RESUMO
Extremely uniform packing of colloidal silica in capillaries is shown. Reversed-phase electrochromatograms of DiI-C(12) exhibit plate heights as low as 0.23 microm and a reduced plate height as low as 0.7, using 75 microm i.d. capillaries packed with 330 nm silica particles. The contribution from the A term is 0 +/- 20 nm in electrochromatography. The particles are shown to form colloidal crystals inside the capillaries. Optical images show Bragg diffraction, indicative of crystallinity. Scanning electron microscopy (SEM) images show face-centered cubic crystallinity, and the porosity is 0.25 +/- 0.01, which is in agreement with that for face-centered cubic crystals. The capillaries are fritless, and 100 microm i.d. capillaries packed with silica colloidal crystals withstand pressures of at least 12,400 psi.
Assuntos
Coloides/química , Dióxido de Silício/química , Eletrocromatografia Capilar , Cristalização , Microscopia Eletrônica de Varredura , PorosidadeRESUMO
A key step in a chemoenzymatic process for the production of high-purity glycolic acid (GLA) is the enzymatic conversion of glycolonitrile (GLN) to ammonium glycolate using a nitrilase derived from Acidovorax facilis 72W. Protein engineering and over-expression of this nitrilase, combined with optimized fermentation of an E. coli transformant were used to increase the enzyme-specific activity up to 15-fold and the biocatalyst-specific activity up to 125-fold. These improvements enabled achievement of the desired volumetric productivity and biocatalyst productivity for the conversion of GLN to ammonium glycolate.
Assuntos
Acetonitrilas/química , Aminoidrolases/química , Aminoidrolases/metabolismo , Betaproteobacteria/enzimologia , Escherichia coli/enzimologia , Glicolatos/síntese química , Engenharia de Proteínas/métodos , Aminoidrolases/genética , Betaproteobacteria/genética , Escherichia coli/genética , Proteínas Recombinantes/metabolismoRESUMO
Hydroxycarboxylic acid monomers can be used to prepare industrially important polymers. Enzymatic production of such hydroxycarboxylic acids is often preferred to chemical production since the reactions are run at ambient temperature, do not require strongly acidic or basic reaction conditions, and produce the desired product with high selectivity at high conversion. However, native enzymes often do not perform desired reactions with the efficiency required for commercial applications. Protein engineering was used to significantly increase the specific activity of nitrilase from Acidovorax facilis 72W for the conversion of 3-hydroxyvaleronitrile to 3-hydroxyvaleric acid. Overexpression of engineered nitrilase enzymes in Escherichia coli, combined with immobilization of whole cells in alginate beads that can be recycled many times has facilitated the development of a commercially viable bioprocess for production of 3-hydroxyvaleric acid.