In many KB calculations we need an estimate of a Molar Volume, MVol. If you have some exact means of getting the value, then use it. Otherwise, the app allows you to estimate if via a well-validated group contribution scheme.


MVol cc/mol
Protein MWt
Protein MVol cc/mol

In many KB apps it is found that the value of a (partial) molar volume, MVol, is required in order to calculate or estimate a KB Integral. Measurement of MVols is not hard (a series of density measurements suffices) but is often not practical (if, for example, the solubility is low) or in the case of interpreting historical data there is no realistic chance of doing the experiments.

In all the apps here, it turns out that an approximate value for MVol is good enough - as can readily be shown by altering these estimates and seeing that the impact on the overall conclusions is small. In the absence of any other technique then just using the MWt is often good enough. Here we provide a group estimation scheme that has been developed carefully and methodically by Lepori and Gianni1 at CNR, Pisa. Their technique includes charged groups but here (for simplicity) we include only neutral groups.

Like all such group contribution schemes "all" you have to do is enter the number of relevant groups ni into the table and the calculated value is based on the group values, Bi and the "ring-dependent" correction factor based on the number mi of rings (in yellow) of type Ri:

MVol = 9.2 + ΣiniBi + ΣimiRi

The app makes this easy by summing all the relevant contributions based on the number of groups you've entered. Note that there is some rounding in the values and cases where two values are in the original paper only show one. The problem is that breaking down a molecule into the relevant groups isn't all that easy for most of us. Unfortunately, automating such a process is not within my capabilities.

A totally unrelated calculation is the MVol of globular proteins from Chalikian and Filfil2 which is useful for KB calculations in biological and food-related systems. The only input is the MWt of the protein, as the formula (using their specific way of expressing it) is:

MVol = 0.602(1200+MWt)+4.7.MWt0.76(0.6-0.24)-1900

Creative Commons BYThe Javascript code is Copyright © 2016 Prof Steven Abbott and is distributed under the Creative Commons BY Attribution license. Users are encouraged to examine the code themselves. All key aspects of the calculation are flagged up with comments.

1Luciano Lepori and Paolo Gianni, Partial Molar Volumes of Ionic and Nonionic Organic Solutes in Water: A Simple Additivity Scheme Based on the Intrinsic Volume Approach, Journal of Solution Chemistry, 29, 405-447, 2000
2Tigran V. Chalikian and Rana Filfil, How large are the volume changes accompanying protein transitions and binding?, Biophysical Chemistry 104 (2003) 489–499