Bioproduct Sciences and Engineering Laboratory, Department of Biological Systems Engineering, Washington State University, Richland, WA 99354, USA.
William R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99354, USA.
Sci Rep. 2017 Mar 14;7:44319. doi: 10.1038/srep44319.
Significant questions remain in respect to cellulose's structure and polymorphs, particularly the cellulose surface layers and the bulk crystalline core as well as the conformational differences. Total Internal Reflection Sum Frequency Generation Vibrational Spectroscopy (TIR-SFG-VS) combined with conventional SFG-VS (non-TIR) enables selectively characterizing the molecular structures of surface layers and the crystalline core of cellulose, revealing their differences for the first time. From the SFG spectra in the C-H and O-H regions, we found that the surface layers of Avicel are essentially amorphous while the surface layers of Iβ cellulose are crystalline but with different structural and spectroscopic signatures compared with its crystalline core. The differences between hydrogen bonding networks of cellulose surface and crystalline core were also shown by the SFG signal. The discovery here represents yet another instance of the importance of spectroscopic observations in transformative advances to understand the structure of the cellulosic biomass.
关于纤维素的结构和多晶型物，仍存在一些重要的问题，尤其是纤维素的表面层和块状结晶核心，以及构象差异。全内反射和频振动光谱（TIR-SFG-VS）与传统的非全内反射和频振动光谱（non-TIR-SFG-VS）相结合，可选择性地对纤维素的表面层和结晶核心的分子结构进行特征描述，这是首次揭示了它们的差异。从 C-H 和 O-H 区域的 SFG 光谱中，我们发现微晶纤维素的表面层基本上是无定形的，而 Iβ纤维素的表面层是结晶的，但与结晶核心相比，其结构和光谱特征不同。纤维素表面和结晶核心的氢键网络之间的差异也通过 SFG 信号表现出来。这里的发现再次证明了光谱观测在推动理解纤维素生物质结构方面的重要性。
