Entropic effects make a more tightly folded conformer of a β-amino acid less stable: UV-UV hole burning and IR dip spectroscopy of L-β3-homotryptophan using a laser desorption supersonic jet technique
Entropic effects make a more tightly folded conformer of a β-amino acid less stable: UV-UV hole burning and IR dip spectroscopy of L-β3-homotryptophan using a laser desorption supersonic jet technique
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熵效应使 β-氨基酸更紧密折叠的构象异构体更不稳定：使用激光解吸超音速喷射技术对 L-β3-同色氨酸进行 UV-UV 烧孔和红外浸入光谱
DOI：
10.1039/c8cp02106f
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发表时间：
2018
影响因子：
3.3
通讯作者：
and Hyuk Kang
中科院分区：
文献类型：
--
作者：
Woon Yong Sohn;Jeong Jin Kim;Myeongwon Jeon;Takuma Aoki;Shun-ichi Ishiuchi;Masaaki Fujii;and Hyuk Kang
采用激光解吸超声射流技术测量了L-β3-高色氨酸的紫外-紫外烧孔光谱和红外吸收光谱，作为一种自下而上的方法来了解β-肽的二级结构。通过UV-UV烧孔光谱分析，发现了14种构象异构体。构象异构体被分为三组，根据其特定的红外光谱中观察到的氢键模式，并通过与量子化学计算进行比较，初步分配。第1组具有自由OH伸缩振动，但没有NH 2反对称伸缩振动跃迁，归属于NH-π氢键结构。第2类构象包括最丰富的构象，显示自由OH和NH 2反对称伸缩振动，属于NH-O氢键构象。第3组构象具有氢键OH伸缩红外跃迁，并具有OH-N氢键。第3组的内部氢键是C6氢键，这是由于在β位置处的额外碳原子，并且显示出比C5氢键的键长更短的键长。当OH-N-C6氢键比NH-O强时，熵效应倾向于更灵活的NH-O氢键结构。预期非天然C6氢键影响β-肽的构象并构建与α-肽完全不同的二级结构。
UV-UV hole burning and IR dip spectra of L-β3-homotryptophan were measured by a laser desorption supersonic jet technique as a bottom-up approach to understand the secondary structures of β-peptides. 14 conformers were found by UV-UV hole burning spectroscopy. The conformers were classified into three groups depending on their hydrogen bonding patterns observed in their conformer-specific IR spectra, and tentatively assigned by comparing with quantum chemical calculations. Group 1 had free OH stretch but no NH2 anti-symmetric stretch vibrational transition and was assigned to NH–π hydrogen bonded structures. Group 2, including the most abundant conformer, showed both free OH and NH2 anti-symmetric stretch vibrations, and belonged to NH–O hydrogen bonded conformations. Group 3 of conformers had hydrogen-bonded OH stretch IR transition and had OH–N hydrogen bonds. The internal hydrogen bond of group 3 is a C6 hydrogen bond due to the additional carbon atom at the β position and shows a shorter bond length than that of a C5 hydrogen bond. While the OH–N C6 hydrogen bond is stronger than NH–O, the entropic effect prefers the more flexible NH–O hydrogen bonded structure. It is expected that the unnatural C6 hydrogen bond influences the conformations of β-peptides and builds totally different secondary structures than those of α-peptides.