In our previous studies of the crystal structure of native cellulose (cellulose I) by solid-state two-dimensional (2D) 13 C-13 C INADEQUATE, it was revealed that cellulose I a contains two kinds of b-D-glucose residues (A and A¢) in the unit cell and that cellulose I b contains another two kinds of residues (B and B¢). In the present study, the sequence of residues A and A¢ along the same chains in cellulose I a and that of residues B and B¢ in I b were investigated by 2D 13 C-13 C rotor-synchronized radiofrequency-driven recoupling (RFDR) experiments using, respectively, uniformly 13 C 6 -labeled (U) 13 C 6 ) bacterial cellulose and the same [U) 13 C 6 ] cellulose sample after thermal treatment at 260°C. The RFDR spectra recorded with a short mixing time (1.0 ms) showed dipolar-coupled 13 C spin pairs of only the neighboring carbon of the both phases, while those recorded with a longer mixing time (3.0-15 ms) provided correlations between weakly coupled 13 C spin pairs as well as strongly coupled 13 C spin pairs such as neighboring carbon nuclei. In the RFDR spectrum of the [U) 13 C 6 ] cellulose recorded with a mixing time of 15 ms, the inter-residue 13 C-13 C correlation between C4 of residue A and C2 of residue A¢ and that between C3 of residue A and C4 of residue A¢ were clearly observed. In the case of cellulose I b , however, inter-residue 13 C-13 C correlations between residues B and B¢ could not be detected in the series of RFDR spectra recorded with different mixing times of annealed [U) 13 C 6 ] cellulose. From these findings, that cellulose I a was revealed to have the -A-A¢-repeating units along the cellulose chain. For cellulose I b , it was revealed that the respective residues B and B¢ are composed of independent chains (-B-B-and -B¢-B¢-repeating units) and that there are no -B-B¢-repeating units in the chain.

Through-bond 13C−13C and 13C−H correlations in the crystal structure of cellulose II were determined by the two-dimensional (2D) refocused INADEQUATE and MAS-J-HMQC spectra of the mercerized cellulose, which was biosynthesized by Acetobacter xylinum ATCC 10245 from the uniformly labeled glucose (d-(U-13C6)glucose). Mercerization of the bacterial cellulose was achieved in a solution of 20% NaOH in water for 2 weeks. In the 2D INADEQUATE spectrum of cellulose II, two sets of the through-bond 13C−13C connectivities from C1 through C6 were clearly observed, which enabled us to completely assign the complex 1D CP/MAS 13C spectrum of cellulose II. Following the 13C assignment, the 1H resonance for the proton(s) attached to each carbon of cellulose II could be assigned by use of the 2D MAS-J-HMQC spectrum of the mercerized cellulose.

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