Solution behavior, carbohydrates

Summary The wetting behavior of liquid siloxanes and aqueous solutions of carbohydrate-modified siloxane surfactants on perfluorinated surfaces has been investigated. Siloxanyl moieties in surfactants level off to a large extent the influences of other structural elements. The donor-acceptor portions of the surface tension and the interfacial tension solid/liquid converge and amount to about 1-2 mN/m. The contact angle is not a linear function of the surface tension. It results from the superposition of surface tension and interfacial tension solid/liquid, both independent of each other. 

The solution behavior of carbohydrates, such as the expression of both terminal and internal chain epitopes, reflects a physicochemical property of a carbohydrate molecule. Carbohydrate molecides are rich in hydroxyl groups, and in an aqueous solution, their hydroxyl groups readily interact with water molecules via hydrogen bonding. Since the glycosidic linkages are more flexible than the peptide bonds in proteins. 

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. 

A coirplete understanding of the role of carbohydrates in biological systems requires knowledge of the distribution at equilibrium of the various conformers in aqueous solution. The conformational behavior of carbohydrates in solution can be examined from different vantage points (1,), but the most relevant approach is, no doubt, study of dilute solutions themselves. At present, high resolution NMR spectroscopy is the primary tool for determination of three-dimensional structure of oligosaccharides in solution. Optical rotation is also very sensitive to conformation (2) and there is a new, semi-enqpirical theory of optical rotation of oligosaccharides ( ). 

While sugar solutions can be a significant item in the diet of ants, parasitoids are often entirely dependent on carbohydrates as an adult food source (Jervis et al., 1993). The parasitoids longevity and fecundity are usually subject to energetic constraints (Leatemia etal., 1995 Stapel etal., 1997 Wackers, 2001), whereas the parasitoids behavior can also be strongly affected by their nutritional state (Wackers, 1994 Takasu and Lewis, 1995). There is strong evidence that the availability of suitable sugar sources can play a key role in parasitoid host dynamics (Krivan and Sirot, 1997 Wackers, 2003). 

There is much to be learned about carbohydrate ionization. Only now are chemists breaking the surface to gain this understanding. Simple explanations for chemical behavior will not always suffice because with carbohydrates the systems are much too complex. Some of the concepts and interpretations of data presented here may be incorrect. A more accurate and detailed description of carbohydrate ionization in alkaline solution, however, will be possible only after much additional research. 

It is difficult to distinguish between these two mechanisms, in which the initial step may be very similar. Furthermore, the occurrence of both mechanisms may also be conceivable. On the other hand, finding model systems, e.g. lignin model compounds showing photocycling behavior both in solution and applied to pulps and other carbohydrate matrices, would support mechanism 1. Efforts will be made in that direction in future work. 

However, another explanation for the differences in behavior between carbohydrates could be their ability to develop a gel-like structure in solution able to... 

CARBON-13 NUCLEAR MAGNETIC RELAXATION AND MOTIONAL BEHAVIOR OF CARBOHYDRATE MOLECULES IN SOLUTION ... 

Variable-temperature 13C NMR spin-lattice relaxation time measurements have been used to probe the motional behavior of 2,3 5,6-di-O-isopropylidene-a-D-mannofuranose (22) in dimethyl sulfoxide solution.67 This carbohydrate deriva-... 

Very few reports have been published on the use of X-rays for modification of starch, although the formation of deoxy compounds on irradiation of solid potato starch with 5 X 106 rads under nitrogen has been described. The amount of deoxy compounds formed is related almost linearly to the irradiation dose, and formation of 2-deoxy-D-arabi no-hexose is the major process there are almost no side-pro-cesses. Similar qualitative, but not quantitative, behavior is shown by 1% aqueous solutions of D-glucose, D-xylose, L-arabinose, D-ribose, sucrose, and cellulose powder (Fig. 14). Starch is the most resistant to irradiation among carbohydrates tested.74... 

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