Sanjay Wategaonkar

Bio: Sanjay Wategaonkar is an academic researcher from Tata Institute of Fundamental Research. The author has contributed to research in topics: Hydrogen bond & Spectroscopy. The author has an hindex of 22, co-authored 68 publications receiving 1421 citations. Previous affiliations of Sanjay Wategaonkar include Rutgers University.

Nature of the N-H...S hydrogen bond.

Abstract: The N−H···S hydrogen-bonded complexes of the model compounds of tryptophan (indole and 3-methylindole) and methionine (dimethyl sulfide, Me2S) have been characterized by a combination of experimental techniques like resonant two-photon ionization (R2PI), resonant ion dip infrared spectroscopy (RIDIRS), and fluorescence dip infrared spectroscopy (FDIRS) and computational methods like ab initio electronic structure calculations, atoms-in-molecules (AIM), natural bond orbital (NBO), and energy decomposition analyses. The results are compared with the N−H···O (M·H2O; M = indole, 3-methyl indole) σ-type and N−H···Φ (M·benzene) π-type hydrogen-bonded complexes. It was shown that the S1−S0 band origin red shifts in the N−H···S hydrogen-bonded complexes correlated well with the polarizability of the acceptor rather than their proton affinity, contrary to the trend observed in most X−H···Y (X, Y = O, N, halogens, etc.) hydrogen-bonded systems. The red shift in the N−H stretching frequency in the N−H···S HB cluster...

Sulfur, Not Too Far Behind O, N, and C: SH···π Hydrogen Bond

Abstract: We report hydrogen-bonded complexes of H(2)S with indole and 3-methyl indole stabilized by the S-H...pi interaction. It is interesting to discover that although sulfur and its hydrides are known as poor hydrogen-bond donor/acceptors, sulfur is not too far behind oxygen, nitrogen, and carbon in regard to forming the pi-type hydrogen bonds. This report also extends the scope of our earlier studies from sigma-type hydrogen-bonded complexes of sulfur (O-H...S and N-H...S sigma-type hydrogen-bonded complexes) to pi-type hydrogen-bonded complexes of sulfur (S-H...pi pi-type hydrogen-bonded complexes). The experiments were carried out using the supersonic jet expansion technique, and the complexes were probed using laser-induced spectroscopy such as laser-induced fluorescence (LIF), resonant two-photon inonization (R2PI), and fluorescence dip infrared spectroscopy (FDIRS). The FDIR spectroscopy revealed that while there was no shift in the N-H stretch, the S-H stretch was red shifted by about 21 cm(-1). For the H(2)O complexes of indole and 3-methylindole, however, there was a significant red shift in the N-H stretch. These observations suggest that H(2)O forms a NH...O type complex, whereas H(2)S prefers to form a SH...pi type complex. The experimental results were complemented by ab initio calculations and energy decomposition analysis. The binding energies for both the sigma-type and pi-type hydrogen-bonded M.L complexes (M = indole and 3-methylindole; L = H(2)O and H(2)S) were calculated by extrapolating MP2 interaction energies to the complete basis set limit. The calculated M.H(2)S (sigma-type) interaction energy (2.74 kcal/mol) was considerably smaller than that of the M.H(2)S pi-type hydrogen-bonded complex (4.89 kcal/mol), which is exactly opposite of the trend found for the M.H(2)O complexes. This is consistent with the experimental observations. Comparison of the S-H...pi interaction with the other type of X-H...pi (X = C, N, and O) shows that the S-H...pi interaction is the strongest among them. In all of the pi-type HB complexes, the dispersion energy component has significant contribution to the total binding energy.

O-H...O versus O-H...S hydrogen bonding I: Experimental and computational studies on the p-cresol x H2O and p-cresol x H2S complexes.

Abstract: The weak hydrogen bonding ability of sulfur-containing hydrides makes it difficult to study their complexes and has not been characterized experimentally so far. In this work, the hydrogen-bonded complexes of H2S and H2O with p-cresol (p-CR) were studied using a variety of techniques such as two-color resonant two-photon ionization (2c-R2PI) spectroscopy, single vibronic level fluorescence (SVLF) spectroscopy, resonance ion dip infrared spectroscopy (RIDIRS), and fluorescence dip infrared spectroscopy (FDIRS), with an aim of comparing the nature and strength of their respective hydrogen bonding abilities. The intermolecular stretch (σ) and the shift in the O−H stretching frequency of p-CR in the complex were taken as the measures of the O−H···O and O−H···S hydrogen bonding strength. The experiments were complemented by the ab initio calculations, atoms in molecules (AIM), natural bond orbital (NBO), and energy decomposition analyses carried out at different levels of theory. The experimental data indicate...

O-H...O versus O-H...S hydrogen bonding. 2. Alcohols and thiols as hydrogen bond acceptors

Abstract: In this paper, the effect of alkyl substitution at the hydrogen bond acceptor and its chain length on the strength and nature of hydrogen bonding is presented. In the present study we combine both experimental and computational methods to investigate the characteristics of O−H···O and O−H···S hydrogen bonding in the complexes of p-cresol (p-CR) with methanol (MeOH), ethanol (EtOH), methanethiol (MeSH), and ethanethiol (EtSH). The results indicate that, with an increase in the alkyl chain length, both O−H···O hydrogen bonding and O−H···S hydrogen bonding become stronger. Energy decomposition analysis emphasizes the dispersive nature of O−H···S hydrogen bonding. In addition, it revealed that the dispersion energy contribution in O−H···O hydrogen bonding increases with an increase in the alkyl chain length of the hydrogen bond acceptor. In the case of O−H···S hydrogen bonding, however, the dispersion energy contribution decreased from 68% for the H2S complex to 53% in the case of the MeSH complex; it remaine...

Nature and strength of sulfur-centred hydrogen bonds: laser spectroscopic investigations in the gas phase and quantum-chemical calculations

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...

Jaguar: A high-performance quantum chemistry software program with strengths in life and materials sciences

Abstract: Jaguar is an ab initio quantum chemical program that specializes in fast electronic structure predictions for molecular systems of medium and large size. Jaguar focuses on computational methods with reasonable computational scaling with the size of the system, such as density functional theory (DFT) and local second-order Moller–Plesset perturbation theory. The favorable scaling of the methods and the high efficiency of the program make it possible to conduct routine computations involving several thousand molecular orbitals. This performance is achieved through a utilization of the pseudospectral approximation and several levels of parallelization. The speed advantages are beneficial for applying Jaguar in biomolecular computational modeling. Additionally, owing to its superior wave function guess for transition-metal-containing systems, Jaguar finds applications in inorganic and bioinorganic chemistry. The emphasis on larger systems and transition metal elements paves the way toward developing Jaguar for its use in materials science modeling. The article describes the historical and new features of Jaguar, such as improved parallelization of many modules, innovations in ab initio pKa prediction, and new semiempirical corrections for nondynamic correlation errors in DFT. Jaguar applications in drug discovery, materials science, force field parameterization, and other areas of computational research are reviewed. Timing benchmarks and other results obtained from the most recent Jaguar code are provided. The article concludes with a discussion of challenges and directions for future development of the program. © 2013 Wiley Periodicals, Inc.

Aromatic rings in chemical and biological recognition: energetics and structures.

Abstract: This review describes a multidimensional treatment of molecular recognition phenomena involving aromatic rings in chemical and biological systems. It summarizes new results reported since the appearance of an earlier review in 2003 in host-guest chemistry, biological affinity assays and biostructural analysis, data base mining in the Cambridge Structural Database (CSD) and the Protein Data Bank (PDB), and advanced computational studies. Topics addressed are arene-arene, perfluoroarene-arene, S⋅⋅⋅aromatic, cation-π, and anion-π interactions, as well as hydrogen bonding to π systems. The generated knowledge benefits, in particular, structure-based hit-to-lead development and lead optimization both in the pharmaceutical and in the crop protection industry. It equally facilitates the development of new advanced materials and supramolecular systems, and should inspire further utilization of interactions with aromatic rings to control the stereochemical outcome of synthetic transformations.

Relevance of Weak Hydrogen Bonds in the Conformation of Organic Compounds and Bioconjugates: Evidence from Recent Experimental Data and High-Level ab Initio MO Calculations

Abstract: Organic chemists tend to consider the conformation of compounds as a consequence of repulsive steric interactions. In other words, “the steric effect” means “repulsive” in many cases. Thus, folded conformations observed in organic molecules have been often regarded as unusual, while the reason remained undecided. However, accurate determinations by modern spectroscopic methods, recent crystallographic data, and high-level ab initio MO calculations have demonstrated that the folded conformation is by no means exceptional. We will show that the gauche or folded conformation prevails in organic compounds bearing at least an electronegative or π-group in the molecule. We consider that the above phenomenon finds its origin, in most cases, in nonconventional hydrogen bonds such as the CH/X (X ) O, halogen, etc.) and the XH/π (X ) O, N, C, etc.) hydrogen bonds. * To whom correspondence should be addressed. E-mail: shu@ hiroshima-u.ac.jp. ‡ Hiroshima University. § Yokohama National University. ⊥ The CHPI Institute. Chem. Rev. 2010, 110, 6049–6076 6049

Supramolecular Luminescent Sensors

Abstract: There is great need for stand-alone luminescence-based chemosensors that exemplify selectivity, sensitivity, and applicability and that overcome the challenges that arise from complex, real-world media. Discussed herein are recent developments toward these goals in the field of supramolecular luminescent chemosensors, including macrocycles, polymers, and nanomaterials. Specific focus is placed on the development of new macrocycle hosts since 2010, coupled with considerations of the underlying principles of supramolecular chemistry as well as analytes of interest and common luminophores. State-of-the-art developments in the fields of polymer and nanomaterial sensors are also examined, and some remaining unsolved challenges in the area of chemosensors are discussed.