Interaction with surface groups

Pulsed ESR was employed to study the (NO)2 triplet-state bi-radical in Na-LTA type zeolite, with the purpose to resolve the interaction with surface groups, and to elucidate the role of the zeolite in stabilizing the triplet state rather than the usual singlet state [12], Measurements performed at 5 K gave rise to FT (Fourier Transformation, see Chapter 2) spectra that were assigned to the (NO)2 bi-radical interacting with one or two Na nuclei (with I = 3/2), with A( Na) = (4.6, 4.6, 8.2) MHz and... 

A similar process occurs on the ensemble of surface atoms that activates dissociation of a molecular k bond. Then, the antibonding unoccupied orbital of the molecule has to interact with surface group orbitals of similar symmetry on the ensemble of surface atoms. When the unoccupied molecular orbital becomes... 

Factors that influence the retentive powers and selectivity of such bonded phases include the surface concentrations of hydrodartenaceous ligates and free silanol groups. The thermodynamic aspectitm solute interactions with the hydrocarbonaceous ligates at the surface, which are hydrophobic interactions in the case of aqueous eluents, are discussed later in this chapter within the framework of the solvophobic theory. In practice, however, solute interactions with surface silanol which may be termed silanophilic interactions can also contribute ]to retention (71, 75, 93), particularly in the case of amino compounds. Consequently the retention mechanism may be different from that which would be ol served with an ideal nonpolar phase. Therefore, increasing attention is paid to the estimation of the concentration of accessible sianols and to their elimination from the surface of bonded phases. 

Adsorption of a specific probe molecule on a catalyst induces changes in the vibrational spectra of surface groups and the adsorbed molecules used to characterize the nature and strength of the basic sites. The analysis of IR spectra of surface species formed by adsorption of probe molecules (e.g., CO, CO2, SO2, pyrrole, chloroform, acetonitrile, alcohols, thiols, boric acid trimethyl ether, acetylenes, ammonia, and pyridine) was reviewed critically by Lavalley (50), who concluded that there is no universally suitable probe molecule for the characterization of basic sites. This limitation results because most of the probe molecules interact with surface sites to form strongly bound complexes, which can cause irreversible changes of the surface. In this section, we review work with some of the probe molecules that are commonly used for characterizing alkaline earth metal oxides. 

The spectral behavior of CO bonded to metal atoms (metal carbonyls) has been used to characterize the surface of solids (61). For instance, it is known that metal carbonyl interacts with surface site of metal oxides and zeolites to form a Lewis-type adduct where a CO ligand of the metal carbonyl interacts (via the oxygen atom) with surface OH groups or with co-ordinatively unsaturated metal ions (surface Lewis acid sites) (62,63). On the other hand, thermal treatment of the metal carbonyl support adducts lead to loss of CO with formation of subcarbonyls, which are anchored to the support (64,65). Papile et al. (66) reported the characterization... 

Further comparison with benzene sorption on this sample yields striking results if the two isotherms are plotted on the same axis, as shown in Figure 1. The fact that these two isotherms may be completely superimposed suggests that the mechanism of tert-butyl alcohol sorption is similar to that observed in benzene sorption. This indicates that the sorption mechanism of tert-butyl alcohol on this material is more influenced by organic interactions with the surface phenyl groups than by polar interaction with surface hydroxyls. (It should be noted, however, that a small amount of rehydroxylation is indicated by the low pressure hysteresis.)... 

Recognition domains often function transiently. For example, SH2 domains are often found in proteins that interact with phosphotyrosyl groups of "activated" cell surface receptors. The receptors become activated... 

IR Studies of the Interaction of Zr (7r-allyl)4 with Silica. There has been substantial growth in the application of IR spectroscopy to the investigation of solid surfaces (17, 18, 19). Many studies of surface hydroxylation and of chemical reaction with surface groups are reported in the literature. Relatively little work, however, has been directed to the study of gas/solid reactions as they occur on support surfaces (70, 71). 

The primary bonding mode of 3-APTHS to the Si and Cr surfaces is via the silanol-end of the molecule, leaving the amine end free. A smaller nitrogen component at about 401 eV is associated with protonated amine species. It is proposed that this feature is due to interaction with surface hydroxyl groups. The results indicate that this feature is not due to interaction of the surface layer with moist ambient CO,. 

One important observation which can be drawn from these spectra is the fact that, at least at low coverages, the removal of molecular water from the surface of the silica does not particularly affect the intensity of the band at 3747 cm 1. Thus, it can be concluded that the water is not specifically interacting with this group during the adsorption at low coverages and is therefore sitting on other parts of the surface. (This view is widely held, but definitive evidence is not available. Interaction certainly occurs at higher partial pressure but this would be expected in a random rather than a specific adsorption process.)... 

Triazines interact with surfaces of inorganic materials in soil environments. The nature and the extent of these interactions depend on both the properties of the inorganic surfaces and the chemistry of the soil solution. Inorganic surfaces in soil environments may be grouped as uncharged, variable charge, and permanent charge surfaces. 

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