Dual Role of Hydrophobic Racemic Thioesters of α-Amino Acids in the Generation of Isotactic Peptides and Co-peptides in Water; Implications for the Origin of Homochirality

Thioesters of α-amino acids are considered as plausible monomers for the generation of the primeval peptides. DL-Leucine-thioethyl esters (LeuSEt), where the L-enantiomer was tagged with deuterium atoms, undergo polycondensation in water or in bicarbonate or imidazole buffer solutions to yield mainly heterochiral (atactic) peptides and diketopiperazine, as analyzed by MALDI-TOF and ESI mass-spectrometry. In variance, when polymerization of DL(d₁₀)-Leu, first activated with N,N′-carbonyldiimidazole, then initiated with ethanethiol or with DL(d₃)-LeuSEt yielded a library of peptides up to 30 detectable residues where those of homochiral sequence (isotactic) are the dominant diastereoisomers. At these conditions, racemic β-sheets are formed and operate as stereoselective templates in the process of chain-elongation. Isotopic L:L(d₁₀)-Leu co-peptides were obtained in the polymerization of L(d₁₀)-Leu with L-LeuSEt. By contrast, mixtures of oligo-D-Leu and oligo-L(d₁₀)-Leu were obtained in the polymerization of mixtures of D-LeuSEt with activated L(d₁₀)-Leu. Isotactic co-peptides containing Leu and Val residues were formed in the polymerization of mixtures of activated DL(d₈)-Val with DL(d₃)-LeuSEt in water, implying that the racemic β-sheets exert regio-enantio-selection but not chemo-selection. A reaction pathway is suggested, where LeuSEt operates both as initiator of the reaction as well as a multimer.     

Simple phosphonic inhibitors of human neutrophil elastase

Herein, we describe the synthesis and resulting activity of a complex series of α-aminophosphonate diaryl esters as irreversible human neutrophil elastase inhibitors and their selectivity preference for human neutrophil elastase over several other serine proteases such as porcine pancreatic elastase, trypsin, and chymotrypsin. We synthesized and examined the inhibitory potency of several new simple Cbz-protected α-aminoalkylphosphonate diaryl esters that yielded several new HNE inhibitors, where one of the obtained compounds Cbz-Val^P(OC₆H₄-4-COOMe)₂ displayed an apparent second-order inhibition value at 33,015 M⁻¹ s⁻¹.     

Nuclear magnetic resonance study of ring conformations of cyclic tetradepsipeptide AM-toxins and related peptides

Cyclic tetradepsipeptides, AM-toxin I and II, are the host-specific phytotoxins of Alternaria mali. In order to elucidate conformation-toxicity relationships, we analyzed the 270-MHz proton nmr spectra of AM-toxins and hydrogenated analogs, (D -Ala²)AM-toxin I (toxic) and (L -Ala²)AM-toxin I (not toxic), in (C²H₃)₂SO. These cyclic tetradepsipeptides do not contain N-substituted amino acid residues, and all the peptide and ester groups have been found to be transoid. Two conformers with very unequal populations have been found for AM-toxin I and II; the C^β?C^α? C?O conformations of the Dha² residues are nonplanar S-trans in the major conformer and nonplanar S-cis in the minor conformer. Only one ring conformation has been found for each of (L -Ala²) and (D -Ala²)AM-toxin I. (L -Ala²)AM-toxin I takes a C₄-type ring conformation; all the C?O groups and C^α-H bonds are oriented to the same side of the ring. (D -Ala²)AM-toxin I takes a new ring conformation; the side chain and C?O group of the L -Amp¹ residue are oriented to the same side of the ring. This new conformation is also found for the major conformers of AM-toxin I and II and thus appears to be required for the toxicity. The ring conformations of Tyr(OCH₃)¹-bearing analog tetradepsipeptides have been found to be much the same as those of Amp¹-bearing depsipeptides. Furthermore, on the basis of the two distinct conformations of (D -Ala²) and (L -Ala²)AM-toxin I, an empirical rule is proposed for the stable ring conformations of cyclic tetra-D ,L -peptides, not containing N-substituted amino acid residues.     

Heterometallic coordination polymers constructed by linear ligands

Eight lanthanide–copper coordination polymers of linear rigid 4-(4-pyridyl)benzoate(L¹) and isonicotinate(L²), [LnCuI(L¹)₂(OAc) (H₂O)]_n (Ln = Pr, 1; Nd, 2; Sm, 3; Eu, 4; Gd, 5), [Ln₂Cu₄I₃(L²)₇ (H₂O)]_n (Ln = La, 6; Pr, 7), and [Nd₂Cu₇I₆(L²)₇ (H₂O)₆]_n·2.5nH₂O (8), were hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. The three-dimensional frameworks of 1–5 can be described as wave-like layer modules of [Ln(L¹)₂(OAc)(H₂O)]_n linking with each other through dimeric units of Cu₂I₂, whereas that of compounds 6 and 7 are constructed by layer modules of and Cu₄I₃ clusters. As for 8, dimeric units of Nd₂(L²)₇(H₂O)₆ connect layered polymeric forming a 3D framework.     

Fluorescence enhancement of rare earth Tb(III) by Tm(III) in benzyl benzoylmethyl sulphoxide complexes

A series of rare earth complexes [(Tb_xTm_y)L₅(ClO₄)₂](ClO₄)·3H₂O (x:y = 1.000:0.000, 0.999:0.001, 0.995:0.005, 0.990:0.010, 0.950:0.050, 0.900:0.100, 0.800:0.200, 0.700:0.300; L = C₆H₅CH₂SOCH₂COC₆H₅) (Tb(III) luminescence ion; Tm(III) doped inert ion) were synthesized and characterized by elemental analysis, infrared spectra (IR) and ¹H‐NMR. The photophysical properties of these complexes were studied in detail using ultraviolet absorption spectra, fluorescent spectra and lifetimes. The fluorescence spectra of complexes indicated that the fluorescence emission intensity was significantly enhanced by Tm(III). The complexes showed the best luminescence properties when the mole ratio Tb(III):Tm(III) was 0.990:0.010. The fluorescence intensity could be increased to 390%. Additionally, phosphorescence spectra and the luminescence mechanisms are discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

Phosphonic analogues of glutamic acid as irreversible inhibitors of Staphylococcus aureus endoproteinase GluC: An efficient synthesis and inhibition of the human IgG degradation

Endoproteinase GluC (V8 protease) is one of many virulence factors released by the Staphylococcus aureus species in vivo. The V8 protease is able to hydrolyze some serpins and all classes of mammalian immunoglobulins. The application of specific and potent inhibitors of V8 protease may lead to the development of new antibacterial agents. Herein, we present the synthesis and the inhibitory properties of novel peptidyl derivatives of a phosphonic glutamic acid analogue. One of the compounds Boc-Phe-Leu-Glu^P(OC₆H₄)₂ displayed an apparent second-order inhibition rate value of 8540 M^?1 s^?1. The Boc-Phe-Leu-Glu^P(OC₆H₄)₂ compound with the highest inhibitory potency showed the ability to prevent V8-mediated human IgG proteolysis in vitro.     

Phenoxyl-copper(II) complexes: models for the active site of galactose oxidase

 The reaction of the macrocycles 1,4,7-tris (3,5-di-tert-butyl-2-hydroxy-benzyl)-1,4,7-triazacyclononane, L¹H₃, or 1,4,7-tris(3-tert-butyl-5-methoxy-2-hydroxy-benzyl)-1,4,7-triazacyclononane, L²H₃, with Cu(ClO₄)₂·6H₂O in methanol (in the presence of Et₃N) affords the green complexes [Cu^II(L¹H)] (1), [Cu^II(L²H)]·CH₃OH (2) and (in the presence of HClO₄) [Cu^II(L¹H₂)](ClO₄) (3) and [Cu^II(L²H₂)] (ClO₄) (4). The Cu^II ions in these complexes are five-coordinate (square-base pyramidal), and each contains a dangling, uncoordinated pendent arm (phenol). Complexes 1 and 2 contain two equatorially coordinated phenolato ligands, whereas in 3 and 4 one of these is protonated, affording a coordinated phenol. Electrochemically, these complexes can be oxidized by one electron, generating the phenoxyl-copper(II) species [Cu^II(L¹H)]^+ ·, [Cu(L²H)]^+ ·, [Cu^II(L¹H₂)]^2+ ·, and [Cu^II(L²H₂)]^2+ ·, all of which are EPR-silent. These species are excellent models for the active form of the enzyme galactose oxidase (GO). Their spectroscopic features (UV-VIS, resonance Raman) are very similar to those reported for GO and unambiguously show that the complexes are phenoxyl-copper(II) rather than phenolato-copper(III) species. Received: 10 February 1997 / Accepted: 7 April 1997     

N-substituted ethylcarbamate complexes of thorium(IV) and lanthanum(III) nitrates

N-substituted ethylcarbamates form with thorium nitrate the complexes Th(NO₃)₄·3RHNC(O)OC₂H₅ (where R = CH₃, C₂H₅, C₆H₅(CH₃)CH) and with lanthanum nitrate the complexes La(NO₃)₃· 2RR′NC(O)OC₂H₅·3H₂O (where R = CH₃, C₂H₅, C₆H₅(CH₃)CH; R′ = H and R = CH₃, C₆H₅; R′ = C₂H₅ or R = R′ = CH₃). In addition the anhydrous La(NO₃)₃·3(C₂H₅)₂NC(O)OC₂H₅ has been isolated. From the IR spectra it is deduced that the carbamates coordinate the metal through the carbonyl oxygen atom and that the nitrato groups act as chelated ligands. ¹H nmr spectral data of the complexes are reported and discussed.     

Structure, solution equilibria and magnetic properties of copper(II) complexes with new sulfurated triazoline derivatives of α-amino acids

Two new sulfurated triazoline ligands have been synthesized by functionalization of glycine and l-alanine (HL¹ and HL², respectively) at the carboxylate site with retention of chirality in the latter case. The ligands and their copper(II) complexes have been characterized by spectroscopic methods and their structures were determined by X-ray diffraction. The compound [Cu(H₂L²)₂](H₅O₂)(SO₄)₂(HSO₄) presents a very disordered structure with regard to the anionic counterion and a very unusual elongated crystal cell. In all the complexes the ligands are (N,S) coordinated to copper(II), while the amino groups remain protonated and uncoordinated. The ligands have also been studied in solution and their dissociation constants were determined both by potentiometry and ¹H NMR titrations. Potentiometric studies on the complex [Cu(H₂L²)₂](H₅O₂)(SO₄)₂(HSO₄) were performed to determine the dissociation constants of the ligand once coordinated to the metal. The complex [CuCl₂(H₂L¹)]Cl was studied also by magnetic susceptibility measurements, showing an interesting antiferromagnetic behavior at low temperature which has been interpreted on the basis of its crystal packing.     

Short-bite aminobis(phosphonite) containing olefinic functionalities, PhN{P(OC6H3(OMe-o)(C3H5-p))2}2: Synthesis and transition metal complexes

Short-bite aminobis(phosphonite) containing olefinic functionalities, PhN{P(OC₆H₃(OMe-o)(C₃H₅-p))₂}₂ (1) was synthesized by reacting PhN(PCl₂)₂ with eugenol in the presence of triethylamine. The ligand 1 acts as a bidentate chelating ligand toward metal complexes [M(CO)₄(C₅H₁₀NH)₂] forming [M(CO)₄{η²-PhN{P(OC₆H₃(OMe-o)(C₃H₅-p))₂}₂}] (M = Mo, 2; W, 3). The reaction between 1 and [CpFe(CO)₂]₂ leads to the cleavage of one of the P-N bonds due to the metal assisted hydrolysis to give a mononuclear complex [CpFe(CO){P(O)(OC₆H₃(OMe-o)(C₃H₅-p))₂}{PhN(H)(P(OC₆H₃(OMe-o)(C₃H₅-p))₂)}] (4). Treatment of 1 with gold(I) derivative, [AuCl(SMe₂)] resulted in the formation of a dinuclear complex, [(AuCl)₂{PhN{P(OC₆H₃(OMe-o)(C₃H₅-p))₂}₂}] (5) with a Au···Au distance of 3.118(2) Å indicating the possibility of aurophilic interactions. An equimolar reaction between 1 and [Ru(η⁶-p-cymene)Cl₂]₂ afforded a tri-chloro-bridged bimetallic complex [(η⁶-p-cymene)Ru(μ-Cl)₃Ru{PhN(P(OC₆H₃(OMe-o)(C₃H₅-p))₂)₂}Cl] (6). The crystal structures of 1-3 and 5 were established by single crystal X-ray diffraction studies.     

Conformational flexibility of 2,6-bis(pyrazol-1-ylmethyl)pyridine (L) in [(L)Co(H2O)3]Cl2 and [(L)Ni(H2O)2Cl]Cl·H2O. Molecular structures and non-covalent interactions

Using a non-planar tridentate ligand 2,6-bis(pyrazol-1-ylmethyl)pyridine (L⁵) two new coordination complexes [(L⁵)Co^II(H₂O)₃]Cl₂ (1) and [(L⁵)Ni^II(H₂O)₂Cl]Cl·H₂O (2) have been synthesized and structurally characterized. Complex 1 has N₃O₃ distorted octahedral environment around Co^II with coordination by L⁵ (two pyrazole and a pyridine nitrogen in a facial mode) and three water molecules. Complex 2 has N₃O₂Cl distorted octahedral geometry around Ni^II with meridional L⁵ coordination, two water molecules, and a Cl⁻ ion. Analysis of the crystal packing diagram reveals the involvement of solvent (water as metal-coordinated and as solvent of crystallization) and counteranion (Cl⁻) to play significant roles in generating 1D chains, involving O-H···Cl, and O-H···O interactions.     

Structure of Rugulovasine A,B and their Derivatives

Culture conditions for the preparation of cells containing high tyrosine phenol lyase activity were studied with Erwinia herbicola ATCC 21434. Adding pyridoxine to the medium enhanced enzyme formation, suggesting that it was utilized as a precursor of the coenzyme, pyridoxal phosphate. Glycerol plus succinic acid; amino acids, such as, DL-methionine, DL-alanine and glycine; and metallic ion, ferrous ion promoted enzyme formation as well as cell growth. Adding L-tyrosine, as inducer, to the culture medium was essential for enzyme formation. However, when large amounts of L-tyrosine were added, the enzyme formation was repressed by the phenol liberated from L-tyrosine. In fact, formation of the enzyme was enhanced by removing phenol during cultivation. L(D)-Phenylalanine or phenylpyruvic acid had a synergistic effect on the induction of enzyme by L-tyrosine.

Cells with high enzyme activity were prepared by growing cells at 28°C for 28 hr in a medium containing 0.2% L-tyrosine, 0.2% KH₂PO₄, 0.1% MgSO₄7H₂O, 0.001% FeSO_4·7H₂O, 0.01% pyridoxine-HC1, 0.6% glycerol, 0.5% succinic acid, 0.1% DL-methionine, 0.2% DL-alanine, 0.05% glycine, 0.1% L-phenylalanine and 120 ml/liter hydrolyzed soybean protein in tap water with the pH controlled at 7.5 throughout cultivation.     

Reactivity of [MO] (M = Tc, Re) core towards 2-mercapto-1,3-azole ligands. Formation of a new organometallic complex of Re(IV) and X-ray crystal structures

Imidazole-2-thiol derivatives H₂L^1-3 (H₂L¹ = 1H-benzoimidazole-2-thiol, H₂L² = 5-methyl-1H-benzoimidazole-2-thiol, and H₂L³ = 1H-imidazole-2-thiol) act as neutral monodentate ligands in a number of technetium and rhenium complexes. Disubstituted M(V) (M = Tc, Re) complexes of the type [AsPh₄]{[MOCl₂(H₂Lⁿ)₂(H₂O)]Cl₂} are formed when [MOCl₄]⁻ react with H₂L^1-3 in 1:2 stoichiometric ratio. Single crystal X-ray structure determinations were carried out on [AsPh₄]{[TcOCl₂(H₂L¹)₂(H₂O)]Cl₂}. The coordination sphere is pseudo-octahedral in which the sulfur atoms of two ligands sit in the equatorial plane and a water molecule is in trans to the TcO multiple bond. All the complexes react with an excess of the corresponding ligand to form tetrasubstituted cationic species {[MO(H₂Lⁿ)₄]Cl₃}. These complexes can be also isolated by reaction of [MOCl₄]⁻ with an excess of ligand. No complex is obtained with benzothiazole-2-thiol (HL⁴) and benzoxazole-2-thiol (HL⁵). Ligand exchange reactions of [ReOCl₃(PPh₃)₂] with HL^4,5 have also been investigated. Treating the oxo-precursor with HL⁴ no product is isolated, while with HL⁵ the chelate oxo-compound [ReOCl₂(L⁵)(PPh₃)] is formed as two isomers. An interesting organometallic complex of Re(IV) [ReCl₃(L^5∗)(PPh₃)₂] is obtained when a slight excess of HL⁵ reacts with [ReOCl₃(PPh₃)₂] in refluxing benzene solution and in air. Geometry about the Re atom is approximately octahedral in which the equatorial plane contains three Cl atoms and the carbon atom of the benzoxazole ligand anion, the apical positions are occupied by two PPh₃. The reaction with O-ethyl S-hydrogen p-tolyl carbonothioimidate HL⁶ which contains the same heteroatoms of HL⁵ does not form an organometallic species, but forms the chelate oxo-Re(V) complex [ReOCl₂(L⁶)(PPh₃)]. The solid-state structure has been authenticated by X-ray crystallography.     

A versatile entry into aqueous niobium chemistry: isolation and structure of the intermediate Nb4(μ2-O)2(μ2-OC2H5)4Cl4(OC2H5)4(HOC2H5)4

The reduction of ethanolic solutions of niobium pentachloride with zinc, followed by treatment with aqueous acids serves as a versatile entry into the aqueous solution chemistry of niobium. From the zinc-reduced solution, the major intermediate, Nb₄(μ₂-O)₂(μ₂-OC₂H₅)₄Cl₄(OC₂H₅)₄(HOC₂H₅)₄, was isolated and the crystal structure determined by X-ray crystallography. The complex crystallizes in the orthorhombic space group Pccn, with Z=4, a=21.0105(9), b=11.0387(5), c=19.1389(8), V=4438.9(3) ų, M_r=1090.19,R₁=0.0327 and wR₂=0.0876. The structure revealed a centrosymmetric tetrameric Nb(IV) complex, consisting of a pair of edge-sharing bi-octahedral Nb₂(μ₂-OC₂H₅)₄Cl₂(OC₂H₅)₂(HOC₂H₅)₂ units that are joined by two axial oxo ligands. The Nb-Nb distance of 2.7458(3) Å is consistent with a single metal-metal bond.     

Two star‐shaped tetranuclear Ru(II) complexes containing uncoordinated imidazole groups: synthesis,characterization, photophysical and pH sensing properties

Tetrapodal ligands H₄L¹ and H₄L² containing imidazole groups have been synthesized by the reaction of 1,10‐phenanthroline‐5,6‐dione with 1,2,4,5‐tetrakis[(4‐formylphenoxy)methyl]benzene and 1,2,4,5‐tetrakis[(3‐formylphenoxy)methyl]benzene, respectively, in presence of NH₄OAc. Two star‐shaped complexes [{Ru(bpy)₂}₄(μ₄‐H₄L¹)](PF₆)₈ and [{Ru(bpy)₂}₄(μ₄‐H₄L²)](PF₆)₈ (bpy = 2,2′‐bipyridine) have been prepared by refluxing Ru(bpy)₂Cl₂·2H₂O and each ligand in ethylene glycol. The deprotonated complexes [{Ru(bpy)₂}₄(μ₄‐L¹)](PF₆)₄ and [{Ru(bpy)₂}₄(μ₄‐L²)](PF₆)₄ have been obtained by the reaction of sodium methoxide with [{Ru(bpy)₂}₄(μ₄‐H₄L¹)](PF₆)₈ and [{Ru(bpy)₂}₄(μ₄‐H₄L²)](PF₆)₈, respectively, in methanol. The pH effects on the UV–vis light absorption and emission spectra of both complexes have been studied, and ground‐ and excited‐state ionization constants of both complexes have been derived. The photophysical properties of both complexes are strongly dependent on the solution pH. They act as proton‐induced off–on–off luminescent sensors through two successive deprotonation processes of imidazole groups, with a maximum on–off ratio of 8 in buffer solution at room temperature. Theoretical calculations for the highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LOMO) orbitals of bridging ligand are also presented for plausible explanations of the fluorescence changes. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and characterization of new lanthanide complexes with hexadentate hydrazonic ligands

In this paper, we report the synthesis and the characterization of a novel series of lanthanide (III) complexes with two potentially hexadentate ligands.The ligands contain a rigid phenanthroline moiety and two flexible hydrazonic arms with different donor atom sets (NNN′N′OO and NNN′N′N″N″, respectively for H₂L¹ (2,9-diformylphenanthroline)bis(benzoyl)hydrazone and H₂L² (2,9-diformylphenanthroline)bis(2-pyridyl)hydrazone).Both nitrate and acetate complexes of H₂L¹ with La, Eu, Gd, and Tb were prepared and fully characterized, and the X-ray crystal structure of the complex [Eu(HL¹)(CH₃ COO)₂] · 5H₂O is presented.The stability constants of the equilibria Ln³⁺ + H₂L¹ = [Ln(H₂L¹)]³⁺ and Ln³⁺ + (L¹)²⁻ = [Ln(L₁)]⁺ (Ln = La(III), Eu(III), Gd(III), and Tb(III)) are determined by UV spectrophotometric titrations in DMSO at t = 25 °C. The nitrate complexes of H₂L² with La, Eu, Gd and Tb were also synthesized, and the X-ray crystal structures of [La(H₂L²)(NO₃)₂(H₂O)](NO₃), [Eu(H₂L²)(NO₃)₂](NO₃) and [Tb(H₂ L²)(NO₃)₂](NO₃) are discussed.     

Supramolecular assembly of coordination networks in silver(I) triple salts containing acetylenediide and some N,O-donor ligands

Five new silver(I) triple salts: (Ag₂C₂)(AgNO₃)₄(AgL¹)₂(L¹H)₂ (1), (Ag₂C₂)(AgCF₃CO₂)₂(AgL¹)₂(L¹H)_1/2 (2), [(Ag₂C₂)(AgCF₃CO₂)₄(L²)(H₂O)] · (L²H₂) (3), (Ag₂C₂)(AgNO₃)₃(AgL³)₂ (4), and [(Ag₂C₂)(AgCF₃CO₂)₄(AgL³)₂(H₂O)₂] · H₂O (5) (L¹H = nicotinic acid, L²H = isonicotinic acid, L³H = 2-pyrazinecarboxylic acid) have been synthesized by the hydrothermal method. All five compounds contain polyhedral silver(I) cages each encapsulating an acetylenediide dianion, . In 1, C₂@Ag₈ cages in the shape of bicapped trigonal prisms are interlinked by nitrate, L¹, and L¹H ligands into a three-dimensional architecture. In 2, silver(I) columns generated from fusion of triangulated dodecahedra are linked by L¹ into a layer structure. Compound 3 provides a rare example of a (L²H₂)⁺-pillared three-dimensional structure via hydrogen bonding. In 4, nitrate ligands together with L³ link the C₂@Ag₇ cages into a three-dimensional architecture. Compound 5 also exhibits a three-dimensional architecture generated from trifluoroacetate and L³-linked C₂@Ag₈ cages.     

Homogeneous green catalysts for olefin oxidation by mono oxovanadium(V) complexes of hydrazone Schiff base ligands

Three mono oxovanadium(V) complexes of tridentate Schiff base ligands [VO(OMe)L¹] (1), [VO(OMe)L²] (2) and [VO(OMe)L³] (3) obtained by monocondensation of 3-hydroxy-2-naphthohydrazide and aromatic o-hydroxyaldehydes have been synthesized (H₂L¹ = (E)-3-hydroxy-N′-(2-hydroxy-3-methoxybenzylidene)-2-naphthohydrazide, H₂L² = (E)-3-hydroxy-N′-(2-hydroxybenzylidene)-2-naphthohydrazide and H₂L³ = (E)-N′-(5-bromo-2-hydroxybenzylidene)-3-hydroxy-2-naphthohydrazide). The complexes were characterized by spectroscopic methods in the solid state (IR) and in solution (UV-Vis, ¹H NMR). Single crystal X-ray analyses were performed with 1 and 2. The catalytic potential of these complexes has been tested for the oxidation of cyclooctene using H₂O₂ as the terminal oxidant. The effects of various parameters including the molar ratio of oxidant to substrate, the temperature, and the solvent have been studied. The catalyst 2 showed the most powerful catalytic activity in oxidation of various terminal, cyclic and phenyl substituted olefins. Excellent conversions have been obtained for the oxidation of cyclic and bicyclic olefins.     

Heteroleptic phthalocyaninato-[2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninato] rare earth(III) triple-deckers: synthesis and spectroscopic characterization

The homo-dinuclear heteroleptic phthalocyaninato-[2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninato] rare earth(III) triple-decker complexes (Pc)M[Pc(OC₈H₁₇)₈]M[Pc(OC₈H₁₇)₈] (M=Pr, Nd, Sm, Eu, Tb, Dy, Y, Ho, Er, Tm) (1a–10a) and (Pc)M[Pc(OC₈H₁₇)₈]M(Pc) (M=Nd, Sm, Eu, Tb, Dy, Y, Ho, Er, Tm) (2b–10b) were obtained by condensation of bis(phthalocyaninato) rare earths M[Pc(OC₈H₁₇)₈]₂ (M=Pr, Nd, Sm, Eu, Tb, Dy, Y, Ho, Er, Tm), Li₂(Pc) and M(acac)₃·nH₂O (M=Pr, Nd, Sm, Eu, Tb, Dy, Y, Ho, Er, Tm). These novel compounds were characterized by ¹H NMR, mass, electronic absorption (UV–Vis), and IR spectroscopic methods.     

Construction of a series of 0D, 2D and 3D inorganic-organic hybrid coordination polymers based on octamolybdate and 2-(2-pyridyl)imidazole and its derivative

Four octamolybdate-based compounds, that is, Cu^II₂(L¹)₄(Mo₈O₂₆) (1), Cu^II₂(HL²)₄(Mo₈O₂₆)₂ (2), [Cu^IIL²(H₂O)(Mo₈O₂₆)_0.5]·2H₂O (3) and [Cu^IIL²(H₂O)(Mo₈O₂₆)_0.5]·2H₂O (4) (L¹ = 2-(2-pyridyl)imidazole, L² = 2-(1-(pyridine-3-ylmethyl)-1H-imidazol-2-yl)pyridine), have been hydrothermally synthesized via changing the reaction conditions and structurally characterized by single-crystal X-ray diffraction. With L¹ ligand, we obtained compound 1, which is a 0D molecule and extends to a 3D supramolecular structure via hydrogen-bonding interactions. By using L² instead of L¹ ligand, compound 2 comes into being which is as well a discrete molecule and further extended to a 3D supramolecular structure by hydrogen bonds. Intriguingly, compounds 3 and 4 are supramolecular isomers: the former is a 2D 4-connected network and the latter is a 3D (3,4)-connected framework. The measurements of diffuse reflectance for compounds 1-4 indicate that they are potential wide gap semiconductors.