Solvent localization

Scleroproteins, insoluble in most solvents. Localized in connective tissue, bone, hair, and skin. The two principal classes are the collagens and keratins Nucleoproteins, nucleic acid... 

Solute-solvent local interactions may play a role in several aspects of the solvation effects. The analysis is delicate because finer aspects of the physics of interacting molecules have to be introduced. 

Eqn.(3.73) suggests that any mixture of two solvents with the same ° value (iso-eluotro-pic solvents) will also have the same eluotropic strength. This would allow the application of a similar strategy for the definition of iso-eluotropic multicomponent mobile phase mixtures as was used for RPLC in section 3.2.2.1. In practice, the situation in LSC has proved to be more complicated, because an effect described as solvent localization limits the validity of eqns.(3.72) and (3.73) if polar components (such as acetonitrile or methyl t-butyl ether) are present in the mobile phase. This makes it difficult to calculate the composition of iso-eluotropic mixtures for LSC with sufficient accuracy for optimization purposes [360-363]. 

C-solvent localization should occur at a surface coverage (6c 0.75) which is the same for all C-solvents. Data for (- versus c reported in Ref. 14 suggest that the function can be approximated well by the empirical fitting expression... 

These polar-solvent systems where (and solvent localization) remain essentially constant show relatively constant values of b and good agreement between experimental and calculated ° values ( 0.020 overall). The implication is that the Q term of Eq. (21) is introducing at most 0.01-... 

Retention in normal-phase chromatography increases as the polarity of the mobile phase decreases. The selectivity of the analytes may arise from the differences in solvent strengths (eq), acidity, basicity, and dipolar nature of the mobile phase. Furthermore, solvent localization of the mobile phase plays a major role in the retention of the analytes [15,16]. These solvent strengths have been shown to be different when used with varied stationary-phase packings such as alumina, diol, and silica [3,17]. 

Values of the function /(2") for various groups k can be obtained directly from Tables 10-2 and 10-6. The a, values of localized sample groups on silica decrease with increasing adsorbent activity, until for a aa 1.0 values of a, are equal to the calculated values of Table 8-4. However, this is of limited importance in practical separations, which generally use water-deactivated silica. This and other aspects of solvent localization on silica and Florisil are further discussed elsewhere (22). 

Since many amino resins contain solvents, local safety codes regarding flammable liquids should be observed. For bulk storage an inert gas atmosphere above the resin should be used [2.162],... 

In the case of co-adsorption of water and organic solvents, localization of bound water can change in comparison with the adsorption of water alone. Addition of 0.4 g CDCI3 per gram of AC leads to disappearance of the signal of water adsorbed in nanopores but the signal of water (SAW) located in mesopores increases (Figure 3.37a). Thus, chloroform displaces water from narrow pores. 

An important topic in supercritical fluid research is the effect of solvent local density augmentation on solute-solute interactions in a supercritical fluid solution. The most important question seems to be whether the supercritical solvent environment facilitates solute-solute clustering, which may be loosely defined as local solute concenttations that are greater than the bulk solute concentration. Unlike solute-solvent clustering discussed in the previous section, solute-solute clustering in supercritical fluid solutions is a more complex and somewhat controversial issue. Following is a summary of the available experimental results and a review of the various explanations and mechanistic proposals on the clustering of solute molecules in supercritical fluid solutions. 

Because the chemical nature of the aliphatic junction points and the stiff aromatic segments is so different, their solubility parameters and affinity to solvents are expected to be different too. Therefore, it is expected that upon swelling in a given solvent, locally selective swelling will occur. In solvents better for the aromatic segments, segment-rich domains will preferrentially absorb more solvent and swell, and in solvents better for aliphatic units, the aliphatic junctions will preferentially swell. Large internal stresses are, hence, expected to appear in such systems. At present, however, not much is known about such systems. 

In contrast to the behavior of noble gases, the radial distribution functions of water around the infinitely dilute anion (Cl ) and cations (Na" " and Li ) show a rather strong solvation, i.e., relative to pure water there is a substantial increase in the local water density around the ions due to strong ion-dipole interactions (Figures 18 and 19). From a microstructural viewpoint, the presence of an ion induces an increase in the solvent local density, relative to the pure solvent, with a consequent decrease of (dP/dxu) j (non-volatile... 

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