So I have to admit that I got it wrong and it looks like Ligand Efficiency (LE) is actually thermodynamically valid after all. You’ll recall my earlier objections to LE on the grounds that the standard concentration of 1 M has been arbitrarily chosen and that our perception of compound quality depends on the units of concentration in which the relevant equilibrium constants are defined. A Russian friend recently alerted me to an article in the Siberian Journal of Thermodynamics in which she thought I might be interested and was kind enough to scan it for me because this journal is not available in the West due to the current frosty relations with Russia. This seminal study by RR Raskolnikov demonstrates unequivocally that the 1 M standard concentration is absolutely and uniquely correct thus countering all known (and even some unknown) objections to LE as a metric of compound quality. The math is quite formidable and the central proof is based on the convergence characteristics of the trace of the partial molar polarizability tensor. Enigmatically, the author acknowledges the assistance of an individual named only as Porfiry Petrovich in helping him to find the truth after a long search. Raskolnikov’s career path appears to have been rather unorthodox. Originally from St Petersburg, he moved east because of some trouble with a student loan and for many years he was dependent on what his wife was able to earn.