Publications by authors named "Poonam Tandon"

51 Publications

Molecular Structure, Spectral Investigations, Hydrogen Bonding Interactions and Reactivity-Property Relationship of Caffeine-Citric Acid Cocrystal by Experimental and DFT Approach.

Front Chem 2021 26;9:708538. Epub 2021 Jul 26.

Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, Sweden.

The pharmaceutical cocrystal of caffeine-citric acid (CAF-CA, Form II) has been studied to explore the presence of hydrogen bonding interactions and structure-reactivity-property relationship between the two constituents CAF and Citric acid. The cocrystal was prepared by slurry crystallization. Powder X-ray diffraction (PXRD) analysis was done to characterize CAF-CA cocrystal. Also, differential scanning calorimetry (DSC) confirmed the existence of CAF-CA cocrystal. The vibrational spectroscopic (FT-IR and FT-Raman) signatures and quantum chemical approach have been used as a strategy to get insights into structural and spectral features of CAF-CA cocrystal. There was a good correlation among the experimental and theoretical results of dimer of cocrystal, as this model is capable of covering all nearest possible interactions present in the crystal structure of cocrystal. The spectroscopic results confirmed that (O33-H34) mode forms an intramolecular (C25 = O28∙∙∙H34-O33), while (O26-H27) (O39-H40) and (O43-H44) groups form intermolecular hydrogen bonding (O26-H27∙∙∙N24-C22, O39-H40∙∙∙O52 = C51 and O43-H44∙∙∙O86 = C83) in cocrystal due to red shifting and increment in bond length. The quantum theory of atoms in molecules (QTAIM) analysis revealed (O88-H89∙∙∙O41) as strongest intermolecular hydrogen bonding interaction with interaction energy -12.4247 kcal mol in CAF-CA cocrystal. The natural bond orbital analysis of the second-order theory of the Fock matrix highlighted the presence of strong interactions (N∙∙∙H and O∙∙∙H) in cocrystal. The HOMO-LUMO energy gap value shows that the CAF-CA cocrystal is more reactive, less stable and softer than CAF active pharmaceutical ingredients. The electrophilic and nucleophilic reactivities of atomic sites involved in intermolecular hydrogen bond interactions in cocrystal have been demonstrated by mapping electron density isosurfaces over electrostatic potential i.e. plotting molecular electrostatic potential (MESP) map. The molar refractivity value of cocrystal lies within the set range by Lipinski and hence it may be used as orally active form. The results show that the physicochemical properties of CAF-CA cocrystal are enhanced in comparison to CAF (API).
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http://dx.doi.org/10.3389/fchem.2021.708538DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8350318PMC
July 2021

Vibrational and conformational analysis of structural phase transition in Estradiol 17β valerate with temperature.

Spectrochim Acta A Mol Biomol Spectrosc 2021 Dec 24;263:120219. Epub 2021 Jul 24.

Instituto de Fìsica de São Carlos, Universidade de São Paulo,C.P 369, 13560-970,São Carlos, S P, Brazil.

Estradiol 17β valerate (E2V) is a hormonal medicine widely used in hormone replacement therapy. E2V undergoes a reversible isosymmetric structural phase transition at low temperature (̴ 250 K) which results from the reorientation of the valerate chain. The reversible isosymmetric structural phase transition follows Ehrenfest's classification when described as first-order and Buerger's classification when classified as order-disorder. The conformational difference also induces changes in molecular torsional angles and on the hydrogen bond pattern. In combination with density functional theory (DFT) calculations, vibrational spectroscopy has been used to correlate the valerate chain modes with the modifications of the dihedral angles on phase transition. We are expecting improvement in our understanding of the phase transition mechanism driven by the temperature. The Conformational analysis reveals the feasible structures corresponding to changes in the dihedral angles associated with the valerate chain. The infrared spectra of calculated conformers are in good agreement with the experimental spectra of E2V structure recorded at room temperature revealing that the changes in valerate chain modes at 1115 cm, 1200 cmand 1415 cm fingerprint the molecular conformation. An investigation made to determine the ligand-protein interaction of E2V through docking against estrogen receptor (ER) reveals the inhibitive and agonist nature of E2V.
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http://dx.doi.org/10.1016/j.saa.2021.120219DOI Listing
December 2021

Molecular structure and quantum descriptors of cefradine by using vibrational spectroscopy (IR and Raman), NBO, AIM, chemical reactivity and molecular docking.

Spectrochim Acta A Mol Biomol Spectrosc 2021 Feb 24;246:118976. Epub 2020 Sep 24.

Department of Physics, University of Lucknow, Lucknow 226 007, India. Electronic address:

This study aims to investigate the structural and vibrational features of cefradine (the first-generation cephalosporin antibiotic) based on spectroscopic experiments and theoretical quantum chemical approach. The fundamental structural aspects of cefradine have been examined based on optimized geometry, spectroscopic behavior, intermolecular interaction, chemical reactivity, intramolecular hydrogen bonding, and molecular docking analysis. The most stable minimum energy conformer of the title molecule was identified by performing a one-dimensional potential energy surface scan along the rotational bonds at B3LYP/6-311++G (d,p) level of theory. The vibrational features of the molecule and information about the coupled modes were predicted. The chemical reactivity and stability of all the possible conformers of cefradine were estimated based on the HOMO-LUMO energy gap and NBO approach. The overall picture of accumulation of charges on individual atoms of the molecule was predicted by molecular electrostatic potential (MEP) surface map which in turn identifies the nucleophilic and electrophilic region or sites. The quantitative analysis of electrophilicity and nucleophilicity indices was done by Hirshfeld charge analysis and it was found that N8 atom is the most prominent site for nucleophilic attack while C14 atom is feasible for electrophilic attack. QTAIM study has also been performed to investigate the nature and strength of hydrogen bonding interactions. Besides, molecular docking studies were performed to examine the active binding residues of the target.
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http://dx.doi.org/10.1016/j.saa.2020.118976DOI Listing
February 2021

Physicochemical and Pharmacokinetic Analysis of Anacardic Acid Derivatives.

ACS Omega 2020 Mar 13;5(11):6021-6030. Epub 2020 Mar 13.

Inorganic Materials Research Laboratory, Department of Chemistry, Jamia Millia Islamia, New Delhi 110025, India.

Anacardic acid (AA) and its derivatives are well-known for their therapeutic applications ranging from antitumor, antibacterial, antioxidant, anticancer, and so forth. However, their poor pharmacokinetic and safety properties create significant hurdles in the formulation of the final drug molecule. As a part of our endeavor to enhance the potential and exploration of the anticancer activities, a detailed study on the properties of selected AA derivatives was performed in this work. A comprehensive analysis of the drug-like properties of 100 naturally occurring AA derivatives was performed, and the results were compared with certain marketed anticancer drugs. The work focused on the understanding of the interplay among eight physicochemical properties. The relationships between the physicochemical properties, absorption, distribution, metabolism, and excretion attributes, and the in silico toxicity profile for the set of AA derivatives were established. The ligand efficacy of the finally scrutinized 17 AA derivatives on the basis of pharmacokinetic properties and toxicity parameters was further subjected to dock against the potential anticancer target cyclin-dependent kinase 2 (PDB ID: 1W98). In the docked complex, the ligand molecules (AA derivatives) selectively bind with the target residues, and a high binding affinity of the ligand molecules was ensured by the full fitness score using the SwissDock Web server. The BOILED-Egg model shows that out of 17 scrutinized molecules, 3 molecules exhibit gastrointestinal absorption capability and 14 molecules exhibit permeability through the blood-brain barrier penetration. The analysis can also provide some useful insights to chemists to modify the existing natural scaffolds in designing new anacardic anticancer drugs. The increased probability of success may lead to the identification of drug-like candidates with favorable safety profiles after further clinical evaluation.
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http://dx.doi.org/10.1021/acsomega.9b04398DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7098041PMC
March 2020

Theoretical Study of Possible Reaction Mechanisms for the Formation of Carbodiimide in the Interstellar Medium (ISM) and Polarizabilities of Carbodiimide.

Orig Life Evol Biosph 2019 Jun 19;49(1-2):89-103. Epub 2019 Jun 19.

Department of Physics, University of Lucknow, Lucknow, India.

The Structure of carbodiimide has been studied by using quantum chemical methods. Carbodiimide (HNCNH) has been detected towards Sagittarius B2 (N) in interstellar medium (ISM). Two reaction mechanisms have been proposed to study the formation of interstellar Carbodiimide. The first reaction mechanism is based on molecule-radical and the second one is a radical-radical mechanism, through previously detected interstellar molecules or radicals. Quantum chemical calculations have been performed by using density functional theory (DFT) and Moller-Plesset second order perturbation (MP2) theory, in gas phase as well as in polarizable continuum model (PCM). The proposed reaction paths are exothermic and barrierless which indicates the possibility of carbodiimide formation in ISM. Several basis sets have been used to verify the validity and accuracy of the results. The isotropic and anisotropic polarizabilities of carbodiimide have been calculated from relevant tensor components for both reaction mechanisms with the help of data obtained by DFT/B3LYP and MP2 methods using aug-cc-pVTZ basis sets in gaseous phase as well as in PCM.
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http://dx.doi.org/10.1007/s11084-019-09577-6DOI Listing
June 2019

Nitrofurantoin-melamine monohydrate (cocrystal hydrate): Probing the role of H-bonding on the structure and properties using quantum chemical calculations and vibrational spectroscopy.

Spectrochim Acta A Mol Biomol Spectrosc 2019 Oct 28;221:117170. Epub 2019 May 28.

Centre for Pharmaceutical Engineering Science and School of Pharmacy and Medical Sciences, University of Bradford, Bradford, West Yorkshire BD7 1DP, United Kingdom. Electronic address:

Cocrystal monohydrate of nitrofurantoin (NF) with melamine (MELA) has been studied as NF is an antibacterial drug used for the treatment of urinary tract infections. The structure of nitrofurantoin-melamine-monohydrate (NF-MELA-HO) is characterized by FT-IR and FT-Raman spectroscopy. The energies and vibrational frequencies of the optimized structures calculated using quantum chemical calculations. Supported by normal coordinate analyses and potential energy distributions (PEDs), the complete vibrational assignments recommended for the observed fundamentals of cocrystal hydrate. With the aim of inclusion of all the H-bond interactions, dimer of NF-MELA-HO has been studied as only two molecules of cocrystal hydrate are present in the unit cell. By the study of dimeric model consistent assignment of the FT-IR and FT-Raman spectrum obtained. H-bonds are of essential importance in an extensive range of molecular sciences. The vibrational analyses depict existence of H-bonding (O-H⋯N) between water O-H and pyridyl N atom of MELA in both monomer and dimer. To probe the strength and nature of H-bonding in monomer and dimer, topological parameters such as electron density (ρ), Laplacian of electron density (∇ρ), total electron energy density (H) and H-bond energy (E) at bond critical points (BCP) are evaluated by quantum theory of atoms in molecules (QTAIM). Natural bond orbitals (NBOs) analyses are carried out to study especially the intra and intermolecular H-bonding and their second order stabilization energy (E). The value of HOMO-LUMO energy band gap for NF-MELA-HO (monomer and dimer both) is less than NF, showing more chemical reactivity for NF-MELA-HO. Chemical reactivity has been described with the assistance of electronic descriptors. Global electrophilicity index (ω = 7.3992 eV) shows that NF-MELA-HO behaves as a strong electrophile than NF. The local reactivity descriptors analyses such as Fukui functions, local softnesses and electrophilicity indices performed to determine the reactive sites within NF-MELA-HO. In MEP map of NF-MELA (monomer and dimer) electronegative regions are about NO and C=O group of NF, although the electropositive regions are around NH, N-H group and HO molecule. Molar refractivity (MR) value of NF-MELA-HO (monomer and dimer) lies within the range set by Lipinski's modified rules. This study could set as an example to study the H-bond interactions in pharmaceutical cocrystals.
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http://dx.doi.org/10.1016/j.saa.2019.117170DOI Listing
October 2019

Study of molecular structure and hydrogen bond interactions in dipfluzine-benzoic acid (DIP-BEN) cocrystal using spectroscopic and quantum chemical method.

Spectrochim Acta A Mol Biomol Spectrosc 2019 Jun 6;216:7-14. Epub 2019 Mar 6.

School of Pharmaceutical Sciences, Hebei Medical University, Shijiazhuang 050017, China.

The purpose of this article is to predict the molecular structure of the cocrystal of dipfluzine-benzoic acid (DIP-BEN) through computational approach (DFT calculations) and validate it using vibrational spectroscopic studies. The molecular structure of the DIP-BEN cocrystal has been predicted by forming models on the basis of the active sites available to form H-bonds between dipfluzine (DIP) and benzoic acid (BEN). Conformational study has been performed and potential energy surface scans are plotted around the flexible bonds of the cocrystal molecule and three stable conformers have been obtained. Quantum theory of atoms in molecules (QTAIM) explains that all the interactions are medium and partially covalent in nature. Natural bond orbital analysis of the second order perturbation theory of the Fock matrix suggests that interactions LP (2) O2 → σ*(O74H75) and LP (2) F1 → σ* (O89H90) are responsible for the stabilization of the molecule. The HOMO and LUMO energies and electronic charge transfer (ECT) confirms that charge flows from BEN to DIP. Global reactivity descriptor parameters suggest that DIP-BEN cocrystal is softer, thus more reactive in comparison to DIP. Local reactivity descriptor parameter is used to predict reactive sites of the cocrystal. The experimental and theoretical results support the formation of cocrystal through strong hydrogen bond (O89H90⋯F1 and O74H75⋯O2) interactions present in cocrystal.
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http://dx.doi.org/10.1016/j.saa.2019.01.092DOI Listing
June 2019

Monitoring the in Vitro Thiazolidine Ring Formation of Antioxidant Drug N-Acetyl-l-cysteine at Basic pH and Detection of Reaction Intermediates: A Raman Spectroscopic and Ab Initio Study.

J Phys Chem B 2018 11 1;122(45):10306-10314. Epub 2018 Nov 1.

Department of Physics , University of Lucknow , Lucknow 226007 , India.

The important cyclization reaction of antioxidant drug N-acetyl-l-cysteine (NAC) has been monitored in vitro at basic pH with the help of time series Raman spectroscopy. The thiazoline ring formation of NAC at acidic pH is a well-known reaction and has been studied extensively. However, the formation of a thiazolidine ring from NAC at basic pH has not been investigated precisely till date. The effect of basicity of the medium on the rate of cyclization has been investigated by studying the reaction at five different basic pH values. Raman signatures of cyclization have been observed with the passage of time and are found to appear faster as the basicity of the medium increases. Ab initio calculations have been done to understand the plausible mechanism of the reaction at basic pH. It is observed that formation of a thiazolidine ring from NAC occurs primarily in four steps, which involve proton abstraction from the thiol (SH) group of NAC and subsequent formation of an S-C bond by a nucleophilic attack of the C-S group on the protonated C-O-H group in NAC. Correlation of the theoretically calculated results with experimental Raman spectral analysis has led to a detailed and proper understanding of this important biochemical reaction.
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http://dx.doi.org/10.1021/acs.jpcb.8b08512DOI Listing
November 2018

Combined spectroscopic and quantum chemical approach to study the effect of hydrogen bonding interactions in ezetimibe.

Spectrochim Acta A Mol Biomol Spectrosc 2019 Jan 13;206:246-253. Epub 2018 Aug 13.

Department of Physics, University of Lucknow, Lucknow 226007, India.

Molecular structure, chemical and physical reactivity, spectroscopic behavior, intermolecular interactions play an important role in understanding the biological nature of pharmaceutical drugs. The objective of the study is to combine the spectroscopic and computational methodology for the investigation of structural behavior of ezetimibe (EZT). Computational study was done on monomeric, dimeric and trimeric models of EZT using B3LYP/6-311G(d,p). Hydrogen bond interactions were taken into consideration to validate the theoretical results with the experimental one. Results obtained for trimeric model were better than monomer and dimer. HOMO-LUMO energy band gap shows that the chemical reactivity calculated using dimeric and trimeric model is higher than that of monomeric model. Higher value of electrophilicity index (ω = 2.5654 eV) also confirms that trimer behaves as a strong electrophile in comparison with monomer and dimer. To examine the hyperconjugation interactions and the stability of the molecule, natural bond analysis (NBO) was done on dimer and trimer of EZT. Nature and the strength of hydrogen bonds were examined by quantum theory of atoms in molecules (QTAIM). Binding energy calculated from counterpoise method was -7.40 kcal/mol for dimer and -21.47 kcal/mol for trimer.
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http://dx.doi.org/10.1016/j.saa.2018.08.023DOI Listing
January 2019

Spectroscopic and molecular structure (monomeric and dimeric model) investigation of Febuxostat: A combined experimental and theoretical study.

Spectrochim Acta A Mol Biomol Spectrosc 2018 Oct 22;203:1-12. Epub 2018 May 22.

Department of Pharmaceutics, National Institute of Pharmaceutical Education and Research (NIPER), Sector-67, S.A.S. Nagar, Punjab 160062, India.

Febuxostat (FXT) is a urate-lowering drug and xanthine oxidase inhibitor which is used for the treatment of hyperuricemia and gout caused by increased levels of uric acid in the blood (hyperuricemia). The present study aims to provide deeper knowledge of the structural, vibrational spectroscopic and physiochemical properties of FXT based on monomeric and dimeric model with the aid of combination of experimental and computational methods. The conformational analysis of form Q has been done to predict the possible structure of unknown form A. Vibrational spectra of form A and Q has been compared to get an idea of hydrogen bonding interactions of form A. A computational study of FXT has been executed at different level (B3LYP, M06-2X, WB97XD) of theory and 6-31 G (d, p) basis set for dimeric model to elucidate the nature of intermolecular hydrogen bond. The red shift observed in the stretching modes of OH, CO groups and blue shift in stretching mode of CN group in experimental as well as in theoretical spectra explains the involvement of these groups in intermolecular hydrogen bonding. NBO analysis shows that change in electron density (ED) in the lone pair orbital to σ* antibonding orbital (LP1 (N39) → σ* (O3-H38)) with maximum value of E(2) energy confirms the presence of hydrogen bond (N39⋯H38-O3) leading to dimer formation. Study of topological parameters was executed for dimer using Bader's atoms in molecules (AIM) theory predicting the partially covalent nature of hydrogen bonds present in the molecule. The study of molecular electrostatic potential surface (MEPS) map ascertains that the CO, CN group are prone to electrophilic attack and OH group is active towards nucleophilic attack. The lower energy band gap and higher value of softness of dimeric model of FXT indicates its more reactivity, polarisability than monomeric model. The local reactivity descriptors predict the order of reactive sites towards electrophilic, nucleophilic and radical attack. An investigation made to determine the ligand protein interaction of FXT through docking with different molecular targets reveals the inhibitive as well as antibacterial nature of FXT.
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http://dx.doi.org/10.1016/j.saa.2018.05.074DOI Listing
October 2018

A combined experimental (IR, Raman and UV-Vis) and quantum chemical study of canadine.

Spectrochim Acta A Mol Biomol Spectrosc 2018 Feb 4;191:249-258. Epub 2017 Oct 4.

Departamento de Fisica, Universidate Federal do Ceará, C. P. 6030, 60.455-900, Fortaleza, CE, Brazil.

Plant based natural products cover a major sector of the medicinal field, as such focus on plant research has been increased all over the world. As an attempt to aid that research, we have performed structural and spectroscopic analysis of a natural product, an alkaloid: canadine. Both ab initio Hartree-Fock (HF) and density functional theory (DFT) employing B3LYP using 6-311++G(d,p) basis set were used for the calculations. The calculated vibrational frequencies were scaled and compared with the experimental infrared and Raman spectra. The complete vibrational assignments were made using potential energy distribution. The structure-activity relation has also been interpreted by mapping electrostatic potential surface and evaluating the reactivity descriptors, which are valuable information for quality control of medicines and drug-receptor interactions. Natural bond orbital analysis has also been performed to understand the stability and hyperconjugative interactions of the molecule. Furthermore, UV-Vis spectra have been recorded in an ethanol solvent (EtOH) and the electronic property has been analyzed employing TD-DFT for both gaseous and solvent phase. The HOMO and LUMO calculation with their energy gap show that charge transfer occurs within the molecule. Additionally, the nonlinear optical properties of the title compound have been interpreted that predicts it's the best candidate for the NLO materials.
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http://dx.doi.org/10.1016/j.saa.2017.10.008DOI Listing
February 2018

Phase transition analysis of V-shaped liquid crystal: Combined temperature-dependent FTIR and density functional theory approach.

Spectrochim Acta A Mol Biomol Spectrosc 2018 Jan 25;188:561-570. Epub 2017 Jul 25.

Centre for Nano and Soft Matter Sciences, Bangalore 560 013, India.

Temperature-dependent Fourier transform infrared spectroscopy (FTIR) combined with density functional theory (DFT) is employed to study the mechanism of phase transitions of V-shaped bent-core liquid crystal. Since it has a large number of flexible bonds, one-dimensional potential energy scan (PES) was performed on the flexible bonds and predicted the most stable conformer I. A detailed analysis of vibrational normal modes of conformer I have been done on the basis of potential energy distribution. The good agreement between the calculated spectrum of conformer I and observed FTIR spectrum at room temperature validates our theoretical structure model. Furthermore, the prominent changes observed in the stretching vibrational bands of CH/CH, CO, ring CC, ring CO, ring CH in-plane bending, and ring CH out-of-plane bending at Iso→nematic phase transition (at 155°C) have been illustrated. However, the minor changes in the spectral features observed for the other phase transitions might be due to the shape or bulkiness of molecules. Combined FTIR and PES study beautifully explained the dynamics of the molecules, molecular realignment, H-bonding, and conformational changes at the phase transitions.
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http://dx.doi.org/10.1016/j.saa.2017.07.043DOI Listing
January 2018

Spectroscopic (far or terahertz, mid-infrared and Raman) investigation, thermal analysis and biological activity of piplartine.

Spectrochim Acta A Mol Biomol Spectrosc 2017 Sep 5;184:368-381. Epub 2017 May 5.

Instituto de Física de São Carlos, Universidade de São Paulo, CP. 369, 13560-970, São Carlos, SP, Brazil.

Research in the field of medicinal plants including Piper species like long pepper (Piper longum L.- Piperaceae) is increasing all over the world due to its use in traditional and Ayurvedic medicine. Piplartine (piperlongumine, 5,6-dihydro-1-[(2E)-1-oxo-3-(3,4,5-trimethoxyphenyl)-2-propenyl]-2(1H)-pyridinone), a biologically active alkaloid/amide was isolated from the phytochemical investigations of Piper species, as long pepper. This alkaloid has cytotoxic, anti-fungal, anti-diabetic, anti-platelet aggregation, anti-tumoral, anxiolytic, anti-depressant, anti-leishmanial, and genotoxic activities, but, its anticancer property is the most promising and has been widely explored. The main purpose of the work is to present a solid state characterization of PPTN using thermal analysis and vibrational spectroscopy. Quantum mechanical calculations based on the density functional theory was also applied to investigate the molecular conformation and vibrational spectrum, which was compared with experimental results obtained by Raman scattering, far (terahertz) and mid-infrared adsorption spectroscopy. NBO analysis has been performed which predict that most intensive interactions in PPTN are the hyperconjugative interactions between n(1) N6 and π*(O1C7) having delocalization energy of 50.53kcal/mol, Topological parameters have been analyzed using 'AIM' analysis which governs the three bond critical points (BCPs), one di-hydrogen, and four ring critical points (RCPs). MEP surface has been plotted which forecast that the most negative region is associated with the electronegative oxygen atoms (sites for nucleophilic activity). Theoretically, to confirm that the title compound has anti-cancer, anti-diabetic and anti-platelet aggregation activities, it was analyzed by molecular docking interactions with the corresponding target receptors. The obtained values of H-bonding parameters and binding affinity prove that its anti-cancer activity is the more prominent than the other properties.
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http://dx.doi.org/10.1016/j.saa.2017.05.007DOI Listing
September 2017

Study of Cr→SmA phase transition and hydrogen bonding in four-ring bent-core liquid crystal.

Spectrochim Acta A Mol Biomol Spectrosc 2017 May 3;178:142-150. Epub 2017 Feb 3.

Departamento de Física, Universidade Federal do Ceará, C.P. 6030, 60.455-900 Fortaleza, CE, Brazil.

A newly designed asymmetrical four-ring bent-core compound (4'-n-decyloxyphenylazo)-phenyl-4-yl-3-[N-(4'-n-octadecyloxy-2-hydroxybenzylidene) amino]-2-methyl benzoate exhibiting liquid crystalline behavior was synthesized and characterized. The thermal and textural morphology were studied using differential scanning calorimetry and polarizing optical microscopy, respectively. The study of hydrogen bonding and dynamics of the phase transition has been performed at the molecular level using temperature dependent Fourier transform infrared (FTIR) spectroscopy. The spectral analysis of OH, CH/CH, CO, and CN stretching vibrational bands revealed clear signatures of Cr→SmA phase transition at 125°C. Density functional theory has been adopted for the geometry optimization and conformational study of the monomer using the B3LYP/6-31G(d) method. The conformational analysis has been performed to predict the most stable conformer along with the possible conformers using one-dimensional potential energy scan employing the same level of theory. The combination of experimental findings and theoretical analysis helped to understand the mechanism of phase transitions at the molecular level.
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http://dx.doi.org/10.1016/j.saa.2017.01.067DOI Listing
May 2017

Conformational Study and Vibrational Spectroscopic (FT-IR and FT-Raman) Analysis of an Alkaloid-Borreverine Derivative.

Anal Sci 2017 ;33(1):99-104

Department of Physics, University of Lucknow.

In the present work, structural and spectroscopic investigations were carried out on a borreverine derivative. Borreverine is a class of alkaloid as well a natural antimalarial drug extracted from Borreria verticillata. With the aim of finding possible conformers, a detailed conformational analysis of a borreverine derivative was conducted utilizing density functional theory employing the B3LYP/6-31G(d,p) method. The crystallographic geometry was used for full geometry optimization, followed by a conformational analysis. The conformational investigation predicted the most stable conformer (conformer I), which was further compared with the initial crystallographic geometry (conformer V). The geometry optimization, vibrational frequency, and intensity of these two conformers (I and V) were calculated in the ground state using density functional theory with the B3LYP functional and 6-31G(d,p) basis set. The spectroscopic investigation was conducted using Fourier transform infrared (FT-IR) and Fourier transform Raman (FT-Raman) techniques. Tentative vibrational assignments of some selective modes were presented utilizing the observed FT-IR, FT-Raman, and calculated spectra. The scaled and observed wavenumbers were found to be in good agreement. The molecular electrostatic potential was computed and plotted so as to elucidate the reactive sites of the molecule. Natural bond orbital studies were performed to investigate the intramolecular charge transfer that results in molecular stability.
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http://dx.doi.org/10.2116/analsci.33.99DOI Listing
June 2018

Evaluation of Structural Isomers, Molecular Interactions, Reactivity Descriptors, and Vibrational Analysis of Tretinoin.

Anal Sci 2017 ;33(1):83-87

Department of Physics, University of Lucknow.

Tretinoin is known to be a pharmaceutical drug for treating acne vulgaris, keratosis pilaris, and acute promyelocytic leukemia. In order to reveal the possible conformers of tretinoin, the energies of all the conformers through rotational bonds have been evaluated by systematic rotor search analysis. The intramolecular interactions ranging from strong hydrogen bonds to weak van der Waals forces present in tretinoin have been distinguished with the help of electron density mapping and wavefunction analysis. The global reactivity descriptors and Fukui functions of tretinoin have been calculated and discussed. The sites suitable for electrophilic attack and nucleophilic attack have been identified with the help of Hirshfeld partitioning. The vibrational spectroscopic signature of tretinoin and mixed mode band assignments have been elucidated with the help of experimental and simulated spectra.
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http://dx.doi.org/10.2116/analsci.33.83DOI Listing
June 2018

Characterization and intramolecular bonding patterns of busulfan: Experimental and quantum chemical approach.

Spectrochim Acta A Mol Biomol Spectrosc 2017 Feb 19;173:390-399. Epub 2016 Sep 19.

Department of Physics, University of Lucknow, 226007 Lucknow, India.

The investigations of structural conformers, molecular interactions and vibrational characterization of pharmaceutical drug are helpful to understand their behaviour. In the present work, the 2D potential energy surface (PES) scan has been performed on the dihedral angles C6O4S1C5 and C25S22O19C16 to find the stable conformers of busulfan. In order to show the effects of long range interactions, the structures on the global minima of PES scan have been further optimized by B3LYP/6-311++G(d,p) method with and without empirical dispersion functional in Gaussian 09W package. The presence of n→σ* and σ→σ* interactions which lead to stability of the molecule have been predicted by natural bond orbital analysis. The strong and weak hydrogen bonds between the functional groups of busulfan were analyzed using quantum topological atoms in molecules analysis. In order to study the long-range forces, such as van der Waals interactions, steric effect in busulfan, the reduced density gradient as well as isosurface defining these interactions has been plotted using Multiwfn software. The spectroscopic characterization on the solid phase of busulfan has been studied by experimental FT-IR and FT-Raman spectra. From the C and H NMR spectra, the chemical shifts of individual C and H atoms of busulfan have been predicted. The maximum absorption wavelengths corresponding to the electronic transitions between the highest occupied molecular orbital and the lowest unoccupied molecular orbital of busulfan have been found by UV-vis spectrum.
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http://dx.doi.org/10.1016/j.saa.2016.09.031DOI Listing
February 2017

Computational approaches to find the active binding sites of biological targets against busulfan.

J Mol Model 2016 06 30;22(6):142. Epub 2016 May 30.

Department of Physics, University of Lucknow, Lucknow, 226 007, India.

Determination of electrophilic and nucleophilic sites of a molecule is the primary task to find the active sites of the lead molecule. In the present study, the active sites of busulfan have been predicted by molecular electrostatic potential surface and Fukui function analysis with the help of dispersion corrected density functional theory. Similarly, the identification of active binding sites of the proteins against lead compound plays a vital role in the field of drug discovery. Rigid and flexible molecular docking approaches are used for this purpose. For rigid docking, Hex 8.0.0 software employing fast Fourier transform (FFT) algorithm has been used. The partial flexible blind docking simulations have been performed with AutoDock 4.2 software; where a Lamarckian genetic algorithm is employed. The results showed that the most electrophilic atoms of busulfan bind with the targets. It is clear from the docking studies that busulfan has inhibition capability toward the targets 12CA and 1BZM. Graphical Abstract Docking of ligand and protein.
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http://dx.doi.org/10.1007/s00894-016-3015-zDOI Listing
June 2016

Reaction between CH2 and HCCN: a theoretical approach to acrylonitrile formation in the interstellar medium.

Orig Life Evol Biosph 2014 Apr 22;44(2):143-57. Epub 2014 Nov 22.

Department of Mathematics & Astronomy, University of Lucknow, Lucknow, India.

Acrylonitrile (CH2CHCN) was first detected in dense molecular cloud SgrB2. The synthesis of this interstellar molecule is reported to be quite difficult. Therefore, in the present work an attempt has been made to explore the possibility of formation of acrylonitrile from some simple molecules and radicals detected in interstellar space by radical-radical interaction scheme, both in the gas phase and in the icy grains. All calculations are performed using quantum chemical methods with density functional theory (DFT) at the B3LYP/6-311G (d,p) level and Møller-Plesset perturbation theory at the MP2/6-311G (d,p) level. In the discussed chemical pathway, the reaction is found to be totally exothermic and barrier less giving rise to a high probability of acrylonitrile formation in Interstellar space.
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http://dx.doi.org/10.1007/s11084-014-9373-6DOI Listing
April 2014

Study of conformational stability, structural, electronic and charge transfer properties of cladrin using vibrational spectroscopy and DFT calculations.

Spectrochim Acta A Mol Biomol Spectrosc 2014 Nov 14;132:615-28. Epub 2014 May 14.

Medicinal and Process Chemistry Division, Central Drug Research Institute, Sector 10, Jankipuram Extension, Lucknow 226 031, Uttar Pradesh, India.

In the present work, a detailed conformational study of cladrin (3-(3,4-dimethoxy phenyl)-7-hydroxychromen-4-one) has been done by using spectroscopic techniques (FT-IR/FT-Raman/UV-Vis/NMR) and quantum chemical calculations. The optimized geometry, wavenumber and intensity of the vibrational bands of the cladrin in ground state were calculated by density functional theory (DFT) employing 6-311++G(d,p) basis sets. The study has been focused on the two most stable conformers that are selected after the full geometry optimization of the molecule. A detailed assignment of the FT-IR and FT-Raman spectra has been done for both the conformers along with potential energy distribution for each vibrational mode. The observed and scaled wavenumber of most of the bands has been found to be in good agreement. The UV-Vis spectrum has been recorded and compared with calculated spectrum. In addition, 1H and 13C nuclear magnetic resonance spectra have been also recorded and compared with the calculated data that shows the inter or intramolecular hydrogen bonding. The electronic properties such as HOMO-LUMO energies were calculated by using time-dependent density functional theory. Molecular electrostatic potential has been plotted to elucidate the reactive part of the molecule. Natural bond orbital analysis was performed to investigate the molecular stability. Non linear optical property of the molecule have been studied by calculating the electric dipole moment (μ) and the first hyperpolarizability (β) that results in the nonlinearity of the molecule.
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http://dx.doi.org/10.1016/j.saa.2014.04.182DOI Listing
November 2014

Molecular structure (monomeric and dimeric) and hydrogen bonds in 5-benzyl 2-thiohydantoin studied by FT-IR and FT-Raman spectroscopy and DFT calculations.

Spectrochim Acta A Mol Biomol Spectrosc 2014 Nov 30;132:15-26. Epub 2014 Apr 30.

Division of Material Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa, Japan.

In the present work the structural and spectral characteristics of 5-benzyl-2-thiohydantoin (5-BTH) have been studied by methods of infrared, Raman spectroscopy and quantum chemistry. Electrostatic potential surface, optimized geometry, harmonic vibrational frequencies, infrared intensities and activities of Raman scattering were calculated by density functional theory (DFT) employing B3LYP with complete relaxation in the potential energy surface using 6-311G++(d,p) basis set. Our results support the hydrogen bonding pattern proposed by reported crystalline structure. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule are calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. UV-vis spectrum of the compound was recorded in methanol solvent. The TD-DFT calculations have been performed to explore the influence of electronic absorption spectra in the gas phase, as well as in solution environment using PCM and 6-311++G(d,p) basis set. In addition, the thermodynamic properties of the compound were calculated at different temperatures and corresponding relations between the properties and temperature were also studied.
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http://dx.doi.org/10.1016/j.saa.2014.04.101DOI Listing
November 2014

Experimental and theoretical (FT-IR, FT-Raman, UV-vis, NMR) spectroscopic analysis and first order hyperpolarizability studies of non-linear optical material: (2E)-3-[4-(methylsulfanyl) phenyl]-1-(4-nitrophenyl) prop-2-en-1-one using density functional theory.

Spectrochim Acta A Mol Biomol Spectrosc 2014 Sep 8;130:41-53. Epub 2014 Apr 8.

Department of Physics, Center for Post Graduate Studies and Research, St. Philomena College, Puttur, India.

A combined experimental and theoretical investigation on FT-IR, FT-Raman, NMR, UV-vis spectra of a chalcone derivative (2E)-3-[4-(methylsulfanyl) phenyl]-1-(4-nitrophenyl) prop-2-en-1-one (4N4MSP) has been reported. 4N4MSP has two planar rings connected through conjugated double bond and it provides a necessary configuration to show non-linear optical (NLO) response. The molecular structure, fundamental vibrational frequencies and intensity of the vibrational bands are interpreted with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) with B3LYP functional and 6-311++G(d,p) basis set combination. The analysis of the fundamental modes was made with the help of potential energy distribution (PED). Molecular electrostatic potential (MEP) surface was plotted over the geometry primarily for predicting sites and relative reactivities towards electrophilic and nucleophilic attack. The delocalization of electron density of various constituents of the molecule has been discussed with the aid of NBO analysis. The electronic properties, such as excitation energies, oscillator strength, wavelengths, HOMO and LUMO energies, were calculated by time-dependent density functional theory (TD-DFT) and the results complement the experimental findings. The recorded and calculated 1H chemical shifts in gas phase and MeOD solution are gathered for reliable calculations of magnetic properties. Thermodynamic properties like heat capacity (C°p,m), entropy (S°m), enthalpy (H°m) have been calculated for the molecule at the different temperatures. Based on the finite-field approach, the non-linear optical (NLO) parameters such as dipole moment, mean polarizability, anisotropy of polarizability and first order hyperpolarizability of 4N4MSP molecule are calculated. The predicted first hyperpolarizability shows that the molecule has a reasonably good nonlinear optical (NLO) behavior.
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http://dx.doi.org/10.1016/j.saa.2014.03.072DOI Listing
September 2014

Molecular structure and vibrational spectra of N-acetylglycine oligomers and polyglycine I using DFT approach.

Biopolymers 2014 Jul;101(7):795-813

Department of Applied Physics, Institute of Engineering and Technology, M. J. P. Rohilkhand University, Bareilly, India.

We have determined the geometric, vibrational, and electronic properties of N-acetylglycine oligomers by performing density functional theory quantum chemical calculations. The normal mode analysis was performed and the potential energy distribution was calculated among the internal coordinates. The optically active vibrational modes of PGI have been determined by selecting the modes from the calculated results of the pentamer and the observed vibrational spectra of PGI have been explained. The molecular electrostatic potential surface of N-acetylglycine pentamer reveals the sites of electrophilic attack and also provides clues for the role of electrostatic interactions involved in the reactivity. Natural bond orbital analysis has been performed to understand the charge transfer and various hyperconjugative interactions in the molecular system. The electronic properties of the oligomers have been discussed by calculating the transitions with the help of time dependent density functional theory method. The global reactivity descriptors such as hardness, chemical potential, and electrophilicity index have also been calculated.
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http://dx.doi.org/10.1002/bip.22458DOI Listing
July 2014

Quantum chemical study on influence of intermolecular hydrogen bonding on the geometry, the atomic charges and the vibrational dynamics of 2,6-dichlorobenzonitrile.

Spectrochim Acta A Mol Biomol Spectrosc 2014 7;121:464-82. Epub 2013 Nov 7.

Department of Chemistry, Lucknow University, Lucknow, India.

FT-IR (4000-400 cm(-1)) and FT-Raman (4000-200 cm(-1)) spectral measurements on solid 2,6-dichlorobenzonitrile (2,6-DCBN) have been done. The molecular geometry, harmonic vibrational frequencies and bonding features in the ground state have been calculated by density functional theory at the B3LYP/6-311++G (d,p) level. A comparison between the calculated and the experimental results covering the molecular structure has been made. The assignments of the fundamental vibrational modes have been done on the basis of the potential energy distribution (PED). To investigate the influence of intermolecular hydrogen bonding on the geometry, the charge distribution and the vibrational spectrum of 2,6-DCBN; calculations have been done for the monomer as well as the tetramer. The intermolecular interaction energies corrected for basis set superposition error (BSSE) have been calculated using counterpoise method. Based on these results, the correlations between the vibrational modes and the structure of the tetramer have been discussed. Molecular electrostatic potential (MEP) contour map has been plotted in order to predict how different geometries could interact. The Natural Bond Orbital (NBO) analysis has been done for the chemical interpretation of hyperconjugative interactions and electron density transfer between occupied (bonding or lone pair) orbitals to unoccupied (antibonding or Rydberg) orbitals. UV spectrum was measured in methanol solution. The energies and oscillator strengths were calculated by Time Dependent Density Functional Theory (TD-DFT) and matched to the experimental findings. TD-DFT method has also been used for theoretically studying the hydrogen bonding dynamics by monitoring the spectral shifts of some characteristic vibrational modes involved in the formation of hydrogen bonds in the ground and the first excited state. The (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the Gauge independent atomic orbital (GIAO) method and compared with experimental results. Standard thermodynamic functions have been obtained and changes in thermodynamic properties on going from monomer to tetramer have been presented.
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http://dx.doi.org/10.1016/j.saa.2013.10.104DOI Listing
September 2014

Conformational analysis and vibrational study of daidzein by using FT-IR and FT-Raman spectroscopies and DFT calculations.

Spectrochim Acta A Mol Biomol Spectrosc 2014 19;120:405-15. Epub 2013 Oct 19.

Medicinal and Process Chemistry Division, Central Drug Research Institute (CDRI), Lucknow 226031, India.

Daidzein (C15H10O4) is a type of isoflavone. It was isolated from Butea monosperma that belongs to the Fabaceae family. Soybeans and soy products are the abundant source of daidzein. It is the subject of investigation for many reasons, as it has got wide applications, such as anti-tumor, anti-estrogen, weak pro-estrogen and anti-cancer activities. In the present study, a complete vibrational assignment is provided for the observed IR and Raman spectra of daidzein. Electronic properties have been analyzed using TD-DFT method for both gaseous and solvent phase. The optimized geometry, total energy, potential energy surface and vibrational wavenumbers of daidzein have been determined using density functional theory (DFT/B3LYP) method with 6-311++G(d,p) basis set and a good correlation was found between observed and calculated values. The double well potential energy curve of the molecule about three bonds, has been plotted, as obtained from DFT/6-31G basis. The HOMO-LUMO energy gap of possible conformers has been calculated for comparing their chemical activity. Global reactivity descriptors have been calculated for predicting the chemical reactivity and the stability of chemical systems. Electrostatic potential surface has been plotted for predicting the structure activity relationship. NBO analysis has also been performed to study the stability of the molecule. NLO study reveals the nonlinear properties of the molecule. 1H and 13C NMR spectra have also been studied. Finally, the calculated results were used to simulate infrared and Raman spectra of the title compound which showed a good agreement with the observed spectra.
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http://dx.doi.org/10.1016/j.saa.2013.10.045DOI Listing
September 2014

Quantum chemical and experimental studies on the structure and vibrational spectra of an alkaloid--Corlumine.

Spectrochim Acta A Mol Biomol Spectrosc 2014 Jan 12;118:470-80. Epub 2013 Sep 12.

Department of Physics, University of Lucknow, Lucknow 226007, India.

The study concentrates on an important natural product, phthalide isoquinoline alkaloid Corlumine (COR) [(6R)-6-[(1S)-1,2,3,4-Tetrahydro-6,7-dimethoxy-2-methylisoquinolin-1-yl] furo [3,4-e]-1,3-benzodioxol-8(6H)-one] well known to exhibit spasmolytic and GABA antagonist activity. It was fully characterized by a variety of experimental methods including vibrational spectroscopy (IR and Raman), thermal analysis (DSC), UV and SEM. For a better interpretation and analysis of the results quantum chemical calculations employing DFT were also performed. TD-DFT was employed to elucidate electronic properties for both gaseous and solvent environment using IEF-PCM model. Graphical representation of HOMO and LUMO would provide a valuable insight into the nature of reactivity and some of the structural and physical properties of the title molecule. The structure-activity relationship have been interpreted by mapping electrostatic potential surface (MEP), which is valuable information for the quality control of medicines and drug-receptor interactions. Stability of the molecule arising from hyper conjugative interactions, charge delocalisation has been analyzed using natural bond orbital (NBO) analysis. Computation of thermodynamical properties would help to have a deep insight into the molecule for further applications.
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http://dx.doi.org/10.1016/j.saa.2013.09.015DOI Listing
January 2014

Spectroscopic and quantum chemical study of an alkaloid aristolochic acid I.

Spectrochim Acta A Mol Biomol Spectrosc 2013 Dec 27;116:258-69. Epub 2013 Jul 27.

Department of Physics, University of Lucknow, Lucknow 226007, India; Department of Physics, Siddhanath Sc. Campus, Tribhuvan University, Nepal.

Aristolochic acids (AAs) (Aristolochiaceae) are used in the traditional Chinese herb medicine. We have presented the geometry optimization, electrostatic potential surface, frontier orbital energy gap and vibrational wavenumbers of aristolochic acid I (AA I) using ab initio Hartree-Fock (HF) and density functional theory (DFT/B3LYP) method employing 6-311G(d,p) basis set. A complete vibrational assignment has been done on the basis of calculations on monomer and dimer of AA I. The UV-vis absorption spectrum has been recorded in ethanol solvent and compared with the calculated one in the gas phase as well as in solvent environment (integral-equation formalism polarizable continuum model; IEF-PCM) using TD-DFT/6-31G basis set. A short outline of the NBO analysis segment with their structural meaning has been presented. The variation of thermodynamic properties with temperature was calculated theoretically and the thermal response of the compound has been recorded with the help of differential scanning calorimetry (DSC) in N2 environment.
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http://dx.doi.org/10.1016/j.saa.2013.07.036DOI Listing
December 2013

Use of vibrational spectroscopy to study 2-[4-(N-dodecanoylamino)phenyl]-5-(4-nitrophenyl)-1,3,4-oxadiazole: a combined theoretical and experimental approach.

Spectrochim Acta A Mol Biomol Spectrosc 2013 Oct 23;114:236-55. Epub 2013 May 23.

Department of Applied Physics, Institute of Engineering and Technology, MJP Rohilkhand University, Bareilly, India.

Quantum chemical calculations of geometric structure and vibrational wavenumbers of 2-[4-(N-dodecanoylamino)phenyl]-5-(4-nitrophenyl)-1,3,4-oxadiazole (AF51) were carried out by using density functional theory (DFT/B3LYP/6-311G(d,p) method. The fundamental vibrational modes were characterized depending on their potential energy distribution (PED). In order to predict the reactive sites for electrophilic and nucleophilic attacks of the title molecule, electrostatic potential surface has been plotted. The UV absorption spectrum was examined in chloroform solvent and compared with the calculated one in gas phase as well as in solvent environment using TD-DFT/ PCM approach. The (1)H NMR spectra was recorded. Comparison between the experimental and the theoretical results is satisfactory. The thermodynamic properties of the title compound at different temperatures have been calculated. A relationship between molecular structural features, non-linear responses and hyperpolarizability of AF51 has been established using vibrational spectra with emphasis on the role of intramolecular charge transfer mechanism in such organic NLO materials.
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http://dx.doi.org/10.1016/j.saa.2013.05.051DOI Listing
October 2013

Study of molecular structure, vibrational, electronic and NMR spectra of oncocalyxone A using DFT and quantum chemical calculations.

Spectrochim Acta A Mol Biomol Spectrosc 2013 Sep 20;113:367-77. Epub 2013 May 20.

Department of Physics, University of Lucknow, Lucknow 226 007, India.

Oncocalyxone A (C17H18O5) is the major secondary metabolite isolated from ethanol extract from the heartwood of Auxemma oncocalyx Taub popularly known as "pau branco". Oncocalyxone A (Onco A) has many pharmaceutical uses such as: antitumor, analgesic, antioxidant and causative of inhibition of platelet activation. We have performed the optimized geometry, total energy, conformational study, molecular electrostatic potential mapping, frontier orbital energy gap and vibrational frequencies of Onco A employing ab initio Hartree-Fock (HF) and density functional theory (DFT/B3LYP) method with 6-311++G(d,p) basis set. Stability of the molecule arising from hyperconjugative interactions and/or charge delocalization has been analyzed using natural bond orbital (NBO) analysis. UV-vis spectrum of the compound was recorded in DMSO and MeOH solvent. The TD-DFT calculations have been performed to explore the influence of electronic absorption spectra in the gas phase, as well as in solution environment using IEF-PCM and 6-31G basis set. The (13)C NMR chemical shifts have been calculated with the B3LYP/6-311++G(d,p) basis set and compared with the experimental values. These methods have been used as tools for structural characterization of Onco A.
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http://dx.doi.org/10.1016/j.saa.2013.05.018DOI Listing
September 2013

FT-Raman, FT-IR, UV spectroscopic, NBO and DFT quantum chemical study on the molecular structure, vibrational and electronic transitions of clopidogrel hydrogen sulfate form 1: a comparison to form 2.

Spectrochim Acta A Mol Biomol Spectrosc 2013 Mar 5;104:409-18. Epub 2012 Dec 5.

Department of Physics, University of Lucknow, University Road, Lucknow, 226 007 Uttar Pradesh, India.

Clopidogrel hydrogen sulfate (+)-(S)-(2-chlorophenyl)-6,7-dihydrothieno[3,2-c]pyridine-5(4H)-acetate sulfate (1:1), is a selective adenosine diphosphate (ADP) receptor antagonist often used in the treatment of coronary artery, peripheral vascular and cerebrovascular diseases. In the present communication, a comparative study of two polymorphic forms (forms 1 and 2) of clopidogrel hydrogen sulfate (CLP) has been reported. There is difference in conformation and intermolecular hydrogen bonding pattern of two forms. These differences are nicely reflected in the vibrational spectra. The molecular structure, fundamental vibrational frequencies and intensity of the vibrational bands of CLP form 1 are interpreted with the aid of structure optimizations and normal mode analysis based on ab initio HF and DFT method employing 6-311++G(d,p) basis. Polymorphism in CLP have been studied using various characterization tools like FT-Raman, FT-IR spectroscopy and DSC in combination with the quantum chemical calculations. UV-vis spectroscopic studies along with HOMO-LUMO analysis of both polymorphs were performed. The solvent effect calculated by TD-DFT/IEF-PCM/6-31G model results complements with the experimental findings. Stability of the molecule arising from hyper conjugative interactions and charge delocalization has been analyzed using natural bond orbital (NBO) analysis.
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http://dx.doi.org/10.1016/j.saa.2012.11.093DOI Listing
March 2013
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