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Separating molecular spin isomers is a challenging task, with potential applications in various fields ranging from astrochemistry to magnetic resonance imaging. A new promising method for spin-isomer separation is magnetic focusing, a method which was shown to be capable of producing a molecular beam of ortho-water. Here, we present results from a modified magnetic focusing apparatus and show that it can be used to separate the spin isomers of acetylene and methane. From the measured focused profiles of the molecular beams and a numerical simulation analysis, we provide estimations for the spin purity and the significantly improved molecular flux obtained with the new setup. Finally, we discuss the spin-relaxation conditions which will be needed to apply this new source for measuring nuclear magnetic resonance signals of a single surface layer. [ABSTRACT FROM AUTHOR]

We recorded infrared (IR) spectra in the CH- and OH-stretching regions of size-selected clusters of methanol (M) with one water molecule (W), represented as MnW, n = 1-4, in a pulsed supersonic jet using the photoionization/IR-depletion technique. Vacuum ultraviolet emission at 118nmserved as the source of ionization in a time-of-flight mass spectrometer to detect clustersMnWas protonated forms Mn-1WH+. The variations in intensities ofMn-1WH+ were monitored as thewavelength of the IR laser light was tuned across the range 2700-3800 cm-1. IR spectra of size-selected clusters were obtained on processing of the observed action spectra of the related cluster-ions according to a mechanism that takes into account the production and loss of each cluster due to IR photodissociation. Spectra of methanol-water clusters in the OH region show significant variations as the number of methanol molecules increases, whereas those in the CH region are similar for all clusters. Scaled harmonic vibrational wavenumbers and relative IR intensities predicted with the M06-2X/aug-cc-pVTZ method for the methanol-water clusters are consistent with our experimental results. For dimers, absorption bands of a structureWMwith H2O as a hydrogen-bond donor were observed at 3570, 3682, and 3722 cm-1, whereas weak bands of MW with methanol as a hydrogen-bond donor were observed at 3611 and 3753 cm-1. For M2W, the free OH band of H2O was observed at 3721 cm-1, whereas a broad feature was deconvoluted to three bands near 3425, 3472, and 3536 cm-1, corresponding to the three hydrogen-bonded OH-stretching modes in a cyclic structure. For M3W, the free OH shifted to 3715 cm-1, and the hydrogen-bonded OH-stretching bands became much broader, with a weak feature near 3179 cm-1 corresponding to the symmetric OH-stretching mode of a cyclic structure. For M4W, the observed spectrum agrees unsatisfactorily with predictions for the most stable cyclic structure, indicating significant contributions from branched isomers, which is distinctly different from M5 of which the cyclic form dominates. [ABSTRACT FROM AUTHOR]

A general formulation for constructing addressable atomic clusters is introduced, based on one or more reference structures. By modifying the well depths in a given interatomic potential in favour of nearest-neighbour interactions that are defined in the reference(s), the potential energy landscape can be biased to make a particular permutational isomer the global minimum. The magnitude of the bias changes the resulting potential energy landscape systematically, providing a framework to produce clusters that should self-organise efficiently into the target structure. These features are illustrated for small systems, where all the relevant local minima and transition states can be identified, and for the low-energy regions of the landscape for larger clusters. For a 55-particle cluster, it is possible to design a target structure from a transition state of the original potential and to retain this structure in a doubly addressable landscape. Disconnectivity graphs based on local minima that have no direct connections to a lower minimum provide a helpful way to visualise the larger databases. These minima correspond to the termini of monotonic sequences, which always proceed downhill in terms of potential energy, and we identify them as a class of biminimum. Multiple copies of the target cluster are treated by adding a repulsive term between particles with the same address to maintain distinguishable targets upon aggregation. By tuning the magnitude of this term, it is possible to create assemblies of the target cluster corresponding to a variety of structures, including rings and chains. [ABSTRACT FROM AUTHOR]

We report infrared (IR) spectra of HOCS+, HSCO+, t-HOCS, and other species produced on electron bombardment of a mixture of carbonyl sulfide (OCS) and para-hydrogen (p-H2) during deposition at 3.2 K. After maintenance of the matrix in darkness for 15 h, the intensities of absorption features of HOCS+ at 2945.9 (ν1), 1875.3 (ν2), and 1041.9 (ν3) cm-1 and those of HSCO+ at 2506.9 (ν1) and 2074.2 (ν2) cm-1 decreased through neutralization with trapped electrons. Lines observed at 3563.4, 1394.8, and 1199.0 cm-1, which decreased slightly in intensity after maintenance in darkness and were nearly depleted after irradiation at 373 nm, are assigned to a t-HOCS radical. The corresponding spectra of their 13C- and D-isotopologues were observed. The IR spectra of HSCO+ and t-HOCS and those of modes ν2 and ν3 of HOCS+ are new. The assignments were made according to the expected chemical behavior and a comparison of experimental and calculated wavenumbers and 13Cand D-isotopic shifts. The wavenumber of the OH stretching mode (2945.9 cm-1) of HOCS+ in solid p-H2 is significantly red-shifted from that (3435.16 cm-1) reported for gaseous HOCS+; this shift is attributed to partial sharing of a proton between OCS and H2. The corresponding p-H2 induced shift is small in HSCO+ because of a much weaker interaction between HSCO+ and H2. [ABSTRACT FROM AUTHOR]

The low-lying isomers of cationic water cluster (H2O)6+ have been globally explored by using particle swarm optimization algorithm in conjunction with quantum chemical calculations. Compared with previous results, our searching method covers a wide range of structural isomers of (H2O)6+ and therefore turns out to be more effective. With these local minima, geometry optimization and vibrational analysis are performed for the most interesting clusters at second-order Møller-Plesset (MP2)/aug-cc-pVDZ level, and their energies are further refined at MP2/aug-cc-pVTZ and coupledcluster theory with single, double, and perturbative triple excitations/aug-cc-pVDZ level. The interaction energies using the complete basis set limits at MP2 level are also reported. The relationships between their structure arrangement and their energies are discussed. Based on the results of thermal simulation, structural change from a four-numbered ring to a tree-like structure occurs at T ≈ 45 K, and the relative population of six lowest-free-energy isomers is found to exceed 4% at some point within the studied temperature range. Studies reveal that, among these six isomers, two new-found isomers constitute 10% of isomer population at 180 K, and the experimental spectra can be better explained with inclusions of the two isomers. The molecular orbitals for six representative cationic water clusters are also studied. Through topological and reduced density gradient analysis, we investigated the structural characteristics and the bonding strengths of these water cluster radical cations. [ABSTRACT FROM AUTHOR]

We study the infrared (IR) resonant heating of neutral niobium carbide clusters probed through ultraviolet photoionization spectroscopy. The IR excitation not only changes the photoionization spectra for the photon energies above the ionization threshold, but also modulates ion yield for energies significantly below it. An attempt to describe the experimental spectra using either Fowler's theory or thermally populated vibrational states was not successful. However, the data can be fully modeled by vibrationally and rotationally broadened discrete electronic levels obtained from Density Functional Theory (DFT) calculations. The application of this method to spectra with different IR pulse energies not only yields information about the excited electronic states in the vicinity of the HOMO level, populated by manipulation of the vibrational coordinates of a cluster, but also can serve as an extra indicator for the cluster isomeric structure and corresponding DFT-calculated electronic levels. [ABSTRACT FROM AUTHOR]

C6H radical is known to exist in the astrophysical environment in linear form; however, it may originate from nonlinear isomeric forms. Potential energy surface of C6H is explored to search isomers of C6H and transition states connecting them. This work reports first-ever identification of reaction pathways for isomerization of C6H. The reaction route search is performed through global reaction route mapping method, which utilizes an uphill walking technique based on an anharmonic downward distortion following approach to search intermediates and transition states. The computations performed at the CASSCF/aug-cc-pVTZ, CCSD(T)/6-311++G(d,p)//DFT/B3LYP/6-311++G(d,p), and DFT/B3LYP/aug-cc-pVTZ levels of the theory identified 14 isomers (including 8 new isomeric forms of C6H) and 28 transition states. Most of the identified isomers are found to have significant multireference character. The kinetic stability and natural bond orbital analysis of the identified isomers is also investigated. The isomeric forms are further characterized using spectral analysis involving rotational constants, vibrational frequencies, and Raman scattering activities as well as analyzing the effect of isotopic substitution of hydrogen on the spectral features. This study proposes that the linear-C6H can readily isomerize to a six-member ring isomer. [ABSTRACT FROM AUTHOR]

The near-edge X-ray absorption fine structure (NEXAFS) spectra and the X-ray photoelectron spectroscopy (XPS), as well as the geometrical structures of two C isomers (C(16), C(17)) and their corresponding chlorinated derivatives (C(16) Cl, C(17)Cl) which were newly purified have been investigated by the density functional theory (DFT). The variations of molecular structure, electronic structure and simulated spectra for C isomers after chlorination have been illustrated. Then, the above-mentioned C isomers and their chlorinated derivatives have been identified by the NEXAFS and XPS spectra which show the dependence on the local structure. Furthermore, we have also traced the source of the features in the total spectra by the spectral exploration of each component, which is very helpful for the further study of newly captured fullerene isomers and their derivatives. In this manuscript, we have performed first-principles simulation of the C1s X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine structure spectra (NEXAFS) for two C86 fullerene isomers and the related chlorinated species. The variations of molecular structure, electronic structure and simulated spectra for C86 isomers after chlorination have been illustrated. The above-mentioned C86 isomers and their chlorinated derivatives were identified by the NEXAFS and XPS spectra which show strong dependence on the local structure. Furthermore, we have also traced the source of the features in the total spectra by the spectral exploration of each component. The investigations on newly synthesized fullerenes and derivatives are effectively valuable and stimulative for the experimental researches in future. [ABSTRACT FROM AUTHOR]

Copyright of Kemija u Industriji is the property of Croatian Society of Chemical Engineers and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Tris(chloropropyl) phosphate (TCPP) is an environmentally abundant organophosphate ester (OPE). TCPP is comprised of four isomers with seven possible structures, eight CAS numbers, and even more common names. A review of 54 studies reporting one or more TCPP isomers confirmed that the most abundant and most often reported TCPP isomer was tris(2-chloro-1-methylethyl) phosphate, also known as tris(chloroisopropyl) phosphate (TCiPP, referred to hereafter as TCPP1). Full-scan gas chromatography-mass spectrometry (GC-MS) was used to identify the other three isomers numbered here according to their elution order on a non-polar GC column (DB-5): bis(2-chloro-1-methylethyl) (2-chloropropyl) phosphate (TCPP2), bis(2-chloropropyl)(2-chloro-1-methylethyl) phosphate (TCPP3), and tris(2-chloropropyl) phosphate (TCPP4). GC with a flame ionization detector (FID) was used to identify the relative abundances of the isomers in commercially available standards with unknown isomer composition. In technical TCPP, TCPP1-4 isomers averaged 71 ± 1, 26 ± 0.4, 3 ± 0.5, and 0.1 ± 0.02%, respectively. When these percent masses are incorporated into GC-MS quantification, response factors (RFs) for TCPP1 and TCPP2 are significantly different from TCPP3 and TCPP4, indicating that the multiple RF approach is more accurate than the commonly employed single RF method. Samples from urban streams and wastewater treatment plant (WWTP) effluent from Toronto, Canada, had isomeric ratios of TCPP1/2 that were not significantly different from a technical mixture whereas rain had a significantly different ratio indicating enrichment in the more volatile TCPP1 isomer. Reporting TCPP isomers can provide insight into sources, transport, and fate of TCPP in the environment. [ABSTRACT FROM AUTHOR]

The geometric and electronic ground-state structures of 30 isomers of six MS4 molecules (M=Group 8 metals Fe, Ru, Os, Hs, Sm, and Pu) have been studied by using quantum-chemical density functional theory and correlated wavefunction approaches. The MS4 species were compared to analogous MO4 species recently investigated (W. Huang, W.-H. Xu, W. H. E. Schwarz, J. Li, Inorg. Chem. 2016, 55, 4616). A metal oxidation state (MOS) with a high value of eight appeared in the low-spin singlet Td geometric species (Os,Hs)S4 and (Ru,Os,Hs)O4, whereas a low MOS of two appeared in the high-spin septet D2 d species Fe(S2)2 and (slightly excited) metastable Fe(O2)2. The ground states of all other molecules had intermediate MOS values, with S2−, S22−, S21− (and O2−, O1−, O22−, O21−) ligands bonded by ionic, covalent, and correlative contributions. The known tendencies toward lower MOS on going from oxides to sulfides, from Hs to Os to Ru, and from Pu to Sm, and the specific behavior of Fe, were found to arise from the different atomic orbital energies and radii of the ( n−1)p core and ( n−1)d and ( n−2)f valence shells of the metal atoms in row n of the periodic table. The comparative results of the electronic and geometric structures of the MO4 and MS4 species provides insight into the periodicity of oxidation states and bonding. [ABSTRACT FROM AUTHOR]

Earlier studies carried out in our laboratory indicated that Tri-sec-butyl phosphate (TsBP) is a potential extractant for U/Th separation. Also, the third phase formation tendency of TsBP is lower compared to its isomers, Tri-n-butyl-phosphate (TBP) and Tri-iso-butyl phosphate (TiBP). In this context, the extraction and third phase formation behaviour of 1.1 M solutions of TiBP and TsBP in n-dodecane in the extraction of Th(IV) from 1 M HNO3 at 303 K over a wide range of Th concentrations were investigated in the present study and the results are compared with the literature data on TBP system. Concentrations of Th(IV) and HNO3 loaded in the organic phase before third phase formation (biphasic region) as well as in third phase and diluent-rich phase after third phase formation (triphasic region) were measured as a function of equilibrium aqueous phase Th(IV) concentration. The density of loaded organic phase was also measured at various Th(IV) concentrations. The extraction profiles in the biphasic region indicated that extraction of Th(IV) by TBP is higher than that of TiBP which in turn is higher than that of TsBP. Extractant concentration in the diluent-rich phase and third phase was measured for the triphasic region. [ABSTRACT FROM AUTHOR]

Controllable synthesis of coordination polymer (CP) isomers and revealing their structure-property relationships remain enormous challenges. Three new supramolecular isomers have been synthesized by tuning the poly(ethylene glycol) (PEG) content in the feed. These supramolecular isomers have the same framework formula of [Cu2I2(tppe)] and different architectures from the classical 2D stacking framework to a 3D entangled system with the coexistence of interpenetration and polycatenation, and a 3D topological framework. Interestingly, these CPs could be utilized for capturing iodine molecules. According to multiple complementary experiments and crystallographic analyses, iodine capture is mainly based on halogen-bond interactions in the inorganic {Cu2I2} building blocks of the framework. The present study describes a structure-property relationship in supramolecular isomerism with distinct topological structures. [ABSTRACT FROM AUTHOR]

Binuclear C^C* cyclometalated NHC platinum(II) compounds with bridging amidinate ligands were synthesized to evaluate their photophysical properties. Their three-dimensional structures were determined by a combination of 2D NMR experiments, mass spectrometry, DFT calculations, and solid-state structure analysis. The bridging amidinate ligands enforce short distances between the platinum centers of the two cyclometalated structures, which gives rise to extraordinary photophysical properties. [ABSTRACT FROM AUTHOR]

Among seven possible nitrogen-in constitutional isomers of porphyrin only one, porphycene, has been obtained so far in the free, unsubstituted form. Herein, the synthesis of another isomer, parent hemiporphycene ( HPc), and its thorough structural, spectral, photophysical, electrochemical, and theoretical characterization are reported. Most of the properties of HPc are intermediate between those of porphyrin and porphycene, as evidenced by the values of inner-cavity dimensions, orbital-energy splittings, absorption coefficients, magnetic circular dichroism parameters, NH-stretching frequencies, fluorescence quantum yields, tautomerization rates, and redox potentials. The largest differences arise with respect to tautomerism, due to the low symmetry of HPc and inequivalence of the four nitrogen atoms that define the inner cavity. Two trans tautomers are observed, separated in energy by about 1 kcal mol−1. Tautomerization from the higher- to the lower-energy form is detected in the lowest-excited singlet state and occurs at a rate that is about four orders of magnitude lower than that observed for porphycene. Hemiporphycene is a very good model for the investigation of inequivalent intramolecular H-bonds present in one molecule; two such bonds in HPc reveal unusual characteristics, and the bond strength results from the interplay between the N ⋅⋅⋅N distance and the N−H−N angle. [ABSTRACT FROM AUTHOR]

Two polymorphic structures have been well determined in a valence tautomeric (VT) dinuclear cobalt complex. These polymorphs showed distinct thermal- and photomagnetic behavior, and are thus ideal for studying the 'pure' intermolecular factors to VT transitions. In polymorph 1A, the VT cations are arranged head-to-waist with their neighbors and exhibit weak π ⋅⋅⋅π interactions, resulting in a gradual and incomplete thermal VT transition. In contrast, the cations in polymorph 1B are arranged head-to-tail and exhibit relatively strong π ⋅⋅⋅π interactions, leading to an abrupt and complete thermal VT transition with adjustable hysteresis loop at around room temperature. The VT process for both polymorphs can be induced by light, but the light-excited state of 1B⋅2H2O has a higher thermal relaxation temperature than that of 1A⋅3H2O. [ABSTRACT FROM AUTHOR]

Organocatalysts displaying a network of cooperative hydrogen bonds (NCHB) have been employed in an enzyme-like manner for a direct, switchable synthesis of enantiopure hexahydropyrimidinones (HHPMs) or dihydropyrimidinones (DHPMs), which starts at a common, easily accessible α-ureidosulfone stage. The NCHB organocatalyst exploits all its potential as a pure hydrogen-bond biomimetic catalyst even in the presence of organic bases. This one-pot, diastereo- and enantioselective synthetic procedure has been proven to be robust, scalable, highly efficient, and environmentally benign. A straightforward and truly practical entry to enantiopure HHPMs is reported for the first time. [ABSTRACT FROM AUTHOR]

Photocrystallographic experiments provide valuable information on how crystalline samples interact with light, yielding light-induced structural changes. Studied processes include, among others, solid state chemical reactions, as well as isolation and characterization of various metastable states. Thus, some instrumentation development efforts in the field have been dedicated to facilitating such experiments using a home X-ray source. In this contribution, a portable, easy-to-use and adjustable light-delivery device for home single-crystal diffractometers is described. The whole system consists of adjustable laser-focusing optics and a holder, which can be conveniently attached to a goniometer, as an additional sample conditioning device. The light-delivery device was designed to reduce any goniometer movement limitations. It allows one to conveniently perform photocrystallographic experiments without violation of the X-ray safety protocols, even when changing the light source is necessary. Test in situ photocrystallographic experiments performed on the literature-reported Ni(NO2)2(dppe) complex [dppe is bis(diphenylphosphino)ethane] confirm the effectiveness and applicability of the device for conducting linkage isomer single-crystal-to-single-crystal transformations. [ABSTRACT FROM AUTHOR]

Achieving strong host-guest interactions between synthetic hosts and hydrophilic guests in solution is challenging because solvation effects overwhelm other effects. To resolve this issue, we transferred complexes of cucurbit[7]uril (CB[7]) and monosaccharides to the gas phase and report here their intrinsic host-guest chemistry in the absence of solvation effects. It was observed that effective host-guest interactions in the gas phase mediated by ammonium cations allow the differentiation of the monosaccharide isomers in complex with CB[7] upon vibrational excitation. The potential of the unique observation was extended to a quantitative supramolecular analytical method for the monosaccharide guests. The combination of host-guest chemistry and phase transfer presented in this study is an effective approach to overcome current limitations in supramolecular chemistry. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Northeastern University (Natural Science) is the property of Dongbei Daxue Xuebao and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the present work, we propose the X3D method that extends the B3LYP method by correcting its errors on heats of formation of hydrocarbons (HCs) with three-dimensional (3D) molecular descriptors. Inspired by the widely used Wiener index, these 3D descriptors are developed to improve over the original B3LYP method for a better description of atom-atom, atom-bond and bond-bond interactions. On top of a training set of only 45 species, the X3D method is validated against various sets of different chemistry, displaying an overall near chemical accuracy. In particular, X3D improves over B3LYP, reducing its mean absolute errors from 28.4 to 0.3 kcal/mol for (Set 1) 21 n-alkanes up to n-C32H66, from 19.3 to 0.6 kcal/mol for (Set 2) n-C7H16 and its branched isomers, from 29.5 to 1.6 kcal/mol for (Set 3) 36 polycyclic saturated HCs, from 8.6 to 1.1 kcal/mol for (Set 4) 41 C6H8 isomers of rings, alkenes, alkynes, and cumulenes, from 20.3 to 0.6 kcal/mol for (Set 5) 41 benzene-based compounds, and 8.1 to 1.3 kcal/mol for (Set 6) 66 radicals, etc. Comparisons with the G4 results are also presented. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Ground state and low lying isomer structures of (Bi2O3) n clusters with n = 6 − 9 were determined by first-principle calculations. These calculations were performed with the LCGTO-ADFT method as implemented in the deMon2k program. Initial structures from Born-Oppenheimer molecular dynamics trajectories were selected as starting points for local geometry optimizations. The optimized structures where identified as minimum structures by frequency analysis. Furthermore, the structural relation between the clusters is presented. This work shows for the (Bi2O3)8 cluster a higher stability then for the other clusters. [ABSTRACT FROM AUTHOR]

During the process development for multigram-scale synthesis of olmesartan medoxomil (OM), two principal regioisomeric process-related impurities were observed along with the final active pharmaceutical ingredient (API). The impurities were identified as N-1- and N-2-(5-methyl-2-oxo-1,3-dioxolen-4-yl)methyl derivatives of OM. Both compounds, of which N-2 isomer of olmesartan dimedoxomil is a novel impurity of OM, were synthesized and fully characterized by differential scanning calorimetry (DSC), infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR) and high-resolution mass spectrometry/electrospray ionization (HRMS/ESI). Their 1H, 13C and 15N nuclear magnetic resonance signals were fully assigned. The molecular structures of N-triphenylmethylolmesartan ethyl (N-tritylolmesartan ethyl) and N-tritylolmesartan medoxomil, the key intermediates in OM synthesis, were solved and refined using single-crystal X-ray diffraction (SCXRD). The SCXRD study revealed that N-tritylated intermediates of OM exist exclusively as one of the two possible regioisomers. In molecular structures of these regioisomers, the trityl substituent is attached to the N-2 nitrogen atom of the tetrazole ring, and not to the N-1 nitrogen, as has been widely reported up to the present. This finding indicates that the reported structural formula of N-tritylolmesartan ethyl and N-tritylolmesartan medoxomil, as well as their systematic chemical names, must be revised. The careful analysis of literature spectroscopic data for other sartan intermediates and their analogs with 5-(biphenyl-2-yl)tetrazole moiety showed that they also exist exclusively as N-2-trityl regioisomers. [ABSTRACT FROM AUTHOR]

In this report, two totally new indium-tetracarboxylate framework isomers based on the same starting tetracarboxylate ligand are presented, namely, [Me2NH2][In(BPTC)]·Guest (InOF-12) and [Hdabco][In(BPTC)]·Guest (InOF-13). Their corresponding crystal structures essentially originated from the guest templates and were then fully characterized and solved by single crystal X-ray diffraction analysis. Through low pressure gas capacity comparison, it is noted that desolvated InOF-12 exhibits a better performance and its H2 isotherm reaches a high uptake capacity value of 1.32 wt% at 77 K and 1.0 bar, and a high carbon dioxide uptake of 82.2 cm3 g−1 (3.67 mmol g−1) at 273 K and 1.0 bar, while InOF-13 has a lower value of 80.4 cm3 g−1 (3.59 mmol g−1) under the same conditions. [ABSTRACT FROM AUTHOR]

The effect of carbenes as Lewis donor groups on the homoaromaticity of mono- and bicyclic organic molecules is surveyed. The search for viable carbene-stabilised homoaromatics resulted in a large amount of rejected candidates as well as nine promising candidates that are further analysed for their homoaromaticity by using a number of metrics. Of these, five appeared to show modest homoaromaticity, whereas another compound showed a level of homoaromaticity comparable with the homotropylium cation benchmark compound. Isoelectronic analogues and constitutional isomers of the lead compound were investigated, however, none of these showed comparable homoaromaticity. The implications of these calculations on the design of donor-stabilised homoaromatics are discussed. [ABSTRACT FROM AUTHOR]

Detected in environmental samples, 1,2-dibromo-4-(1,2-dibromoethyl) cyclohexane (DBE-DBCH) is a bioaccumulative isomer of a current-use brominated flame retardant. All 4 structural isomers are androgen agonists; however, little toxicological information exists for this compound. The objective of the present study was to determine if β-DBE-DBCH, the isomer found most prominently in animal tissue, affects androgen-dependent behavior of breeding American kestrels ( Falco sparverius). The authors hypothesized that if β-DBE-DBCH acts as an androgen agonist in kestrels, androgen-dependent behaviors (i.e., copulation, courtship, aggression) would increase and behaviors inhibited by androgens (i.e., parental care behaviors) would decrease. Sixteen captive experimental kestrel pairs were exposed to 0.239 ng β-DBE-DBCH/g kestrel/d by diet from 4 wk prior to pairing until their nestlings hatched (mean 82 d) and compared with vehicle only-exposed control pairs ( n = 15). Androgen-dependent behaviors were significantly increased in β-DBE-DBCH-exposed birds, consistent with the authors' hypothesis. These behavioral changes included copulation and other sexual behaviors in males and females and aggression in males, suggesting that β-DBE-DBCH may have acted like an androgen agonist in these birds. Parental behaviors were not reduced in exposed birds as predicted, although dietary exposure had ceased before chicks hatched. Further assessment of β-DBE-DBCH is recommended given these behavioral changes and the previously reported reproductive changes in the same birds. Environ Toxicol Chem 2015;34:2395-2402. © 2015 SETAC [ABSTRACT FROM AUTHOR]

(6-4) Photolesions between adjacent pyrimidine DNA bases are prone to secondary photochemistry. It has been shown that singlet excited (6-4) moieties form Dewar valence isomers as well as triplet excitations. We here report on the triplet state of a minimal model for the (6-4) photolesion, 1-methyl-2(1H)-pyrimidinone. Emphasis is laid on its ability to abstract hydrogen atoms from alcohols and carbohydrates. Steady-state and time-resolved experiments consistently yield bimolecular rate constants of ∼104 M−1 s−1 for the hydrogen abstraction. The process also occurs intramolecularly as experiments on zebularine (1-(β-d-ribofuranosyl)-2(1H)-pyrimidinone) show. [ABSTRACT FROM AUTHOR]

Phosphine-catalyzed [4+1] annulation of 2-tosylaminochalcones with allenoates has been achieved, giving trans-2,3-disubstitued indolines as major diastereoisomers in moderate to good yields. [ABSTRACT FROM AUTHOR]

D5h star-like CsF5, formally isoelectronic with known XeF5- ion, is computed to be a local minimum on the potential energy surface of CsF5, surrounded by reasonably large activation energies for its exothermic decomposition to CsF+ 2F2, or to CsF3 (three isomeric forms)+F2, or for rearrangement to a significantly more stable isomer, a classical Cs+ complex of F5-. Similarly the CsF2+ ion is computed to be metastable in two isomeric forms. In the more symmetrical structures of these molecules there is definite involvement in bonding of the formally core 5p levels of Cs. [ABSTRACT FROM AUTHOR]

This study verified the usefulness of additives for the stabilization of dissolved material in the liquid stage as in the case of crystallization. Additives were introduced to prevent dissolved crystals from isomerization and degradation. The case study here is astaxanthin, a carotenoid occurring in different isomers. The molecule structure is susceptible to a plethora of substances and factors which cause transformation and degradation of the isomers. The aim was to examine whether foreign materials (additives) would induce a change of the kinetics of a system consisting of crystalline all- trans astaxanthin dissolved in chloroform. The results show that K2CO3 and CH3COOK increase the stability of all- trans astaxanthin in solution. [ABSTRACT FROM AUTHOR]

The connection of bowl-shaped aromatic boron subphthalocyanines with anti-[2.2]paracyclophane resulted in the first observation of electronic communication between convex and concave surfaces. Three isomers of anti-[2.2](1,4)subphthalocyaninophane, described as concave-concave ( CC), convex-concave ( CV), and convex-convex ( VV) according to the orientation of the subphthalocyanine units, were synthesized and characterized by various spectroscopic techniques, including 1H NMR, electronic absorption, fluorescence, and magnetic circular dichroism spectroscopy and X-ray crystallography, together with molecular-orbital calculations. On going from the CC system to CV and further to VV, the Q band broadened and finally split as a result of through-space expansion of the conjugated systems, which were also reproduced theoretically. [ABSTRACT FROM AUTHOR]

Methyl aroylpyruvates reacted with 4-amino- N-carbamimidoylbenzene-1-sulfonamide in acetic acid-ethanol (1: 1) to give methyl 4-aryl-2-{[4-(carbamimidoylsulfamoyl)phenyl]amino}-4-oxobut-2-enoates which were found to exist in solution as mixtures of Z and E isomers. [ABSTRACT FROM AUTHOR]

The article discusses the stereodynamics and molecular structure of nickel (II) bis (chelate) complexes based on aromatic azomethines. Topics discussed include the state of low-spin complex which has a trans and cis planar structures, the geometric characteristics of the trans and cis isomers which shows that the planar cis configuration is due to mutual repulsion at the azomethine nitrogen atoms, and the tables that shows the bending angles of the chelate rings in the singlet electronic state.

The known complex [Ni(medpt)(η¹-NO2)(η²-ONO)] 1 (medpt = 3,3'-diamino-N-methyldipropylamine) crystallises in the monoclinic space group P21/m with 1.5 molecules in the asymmetric unit with two different η¹-NO2 ligand environments in the crystal structure. At 298 K the molecule (A) sitting in a general crystallographic site displays a mixture of isomers, 78% of the η¹-NO2 isomer and 22% of an endo-nitrito--(η¹-ONO) form. The molecule (B) sitting on a crystallographic mirror plane adopts the η¹-NO2 isomeric form exclusively. However, a variable temperature crystallographic study showed that the two isomers were in equilibrium and upon cooling to 150 K the η¹-ONO isomer converted completely to the η¹-NO2 isomer, so that both independent molecules in the asymmetric unit were 100% in the η¹-NO2 form. A kinetic analysis of the equilibrium afforded values of ΔH = -9.6 (±0.4) kJ mol-1, ΔS = -21.5 (±1.8) J K-1 mol-1 and EA = -1.6 (±0.05) kJ mol-1. Photoirradiation of single crystals of 1 with 400 nm light, at 100 K, resulted in partial isomerisation of the η¹-NO2 isomer to the metastable η¹-ONO isomer, with 89% for molecule (A), and 32% for molecule (B). The crystallographic space group also reduced in symmetry to P21 with Z' = 3. The metastable state existed up to a temperature of 150 K above which temperature it reverted to the ground state. An analysis of the crystal packing in the ground and metastable states suggests that hydrogen bonding is responsible for the difference in the conversion between molecules (A) and (B). [ABSTRACT FROM AUTHOR]

Trifluoromethylated derivatives of Sc3N@Ih-C80 and Sc3N@D5h-C80 were synthesized by the reaction with CF3I at 440°C. HPLC separation of the mixture of Sc3N@D5h-C80(CF3)n derivatives resulted in isolation and Xray structure determination of Sc3N@D5h-C80(CF3)16, which represents a precursor of the known Sc3N@D5h-C80(CF3)18. Among the CF3 derivatives of Sc3N@Ih-C80, two new isomers of Sc3N@Ih-C80(CF3)14 (Sc-14-VI and Sc-14-VII) were isolated by HPLC, and their molecular structures were determined by X-ray diffraction, thus enabling a comprehensive comparison of altogether seven isomers. Two types of addition patterns with different orientations of the Sc3N cluster relative to the Ih-C80 fullerene cage were established. In particular, Sc-14-VII represents a direct precursor of the known Sc3N@Ih-C80(CF3)16-II. All molecular structures exhibit an ordered position of a Sc3N cluster inside the fullerene C80 cage. [ABSTRACT FROM AUTHOR]

The crystal structures of three pairs of "bridge-flipped isomers" are compared here in the context of whether their similarity in molecular space-filling requirements in combination with the tendency of centrosymmetric molecules to occupy crystallographic inversion centers might lead to their isomorphism. The possibility that similar fluorine-based supramolecular synthons occurring in the crystal structures of both members of a pair might promote their isomorphism is also considered. The compounds are the bis-benzylideneanilines formed by reaction of 2-fluoroaniline, 3-fluoroaniline, and 4-fluoroaniline respectively with terephthaldehyde (1-3) and by reaction of 2-fluorobenzaldehyde, 3-fluorobenzaldehyde, and 4-fluorobenzaldehyde respectively with phenylenediamine (4-6). The crystal structure of 2 is disordered, with the fluorine atom occupying two sites (95 : 5 occupation) related by rotation about the bond between the bridge nitrogen atom and the 3-fluorophenyl group. The crystal structure of 6 (HEWHAU) has been reported by previous workers. The structures of the 1:4, 2:5, and 3:6 pairs are compared to each other and to those of fluorinated simple (one-bridge) benzylideneanilines and fluorinated bis-benzylideneanilines recently described in the literature. No isomorphism is found among the bridge-flipped isomeric pairs, and none is found between positional isomers within the 1-3 or 4-6 series. The supramolecular synthon defined by a 2-F⋯bridge H contact is found in several of the benzylideneaniline crystal structures, but it does not compel isomorphism, nor is it specific to one type (terephthaldehyde-based or phenylenediamine-based) of isomer. Conformational variability and supramolecular synthon variety apparently serve as structure differentiators, not as isomorphism facilitators, among these bis-benzylideneanilines. [ABSTRACT FROM AUTHOR]

The FTIR spectra of 2-deoxyadenosine (dA) molecules isolated in low-temperature Ar matrices were obtained in the range of 3800-180 cm-1 with a resolution of 0.3 cm-1. The population analysis of the major structural isomers of dA was carried out by MP2 and DFT quantum-mechanical calculation methods. It was established that dA can sustain prolonged evaporation at 440K without undergoing thermal decomposition. For the first time, it was shown that the populations of dA syn-conformers with the intramolecular hydrogen bond O5'H-N3 is close to (76 ± 5)% in the gas phase and matrix. Upon freezing in the matrix the syn-conformers with the intramolecular hydrogen bond O5'H-N3 and C3'-endo structure of the deoxyribose ring were fully transformed into the subset of syn-conformers with the C2'-endo structure of the deoxyribose ring. Only two structures from this subset with different rotation angles of the O3'H-group can be stabilized in the matrix. Unlike pyrimidine nucleosides, the dA conformers with the intramolecular hydrogen bonds O3'H-O5 or O5'H-O3 were not found. [ABSTRACT FROM AUTHOR]

Many plants accumulate large quantities of specialized metabolites in secretory glandular trichomes (SGTs), which are specialized epidermal cells. In the genus Solanum, SGTs store a diverse collection of glucose and sucrose esters. Profiling of extracts from two accessions (LA1777 and LA1392) of Solanum habrochaites using ultra-high performance liquid chromatography-mass spectrometry (UHPLC/MS) revealed wide acylsugar diversity, with up to 11 isomers annotated for each individual elemental formula. These isomers arise from differences in ester chain lengths and their positions of substitution or branching. Since fragment ion masses were not sufficient to distinguish all isomers, 24 acylsucroses were purified from S. habrochaites accessions and cultivated tomato ( Solanum lycopersicum M82) and characterized using NMR spectroscopy. Two-dimensional NMR spectra yielded assignments of positions of substitution of specific acyl groups, and locations of branching. The range of substitution was wider than reported earlier, and in contrast to previous reports, tetra- and penta-acylsucroses were substituted at position 2 with acyl groups other than acetate. Because UHPLC/MS fails to yield sufficient information about structure diversity, and quantitative NMR of acylsugar mixtures is confounded by structural redundancy, the strategic combination of NMR and UHPLC/MS provides a powerful approach for profiling a class of metabolites with great structural diversity across genotypes. [ABSTRACT FROM AUTHOR]

An understanding of the aggregates and properties of positional isomers can not only uncover how a slight difference in molecular structure alter crystal packing and bulk solid-state properties, but also plays an important role in developing new types of molecule-based functional materials. Herein, we report a study of the molecular packing and static/dynamic luminescence properties of three cyanostilbene (CS)-based isomers (CS1, CS2, CS3) within their single- and two-component molecular solids. Changing the positions of the cyano substitutents in the CS isomers has a marked influence on their packing modes and luminescent properties. Moreover, two-component CS-based materials have been constructed, which exhibit tunable conformations and packing fashions, as well as fluorescence properties, which differ from the pristine CS solids. The CS-based two-component molecular materials show solvent-responsive luminescence due to the dynamic disassembly of the samples. Moreover, it was found that the system based on CS2 and octafluoronaphthalene shows reversible photochromic fluorescence upon alternating light illumination and grinding. Such co-assembly procedures provide a facile way to fabricate patterned luminescent film materials. Therefore, this work not only affords new insight into the relationship between isomers and luminescence from molecular and supramolecular perspectives, but provides an effective strategy to develop multiple-stimuli-responsive luminescent materials. [ABSTRACT FROM AUTHOR]

The syntheses, calculated surface areas and N2 uptakes of two highly augmented {Cu}2 'paddlewheel'-based MOFs provide a direct comparison of tbo and pto framework polymorphs with identical composition. [ABSTRACT FROM AUTHOR]

ABSTRACT The nanostructure of sulfonated polyimide (SPI)/dihydroxynaphthalene (DHN) derivative charge-transfer (CT) complex hybrid films, which are noble alternative polymer electrolyte membranes (PEMs), is determined by a combined visible spectroscopy/quantum mechanical approach. From the visible spectra of SPI/2,6-dihydroxynaphthalene (2,6-DHN) and 1,5-dihydroxynaphthalene (1,5-DHN) CT complex hybrid films, it is confirmed that these films have different maximum wavelength, although difference of the molecular structure is small. From the calculation based on the experimental result, SPI and DHNs form multiple interactions consisting of not only CT interaction, but also hydrogen bonding in multilayered structures. CT interaction between SPI and DHN defines the DHN position in the SPI matrix, with DHN sitting in the cavity formed between SPIs. The molecular structure of the CT films derived from the multiple and complex interactions can recognize small differences in the structural isomers and bring changes of the optical property. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 293-298 [ABSTRACT FROM AUTHOR]

In order to understand the substitution effects of pyrazolylpyridine (pzpy) on the coordination reaction equilibria, the interactions between a series of pzpy-like ligands and biperoxidovanadate ([OV(O2)2(D2O)]−/[OV(O2)2(HOD)]−, abbrv. bpV) have been explored using a combination of multinuclear (1H, 13C, and 51V) magnetic resonance, heteronuclear single quantum coherence (HSQC), and variable temperature NMR in a 0.15 mol L−1 NaCl D2O solution that mimics the physiological conditions. Both the direct NMR data and the equilibrium constants are reported for the first time. A series of new heptacoordinated peroxidovanadate species [OV(O2)2L]− (L = pzpy-like chelating ligands) are formed due to several competitive coordination interactions. According to the equilibrium constants for products between bpV and the pzpy-like ligands, the relative affinity of the ligands is found to be pzpy > 2-Esterpzpy ≈ 2-Me-pzpy ≈ 2-Amide-pzpy > 2-Et-pzpy. In the interaction system between bpV and pzpy, a pair of isomers (Isomers A and B) are observed in aqueous solution, which are attributed to different types of coordination modes between the metal center and the ligands, while the crystal structure of NH4[OV(O2)2(pzpy)]·6H2O (CCDC 898554) has the same coordination structure as Isomer A (the main product for pzpy). For the N-substituted ligands, however, Isomer A or B type complexes can also be observed in solution but the molar ratios of the isomer are reversed (i.e., Isomer B type is the main product). These results demonstrate that when the N atom in the pyrazole ring has a substitution group, hydrogen bonding (from the H atom in the pyrazole ring), the steric effect (from alkyl) and the solvation effect (from the ester or amide group) can jointly affect the coordination reaction equilibrium. [ABSTRACT FROM AUTHOR]

The potential energy surface of C6Li6 was re-examined and a new non-symmetric global minimum was found. The new structure can be described as three C22− fragments strongly aggregated through lithium bridges. At high temperatures, fluxionality is perceived instead of dissociation. At 600 and 900 K, the BOMD simulations show that the lithium mobility is high, indicating that the cluster behaves in a liquid-like manner (BOMD=Born-Oppenheimer molecular dynamics). [ABSTRACT FROM AUTHOR]

Isomers of 1-nitroso-3-nitro-1,2,4-triazol-5-one-2-oxide are of interest in the contest of high explosives and were found to have true local energy minima at the hybrid DFT-B3LYP/aug-cc-pVDZ level. The optimised structures, vibrational frequencies and thermodynamic values for triazol-5-one-N-oxides have been obtained in the ground state. Kamlet–Jacob equations were used to evaluate the performance of model compounds based on the predicted density and the calculated heat of explosion. The detonation properties (D = 10.15–10.46 km/s,P = 50.86–54.25 GPa) of designed compounds were found to be promising compared with 1,3,5-trinitro-1,3,5-triazine (D = 8.75 km/s,P = 34.7 GPa), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (D = 8.96 km/s,P = 35.96 GPa), 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (D = 9.20 km/s,P = 42.0 GPa) and octanitrocubane (D = 9.90 km/s,P = 48.45 GPa). The replacement of secondary hydrogen by nitroso group appears to be a particularly promising area for investigation since it may lead to the desirable consequences of higher heat of explosion, higher density and thus detonation performance. [ABSTRACT FROM AUTHOR]

The stabilities and electronic properties of gold clusters containing up to six atoms trapped inside cyclo[8]thiophene (CS8), cyclo[8]selenophene (CSe8), and cyclo[8]tellurophene (CTe8) nanoaggregates have been studied using the M06 functional. The 6-31G(d) basis set was used for all atoms except Au and Te, for which the LANL2DZ(d,p) pseudopotential basis set was applied. Single-point energy calculations were performed with the 6-311G(d,p) basis set for all atoms except for Au and Te, for which the cc-TZVP-pp pseudopotential basis set was used. Among the three studied macrocycles, only CS8 and CSe8 were found to be capable of nanoaggregate formation. In the lowest-energy conformer of CTe8, the tellurophene fragments adopt an anti orientation, thus impeding a tubular arrangement of the macrocycles. The formation of gold clusters inside the CS8 and CSe8 nanoaggregates is a thermodynamically favorable process, and could represent a potentially useful method of stabilizing metal nanowires. The binding energy between the nanoaggregate and the gold cluster is always higher for selenium-containing complexes than for sulfur-containing ones because Se has a higher affinity than S for Au in such complexes. Interactions of the gold cluster with the nanoaggregate walls can change the geometry of the most stable isomer for the cluster. The relative energies of different isomers are rather similar, suggesting that they coexist. For nanoaggregates containing Au clusters, the cluster geometry when it is inside a nanoaggregate is different from the geometry of the cluster when it is not inside the nanoaggregate, due to the geometric restrictions imposed by the nanoaggregate cavity. The reorganization energy needed to change the geometry leads to lower binding energies for these complexes compared to those of some smaller systems, although the formation of a complex between Au and a nanoaggregate with six CS8 or CSe8 macrocycles is still thermodynamically viable. [ABSTRACT FROM AUTHOR]

Two supramolecular isomers, {[Cd2(pda)2(1,10'-phen)2]H2O}n (1) and {[Cd2(pda)2(1,10'-phen)2]4-H2O}n (2) (1,10'-phen= 1,10-phenanthroline, pda = phenylenediacrylate dianion), have been synthesized and characterized by single-crystal X-ray analysis. Complex 1 exhibits a 3D network constructed from 1D rod-shaped secondary building units, while 2 shows a 3D, twofold interpenetrated framework. There exists a reversible transformation between the pair of isomers: when yellow block crystals of 1 are treated under microwave irradiation, colorless plate crystals of 2 are formed; in turn, if crystals of 2 are dissolved in water and left undisturbed about two weeks at room temperature, crystals of 1 reappear. Fluorescence properties of 1 and 2 have also been studied. [ABSTRACT FROM AUTHOR]

Isomeric diamondoids with the same number $$n$$ of adamantane units (or cells), which share the same molecular formula $$\text{ C}_\mathrm{Q}(\text{ CH})_\mathrm{T}(\text{ CH}_{2})_\mathrm{S}$$, can be divided into valence isomers by partitioning the number $$C $$ of their carbon atoms according to whether they are Quaternary, Tertiary, or Secondary: $$C =Q +T +S$$. Each [ $$n$$]diamondoid has a dualist (or inner dual) with $$n$$ vertices (situated at centers of adamantane units), and edges connecting vertices of adjacent adamantane units sharing a chair-shaped hexagon of carbon atoms. Such a dualist is characterized by a quadruplet of indices (denoted as p, s, t, q for primary, secondary, tertiary, or quaternary) specifying again the connectivity of each vertex by assimilating it with a virtual carbon atom. The diamond lattice is self-dual. Dualists help in classifying diamondoids as catamantanes with acyclic dualists, perimantanes with dualists having chair-shaped six-membered rings, or coronamantanes with dualists having only higher-membered rings. In turn, catamantanes can be either regular when they have formulas $$\text{ C}_{4n+6}\text{ H}_{4n+12}$$, or irregular when the numbers of carbon and hydrogen atoms are lower than the above values for the given numbers $$n$$ of adamantane units. Regular catamantanes can have branched or non-branched dualists and they are isomeric when having the same $$n$$. Partitioned formulas reflect the branching patterns, encoded in their dualists. Partition formulas and codes are presented for all possible diamondoids with up to 7 adamantane units. A remarkable symmetry is observed for the table of partition periodic table of regular catamantanes with up to 7 adamantane units. Isomeric irregular catamantanes with six or more adamantane units may be valence-isomeric (or homomeric, sharing both the molecular and the partitioned formulas), or heteromeric when they have different partitioned formulas. [ABSTRACT FROM AUTHOR]

Density-functional theory calculations are presented for low-energy La@C72, La@C74 and La@C76 isomers with IPR (isolated pentagon rule) and non-IPR cages. The relative isomeric production yields at high temperatures are evaluated using the calculated terms, and the relationships to observations are discussed [ABSTRACT FROM AUTHOR]

At the DFT level with the B3LYP hybride functional the structure and relative stability of geometric isomers of bi- and trithiazolidine-4-ones are calculated. Based on Bader's analysis of the electron density distribution the presence of intramolecular hydrogen bonds and van der Waals interactions is found in the studied isomers. Energies of these interactions are calculated. It is shown that the presence of a substituent in the thiazolidine ring affects the stabiliyty of the studied geometric isomers. [ABSTRACT FROM AUTHOR]