Superoxide dismutase: Improved assays and an assay applicable to acrylamide gels☆

In this review, we highlight the use of organic photoredox catalysts in a myriad of synthetic transformations with a range of applications. This overview is arranged by catalyst class where the photophysics and electrochemical characteristics of each is discussed to underscore the differences and advantages to each type of single electron redox agent. We highlight both net reductive and oxidative as well as redox neutral transformations that can be accomplished using purely organic photoredox-active catalysts. An overview of the basic photophysics and electron transfer theory is presented in order to provide a comprehensive guide for employing this class of catalysts in photoredox manifolds.

Organic Photoredox Catalysis

Due to their small size, nanoparticles have distinct properties compared with the bulk form of the same materials. These properties are rapidly revolutionizing many areas of medicine and technology. Despite the remarkable speed of development of nanoscience, relatively little is known about the interaction of nanoscale objects with living systems. In a biological fluid, proteins associate with nanoparticles, and the amount and presentation of the proteins on the surface of the particles leads to an in vivo response. Proteins compete for the nanoparticle "surface," leading to a protein "corona" that largely defines the biological identity of the particle. Thus, knowledge of rates, affinities, and stoichiometries of protein association with, and dissociation from, nanoparticles is important for understanding the nature of the particle surface seen by the functional machinery of cells. Here we develop approaches to study these parameters and apply them to plasma and simple model systems, albumin and fibrinogen. A series of copolymer nanoparticles are used with variation of size and composition (hydrophobicity). We show that isothermal titration calorimetry is suitable for studying the affinity and stoichiometry of protein binding to nanoparticles. We determine the rates of protein association and dissociation using surface plasmon resonance technology with nanoparticles that are thiol-linked to gold, and through size exclusion chromatography of protein-nanoparticle mixtures. This method is less perturbing than centrifugation, and is developed into a systematic methodology to isolate nanoparticle-associated proteins. The kinetic and equilibrium binding properties depend on protein identity as well as particle surface characteristics and size.

https://www.pnas.org/content/pnas/104/7/2050.full.pdf

Understanding the nanoparticle-protein corona using methods to quantify exchange rates and affinities of proteins for nanoparticles.

The use of biocatalysis for industrial synthetic chemistry is on the verge of significant growth. Biocatalytic processes can now be carried out in organic solvents as well as aqueous environments, so that apolar organic compounds as well as water-soluble compounds can be modified selectively and efficiently with enzymes and biocatalytically active cells. As the use of biocatalysis for industrial chemical synthesis becomes easier, several chemical companies have begun to increase significantly the number and sophistication of the biocatalytic processes used in their synthesis operations.

Industrial biocatalysis today and tomorrow

Over the past ten years, scientific and technological advances have established biocatalysis as a practical and environmentally friendly alternative to traditional metallo- and organocatalysis in chemical synthesis, both in the laboratory and on an industrial scale. Key advances in DNA sequencing and gene synthesis are at the base of tremendous progress in tailoring biocatalysts by protein engineering and design, and the ability to reorganize enzymes into new biosynthetic pathways. To highlight these achievements, here we discuss applications of protein-engineered biocatalysts ranging from commodity chemicals to advanced pharmaceutical intermediates that use enzyme catalysis as a key step.

Engineering the third wave of biocatalysis

Immobilized enzymes: crystals or carriers?

Mechanism and yields in enzyme catalysed equilibrium and kinetically controlled synthesis of β-lactam antibiotics, peptides and other condensation products

Preface Introduction to enzyme technology Basics of enzymes as biocatalysts Enzyme discovery and protein engineering Enzymes in organic chemistry Cells designed by metabolic engineering as biocatalysts for multi-enzyme biotransformations Enzyme production and purification Application of enzymes in solution: Soluble enzymes and enzyme systems Immobilization of enzymes (Including Applications) Immobilization of microorganisms and cells Characterization of immobilized biocatalysts Reactors and process technology Case study: The one-step enzymatic process to produce 7-ACA from cephalosporin C Appendix I The World of Biotechnology Information: Seven Points for Reflecting on Your Information Behavior Appendix II Solutions to exercises Appendix III Symbols, additional Symbols

Biocatalysts and Enzyme Technology

The kinetics of phytochrome conversion.

— Photochemical reactions of eosin in aqueous solution were studied using the flash photolysis technique. In deaerated solution the dye was converted quantitatively to the triplet state during flashing. The triplet dye decayed by first and second order reactions which partly regenerated the dye in the ground state and partly produced semioxidized and semireduced eosin. These radical species were formed in an electron dismutation reaction between two triplet molecules and also in a reaction between one triplet and one unexcited molecule. The radicals recombine rapidly to give the dye in the ground state.



An efficient reversible photooxidation reaction was observed in eosin solutions containing potassium ferricyanide. Semioxidized eosin was formed in high yield by reaction between the triplet dye and the oxidant. The dye was regenerated rapidly in a reverse reaction between the products of the oxidation reaction.



An analogous type of reaction was found to occur in eosin solutions containing p-pheny-lene diamine. This reagent reduced the triplet dye to semireduced eosin; the dye was regenerated in the ground state in a very efficient reverse reaction. The protolytic behaviour of semireduced eosin was studied by varying the pH.



Absorption spectra of the transient products were determined and rate constants for the observed reactions were measured. The results are compared with results from previous studies of fluorescein.

Volker Kasche

Papers

Immobilized enzymes: crystals or carriers?

Mechanism and yields in enzyme catalysed equilibrium and kinetically controlled synthesis of β-lactam antibiotics, peptides and other condensation products

Biocatalysts and Enzyme Technology

The kinetics of phytochrome conversion.

Transient species in the photochemistry of eosin