Browsing by Author "C. Gopi Mohan"

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An optimized approach to compute hybridization displacement charge and a study of its effects on electrostatic potentials of some biologically important molecules
(John Wiley and Sons Inc., 1996) C. Gopi Mohan; Anil Kumar; P.C. Mishra
Electrostatic potential maps of certain biologically important molecules (guanine, adenine, cytosine, thymine, and two conformers of glycine) were studied employing a "hybridization displacement charge (HDC)" correction to Löwdin charge distributions and using the conventional Mulliken charge distributions of the molecules. In these calculations, the magnitude of each of the point charges was distributed in 3-dimension in a spherically symmetric manner. The method of computing HDC using MNDO wave functions was optimized by introducing two adjustable parameters. It has been clearly demonstrated that HDC-corrected Löwdin charge distributions of the molecules mentioned above are able to reproduce most of the important features of their ab initio MEP maps, while the conventional Mulliken charge distributions fail in many respects. Thus, HDC-corrected Löwdin charge distributions are shown to be quite reliable for the study of molecular electrostatic properties, particularly for molecules with more than one competing electrophilic site. © 1996 John Wiley & Sons, Inc.
Effect of optimised hybridization displacement charge on the description of molecular electrostatic potentials of some substituted acetaldehydes
(1996) C. Gopi Mohan; C.H. Suresh; P.C. Mishra
Molecular electrostatic potential (MEP) maps of acetaldehyde, fiuoroacetaldehyde, trifluoroacetaldehyde, hydroxyacetaldehyde and amihoacetaldehyde were studied using ab initia SCF wavefunctions with 6-3 IG** basis set as well as a recently developed and optimised new method in which a combination of Löwdin and hybridization displacement charges (HDC) at the MNDO level is used. An important point of this method is the distribution of electronic charges continuously and spherically in three dimensions, which helps reproduce most of the important features of the corresponding ab initia MEP maps that cannot be achieved using point charges. Electrophilic reactivity of the molecules has been discussed using the MEP results.
Electric field mapping and structure-activity relationship for cardiotonic activities of medorinone and some of its analogs
(1997) C. Gopi Mohan; P.C. Mishra
Medorinone 5-methyl-1,6-napthyridin-2(1H)-one and some of its analogs having varying degrees of cardiotonic potency have been studied by molecular orbital and electric field mapping methods. Ground state geometries of the molecules were optimized using the MNDO molecular orbital method. Hybridization displacement charges (HDC) combined with Löwdin charges as well as Mulliken charges were used for electric field mapping around the molecules. Electric fields near the O2 site of medorinone and its analogs correlate well with their observed cardiotonic potencies. This result is in agreement with certain pharmacological models for cardiotonics.
Electrostatic potential mapping using hybridization displacement charge: Atomic parameters and transferability of charge and potential
(John Wiley and Sons Inc., 1998) C. Gopi Mohan; P.C. Mishra
Molecular electrostatic potential (MEP) maps and MEP-derived charges for certain molecules were studied by the ab initio approach using the 6-31G basis set. These results were used to obtain the parameters (K and ) for fluorine, sulfur, and chlorine required for the hybridization displacement charge (HDC) calculations employing the MNDO and AMI methods. The HDC combined with Löwdin charges, distributed continuously in three-dimension spherically and symmetrically, were shown to reproduce ab initio MEP features of molecules fairly well. This method of computing the MEP was applied to two molecules of pharmacological importance, namely, dimaprit and mustard gas. It is shown by studying the as and trans forms of two amino acids that transferability of the MEP is appreciably less acceptable than that of charges in going from one conformation to the other. © 1998 John Wiley & Sons, Inc.
Influence of hybridization displacement charge on the description of electrostatic potentials of molecules with multiple electrophilic sites
(John Wiley and Sons Inc., 1997) C. Gopi Mohan; Anil Kumar; P.C. Mishra
The importance of the hybridization displacement charge (HDC) in describing molecular electrostatic potential (MEP) maps was demonstrated by studying six molecules; pyrazine N-oxide, para-nitropyridine, 5-nitropyrimidine, 3-nitropyridazine, N2, and N2O. It is shown that continuously distributed HDC-corrected Löwdin charges reproduce the MEP features of these molecules, most of which have competing electrophilic sites, in agreement with ab initio results. Further, it is found that for homonuclear diatomic molecules MEP minima can be located properly using HDC-corrected Löwdin (or HDC-corrected Mulliken) continuously distributed charges, but these features cannot be obtained using the conventional Löwdin (or Mulliken) charges. It was shown that the order of molecular electric field (MEF) values near the different electrophilic sites becomes changed when one moves away from the molecules. Thus, pyridine-type nitrogen atoms are the preferred binding sites close to the molecules, while at large distances, effects of oxygen atoms of the NO groups become dominant. © 1997 John Wiley & Sons, Inc.
Molecular electrostatic potential and field as descriptors of hydrogen bonding and molecular activity. Effects of hybridization displacement charge
(Elsevier, 1996) Anil Kumar; C. Gopi Mohan; P.C. Mishra
Molecular electrostatic potential (MEP) and field (MEF) maps have been studied for certain epoxides, ethers and nitriles. The MNDO method was used to optimize geometries of the molecules fully. Hybridization displacement charges (HDC) recently defined by us, which preserve atomic contributions to molecular hybridization dipole moment, were combined with the Mulliken and Löwdin charges to compute the MEP and MEF maps. Linear correlation coefficients between our MEP and MEF values and the observed hydrogen bond accepting parameters (β) for ethers and nitriles, and the corresponding ab initio MEP values for epoxides were found to be quite high (>0.9). Thus it has been shown that combination of HDC with the Mulliken and Löwdin charges usually improves the quality of MEP and MEF maps appreciably in comparison with those computed using the Mulliken and Löwdin charge distributions alone. Furthermore, the study demonstrates great utility of MEP and MEF in describing hydrogen bonding and molecular activity. © 1996 Elsevier Science B.V. All rights reserved.
Molecular structure-activity relationship study of some non-steroidal anti-inflammatory agents using electrostatic potential mapping
(2000) C. Gopi Mohan; P.C. Mishra
A series of 6,11-dihydro-11-oxodibenz[b,e]oxepin-2-acetic acids (DOAA) which are known to be anti-inflammatory agents were studied. The geometries of some of the molecules obtained from X-ray crystallography were used in the calculations as such while the geometries of their derivatives were obtained by local, partial geometry optimization around the sites of substitution employing the AMI method, keeping the remaining parts of the geometries the same as those in the parent molecules. Molecular electrostatic potential (MEP) mapping was performed for the molecules using optimized hybridization displacement charges (HDC) combined with Löwdin charges, as this charge distribution has been shown earlier to yield near ab initio quality results. A good correlation has been found between the MEP values near the oxygen atoms of the hydroxyl groups of the carboxy groups of the molecules and their anti-inflammatory activities. The result is broadly in agreement with the model proposed earlier by other authors regarding the structure-activity relationship for other similar molecules.
Synthesis, biological evaluation and molecular modeling study of pyrazole derivatives as selective COX-2 inhibitors and anti-inflammatory agents
(Academic Press Inc., 2014) Ashish Kumar Tewari; Ved Prakash Singh; Pratima Yadav; Garima Gupta; Amit Singh; Raj Kumar Goel; Pravin Shinde; C. Gopi Mohan
A novel series of pyrazole derivatives were synthesized and evaluated in vivo for their anti-inflammatory activity in carrageenan-induced rat paw edema model. Among all compounds, 5a, and 5b showed comparable anti-inflammatory activity to Nimesulide, the standard drug taken for the studies. In silico (docking) studies were carried out to investigate the theoretical binding mode of the compounds to target the cyclooxygenase (COX-2) using Autodock 4.2. © 2014 Elsevier Inc. All rights reserved.