Solvate-separated

From a thermodynamic perspective, the solvation of ionic species (see Equations 10.6 and 10.7), such as crown-ether complexes, NO3, and SO 4, in the ILs, should be much more favored thermodynamically than those of conventional solvent extractions (Equations 10.1 and 10.2). This is one of the key advantages of using ILs in separations involving ionic species. In this case, cationic crown-ether complexes and their counter anions are not expected to form ion pairs, but to be solvated separately by ionic species from the ILs. Therefore, the extraction process using crown ethers in ILs may not be an ion-pair extraction process. 

For formation of resin 3, the resin is washed in NMP (20ml/g of resin), filtered, and left solvated. Separately, tin(II) chloride dihydrate (approximately 40 equivalents with respect to resin-bound nitro groups) is dissolved in NMP with vigorous stirring, then the solution is added to the resin and mixed by nitrogen bubbling for 12 h at room temperature. The resin is filtered, washed, and left solvated prior to the next synthetic step. 

For reduction of resin 8, concerns about the possibility of traces of tin by-products contaminating subsequent assays led to the adoption of a different reduction procedure for library production.15 The tagged resins 8 are combined into one pool in a large peptide synthesis vessel, washed with methanol, filtered, and the resin left solvated. Separately, an aqueous solution of 0.5 M aqueous sodium hydrosulfite/0.5 M potassium carbonate is prepared and added to the resin (40ml/g of resin) and then the resin/solu-tion is bubbled with nitrogen at room temperature for 16 h. The resulting resin is washed with water, water/MeOH (1 1), MeOH, MeOH/NMP (1 1), NMP, DCM, MeOH, and ether, then filtered and dried overnight in vacuo prior to the next step. 

The tagged resins are pooled into one large batch in a 2-liter peptide vessel, washed with methanol, and then left solvated. Separately, solid Ox-one is dissolved in water (to a final concentration of 0.4 M), sonicating for 5 min to aid in solvation. The aqueous Oxone solution (10 equivalents with respect to the nitro group loading of the resin) is added to the methanol-solvated resin and stirred/bubbled for 16 h at room temperature. The resulting resin 10 was then washed with water, MeOH/water (1 1), MeOH, MeOH/NMP, NMP, DCM, and ether, then dried in vacuo overnight prior to the next step. 

The structures of lithiated phenylacetonitrile and 1-naphthylacetonitrile have been studied in THF and HMPA-THF solution. In pure THF, Fi-NMR line width studies suggest that these species exist as contact ion pairs. In the presence of 0.25-2 equivalents of HMPA, HMPA-solvated monomeric and dimeric contact ion pairs can be identified with P and Fi-NMR spectroscopy, but with four to six equivalents of added HMPA, NMR spectra provide direct evidence for the formation of HMPA-solvated separated ion pairs. 

Peat materials are often richer in nonhumified plant residues than in humus. Exhaustive alkaline extraction and estimation of humic substances are therefore hampered by the presence of hydrophobic lipids, and by coextraction of phenolic compounds from undecomposed plant residues, particularly from lignihed tissues. Artifacts may occur also during the solvation, separation, or concentration steps of the procedure, as discussed by Hayes in Chapter 13. Some of the problems can be mitigated by prior extraction of the lipids, soluble phenols, and sugars, as in the various schemes of proximate analysis discussed by Walmsley (1973). 

For a dissociative heterolytic mechanism, the reactant is solvated, and heterolysis forms an ion pair (termed an intimate ion pair ) that is contained within the original solvation shell. The ions are then solvated separately but remain associated ( solvent-separated ion pair ). The ions dissociate, and the incoming nucleophile reacts by a reversal of this process with the electrophile. The presence of up to three intermediate types accounts for many of the complexities associated with dissociative reaction mechanisms. For example, the separated ions are stereochemically distinct from the reactant, and in the case of carbonium ions or metaphosphate intermediates the intermediate is expected to be planar. 

Complexes of macroopen-chain analogues with metal ions possess imique properties, and interest in these compounds is continuously growing [103, 109]. The catalytic action of crown-ethers and their analogues as catalysts of phase transfer consists in activation of reagents due to the increase of ion pair dissociation with the formation of nonsolvated reactive anions owing to the transformation of contact ion pairs into solvation-separated ones. 

In a solution an equilibrium "solvate-separated ionic pair - contact ionic pair" evidently exists [73] ... 

The molecular weight studies and the infrared studies indicate that in a THF solution the dimer is split into two monomeric molecules retaining the Ce-OC-W linkage. In a more polar solvent such as MeCN, the complex is presumed to exist as a solvate-separated ion pair [61] ... 

An additional complexity is that as the particle is moving, it is solvated , i.e. it incorporates molecules from the dispersion medium, e.g. water (hydration). The friction coefficient is affected by both nonsphericity and solvation. Separate evaluation of the contribution of asymmetry and hydration (solvation) is often difficult, but an assessment of the joint effect of these two factors is shown for one specific case in Figure 8.5 for proteins in water. 

Contact (tight, nonseparated) and solvate-separated ion pairs are distinguished. In the contact pair the anion replaces one or several solvent molecules in the solvate shell of the cation, so that the cation and anion are nearest neighbors. In the solvate-separated ion pair the anion and cation are separated by solvent molecules, that is, each anion is surrounded by its solvate shell. 

The transition from the solvate-separated to contact ion pair is accompanied by a change in the electrostatic energy. If in the contact pair the distance between ions is equal to + rg and in the solvate-separated pair it is ta + rg + Ar, then the transition to the contact pair is accompanied by the release of an energy equal to z z e Mzir + + Ar)(rA + r. At Ta and ta + Ar, this energy becomes... 

The rearrangement of the tight pair into the solvate-separated pair is considered as a two-stage process at first a hole is formed between ions due to their thermal motion, and then a solvent molecule enters the hole... 

The formation of independently diffusing ions occurs through the stage of contact and solvate-separated ion pairs... 

The solvate-separated pair of CgHj and HsO then dissociates to individual ions. In this polymer ionization represents, in essence, the heterolytic abstraction of a proton from the phenoxyl group with the simultaneous formation of the H30 ion, which is transformed then into the more stable HsOj ion. Bases (/.e., ammonia), by contrast, abstract the proton from water... 

Most frequently carbanions in a solution exist as contact or solvate-separated ion pairs. The stability of the R carbanion is characterized by pKa = -log o, where K is the constant of acid dissociation of RH K = [R ][H /[ ]. At this dissociation the proton adds to the solvent molecule... 

Supramolecular dyad molecules are also available by utilizing host-guest chemistry. Konishi et al. reported that improvement of electron-transfer efficiencies could be attained in the electron-transfer systems composed of donors and fuUerenes connected with calixarene, in which calixarene could capture the electron donor [136]. It is interesting to note that back electron transfer in these systems obeyed second order kinetics, indicating that the generated radical ions are solvated separately after electron transfer by deforming the supramolecular. 

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