Disaccharides modeling results

About a decade ago, Pensak and French investigated this flexibility with the program MMl and a limited set of crystallographic results (9,). Since then, the number of crystal studies has increased, and new modeling software was developed in attenpts to improve accuracy. Therefore, we have reinvestigated this problem. While we focus on changing D, we believe that the abilities and deficiencies disclosed in our study will apply to other modeling studies such as conformational analyses of disaccharides with flexible residues. 

In model studies,224,225 oligosaccharides have been separated as their trifluoroacetates, and Vilkas and coworkers224 found that a tetra-saccharide so esterified had a retention time of six minutes at 250°. Similar results were obtained by Nakamura and Tamura,49 who showed that, on a column of OV-1 at 220°, the retention time of per-0-(trimethylsilyl)sucrose was 12 min, whereas, at 140°, the per(tri-fluoroacetate) required only 7 min. Other comparative data were provided for the common disaccharide alditols. A study of the concentration of lactose in blood was made by using this method 48 it was also shown48 that trifluoroacetylation of disaccharides proceeds more rapidly and satisfactorily in N,N-dimethylformamide than in ethyl acetate. 

Model building in the computer is used to analyze the conformational effects of steric interactions between atoms of the polymer skeleton for x-carrageenan, t-carrageenan, A-carrageenan, agar, chondroltin, chondroitin sulfates, dermatan sulfate, keratan sulfate, hyaluronic acid, and related polysaccharides. Over 99% of the conformations are thus excluded and virtually all of the remainder for each polysaccharide lie close together. Predictions are also made from disaccharide crystal structures and checked against experimental results. 

The disaccharides such as trehalose, maltose, and leucrose are useful in biopreservation and life science, and the polysaccharides are important in other areas. On elevating pressure, fructose, D-ribose, 2-deoxy-D-ribose , and leucrose have a secondary relaxation shifting to lower frequencies with applied pressures, mimicking the behavior of the a-relaxation. The one in leucrose is sensitive to the thermodynamic history of measurements. There is also good agreement of the observed relaxation time of the secondary relaxation with the primitive relaxation time calculated from the Coupling Model for D-ribose and 2-deoxy-D-ribose. These results indicate that this secondary relaxation in the mono- and di-saccharides is connected to the a-relaxation in the same way as in ordinary glassformers, and hence it is the JG p-relaxation of... 

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