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Cooperative effects in α‐helices: An ab initio molecular‐orbital study
Author(s) -
Van Duijnen P. T.,
Thole B. T.
Publication year - 1982
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360210906
Subject(s) - chemistry , cooperativity , intramolecular force , dipole , molecular orbital , protonation , ab initio , crystallography , hydrogen bond , helix (gastropod) , computational chemistry , proton affinity , molecule , stereochemistry , ion , ecology , biochemistry , organic chemistry , snail , biology
Some properties of α‐helices of polyclycine and polyalanine, up to the decapeptide, were investigated by ab initio molecular‐orbital calculations. These helices were found to be unstable relative to the corresponding “fully extended chain” conformation. The electric field of helices of 8–10 residues is about 20% stronger than that of models built from noninteracting monomers, for example. This is a result of cooperativity, which is essentially governed by the intramolecular hydrogen bonds. The cooperativity is manifest in all properties of the helices: relative stability, dipole moment, proton affinity, electrical potential. The electric potential of helices of three and four residues is such that their instability can be compensated for by a single charged group acting as an “initiator.” The computed proton affinity of the (Ala) 8 α‐helix is about 45 kcal/mol larger than that of formamide, which confirms that long helices may be protonated at the carboxyl end in solution.