Tetrapeptides containing a Cys-Gly-Cys motif and a propensity to adopt a reverse-turn structure were synthesized to evaluate how O-, N-, H-, and aromatic π donor groups might contribute to mercury(II) complex formation. Tetrapeptides Xaa-Cys-Gly-Cys, where Xaa is glycine, glutamate, histidine, or tryptophan, were prepared and reacted with mercury(II) chloride. Their complexation with mercury(II) was studied by spectroscopic methods and computational modeling. UV-vis studies confirmed that mercury(II) binds to the cysteinyl thiolates as indicated by characteristic ligand-to-metal-charge-transfer transitions for bisthiolated S-Hg-S complexes, which correspond to 1 : 1 mercury-peptide complex formation. ESI-MS data also showed dominant 1 : 1 mercury-peptide adducts that are consistent with double deprotonations from the cysteinyl thiols to form thiolates. These complexes exhibited a strong positive circular dichroism band at 210 nm and a negative band at 193 nm, indicating that these peptides adopted a β-turn structure after binding mercury(II). Theoretical studies confirmed that optimized 1 : 1 mercury-peptide complexes adopt β-turns stabilized by intramolecular hydrogen bonds. These optimized structures also illustrate how specific N-terminal side-chain donor groups can assume intramolecular interactions and contribute to complex stability. Fluorescence quenching results provided supporting data that the indole donor group could interact with the coordinated mercury. The results from this study indicate that N-terminal side-chain residues containing carboxylate, imidazole, or indole groups can participate in stabilizing dithiolated mercury(II) complexes. These structural insights on peripheral mercury-peptide interactions provide additional understanding of the chemistry of mercury(II) with side-chain donor groups in peptides.

中文翻译：

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Hg(II) 与某些双半胱氨酰四肽络合的光谱和理论研究

合成包含 Cys-Gly-Cys 基序和采用反向结构的倾向的四肽，以评估O -、N -、H - 和芳香π捐助团体可能有助于汞(II) 复合物的形成。制备四肽 Xaa-Cys-Gly-Cys，其中 Xaa 是甘氨酸、谷氨酸、组氨酸或色氨酸，并与氯化汞 (II) 反应。通过光谱方法和计算模型研究了它们与汞 (II) 的络合。UV-vis 研究证实，汞 (II) 与半胱氨酰硫醇盐结合，如双硫醇化 S-Hg-S 复合物的特征配体-金属-电荷转移跃迁所表明的，这对应于 1:1 的汞-肽复合物形成。ESI-MS 数据还显示了主要的 1:1 汞-肽加合物，这与半胱硫醇双去质子化形成硫醇盐一致。这些复合物在 210 nm 处表现出很强的正圆二色性带，在 193 nm 处表现出负带，表明这些肽采用了结合汞(II)后的β-转角结构。理论研究证实，优化的 1:1 汞肽复合物采用由分子内氢键稳定的β-转角。这些优化的结构还说明了特定的N端侧链供体基团如何承担分子内相互作用并有助于复杂的稳定性。荧光猝灭结果提供了吲哚供体组可以与配位汞相互作用的支持数据。本研究结果表明，N含有羧酸根、咪唑或吲哚基团的末端侧链残基可以参与稳定二硫醇化汞 (II) 配合物。这些关于外周汞-肽相互作用的结构见解提供了对汞 (II) 与肽中侧链供体基团的化学的进一步理解。