4hJCHOCH Spin Coupling in a Lewisx Trisaccharide as Evidence of Inter-Residue C-H···O Hydrogen Bonding in Aqueous Solution.

IF 14.4 1区 化学 Q1 CHEMISTRY, MULTIDISCIPLINARY Journal of the American Chemical Society Pub Date : 2024-11-13 Epub Date: 2024-10-29 DOI:10.1021/jacs.4c11948
Mi-Kyung Yoon, Pradip Shit, Wenhui Zhang, Reagan J Meredith, Hannah Kang, Ian Carmichael, Anthony S Serianni
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Abstract

Prior studies of the solution conformation of the Lewisx (Lex) trisaccharide, αFuc-(1→3)[βGal-(1→4)]-βGlcNAc, suggest that nonclassical inter-residue C-H···O hydrogen bonding in aqueous solution contributes to the stabilization of its 3D structure and affects its biological properties. Experimental evidence for this hydrogen bond in aqueous solution has been reported in the form of a 4hJCHOCH NMR spin-coupling constant between C5'Fuc and H1″Gal measured by 2D NMR methods in unlabeled samples. A methyl glycoside of Lex (MeβLex) was prepared containing selective 13C-labeling at C5'Fuc, and the H1″Gal signal was examined in high-field 1H NMR spectra for evidence of splitting or line-broadening caused by the 13C at C5'Fuc. High-resolution 1H NMR spectra obtained at high field and at different temperatures using different FID processing parameters showed no resolved splitting of the H1″Gal signal or evidence of line-broadening. Spectral simulation showed that this splitting and/or line-broadening would be observable if the reported J-value (∼1.1 Hz) is correct. DFT calculations on MeβLex and a carbon analog (O5″Gal replaced by a CH2 group) gave very small and nearly identical calculated 4hJC5',H1″ values, suggesting that the coupling is essentially zero. DFT calculations also showed that an alternate inter-residue 3hJH5',H1″ is small. Based on NMR analyses and DFT calculations, we found that 4hJC5',H1″ in MeβLex has an upper limit of ∼0.4 Hz and that the value could be lower, possibly zero, calling into question its value as experimental proof of persistent nonclassical hydrogen bonding in aqueous solutions of MeβLex and related structures.

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路易斯三糖中的 4hJCHOCH 自旋耦合是水溶液中残基间 C-H-O 氢键的证据。
之前对 Lewisx(Lex)三糖 αFuc-(1→3)[βGal-(1→4)]-βGlcNAc 的溶液构象的研究表明,水溶液中的非经典残基间 C-H-O 氢键有助于稳定其三维结构并影响其生物特性。通过二维核磁共振方法测量未标记样品中 C5'Fuc 和 H1″Gal 之间的 4hJCHOCH NMR 自旋耦合常数,报告了水溶液中这种氢键的实验证据。制备了一种含有选择性 C5'Fuc 13C 标记的 Lex 甲基糖苷(MeβLex),并在高场 1H NMR 光谱中检测了 H1″Gal 信号,以确定是否存在由 C5'Fuc 13C 标记引起的分裂或线宽。使用不同的 FID 处理参数在不同温度和高场条件下获得的高分辨率 1H NMR 图谱显示,H1″Gal 信号没有明显的分裂,也没有线变宽的迹象。光谱模拟显示,如果报告的 J 值(∼1.1 Hz)是正确的,则可以观察到这种分裂和/或线宽。对 MeβLex 和一种碳类似物(O5″Gal 被一个 CH2 基团取代)进行的 DFT 计算显示,4hJC5',H1″ 的计算值非常小且几乎相同,这表明耦合基本上为零。DFT 计算还表明,另一种残基间的 3hJH5',H1″ 值也很小。根据核磁共振分析和 DFT 计算,我们发现 MeβLex 中的 4hJC5',H1″ 的上限为 ∼0.4 Hz,该值可能更低,甚至可能为零,这使我们对其作为 MeβLex 和相关结构水溶液中持续存在非经典氢键的实验证明的价值产生了怀疑。
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来源期刊
CiteScore
24.40
自引率
6.00%
发文量
2398
审稿时长
1.6 months
期刊介绍: The flagship journal of the American Chemical Society, known as the Journal of the American Chemical Society (JACS), has been a prestigious publication since its establishment in 1879. It holds a preeminent position in the field of chemistry and related interdisciplinary sciences. JACS is committed to disseminating cutting-edge research papers, covering a wide range of topics, and encompasses approximately 19,000 pages of Articles, Communications, and Perspectives annually. With a weekly publication frequency, JACS plays a vital role in advancing the field of chemistry by providing essential research.
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