Ascorbate to tartrate

The grape is a seasonal plant. Moreover, conversion of ascorbate to tartrate, as noted above, is limited to certain stages of growth and development. EflForts to find an alternative species of Vitaceae more amenable to research led us to Virginia Creeper (Parthenocissus quinque-folia). In a controlled environment, this plant retains its leaves and continues to lengthen its vines indefinitely, an ideal system for study of Vitaceae-type ascorbic acid metabolism on a year-around basis. 

Acetate, (reduction with) ascorbic acid + KI, citrate, V,V-dihydroxyethylglycine, EDTA, F , formate, NaOH + H2O2, oxidation to CrOJ , NagP30io, sulfosalicylate, tartrate, triethylam-ine, tiron... 

Acetylacetone, ascorbic acid, citrate, C20j, EDTA, F , H2O2, hydrazine, mannitol, NagP30io, NH2OH HCI, oxidation to molybdate, 8CN , tartrate, tiron, triphosphate... 

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... 

The determination of the orthophosphate was carried out by using the automated systems described by the Technicon Instruments Corporation. The manifolds used are shown in Fig. 12.3. The procedures referred to below as methods I and II are Technicon industrial methods Nos. 94-70W and 155-71W, respectively. Method I includes ascorbic acid alone for the reduction of the molybdophosphoric acid whereas in method II the mixed reagents ascorbic acid, sulphuric acid, ammonium molybdate and antimony potassium tartrate are used. Method I is intended for use for high levels of phosphorus (up to lOpg ml4) and method II for low levels (less than 0.5pg ml4). The wetting agent (Levor IV) used in order to obtain a smooth bubble pattern, is present in the ascorbic acid reagent line for method I whereas it is added externally Fig. 12.3) in the water line (0.5pg ml4 of Levor) in method II. 

Note In this experiment, the phosphorus in water samples is determined by visible spectrometry following a reaction of the phosphates in the sample with potassium antimonyl tartrate, ammonium molybdate, and ascorbic acid. All glassware should be washed in phosphate-free detergent prior to use to avoid phosphate contamination. 

Ortho-phosphate reacts with molybdate and ascorbic acid to form a blue compound measured at 660 nm. Antimony potassium tartrate is used as a catalyst. 

In plants, ascorbate is required as a substrate for the enzyme ascorbate peroxidase, which converts H202 to water. The peroxide is generated from the 02 produced in photosynthesis, an unavoidable consequence of generating 02 in a compartment laden with powerful oxidation-reduction systems (Chapter 19). Ascorbate is a also a precursor of oxalate and tartrate in plants, and is involved in the hydroxylation of Pro residues in cell wall proteins called extensins. Ascorbate is found in all subcellular compartments of plants, at concentrations of 2 to 25 mM—which is why plants are such good sources of vitamin C. 

In order to prevent the reduction between iron(II) and formaldoxime occurring, another iron complexing agent (potassium cyanide) was used in the presence of a reductant (ascorbic acid) that reduces iron(III) to iron(II). Aluminium, titanium, uranium, molybdenum and chromium also form light-coloured complexes that normally do not interfere in the determination of manganese in water or plant material by this method. If the aluminium or titanium concentrations are higher than 40 ppm an additional masking flow of tartrate is recommended [31]. 

To prepare the colorimetric reagent, sulfuric acid (250 ml 2.5 M) is added to ammonium molybdate (75 ml) and mixed. Then, ascorbic acid (50 ml) is added and mixed, followed by antimony potassium tartrate (25 ml) and further thorough mixing. The volume is finally adjusted to 500 ml. 

Section V Stabilising Agents Recommended none are recommended Tolerated citric, tartaric, malic, ascorbic, fiimaric acids from nonsynthetic sources according to BATF standards. Low temperatures for tartrate stabilisation (cold stabilisation). Flash pasteurisation with technical justification Prohibited potassium ferrocyanide, synthetic citric acid, metatartaric acid, sorbic acid and sorbates... 

Within experimental limits, leaves labeled with l-[5- C]- or l-[6- C]ascorbic acid gave comparable results (Table III). Additively, the C in CO2, sugars, and malic acid accounted to 62-63% of that present in the leaves. Another 7% appeared in the residue as glycans. The total amount of C found in hexose or products of hexose metabolism of l-[5- C]- or L-[6- C]ascorbic acid labeled leaves was similar to that found in tartrate (and CO2) after labeling with l-[1- C]- or l-[4- C]-ascorbic acid. Cleavage of the carbon chain of ascorbic acid at the C4-C5 bond accounts for these observations. 

Further evidence that the tartaric acid arose from a G4 fragment of L-ascorbic acid corresponding to C3 through G6 was obtained from studies with l-[4- G]- and l-[6- C]ascorbic acid (Table IV) (9). The former was converted to carboxyl-labeled tartrate in grape and Virginia... 

The influence of stereochemical differences of natural products on biological systems has already been studied by Pasteur who recognized that dextro ammonium tartrate was digested more rapidly by the fungus Penicillium glaucum than the levo isomer [56]. Ascorbic acid, also known as vitamin C, only exhibits redox activity as the (-I-)-isomer, whereas the (-)-isomer is inactive and cannot be used to treat scurvy [57]. 

To a weakly acidic solution containing not more than 50 pg of Mn, add 20% potassium sodium tartrate solution (in the presence of Al, Cr, Ti, or U), about 10 mg of ascorbic acid (in the presence of Fe), and about 20 mg of KCN (in the presenee of Ni, Co, Fe, or Cu). Next, add 1 ml of 1 M formaldoxime, followed immediately by 1 ml more of 1 M NaOH than is required for neutralization. Dilute the solution with water to the mark in a 25-ml standard flask. After 10 min, measure the absorbance of the solution at 455 nm, using water or a blank solution as reference. 

Most interfering cations are masked with EDTA. Tartrate masks milligram quantities of Ta, Ti, W, Mo, Sb(V), and Sn(IV) U(VI) and Zr can be masked with phosphate fluoride masks A1 and Th cyanide masks any silver present. The interfering effect of Ce(IV) and V(V) can be eliminated by addition of ascorbic acid which reduces them to Ce(III) and V(IV), respectively. Thus, the BPR method can be regarded as specific, provided that... 

Interfering metals [e.g., Fe(III), Cd, Cu, Pb, Hg, Mo] can be masked with iodide, thiosulphate, or tartrate. Iron(III), which interferes, is reduced to Fe(Il) by means of ascorbic acid. 

The very weak complexing of iron(ll) by tartrate suggested that iron(II) might be determined quantitatively by cation chromatography. This was proved to be true by Fritz and Sevenich [14] who determined iron(II) in the presence of iron(III) and several other metal ions. Total iron in solution was determined after a preliminary reduction to iron(II) with ascorbic add. 

The activity of the tartrate-resistant acid phosphatase enzyme is affected by the strength of reducing agents. Whereas mild-reducing agents, such as ascorbate or p-mercaptoethanol, lead to... 

Standard methods for phosphates, polyphosphates, and organic phosphates in environmental samples are predominantly nonchromatographic methods, which are based upon the molybdenum blue method. Within this colorimetric method ammonium molybdate and antimony potassium tartrate react under acidic conditions with dilute solution of phosphorous to form an antimony-phospho-molybdate complex which is then reduced to an intensely blue-colored complex by ascorbic acid. U.S. EPA Methods 365.1 to 365.4 are based upon this chemistry. 

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