Curdlan solid state

Figure 15 75.46 MHz 13CCPMAS NMR spectra of curdlan in the solid state. (A) anhydrous, (B) hydrate, (C) annealed at 180 °C followed by slow cooling. From Ref. 120 with permission.

Curdlan adopts a triple helix conformation in the dispersed and solid states (Deslandes et al., 1980) and reverts to a random coil in 0.25-M sodium hydroxide (Stipanovic and Giammatteo, 1989). Some glucans are ordered in dilute alkali and disordered at higher concentrations (Ogawa et al., 1972). 

It is more difficult to envision that the H-6A-H-2, 4, 5 cross peak displayed in Figure 7b resulted from an interresidue interaction. Calculations show that both C-6 protons are 5-8 A removed from H-2, H-4, and H-5 of the successive residue. However, an 0-4-0-6 intertriplex hydrogen bond that exists in the solid state of curdlan 15, 16) may also persist in 0.1 M NaOD and yield an NOE cross peak resulting from a H-6-H-4 interaction between helices in an aggregated network structure. 

NMR spectroscopy allowed to determine that the native SSG glucan from Sclerotinia sclerotiorum IFO 9395 and regenerated SSG obtained by neutralization of the alkaline solution had different conformations, since their C-3 signals appeared at 86 and 89 ppm, respectively. These values imply that while regenerated SSG possesses helical structure similar to that of curdlan, the native SSG in solid state has random-coil conformation [69]. 

C-1-0 and C-3-0 linkages is allowed (6). We attempted here to compare the chemical shifts of the gel with those of solid state curdlan, the conformation of which is mainly single helix at ambient temperature and triple-helix at higher temperature above 120°, as studied by X-ray diffraction (14>I5)- The newly emerging technique, cross-polarization magic angle spinning (CPMAS) ... 

Figure 6 shows the CPMAS NMR spectrum of curdlan powder, taken by courtesy of Professor Gary Maciel and Dr. Victor Bartuska of Colorado State University. Interestingly, the most mobile C-6 carbon gives rise to the least intense signal in the solid state because of insufficient CP transfer between proton and carbon. It was again found that the C chemical shifts of C-1 and C-3 are displaced downfield appreciably in the solid state compared with the peak-positions of liquid state D-glucan, as shown in Table I. 

Comparison of C chemical shifts of curdlan gbserved in aqueous solution, elastic gel and solid state°... 

Figure 6. 15.03-MHz CPMAS C-13 NMR spectrum of solid-state curdlan, re-...

The solid-state %-NHR spectra of curdlan, amylose and chitin have also been reported (26), and generally C-1 and C-4, or C-3 in... 

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