Dextrins structure

Finally, French and Mclntire studied the periodate oxidation of alpha, beta, and gamma dextrin, found that neither formic acid nor formaldehyde was produced, and concluded that all three have a cyclic structure, as earlier proposed by Freudenberg. Also supported was the gamma dextrin structure proposed by Freudenberg, on the basis of acid... 

Figure 24. Dimensional representation of phosphorylase limit dextrin structure and changes produced by action of the debranching enzyme...

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... 

The preparation of true, /8-limit dextrins is difficult. The extent of /3-amylolysis after 2 or 24 hr. may be identical, but, after 48 or 72 hr., there may be a 1 or 2% increase which may continue for many hours. Despite the use of the most-highly purified enzymes, it is often impossible to tell whether this small increase represents the action of a minute trace of another enzyme (for example, a-amylase or a debranching enzyme), the hydrolysis of chains which are not freely accessible (for example, buried A-chains ), or a slow action on linkages near to the branch point, for which the enzyme has a lowered affinity. Caution is clearly required in the deduction of limit-dextrin structures. 

Only the hydrophobic and steric terms were involved in these equations. There are a few differences between these equations and the corresponding equations for cyclo-dextrin-substituted phenol systems. However, it is not necessarily required that the mechanism for complexation between cyclodextrin and phenyl acetates be the same as that for cyclodextrin-phenol systems. The kinetically determined Kj values are concerned only with productive forms of inclusion complexes. The productive forms may be similar in structure to the tetrahedral intermediates of the reactions. To attain such geometry, the penetration of substituents of phenyl acetates into the cyclodextrin cavity must be shallow, compared with the cases of the corresponding phenol systems, so that the hydrogen bonding between the substituents of phenyl acetates and the C-6 hydroxyl groups of cyclodextrin may be impossible. 

Attempts to stabilize anthocyanins by complex inclusion with a- and P-cyclo-dextrins failed on the contrary, a discoloration of anthocyanin solutions was observed.Thermodynamic and kinetic investigations demonstrated that inclusion and copigmentation had opposite effects. In the anthocyanins, the cw-chalcone colorless structure is the best species adapted to inclusion into the P-dextrin cavity, shifting the equilibrium toward colorless forms. "... 

Pacsu4 5 has suggested a structure for starch involving a small number of non-cyclic hemiacetal linkages, the number being presumably sufficient to account for the number of endgroups determined by the methylation method. Halsall, Hirst and Jones6 have commented on this structure, however, and have shown it to be incompatible with the results of periodate-oxidation studies. In addition, these authors pointed out that it would be difficult to explain enzymic hydrolysis and dextrin formation on the basis of such a structure. 

The only example of this technique applied to the amylose component is that already described, of the action of Z-enzyme on the /3-limit dextrin. In the case of amylopectin, enzymic methods enable a distinction to be made between the proposed laminated and highly ramified structures (I and III, in Fig. 1, page 352). The method used by Peat and coworkers101 involves the successive action of /3-amylase and R-enzyme on waxy maize starch. /3-Amylolysis will degrade A-chains down to two or three units from the 6 —> 1-a-D interchain linkages. These latter linkages will protect the... 

B-chains until they are acted on by R-enzyme, when maltose or malto-triose will be produced from the residual A-chain, and linear dextrins from the B-chains. The amount of maltose or maltotriose liberated on treating the /3-limit dextrin with R-enzyme will be a measure of the number of A-chains in the molecule, and from these data, the ratio of A B chains in the molecule can be calculated.220 Peat concluded that multiple branching is an intrinsic part of the amylopectin structure, as the observed yield of these sugars was greater than expected for a singly-branched structure. It should be noted that glycogen has been shown by similar enzymic methods to possess a truly random structure.221... 

Calculations based on simple molecular models and the charge density of the layers suggest that sulfopropylated-//-cyclodextrin and carboxyethylated-/3-cyclodextrin are arranged in the interlayer galleries with their conical axis parallel to the layers with a packing structure which is similar to that in crystalline cyclo dextrin complexes, where the molecules are arranged in a brickwork pattern [202]. 

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. 

Although Schardinger did not propose a structure for his crystalline dextrins, he made several observations that can now be attributed to their cyclic structure. For example, he discovered their ability to engage in complex-formation "With various substances, the crystalline dextrins form loose complexes which, like those produced with alcohol, ether, and chloroform, are indeed partly decomposed by water, while the iodine complexes are more stable toward water. He also found, as previously mentioned, that the crystalline dextrins were nonreducing toward copper salts and nonfermentable by yeast. This last observation he considered was "... the most essential thing that I was able to mention concerning the formation of crystalline dextrins by microbes. Both of these observations can be explained by the lack of a chain termination. 

Freudenberg later concurred with French s results, after studying the X-ray measurements of Borchert and also his and Cramer s optical rotation data. He also proposed that the gamma dextrin consisted of eight d-glucosyl residues joined by a linkages in a cyclic structure, as in the case of the alpha and beta dextrins. 

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. 

This study also suggests that molecular size and structure play a role in this interaction. The binding behaviors of dextrin oligomers for four different pharmaceuticals (ibuprofen, ketoprofen, furosemide, and warfarin) were observed under the same experimental conditions. Ibuprofen and ketoprofen, two compounds that are similar in chemical structure and pharmaceutical use, showed obvious differences in interaction patterns (Fig. 13A and B). Ketoprofen, having an extra aromatic ring, required an octa-saccharide (DP = 8) for binding, whereas ibuprofen required a heptasac-... 

Jane, J. L., Wong, K. S., McPherson, A. E. (1997). Branch-structure difference in starches of A- and B-type X-ray patterns revealed by their Naegeli dextrins. Carbohydr. Res., 300,219-227. 

Yusuph, M., Tester, R. F., Ansell, R., Snape, C. E. (2003). Composition and properties of starches extracted from tubers of different potato varieties grown under the same environmental conditions. Food Chem., 82,283-289. Zhu, Q., Bertoft, E. (1996). Composition and structural analysis of alpha-dextrins from potato amylopectin. Carbohydr. Res., 288, 155-174. 

A real breakthrough in this field occurred when enantio-cGC became more and more available. In particular, since 1988 selectively modified cyclodextrins have been synthesised, serving as chiral stationary phases in enantio-cGC, reported by Schurig and Novotny [I], Konig et al. [2, 3], Armstrong et al. [4], Dietrich et al. [5,6 ], Saturin et al. [7], and Bicchi et al. [8]. 6-O-silylated modified /I-cyclo dextrin and y-cyclodextrin derivatives of well-defined structure and purity were synthesised and have proved to be chiral stationary phases of unique selectivity and versatility and, therefore, are successfully used in simultaneous enantio-cGC analysis [5,6]. Further derivatives were recently reported by Taka-hisa and Engel [9, 10], dealing with 2,3-di-0-methoxymethyl-6-0-tert-butyldi-methylsilyl modified cyclodextrins as chiral stationary phases in enantio-cGG. 

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