振动圆二色性作为环状β-氨基酸衍生物固态结构的探针:顺式和反式 2-氨基环丁烷-1-羧酸。
Vibrational circular dichroism as a probe of solid-state organisation of derivatives of cyclic β-amino acids: Cis- and trans-2-aminocyclobutane-1-carboxylic acid.
机构信息
CP3A Organic Synthesis Group and Services Communs, ICMMO, UMR 8182, Université Paris Sud, Université Paris-Saclay, Orsay, France.
Institut des Sciences Moléculaires d'Orsay (ISMO), CNRS, Univ. Paris-Sud, Université Paris-Saclay, Orsay, France.
出版信息
Chirality. 2019 Aug;31(8):547-560. doi: 10.1002/chir.23083. Epub 2019 Jun 26.
Peptide models built from cis- and trans-2-aminocyclobutane-1-carboxylic acids (ACBCs) are studied in the solid phase by combining Fourier-transform infrared spectroscopy (FTIR) absorption spectroscopy, vibrational circular dichroism (VCD), and quantum chemical calculations using density functional theory (DFT). The studied systems are N-tert-butyloxycarbonyl (Boc) derivatives of 2-aminocyclobutanecarboxylic acid (ACBC) benzylamides, namely Boc-(cis-ACBC)-NH-Bn and Boc-(trans-ACBC)-NH-Bn. These two diastereomers show very different VCD signatures and intensities, which of the trans-ACBC derivative being one order of magnitude larger in the region of the ν (CO) stretch. The spectral signature of the cis-ACBC derivative is satisfactorily reproduced by that of the monomer extracted from the solid-state geometry of related ACBC derivatives, which shows that no long-range effects are implicated for this system. In terms of hydrogen bonds, the geometry of this monomer is intermediate between the C6 and C8 structures (exhibiting a 6- or 8-membered cyclic NH⋯O hydrogen bond) previously evidenced in the gas phase. The benzyl group must be in an extended geometry to reproduce satisfactorily the shape of the VCD spectrum in the ν (CO) range, which qualifies VCD as a potential probe of dispersion interaction. In contrast, reproducing the IR and VCD spectrum of the trans-ACBC derivative requires clusters larger than four units, exhibiting strong intermolecular H-bonding patterns. A qualitative agreement is obtained for a tetramer, although the intensity enhancement is not reproduced. These results underline the sensitivity of VCD to the long-range organisation in the crystal.
采用傅里叶变换红外光谱(FTIR)吸收光谱、振动圆二色性(VCD)和基于密度泛函理论(DFT)的量子化学计算相结合的方法,在固态相中研究了顺式和反式 2-氨基环丁烷-1-羧酸(ACBC)构建的肽模型。研究的体系是 2-氨基环丁烷羧酸(ACBC)苄酰胺的 N-叔丁氧羰基(Boc)衍生物,即 Boc-(顺式-ACBC)-NH-Bn 和 Boc-(反式-ACBC)-NH-Bn。这两个非对映异构体表现出非常不同的 VCD 特征和强度,反式 ACBC 衍生物在 ν(CO)伸展区域的强度大一个数量级。顺式 ACBC 衍生物的光谱特征可以通过从相关 ACBC 衍生物的固态几何结构中提取的单体的光谱特征来很好地再现,这表明该体系没有涉及远程效应。在氢键方面,该单体的几何形状介于气相中先前证明的 C6 和 C8 结构(表现出 6 或 8 元环 NH⋯O 氢键)之间。为了很好地再现 VCD 光谱在 ν(CO)范围内的形状,苄基基团必须处于伸展的几何形状,这使得 VCD 成为色散相互作用的潜在探针。相比之下,要再现反式 ACBC 衍生物的 IR 和 VCD 光谱,需要大于四个单元的团簇,表现出强烈的分子间氢键模式。虽然强度增强没有再现,但对于四聚体可以获得定性的一致性。这些结果强调了 VCD 对晶体中远程组织的敏感性。