(gly) N (n = 2,3,4) Closed Into The Cyclo (gly) N (n = 2, 3, 4) Reaction Mechanism Of Chemical Research

Cyclopeptide, a kind of biological cyclic molecules, exists widely in nature. They exist in low life-form such as poriferan and arthropod , microorganism, epiphyte, algae and high plant. They play an important role in many biologically relevant processes. The main properties and uses of cyclopeptide include supramolecular recognition, simulation of enzymatic catalyze, nanotube and ionic transporting, bioactivity. Cyclopeptides have shown broad potentials in many areas including such as biomedicine and pharmaceutical research. Many cyclopeptides and cyclodepsipeptides present bioactivities. Bioactive cyclopeptides can form restricted conformations and have more favorable capabilities of antienzymolysis and antidegradation. Thus, the theoretical research on the mechanism for the cyclization reaction of peptide and conformation of cyclopeptide are very useful for cyclopeptide synthesis and investigating their supramolecular properties and bioactivity. The graphical function of GaussView is used to produce original structure and Gaussian 03 program is used to do the calculation in process of all researches.The transition states of two reactions were found using HF method at the 6-31G(d) level and verified by frequency analysis. The minimum energy paths(MEP) were affirmed by intrinsic reaction coordinate (IRC) method and the imaginary vibration modes were discussed. On this basis, full geometry optimization was carried out to find preferred conformations of the stationary point structures at B3LYP/6-31G(d) level, and their energies including ZPE and thermodynamic parameters were obtained at MP2/6-31G(d,p) level. Δ_rH_m^θ,Δ_rG_m^θ and E_a of two reactions were calculated. The results show that cyclization reaction of (Gly)2 is exothermal, Δ_rG_m^θ<0, with comparative low activation energy and easy to proceed, whereas (Gly)3 is endothermic, Δ_rG_m^θ>0, with higher activation energy and difficult to proceed.The mechanisms of cyclization reaction of (Gly)₄ ( conformation...