In situ Raman monitoring of electroreductive dehalogenation of aryl halides at an Ag/aqueous solution interface.

Electroreductive dehalogenation as an efficient and green approach has attracted much attention in pollution remediation. Herein, we have employed a shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) technique to in situ probe the electroreductive dehalogenation process of aryl halides with thiol groups at Ag/aqueous solution interfaces. It is found that 4-bromothiophenol (BTP) and 4-chlorothiophenol (CTP) can turn into mixed products of 4,4'-biphenyldithiol (BPDT) and thiophenol (TP) as the electrode potential decreases. The conversion ratios estimated from the Raman intensity variations of C-Cl and C-Br vibrations are 44% and 58% for CTP and BTP in neutral solution, respectively. Furthermore, the quantitative analysis of benzene ring vibrations reveals a C-C cross coupling between the benzene free radical intermediate and adjacent TP product, which results in increased selectivity for biphenyl products at negative potentials.

Guanidyl-implanted UiO-66 as an efficient catalyst for the enhanced conversion of carbon dioxide into cyclic carbonates.

The development of heterogeneous catalysts for promoting epoxide cycloaddition with carbon dioxide is highly desirable for recycling CO2 and achieving the goal of carbon neutrality. Herein, we designed and synthesized Zr-based metal organic frameworks (MOFs) by implanting functional guanidyl into the framework via mixing different molar ratios of 4-guanidinobenzoic acid (Gua) with 1,4-benzenedicarboxylic acid (BDC). Consequently, a small sized Zr-MOF (∼350 nm) can be prepared by implanting Gua with 20% molar ligands, denoted as UiO-66-Gua0.2(s). Compared to large sized and different guanidyl Zr-MOFs, UiO-66-Gua0.2(s) exhibited an optimal activity on catalyzing epoxide cycloaddition with CO2 in the presence of the Bu4NBr cocatalyst. A yield of 97% for the product of chloropropene carbonate was achieved at 90 °C under 1 atm CO2. The great performance of UiO-66-Gua0.2(s) might be attributed to the synergistic effect of guanidyl groups as hydrogen-bond donors and Zr centers acting as Lewis-acidic sites. In addition, the heterogeneous catalyst of UiO-66-Gua0.2(s) exhibited a great versatility towards converting other epoxides and a satisfactory recyclability for five consecutive runs. Moreover, a plausible reaction mechanism has been proposed for UiO-66-Gua0.2(s) in promoting CO2 epoxide cycloaddition reactions.

MIL-101(Cr) with incorporated polypyridine zinc complexes for efficient degradation of a nerve agent simulant: spatial isolation of active sites promoting catalysis.

Development of an efficient catalyst for degradation of organophosphorus toxicants is highly desirable. Herein, an MIL-101(Cr)LZn catalyst was fabricated by incorporating polypyridine zinc complexes into a MOF to achieve the spatial isolation of active sites. Compared with a terpyridine zinc complex without an MIL-101 support, this catalyst was highly active for detoxification of diethyl-4-nitrophenylphosphate.

Cleaving DNA-model phosphodiester with Lewis acid-base catalytic sites in bifunctional Zr-MOFs.

Organophosphates exist in many biomolecules. The design of artificial nucleases for efficient P-O bond cleavage is essential for the fields of genetic engineering and molecular biology. Herein, metal-organic frameworks (MOFs) with cooperatively isolated multi-catalytic active sites were utilized as heterogeneous catalysts for the hydrolytic cleavage of bis(p-nitrophenyl) phosphate (BNPP).

Low-cost CuNi@MIL-101 as an excellent catalyst toward cascade reaction: integration of ammonia borane dehydrogenation with nitroarene hydrogenation.

Bimetallic CuNi nanoparticles (NPs) with low cost were rationally confined inside MIL-101 to give CuNi@MIL-101, which exhibits high efficiency and excellent recyclability toward the hydrogenation of nitroarenes under mild conditions on coupling with ammonia borane dehydrogenation. This is the first report on MOF-stabilized base metal NPs for cascade reactions.

Effective cleavage of phosphodiester promoted by the zinc(II) and copper(II) inclusion complexes of ß-cyclodextrin.

To construct the model of metallohydrolase, two inclusion complexes [MLCl2(ß-CD)] (1, M=Zn(II); 2, M=Cu(II); L=N,N'-bis(2-pyridylmethyl)amantadine; ß-CD=ß-cyclodextrin) were synthesized by mixing ß-CDs with the pre-synthesized complexes G1, [ZnLCl2] and G2, [CuLCl2]. Structures of G1, G2, 1 and 2 were characterized by X-ray crystallography, respectively. In solution, two chloride anions of G1 and G2 underwent ligand exchange with solvent molecules according to ESI-MS analysis. The chemical equilibrium constants were determined by potentiometric pH titration. The kinetics of bis(4-nitrophenyl) phosphate (BNPP) hydrolysis catalyzed by G1, G2, 1 and 2 were examined at pHs ranging from 7.50 to 10.50 at 308±0.1K. The pH profile of rate constant of BNPP hydrolysis catalyzed by 1 exhibited an exponential increase with the second-order rate constant of 2.68×10-3M-1s-1 assigned to the di-hydroxo species, which was approximately an order of magnitude higher than those of reported mono-Zn(II)-hydroxo species. The high reactivity was presumably hydroxyl-rich microenvironment provided by ß-CDs, which might effect in stabilizing either the labile zinc-hydroxo species or the catalytic transition state.

[1-tert-Butyl-3-(pyridin-2-ylmethyl-κN)imidazol-2-yl-idene-κC]carbonyl-dichlorido(dimethyl sulfoxide-κS)ruthenium(II).

In the title complex, [RuCl(2)(C(13)H(17)N(3))(C(2)H(6)OS)(CO)], the coordination environment around the Ru atom is slightly distorted octa-hedral. The Cl atoms are mutually trans to the dimethyl sulfoxide ligand and the imidazole carbene C atom, respectively. The carbonyl ligand is located trans to the pyridine N atom.

Poly[µ(3)-hydroxido-µ-(pyridine-2,4,6-tricarboxyl-ato)-dilead(II)].

The asymmetric unit of the title coordination polymer, [Pb(2)(C(8)H(2)NO(6))(OH)](n), contains two crystallographically independent Pb(II) ions, one pyridine-2,4,6-tricarboxyl-ate (ptc) trianion and one hydroxide anion. One of the Pb(II) atoms is coordinated by one pyridine N and four carboxyl-ate O atoms from the ptc trianion and a hydroxide O atom in a distorted octa-hedral geometry. The other Pb(II) atom is five-coordinated by three carboxyl-ate O atoms and two hydroxide O atoms in a distorted tetra-gonal-pyramidal geometry. Four neighbouring Pb(II) atoms are bridged through two µ(3)-hydroxide ligands, forming the centrosymmetric Pb(4)(OH)(2) core. The three-dimensional structure is further achieved through bridging carboxyl-ate groups. There are also O-H⋯O hydrogen bonds between the hydroxide ligand and the carboxyl-ate group.

Ester hydrolysis by a cyclodextrin dimer catalyst with a tridentate N,N',N''-zinc linking group.

A new beta-cyclodextrin dimer, 2,6-dimethylpyridine-bridged-bis(6-monoammonio-beta-cyclodextrin) (pyridyl BisCD, L), is synthesized. Its zinc complex (ZnL) is prepared, characterized, and applied as a catalyst for diester hydrolysis. The formation constant (log K(ML)=7.31+/-0.04) of the complex and deprotonation constant (pK(a1)=8.14+/-0.03, pK(a2)=9.24+/-0.01) of the coordinated water molecule were determined by a potentiometric pH titration at (25+/-0.1) degrees C, indicating a tridentate N,N',N''-zinc coordination. Hydrolysis kinetics of carboxylic acid esters were determined with bis(4-nitrophenyl)carbonate (BNPC) and 4-nitrophenyl acetate (NA) as the substrates. The resulting hydrolysis rate constants show that ZnL has a very high rate of catalysis for BNPC hydrolysis, yielding an 8.98x10(3)-fold rate enhancement over uncatalyzed hydrolysis at pH 7.00, compared to only a 71.76-fold rate enhancement for NA hydrolysis. Hydrolysis kinetics of phosphate esters catalyzed by ZnL are also investigated using bis(4-nitrophenyl)phosphate (BNPP) and disodium 4-nitrophenyl phosphate (NPP) as the substrates. The initial first-order rate constant of catalytic hydrolysis for BNPP was 1.29x10(-7) s(-1) at pH 8.5, 35 degrees C and 0.1 mM catalyst concentration, about 1600-fold acceleration over uncatalyzed hydrolysis. The pH dependence of the BNPP cleavage in aqueous buffer was shown as a sigmoidal curve with an inflection point around pH 8.25, which is nearly identical to the pK(a) value of the catalyst from the potentiometric titration. The k(BNPP) of BNPP hydrolysis promoted by ZnL is found to be 1.68x10(-3) M(-1) s(-1), higher than that of NPP, and comparatively higher than those promoted by its other tridentate N,N',N''-zinc analogues.

Ester hydrolysis by a cyclodextrin dimer catalyst with a metallophenanthroline linking group.

A novel beta-cyclodextrin dimer, 1,10-phenanthroline-2,9-dimethyl-bridged-bis(6-monoammonio-beta-cyclodextrin) (phenBisCD, L), was synthesized. Its zinc complex (ZnL) has been prepared, characterized, and applied as a new catalyst for diester hydrolysis. The formation constant (logK(ML)=9.56+/-0.01) of the complex and deprotonation constant (pK(a)=8.18+/-0.04) of the coordinated water molecule were determined by a potentiometric pH titration at (298+/-0.1) K. Hydrolytic kinetics of carboxylic acid esters were performed with bis(4-nitrophenyl) carbonate (BNPC) and 4-nitrophenyl acetate (NA) as substrates. The obtained hydrolysis rate constants showed that ZnL has a very high rate of catalysis for BNPC hydrolysis, giving a 3.89x10(4)-fold rate enhancement over uncatalyzed hydrolysis at pH 7.01, relative to only a 42-fold rate enhancement for NA hydrolysis. Moreover, the hydrolysis second-order rate constants of both BNPC and NA greatly increases with pH. Hydrolytic kinetics of a phosphate diester catalyzed by ZnL was also investigated by using bis(4-nitrophenyl) phosphate (BNPP) as the substrate. The pH dependence of the BNPP cleavage in aqueous buffer shows a sigmoidal curve with an inflection point around pH 8.11, which was nearly identical to the pK(a) value from the potentiometric titration. The k(cat) of BNPP hydrolysis promoted by ZnL was found to be 9.9x10(-4) M(-1) s(-1), which is comparatively higher than most other reported Zn(II)-based systems. The possible intermediate for the hydrolysis of BNPP, BNPC, and NA catalyzed by ZnL is proposed on the basis of kinetic and thermodynamic analysis.

Synthesis, structure, and activity of supramolecular mimics for the active site and arg141 residue of copper, zinc-superoxide dismutase.

Two supramolecular complexes, [Cu(L)(H2O)2(beta-CD)](ClO4)2.10.5H2O.CH3OH (1) and [Cu(L)(H2O)2(beta-GCD)](HClO4)(ClO4)2.10H2O (2) (L = 4-(4'-tert-butyl-benzyl)diethylenetriamine, beta-CD = beta-cyclodextrin, and beta-GCD = mono-6-deoxy-6-guanidinocycloheptaamylose cation), have been synthesized. The structure of 1 has been characterized by X-ray crystallography. The 4-tert-butyl-benzyl of [Cu(L)(H2O)2]2+ moiety in 1 as a guest inserts into the hydrophobic cavity of the beta-CD as a host along the primary hydroxyl side. On the basis of the structure data of 1, complex 2 was modeled, which showed that the distance between the Cu and C atom of the guanidinium is 5.2 A, comparable to the corresponding distance in bovine erythrocyte Cu, Zn-SOD (5.9 A) (SOD = superoxide dismutase). Apparent inclusion stability constants of the host and the guest were measured to be 0.66 (+/-0.01) x 104 and 1.15 (+/-0.03) x 104 M-1 for 1 and 2 respectively. The electronic absorption bands and electronic reflection bands of each complex are almost the same, indicating an identical structure of the complex in aqueous solution and in solid state. The two complexes showed quasi-reversible one-electron Cu(II)/Cu(I) redox waves with redox potentials of -0.345 and -0.338 V for 1 and 2, respectively. Their SOD-like activities (IC50) were measured to be 0.30 +/- 0.01 and 0.17 +/- 0.01 microM by xanthine/xanthine oxidase-NBT assay. The enhanced SOD activity of 2 by approximately 40% compared with 1 suggests that the guanidyl cation in the host of the supramolecular system of 2 can effectively mimic the side chain of Arg141 in the enzyme, which is known to be essential for high SOD activity possibly through steering of the superoxide substrate to and from the active copper ion.

An effective metallohydrolase model with a supramolecular environment: structures, properties, and activities.

A supramolecular inclusion complex, [Zn(L1)(H2O)2(beta-CD)](ClO4)2.9.5 H2O (1) was synthesized and characterized structurally and its first-order active species for hydrolysis of esters, [Zn(L1)(H2O)(OH)(beta-CD)](ClO4) (2), was isolated (L1=4-(4'-tert-butylbenzyl)diethylenetriamine; beta-CD=beta-cyclodextrin). The apparent inclusion stability constant of the host and the guest measured in aqueous solution was (5.91+/-0.03)x10(3) for 1. The measured values of the first- and second-order pK(a) values of coordinated water molecules were 8.20+/-0.08 and 10.44+/-0.08, respectively, and were assigned to water molecules occupying the plane and remaining axial positions in a distorted trigonal bipyramid of the [Zn(L1)(H2O)2(beta-CD)]2+ sphere according to the structural analysis of [Zn(L2)(H2O)}2(mu-OH)](ClO4)3 (3) (L2=4-benzyldiethylenetriamine). p-Nitrophenyl acetate (pNA) hydrolysis catalyzed by 1 at pH 7.5-9.1 and 25.0+/-0.1 degrees C exhibited a first-order reaction with various concentrations of pNA and 1, but the pH profile did not indicate saturated kinetic behavior. Second-order rate constants of 0.59 and 24.0 M(-1) s(-1) were calculated for [Zn(L1)(H2O)(OH)(beta-CD)]+ and [Zn(L1)(OH)2(beta-CD)], respectively; the latter exhibited a potent catalytic activity relative to the reported mononuclear and polynuclear Zn(II) species.

Complexation, structure, and superoxide dismutase activity of the imidazolate-bridged dinuclear copper moiety with beta-cyclodextrin and its guanidinium-containing derivative.

An imidazolate-bridged homodinuclear complex, {[Cu(L)(H2O)]2(im)}(ClO4)3 (1), assembled with beta-cyclodextrin (betaCD) and its guanidinium-containing derivative (betaGCD), and thus a helical inclusion complex, {[Cu(L)(H2O)(betaCD)]2(im)}(ClO4)3 (2), were successfully isolated and structurally characterized. Structural analysis showed that each Cu(II) ion has a distorted square pyramidal N4Ow coordination sphere and forms a chiral chain through hydrogen-bonding and hydrophobic interactions. The UV-vis data showed that such a chain can provide the imidazolate bridge additional stability and results in the dissociation equilibrium taking place at the physiological pH. The obtained IC50 value for 2 (0.23 muM) showed a high superoxide dismutase (SOD) activity, which corresponds to a highly stable imidazolate bridge. Interestingly, the guanidinium-containing 1/betaGCD system showed higher SOD activity (IC50 = 0.16 muM), which is enhanced at least by 30% in comparison with that of guanidinium-lacking 2. This result supports that the positive guanidinium plays a role in the catalytic mechanism of Cu,Zn-SOD by ensuring that superoxide enters and peroxide leaves rapidly from the coordination sphere of the copper ion.