First-Principle Computational Study on the Full Conformational Space of L-Threonine Diamide, the Energetic Stability of Cis and Trans Isomers
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- 作者：Michelle A. Sahai ; Szilard N. Fejer ; Bela Viskolcz ; Emil F. Pai ; Imre G. Csizmadia
- 刊名：Journal of Physical Chemistry A
- 出版年：2006
- 出版时间：October 12, 2006
- 年：2006
- 卷：110
- 期：40
- 页码：11527 - 11536
- 全文大小：1005K
- 年卷期：v.110,no.40(October 12, 2006)
- ISSN：1520-5215
文摘
First-principle computations were carried out on the conformational space of trans and cis peptide bond isomersof HCO-Thr-NH2. Using the concept of multidimensional conformational analysis (MDCA), geometryoptimizations were performed at the B3LYP/6-31G(d) level of theory, and single-point energies as well asthermodynamic functions were calculated at the G3MP2B3 level of theory for the corresponding optimizedstructures. Two backbone Ramachandran-type potential energy surfaces (PESs) were computed, one each forthe cis and trans isomers, keeping the side chain at the fully extended orientation (
1 = 2 = anti). Similarly,two side chain PESs for the cis and trans isomers were generated for the (
= 
= anti) orientationcorresponding to approximately the 
L backbone conformation. Besides correlating the relative Gibbs freeenergy of the various stable conformations with the number of stabilizing hydrogen bonds, the process oftrans 
cis isomerization is discussed in terms of intrinsic stabilities as measured by the computedthermodynamic functions.
1 = 2 = anti). Similarly,two side chain PESs for the cis and trans isomers were generated for the ( = = anti) orientationcorresponding to approximately the L backbone conformation. Besides correlating the relative Gibbs freeenergy of the various stable conformations with the number of stabilizing hydrogen bonds, the process oftrans cis isomerization is discussed in terms of intrinsic stabilities as measured by the computedthermodynamic functions.