水溶液中几种芳香族氨基酸π-π自堆叠作用

利用精密的流动混合微量热法测定了298.15 K时D/L-色氨酸、L-色氨酸、L-组氨酸和L-苯丙氨酸四种天然芳香族氨基酸水溶液的稀释焓, 根据所建立的拟等步自堆叠作用的化学模型对实验数据进行了处理, 计算得到模型参数K△Hm. 该化学作用参数与McMillan-Mayer理论模型中的焓对作用系数具有高度一致性, 即hxx=K△Hm. 结合文献报道的结果, 认为芳核π-π自堆叠作用在本质上是一种特殊的疏水-疏水作用, 一般表现为吸热效应; 取代基空间位阻、芳核以外部分的静电、氢键和手性选择性作用等对芳核π-π自堆叠作用有显著影响; 组合参数K△Hm实际上描述了芳核π-π自堆叠作用平衡及焓变的综合效应.

Aromatic π-π Self-Stacking of Some Aromatic Amino Acids in Aqueous Solutions

Dilution enthalpies of some aromatic amino acids such as D/L-α-tryptophan, L-α-tryptophan, L-α-tyrosine and L-α-phenylalanine in aqueous solutions at 298.15 K were determined by sensitive mixing-flow microcalorimetry. A chemical interaction model for quasi-isodemic self-stacking was proposed and used to process the calorimetric data from which the model parameter K△Hm was calculated. The chemical interaction parameter (K△Hm) agrees well with and provides good insights into the pairwise enthalpic interaction coefficient (hxx) in the McMillan-Mayer approach for the existence of the equation K△Hm=hxx. Combined with results from literature we considered that aromatic π-πself-stacking is essentially a kind of special hydrophobic interaction manifesting commonly as an endothermic effect. Noteworthy effects arising from substituent hindrance, electrostatic interaction, hydrogen bonding and chiral recognition which are directed away from the aromatic core exert on aromatic π-πself-stacking. In nature, the composite parameter K△Hm describes a complex effect between the equilibrium and an enthalpic change of aromatic π-πself-stacking.