Question

How to calculate molecular weight using partial specific volume?

Answer 1

Answer:

A method is described for the simultaneous measurement of partial specific volumes and molecular weights of proteins and other substances by sedimentation equilibrium experiments in H 2 O and D 2 O (or D 2 O 18) solutions. In effect, the method is a differential …

Answer 2

Answer:

Explanation:

The estimation of molecular weight by sedimentation requires a knowledge

of the partial specific volume of the sedimenting material. With purified

protein preparations a satisfactory value of the partial specific volume, v,

call often be assumed from published results. However this is not possible for

macromolecules that have not been extensively studied. The classical pycnometer (19) and float (6) methods require more material than may be available

and the density gradient column (11) has limitations when applied to such

materials as lipoproteins.

NIcBain (14) postulated that v of macromolecules could be estimated from

their differential sedimentation rate in media of differing density. Obviously

such estimates will be subject to the combined errors of at least two sedimentation determinations and these will be in general greater than the errors

applicable to the classical methods of determining density. The classical

methods, however, are far more sensitive than the sedimentation method to

errors in concentration or residual hydration and small percentages of impurities. Such errors are inevitable with macro~nolecules that have a great

affinity for water, decompose at elevated temperatures, or associate with other

substances. The sedimentation method is attractive, therefore, since it is less

subject to the errors often inherent in the material itself and since it requires

only a small sample.

Evaluation of v of macromolecules by the sedimelltation method has been

made from experimelzts in which glycerol, sucrose, serum albumin, or deuterium oxide (4,12, 13) was used to vary the density of the sedimelltatioll medium.

Although the range of density obtainable with deuterium oxide is limited, it can

be assumed to behave in the same manner as water and thus avoids the

uncertainties of differential interaction between solvent and solute illherent

in the use of other materials. With the exception of polystyrene latex spheres,

previous experiments with deuterium oxide were made on materials of uncertaill

physical characteristics