Interactions biopolymer-water

A possible explanation of the hysteresis could be the non-equilibrium of the DNA hydration. In that case the value of hysteresis has to depend on the size of the experimental sample. However, such a dependence is not observed in the wide range of DNA film thicknesses (0.05-0.2 fmi) [14], [12]. Thus, hysteresis cannot be a macroscopic phenomenon and does reflect the molecular interaction of water and the biopolymer. 

Fig. 7. Besides direct interactions between functional groups of the biopolymer molecule itself there are also various kinds of interactions with water molecules. These hydrophilic and hydrophobic interactions are essential for stabilizing the native conformation of biopolymers. In the last few years some progress was made in elucidating the hydration of these molecules.

The characteristics of the isolated biopolymers depend on their structure. Cellulose and amylose are linear polymers, whereas amylopectin, pectin and hemicelluloses are branched polymers. Pectin and amylopectin contain carboxylic groups, which make interactions with water molecules very important. Amylose has a helix structure, whereas the cellulose molecule looks like a ribbon. The interactions with water and other neighbouring molecules are therefore different. 

Bustamante C, Gurrieri S, Pasternack RF et al (1994) Interaction of water-soluble porphyrins with single- and double-stranded polyribonucleotides. Biopolymers 34 1099-1104... 

Hermans, J., H.J.C. Berendsen, W.F. van Gunsteren, and J.RM. Postma. 1984. A consistent empirical potential for water-protein interactions. Biopolymers 23 1513-1518. 

Water soluble polymers behave like other solutes, i.e. radiation interacts with water principially and products of radiolysis react with the polymer. If the polymer is composed from different meres, what is the case with biopolymers, different segments of the polymer can have different rate constants of reaction with water derived radicals, c.f. the case of gelatin zols and gels [8], The radiation chemistry of polymers dissolved in water is the chemistry of reactions with OH, H, eaq, H2O2 and not, sensu stricto, of the polymer itself. Experiment shows clearly, that the radiation chemistry of the same polymer, but in the dry or almost dry state is completely different from radiation chemistry of its aqueous solution. Spurs are formed in the dry polymer and not in water. 

Berendsen, H. J. C. 1975. Specific interactions of water with biopolymers. In F. 

Cacace et al. (1997) stressed several aspects of the Hofmeister series. The underlying concept is that biopolymer interactions are water-mediated and the anions affect both the surface of the biopolymer and the structure of the water. When a protein folds, aggregates or adsorbs, the solvent/protein interfacial area Awp is diminished. Contrarily, when a protein is denatured, Awp increases. Work needs to... 

DAN Dan, A., Ghosh, S., and Moulik, S.P., Physicochemical stndies on the biopolymer inulin A critical evaluation of its self-aggregation, aggregate-morphology, interaction with water, and thermal stabihty. Biopolymers, 91, 687,2009. 

Protein crystals contain between 25 and 65 vol% water, which is essential for the crystallisation of these biopolymers. A typical value for the water content of protein crystals is 45% according to Matthews et al. l49,150). For this reason it is possible to study the arrangement of water molecules in the hydration-shell by protein-water and water-water interactions near the protein surface, if one can solve the structure of the crystal by X-ray or neutron diffraction to a sufficiently high resolution151 -153). 

Adsorption of (bio)polymers occurs ubiquitously, and among the biopolymers, proteins are most surface active. Wherever and whenever a protein-containing (aqueous) solution is exposed to a (solid) surface, it results in the spontaneous accumulation of protein molecules at the solid-water interface, thereby altering the characteristics of the sorbent surface and, in most cases, of the protein molecules as well (Malmsten 2003). Therefore, the interaction between proteins and interfaces attracts attention from a wide variety of disciplines, ranging from environmental sciences to food processing and medical sciences. 

Polyelectrolytes are long chain molecules bearing ionisable sites. It is not always possible to predict with confidence the extent to which polyelectrolytes behaviour is exhibited. Thus, polyacrylic acid in water is only weakly ionised and in dioxan it behaves as a typical non-electrolyte. It is usual to overcome the complications imposed by ionic interactions by the inclusion of simple salts and LS studies in salt-free solutions are rather rare. The problems have been discussed recently by Kratochvil137), whilst the review of Nagasawa and Takahashi138 constitutes one of the few devoted exclusively to LS from polyelectrolyte solutions. LS from many biopolymers such as proteins is, of course, extremely relevant in this context. 

Proteins are water-soluble biopolymers with a huge number of potential donor atoms and coordination sites which could make them useful carriers of metal complex catalysts. Indeed, a few successful attempts can be found in the literature [139] but often the interaction of proteins and metal complexes lead to a loss of catalytic activity [140]. This was not the case with human serum albumin (HSA) which formed a stable and active catalytically active complex with [Rh(acac)(CO)2]. In the hydroformylation of 1-octene and styrene the selectivity towards aldehydes was excellent, moreover styrene reacted with high regioselectivity (b/1 = 19). The activity... 

Bioreactions. The use of supercritical fluids, and in particular C02, as a reaction media for enzymatic catalysis is growing. High diffusivities, low surface tensions, solubility control, low toxicity, and minimal problems with solvent residues all make SCFs attractive. In addition, other advantages for using enzymes in SCFs instead of water include reactions where water is a product, which can be driven to completion increased solubilities of hydrophobic materials increased biomolecular thermostability and the potential to integrate both the reaction and separation bioprocesses into one step (98). There have been a number of biocatalysis reactions in SCFs reported (99—101). The use of lipases shows perhaps the most commercial promise, but there are a number of issues remaining unresolved, such as solvent—enzyme interactions and the influence of the reaction environment. A potential area for increased research is the synthesis of monodisperse biopolymers in supercritical fluids (102). 

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