Biopolymers sulfates Polysaccharides

Figure 8.12 illustrates the effect of complex formation between protein and polysaccharide on the time-dependent surface shear viscosity at the oil-water interface for the system BSA + dextran sulfate (DS) at pH = 7 and ionic strength = 50 mM. The film adsorbed from the 10 wt % solution of pure protein has a surface viscosity of t]s > 200 mPa s after 24 h. As the polysaccharide is not itself surface-active, it exhibited no measurable surface viscosity (t]s < 1 niPa s). But, when 10 wt% DS was introduced into the aqueous phase below the 24-hour-old BSA film, the surface viscosity showed an increase (after a further 24 h) to a value around twice that for the original protein film. Hence, in this case, the new protein-polysaccharide interactions induced at the oil-water interface were sufficiently strong to influence considerably the viscoelastic properties of the adsorbed biopolymer layer. 

Mucopolysaccharides (MPS, also called glycosaminoglycans) are ani nic biopolymers widespread in animal tissues, especially in the intercellular matrix of connective tissues. These polysaccharides arc built up from amino sugars, either D-glucosamine or D-galactosamine, together with uronic acids, either D-glucuronic acid or L-iduronic acid and may have N-acetyl, 0- or N-sulfate groups. 

GAGs are an important class of polysaccharides that are involved in myriad physiological processes, such as biolubrication, cell division, adhesion, inflammation, and wound healing [117,119, 183-188]. Although the disaccharide repeat units of these macromolecules have been characterized, the natural biopolymers are typically heterogeneous in molecular weight and sulfation levels [183,185]. 

Soon after the original work was published, unique properties of the new biopolymer were discovered, which proved it different from other similar glycosaminoglycans. According to Meyer and Palmer, the isolated polysaccharide contained uronic acids and amino sugars, as well as pentose, and was not sulfated [1], They also decided that the molecular mass of the repeatable unit is approximately 450 Da. It was later proved that HA in fact does not contain sulfate groups or pentose. It was also established that the molecular mass of the repeatable disaccharide residue is 397 Da. 

In carbohydrate chemistry, a polysaccharide is a molecule having more than ten monosaccharide units [18]. Polysaccharides belong to one of three important classes of naturally occurring biopolymers, the other two being nucleic acids (DNA and RNA) and proteins. Cellulose, amylose, xylan, chitin, hyaluronic acid (hyaluronan), chondroitin, and chondroitin sulfate can be cited as typical natural polysaccharides (Scheme 1). 

It turned out that the dynamical behaviour of polyelectrolyte solutions is even more spectacular then theoretically anticipated. In the early 1970s mostly biopolymers such as DNA were studied and often two separate relaxations were observed which were then attributed to internal relaxations [197-202]. During the past twenty years numerous studies on synthetic polyelectrolytes (NaPSS, NaPMA, NaPAA, QPVP), proteins (BSA, PLL), polynucleotides (DNA, RNA) and charged polysaccharides (heparin, chondroitin-6-sulfate, proteoglycan hyal-onurate) have been performed. The dynamical behaviour of all these polymers exhibits common features which are attributed to the ionic character of the polyelectrolytes. So far, most studies have focused on the dependence of the apparent diffusion coefficient on polyelectrolyte concentration, salt concentra-... 

Other than the above-mentioned biopolymers, research continues to examine the usefulness of other polysaccharides as well. The use of hyaluronic acid and chon-droitin sulfate as membranes has so far been limited to tissue engineering and biomedical applications. However, these materials will also be seen in the mainstream membrane market for water purification in future. 

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