Amylose hybrids

Amylose Hybrids with Short Alkyl Chains... 

Amylose Hybrids with Short Alkyl Chains Pfannemuller et al. showed that it is possible to obtain carbohydrate-containing amphiphiles with various alkyl chains via amide bond formation. For this, maltooligosaccharides were oxidized to the corresponding aldonic acid lactones which could subsequently be coupled to alkylamines [52-60]. Such sugar-based surfactants are important industrial products finding their applications in cosmetics, medical applications etc. [61-63]. The authors were also able to extend the attached maltooligosaccharides with enzymatic polymerization with potato phosphorylase which resulted in products with very interesting solution properties [64, 65]. 

Amylose hybrids with short alkyl chains... 

Another tjqie of comb like amylose hybrids synthesized via enzymatic grafting with phosphorylase is based on polysiloxane backbones. To achieve these structures double bonds were incorporated to the reducing end of oligosaccharides which were then attached to poIy(dimethylsiloxane-co-methylsiloxane) copolymers via hydrosililation or to silane monomers which were subsequently polymerized to polysiloxanes . Various mono-, d>-, tri and oligosaccharides were attached to siloxane backbones and their solution properties were studied with viscosimetry and static and dynamic light... 

The glycogen phosphorolysis of phosphorylase can be reverted, which makes it possible to enzymatically polymerize amylose as well as hybrid structures with amylose as outlined in the following section. 

The strict primer dependence of the glycogen phosphorylases makes them ideal candidates for the synthesis of hybrid structures of amylose with non-natural materials... 

Fig. 7 Maltotetraose hybrids with various carriers resulting in different chain architectures A poly(ethylene oxide) Ba and Bb poly(acrylic acid), amylose, cellulose, and other polysaccharides Ca cyclodextrin and multifunctional acids Cb amylopectin D crosslinked poly(acryl amide) [156] - Reproduced by permission of Wiley...

High-amylose com having starch which contains 55-80% of the linear starch fraction, amylose, has also been developed65 (see Chapter 3) and must also be grown under contract. Production of amylomaize is even smaller than it is for waxy hybrids because of limited uses for the starch. Starch yields of high-amylose com are lower than those of dent com.66... 

Protein Not more than 0.5% except in high-amylose and other hybrid starches, not more than 1%. 

Inclusion protects unsaturated fatty acids from aging however, this protection is not perfect, as amylose itself also complexes oxygen753 756 (see Fig. 48). Unsaturated acids have a specific pattern of the carbon chain because at least two sp2-hybridized carbon atoms are present, causing geometrical isomerism. The frans-isomer does not fit perfectly into the cavity of amylose. Another report indicates that starch complexation with tannic acid has no effect on its activity against experimental ulcers in laboratory rats.757... 

The strict primer dependence of the glycogen phosphorylases makes them ideal candidates for the synthesis of hybrid structures of amylose with non-natural materials (e.g., inorganic particles and surfaces, synthetic polymers). For this, a primer functionality (maltooligosaccharide) can be coupled to a synthetic structure and subsequently elongated by enzymatic polymerization resulting in amylose blocks. 

The monomer-up approach opens up the possibility of enzymatically grafting branched polysaccharides from functionalized substrates in order to make hybrid materials bearing a highly branched amylose part. Following the same route we are currently synthesizing hybrid materials bearing (hyper)branched polysaccharide structures as shown in Figure 9.11 with the described tandem reaction of two enzymes. 

The examples reviewed in this chapter prove that enzymatic polymerizations using glycosyltransferases and glycosidases are powerful techniques for synthesizing various well-defined polysaccharides ranging from natural saccharides such as cellulose, amylose, amylopectin etc. to non-natural hybrid polysaccharides. 

Biocatalysis is a key route to both natural and non-natural polysaccharide structures. Research in this area is particularly rich and generally involves at least one of the following three synthetic approaches 1) isolated enzyme, 2) whole-cell, and 3) some combination of chemical and enzymatic catalysts (i.e. chemoenzymatic methods) (87-90). Two elegant examples that used cell-fi-ee enzymatic catalysts were described by Makino and Kobayashi (25) and van der Vlist and Loos (27). Indeed, for many years, Kobayashi has pioneered the use of glycosidic hydrolases as catalysts for polymerizations to prepare polysaccharides (88,91). In their paper, Makino and Kobayashi (25) made new monomers and synthesized unnatural hybrid polysaccharides with regio- and stereochemical-control. Van der Vlist and Loos (27) made use of tandem reactions catalyzed by two different enzymes in order to prepare branched amylose. One enzyme catalyzed the synthesis of linear structures (amylose) where the second enzyme introduced branches. In this way, artificial starch can be prepared with controlled quantities of branched regions. 

The amount of amylose and amylopectin in a starch depends on the source of the starch. Most starches contain 20 to 30% by weight of amylose, although certain hybrids can contain more than 80% amylose. The most commonly available industrial starches are waxy cornstarch, regular cornstarch, high-amylose cornstarch type V, and high-amylose cornstarch type VII, with amylose concentrations of 0, 28, 55, and 70%, respectively [7]. 

Natural polysaccharides like cellulose or amylose can be obtained via polycondensation reactions, while chitin and glycosaminoglycans (GAGs) are synthesized by ROP [49]. One group of uimatural polysaccharides is hybrid polysaccharides obtained from two different polysaccharide components and is very difficult to synthesize via conventional chemical synthesis. 

The oc-amylase from a wheat-rye hybrid [triticale ( x Triticosecaley has been purified by affinity chromatography on cyclohepta-amylose immobilized on a derivative of macroporous agarose. Contaminating proteins were eluted with a sodium acetate buffer, whereafter a-amylase was eluted with a buffer containing cyclohepta-amylose. This chromatographic procedure gave a yield of 90% and < 180-fold purification. 

The characteristics of these cooked viscous solutions vary from starch to starch. After cooling to room temperature, the starch from roots are clearer and more fluid, while starch from the cereal grains yield a cloudy less fluid paste that tends to be jellylike. These characteristics are dependent upon the amylose and amylopectin content of the starch and upon the size of the amylose and amylopectin molecule. Some hybrids—waxy hybrids—of corn and sorghum have been developed which yield starch that is almost entirely amylopectin, while other hybrids have a high amylose content. Overall, the tendency to thicken or gel upon cooling, and to become opaque is caused by the presence of amylose. 

---