Phosphates, cyclic linear

Aldolases catalyze asymmetric aldol reactions via either Schiff base formation (type I aldolase) or activation by Zn2+ (type II aldolase) (Figure 1.16). The most common natural donors of aldoalses are dihydroxyacetone phosphate (DHAP), pyruvate/phosphoenolpyruvate (PEP), acetaldehyde and glycine (Figure 1.17) [71], When acetaldehyde is used as the donor, 2-deoxyribose-5-phosphate aldolases (DERAs) are able to catalyze a sequential aldol reaction to form 2,4-didexoyhexoses [72,73]. Aldolases have been used to synthesize a variety of carbohydrates and derivatives, such as azasugars, cyclitols and densely functionalized chiral linear or cyclic molecules [74,75]. 

Espelt, L., Parella, T., Bujons, J., Solans, C., Joglar, J., Delgado, A. and, Clapes, P., Stereoselective aldol additions catalyzed hy dihydroxyacetone phosphate-dependent aldolases in emulsion systems preparation and structural characterization of linear and cyclic iminopolyols from aminoaldehydes. Chem. Eur. J., 2003, 9, 4887. 

Takamura et al. have reported a voltammetric method for the determination of chlorpromazine using an anodically oxidized carbon electrode [167]. A vitreous-carbon electrode was maintained at +1.6 V vi. S.C.E. for 2 minutes (in 0.5 M phosphate buffer at pH 6.8). Under these conditions, chlorpromazine gave an oxidation peak current on cyclic voltammograms that varied linearly with concentration over the range of 50 nM to 1 pM. 

The linear peptide thioester was dissolved in 0.2 M phosphate buffer (pH 7.2, 0.1-0.6 mM soln) containing 50% DMF and TCEP (6 equiv). After completion of the reaction (3-24 h, monitored by HPLC) the cyclic peptide was purified by preparative HPLC (small amounts of byproducts result from hydrolysis of the peptide thioester). 

No studies were located that specifically address white phosphorus metabolism in humans after oral exposure. However, since orthophosphate is a stable end-product of the inorganic oxidation and hydrolysis of white phosphorus, it is appropriate to examine data on serum phosphate levels in humans following oral ingestion of white phosphorus (these data are discussed further in Section 2.2). Although orthophosphate is the stable end-product, linear and cyclic phosphorus compounds do exist that are stable for relatively long periods, and these may be metabolic blockers especially where phosphorus metabolism is on-going. 

Richardson 1992 Spanggord et al. 1985). It should be mentioned that although microorganisms that biodegrade elemental phosphorus under anaerobic conditions could not be grown, both linear polyphosphates and cyclic meta-phosphates could be microbially hydrolyzed to simpler phosphates in water and soil under aerobic and anaerobic conditions... 

Figure 5.2 Reactions catalyzed by deoxyribozymes that ligate RNA to form linear products. (A) Reaction of a 2,3,-cyclic phosphate with a 5 -OH group, leading to either a native S —S linkage or a nonnative 2 —S linkage. (B) Reaction of a 2,3,-diol with a S -triphosphate, again leading to either a S —S or 2 —S linkage.

When a ferrocene derivative loaded Pt/Nafion-GOD electrode is transferred to a phosphate buffer solution containing no ferrocene derivatives, the observed redox waves reflect their electrochemical behavior in the film. The scan rate dependence of the cyclic voltammetry for the Pt/Nafion-GOD incorporated with different ferrocene derivatives was studied. A linear plot of the anodic peak current against the square root of the scan rate was obtained in all cases, which is indicative of diffusion controlled redox process. Typical chronoamperometric... 

Hale et al. reported the use of an enzyme-modified carbon paste for the determination of acetylcholine [21], The sensor was constructed from a carbon paste electrode containing acetylcholineesterase and choline oxidase, and the electron transfer mediator tetrathiafulvalene. The electrode was used for the cyclic voltammetric determination of acetylcholine in 0.1 M phosphate buffer at +200 mV versus saturated calomel electrode. Tetrathiafulvalene efficiently re-oxidized the reduced flavin adenine dinucleotide centers of choline oxidase. The calibration graph was linear up to 400 pM acetylcholine, and the detection limit was 0.5 pM. 

Figure 1.3 Distribution curve (by size) obtained for sodium polyphosphate molecules (Graham s salt, n 193) after fractional precipitation, after Van Wazer (1958) (a) cyclic phosphates (b), (c) and (d) linear polyphosphates.

Figure 1.9 Results of a chromatographic examination of the hydrolysis products of Graham s salt at pH 4 and 90 °C (a) high-molecular-weight polyphosphates (b) cyclic phosphates containing four to six phosphorus atoms (c) cyclotriphosphate (d) pyrophosphate (e) tripolyphosphate (f) linear polyphosphates containing four to 15 phosphorus atoms (g) orthophosphate (Van Wazer, 1958).

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