Adsorption of Bio polymers

Assume a (solid) surface, for example, the outer wall of a bacterial cell, of which the charge is determined by dissociation or association of protons in an aqueous medium containing NaCl as the only low-molecular-weight electrolyte. The charge density Oq at the surface of the solid is given by 

Cross-differentiation between the first and the third term, at constant CNaci or pnaci gives 

Using Equation 3.100 the variation of with pH, at constant can t e computed from the experimentally accessible variation of Oq with at constant pH. As the relation between Oq and pH is also known, the dependence of on Oq can be established, even if this cannot be directly measured. 

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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. 

Adsorption of (Bio)Polymers, with Special Emphasis on Globular Proteins 279... 

Another attractive application of polymer brushes is directed toward a biointerface to tune the interaction of solid surfaces with biologically important materials such as proteins and biological cells. For example, it is important to prevent surface adsorption of proteins through nonspecific interactions, because the adsorbed protein often triggers a bio-fouling, e.g., the deposition of biological cells, bacteria and so on. In an effort to understand the process of protein adsorption, the interaction between proteins and brush surfaces has been modeled like the interaction with particles, the interaction with proteins is simplified into three generic modes. One is the primary adsorption. 

Gel permeation chromatography is an excellent technique for the practically quantitative separation of compounds up to a molecular mass of 400 u (e.g., OCPs) from macromolecular compounds, such as lipids (600-1500 u). The GPC column, which consists of porous polymer beads, retains molecules that are small enough to enter the pores. Lipid molecules that are too large to enter these pores are not retained and are therefore eluted from the column first. Separation is generally performed using divinylbenzene-linked polystyrene gels, mostly Bio-Beads SX-3. It is suitable for OCPs and OPPs and nearly all other types of pesticides and does not involve any losses by adsorption. 

We propose the following mechanism for adsorption of Hg by modified bio polymers. 

Table 1 Effect of adsorbent s pore size on adsorption of a bio-related polymer...

Polymers are our molecular views on certain chemical substances. The views have been established in our long-lasting exploration and exploitation of materials in nature. The term polymers is commonly used to describe a broad range of materials, from synthetic materials, such as plastics, rubbers, fibers, coatings, filtration membranes, adsorption resins and adhesives to natural materials, such as cellulose, starches, natural rubbers, sOks, hairs, and chitins and even to the prototypes of bio-macromolecules, such as DNA, RNA and proteins, which are the basic substances for highly diverse creatures. 

Most theories for polymer adsorption kinetics start from (combinations of) the models discussed earlier. Other theories, often proposed for (bio)polymer adsorption, are based on the random sequential adsorption (RSA) model. According to this model, the adsorbate molecules arrive randomly at the interface and they stick where they hit. It implies that both desorption and tangential motion of the adsorbate at the interface are absent. Because the center of a newly arriving spherical molecule cannot be accommodated within the shaded areas enclosed by the dashed circles shown in Figure 15.6, only the unshaded fraction < ) of the surface is available for adsorption. It is obvious that ( ) is a function of 0, the fraction of the surface that is covered by the adsorbate. For sphere-like molecules, 0 = niUi (R being the radius of the molecule). The following expressions for the available surface function < )(0) can be derived from the RSA theory ... 

It is evident from our literature survey that chitosan and its derivatives have demonstrated outstanding removal capabilities of metal ions as compared to other low-cost sorbents and commercial activated carbons. Biopolymer adsorbents are efficient and can be used for the decontamination of effluents, for separation processes, and also for analytical purposes. The literature data show that the sorption capacity, speciflcity and adsorption kinetics are mainly influenced by chemical stmcture and composition of the bio polymer, and also by the accessibility of chelating or complexing groups. 

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