Renewable Resources and Enabling Sciences Center, 15013 Denver West Parkway, Golden, Colorado 80401, United States.
Department of Chemistry and Biochemistry, San Diego State University, San Diego, California 92182-1030, United States.
J Phys Chem B. 2020 Nov 5;124(44):9870-9883. doi: 10.1021/acs.jpcb.0c07759. Epub 2020 Oct 22.
Two-dimensional (2D) and 3D through-space C-C homonuclear spin-diffusion techniques are powerful solid-state nuclear magnetic resonance (NMR) tools for extracting structural information from C-enriched biomolecules, but necessarily long acquisition times restrict their applications. In this work, we explore the broad utility and underutilized power of a chemical shift-selective one-dimensional (1D) version of a 2D C-C spin-diffusion solid-state NMR technique. The method, which is called 1D dipolar-assisted rotational resonance (DARR) difference, is applied to a variety of biomaterials including lignocellulosic plant cell walls, microcrystalline peptide fMLF, and black widow dragline spider silk. 1D C-C spin-diffusion methods described here apply in select cases in which the 1D C solid-state NMR spectrum displays chemical shift-resolved moieties. This is analogous to the selective 1D nuclear Overhauser effect spectroscopy (NOESY) experiment utilized in liquid-state NMR as a faster (1D instead of 2D) and often less ambiguous (direct sampling of the time domain data, coupled with increased signal averaging) alternative to 2D NOESY. Selective 1D C-C spin-diffusion methods are more time-efficient than their 2D counterparts such as proton-driven spin diffusion (PDSD) and dipolar-assisted rotational resonance. The additional time gained enables measurements of C-C spin-diffusion buildup curves and extraction of spin-diffusion time constants , yielding detailed structural information. Specifically, selective 1D DARR difference buildup curves applied to C-enriched hybrid poplar woody stems confirm strong spatial interaction between lignin and acetylated xylan polymers within poplar plant secondary cell walls, and an interpolymer distance of ∼0.45-0.5 nm was estimated. Additionally, Tyr/Gly long-range correlations were observed on isotopically enriched black widow spider dragline silks.
二维（2D）和三维（3D）通过空间 C-C 同核自旋扩散技术是从富含 C 的生物分子中提取结构信息的强大固态核磁共振（NMR）工具，但必要的长采集时间限制了它们的应用。在这项工作中，我们探索了二维 C-C 自旋扩散固态 NMR 技术的一维（1D）化学位移选择版本的广泛应用和未充分利用的能力。该方法称为一维偶极辅助旋转共振（DARR）差谱，应用于各种生物材料，包括木质纤维素植物细胞壁、微晶肽 fMLF 和黑寡妇拖丝蜘蛛丝。这里描述的一维 C-C 自旋扩散方法适用于某些情况下，其中一维 C 固态 NMR 谱显示化学位移分辨部分。这类似于在液态 NMR 中使用的选择性 1D 核 Overhauser 效应光谱（NOESY）实验，作为更快（1D 而不是 2D）和通常更明确（直接采样时域数据，同时增加信号平均）的替代方案 2D NOESY。选择性 1D C-C 自旋扩散方法比其二维对应物（如质子驱动的自旋扩散（PDSD）和偶极辅助旋转共振）更有效率。额外的时间增益使能够测量 C-C 自旋扩散积累曲线并提取自旋扩散时间常数，从而获得详细的结构信息。具体来说，应用于富含 C 的杂交杨树木质茎的选择性 1D DARR 差积累曲线证实了木质素和乙酰化木聚糖聚合物在杨树次生细胞壁之间具有很强的空间相互作用，并估计了聚合物间的距离约为 0.45-0.5nm。此外，在同位素富集的黑寡妇蜘蛛拖丝丝上观察到 Tyr/Gly 长程相关。
