Salts, exclusion

FIG. 8 Salt exclusion as a function of surface charge in a cylindrical pore in equilibrium with a 0.1 molar electrolyte. The open circles are GCMC results for 1 1 RPM electrolyte in a pore ofR = 5d The circles with a centered cross are results for a 2 1 electrolyte in a pore of = 5d. The up-trian-gles are results for a 2 1 electrolyte in a pore ofR = lOd. The solid circles are results for a 1 1 SPM model with 0.3 solvent packing fraction in a pore of = 5d. The solid squares are the same results for a pore of R = Id. 

Using a dilute aqueous solution of the polymer in the absence of external salt, a molecular weight distribution was obtained, although it was perturbed by electrostatic exclusion. When CaCh was added, a salt exclusion corresponding to NaCl was formed, i.e., an exchange process occurred up to at least 40% of the stoichiometry, where in each case one Ca2+ expelled two Na+ (10). 

Earlier, we examined the movement of salts through a Martian regolith under a freezing regime (Fig. 5.18). Initially, each layer (0.5km) was separately equilibrated this initial step removed virtually all the Fe(II) as siderite, most of the Ca as calcite, and a lesser percent of Mg as hydromagnesite. In a second step, we froze the system from the top down, which led to salt exclusion, increasing salt concentrations with depth, and additional precipitation of calcite and hydromagnesite (Fig. 5.18). 

In papers on the Walden inversion, Ingold s group (Harvey et al., 1960) established that electrostatic forces do not contravene the normal stereochemistry of SN2 reactions. Even in the favorable case of negative nucleophile (azide) and positive substrate (sulfonium salt), exclusive inversion occurs. Obviously, the quantal forces of orbital symmetry and energy obliterate the coulombic factor here. 

Bonnet-Gonnet C, Leikin S, Chi S, Rau DC, Parsegian VA. Measurement of forces between hydroxypropylcellulose polymers temperamre favored assembly and salt exclusion. J. Phys. Chem. B 2001 105 1877-1886. 

Dithiolylium salts as well as l,3-dithiolylium-4-olates react with a variety of C-, N-, 0-, P-, and S-nucleophiles as a 6 t-electron system with a positively charged five-membered ring the reactions occur for the 1,3-dithiolylium salts exclusively at the 2-position while the 1,3-dithiolylium-... 

Most mechanistic thinking in the area of glycoside synthesis is shaped by a seminal paper by Lemieux et al, in which an array of solvent-separated and intimate ion pairs is invoked, in heroic defiance of Occam s razor . The key discovery was that, whereas tetraacetyl a-D-glucopyranosyl bromide in a mixture of phenol and pyridine gave the p-pyridinium salt exclusively, in anhydrous pyridine anomeric mixtures were produced, and addition of tetra-ethylammonium bromide gave exclusively the a-anomer (Figure 3.38). Similar... 

A single sulfonium ylide is beUeved to be formed as alkylation of oxathiane 3a gave the equatorial sulfonium salt exclusively [29]. Ylide conformation has been studied by X-ray, NMR, and computation [30]. All of these studies indicate that the preferred conformation of sulfur yUdes is one in which the filled orbital on the ylide carbon is orthogonal to the lone pair on sulfur. The barrier to rotation around the C-S bond of the semi-stabilized ylide, dimethylsulfonium fluorenide, has been found to be 42 1.0 kJmol [30]. This impHes that the ylide will adopt conformations 6a and 6b and that these will be in rapid equilibrium at room temperature. Of these two, conformation 6b will be favored as 6a suffers from... 

Some triplet photosensitizers also undergo electron transfer with iodo-nium and sulfonium salts. Manivannan et al. [104] have demonstrated that ketocoumarins sensitize photolysis of diphenyliodonium salts exclusively from their triplet states. An electron transfer mechanism was inferred from observation of a light absorbing transient assignable to the ketocoumarin radical cation, on laser flash photolysis of a ketocoumarin onium salt mixture in methanol. 

Keteniminium salt lb reacts with ( )-2-butene to give the /ran.Mctramethylcyclobutaniminium salt exclusively with d.r. (trans eis) >97 333a. Hydrolysis occurs with partial isomerization at the carbon a to the carbonyl group giving a transjeis mixture of 2,2,3,4-tetramethylcyclobu-... 

The Donnan salt exclusion parameter f expresses a property of polyelectrolyte solutions. It describes the bias when a salt is present in the bulk of the solution against the presence of mobile ions in the vicinity of the polyelectrolyte. In the case of the two phase system of a cross-linked ion exchange gel and an outer solution the exclusion is directly measurable experimentally. If the concentration of the salt in the external solution is CEex and that in the vicinity of the polyelectrolyte is CEnear, then the limiting value of Tfor a concentration Cpoiy of the polyelectrolyte tending to zero is formally defined by ... 

Values computed by displacement, on the assumption that the water in the clay pack had the same composition as the supernatant solution, were somewhat higher, by 0.04 to 0.08 equiv/kg, than by the modified isotope dilution procedure. As we described earlier, the solution displaced from the clay pack and associated water was also analyzed for chloride, and it was found the concentration of anion in the pack water was significantly less than in the supernatant solution, i.e., there appeared to be some salt exclusion. Computation of cation-exchange capacity by subtracting from total... 

In addition to a sample peak, some anomalous peaks often appear in chromatograms. when multicomponent eluent is used [ref. 71, 72]. Such an induced peak can be observed when polyelectrolyte is chromatographed using a simple electrolyte solution as eluent the first peak corresponds to polyelectrolyte and the second to an induced peak which has the elution volume exactly the same as that of the eluent salt [ref. 33, 45-48, 73-76]. This effect of polyelectrolytes in exclusion chromatography has been explained in terms of Donnan salt exclusion established on the gel [ref. 33, 45-48, 73-76] a polyelectrolyte is barred from the gel interior and thus promote the diffusion of the penetrable eluent coion into the inner volume of the gel, the gel matrix acting as a semipermeable membrane. The eluent coion thus excluded from the polyelectrolyte zone produces an induced peak. It has been reported that the area of the induced peak allows to calculate the Donnan salt exclusion parameter [ref. 33, 74] or the osmotic coefficient [ref. 46-48, 76] of the polyelectrolyte. 

However, these interpretations in terms of the Donnan salt exclusion effect seem to be still open to discussion, because the difference in elution volume between small inorganic ions, such as chloride and nitrate ions, on tightly crosslinked hydrophilic gels cannot be attributed to their size differences, and furthermore, the eluent salt peak can also be produced by the injection of the sample ion which elutes slower than the eluent coion [ref. 16, 23, 26]. 

Salicyloylguanidines 19, 459 Salts, exclusive of — 19, 739 —, fused, reactions in — 18, 942 —, inner s. Betaines, Mercury-carboxylic acid inner salts —, organic... 

The successful applications of GPC to aqueous polymer solutions are few in number. Salt-exclusion effects have been examined by Rinaudo and co-workers, who found that the elution peak was dependent on sample concentration and ionic strength for polyelectrolytes. The universal calibration was valid as soon as the ionic strength exceeded 5 x 10 molar, when screening of electrostatic repulsions was achieved. Similar observations were made for aqueous polyacrylamide. The dependence of elution volume on ionic strength has been used to increase resolution in low molar mass charged polymra and it was noted that non ionic species were unaffected by ionic strength. Water soluble polymers have also been studied by Barth et aL ... 

Walker R R, Sedgley M, Belsing M A, Douglas T J 1984 Anatomy, ultrastructure and assimilate concentrations of roots of Citrus genotypes differing in ability for salt exclusion. J Exp Bot 35 1481-1494... 

Nonrandomness parameter (in model of Nagvekar and Danner) Nonrandomness parameter (in model of Nagvekar and Danner) Dimensionless parameter Salt-exclusion parameter... 

V. Vlachy and A. D. J. Haymet, /. Electroanal. Chem., 283, 77 (1990). Salt Exclusion from Charged and Uncharged Micropores. 

Note that the coefficient of in Equation (101), i.e., thejth virial coefficient, is exactly equal to minus two times the coefficient of in Equation (100). Thus, the virial coefficients may be found either directly from tid or from the salt exclusion. 

The synthesis, structure, and physical and chemical properties of various hydrazinium salts have been documented [6]. Several processes have been developed for the synthesis of these salts but, typically, the method of preparation varies with the type of salt made. Furthermore, acids hke H2SO4 and HF form N2He salts exclusively when they react with N2H4 H2O because of their low solubility. 

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