Lin Chen-Jui, Wang Po-Yen, Lin Yi-Liang, Chang Sheng-Te, Hsu Chao-Sheng, Wu Shu-Pao, Wu Chien-Hou
Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu 30013, Taiwan.
Department of Civil Engineering, Widener University, Chester, Pennsylvania 19013, United States.
ACS Omega. 2021 Oct 13;6(42):28194-28202. doi: 10.1021/acsomega.1c04277. eCollection 2021 Oct 26.
Photochemical redox reactions of Cu(II) complexes of eight amino acid ligands (L) with nonpolar side chains have been systematically investigated in deaerated aqueous solutions. Under irradiation at 313 nm, the intramolecular carboxylate-to-Cu(II) charge transfer within Cu(II)-amino acid complexes leads to Cu(I) formation and the concomitant decomposition of amino acids. All amino acid systems studied here can produce ammonia and aldehydes except proline. For the 1:1 Cu(II) complex species (CuL), the Cu(I) quantum yields at 313 nm (Φ) vary by fivefold and in the sequence (0.10 M ionic strength at 25 °C) alanine (0.094) > valine (0.059), leucine (0.059), isoleucine (0.056), phenylalanine (0.057) > glycine (0.052) > methionine (0.032) > proline (0.019). This trend can be rationalized by considering the stability of the carbon-centered radicals and the efficient depopulation of the photoexcited state, both of which are dependent on the side-chain structure. For the 1:2 Cu(II) complex species (CuL), the Cu(I) quantum yields exhibit a similar trend and are always less than those for CuL. The photoformation rates of ammonia, Cu(I), and aldehydes are in the ratio of 1:2.0 ± 0.2:0.7 ± 0.2, which supports the proposed mechanism. This study suggests that the direct phototransformation of Cu(II)-amino acid complexes may contribute to the bioavailable nitrogen for aquatic microorganisms and cause biological damage on cell surfaces in sunlit waters.
在除氧水溶液中，系统研究了八种具有非极性侧链的氨基酸配体（L）的铜（II）配合物的光化学氧化还原反应。在313nm光照下，铜（II）-氨基酸配合物分子内的羧酸盐到铜（II）的电荷转移导致铜（I）的形成以及氨基酸的伴随分解。除脯氨酸外，这里研究的所有氨基酸体系都能产生氨和醛。对于1:1的铜（II）配合物物种（CuL），在313nm处的铜（I）量子产率（Φ）变化了五倍，顺序为（25℃下离子强度为0.10M）丙氨酸（0.094）＞缬氨酸（0.059）、亮氨酸（0.059）、异亮氨酸（0.056）、苯丙氨酸（0.057）＞甘氨酸（0.052）＞甲硫氨酸（0.032）＞脯氨酸（0.019）。通过考虑以碳为中心的自由基的稳定性和光激发态的有效去极化可以解释这种趋势，这两者都取决于侧链结构。对于1:2的铜（II）配合物物种（CuL），铜（I）量子产率呈现类似趋势，且总是低于CuL的量子产率。氨、铜（I）和醛的光形成速率之比为1:2.0±0.2:0.7±0.2，这支持了所提出的机理。这项研究表明，铜（II）-氨基酸配合物的直接光转化可能有助于为水生微生物提供生物可利用的氮，并对阳光照射水体中的细胞表面造成生物损伤。
