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Abstract Deficiency of vitamin-E or tocopherol causes neurological disorders in humans. α-tocopherol possessing the highest vitamin-E activity is present in low concentration in maize kernel. Nine lines and four testers possessing favourable allele of ZmVTE4 that significantly enhances vitamin-E activity were used to generate 36 hybrid combinations. Significant variation was observed for α- (5.95–39.03 μg/g), γ- (11.69–50.82 μg/g), δ- (4.09–10.76 μg/g) and total-tocopherol (33.18–90.53 μg/g). α-, γ- and δ-tocopherol constituted 36%, 53% and 11% of the total tocopherol, respectively. Majority of the experimental hybrids possessed significantly higher α-tocopherol (mean: 21.37 μg/g) than the check hybrids (mean: 11.16 μg/g). AMMI analysis revealed that across tocopherols, genotype and interaction effect accounted 35–77% and 23–45% of variation, respectively. The environmental effects were of minor magnitude. Non-additive gene action was predominant for α-, γ-, and total-tocopherol, while δ-tocopherol was conditioned predominantly by additive gene action. The information generated here assumes great significance in biofortification programme. This is the first report of variability, G × E interactions and combining ability for kernel tocopherol using maize hybrids possessing novel allele of ZmVTE4. Highlights • In maize, the level of α-tocopherol (efficient form of vitamin-E) is very low. • The novel and the favourable allele of γ-tocopherol methyl transferase (ZmVTE4) enhance α-tocopherol in maize grain by 2–3 folds. • Here, maize inbreds with favourable allele of ZmVTE4 were used to generate single cross hybrids. • These hybrids were evaluated at multi-locations to study the variability of different tocopherol components, their G × E interactions and nature of gene action. • The results obtained holds immense significance in maize biofortification programme for the development of vitamin-E rich maize. [ABSTRACT FROM AUTHOR]

Superalkalis are unusual species having ionization energies lower than that of the alkali metals. These species with various applications are of great importance in chemistry due to their low ionization energies and strong reducing property. A typical superalkali contains a central electronegative core decorated with excess metal ligands. In the quest for novel superalkalis, we have designed the superalkalis HLi2, HLiNa and HNa2 using hydrogen as central electronegative atom for the first time employing high level ab initio (CCSD(T), MP2) and density functional theory (ωB97X‐D) methods. The superalkalis exhibit very low ionization energies, even lower than that of cesium. Stability of these species is verified from binding energy and dissociation energy values. The superalkalis are capable of reducing SO2, NO, CO2, CO and N2 molecules by forming stable ionic complexes and therefore can be used as catalysts for the reduction or activation of systems possessing very low electron affinities. The superalkalis form stable supersalts with tailored properties when interact with a superhalogen. They also show remarkably high non‐linear optical responses, hence could have industrial applications. It is hoped that this work will enrich the superalkali family and spur further theoretical and experimental research in this direction. [ABSTRACT FROM AUTHOR]

Abstract: Orientation of water molecules around ionic arsenic has been studied in detail using density functional B3LYP method. Both trivalent and pentavalent ionic states of arsenic are considered to investigate the orientations. The structure, stability and energetics of the ionic arsenic–water complexes, As3+–nH2O (n =1–6) and As5+–nH2O (n =3–6) have been investigated with increasing number of water molecules. The change in binding energy (BE) of the arsenic–water complexes has been discussed in detail. Symmetry, hybridization and charge transfer in these complexes have been illustrated with the help of natural electron configuration. Both donation and back-donation processes involving the orbitals of oxygen and arsenic are analyzed to explain the charge transfer. [Copyright &y& Elsevier]

Using density functional theory, we have designed novel metal-free organic superalkalis by rational modification of the aromatic molecule benzene. The superalkalis exhibit very low ionization energies, even lower than the ionization energy of the alkali metal, cesium. The Hückel's aromaticity rule is seen to play an important role in the design strategy of the organic superalkali compounds. The superalkalis are devised by replacing the core C atom and the H atoms of benzene with proper substituents. Nitrogen atom is used as core substitution, and two different electron-donating groups, –NH2 and –CH3, are employed to substitute the H atoms. It is noticed that the ionization energies of these organic superalkalis are considerably lower compared to that of the commonly used organic reducing agents. To predict their stability, we have evaluated the binding energy per atom values of the systems. It is also observed that the superalkalis show nonlinear optical property and may have industrial importance. [ABSTRACT FROM AUTHOR]

Levodopa, a widely prescribed drug in Parkinson's disease treatment, stands as the foremost prodrug of dopamine. An affordable self‐testing kit is utilized to monitor levodopa content in anti‐parkinson drugs in human serum. A photoluminescent trinuclear Zn(II) complex [Zn3(L)2(κ1‐OAc)2(κ2‐OAc)2] has been synthesized, which cleaves into mononuclear ZC in aqueous solution. ZC was found to detect L‐Dopa in Tris‐HCl buffer, exhibiting a moderate decrease in PL‐emission. The real‐life utility of the ZC probe is limited, for its lower sensitivity (LOD 35.3 μM) and separation challenges. Therefore, an interface between homogeneous and heterogeneous supports has been explored, leading to the strategic development of NGOZC, where ZC was grafted onto NGOQD (Graphene oxide quantum dots). This material enables naked‐ eye detection under both ambient and UV light with color change from bright cyan to green, followed by dark. The nitrogen doping effect was investigated by several comparative investigations involving the synthesis of ZC‐grafted GOQD, leading to enhanced quenching performance. Steady‐state and time‐resolved fluorescence titration study, morphological analysis, and computational calculations have been performed to get insights into the sensing mechanism. To the best of our knowledge, this as‐synthesized NGOZC (LOD 1.78 nM) represents a promising strategy and platform for applications in biosensors, especially for Parkinson's and Alzheimer's diseases. [ABSTRACT FROM AUTHOR]

• Significant variation for α-, γ-, δ- and total-tocopherol was observed. • α-/total-tocopherol & α-/γ-tocopherol was high in 0/0 class over other haplotypes. • First report on relationship of haplotypes of vte4 with tocopherols in India. Vitamin-E deficiency is a serious health problem worldwide. In maize, α-tocopherol possessing the highest vitamin-E activity is regulated by vte4 gene. Here, 54 maize inbreds possessing three favourable (0/0, 7/0 and 0/118) and one unfavourable (7/118) haplotypes of vte4 were evaluated at three locations. Significant variation was observed for α-, γ-, δ- and total-tocopherol. Variation in β-tocopherol was narrow. The mean α-tocopherol of 0/0, 7/0 and 0/118 haplotypes was much higher than the unfavourable (7/118) haplotype. Further, 0/0, 0/118 and 7/0 haplotypes possessed higher proportion of α-tocopherol/ total tocopherol than 7/118 haplotype. α-, γ- and δ- tocopherols were positively correlated (r = 0.56, 0.88 and 0.45, respectively) with total tocopherol. Across tocopherols, genotypes explained 34.7–90.4 %, while environment represented 0.3–21.7 % of total variation. β- and δ-tocopherols were minute in concentration, and α- and γ- tocopherols were the predominant fractions. This is the first report on genetic analysis of tocopherols among maize inbreds possessing four haplotypes of vte4 for use in biofortification programs in India. [ABSTRACT FROM AUTHOR]

In this study, three different solvent systems have been employed to investigate the effect of reaction parameters on the synthesis of four alkaline earth metal-based MOFs namely [Ca(0.5 1,4-phenyl diacetic acid)2(H2O)DMF]∞ (Ca-MOF-1), [Ca(1,4-naphthalene dicarboxylate)DMF]∞ (Ca-MOF-2), [Ca2(0.5 1,2,4,5-benzene tetracarboxylate)2(H2O)3DMF]∞ (Ca-MOF-3) and [Ca2(2,6-naphthalene dicarboxylate)2(H2O)6]∞ (Ca-MOF-4). The crystal structures of these four MOFs have been resolved through single crystal X-ray analysis and the bulk phase purity of these MOFs was assessed using PXRD and FT-IR analysis. To check the stability of these MOFs, thermogravimetric analysis (TGA) was carried out. To analyze the robustness of these MOFs, the PXRD of the samples was also collected at different pH levels. These MOFs were further explored as Lewis acid catalysts for the alcoholysis of epoxides and the activity of these catalysts depend on the open metal sites present in the MOFs. The catalytic activity follows the order: Ca-MOF-2 > Ca-MOF-4 > Ca-MOF-1 > Ca-MOF-3. The activity was also checked with various epoxide substrates using Ca-MOF-2. Density functional theory (DFT) calculations also support this trend with the help of the thermodynamic feasibility of epoxide binding, considering model MOF structures. The weak interaction between the epoxide oxygen and the metal centre of the most stable MOF structure has also been clarified by computational studies. [ABSTRACT FROM AUTHOR]

Herein, we present a dark-green crystalline tetranuclear Cu(II) Schiff base complex {C1 = [Cu4L4](ClO4)4(DMF)4(H2O)} using a N,N,O donor ligand (HL), namely 2-(((2-hydroxypropyl)imino)methyl)-6-methoxyphenol. Spectro-photometrical investigation on the β-lactamase-like activity of this coordinately saturated system revealed its catalytic inefficiency towards hydrolysis of nitrocefin as a model substrate. This complex has attracted significant interest as a promising photo-catalyst owing to its narrow band gap (2.40 eV) as predicted from DFT calculations and its higher responsivity towards UV light. Therefore, C1 is effectively involved in the photocatalytic reduction of perchlorate to Cl− in the presence of a hole scavenger (H2O–MeOH) under prolonged UV irradiation and itself becomes photo-cleaved to yield a new dark-brown colored chlorobridged dinuclear crystalline complex C2 {[CuL(H2O)2Cl3]H2O}. Furthermore, C2 was deployed as a functional β-lactamase model and was found to show a remarkable catalytic proficiency towards the hydrolysis of nitrocefin in 70 : 30 (V/V) MeOH–H2O medium. This pro-catalyst C2 has been speculated to generate an aqua bridged active catalyst that plays a crucial factor in hydrolysis. This phenomenon was again experimentally established by potentiometric pH titration where C2 displays only one pKa value (7.11) in the basic pH range, indicating the deprotonation of the bridged water molecule. Based on several other kinetic studies, it may be postulated that the hydrolysis of nitrocefin is initiated by the nucleophilic attack of a bridging hydroxide, followed by very fast protonation of the intermediate to furnish the hydrolyzed product. It is noteworthy that the rate of nitrocefin hydrolysis is greatly inhibited in the presence of external chloride concentration. To the best of our knowledge, this is the first report on the photochemical behavior of such a tetranuclear copper(II) Schiff base complex. Our current interest is focused on inventing a potent β-lactamase inhibitory therapeutic as well as elucidating its mechanism through comprehensive chemical analysis. [ABSTRACT FROM AUTHOR]

Bimetallic sandwich complexes based on the borazocine (B4N4H8) ligand have been studied using density functional theory (DFT). The studied Ca–Ca covalent bond length agrees well with the experimental Ca2 bond length. For the studied complexes, the non-nuclear attractor (NNA) is found at the Ca–Ca bond of K2(B4N4H8)2Ca2 and Na2(B4N4H8)2Ca2. The negative Laplacian at the NNA is noticed for these two complexes, indicating that these complexes are electrides. This study for the first time reports the electride complexes based on the B4N4H8 ligand. Interestingly, upon asymmetric doping with Na and K, no NNA point is found for the complex NaK(B4N4H8)2Ca2, indicating that this complex is not an electride. Our study points out one of the fascinating outcomes that asymmetric doping can affect the occurrence of the NNA in a system. The complex Na2(B4N4H8)2Ca2 exhibits the highest second hyperpolarizability value of 2.2 × 106 au at the ωB97XD/6-311++G(3df,3pd) level among the studied sandwich complexes. [ABSTRACT FROM AUTHOR]

The conversion mechanisms of CO into methanol through hydrogenation and CO2 through hydrolysis catalyzed by (PNP)RuH2CO (1) pincer complex have been explored employing density functional theory (DFT). For both the reactions, we have identified two pathways. In pathway‐I, at first the CO takes part in the reaction by interacting with the Ru‐center of pincer complex and after that the H2/H2O molecule participates in the reaction, whereas in pathway‐II, the generation of hydrogenated/hydrolyzed pincer from initial pincer via the assistance of H2 or H2O molecule occurs first, followed by the reaction with CO. In case of hydrogenation, for both the pathways, CO is first converted to HCHO through hydrogenation which further undergoes hydrogenation to form methanol. In pathway‐I, the reaction of HCHO with H2 in presence of dehydrogenated pincer leads to produce methanol, whereas for pathway‐II the hydrogenated pincer formed at the beginning of this pathway carries out the aforementioned conversion. Further in presence of methanol, CO is catalytically converted to methyl formate. On the other hand, in case of hydrolysis, the conversion of CO to CO2 can be achieved in two ways, where 2nd step, i. e. formic acid to CO2 via formate ion formation follows similar mechanism for both the pathways. Overall, from our study it is revealed that the Ru‐pincer complex acts as a promising homogeneous catalyst for converting CO to various organic chemical commodities. [ABSTRACT FROM AUTHOR]

Context: Phytic acid is the major storage form of phosphorus in cereals and is considered an anti-nutritional factor because it chelates major mineral micronutrient cations, resulting in micronutrient malnutrition in humans. For monogastric animals fed maize (Zea mays L.) grains, the stored phosphorus does not release into the digestive tract, leading to phosphorus deficiency and environmental pollution. Aims: The aim of the study was to develop maize lines with a lower level of phytic acid that might substantially enhance the nutritional value of maize. Methods: The lpa1 mutant allele conferring low phytic acid was transferred into the parental lines of popular maize hybrid DMH 121 (i.e. BML 6 and BML 45) through marker-assisted backcross breeding. Foreground selection was performed using a co-dominant single nucleotide polymorphism marker through a high-resolution melting approach, and background selection was undertaken using 50–55 polymorphic sequence-tagged microsatellite site markers. Key results: Near-isogeneic lines were produced with >90% recurrent parental genome and reduction of phytic acid content by up to 44–56% compared with the original lines. Conclusions: The near-isogeneic lines carrying lpa1 can be used to reconstitute DHM 121 with low phytate content. Implications: The low-phytate maize hybrids produced can be useful in reducing micronutrient malnutrition in humans, as well as environmental pollution. Phytic acid is an anti-nutritional factor that chelates major mineral micronutrient cations, resulting in micronutrient malnutrition in humans. In this study, the lpa1 mutant allele was transferred into the parental lines of DMH 121 (i.e BML 6, and BML 45) through marker-assisted backcross breeding. Near-isogeneic lines were produced with 44–56% reduction of phytic acid content relative to the original lines. [ABSTRACT FROM AUTHOR]

[Display omitted] • DFT-employed gas phase catalytic hydrogenation of CO has been explored. • A total of six phosphorus compounds have been chosen for the study. • Effect of ONO-ligand substitution and ONO-framework modification have been explored. • Catalytic efficiencies have been compared based on the activation barrier of RDS. The catalytic hydrogenation of carbon monoxide (CO) with ammonia-borane (NH 3 BH 3) using a series of phosphorus compounds (1) has been explored computationally. The formation of an active phosphorus compound (1-H) via the subsequent transfer of protic and hydridic hydrogens from NH 3 BH 3 to 1 is the initiation step. The newly formed catalyst (1-H) further carries out the conversion of CO to formaldehyde (HCHO) to methanol (MeOH). The impact of ONO-ligand substitution and ONO-framework modification on the catalytic efficiency is also studied. The catalytic efficiencies of the phosphorus compounds have been compared based on the calculated activation barriers of rate-determining step (RDS). [ABSTRACT FROM AUTHOR]

Effects of complexant number on static and dynamic second hyperpolarizability of diffuse electron systems comprising aziridine (complexant) and alkaline earth metal dopant (i.e., Be, Mg, and Ca) are explored theoretically. Accordingly, the number of the complexant is increased up to three in a stepwise fashion. Aziridine unit, which is non-covalently linked with dopant, polarizes the ns electron of dopant. This polarizing effect results in higher second hyperpolarizability value of the complexes. Compared to pristine aziridine moiety, the γavg of Be-aziridine complex enhances significantly. Interestingly, with increase in complexant number, the static and dynamic second hyperpolarizability values enhance monotonically and attain the maximum value when three complexants are employed. Among the studied systems, the shamrock-shaped complex (Ca@(aziridine)3) exhibits higher non-linear refractive index as well as remarkably high second hyperpolarizability value (1.83 × 107 au). [ABSTRACT FROM AUTHOR]

The effect of metal-alkoxide functionalization of different organic linkers on the H 2 binding is investigated employing DFT approach. While analyzing the H 2 binding interaction of magnesium-alkoxide modified benzene, naphthalene, anthracene and pyrene linkers, we find their comparable affinity toward H 2 molecules. Six-member alkoxide ring containing naphthalene and pyrene systems interact with the H 2 molecules in a comparatively better way than their five-member analogues. AIM, NBO and LMO-EDA analyses have been performed to comprehend the bonding nature between Mg center and the H 2 molecules. Polarization along with the charge transfer interactions play significant role in stabilizing the systems. [ABSTRACT FROM AUTHOR]

A highly fluorescent zinc probe of reduced Schiff base (rBDZn) has been identified as promising chemosensor towards cadmium ion sensing supported by theoretical and experimental approaches, where rBDZn captures Cd2+ and crystallize out from the system. [Display omitted] • A zinc-based fluorescent probe (rBDZn) having reduced Schiff base backbone with N,O-donor atoms has been synthesized. • Single Crystal X-Ray diffraction study revealed a trimeric structure linearly bridged by azide ion. • The fluorescent probe has been found to exhibit a cyan blue fluorescence getting 'turned-off' in presence of Cd2+ selectively. • A naked-eye visible colour change from pale yellow to colourless is observed. • Single crystal of Cd-substituted complex have been isolated and verified with single crystal XRD and computational calculations. • Selective Cd2+ probe with a very low detection limit of 1.72 nM enables its genuine implications in pollution management. Alarmingly increasing population and industrial growth has immensely affected water bodies and potable water sources by elution of many heavy toxic metal ions, including cadmium (II). The rising threat has demanded easy and cost-effective detection of this heavy metal ion so as to spread widely across the masses and eliminate the poisoning of water. With this aim, we have synthesized a zinc-based fluorescent probe (rBDZn) having reduced Schiff base backbone with N- and O- donor atoms derived from 5-bromosalicaldehyde and 2,2-dimethylpropane-1,3-diamine, characterized with the aid of single crystal X-ray analysis, revealing a trimeric structure linearly bridged by azide ion. The complex has been found to exhibit a cyan blue fluorescence getting 'turned-off' in the presence of cadmium ion selectively along with many other cations in the aqueous solution together with a naked-eye visible color change from pale yellow to colorless. Steady-state and time-resolved fluorescence titration, and absorption titration experiments were performed. During the investigation of the sensing pathway it is observed that the detection of Cd2+ is being associated with the formation of the cadmium complex rBDCd from the probe rBDZn and this has been explained though a probable mechanism. In support of the fact a single crystal of Cd-substituted complex have been isolated and verified with single crystal XRD and computational calculations. Proper justification of the selectivity of the probe towards cadmium ion with a very low detection limit of 1.72 nM enables its genuine impact in the pollution management. [ABSTRACT FROM AUTHOR]

CO2 gasification process on different active edges of a particular coke model surface has been explored computationally. It is observed that the adsorption through carbon and oxygen end of CO2 (CO‐mode) through formation of four‐ and five‐membered ring on the active sites is the favoured one. Our calculation also reveals that the strength of adsorption depends on nature and position of the active sites. The exergonic adsorption energy of CO‐mode drives the first CO release process and also makes it favoured compared to the adsorption mode where CO2 has been absorbed through its two‐oxygen end (OO‐mode). Among all the intermediates, intermediate having oxygen attached to the middle‐carbon of the coke (middle‐oxygenated coke) is found to be the most stable intermediate. The energy barrier for the second CO release also depends on the attachment sites of the oxygen on the coke surface. It is noteworthy that first principles investigations of coke gasification reactions with CO2 reported to date are found to consider different coke active sites separately on different coke model surfaces. In this context, our work is believed to be the first of its kind where complete characterization of CO2 gasification reactions has been performed considering all the active sites in a single coke model, thus providing a more coherent picture of it. [ABSTRACT FROM AUTHOR]

The spectroscopic constants and molecular properties of low‐lying isomers of CaC6H2 have been studied using dispersion‐corrected density functional theory, MP2 and high‐level coupled‐cluster (CC) methods. 60 isomers have been identified, among which three low‐lying isomers having energy differences within 1 eV have been re‐optimized at MP2/cc‐pVTZ level. Isomer 1 (1‐calciacyclohepta‐4‐en‐2,6‐diyne) is found to be the most stable one, followed by isomer 3 (3‐calciahepta‐1,4,6‐triyne) and isomer 2 (1‐calciacyclohepta‐2,3,4‐trien‐6‐yne) that lie 20.9 and 19.7 kcal/mol above 1, respectively at MP2/cc‐pVTZ level. All three isomers are polar with a permanent electric dipole moment. Molecular properties like electron affinity, ionization potential as well as GCRD parameters, i. e., chemical potential, global hardness, etc. have been calculated at ae‐CCSD(T)/cc‐pVTZ level. NBO and AIM analyses have been performed to predict the nature of bonds in the isomers. The spectroscopic constants such as rotational and centrifugal distortion constants, inertial axis dipole moment components, etc. have been calculated using the frozen core (fc)‐CCSD(T) and all electron (ae)‐CCSD(T) methods with cc‐pVTZ basis. The ae‐CCSD(T) method with cc‐pwCVTZ‐X2C basis set has also been used to calculate spectroscopic constants. The predicted spectroscopic constants and molecular properties will facilitate in detecting these isomers in the laboratory as well as in interstellar medium (ISM). [ABSTRACT FROM AUTHOR]

Efficient detection of arsenate (AsO43-) from contaminated drinking water extracted from underground has become a matter of utmost necessity and an exquisite challenge owing to the growing public health issue due to arsenicosis. In order to combat this we planned to detect arsenate with the naked eye under UV light using a novel chemosensor material whose structure and functioning as a sensor could be certified mechanistically. Hence we were encouraged to synthesize two differently O-substituted imidazole based homologous ligands: C1 (HL¹ = 2-((E)-(3-(1H-imidazole-1-yl)propylimino)methyl)-6-ethoxyphenol) and C2 (HL² = 2-((E)-(3-(1H-imidazole-1-yl)propylimino)methyl)-6-methoxyphenol). To accomplish the purposeful exploration of the luminescent sensor, we considered Chelation Enhanced Fluorescence (CHEF) and kept on searching for a metal cation that would be able to turn on the fluorescence of the ligands. Considering Zn(II) as the most suitable candidate, luminescent complexes D1 and D2 ({[Zn2(L¹)2(I)2](DMF)} and [Zn2(L²)2(I)2](DMF), respectively) were synthesized and characterized by SXRD, UV-Vis, FT-IR, and photoluminescence spectroscopy. In spite of the resemblance in the solid state structures of D1 and D2, the selective response of D1 towards arsenate with high quenching constants (2.13 x 106), unlike D2, has been demonstrated mechanistically with steady state and time resolved fluorescence titration, solution phase ESI-MS spectral analysis and DFT studies. The selectivity and sensitivity of the sensor D1 explicitly make this material a potent candidate for arsenate detection due to its very low detection limit (8.2 ppb), low cost and user friendly characteristics. Real life implementation of this work in a test strip is expected to prove beneficial for public health to identify arsenate polluted water. [ABSTRACT FROM AUTHOR]

Abstract: Mechanism and kinetics for the reaction of DMSO with O(3P) have been investigated by M06-2X/MG3S, CBS-QB3 and G4MP2 methods. Four possible reaction pathways are identified. Among them, the O(3P) addition to S-atom followed by CH3 elimination is almost exclusive. Four pre-reactive complexes have been located. AIM theory is used to determine the nature of interactions in these complexes. Considering the formation of pre-reactive complex, the rate constant for major pathway is calculated using transition state theory applied to a two-step mechanism. Enthalpies of formation at 298.15K (Δf H°298.15) have been calculated using the composite CBS-QB3, G4MP2 and G3B3 methods. [Copyright &y& Elsevier]

Ab initio and density functional theory (DFT) calculationshavebeen performed to understand the destruction chemistry of an importantorganophosphorus insecticide O,O-dimethyl O-(3-methyl-4-nitrophenyl) phosphorothioate,fenitrothion (FN), toward nucleophilic attack. Breakingof the P–OAr linkages through nucleophilic attack is consideredto be the major degradation pathway for FN. One simplenucleophile, hydroxide (OH–), and two differentα-nucleophiles, hydroperoxide (OOH–) and hydroxylamineanion (NH2O–), have been considered forthis study. Nucleophilic attack at the two different centers, SN2@P and SN2@C, has been monitored, and the computedreaction energetics confirms that the SN2@P reactions arefavorable over the SN2@C reactions for all the nucleophiles.All electronic structure calculations for the reaction are performedat DFT-B3LYP/6-31+G(d) level of theory followed by a refinement ofenergy at ab initio MP2/6-311++G(2d,2p) level. The effect of aqueouspolarization on both the SN2 reactions is taken into accountemploying the conductor-like screening model (COSMO) as well as polarizationcontinuum model (PCM) at B3LYP/6-31+G(d) level of theory. Relativeperformance of the two α-nucleophiles, OOH–and NH2O–, at the P center has furtherbeen clarified using natural bond orbital (NBO), conceptual DFT, andatoms in molecules (AIM) approaches. The strength of the intermolecularhydrogen bonding in the transition states and topological propertiesof the electron density distribution for −X–H···S(X = O, N) intermolecular hydrogen bonds are the subject of NBO andAIM analysis, respectively. Our calculated reaction energetics andelectronic properties suggest that the relative order of nucleophilicityfor the nucleophiles is OOH–> NH2O–> OH–for the SN2@P,whereas for the SN2@C the order, which gets little altered,is NH2O–> OOH–>OH–. [ABSTRACT FROM AUTHOR]

The complexes of PbII(S2COR)2 [R = Me, Et, Ph] having three possible coordination patterns S,S/S,S or S,O/S,S or S,O/S,O are studied. The formation energy and relative energy of these isomers reveal that the order of stability is S,S/S,S > S,O/S,S > S,O/S,O. Complexation energy of the isomers decreases substantially from gas phase to water. The natural bond orbital (NBO) analysis has been performed to explore the metal–ligand coordination. Similar types of metal–ligand coordinations are observed for methyl and ethyl substituent. In S/S,S/S coordination, lead mainly uses its 6p sub-shells along with 6d and 7s orbitals to coordinate with 3p sub-shells of the surrounding sulfur atoms. Significant mixing of 6p and 6d orbitals of lead is also observed. In contrast, for phenyl substituent, lead uses only its 6p sub-shells to coordinate with sulfur atoms. In S,O/S,O or S,O/S,S coordination, oxygen uses its 2s and 2p sub-shells while sulfur uses its 3p sub-shells to coordinate with 7s and 6p sub-shells of lead. The binding energy and NBO analysis of these chelates indicate that lead–sulfur (soft–soft) coordination is preferred over lead–oxygen (soft–hard). In all these chelates, valence 6s orbital of lead shows inert pair effect with no participation in chelation. [ABSTRACT FROM PUBLISHER]

A systematic theoretical study has been performed on the low pressure thermal decomposition pathways of t-BuS(O)St-Bu using the CCSD(T)/cc-pV(D+d)Z//B3LYP/6-311++G(2d,2p), CCSD(T)/cc-PV(D + d)Z//PBEPBE/6-3Il++G(2d,2p)l and G3B3 level of theories. Rate constants for the unimolecular decomposition pathways are calculated using Rice-Ramsperger-Kassel-Marcus (RRJCM) theory. On the basis of the experimental observation and theoretical predictions, the pyrolysis channels are considered as primary and secondary pyrolysis reactions. The primary decomposition via a five-membered transition state leads to the formation of tert-butanethiosulfoxylic acid (i-BuSSOH) and 2-methylpropene (C4H8) almost exclusively having low-pressure limit rate constant κ10 = 4.67 x 10-6T-4.67 exp(-11.64 kcal mol-1/RT) cm3 mol-1s-1 (T = 500-800 K). The primary decomposition via a six-membered transition state is also identified, and that leads to the tert-butanethiosulfinic acid t- BuS(OH )S, which is the branched chain isomer of t-BuSSOH. The formation of t-BuSSOH is thermodynamically as well as kinetically favorable over t-BuS(OH)S formation, and therefore the second product could not be found experimentally. Furthermore, calculation on secondary pyrolysis pathways involving the decomposition of t-BuSSOH leads to the formation of 1-oxatrisulfane (trans-HSSOH and cis-HSSOH) and their branched isomer S(SH)OH. These three secondary product formation rates are competitive, but thermodynamics do not favor the formation of the branched isomer. Among the secondary pyrolysis products, trans-HSSOH is the most stable one, and its formation rate constant at low pressure is calculated to be κ30 = 5-49 x 1028T-10.70 exp(-36.22 kcal mol-1/RT) cm3 mol-1 s-1 (T = 800-l500 K). Finally, the secondary pyrolysis pathway from less stable product t-BuS(OH)S is also predicted, and that leads to trans-HSSOH and cis- HSSOH products with almost equal rates. A bond-order analysis using Wiberg bond indexes obtained by natural bond orbital (NBO) calculation predicts that the primary and secondary pyrolysis of t-BuS(O)St-Bu occur via E1-like mechanism. [ABSTRACT FROM AUTHOR]

Abstract: The spectroscopic properties of I2–Rg (Rg=He, Ne, Ar) van der Waals complexes have been studied in detail using ab initio MP2 and CCSD(T) methods in conjunction with the correlation consistent quadruple-ζ quality basis sets. The dissociation energy and depth of the potential well have been calculated using potential method and supermolecular approach in order to remove the discrepancy among the existing theoretical and experimental values. Most of the spectroscopic properties are first reported and the rest agree very well with the theoretical and experimental values wherever available. [Copyright &y& Elsevier]

The intermediates [Si,O,C,O] of the Si + CO reaction have been studied in detail using high level ab iniitio methods. Both singlet and triplet [Si,O,C,O] species are characterized structurally and energetically. On the singlet potential energy surface (PES), the vdw-OSi-CO isomer and in the triplet PES, the bent-SiOCO isomer is found to be thermodynamically as well as kinetically most stable species. All possible isomerization transition states (TS) are located on both singlet and triplet potential surfaces. On the triplet surface, the stability of the trans-OSiCO isomer is comparable with that of the bent-SiOCO isomer. A non-planar cis-SiOCO isomer is located on the triplet PES, which is predicted for the first time. Heats of formation at 0 K (Δ H°, 0 K) for all singlet and triplet species are computed using G3B3, G3MP2, and CBS-Q theories. The discrepancy between G3B3 and the other two methods for the heat of formation value for triplet trans-OSiCO is discussed. The PESs for singlet as well as triplet species with their dissociation asymptotes are explored at the CCSD(T)/6-311G(d,p)//MP2/6-311G(d,p) level of theory. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

Abstract: The structures, stability, thermochemistry and dissociation of the doublet [H,S,Si,O] species are studied using UMP2-FC and UCCSD(T)-FC methods. Twelve isomers connected with sixteen interconversion transition states are located on the doublet potential energy surface (PES). All isomers are planar except two cyclic isomers. The trans-HOSiS isomer is found to be the kinetically most stable species with the least interconversion barrier of 42.80kcal/mol whereas the thermodynamically most stable cis-HOSiS isomer is the next kinetically stable species. Among the located isomers, five are found to be kinetically stable and should be observable experimentally. The dissociation processes of the [H,S,Si,O] species to the low-lying molecular fragments are investigated. The results are compared with those of analogous HOCO and HOCS species. Implications of these species in the laboratory and in interstellar medium are discussed. Finally the standard Enthalpies of formation at 0K (Δ fH°, 0K) is calculated for all [H,S,Si,O] species and their fragments. [Copyright &y& Elsevier]

Abstract: An ab initio study has been performed to characterize the probable magnesium containing interstellar species MgSiN, MgNSi and their ionized, hydrogenated and protonated forms. We are able to locate four protonated and four hydrogenated magnesium species with planar geometry at MP2(Full)/cc-pVTZ level of theory. MgNSi is found to be more stable than MgSiN and their connecting transition state is also located. The ionization potential for both MgSiN and MgNSi are small, 7.91eV and 7.01eV, respectively. All possible protonation sites are considered for these two species but the preferred protonation sites are found to be silicon for MgNSi and nitrogen for MgSiN. Enthalpies of formation at 0K (Δf H°) and bond dissociation energies (D o(X–Y)) are computed for all the species at G3 and G3MP2 level of theory. Finally, the reaction enthalpies for ion–molecule processes are calculated and most of the processes are found to be exothermic and hence thermodynamically favorable in interstellar region. [Copyright &y& Elsevier]

Abstract: Reaction between SiO2 and water has been studied extensively using ab initio methods. The mechanism for formation of metasilicic acid SiO(OH)2 and orthosilicic acid Si(OH)4 has been explored and a new pathway for formation of Si(OH)4 is predicted. Heats of reaction () and heats of formation () at 298K for the related reactions and species calculated at two different theoretical levels G3B3 and G3MP2B3 agree well with the literature values. It is found that when SiO2 reacts simultaneously with two water molecules, the thermodynamic as well as kinetic feasibility of the process is much greater than that when SiO2 reacts with one molecule of water. [Copyright &y& Elsevier]

Stability, spectroscopic constants, and dissociation of CO2+ have been studied in detail using ab initio MP2, CCSD and CCSD(T) methods, and density functional B3LYP method. The stability and the ambiguity between the ground and metastable state of the molecular dication have been discussed. The spectroscopic constants of the molecular dication have been compared with the experimental and theoretical values wherever available. Various charge symmetric and charge asymmetric dissociation pathways of CO2+ have been investigated. After dissociation, the fragmented atoms and ions are considered to be either in their ground or in their metastable state. Interesting results have been obtained for the charge symmetric and charge asymmetric dissociation of the diatomic dication. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

The exohedral functionalization of encapsulated fullerenes (such as Diels–Alder reaction) gives rise to wide‐ranging derivatives that are useful for potential applications. Though the oligo‐adducts have significant uses in material and biological sciences, they are hardly investigated due to experimental limitations. To shed light on that unexplored area, we have computationally investigated the sequential Diels–Alder reactions, that is, multi‐Diels–Alder (MDA) reaction of neutral C60 and its Li+‐encapsulated derivative with 1,3‐butadiene in the present venture employing density functional theory. The computational reports available to date illustrate that the reactivity of neutral C60 can be significantly stimulated by the encapsulation of alkali/alkaline earth metal atoms/ions within the fullerene cage. However, the effect of encapsulation has been examined for the Diels–Alder reaction of fullerene derivatives up to bis‐functionalization. Therefore, in the present study, we aim to investigate the kinetic and thermodynamic feasibility of multiple butadiene attachments (beyond two) to the neutral C60 surface and also the impact of Li+ encapsulation on the reaction mentioned above. We have shown that the MDA reaction initiates with the formation of an encounter complex between the mono‐functionalized fullerene product and the second butadiene molecule. In this context, two different approaches, namely "direct" and "alternative" have been considered depending on the second butadiene attachment to check whether the first functionalization makes the rest of the double bonds in‐equivalent toward the second butadiene addition or not. Each of the reaction steps following these two approaches eventually forms the same tetra‐functionalized final product with a high degree of exothermicity value, thus making the overall reaction thermodynamically facile. The positive impact of Li+ encapsulation is well‐understood from the diminished activation barrier and more negative exothermicity value compared to neutral C60 in each step of the MDA procedure. Moreover, just like the mono‐ and bis‐functionalization reported earlier, the regio‐selectivity is also retained in the MDA procedure. Overall, the present study will foresee an extensive idea about the detailed mechanism of the MDA reactions on neutral C60 and its Li+ encapsulated analogue, which will be helpful for further progress in the field of fullerene chemistry. [ABSTRACT FROM AUTHOR]

A gas phase mechanistic investigation has been carried out theoretically to explore the hydrolysis pathway of ammonia borane (NH3BH3) and metal amidoboranes (MNH2BH3, M = Li,Na). The Solvation Model based on Density (SMD) has been employed to show the effect of bulk water on the reaction mechanism. Gibbs free energy of solvation has also been computed to evaluate the stabilization of the participating systems in water medium which directly affects the barrier heights in the potential energy surface of hydrolysis reaction. To validate the experimentally observed kinetics studies, we have carried out transition state theory calculations on these hydrolysis reactions. Our result shows that the hydrolysis of both the metal amidoboranes exhibits greatly improved kinetics over the neat NH3BH3 hydrolysis which corroborates well with the experimental observation. Between the two amidoboranes, hydrolysis of LiNH2BH3 is found to be kinetically favored over that of NaNH2BH3, making it a better candidate for releasing molecular hydrogen. [ABSTRACT FROM AUTHOR]

The structures, energies, isomerization, and decomposition pathways of small ionic silicon oxide clusters, SiOn+ (n = 3, 4), on doublet and quartet energy surfaces are investigated by density functional theory. New structural isomers of these ionic clusters have been obtained with this systematic study. The energy ordering of the isomeric cluster ions on doublet spin surface is found to follow the same general trend as that of the neutral ones, while it differs on the quartet surface. Our computational results reveal the energetically most preferred decomposition pathways of the ionic clusters on both spin surfaces. To comprehend the reaction mechanism, bonding evolution theory has also been employed using atoms in molecules formalism. The possible reasons behind the structural deformation of some isomers on quartet surface have also been addressed. Our results are expected to provide important insight into the decomposition mechanism and relative stability of the SiOn+ clusters on both the energy surfaces. [ABSTRACT FROM AUTHOR]

Activation of C–H, B–H as well N–H sigma bonds has been a subject of fundamental interest due to potential feedstock in chemical industry. The co-operative effect of the metal centers in a di-nuclear carbide cluster Ta 2 C 4 − for methane C–H activation and dissociation has recently been revealed, in which a molecule of hydrogen is evolved. Based on that, we have explored reaction pathways for 'E−H' sigma bond activation and dissociation processes of gaseous Ammonia (E: N) and Borane (E: B) using the stable form of the aforesaid complex at DFT levels. The geometries and energetics associated with the reactions are found to be method insensitive. The course of the reaction is initiated by a 1:1 precursor complex formed between the cluster and N (/B)H 3. This complex formation is found to be more exothermic than that of its methane counterpart. In case of BH 3 , considerable lengthening of two B–H bonds in the first step is observed which implies that the two B–H bonds are activated simultaneously under the influence of Ta 2 C 4 −. But for NH 3 , N–H bond lengthening as well as activation is observed to be insignificant in this precursor complex. The chemical nature of the participating hydrogen atoms is inspected by NPA analysis (' protic ' type in NH 3 and 'hydride ' type in BH 3).The overall dehydrogenation procedures for both the molecules are found to be multi-step with high exothermicity. Highly negative net energy change in terms of Gibbs Free Energy (−31.03 kcal/mol for ammonia and −31.36 kcal/mol for borane) as well as Enthalpy (−33.68 kcal/mol for ammonia and −34.13 kcal/mol for borane), in forming a H 2 molecule with stable Ta 2 C 4 N(/B)H− complex, with respect to the reactant pair govern the thermodynamic feasibility of the overall process. In a nutshell, this computational study provides a detail understanding of the activation and dissociation processes of the concerned gaseous molecules, which will be beneficial for further experimental studies. Image 1 • Dehydrogenation of gaseous NH 3 and BH 3 by Tantalum carbide cluster anion (Ta 2 C 4 -). • The participating hydrogen atoms are ' protic ' type in NH 3 and 'hydride ' type in BH 3. • The multi-step reaction is initiated by a 1:1 precursor complex (Exothermic). • Primarily, significant activation of two B-H sigma bonds is noted though N-H sigma bond activation is inconsequential. • Overall H 2 release process, for both the molecules is highly exothermic making the procedure to be thermodynamically facile. [ABSTRACT FROM AUTHOR]

Reaction pathways involved in catalytic Cross Dehydrogenative Coupling (CDC) reactions leading to formation of Si−O and Si−S bonds have been formulated and explored theoretically using Density Functional Theory (DFT). The advantage of the weak Si−H bond has been exploited to carry out coupling with water, alcohol and thiol, along with H2 release. Ru complex, [K(dme)2][Ru(H)(trop2dad)] when reacts with water generates a neutral complex, [Ru(trop2dad)]. This neutral complex has been employed to act as a catalyst in CDC reactions. It has also been found that the complex, [Ru(H2)(trop2dad)] formed within the catalytic cycle may also be used for hydrogenation of C=O, C=N and N=N bonds. The optimized geometries of all the complexes and transition states have been obtained using wB97xd functional in conjunction with 6‐31++G(d,p) basis set. The whole assisting phenomena in solvent medium has been investigated through the implementation of conductor‐like screening solvation model (COSMO) considering tetrahydrofuran as the bulk solvent medium. The Turnover frequency (TOF) has been calculated by Energetic Span Model. The theoretical investigation extends the role of the ruthenium catalyst to the regime of 'element to element' bond formation, along with H2 release, which may be significant in the field of energy storage, and also triggers an alternative possibility of hydrogenation of carbonyls, imines and diazo compounds. [ABSTRACT FROM AUTHOR]

The interaction of four moderately reactive molecules (MRMs), benzene (BZ), water, ammonia and silicon dioxide, with three aromatic organic superhalogens (OSHs) has been investigated at the density functional theory (DFT) level. The strength of the interaction is analysed from the distortions in the structures of both the MRMs and OSHs after complexation and the calculated binding energy (BE) values between the two interacting moieties. The interaction becomes stronger as we move from BZ to H2O to NH3 and strongest for SiO2 molecule. Contributions from different terms in total interaction energy have been examined by energy decomposition analysis (EDA). The charge flow values between MRMs and OSHs, and Mulliken spin density localised on the moderately reactive molecules have been evaluated to ensure whether the interaction is ionic or not. Atoms in Molecules (AIM) analysis has been performed to characterise the bonds formed between the two. Overall, our study gives a comprehensive account of the interaction between the moderately reactive molecules and three theoretically designed aromatic organic superhalogens, which will further motivate researchers in the field of superhalogen chemistry. [ABSTRACT FROM AUTHOR]

• Doping with Al and Ga substituting one of the B atoms of the B 12 N 12 and B 12 P 12 nanocages increases the reactivity of the cage. • THF/F adsorbed complexes show the highest adsorption energy for Al-doped nanocages. • For a given nanocage, THF molecule is adsorbed strongly than F. • B 12 P 12 complexes show higher optical responses compared to its B 12 N 12 counterparts. Removing pollutants like furan (F) and tetrahydrofuran (THF) from the environment is challenging, and adsorption can efficiently remove pollutants. Fullerene like inorganic nanocages B 12 N 12 and B 12 P 12 are known for their efficient adsorption capability. To address these concerns, we report here the adsorption of the F and THF on the pristine and Al and Ga-doped B 12 N 12 and B 12 P 12 nanocages and consequently the change in the electronic structure, property and optical responses. Doping Al and Ga at the nanocage diminishes the HOMO-LUMO energy gap by 2.9 to 0.4 eV compared to the pristine cage, making the doped cage surface more reactive. The doped surface of nanocage adsorbs F (F@AlB 11 N 12 (-130.1 kJ/mole) and THF (THF@AlB 11 N 12 (-202.3 kJ/mole) more effectively compared to pristine ones (F@B 12 N 12 -28.7 kJ/mole, THF@B 12 N 12 (-98.3 kJ/mole) at ωB97XD/6–31+ G (d,p) level. For a given cage, THF is more strongly adsorbed (THF@B 12 N 12 (-98.3 kJ/mole)) on the cage surface than F (F@B 12 N 12 -28.7 kJ/mole). Interestingly, Al-doped cages exhibit the highest adsorption energy value ranging from -68.5 kJ/mole to -202.3 kJ/mole. Natural bonding orbital analysis, global reactivity descriptor, molecular electrostatic potential, frontier molecular orbital, etc. have been employed to comprehend the distinctive patterns of adsorption. The optical response properties of the studied complexes show that the complexes of B 12 P 12 nanocages exhibit higher polarizability and second hyperpolarizability value (1.51 × 105 to 1.62 × 105 au) compared to its analogous B 12 N 12 complex (3.62 × 104 to 4.15 × 104 au) at ωB97XD/6–311+ G (d,p) level. Our theoretical results further demonstrate the capability of AlB 11 N 12 and AlB 11 P 12 as promising adsorbents of the toxic organic pollutants F and THF, and the computed higher second hyperpolarizability value of the B 12 P 12 complexes indicates these nanomaterials could be used as potential optoelectronic materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Reaction pathways for dehydrogenation and hence cyclization of diamine-monoborane and amine-borane alcohol have been explored theoretically using Density Functional Theory (DFT). The diamine-monoborane and amine-borane alcohol chosen for investigation in the present venture are N -(tert -butyl)(BH 3)– N′ - tert -butyl-ethylenediamine and α,α -Diphenyl-2-pyrrolidinemethanol-borane. Alkali metal catalysts, viz., 1-lithio-2- tert -butyl-1,2-dihydropyridine and its sodium and potassium analogues have been employed for the removal of two equivalents of H 2. The optimized geometries of all the reactant complexes, intermediates, transition states and product complexes have been obtained using ωB97xd functional in conjunction with 6–31++G(d,p) basis set. The whole assisting phenomena in solvent medium has been investigated through the implementation of conductor-like screening solvation model (COSMO) primarily considering benzene as the bulk solvent medium. The investigation has further been extended to solvents tetrahydrofuran and pyridine to examine the participation of solvent molecules in bringing any change in reaction mechanism and catalytic cycle of the lithium catalyst over diamine-borane. The intramolecular and all possible intermolecular (catalytic) pathways have been studied in detail. Our study supports previous experimental studies and elucidates key role in the catalytic regime of 1,2-dihydropyridine, which is able to store and deliver Li–H on demand. Image 1 • Dehydrocyclization of diamine-borane and amine-borane alcohol. • Catalysts considered are 1-lithio-2-alkyl-1,2-dihydropyridine and its Na & K analogues. • Implementation of solvent medium (benzene, THF, pyridine) on reaction mechanism through COSMO. • Investigation of all possible pathways involved in H 2 -release. • Activation barriers and Turnover frequencies suggest effective catalytic activity. [ABSTRACT FROM AUTHOR]

The possibility of ionization of six moderately reactive molecules (Y), namely silicon dioxide (SiO2), ammonia (NH3), water (H2O), carbon dioxide (CO2), chloroform (CHCl3) and dichlorodifluoromethane (CCl2F2) by two properly chosen superhalogens (SHs), gold tetrafluoride (AuF4), and gold hexafluoride (AuF6) denoted as AuXn (n = 4 and 6) has been explored at density functional theory (DFT) level. With increasing electron affinity (EA) of superhalogen, its capability to oxidize molecules with higher ionization potential also increases. We have demonstrated that this competition between the electron-binding energy of the superhalogen system and the ionization potential (IP) of the molecule with which the superhalogen combines is a key factor to predict the stability and nature of the formed complex. Binding energies have been evaluated to predict the stability of the formed complexes. The charge flow between Y and AuXn and localization of spin density distribution on the Y molecules have been estimated to verify the nature of interaction between the two. Atom in molecule (AIM) analysis has been performed to predict the nature of the bonds formed between the two interacting species. Overall, our study gives a comprehensive idea about the nature and stability of the complexes formed when moderately reactive (or inert) molecules interact with superhalogens containing coinage metal. [ABSTRACT FROM AUTHOR]

The role of Ti(II) sandwich complex, [Cp2Ti], generated by the combination of [Cp2TiCl2] and two equivalents of nBuLi, in situ, in toluene has been investigated theoretically for the release of H2 from a series of liquid organic hydrogen carriers (LOHCs), mainly alcohols or diols of low molecular weights. The compounds with hydroxyl functionality considered here are methanol, ethanol, isopropanol, methanediol, and ethylene glycol. Satisfactory results have also been obtained on applying the same mechanism to two other compounds with amino functionality, viz., methanediamine and ethylene diamine. The exploration has been carried out using density functional theory (DFT). Our findings reveal that the reaction is initiated with the formation of an adduct of the Ti center of sandwich complex, [Cp2Ti], with O/N atom of the compound under investigation. From the adduct thus formed, H2-release is possible via two routes. In one of the paths, O/N–H bond breaks first, followed by the cleavage of C–H bond, and in the other path, C–H bond breaking takes place prior to the scission of O/N–H bond. Our results show that the second path is thermodynamically and kinetically more preferable for the release of H2. Thus, [Cp2Ti] can be highly effective in releasing one equivalent of H2 from alcohols and compounds with amino functionalities, and more importantly, removal of two equivalents of H2 from methanediol is possible using [Cp2Ti], which is significant in terms of hydrogen storage purpose. [ABSTRACT FROM AUTHOR]

• Ester synthesis from primary alcohol. • (PNP)Ru pincer complex acts as effective catalyst. • Investigation of thermal and kinetic feasibility by DFT. • Involves release of two equivalent of hydrogen. • Comparative study with isoelectronic (PNP)Os and (PNP)Rh+pincer complex. Mechanistic pathway of (PNP)Ru {PNP = bis[(2- dimethylphosphino)- ethyl ]amine} mediated synthesis of an ester (2-methoxyethyl-2-methoxyacetate) from two equivalent of a primary alcohol (3-oxabutanol) is investigated using density functional theory. A ten-stage catalytic cycle is proposed. The key steps of this process is broadly described as the oxidation of first equivalent of primary alcohol into aldehyde with the elimination of H 2 molecule, coupling of the aldehyde with second equivalent of alcohol to form an ester followed by the regeneration of the pincer catalyst with the liberation of second H 2 molecule. Two isoelectronic pincer complexes (PNP)Os and (PNP)Rh+ are also considered to shed light on the variation of the energetics. Prior to H 2 elimination, a η2-bonded metal-dihydride complex is obtained for (PNP)Ru and (PNP)Rh+, whereas pure Os-H bonds are observed in case of (PNP)Os. Theoretical catalytic efficiency and TOF values infer that (PNP)Ru is the best amongst the three pincer complexes considered here. [Display omitted] [ABSTRACT FROM AUTHOR]

Tautomerizations of biologically and medicinally important heterocyclic compound, 2,5-pyrrolidinedione, commonly known as succinimide and two of its analogous compounds, 2,4-pyrrolidinedione and 3,4-pyrrolidinedione have been investigated at the density functional theory (DFT)/M06-2X level in aqueous medium, implementing polarizable continuum model (PCM). We have extended our investigation of tautomerism to the sulfur analogues of the aforementioned compounds also, i.e., 2,5-pyrrolidinedithione, 2,4-pyrrolidinedithione, and 3,4-pyrrolidinedithione. Tautomerism observed in these compounds are mainly keto-enol, thio-thiol and amine-imine, but we have detected two new kind of tautomerization shown by some of the abovementioned compounds, named as keto-epoxy (for the oxygen analogue) and thio-thioepoxy (for the sulfur analogue) which have not yet been reported in the literature. Relative energies (Er) and activation energies (Ea) have been calculated for all the tautomers and tautomerization processes. The potential energy surfaces (PESs) have been constructed using the M06-2X energy values. It has been observed that the energy difference found in the tautomers of sulfur analogues is relatively lower than that of the corresponding oxygen analogues, so does the activation energy barrier. As one-electron redox properties play an important role in biological systems, we have also explored the effect of conformational changes on the overall redox properties of the said compounds by calculating the adiabatic and vertical ionization potentials (AIPs and VIPs, respectively) and adiabatic electron affinities (AEAs). [ABSTRACT FROM AUTHOR]

The stabilization of non-IPR fullerenes for their isolation and characterization is an area of recent interest. In the present study, we have explored the stabilization techniques of C 72 isomers via endo and exo-modifications and finally approached dual modification. A total of four isomers of C 72 have been considered in this study; among them, one is IPR derivative (1), and the rest are non-IPR derivatives with one (2) and two (3 and 4) fused pentagon rings. First, we have studied the endohedral modification by encapsulating one and two La atoms in the C 72 cavity. Secondly, we have exohedrally modified the C 72 isomers via chlorination by adding four and eight chlorides, respectively. Our final approach is to study the dual modification, where we have implemented both endo exo-modifications together. This dual modification can be achieved in two ways: exo followed by endo and endo followed by exo. For each modification, the relative stability of every modified C 72 derivative has been checked by calculating the relative energy with respect to the most stable modified analogue. To find out whether these modifications are energetically feasible or not, we have calculated the binding energy of each modified C 72 isomer. The binding energy calculation reveals that the encapsulation and exo-modification techniques are good enough to stabilize the non-IPR C 72 derivatives. Moreover, the effectiveness of dual modification has also been established from the enhanced binding energy compared to either endo- or exo-modification. We have also studied the NPA charges on the encapsulated La atoms for each endo- and dual-modified C 72 derivative. Furthermore, the AIM study has also been perceived to find out the interaction between the La atom and the fullerene cages for both mono- and di-encapsulated fullerene derivatives and also between La–La centres for di-encapsulated derivatives. Overall, the present theoretical study will provide an idea about the stability of the modified C 72 derivatives, which will help the experimentalists to design new strategies for synthesizing modified non-IPR fullerene derivatives that have vast applications in the medicinal and industrial fields. [Display omitted] • The stabilization techniques of Non-IPR C 72 isomers have been discussed in the light of DFT. • Both endo- and exo-modifications have been considered separately before going into the dual modification approach. • The thermodynamic feasibility of these modifications has been checked by binding energy calculations. • Enhanced binding energy has predicted effectiveness of dual modification compared to each modification in separation. • The present study will be helpful for experimentalists to design modified non-IPR fullerene derivatives. [ABSTRACT FROM AUTHOR]

Using the first-principles density functional theory approach, a detailed gas phase dehydrogenation analysis has been carried out for the monomeric as well as the dimeric units of lithium hydrazinidoborane (LiN 2 H 3 BH 3 ). Atoms in molecules formalism (AIM) has been employed in order to get bonding features along the desired reaction pathways. The exploration of potential energy surfaces from different structural isomers of both monomeric and dimeric hydrazinidoborane (LiHB) suggests that all the dehydrogenation reactions are endothermic in nature. Hydrogen generation from the dimeric lithium hydrazinidoborane provides an idea about the effect of neighbouring molecules on the dehydrogenation process occurring in the solid state. The lithium ion plays the central role in transferring the hydride in the dehydrogenation of both the monomeric and dimeric form of hydrazinidoborane. In summary our theoretical calculations are expected to shed light on the decomposition mechanism of alkali metal substituted hydrazine-borane type of compounds. [ABSTRACT FROM AUTHOR]

Agostic interactions have been investigated through NBO analysis tuning each part of H2LMMZCHR2 by varying metal centre and intramolecular groups in different positions of the molecule. We have calculated the energy transfer phenomena between donor and acceptor orbitals associated with the agostic bond by second-order perturbation analysis and characterized the acceptor orbitals for whether it is a vacant metal lone pair or molecular orbital associated with both metal and ligand. The investigation of agostic phenomenon by altering the orientation of the metal-associated ligand is another aspect of this work to reveal the orientation effect as one of the controlling factors of the agostic interaction. We have further studied the impact of agostic interaction on the two well-recognized reaction processes, namely β-hydride elimination and dehydrogenation for all the d0 systems under investigation. Both the reactions are found to be facilitated by agostic interaction, where the nature of agostic hydrogen varies from reaction to reaction. The complete work furnishes both characterization and reaction pathways to portray agostic phenomena by interconnecting the molecular geometry with the reaction processes. [ABSTRACT FROM AUTHOR]

We have determined the electronic, thermodynamic and geometrical properties of Lin@Cx fullerenes by employing DFT study, which are better known as endohedral metallofullerenes (EMFs). In this work, we have considered C20, C32, C42 and C60 fullerenes and predicted the maximum number of Li atoms that can be encapsulated in their respective cavities. The identification of the geometrical structures of Lin clusters formed inside the fullerene cavity has been also included in our study. The binding energies as well as the thermodynamic properties (enthalpy, entropy and Gibbs free energy) of each EMF have been determined to acquire an idea about the stability of the EMFs. Further to ensure the stability of the EMFs, we have also calculated the deformation energy of the EMFs with respect to normal C60. By analyzing the results obtained from our calculation, we have shown that our results are in reasonably good agreement with the earlier available theoretical results. We have also performed the NPA analysis to calculate the charges on both the fullerene surface and the encapsulated Lin clusters for each Lin@Cx and further investigated its variation with respect to n and x. Energy transfer phenomena from MO C - C → LP Li ∗ have been observed by employing second-order perturbation analysis. Overall, the work has provided a comprehensive idea about the characteristics and stability of all the Lin@Cx-type EMFs which can be set as a benchmark for further work on the EMFs. [ABSTRACT FROM AUTHOR]

We have theoretically explored the entire binding phenomena of d-penicillamine and its O- and Se-analogues with Cu2+ in both gas and aqueous phases. At first, a brief conformational analysis has been performed via −XH and −COOH rotations to investigate such conformers that are suitable for binding in both bidentate as well as tridentate fashions. The stability of each bidentate and tridentate complex is determined on the basis of relative energy (ΔE) and gas phase metal ion affinity (MIA) along with the bonding analysis by using atoms in molecule theory. The effect of conformational change on the stability of the complexes is also examined thoroughly. By analyzing the MIA values, we have shown that the side chain substitution makes an impact on the binding process. To delve into the binding phenomena in aqueous phase, we have introduced both the first and second hydration sphere models. In first hydration sphere model, to realize the precise effect of water molecules we have considered stable octahedral hexa-aqua copper complex, [Cu(H2O)6]+2 and accordingly substituted water molecules depending on the bidentate or tridentate nature of the chelating agents. The influence of bulk water molecules on the energetics and geometries of the first hydrated sphere complexes have also been investigated by employing second hydration sphere model assuming physiological pH through the implementation of implicit COSMO and polarizable continuum models, respectively. In the second hydration sphere model, the zwitterionic structures of the amino acids and their side chain deprotonated forms are also included to study the binding phenomena with Cu2+. The complete work furnishes both the binding properties and the energetics of the copper-artificial amino acid complexes in both gas and aqueous phases that will reflect a realistic overview of the entire binding phenomena. [ABSTRACT FROM AUTHOR]

A detailedmechanistic investigation of Si–Me formationover the silicon (100)-2 × 1 surface using the Si9H12cluster model has been performed using various reagents,based on two basic mechanisms: dissociation and substitution. Thereagents CH4, CH3Cl for dissociation and CH3Li, CH3MgBr for substitution mechanism are usedto explore the methylation process on the silicon surface at the M062X/6-311+G(2d,p) level of theory. The associated potential energy surfaces exploredhere are aimed to unveil the most favored pathway of methylation withappropriate reagents. Dissociation of methane forms a monomethylatedproduct (D1) through an energetically unfavorable pathway. All theadsorption modes of CH3Cl over the silicon surface arealso detected and analyzed. Methyl chloride dissociates to form anothermonomethylated product D2 and its derivative D3 in the entrance channel,while, in the next step, bridged compounds I1 (Cl-bridged) and I2(H-bridged) are produced from them, respectively. The C–Cldissociation leads to the formation of D2 having a lower activationbarrier. With a comparably high activation barrier in the C–Hdissociation, producing D3, very interestingly carbene intermediatehas been detected in the reaction pathway. Detection of energeticallyunfavored conversions from D2 to I1 and D3 to I2 ensured that themethylation process will not be hampered through these interconversions.For substitution, HCl- and Cl2-passivated Si surfaces aretaken, where chlorine is to be substituted by the methyl group ofboth of the methylating agents. With both substituents, HCl-passivatedSi9H12gives D1. The substitution process onCl2-passivated Si9H12leads to theformation of D2 in the first step and dimethylated product (S1) inthe final step. In all the above substitution processes, methyl lithiumproved to be the better substituent for the formations of D1, D2,and S1 on HCl- or Cl2-passivated surfaces. The presentwork not only demonstrated methyl lithium as one of the best methylatingagents but also revealed the interrelation among the dissociativeadsorption modes of CH3Cl, reported earlier, in a singlepotential energy surface with a remarkable detection of carbene intermediateformed in the pathway of C–H dissociation. [ABSTRACT FROM AUTHOR]

A gas phase mechanistic investigation of the chemical vapor deposition (CVD) of titanium nitride (TiN) from the decomposition of Ti(NMe2)4, tetrakis(dimethylamido)titanium (TDMAT) as a single source precursor as well as from the reaction of Ti(NMe2)4 with NH3, i.e., the ammonia assisted mechanism is carried out and reported herein within the framework of density functional theory. Contrary to the theoretical result reported previously for a model TDMAT, metallacycle formation and β-H elimination pathways are found to be the major decomposition pathways responsible for the decomposition of TDMAT, and this finding is in accord with the experimental observation. Interestingly, agostic interaction is found to play a key role in promoting β-H elimination in the decomposition of TDMAT. A new additional pathway of decomposition of TDMAT has been identified theoretically in this present study. Exploration of the complex gas phase mechanism and thereby a detailed identification of the reaction intermediates enable us in realizing the origin of incorporation of carbon contamination in TiN films produced from TDMAT alone and then how the contamination is removed in the presence of ammonia. The ammonia assisted mechanism is found to proceed through the formation of a pre-equilibrium complex. The computed barrier height of 7.3 kcal mol-1 for the initial transamination process associated with the Ti(NMe2)4 + NH3 reaction is found to be in very good agreement with the experimental activation energy. The total rate constant ktot for the ammonia assisted mechanism is calculated to be 1.28 × 10-51 cm³ molecule-1 s-1 at 298.15 K. [ABSTRACT FROM AUTHOR]

The interaction between the metal cations and H2molecule has been investigated using dispersion-corrected and -uncorrected hybrid density functional and CCSD(T) methods in conjunction with the correlation consistent triple-ζ quality basis sets for the storage of the H2molecule. The molecular properties, potential energy surfaces, stability, binding energy and well-depth have been computed for the metal cation–dihydrogen (M+–H2, M = Mg, Ca, and Ag) complexes in the gas phase. The results obtained by the dispersion-corrected hybrid density functional B2PLYP-D method agree very well with the earlier experimental and theoretical results wherever available. Different components of the interaction energy have been estimated by the symmetry adapted perturbation theory (SAPT) to get physical insight into the interaction energy. Among the three complexes, only Ag+–H2is the most stable complex and it accumulates more H2molecules as the interaction between the metal cation Ag+and the H2molecule is the greatest. [ABSTRACT FROM PUBLISHER]

The binding properties of a series of benzenesulfonamide inhibitors (4-substituted-ureido-benzenesulfonamides, UBSAs) of human carbonic anhydrase II (hCA II) enzyme with active site residues have been studied using a hybrid quantum mechanical/molecular mechanical (QM/MM) model. To account for the important docking interactions between the UBSAs ligand and hCA II enzyme, a molecular docking program AutoDock Vina is used. The molecular docking results obtained by AutoDock Vina revealed that the docked conformer has root mean square deviation value less than 1.50 Å compared to X-ray crystal structures. The inhibitory activity of UBSA ligands against hCA II is found to be in good agreement with the experimental results. The thermodynamic parameters for inhibitor binding show that hydrogen bonding, hydrophilic, and hydrophobic interactions play a major role in explaining the diverse inhibitory range of these derivatives. Additionally, natural bond orbital analysis is performed to characterize the ligand-metal charge transfer stability. The insights gained from this study have great potential to design new hCA-II inhibitor, 4-[3-(1-p-Tolyl-4-trifluoromethyl-1H-pyrazol-3-yl)-ureido]-benzenesulfonamide, which belongs to the family of UBSA inhibitors and shows similar type of inhibitor potency with hCA II. This work also reveals that a QM/MM model and molecular docking method are computationally feasible and accurate for studying substrate-protein inhibition. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Vinyl acetate [VA (CH3COOC2H3)]is an important unsaturated and oxygenated volatile organic compoundresponsible for atmospheric pollution. In this work, possible reactionmechanisms for the degradation of OH-initiated atmospheric oxidationof VA are investigated. The potential energy surfaces (PESs) for thereaction of OH radical with VA in the presence of O2andNO have been studied using the M06-2X/6-311++G(d,p) method. The initialaddition reactions of more and less substituted ethylenic C-atomsof VA are treated separately, followed by a conventional transitionstate theory (TST) calculation for reaction rates. The direct H-abstractionmechanism and kinetics have also been studied. The initial OH additionoccurs through a prereactive complex, and the calculated rate constantsin the temperature range 250–350 K for both the addition reactionsare found to have negative temperature dependence. The calculationindicates that the reaction proceeds predominantly via the additionof OH radical to the double bond rather than the direct abstractionof H-atoms in VA. IM1 [CH3C(O)O•CHCH2OH] and IM2 [CH3C(O)OCH(OH)•CH2], the OH adduct complexes formed initially, react with ubiquitousO2followed by NO before their rearrangement. The formationof the prereactive complex plays an important role in reaction mechanismand kinetics. The calculated rate constant, k298K= 1.61 × 10–11cm3molecule–1s–1, is well harmonized with theprevious experimental data, k298K= (2.48± 0.61) × 10–11cm3molecule–1s–1(Blanco et al.) and k298K= (2.3 ± 0.3) × 10–11cm3molecule–1s–1(Picquet-Varrult et al.). Additionally, consistent and reliableenthalpies of formation at 298.15 K (ΔfH°298.15) have been computed for all the species involvedin the title reaction using the composite CBS–QB3 method. Thetheoretical results confirm that the major products are formic aceticanhydride, acetic acid, and formaldehyde in the OH-initiated oxidationof VA in the presence of O2and NO, which are in excellentagreement with the experimental findings. [ABSTRACT FROM AUTHOR]