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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Role of ring-constrained γ-amino acid residues in α/γ-peptide folding: Single-conformation UV and IR spectroscopy
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Role of ring-constrained γ-amino acid residues in α/γ-peptide folding: Single-conformation UV and IR spectroscopy

机译：环受限的γ-氨基酸残基在α/γ肽折叠中的作用：单构型紫外和红外光谱

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The capped α/γ-peptide foldamers Ac-γACHC-Ala- NH-benzyl (γα) and Ac-Ala-γACHC-NH-benzyl (αγ) were studied in the gas phase under jet-cooled conditions using single-conformation spectroscopy. These molecules serve as models for local segments of larger heterogeneous 1:1 α/γ-peptides that have recently been synthesized and shown to form a 12-helix composed of repeating C12 H-bonded rings both in crystalline form and in solution [Guo, L.; et al. J. Am. Chem. Soc. 2009, 131, 16018]. The γα and αγ peptide subunits are structurally constrained at the Cβ-Cγ bond of the γ-residue with a cis-cyclohexyl ring and by an ethyl group at the Cα position. These triamides are the minimum length necessary for the formation of the C12 H-bond. Resonant two-photon ionization (R2PI) provides ultraviolet spectra that have contributions from all conformational isomers, while IR-UV hole-burning (IR-UV HB) and resonant ion-dip infrared (RIDIR) spectroscopies are used to record single-conformation UV and IR spectra, respectively. Four and six conformers are identified in the R2PI spectra of the γα and αγ peptides, respectively. RIDIR spectra in the NH stretch, amide I (C? -O stretch), and amide II (NH bend) regions are compared with the predictions of density functional theory (DFT) calculations at the M05-2X/6-31+G* level, leading to definite assignments for the H-bonding architectures of the conformers. While the C12 H-bond is present in both γα and αγ, C9 rings are more prevalent, with seven of ten conformers incorporating a C9 H-bond involving in the γ-residue. Nevertheless, comparison of the assigned structures of gas-phase γα and αγ with the crystal structures for γα and larger α/γ-peptides reveals that the constrained γ-peptide backbone formed by the C9 ring is structurally similar to that formed by the larger C12 ring present in the 12-helix. These results confirm that the ACHC/ethyl constrained γ-residue is structurally preorganized to play a significant role in promoting C12 H-bond formation in larger α/γ-peptides.
机译：在气相冷却条件下，采用单组分光谱法研究了封端的α/γ-肽折叠剂Ac-γACHC-Ala-NH-苄基（γα）和Ac-Ala-γACHC-NH-苄基（αγ）。这些分子可作为较大的异质1：1α/γ肽局部片段的模型，这些片段最近已合成，并显示出形成12个螺旋结构，该结构由重复的C12 H键合环以晶体形式和溶液形式组成[Guo， L .;等。 J.上午化学Soc。 2009，131，16018]。 γα和αγ肽亚基在结构上限制在具有顺式环己基环和Cα位置的乙基的γ-残基的Cβ-Cγ键上。这些三酰胺是形成C12 H键所需的最小长度。共振双光子电离（R2PI）提供了所有构象异构体的贡献的紫外光谱，而IR-UV空穴燃烧（IR-UV HB）和共振离子浸入红外（RIDIR）光谱仪用于记录单形态UV和红外光谱。在γα和αγ肽的R2PI光谱中分别鉴定出四个和六个构象体。将NH延伸区，酰胺I（C1-O延伸区）和酰胺II（NH弯曲区）中的RIDIR光谱与M05-2X / 6-31 + G *处的密度泛函理论（DFT）计算的预测值进行比较级别，从而为构想者的H键结体系结构确定分配。尽管C12 H键同时存在于γα和αγ中，但C9环更为普遍，在十个构象异构体中，有七个构象掺入了C 9 H键并参与了γ残基。然而，将气相γα和αγ的分配结构与γα和较大的α/γ肽的晶体结构进行比较后发现，由C9环形成的受约束γ肽骨架与较大的C12形成的结构相似。环存在于12螺旋中。这些结果证实，ACHC /乙基约束的γ-残基在结构上被预先组织成在促进较大的α/γ-肽中的C12 H键形成中起重要作用。

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