Adsorption of biopolymers

Chapter 4 Adsorption of Biopolymers, with Special Emphasis on... 

Effect of Degree of Ligand Polymerization on Adsorption of Biopolymer... 

The adsorption of biopolymers onto a surface 190], the attraction and adhesion of bacteria to that surface, their subsequent multiplication and exopolymer production leads to the formation of biofilms 191]. The original conditioning film can influence the type and number of settling microorganisms, which in turn can affect the settlement of larvae of marine fouling organisms (92, 93]. 

The rapid initial phase of salivary protein adsorption is followed by a second, comparatively slower phase of protein adsorption onto the protein-coated enamel surface. The second stage of pellicle formation is characterised by a continuous adsorption of biopolymers from saliva. This process involves protein-protein interactions between already adsorbed proteins, immobilised in the pellicle layer, and proteins as well as protein aggregates from saliva. Amino acid and Auger analyses of the pellicle layer formed on buccally carried enamel slabs [18] indicate that the adsorbed proteins reach an initial thickness in about 2-3 min, and stay at that level for about 30 min. The thickness of the pellicle then increases to about three times its initial thickness and reaches a plateau after 30-90min [5, 18, 27], Within 60min, the thickness of the in situ-formed pellicle will further increase to between 100 and lOOOnm [17, 28], dependent on the supply of locally available salivary biopolymers and the prevailing intraoral conditions [17,28,29] (fig. 2). 

Matsui M, Kiyozumi Y, Yamamoto T, Mizushina Y, Mizukami F, Sakaguchi K. Selective adsorption of biopolymers on zeolites. Chem EurJ 2001 7(7) 1555-1560. 

Surface density, orientation and/or molecular conformation of the immobilized bioactive components, and/or nonspecific adsorption of biopolymers will control the performance of biofunctional surfaces. Options to address... 

Further advances in technology offered the solution of surface modification of the metal structure of the DES by chemical or physical adsorption of biopolymers or synthetic polymers that would allow enhanced cell adhesion following placement of the stent. Thus, pharmaceutical polymers may be used not only in the design of the actual stent, but also to coat stent surfaces to augment tissue compatibility. At the present time there are a few DES which are approved by the Food and Drug Authority (FDA) for use in humans. These are further discussed below. 

The problem of the theoretical description of biopolymer water adsorption isotherms has drawn the attention of researchers for a long time. In the works [19], [20] a rigorous statistical basis for equations describing the isotherms for the case of homogeneous adsorption surfaces and noninteracting adsorption sites of N different types has been suggested. The general equation is ... 

Figure 11.15 Cation-exchange mia O-LC analysis of a mixture of model proteins (a) the original sample consisting of myoglobin (M), cytochrome C (C) and lysozyme (L) (b) and (c) proteins adsorbed on to and then released from the polyaaylic acid coated fibre with exti ac-tion times of 5 and 240 s, respectively. Reprinted from Journal of Microcolumn Separations, 8, J.-L. Liao et al., Solid phase mia O exti action of biopolymers, exemplified with adsorption of basic proteins onto a fiber coated with polyaaylic acid, pp. 1-4, 1996, with permission from Jolm Wiley Sons, New York.

J.-L. Liao, C-M. Zeng, S. Hjeiten and J. Pawliszyn, Solid phase micro exti action of biopolymers, exemplified with adsorption of basic proteins onto a fiber coated with polyacrylic acid , ]. Microcolumn Sep. 8 1-4. (1996)... 

The consideration made above allows us to predict good chromatographic properties of the bonded phases composed of the adsorbed macromolecules. On the one hand, steric repulsion of the macromolecular solute by the loops and tails of the modifying polymer ensures the suppressed nonspecific adsorptivity of a carrier. On the other hand, the extended structure of the bonded phase may improve the adaptivity of the grafted functions and facilitate thereby the complex formation between the adsorbent and solute. The examples listed below illustrate the applicability of the composite sorbents to the different modes of liquid chromatography of biopolymers. 

These sorbents may be used either for selective fixation of biological molecules, which must be isolated and purified, or for selective retention of contaminants. Selective fixation of biopolymers may be easily attained by regulation of eluent polarity on the basis of reversed-phase chromatography methods. Effective isolation of different nucleic acids (RNA, DNA-plasmid) was carried out [115, 116]. Adsorption of nucleosides, nucleotides, tRN A and DNA was investigated. It was shown that nucleosides and nucleotides were reversibly adsorbed on... 

Silica gels with mean pore diameters of 5-15 nm and surface areas of 150-600 m /g have been preferred for the separation of low molecular weight samples, while silica gels with pore diameters greater than 30 nm are preferred for the separation, of biopolymers to avoid restricting the accessibility of the solutes to the stationary phase [15,16,29,34]. Ideally, the pore size distribution should be narrow and symmetrical about the mean value. Micropores are particularly undesirable as they may give rise to size-exclusion effects or irreversible adsorption due to... 

Fig. 3.5 Representation of a scheme of an experiment (upper set of drawings) and the obtained experimental results presented as AFM images (middle part) and cross-sectional profiles (bottom) that provides evidence of silica nucleation and shell formation on biopolymer macromolecules. Scheme of experiment. This includes the following main steps. 1. Protection of the mica surface against silica precipitation. It was covered with a fatty (ara-chidic) acid monolayer transferred from a water substrate with the Langmuir-Blodgett technique. This made the mica surface hydrophobic because of the orientation of the acid molecules with their hydrocarbon chains pointing outwards. 2. Adsorption of carbohydrate macromolecules. Hydrophobically modified cationic hydroxyethylcellulose was adsorbed from an aqueous solution. Hydrocarbon chains of polysaccharide served as anchors to fix the biomacromolecules firmly onto the acid monolayer. 3. Surface treatment by silica precursor. The mica covered with an acid mono-...

In view of the conductive and electrocatalytic features of carbon nanotubes (CNTs), AChE and choline oxidases (COx) have been covalently coimmobilized on multiwall carbon nanotubes (MWNTs) for the preparation of an organophosphorus pesticide (OP) biosensor [40, 41], Another OP biosensor has also been constructed by adsorption of AChE on MWNTs modified thick film [8], More recently AChE has been covalently linked with MWNTs doped glutaraldehyde cross-linked chitosan composite film [11], in which biopolymer chitosan provides biocompatible nature to the enzyme and MWNTs improve the conductive nature of chitosan. Even though these enzyme immobilization techniques have been reported in the last three decades, no method can be commonly used for all the enzymes by retaining their complete activity. 

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. 

In addition, the composition of the electrolyte solution can strongly influence sample solubility and detection, native conformation of biopolymers, molecular aggregation, electrophoretic mobility, and EOF, which can be altered as a consequence of the adsorption of the components of the BGE onto the capillary wall. Consequently, selecting the proper composition of the electrolyte solution... 

Another characteristic property of many biopolymers (proteins, modified starch, chitosan, etc.) which is useful for the encapsulation of bioactive molecules is their ability to adsorb at the oil-water interface and to form adsorbed layers that are capable of stabilizing oil-in-water (OAV) emulsions against coalescence (see Table 2.2). It is worthwhile to note here that the formation of an emulsion is one of the key steps in the encapsulation of hydrophobic nutraceuticals by the most common technique used nowadays in the food industry (spray-drying). The adsorption of amphiphilic biopolymers at the oil-water interface involves the attachment of their hydrophobic groups to the surface of the oil phase (or even their slight penetration into it), whilst their hydrophilic parts protrude into the aqueous phase providing a bulky interfacial layer. 

Information on the chemical potentials of components in a solution of biopolymers can serve as a guide to trends in surface activity of the biopolymers at fluid interfaces (air-water, oil-water). In the thermodynamic context we need look no further than the Gibbs adsorption equation,... 

In Part Four (Chapter eight) we focus on the interactions of mixed systems of surface-active biopolymers (proteins and polysaccharides) and surface-active lipids (surfactants/emulsifiers) at oil-water and air-water interfaces. We describe how these interactions affect mechanisms controlling the behaviour of colloidal systems containing mixed ingredients. We show how the properties of biopolymer-based adsorption layers are affected by an interplay of phenomena which include selfassociation, complexation, phase separation, and competitive displacement. 

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