Restricted internal rotation of amino acid esters. Quantitative evaluation of rigidity of a molecule in terms of internal rotation entropy

Tadashi Mizutani, Tadashi Ema, Hisanobu Ogoshi

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)

Abstract

As a model of molecular recognition of a flexible guest through multi-point recognition, the two-point fixation of the NH2 group and the C=O group of amino acid esters to porphyrin host was investigated from thermodynamic point of view. The negative entropy change owing to restriction of internal rotation around the Cα-C(carbonyl) bond of guest as driven by the two-point fixation was calculated from the following steps: (1) ab initio molecular orbital calculations at the 3-21G level to generate a potential energy surface for internal rotation along the Cα-C(carbonyl) bond and the Cα-Cβ bond, and (2) a calculation of partition function of the system based on classical statistical mechanics. The entropy loss due to the restriction of a rotation around the Cα-C(carbonyl) bond was 5.0 cal·K-1·mol-1 for alanine methyl ester and 1.9 cal·K-1·mol-1 for valine methyl ester, indicating that valine methyl ester is more rigid with respect to the Cα-C(carbonyl) rotation. This entropy loss was found to originate from the correlated rotation of the Cα-C(carbonyl) bond and the Cα-Cβ bond.

Original languageEnglish
Pages (from-to)473-484
Number of pages12
JournalTetrahedron
Volume51
Issue number2
DOIs
Publication statusPublished - Jan 9 1995
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Drug Discovery
  • Organic Chemistry

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