Adsorption multi point

The unique practical properties of adsorption have promoted its extensive use in genetic analysis. The disadvantages of adsorption with respect to covalent immobihzation are mainly that (1) nucleic acids may be readily desorbed from the substrate, and (2) base moieties may be unavailable for hybridization if they are bonded to the substrate in multiple sites [34]. However, the electrochemical detection strategy based on the intrinsic oxidation of DNA requires the DNA to be adsorbed in close contact with the electrochemical substrate by multi-point attachment. This multi-site attachment of DNA can be thus detrimental for its hybridization but is crucial for the detection based on its oxidation signals. 

Polymer Adsorption. A review of the theory and measurement of polymer adsorption points out succinctly the distinquishing features of the behavior of macromolecules at solid - liquid interfaces (118). Polymer adsoiption and desorption kinetics are more complex than those of small molecules, mainly because of the lower diffusion rates of polymer chains in solution and the "rearrangement" of adsorbed chains on a solid surface, characterized by slowly formed, multi-point attachments. The latter point is one which is of special interest in protein adsoiption from aqueous solutions. In the case of proteins, initial adsoiption kinetics may be quite rapid. However, the slow rearrangement step may be much more important in terms of the function of the adsorbed layer in natural processes, such as thrombogenesis or biocorrosion / biofouling caused by cell adhesion. 

D-3363 Surface Area of Catalysts Multi-point volumetric (BET) surface area by nitrogen adsorption ... 

The specific surface area (ssa) of the solids (m g ) obtained after hydrolysis and drying at various temperatures was measured routinely by multi-point BET method at 77K by N2 adsorption in a Fisons Sorptomatic 1900 system. From these isotherms the BET ssa s were determined and the corresponding pore size distribution was also found. Typical results including the adsorption-desorption isotherms as well as the corresponding pore size distributions are shown in Fig.2... 

Supports and Catalysts. The catalyst supports used in this work are described in Table I. The surface areas, except for the sillcalite, were measured by the multi-point BET method. The surface area for the sillcalite was obtained from the manufacturer. Silicalite is an essentially aluminum-free pentasil zeolite (14) manufactured by Union Carbide. The chlorine contents of the supports were determined by neutron activation analysis, and sulfur contents were obtained with a Leco sulfur analyser. Sulfur and chlorine contents were measured since these elements may influence subsequent hydrogen adsorption on the supported platinum catalysts (15). 

BET surface areas were measured using a multi-point Coulter SA 3100 instrument with data collected over the P/Po range of0.02-0.2. Adsorption of N2 at 77 K was carried out after outgassing the samples at 573 K. BJH pore distributions were determined using 45 data points over a full adsorption desorption isotherm. 

Figure 3.6 Single-versus multi-point interacl ion. Both mechanisms of adsorption have been determined in peptide ligand affinity chromatography...

In order to understand HDS reactions, it is important to define the ways in which thiophenes are bonded to metal centers on catalytic surfaces. A number of modes in which T interacts with surfaces have been proposed, the most important ones being the one-point adsorption , that is, a strong interaction between the S atom and a vacancy on the surface, and the multi-point adsorption involving the S atom plus one or both of the C=C bonds in a delocalized rr-bonding. While it is difficult to experimentally obtain detailed information on the bonding of thiophenes to surface sites, several coordination modes of thiophenes have been authenticated in metal complexes (Figure 2). 

This effect can be explained with a reversible adsorption of resin molecules to the freshly provided surfaces of silica particles produced by shearing down the cluster structure of the N20 network. The re-formation of the netwoik requires at least a partial desorption of the resin molecules which is a slow and time-consuming process due to the multi-point interaction of the resin chains with the silica surface [12]. 

Figure 2.14. Multi-point adsorption of heptane on a metal surface. Surface ensemble requirement for the hydrogenolysis reaction.

In the work mentioned previously, Liauw and co-workers also examined the adsorption of acrylic, linoleic, linolenic and oleic, acids from organic solution onto a magnesium hydroxide filler [8]. Salt formation was observed for all the acids. All the unsaturated long chain acids gave lower apparent mono-layer levels than stearic acid, which was thought to be due to steric effects and even multi-point adsorption through the unsaturation. 

From the point of view of solute interaction with the structure of the surface, it is now very complex indeed. In contrast to the less polar or dispersive solvents, the character of the interactive surface will be modified dramatically as the concentration of the polar solvent ranges from 0 to l%w/v. However, above l%w/v, the surface will be modified more subtly, allowing a more controlled adjustment of the interactive nature of the surface It would appear that multi-layer adsorption would also be feasible. For example, the second layer of ethyl acetate might have an absorbed layer of the dispersive solvent n-heptane on it. However, any subsequent solvent layers that may be generated will be situated further and further from the silica surface and are likely to be very weakly held and sparse in nature. Under such circumstances their presence, if in fact real, may have little impact on solute retention. 

Flowever, the focus of the major part of the chapters lies on the couphng chemistry used for DNA immobilization. Successful immobihzation techniques for DNA appear to either involve a multi-site attachment of DNA (preferentially by electrochemical and/or physical adsorption) or a single-point attachment of DNA (mainly by surface activation and covalent immobihzation or (strept)avidin-biotin linkage). Immobilization methods described here comprise physical or electrochemical adsorption, cross-linking or entrapment in polymeric films, (strept)avidin-biotin complexation, a surface activation via self-assembled monolayers using thiol linker chemistry or silanization procedures, and finally covalent coupling strategies. 

The most successful immobilization techniques for DNA or oligonucleotides appear to be those involving multi-site attachment—either electrochemical or physical adsorption—or single-point attachment— mainly covalent immobilization or strept(avidin)/biotin linkage [26]. As an example, single-point covalent immobilization can be performed on... 

The reason for initially decreasing sticking probability is a dynamical process which had been proposed before [45] but whose efficiency had been grossly underestimated dynamical steering. This process can only be understood if one takes into account the multi-dimensionality of the PES. The PES of H2/Pd(l 00) shows purely attractive paths towards dissociative adsorption, but the majority of reaction paths for different molecular orientations and impact points exhibits energetic barriers hindering the dissociation. 

The Frumkin epoch in electrochemistry [i-iii] commemorates the interplay of electrochemical kinetics and equilibrium interfacial phenomena. The most famous findings are the - Frumkin adsorption isotherm (1925) Frumkin s slow discharge theory (1933, see also - Frumkin correction), the rotating ring disk electrode (1959), and various aspects of surface thermodynamics related to the notion of the point of zero charge. His contributions to the theory of polarographic maxima, kinetics of multi-step electrode reactions, and corrosion science are also well-known. An important feature of the Frumkin school was the development of numerous original experimental techniques for certain problems. The Frumkin school also pioneered the experimental style of ultra-pure conditions in electrochemical experiments [i]. A list of publications of Frumkin until 1965 is available in [iv], and later publications are listed in [ii]. 

The type II isotherm is associated with solids with no apparent porosity or macropores (pore size > 50 nm). The adsorption phenomenon involved is interpreted in terms of single-layer adsorption up to an inversion point B, followed by a multi-layer type adsorption. The type IV isotherm is characteristic of solids with mesopores (2 nm < pore size < 50 nm). It has a hysteresis loop reflecting a capillary condensation type phenomenon. A phase transition occurs during which, under the eflcct of interactions with the surface of the solid, the gas phase abruptly condenses in the pore, accompanied by the formation of a meniscus at the liquid-gas interface. Modelling of this phenomenon, in the form of semi-empirical equations (BJH, Kelvin), can be used to ascertain the pore size distribution (cf. Paragr. 1.1.3.2). 

---