摘要:

AbstractThe computer program PRODIS is used to find low energy conformations of flexible molecules by searching the potential energy surface(s) of one or more torsion angles via rigid rotation. Then‐dimensional grid of energy versus torsion angles is then converted to a Boltzman probability distribution, with the probability being represented not as a function of torsion angle, but rather a distance between two atoms. These atoms are chosen by comparison with a known, active analogue in which certain atoms have previously been determined as requirements for drug activity. PRODIS produces a list of low energy conformations, their corresponding interatomic distances and the Boltzman probability for each distance ±0.125, as well as the total probability for each conformation. The user also specifies a target interatomic distance and range (usually derived from a more rigid analogue) for which PRODIS lists all conformations and their Boltzman probability that meet this distan

ISSN:0192-8651    

DOI:10.1002/jcc.540080802

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractMolecular orbital calculation by the MINDO/3 method are reported for 50 compounds used as solvents in chemical reactions. Relationships between various parameters of electronic structure and molecular properties such as dipole moment, polarizability and Taft solvent parameters are presented. Comparison between experimental values of π* and calculated values is given

ISSN:0192-8651    

DOI:10.1002/jcc.540080803

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe additional energy stabilization due to cooperative effects was calculated in extended hydrogen bonded systems OH ⃛OH ⃛OH with unidirectional (homodromic) orientation of the OH groups.Ab initiorestricted Hartree Fock, MP2 and MP3 calculations with geometry optimization and BSSE correction have been performed using theGAUSSIAN83 program package for the ground states of the linear water dimer with Cssymmetry and the cyclic water tetramer with S4symmetry. The latter represents the smallest possible, experimentally observed cooperative structure. A new definition for a cooperativity parameter is proposed. The definition is based on the two‐body, non‐neighbour interaction energy, plus three‐ and four‐body contributions, including one‐body deformation terms in relation to the total interaction energy of the water tetramer. The advantage of this definition is its independence of the reference system, which is necessary in complicated molecular systems with an undefined number of hydrogen bonds, such as disordered or flip‐flop systems. According to this definition the energy gain based on cooperativity in the S4water tetramer is 29% with the MP3/6‐31G** approximation, (30% with HF/4‐31G* and 46% with HF/3‐21G). The largest contribution of 18% is due to the three‐body term on the MP3/6‐31G** level, followed by the two‐body, non‐neighbour term with 11%. The four‐body term and the deformation term are in the order of 1% and cancel eac

ISSN:0192-8651    

DOI:10.1002/jcc.540080804

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractIt is shown how the Lagrange Multiplier method for constrained minimization can be implemented in a molecular mechanics program using the common approximations to the full‐matrix Newton‐Raphson minimization. The method reduces the number of cycles to achieve convergence, and also stabilizes the refinement process. Increases in computer memory requirements are small. As an application, the conformational surface of cycloheptane is calcula

ISSN:0192-8651    

DOI:10.1002/jcc.540080805

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractMyelin basic protein (MBP) is the major extrinsic protein of the myelin sheath in the central nervous system. We have examined the predicted structure of segments of MBP using the molecular mechanics program ECEPP83 developed by Scheraga and coworkers as modified by Chuman, Momany, and Schafer. We have focused upon segments containing the Pro‐Pro‐Pro sequence (residues 100‐102), which have been predicted from standard algorithms to exist in a hairpin loop connecting anti‐parallelbeta‐strands. Both the shorter (98‐105, 99‐105, and 100‐105) and longer segments (87‐109, 87‐118, and 87‐120) have been examined. These results indicate potential for a chain reversal in this region. The shorter segments have been studied by others using NMR techniques and the

ISSN:0192-8651    

DOI:10.1002/jcc.540080806

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe energetic effects of the addition of diffuse functions to molecules with second‐row elements are much less dramatic than those for their first‐row counterparts. Although diffuse functions on second‐row elements have little effect on the geometries and vibrational frequencies of neutral molecules, significant changes are found for anions. While the largest basis set, 6‐31 + G*, generally performs best, the results at 3‐21 + G* are comparable, and this basis can be recommended for practical app

ISSN:0192-8651    

DOI:10.1002/jcc.540080807

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe MNDO Hamiltonian as incorporated within MOPAC has been utilized to predict dynamics for some simple reactions. In one option, the intrinsic reaction coordinate has been followed along the path of steepest descent from the transition state backward to reactants and forward to products. In a second option, dynamics of isolated molecular systems have been calculated. In each case, the potential surface (as predicted by the MNDO Hamiltonian) is calculatedin situas the atomic trajectories are calculated from Newton's Laws of Motion. Several specific examples are given and discussed.

ISSN:0192-8651    

DOI:10.1002/jcc.540080808

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe hydrogen‐hydrogen nonbonded potential which may be derived from the calculated interactions between hydrogen molecules has been obtained. The best three‐parameter Buckingham function gave an RMS error of 0.18 kcal/mol in fitting Price and Stone'sab initiodata for 130 pairs of hydrogen molecules, which may be compared with an RMS error of 0.74 kcal/mol using the parameters in the MM2 force field. Burton's basis set is also considered. A better fit to these data requires that the angular relationship between the bonds be included. The data for hydrogen as well as experimental data for chlorine show that these atoms appear “larger” normal to the bond axis than along the axis, and this is probably also the case for other atoms. When simple angular terms are added it is possible to fit the Price and Stone data set with an RMS error of less than 0.06 kcal/mol. The preferred function was:V= [a0+a1(sin θ1+ sin θ2)4+a2r]e−3r− [c0+c1(1 + sinθ1sinθ2)]/r5. Deficiencies in the currentab initiodat

ISSN:0192-8651    

DOI:10.1002/jcc.540080809

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractSets of hydrogen molecule equivalents have been developed which permit the calculation of hydrogenation of different types of carbon‐carbon bonds fromab initiototal energies (3‐21G and 6‐31G* basis sets, and, to a more limited extent, for MP2/6‐31G* data) of reactants and products. The calculated enthalpies of hydrogenation are in good agreement with experiment for unstrained molecules, with average errors on the order of 2 kcal/mol. The 6‐31G* equivalents allow the enthalpies for strained molecules to be calculated accurately, but the 3‐21G equivalents do not. The equivalents for both basis sets have been tested by calculating the enthalpies of hydrogenation of carbon‐carbon bonds in nitrogen‐ and oxygen‐containing organic molecules, free radicals, and classical carbocations. The results are in good agreement with experim

ISSN:0192-8651    

DOI:10.1002/jcc.540080810

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe MM2/MMP2 force‐field gives an incorrect description of benzene‐benzene interactions. This deficiency may be overcome by the addition of electrostatic interactions. Using point charges of −0.15 on carbon and +0.15 on hydrogen, a good agreement between benzene dimer potentials calculated by MMP2 andab initioSCF CI potentials is obtained. The influence of the addition of point charges on calculated structures and conformational energies has been studied. Examples are given in which the addition of electrostatic interactions between phenyl groups substantially improves calculated conformational ene

ISSN:0192-8651    

DOI:10.1002/jcc.540080811

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY