ENTHALPY OF SOLUTION OF CARBOHYDRATES USING A MODIFIED DIFFERENTIAL SCANNING CALORIMETER

A differential scanning calorimeter (DSC) was modified for the determi nation of enthalpies of solution. The measurements were performed opt aqueous solutions of the deoxy- and fluoro-deoxy derivatives of D-gluc opyranose (Glu) where the OH group on the C1, C2, C3, and C6 is replac ed by H (1HGlu, 2HGlu, 3HGlu, and 6HGlu) and by F (1FGlu, 2FGlu, 3FGlu , and 6FGlu), 4-deoxy 4-fluoro-alpha-D-glucopyranoside (4FGlu), 1-meth oxy-alpha-D-glucopyranoside (alpha MeOGlu), 1-phenoxy-alpha-D-glucopyr anoside (alpha PheOGlu), D-mannopyranose (Man), and 3-methoxy-alpha-D- glucopyranoside (3MeOGlu) at 15.1, 25.0, 35.0, and 45.1 degrees C. The enthalpies of solution Delta(s)H(0)(T) ranged from 1.00 +/- 0.25 kJ-m ol(-1) for 6HGlu at 15.1 degrees C to 20.4 +/- 1.4 for alpha PhOGlu at 45.1 degrees C and were in good agreement with literature values for Man, alpha Glu, alpha MeOGlu, and 3MeOGlu at 25.0 and 35.0 degrees C a nd for alpha MeOMan and 2HGlu at 35.0 degrees C. Delta(s)H(0)(T) for t he derivatives were then extrapolated up to the melting temperature T- m and compared with their enthalpies of fusion, Delta(f)H, also determ ined from DSC measurements. If the agreement between Delta(s)H(0)(T-m) and Delta(f)H was within the 95% confidence level, then it was conclu ded that intermolecular interactions between the carbohydrate molecule s in the liquid phase were the same as between the carbohydrate and wa ter molecules in the solution phase. This agreement was observed for a queous solutions of Man, alpha Glu, alpha MeOGlu, 3HGlu, 3FGlu, and 6F Glu.