Theoretical Analysis on the Conformational Features of the HCO—Gly—L—Leu—NH2 Protected Dipeptide Motif: Ab initio and DFT Exploratory

Subject Areas : Journal of Physical & Theoretical Chemistry

B. Chahkandi ¹ , M. Chahkandi ² , S. M. Sadati Amin ³ , M. Giahi ⁴

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Received: 2015-05-31 Accepted : 2015-05-31 Published : 2011-11-01

Keywords: Dipeptide structures, Ab initio, DFT calculations, Conformational stability,

Abstract :

For better understanding of conformational stability of the dipeptide model HCO—Gly—L—Leu—NH2,ab initio and DFT computations at HF/6-31G(4 6-311++G(d,p) and B3LYP/6-31G(d) levels oftheory were carried out. Geometry optimization of the dipeptide within the leucine (Leu) side chainangles (x2 ,x2) resulted in three stable conformations as followings: anti-anti, the most stable one,(Xi = 180°, x2 = 180°), Gauche (+)-trans (xi= 60°, x2 = 210°) and 270°-Gauche (-)(x4 = 270°, x2 =3001. The thermodynamic properties E, H, G, and S by changing dihedral angles '111 (DO and (Di(D11) of glycine (Gly), ‘1J2 (D6), and (62 (D4) of Leu and keeping the SC dihedral angles of the anti--anti conformer were obtained by frequency calculations at the same levels. The calculations indicatethat the BB has the highest stability bearing 'P I (DO = 180°, (1:11 (D11 ) = 180°, T2 (D6) = 150°, and 02(D4) = 210°.