Photophysical Processes in Cyanobiphenyl Derivatives. II. Cyanobiphenyl Derivatives as Fluorescent Probes in Micellar Environment

Preparation of Optically Active Biphenyl Compounds via an Albumin- Mediated Asymmetric Nitroaldol Reaction

Abstract:

Human serum albumin (HSA) was found to catalyze the asymmetric nitroaldol reaction of biphenyl aldehydes with nitromethane to afford the corresponding optically active 2-nitro alcohols. Careful optimization of the conditions for the reaction of 4-phenylbenzaldehyde with nitromethane in water at a neutral pH improved both the reactivity and the enantioselectivity. Finally, the reaction of 4-phenylbenzaldehyde (56 mg, 0.30 mmol) in nitromethane (2.8 mL) and water (1.1 mL) using HSA (68 mg) at 5 °C for 240 h gave (R)-1-([1,1'-biphenyl]-4-yl)-2-nitroethanol in 71% yield (52 mg), with an ee up to 85% ee. Subsequent recrystallization improved the ee up to 95%. The reaction was useful in a preparative-scale operation, and the biocatalyst could be reused several times. The procedure was also applicable to other substrates with different substitution patterns. Although the nitroaldol reaction of 2-phenylbenzaldehyde with nitromethane proceeded with low enantioselectivity to afford the corresponding (R)-2-nitroalcohols (35% ee), the reactions of the substrates bearing Br, Me, OMe, or CN group at the 4'-position of the benzene ring gave the corresponding optically active compounds with high enantioselectivities (80-88% ee).

Interactions of neutral molecules with ionic micelles

The interactions of neutral molecules with ionic micelles are analyzed. The cell and mass action models are presented in order to provide a semi-quantitative description of the solubilization process. Both approaches are discussed from a thermodynamic and kinetic point of view and the different definitions of solute incorporation constants are also discussed and compared. An extensive compilation of standard free energies of transfer from water to micelles is provided and the basis of the employed methods to obtain them is presented. Several aspects of the solubilization process such as its dynamics, the effect of additives, the probe microenvironment and its dependence with the solute mean occupation number are reviewed and critically discussed. The effect of solute incorporation upon the micelle shape and size is also briefly reviewed.