Adsorption solvents, effect

Donor strengths, taken from ref. 207b, based upon the solvent effect on the symmetric stretching frequency of the soft Lewis acid HgBr2. Gutmann s donor number taken from ref 207b, based upon AHr for the process of coordination of an isolated solvent molecule to the moderately hard SbCL molecule in dichioroethane. ° Bulk donor number calculated as described in ref 209 from the solvent effect on the adsorption spectrum of VO(acac)2. Taken from ref 58, based on the NMR chemical shift of triethylphosphine oxide in the respective pure solvent. Taken from ref 61, based on the solvatochromic shift of a pyridinium-A-phenoxide betaine dye. 

The molecular modelling approach, taking into account the pyruvate—cinchona alkaloid interaction and the steric constraints imposed by the adsorption on the platinum surface, leads to a reasonable explanation for the enantio-differentiation of this system. Although the prediction of the complex formed between the methyl pyruvate and the cinchona modifiers have been made for an ideal case (solvent effects and a quantum description of the interaction with the platinum surface atoms were not considered), this approach proved to be very helpful in the search of new modifiers. The search strategy, which included a systematic reduction of the cinchona alkaloid structure to the essential functional parts and validation of the steric constraints imposed to the interaction complex between modifier and methyl pyruvate by means of molecular modelling, indicated that simple chiral aminoalcohols should be promising substitutes for cinchona alkaloid modifiers. Using the Sharpless symmetric dihydroxylation as a key step, a series of enantiomerically pure 2-hydroxy-2-aryl-ethylamines... 

Electroneutral substances that are less polar than the solvent and also those that exhibit a tendency to interact chemically with the electrode surface, e.g. substances containing sulphur (thiourea, etc.), are adsorbed on the electrode. During adsorption, solvent molecules in the compact layer are replaced by molecules of the adsorbed substance, called surface-active substance (surfactant).t The effect of adsorption on the individual electrocapillary terms can best be expressed in terms of the difference of these quantities for the original (base) electrolyte and for the same electrolyte in the presence of surfactants. Figure 4.7 schematically depicts this dependence for the interfacial tension, surface electrode charge and differential capacity and also the dependence of the surface excess on the potential. It can be seen that, at sufficiently positive or negative potentials, the surfactant is completely desorbed from the electrode. The strong electric field leads to replacement of the less polar particles of the surface-active substance by polar solvent molecules. The desorption potentials are characterized by sharp peaks on the differential capacity curves. 

Another example of the solvent effect in interfacial processes has come from the investigation of the adsorption of acetone on the mercury... 

Perhaps, unsurprisingly, the effects of polymer matrix on the reaction rate are probably at least as complex as solvent effects in solution-phase reactions, and broad generalizations about the characteristics of any given support in a series of different reactions are inappropriate. Reaction rates on supports depend on solvent swelling, selective adsorption, hydrogen bonding, hydrophobicity, and polarity. No single polymer support is best for all reactions. 

Retention on these supports is adaquetely described by the adsorption displacement model. Nevertheless, the adsorption sites are delocalized due to the flexible moiety of the ligand, and secondary solvent effects play a significant role. The cyano phase behaves much like a deactivated silica toward nonpolar and moderately polar solutes and solvents. Cyano propyl columns appear to have basic tendencies in chloroform and acidic tendencies in methyl tertiobutyl ether (MTBE)... 

Keywords Solution properties Conformational analysis Theta condition Excluded volume Good and poor solvent Thermodynamic theories Preferential adsorption Cosolvent effect... 

The wide use of these bonded phases has also stimulated a large effort to explain their surface structure and how they work. The so-called solvophobic theory of RPLC was elaborated originally by Horvath and Me-lander.16 Their model assumes that the nonpolar bonded phase acts more like a solid than a liquid and attracts analytes by adsorption. The binding of an analyte to the surface reduces the surface area of the analyte exposed to the mobile phase, and it can be considered to be sorbed partially because of this solvent effect that is, the analyte is sorbed because it, is solvophobic. Sorption increases as the surface tension of the mobile phase increases. 

Abstract. Adsorption of antioxidants (vitamins C and E) from aqueous and ethanol solutions on unmodified and partially hydrophobized nanosilica A-200 was studied using UV spectroscopy and quantum chemical methods with consideration for the solvent effects. Antioxidant power of silica nanocomposites with immobilized vitamins was evaluated by measuring the total polyphenolic index following the Folin-Ciocalteu method. It has been shown that immobilization of vitamins on silica surface leads to their stabilization. Being released from the carrier molecules of vitamins do not lose their antioxidant properties... 

R. M. Narske, K. J. Klabunde, and S. Fultz, Solvent effects on the heterogeneous adsorption and reactions of (2-chloroethyl) ethyl sulfide on nanocrystalline magnesium oxide, Langmuir 18, 4819-4825 (2002). 

Br-PADAP showed a significant adsorption at the interface of heptane-water under HSS conditions (5000 rpm). On the other hand, the adsorptivity at the toluene-water interface was very low. Hpan did not adsorb at the toluene-water interface at all. The adsorption constants of 5-Br-PADAP (HL) at the heptane-water and toluene-water interfaces were obtained as log K A, (cm3) = 1.64 and log KAi (cm3) =—0.367 [21]. The solvent effect on the adsorptivity of the ligand affected directly the interfacial reaction rate. In the heptane system, the Ni(II) complex was not extracted into the heptane phase. On the other hand, in toluene system, the complex was extracted very slowly. Recently, the extraction rates of Ni(II) and Zn(II) with 5-Br-PADAP were studied by means of CLM [67]. Based on the reaction mechanism shown in Scheme I, the initial formation rate was represented by... 

This publication arranges the published papers on adsorption of polymers with special regard to experiment and theory. A summary of all investigated systems is given. The experimental methods are outlined and the amounts adsorbed are discussed as a function of the system and experimental parameters (polymer, adsorbent, solvent, molecular, concentration, time, weight and temperature). Calculated and experimental amounts of saturation, the number of contact points per molecule adsorbed, the thickness of the adsorbed layer, the adsorption isotherms, the heats of adsorption, the effects of desorption are compared. Assumptions on the structur of the adsorbed layer and the mechanism of polymer adsorption are made and discussed. 

Solvent Effects on Adsorption at the Polymer/ Solid Interface... 

The carrier liquid can also influence the FFF results as it can alter solute-solute or solute-wall interactions as well as the extension of a polymer in solution [266]. This in turn influences the diffusion and retention of the sample. Limited efforts have been made to describe these phenomena so that their influence still cannot be quantitatively treated. The practical importance of solvent effects becomes clear for the example of proteins which can be switched from positive to negative polyelectrolytes by pH variation. In any case, the pH should be chosen outside the range of the isoelectric point to avoid adsorption problems. 

Huebner and Venkataraman69 demonstrated that starch can adsorb iodine from nonaqueous and not necessarily polar solvents, as shown in Table IV. Iodine adsorption by starch in aqueous ethanol increases as the ethanol content increases. Again, the solvent effect depends on the origin of the starch (Table II). The varying effects observed using benzene, ethanol, and chloroform may also be ascribed to the use of starches of different origin... 

T8.n Adsorption, Active Species and Oxidation Mechanisms 741 Table 18.13 Solvent effects in the oxidation of n-hexane on TS-1. ... 

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