Covalent adsorption

Fig. 6-7. Electron energy levels of an adsorbed particle on adsorbent metal (c) localized covalent adsorption, (d) anionic adsorption. [From Benard, 1983.]...

Both cationic adsorption and anionic adsorption belong to what is called ionic adsorption. Covalent adsorption is due to the localized covalent bonding, and metallic adsorption is due to the delocalized covalent bonding. The distinction among these three modes of chemisorption, however, is not so definite that the transition from the covalent through the metallic to the ionic adsorption may not be discontinuous, but rather continuous, in the same way as the transition of the three-dimensional solid compounds between the covalent, metallic, and ionic bonding. 

Capillary coating can also stabilize the migration times and resolutions. This is in particular necessary in the case of peptide and protein analysis, because proteins tend to stick to capillary walls. Often low-concentration polyethylene oxide solutions are recommended as well as dynamic bilayer coating formed by a non-covalent adsorption of polybrene and polyvinylsulfonate (PVS). Due to the stability of the EOF, the variation of intra- and intercapillary migration time was less than 1% relative standard deviation (RSD) with basic analytes and peptides. 

Fig. 9. Dipoles at a metal surface (a) van der Waals , (b) ionic, and (c) covalent adsorption.

Covalent Adsorption with Ionic Character). If it is assumed that metallic conduction starts at the metal surface, the effective dipole length is diiJkl I , where duA is equal to the distance between the adsorbate and metal atoms as shown in Fig. 9c. Thus, for a dipole moment M = eduA, ... 

Concerning label attachment, all types of binding (covalent, adsorption, biospecific interactions, etc.) are included in the labeling techniques used. 

Chambers E, Mitrigotri S. Prolonged circulation of large polymeric nanoparticles by non-covalent adsorption on erythrocytes. J Control Release 2004 100 111-119. 

The interaction of nanoparticles with the proteins is governed from the same type of interactions described for carbon nanotubes. Since NPs carry charges, they can electrostatically adsorb biomolecules with different charges, which depend on the pH that the immobilization takes place and the pi of the protein [3,191]. Moreover, hydrophobic interactions, hydrogen bonds and non-specific absorption can play a role for enzyme non-covalent adsorption onto the surface of nanoparticles. 

Immobilization may take place as part of the actual formation of the sensor active surface, or may be done after a base layer is established on the transducer. For example, entrapment and cross-linking immobilization methods involve the mixture of active component with carriers and polymerizing agent(s) and application of the mixture directly to the transducer to form the active surface. Covalent, adsorption, and biological immobilization methods attach the active component to a previously prepared surface, such as activated silica. 

A series of close-to-spherical styrene/DVB resins of varying particle size and pore diameter were employed as supports for non-covalent adsorptive attachment of CALB by hydrophobic interaction. The effect of matrix particle and pore size on CALB i) adsorption isotherms, ii) fraction of active sites, iii) distribution within supports, and iv) catalytic activity for s-CL ring-opening polymerizations and adipic acid/l,8-octanediol polycondensations is reported. Important differences in the above for CALB immobilized on methyl methacrylate and styrene/DVB resins were found. The lessons learned herein provide a basis to others that seek to design optimal immobilized enzyme catalysts for low molar mass and polymerization reactions. 

This paper reviews the present status of affinity separation of cells based on the biospecific interaction of cellular receptors with proteinaceous ligands immobilized on a solid-phase matrix. Special emphasis was placed on the development of new matrix materials for immuno-affinity chromatography of lymphocyte subpopulations. Our newly developed matrix of poly(2-hydroxyethyl methacrylate)/polyamine graft copolymer offered novel advantages in (1) elimination of non-specific adsorption of lymphocytes and (2) simple immobilization procedure of ligand protein through non-covalent adsorption. This matrix allowed a rapid separation of preparative quantities of pure and vital lymphocyte subpopulations (IgG-positive and -negative cells) in excellent yield. 

Another paper " reported the development of two main strategies (i) the covalent grafting of hydrolyzable Si(OEt)3 groups on oxidised CNTs and (ii) the non-covalent adsorption of a polycation on pristine CNTs (Figure 4.9). These approaches enabled the performance of further sol-gel processing of functionalised CNTs and their incorporation into poly(methyl methacrylate)... 

Cellulose has been converted into more reactive forms by chelation with titanium(m), iron(ni), tin(iv), vanadium(m), and zirconium(iv) salts. The unsubstituted ligands of the bound metals could be replaced by electron-donating groups of antibiotics e,g. ampicillin, gentamicin, kanamycin, neomycin, paro-mycin, etc.) to yield materials possessing antimicrobial activity the original chelated celluloses were inactive. The chelation procedure offers an easy way of rendering cellulose more resistant to microbial attack than that afforded by non-covalent adsorption of the antibiotic. 

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