Solid-State 13C NMR Investigation of Molecular Ordering in the Cellulose of Apple Cell Walls

Abstract

A resolution-enhanced 13C nuclear magnetic resonance (NMR) spectrum of cell wall material isolated from Braeburn apples has revealed a pair of signals assigned to cellulose chains exposed on crystal surfaces, providing evidence for a high degree of molecular ordering on those surfaces. Proton spin relaxation editing revealed no detectable amorphous cellulose and provided an estimate of about 23 chains in a typical crystallite. Cellulose in apple cell walls was found to be distinctive, with triclinic and monoclinic Id crystalline forms present in similar proportions. Hence, its composition is intermediate between the family of bacterial and Valonia celluloses, rich in the triclinic crystalline form, and the family of cotton and ramie celluloses, in which the monoclinic form is dominant. Implications for apple crispness are discussed.

Solid-State 13C Nuclear Magnetic Resonance Characterization of Cellulose in the Cell Walls of Arabidopsis thaliana Leaves

“…These signal assignments follow Newman et al (1994). The values of T,(C) fall below the range 15 to 25 s observed for C-4 of cellulose in secondary cell walls of the wood of the dicotyledon Eucalyptus delegatensis and the gymnosperm Pinus radiata (Newman, 1992).…”

“…10a) showed a pair of peaks 84.0 and 85.1 ppm, assigned to C-4 in chains exposed on crystallite surfaces. These peaks were resolved in earlier studies of cellulose (Newman, 1994;Newman et al, 1994), and the relative heights were found to be independent of the relative proportions of I, and I, forms (Newman, 1994). The pair of peaks has therefore been assigned to pairs of crystallographically nonequivalent sites on well-ordered crystallite surfaces, regardless of whether the interior is in the I, or I, form .…”

“…10). The pattern is interpreted as a sum of two overlapping doublets, assigned to the two distinct crystal forms (Atalla and VanderHart, 1984;Newman et al, 1994). The peaks at 90.4 and 88.5 ppm are assigned to I, and I cr stal forms, respectively, and the peak at 89.4 ppm is assigned to a combination of the two.…”

“…The heights of the peaks at 84.0 and 85.1 ppm, relative to those at 88.5, 89.4, and 90.4 ppm, are consistent with cellulose crystallites containing so few chains that most of the chains are exposed on crystallite surfaces. Newman et al (1994) illustrated this point by drawing a cross-section of a crystallite containing just 23 chains.…”

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

“…Solid-state NMR spectroscopy of cellulose produces doublet d 13 C4 peaks that have been used to estimate the degree of crystallinity of cellulose as well as the number of glucan chains in elementary cellulose microfibrils (Kennedy et al 2007;Newman et al 1994Newman et al , 1996Park et al 2009;Teeäär et al 1987;Wang et al 2015). Two d 13 C4 peaks, centered at * 89 and * 85 ppm, have been assigned to ordered (crystalline) and disordered (amorphous) regions, respectively (Atalla et al 1980;Earl and VanderHart 1980).…”