Showing papers by "Sanjay Wategaonkar published in 2015"
TL;DR: In this paper, the authors presented laser spectroscopic investigations of isolated binary complexes of H-bond donor-acceptor molecules containing Sulfur atom and found that electronegativity is a controlling factor to be a potent H-Bond donor/acceptor.
Abstract: The importance of Sulfur centred hydrogen bonds (SCHBs) cannot be underestimated given the current day knowledge of its non-covalent interactions prevalent in many biopolymers as well as in organic systems. Based on the distance/angle constraints available from the structural database, these interactions have been interchangeably termed as van der Waals/hydrogen bonded complexes. There is a lack of sufficient spectroscopic evidence that can unequivocally term these interactions as hydrogen bonding interactions. In this review we present laser spectroscopic investigations of isolated binary complexes of H-bond donor-acceptor molecules containing Sulfur atom. The complexes were formed using supersonic jet expansion method and the IR/UV spectroscopic investigations were carried out on mass selected binary complexes. The pertinent questions regarding SCHBs addressed herein are (1) Is electronegativity the controlling factor to be a potent H-bond donor/acceptor? (2) How do SCHBs compare with their oxygen count...
66 citations
TL;DR: The experiments identify a new conformer (conformer A) in the gas phase for the first time which has also been reported in crystal structures of histidine containing proteins, and no spectral evidence was found for either the C(4)-H∙�’∙ ∼’O or theC(2)-H ∼“∙O interaction.
Abstract: We present the IR spectroscopic investigations of benzimidazole (BIM), N-methylbenzimidazole (MBIM), and their monohydrates (W1) carried out in a supersonic jet in the region of N–H, C–H, and O–H stretching fundamentals. The C–H stretching modes in the monomers were studied with the aim of identifying the C(2)H mode (the C atom between the two N atoms in the imidazole moiety) which is known to play an important role as a H-bond donor in enzymes and ionic liquids. The assignment was aided by quantum chemical calculations as well as the literature data for FTIR measurements in the matrix. The monohydrated clusters were investigated for a global comparison with previously reported conformations of hydrated imidazole and related derivatives in the gas phase, matrices, and He nanodroplets. The BIM–W1 complex showed the presence of three conformers; an N–H⋯O bound conformer (A′) and two O–H⋯N bound conformers, tilted towards the phenyl side (A) and the imidazole side (B), respectively. Although both A′ and B type conformers have been reported in the literature, our experiments identify a new conformer (conformer A) in the gas phase for the first time which has also been reported in crystal structures of histidine containing proteins. The binding energies of the three conformers were found to be of comparable magnitude, with the N–H⋯O bound structure lying in between (∼0.02–0.04 kcal mol−1) the O–H⋯N bound ones at the counterpoise corrected (cp) MP2/aug-cc-pVDZ level of theory. The formation of two distinct but closely related O–H⋯N bound conformers (A and B) was additionally confirmed by studying the MBIM–W1 complex. Binding energies of the MBIM–W1 conformers were found to be higher than those of the analogous BIM–W1 conformers by 0.2 kcal mol−1 at the cp-MP2/aug-cc-pVDZ level. The C(2)–H⋯O or π bound water structures were not observed in the beam for monohydrated clusters of either monomer. While QTAIM calculations predicted secondary stabilization in the A type conformer by a C(4)–H⋯O hydrogen bond, such an effect due to a possible C(2)–H⋯O interaction was not found for conformer B. Experimentally, however, no spectral evidence was found for either the C(4)–H⋯O or the C(2)–H⋯O interaction.
25 citations
TL;DR: The sulfhydryl (S-H) group, like O-H, is found to conform to the widely accepted acid-base nature of hydrogen-bonding interactions in 1:1 complexes of H2S with diethyl ether, dibutyl ether and 1,4-dioxane.
Abstract: The role of sulfhydryl (S–H) group as hydrogen bond donor is not as well studied as that of hydroxyl (O–H). In this work we report on the hydrogen-bonding properties of S–H donor in 1:1 complexes of H2S with diethyl ether (Et2O), dibutyl ether (Bu2O), and 1,4-dioxane (DO). The complexes were prepared in supersonic jet and investigated using infrared predissociation spectroscopy based on VUV photoionization detection. The IR spectra of all the complexes showed the presence of a broad, intensity-enhanced, and red-shifted hydrogen-bonded S–H stretching transition. The S–H stretching frequency was red-shifted by 46, 63, and 49 cm–1 in H2S–Et2O, H2S–Bu2O, and H2S–DO complexes, respectively, suggesting that all the complexes are S–H···O bound. Computationally, two different S–H···O bound structures, namely, “coplanar” and “perpendicular”, were obtained as the minimum energy structures for these complexes at the MP2/6-311++G** level, with the former being the global minimum. However, with Dunning-type basis sets...
25 citations
TL;DR: One of the important findings is that ωB97X-D functional, which is a dispersion corrected DFT functional, was able to predict the dissociation energies in both the cationic as well as the ground electronic state very well for almost every case.
Abstract: In this work we have determined dissociation energies of O-H···S hydrogen bond in the H2S complexes of various phenol derivatives using 2-color-2-photon photofragmentation spectroscopy in combination with zero kinetic energy photoelectron (ZEKE-PE) spectroscopy This is the first report of direct determination of dissociation energy of O-H···S hydrogen bond The ZEKE-PE spectra of the complexes revealed a long progression in the intermolecular stretching mode with significant anharmonicity Using the anharmonicity information and experimentally determined dissociation energy, we also validated Birge-Sponer (B-S) extrapolation method, which is an approximate method to estimate dissociation energy Experimentally determined dissociation energies were compared with a variety of ab initio calculations One of the important findings is that ωB97X-D functional, which is a dispersion corrected DFT functional, was able to predict the dissociation energies in both the cationic as well as the ground electronic state very well for almost every case
14 citations