ASCORBIC ACID as an analytica Sveh1a.l MildThe kinetics of reduction of silver([) have been studied in perchloric acid solution using ascorbic acid (AH,) as the reducing agent. First-order dependences on ascorbic acid and silver(i) concentrations are exhibited, together with an inverse first-order dependence on [H+]. The influence of ionic strength (1 < 0 . 0 8 ~) is negligible. The activation energy is 10.6 A 0.2 kcal mot-l. A mechanism for the reduction process is proposed which invoives bimolecular rate-determining reaction between ascorbate ion and silver(1).
Kinetics of the osmium(v1il) -catalysed oxidation of glycollic, lactic, and mandelic acids have been investigated in alkaline media. First-order rate plots in chloramine-Twere linear up to two half-lives. However, under pseudofirst-order conditions the rate constants showed a slight decrease with increase in chloramine-T concentration. The rate of reaction was independent of a-hydroxy-acid concentration and directly proportional to the osmium-(VIII) and the reciprocal of the hydroxide ion concentrations. The formation of a complex between N-chlorotoluene-p-sulphonamide and osmium(V1li) is rate-determining and is followed by the rapid transfer of a hydride ion from the substrate to this complex.
Although cercarial dermatitis is an emerging disease world-wide, cases of such dermatitis may often go undiagnosed, especially in communities that are affected by various skin infections. Between August 2001 and July 2002, 1336 individuals from tribal villages in central India were examined for dermatitis. Skin scrapings were collected and examined for Sarcoptes scabiei and each subject's response to antiscabies treatment was recorded. Freshwater snails were collected from the local ponds used for bathing, and examined for cercariae. The recorded prevalence of dermatitis ranged between 2.1% and 12.5% during the study year, peaking at the end of winter (February-March) and during the rainy season (August-October). Snail positivity for cercariae peaked in the rainy season. The prevalence and the severity of dermatitis were both higher in children than in adults. As most recorded cases of dermatitis were associated with a rash that developed soon after bathing in the local pond, all the skin scrapings were negative for itch mites, and the response to antiscabies treatment was poor, most if not all of the dermatitis observed was probably cercarial. Cercarial dermatitis therefore appears to be a significant health problem among the tribal populations of central India.
The reduction of hexacyanoferrate(II1) has been studied in an acidic medium using ascorbic acid (AH2) as the reducing agent. The reaction has been found to have first-order dependence in both AH2 and Fe(CN)&. Acid concentrations retard the rate and the inverse order with respect to H+ is unity, The effect of addition of neutral salts like potassium chloride and potassium sulfate is positive and an increase in the dielectric constant of the medium also shows an accelerating effect on the reaction rate. The energy and entropy of activation for the reduction process have been calculated as 10.8 kcal and -39.8 cal d e g l mol-', respectively. A mechanism involving intermediate formation of ascorbate radical (AH-) has been proposed and the derived rate law agreed well with the experimental observations.
India is uniquely positioned with regard to schistosomes and schistosomiasis—discovering seven new mammalian species with the existence of three more schistosome species: Orientobilharzia turkestanicum, O. harinasutai, and Schistosoma haematobium(?). An endemic focus of urinary schistosomiasis was reported from Gimvi village of Ratnagiri, Maharashtra with infrequent occurrence of schistosome eggs in human stools. Cercarial dermatitis has been reported to be more abundant in rural population using ponds, tanks, and so forth, for their domestic purposes. Few dermatitis cases were tested positive by CHR. Schistosome antigen was also detected in urine of five cases suggesting existence of active schistosomiasis in India. Nevertheless, human kind does not appear to be the usual host for Indian schistosomes in contrast to S. haematobium, S. mansoni, or S. japonicum. Various reasons for this phenomenon are discussed including evolution of Indian schistosomes, immune mechanisms, and environmental conditions. These and other aspects such as seasonal effect on the prevalence, snail infectivity, heterologous mating, existence of hybrids, and number of schistosomes in heterologous infections need further investigations with application of molecular techniques. Joint efforts by the national as well as international scientific community would be much more rewarding for better understanding of the parasite and the infection.
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