Silica–enzyme–ionic liquid composites for improved enzymatic activity

Abstract

Trypsin and pepsin enzyme-catalyzed precipitation of silica, synthesized by sol–gel chemistry in an ionic liquid, produces a composite material that demonstrates high enzymatic activity. This study investigates the structural properties of this silica–enzyme–ionic liquid composite material that allows for the retention of enzyme hydrolysis and condensation activity. The composite was prepared from a mixture of organo-functionalized triethoxysilane and tetraethoxysilane in an ionic liquid via enzyme-catalyzed direct hydrolysis and polycondensation reactions. The composite samples have been fully characterized with SEM, TEM, TG–DTA, IR, and N2 isotherms, and incorporation of the composite's organic function has been demonstrated by 29Si and 13C nuclear magnetic resonance. The presented systematic approach provides valuable information on the influence of the enzyme and ionic liquid on the properties of the silica gel and nature of the silica network as well as on the extent of enzyme and ionic liquid encapsulation. SEM and TEM reveal that the silica–enzyme–ionic liquid composites prepared from trypsin are composed of an aggregate of closely packed spherical structures ∼20 nm in diameter; however, the composites from pepsin consist of larger particles of ∼1 μm having a smooth surface. In addition, after encapsulation within the silica–ionic liquid composite, enzymes showed extremely high hydrolysis and condensation activities using trimethylethoxysilane as an enzyme substrate, and these activities were better than those of corresponding free enzyme solutions. The simple route employed can yield materials with high enzymatic activities, and this may offer very promising application prospects.