脉冲升温纳秒时间分辨中红外光谱研究氨基酸重水溶液的分子间氢键

应用变温傅立叶变换红外光谱和脉冲升温纳秒时间分辨红外差谱研究了组氨酸和甘氨酸的重水溶液的羧基负离子的振动．结果表明不仅氨基酸分子之间形成氢键，而且氨基酸分子和溶剂分子之间也形成氢键．当温度升高时，羧基负离子在1600?1610 cm?1 附近的反对称伸缩振动发生蓝移，说明高温使氢键减弱．温度从10℃突然升高到20℃，组氨酸的时间分辨瞬态光谱出现两个漂白峰，一个在1604 cm?1，指认为形成氨基酸分子间氢键的羧基负离子的峰；另一个在1612 cm?1，指认为氨基酸分子和溶剂分子形成氢键的羧基负离子的峰．前

Intermolecular Hydrogen Bonds Formed Between Amino Acid Molecules in Aqueous Solution Investigated by Temperature-jump NanosecondTime-resolved Transient Mid-IR Spectroscopy

Carboxyl (COO?) vibrational modes of two amino acids histidine and glycine in D2O solution were investigated by temperature-dependent FTIR spectroscopy and temperature-jump nanosecond time-resolved IR di?erence absorbance spectroscopy. The results show that hydrogen bonds are formed between amino acid molecules as well as between the amino acid molecule and the solvent molecules. The asymmetric vibrational frequency of COO? around 1600-1610 cm?1 is blue shifted when raising temperature, indicating that the strength of the hydrogen bonds becomes weaker at higher temperature. Two bleaching peaks at 1604 and 1612 cm?1 were observed for histidine in response to a temperature jump from 10 ±C to 20 ±C. The lower vibrational frequency at 1604 cm?1 is assigned to the chain COO? group which forms the intermolecular hydrogen bond with NH3+ group, while the higher frequency at 1612 cm?1 is assigned to the end COO? group forming hydrogen bonds with the solvent molecules. This is because that the hydrogen bonds in the former are expected to be stronger than the latter. In addition the intensities of these two bleaching peaks are almost the same. In contrast, only the lower frequency at 1604 cm?1 bleaching peak has been observed for glycine. The fact indicates that histidine molecules form a dimer-like intermolecular chain while glycine forms a relatively longer chain in the solution. The rising phase of the IR absorption kinetics in response to the temperature-jump detected at 1604 cm?1 for histidine is about 30§10 ns, within the resolution limit of our instrument, indicating that breaking or weakening the hydrogen bond is a very fast process.