Infrared Laser Spectroscopy Section, Bhabha Atomic Research Centre, Trombay, Mumbai 85, India; Homi Bhabha National Institute, Anushaktinagar, Mumbai 94, India.
High Pressure & Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 85, India; Homi Bhabha National Institute, Anushaktinagar, Mumbai 94, India.
Spectrochim Acta A Mol Biomol Spectrosc. 2022 Feb 5;266:120438. doi: 10.1016/j.saa.2021.120438. Epub 2021 Sep 27.
Trans-urocanic acid (t-UCA) is an important epidermal UV protector predominantly found in human skin. Exposure of UV radiation triggers photoisomerization of t-UCA into its other conformer, cis-urocanic acid (cis-UCA), which has been shown to be a mediator of UV-induced immune-suppression leading to skin cancer. In this report, we present the investigation of molecular changes of t-UCA under high pressures by in-situ high pressure Raman spectroscopy. The study indicates onset of ring opening polymerization of t-UCA at pressure above 1.4 GPa. At pressures beyond 5 GPa, a well discernible characteristic vibrational mode (CC stretch) accompanied by several other spectral features such as δ CO and δ NH modes of cis-UCA point towards the isomerization of residual t-UCA monomers into cis-UCA. The content of cis-UCA gradually increased with increase in pressure. On release to ambient conditions, the spectrum of the quenched sample showed Raman modes of polymer and cis-UCA indicating that the changes are irreversible.
反式尿刊酸（t-UCA）是一种重要的表皮紫外线保护剂，主要存在于人体皮肤中。紫外线辐射的暴露会触发 t-UCA 向其顺式异构体顺式尿刊酸（cis-UCA）的光异构化，顺式尿刊酸已被证明是介导紫外线诱导免疫抑制导致皮肤癌的物质。在本报告中，我们通过原位高压拉曼光谱研究了 t-UCA 在高压下的分子变化。研究表明，t-UCA 在压力高于 1.4GPa 时开始开环聚合。在超过 5GPa 的压力下，一个明显的特征振动模式（CC 伸展）伴随着 cis-UCA 的几个其他光谱特征，如δCO 和δNH 模式，表明残余 t-UCA 单体异构化为 cis-UCA。cis-UCA 的含量随压力的增加而逐渐增加。在释放到环境条件下，淬火样品的光谱显示聚合物和顺式尿刊酸的拉曼模式，表明这些变化是不可逆的。
