Denaturation by organic solvents

A RM is a nanometer size droplet of an aqueous solution stabiHzed in an apolar environment by the surfactant present at the interface. In these systems, the proteins are solubiHzed inside the polar core of surfactant shell that protects the biomaterials from denaturation by organic solvent. The RMs formed in ternary... 

Khmelnitsky YL, Belova AB, Levashov AV, and Mozhaev W. Relationship between Surface Hyrophobicity of a Protein and its Stability agains Denaturation by Organic Solvents. FEES 1991 284 267-269. 

YL Khmelnitzki, AB Belova, AV Levashov, W Mozhaev. Relationship between surface hydrophilicity of a protein and its stability against denaturation by organic solvents. FEBS Lett 284 267-269, 1991. 

Aqueous-organic High substrate and product solubilities Biocatalyst denaturation and/or inhibition by organic solvent... 

The forces which hold a protein molecule together can be disrupted by changes in temperature and pH as well as by organic solvents and mechanical manipulation. This is known as denaturation. 

The hydrophilic character of a solid support is desirable not only because of the necessity of minimizing non-specific sorption but also because the hydrophobic character of a support can decrease the stability of some bound proteins on the basis of denaturation analogous to that produced by organic solvents. 

The crude ketal from the Birch reduction is dissolved in a mixture of 700 ml ethyl acetate, 1260 ml absolute ethanol and 31.5 ml water. To this solution is added 198 ml of 0.01 Mp-toluenesulfonic acid in absolute ethanol. (Methanol cannot be substituted for the ethanol nor can denatured ethanol containing methanol be used. In the presence of methanol, the diethyl ketal forms the mixed methyl ethyl ketal at C-17 and this mixed ketal hydrolyzes at a much slower rate than does the diethyl ketal.) The mixture is stirred at room temperature under nitrogen for 10 min and 56 ml of 10% potassium bicarbonate solution is added to neutralize the toluenesulfonic acid. The organic solvents are removed in a rotary vacuum evaporator and water is added as the organic solvents distill. When all of the organic solvents have been distilled, the granular precipitate of 1,4-dihydroestrone 3- methyl ether is collected on a filter and washed well with cold water. The solid is sucked dry and is dissolved in 800 ml of methyl ethyl ketone. To this solution is added 1600 ml of 1 1 methanol-water mixture and the resulting mixture is cooled in an ice bath for 1 hr. The solid is collected, rinsed with cold methanol-water (1 1), air-dried, and finally dried in a vacuum oven at 60° yield, 71.5 g (81 % based on estrone methyl ether actually carried into the Birch reduction as the ketal) mp 139-141°, reported mp 141-141.5°. The material has an enol ether assay of 99%, a residual aromatics content of 0.6% and a 19-norandrost-5(10)-ene-3,17-dione content of 0.5% (from hydrolysis of the 3-enol ether). It contains less than 0.1 % of 17-ol and only a trace of ketal formed by addition of ethanol to the 3-enol ether. 

Aqueous solutions are not suitable solvents for esterifications and transesterifications, and these reactions are carried out in organic solvents of low polarity [9-12]. However, enzymes are surrounded by a hydration shell or bound water that is required for the retention of structure and catalytic activity [13]. Polar hydrophilic solvents such as DMF, DMSO, acetone, and alcohols (log P<0, where P is the partition coefficient between octanol and water) are incompatible and lead to rapid denaturation. Common solvents for esterifications and transesterifications include alkanes (hexane/log P=3.5), aromatics (toluene/2.5, benzene/2), haloalkanes (CHCI3/2, CH2CI2/I.4), and ethers (diisopropyl ether/1.9, terf-butylmethyl ether/ 0.94, diethyl ether/0.85). Exceptionally stable enzymes such as Candida antarctica lipase B (CAL-B) have been used in more polar solvents (tetrahydrofuran/0.49, acetonitrile/—0.33). Room-temperature ionic liquids [14—17] and supercritical fluids [18] are also good media for a wide range of biotransformations. 

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