Pseudo-dilution effect

The principle of oxidation of bis-cysteine peptides on resin consists of deprotection and oxidation of a cysteine pair in a single step or in two separate steps to form the disulfide bond while the peptide chain remains attached to the solid support. The strategy is especially effective for the formation of intramolecular disulfides since the solid support simulates high dilution via the pseudo-dilution effect, thus, largely preventing intermolecular reactions. 163 98 10° ... 

It should be mentioned, however, that high dilution is still mandatory in order to obtain high yields [15, 16], which can be achieved either by low feeding rates of the substrate into the solution containing the catalyst or by exploiting the pseudo-dilution effect of polymer bound Pd° [41]. This experimental requirement shows that the palladium center itself does not shape the substrate but just stabilizes the reactive eonformation once it is adopted (Scheme 9-21). Therefore the observed template effect must be largely attributed to electrostatic attraction and/or favorable ion pairing properties of the intermediates. 

This reaction is however retarded by the presence of inert solvents due to dilution effects. The presence of ketones has also been shown to retard the reactions either due to pseudo-SchilTs-base or ketimine formation. 

Although the odour of the pseudo-ionone does not appear to render it of great importance for its direct use in perfumery, it is capable of serving as raw material lor the production of perfumes, the pseudo-ionone being converted by the action of dilute acids into an isomeric ketone, which I term lonone, and which has most valuable properties for perfumery purposes. This conversion may be effected, for example, by heating for several hours in an oil-bath 20 parts of pseudo-ionone with 100 parts of water, 2-5 parts of sulphuric acid, and 100 parts of glycerine, to the boiling-point of the mixture. 

A procedure is presented for correlating the effect of non-volatile salts on the vapor-liquid equilibrium properties of binary solvents. The procedure is based on estimating the influence of salt concentration on the infinite dilution activity coefficients of both components in a pseudo-binary solution. The procedure is tested on experimental data for five different salts in methanol-water solutions. With this technique and Wilson parameters determined from the infinite dilution activity coefficients, precise estimates of bubble point temperatures and vapor phase compositions may be obtained over a range of salt and solvent compositions. 

Control of an evaporator requires more than proper instrumentation. Operator logs should reflect changes in basic characteristics, as by use of pseudo heat-transfer coefficients, which can detect obstructions to heat flow, hence to capacity. These are merely the ratio of any convenient measure of heat flow to the temperature drop across each effect. Dilution by wash and seal water should be monitored since it absorbs evaporative capacity. Detailed tests, routine measurements, and operating problems are covered more fully in Testing Procedure for Evaporators (loc. cit.) and by Standiford [Chem. Eng. Prog., 58(11), 80 (1962)]. 

The shapes of the d (r) curves in flg. 5.24 have a number of consequences that are important in the interpretation of experiments. If, for a given polymer, is measured as a function of the adsorbed amount F, there should (in dilute solutions) be no effect of the molar mass Af. However, in the steep part of the d (r) curve, which is In the (pseudo)plateau region of the adsorption isotherm. F... 

Even within a monolayer there is the possibility of in-plane intermolecular interaction [12]. Adjacent 7t-systems can interact to form a 2D band or a pseudo-ID band structure within the layer, resulting in dispersion of the individual molecular orbital levels. It should be possible to isolate single-molecule effects by diluting the rectifier material in an inert matrix, e.g., a fatty acid. The current should then scale with the area fraction of active molecules within the matrix, if it is assumed that the rectifying current is the dominant conduction mechanism. 

In comparison, the effect of the alkyl chain length on the cation on the solubility of solutes capable to exhibit n- or jt-dispersion interactions compares well to the trends found in the study on the activity coefficient at pseudo-infinite dilution With respect to the anion effect on the solubility of either hexene [43] or alcohols [54], the trends observed in the solubility data match that from the y °° study within this narrow set of examples. 

When very dilute solutions of benzophcnonc in ether (pseudo first-order concentrations) react with solutions of /-butyl- and isopropylniagnc-sium halide of increasing concentrations, a rate-levelling effect is observed at 0.1-0.2 M 26 The use of benzophenone in excess leads to extremely high reaction rates. These phettomena are of course remini.scent of the complex-type kinetics of acetone 42. As will be described below, /-butyl- and isopropylmagnesium halides react with benzophenone by an ET-radical mechanism (ET is electron transfer) and acetone by a concerted mechanism. It therefore seems strange to have complex effects for both. 

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