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Handbook of Solvents - George Wypych - ChemTech - Ventech!

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14.4.3 Choice <strong>of</strong> solvent for enzymatic reaction 873<br />

Table 14.4.3.1. Classification <strong>of</strong> solvents commonly used for enzymatic reactions in<br />

organic media. [Adapted, by permission, from T. Yamane, Nippon Nogeikagaku<br />

Kaishi, 65, 1104(1991)]<br />

1) Water-miscible organic solvents<br />

Methanol, ethanol, ethylene glycol, glycerol, N,N’-dimethylformamide, dimethylsulfoxide,<br />

acetone, formaldehyde, dioxane, etc.<br />

2) Water-immiscible organic solvents (water solubility [g/l] at the temperature indicated)<br />

• alcohols<br />

(n-, iso-) propyl alcohol, (n-, s-, t-) butyl alcohol, (n-, s-, t-) amyl alcohol,<br />

n-octanol, etc.<br />

• esters<br />

methyl acetate, ethyl acetate (37.8, 40 o C), n-butyl acetate, hexyl acetate, etc.<br />

• alkyl halides<br />

dichloromethane (2, 30 o C), chlor<strong>of</strong>orm, carbon tetrachloride, trichloroethane<br />

(0.4, 40 o C), etc.<br />

• ethers<br />

diethyl ether (12, 20 o C), dipropyl ether, diisopropyl ether, dibutyl ether, dipentyl<br />

ether, etc.<br />

3) Water-insoluble organic solvents (water solubility [ppm] at the temperature indicated)<br />

• aliphatic hydrocarbons<br />

n-hexane (320, 40 o C), n-heptane (310, 30 o C), isooctane (180, 30 o C), etc.<br />

• aromatic hydrocarbons<br />

benzene (1200, 40 o C), toluene (880, 30 o C), etc.<br />

• allicyclic hydrocarbons<br />

cyclohexane (160, 30 o C), etc.<br />

These organic solvents have noticeable but limited solubility <strong>of</strong> water, ranging<br />

roughly 0.1 - 10 % its solubility. The water solubility is <strong>of</strong> course increased as the temperature<br />

is raised.<br />

3) Water-insoluble organic solvents<br />

These solvents are also water-immiscible and have very low water solubility so that<br />

they are regarded as water-insoluble, i.e., water is practically insoluble in the organic solvents.<br />

Most aliphatic and aromatic hydrocarbons belong to this category.<br />

In Table 14.4.3.1 organic solvents <strong>of</strong>ten used for enzymatic reactions are listed together<br />

with their water solubilities (although not for all <strong>of</strong> them).<br />

14.4.3.3 Influence <strong>of</strong> solvent parameters on nature <strong>of</strong> enzymatic reactions<br />

in organic media<br />

Factors that influence the activity and stability <strong>of</strong> enzymes in organic media have been<br />

mostly elucidated. Several <strong>of</strong> them are mentioned below.<br />

1) Water activity, aw Among factors, the amount <strong>of</strong> water existing in the reaction system is no doubt the most influential.<br />

To emphasize the effect <strong>of</strong> water, the author once proposed to say ‘enzymatic reaction<br />

in microaqueous organic solvent’, instead <strong>of</strong> merely say ‘enzymatic reaction in<br />

organic solvent’. 3-5

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