高压下L-丝氨酸的拉曼光谱研究

High-Pressure Raman Spectroscopy Study of L-Serine

压力可以引起蛋白折叠与变性。作为蛋白质的基本构成单位,氨基酸在高压下的变化近来年备受关注。在常见的20种氨基酸中,学者们利用高压拉曼技术已研究了多种氨基酸在高压下的变化,研究的最高压力达到30 GPa。为了探究L-丝氨酸(C_3H_7NO_3)在极高压力下的结构变化情况,采用原位高压拉曼技术在常温下对L-丝氨酸晶体进行研究,最高压力达到22.6 GPa。研究发现,当压力达到2.7 GPa时,在102 cm^(-1)处出现新峰,在1 123 cm^(-1)(NH_3反对称摇摆振动)处的特征峰出现劈裂;当压力达到5.4 GPa时, L-丝氨酸晶体在574 cm^(-1)处出现新峰,同时原来164 cm^(-1)处峰消失;当压力达到6.0 GPa时,位于226, 456, 770和2 968 cm^(-1)(CH_2伸缩振动)等处出现新峰, 877 cm^(-1)处的CC伸缩振动峰发生劈裂,产生894 cm^(-1)新峰;当压力达到7.9 GPa时,在145, 151和2 946 cm^(-1)等出现新峰,同时原在CO_2摇摆振动峰的肩峰531 cm^(-1)消失;当压力达到11.0 GPa时,位于249 cm^(-1)处的振动峰开始劈叉,在241 cm^(-1)处形成新峰,位于2 956 cm^(-1)(CH_2伸缩振动)同时原位于391和431 cm^(-1)处的峰消失;当压力达到17.5 GPa时,在200 cm^(-1)处出现新峰。通过进一步分析L-丝氨酸的拉曼波数随压力的变化,发现很多拉曼峰在1.37, 2.2, 5.3, 7.46和11.0 GPa以及15.5 GPa等压力点处都出现了拐点。其结果表明:L-丝氨酸在0.1～22.6 GPa之间共发生7处结构相变,分别位于压力区间0.1～1.37, 2.2～2.7, 5.3, 6.0, 7.46～7.9, 10.1～11.0和15.5～17.5 GPa之间。而且,在6.0 GPa新的相变点在之前文献中未论述过。由于L-丝氨酸晶体在6.0 GPa时CC伸缩振动峰发生劈裂,这现象可能是由于压力引起L-丝氨酸晶体分子发生重排导致的,同时L-丝氨酸晶体分子重排导致氢键发生重排,使得L-丝氨酸晶体出现新的CH_2伸缩振动峰。L-丝氨酸晶体在10.1～11.0 GPa之间的拉曼光谱变化主要集中在低波数段,该波数段的拉曼振动模式主要与晶体晶格振动等低能量振动有关。同时在高波数段出现新的CH_2峰,由此可推测在10.1～11.0 GPa之间, L-丝氨酸晶体的晶格振动发生变化,产生了新的氢键,从而导致了L-丝氨酸晶体结构的改变。L-丝氨酸晶体在15.5～17.5 GPa之间,由于没有发现直接证据证明其发生结构相变,只是在拉曼波数随压力变化中,发现其在17.5 GPa时出现拐点,因此推测L-丝氨酸晶体在15.5～17.5 GPa之间可能发生结构相变。

Pressure can lead to protein fold and denaturation.As for the element of protein,the study of amino acid under high pressure has attracted attention of scholars in recent years.The properties of some amino acids among 20 common amino acids have been studied by using high-pressure Raman spectroscopy techniquewith the maximum pressure reaching to 30 GPa.In order to investigate the structural change of L-serine(C 3H 7NO 3)under ultra-high pressure,L-serine crystal was studied at room temperature by in-situ high pressure Raman spectroscopy,and it was submitted to pressure up to 22.6 GPa.The results showed that a new peak appears at 102 cm^-1 when the pressure reaches 2.7 GPa,and the peak splits at 1 123 cm^-1(NH 3 antisym rocking).Furthermore,a new peak appears at 574 cm^-1 as the pressure reaches 5.4 GPa,and the original peak at 164 cm^-1 disappears.While the pressure reaches 6.0 GPa,new peaks appear at 226,456,770,2 968 cm^-1(CH 2 stretching).And one peak splits at 877 cm^-1,which produces a new peak at 894 cm^-1.When the pressure reaches 7.9 GPa,new peaks appear at 145,151 and 2 946 cm^-1.With the pressure reaching 11.0 GPa,the vibration peak at 249 cm^-1 begins to split and a new peak appears at 241 cm^-1,which is located at 2 956 cm^-1(CH 2 Stretching)while the original peak at 391 cm^-1 and 431 cm^-1 disappears.When the pressure reaches 17.5 GPa,a new peak emerges at 200 cm^-1.By further analyzing the Raman spectroscopy,many Raman peaks have inflexed at pressure of 1.37,2.2,5.3,7.46,11.0 and 15.5 GPa.These results showed that the crystals undergo seven structural phase transitions,which are in the pressure range of 0.1~1.37,2.2~2.7,5.3,6.0,7.46~7.9,10.1~11.0 and 15.5~17.5 GPa,respectively.Moreover,a new phase transition that was found at 6.0 GPa has never been discussed before.This Structural change may be caused by rearrangement of molecules,which is induced by pressure.And molecular rearrangement leads to hydrogen bond rearrangement,which causes new CH2 stretching vibration peak.The Raman spectra in the range of 10.1~11.0 GPa focus on the low wavenumber,which is assigned to the low-energy vibration such as crystal lattice vibration and the new CH 2 stretching vibration.So the crystal lattice vibration of L-serine crystal change within 10.1~11.0 GPa,which causes the new hydrogen bond of L-serine crystal to change its structure.No direct evidence of structural phase transition has been found in the 15.5~17.5 GPa pressure range,except for the inflection point at 17.5 GPa.Therefore,it is speculated that L-serine crystals undergo a structural phase transition.