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Selected Publication:

Yoneda, Y; Mereiter, K; Jaeger, C; Brecker, L; Kosma, P; Rosenau, T; French, A; .
(2008): Van der Waals versus hydrogen-bonding forces in a crystalline analog of cellotetraose: cyclohexyl 4"-O-cyclohexyl beta-D-cellobioside cyclohexane solvate.
J Am Chem Soc. 2008; 130(49):16678-16690 FullText FullText_BOKU

Abstract:
Hydrogen bonding is important in cellulosic and other carbohydrate structures, but the role of interactions between nonpolar groups is less understood. Therefore, we synthesized cyclohexyl 4'-O-cyclohexyl beta-D-cellobioside (8), a molecule that has two glucose rings and two nonpolar cyclohexyl rings. Key to attaching the 4'-O-cyclohexyl group was making the 4'-O,6'-O-cyclohexylidene ketal. After peracetylation, the cyclohexylidene ketal ring was opened regioselectively, providing 65% of 8 after final deacetylation. Comparison of the crystal structure of 8, as the cyclohexane solvate, with those of cellulose and its fragments, especially cellotetraose with four glucose rings, revealed extensive effects from the cyclohexyl groups. Three conformationally unique molecules (A, B, and C) are in the triclinic unit cell of 8, along with two solvent cyclohexanes. When viewed down the crystal's a-axis, the array of C, A, and B looks like the letter N, with A inclined so that its cyclohexyl groups can stack with those of the reducing ends of the B and C molecules. The lower left and upper right points of the N are stacks of cyclohexyl rings on the nonreducing ends of B and C, interspersed with solvent cyclohexanes. Whereas cellotetraose has antiparallel (up-down) packing, A and B in 8 are oriented "down" in the unit cell while C is "up". "Down-down-up" (or, alternatively, "up-up-down") packing is rare for carbohydrates. Other unusual details include 06 in all three staggered orientations: one is tg, two are gg, and three are gt, confirmed with CP/MAS C-13 NMR. The tg O6 donates a proton to an intramolecular hydrogen bond to O2', opposite to the major schemes in native cellulose I. A similar but novel O6B-H center dot center dot center dot O2'B hydrogen bond is based on a slightly distorted gg orientation. The hydrogen bonds between parallel molecules are unique, with linkages between O2'A and O2'B, O3'A and O3'B, and O6A and O6B. Other details, such as the bifurcated O3 center dot center dot center dot O5' and center dot center dot center dot O6' hydrogen bonds are similar to those of other cellulosic structures. C-H center dot center dot center dot O hydrogen bonds are extensive along the [110] line of quarter-staggering. The unusual features described here expand the range of structural motifs to be considered for as-yet undetermined cellulose structures.
Authors BOKU Wien:
Kosma Paul
Rosenau Thomas
BOKU Gendermonitor:

Find related publications in this database (using NML MeSH Indexing)
Carbohydrate Conformation;Cellobiose/analogs & derivatives*;Cellobiose/chemical synthesis;Cellobiose/chemistry;Cellulose/analogs & derivatives*;Cellulose/chemistry;Crystallography, X-Ray;Cyclohexanes/chemistry;Hydrogen Bonding;Solvents/chemistry*;Tetroses/chemistry*;



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