Electrostatic effects, measurements

The reaction between Fe(IlI) and Sn(Il) in dilute perchloric acid in the presence of chloride ions is first-order in Fe(lll) concentration . The order is maintained when bromide or iodide is present. The kinetic data seem to point to a fourth-order dependence on chloride ion. A minimum of three Cl ions in the activated complex seems necessary for the reaction to proceed at a measurable rate. Bromide and iodide show third-order dependences. The reaction is retarded by Sn(II) (first-order dependence) due to removal of halide ions from solution by complex formation. Estimates are given for the formation constants of the monochloro and monobromo Sn(II) complexes. In terms of catalytic power 1 > Br > Cl and this is also the order of decreasing ease of oxidation of the halide ion by Fe(IlI). However, the state of complexing of Sn(ll)and Fe(III)is given by Cl > Br > I". Apparently, electrostatic effects are not effective in deciding the rate. For the case of chloride ions, the chief activated complex is likely to have the composition (FeSnC ). The kinetic data cannot resolve the way in which the Cl ions are distributed between Fe(IlI) and Sn(ll). 

If only electrostatic effects are responsible for polymer adsorption and flocculation, our results can be explained according to the same scheme as that used by Furusawa et Al.(20) to interprete the destabilization of negatively charged latex by a cationic polymer. In a first step, the adsorption of the polymer leads to the neutralization of the particles which are no more stabilized by electrostatic repulsions and there is flocculation (we have not studied this step since in our experiments polymer was always in large excess with respect to Al(0H)3). In a second step the adsorption inverses the charge and (we have indeed measured by... 

Fitzgerald et al. (1984) measured pressure fluctuations in an atmospheric fluidized bed combustor and a quarter-scale cold model. The full set of scaling parameters was matched between the beds. The autocorrelation function of the pressure fluctuations was similar for the two beds but not within the 95% confidence levels they had anticipated. The amplitude of the autocorrelation function for the hot combustor was significantly lower than that for the cold model. Also, the experimentally determined time-scaling factor differed from the theoretical value by 24%. They suggested that the differences could be due to electrostatic effects. Particle sphericity and size distribution were not discussed failure to match these could also have influenced the hydrodynamic similarity of the two beds. Bed pressure fluctuations were measured using a single pressure point which, as discussed previously, may not accurately represent the local hydrodynamics within the bed. Similar results were... 

Electrostatics in Non-Aqueous Media. A popular misconception in studies of non-aqueous dispersions concerns electrostatic effects. Because these are more difficult to measure than in aqueous media, there has been a general tendency to ignore them completely. However, the few investigators who have measured zeta-potentials or electrodeposition with these systems have become convinced of their importance. With the advent of modern commercial instrumentation for zeta-potentials in non-aqueous media it is to hoped that these effects will be measured rather than ignored. 

X-ray crystallography, docking modes can be validated by various NMR techniques NOEs may be observed between the ligand and the receptor protein by heteronuclear-filtered NOE spectroscopy [51], chemical shift changes of protein resonances upon binding can be analyzed by simulation of shifts caused by ring currents and electrostatic effects [52], and saturation transfer difference measurements indicate which part of the ligand is in direct contact with the protein [52]. 

The calculation of the energy for the interaction between the solvent and solute is more complicated. Formally, the free energy for the process, AC/ini, is composed of two chemical parts and an essentially entropic term. The chemical terms are associated with van der Waals interactions AGvdw> electrostatic effects, AG, between solute and solvent. The entropic term measures the free volume i.e., the volume a molecule explores before encountering another, which is assumed to be proportional to the molar volume of the solvent. Thus, the free energy change associated with solute-solvent interactions at temperature T is given by... 

The activity coefficient, y, is a measure of the change in free energy of a component at fixed concentration x in a mixture due to nonideal behavior. In this case, nonideality is due to electrostatic effects. The general expression for free energy of a componenl including this effeci is... 

Rietra et al. (2001) measured the simultaneous adsorption of phosphate and calcium on goethite over the pH range 4-11 and modelled the data with the CD-MU-SIC model. They concluded that the observed adsorption took place in response to electrostatic effects and that ternary adsorption was not involved. 

Developments in the study of carbocations in superacid media over the past 30 years have been reviewed.1 The thermodynamics [AG(g)] of the reaction R+(g) + Rref OH(g) -> ROH(g) + R+ref(g) involving Rref = f-butyl and 21 R+ has been studied by high-level computation.2 A plot of AG(g) versus AG(solution) shows an excellent correlation, except for phenyl-substituted R+, which form a separate correlation family. The magnitude of the most positive surface electrostatic potential was proposed as an effective measure of the stability of gas-phase carbocations, with results presented for a number of structurally diverse cations.3 The electrostatic potential directly... 

In conclusion, extensive work on solvent properties has revealed that simple physical properties, such as the dielectric constant or dipole moment, are inadequate measures for solvent polarity (which can correlate well with the influence of solvents on thermodynamic and kinetic reaction parameters in them). Better solvent parameters, which correlate well with the impact of the solvent chosen on electrochemical and chemical reactions, are donor and acceptor numbers or parameters based on solvatochromic effects, because these reflect not only pure electrostatic effects but rather the entire electronic properties of a solvent. 

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