Differential regulation of chemical reactions in a microchannel reaction system

Microchannel reactors have continued to attract attention in the fields of analytical and synthetic chemistry. An important feature of microchannel systems is their superior controllability of fluidic systems, which cannot be created in the batchwise reaction system with larger reaction apparatus. This study is designed to examine whether the superior controllability of microfluidics allows the use of microchannel reactors as a novel reaction control apparatus. Microfluidic analysis of ceramic microreactors using a solvatochromic dye demonstrated that the mixing of two solvents was strongly affected by the secondary flow that occurs at the corners of a microchannel. We examined the effects of such a microfluidic system on chemical reactions using amino acid substitution as a model reaction. Substitution of phenylalanine in a microreaction system using separate solutions was more efficient than in a batchwise reaction or in microchannel reaction using a homogeneous solution. Substitution of other amino acids showed that this enhancement is caused by localization of hydrophobic amino acids at the DMF–H2O interface. Using the rapid Michael addition reaction of the SH group of cysteine to a maleimide group, we also demonstrated that such a reaction involving hydrophilic amino acids was diminished in this microreaction system. These results show that the microreaction system is a novel apparatus for regulating chemical reactions, depending on the structure of the reactant molecules, by controlling the mixing of two different solutions.