Surface modification of cotton fabrics by transesterification with ion-paired subtilisin Carlsberg in solvents

The transesterification-active enzyme subtilisin Carlsberg was successfully solubilized into organic solvents such as isooctane by enzyme–bis(2-ethylhexyl) sulfosuccinate (AOT) ion-pairing while retaining its natural secondary structure and catalytic activity. The optimal CaCl₂ concentration and pH for enzyme extraction were 2 mM and 5.0, respectively, while the optimal pH for transesterification capability of enzyme was around 7.5. Within the critical micellar concentration (CMC) of AOT in isooctane, increasing the initial AOT concentration enhanced the extraction efficiency. As the hydrophobicity of the solvent decreased, so did the catalytic efficiency of the enzyme, while transesterification of cotton fabrics (medical gauze and knitted cotton cloth) occurred only in less hydrophobic solvents such as toluene. Transesterification was verified by infrared spectral analysis. The final degree of substitution (DS, the number of propionate groups per cellulose monosaccharide unit) of the medical gauze and knitted cotton cloth was 0.00282 and 0.00228, respectively. The surface properties of the modified cotton fabrics were characterized using X-ray diffraction, scanning electron microscopy, thermogravimetry, water contact angle, etc.