Oxidation losses

Biooxidation Oxidation (loss of electrons) process accelerated by a biocatalyst. 

Oxidation loss of electrons by a species during a chemical or electrochemical reaction addition of oxygen or removal of hydrogen from a substance. 

In biologic systems, as in chemical systems, oxidation (loss of electrons) is always accompanied by reduction of an electron acceptor. 

Any reaction of the type described herein can, in principle, form the basis of electricity generation. The only requirement is that site of oxidation (loss of electrons or deelectronation) be physically separated from the site of reduction (gain of electrons or electronation) so that the reaction cannot be completed without the passage of an electric current from one site to the other, except through the external circuit. If there is no external connection between the electrodes, equilibria will exist and each of the metals concerned will have a potential relative to the corresponding electrolyte. These potentials will be different for the two metals. 

Cakes are in principle subject to all the threats to a long shelf life that any other bakery product is subject to. The product can dry out, the starch can retrograde or mould can grow. These are in addition to the threats of oxidation, loss of flavour and lipolysis by any enzymes present. 

Oxidation loss of electrons reduction gain of electrons (OIL RIG). 

Photolysis of three 2,4-dinitroanilino-substituted carbohydrates, compounds that differ considerably from each other in photochemical reactivity, has been reported.150,151 l-Deoxy-l-(2,4-dinitroanilino)-D-glucitol (73) is photochemically unreactive in contrast, sodium 2-deoxy-2-(2,4-dinitroanilino)-D-gluconate (74) produces D-arabinose in 52% yield upon irradiation.150 The behavior of compounds 73 and 74 indicates that oxidative loss of the 2,4-dinitroanilino group during photolysis is only possible when it is accompanied by simultaneous decarboxylation. The evidence gathered from the considerable study of this reaction for noncarbohydrate systems suggested that this process is quite complex. Although useful, mechanistic proposals have... 

Little is known about the mode of action of nitrosothiols regarding their biological properties. There appears to be no direct connection between their reactivities towards nitric oxide loss and biological activity38,48. However, the experiments which have been carried out in these studies relating to rates of nitric oxide formation do not recognize... 

To learn that there are two basic types of electrode reaction, namely oxidation (loss of electrons) and reduction (gain of electrons). These reactions are the sum total of redox chemistry. 

The extremely low yield of vincristine (2) from intact plants has made pursuit of its biosynthesis a very challenging problem, which at this point in time remains unsolved. Kutney et al. have used both anhydrovinblastine (8) (227) and catharanthine N-oxide (107) (233) as precursors to vincristine (2) in a cell-free preparation, but incorporation levels were extremely low. Therefore, the question of whether vinblastine (1) is an in vivo, as well as an in vitro, precursor remains to be answered. Several possibilities exist for the overall oxidation of vinblastine (1) to vincristine (2), including a direct oxidation of the A-methyl group or oxidative loss of the N-methyl group followed by N-formylation. 

Oxidation Loss of electrons from a chemical species. Any process which increases the proportion of electronegative constituents in a compound such as increasing the proportion of oxygen in organic compounds. 

Oxidation of 6-methylphenanthridines with potassium dichromate in acetic acid results in oxidative loss of the methyl group, the product being the phenanthridone (e.g. 67 Scheme 62) (61JCS3771). If a second methyl group is present it remains unchanged. Selenium dioxide oxidizes the 6-methyl group to the aldehyde. 

Redox pairs Oxidation (loss of electrons) of one compound is always accompanied by reduction (gain of electrons) of a second substance. For example, Figure 6.11 shows the oxidation of NADH to NAD+ accompanied by the reduction of FAD to FADH2. Such oxidation-reduction reactions can be written as the sum of two halfreactions an isolated oxidation reaction and a separate reduction reaction (see Figure 6.11). NAD+ and NADH form a redox pair, as do FAD and FADH2. Redox pairs differ in their tendency to lose electrons. This tendency is a characteristic of a particular redox pair, and can be quantitatively specified by a constant, E (the standard reduction potential), with units in volts. 

Oxidation loss of electrons Reduction gain of electrons Oxidizing agent takes electrons Reducing agent gives electrons... 

The reaction of thiophene and its derivatives with diisopropyl peroxydicarbonate has been investigated (74JOC504). In the presence of CuCl2 as oxidant, 2-thienyl isopropyl carbonate is formed in 70% yield (Scheme 62). In the absence of added oxidant, loss of a hydrogen atom from the a-complex radical is less efficient. 

Samples, even at moderate concentrations, injected into the HPLC column may precipitate in the mobile phase or at the column frit. In addition, the presence of other compounds (e.g., lipids) in the injection sample may drive the carotenoids out of solution or precipitate themselves in the mobile phase, trapping carotenoids. It is best to dissolve the sample in the mobile phase or a slightly weaker solvent to avoid these problems. Centrifugation or filtration of the samples prior to injection will prevent the introduction of particles that may block the frit, fouling the column and resulting in elevated column pressure. In addition to precipitation, other sources of on-column losses of carotenoids include nonspecific adsorption and oxidation. These can be minimized by incorporating modifiers into the mobile phase (Epler et al., 1993). Triethylamine or diisopropyl ethylamine at 0.1% (v/v) and ammonium acetate at 5 to 50 mM has been successful for this purpose. Since ammonium acetate is poorly soluble in acetonitrile, it should be dissolved in the alcoholic component of the mobile phase prior to mixing with other components. The ammonium acetate concentration in mobile phases composed primarily of acetonitrile must be mixed at lower concentration to avoid precipitation. In some cases, stainless steel frits have been reported to cause oxidative losses of carotenoids (Epler et al., 1992). When available, columns should be obtained with biocompatible frits such as titanium, Hastolloy C, or PEEK. 

For a compound which contains dimethylpyperidine substructure (shown on the left), isomeric metabolites oxygenated at positions 1, 2, and 3 can be easily distinguished without NMR by conducting a single LC-APCI-MS experiment on the TSQ Quantum. Loss of 16 is observed for oxidation at position 1 (/V-oxide), loss of 18 (H20) for aliphatic hydroxylation at position 3, while for aromatic hydroxylation at position 2 no significant in-source fragmentation is observed. 

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