配体间相互作用研究: 氨基酸与二肽配体形成 质子复合物的稳定性

用pH电位滴定法测定了苯丙氨酰亮氨酸(PL)与甘氨酸(Gly)、丙氨酸(Ala)、缬氨酸(Val)、亮氨酸(Leu)、异亮氨酸(Ile)、苯丙氨酸(Phe)在离子强度为0.1mol/L(NaNO~3)，(25.0±0.1)℃时形成质子复合物的稳定常数，并对苯丙氨酰亮氨酸与六种氨基酸相互作用体系进行了量子化学和分子力学计算。从配体间弱相互作用的观点，讨论了二肽配体对氨基酸分子的识别。结果表明，二肽与氨基酸配体间的结合主要受到配体间静电、氢键作用的控制，同时受到范德华力和键间排斥能等弱相互作用的影响。

Studies on ligand-ligand interaction: Formation and stability of proton-dipeptide-amino acid complexes

Potentiometric titration method was used to determine the stabilities of proton complexes forming between phenylalanyl-L- leucine and six amino acids(glycine, alanine, valine, leucine, isoleucine and phenylalanine) at ionic strength of 0.1 mol/L (NaNO~3) and 25℃. The results show that the order of stability of the two forms of complexes is valine>alanine>leucine>isoleucine>phenylalanine> glycine. For further understanding of these results, semiempirical calculations at PM3 level and molecular mechanic (AMBER force field) method were used to optimize the conformation and the energy of proton complexes. In the view of weak interligand interaction, the recognitions of amino acids by phenylalanyl-L-leucine are discussed. The results show that the electrostatic forces and hydrogen bond give main contributions to the stabilities of the complexes. The van der Waals interactions and the bonding interactions also play a very important role in the complexation.