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Title: Structural factors affecting 13C NMR chemical shifts of cellulose: a computational study

Here, the doublet C4 peaks at ~ 85 and ~ 89 ppm in solid-state 13C NMR spectra of native cellulose have been attributed to signals of C4 atoms on the surface (solvent-exposed) and in the interior of microfibrils, designated as sC4 and iC4, respectively. The relative intensity ratios of sC4 and iC4 observed in NMR spectra of cellulose have been used to estimate the degree of crystallinity of cellulose and the number of glucan chains in cellulose microfibrils. However, the molecular structures of cellulose responsible for the specific surface and interior C4 peaks have not been positively confirmed. Using density functional theory (DFT) methods and structures produced from classical molecular dynamics simulations, we investigated how the following four factors affect 13C NMR chemical shifts in cellulose: conformations of exocyclic groups at C6 ( tg, gt and gg), H 2O molecules H-bonded on the surface of the microfibril, glycosidic bond angles (Φ, Ψ) and the distances between H4 and HO3 atoms. We focus on changes in the δ 13C4 value because it is the most significant observable for the same C atom within the cellulose structure. DFT results indicate that different conformations of the exocyclic groups at C6 have the greatestmore » influence on δ 13C4 peak separation, while the other three factors have secondary effects that increase the spread of the calculated C4 interior and surface peaks.« less
Authors:
 [1] ;  [2] ;  [3] ; ORCiD logo [4] ;  [5] ;  [6]
  1. Pennsylvania State Univ., University Park, PA (United States)
  2. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Louisiana State Univ., Baton Rouge, LA (United States)
  3. Univ. of Melbourne, Melbourne (Australia)
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  5. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  6. Univ. of Texas at El Paso, El Paso, TX (United States)
Publication Date:
Grant/Contract Number:
AC05-00OR22725; SC0001090
Type:
Published Article
Journal Name:
Cellulose
Additional Journal Information:
Journal Volume: 25; Journal Issue: 1; Journal ID: ISSN 0969-0239
Publisher:
Springer
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; 59 BASIC BIOLOGICAL SCIENCES; Cellulose; NMR; DFT; MD simulation; Microfibril
OSTI Identifier:
1406658
Alternate Identifier(s):
OSTI ID: 1407765