Vibrational and electronic couplings in ultraviolet resonance Raman spectra of cyclic peptides
Vibrational and electronic couplings in ultraviolet resonance Raman spectra of cyclic peptides
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DOI：
10.1016/s0301-4622(03)00108-x
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发表时间：
2003-09-01
影响因子：
3.8
通讯作者：
Spiro, TG
中科院分区：
文献类型：
--
作者：
Wang, Y;Spiro, TG
本文报道了一系列环酰胺的紫外共振拉曼光谱。具有13元环的2-氮杂环十三烷酮显示出经典的反式酰胺UVRR光谱模式，酰胺模式11、111和S的增强相当。当环减少到八个（ε-己内酰胺）或七个（2-氮杂环辛酮）成员时，这种模式被1497 cm（-1）附近的单一强带所取代，这是顺式酰胺振动（酰胺IIc）的C-N伸缩的特征。环的进一步收缩降低酰胺IIc频率。在4元环（2-氮杂环丁烷）中，它降低了100至1389 cm（-1），反映了由于环张力和C和N原子的非对称化，C-N键级减少。同时，酰胺Ic（C=O伸缩）频率增加，反映了C=O双键的局部化。此外，随着环尺寸的减小，酰胺Ic和IIc模式对氢-氘交换的敏感性反转。的UV吸收最大值，这是红移的顺式相对于反式酰胺，越来越多地转移到蓝色的环尺寸减小，再次反映本地化的π键。在5-和6-元环的酰胺（2-吡咯烷酮和delta-vareloctam）的情况下，多个UVRR带中看到的酰胺IIc区域，其相对强度是温度依赖性的。这些被分配到构象，其中不同的成员的环是出了平均平面，导致变量扰动的酰胺键。环状二肽环（Gly-Gly）和环（Gly-Pro）具有扰动的酰胺IIc频率，反映了酰胺坐标在同相和异相模式中的运动学混合。激发配置文件揭示电子混合，以及过渡偶极子添加的同相和取消的相位模式。(C)2003 Elsevier Science B. V.保留所有权利。
Ultraviolet resonance Raman (UVRR) spectra are reported for a series of cyclic amides. 2-Azacyclotridecone, which has a 13-membered ring, shows a classic trans-amide UVRR spectral pattern, with comparable enhancement of the amide modes 11, 111 and S. When the ring is diminished to eight (epsilon-caprolactam) or seven (2-azacyclooctanone) members, this pattern is replaced by a single strong band near 1497 cm(-1), characteristic of the C-N stretch of a cis-amide vibration (amide IIc). Further shrinkage of the ring decreases the amide IIc frequency. It is lowered over 100 to 1389 cm(-1) in the case of a 4-membered ring (2-azaidine), reflecting diminution of the C-N bond order due cm to ring strain and pyramidalization of the C and N atoms. At the same time the amide Ic (C=O stretching) frequency increases, reflecting the localization of the C=O double bond. Also the sensitivity to hydrogen-deuterium exchange reverses for amide Ic and IIc modes as ring size decreases. The UV absorption maximum, which is red-shifted for cis-relative to trans-amides, shifts increasingly to the blue as the ring size decreases, again reflecting localization of the pi bonding. In the case of amides with 5- and 6-membered rings (2-pyrrolidinone and delta-vareloctam) multiple UVRR bands are seen in the amide IIc region, whose relative intensities are temperature-dependent. These are assigned to conformers in which different members of the ring are out of the mean plane, resulting in variable perturbations of the amide bond. The cyclic dipeptides cyclo(Gly-Gly) and cyclo(Gly-Pro) have perturbed amide IIc frequencies, reflecting the kinematic mixing of the amide coordinates into in- and out-of-phase modes. Excitation profiles reveal electronic mixing as well, with the transition dipoles adding for the in-phase and canceling for the out-of-phase modes. (C) 2003 Elsevier Science B.V. All rights reserved.