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A quantum mechanical study of the folding of methylene units in compounds with several glutaramide units: nylon 1,5
Author(s) -
Alemán Carlos,
Puiggalí Jordi
Publication year - 1998
Publication title -
macromolecular theory and simulations
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.37
H-Index - 56
eISSN - 1521-3919
pISSN - 1022-1344
DOI - 10.1002/(sici)1521-3919(19980501)7:3<367::aid-mats367>3.0.co;2-x
Subject(s) - conformational isomerism , methylene , ab initio , chemistry , crystallography , folding (dsp implementation) , quantum , quantum chemical , protein folding , computational chemistry , molecule , physics , organic chemistry , quantum mechanics , electrical engineering , engineering , biochemistry
Three conformers of N,N ′‐dimethylglutaramide and two conformers of N,N ′‐dimethylsuccinamide have been studied by ab initio methods at the HF (Hartree‐Fock) and MP (Møller‐Plesset) levels using a number of different basis sets. These two compounds were previously studied in solid state by X‐ray crystallography and in vacuo by high‐level quantum mechanical methods, indicating the intrinsic tendency of the central methylene units to adopt a gauche conformation rather than the all‐ trans ‐conformation expected in polymethylenic segments. The present results indicate that HF/6‐31G is the minimum level of theory required to provide a reasonable description of the folding of methylene units in glutaramide analogues. In order to investigate the conformational preferences of compounds with several glutaramide residues, nylon 1,5 model oligopeptides from 1 to 4 residues were constructed. Energy calculations revealed that the six‐fold helix, which has been observed by X‐ray diffraction experiments, is stabilized with respect to the conformation with a folding of methylene units when the number of residues is 4.