Enhancement of lipase activity in non-aqueous media upon immobilization on multi-walled carbon nanotubes

<p>Abstract</p> <p>Background</p> <p>Immobilization of biologically active proteins on nanosized surfaces is a key process in bionanofabrication. Carbon nanotubes with their high surface areas, as well as useful electronic, thermal and mechanical properties, constitute important building blocks in the fabrication of novel functional materials.</p> <p>Results</p> <p>Lipases from <it>Candida rugosa </it>(CRL) were found to be adsorbed on the multiwalled carbon nanotubes with very high retention of their biological activity (97%). The immobilized biocatalyst showed 2.2- and 14-fold increases in the initial rates of transesterification activity in nearly anhydrous hexane and water immiscible ionic liquid [Bmim] [PF6] respectively, as compared to the lyophilized powdered enzyme. It is presumed that the interaction with the hydrophobic surface of the nanotubes resulted in conformational changes leading to the 'open lid' structure of CRL. The immobilized enzyme was found to give 64% conversion over 24 h (as opposed to 14% with free enzyme) in the formation of butylbutyrate in nearly anhydrous hexane. Similarly, with ionic liquid [Bmim] [PF6], the immobilized enzyme allowed 71% conversion as compared to 16% with the free enzyme. The immobilized lipase also showed high enantioselectivity as determined by kinetic resolution of (±) 1-phenylethanol in [Bmim] [PF6]. While free CRL gave only 5% conversion after 36 h, the immobilized enzyme resulted in 37% conversion with > 99% enantiomeric excess. TEM studies on the immobilized biocatalyst showed that the enzyme is attached to the multiwalled nanotubes.</p> <p>Conclusion</p> <p>Successful immobilization of enzymes on nanosized carriers could pave the way for reduced reactor volumes required for biotransformations, as well as having a use in the construction of miniaturized biosensensor devices.</p

Pore-diffusion: Dependence of the Effective Diffusivity on the Initial Sorbate Concentration in Single and Multisolute Batch Adsorption Systems

The present work studies the intraparticle diffusivity in batch adsorption systems as a function of the initial sorbate concentration. The systems under investigation are basic dyes, namely Basic Blue 69, Basic Red 22 and Basic Yellow 21 and their binary and ternary combinations, all adsorbing onto activated carbon Filtrasorb 400. They study is based on the film-pore diffusion model and the output is a combination of the external mass transfer coefficient, k(f) and the effective diffusivity, D(eff) that yields congruent experimental and theoretical kinetic data

Prediction of Binary System for Kinetics of Batch Adsorption using Basic Dyes onto Activated Carbon

The present work develops the film-homogeneous diffusion model for multicomponent batch adsorption and applies to it two binary mixtures of basic dyes, namely (Basic Red 22 + Basic Yellow 21) and (Basic Red 22 + Basic Blue 69), onto activated carbon F400. The adsorption rate of each component j is measured by the external mass transfer coefficient kfj and intraparticle solid diffusivity Dsj. A single kfj has succeeded to describe the whole experimental range of each component while Dsj has increased exponentially with the initial sorbate concentration Coj. Equilibrium has been successfully described by the empirically extended Freundlich isotherm. © 1990

Prediction of Bisolute Adsorption Isotherms using Single Component Data for Dye Adsorption onto Carbon

Equilibrium isotherms have been determined for the adsorption of dyes in solution onto activated carbon. Single-component isotherms were measured for three basic dyes and then the three possible bisolute isotherms from the dyes were determined. Methods of predicting multicomponent dye isotherms were developed and applied using the single-component dye adsorption data to predict the bisolute equilibrium data. A comparison was made between predicted and experimental results. A simplified proximate method and a more rigorous method incorporating a Langmuir isotherm approach failed to give accurate predictions. However, the same rigorous method using a modified Freundlich isotherm proved successful in predicting bisolute isotherm data for a number of two-component dye mixtures adsorbing onto activated carbon. © 1988