Oxygen atom transfer promoted nitrate to nitric oxide transformation: a step-wise reduction of nitrate → nitrite → nitric oxide

Nitrate reductases (NRs) are molybdoenzymes that reduce nitrate (NO₃⁻) to nitrite (NO₂⁻) in both mammals and plants. In mammals, the salival microbes take part in the generation of the NO₂⁻ from NO₃⁻, which further produces nitric oxide (NO) either in acid-induced NO₂⁻ reduction or in the presence of nitrite reductases (NiRs). Here, we report a new approach of VCl₃ (V³⁺ ion source) induced step-wise reduction of NO₃⁻ in a Co^II-nitrato complex, [(12-TMC)Co^II(NO₃⁻)]⁺ (2,{Co^II–NO₃⁻}), to a Co^III–nitrosyl complex, [(12-TMC)Co^III(NO)]²⁺ (4,{CoNO}⁸), bearing an N-tetramethylated cyclam (TMC) ligand. The VCl₃ inspired reduction of NO₃⁻ to NO is believed to occur in two consecutive oxygen atom transfer (OAT) reactions, i.e., OAT-1 = NO₃⁻ → NO₂⁻ (r₁) and OAT-2 = NO₂⁻ → NO (r₂). In these OAT reactions, VCl₃ functions as an O-atom abstracting species, and the reaction of 2 with VCl₃ produces a Co^III-nitrosyl ({CoNO}⁸) with V^V-Oxo ({V^V O}³⁺) species, via a proposed Co^II-nitrito (3, {Co^II–NO₂⁻}) intermediate species. Further, in a separate experiment, we explored the reaction of isolated complex 3 with VCl₃, which showed the generation of 4 with V^V-Oxo, validating our proposed reaction sequences of OAT reactions. We ensured and characterized 3 using VCl₃ as a limiting reagent, as the second-order rate constant of OAT-2 (k₂^/) is found to be ∼1420 times faster than that of the OAT-1 (k₂) reaction. Binding constant (K_b) calculations also support our proposition of NO₃⁻ to NO transformation in two successive OAT reactions, as K_{b(Co^II–NO2⁻)} is higher than K_{b(Co^II–NO3⁻)}, hence the reaction moves in the forward direction (OAT-1). However, K_{b(Co^II–NO2⁻)} is comparable to K_b{CoNO}⁸, and therefore sequenced the second OAT reaction (OAT-2). Mechanistic investigations of these reactions using ¹⁵N-labeled-¹⁵NO₃⁻ and ¹⁵NO₂⁻ revealed that the N-atom in the {CoNO}⁸ is derived from NO₃⁻ ligand. This work highlights the first-ever report of VCl₃ induced step-wise NO₃⁻ reduction (NRs activity) followed by the OAT induced NO₂⁻ reduction and then the generation of Co-nitrosyl species {CoNO}⁸.

Single metal-induced reduction of NO₃⁻ → {NO₂⁻} → NO via oxygen atom transfer reaction.     

Selenophilicity of Copper in Selenium-Carbon Bond Formation from Selenous Acid Using Cu(II)/Sn(II) Reagent

A selenium transfer reaction from selenous acid to benzyl and alkyl halides is initiated in the presence of stannous chloride and a catalytic amount of cupric chloride resulting in the formation of the corresponding diorganoselenides and/or diorganodiselenides as the major products as indicated by ¹ H, ¹³ C, ⁷⁷ Se NMR, and MS. The reaction is characterized by a dual-metal effect at the selenium activation and transfer step. Thus, initial reaction of stannous chloride, cupric chloride, and selenous acid gives rise to α-Cu ₂ Se. Selenium transfer from the latter to the organic halide takes place with additional assistance of stannous chloride.     

Electrokinetic Behavior of Fluorite

The electrokinetic behavior of fluorite mineral was studied under various partical sizes and different concentrations of oleic acid at constant pH. The particle size has been reduced with an increase in activation time. The surface energies of milled fluorite minerals were calculated theoretically and experimentally. The zeta potential of the fluorite/water system has shifted to lower side with an increase in particle size. The isoelectric point (iep) of fluorite minerals has been shifted to lower side with increase in oleic acid concentration. This indicates the chemisorbed oleate formation on fluorite. A sharp decrease in zeta potential in the pH range of 6.5–8.4 and the decrease in calculated free energy of adsorption shows the formation of calcium dioleate precipitate on fluorite.     

A Stereo Flexible Total Synthesis of Karalicin,an Antiviral Agent

Abstract: The first stereo flexible total synthesis of Karalicin, an antiviral agent recently isolated from a fermentation broth of the Pseudomonas Fluoriscens/Putida strain SS-3 (CCM 4430), from readily available starting materials is described.

     

One-pot,solvent-free Pd(II)-catalyzed direct β-C-H arylation of carboxamides involving anhydrides as substrates via in situ installation of directing group

A one-pot, multicomponent-type, solvent-free Pd(II)-catalyzed direct β-C-H activation/arylation of carboxamides involving anhydrides as substrates via in situ installation of directing group (DG) is reported. Typically, the DG-assisted β-C-H activation/arylation of carboxamides is a two-step process comprising the installation of DG and Pd(II)-catalyzed CH arylation. We attempted a multicomponent-type reaction comprising an anhydride, a DG (e.g. 8-aminoquinoline), an aryl iodide in the presence of the Pd(II) catalyst and an appropriate additive. Different anhydrides, DGs, aryl iodides, catalysts and additives were screened to reveal the scope of this multicomponent-type CH arylation reaction process and various β-C-H arylated carboxamides were obtained in satisfactory to good yields.     

Delaying of cataract through intervention of Hemidesmus indicus in STZ induced diabetic rats

Hemidesmus indicus (L.) R. Br. was extensively used as hypoglycaemic agent and significance of this plant on secondary complications of diabetes remained unknown. The present study was to investigate the anti-cataractous activity of H. indicus against streptozotocin (STZ)-induced diabetic cataract in rodent model. Root extracts have been prepared and tested for inhibition of rat lens aldose reductase (AR) activity. In addition, its pharmacological potential has been investigated in STZ-induced diabetic cataract. Methanol extract of H. indicus-inhibited AR activity in vitro decreased the blood glucose levels, inhibited the AR activity and delayed the onset and progression of cataract in a dose-dependent manner in in vivo and the antioxidant markers have been normalised. Our results demonstrate that H. indicus has decrease the osmotic stress by inhibiting the AR activity and prevented the loss of antioxidants and delayed the progression of diabetic cataract in STZ-induced diabetic rats.     

Electrospray ionization mass spectral studies of N,N-dialkylaminoethane-2-sulphonic acids

Oxidative reactions of VX type compounds and N,N-dialkylaminoethane-2-thiols that are precursors for VX compounds produce N,N-dialkylaminoethane-2-sulphonic acids, N(R(1))(R(2))-CH(2)-CH(2)SO(3)H (where R(1) and R(2) = methyl, ethyl, n-propyl and isopropyl, 1-10), as the degradation products, and these degradation products are considered as markers for the detection of chemicals listed in the schedules of Chemical Weapons Convention (CWC) chemicals. Off-site detection of such degradation products in aqueous samples is an important task in the verification of CWC-related chemicals. Here we report a simple method involving the direct analysis of aqueous samples using positive and/or negative ion electrospray ionization (ESI) for the screening, detection and identification of N,N-dialkylaminoethane-2-sulphonic acids, avoiding sample preparation and chromatographic steps. The positive ion ESI mass spectra of all the compounds result in abundant [M+Na](+) ions, and the negative ion spectra show abundant [M-H](-) ions to confirm their molecular weight. The collision-induced dissociation spectra of [M+Na](+) and [M-H](-) give characteristic product ions by which it is easy to detect and identify all the studied N,N-dialkylaminoethane-2-sulphonic acids including those of isomeric compounds. The method is successfully applied to detect the spiked chemical, N,N-diisopropylaminoethane-2-sulphonic acid, present in a water sample received in a proficiency test.     

Synthesis and evaluation of analgesic and anti-inflammatory activities of most active free radical scavenging derivatives of embelin-A structure-activity relationship

Antioxidant and related properties of the plant Embelia ribes and embelin are well known. In the present study embelin was condensed with various aromatic substituted primary amines to yield ten new and one reported derivatives along with monomethyl embelin. All these compounds along with embelin were evaluated for in vitro antioxidant activity using 2,2'-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) diammonium salt (ABTS) and 2,2'-diphenyl-1-picryl hydrazyl (DPPH) methods. Two para-substituted embelin derivatives showed potent antioxidant activity. These compounds along with embelin were studied for analgesic and anti-inflammatory activities at 10 and 20 mg/kg doses by standard methods. Potent analgesic activity higher than the standard pentazocine was observed. Embelin and both of its derivatives almost completely abolished the acetic acid induced writhing. p-Sulfonylamine phenylamino derivative showed better anti-inflammatory activity than embelin.