Benzoquinone adsorption

A small peak at 288.0 eV was also observed and is most likely that of the unperturbed carbonyl of the ketone. Previous results for formaldehyde adsorption at 170 K on fully oxidized TiO2(001) surfaces gave a C(1s) peak at 288.0 [11]. The curve fits of figure 3C (after p-benzoquinone adsorption) gave four peaks centered at 284.5, 286.1, 288.0 and ca. 290.5 eV. These peaks can be tentatively assigned... 

To elucidate some enzymatic characteristics of the isolated laccases I, II, and III, substrate specificities for several simple phenols, electrophoresis patterns, ultraviolet spectra, electron spin resonance spectra, copper content, and immunological similarities were investigated. Tyrosine, tannic acid, g c acid, hydroquinone, catechol, pyrogallol, p-cresol, homocatechol, a-naphthol, -naphthol, p-phenylenediamine, and p-benzoquinone as substrates. No differences in the specificities of these substrates was found. The UV spectra for the laccases under stucfy are shown in Figure 4. Laccase III displays three adsorption bands (280, 405, and 600nm), laccase II shows one band 280nm), and laccase I shows two bands (280 and 405 nm). These data appear to indicate differences in chemical structure. The results of the copper content analysis (10) and two-dimensional electrophoresis also indicate that these fractions are completely different proteins (10), Therefore, we may expect differences in substrate specificities between the three laccase fractions for more lignin-like substrates, yet no difference for some simple phenolic substrates. 

Waugh et al.131 discussed the selective oxidation of benzene to maleic anhydride on the basis of a detailed study of maleic anhydride and benzene adsorption on a V-Mo oxide catalyst supported on a-Al203. Hydroquinone is found to be an intermediate in this reaction and p-benzoquinone, formed from the hydroquinone, is the main intermediate in the non-selective pathway. The maleic anhydride is observed to be immobile adsorbed and the surface oxidation reaction has a relatively low activation energy. From this the authors conclude that it is not lattice oxygen but weakly bound molecular 02 which is responsible for the selective oxidation and a detailed mechanism, in which use is made of orbital symmetry arguments, is presented. 

Adsorption and electrochemical oxidation of a series of compounds related to hydroquinone (HQ) at Pt(lll) in aqueous solutions has been studied [81, 82], including benzoquinone (BQ), phenol (PL), perdeuterophenol (PDPL), tetrafluorohydroquinone (TFHQ), 2,2, 5,5 -tetrahydroxygiphenyl (THBP), and 2,2, 5,5 -tetraketodicyclohexadiene (TKCD). 

The presence of various functional surface groups and the high conductivity and porosity of carbon material permit effective enzyme adsorption. Glucose oxidase has been irreversibly adsorbed to a graphite electrode by drying a concentrated enzyme solution on the surface (Ikeda et al., 1984). In the presence of p-benzoquinone an electrocatalytic current was observed at 500 mV vs SCE. The measuring signal was... 

Another article concerning liquid-phase reactions catalyzed by perovskites is that by Sugunan and Meera (1995). They studied the reduction of ketones and oxidation of alcohol using RBO3 (R = La, Pr or Sr, B = Cr, Mn, Co or Ni) perovskites. Their goal was, however, to correlate data from these test reactions with surface electron-donor properties of these oxides. The electron-donor properties were investigated by the adsorption of electron acceptors with different electron affinities such as para- and /n-dinitrobenzene, benzoquinone, etc. They adsorbed these electron acceptors on both the mixed and the individual oxides. The results obtained are not conclusive to explain the catalytic behavior of the solids studied on the basis of this single property, as is often the case in many catalytic systems. 

Figure IB presents the Ti(2p) region of the same crystal after adsorption of cyclohexenone at room temperature. An increase of the Ti+4 line at 459.1 eV was accompanied by a simultaneous decrease of the lines corresponding to the lowest oxidation state Ti+x cations (0

Figure 3. XPS C(1s) after adsorption of cyclohexanone (A), cyclohexenone (B), and p-benzoquinone (C) at 300 K.

Any species showing infrared active vibrational modes adsorbed on a reflecting surface can be studied with infrared spectroscopy. The beam of light will interact absorptively with the species when passing through the adsorbate layer before and after the point of reflection. This enables studies of all kinds of adsorbates on many surfaces. Of particular interest in electrochemistry are surfaces of metals and semiconductors employed as electrodes. Thus the following text deals only with reflection at these surfaces other surface and interfaces are not treated. Attempts to record infrared spectra of emersed electrodes (i.e. ex situ measurements) have been reported infrequently in studies of adsorption of hydroquinone and benzoquinone on a polycrystalline platinum electrode [174-177]. Further development of this approach has... 

The concentration dependence for ij as discussed above was confirmed for these photocurrent transient measurements, and a Langmuir adsorption isotherm according to Eq. 3a was successfully used to fit the data for the photoreduction of benzoquinone at the surface of PcZn [44] and for the photooxidation of Ce " at the surface of FisPcZn [129]. In these studies quite remarkable differences were seen in the dependence or independence of charging and discharging currents on the... 

Medical pharmaceutical rubber Phenolic antioxidants Silica gel Ce,H , Ce,H6-C6H,4 (75 25) CftHft-EtOAc- MejCO (100 5 1) A-chloro-2,6- dichloro-p- benzoquinone- monooxime Adsorption 3 8 hindered phenols found (in 102 samples)... 

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