Carbohydrates, theoretical prediction

These examples of simulations of the molecular dynamics of carbohydrates show the possibility of predicting their behavior in different solvents. Experimental work has confirmed these findings. While theoretical prediction is becoming more reliable, it is only qualitative and we must consider the theoretical results within the framework of the actual capability of the methods. Current minicomputers allow simulation of large system. Polysaccharides, for instance, are being studied by this technique. However, the description of carbohydrate solutions is still poor, and simple systems can help in the understanding of the problems. 

Jeffrey, G. A., J. A. Pople, and L. Radom The Application of ab initio Molecular Orbital Theory to the Anomeric Effect. A Comparison of Theoretical Predictions and Experimental Data on Conformations and Bond Lengths in Some Pyranoses and Methyl Pyranosides. Carbohydr. Res. 25, 117 (1972). 

Numerous experimental and theoretical studies have addressed the observation that in pyranosides, an electronegative substituent (OFI, OR, halogen) at the anomeric carbon atom C-1 prefers the axial configuration in contrast to that predicted on steric grounds alone (Figure 1). This so-called anomeric effect is one of several electronic and stereoelectronic effects that influence the conformational properties of carbohydrates.Related to the anomeric effect is the... 

Another critical strength of this paper was that it used the electronic calculations in conjunction with a simple steric model to successfully rationalize 18 different pyranose crystal structures. While this latter aspect cannot be discussed here in any detail owing to space limitations, this careful comparison of the model to experiment had a tremendous impact on experimental carbohydrate chemists, who were impressed to see theory being used to make predictions about exactly the same crystal structures they were concerned with from their own perspectives. Indeed, JP R set a remarkably high standard to be emulated in future theoretical papers, and contributed to the generally good reputation theory has enjoyed within the carbohydrate community. The calculations of JP R, described below, were carried out at the HF/4-31G level [18]. 

A theoretical framework has been proposed for the analysis of adhesion between cells, or of cells to surfaces, when the adhesion is mediated by reversible bonds between specific molecules such as antigen and antibody, lectin and carbohydrate, or enzyme and substrate. Two models have been developed for predicting the rate of bond formation between cells, from the measurements of reaction rates for membrane-bound reactants. 

If our food was a dietetic beverage (almost a pure aqueous solution), we could readily predict kg, for an aroma compound (and therefore recovery during isolation). Unfortunately, the presence of various solutes in the food (simple sugars, complex carbohydrates, lipids, proteins, water, minerals, etc.) enormously complicates this equation and our task.. Some factors can be predicted and thus understood, for example, lipid effects. Others, for example binding by proteins or salting out by simple sugars, are not predictable and thus cannot currently be accounted for in a theoretical treatment. 

A symposium report has been published on the conformational properties of deo genated sugars, with emphasis on furanose derivatives. A review with 18 references is concerned with certain stereochemical problems associated with small carbohydrate molecules and aims to show how the combination of experimental n.m.r. studies and theoretical computer simulation can be brought to bear on their resolution. In connection with the total synthesis of palytoxin, a review has been written covering the conformational anal is of O-and C-disaccharides and presents a useful mode (diamond lattice diagrams) for predicting the solution conformations of these compounds. A further review deals with C-n.m.r. studies, especially by use of relaxation probes, of the interaction between metal ions and carbohydrates. ... 

Developmental stages of several fish species have been evaluated with calorespirometry. The CR ratios for developing turbot Scophthalmus maximus) embryos and larvae [43] fell within the theoretical scope for oxycaloric equivalents that reflected a fully aerobic metabolism (Table 1). TTie total measured heat dissipation over the first 19 h post-fertilization matched the expected heat dissipated calculated from aerobic glycogen consumption across the same period (measured, -1.80 to -1.91 mJ biochemically predicted, -1.90 mJ). Lactate was low and constant across this period of development. The energetic role played by carbohydrates diminished after commencement of epiboly. Similar CR ratios to those of the turbot (Table 1) have been reported for embryos of the arctic char [44],... 

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