Search

Here, we present a detailed investigation on the interaction of 4-chloro-7-nitro-1,2,3-benzoxadiazole (NBD) embedded olanzapine derivative (OLA-NBD) with a model transport protein, human serum albumin (HSA). The thermodynamic parameters, Δ

We report a novel phenazine-embedded fluorescent probe (2-[2-(pyridin-2-ylmethoxy)-phenyl]-1H-imidazo[4,5-b]phenazine, PIP), which upon complexation with Cu(II)-ion-forming [(PIP)CuII(Cl)] becomes ...

A dual-emission pyrene-based new fluorescent probe (N-(4-nitro-phenyl)-N′-pyren-1-ylmethyl-ene-ethane-1,2-diamine (PyDA-NP)) displays green fluorescence for nitric oxide (NO) sensing, whereas it exhibits blue emission in the aggregated state. The mechanism of nitric oxide (NO/NO+) sensing is based on N-nitrosation of aromatic secondary amine, which was not interfered by reactive oxygen species and reactive nitrogen species. The aggregation-induced enhancement of emission (AIEE) behaviors of the PyDA-NP could be attributed to the restriction of intramolecular rotation and vibration, resulting in rigidity enhancement of the molecules. The AIEE behavior of the probe was well established from fluorescence, dynamic light scattering, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, optical fluorescence microscopy, and time-resolved photoluminescence studies. In a H2O/CH3CN binary mixture (8:2 v/v), the probe showed maximum aggregation with extensive (833-fold) increases in fluorescence intensity and high quantum yield (0.79). The aggregated state of the probe was further applied for the detection of nitroexplosives. It displayed efficient sensing of 2,4,6-trinitrophenol (TNP), corroborating mainly the charge-transfer process from pyrene to a highly electron-deficient TNP moiety. Furthermore, for the on-site practical application of the proposed analytical system, a contact-mode analysis was performed.

The Mn(II)-mediated transformation of 2-cyanopyrimidine to methylimidate in the presence of inorganic azide is proven through isolation and structural characterization of a metal complex. Though the reaction conditions are favorable for a "click" reaction leading to the formation of tetrazole, as evidenced from recent studies, we are astonished to see the formation of methylimidate in MeOH instead of tetrazole, which is supposed to form only in the presence of catalytic amount of corresponding alkoxide ion as base. The catalytic nature of this transformation reaction was confirmed by performing these experiments under catalytic conditions and analyzing the products using liquid chromatography-mass spectrometry techniques, which clearly showed ∼96% and ∼60% selectivity of methylimidate along with almost 100% conversion in the presence of Mn(II) and Co(II) as catalysts, respectively. In absence or presence of other metal ions like Cu(II), Ni(II), Fe(II), Zn(II), etc. only tetrazole formation takes place. So the present findings extended the formation of methylimidate catalyzed by metal ions in the presence of azide ion in alcoholic medium. Importantly, a probable mechanism for this unexpected transformation was framed based on the structural analysis and high-resolution mass spectrometry (electrospray ionization MS(+)) studies. The magnetic studies were also performed on complexes [Mn(L)(N3)2]n (1) and [Cu (L(2))2]n (2a), showing anti-ferromagnetic character for compound 1 and negligible coupling for the copper complex 2a.

A new, easily synthesizable rhodamine-based chemosensor with potential N2O2 donor atoms, L(3), has been characterized by single-crystal X-ray diffraction together with (1)H NMR and high-resolution mass spectrometry (HRMS) studies. L(3) was found to bind selectively and reversibly to the highly toxic Hg(2+) ion. The binding stoichiometry and formation constant of the sensor toward Hg(2+) were determined by various techniques, including UV-vis, fluorescence, and Job's studies, and substantiated by HRMS methods. None of the biologically relevant and toxic heavy metal ions interfered with the detection of Hg(2+) ion. The limit of detection of Hg(2+)calculated by the 3σ method was 1.62 nM. The biocompatibility of L(3) with respect to its good solubility in mixed organic/aqueous media (MeCN/H2O) and cell permeability with no or negligible cytotoxicity provides good opportunities for in vitro/in vivo cell imaging studies. As the probe is poorly soluble in pure water, an attempt was made to frame nano/microstructures in the absence and in the presence of sodium dodecyl sulfate (SDS) as a soft template, which was found to be very useful in synthesizing morphologically interesting L(3) microcrystals. In pure water, micro-organization of L(3) indeed occurred with block-shaped morphology very similar to that in the presence of SDS as a template. However, when we added Hg(2+) to the solution of L(3) under the above two conditions, the morphologies of the microstructures were slightly different; in the first case, a flowerlike structure was observed, and in second case, a simple well-defined spherical microstructure was obtained. Optical microscopy revealed a dotlike microstructure for L(3)-SDS assemblies, which changed to a panicle microstructure in the presence of Hg(2+). UV-vis absorption and steady-state and time-resolved fluorescence studies were also carried out in the absence and presence of Hg(2+), and also the SDS concentration was varied at fixed concentrations of the receptor and guest. The results revealed that the fluorescence intensity increased steadily with [SDS] until it became saturated at ∼7 mM SDS, indicating that the extent of perturbation to the emissive species increases with the increase in [SDS] until it becomes thermodynamically stable. There was also an increase in anisotropy with increasing SDS concentration, which clearly manifests the restriction of movement of the probe in the presence of SDS.

A novel water-stable (t1/2 ∼ 6.8 days) mononuclear manganese(IV) complex of a hexacoordinating non-Schiff-base ligand (H4L) with N2O4-donor atoms has been synthesized and characterized crystallographically. High-frequency electron paramagnetic resonance experiments performed on a single crystal reveal a manganese(IV) ion with an S = 3/2 ground spin state that displays a large single-ion anisotropy, setting the record of mononuclear manganese(IV) complexes reported so far. In addition, spin-echo experiments reveal a spin-spin relaxation time T2 ∼ 500 ns.

A new transition-metal-free, sodium metaperiodate (NaIO4)-mediated direct oxidation of methylarenes and benzylic bromides to the corresponding aromatic carboxylic acids is described. Under the same reaction conditions, benzylic alcohols are selectively oxidized to afford the corresponding aldehydes in good yields without undergoing overoxidation. Unprecedentedly, oxidation of benzyl bromide, toluene, or benzyl alcohol with NaIO4 underwent nuclear bromination followed by oxidation to give 4-bromobenzoic acid in 60−79% yields.

Rate constants for the attachment of CH(CN)2- to Fischer carbene complexes of the type (CO)5MC(XR)C6H4Z with M = Cr, W and XR = OMe, OEt, SMe in 50% MeCN−50% water (v/v) at 25 °C are reported. The ...

Acidity constants of six substituted 1-benzyl-1-methoxy-2-nitroethylenes (2-Z with Z = m-NO(2), m-CF(3), m-Cl, H, p-Me, p-MeO) and their respective nitronic acids were determined in 50% DMSO-50% water (v/v) at 20 degrees C. Kinetic data were obtained on the reversible deprotonation of all six 2-Z by OH(-) and piperidine and on the reversible deprotonation of 2-NO(2)() by piperazine, 1-(2-hydroxyethyl)piperazine, and morpholine in the same solvent. These data allowed a determination of the Brønsted coefficients alpha (dependence on acidity of 2-Z) and beta (dependence on amine basicity). The fact that alphabeta indicates the presence of a transition state imbalance which, however, is much smaller than that for the deprotonation of arylnitromethanes. The reasons for this reduction in the imbalance and their relevance to a recent study of the deprotonation of Fischer carbene complexes are discussed.

A kinetic study of the reversible cyclization of (((2-hydroxyethyl)thio)arylcarbene)pentacarbonyltungsten(0) complexes, 2-SR(Z), in 50% MeCN−50% water (v/v) at 25 °C is reported. The results are co...

Rate and equilibrium constants for the conversion of (CO)5CrC(OCH2CH2OH)Ph (8-CrOOH), (CO)5WC(OCH2CH2OH)Ph (8-WOOH), (CO)5CrC(SCH2CH2OH)Ph (8-CrSOH), and (CO)5WC(SCH2CH2OH)Ph (8-WSOH) into the corresponding cyclic adducts (9-CrOO- for M = Cr, X = O; 9-WOO- for M = W, X = O; 9-CrSO- for M = Cr, X = S; 9-WSO- for M = W, X = S) are reported. Under basic conditions the reaction occurs via the respective oxyanions, (CO)5CrC(OCH2CH2O-)Ph (8-CrOO-), etc.; under acidic conditions the reaction may either be concerted with water acting as a general base catalyst or stepwise via a zwitterionic intermediate. The absence of buffer catalysis suggests but does not prove the operation of the stepwise mechanism. The equilibrium constants for cyclization of 8-CrSO- and 8-WSO- are about 1 order of magnitude higher than for 8-CrOO- and 8-WOO-, respectively. For the rate constants the situation is reversed, with 8-CrOO- and 8-WOO- being substantially more reactive than 8-CrSO- and 8-WSO-, respectively. These results reflect t...

Rate constants for the reversible deprotonation of (CO)5CrC(SCH3)CH3 (9-Cr) and (CO)5WC(SCH3)CH3 (9-W) by OH-, water, a number of primary aliphatic and secondary alicyclic amines, and a series of carboxylate ions have been determined in 50% MeCN−50% water at 25 °C. This represents the first such study of Fischer carbene complexes stabilized by a thioalkoxy group. Comparison of our results to those of the corresponding methoxy derivatives (CO)5CrC(OCH3)CH3 (2-Cr) and (CO)5WC(OCH3)CH3 (2-W) reveals that the change in the π-donor group from MeO to MeS leads to (1) a strong increase in the thermodynamic acidity, (2) an increase in the dependence of the pKa on the nature of the metal, (3) a decrease in the intrinsic rate constants for proton transfer, and (4) a decrease in the dependence of the intrinsic rate constant on the metal. Observations 1, 2, and 4 can be attributed to the weaker π-donor capability of the MeS group while observation 3 is the combined result of a steric effect due to the larger size of ...

Oxidation of trans-I−NiIIL, or NiIILout, by •OH radicals was carried out by irradiating N2O saturated solutions containing the complex, prepared by mixing equimolar concentrations of the metal ion and the ligand at pH 3.50. The intermediate thus formed has a strong absorption band at 310 nm and is stable for hours. That this unstable complex is a nickel(III) species was verified by EPR spectroscopy and its chemical reduction with ascorbic acid, which was found to be instantaneous. The most striking feature of the oxidation by •OH radicals, which are powerful single electron oxidizing agents, is that it produces a nickel(III) species which is different from the electrochemically produced one as manifested by their absorption spectra and EPR signals. The radiolytically produced nickel(III) species undergoes decarboxylation leading to the production of CO2, CH2O, NiIIL‘ and NiIIL (L‘ = the new ligand produced after oxidative degradation of one of the N-acetate groups of the ligand). The electrochemical oxida...

Rate and equilibrium constants for the nucleophilic attachment of various thiolate ions to (CO)5MC(SMe)Ph (M = Cr and W) and for the attachment of HOCH2CH2S- to (CO)5WC(SCH2CH2OH)C6H4Z (Z = CF3, Cl, F, H, Me, MeO, and Me2N) have been determined in 50% MeCN−50% water (v/v) at 25 °C. For some of the adducts, those of the general structure (CO)5MC(SR,SR‘)C6H4Z, a kinetic determination of the pKa of their metal-protonated conjugate acid, (CO)5M(H)C(SR,SR‘)C6H4Z, is also reported. On the basis of Bronsted coefficients, Hammett ρ values and comparisons with the reactions of the same thiolate ions with methoxy carbene complexes such as (CO)5MC(OMe)Ph, insights into the role played by desolvation of the nucleophile prior to C−S bond formation, by the smaller π-donor and inductive but larger steric effects of the MeS compared to the MeO group, by transition state imbalances, etc. are discussed. The pKa values obtained for (CO)5M(H)C(SR,SR‘)C6H4Z were used to resolve a mechanistic ambiguity in the hydrolysis of Fi...