Tara P. Dasgupta

Decreased insulin binding to mononuclear leucocytes and erythrocytes from dogs after S-Nitroso-N-Acetypenicillamine administration

BackgroundNitric oxide (NO) and oxygen free-radicals play an important part in the destruction of beta-cells in auto- immune diabetes although the precise mechanism of interaction is still not known. This study was designed to examine any possible diabetogenic effect of NO by investigating any differences in cellular binding of insulin to its receptor on the cell membranes of erythrocytes and mononuclear leucocytes of dogs treated with the NO donor, S-nitroso-N-acetylpenicillamine (SNAP) and controls treated with captopril.ResultsThe result obtained showed decreased binding of insulin to its receptor on the cell membranes of erythrocytes and mononuclear leucocytes. Mononuclear leucocytes from SNAP-treated dogs had decreased ability to bind insulin (16.30 ± 1.24 %) when compared to mononuclear leucocytes from captopril-treated controls (20.30 ± 1.93 %). Similar results were obtained for erythrocytes from dogs treated with SNAP (27.20 ± 1.33 %) compared with dogs treated with captopril (34.70 ± 3.58 %). Scatchard analysis demonstrated that this decrease in insulin binding was accounted for by a decrease in insulin receptor sites per cell, with mononuclear leucocytes of SNAP-treated dogs having 55 % less insulin receptor sites per cell compared with those of captopril-treated controls (P < 0.05). Average affinity and kinetic analysis revealed a 35 % decrease in the average receptor affinity, with mononuclear leucocytes from captopril-treated controls having an empty site affinity of 12.36 ± 1.12 × 10-8 M-1 compared with 9.64 ± 0.11 × 10-8 M-1 in SNAP-treated dogs (P < 0.05).ConclusionThese results suggest that acute alteration of the insulin receptor on the membranes of mononuclear leucocytes and erythrocytes occurred in dogs treated with S-nitroso-N-acetylpenicillamine. These findings suggest the first evidence of the novel role of NO as a modulator of insulin binding and the involvement of NO in the aetiology of diabetes mellitus.

Acrylamide in Caribbean foods - residual levels and their relation to reducing sugar and asparagine content.

The acrylamide levels in commercial and homemade Caribbean foods were determined by pre-derivatisation of acrylamide to 2-bromopropenamide and analysed by gas chromatography with mass spectrometric (GC/MS) detection. Over 100 Caribbean food samples were analysed for the presence of acrylamide. These samples include: biscuits, breakfast cereals, banana chips and home-prepared foods: breadfruit; Artocarpus altilis, banana fritters, and dumplings. The limit of detection (LOD) for the GC/MS method was found to be dependent on the type of column used for the GC/MS analysis. The DB-1701 and the DB-VRX columns gave LODs of 20 and 4 μg/kg, respectively. Acrylamide has not been found in raw foods or foods which have been cooked by boiling. Its content in all other foods had concentrations in the range, 65-3,640 μg/kg. The relationship between acrylamide levels and precursor concentration as well as the health implications of our findings are discussed.

A correlation between infrared stretching mode absorptions and structural angular distortions for the carbonato ligand in a wide variety of complexes

The i.r. spectra of several new carbonato complexes of cobalt(III) are reported and it has been found that the bridging carbonato ligand can be distinguished from the bidentate species and possibly from the monodentate species. By comparing available X-ray structural and i.r. spectral data for a large variety of carbonato complexes a strong correlation has been found between the angular distortion (from D3h) within the carbonato ligand and the separation between the two highest energy CO stretching modes.

Mechanisms of nitric oxide release from nitrovasodilators in aqueous solution: reaction of the nitroprusside ion ([Fe(CN)5NO]2−) with l-ascorbic acid

Nitric Oxide (NO) is a very diverse endogenous molecule and is responsible for a number of mammalian physiological activities. Sodium nitroprusside (SNP) is a long known hypotensive agent due to its ability to produce NO in situ. In this study, we have carried out a detailed investigation on the kinetics and mechanism of the decomposition of SNP by L-ascorbic acid to afford NO in aqueous medium. Spectrophotometric and electrochemical methods were employed in these studies. Experiments were performed under an argon atmosphere and reaction rates were strongly pH dependent and increases with pH. NO release increases up to about pH 7 after which it decreases at higher pHs. The two ionized forms of ascorbate present in aqueous solution reduce SNP in the order A2->>HA->>H2A (H2A=L-ascorbic acid) to release NO. The outer-sphere reduction of SNP by ascorbate involved three clear stages with NO being released in the last stage. Our kinetic results also show catalysis by group 1 alkali metal ions to increase down the group from Li+ to Cs+. A detail study presented here, strongly illustrate the possibility of the biological antioxidant, L-ascorbic acid, to play a vital role in the in situ metabolism of nitrosocompounds such as SNP to produce NO.

Kinetics and mechanism of acid-catalyzed aquation of carbonato-(1,4,8,5,11-tetra-azacyclotetradecane)cobalt(II) ion

Abstract The acid-catalyzed aquation of the title compound has been studied over the range of 0.05 + ] + for the range of acidity studied. The results have been interpreted in terms of mechanism involving acidcatalyzed dechelation followed by a rapid decarboxylation of the monodentate intermediate. At 25°C, the acid-catalyzed ring-opening rate constant, k 1 , is 1.3 × 10 −3 M −1 sec −1 and the temperature variations describing this constant are ΔH*, 20.6 ± 0.4 kcal/mol and Δ* = -2.6±1.3 cal/deg mol. The results are compared with those obtained for similar carbonato (tetramine)cobalt(III) complexes.

Mechanism of the oxidation of l-ascorbic acid by the molyb-datopentaamminecobalt(III) ion in aqueous solution

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Fate and transport of ethoprophos in the Jamaican environment

The hydrolytic half lives of ethoprophos in distilled, river, brackish and open sea water were 25, 133, 65 and 81 days, respectively. Under laboratory conditions, volatilisation of the residues after 12 h was 1.4-3.6, 2.3-4.5 and 6.5-20.2% from a sandy loam soil with 1, 10 and 20% moisture levels, respectively. Photolysis in soil was significantly faster (P < 0.05) in direct sunlight (T1/2 of 4.7 days) than in the shade (T1/2 of 12.3 days). The microbial degradation of ethoprophos was more than two-fold faster in unsterile soil (T1/2 of 10.9 days) than in sterile soil (T1/2 of 28.8 days). The runoff of ethoprophos from unweeded plantation soil at 23 degrees slope was significantly (P = 0.015) less than at 38 degrees slope; the amounts lost after 9 weeks and 27.5 mm of rainfall were 89.4 and 91.2%, respectively, of the applied amount from the two respective slopes. In the weeded plots, 93.6 and 92.4% of the applied insecticide were lost from 23 degrees and 38 degrees slopes, respectively. Under laboratory conditions, between 67.0 and 85.1% of ethoprophos leached through the soil columns. Under field conditions, after 9 weeks and 25 mm of rainfall, only 2.8 and 2.0% residues were recovered at a depth of 10-15 cm from unweeded and weeded slopes, respectively at 23 degrees slope, and 2.2 and 1.9% from the two respective plots at 38 degrees slope.

Kinetics and mechanism of the aquation of a series of mixed-metal oxo-centered trinuclear cations, μ3-oxo-triaqua-hexakis(carboxylato)bis-(chromium(III)(iron(III))+, [ (RCOO)6(H2O)3]+, (R=H, CH3, CH3CH2 and (CH3)2CH) in perchloric acid media

The aquation of a series of [Cr2Fe(µ3-O)µ2-(RCO2)6(H2O)3]+ cations, where R = H, CH3, CH3CH2, and (CH3)2CH was investigated in aqueous perchloric acid, 0.01 ≤ [H+] ≤ 0.17 mol dm−3 and 25 ≤ θ ≤ 35°C. The mechanism is postulated as an equilibrium between the protons and the complex cation, where the oxygens of the carboxylate coordinated to the metal center are protonated, followed by Fe–O bond cleavage. This is followed by rapid decomposition to produce aqueous iron(III), a dinuclear chromium(III) species (which is further hydrolyzed), and carboxylate ions. First-order rate constants for the reactions at 25°C and 0.5 mol dm−3 ionic strength (NaClO4) and corresponding activation parameters are: R = (CH3)2CH; k 1 = (7.18 ± 0.07) × 10−5 s−1 (ΔH ‡= 52 ± 2 kJ mol−1, ΔS ‡= −151 ± 8 J K−1 mol−1), R = CH3CH2; k 1 = (13.67 ± 0.02) × 10−5 s−1 (ΔH ‡= 57.8 ± 0.6 kJ mol−1, ΔS ‡= −125 ± 2 J K−1 mol−1), R = CH3; k 1 = (17.6 ± 0.3) × 10−5 s−1 (ΔH ‡= 30 ± 5 kJ mol−1, ΔS ‡= −216 ± 16 J K−1 mol−1), R = H; k 1 = (3.86 ± 3.01) × 10−2 s−1 (ΔH ‡= 75 ± 1 kJ mol−1, ΔS ‡= −22 ± 5 J K−1 mol−1). Spontaneous hydrolysis rate constants and activation parameters were also determined at 25°C and 0.5 mol dm−3 ionic strength (NaClO4): R = (CH3)2CH; k 0 = (3.18 ± 0.05) × 10−5 s−1 (ΔH ‡= 12.0 ± 0.1 kJ mol−1, ΔS‡= −291 ± 1 J K−1 mol−1), R = CH3CH2; k 0 = (4.04 ± 0.01) × 10−5 s−1 (ΔH ‡= 22.4 ± 0.9 kJ mol−1, ΔS ‡= −254 ± 3 J K−1 mol−1), R = CH3; k 0 = (4.05 ± 0.17) × 10−5 s−1 (ΔH ‡= 34.1 ± 0.1 kJ mol−1, ΔS ‡= −214 ± 1 J K−1 mol−1), R = H; k 0 = (3.4 ± 0.2) × 10−3 s−1 (ΔH ‡= 25.3 ± 0.4 kJ mol−1, ΔS ‡= −207 ± 1 J K−1 mol−1).

Properties and kinetics of dihydroxy- and diaminoanthraquinone ruthenium bipyridyl dimers

Ru(bpy)2Cl2 (bpy: 2,2′-bipyridine) reacts with 1,4-diaminoanthraquinone (1,4-DAAQ) to produce a dimeric complex which precipitates from solution in its mixed-valence form. Redox couples show that the rutheniums are easier to oxidize than those in the corresponding 1,4-DHAQ (1,4-dihydroxyanthraquinone) and 1,4-AHAQ (1-aminon-4-hydroxyanthraquinone) dimers and give a value of 2.8 × 106 for Kcom. Visible absorption bands are broad and may be combinations of transitions. The IT band in acetonitrile shows structure with λmax (log ϵ) and 845 nm (3.5), 1493 nm (4.11) and 2028 nm (4.04). Preliminary kinetic studies of the S2O82 oxidation of the 1,4-DHAQ, 1,4-AHAQ and 1,4-DAAQ dimers show a faster oxidation of the fully reduced form (|2.2|) followed by a slower oxidation of the mixed-valence form (z.sfnc;2.3z.sfnc;). No mechanism could be determined for the faster oxidation. However, the slower oxidation appeared to be first order in both dimer and S2O82−, and involved ion pairing, Kip was determined to be 13 for the 3+,2− ion pair. Values for ket were found to parallel the second ruthenium oxidation potential for the dimers, and were found to be 6 × 10 4, 8 × 10 4 and 1.1 × 10 2 M 1 s 1 for the 1,4-DHAQ, 1,4-AHAQ and 1,4-DAAQ dimers, respectively, at 25°C.

Mechanism of Nitric Oxide Release. I. Two-electron Reduction of Sodium Nitroprusside by l -cysteine in Aqueous Solution

Sodium nitroprusside (SNP) is a well-known vasodilator, which activates the cytosolic isozyme guanylate cyclase. It is quite stable by itself in aqueous solution and in the dark, but produces nitric oxide spontaneously under the appropriate reducing conditions. Both the neutral nitric oxide (NO) and the nitroxyl anion (NO m ) can be produced from SNP depending on the condition employed. NO release is favored at lower pH and cysteine concentration while NO m formation is more likely to occur at higher pH (>7) and cysteine concentration. NO was measured by electrochemical method and the chemical detection of NH 2 OH and NO 2 m are evidences of NO m formation. The mechanism of the reaction was found to be very complicated and involved three clear stages. NO and NO m are postulated to form in the first and third stages, respectively. All three stages showed cysteine dependence and were also affected by the pH of the solution. The first two stages resembled stepwise reversible two-electron reduction of NO + to...