Enzymatic surface-initiated

Enzymatic, surface-initiated polymerizations of aliphatic polyesters was reported for wider clinical use of aliphatic polyesters 84). The hydroxyl terminated SAM acted as an initiation site for lipase B catalyzed ROP of aliphatic polyesters, such as poly(e-caprolactone) and poly (p-dioxanone) (Scheme 3). Another example of enzymatic SIP is the polymerization of poly (3-hydroxybutyrate) (PHB), where PHB synthase, fused with a His-tag at the N-terminus, was immobilized onto solid substrates through transition-metal complexes, Ni (II)-NTA, and the immobilized PHB synthase catalyzed the polymerization of 3-R-hydroxybutyry 1-coenzyme A (3HB-CoA) to PHB 85). 

With the development of enzymatic polymerization in solution, also first accounts for SIP appeared. Loos et al. [350] reported on enzymatic surface polymerization of glucose-l-phosphate with potato phosphorylase as the catalyst resulting in oligo- or poly-(a,l- 4)-D-glucopyranose. As initiator sites, immobilized malto-heptaose was used. Enzymatic grafting of hexyloxyphenol onto chitosan is reported by Payne and coworkers [351]. 

The first surface-initiated enzymatic polymerization reported was the synthesis of amylose brushes on planar and spherical surfaces [145]. For this, silica or silicone surfaces were modified with self-assembled monolayers of (3 amino-propyl)trimethoxysilane or chlorodimethylsilane, respectively. To these functionalities, oligosaccharides were added via (a) reductive amidation of the oligosaccharides to surface-bound amines, (b) conversion of the oiigosaccharide to the according aldonic acid lactone and reaction with surface bound amines, and (c) incorporation... 

A novel system for surface-initiated enzymatic polymerization to a PHA film on solid surfaces was demonstrated [131]. PHA synthase from Ralstonia eutropha H16 was expressed as a poly-histidine fusion in Escherichia coli and immobilized onto several solid substrates through Ni " -nitrilotriacetic acid. The surface-initiated polymerization of 3-(R)-hydroxybutyryl CoA by immobilized PHA synthase on silicon produced a polymer film with a uniform thickness on the surface. 

A surface-initiated enzymatic ROP has also been reported, whereby CL and DXO were grafted from hydroxyl-terminated self-assembled monolayers (SAMs) on gold, using Novozym 435 [117], while polycaprolactone-modified hydroxyethylcel-lulose films were prepared by the enzymatic ROP of CL [118]. 

Various factors that influence the release of drugs from particulate carriers are listed in Table 10. Drugs can be released by diffusion or by surface erosion, disintegration, hydration, or breakdown (by a chemical or an enzymatic reaction) of the particles. The release of drugs from microspheres follows a biphasic pattern that is, an initial fast release followed by a slower... 

Recent work by Atalla(H) supports the idea that lignin is at least a semi-ordered substance in wood with the plane of the aromatic ring parallel to the cell wall surface. Woody plants synthesize lignin from trans-coniferyl alcohol (pines), trans-sinapyl alcohol 2 (deciduous), and trans-4-coumaryl alcohol 3 by free radical crosslinking initiated by enzymatic dehydrogenation(l2). Structures of these alcohols are given in Figure 1. 

The classic pathway is triggered by the formation of factor Cl at IgG or IgM on the surface of microorganisms (left). Cl is an 18-part molecular complex with three different components (Clq, Clr, and Cls). Clq is shaped like a bunch of tulips, the flowers of which bind to the Fc region of antibodies (left). This activates Clr, a serine proteinase that initiates the cascade of the classic pathway. First, C4 is proteolytically activated into C4b, which in turn cleaves C2 into C2a and C2b. C4B and C2a together form C3 convertase [1], which finally catalyzes the cleavage of C3 into C3a and C3b. Small amounts of C3b also arise from non-enzymatic hydrolysis of C3. 

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