Hydroxyl group orientation

Fig. 4 shows c.d.-difference spectra that are due to the presence of a hydroxymethyl group in one member of the pair. The pairs of pyranoses have the same conflguration about each asymmetric carbon atom that is part of the ring. Three related pairs have the same conflguration at the carbon atoms near the hydroxymethyl group and give very similar difference spectra. The similarity indicates that the rotameric distribution for the hydroxymethyl group is similar for each of these pairs. This is to be expected, as all three sugars have 4-hydroxyl groups oriented equatorially, but the relationship is certainly not obvious from the c.d. spectra themselves (see Fig. 3). In contrast, when the conflguration near the hydroxymethyl group...

Hydroxyl group orientation in computational studies of carbohydrates still remains a problem. This study has... 

After rigidly rotating to < ) -180, - -180 and optimizing at increments of 20 over 360 , the smallest energy found was 32.8 kcal/mol. The secondary hydroxyl group orientations were changed at an early < ), conformation and not restored. Another manifestation of the deformation is that the energy values at < > = -180, = 140 and at < ) = +180, 140, differ by 5 kcal/mol. As... 

S. D. Markad, S. M. Miller, M. Morton, and M. W. Peczuh, Hydroxyl group orientation affects hydrolysis rates of methyl [alpha]-septanosides, Tetrahedron Lett., 51 (2010) 1209-1212. 

Organic solvents also induce changes in the properties of surfactant-coated stationary phases, such as polarity, surface area, or pore volume. Several studies have demonstrated that /i-alcohols interpenetrate the Cig-bonded alkyl chains to form a single monolayer, structurally similar to an opened micelle (i.e., the hydroxyl group orientated toward the aqueous phase). The competition between organic solvent and surfactant molecules for the active sites on the column explains the reduction of adsorbed surfactant at increasing concentration of organic solvent in the mobile phase. For ionic surfactants, this... 

Figure 6 A semi-rigid analog, 13, of isoproterenol is a potent 3-adrenergic agonist. A comparable conformation of 2-F-NE has the hydroxyl group oriented away from fluorine.

Cyclodextrins (CDs) have the ability to include the hydrophobic area of a compound, and the formed complex becomes soluble in water due to hydroxyl groups orientated on the surface of CDs. Thus, it was proposed that CDs would have similar properties as surfactants in enzymatic glycosylations. Nishimura etuL studied the utility of simple CDs for the synthesis of neoglycolipids using glycosyltransferase. In this approach, the authors attempted to use cell-media synthesis, which was named cellular-chemoenzymatic synthesis, as a triple-factor combination method, to construct oligosaccharide easily. Three types of CD, a-CD, /3-CD, and... 

Oils that contain high levels of essential fatty acids, EFAs, are prized for their ability to replenish lipids (oils) that are found naturally within the sldn layers. Linoleic acid is an example of an EFA. Long-chain alcohols, also called fetty alcohols, are useful as emollients and emulsion stabilizers. Their polar hydroxyl groups orient to the water phase with their fatty chains oriented towards the oil phase. Esters of fatty alcohols and fatty acids make excellent emollients becanse of their low reactivity and good stabibty. 

Ionic compounds added to the micellar system for pH or ionic strength adjustment increase usually the surfactant adsorption. Organic solvents, in contrast, decrease the amount of adsorbed surfactant. The alkyl chains of propanol and longer -alcohols form on the stationary phase a monolayer similar to that of adsorbed surfactant molecules, with the hydroxyl group oriented toward the aqueous phase. Alcohol and surfactant molecules compete for adsorption sites. For ionic surfactants, the desorbing ability depends on the organic solvent polarity (methanol adsorbed surfactant molecules decreases linearly with the organic solvent concentration. 

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