What I understand from your problem is that you want to calculate log P value for any enzyme in a mixture of solvents i.e. Hexane:THF in the mentioned proportion.You can calculate the partition coefficient by taking each layer of solvent separately and calculate the concentration of enzyme in it by taking O.D of the solution .You have to first calculate the absilon value of the enzyme and from that calculate the concentration using equation, Absorption(O.D)=absilonXconcentrationXlength of the optical cell used.Calculate value of "C" for each layer and divide to find the Partition coefficient.

The log P-value is often determined in pharmaceutical mixed substances using potentiometry.

See following literature:

Interlaboratory study of log< i> P determination by shake-flask and potentiometric methods

K Takács-Novák, A Avdeel - Journal of pharmaceutical and biomedical Analysis, 1996 - Elsevier

Abstract

The pKa and log P values of 23 structurally diverse compounds, including well known drugs and two pharmacons under development, were determined by potentiometry. Also, the log P data were measured by the shake-flask method. Many of the samples were investigated at both of the participating laboratories in order to evaluate the reproducibility of the pH-metric log P technique. The interlaboratory evaluation of pKa and log P data obtained by potentiometry showed excellent agreement (average ΔpKa = ± 0.02 and Δ log P = ± 0.07). The log P values obtained by the two different methods, ranging from −1.84 to 5.80 (nearly eight orders of magnitude), were in very good concordance, as shown by the linear regression analysis: log PpH-metric = 0.9794 log Pshake-flask −0.0397 (r = 0.9987, s = ± 0.091, F = 8153). The advantages of potentiometric log P determination are discussed.

Sighart Walter Golf

the substance released on LogP is dissolved in a solvent in which it is soluble, using a HPLC and performs a calibration curve, footage from the lowest to the highest value (your place the lower limit and the maximum). Then compound to investigate what you put in your solvent mixture, stirring leave it overnight. Then take a syringe with a portion of each mecla and analyze by hplc and you determine the calibration curve that is in each phase, then performs the calculation

As far as I know, it can be determined experimentaly. For calculation You can ask Prof Dr Michael Abraham, Department for Organic Chemistry, University College London. Best regards.

Here ananother publication on calculation of log P.

Programs and Methods for Calculation of log P-values

Han van De Waterbeemd1,

Raimund Mannhold2

Article first published online: 19 SEP 2006

DOI: 10.1002/qsar.19960150507

Copyright © 1996 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Issue

Quantitative Structure-Activity Relationships

Volume 15, Issue 5, pages 410–412, 1996

I calculated it with a equation which recommended by Dordick. You can find it with detailed in my publication: Water Miscible Mono Alcohols' Effect on the Proteolytic Performance of Bacillus clausii Serine Alkaline Protease.

Applied biochemistry and biotechnology (Impact Factor: 1.94). 10/2013; DOI:10.1007/s12010-013-0525-3

Regardless of the problem of logP-calculation, I'd like to advice you to rethink whether you really require this value. It has become obvious for quite some time now, that the results of Laane et al., to which you obviously refer, have only a very limited application range. There actually seems to be a relation between enzyme behaviour and log P as long as you compare solvents of the same type. When comparing solvents with essentially different functional groups logP is not really an option to estimate the enzyme behaviour.

WARNING: THF and n-hexan give an AZEOTROPE!!

At first, please use THF PEROXIDE FREE and fresh destillated. and water free. When you use n-hexan, water free and fresh destillated too.

Why are you using the mixture : 7.3 / 1.1. ?

PLEASE NOTE that THF and n-hexan give an azeotrope (azeotrope pair) B.p. 63 ° C. and it cannot be alterered by destillation.

If you take the distillate at 63 °C you have a liquid with definable properties like a single liquid for your logP measurement. However your enzym must be water free too. Please check this aspect because a trace of water can give false results.

Good luck

JRG

Thank You all for help. The THF:hexane mixture in these proportions comes purely from the fact, that any lower concentration of THF is not enough to dissolve the substrate in a reasonable amount of solvent.

As for now I - according to some suggestions - decided to actually dump the logP comparison, just sticking to the structural aspects of solvents. It actually seems to make more sense when looking at the results. THF:Hexane mix allows for a higher proces enantioselectivity and reaction rate, similar situation is for MTBE, which has a not too high logP value. In theory, according to the theory by Laane the enzyme should behave better, giving a faster reaction in 1,2-dichloroethane, which in my particular case is not true. Thus, I decided to explain the changes in reaction behawior in different solvents basing only on their structure.

Thank You all again for help