Carbanilation of cereal beta-glucans for molecular weight determination and conformational studies.
Cereal beta-glucans can form aggregates in aqueous solution. The presence of aggregates in cereal beta-glucan solutions led to inaccurate determination of molecular weights and it was believed that intermolecular hydrogen bonding caused the aggregation. To eliminate aggregates, a carbanilation method for molecular weight determination of cereal beta-glucans was developed. Wheat beta-glucan samples were selected for investigation. The carbanilation method can prevent intermolecular hydrogen bonding by blocking hydroxyl groups with phenyl carbamate groups. The carbanilates of cereal beta-glucans were prepared by the reaction of cereal beta-glucans with phenylisocyanate catalyzed by DMSO and pyridine. To avoid degradation during the carbanilation reaction, relatively mild conditions were used, which led to incomplete substitution (DS: approximately 2). However, after the carbanilation reaction, the carbanilates dissolved completely in 1,4-dioxane solution without any detectable aggregates, which allowed accurate molecular weight determination. The degree of substitution (DS) of carbanilates was determined by both a nitrogen content method and an FT-IR method. The FT-IR method proved to be the more effective for DS estimation. Using this method, the converted molecular weights of cereal beta-glucans were in good agreement with the results measured in 0.5M NaOH solution, which previously was shown to be a good solvent for cereal beta-glucans. After the carbanilation reaction, conformational changes of carbanilates were studied by static and dynamic light scattering techniques. The fractal dimension (d(f)=2.27) and the structure sensitive parameters (rho >2) suggested a porous globular structure for partially carbanilated beta-glucans.
Li
Wei
W
Food Research Program, Agriculture and Agri-Food Canada, Guelph, ON, Canada N1G 5C9.
Wang
Qi
Q
Cui
Steve W
SW
Burchard
Walther
W
Yada
Rickey
R
D002219:Carbamates / Q000737:chemistry / Q000378:metabolism; D002236:Carbohydrate Conformation; D004146:Dioxanes / Q000737:chemistry / Q000378:metabolism; D006860:Hydrogen Bonding; D008027:Light; D008970:Molecular Weight; D012542:Scattering, Radiation; D017550:Spectroscopy, Fourier Transform Infrared; D014908:Triticum / Q000737:chemistry* / Q000378:metabolism; D047071:beta-Glucans / Q000737:chemistry* / Q000378:metabolism
D002219:Carbamates; D004146:Dioxanes; D047071:beta-Glucans; C025223:1,4-dioxane; C059692:phenylcarbamic acid