Hydroquinone group

Yousaf and coworkers used an OEG-based surface bearing hydroquinone groups for electrochemical control of cell adhesion [186]. The hydroquinone groups were electrochemically converted into quinones, to which a cyclopentadienyl-modified RGD motif was then coupled via a Diels-Alder reaction. Although the hydroquinone-bearing surface was cell-repellent, fibroblasts attached to the areas... 

The data also correlate with the electrochemical investigations of Epstein, et al., ( ), i.e., that quinone-hydroquinone groups are most likely present on LTI carbon surfaces. They further concluded that such groups can be readily converted electrochemically from one to the other. As previously noted, our data indicates that approximately 25% of the surface oxygen is quinone-like in nature. 

The addition of semiquinone to cellulose macroradicals gives rise to low-substituted derivatives containing 5 to 10 hydroquinone groups per 100 cellulose units. 

Further progress was achieved with the subsequent synthesis of the bis(2-oxypropylenedithio)tetrathiafulvalene-containing [2]-rotaxane 33. An electron-rich tetrathiafulvalene derivative appeared an attractive candidate for incorporation into the linear component. The parent tetrathiafulvalene is of comparable bulk to a hydroquinone group and has also been demonstrated to exhibit reversible redox behaviour at low potentials. Further, the green 1 1 complex between tetrathiafulvalene and the above cyclophane tetracation had been characterised previously -... 

Moreno-Castilla and coworkers [139,140] did clarify the relationship between carbon surface chemistry and chromium removal. Table 3 summarizes some of the key results. Upon oxidation of carbon M in nitric acid (sample MO), the surface has become much more hydrophilic and more acidic, and the uptakes increased despite a decrease in total surface area. The enhancement in Cr(III) uptake was attributed to electrostatic attraction between the cations and the negatively charged surface. The enhancement in Cr(VI) uptake (at both levels of salt concentration) was attributed to its partial reduction on the surface of carbon MO (perhaps due to the presence of phenolic or hydroquinone groups), which is favored by the lower pH. The increase in uptake on carbon MO with increasing NaCl concentration is consistent with this explanation, from a straightforward analysis of the Debye-Hvickel and Nemst equations the decrease in uptake on carbon M was attributed to the competition of specifically adsorbed Cl and CrOj- ions on the positively charged surface. 

It was thus proposed that the uptake of Hg(II) by activated carbons occurs by the parallel mechanisms of adsorption of molecular HgCE and reduction. Upon H 0 oxidation, the beneficial phenolic and hydroquinone groups were hypothesized to be lost and converted to carboxyl groups. In contrast to the earlier report by Sinha and Walker [219], significant uptake increase was observed upon sul-phurization (saturation with CS at 288 K and subsequent heating to 773 K) of the as-received (AS), and especially so, the oxidized carbon (AOS). This effect was attributed to the analogous reduction reaction ... 

V versus RHE [255,259,266], which is ascribed to quinone-hydroquinone groups [8] ... 

A few attempts have also berxi made to quantify the concenttalion of the electrochemically active groups by means of voltammetry and polarograply [188, 189], Kinoshita and co-workas attempted to quantify the quinone and hydroquinone groups detected by voltammetry on carbon blacks [190], An excellent agreement with data available fiom TPD analysis was reported, although the authors themselves acknowledge that such... 

A chronic toxicity test of hydroquinone in mice and rats indicated some adverse effects after long-term administration as 0.8% of the diet for 2 years. In the hydroquinone group, renal tubular hyperplasia occurred in 100% of male rats, 30% of male mice, and 7% of female rats adenomas occurred in 47% of male rats and 10% of male mice (Shibata et al. 1991). 

The high adsorption capacity of Ag+ ions by all the activated carbons was attributed to the reduction of Ag+ ions to metallic silver by the hydroquinone groups present on the carbon surface, which in turn are oxidized to quinone groups. This redox process is supported by the standard reduction potentials of Ag+ (Ag+ + e Ag, E = 0.7996 V) and quinhydrone electrode, = 0.6995 V. The increase in adsorption of Ag+ ions by the ammonia-treated sample was attributed to the formation of silver amino complexes which are quite stable under the conditions used in these studies. 

Poly(hydroxy hydroquinones) break down by oxidation of hydroquinone groups to quinones, followed by dehydroxylation and finally by decomposition of quinone rings. Two competing processes, heterolytic and homolytic, are operative in the degradation of polyisocyanurates the former dominates at low temperatures and the latter becomes steadily more important as the temperature is raised. ... 

CVs in aqueous KCl solutions show a pH-dependent electroactivity of the hydroquinone group in the copolymer film and plots of versus pH are linear. The chemical structure of the copolymer is given in Figure 11.19. 

Association of these two components is mediated by the chloride anion via N-H -Cl" and C-H -Cl hydrogen bonding and further stabilized by donor-acceptor interactions between the electron-rich hydroquinone groups of 9 and electron-deficient pyridinium axle 8. Conversion of this orthogonal association complex into a permanently interlocked rotaxane was achieved by RCM clipping to afford 10 in 47% yield. 

Recently, the synthesis of a similar type of ladder polysilox-anes described in Reference 102 was reported, but hydroquinone groups were changed to 9,10-diphenylanthryl groups. 

Scheme 16 Polycondensation of methylosiloxanes with hydroquinone groups.

---