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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Laser Spectroscopy of Conformationally Constrained r/-Peptides: Ac-ACPC-Phe-NHMe and Ac-Phe-ACPC-NHMe
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Laser Spectroscopy of Conformationally Constrained r/-Peptides: Ac-ACPC-Phe-NHMe and Ac-Phe-ACPC-NHMe

机译：构象受约束r /肽的激光光谱：Ac-ACPC-Phe-NHMe和Ac-Phe-ACPC-NHMe

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摘要

Single-conformation ultraviolet and infrared spectra have been recorded under the isolated molecule conditions of a supersonic expansion for three conformationally constrained R/-peptides, Ac-L-Phe-ACPC-NHMe (rLACPC), Ac-ACPC-L-Phe-NHMe (ACPCrL), and Ac-ACPC-D-Phe-NHMe (CPCrD). These three molecules are close analogues of the hAla-containing R/-peptide counterparts Ac-L-Phe-3-hAla-NHMe, Ac-3-hAla- L-Phe-NHMe, and Ac-3-hAla-D-Phe-NHMe, which have been studied recently by James et al. (J. Am. Chem. Soc. 2009, 131, 6574). Incorporation of the -amino acid trans-2-aminocyclopentanecarboxylic acid (ACPC) constrains the-peptide backbone via the cyclopentane ring, producing clear changes in the conformational preferences relative to the unconstrained analogues. The conformational control is manifested most obviously in the complete absence of C6 H-bonded rings, which were dominant in the unconstrained R/-peptides. The most stable C6 ring structure (C6a) in the absence of the ACPC ring cannot be formed in its presence, while a secondary C6 ring (C6b) has its energy destabilized by 20 kJ/mol. In rLACPC, the preference for C5 structures in the N-terminal position, combined with the strong preference for C8 structures in the -peptide subunit, leads to the observation of two C5/C8 bifurcated double ring conformers. Both C8/C7 sequential double rings and C11 single rings are observed in ACPCrL and ACPCrD. Here, the ACPC ring selectively stabilizes the C8a ring over other possible C8 structures. Finally, the combined evidence from IR and UV spectra lead to tentative assignments for diastereomeric pairs, exhibiting small but understandable shifts in the IR and UV spectra induced by the change in chirality at the R-peptide chiral center.
机译：在超音速膨胀的分离分子条件下已记录了三个构象受约束的R /肽，Ac-L-Phe-ACPC-NHMe（rLACPC），Ac-ACPC-L-Phe-NHMe的单形态紫外和红外光谱（ACPCrL）和Ac-ACPC-D-Phe-NHMe（CPCrD）。这三个分子是含hAla的R /肽对应物Ac-L-Phe-3-hAla-NHMe，Ac-3-hAla-L-Phe-NHMe和Ac-3-hAla-D-Phe的紧密类似物。 -NHMe，James等人最近进行了研究。 （J.Am.Chem.Soc.2009，131，6574）。 -氨基酸反式-2-氨基环戊烷羧酸（ACPC）的掺入通过环戊烷环约束肽主链，相对于不受约束的类似物在构象偏好方面产生明显的变化。构象控制最明显地表现在完全不存在C6 H键环的情况下，该环在不受约束的R /肽中占主导地位。在没有ACPC环的情况下，无法在其存在下形成最稳定的C6环结构（C6a），而次级C6环（C6b）的能量不稳定了20 kJ / mol。在rLACPC中，对N末端位置C5结构的偏爱，再加上对肽亚基中C8结构的偏爱，导致观察到两个C5 / C8分叉的双环构象体。在ACPCrL和ACPCrD中都观察到C8 / C7顺序双环和C11单环。在此，ACPC环相对于其他可能的C8结构选择性地使C8a环稳定。最后，来自红外光谱和紫外光谱的综合证据导致对映体对的初步分配，在R肽手性中心的手性变化引起的红外光谱和紫外光谱中显示出微小但可以理解的变化。

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