Dextrin synthetic

Hydroxyethylstarch is widely used with synthetic latexes in the surface sizing of paper and as a coating binder. For these uses, the hydroxyethylstarch is acid-thinned, oxidized, or dextrinized. Hydroxypropylstarch is used in foods to provide viscosity stabiHty and to ensure water-holding during low temperature storage. 

While nature uses coenzyme-dependent enzymes to influence the inherent reactivity of the coenzyme, in principle, any chemical microenvironment could modulate the chemical properties of coenzymes to achieve novel functional properties. In some cases even simple changes in solvent, pH, and ionic strength can alter the coenzyme reactivity. Early attempts to present coenzymes with a more complex chemical environment focused on incorporating coenzymes into small molecule scaffolds or synthetic host molecules such as cyclophanes and cyclo-dextrins [1,2]. While some notable successes have been reported, these strategies have been less successful for constructing more complex coenzyme microenvironments and have suffered from difficulties in readily manipulating the structure of the coenzyme microenvironment. 

Prior to 1939, however, it was not known whether the cyclodextrins were products of the synthetic metabolism of Bacillus macerans, and therefore, perhaps, quite different from the components of starch, or whether they were formed by a single enzyme and therefore closely related to the starch structure. Then, Tilden and Hudson announced the discovery of a cell-free enzyme preparation from cultures of Bacillus macerans which had the ability to convert starch into the Schardinger dextrins without the production of maltose, glucose, or any other reducing sugars. They thus concluded that the Schardinger dextrins were either the true components of starch or closely related to such true components. 

Biomimetic Chemistry, including that involved in the synthesis and study of artificial enzymes, has grown to enormous proportions. Even the part of the field using cyclo-dextrins as binding groups in synthetic catalysts that mimic enzymes has been the subject of a large review article [1]. Thus in this chapter I will focus mainly, but not exclusively, on work from our own laboratory. Other chapters will help make up for this somewhat narrow focus. I have published several reviews of our work elsewhere [2-51]. 

The 5,8-disubstituted indolizidines and 1,4-disubstituted quinolizidines are the more common structural patterns found in amphibian skin[21]. None of these alkaloids has so far been reported from any other source. In addition, the biological activity of only a few 5,8-disubstituted indolizidines has been investigated due to the isolation in minute quantities from the skin. Among them, the relative stereochemistry of quinolizidine 2071 was anticipated to be 75 by our chiral synthesis of 76[35] followed by stereocontrolled synthesis of 75[36]. A sample of synthetic racemate of 75 had produced the best separations on GC analysis with (3-dextrin chiral column[36]. 

We are grateful to Dr. John H. Cardellina, II, National Cancer Institute, Prof. D. John Faulkner, University of California, San Diego, and Prof. Raymond J. Andersen, University of British Columbia, for kindly providing us with H, l3C NMR spectra of natural clavepictines A, B, Pictamine, and lepadin B. We are also indebted to Dr. Thomas F. Spande, National Institute of Health, for measurement of the GC analysis of synthetic, racemic, and natural quinolizidine 2071 with (3-dextrin chiral column, and to Prof. Andre Rassat, Ecole Normale Superieure, for kindly providing us with racemic quinolizidine 2071. 

Since these species were conceptual, there were no well-characterized synthetic examples of such regular architecture. Meyer [73] proposed such a symmetrically, ordered architecture for amylopectin, but subsequent work by Erlander and French [74] and Burchard et al. [75], showed that neither amylopectin nor glycogen is so regular, but are instead, random f-functional polycondensates possessing a large, hyperbranched dextrin core (in Fig. 13). 

Despite present trends toward use of synthetic polymers developed over the last 10 or 20 years, starches are still being widely used as an adhesive in such applications as the production of paper and paperboard products, warp sizing, and bonding charcoal briquettes. Because of a unique combination of properties and low cost, these adhesives are almost impossible to exclude from many applications, especially those involving the use of hot paste (size) for anchoring fibers. For starch molecules to act as an adhesive, they must be chemically or thermally hydrated. Then, their adhesive character is developed and modified in different ways by chemicals or other additives for different end uses. As renewable resources that are both economical and reliable, starch and dextrin are likely to continue to be significant factors in the adhesive market for many years. 

Scheme 4. Synthetic sequence leading from a-cyclo-dextrin to a-cycloaltrin. TBAF = tetrabutylammonium fluoride.

ADHERE-TEX 1500 adhesive is used when pigment printing cotton, cotton blends, and most synthetic fabrics including fiberglass. The problem of mildew formation is eliminated with this adhesive, since it is not a starch or dextrin-base product. 

Synthetic polyelectiolytes as models for enzymes have been reported recently The hydrolysis of dextrin in the presence of copolymers of vinyl alcohol and vinyl-sulfonic acid has been found to increase with increasing content of vinyl alcohol in the copolymers ... 

When making very dehcate materials it may be necessary to use a yam which is so fine that it would break down under the stresses imposed on it during manufacture. The strength, however, is sufficient once the fabric is made because of the mutual support of adjacent threads. In such cases it is customary to impart temporary strength to the yam by a process known as sizing. This consists of impregnating the thread with some easily removed substance such as starch or dextrine and, in the case of the more modern man-made fibres, with a synthetic product such as polyvinyl alcohol or polyacrylic acid. The size is usually removed before the article is dyed or bleached. Yarns are frequently referred to as warp or weft yarns. In a... 

Believing that the chemical modification of natural biopolymers could produce materials having many of the physical properties desired for technical applications, he pursued structural studies of synthetic gums, such as the dextrins from pyrolysis of starch (with G. M. Christensen,... 

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