The photocatalytic degradation processes of ethylene glycol (EG) during the UV or visible light irradiation of pure anatase and nitrogen (N)-doped TiO2 powders (TiO(2-x)N(x), x = 0, 0.002, 0.003, and 0.007) were investigated using time-resolved diffuse reflectance (TDR) and solid-state NMR spectroscopies. The TDR spectra and time traces observed for the charge carriers indicated that the scavenging of photogenerated holes (h+) by EG occurred during the 355-nm laser photolysis of the N-doped TiO2 powders, while no direct oxidation reaction of EG by h+ occurred during the 460-nm laser photolysis, although the charge carriers were sufficiently generated upon excitation. The solid-state magic-angle spinning (MAS) NMR measurements revealed that EG is preferentially chemisorbed on the surface of the N-doped TiO2 powders, in contrast to the pure TiO2, and degrades under visible light irradiation.

Chiral recognition in host-guest complexations between crown ether hosts (H) and amino acid ester ammonium ion guests (G+) has been evaluated by fast atom bombardment @AB) mass spectrometry (m-nitrobenzyl alcohol matrix). The method uses a 1/1 mixed (for example, GR' and Cis-&+) solution of the guest whose enantiomer is isotopically (deuterium) labeled. Chiral recognition of a given host is simply measured with a given guest from the peak intensity ratio of the two diastereomeric host-guest complex ions as I [(H f GR)+]/I[(H -I-Gs-d,)'] 3 IR/&-d,.Both the degree and the direction of chiral recognition are characterized by the I,&-d, values in the range from 0.5 to 5.4 (IR/&-d3) for the present host-guest combination systems studied. b o n g several synthetic chird crown ethers and related natural host compounds, it has been found that host 5 possesses remarkably large guest dependence upon the chiral recognition properties: (1) toward primary amino acid ester guests 14-21, a high degree of (R)-enantiomer preference (I,& = 3.2-5.4), (2) toward phenylglycine ester guest 22, almost no enantiomer recognition (IR/ZS = l.l), and (3) toward secondary amino acid ester guest 24, a weak (S)-enantiomer preference (IR/ZS = 0.7). It is also shown that the IR/Z~ values measured with the present concentrations are reasonably correlated with the relative thermodynamic stabilities in the corresponding host-guest equilibria in solution (IR/IS I KR/KS) for three typical host-guest combination systems selected (1-22,4-16, and 5-16). Accordingly, the present FABMS/ EL (enantiomer-labeled guest) method can be proposed as a new and practically useful technique for determining chiral recognition properties in the highly structured chiral host-chiral guest complexations.

Chiral recognition of crown ethers toward amino acids and their esters is detected both by electrospray ionization (ESI) and by fast atom bombardment (FAB) mass spectrometry (MS) and then compared as a series of host (H)-guest (G) pairs. A racemic guest (G R؉ : [ 2 H n ]G S ؉ ‫؍‬ 1 : 1, of which one enantiomer is deuterium-labelled), is mixed with the target host. The chiral amino acid recognition of the host is determined from the relative peak intensities of the corresponding diastereomeric host-guest complex ions, [eqn. (a)]:For the complexation between chiral host 1 and guest MetOMe ؉ , FABMS gives IRIS ‫؍‬ 5.0 (NBA matrix), which is practically equal to the corresponding equilibrium constant ratio (K R /K S ) in solution. However, ESIMS gives IRIS ‫؍‬ 1.5 for the same complexation (MeOH), which is a remarkable decrease in the IRIS value. Another complex between chiral host 8 and guest MetOMe ؉ , gives IRIS ‫؍‬ 2.0 by FABMS but IRIS ‫؍‬ 1.2 by ESIMS. Moreover, in a much simpler system, the amino ester ion selectivity, Leu t OMe ؉ / MetOMe ؉ , of host 18-crown-6 is depressed to such an extent that we must conclude that ammonium ion selectivity cannot be evaluated by ESIMS, but the metal ion selectivity, K ؉ /Na ؉ , of the same host 18-crown-6 gives a good qualitative evaluation of the relative concentrations of the corresponding H-G complex ions in solution. It is demonstrated that the IRIS values from the FABMS coupled with the enantiomer-labelled (EL) amino ester guest method are the most reliable and generally useful of the measures considered for the chiral amino acid recognition.

The local structure of the TiO2 surface modified with electron-donating bidentate ligands, such as catechols, has been investigated by solid-state NMR spectroscopy. The adsorption and degradation processes of catechols at the TiO2 surface were observed. The photocatalytic degradation mechanism of catechols at the TiO2 surface was interpreted in terms of the interfacial charge recombination reaction with conduction band electrons.