Search

The electrochemical reduction of CO2 on single atom catalysts (SAC) has emerged as a highly promising yet intricate process, requiring an in-depth understanding of each elementary step of the reaction. Most of the theoretical studies pertaining the screening of new efficient catalysts neglect important effects such as the capability of the catalytic site to bind and activate CO2, the occurrence of competing reaction paths via formation of different isomers in the intermediate steps, and the role of water. In this work we will show that these are key aspects of the CO2 reduction reaction (CO2RR). Employing density functional theory, we investigated a series of Transition Metal atoms (Sc-Cu, Mo-Ag, W-Au) embedded in nitrogen doped graphene (TM@4N-Gr) and their activity in the CO2 reduction. Our results show that water is not only solvating the reaction intermediates, but it acts as a ligand itself, competing with CO2 when binding to the catalytic site. This coordination chemistry effect largely affects the stability of the chemical intermediates. Furthermore, only a small fraction of the investigated SACs can bind and activate CO2, and that in most cases the reaction proceeds via formation of the OCHO intermediate and not of the COOH one, as often assumed.

The influence of solvents on intramolecular interactions in 5- or 6-substituted nitro and amino derivatives of six tautomeric forms of uracil was investigated. For this purpose, the density functional theory (B97-D3/aug-cc-pVDZ) calculations were performed in ten environments (1 > ε > 109) using the polarizable continuum model (PCM) of solvation. The substituents were characterized by electronic (charge of the substituent active region, cSAR) and geometric parameters. Intramolecular interactions between non-covalently bonded atoms were investigated using the theory of atoms in molecules (AIM) and the non-covalent interaction index (NCI) method, which allowed discussion of possible interactions between the substituents and N/NH endocyclic as well as =O/−OH exocyclic groups. The nitro group was more electron-withdrawing in the 5 than in the 6 position, while the opposite effect was observed in the case of electron donation of the amino group. These properties of both groups were enhanced in polar solvents; the enhancement depended on the ortho interactions. Substitution or solvation did not change tautomeric preferences of uracil significantly. However, the formation of a strong NO∙∙∙HO intramolecular hydrogen bond in the 5-NO2 derivative stabilized the dienol tautomer from +17.9 (unsubstituted) to +5.4 kcal/mol (substituted, energy relative to the most stable diketo tautomer).

A model complex of dysprosium, Dy(N2O2C7H11)3 (Dy2) was built by successive capping of the peripheral aromatic ring of a butterfly-shaped dysprosium complex of a schiff base ligand, Dy(N4O5C14H11)3 (Dy1). The structural modifications were carried out in order to investigate the effect of the chemical surroundings like aromaticity on the observation of single-molecule magnet (SMM) behaviour in a lanthanide-based complex (Dy1). Experimental techniques were combined with theoretical tools to investigate the dynamics of magnetic properties of the Dy1 and compared with the theoretical results for Dy2 to gain insight on the contribution of covalency, crystal field effect and the role of aromaticity in stabilizing the excited magnetic levels of a single-molecule magnet. Dy1 showed frequency-dependent slow magnetic relaxation characteristics of a single-molecule magnet with and without applied dc field and a blocking temperature of about 8 K. The obtained results showed that despite f−electrons having weak interactions with ligand field, it is possible to tune the magnetic properties of lanthanide-based complexes using ring currents, control of covalency and peripheral ligand substitution. Furthermore, di-nuclear acetate bridged lanthanide complexes with two different structural motifs, Er1 = [Er(CH3COO)(CH3COO)2(H2O)2]2 · 4H2O and [Ln(CH3COO)(CH3COO)(CH3COO)(H2O)CH3COOH]2 · 2CH3COOH (Ln = Er (Er2), Y0.8Er0.2 (Er3)) were characterised. The solvent effects on the structure, electronic and magnetic properties were studied by experiments and theoretical methods. The tetraacetate-bridged erbium (Er2) showed a shorter intra-molecular Er – Er distance of 3.878 Å compared to the doubly-bridged counterpart (Er1) with Er – Er intra-molecular separation of 4.152 Å. Er2 exhibited weak ferromagnetic ordering at very low temperature in the dc magnetic measurement due to the short proximity of the Er centres. A field-induced slow magnetic relaxation for spin reversal characteristics of single-molecule magnet behaviour with relaxation dynamics dominated by Orbach process was observed for Er2. Er1 showed very fast slow magnetic relaxation dominated by quantum tunnelling of magnetization as evidenced in the Cole-Cole plot and the observed plateau in the susceptibility curve. The role of inter-molecular interactions between Er centres was investigated using yttrium diluted sample (Er3). The enhanced magnetic property of Er2 and Er3 over Er1 is attributed to the structural changes accompanying the choice of synthetic solvents used as well as the stronger interactions between Er and oxygen donor atoms of the acetate/acetic acid over that of water molecule as ligands. The present study presents an interesting result on solvent effects in the design of single-molecule magnets. In addition to the peripheral, aromatic, solvent effect and accompanying lanthanide-lanthanide coupling investigated, the role of hetero-metallic Pd-Ln bonding interaction was investigated using a set of tetranuclear acetate-bridged palladium-lanthanide complexes of the formula [Pd2Ln2(H2O)2(AcO)10] · 2AcOH (AcO = CH3COO– , Ln = Ce, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm and Yb) by theoretical means and compared with experimental results for the lanthanide series to establish an interesting alternating trend in the observation of slow magnetic relaxation between Kramers and non-Kramers ions along the series. The role of axial perturbation, electron-cloud distortion and utility of metal as a ligand to upset the electronic properties of lanthanide complexes and their implication to the observation of slow magnetic relaxation were investigated. Results showed that transition metal–lanthanide bonding interaction presents a unique way to control the ligand field of lanthanide at varying degrees while confirming the role of rigidity in SMM design., Cambridge Trust, Cambridge- Africa, IsDB

In this study, hexane and ethanol were used separately as solvent in the extraction of different part of fresh fruit of Cucurbita pepo L. For each solvent, total phenolic content, total flavonoid content, total flavanol content and antioxidant activity in skin, pulp and whole fruit extract were investigated using invitro assays. The results showed that skin part is the rich one en compounds and ethanol is the best solvent for the extraction of total phenolics (231.16 mgGAE/g), total flavonoids (8,4 mgRE/g) and total flavanols (4,16 mgQE/g). For evaluation of antioxidant activity, using DPPH• radical scavenging and total antioxidant activity, skin extract obtained by ethanol showed the highest value respectively (IC50= 0,42 mg/mL) and (19,72 mg/g). The superoxide scavenging assay of ethanol extract of whole fruit and skin showed the highest value respectively (IC50= 0,015 mg/ml) and (0.016 mg/ml).

Hierarchical helicates based on ketone‐substituted titanium(IV)triscatecholates show different monomer‐dimer behavior depending on different solvents. The dimerization constants of a whole series of differently alkyl‐substituted complexes is analyzed to show that the solvent has a very strong influence on the dimerization. Hereby, effects like solvophobicity/philicity, sterics, electronics of the substituents and weak side‐chain—side‐chain interactions seem to act in concert., The behavior of the monomer–dimer equilibrium of hierarchical helicates formed from keto‐catechol ligands strongly depends on the solvent that is used. Based on the respective solvents, different side‐chain—side‐chain interaction modes such as sterics, solvophobicity/philicity and probably even London dispersion become highly influential for the stabilization or destabilization of the dimers.

Bu çalışmada, çeşitli aromatik aminler ile hazırlanan diazonyum tuzlarının, 2-(4-metilfenil)-1H-indol ve 2-(4-klorfenil)-1H-indol bileşikleri ile azo kenetlenmesi sonucu, bir dizi yeni hetarilazo indol boyası sentezlendi. Hazırlanan boyarmaddelerin, Mitsunobu reaksiyonu ile N-pozisyonundan izopropil alkol ile alkillenmesi sonucu N-sübstitue indol türevlerinin sentezi gerçekleştirildi. Sentezlenen bileşiklerin kimyasal yapıları, NMR, FT-IR, UV-vis, kütle spektrometresi ve elementel analiz ile aydınlatıldı. Elde edilen boyarmaddelerin fotofiziksel özelliklerini belirlemek için, farklı polariteye sahip çözücüler içerisinde görünür bölge absorpsiyon spektrumları incelendi. Ek olarak, asit ve baz ilavesinin absorpsiyon maksimumları üzerine etkileri ayrıntılı olarak incelendi., In this study, as a result of azo coupling of diazonium salts prepared with various aromatic amines with 2-(4-methylphenyl)-1H-indole and 2-(4-chlorophenyl)-1H-indole compounds, a series of new hetarylazo indole dyes were synthesized. N-substituted indole derivatives were synthesized by alkylation of the prepared dyes with the isopropyl alcohol from the N-position by Mitsunobu reaction. The chemical structures of the synthesized compounds were determined by NMR, FT-IR, UV-vis, mass spectrometry and elemental analysis. In order to determine the photophysical properties of the dyes obtained, visible region absorption spectra were examined in solvents of different polarity. In addition, the behavior of acid and base addition on absorption maxima were examined in detail.

The different activity of a 1% Pd/carbon catalyst towards aromatic and aliphatic aldehydes hydrogenation has been explored by 13C NMR relaxation. The ratio between T1 relaxation times of adsorbed (ads) and free diffusing (bulk) molecules (T1ads/T1bulk) can be used as an indicator of the relative strength of interaction between the reactant and the catalytic surface, where the lower the T1ads/T1bulk, the higher the adsorption strength. It can be seen that 1% Pd/carbon showed a reverse catalytic behaviour towards benzaldehyde and octanal hydrogenation, which can be explained by analysing the T1 relaxation times related to each substrate in the presence of the catalyst. Comparing and correlating the different T1ads/T1bulk values, we were able to prove that the different catalytic results mainly depend on the contrasting adsorption behaviour of substrates on the catalyst. Moreover, the role of the solvent has been disclosed, as NMR results revealed that the adsorption of the reactants was strongly affected by the choice of solvent, which is revealed to be critical in modulating catalytic activity. As a consequence, T1ads/T1bulk measurements can provide a guide to the selection of appropriate reaction conditions for improving catalytic activity.

A combination of transient methods in a laboratory-scale trickle bed reactor and attenuated total reflection (ATR)-infrared spectroscopy was applied to gain insight into the reaction mechanism of the direct synthesis of hydrogen peroxide (DSHP) on a commercial 5 %Pd/C catalyst, with water and methanol used as solvents. During the transient studies, after the switch from water to methanol, an oscillatory pattern was observed in which methoxy and hydroxymethyl species were observed prior to the peroxide species. From the specific position and the maxima in the intensities of these species over time, an augmented reaction scheme for the DSHP in methanol was proposed, in which methanol can form hydroxymethyl species which act as co-catalysts to reduce absorbed oxygen species.

In this work, 242 NMR spin-spin coupling constants (SSCC) in 20 molecules have been calculated either with correlated wave-function methods, SOPPA and HRPA(D), or with density functional theory based on the B3LYP, BHandH, or PBE0 functionals. The calculations were carried out with and without treatment of solvation via a polarizable continuum model in both the geometry optimization step and/or the SSCC calculation, and thereby four series of calculations have been considered (the full-vacuum calculation, the full-solvent calculation, and the two cross combinations). The results were compared with the experimental results measured in a solvent. With the goal of reproducing experimental values, we find that the performance of the PBE0 and BHandH SSCCs improves upon including solvation effects. On the other hand, the quality of the B3LYP SSCCs worsens with the inclusion of solvation. The performance of the SOPPA and HRPA(D) calculations was almost not affected by whether solvation was included. We find the PBE0-based calculations of the spin-spin coupling constants to have the best agreement with the experimental data.

Amino derivatives of purine (2-, 6-, 8-, and N-NH2) have found many applications in biochemistry. This paper presents the results of a systematic computational study of the substituent and solvent effects in these systems. The issues considered are the electron-donating properties of NH2, its geometry, π-electron delocalization in purine rings and tautomeric stability. Calculations were performed in ten environments, with 1 < ε < 109, using the polarizable continuum model of solvation. Electron-donating properties were quantitatively described by cSAR (charge of the substituent active region) parameter and π-electron delocalization by using the HOMA (harmonic oscillator model of aromaticity) index. In aminopurines, NH2 proximity interactions depend on its position and the tautomer. The results show that they are the main factor determining how solvation affects the electron-donating strength and geometry of NH2. Proximity with the NH∙∙∙HN repulsive interaction between the NH2 and endocyclic NH group results in stronger solvent effects than the proximity with two attractive NH∙∙∙N interactions. The effect of amino and nitro (previously studied) substitution on aromaticity was compared; these two groups have, in most cases, the opposite effect, with the largest being in N1H and N3H purine tautomers. The amino group has a smaller effect on the tautomeric preferences of purine than the nitro group. Only in 8-aminopurine do tautomeric preferences change: N7H is more stable than N9H in H2O.

Small molecule thin films are the core of some organic optoelectronic devices. Their deposition by solution processes is an advantage for device fabrication and can be achieved via spin coating for small areas and slot-die or doctor blade for larger areas. Solution deposition of small molecule thin films is usually processed only with medium polarity solvents. Herein, the use and influence of solvents with several polarities and physicochemical properties to form small-molecule homogeneous thin films via the doctor blade technique over an area of 25 cm2 have been explored. Solvents with different polarity, heptane, chlorobenzene, N,N-dimethylformamide, acetonitrile, and methanol were used along with different deposition temperatures, from room temperature up to near the boiling temperature for each solvent. With heptane and chlorobenzene, smooth films with an average roughness of 3 nm and thickness of 100–120 nm were obtained. The film was homogeneous over the whole substrate for temperatures from room temperature to close to the boiling temperature of both solvents. On the other hand, with dimethylformamide, a film is observed when the deposition is conducted only at room temperature; when the deposition temperature increases, the formation of agglomerates of several sizes from 1 to 5 nm was observed. With acetonitrile, and methanol, no films were formed, and only nanoaggregates were created on the substrate due to the solvent high vapor pressure, and the agglomerate size depends on the deposition temperature. The measure of the contact angle of pure solvent and solutions indicated that wettability helps to film formation over the whole substrate. For heptane and chlorobenzene, a small angle was measured; meanwhile, the contact angle is large in acetonitrile leading to the formation of nanoaggregates. In the case of methanol solution, although it wets very well, no film is deposited because it has high volatility.

The role of solvents is crucial in catalyst preparation. With regard to catalysts prepared with activated carbon (AC) as the carrier, when water is used as a solvent it is difficult for the solution to infiltrate the AC. Because AC comprises a large number of C atoms and is a nonpolar material, it is more effective for the adsorption of nonpolar substances. Since the water and active ingredients are polar, they cannot easily infiltrate AC. In this study, the dispersion of the active component was significantly improved by optimizing the solvent, and the particle size of the active component was reduced from 33.08 nm to 15.30 nm. The specific surface area of the catalyst is significantly increased, by 10%, reaching 991.49 m2/g. Under the same reaction conditions, the conversion of acetic acid by the catalyst prepared with the mixed solvent was maintained at approximately 65%, which was 22% higher than that obtained using the catalyst prepared with water as the solvent.

More than 85% yield of (E)-1,2,3-triphenylprop-2-en-1-ones were synthesized using disodium hydrogen phosphate (Na2HPO4) catalyzed ultrasound assisted aldol condensation of 1,2-diphenylethanone and various substituted benzaldehydes. Synthesized (E)-1,2,3-triphenylprop-2-en-1-ones were examined by their spectroscopic data, yield, micro analysis and physical constants. The effect of solvent on the yield was investigated. The pharmacological effects such as antibacterial and antifungal activities of synthesized enones were evaluated with Bauer-Kirby disc diffusion method.

Levulinic acid derived from biomass is a versatile platform molecule, which can be used in manufacturing different compounds to replace fossil-based chemicals. In this study, the effect of sulfolane as solvent in sulphuric acid catalysed levulinic acid production from glucose was investigated. The broad sulfolane concentration range was systematically studied and a kinetic model was developed to describe the levulinic acid production. A significant increase in glucose conversion rate was observed when the proportion of sulfolane in the solvent mixture was increased. The maximum selectivity of the levulinic acid production was found to be slightly over 50% and independent of the solvent composition. Thus, with sulfolane solvent, the same yields can be obtained in a significantly shorter time or at a lower temperature as when water is used as solvent. Sulfolane was also found to keep the generated by-products in soluble form. This will decrease fouling of the process equipment, which has been a major issue in designing of levulinic acid production processes.

Solvent selection is key in extractive distillation process development and solvent effects are often predicted based on the activity coefficients at infinite dilution. For close-boiling polar systems with strong or specific interacting species, standard simulation tools, e.g. using UNIFAC or COSMO-RS, often predict poor as the activity coefficients at infinite dilution not always reflect the selectivity in the process. For these systems, a heuristic solvent selection method in which molecular properties such as acidity, hydrogen bonding and polarity are applied is desired as first estimate in the solvent selection. To explore the key parameters for such a first selection, solvent effects on the relative volatility ( α ) were measured for three different industrially relevant polar mixtures, valeric acid – 2-methylbutyric acid, diethylmethylamine – diisopropylether, and 2-butanol – 2-butanone. For each of the cases the effect of potential solvents on α was measured in an ebulliometer. For the acids, the difference in p K a of 0.1 was too small to separate based on acidity with a moderately basic solvent. Stronger basic solvents resulted in thermal and chemical instability. Although the solvent methyl-2-methyl butyrate is not suitable as a solvent because of reactivity, this structurally similar solvent showed selectivity, indicating also in extractive distillation the like dissolves like phenomenon can be applied to induce selectivity. A larger difference in basicity of the mixture components (amine–ether mixture) and a difference in hydrogen bonding affinity between the mixture components (ketone–alcohol mixture) allowed for increasing α based on differences in acidity and hydrogen bonding, respectively.

Fabrication of surfactant-modified DNA thin films with high uniformity, specifically DNA–CTMA, has been well considered via drop-casting and spin-coating techniques. However, the fabrication of thin films with pure DNA has not been sufficiently studied. We characterize the uniformity of thin films from aqueous salmon DNA solutions mixed with ethanol, methanol, isopropanol, and acetone. Measurements of thickness and macroscopic uniformity are made via a focused-beam ellipsometer. We discuss important parameters for optimum uniformity and note what the effects of solvent modifications are. We find that methanol- and ethanol-added solutions provide optimal fabrication methods, which more consistently produce high degrees of uniformity with film thickness ranging from 20 to 200 nm adjusted by DNA concentration and the physical parameters of spin-coating methods.

In the current study, the toxic material Poly-hexamethylene biguanide hydrochloride (PHMB) has been characterized by UV–Visible and infrared spectroscopy in different solvent environments. The nature of the molecular interactions between solvent molecules and PHMB via hydrogen bonds has been investigated using the Atoms in Molecules (AIM) and non-covalent reduced density gradient (NC-RDG) analyses. Intermolecular interactions are further supported by the Natural Bond Orbital (NBO) analysis, which was carried out to provide information about the delocalization of charge and energy density of the atoms. The Osingle bondH···Cl and Nsingle bondH···Cl hydrogen bond types of interaction in solvent complexes have indicated weak hydrogen bonds. Moreover, we studied the endocrine disrupting potential of PHMB by using VirtualToxLab technology.

Herein we report the synthesis and characterization of a new series of styryl-based push-pull dyes containing a free amino group and their Schiff base derivatives. The dyes include the dicyanomethylene group as an acceptor and different para-substituted alkylamines as donors. Morever as a proton-sensitive group a pyridin-2-yl substituent was attached to the para-position of the phenyl moiety in both series of compounds. The photophysical properties of the dyes were examined in various solvents with different polarities and showed absorption in the visible region and green-red emission with low quantum yields. The absorption and the emission maxima were shifted bathocromically by increasing the solvent’s polarity. However, there was no correlation with the polarity parameters of the solvents. The pH-sensitive properties of all prepared Schiff bases were examined against TBAOH in DMSO, via deprotonation of the OH group in the salicylidene moiety and their reverse protonation was also investigated using TFA. The Schiff bases exhibited a bathochromic shift upon the addition of TBAOH to their solutions in DMSO. Therefore, they showed potential to be utilized as colorimetric and luminescence pH sensors. The second-order nonlinear optical (NLO) responses of the dyes were measured by the electric field-induced second harmonic (EFISH) generation method. The highest μβ values were obtained for the dyes bearing the julolidine donor as 1430 × 10−48 esu (for free amino derivative) and 1950 × 10−48 esu (for Schiff base derivative), respectively. The structural and electronic properties of the dyes as well as their NLO properties were further studied using DFT calculations. The thermal stabilities of all dyes were evaluated by thermogravimetric analysis (TGA). The TGA data showed that all dyes were thermally stable up to 250 °C.

Kinetics and thermodynamics of $$\alpha$$ -pinene oxide isomerization was investigated both theoretically and experimentally in different solvents in the temperature range of 50–140 °C using different zeolites, iron modified zeolites, Fe–H–MCM-41 and micro-mesoporous ZSM-5 derived catalysts. The aim was to elucidate the effect of solvent basicity and polarity on the product distribution in this reaction giving as the main value-added products campholenic aldehyde and trans-carveol, which are used as fragrances and perfumes. A generic kinetic first order model was developed composed of both parallel and consecutive routes. A thermodynamic analysis showed that product selectivity is determined by kinetic control and not by thermodynamics. Formation of campholenic aldehyde was favored in non-polar solvents, whereas basic solvents promoted formation of trans-carveol independent on temperature.

The gas phase proton affinities and basicities of a [1.1.1]‐(2, 6)‐pyridinophane and its derivatives having one ‐CH2‐ bridge replaced by ‐CH=CH‐ and ‐CH2‐CH2‐ are examined by the DFT B3LYP/6‐311+G(2df, p)//B3LYP/6‐31G(d) method. The calculated proton affinities are within the range of 253.8 and 294.8 kcal mol−1. The upper‐scale basicity is consequence of unfavorable steric interactions in neutral bases and diminishing of former in conjugate acids with forming of intramolecular hydrogen bonds (IMHB) being amplified by substitution in the para position of pyridine rings by electron‐releasing substituents. The inspection of the nature of IMHBs reveals that IMHB is of a bifurcated type with energy spanning a range between 5.7 and 7.4 kcal mol−1. The basicities of pyridinophanes are examined in acetonitrile. It is found that their pKa values span a range between 18.9 and 31.3 units.

WOS: 000428915800018, Solvent dependent structural properties of 4-carboxy phenylboronic acid (4-cpba) were investigated by X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) spectroscopic methods. The molecular structure and geometric parameters were determined by some computational methods such as B3LY P/6-31 + G(3df,p), HF/aug-cc-pvtz and MP2/6-31G(d). Detailed elucidation of the structural and spectroscopic properties of 4-cpba was carried out with H-1, HETCOR and DOSY NMR experiments. Solvent effects on the structural properties were monitored on the changes of 1H NMR spectra by using various solvents and it was observed that 4-cpba shows serious structural preferences depending on the solvent used

The past two decades have seen considerable attention given to chemical sensing due to its quick, reproducible, and accurate results. These are extensively used for the detection of cations and anions in different environmental matrices. Organic-molecule-based sensors have proved to be a great promising tool in determining target species. This communication demonstrates the use of triphenylether derivatives (L1–L4) as receptors for the sensing of cations and anions, using voltammetry as a sensing tool. The effect of the oxidative/reductive nature of the ionophores and, hence, their selectivity behavior was studied in MeCN and MeOH solvents. Three receptors (L2–L4) responded selectively towards cyanide ions following the intramolecular charge-transfer mechanism, while sensing in the case of L1 was not studied because it lacked a proper cavity size.

Accurate modeling of the solvent environment for biological molecules is crucial for computational biology and drug design. A popular approach to achieve long simulation time scales for large system sizes is to incorporate the effect of the solvent in a mean-field fashion with implicit solvent models. However, a challenge with existing implicit solvent models is that they often lack accuracy or certain physical properties compared to explicit solvent models, as the many-body effects of the neglected solvent molecules is difficult to model as a mean field. Here, we leverage machine learning (ML) and multi-scale coarse graining (CG) in order to learn implicit solvent models that can approximate the energetic and thermodynamic properties of a given explicit solvent model with arbitrary accuracy, given enough training data. Following the previous ML--CG models CGnet and CGSchnet, we introduce ISSNet, a graph neural network, to model the implicit solvent potential of mean force. ISSNet can learn from explicit solvent simulation data and be readily applied to MD simulations. We compare the solute conformational distributions under different solvation treatments for two peptide systems. The results indicate that ISSNet models can outperform widely-used generalized Born and surface area models in reproducing the thermodynamics of small protein systems with respect to explicit solvent. The success of this novel method demonstrates the potential benefit of applying machine learning methods in accurate modeling of solvent effects for in silico research and biomedical applications., 16 pages, 6 figures

An optimized spectroscopic methodology for the quantification of urea using p -dimethylaminobenzaldehyde (DMAB) as a derivatizing reagent is proposed to avoid changes in reproducibility caused by aging of acidic DMAB solutions, and the unintended use of different solvents. Four solvents; ethanol, methanol, 2-propanol and acetonitrile are evaluated. Acetonitrile has never been reported for the determination of urea with DMAB, and it is found to be the best medium for the quantification of urea due to its aprotic nature. The use of acetonitrile allows a more stable reaction system, which results in a faster urea quantification, less acid consumption and a more sensitive spectroscopic method. Taking into account that polymer matrices of chitosan are being used recently to develop controlled release fertilizers of urea, a complementary study is carried out to determine any interference by released chitosan macromolecules with different molecular mass and degree of deacetylation in the optimized system. The results show no appreciable changes in the sensitivity and accuracy of the methodology being other available application of this work.

The oxidation of seven aliphatic aldehydes by benzimidazolium fluorochromate (BIFC) in dimethyl sulphoxide (DMSO) leads to the formation of the corresponding carboxylic acids. The reaction is first order in BIFC. The Michaelis–Menten type kinetics was observed with respect to the aldehyde. The reaction is catalysed by hydrogen ions. The hydrogen-ion dependence has the form: k obs = a + b [H + ]. The oxidation of deuterated acetaldehyde, CH 3 CDO, exhibited a substantial primary kinetic isotope effect ( k H / k D = 6.05 at 303 K). Oxidation of acetaldehyde has been studied in eighteen different organic solvents. Various thermodynamic parameters are discussed along with isokinetic temperature. The solvent effect has been analysed using multi parametric equations. A mechanism involving transfer of hydride ion has been suggested. The linear isokinetic correlation implies that all the aldehydes are oxidized by the same mechanism.

Efficient fluorescence on/off switching of a dyad consisting of a photochromic diarylethene and a fluorescence dye based on excited state intramolecular proton transfer (ESIPT) was designed and demonstrated. Diarylethenes linked to (2-(2-methoxy-5-methylphenyl)benzothiazol-6-yl)- and (2-(2-hydroxy-5-methylphenyl)benzothiazol-6-yl)-9,9-dioctylfluorene moieties (1a and 2a, respectively) exhibited fluorescence on/off switching upon alternating irradiation with ultraviolet and visible light in various solvents. The fluorescence on/off contrast of 2a was found to be higher than that of 1a in n-hexane because the overlap integral between the absorption spectrum of the diarylethene closed-ring form and the fluorescence spectrum of 2a is larger than that of 1a. Diarylethene 2a exhibited green fluorescence with large Stokes shift in n-hexane, which is ascribed to the ESIPT process from the enol form to the keto form. In contrast, the fluorescence of 2a in N,N-dimethylsulfoxide (DMSO) was mainly observed as blue fluorescence from enol form, while diarylethene 1a exhibited blue fluorescence in n-hexane and DMSO. The fluorescence on/off contrast of 2a in n-hexane was higher than that in DMSO because of the difference in the spectral overlaps in n-hexane and DMSO.

Four new organoruthenium(II) compounds of 2’-hydroxychalcones, differing in the position of the chloro substituent at chalcone moiety, were prepared by solution synthesis and characterized by chemical analysis, infrared and electron spectroscopy, mass spectrometry and 1D and 2D NMR spectroscopy, as biomimetic functional models of catechol oxidase. The molecular and crystal structures of three compounds were determined by single crystal X-ray diffraction. The organometallics are neutral species having piano-stool pseudo octahedral geometry with ruthenium(II) coordinated by η6-cymene, bidentate monobasic 2’-hydroxychalcone ligand, and chloride ion. The catecholase activity of new organometallics was investigated by electron spectroscopy in three solvents at three temperatures. The kinetic measurements were done under pseudo first order conditions and vmax, kcat, KM, TON, TOF, and Ea values are determined. Compounds (1) – (4) have solvent-dependent catecholase activity with activity decreasing in order ethanol > methanol ≫ acetonitrile. The highest kcat value and the lowest activation energy were found for the reaction catalyzed by organometallic (4), having a chloro substituent at the B ring of the chalcone ligand in the para position. The kcat values of 104 h−1 and 105 h−1 order at 297 K and 307 K, respectively classify these organometallics among the best artificial functional models of catechol oxidase. The results indicate that the catechol oxidation mediated by organometallics (1) – (4) proceeds via semiquinone radical formation.

Keto-enol prototropic conversions for carbonyl compounds and phenols have been extensively studied, and many interesting review articles and even books appeared in the last 50 years. Quite a different situation takes place for derivatives of biologically active azulene, for which only scanty information on this phenomenon can be found in the literature. In this work, quantum-chemical studies have been undertaken for symmetrically and unsymmetrically substituted azulenols (constitutional isomers of naphthols). Stabilities of two enol (OH) rotamers and all possible keto (CH) tautomers have been analyzed in the gas phase {DFT(B3LYP)/6-311+G(d,p)} and also in aqueous solution {PCM(water)//DFT(B3LYP)/6-311+G(d,p)}. Contrary to naphthols, for which the keto forms can be neglected, at least one keto isomer (C1H, C2H, and/or C3H) contributes significantly to the tautomeric mixture of each azulenol to a higher degree in vacuo (non-polar environment) than in water (polar amphoteric solvent). The highest amounts of the CH forms have been found for 2- and 5-hydroxyazulenes, and the smallest ones for 1- and 6-hydroxy derivatives. The keto tautomer(s), together with the enol rotamers, can also participate in deprotonation reaction leading to a common anion and influence its acid-base properties. The strongest acidity in vacuo exhibits 6-hydroxyazulene, and the weakest one displays 1-hydroxyazulene, but all azulenols are stronger acids than phenol and naphthols. Bond length alternation in all DFT-optimized structures has been measured using the harmonic oscillator model of electron delocalization (HOMED) index. Generally, the HOMED values decrease for the keto tautomers, particularly for the ring containing the labile proton. Even for the keto tautomers possessing energetic parameters close to those of the enol isomers, the HOMED indices are low. However, some kind of parallelism exists for the keto forms between their relative energies and HOMEDs estimated for the entire molecules.

Dye-sensitized solar cells (DSSCs) that use an aqueous (40 % w/w water content) choline chloride based deep eutectic solvent as an electrolyte medium have been investigated. The joint combination of the eutectic mixture and an appropriate hydrophilic sensitizer afforded a DSSC with a power conversion efficiency comparable to that using the same electrolyte composition but with conventional, toxic, and volatile solvents as the medium, which thereby paves the way to a new generation of eco-friendly, nature-inspired, low-cost solar devices.

In the present work, the electrochemical oxidation of acid orange 7 (AO7) on a glassy carbon (GC) electrode has been investigated by cyclic voltammetry in different solvents: aqueous solvent (H2O), dimethyl sulfoxide (DMSO) and acetone (ACE), using sulfuric acid as a supporting electrolyte. The analysis of AO7 oxidation voltammograms in different solvents showed that the more donor numbers, the easier it becomes the oxidation of AO7. The experimental parameters show that the oxidation peak current of AO7 was linearly proportional to its concentration in a range from 0.04 mM to 0.2 mM. The limit of detection was estimated by gradually decreasing the concentration levels of AO7, and was found to be 6.6 μM.

WOS: 000415108300009, Eight novel 3-(4-(benzyloxy)phenyl)-5-(4-bromophenyl)-1-(4-substituted-phenyl)formazan (4a 4h) were synthesized by coupling of substituted phenylhydrazones with diazonium salts of 4-bromoaniline. The substituted phenylhydrazones, which are intermediate products, were obtained from the condensation of substituted phenylhydrazines with 4-(benzyloxy)benzaldehyde. All target compounds were characterized by using FTIR, H-1 NMR, C-13 NMR, LC-MS spectrometry, and elemental analysis. Absorption spectra of these compounds in solvents with different polarities were investigated thoroughly. Time-dependent density functional theory (TD-DFT) studies were conducted to shed light on their electronic structures, Kohn-Sham orbitals, and electronic transitions., Anadolu University Research Council, GT would like to express her deep thanks to Asst Prof Halil Berber, Faculty of Science, Department of Chemistry, Anadolu University, for his kind advice and valuable help. GT is grateful to Anadolu University Research Council for its financial support. We are indebted to the High-Performance-Computing (HPC) Linux Cluster HorUS of the University of Siegen for the computer time provided.

WOS: 000404241800005, This research deals with some antiepileptic agents that are used to treat antiepileptic seizures. Stable conformational structures corresponding to potential energy minima for each molecule are determined in the gas phase with both Hartree-Fock and density functional methods. Polarizable continuum models have been employed to assess solvent effects on the activity of global minimum structures, and each molecule has become stabilized with increasing solvent dielectric constant. To examine structure-activity relationships, electron propagator calculations of ionization energies, electron affinities, and corresponding energy gaps with the Outer Valence Green's Function (OVGF) and Partial Third Order (P3) approximations have also been performed to compare with Koopmans's Theorem results. The best correlation between logED(50) and electron affinity values, with a linear regression coefficient of 0.98 and a standard deviation of 0.19, is obtained for Koopmans's Theorem with the 6-311++g** basis set in chloroform.

A Schiff-base ligand, 4-bromo-2-[(2-hydroxy-1,1-dimethylethylimino)methyl]phenol (HL1), and its reduced analogue 4-bromo-2-[(2-hydroxy-1,1-dimethylethylamino)methyl]phenol (HL2) have been synthesized. Treatment of HL1 and HL2 with Cu(ClO4)2·6 H2O in the presence of sodium dicyanamide in MeOH and MeCN has been investigated. HL1 generates [Cu(L1)(MeOH)(dca)] (1) in MeOH (dca = dicyanamide) but [Cu2(L1)2(dca)2] (2) in MeCN. HL2 in MeOH produces [Cu4(L2)4(MeOH)2(ClO4)2] (3). On the other hand, in MeCN an interesting redox reaction is observed. CuII undergoes reduction, and [CuI(MeCN)4](ClO4) (4) is formed with concomitant oxidation of HL2 to HL1. The solvent-dependent nuclearity change (i.e, conversion of mononuclear species 1 into dinuclear species 2) has been investigated by ESI-MS, through the addition of MeCN to a methanolic solution of 1, and the origin of the conversion has been explained by means of DFT calculations. The catecholase activity of 1, 2 and 3 in MeCN and DMF has been investigated with the model substrates 3,5-di-tert-butylcatechol (3,5-DTBC), tetrachlorocatechol (TCC) and pyrocatechol (PRC). Compound 1 is inactive with all substrates, whereas 2 is active only with 3,5-DTBC in DMF. In contrast, 3 – which exists as a dinuclear species in solution, as is evident from ESI-MS – is highly active with all three substrates, especially in MeCN. The exceptionally high catalytic activity of 3 over 2 is likely to be due to the higher flexibility of the reduced Schiff-base ligand in comparison with its Schiff base analogue.

none 4 si Hydroperoxyl (HOO.) and alkylperoxyl (ROO.) radicals show a different behavior in H-atom-transfer processes. Both radicals react with an analogue of α-tocopherol (TOH), but HOO., unlike ROO., is able to regenerate TOH by a fast H-atom transfer: TO.+HOO.→TOH+O2. The kinetic solvent effect on the H-atom transfer from TOH to HOO.is much stronger than that observed for ROO.because noncovalent interactions with polar solvents (Solv⋅⋅⋅HOO.) destabilize the transition state. Cedrowski, Jakub; Litwinienko, Grzegorz; Baschieri, Andrea; Amorati, Riccardo Cedrowski, Jakub; Litwinienko, Grzegorz; Baschieri, Andrea; Amorati, Riccardo

WOS: 000399466200011, Conformers of N-methacryloyl-(L)-glutamic acid (MAGA, C9H13NO5) in the gas phase, benzene or methanol environment were searched by the density functional theory (DFT) and time-dependent DFT. Selected conformational isomers based on potential energy surface analysis were studied by considering the structural and electronic properties. B3LYP functional, and HF and MP2 levels were used with the 6-31+G(d,p), 6-311+G(3df,p) and aug-cc-pVDZ basis sets. We explored the effect of medium on the conformational preferences, UV spectra and frontier molecular orbitals of the conformers. The outcomes of this research will be useful for future studies including moieties analogous to MAGA.

WOS: 000378360000049, A new azo-chromophore group containing a hydrazine-Schiff base compound, 2-[(E)-hydrazinylidenemethyl]-6-methoxy-4-[(E)-phenyldiazenyl]phenol, was synthesized and structurally characterized by single crystal X-ray diffraction study. The compound was found to crystallise in orthorhombic crystal system with Pca2(1) space group. In the structure, the molecule exhibits a phenol-imine intramolecular hydrogen bond and the -NH2 group also involves in intermolecular hydrogen bonding with one of the nitrogen atom of the azo group (-N=N-) forming a 1D zigzag chain. Computational studies were performed on the titled compound and its tautomers. As computationally, this compound and its tautomers were optimized by using M062X/6-311G(d,p) level. According to thermodynamic parameters, the most stable tautomer was found to be azo-enol form. This result was then taken into account and spectral studies, which are IR, UV-Vis and NMR spectra, of this compound were performed and examined in detail. All calculations were performed at gas phase (epsilon = 1.000), 2-propanol (epsilon = 19.264), 1,2-ethanediol (epsilon = 40.245), water (epsilon = 78.355), formamide (epsilon = 108.940) and N-methylformamide-mixture (epsilon = 181.560). (C) 2016 Elsevier B.V. All rights reserved., Kahramanmaras Sutcu Imam University, Kahramanmaras, Turkey [2015/1-1 YLS], The authors thank to Kahramanmaras Sutcu Imam University for financial support (project no: 2015/1-1 YLS), Kahramanmaras, Turkey. The numerical calculations reported in this paper are performed at TUBITAK ULAKBIM, High Performance and Grid Computing Center (TRUBA Resources).

In this work, the structural, electronic properties, 14N NQR parameters and first hyperpolarizability of W(CO)5L, L=(4-pyridylmethylene)malononitrile complex were computed in gas phase by hybrid functional PBE method with LanL2DZ, and 6-311G(d,p) basis sets for transition metal and man group elements, respectively. Also, the solvent effect on structural parameters, frontier orbital energies of complexes has been carried out based on Polarizable Continuum Model (PCM). The results indicate that the polarity of solvents has played a significant role on the structures and properties of complex. ¹H and 13C NMR chemical shifts were calculated by using the Gauge-invariant atomic orbital (GIAO) method. By analyzing the structural characteristics of this structure, W-C and W-N bonds were identified and characterized in details by topological parameters such as electron density ρ(r) and Laplacian of electron density 2® ∇2ρ(r) from Bader's atom in molecules theory.

In this work, the antioxidant activity, free radical-scavenging capacity, molecular geometry and intramolecular hydrogen bonding interaction were explored for three natural flavonoid compounds of Arbutus unedo L. plant, Fisetin (3,3′,4′,7-tetrahydroxy flavone), Catechin (Flavan-3,3′,4′,5,7-pentol) and Apigenin (4′,5,7-trihydroxy flavone). Three potential mechanisms of antioxidant activity, hydrogen atom transfer (HAT), single electron transfer-proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET), have been explored. The physicochemical parameters (BDE, IP, PA, PD, ETE, HOMO and LUMO), as well spin density distribution, were calculated in different solvents. The mechanisms involved in the radical scavenging activity, taking into account the position of the most active OH hydroxyl group, are in accordance with the experimental tests. HAT mechanism is most favorable in the gas phase and benzene solvent. B-ring of the three flavonoids is the active center for the antioxidant activity. Fisetin presents the best antioxidant activity with high free radical scavenging capacity followed by Catechin and Apigenin, respectively.

The lithium-sulfur (Li-S) battery is one of the promising energy storage alternatives because of its high theoretical capacity and energy density. Factors governing the stability of polysulfide intermediates in Li-S batteries are complex and are strongly affected by the solvent used. Herein, the polysulfide reduction and the bond cleavage reactions are calculated in different solvent environments by the density functional theory (DFT) methods. We investigate the relationship between the donor numbers (DN) as well as the dielectric constants (ε) of the solvent system and the relative stability of different polysulfide intermediates. Our results show that the polysulfide reduction mechanism is dominated by its tendency to form the ion-pair with Li+ in different organic solvents.

This study describes photolysis of 1 × 10–4 M methomyl solution in deionized water and in eleven organic solvents, both polar and nonpolar: methanol, ethanol, n-propanol, isopropanol, sec-butanol, tert-butanol, isobutanol, isopentanol, n-hexane, acetonitrile, and dichloromethane. Photolysis of methomyl at 254 nm was performed using Osram mercury lamp (6 × 8 W) by exposing to irradiation for five hours. All photolytic methomyl reactions were studied by UV/Vis spectroscopy within a wavelength range of 190−300 nm (Spectrum Mode), and at 233.4 nm (Quantitative Mode), while the rate of photodecomposition of methomyl was measured using UV spectroscopy and HPLC. In order to get better insight in the photolysis of methomyl, a liquid chromatography-mass spectrometry (LC–MSn) was used. The rate of methomyl photolysis was solvent-specific and the following reaction rate order was established: deionized water > tert-butanol > n-hexane > sec-butanol > ethanol > isopentanol > isobutanol > isopropanol > methanol > acetonitrile > dichloromethane > n-propanol. Both nonspecific and specific solvent-solute interactions contribute mutually to the differences in the obtained quantum yields. Results of quantum chemical calculations, using CBS-QB3 method, provided insights into the solvent effects on both ground and excited state. The LC/MSn analysis showed the formation of several photolytic products. Supplementary material: [http://cherry.chem.bg.ac.rs/handle/123456789/3833]

The development of homogeneous, endurable and low cost SERS (Surface Enhancement Raman Spectroscopy) substrates is becoming of outmost importance due to growing interest in SERS technique for analytical applications. Here, we use the Langmuir-Schaefer technique to produce, as demonstrated by Atomic Force Microscopy and Scanning Electron Microscopy, homogeneous tightly-packed films of 27 nm in diameter octadecylthiolate capped gold nanoparticles in a reproducible and simple manner. The fabricated Au-based SERS substrates result in an analytical enhancement factor (AEF) of 4.3 × 108 and enable the detection of Rhodamine 6G in a 10−11 M aqueous solution, with remarkable spatial uniformity of the SERS response over a scanned area of 0.4 cm2. In addition, the developed procedure is highly reproducible from batch to batch with a standard deviation below 10% in the SERS signal. Finally, these substrates exhibit durable SERS properties, i.e. experimentally validated 16 months after its fabrication., P.C. and S.R-R. are grateful for financial assistance from DGA/Fondos FEDER (construyendo Europa desde Aragón) for funding PLATON (E31_17R) research group. M.P.P., R.M. and M.L. are grateful for financial support from MICINN (CTQ2013-49068-C2-1-R and CTQ2016-79419-R).

The effect of solvent on the activity and selectivity of SiO2-Al2O3 in the liquid-phase acid-catalyzed isomerization/cyclization of citronellal (CNAL) to isopulegol was investigated using non-polar (cyclohexane, toluene), weakly polar (chloroform), polar protic (ethanol, 2-propanol) and polar aprotic (acetonitrile) solvents. The catalyst activity and selectivity greatly depended on the solvent nature. The CNAL conversion rate was higher in weakly and non-polar (chloroform > toluene > cyclohexane) than in polar solvents (ethanol > acetonitrile > 2-propanol). To interpret this activity pattern, the solvent-CNAL interactions were analyzed by measuring the shift of the infrared C[dbnd]O absorption band of CNAL in CNAL/solvent mixtures, while the solvent-catalyst interactions were characterized by both determining the solvent adsorption enthalpies by calorimetry and following the product evolution from temperature-programmed desorption of solvents. In the case of polar solvents, both the strong solvation effect in the liquid phase and the adsorption strength of solvents on SiO2-Al2O3 contributed to decrease the catalyst isomerization activity. In particular, the selectivity to isopulegol was clearly lower in polar protic solvents (ethanol and 2-propanol) because secondary reactions producing carbon deposits took place. In contrast, in non-polar solvents the selectivity to isopulegol was higher than 97% in all the cases. The highest isomerization rate was obtained in chloroform that partially adsorbs dissociatively on SiO2-Al2O3, leading to a higher density of acid sites available for the isomerization reaction. Fil: Bertero, Nicolas Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina Fil: Trasarti, Andres Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina Fil: Acevedo, Maria Cristina Dominga. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina Fil: Marchi, Alberto Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina Fil: Apesteguia, Carlos Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina

The complexation of molybdenum(VI) with methyliminodiacetic acid (MIDA) at pH = 6.00, T = 298 K , I = 0.1 mol.dm-3 of sodium chloride and different water + methanol solutions (0-45% v/v) was studied by using potentiometric and UV spectrophotometric measurements. The stability constants values were calculated and their trends have been interpreted by using the Kamlet-Abboud-Taft (KAT) model in order to investigate the role of different specific and non-specific interactions in the aqueous solutions of methanol. Hyperquad 2013 and Microsoft Excel 2010 softwares have been used for the calculations.

The rate and, more importantly, selectivity (ketone vs aromatic ring) of the hydrogenation of 4-phenyl-2-butanone over a Pt/TiO2 catalyst have been shown to vary with solvent. In this study, a fundamental kinetic model for this multi-phase reaction has been developed incorporating statistical analysis methods to strengthen the foundations of mechanistically sound kinetic models.A 2-site model was determined to be most appropriate, describing aromatic hydrogenation (postulated to be over a platinum site) and ketone hydrogenation (postulated to be at the platinum–titania interface). Solvent choice has little impact on the ketone hydrogenation rate constant but strongly impacts aromatic hydrogenation due to solvent-catalyst interaction. Reaction selectivity is also correlated to a fitted product adsorption constant parameter. The kinetic analysis method shown has demonstrated the role of solvents in influencing reactant adsorption and reaction selectivity.

Water-in-oil (w/o) emulsions are used as a cellular model because of their unique cell-like architecture. Previous works showed the capability of eukaryotic-cell-sized w/o droplets (5-50 μm) to support protein synthesis efficiently; however data about smaller w/o compartments (

WOS: 000355041400009, Quantum chemical calculations using Density Functional Theory (DFT) at the B3LYP/6-31++G(d,p) basis set level were performed to investigate the azide group rotation from the trans to the cis isomer and the azido-tetrazole ring-chain isomerism equilibrium of 2-azido-1,3-azoles in the gas phase, carbon tetrachloride (CCl4), acetonitrile (CH3CN) and water (H2O). The solvent effect on the relative stabilities of each species was analyzed within the self-consistent field theory using the Polarized Continuum Model (PCM). The transition states (TSs) of each step was identified and confirmed. The azido-tetrazole ring-chain isomerism equilibrium was investigated in detail. In addition, the electronic characteristics of each species were analyzed by means of Molecular Electrostatic Potential (MEP) and Natural Bond Orbital (NBO) analyses. The relative energies were increased with the increasing electronegativity of X atom in the 1,3-azole ring. The study confirmed that the relative stability of the tetrazole isomers could be maximized to a great extent by increasing the polarity of solvent, and vice versa for the azido isomers. The low rotational barrier of the azido group in the trans reversible arrow cis isomerization and the significant increase of the dipole moment of the tetrazole isomers were determined factors in ring-chain isomerization. The results obtained in advance for 2-azido-1,3-thiazoles were found to be consistent with the experimental and theoretically data reported. (C) 2015 Elsevier B.V. All rights reserved.

The kinetics of oxidation of methionine (Met) by tetraethylammonium chlorochromate (TEACC) in dimethyl sulfoxide (DMSO) leads to the formation of the corresponding sulfoxide. The reaction is first order each in Met and TEACC. The reaction is catalyzed by hydrogen ions. The hydrogen ion dependence has the form : kobs = a + b [H+]. The reaction rate has been determined at different temperatures and activation parameters are calculated. The solvent effect has been analyzed using Kamlet’s multi parametric equation. A correlation of data with Kamlet–Taft solvatochromic parameters (α, β, π∗) suggests that the specific solute–solvent interactions play a major role in governing the reactivity. The reaction does not induce polymerization of acrylonitrile. A suitable mechanism has been proposed.

The conformational equilibrium of methyl 4-nitrophenyl sulfoxide (MNPSO) was experimentally investigated in the gas phase by using microwave spectroscopy and in isotropic and nematic liquid-crystal solutions, in which the solvents are nonaqueous and aprotic, by using NMR spectroscopy; moreover, it was theoretically studied in vacuo and in solution at different levels of theory. The overall set of results indicates a significant dependence of the solute conformational distribution on the solvent dielectric permittivity constant: when dissolved in low-polarity media, the most stable conformation of MNPSO proved to be strongly twisted with respect to that in more polar solvents, in which the conformational distribution maximum essentially coincides with that obtained in the gas phase. We discuss a possible explanation of this behavior, which rests on electrostatic solute-solvent interactions and is supported by calculations of the solute electric dipole moment as a function of the torsional angle. This function shows that the least polar conformation of MNPSO is located at a twist angle close to that of the conformational distribution maximum found in less-polar solvents. This fact, associated with a relatively flat torsional potential, can justify the stabilization of the twisted conformation by the less-polar solvents.

The conformational analysis of some 4'-substituted 2-(phenylselanyl)-2-(ethylsulfanyl)-acetophenones bearing the substituents NO2 (1), Br (2), H (3), Me (4) and OMe (5) was performed by ν(CO) IR analysis, B3LYP/6-31+G(d,p) and single point polarisable continuum model (PCM) calculations, along with NBO analysis for 1, 3 and 5. Calculations for 1-5 indicate the existence of three stable conformations, c1, c2 and c3, whose stability depends on the balance between electrostatic and orbital interactions that are strictly related to the geometrical arrangement. The comparison between the experimental IR spectra in solution and the computed data in gas phase for 1-5 allows the c1 conformer to be assigned to the less intense component at higher frequency of the carbonyl doublet and both the c2 and c3 ones to the more intense lower frequency component. The sum of the calculated molar fraction of c2 and c3 conformers decreases from 95% to 63% on going from 1 to 5 (in gas phase), and this trend compares well with the PCM calculations and the IR experimental data for the majority of the solvents for all compounds 1-5. The NBO analysis for 1, 3 and 5 shows that the sum of the relevant orbital delocalization energies for the c1, c2 and c3 conformers is almost constant and does not match the computed stability order. The lowest stability of the c1 conformer for 1-3 can be related to the small value of the α dihedral angle that enables a strong electrostatic destabilizing repulsion between the O(CO)(δ-)…S(δ-) atoms. The relative stability of the c1 conformer increases for 4 and 5 as the α dihedral angle enlarges and the repulsion is minimized. Moreover, the strong repulsive field effect between the C(δ+)=O(δ-) and C(δ+)-S(δ-) dipoles exerted to a greater extent on the c1 conformers of 1-3 with respect to 4 and 5, causes a major increase of the corresponding C=O bond orders and related carbonyl frequencies. For the c2 conformer, the electrostatic destabilizing repulsion between the O(δ-)…Se(δ-) atoms is weaker than that involving the O(δ-)…S(δ-) atoms in the c1 conformer and therefore has negligible effects on the conformer stability that is mainly determined by the sum of the orbital interactions. The c3 conformer has the shortest S(δ-)…Se(δ-) contact for all compounds and thus the related electrostatic repulsion seems to be the most important factor that affects its stability. In conclusion, the computed order of stability of the three conformers for 1-5 depends on the electrostatic repulsions between close charged atoms rather than on the sum of the orbital delocalization energies that are quite similar for all the conformers.

A conformational study of some 4′-substituited 2-(phenylselanyl)-2-(methoxy)-acetophenones (OMe 1, H 2, and Cl 3) was performed using IR carbonyl stretching band analysis supported by NBO and PCM calculations at the B3LYP/6-31 + G (d,p) level for 1–3 and using X-ray diffraction for 1 and 2. The computational results indicated the existence of three stable conformers for the series (c2, c3, and c1 in order of decreasing stability), whose relative abundance changes with solvent permittivity. The experimental trend observed for the components of the triplet carbonyl band in all solvents matches well with computational results and thus allows for their assignment to distinct conformers. The relative population of the c1 conformer increases in more polar solvents, becoming the most stable conformer in the highest permittivity solvent, acetonitrile, as indicated by IR spectra and PCM calculations. These findings are related to the quasi parallel geometry assumed by the Cδ+ = Oδ− and Cδ+-Oδ- dipoles, which favour stronger solvation. NBO analysis shows that the sum of the energies (ΣE) of the relevant orbital interactions stabilizes the c3 conformer of 1–3 slightly, likely due to the minor contribution of the LPO5→σ*C3 Se10 interaction. However, only the c1 conformer is significantly destabilized by the Oδ−(1)CO … Oδ−(5)OMe short contact electrostatic repulsion, which is also responsible for its highest νCO frequency. In addition, the LPO5→ σ*C2 C3 orbital interaction accounts for the lowest νCO frequency of c3 conformer. X-ray single crystal analysis of compounds 1 and 2 indicates that in the solid state they assume the least stable c1 conformation found in the gas phase. Molecules of these compounds are stabilized in the crystal through a series of C H⋯O and C H … π intermolecular interactions.