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    188宝金博页面版: Quantum mechanical studies of environmental effects on biomolecules

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    内容提示： Theoret. Chim. Acta (Berl.) 54, 73-82 (1979) THEORETICA CHIMICA ACTA ?9 by Springer-Verlag 1979 Quantum Mechanical Studies of Environmental Effects on Biomolecules IX. Structure and Hydration of Thiourea Yoshimasa Orita, Akio Ando, Hiroshi Abe Department of Medicine, Osaka University Medical School, 1-1-50, Fukushima, Fukushima-ku, Osaka, 553 Japan Shin-ichi Yamabe Department of Chemistry, Nara University of Education, Takabatake-cho, Nara, 630 Japan H616ne Berthod and Alberte Pullman Institut de Biologie ...

    文档格式：PDF | 页数：10 | 浏览次数：11 | 上传日期：2018-05-03 19:36:32 | 文档星级：
    Theoret. Chim. Acta (Berl.) 54, 73-82 (1979) THEORETICA CHIMICA ACTA ?9 by Springer-Verlag 1979 Quantum Mechanical Studies of Environmental Effects on Biomolecules IX. Structure and Hydration of Thiourea Yoshimasa Orita, Akio Ando, Hiroshi Abe Department of Medicine, Osaka University Medical School, 1-1-50, Fukushima, Fukushima-ku, Osaka, 553 Japan Shin-ichi Yamabe Department of Chemistry, Nara University of Education, Takabatake-cho, Nara, 630 Japan H616ne Berthod and Alberte Pullman Institut de Biologie Physico-Chimique, Laboratoire de Biochimie Th6orique, associ6 au C.N.R.S., 13, rue Pierre et Marie Curie, F-75005 Paris, France SCF ab initio computations have been performed on the structure, molecular potential and hydration scheme of thiourea in view of a comparison with urea and more generally as a model of the conjugated S=CNH-- group as compared to O=CNH--. In contrast to the carbonyl oxygen, both a and ~r acceptor, the sulfur atom of the thiocarbonyl is a a donor but a ~r acceptor and this results in an enhancement of the double-bond character of thiourea. The CN bond is less attractive for a proton than urea. The hydration scheme indicates a maxi- mum number of four water molecules directly bound to thiourea. Key words: Thiourea - Conjugated thiocarbonyl - Thioanalogs - Hydration of thiocarbonyls 1. Introduction As a continuation of previous studies on the molecular structure and hydration properties of urea [1 ], acetamide [2], N-methylacetamide [3], and formamide [4, 5], we report presently the results of a similar investigation of the corresponding properties of thiourea, the thiocarbonyl analog of urea. This compound is one of the simplest molecules where a C=S double bond is part of a conjugated system involving the rr lone-pairs of planar amine nitrogens. Thus, aside from its interest per se in comparison to urea [6, 7], thiourea provides also an appropriate model for the study of the properties of the S=C--NH-- group, a fundamental building block in the chemical skeleton of thiopurines and thiopyrimidines. Some of these compounds, which differ from the usual natural bases of the nucleic acids only by substitution of the thiocarbonyl for the carbonyl double bond, have been found recently to occur naturally as minor components of the structure of transfer- 0040-5744/79/0054/0073/$02.00

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