Specific chemical interactions

Finally, values of n must be obtained when specific ("chemical") interactions can occur. These are difficult to estimate a priori but reasonable approximations can often be made by choosing a value (Appendix C) for a chemically similar system. 

Equation (8.49) accounts only for endothermic mixing. It is not too surprising that we are thus led to associate exothermic values with more specifically chemical interactions between solvent and solute as opposed to the purely physical interactions we have been describing in this approximation. 

The two steps in the removal of a particle from the Hquid phase by the filter medium are the transport of the suspended particle to the surface of the medium and interaction with the surface to form a bond strong enough to withstand the hydraulic stresses imposed on it by the passage of water over the surface. The transport step is influenced by such physical factors as concentration of the suspension, medium particle size, medium particle-size distribution, temperature, flow rate, and flow time. These parameters have been considered in various empirical relationships that help predict filter performance based on physical factors only (8,9). Attention has also been placed on the interaction between the particles and the filter surface. The mechanisms postulated are based on adsorption (qv) or specific chemical interactions (10). 

Finally, a fourth motivation for exploring gas solubilities in ILs is that they can act as probes of the molecular interactions with the ILs. Information can be discerned on the importance of specific chemical interactions such as hydrogen bonding, as well as dipole-dipole, dipole-induced dipole, and dispersion forces. Of course, this information can be determined from the solubility of a series of carefully chosen liquids, as well. FLowever, gases tend to be of the smallest size, and therefore the simplest molecules with which to probe molecular interactions. 

Although it is difficult to predict exactly which solute molecules will form clathrate solutions in any given host lattice, the general principle is quite clear. All molecules which fit into the cavities will be able to stabilize the host lattice, unless they show a specific chemical interaction with the solvent molecules. HC1 (or the other hydrogen halides), for instance, does not form a clathrate with water, but rather the stoichiometric compounds HC1 H20,... 

It has been observed by Koleske et al. [76] that factors other than specific chemical interaction can influence adhesion measurements. They studied a film of mixed-chain-length fatty acid and found that the adhesion of the tip over the shorter chain was 20% larger than over the longer chain, despite the fact that both had the same CH3 terminating... 

The surface complexation approach is distinct from the Stern model in the primacy given the specific chemical interaction at the surface over electrostatic effects, and the assignment of the surface reaction to the sorption reactions themselves (Dzombak and Morel, 1990). 

The "classical" theory of nucleation concentrates primarily on calculating the nucleation free energy barrier, AG. Chemical interactions are included under the form of thermodynamic quantities, such as the surface tension. A link with chemistry is made by relating the surface tension to the solubility which provides a kinetic explanation of the Ostwald Step Rule and the often observed disequilibrium conditions in natural systems. Can the chemical model be complemented and expanded by considering specific chemical interactions (surface complex formation) of the components of the cluster with the surface ... 

In the o.s. reaction, the ion pair A+ - B is formed in a first step. The corresponding equilibrium constant can usually be obtained from simple electrostatic models. In this "ideal" case specific chemical interactions can be neglected and the rate constant of the E.T. step follows the theory of R.A. Marcus (see for example Marcus, 1975, or Cannon, 1980). In the i.s. reaction each of the three steps in reaction (9.2) may determine the reaction rates. The lability of the coordinated ligands at the... 

Stumm, W., C. P. Huang, and S. R. Jenkins (1970), "Specific Chemical Interaction Affecting the Stability of Dispersed Systems", Croat. Chem. Acta 42, 223-245. 

Although adsorption of many types of species could be considered, this discussion will focus on surface hydrolysis reactions, that is, adsorption of H+ and OH . Virtually all surface hydrolysis experiments are carried out in the presence of a "background electrolyte," many of which appear to exhibit weak specific chemical interactions (e.g., ion-pair formation) with the surface (10-12). While consideration of these interactions is essential to a complete understanding of the interfacial chemistry, the topic is a subject in itself, and will not be considered in detail here. Treatment of these interactions is readily incorporated within the framework that is presented here. 

Beyond the surface plane is a layer of ions attracted to the surface by specific chemical interactions. The locus of the center of these ions is known as the inner Helmholtz plane (IHP). The charge in this plane, which results from the specifically adsorbed ions is denoted by a2, and the electrostatic potential at the IHP by The species usually assigned to this plane include... 

Chemical force microscopy (CFM) [26] is a progression from the physicochemical based detection of LFM to specific chemical detection. CFM performs the nanoscale chemical analysis of the sample, through the measurement of forces related to specific chemical interaction between a chemically functionalised tip (e.g., with carbon nanotubes or oligonucleotides) and a surface that is chemically functionalised with complementary (or non-complementary) chemical species, e.g., complementary oligonucleotides. 

Specific chemical interactions affecting the stability of dispersed systems. Croatica Chem. Acta 42 223-245 Su, C. Puls, R.W (2001) Arsenate and arsenite removal by zerovalent iron Kinetics, Redox transformation, and implications for in situ groundwater remediation. Environ. Sd. 

The Stern theory is difficult to apply quantitatively because several of the parameters it introduces into the picture of the double layer cannot be evaluated experimentally. For example, the dielectric constant of the water is probably considerably less in the Stern layer than it would be in bulk because the electric field is exceptionally high in this region. This effect is called dielectric saturation and has been measured for macroscopic systems, but it is difficult to know what value of e6 applies in the Stern layer. The constant K is also difficult to estimate quantitatively, principally because of the specific chemical interaction energy . Some calculations have been carried out, however, in which the various parameters in Equation (97) were systematically varied to examine the effect of these variations on the double layer. The following generalizations are based on these calculations ... 

Specific chemical interaction between the chloride ion and metal ions present at the pore surfaces has also been considered as a possible factor contributing to retardation of HC1 diffusion. To evaluate this possibility, one portion of the coconut carbon was washed with acetic acid to reduce its ash content from 0.7% to 0.6%, and another portion with hydrochloric acid to reduce its ash content from 0.7% to 0.3%. The finite bath technique was used to study these two carbons in otherwise identical systems consisting of 10 -M NaCl, 1.5 grams carbon per liter, an initial pH of 3.50 (HC1), at a temperature of 25 °C. The corresponding isotherms show no significant difference between these carbons and the... 

Chromatography and electrophoresis are used to separate dissolved constituents in seawater. Chromatography is based on partition of the individual components between gas or liquid passed through a column and the liquid or solid stationary phase. This partition is based on solubilities of dissolved material in the different phases and specific chemical interactions with column components. Electrophoresis separates materials on the basis of electrical charge and size as solvents flow through the plate. 

Figure 13.4 The double sieve analogy for the editing mechanism of the isoleucyl-tRNA synthetase. The active site for the formation of the aminoacyl adenylate can exclude amino acids that are larger than isoleucine but not those that are smaller. On the other hand, a hydrolytic site that is just large enough to bind valine can exclude isoleucine while accepting valine and all the smaller amino acids. (In some enzymes, the hydrolytic site offers specific chemical interactions that enable it to bind isosteres of the correct amino acid as well as smaller amino acids.)...

Since the functional groups of the coupling agent that form specific chemical interactions with the metal are hydrophilic in nature (in all cases known to us), an... 

Of particular interest are the specific chemical interactions that occur between the coupling agent s active functionality and either the metal oxide or the polymeric top-coat. Recently, reflection angle infrared spectroscopy (RAIRS) [12, 13] and... 

Fundamental studies by reflection angle infrared spectroscopy of the bonding of EME coupling agents to metal oxides reveal a significant shift in the carbonyl absorbance band when the coupling agent is applied as a very thin layer on a metal oxide. The shift is reproducible and the extent varies with the type of oxide. These results were obtained both by use of copper mirrors and from CuzO powder coated with very thin layers of model compounds. The compounds were not removable by isopropanol, a solvent for the bulk compound. The thiol absorbances of thin layers of model compounds were also found to decrease in relative intensity with time. This illustrates that a specific chemical interaction has occurred. 

The mechanical properties of a fiber-matrix interphase composed of high concentrations of sizing, exclusive of the presence or absence of specific chemical interactions between the fiber surface and the surrounding matrix, have been demonstrated to be potentially responsible for the level of fiber-matrix adhesion. 

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