Glucose conformation

Initial rate kinetics of bovine brain hexokinase (A) with glucose and ATP as substrates, and (B) with fructose and ATP. Note that the apparent parallel-line kinetics observed with glucose conform to a rate equation lacking a < 12 term. 

Table 6.2 Mean unsigned errors (kcal rnol ) in 11 predicted glucose conformational energies for various basis sets at the HF level in order of basis set size...

The radii of gyration of amylose and cellulose are calculated by a method of Lifson for different glucose conformations. It is found that the radii of gyration differ widely and it can be determinated clearly by means of viscosity and light-scattering measurements which kind of glucose conformation is present in the polysaccharides. The effects of twisting upon the linear molecule is discussed. 

In Section 6.2.6, we considered approaches to the HF limit derived under the assumption that various various aspects of basis-set incompleteness (radial, angular, etc.) could be accounted for in some additive fashion (see Eq. (6.5)). In essence, multilevel methods carry this approach one step further, and assume a similar behavior for the correlation energy. For instance, the QM energies for glucose conformers that have served as a benchmark for comparison with lower levels of theory in preceding chapters were computed at a composite (C) level as... 

The way we have represented some of these molecules may be unfamiliarto you we have shown stereochemistry (whether bonds come out of the paper or into it— the wiggly lines indicate a mixture of both) and, for the cyclic glucose, conformation (the actual shape the molecules adopt). These are very important in the sugars we devote Chapter 16 to stereochemistry and Chapter IB to conformation. 

The agreement in the anomeric populations between experimental and computational studies is certainly encouraging. The computations correctly predict the inversion of anomeric preference between the gas and solution phases. However, there are some underlying concerns. Solution-phase NMR studies have determined the populations of the glucose conformations. The experimental populations of the gg (6a, 6f, 7a, 7b), gt (6b, 7c, 7d), and tg (6c, 7e, 7h) conformations is 51 47 2 for the a anomer and 53 45 2 for the p anomer.The computational studies of Table 7.11 predict that the gt conformations will dominate the populations for both the a and p anomers. 

Water molecules located in the immediate vicinity of dispersed monosaccharide molecules are relatively tightly bound and contribute to the stability of some conformers or anomers. A glucose molecule, for example, is associated with 3.7 molecules of water. The glucose conformation (more than 99% of molecules)... 

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