Developing agents ascorbic acid

Ascorbic Acid Developing Agent or Anti-oxidant ... 

M.p. 190-192 C. The enolic form of 3-oxo-L-gulofuranolactone. It can be prepared by synthesis from glucose, or extracted from plant sources such as rose hips, blackcurrants or citrus fruits. Easily oxidized. It is essential for the formation of collagen and intercellular material, bone and teeth, and for the healing of wounds. It is used in the treatment of scurvy. Man is one of the few mammals unable to manufacture ascorbic acid in his liver. Used as a photographic developing agent in alkaline solution. 

Since many essential nutrients (e.g., monosaccharides, amino acids, and vitamins) are water-soluble, they have low oil/water partition coefficients, which would suggest poor absorption from the GIT. However, to ensure adequate uptake of these materials from food, the intestine has developed specialized absorption mechanisms that depend on membrane participation and require the compound to have a specific chemical structure. Since these processes are discussed in Chapter 4, we will not dwell on them here. This carrier transport mechanism is illustrated in Fig. 9C. Absorption by a specialized carrier mechanism (from the rat intestine) has been shown to exist for several agents used in cancer chemotherapy (5-fluorouracil and 5-bromouracil) [37,38], which may be considered false nutrients in that their chemical structures are very similar to essential nutrients for which the intestine has a specialized transport mechanism. It would be instructive to examine some studies concerned with riboflavin and ascorbic acid absorption in humans, as these illustrate how one may treat urine data to explore the mechanism of absorption. If a compound is... 

This ammonium phosphomolybdate complex is yellow, but if mildly reduced by ascorbic acid in the presence of potassium antimonyl tartrate a solution of stable bluish-purple color ( molybdenum blue ) develops after about ten minutes, which has its strongest absorption at 882 pm (Fig. 4.6). Other mild reducing agents have also been used, including tin(II) chloride, or hydrazine sulfate, which give maximum absorbances at slightly different wavelengths. The intensity of the color which develops is linearly proportional to the... 

A useful copper physical developer consists of a mixture of a copper(II) salt [Cu(N03)J, an amine such as triethanolamine to make the system basic as well as to sequester Cu11, and a reducing agent (ascorbic acid). It can be used to develop Cu, Ag, Pd, Pt and Au nuclei.180... 

All of the above developing agents have unique characteristics, and some have a special purpose. The shortening of the list of modern developing agents has more to do with ease of manufacture, storage, and shipping than it does with their usefulness. The superadditive effects of hydroquinone, metol, Phenidone, and ascorbic acid (see discussion of superadditivity later in this chapter) has also added to their popularity with manufacturers. 

Developing agents for film can be used for paper and vice versa. In practical terms, some developing agents are more advantageous to use in one process than another. For example, ppd is better suited for film development than for paper development, while chlorhydroquinone is better suited for paper than film. Hydroquinone, metol, ascorbic acid, and Phenidone are well suited for either film or paper. This is an additional reason they are preferred by manufacturers. It is worthwhile to familiarize yourself with the brief description of each developing agent in Appendix 3 Pharmacopoeia. 

The third method developed for preparing DENs is known as the sequential reduction method. This method, shown in Scheme 3 involves the initial complexation and reduction of a seed metal (Ma), followed by the com-plexation and subsequent reduction of the second metal (Mb) to produce the MaMb system. The synthetic utility of this method is that it provides the means to access both well mixed and core/shell-type DENs. When the reducing agent used for Mb is a mild reductant, such as H2 or ascorbic acid, core/shell nanoparticles with an Ma core and Mb shell can be selectively pre-... 

The early functional models for this oxidation chemistry were rather simple Udenfriend used iron(II), EDTA, ascorbic acid (as the reducing agent) and O2 to hydroxylate arenes, while Hamilton showed that the same system hydroxylates unactivated C—H bonds (e.g. androsten-3-ol-17-one is converted to androsten-3,7-diol-17-one). Mimoun developed the use of an iron(II)/PhNHNHPh/ H1CO2H/O2 system which is also active for alkane hydroxylation. Curiously, other metals [copperfll), manganese(II), vanadium(II), cobalt(II)] are also active. In the hydroxylation of arenes, an arene oxide is believed to be the intermediate in P-450 dependent systems, because a 1,2-shift of a proton in the arene, the NIH shift is often observed. Neither the Udenfriend nor Mimoun models show such a shift, however. 

Effective superadditive mixtures result from combinations of l-phenyl-3-pyrazolidinone (Phenidone) [48] and its derivatives with hydroquinone, ascorbic acid, /7-hydroxyphenylaminoacetic acid, hydroxylamines, pyrogallol, and other agents. In general, superadditivity is a phenomenon primarily used in black-and-white developers but it has also been observed in color development [49]. 

Figure 26. Dependence of the specific rate constant upon developing agent (ascorbic acid) concentration [107].

Figure 27. Dependence of specific rate constant for pre-filamentary center growth upon bromide ion concentration, showing conformity with the Butler-Volmer law of electrode kinetics. Developing agent, 10 m ascorbic acid [107].

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