Multilayer binding

Figure 4 Multilayer binding of proteins in polymer chain grafted onto pore surface.

Second, the degree of multilayer binding of protein onto the pore surface, as defined by equation (3), can be determined by dividing Qe by the theoretical monolayer binding capacity, Qj. 

We can visualize that when our hair is rubbed with a plastic plate, strands of hair stand up from the scalp due to electrostatic repulsion among them. Similarly, when charged functional groups, such as diethylamino groups, are introduced onto the graft chains, the polymer chains extend from the pore surface due to their mutual repulsion. This extended polymer brush conformation provides the protein with three-dimensional binding sites. The multilayer binding of various proteins onto the ion-... 

Figure 9 Degree of multilayer binding of BSA vs DEA-group mole fraction.

The membrane of a hollow-fiter form is a convenient polymeric material in that expansion from a laboratory to a plant scale can be carried out simply by bundling the hollow fibers into a hollow-fiber membrane module [14,15]. The phenomenon of multilayer binding of the enzymes into the polymer chains grafted onto the porous hollow-fiber membrane is applicable to other enzymatic reactions at a high throughput. 

Insuffident characterization of the graft chains does not mean unsatisfactory materials with resped to spedfic fundionality. The high performance of fundional polymeric materials prepared by radiation-induced graft polymerization and subsequent chemical modifications has been verified experimentally. Moreover, phenomena such as multilayer binding of proteins to the graft chains [7-11,16-18] and... 

F) antibody spaced too widely to allow adjacent molecules to bind bivalently via Fc (G) as in (E) except that orientation is via Fc or Fab, (H) more extreme case of (C) with less antibody and more molecules inactive owing to orientation, (I) multilayered binding in excess leading to binding... 

Figure 5.15 Electron beam grafting of polyethylene with glycidyl methacrylate and multilayer binding of bovine serum albumin (BSA) after conversion of the epoxide groups. Adapted with permission from Ref. [163] 2001, Elsevier.

Adsorption may in principle occur at all surfaces its magnitude is particularly noticeable when porous solids, which have a high surface area, such as silica gel or charcoal are contacted with gases or liquids. Adsorption processes may involve either simple uni-molecular adsorbate layers or multilayers the forces which bind the adsorbate to the surface may be physical or chemical in nature. 

Organosilanes, such as trichlorosilanes or trimethylsilanes, can establish SA monolayers on hydroxylated surfaces. Apart from their (covalent) binding to the surface these molecules can also establish a covalent intennolecular network, resulting in an enlranced mechanical stability of the films (figure C2.4.11). In 1980, work was published on the fonnation of SAMs of octadecyltrichlorosilane (OTS) 11171. Subsequently, the use of this material was extended to the fonnation of multilayers 11341. 

Room temperature deposition of silver on Pd(lOO) produces a rather sharp Ag/Pd interface [62]. The interaction with a palladium surface induces a shift of Ag 3d core levels to lower binding energies (up to 0.7 eV) while the Pd 3d level BE, is virtually unchanged. In the same time silver deposition alters the palladium valence band already at small silver coverage. Annealing of the Ag/Pd system at 520 K induces inter-diffusion of Ag and Pd atoms at all silver coverage. In the case when silver multilayer was deposited on the palladium surface, the layered silver transforms into a clustered structure slightly enriched with Pd atoms. A hybridization of the localized Pd 4d level and the silver sp-band produces virtual bound state at 2eV below the Fermi level. 

Fluorescent nanotubes of polyethyleneimine (PEI) and 3,4,9,10-perylenetetra-carboxylicdianhydride (PTCDA) have been prepared through the alternating deposition of polymers and small functional molecules that form covalent bonds (Figure 7.10) [ 120]. The nanotube synthesis starts with the deposition of P EI in the pores of an AAO membrane as the first layer. The PTCDA solutionis then used to bind to the PEI via covalent bonding (Figure 7.10). The electro-optical properties of the small molecule (PTCDA) are retained in the multilayer films of PEI/PTCDA. The prepared nanotubes retain their fluorescent properties for up to 10 months without... 

The low nonspecificity of PEG layers also was used to eliminate biomolecule binding to certain areas of an array. Kidambi et al. (2004) patterned an mPEG-carboxylate molecule onto polyelectrolyte multilayers to mask portions of the surface. The extremely low binding character of PEG provides advantages for creating patterned surfaces that other modifiers using aliphatic alkyl linkers do not provide. 

The results obtained with PE multilayers as well as DNA on top of the capacitive EIS sensor could verify their feasibility as transducer for a label-free detection of adsorption, binding, and interactions of charged macromolecules. Nevertheless, our experiments do not enable us to clearly distinguish between the contributions in the signal generation from each of the mechanisms discussed in sections 7.3 and 7.4. Probably, both basic mechanisms, namely, the intrinsic charge of molecules and the ion-concentration redistribution in the intermolecular spaces or in the multilayer, affect the sensor signal by superposition. 

Occupied molecular orbitals of the adsorbate with ionization potentials between 0 and hv- (p become visible. If one compares their binding energies with those in a UPS spectrum of a physisorbed multilayer of the same gas, one readily recognizes which of the molecular orbitals are involved in the chemisorption bond. For example, the adsorbate level in Fig. 3.19 has shifted a few eV with respect to its position indicated in the density of states picture (taken as the position in a physisorbed gas), indicating that the level is involved in the chemisorption bond. 

Dai J, Baker GL, Bruening ML (2006) Use of porous membranes modified with polyelectrolyte multilayers as substrates for protein arrays with low nonspecific binding. Anal Chem 78 135-140... 

A wide range of reversible adsorption kinetic rates was also found by TIR/FRAP for another protein, lysozyme, on a substrate with a different surface charge, alkylated silicon oxide.(61) It is possible that the wide range of rates results from a spectrum of surface binding site types and/or formation of multilayers of adsorbed protein. 

The first report of surface-immobilized dendrimers was in 1994 [54]. Subsequently, our research group showed that the amine-terminated PAMAM and PPl dendrimers could be attached to an activated mercaptoimdecanoic acid (MUA) self-assembled monolayer (SAM) via covalent amide linkages [55, 56]. Others developed alternative surface immobilization strategies involving metal com-plexation [10] and electrostatic binding [57]. These surface-confined dendrimer monolayers and multilayers have found use as chemical sensors, stationary phases in chromatography, and catalytic interfaces [41,56,58,59]. Additional applications for surface-confined dendrimers are inevitable, and are dependent only on the synthesis of new materials and the development of clever, new immobilization strategies. 

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