Multi site adsorption

The common methods for the multi-site adsorption of DNA on carbonaceous-based material can be classified into physical (dry and wet) adsorption and electrostatic adsorption. 

Multi-site adsorption of cadmium on goethite. J. Coll. Int. Sci. 183 515-527... 

Koretsky C. M., Sveijensky D. A., and Sahai N. (1998) A model of surface site types on oxide and sihcate minerals based on crystal chemistry imphcations for site types and densities, multi-site adsorption, surface infrared spectroscopy, and dissolution kinetics. Am. J. Sci. 298(5), 349-438. 

Due to this were proposed models of multi-site adsorption or multireaction. Their substance is in the differentiation of adsorption sites on the mineral surface in correlation with the rate of their exchange. 

We start this book with a chapter (Chapter 2) on the fundamentals of pure component equilibria. Results of this chapter are mainly applicable to ideal solids or surfaces, and rarely applied to real solids. Langmuir equation is the most celebrated equation, and therefore is the cornerstone of all theories of adsorption and is dealt with first. To generalise the fundamental theory for ideal solids, the Gibbs approach is introduced, and from which many fundamental isotherm equations, such as Volmer, Fowler-Guggenheim, Hill-de Boer, Jura-Harkins can be derived. A recent equation introduced by Nitta and co-workers is presented to allow for the multi-site adsorption. We finally close this chapter by presenting the vacancy solution theory of Danner and co-workers. The results of Chapter 2 are used as a basis for the... 

The theory of Nitta et al. (1984) assumes a localised monolayer adsorption on surface with an allowance for multi-site adsorption. This is an extension of the Langmuir isotherm for localised monolayer adsorption. Nitta et al. s theory is based on the statistical thermodynamics, and its derivation is given briefly below. 

The last section deals with the multi-site adsorption model of Nitta and his coworkers. In such model each adsorbate molecule is adsorbed onto n active sites and the adsorption is localised. For surfaces where mobile adsorption is possible, the approach using the scaled particle theory can be used in the statistical thermodynamics to obtain the required adsorption isotherm equation. This has been addressed by Nitta and co-workers and what to follow is the brief account of then-theory (Nitta et al., 1991). 

Multi-site adsorption model.Upon the assumption that there are two sites with different natures, in the course of TPD, and they only take place adsorption and desorption, it can be imagined that following adsorption-desorption process can occur on the surface (Fig. 7.17). The adsorption rate equation for each adsorption site is ... 

Adsorption of the EBF A) follows a classical multi-site adsorption behavior ... 

Additional applications of the transfer matrix method to adsorption and desorption kinetics deal with other molecules on low index metal surfaces [40-46], multilayers [47-49], multi-site stepped surfaces [50], and co-adsorbates [51-55]. A similar approach has been used to study electrochemical systems. 

In this review article we have tried to show that an analytical approach to the thermodynamics and the kinetics of adsorbates is not restricted to simple systems but can deal with rather complicated situations in a systematic approach, such as multi-site and multi-component systems with or without precursor-mediated adsorption and surface reconstruction, including multi-layers/subsurface species. This approach automatically ensures that such fundamental principles as detailed balance are implemented properly. 

Summarizing, it is clear that the indirect interaction between adatoms has a significant effect on the chemisorption properties of the system. Most noticeably, the chemisorption energy has a damped, oscillatory dependence on the adatom separation, as first quantified in (8.1) by Grimley. Thus, multi-atom adsorption occurs preferentially with the atoms at certain sites relative to one another. 

Electrochemical detection of successful DNA hybridization events should be also considered. Although it is based mostly on external electrochemical markers, such as electroactive indicators or enzymes, the exploitation of the intrinsic DNA oxidation signal requires a multi-site attachment such as adsorption as the immobihzation technique. 

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. 

Moreover, the unique adsorption properties of GEC allowed the very sensitive electrochemical detection of DNA based on its intrinsic oxidation signal that was shown to be strongly dependent of the multi-site attachment of DNA and the proximity of G residues to GEC [100]. The thick layer of DNA adsorbed on GEC was more accessible for hybridization than those in nylon membranes obtained with genosensors based on nylon/GEC with a changeable membrane [99,101,102]. Allhough GEC has a rough surface, it is impermeable, while nylon is more porous and permeable. DNA assays made on an impermeable support are less complex from a theoretical standpoint [7] the kinetics of the interactions are not compUcated by the diffusion of solvent and solutes into and out of pores or by multiple interactions that can occur once the DNA has entered a pore. This explained the lower hybridization time, the low nonspecific adsorplion and the low quantity of DNA adsorbed onto GEC compared to nylon membranes. 

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... 

Narkiewicz-Michalek, J. Electrostatic theory of ion-pair chromatography multi-site occupancy model for modifier and solute adsorption. Chmmatographia 1993, 35, 527-538. 

Recently the new SRT approach has been generalized further to take into account the energetic heterogeneity of the actual adsorption systems and the possible role of the interactions between the adsorbed molecules. [10-20] Most recently, the authors have shown, that the SRT approach can be successfully applied to describe the multi-site-occupancy adsorption of molecules which do not dissociate after being adsorbed. [14] Compact simple analytical expressions were developed, and next used successfully to correlate experimental data for adsorption/desorption kinetics in various gas/solid systems. The purpose of this presentation is to show, that the new SRT approach can be also applied to represent the kinetics of dissociative gas adsorption on solids. That kinetics is of a crucial importance in a variety of catalytic reactions occurring on solid surfaces. 

Panczyk T. and Rudzinsld W., Kinetics of Multi-Site-Occupancy Adsorption on Heterogeneous Solid Sur ces A Statistical Rate Theory Approach, J. Phys. Chem., 106(2002) pp.7846-7851. 

It may be noted that the potentials used in the simulations are approximations, and that the selected equation of state for N2 is only applicable over restricted ranges of pressure and temperature. Like many other authors we have used these simple approximations to reveal broad patterns of behaviour. However, we are currently exploring more realistic models (e.g., multi-site LJ potentials) to explore the detail of adsorption in nanotubes. 

Quantum chemistry approaches to zeolites are complemented by an active research community that uses classical force-field methods to study molecular adsorption and diffusion in zeolites and similar materials. This topic was comprehensively reviewed by Keil, Krishna, and Coppens in 2000.262 For more recent examples of activity in this area, see References 263-270. Examples of impressive agreement between adsorption isotherms and molecular dilfusivities predicted with calculations of this type and experimental data are available.271,272 There appear to be many future opportunities for linking the detailed understanding of multi-component adsorption and diffusion that is now emerging from this area with detailed quantum chemistry approaches to reactivity at active sites inside zeolites. 

Siegel, M. D., V. S. Tripathi, M. G. Rao, and D. B. Ward. 1992. Development and validation of a multi-site model for adsorption of metals by mixtures of minerals 1 Overview and preliminary results. Proc. 7th inti. symp. water rock interaction, ed Y. K. Kharaka and A. S. Maest, I, pp. 63-67. Rotterdam A. A. Balkema. 

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