In Hong Hwang

Selective fluorescence assay of aluminum and cyanide ions using chemosensor containing naphthol

The selective assay of aluminum and cyanide ions is reported using fluorescence enhancement and quenching of a phenol–naphthol based chemosensor (PNI) in aqueous and nonaqueous solvents, respectively. PNI gave no significant fluorescence in water. The binding properties of PNI with metal ions were investigated by UV-vis, fluorescence, and electrospray ionization mass spectrometry in a Bis–Tris buffer solution. The addition of aluminum ions switches on the fluorescence of the sensor PNI in water, comparable to relatively very low fluorescence changes in the presence of various other metal ions. The complex stability constant (Ka) for the stoichiometric 1 : 1 complexation of PNI with aluminium ions was obtained by fluorimetric titrations and NMR experiments. However, upon treatment with cyanide ions, the fluorescence of PNI was selectively turned off and the yellow solution of PNI turned to red in methanol. Other comparable anions, such as F−, Cl−, Br−, I−, CH3COO−, and H2PO4−, afforded no apparent fluorescence quenching. The interaction of PNI with cyanide ions was studied by NMR experiments.

A highly selective and sensitive fluorescent turn-on Al3+ chemosensor in aqueous media and living cells: experimental and theoretical studies

A highly selective and sensitive fluorescent chemosensor (1) based on a 2-aminobenzoic acid Schiff base has been synthesized in one step. The binding properties of 1 with metal ions were investigated by fluorescence, UV-vis, 1H NMR and electrospray ionization mass spectra. This sensor exhibited enhanced fluorescence in the presence of Al3+ in aqueous solution and also in living cells. The sensing mechanism of 1 toward Al3+ was explained by DFT/TDDFT calculations. The binding constant was determined to be 3.1 × 108 M−1 which is one of the highest binding affinities among such simple Schiff bases for Al3+ in buffer solution. The calibration curve for the analytical performance of Al3+ was found to be linear over a concentration range with a very low detection limit of 290 nM (3σ).

Remarkable Solvent, Porphyrin Ligand, and Substrate Effects on Participation of Multiple Active Oxidants in Manganese(III) Porphyrin Catalyzed Oxidation Reactions

The participation of multiple active oxidants generated from the reactions of two manganese(III) porphyrin complexes containing electron-withdrawing and -donating substituents with peroxyphenylacetic acid (PPAA) as a mechanistic probe was studied by carrying out catalytic oxidations of cyclohexene, 1-octene, and ethylbenzene in various solvent systems, namely, toluene, CH(2) Cl(2) , CH(3) CN, and H(2) O/CH(3) CN (1:4). With an increase in the concentration of the easy-to-oxidize substrate cyclohexene in the presence of [(TMP)MnCl] (1a) with electron-donating substituents, the ratio of heterolysis to homolysis increased gradually in all solvent systems, suggesting that [(TMP)Mn-OOC(O)R] species 2a is the major active species. When the substrate was changed from the easy-to-oxidize one (cyclohexene) to difficult-to-oxidize ones (1-octene and ethylbenzene), the ratio of heterolysis to homolysis increased a little or did not change. [(F(20) TPP)Mn-OOC(O)R] species 2b generated from the reaction of [(F(20) TPP)MnCl] (1b) with electron-withdrawing substituents and PPAA also gradually becomes involved in olefin epoxidation (although to a much lesser degree than with [(TMP)Mn-OOR] 2a) depending on the concentration of the easy-to-oxidize substrate cyclohexene in all aprotic solvent systems except for CH(3) CN, whereas Mn(V)=O species is the major active oxidant in the protic solvent system. With difficult-to-oxidize substrates, the ratio of heterolysis to homolysis did not vary except for 1-octene in toluene, indicating that a Mn(V)=O intermediate generated from the heterolytic cleavage of 2b becomes a major reactive species. We also studied the competitive epoxidations of cis-2-octene and trans-2-octene with two manganese(III) porphyrin complexes by meta-chloroperbenzoic acid (MCPBA) in various solvents under catalytic reaction conditions. The ratios of cis- to trans-2-octene oxide formed in the reactions of MCPBA varied depending on the substrate concentration, further supporting the contention that the reactions of manganese porphyrin complexes with peracids generate multiple reactive oxidizing intermediates.

Terminal and Internal Olefin Epoxidation with Cobalt(II) as the Catalyst: Evidence for an Active Oxidant CoII–Acylperoxo Species

A simple catalytic system that uses commercially available cobalt(II) perchlorate as the catalyst and 3-chloroperoxybenzoic acid as the oxidant was found to be very effective in the epoxidation of a variety of olefins with high product selectivity under mild experimental conditions. More challenging targets such as terminal aliphatic olefins were also efficiently and selectively oxidized to the corresponding epoxides. This catalytic system features a nearly nonradical-type and highly stereospecific epoxidation of aliphatic olefin, fast conversion, and high yields. Olefin epoxidation by this catalytic system is proposed to involve a new reactive Co(II)-OOC(O)R species, based on evidence from H(2)(18)O-exchange experiments, the use of peroxyphenylacetic acid as a mechanistic probe, reactivity and Hammett studies, EPR, and ESI-mass spectrometric investigation. However, the O-O bond of a Co(II)-acylperoxo intermediate (Co(II)-OOC(O)R) was found to be cleaved both heterolytically and homolytically if there is no substrate.

CO2 selective dynamic two-dimensional ZnII coordination polymer

A CO2 selective dynamic two-dimensional (2D) MOF system, [Zn(glu)(μ-bpe)]·2H2O (·2H2O) (glu = glutarate, bpe = 1,2-bis(4-pyridyl)ethylene), is prepared. Based on variable temperature PXRD patterns, I·2H2O exhibits a structural transformation of the framework upon desolvation. Various gas sorption analyses at low temperatures reveal that solvent-free I selectively adsorbs CO2 over N2, H2, and CH4. Stepped CO2 isotherms for solvent-free I with a large hysteresis between adsorption and desorption branches at 196 K indicate that I is a dynamic framework. Moreover, I·2H2O shows efficient heterogeneous catalytic reactivity for transesterification of various esters. The catalyst can be recycled multiple times without losing its original activity.

Synthesis, DNA binding profile and DNA cleavage pathway of divalent metal complexes

Complexes of dipyridylamine based ligand with an anthracene moiety containing divalent metal ions Co(II), Cu(II), Ni(II), Zn(II) and Cd(II) were characterized structurally. The experimental results showed that they can induce considerable oxidative DNA cleavage in the presence of hydrogen peroxide and dioxygen. The Zn(II) complex did not show any appreciable cleavage activity, whereas the Cd(II) and Ni(II) complexes were moderately active. On the other hand, Cu(II) and Co(II) complex showed the formation of a significant quantity of linear DNA resulting from the double-strand breaks. Mechanistic studies revealed the involvement of HO˙ and the superoxide anion to be the reactive species in the scission process in aerobic media. A mechanism involving either the Fenton or the Haber–Weiss reaction was proposed for the DNA cleavage mediated by these complexes. The Cu(II) complex could also cleave the double stranded calf thymus DNA (ds DNA) in the presence of activators, most likely via an oxidative mechanism, whereas the activity of the other complexes was negligible under similar reaction conditions. The kinetic aspects of ds DNA cleavage with the Cu(II) are detailed. The interaction of the five metal complexes with ds DNA was investigated by UV absorption and linear dichroism studies, and the mode of complexes binding to ds DNA is proposed.

Bis(μ-3-carb-oxy-2-hy-droxy-propane-1,2-dicarboxyl-ato)bis(diaquazinc)-1,2-bis-(pyridin-4-yl)ethene-water (1/1/2).

The asymmetric unit of the title compound, [Zn2(C6H6O7)2(H2O)4]·C12H10N2·2H2O, comprises half of a centrosymmetric complex dimer, half of a 1,2-bis(pyridin-4-yl)ethene molecule, which lies across an inversion centre, and one lattice water molecule. Carboxylate groups of two dianionic citrate ligands bridge two ZnII ions to give the cyclic dimer, with each ZnII ion coordinated by four O atoms from the chelating citrate ligand (one hydroxy and three carboxylate, with one bridging) and two water O atoms, forming a distorted octahedral environment [Zn—O = 2.040 (3)–2.244 (3) Å]. In the crystal, O—H⋯O and O—H⋯N hydrogen bonds involving hydroxy groups and both coordinating and lattice water molecules link the dimers to give a three-dimensional framework structure.

Bis(μ-2-carboxymethyl-2-hydroxy-butane-dioato)bis-[diaqua-manganese(II)]-1,2-bis-(pyridin-4-yl)ethane-water (1/1/2).

The asymmetric unit of the title compound, [Mn2(C6H6O7)2(H2O)4]·C12H12N2·2H2O, comprises half of a centrosymmetric dimer, half of a 1,2-bis(pyridin-4-yl)ethane and one water molecule. Two citrate ligands bridge two MnII ions, the MnII ion being coordinated by four O atoms from the citrate(2−) ligands and two water O atoms, forming a distorted octahedral environment. In the crystal, O—H⋯O hydrogen bonds link the centrosymmetric dimers and lattice water molecules into a three-dimensional structure which is further stabilized by intermolecular π–π interactions [centroid–centroid distance = 3.792 (2) Å].

Bis(μ-2-carb-oxy-methyl-2-hy-droxy-butane-dioato)bis-[diaqua-manganese(II)]-1,2-bis-(pyridin-4-yl)ethene-water (1/1/2).

The asymmetric unit of the title compound, [Mn2(C6H6O7)2(H2O)4]·C12H10N2·2H2O, contains half of the centrosymmetric Mn complex dimer, half of a 1,2-bis(pyridin-4-yl)ethene molecule, which lies across an inversion center, and one water molecule. Two citrate ligands bridge two MnII ions, and each MnII atom is coordinated by four O atoms from the citrate ligands (one from hydroxy and three from carboxylate groups) and two water O atoms, forming a distorted octahedral environment. In the crystal, O—H⋯O and O—H⋯N hydrogen bonds link the centrosymmetric dimers and lattice water molecules into a three-dimensional structure which is further stabilized by intermolecular π–π interactions [centroid–centroid distance = 3.959 (2) Å]. Weak C—H⋯O hydrogen bonding interactions are also observed.