Rules for optimization of biocatalysis in organic solvents

Abstract

General rules for the optimization of different biocatalytic systems in various types of media containing organic solvents are derived by combining data from the literature, and the logarithm of the partition coefficient, log P, as a quantitative measure of solvent polarity. (1) Biocatalysis in organic solvents is low in polar solvents having a log P < 2, is moderate in solvents having a log P between 2 and 4, and is high in a polar solvents having a log P > 4. It was found that this correlation between polarity and activity parallels the ability of organic solvents to distort the essential water layer that stabilizes the biocatalysts. (2) Further optimization of biocatalysis in organic solvents is achieved when the polarity of the microenvironment of the biocatalyst (log P(i)) and the continuous organic phase (log P(cph)) is tuned to the polarities of both the substrate (log P(s)) and the product (log P(p)) according to the following rules: |log P(i) - log P(s)| and |log P(cph) - log P(p)| should be minimal and |log P(cph) - log P(s)| and |log P(i) - log P(p)| should be maximal, with the exception that in the case of substrate inhibition log P(i), should be optimized with respect to log P(s) In addition to these simple optimization rules, the future developments of biocatalysis in organic solvents are discussed.

Enzymatic synthesis optimization of isoamyl butyrate

“…It has been asserted that acids may cause acidification of the micro-aqueous interface, leading to enzyme inactivation. 24,25 The highest values for percent esterification were found between 0.15 and 0.6 mol L -1 with the enzyme concentration in the range from 0.012 to 0.024 g mL -1 .…”

“…It has been asserted that alcohols are terminal inhibitors of lipases and acids, and may cause acidification of the micro-aqueous interface, leading to enzyme inactivation. 24,25 At a fixed temperature, esterification showed little variation with increased enzyme concentrations, but with 0.021 g mL -1 enzyme, a temperature of 30 °C, and the other conditions at the central point, total esterification from the acid substrate could occur. Even an increase in enzyme concentration had no significant effect at the higher temperatures.…”

Imobilização de lipases em filme de caseinato de sódio/glicerol: aplicação na síntese de ésteres

“…Segundo Laane et al 39 os solventes que possuem log P ≤ 2 são hidrofílicos, não sendo adequados para biocatálise porque alteram fortemente a interação água/biocatalisador, tornando-o inativo ou ocasionando a desnaturação. Os solventes com log P entre 2 e 4 são também hidrofílicos, mas perturbam menos a interação água/biocatalisador.…”

“…Os resultados obtidos neste trabalho, em geral, corroboram com os de Laane et al 39 mostrando que a conversão a produto foi dependente do solvente orgânico e, também, da massa de lipase. Os solventes com log P acima de 2,50, ou seja, os menos polares, foram os mais eficientes na catálise enzimática, formando os oleatos de npentila e de n-propila com conversões entre 24-58% e 53-60%, respectivamente.…”

“…Usando solventes com log P menores que 2,50, ou seja os mais polares, os produtos foram obtidos em menores conversões (0-17% para o oleato de n-pentila e 0-35% para o oleato de npropila). A baixa conversão em éster nos solventes mais polares devese provavelmente ao fato destes retirarem a camada de água essencial ao redor da enzima, causando distorção na conformação nativa e, portanto, alterando a atividade catalítica do biocatalisador 1,6,13,39 .…”