Sugars model studies

Fig. 2. A representation of the cellulose chain ia solution, projected against three two-dimensional surfaces. The circles represent the oxygen atoms that link the iadividual glucose residues, and the lines take the place of the sugar residues. This result of a modeling study (39) iadicated a molecule somewhat more...

As in the previous categories in this section, there are numerous compounds which have been prepared based on a sugar subunit. Examples may be found in Refs. 7,35,42-45, 57, 82-85, 117—121,175,176,193 and 208. Much of the work in these references has been reported by Stoddart and his coworkers, who have pioneered this field. As with the compounds prepared by Cram, the goal was to prepare a chiral receptor for ammonium ions which could be utilized in enzyme model studies. 

At best, van der Waals interactions are weak and individually contribute 0.4 to 4.0 kj/mol of stabilization energy. ITowever, the sum of many such interactions within a macromolecule or between macromolecules can be substantial. For example, model studies of heats of sublimation show that each methylene group in a crystalline hydrocarbon accounts for 8 k[, and each C—IT group in a benzene crystal contributes 7 k[ of van der Waals energy per mole. Calculations indicate that the attractive van der Waals energy between the enzyme lysozyme and a sugar substrate that it binds is about 60 k[/mol. 

Only model studies have so far been reported, and the method has not yet been applied to the analysis of sugar mixtures, with the exceptions noted.48,49 The recovery of glucose-14C trifluoroacetate from a column of Carbowax 20 M or SF-96 has been shown to be 5 to 14% and 3 to 5%, respectively.208 Table III (p. 112) records further details of the separation of sugars and their derivatives as trifluoroacetates. 

In a paper concerned primarily with the determination of neutral sugars, Richey and coworkers examined the O-trimethylsilyl derivatives of 2-acetamido-2-deoxy-D-glucose and 2-acetamido-2-deoxy-D-galactose.171 Similar methods for determining these compounds have also been used in studies on human milk,545 yeasts and bacteria,1,2 blood-group oligosaccharides,405 and urine.118 These methods were also included in a model study on the isothermal determination of sugars.256... 

The chemistry is more straightforward with the aromatic series. From modeling studies, we saw that the sugar binding pocket could be filled more... 

During AEDA, interactions between the odorants are not taken into consideration, since every odorant is evaluated individually. Therefore, it may be possible that odorants are recognized which are possibly masked in the food flavor by more potent odorants. Furthermore, the odor activity values only partially reflect the situation in the food, since OAVs are mostly calculated on the basis of odor thresholds of single odorants in pure solvents. However, in the food system, the threshold values may be influenced by nonvolatile components such as lipids, sugars or proteins. The following examples will indicate that systematic sensory model studies are important further steps in evaluating the contribution of single odorants to the overall food aroma. 

Neyhart GA, Cheng C-C, Thorp HH (1995) Kinetics and mechanism of the oxidation of sugars and nucleotides by oxoruthenium(IV) model studies for predicting cleavage patterns in polymeric DNA and RNA. J Am Chem Soc 117 1463-1471... 

S/N equilibrium for the C sugar in 5/-(CA )-3/. In previous modeling studies, a change from direct to water-mediated NH3-phosphate hydrogen bonding was found to change the sugar pucker of the residue 5 to 5 -G [72]. 

Ab initio molecular orbital calculations on these systems have been confined to the 1,2,3-triazolo[4,5-d]pyrimidines (7), the so-called 8-azapurines , and references to this subject may be found in the previously mentioned review <86AHC(39)ii7>. In 1989, quantum mechanical perturbation methods have been used to study the activity of 8-azapurine nucleoside antibiotics in transcription processes <89Mi 7i3-oi>. The l,2,3-thiadiazolo[5,4-d]pyrimidine derivative (51), a rearrangement product of 8-aza-6-thioinosine, has been used in a molecular modeling study of the antitumor activity of sugar derivatives of pyrimidopyrimidines <89PNA(86)8242>. 

Studies on isolated DNA and sugar model compounds have allowed the determination of the main OH-mediated degradation pathways to the 2-deoxyribose moiety. In addition, data are also available on the influence ofthe double-helix structure on the fate of purine and pyrimidine base radicals. 

The available amino groups in proteins are the s-amino group of lysine and the N-terminus. Many model studies of the Maillard reaction, however, use free amino acids, which can decarboxylate, particularly when the a-nitrogen has combined with a sugar moiety to provide an electron sink. This then produces aldehydes from the alkyl residue of the amino acid (Strecker reaction). ... 

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