Department of Chemistry, University of Utah, 315 S. 1400 E. Rm 2020, Salt Lake City, Utah 84112, USA.
Phys Chem Chem Phys. 2010 Nov 7;12(41):13419-33. doi: 10.1039/c0cp00302f. Epub 2010 Jul 6.
Absolute bond dissociation energies of water to sodium cysteine (Cys) cations and cysteine to hydrated sodium cations are determined experimentally by collision-induced dissociation of Na(+)Cys(H(2)O)(x), where x = 1-4, complexes with xenon in a guided ion beam mass spectrometer. Experimental results show that the binding energies of water and cysteine to the complexes decrease monotonically with increasing number of water molecules. Quantum chemical calculations at three different levels show reasonable agreement with the experimental bond energies. The calculations indicate that the primary binding site for Na(+) changes from charge-solvated tridentate chelation at the amino nitrogen, carbonyl oxygen, and sulfur side-chain for x = 0 and 1 to the C terminus of zwitterionic cysteine for x = 4, whereas different levels of theory provide conflicting predictions for x = 2 and 3. The first solvent shell of Na(+)Cys is found to be complete at four waters. This is fewer than needed for the aliphatic amino acid glycine, because the functionalized side-chain of Cys provides an internal solvation site, a binding motif that probably applies for most other functionalized amino acids.
通过在引导离子阱质谱仪中用氙气碰撞诱导分解 Na(+)Cys(H(2)O)(x)（其中 x = 1-4）复合物，实验测定了水与半胱氨酸阳离子（Cys）和半胱氨酸与水合钠离子的绝对键离解能。实验结果表明，水和半胱氨酸与配合物的结合能随水分子数的增加而单调下降。在三个不同水平上的量子化学计算与实验键能吻合较好。计算表明，Na(+)的主要结合位点从 x = 0 和 1 时带电荷的三配位螯合作用（氨基氮、羰基氧和硫侧链）变为 x = 4 时两性离子半胱氨酸的 C 末端，而不同理论水平对半胱氨酸的 x = 2 和 3 提供了相互矛盾的预测。发现 Na(+)Cys 的第一个溶剂壳在四个水分子时就已完全形成。这比脂肪族氨基酸甘氨酸所需的少，因为 Cys 的官能化侧链提供了内部溶剂化位点，这是一种结合模式，可能适用于大多数其他官能化氨基酸。
