ULTRAVIOLET RESONANCE RAMAN ENHANCEMENT OF THE CARBOXYLATE AND GUANIDINIUM GROUPS IN AMINO-ACIDS
ULTRAVIOLET RESONANCE RAMAN ENHANCEMENT OF THE CARBOXYLATE AND GUANIDINIUM GROUPS IN AMINO-ACIDS
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DOI：
10.1002/jrs.1250201003
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发表时间：
1989-10-01
影响因子：
2.5
通讯作者：
SPIRO, TG
中科院分区：
文献类型：
--
作者：
HILDEBRANDT, P;CZERNUSZEWICZ, RS;SPIRO, TG
用紫外共振拉曼光谱（UVRR）研究了氨基酸的羧酸基和胍基。在近共振激发下（192nm），进入羧酸盐发色团允许的π -π *跃迁，天冬氨酸的振动谱显示只有一个来自COO -对称拉伸模式的波段，与anA -项增强机制一致。胍离子的UVRR光谱显示出复杂的振动模式，并借助正坐标分析对其谱带进行了分配。在非对称（E ‘）和完全对称（A1 ’）模式下，以及在平面外cn3弯曲模式的泛音Γ（A2″）中，都观察到了紫外增强。在第一次允许的电子跃迁中，我们提出了E '增强以反映Jahn-Teller分裂A2″←E″，而2Γ（A2″）增强需要降低激发态中面外弯曲的力常数，这与预期的金字塔化趋势一致。在甲基胍和精氨酸中的胍发色团的UVRR光谱中也可以看到类似的增强模式，此外，由于取代基的存在，它们还出现了分裂和强度重分布。胍和精氨酸的激发谱显示出一种复杂的结构，可能是由激发态Jahn-Teller效应引起的。拉曼增强过低，无法在蛋白质的UVRR光谱中检测到胍或羧酸盐，即使波长低至192nm。
Carboxylate and guanidinium groups of amino acids have been studied by ultraviolet resonance Raman (UVRR) spectroscopy. On near‐resonant excitation (192 nm) into the allowed π–π* transition of the carboxylate chromophore, the vibrational spectrum of aspartate displays only one band originating from the COO−symmetric stretching mode, consistent with anA‐term enhancement mechanism. The UVRR spectra of the guanidinium ion reveals a complex vibrational pattern, and the bands have been assigned with the aid of a normal coordinate analysis. UV enhancement is observed for both asymmetric (E′) and totally symmetric (A1′) modes, and also for the overtone of the out‐of‐plane CN3bending mode, Γ(A2″). TheE′ enhancement is suggested to reflect Jahn—Teller splitting in the first allowed electronic transitionA2″ ←E″, whereas the 2Γ(A2″) enhancement requires a lowering of the force constant for out‐of‐plane bending in the excited state, consistent with its expected tendency toward pyramidalization. Similar enhancement patterns are seen in the UVRR spectra of the guanidinium chromophore in methylguanidinium and arginine, which show, in addition, splittings and intensity redistribution due to the substituents. The excitation profiles of guanidinium and arginine reveal a complex structure that may arise from an excited‐state Jahn—Teller effect. The Raman enhancements are too low to permit detection of guanidinium or carboxylate in the UVRR spectra of proteins, even at wavelengths as low as 192 nm.