Normal phase hydrogen bonding

Figure 5.1. Hydrogen bonding normal-phase mechanism in SPE using a cyanopropyl sorbent.

Liquid-crystalline materials of types A-I and A-II exhibit homogeneous (non-phase separated) mesophases by the association of identical or different molecules. A new class of mesomorphic H-bonded materials, anisotropic liquid-crystalline gels (Fig. 2, Type B), has recently been prepared by the selfaggregation of H-bonded molecules in non-hydrogen-bonded normal liquid crystals [29, 30]. These materials are macroscopically soft solids and form heterogeneous (phase-separated) structures consisting of liquid crystals and fibrous solids. 

Normal-phase LC tends to separate according to solute polarity since the stationary phase is polar and retention is often dominated by hydrogen bonding. Thus, normal-phase LC is useful in sorting out classes of materials according to the polarity of the solutes. Fatty acids are easily separated from monoglycerides, but the separation of individual saturated fatty acids from each other on the basis of their carbon... 

The brush-type (Pirkle-type) CSPs have been used predominantly under normal phase conditions in LC. The chiral selector typically incorporates tt-acidic and/or n-basic functionality, and the chiral interactions between the analyte and the CSP include dipole-dipole interactions, n-n interactions, hydrogen bonding, and steric hindrance. The concept of reciprocity has been used to facilitate the rational design of chiral selectors having the desired selectivity [45]. 

This relatively new class of CSPs incorporates glycopeptides attached covalently to silica gel. These CSPs can be used in the normal phase, reversed phase, and polar organic modes in LC [62]. Various functional groups on the macrocyclic antibiotic molecule provide opportunities for tt-tt complexation, hydrogen bonding, and steric interactions between the analyte and the chiral selector. Association of the analyte... 

Hong, J.H., Malone, P.V., Jett, M.D., and R. Kobayashi, "The measurement and Interpretation of the Fluid Phase Equilibria of a Normal Fluid in a Hydrogen Bonding Solvent The Methane-Methanol System", Fluid Phase Equilibria, 38,83-86(1987). 

On Pt(lll) the HREELS features due to water are unchanged by the presence of CO. These observations indicate that water and CO adsorb onto separate patches on the surface, in a form of hydrophobic coadsorption. Water condenses into hydrogen-bonded islands, as indicated by the low 0-H stretching frequency. CO spreads to cover the rest of surface, giving a phase similar to that for CO alone, but with a coverage normalized to the water-free, not total, surface area. COCO repulsions, which have been well documented on Pt(lll) (10), produce a surface pressure within the CO patches which bears upon the edges of the water islands. It is this lateral pressure which causes water to desorb from Pt(lll) at lower temperatures in the presence of coadsorbed CO. 

The term polarity refers to the ability of a sample or solvent molecule to interact by combination of dispersion, dipole, hydrogen bonding, and dielectric interactions (see Chapter 2 in reference 5). The combination of these four intermolecular attractive forces constitutes the solvent polarity, which is a measure of the strength of the solvent. Solvent strength increases with polarity in normal phase, and adsorption HPLC decreases with polarity in reversed-phase HPLC. Thus, polar solvents preferentially attract and dissolve polar solute molecules. 

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