Quinones chemical structures

Oxidation of P-nicotinamide adenine dinucleotide (NADH) to NAD+ has attracted much interest from the viewpoint of its role in biosensors reactions. It has been reported that several quinone derivatives and polymerized redox dyes, such as phenoxazine and phenothiazine derivatives, possess catalytic activities for the oxidation of NADH and have been used for dehydrogenase biosensors development [1, 2]. Flavins (contain in chemical structure isoalloxazine ring) are the prosthetic groups responsible for NAD+/NADH conversion in the active sites of some dehydrogenase enzymes. Upon the electropolymerization of flavin derivatives, the effective catalysts of NAD+/NADH regeneration, which mimic the NADH-dehydrogenase activity, would be synthesized [3]. 

These quinone methide structures are capable of polymerisation and of other chemical reactions. 

Isoviolanthrone (109) is an highly anellated polycyclic quinone system. It is derived from the chemical structure of isodibenzanthrone, which may be visualized as being obtained by unsymmetrical condensation of two benzanthrone molecules. The compound itself affords an intense blue shade. 

Senesi and Testini [147,156] and Senesi et al. [150,153] showed by ESR the interaction of HA from different sources with a number of substituted urea herbicides by electron donor-acceptor processes involves organic free radicals which lead to the formation of charge-transfer complexes. The chemical structures and properties of the substituted urea herbicides influence the extent of formation of electron donor-acceptor systems with HA. Substituted ureas are, in fact, expected to act as electron donors from the nitrogen (or oxygen) atoms to electron acceptor sites on quinone or similar units in HA molecules. 

Chemistry.—The chemical structures of several bacterial menaquinones (MKs) with partly saturated isoprenoid side-chains have been studied. Spectroscopic (u.v., i.r., m.s., and H n.m.r.) and chromatographic data have been recorded for the tetrahydro-MK8 and -MK9 mixture of some nocardioform and coryneform bacteria.The main component tetrahydro-MK9 has the second and third iso-prene residues from the quinone ring saturated, i.e. has structure (159), 2-... 

Caldariellaquinone, from an extremely thermophilic and acidophilic bacterium Caldariella acidophila, is a unique sulphur-containing benzoquinone with structure (161), 6-(3,7,11,15,19,23-hexamethyltetracosyl)-5-methylthiobenzo[( ]thiophen-4,7-quinone. The structure was deduced from spectroscopic data (including H and n.m.r.) and chemical degradation. 

Chemical Attachment. The initial step in chemically attaching enzymes to electrodes involves an activation (derivatization) of the support to introduce appropriate functional groups, such as carboxy, phenol, and quinone-like structures. This step is critical and must be controlled rigorously since the greater the number of functional groups, the higher will be the amount of immobilized enzymes attched and the better the final electrode activity. The electrode surface may be activated by different ways ... 

The treatment of the raw sample produces an increase in oxygen functionalities as can be deduced from Table 2 where amounts of CO and CO2 evolved during a TPD experiment are reported. The surface chemical structures that evolve CO2 are less stable and are related to carboxylic, anhydride or lactonic functions. The evolution of CO is attributable to fairly stable structures and could be postulated as phenols, quinones, ethers and carbonyls (3, 8). CO is more abundant than CO2 during decomposition of surface oxides for both samples, indicating the presence of more stable groups on the samples surface. Moreover, sample SC900R was heated up to 400 C after chemical treatment, so an important part of C02-evolving structures had disappeared before TPD experiments. 

Variability in the effectiveness of humic substances as electron shuttling compounds is expected due to differences in their chemical structure. For example, the electron-accepting capacity of humic substances from three distinct sources varied nearly 700-fold in the following order soils > sediments > dissolved river-borne (Scott et al., 1998 Figure 19). Microorganisms are a source of quinone moities and other electron shuttling compounds. For example, S. oneidensis... 

Metabolic activation of carcinogens involves many enzymatic systems, known as phase I enzymes. The most important is the cytochrome P450 complex, consisting of several different isoenzymes, which are particularly active in the liver. Other enzymes include peroxidases, quinone reductases, epoxide hydrolases, sulfotrans-ferases, and others. Their variety reflects the diversity of chemical structures of compounds to which an organism is exposed. These may be harmful substances or needed ones, or even those indispensable for its proper functioning. One could argue that the activation of carcinogens is an undesirable side effect of metabolic pathways,... 

Melanins are classified according to their chemical structure into the insoluble black eumelanins (poly-5,6-indole quinones) and the alkali-soluble red phaeomelanins (polydihydrobenzothiazines). Nicolaus (5) includes another group, the homoaromatic phenolic allomelanins (per-... 

Oxidation mechanisms for drug substances depend on the chemical structure of the drug and the presence of reactive oxygen species or other oxidants. Catechols such as methyl-dopa180 and epinephrine181 are readily oxidized to quinones, as shown in Scheme 45. 5-Aminosalicylic acid undergoes oxidation and forms quinoneimine,182 which is further degraded to polymeric compounds (Scheme 46).183 Ethanolamines such as procaterol are oxidized to formyl compounds (Scheme 47),184 whereas thiols such as 6-mercaptopurine,185... 

ABSTRACT Quinones constitute a structurally diverse class of phenolic compounds with a w ide range of pharmacologial properties, which are the basis for different applications in the broad field of pharmacy and medicine. In traditional medicine all over the world, plants which are rich in quinones are used for the treatment of a variety of diseases. Besides the classical applications of these plants in industry (dyestuffs) and pharmaceutical (laxatives) practice, the relatively new field of biologically active quinones will be discussed. This review gives an account of the work done on naturally occurring bioactive quinones from 1992 to the present date. The biological activity detected in quinones from natural and synthetic sources has been discussed in relation to chemical structure under the respective titles. 

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