Characterization of sol-gel silica glass and its composites through study of physical and chemical properties of entrapped molecules
Controlled hydrolysis of alkoxides and polymerization of the resulting oxyacids, the sol-gel, method is very useful in many branches of chemistry and material science. Moderate processing conditions enable encapsulation of various organic, inorganic and biological molecules in glasses having adjustable properties. This method is used for fabrication of sensors, catalyst supports, optical elements, coatings, and special polymers.;Thoughtful understanding of local environments around dopant molecules and interactions at molecular level between dopants and silica glass matrix are essential in achieving desired properties of these materials.;In our work we took advantage of silica glass transparency as well as high sensitivity of electronic spectroscopy techniques (absorption, emission, and circular dichroism spectroscopy) to study physico-chemical behavior of low-concentrated organic and biological dopant molecules under the controlled various conditions. Hence, we studied the effects of sol-gel silica glass on activity and conformational stability of the encapsulated bovine carbonic anhydrase. A porous silica monolith limits access of an ester substrate to the enzyme embedded in the silica, and hence modulates the activity of the encapsulated enzyme. The conformational stability of the enzyme seems to be retained upon the encapsulation in this inorganic matrix. The classical hydrogen bonding interactions between silica glass and different organic compounds diffused into the glass modulate mobility and chemical reactivity of these compounds. Hydrogen bonding, also, causes immense accumulation of organic molecules from their solution into the silica matrix. Unexpectedly, hydrophobic aromatic hydrocarbons get accumulated into hydrophilic sol-gel silica matrix due to the hydrogen bonding between their aromatic It system and hydroxyl groups on the silica surface. We achieved full control over these interactions by using organic solvents with different hydrogen bonding propensity. In study of chemical reactivities of azo compounds inside micelle/silica composites, we discovered that these compounds partition between SDS/silica composite and a surrounding solution and that modulates their reactivity. Upon the ionic strength adjustment, the partitioning can be suppressed and the reactivity normalized. The partitioning of azo-compounds was not observed in case of CTAB/micelle composite.