SUBJECTS dextrin

Schardinger brought his work on the crystalline dextrins to a close in 1911. He ended his work with the statement I realise that still very many questions remain unsolved. The answer to these I must leave to another, who, owing to more favorable external conditions, can deal with the subject more intensively. It was to be another twenty-five years before the cyclic nature of Schardinger s dextrins was recognized. 

We subject envelope and stamp adhesives to stringent safety requirements. Since we re likely to swallow traces of the stuff, we have to regulate it as a food. Gum arable from the acacia tree, dextrin from corn starch, and the water soluble resin polyvinyl alcohol are the adhesives we use most often. We also... 

Starch octenylsuccinates offer excellent emulsifying properties, flavor oil retention and good oxidation resistance versus gum arabic. They can be made on a variety of starch bases, dextrins or fluidities which provide versatility and improved spray-drying costs. Starch octenylsuccinate are low in cost, domestically produced and are not subject to the market fluctuations that gum arabic encounters. 

All chapters/subjects that were also in the previous edition have been updated. Chapters have been added on the biochemistry and molecular biology of starch biosynthesis, structural transitions and related physical properties of starch, and cyclo-dextrins. There are two chapters on the structural features of starch granules that present not only advances in understanding the organization of starch granules, but also advances in understanding the fine structures of amylose and amylopectin, both of which are based on techniques that have been developed since 1984. 

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]. 

In his closing paragraphs on the crystalline dextrins Schardinger notes I realize that there are many questions which have not yet li)een answered. I must leave the answering of them to the person who, thanks to more favorable circumstances, can engage himself more intensively with the subject. ... 

In an effort to see how far the Schardinger dextrin series extends, French subjected radioactive glycogen to the prolonged action of B. macerans... 

In 1992, Harada et al. prepared a compound in which many cyclodextrins are threaded on a single PEG chain and are trapped by end-capping groups at both termini of the main chain (Scheme 16) [111]. The pseudopolyrotax-ane formed in water from PEG bisamine (mass 3350) and a large excess of a-cyclo dextrin in an aqueous solution was isolated and then subjected to end-capping reaction with 2,4-dinitrofluorobenzene in DMF to yield polyro-... 

The effect of an electric field on dextrinated lead azide pellets as a function of density and thickness was also studied [11]. The explosive was pressed in a nylon sleeve between two 0.48-mm (0.187-in) -diam, flat-surface steel rods with rounded edges. The explosive was subjected to a one-minute-on, onc-minutc-off application of voltage, increasing the voltage in 100-V increments until the sample detonated. The current was monitored continuously. 

The Hugoniot equation of state and the sensitivity of dextrinated lead azide to shocks of long duration were determined by subjecting lead azide pellets to... 

The threshold for the detection of reaction in the dextrinated lead azide (3.4 g/ml) subjected to 3,5-psec pulses was dependent upon sample thickness (Figure 25). No reaction was noted in 1-mm-thick samples even at the highest impact stresses (8.9 kbar) tested, whereas the threshold for 4-mm-thick samples was between 4 and 6 kbar. 

Evans and Caldwell introduced an index called the Blue staining residue (B.s.r.) which is related to the intensity of the color developed by a dextrin with iodine. B.s.r. values decrease together with the thixotropy of gels from dextrins. It should be noted that fatty acids present in the dextrinized starch favor the formation of dextrins having a high B.s.r., that is, dextrins of good thixotropic properties. For studies on a related subject, see an article by Tsuji and Mochizuki. ... 

Maturation is the next stage in the preparation of dextrins. It is necessary to allow the catalyst to penetrate into the starch granule, in order to correct imprecise distribution of acid, should this have happened in the first stage. The matured source is then subjected to drying, to avoid hydrolytic scission of the starch in the first period of roasting (as well as gelatinization, or... 

Smith and coworkers - have subjected starch dextrins to the classical techniques of structural carbohydrate chemistry. In one study, four commercial maize-dextrins were fractionated from aqueous ethanol to obtain a sub-fraction which was the most resistant to periodate oxidation. This material was then methylated, the product hydrolyzed, and the resulting methylated sugars analyzed by column chromatography. Table II shows the results. The complexity of the dextrin structure is shown by the fact that only components 1, 2, and 5 arise in any large proportion from the methylation of maize starch. It is of interest that no traces of a methyl... 

Comparable results were obtained from a structural study of a wheat-starch dextrin. The major fraction from aqueous ethanol solution (37%) was purified by acetylation, and then the deacetylated product was subjected to (a) methylation and hydrolysis, and (6) periodate oxidation, sodium borohydride reduction, and hydrolysis. Both procedures indicated a chain-length of about 8 D-glucose residues. Furthermore, the methylation products were identical with those in Table II, again showing the highly branched structure of the dextrin. 

Chemically the process is a hydrolysis. That is, by the addition of water to the starch molecules, the latter are split into more soluble materials. The products obtained depend upon the agent used, and, also, upon whether the action is allowed to go to completion. Many researches have been made in the study of this subject. C. O Sullivan (J.C.S. 1872, S79> 1876, 725), showed that the products of diastatic action are maltose and dextrin, and that the proportion of maltose in the product decreases as the temperature of conversion is raised above 63°C. According to Brown, Heron and Morris (J.C.S. 1879,596), malt extract at room temperature converts starch paste into 80.9 parts of maltose and 19.1 parts of dextrin, and the same change occurs at all temperatures to 6o°C. The intermediate dextrins were investigated by Brown and Morris (J.C.S. 1885, S27>... 

This procedure is not subject to any of the criticisms resulting from incorrect assumptions regarding the mechanism of debranching or the structure of the phosphorylase limit-dextrin discussed previously, and it has been used routinely with successful results. A deterrent to the use of the procedure is that it requires two purified enzymes, both of which are rather difiBcult to obtain (particularly, free from branching enzyme, which would interfere with the results). Carter and Lee used the same method with yeast glucosidase-transferase instead of muscle glucosidase-transferase. 

Phenoxy acid herbicides, sulfonyl ureas, quaternary ammonium derivatives (quats), and aryloxy propanoic acids are the main classes of compounds subjected to capillary zone electrophoresis (CZE). Triazines are also separated using nonaqueous CZE, while low pfCa characterized chlorotriazines require an ion-pair-like solubilization using cationic surfactants (tetradecylammonium bromide, dodecyltrimethyl-ammonium bromide). Chiral selectors are added in CZE for obtaining enantioselectivity. Chiral selectors used for herbicide enantiomeric discrimination are vancomycin, y-cyclodextrin, ethyl carbonate -cyclo-dextrin, cyclohexyl-alkyl-)S-D-maltoside, sulpropyl ether a-cyclodextrin, and hexakis(2,3-di-0-methyl)-a-cyclodextrin. 

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