Conformational analysis of cyclo (L-cystine).
Conformational analysis of cyclo (L-cystine).
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环（L-胱氨酸）的构象分析。
DOI：
10.1111/j.1399-3011.1977.tb01739.x
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
R. Chandrasekaran
中科院分区：
文献类型：
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作者：
A. Mitra;R. Chandrasekaran
环（L-胱氨酸）的构象分析表明，二酮哌嗪环必须仅以船形存在。有了这种几何形状，分子可以采取两种不同的形式，主要是在二硫桥的手性不同。在P-和M-模型中，分别对应于S-S-键的近+90度和-90度的二面角，分子显示出近似的双重对称性。根据我们的半经验能量计算，M模型的最低能量为9.2kcal/mol，仅比P模型低0.3kcal/mol。因为两个最小值之间的差异很小，所以没有一种形式明显上级另一种。然而，在允许的构象空间中，M-模型的低能构象的数量明显大于P-模型的数量，比例为3：1，因此前者很可能是有利的。
Conformational analysis of cyclo(L-cystine) shows that the diketopiperazine ring has to exist only in the boat form. With this geometry, the molecule can adopt two distinct forms differing mainly in the chirality of the disulphide bridge. In both the P- and M-models, corresponding to dihedral angles of nearly +90 degrees and -90 degrees respectively about the S-S- bond, the molecule displays an approximate two-fold symmetry. According to our semi-empirical energy calculations, the minimum energy of the M-model is --9.2 kcal/mol, only 0.3 kcal/mol lower than that of the P-model. Because the difference between the two minima is so small, neither form is clearly superior to the other. However, the number of low energy conformations of the M-model in the allowed conformational space is significantly larger than that of the P-model by a ratio of 3 to 1, and therefore the former is likely to be thermodynamically favoured.