Surface Enhanced Raman Spectroscopy Study of Complexes of Metal Ions with L-Cysteine
利用拉曼光谱仪测定L-半胱氨酸(L-Cys)的常规拉曼光谱(NRS)和表面增强拉曼光谱(SERS), 发现L-Cys在纳米银棒上有明显的拉曼增强效应, 对分子特征峰进行了归属, 研究L-Cys在银纳米棒基底表面吸附机理, 在固体NRS中在2 576 cm-1出处有明显的S—H伸缩振动峰, 而SERS中没有出现, 实验表明纳米银棒与L-Cys巯基上的S原子形成了Ag—S键, C—O和C—N伸缩振动有明显的增强。 在不同pH值条件下, 分析了L-Cys的拉曼光谱差异, 探讨吸附行为的变化。 在pH值为6时, S—H的伸缩振动峰基本消失, 形成了稳定的S—Ag键； 随着pH值增加趋于碱性时, 羧基易失去H原子形成—COO-易与银发生吸附作用且振动峰增强。 在pH值为7时, S原子与Ag形成稳定的S—Ag键, C—O和C—N的振动峰也最稳定。 选择在pH值为7的条件下, 在L-Cys溶液中加入Na+, Mg2+和Cu2+ 等10种金属盐, 发现Al3+, Cu2+, Zn2+, Cd2+和Hg2+ 使L-Cys分子的结构发生了改变, 金属离子与L-Cys另一端羧基发生作用, 其中Cu2+, Zn2+, Cd2+和Hg2+随半径增大与S原子的孤电子发生作用越大。 探讨了在不同pH值、 不同比例和不同浓度下, 金属离子与L-Cys作用SERS的变化, 随着pH值、 比例和浓度的增大, 峰的强度有减小趋势。 Cu2+与L-Cys作用的SERS信号很弱, Hg2+与L-Cys作用只出现了一个C—O的振动峰, 说明Hg2+完全破坏了L-Cys的空间构型。 该研究对蛋白质变性等的研究提供了重要参考信息。
In the present article, normal Raman spectra (NRS) and surface-enhanced Raman spectra (SERS) of L-cysteine (L-Cys) included liquid and solid sample, the unique possessing the reducing group, on the silver nanorodes were analyzed. The results showed that the strengthen of peaks were enhanced relatively. The vibrational and enhanced peaks were assigned. Adsorption models of L-Cys on the silver nanorodes have been investigated. The S—H stretching vibration absorption of solid NRS was found, which was disappeared on the SERS, which showed that the ν(S—H) bond was formed by drawing lone pairs of electrons on the sulfur atoms and silver nanorodes. The vibrations of ν(C—O) and ν(C—N) was enhanced obviously. The results explain that the long pair electrons of L-Cys were adsorbed on the silver nanorodes with moving to the low wave numbers. At the different pH values, all the different shifts were expressed and adsorption behaviors were changed. When the pH values reached number of 6, the vibrations of ν(S—H) were disappeared, it is shown that it was formed the stable vibrations of ν(Ag—S). With the pH values tended an alkalinity, but carboxyl groups were enhanced because of connection with silver nanoeodes. Under the condition of pH values 7, vibrations of ν(Ag—S) were constituted meanwhile had the stable vibrations of ν(C—O) and ν(C—N), so it was selected the pH values 7. In the systems containing different metal salts including Na+, Mg+, Cu2+, etc, it was found that the molecular structure of the L-Cys was changed under adding metal salts with Al3+, Cu2+, Zn2+, Cd2+ and Hg2+, the ability depends on metal ions and carboxyl groups were conjugated. UV-Vis absorption of silver nanorods was observed at 414nm, when it was changed under adding the metal salts. But the maximum absorption peaks were small changed, which had not assembled. Cu2+, Zn2+, Cd2+ and Hg2+ were all created that the groups ν(C—S) was appeared the two weak peaks near for 661 cm-1. The Al3+ came into precipitation with carboxyl groups easily, so the SERS was the weakest to low resolution. With the radius of metals (Cu2+, Zn2+, Cd2+, Hg2+) grow, the interaction was enhanced with sulfur atom. The Cd2+ and Hg2+ belonged to soft acid and S2- to soft base, so both were had large force. The SERS of complexes of cupric ion because of unstable (n-1)d9 electron configurations with L-Cys were reduced because of precipitation combining cupric ion with sulfhydryl groups to obtain the insoluble thiolate salts. The SERS of complexes of mercury ion with L-Cys only appeared the vibrations of ν(C—O), without any other vibration. The structure of L-Cys to join the mercury ion was destroyed completely. Though alternating the condition of pH value, proportion and concentration, the SERS of complexes of metal ions with L-Cysteine was changed. The results show that the strengthen of peaks were decreased as the pH value, proportion and concentration increased, which provides important information for the protein denaturation and heavy metal pollution.
周光明：发光与实时分析教育部重点实验室, 西南大学化学化工学院, 重庆 400715
程洪梅：发光与实时分析教育部重点实验室, 西南大学化学化工学院, 重庆 400715
张璐涛：发光与实时分析教育部重点实验室, 西南大学化学化工学院, 重庆 400715
于 璐：发光与实时分析教育部重点实验室, 西南大学化学化工学院, 重庆 400715
高 意：发光与实时分析教育部重点实验室, 西南大学化学化工学院, 重庆 400715
备注：张彩红, 女, 1990年生, 西南大学化学化工学院硕士研究生
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ZHANG Cai-hong,ZHOU Guang-ming,CHENG Hong-mei,ZHANG Lu-tao,YU Lu,GAO Yi. Surface Enhanced Raman Spectroscopy Study of Complexes of Metal Ions with L-Cysteine[J]. Spectroscopy and Spectral Analysis, 2017, 37(7): 2079-2086
张彩红,周光明,程洪梅,张璐涛,于 璐,高 意. L-半胱氨酸-金属离子配合物的表面增强拉曼光谱研究[J]. 光谱学与光谱分析, 2017, 37(7): 2079-2086