Low Acid Medium Research Articles

Synergistic antimalarial activity of dapsone/dihydrofolate reductase inhibitors and the interaction of antifol, antipyrimidine and antipurine combinations against Plasmodium falciparum in vitro

Using low folate, low p-aminobenzoic acid medium, 2 isolates of Plasmodium falciparum were tested in vitro against a wide range of antimetabolite compounds with known or potential antimalarial activity. ID 50 values (the concentration of compound causing 50% inhibition of [ 3H]hypoxanthine incorporation) were determined for each compound against both isolates. The compounds tested may affect folate, pyrimidine or purine metabolism in malaria parasites and various combinations of compounds were examined for further synergistic antimalarial effects. The combination of any of the dihydrofolate reductase inhibitors cycloguanil, pyrimethamine or WR 99210 with the sulphone drug dapsone demonstrated strongly synergistic antimalarial activity. Combinations of dihydrofolate reductase inhibitors with the antipyrimidine compounds pyrazofurin or menoctone, or with the antipurine compounds tubercidin, bredinin or hadacidin, or with primaquine, failed to demonstrate synergistic activity. Most combinations of an antipurine with an antipyrimidine compound also failed to show any synergistic effect. However, weak synergism was consistently seen in the tubercidin/pyrazofurin and tubercidin/menoctone combinations. Over the 48 h intraerythrocytic cycle using tightly synchronized parasites, tubercidin demonstrated both a cytotoxic and a cytostatic effect.

Redox determination of uranium in presence of plutonium in low phosphoric acid medium and the recovery of plutonium

Quantitative determination of uranium in (U, Pu)O2 fuels is usually done by the DAVIES-GRAY method. High concentrations of phosphoric acid in the analytical waste generated by this method make the revocery of plutonium rather complex. Studies on the recovery of plutonium from nitric acid medium containing different concentrations of H3PO4 by conventional anion-exchange procedure reveal that more than 90% of the plutonium can be easily recovered when the phosphoric acid concentration is less than 0.5 M in the solution. A method was developed for the determination of uranium in the presence of plutonium, which involves the reduction of U(VI) to U(IV) by Fe(II) in a medium of 3.5M H3PO4 +4.5M H2SO4 instead of 10–11M H3PO4 so as to have the H3PO4 concentration ∼0.6M in the waste. A number of determinations of uranium in UO2(NO3)2 working standard solutions and (U, Pu) synthetic solutions with uranium at the 3–7 mg level were carried out by this method. The precision obtained was better than ±0.2% and the accuracy was also within the precision limits. The resulting analytical waste generated was directly subjected to anion exchange separation for the recovery of plutonium which was found to be more than 90%.

Electrochemical reduction of tetraphenylphosphonium cation in low acidity media

The electrochemical reduction on mercury of P + φ 4 in low acidity solvents is studied using polarography, cyclic voltammetry, coulometry and preparative-scale electrolysis. Triphenylphosphine oxide is a major product besides triphenylphosphine and benzene. The reduction process involves the cleavage of a PC bond leading to an unstable carbanion which reacts on the residual water to give OH −. Pφ 3O is then formed by reaction of OH − on the starting P + φ 4. The formation of a small amount of biphenyl through a one-electron process is a distinct but minor alternative pathway.

Electrodimerization X. Solvation and protonation in the EHD of activated olefins in low acidity media

Electrodimerization X. Solvation and protonation in the EHD of activated olefins in low acidity media

ElectrodimerizationX. Solvation and protonation in the EHD of activated olefins in low acidity media

ElectrodimerizationX. Solvation and protonation in the EHD of activated olefins in low acidity media

Solvent extraction of some actinides by trilaurylamine oxide

The solvent extraction of uranium(VI) from nitric or hydrochloric acids, and plutonium(IV) and thorium(IV) from nitric acid by trilaurylamine oxide (TLAO) in benzene or xylene has been studied. A very high distribution of uranium(VI) in low acid media was observed. An examination of the mechanism of extraction(VI) was made using extraction i.r. and NMR measurement. Two mechanisms of extraction of uranium(VI) in low and high acid media are postulated.

The kinetics and mechanism of the electrophilic substitution of heteroaromatic compounds. Part XXX. The orientation of the nitration of 2-pyridones

The nitration of 2-pyridone yields largely the 3-nitro-derivative in low acidity media and largely the 5-nitro-compound in high acidity media. However, both reactions occur on the free base species. This behaviour is compared with similar phenomena in the literature.