With dithionite

The most common chemical bleaching procedures are hypochlorite bleach for cotton hydrogen peroxide bleach for wool and cotton sodium chlorite bleach for cotton, polyamide, polyester, and polyacrylonitrile and reductive bleaching with dithionite for wool and polyamide. 

Reaction of free-base porphyrin compounds with iton(II) salts in an appropriate solvent results in loss of the two N—H protons and insertion of iron into the tetradentate porphyrin dianion ligand. Five-coordinate iton(III) porphyrin complexes (hemins), which usually have the anion of the iton(II) salt for the fifth or axial ligand, ate isolated if the reaction is carried out in the presence of air. Iron(II) porphyrin complexes (hemes) can be isolated if the reaction and workup is conducted under rigorously anaerobic conditions. Typically, however, iton(II) complexes are obtained from iton(III) porphyrin complexes by reduction with dithionite, thiolate, borohydtide, chromous ion, or other reducing agents. 

Nitro groups in the pyridine ring are reduced to amines catalytically, but side reactions can occur with dithionite, leading to, e.g. (92) (75JOC3608). 

Some aspects of the Lowe-Thomeley mechanism for nitrogenase action, which has served us well over the past 15 years, are being called into question. In particular, the necessity for protein-protein dissociation after each electron transfer, the rate-determining step with dithionite as reductant, is being questioned when the natural electron donor flavodoxin or other artificial systems are used. Some aspects of the mechanism should be reinvestigated. 

Fig. 4. EPR redox titration of ZJ. vulgaris Fepr protein at pH 7.5 of S = J components with dithionite and ferricyanide in the presence of mediators, [from (ZZ)]. ( , ) The Fepr protein-fingerprint signal (the 3+ state) monitored at g = 1.825 (O, ) signal with aU < 2 (the 5+ state) monitored atg = 1.898 ( , ) Titration in two directions starting from the isolated protein, which corresponds approximately to the top of the bell-shaped curve. ( , O) A titration starting from the fully preoxidized state. EPR conditions microwave frequency, 9.33 GHz microwave power, 13 mW modulation amplitude, 0.63 mT temperature, 15 K.

Dithionite-mediated reductive activation of mitomycin C has been employed in the study of its DNA alkylation chemistry.6,63 However, dithionite activated mitomycin C possesses different DNA alkylation properties than that activated by catalytic hydrogenation and enzymatic reduction. We postulated that a new alkylating species is produced by dithionite reductive activation resulting in different reactivity than the iminium methide species. To investigate dithionite-mediated reductive activation further, we treated 13 C-labeled analogues of WV-15 with dithionite and carried out spectral and product studies. 

Enzymes modified with N -carbonyldiimidazole (CDI) include horseradish peroxidase 761 /1-lactamase after nitration and reduction,[771 lysozyme, and urease.[781 Ref. [77] describes how the tyrosine side chain of a protein was nitrated, reduced with dithionite to an amino group, and then treated with CDI or A/-(2,2,2-trifluoro-ethoxycarbonyl)imidazole to give the benzoxazolinonyl alanine moiety ... 

For satisfactory whiteness on wool, it is essential for the fibre to be well scoured and bleached, either oxidatively with hydrogen peroxide or by reduction using stabilised sodium dithionite. Brightener is usually applied together with the dithionite bleach. To achieve the highest possible whiteness, the wool should first be scoured to remove natural waxes and other contaminants, then bleached with peroxide and finally treated with FBA during a second bleach with dithionite. 

Sodium hydroxide is the alkali usually used in conjunction with dithionite. Sodium carbonate is a possible alternative when Cl Solubilised Sulphur dyes are used but is insufficiently alkaline for the Cl Sulphur brands, requiring careful control if over-reduction and the associated lower yields are to be avoided [30]. Typical concentrations are given in Table 12.24. The system of sodium carbonate and sodium dithionite used to reduce blue and black Cl Solubilised Sulphur dyes is particularly suitable for flame-retardant viscose fibres that are sensitive to strong alkalis, since it preserves a satisfactory level of flame retardancy [30]. It is also possible to use a mixture of dithionite with sodium sulphide in alkaline media. 

COD values for hydroxyacetone are after treatment in a bioreactor such treatment is not possible with dithionite. 

FIGURE 13.1 An EPR-monitored redox titration of two [2Fe-2S] clusters. A 2Fe cluster in a ferredoxin (E° = -170 mV) and one in an oxygenase enzyme (E° = -20 mV) from Pseudomonas maltophilia were each titrated with dithionite in the presence of a mediator mix. Each point is the EPR amplitude from an individual sample drawn at the indicated solution ii-value. The fit is based on Equation 13.12. (Data from Chakraborty et al. 2005.)... 

Selected examples of the reduction of methylcyclohexanones with dithionite ... 

Cytochrome P-450 spectra (reduced + CO) show the 2-nm shift to the blue as a result of 3-MC induction. No such shift is observed in the trout, control rat, and PB-induced rat liver microsomes. Cytochrome P-450 EtNC spectra were recorded at pH 7.4, 2 min after the samples were reduced with dithionite. The absorption peaks are at 430 and 455 nm. For pH curves the A Absorbance represents A A (430—490 nm) and A A (455— 490 nm). The number of (+) signifies only the relative activity or inhibition with respect to BP hydroxylation and covalent binding of BP to DNA ( ++-(-) signifies 2-4 times and (+-H—h) signifies 10-36 times the control rat microsomal activity (n.d.), not determined. 

Figure 9.3. EPR spectra of membrane preparations of T. foetus and N. frontalis, reduced with dithionite and recorded at 30 K and microwave frequency 9.38 GHz.

Reduction of the nicotinoyl group with dithionite at pH 7 was followed by both NMR and UV/vis spectroscopy. This analysis showed that the lifetime of the generated dihydropyridine group had been extended relative to 1-methyl-nicotinamide by more than a factor of 3. This system has not yet been shown to be capable of supporting nicotinamide-catalyzed reduction of carbonyl compounds however, the successful inclusion of this functionality within a stable... 

In particular, poly(amidoamine) dendrimers were peripherally modified with diimide moieties (see the structure shown in Scheme 1.43). After rednction with dithionite, this dendrimer was cast into a film, the electronic properties of which were isotropic. (This means that on the molecular and macroscopic levels, there is a three-dimensional (3-D) electron delocalization.) The conductivity was humidity dependent. Water molecules integrate into the material s crystal structure and take part in long-distance electron transfer. Such an effect of water was also observed to enhance electric... 

One-electron reduction at the cathode in the presence of cyanide leads to anion-radical of 4-iodonitrobenzene. Like other halide derivatives, 4-iodonitrobenzene in the anion-radical state easily expels the halide ion and converts into 4-nitrophenyl radical. The latter reacts with cyanide ion and produces anion-radical of 4-cyanonitrobenzene. The same anion-radical can be obtained by reducing the 4-cyanobenzenediazonium salt with dithionite in the presence of nitrite. One-electron oxidation with the initial substrate converts this anion-radical into 4-cyanonitrobenzene. 

Fig. 3. EPR spectra of 100 pairs of Rhodnius salivary glands homogenized in 125 xl of phosphate-buffered saline at pH 7.2 (A) before argon equilibration (B) after equilibration in an argon atmosphere for 4 h (C) after equilibration of (B) with NO for 2 min. (D) difference spectrum, that is B — C. (E) homogenate as in (B) treated with dithionite (DT) to reduce Fe(III) to Fe(II), followed by equilibration with NO for 2 min. (The small signal at g = 2 in A-C is due to copper oxide in the liquid helium which had been condensed at the University of Arizona in a copper-plumbed helium liquiflcation apparatus ) All spectra are plotted on the same scale except (E), which is reduced in amplitude by a factor of 3. Reproduced with permission from Ref 24).

Figure 3. Mossbauer absorption spectra of aconitase at 4.2 K in zero field. (A) Dithionite reduced enzyme activated with 99.9% enriched Fe. (B) Dithionite reduced enzyme activated with >90% enriched Fe. (C) Apoaconitase incubated with dithionite and Fe. (Reproduced with permission from ref. 39. Copyright 1982 the authors.)...

The only complex of Tc containing two phenanthroline ligands is [TcOCl(phen)2] (122), which is obtained either electrochemically by controlled potential cathodic reduction or by reduction of [Tc04] with dithionite in the presence of phenanthroline. Its formulation as a mono-oxo species is suggested by the Tc=0 stretch at 895 cm in the IR. From the observation that all protons in the phenanthroline ligands are nonequivalent, chloride must be cis to the oxo group. ... 

A nonbiological reductant (8204 ) that has proven to be of immense value in converting uncomplexed and porphyrin-bound Fe(III) to the +2 oxidation state with the concomitant formation of two molecules of SO2 gas. Dithionite also reacts with heme-bound oxygen to produce deoxyhemoglobin, and treatment of intact red blood cells with dithionite can induce sickling in cells containing hemoglobin S. Dithionite also reduces NAD+ to NADH. 

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