Abhay Vaze

Paper-based electrochemical immunoassay for rapid, inexpensive cancer biomarker protein detection

Inexpensive, reusable electrochemical sensor chips were fabricated from gold CDs. All reagents were loaded onto a paper disk sequentially, then placed on the chip to detect cancer biomarker prostate specific antigen (PSA) in serum at pg mL-1 levels in ∼15 mins.

Vitamin B12-mediated electrochemical cyclopropanation of styrene

Abstract Vitamin B 12 (a cobalt corrin complex) mediated the reduction of methylene chloride in the presence of styrene to give cyclopropylbenzene in quantitative yields in DMF containing tetrabutylammonium bromide (TBAB) and acetic acid with current efficiency 45% and turnover rate 4-fold larger than a typical vitamin B 12 -mediated 6-membered ring cyclization. A pathway involving formation and electroreductive cleavage of a chloromethylene-Co III intermediate to yield a chloromethylene radical that adds to styrene is suggested. The reaction is highly sensitive to solvent composition, and water in the solvent acts as a proton donor to facilitate production of 1-chloro-3-phenylpropane in a competitive pathway.

Optimizing Turnover of a Cobalt Corrin-Polyion Scaffold on Electrodes in Microemulsions with a Flow Reactor

Electrochemical reactors employing catalytic films of the cobalt corrin vitamin B 12 hexucarboxylic acid [B 12 (COOH) 6 ] attached to poly(L-lysine) (PLL) covalently bound to carbon cloth electrodes were optimized for the reduction of 1,2-dibromocyclohexane (DBCH) to cyclohexene in a microemulsion. An improved initial electrode oxidation method enabled attachment of films with higher surface concentrations of catalyst than previously. A parallel plate flow reactor containing a catalyst-coated carbon cloth cathode gave sixfold larger turnover rates compared to a simple stirred hatch reactor, especially for 20 and 90 nm thick films of B 12 (COOH) 6 -PLL. The 90 nm thick films showed high turnover rates in the flow reactor while maintaining 100% current efficiency, whereas in the batch reactor current efficiency dropped well below 100% at the higher applied currents. Significantly thicker films of B 12 (COOH) 6 -PLL on carbon cloth than reported in previous work were shown to operate efficiently in microemulsions for catalyzing DBCH conversion to cyclohexene. The key factor was eliminating mass transport limitations in the microemulsion by using an efficient flow reactor, resulting in turnover rates up to 3000 min 1 at 100% current efficiency.

Interfacial and mass transport enhancement effects on rates of styrene epoxidation catalyzed by myoglobin films in microemulsions

Biocatalytic surfaces hold promise for future clean methods of chemical synthesis. Biocatalyst films utilizing inexpensive redox proteins can operate in low-toxicity microemulsions with high capacities to dissolve nonpolar reactants. Crosslinked films of myoglobin (Mb) and poly(L-lysine) (PLL) attached to oxidized carbon cathodes gave up to 40-fold larger turnover rates in bicontinuous microemulsions compared to o/w microemulsions and micelles. Larger synthetic turnover rates are correlated with up to 10-fold faster diffusion of solutes in oil phases of the bicontinuous fluids, as measured by voltammetry. Visible and circular dichroism spectra suggest that myoglobin resides in the film in a largely aqueous environment. The reactant sites in films monitored by a fluorescent probe were more polar when films were in CTAB than in SDS microemulsions. These combined results suggest that larger mass transport rates in the bicontinuous fluids is a major factor for enhanced turnover rates. Electrostatic interactions between the charged films and oppositely charged surfactants may significantly influence turnover rates when reactant mass transport is not fast enough.