Zhang, Juner;Huang, Xiongyi;Zhang, Ruijie K.;Arnold, Frances H.
来源期刊：Journal of the American Chemical Society
年/卷/期：2019 / 141 / 25
The introduction of fluoroalkyl groups into organic compounds can significantly alter pharmacological characteristics. One enabling but underexplored approach for the installation of fluoroalkyl groups is selective C(sp(3))-H functionalization due to the ubiquity of C-H bonds in organic molecules. We have engineered heme enzymes that can insert fluoroalkyl carbene intermediates into alpha-amino C(sp(3))-H bonds and enable enantiodivergent synthesis of fluoroalkyl-containing molecules. Using directed evolution, we engineered cytochrome P450 enzymes to catalyze this abiological reaction under mild conditions with total turnovers (TTN) up to 4070 and enantiomeric excess (ee) up to 99%. The iron-heme catalyst is fully genetically encoded and configurable by directed evolution so that just a few mutations to the enzyme completely inverted product enantioselectivity. These catalysts provide a powerful method for synthesis of chiral organofluorine molecules that is currently not possible with small-molecule catalysts.
会议集名/来源：2017 Progress in Electromagnetics Research Symposium - Spring: PIERS 2017, St Petersburg, Russia, 22-25 May 2017, pages 1-804, [v.1]
The problem of electromagnetic wave diffraction by perfectly conducting body of small thickness is considered. The classic model, based on the solution of the boundary value problem for the Maxwell equations by the method of boundary integral equations is used. The authors applied an approach, based on reducing the problem to integral equations with hypersingular integrals in the sense of the Hadamard finite value. These equations are solved numerically using the methods of piecewise constant approximations and collocations. The numerical experiment shows that in the case of objects with a small bodily thickness, to improve the accuracy of the numerical solutions, it is necessary to improve the accuracy of calculating the integrals with weak singularity. We used the quadrature formulas, based on the additional splitting of main surface mesh cells into smaller cells and smoothing of singularity of integrand function in small neighborhood of the singular point.
Integral equations;Electromagnetics;Springs;Magnetic domains;Radiation effects;Electromagnetic scattering;Conductors