摘要
采用B3I。YP／6—31＋＋G＊＊方法研究甘氨酸构象间转化机理，进而解释实验结果．优化得到了7个稳定极小，稳定次序为Ip〉Ⅱn〉1Vn〉Ⅲp〉Vn〉Ⅵp〉Wn；找到了9个过渡态．分子内C—N键、C—C键和c一0键的旋转导致构象转变，能垒分别处于0．25～9．43kJ／tool、10．53～15．79kJ／mol和23．96～61．43kl／mol范围内．为了理解实验结果，计算了445K（实验温度）各构象的热动力学性质，认识到：构象VIP和Ⅶn单向转化为低能构象，很快消失；构象ⅢP和Vn沿着Ⅲp→Vn→Ⅳn→IP方向快速转变为低能构象，数量迅速减少，导致谱图上难以分辨．构象IP是最稳构象，Ⅱn不能转化（能垒过高），Ⅳn可由IP直接转化，所以实验上只观测到3种构象．
B3LYP/6-31＋＋G ＊＊ method was applied to investigate the isomerization re- action mechanism of glycine conformers to understand experimental results. 7 minima （stabili- ty order is Ip〉Ⅱn〉1Vn〉Ⅲp〉Vn〉Ⅵp〉Wn） and 9 transition states were obtained after the full optimization and the reaction paths were found. It is found that isomerization reaction is induced by the rotation of C--N, C--C and C--O bond, and energy barrier range is separate- ly 0.25-9.43 kJ/mol, 10.54-15.82 kJ/mol and 23.96~61.43 kJ/mol. To understand exper- imental results, thermokinetic property of conformers at 390 K and 445 K （experimental tem- perature） was calculated and analyzed detailedly. It is found that Vip and ~n can rapidly and unidirectionally convert into other conformers, so both of them will vanish immediately, ill p and V n will rapidly and preponderantly convert into more stable conformers along the path of Ⅲp→Vn→Ⅳn→IP, so the quantity of these two conformers will be decreased quickly to the extent that they can not be distinguish by spectrum chart. I p is the most stable conformer, II n can not convert into other conformer due to the higher energy barrier, IV n can obtained di- rectly from single bond rotation of I p. So only 3 conformers were detected by experiment.
出处
《南开大学学报（自然科学版）》
CAS
CSCD
北大核心
2013年第3期15-22,共8页
Acta Scientiarum Naturalium Universitatis Nankaiensis
基金
河北省教育厅科学研究基金(Z2007205)
唐山市应用基础研究基金(06234501A-10)
关键词
甘氨酸
异构化
过渡态
机理
密度泛函计算
glycine
isomerization ~ transition state ~ mechanism ~ DFT calculation
