重金属镉与氨基酸类单体相互作用的亲合方式和驱动力研究

Affinity mode and driving force of interaction between heavy metal cadmium and amino acid monomers

采用等温滴定量热法,研究了重金属镉与氨基酸类单体相互作用的亲合方式、驱动力,并探讨了环境条件变化对二者亲合的影响。结果显示:除脯氨酸外,其它氨基酸与镉离子都可以相互亲合。其中,半胱氨酸与镉离子的亲合能力最强,二者的作用方式为配位键和静电相互作用,驱动力为焓熵双驱动和熵驱动两种;其他氨基酸与镉的作用方式均为静电相互作用,驱动力为熵驱动,所有的亲合过程均是可以自发进行的。氨基酸结构中的巯基为放热结合位点,结合能力最强;咪唑基、羧基为吸热结合位点,结合能力次之;氨基为微弱的吸热位点,结合能力最弱。此外,pH 6.0~7.5范围利于Cd(Ⅱ)与半胱氨酸的结合;升高温度不利于Cd(Ⅱ)与半胱氨酸的放热结合,离子强度的变化(25 mmol/L~100 mmol/L)对Cd(Ⅱ)与半胱氨酸的结合影响很小。

The affinity mode and driving force of interaction between heavy metal cadmium and amino acid monomer were studied by isothermal titration calorimetry,and the effects of environmental conditions on their affinity were discussed.The results showed that except proline,other amino acids and cadmium ions could be mutually affinitive.Among them,cysteine and cadmium ion had the strongest affinity.The interaction mode of cysteine and cadmium ion was coordination bond and electrostatic interaction,and the driving forces were enthalpy entropy double drive and entropy drive.While the interaction between other amino acids and cadmium was electrostatic interaction,the driving force was entropy drive,and all the affinity processes could be carried out spontaneously.The sulfhydryl group in amino acid structure was the exothermic binding site with the strongest binding ability.Imidazole and carboxyl groups were endothermic binding sites,followed by binding ability.The amino group was weak endothermic site with the weakest binding ability.In addition,the pH range from 6.0 to 7.5 was favorable for Cd(Ⅱ)binding to cysteine.The increase of temperature was not conducive to exothermic binding of Cd(Ⅱ)to cysteine,and the change of ionic strength(25 mmol/L~100 mmol/L)had little effect on the binding of Cd(Ⅱ)to cysteine.