Mahammad Ali

Electron exchange and transfer reactions of heteropoly oxometalates

A. Introduction B. Electron exchange in dodecatungstocobaltate(II/III) and dodecatungstocuprate(I/II) C. Electron transfer reactions of dodecatungstocobaltate(II1) (i) Reactions with inorganic reagents (ii) Reactions with thiols and related species (iii) Reactions with carboxylates, cc-hydroxycarboxylates and amine-N-polycarboxylates (iv) Reactions with carbonyl compounds and esters (v) Reactions with carbohydrates (vi) Reactions with substituted alkyl aromatic compounds (vii) Miscellaneous reactions D. Electron transfer reactions of dodecatungstocobaltate(I1) (i) Reactions of [CO”W,,O,,]~with peroxodisulphate and periodate (ii) Reactions of [Co”W,,O,,]‘~ and [CO”W,,O,,]~with polyhalogenated alkanes E. Electron transfer reactions of dodecamolybdocerate(IV) F. Electron transfer reactions of nonamolybdonickelate(IV) and nonamolybdomanganate(IV) G. Conclusions Note added in proof References . . . .._..._ _........__._.......__.....

Morphology-Directing Synthesis of Rhodamine-Based Fluorophore Microstructures and Application toward Extra- and Intracellular Detection of Hg2+

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 Jobs 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.

Synthesis, crystal structure, EPR and magnetic properties of a cyano-bridged CuII–NiII heterobimetallic complex: an unusual structure with long-range ferromagnetic exchange through hydrogen bonding

A cyano-bridged CuII–NiII dimeric complex [Cu(Me6Cy)][Ni(CN)4] has been synthesized and characterized by its single crystal X-ray structure determination. The square planar [Cu(Me6Cy)]2+ cation is converted to a distorted trigonal bipyramidal (TBP) geometry through ligation to one of the cyano groups of [Ni(CN)4]2− in the equatorial plane, keeping the other three as terminal. Inspection of the X-ray data reveals that the Cu–N(6)–C(6) angle of the bridging cyano group is perfectly linear (180°). The room temperature (RT) EPR spectrum of polycrystalline [Cu(Me6Cy)][Ni(CN)4] is typical for mononuclear copper(II) complexes of axial symmetry, where the flattened out symmetry axis is characterized by g⊥ = 2.143 ± 0.005 and g‖ = 2.002 ± 0.005. No half field (ΔM = 2) signals were observed. RT EPR spectrum of polycrystalline [CuII(Me6Cy)](ClO4)2 yields an EPR signal with g‖ = 2.394 ± 0.005 and g⊥ = 2.045 ± 0.005, indicating that this parent compound has a different geometry than [Cu(Me6Cy)][Ni(CN)4]. Variable temperature magnetic moment studies on [Cu(Me6Cy)][Ni(CN)4] indicate a very weak long-range ferromagnetic exchange through hydrogen bonding between copper(II) ions (S = ½). The present investigation provides a unique example where the original square planar [Cu(Me6Cy)]2+ moiety rearranges itself to a trigonal bipyramidal geometry under the influence of [Ni(CN)4]2−. This is probably only the second, rare example, and perhaps the first, for a macrocyclic precursor using only one cyano group of [Ni(CN)4]2− for bridging, leading to a discrete dinuclear complex.

ESIPT blocked CHEF based differential dual sensor for Zn2+ and Al3+in a pseudo-aqueous medium with intracellular bio-imaging applications and computational studies

A novel 3-hydroxymethyl-5-methylsalicylaldehydenaphthyl-hydrazone (H3SAL-NH) exhibits ESIPT behaviour due to proton transfer from the phenolic OH group to the azomethine N atom in the excited state. Through this ESIPT behaviour together with cis–trans isomerization of the azomethine group, the free ligand becomes very weakly fluorescent. However, in the presence of Zn2+ and Al3+ the ESIPT and isomerization are blocked due to coordination to the metal ions thereby causing turn on fluorescence for Al3+ and Zn2+. Moreover, Zn2+ can easily be displaced from the [H2SAL-NH–Zn2+] complex by Al3+ thereby enhancing the differential selectivity for Al3+ over Zn2+. This probe was found to be selective for Al3+ over Zn2+ in the presence of Na2H2EDTA, under both intra- and extracellular conditions. The LODs for Zn2+ and Al3+ were determined by 3σ methods and were found to be 3.1 nM and 0.92 nM, respectively. Thus, the differentially selective turn-on fluorescence behaviour of H3SAL-NH for Zn2+ and Al3+ is based on the combined blocking of ESIPT and CN isomerization, and a chelation-enhanced fluorescence (CHEF) effect. The coordination modes of the complexes were investigated through spectroscopic and computational studies. H3SAL-NH also exhibits good photostability and very low cytotoxicity and is useful for fluorescence imaging of Zn2+ and Al3+ ions in live HepG2 cells.

Oxidation reactions of mononuclear manganese (III) complexes

Abstract This review encompasses the oxidation reactions of various manganese(III) coordinated molecules. The reactions have been categorized primarily with respect to the type of manganese(III) complexes. Emphasis has been given to the reactivity of the manganese(III) complexes derived from aminopolycarboxylic acids, acetylacetone, porphyrins, bipyridine and pyrophosphoric acid with various organic, inorganic and biochemical electron donors. Kinetic and mechanistic features associated with the interactions have been highlighted and analysed critically. The utility and scope of the catalytic oxidation of hydrocarbons and secondary amines by manganese(III) porphyrins are discussed at length.

A novel rhodamine-3,4-dihydro-2H-1,3-benzoxazine conjugate as a highly sensitive and selective chemosensor for Fe3+ ions with cytoplasmic cell imaging possibilities

A novel, highly sensitive and selective fluorescent chemosensor ‘rhodamine-3,4-dihydro-2H-1,3-benzoxazine’ [RH-BZN (1)] has been synthesized and characterized by single crystal X-ray diffraction and other physicochemical techniques. In 3:7 water:MeCN (v/v) at pH 7.2 (10 mM HEPES buffer, μ = 0.05 M LiCl) it selectively recognizes Fe3+ through 1:1 complex formation resulting in a 240-fold fluorescence enhancement and a binding constant (Kf) of 1.50 × 104 M−1. The otherwise non-fluorescent spirolactam form of the probe results in dual changes in absorbance and fluorescence arising out of opening of the spirolactam ring through coordination to Fe3+ ions. This probe could suitably be employed for cytoplasmic intracellular imaging of Fe3+ without notable cytotoxicity. The reversible binding of RH-BZN to Fe3+ was confirmed by reacting with tetra-n-butylammonium fluoride both in extra- and intra-cellular conditions.

Kinetics and mechanism of the oxidation of histidine by dodecatungstocobaltate(III) and trans-cyclohexane-1,2-diamine-N,N,N′,N′-tetraacetatomanganate (III) in aqueous medium

The oxidation of histidine with dodecatungstocobaltate(III), CoW12O405– and trans-cyclohexane-1,2-diamine-N,N,N′,N′-tetraacetatomanganate(III), [MnIII(cdta)]– have been investigated in the range pH 3.0–9.5 at variable reductant concentrations, at a constant ionic strength and temperature. Both reactions are found to be dependent on the first powers of the concentration of the substrate and oxidants and follow the general rate law, -d[Ox]/dt= 2k[Ox][Hist], where 2 is the stoichiometric factor. In the reduction of [MnIII(cdta)]–, a bell-shaped curve is obtained for the variation of second-order rate constant (K) as a function of pH, and this has been explained by considering the hydroxo form of the complex as being unreactive towards the reductant. An attempt has been made to verify the effect of alkali cation catalysis on the reaction rate. The observed alkali cation catalysis for the reduction of CoW12O405– is consistent with a rate law, k=k0+kc[M+] where k0 and kc are the rate constants for the spontaneous and catalysed paths respectively. For the reduction of [MnIII(cdta)]–, a negligible dependence of rate on [M+] was noted. All the observations are successfully explained by considering outer-sphere mechanistic pathways for both reactions.

A rhodamine based fluorescent trivalent sensor (Fe3+, Al3+, Cr3+) with potential applications for live cell imaging and combinational logic circuits and memory devices

A sensor (HL5) based on rhodamine 6G–en and 3-(3,5-dimethyl-pyrazol-1-ylmethyl)-2-hydroxy-5-methyl-benzaldehyde (HL4) has been developed for a highly sensitive and selective CHEF based recognition of trivalent metal ions M3+ (M = Al, Fe and Cr) over mono- and di-valent and other biologically abundant trivalent metal ions with prominent enhancement in absorption and emission intensities. A large enhancement of fluorescence intensities for Fe3+ (21 fold), Al3+ (14 fold) and Cr3+ (10 fold) was observed upon addition of 1.8 equivalents of these metals into the probe in methanol/H2O (1 : 1, v/v, pH 7.2) with the possibility of naked eye detection. The corresponding Kf values were evaluated to be 6.7 × 104 M−1 (Fe3+); 8.2 × 104 M−1 (Al3+) and 6.0 × 104 M−1 (Cr3+). The quantum yields of HL5 and [HL5–Fe3+] and [HL5–Cr3+] and [HL5–Al3+] complexes in methanol/H2O (1 : 1, v/v, pH 7.2) are found to be 0.013, 0.290, 0.120, and 0.158, respectively, using rhodamine-6G as the standard. The LOD for Fe3+, Al3+ and Cr3+ were determined by 3σ methods with values 0.29, 0.34 and 0.31 μM, respectively. An arsenate ion snatches Al from the Al–HL5 complex and quenches its fluorescence via its ring closed spirolactam form. Advanced level molecular logic devices using the inputs 2 and 4 and memory devices, have been constructed. The low cytotoxicity and large enhancement in fluorescence intensity of HL5 upon complexation with M3+ metal ions make the probe suitable for bio-imaging of M3+ (M = Al, Fe and Cr) in living cells and native cellular iron pools.

A novel 8-hydroxyquinoline-pyrazole based highly sensitive and selective Al(III) sensor in a purely aqueous medium with intracellular application: experimental and computational studies

A new 8-hydroxyquinoline-pyrazole based highly sensitive and selective Al3+ sensor, 8Q-NH-Pyz (H2L3), was found to exhibit a turn-on fluorescence enhancement (FE) as high as 157 fold with Kd = (1.76 ± 0.06) × 10−5 M. The 1:1 binding stoichiometry was revealed from the linear fit of (Fmax − F0)/(F − F0) vs. 1/[Al3+] of the fluorescence titration data which was further substantiated by Jobs method and HRMS studies. The LOD determined by 3σ methods was found to be 4.29 nM and quantum yields were determined to be 0.002 and 0.28 for the ligand and its Al3+ complex, respectively. The tentative coordination environment in the [Al(L3)(H2O)]+ complex was delineated by DFT calculations. TDDFT calculations reveal spectral features comparable to the experimental ones. This constitutes the first report on the fluorescence sensing of Al3+ and hence F− in a purely aqueous medium.

A novel pyrene-2-(pyridin-2-ylmethylsulfanyl)ethylamine based turn-on dual sensor for Al3+: experimental and computational studies

A new pyrene based highly sensitive and selective Al3+ sensor, pyrene-2-(pyridin-2-ylmethylsulfanyl)-ethylamine (PP), was found to exhibit a turn-on fluorescence enhancement (FE) as high as 7.4 fold with Kd (2.55 ± 0.10) × 10−4 M and n = 1. This probe binds reversibly with Al3+ in the presence of H2EDTA2−, both under intra- and exctracellular conditions. LOD determined by 3σ methods was found to be 15 nM while LOQ = 52.8 nM. The tentative coordination environment in the Al3+–PP complex was delineated by DFT calculations both on the free ligand and complex. The TDDFT calculations reveal spectral features comparable to the experimental ones.