- Competitive behavior of nitrogen based axial ligands in the oxovanadium(IV)-salen catalyzed sulfoxidation of phenylmercaptoacetic acid
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The sulfoxidation of twelve phenylmercaptoacetic acids (PMAA) by H2O2 catalyzed by three oxovanadium(IV)-salen complexes, having varied substituents on PMAA and salen with regard to their position, size and inductive effect, has been performed spectrophotometrically in 100percent acetonitrile medium. Three nitrogen bases (NB), pyridine (Py), imidazole (ImH) and 1-methylimidazole (MeIm), were used as axial ligands. It has been found that the rate of sulfoxidation is not only tuned by the substituents on PMAA and salen, but it is also varied by the addition of nitrogen bases. The observed order of retardation found among the different nitrogen bases is ImH > MeIm > Py. The rate of reaction decreases with the increase in concentration of the NB axial ligands. The strongly binding ImH shows the least reactivity. Hydroperoxovanadium(V)-salen has been proposed as the sole active oxidizing species. A detailed mechanistic study reveals that the low rate constant values in the presence of the nitrogen base is due to the existence of competition of NB with H2O2 and PMAA during the formation of active species and the coordination of PMAA with active species, respectively. Both electron donating and electron withdrawing substituents on PMAA retard the sulfoxidation rate significantly. The Hammett correlation between the rate constants and substituent constants shows a non-linear concave downward curve which is explained by the existence of two different rate determining steps within the same mechanism; coordination of PMAA with the active species for electron withdrawing substituents and transfer of oxygen to PMAA for electron donating substituents. All the experimental observations are explained by proposing a suitable mechanism.
- Kavitha, C.,Subramaniam, P.
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- 2-(4′-Pyridyl-N-oxide)-Substituted Hemithioindigos as Photoresponsive Guests for a Super Aryl-Extended Calix[4]pyrrole Receptor
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We report the synthesis of two 2-(4′-pyridyl-N-oxide)-substituted hemithioindigos (HTIs). We probed their photoisomerization by using UV/Vis and 1H NMR spectroscopy techniques. Light irradiation at λ=450 nm provoked the isomerization of the HTI Z isomer to the E counterpart to a large extent (≈80 % at the photostationary state). 1H NMR titration experiments revealed the formation of thermodynamically and kinetically stable 1:1 inclusion complexes of the (Z)-HTI isomers with a super aryl-extended host (association constant>104 m?1). Photoirradiation at λ=450 nm of the inclusion complexes induced the isomerization of the bound HTI N-oxide to afford the (E)-HTI?calix[4]pyrrole complex. We determined accurate association constant values for the 1:1 inclusion complexes of the (Z)- and (E)-HTI isomers by using isothermal titration calorimetry experiments. The results showed that the stability constants of the (E)-HTI complexes were 2.2–2.8-fold lower than those of the (Z)-HTI counterparts, which explains the lack of light-induced release of the former to the bulk solution.
- Moncelsi, Giulia,Escobar, Luis,Dube, Henry,Ballester, Pablo
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supporting information
p. 1632 - 1639
(2018/05/30)
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- Modulation of catalytic activity by ligand oxides in the sulfoxidation of phenylmercaptoacetic acids by oxo(salen)chromium(V) complexes
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Mechanism of sulfoxidation of eleven para-substituted phenyl mercaptoacetic acids (PMAAs) by three oxo(salen)chromium(V)+PF6?complexes in the presence of different ligand oxides (LOs) such as triphenylphosphine oxide, pyridine N-oxide and 4-picoline N-oxide have been studied spectrophotometrically in 100% acetonitrile medium. Spectral and kinetic profiles establish the formation of adduct, O[dbnd]Cr(V)(salen)+-LO as the reactive intermediate in the catalytic cycle. The rate of sulfoxidation is found to be enhanced significantly by the addition of LOs and introduction of substituent in PMAA and salen complex. Both electron releasing and electron withdrawing substituents in the substrate and oxidant facilitate the rate of sulfoxidation. Correlation with Hammett constants yields a non-linear concave upward curve. Based on the experimental results and substituent effects two different mechanisms, a direct oxygen atom transfer (DOT) for PMAAs with electron withdrawing substituents and a single electron transfer for PMAAs with electron donating substituents have been postulated.
- Subramaniam,Anbarasan,Sugirtha Devi,Ramdass
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- A paradigm shift in rate determining step from single electron transfer between phenylsulfinylacetic acids and iron(III) polypyridyl complexes to nucleophilic attack of water to the produced sulfoxide radical cation: a non-linear Hammett
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Mechanism of oxidative decarboxylation of phenylsulfinylacetic acids (PSAAs) by iron(III) polypyridyl complexes in aqueous acetonitrile medium has been investigated spectrophotometrically. An initial intermediate formation between PSAA and [Fe(NN)3]3+ is confirmed from the observed Michaelis–Menten kinetics and fractional order dependence on PSAA. Significant rate retardation with concentration of [Fe(NN)3]3+ is rationalized on the basis of coordination of a water molecule at the carbon atom adjacent to the ring nitrogen of the metal polypyridyl complexes by nucleophilic attack at higher concentrations. Electron-withdrawing and electron-releasing substituents in PSAA facilitate the reaction and Hammett correlation gives an upward ‘V’ shaped curve. The apparent upward curvature is rationalized based on the change in the rate determining step from electron transfer to nucleophilic attack, by changing the substituents from electron-releasing to electron-withdrawing groups. Electron-releasing substituents in PSAA accelerate the electron transfer from PSAA to the complex and also stabilize the intermediate through resonance interaction leading to negative reaction constants (ρ). Conversely, electron-withdrawing groups, while retarding the electron transfer exert an accelerating effect on the nucleophilic attack of H2O which leading to low magnitude of ρ+ compared to high ρ? values of electron-releasing groups. Marcus theory is applied, and a fair agreement is seen with the experimental values. Copyright
- Subramaniam, Perumal,Janet Sylvia Jaba Rose, Jebamoney,Jeevi Esther Rathinakumari, Rajasingh
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p. 496 - 504
(2016/09/21)
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- Spectral and mechanistic investigation of Oxidative Decarboxylation of Phenylsulfinylacetic Acid by Cr(VI)
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The oxidative decarboxylation of phenylsulfinylacetic acid (PSAA) by Cr(VI) in 20% acetonitrile - 80% water (v/v) medium follows overall second order kinetics, first order each with respect to [PSAA] and [Cr(VI)] at constant [H+] and ionic strength. The reaction is acid catalysed, the order with respect to [H+] is unity and the active oxidizing species is found to be HCrO3+. The reaction mechanism involves the rate determining nucleophilic attack of sulfur atom of PSAA on chromium of HCrO3+ forming a sulfonium ion intermediate. The intermediate then undergoes a,β-cleavage leading to the liberation of CO2. The product of the reaction is found to be methyl phenyl sulfone. The operation of substituent effect shows that PSAA containing electron-releasing groups in the meta- and para-positions accelerate the reaction rate while electron withdrawing groups retard the rate. An excellent correlation is found to exist between log k2 and Hammett s constants with a negative value of reaction constant. The p value decreases with increase in temperature evidencing the high reactivity and low selectivity in the case of substituted PSAAs.
- Subramaniam, Perumal,Selvi, Natesan Thamil,Devi, Soundarapandian Sugirtha
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- NOVEL COMPOUNDS, ISOMER THEREOF, OR PHARMACEUTICALLY ACCEPTABLE SALTS THEREOF AS VANILLOID RECEPTOR ANTAGONIST; AND PHARMACEUTICAL COMPOSITIONS CONTAINING THE SAME
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This present invention relates to novel compounds, isomer thereof or pharmaceutically acceptable salts thereof as vanilloid receptor (Vanilloid Receptor 1; VR1; TRPV1) antagonist; and a pharmaceutical composition containing the same. The present invention provides a pharmaceutical composition for preventing or treating a disease such as pain, inflammatory disease of the joints, neuropathies, HIV-related neuropathy, nerve injury, neurodegeneration, stroke, urinary bladder hypersensitivity including urinary incontinence, cystitis, stomach duodenal ulcer, irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD), fecal urgency, gastro-esophageal reflux disease (GERD), Crohn's disease, asthma, chronic obstructive pulmonary disease, cough, neurotic/allergic/inflammatory skin disease, psoriasis, pruritus, prurigo, irritation of skin, eye or mucous membrane, hyperacusis, tinnitus, vestibular hypersensitivity, episodic vertigo, cardiac diseases such as myocardial ischemia, hair growth-related disorders such as effluvium, alopecia, rhinitis, and pancreatitis.
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Page/Page column 73
(2010/11/28)
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- Propenyl cephalosporin derivatives and process for the manufacture thereof
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Disclosed are cephalosporin derivatives of the general formula wherein R is an organic residue with a molecular weight not exceeding 400 bonded to the adjacent sulphur atom via carbon and consisting of carbon, hydrogen, and optional oxygen, sulfur, nitrogen and/or halogen atoms; R1 is hydrogen, lower alkyl or phenyl; and A is a secondary, tertiary or quaternary nitrogen atom bound directly to the propenyl group and being substituted by an organic residue with a molecular weight not exceeding 400 and consisting of carbon, hydrogen, and optional oxygen, sulfur, nitrogen and/or halogen atoms,as well as readily hydrolyzable esters thereof, pharmaceutically acceptable salts of said compounds and hydrates of the compounds of formula I and of their esters and salts.
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- PHENYLSULFONYL NITROMETHANES AS ALDOSE REDUCTASE INHIBITORS
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The invention concerns novel pharmaceutical compositions for use in the treatment of certain complications of diabetes and galactosemia and which contain a nitromethane derivative (or its non-toxic salt) as active ingredient. The nitromethane derivatives
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- Theoretical and Spectroscopical Investigations of Indigo Dyes, XXII. - Preparations of 5,5'- and 6,6'-Dialkylated Indigo Dyes
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The manifolded applicabilities of indigo dyes are strongly restricted by the low solubility of most of their representatives.We describe in this paper the preparation of a series of dialkylated indigos 1, thioindigos 2, dyes of the cibaviolett-type 3, and of the corresponding vinylogues 4, 5, and 6 by different synthetic methods.Some of the prepared compounds show a remarkable solubility and can be used for spectroscopic measurements even in non-polar solvents.
- Meier, Helmut,Luettke, Wolfgang
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p. 1303 - 1333
(2007/10/02)
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