Reaction of the triethylammonium salt of the substituted diphenyldithiophosphate ligands with AsCl3 in a 3:1 ratio results in the formation of the arsenic complexes As[S2P{OC6H4(4-C2H5)}(2)](3) (1), As[S2P{OC6H4(4-(CH3)(3)C)}(2)](3) (2), As[S2P{OC6H3(2,4-CH3)(2)}(2)](3) (3), As[S2P{OC6H3(2,5-CH3)(2)}(2)](3) (4), As[S2P{OC6H3(3,4-CH3)(2)}(2)](3) (5), and As[S2P{OC6H3(3,5-CH3)(2)}(2)](3) (6). The characterization of all the synthesized complexes was done by IR and multinuclear NMR (H-1, C-13, and P-31) spectroscopies. Complexes 1 and 2 were structurally elucidated by single-crystal X-ray analysis. The X-ray data reveals that 1 and 2 were crystallized in triclinic crystal system with space group P(-)1 and monoclinic crystal system with space group C2/c, respectively. In 1 and 2, the coordination geometry around the central arsenic atom is pseudo-trigonally distorted octahedral with a lone pair of electrons positioned on one of the triangular faces of the octahedral. The central As atom in both complexes is surrounded by six sulfur atoms of the chelating anisobidentate ligands. The density functional theory computations are also carried out to further analyze the geometry and quantum chemical parameters in order to support the experimental and structural data. Finally, to estimate the effect of alkyl steric bulk in diphenyldithiophosphate complexes 1 and 2 on the intermolecular contacts contributions to the Hirshfeld surface analysis and 2-D finger-print plots analysis have been employed.

An accurate quantitative prediction for concentration-dependent adsorption of organic compounds by carbon-nanotubes (CNTs) is increasingly in demand to evaluate not only their applications but also risk associated using CNTs. This is often carried out using poly-parameter linear-solvation-energy-relationships (pp-LSERs) based on adsorbate descriptors. This work examines the predictivity of existing pp-LSERs in the prediction of adsorption of aromatic organic compounds by multi-walled CNTs (MWCNTs) at five different adsorbate concentrations, and compares that with the predictivity of quantum-mechanical models while revealing an essential role of electron-correlation. Notably, the most influencing descriptor for the adsorption was found to be the mean polarizability but that arising from the quantum-mechanical exchange interactions between electrons of the same spin. This work also proposes reliable predictive models based on a combination of the quantum-mechanical descriptors and pp-LSER's descriptors, which were applied to predict the adsorption of nucleobases and steroid hormones, with Progesterone found to be maximally adsorbed.

Solubility of fullerenes in diverse solvents is difficult to model owing to the involvement of inherent quantum-mechanical interactions. This work proposes pure quantum mechanical models for predicting the solubility of C-70 fullerenes. The models are developed using single-molecule quantum mechanical properties of solvents,which includes electron-correlation based descriptors accounting for the instantaneous inter-electronic interactions responsible for the origin of these properties. The external predictivity of the models was validated using an external prediction set of compounds not exposed to the model during its development. The most influential factor affecting the solubility was found to be electron-correlation contribution to the energy of highest occupied molecular orbital of solvents, which in fact, has been analyzed to suppress the solubility of fullerenes. However, the polarizability of the solvents, particularly that due to the quantum-mechanical exchange interactions between the electrons, is observed to drive the solubility of C-70 fullerenes. The present work also found several other quantum mechanical properties affecting the solubility of fullerenes, which pay valuable insights towards the origin of the solubility of carbon-based nanomaterials.

Graphene oxide is most often chosen as an alternative to graphene in the applications of carbon-based nanomaterials where adsorption is the primary process. However, its adsorption properties are poorly understood. The existing reports on the adsorption mechanism of graphene oxide rely on the linear free-energy/solvation-energy relationship (LFER/LSER) models. This computational work explores the role of quantum mechanical descriptors in the adsorption of aromatic organic compounds by graphene-oxide. For this, externally predictive quantitative models based on quantum-mechanical descriptors are developed and compared with the existing LSERs for the prediction of adsorption coefficients of organic compounds at three different adsorbate concentrations. The predictivity of the models is assessed using an external prediction set of compounds not used for developing the models. Notably, the mean polarizability, but originating from the quantum mechanical exchange interactions (between electrons of parallel spin), is found to be the most significant factor in driving the adsorption on graphene oxide. The present work also proposes quantum-mechanical-LSER models based on a combination of quantum-mechanical and LSER descriptors, which are in fact found to be equally predictive as the existing LSERs. The quantum-mechanical models proposed in this work are further utilized for the prediction of adsorption coefficients of aliphatic compounds.

Enantiomeric excess of amino acids observed in the meteoritic samples of carbonaceous chondrites has incited many researchers to search for an extra-terrestrial origin of life on prebiotic Earth. However, in a non-catalytic environment, only racemic amino acids are synthesized. This computational quantum-mechanical study explores non-catalytic mechanistic pathways for stereoinversion in proteinogenic L-glutamic acid, which may be observable under gas-phase conditions of interstellar medium (ISM). The multi-step stereoinversion pathways proposed in this study are traced through a global reaction route mapping (GRRM) strategy utilizing density-functional and coupled-cluster theories. Notably, a few of the pathways are observed to proceed through simultaneous intramolecular hydrogen atom and proton transfer as well as through a proton-coupled electron transfer mechanism. The intermediates explored along the stereoinversion pathways resemble ammonium ylide and imine, the key ingredients in Strecker synthesis of amino acids. The thermodynamic and kinetic analysis of the stereoinversion pathways in different temperature regions of ISM are also carried out, predicting the streoinversion to proceed over any dissociation of intermediates and conformers of glutamic acid along the pathways. However, initial step of the pathways involves an unsurmountable energy barrier though the key step responsible for stereoinversion has a very low energy barrier and is predicted to proceeds with significant rates. The work suggests the possibility of observing stereoinversion of glutamic acid in the warmer regions of ISM.

Carbon nanotubes (CNTs) have taken precedence over activated carbon in various applications where adsorption is the primary process. The adsorption of chemical compounds by CNTs and activated carbon is most often predicted through linear free energy/solvation energy relationships (LFERs/LSERs). This work proposes quantum-mechanical LSER models based on a combination of quantum-mechanical descriptors and solvatochromic descriptors of LSERs for predicting the adsorption of aromatic organic compounds by activated carbon at varying adsorbate concentrations. The models are validated using state-of-the-art procedures employing an external prediction set of compounds. This work reveals the hydrogen bond donating and accepting ability of compounds to be the most influencing – but a negative – factor in the adsorption process of activated carbon. The quantum-mechanical LSERs proposed in this work are analysed and found to be equally reliable as the existing LSERs. These were further used to predict the adsorption of nucleobases, steroid hormones, agrochemicals, endocrine disruptors and pharmaceutical drugs. Notably, agrochemicals and endocrine disruptors are predicted to be adsorbed more strongly by activated carbon when compared with their adsorption by CNTs. However, quantum-mechanical LSERs predict the adsorption strength of biomolecules on activated carbon to be similar to that on the CNTs, which can be used to assess the risk associated with using carbon materials.

The gas-phase stereoinversion of amino acid threonine under the condition of interstellar medium (ISM) has been predicted to proceed through isomeric species with diverse chemistry. These species including ammonium ylides, epoxides, contain a variety of functional groups such as geminal-diol, triol besides alkenyl, carboxy, keto, hydroxy, and amino groups. The detection of these species in ISM can help in unravelling the enantiomeric excess observed in meteoritic samples. Towards this, the present work reports rotational and vibrational spectroscopic data computed for the conformers and isomeric intermediates predicted along the stereoinversion pathways of proteinogenic threonine under conditions akin to ISM. The rotational parameters are computed using quantum mechanical methods employing Møller–Plesset perturbation theory whereas for the vibrational analysis, density functional computations are performed using dispersion corrected exchange-correlation functionals. The anharmonic corrections are also computed using vibrational second-order perturbation theory, which, however, fails to account for the hydrogen bonded interactions in the species investigated. The rotational and vibrational transitions predicted for the conformers of threonine are observed to be in good agreement with the available experimental data. The gas-phase spectroscopic data computed for other isomeric species of threonine is quite reliable and can be used to search threonine or other amino acids in ISM by resolving the astrophysical data observed in the microwave and mid-infrared regions.

Noncatalytic reaction pathways for the gas-phase stereoinversion in aspartic acid are mapped employing a global reaction route mapping strategy using quantum mechanical computations. The species including the transition states (TSs) traced along the stereoinversion pathways are characterized using rotational and vibrational computational spectroscopic analysis while accounting for the vibrational corrections to rotational constants and anharmonic effects. Notably, the TS structures traced along the stereochemical pathways resemble the achiral ammonium ylide and imine intermediates as observed in the Strecker synthesis of chiral amino acids. A few of the probable stereoinversion pathways proposed proceed through the proton or hydrogen atom transfer. The feasibility of the pathways under conditions akin to interstellar medium (ISM) is further discussed in terms of natural bond orbital analysis. The stereoinversion pathways proposed in this work may proceed via photoirradiation in the ISM, which though can be revealed by exploring the excited-state potential energy surface. In this context, the spectroscopic data generated in this work can provide valuable assistance toward the astrophysical detection of chiral molecules in outer space.

There are some unsettled issues regarding the mechanism and kinetics of an important atmospheric reaction of NO2 radical with the SH radical. The existing mechanism is based on the formation of HSO and NO radicals, both of which can result only along one barrierless channel. However, the detection of NO radical has never been reported though the formation of HSO radical has been followed in some studies to determine the rate constants. The latter are mainly obtained by monitoring the SH decay, but rate constants are reported to be highly conflicting among the existing studies reporting its value ranging from 10(-10) to 10(-12) cm(3) molecule(-1) sec(-1). The present work attempts to resolve these issues by exploring various reaction pathways through the global reaction route mapping of the potential energy surface at the level of spin-unrestricted and spin-restricted coupled-cluster and density functional theories. The initial association of two radicals was found to proceed via two barrierless modes: (1) S-N association leading to HSNO2 and, (2) S-O association resulting in HSONO, in particular the cis-isomer. The kinetics of the barrierless pathways was investigated through rate constants computed using canonical variational transition state theory (CVTST) along with their temperature and pressure dependence investigated using the master equation. The rate constants calculated using spin-unrestricted methods are found to be in agreement with experimentally observed range of rate constant, and the formation of cis-HSONO (via mode 2) is observed to be the main contributing channel. Contrary to the results of spin-restricted calculations, the barrierless channel (mode 1) leading to the formation of HSNO2 is predicted to involve two bottlenecks when results using spin-unrestricted calculations were analyzed. Notably, the spin-unrestricted calculations predict a prereaction complex for the formation of S-N bond (via mode 1) which has been treated using Miller's unified transition state theory with a two transition state model. The fate of all the species involved in the reaction is critically evaluated in the present work, and the predictions made can be a subject of further experimental and theoretical studies involving radical-radical reactions.

For evaluating the environmental risk associated using carbon nanotubes (CNTs), a successful prediction is desired for the adsorption of organic compounds (OCs) by CNTs at different adsorbate concentrations. This is most often achieved through poly-parameter linear solvation energy relationships (LSERs) based on solvatochromic descriptors. This study examines the real predictivity of the existing LSERs for predicting the adsorption of OCs by single-walled CNTs (SWCNTs) while comparing it with that of the models developed in the present work using quantum-mechanical descriptors. The real predictivity of the quantum-mechanical models and existing LSERs is compared using state-of-the-art statistical procedures employing an external prediction set of compounds not used in the model development. The quantum-mechanically computed mean polarizability, but originating from the interactions between electrons of parallel spin, is found to play an essential role in the adsorption of OCs by SWCNTs. Besides the solvatochromic descriptors (McGowan volume and molar excess refractivity), the instantaneous inter-electronic interactions, captured through electron-correlation based quantum-mechanical descriptors, are found to significantly affect the adsorption at varying adsorbate concentration. The models developed using a combination of quantum-mechanical and solvatochromic descriptors are found to be quite reliable. The models proposed were further employed to predict the adsorption of agrochemicals such as insecticides, pesticides, herbicides, as well as adsorption of endocrine disruptors and biomolecules such as nucleobases and steroid hormones. These are predicted to be strongly adsorbed by SWCNTs with Progesterone and Guanine exhibiting maximal interaction with the SWCNTs among biomolecules. The quantum-mechanical descriptors proposed in this work can be used for the risk assessment of SWCNTs in systems where adsorption is the primary process.

Quantum-mechanical computations are performed to trace the mechanistic pathways for the gas-phase stereoinversion in proteinogenic L-threonine, an amino acid with two stereocenters. The pathways are explored employing density functional and coupled cluster theories along with a global reaction route mapping strategy to locate various intermediates and transition states along the stereoinversion pathways on the complex potential energy surface of L-threonine. A simultaneous intramolecular proton and hydrogen atom transfer is observed to drive the stereoinversion in threonine. The kinetics analysis of the stereoinversion pathways is also carried out using transition state theory while accounting for the quantum mechanical tunnelling under conditions akin to various temperature regions of interstellar medium (ISM). The key step leading to stereoinversion through an achiral intermediate or transition state is predicted to involve a low energy barrier with high stereoinversion rates. The temperature region of 500-1000 K corresponding to protoplanetary disks was found to be an optimum region for stereoinversion to occur in L-threonine with quite significant reaction rates. However, in the cold molecular clouds of ISM the stereoinversion is predicted to be a less likely event despite involving significant proton tunnelling. The stereoinversion pathways proposed in this work pay gainful insights, particularly, to the researchers looking for the complex organic molecules in outer space.

Aryldithiocarbonates of titanium(IV) and zirconium(IV) corresponding to [(ROCS2)(2)MCl2] (R = o-, m- or p-CH3C6H4 and 4-CI-3-CH3C6H3; M = Ti or Zr) have been isolated by the reaction of sodium salt of dithiocarbonates with titanium or zirconium tetrachloride in 1:2 M ratio in CHCl3. Donor stabilized addition complexes of titanium/zirconium with aryldithiocarbonates were also successfully isolated in chloroform. These have been characterized by elemental analyses, IR, mass, TGA/DTA, SEM and heteronuclear NMR (H-1, C-13 and P-31) spectroscopic studies. The antimicrobial test of these complexes has also been conducted against the bacteria Klebsiella pneumonia and Enterococcus faciolus and fungus Fusarium oxysporium, which indicate potential antimicrobial activity. In addition, the antioxidant activities of the complexes were also investigated through their scavenging effect on DPPH radicals. Density Functional Theory (OFT) calculations have been carried out to investigate geometry parameters of the complexes using B3LYP method and LANL2DZ basis set. HOMO (Highest Occupied Molecular Orbital), LUMO (Lowest Unoccupied Molecular Orbital) energies are analyzed. Based on analytical and theoretical results, a hexacoordinate geometry is concluded around the Ti or Zr atom. (C) 2017 Elsevier B.V. All rights reserved.

A single water molecule is known to significantly lower the potential energy barrier in the atmospheric reactions of hydroxyl radical with volatile organic compounds but except at extremely low temperatures, it has never been observed to accelerate the reactions investigated so far. This quantum-mechanical computational work reveals a probable case of observing a single water molecule accelerating the atmospheric reactions of Trifluoroacetic acid and Trifluoroacetaldehyde at temperatures near 200 K under tropospheric conditions. (C) 2017 Elsevier B.V. All rights reserved.

In order to assess the potential role of a single water molecule as a catalyst, the gas-phase oxidation reaction of hydroxyl radical with glyoxylic acid has been investigated by the means of quantum mechanical computations using CCSD(T), MP2 and DFT methods. The pre-reaction complexes along the oxidation pathways are systematically explored through a global reaction route mapping method. The computations reveal that a single water molecule stabilizes the pre-reaction complexes as well as respective transition states, resulting in the lowering of the energy barrier, however, the transition state theory computed rate constants for the water-catalysed pathways are found to be an order of magnitude lower than that for the water-free pathways. Notably, the abstraction of formyl hydrogen is observed to be most favourable both in the presence and absence of a single water molecule. Besides these, a couple of triple-proton exchange pathways involving simultaneous proton transfer between the glyoxylic acid, OH radical and a single water molecule are also explored. All the pathways are observed to proceed through conventional free radical mechanism when analysed using BHandHLYP exchange–correlation (XC) functional of DFT. However, DFT method using other XC functionals revealed that one of the relevant acidic H-abstraction pathways proceeds through a proton-coupled electron-transfer mechanism and also results in the dissociation of glyoxylic acid. The pathways for trans form of glyoxylic acid has also been compared with those explored for the cis form. The standard Gibbs free-energy profiles for the reactions studied indicate that the hydrogen abstraction, particularly in trans-glyoxylic acid, may be more feasible than the dissociation, particularly at lower temperatures. This study may assist future investigation of similar atmospheric reactions.

The dianions and trianions of doubly- and triply-deprotonated naphthalenes are investigated using density functional theory (DFT) computations employing hybrid, long-range, and dispersion corrected exchange-correlation functionals. The investigated polyanionic species are found to be metastable with negative electron affinity and are further treated using a nuclear-charge stabilization method. The tunneling lifetimes of these anionic species were estimated to be a few femtoseconds. Notably, the deprotonated energies (DPEs) of naphthalene leading to the formation of triply deprotonated trianions are observed to be affected by the metastability of the dianions and trianions. For the deprotonation of doubly deprotonated dianions, the DPE calculated using the improved methodology based on the stabilization method is found to be nearly 100 kcal/mol more than that computed using the conventional procedure. Though the various DFT approximations employed are in a good agreement for predicting the lifetimes of the metastable species but in the prediction of electron-affinities and deprotonation energies, the dispersion-corrected DFT-D3 significantly disagrees with the long-range corrected DFT methods employing cam-B3LYP and ωB97XD exchange-correlation functionals.

This work reveals that though a single-water molecule decelerates the atmospheric reaction between the glycolaldehyde and OH radical, however, it facilitates thecis–​transinterconversion along the hydrogen-abstraction pathways.

The role of dynamic interactions between electrons (the electron-correlations) in the prediction of inhibitory growth concentration of alkyl- and halogen-substituted nitrobenzenes against Tetrahymena pyriformis is analyzed through the quantitative structure–activity relationships (QSARs) based on the widely used quantum-chemical descriptors. The advanced semi-empirical and ab initio quantum-mechanical methods are employed for the computation of the descriptors and their electron-correlation contribution. The statistical quality of the proposed QSAR models is assessed through the state-of-the-art external validation parameters via employing an external prediction set of compounds. This study revealed that the models based on the quantum-chemical descriptors incorporating mainly the effect of dynamical electron-correlation are significantly robust and externally predictive, in particular, the models based on the electron-correlation energy are found to be highly reliable. Besides this, the electron-correlation contributions to the orbital energies and to the electrophilicity index are also observed to be significant. The present work emphasizes that the biological activities of chemicals are significantly influenced by the “correlated” motion of electrons in the molecule.

Quantum-mechanical exchange and correlation interactions between electrons are quite crucial in deciding molecular geometry and properties. Such electronic interactions can have a significant role in the reliability of a quantitative structure–activity relationship (QSAR) because the biological activities of the chemicals can be described as a function of the molecular structure through the QSARs which are routinely based on the quantum-mechanical molecular descriptors. In this work, we present a detailed analysis of the effect of the quantum-mechanical exchange and correlation on the internal stability and external predictivity of a QSAR model based on the quantum-mechanical molecular descriptors while modeling the mutagenic activity of a set of 51 nitrated-polycyclic aromatic hydrocarbons (PAHs). For this, various molecular descriptors are computed using electronic structure methods such as the Hartree–Fock (HF) method, and density functional theory (DFT) employing only the exchange functionals (HFX, B88), pure exchange and correlation functionals (HFX + LYP, BLYP), hybrid (B3LYP), meta (M06-L), and meta-hybrid (M06, M06-2X) exchange–correlation (XC) functionals. To further analyze the role of electron-correlation, QSAR models are also developed using the descriptors incorporating mainly the effect of electron-correlation. The external predictivity of the developed models is assessed through state-of-the-art external validation parameters employing an external prediction set of compounds. A comparison of the quality of the models developed with the descriptors computed using different electronic structure methods revealed that the exchange interactions are quite critical along with the electron-correlation in modeling the mutagenicity. Notably, for most of the models, electron-correlation based descriptors are found to be highly reliable when computed using the hybrid XC functionals, particularly B3LYP and M06-2X.

A systematic exploration for d–l interconversion in serine reveals uncovered stereochemical pathways at the DFT, MP2 and CCSD(T) levels of theory. The computations explored three feasible multi-step reaction pathways involving the interchange of functional groups, namely, [H, NH2], [CH2OH, NH2] and [H, COOH] around the chiral carbon-atom in serine. The [CH2OH, COOH] interchange, however, is observed to be hindered for the d–l interconversion in case of serine, contrary to that observed in the case of alanine. Notably, one of the feasible pathways in serine proceeds through an unconventional 1,4-proton shift.

This work reveals interesting pathways for water-migration and neutral ↔ zwitterionic isomerisation in the water complexes of l-proline.