There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Herein we review recent advances in the asymmetric reduction of ketones by biocatalysts. Included are discussions on recent developments in methodologies to control enantioselectivities of catalytic reactions, and examples of practical applications that reduce various types of ketones are also shown.

Recent developments in asymmetric reduction of ketones with biocatalysts

Recent developments in pyridine nucleotide regeneration.

Enzymes are able to perform reactions under mild conditions, e.g., pH and temperature, with remarkable chemo-, regio-, and stereoselectivity. Because of this feature, the number of biocatalysts used in organic synthesis has rapidly increased during the last decades, especially for the production of chiral compounds. The present review highlights biotechnological processes for the production of chiral alcohols by reducing prochiral ketones. These reactions can be catalyzed by either isolated enzymes or whole cells that exhibit ketone-reducing activity. The use of isolated enzymes is often preferred because of a higher volumetric productivity and the absence of side reactions. Both types of catalysts have also deficiencies limiting their use in synthesis of chiral alcohols. Because reductase-catalyzed reactions are dependent on cofactors, one major task in process development is to provide an effective method for regeneration of the consumed cofactors. In this paper, strategies for cofactor regeneration in biocatalytic ketone reduction are reviewed. Furthermore, different processes carried out on laboratory and industrial scales using isolated enzymes are presented. Attention is turned to process parameters, e.g., conversion, yield, enantiomeric excess, and process strategies, e.g., the application of biphasic systems or methods of in situ (co)product recovery. The biocatalytic production of chiral alcohols utilizing whole cells is presented in part II of this review.

Biocatalytic ketone reduction--a powerful tool for the production of chiral alcohols--part I: processes with isolated enzymes

Due to their ability to perform reactions in a stereo- and regiospecific manner, while functioning under mild conditions of temperature and pH, enzymes are increasingly used for chiral synthesis in the pharmaceutical industry, in medicinal chemistry, agriculture, cosmetic and food industry. The oxidoreductases as catalysts require a coenzyme (cofactor) which functions as an electron carrier. If used in stoichiometric amounts the cost of coenzymes makes synthetic applications of redox enzymes prohibitively expensive for industrial applications. The present review updates previous discussions about the objectives of cofactor regeneration as a requirement for the applicability of enzymatic redox reactions, and about the strategies customarily used to this end. Different types of chiral syntheses coupled successfully to coenzyme regeneration (amino acid synthesis, lactone synthesis, synthetic reactions involving alcohols, hydroxy acid and steroid synthesis, deracemization) are then discussed. New catalysts, cross-linked enzyme crystals, prepared from redox enzyme are presented in a small paragraph together with some of their applications. Special attention is given to whole cells used in this type of synthesis and their advantages and disadvantages are presented in one paragraph. Finally, different reactors, within which were conducted chiral syntheses catalyzed by oxireductases and coupled to cofactor regeneration, are briefly discussed.

Redox enzymes used in chiral syntheses coupled to coenzyme regeneration.

Antibacterial hop extracts encapsulated in nanochitosan matrices

Chitosan nanoparticles (CNP) were prepared by ionic gelation using sodium tripolyphosphate. Metal-enhanced CNP were prepared using the same procedure in the presence of Cu 2+ and Ag+, respectively. The nanoparticulate materials were characterised by FTIR, SEM and antimicrobial assays. The CNP showed higher antimicrobial effect than chitosan against S. saprophyticus and E. coli . The effect did not seem to depend on the molecular weight of the starting chitosan. Cu 2+ and Ag+, both known as antimicrobial agents, showed synergistic effects with chitosan against both organisms. The skin regenerative potential of CNP and metal-enhanced CNP was tested by assessing skin cell (fibroblast, keratinocyte) proliferation. The present study also suggests that chitosan and its nanoparticles inhibits MMP-1 expression in skin fibroblasts and keratinocytes, and may thereby inhibit skin aging and facilitate the ECM remodelling phase of wound healing.

Mihaela D. Leonida

Papers

Redox enzymes used in chiral syntheses coupled to coenzyme regeneration.

Antibacterial hop extracts encapsulated in nanochitosan matrices

Nanocomposite materials with antimicrobial activity based on chitosan

Self-stabilized chitosan and its complexes with carboxymethyl starch as excipients in drug delivery.

Bionanomaterials for Skin Regeneration