Aluminol group

Figure 2. Thymidylic acid bound through its phosphate group to aluminum-exchanged mica. The thymidylic acid further adsorbs a poly-A tail of messenger RNA by hydrogen bonding, represented on top. The necessary active center for thymidylic acid are surface aluminol groups as discussed in text.

Figure 4.5. Schematic of the kaolinite surface hydroxyls. In addition to the basal OH groups, the schematic is showing the aluminol groups, the silanol groups, and the Lewis acid sites contributing to water adsorption (from Sposito, 1984a, with permission).

It suggests that water adsorption occurs mainly on structural defects of the clay mineral crystal rather than on the basal surfaces because, due to the presence of aluminol groups on one face of kaolinite, kaolinite would be, in principle, more hydrophylic than illite which exhibits only siloxane bridges on both faces of the crystal. 

Coming back to oil adsorption, we have evidence that the asphaltenes adsorption dissolved in the water saturated toluene, is more strongly on kaolinite than on illites. It is obvious that the size of an asphaltene molecule does not permit its access to the sites of adsorption that are responsible for the water adsorption. In other words, only basal surfaces are accessible to the large and planar asphaltene molecules that interact preferentially with the aluminol groups of the kaolinite while water deactivates the more energetic and certainly less accessible sites of illites. 

Figure 1.10. Surface hydroxyl groups (shaded) on kaolinite. Besides the OH groups on the basal plane, there are aluminol groups, associated with Lewis acid sites, and silanol groups protruding from the edge surface. The right side of the figure shows an outer-sphere surface complex between an ionized H2O and Na" ", as well as complexes between the silanol groups and OH (i.e., proton dissociation).

These spectral features have received controversial assignments. In early reports (414), the new v(OH) bands formed upon water adsorption were assigned to new types of silanol or aluminol groups. In more recent publi-... 

HBEA is a zeolite that is easily dealuminated and various aluminol groups are often observed in samples. The band at 3782 cm disappears fully after adsorption of pyridine or pivalonitrile, which indicates that the respective species are not located in the small channels (587). However, only half of the band is affected by adsorption of DTBP (159), indicating some variation in the location of these species. 

Data on the location of aluminol groups (3665 cm ) were reported in Ref (196). These hydroxyls were not affected by 2,4,6-coUidine adsorption, and it was concluded that their location must be at the internal surface. 

The ion-binding capacity of silicate minerals is mainly given by electrostatic interactions (i.e., ionic exchange), and there is relatively little specific binding, mainly through edge silanol and aluminol groups. 

The interlayer aluminol groups (Al-OH) present in the internal surfaces of kaolinite can be grafted by reaction with alkanols and polyols. Tunney and Detel-lier (108), using previously expanded kaolinite with DMSO or NMF, obtain organic derivatives of this silicate trough A1—O—C bonds. Surprisingly, some of these hybrid materials (e.g., methoxy-kaolinite) show high thermal stability (>350°C) as well as elevated resistance to water hydrolysis. 

Hydrolyzed ASP and the surface hydroxyl groups of HNTs consisting of aluminol groups at the internal surface of the lumen are grafted to potentially improve the dmg loading and delay of drug release (Levis and Deasy, 2003) in drag-delivery application. 

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