Empirical conformational energy

The Empirical Conformational Energy Program for Peptides, ECEPP [63, 64], is one of the first empirical interatomic potentials whose derivation is based both on gas-phase and X-ray crystal data [65], It was developed in 1975 and updated in 1983 and 1992. The actual distribution (dated May, 2000) can be downloaded without charge for academic use. 

D.R. Ripoll, H.A. Scheraga, ECEPP Empirical Conformational Energy Program for Peptides, in The Encyclopedia of Computational Chemistry, Vol. 2,... 

Empirical conformational energy program for peptides (ECEPP) is the name of both a computer program and the force field implemented in that program. This is one of the earlier peptide force fields that has seen less use with the introduction of improved methods. It uses three valence terms that are fixed, a van der Waals term, and an electrostatic term. 

ECEPP Empirical conformational energy program for peptides... 

Empirical conformational energy calculations are performed on helical poly(2,3-quinoxaline)s to predict stable conformations. Two energy minimum conformations are found by varying the dihedral angle, y, between two adjacent quinoxaline units from 5 to 180°. Circular dichroism spectra are calculated for the two stable conformations (v - 45 and 135°) on the basis of exciton theory. 

Some of the parameters that are used in the computer program ecepp (empirical conformational energy program for peptides) of Momany et al. (J. Phys. Chem. 1975, 79, 2361) are updated. The changes are based on experimental information that has become available since 1975,... 

The energy levels in the semi-empirical conformational energy calculations may be used to derive conditional probabilities using the statistical weights method described by Flory (13). 

This work has shown that wide-angle X-ray scattering is a sensitive tool for evaluating the structure of non-crystalline polymers. The structure determination is only successfully approached by considering first the persistent conformation and then the packing which must to some extent be a consequence of such conformations. The method does not need to place any reliance on the semi-empirical conformational energy calculations. 

An empirical conformation energy calculation based on the ECEPP functions indicated two stable side-chain orientations (A and B) are possible for a-helical main chain. A theoretical CD computation, however, suggested that orientation B = 290°, X2 285°) is more populated than A. 

The semi-empirical conformational energy calculations of poly-cis-5-ethylproline (PC5EP) predict that the helical structure may exist in two conformational forms such as I and II. Experimental results confirmed that in solution two major conformations may be assumed by the poly-cis-5-ethyl-D-proline. However, the calculations for poly-trans-5-ethyl-D-proline indicated that only one form may be allowed.Spectroscopic data (Circular Dichroism, NMR) showed the polypeptide exists in a poly-L-proline form-I-type helix and changes slowly to some intermediate conformation. The slow muta-rotation is partially due to the steric interactions of the ethyl group with the carbonyl group of the amide during the mutarotation. 

For a significant portion of this work, the ECEPP/3 (Empirical Conformational Energy Program for Peptides) [38] potential model is utilized. In this force field, it is assumed that the covalent bond lengths and bond angles are fixed at their equilibrium values. Then, the conformation is only a function of... 

ECEPP/3 Empirical Conformational Energy Program for Peptides... 

Abstract The conformationel properties of a series of asymmetric diamides and polyamides derived from cyclic r/- z s-l,2-dicarboxylic acid and either piperidine, piperazine, trans-2,5-dimethyl piperazine orA, A -dimethylethylendiamine have been extensively investigated with disparate techniques such as NMR spectroscopy, dipole moment measurements, hydrodynamic properties and empirical conformational energy calculations. 

ECEPP EMPIRICAL CONFORMATIONAL ENERGY PROGRAM FOR PEPTIDES... 

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