Quinones adsorption

McDermott, M.T. and McCreery, R.L. (1994). Scanning tunneling microscopy of ordered graphite and glassy carbon surfaces electronic control of quinone adsorption. Langmuir, 10, 4307-14. 

Hurst (19) discusses the similarity in action of the pyrethrins and of DDT as indicated by a dispersant action on the lipids of insect cuticle and internal tissue. He has developed an elaborate theory of contact insecticidal action but provides no experimental data. Hurst believes that the susceptibility to insecticides depends partially on the cuticular permeability, but more fundamentally on the effects on internal tissue receptors which control oxidative metabolism or oxidative enzyme systems. The access of pyrethrins to insects, for example, is facilitated by adsorption and storage in the lipophilic layers of the epicuticle. The epicuticle is to be regarded as a lipoprotein mosaic consisting of alternating patches of lipid and protein receptors which are sites of oxidase activity. Such a condition exists in both the hydrophilic type of cuticle found in larvae of Calliphora and Phormia and in the waxy cuticle of Tenebrio larvae. Hurst explains pyrethrinization as a preliminary narcosis or knockdown phase in which oxidase action is blocked by adsorption of the insecticide on the lipoprotein tissue components, followed by death when further dispersant action of the insecticide results in an irreversible increase in the phenoloxidase activity as a result of the displacement of protective lipids. This increase in phenoloxidase activity is accompanied by the accumulation of toxic quinoid metabolites in the blood and tissues—for example, O-quinones which would block substrate access to normal enzyme systems. The varying degrees of susceptibility shown by different insect species to an insecticide may be explainable not only in terms of differences in cuticle make-up but also as internal factors associated with the stability of oxidase systems. 

FIGURE 10.12 Adsorption data of buspirone (o), doxepin (V), and diltiazem ( ) and best Bilangmuir isotherms (continuous and dotted lines). Mobile phase is acetonitrile buffer=35 65 buffer is 0.1 M phosphate, pH 3.0, T = 25°C. (Reproduced from Quinones, I. et al., J. Chromatogr. A, 877, 1, 2000. With permission from Elsevier.)... 

The adsorption of electron acceptors (quinone, chloranil) from the gas phase does not substantially influence the photo-emf of PAC but decreases the dark conductivity and the photoconductivity. The same compounds, however, adsorbed on certain polyacetylenides from solution, increase the photo emf without causing any appreciable change in the spectral distribution. Mercury vapor depresses reversibly the dark conductivity and photoconductivity [276-278]. 

A wide variety of quinones spontaneously adsorb onto various electrodes, including gold, platinum, carbon, and especially mercury. On mercury electrodes, these quinonoid monolayers often exhibit nearly ideal electrochemical responses in low-pH electrolytes, so making them attractive model systems for probing the thermodynamics of adsorption. In low-pH electrolytes, both the oxidized and... 

Figure 4.6 Dependence of the surface coverage on the bulk concentration of the quinone (where and A denote the areas under the anodic and cathodic peaks, respectively) and hydroquinone (where denotes both anodic and cathodic data) forms of 1,2,4-AQASH. The supporting electrolyte is 1.0 M HCIO4. The dashed lines represent the best fits to the Frumkin adsorption isotherm where error bars are not shown, the errors determined from at least three independently formed monolayers are comparable to the sizes of the symbols. Reprinted with permission from R.J. Foster, T.E. Keyes, M. Farrell and D. O Hanlon, Langmuir, 16, 9871 (2000). Copyright (2000) American Chemical Society...

Reaction 5.1 is meant to represent a nonspecific electrostatic interaction (presumably responsible for double-layer charge accumulation) Reaction 5.2 symbolizes specific adsorption (e.g., ion/dipole interaction) Reaction 5.3 represents electron transfer across the double layer. Together, these three reactions in fact symbolize the entire field of carbon electrochemistry electric double layer (EDL) formation (see Section 5.3.3), electrosorption (see Section 5.3.4), and oxidation/reduction processes (see Section 5.3.5). The authors did not discuss what exactly >C, represents, and they did not attempt to clarify how and why, for example, the quinone surface groups (represented by >CxO) sometimes engage in proton transfer only and other times in electron transfer as well. In this chapter, the available literature is scrutinized and the current state of knowledge on carbon surface (electrochemistry is assessed in search of answers to such questions. 

In addition to quinone reduction and hydroquinone oxidation, electrode reactions of many organic compounds are also inner-sphere. In these charge transfer is accompanied by profound transformation of the organic molecules. Some reactions are complicated by reactant and/or product adsorption. Anodic oxidation of chlorpro-mazine [54], ascorbic acid [127], anthraquinone-2,6-disulfonate [128], amines [129], phenol, and isopropanol [130] have been investigated. The latter reaction can be used for purification of wastewater. The cyclic voltammogram for cathodic reduction of fullerene Cm in acetonitrile solution exhibits 5 current peaks corresponding to different redox steps [131]. 

Other reactions leading to NH4 removal from soil solution besides microbial nitrogen assimilation, metal-ammine formation, or adsorption onto mineral surfaces, involve NH3 fixation by incorporating it as NH2 in aromatic rings of humic acids (quinone) followed with aromatic ring condensation. 

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