Determination of molecular weights by differential cryoscopy on small volumes of dilute solutions of oligopeptides.
A differential cryoscope of the equilibrium type is described. It requires only 1 ml of sample for a molecular-weight determination of a solute in a solvent that freezes below room temperature. The instrument is sensitive to +/- 0.0002 degrees C, which corresponds to +/- 0.0001 mol of solute per 1000 g of water. The apparatus was evaluated by measuring the freezing point depressions of 0.015 M urea and 0.01 M alanine in water, the measured molecular weights being accurate to within +/- 5%. The molecular weights of the following oligopeptides were then measured to determine their states of aggregation in the cited solvents: Ac-Asn-Pro-Tyr-NHMe in H2O and dimethyl sulfoxide and cyclo(L-alanyl-L-alanyl-epsilon-aminocaproyl), cyclo(L-alanyl-D-alanyl-epsilon-aminocaproyl), cyclo(L-alanyl-L-analyl-omega-capryl), cyclo(L-alanyl-D-alanyl-omega-capryl), and Ac-Tyr-Pro-Asn-NHMe in dimethyl sulfoxide.
D004121:Dimethyl Sulfoxide; D005615:Freezing; D008970:Molecular Weight; D009842:Oligopeptides; D012997:Solvents; D013816:Thermodynamics; D014867:Water
D009842:Oligopeptides; D012997:Solvents; D014867:Water; D004121:Dimethyl Sulfoxide