Dynamics of Cellulose-Water Interfaces: NMR Spin-Lattice Relaxation Times Calculated from Atomistic Computer Simulations
2008 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 112, no 9, 2590-2595 p.Article in journal (Refereed) Published
Solid-state nuclear magnetic resonance (CP/MAS 13C NMR) spectroscopy has often been used to study cellulose structure, but some features of the cellulose NMR spectrum are not yet fully understood. One such feature is a doublet around 84 ppm, a signal that has been proposed to originate from C4 atoms at cellulose fibril surfaces. The two peaks yield different T1, differing by approximately a factor of 2 at 75 MHz. In this study, we calculate T1 from C4-H4 vector dynamics obtained from molecular dynamics computer simulations of cellulose Iβ-water interfacial systems. Calculated and experimentally obtained T1 values for C4 atoms in surface chains fell within the same order of magnitude, 3-20 s. This means that the applied force field reproduces relevant surface dynamics for the cellulose-water interface sufficiently well. Furthermore, a difference in T1 of about a factor of 2 in the range of Larmor frequencies 25-150 MHz was found for C4 atoms in chains located on top of two different crystallographic planes, namely, (110) and (10). A previously proposed explanation that the C4 peak doublet could derive from surfaces parallel to different crystallographic planes is herewith strengthened by computationally obtained evidence. Another suggested basis for this difference is that the doublet originates from C4 atoms located in surface anhydro-glucose units with hydroxymethyl groups pointing either inward or outward. This was also tested within this study but was found to yield no difference in calculated T1.
Place, publisher, year, edition, pages
Washington: ACS Publications , 2008. Vol. 112, no 9, 2590-2595 p.
cellulose-water interface, spin-lattice relaxation times, molecular dynamics
Physical Chemistry Polymer Chemistry
IdentifiersURN: urn:nbn:se:kth:diva-9475DOI: 10.1021/jp074641tISI: 000253511900006ScopusID: 2-s2.0-41549090192OAI: oai:DiVA.org:kth-9475DiVA: diva2:114134
QC 201006182008-11-172008-11-062015-05-26Bibliographically approved