NEXAFS Sensitivity to Bond Lengths in Complex Molecular Materials: A Study of Crystalline Saccharides

Abstract

Detailed analysis of the C K near-edge X-ray absorption fine structure (NEXAFS) spectra of a series of saccharides (fructose, xylose, glucose, galactose, maltose monohydrate, α-lactose monohydrate, anhydrous β-lactose, cellulose) indicates that the precise determination of IPs and σ* shape resonance energies is sensitive enough to distinguish different crystalline saccharides through the variations in their average C-OH bond lengths. Experimental data as well as FEFF8 calculations confirm that bond length variations in the organic solid state of 10(-2) Å can be experimentally detected, opening up the possibility to use NEXAFS for obtaining incisive structural information for molecular materials, including noncrystalline systems without long-range order such as dissolved species in solutions, colloids, melts, and similar amorphous phases. The observed bond length sensitivity is as good as that originally reported for gas-phase and adsorbed molecular species. NEXAFS-derived molecular structure data for the condensed phase may therefore be used to guide molecular modeling as well as to validate computationally derived structure models for such systems. Some results indicate further analytical value in that the σ* shape resonance analysis may distinguish hemiketals from hemiacetals (i.e., derived from ketoses and aldoses) as well as α from β forms of otherwise identical saccharides.

Resonant soft X-ray scattering reveals cellulose microfibril spacing in plant primary cell walls

“…We use published Partial Electron Yield (PEY) NEXAFS data 64 to obtain β and δ for cellulose (Fig. 4a ).…”

X-ray Raman scattering: a newin situprobe of molecular structure during nucleation and crystallization from liquid solutions

“…66,67 The sensitivity of δ values to bond length variations as low as 0.001 Å have been previously illustrated for p-aminobenzoic acid 68 and saccharides. 69 Non-linear least-squares fitting using Fityk software 70 was utilized for the deconvolution of the near edge K-edge spectra ( Fig. 3).…”

Near-Edge X-Ray Absorption Fine Structure Spectroscopy of Agarose with a Compact Laser Plasma Soft X-Ray Source

“…Each element has a characteristic energy of core bonding, therefore NEXAFS spectra contain element-specific information. Additionally, the energy levels of initial and final states are strongly dependent on the involved molecular bonds [2]. Currently, the majority of large-scale facilities have a beamline dedicated to studying X-ray absorption.…”