Icosahedron cage occupancy of structure-H hydrate helped by Xe -1,1-, cis -1,2-, trans-1,2-, and cis-1,4-dimethylcyclohexanes

Four mixtures of 1,1-, cis-1,2-, trans-1,2-, and cis-1,4-dimethylcyclohexanes (hereafter abbreviated DMCH) including H₂O and Xe have been investigated in a temperature range over 274.5 K and a pressure range up to 2.7 MPa. The 1,1-DMCH and cis-1,2-DMCH generate the structure-H hydrate in the temperature range up to 295.2 and 280.2 K, respectively. Especially, very large depression of equilibrium pressure has been observed in the structure-H 1,1-DMCH hydrate system. On the other hand, neither trans-1,2-DMCH nor cis-1,4-DMCH generates the structure-H hydrate in the present temperature range. It is an important finding that the cis-1,4-DMCH does not generate the structure-H hydrate in the presence of Xe, while the mixture of cis-1,4-DMCH and methane generates the structure-H hydrate.     

Synthesis,characterization, and catalytic activity of 4 mol % N,N′‐methylene bisacrylamide crosslinked poly(acrylic acid)–metal complexes

The metal‐ion complexation behavior and catalytic activity of 4 mol % N,N′‐methylene bisacrylamide crosslinked poly(acrylic acid) were investigated. The polymeric ligand was prepared by solution polymerization. The metal‐ion complexation was studied with Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) ions. The metal uptake followed the order: Cu(II) > Cr(III) > Mn(II) > Co(II) > Fe(III) > Zn(II) > Ni(II). The polymeric ligand and the metal complexes were characterized by various spectral methods. The catalytic activity of the metal complexes were investigated toward the hydrolysis of p‐nitrophenyl acetate (NPA). The Co(II) complexes exhibited high catalytic activity. The kinetics of catalysis was first order. The hydrolysis was controlled by pH, time, amount of catalyst, and temperature. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 272–279, 2004     

Effect of the nature and degree of crosslinking on the catalase‐like activity of polystyrene‐supported schiff base‐metal complexes

Catalase‐like activity of the metal complexes of various crosslinked polystyrene‐supported Schiff bases were carried out and correlated with the nature and degree of crosslinking in the polymer support. Polystyrenes with 2–20 mol % ethyleneglycol dimethacrylate (EGDMA), 1,4‐butanediol dimethacrylate (BDDMA) and 1,6‐hexanediol diacrylate (HDODA) were used as polymer supports. functions of diethylenetriamine and salicylaldehyde were incorporated to the chloromethylpolystyrene by polymer analogous reactions and complexed with Fe(II), Fe(III), Co(II), Ni(II), and Cu(II) ions. The metal uptake decreased in the order: Cu(II) > Co(II) > Ni(II) > Fe(III) > Fe(II), and extent of metal uptake by the various crosslinked system varied with the nature and degree of the crosslinking agent. The polymeric ligands and the metal complexes were characterized by various analytical techniques. The catalytic activities of these metal complexes were investigated towards the decomposition reaction of hydrogen peroxide. Generally among the various metal complexes, the catalytic activities decreased in the order: Co(II) > Cu(II) > Ni(II) > Fe(III) ? Fe(II). With increasing rigidity of the crosslinking agent their catalytic activity also decreased. Of the various crosslinked systems, the catalytic activity decreased in the order: HDODA‐ > BDDMA‐ > EGDMA‐crosslinked system. Also, the catalytic activity is higher for low crosslinked systems and decreased further with increasing degree of crosslinking. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1271–1278, 2004     

Highly active and stereospecific polymerizations of 1,3-butadiene by using bis(benzimidazolyl)amine ligands derived Co(II) complexes in combination with ethylaluminum sesquichloride

A family of cobalt(II) complexes supported on tridentate dibenzimidazolyl ligands having a general formula: [N(CH₃)(CH₂)₂(Bm-R)₂]CoCl₂ (where Bm = benzimidazolyl, R = H; -Me; -Bz), have been prepared by the condensation of o-phenylene diamine with methyliminodiacetic acid. The Co(II) complexes exhibited high activities for the polymerization of 1,3-butadiene, on activation with ethylaluminum sesquichloride (EASC), to yield predominantly cis-1,4 microstructure. The polymers are characterized by high molecular weight with polydispersity values between 2.35 and 3.37. The ligand modification shows remarkable influence on polymerization activity. The stereospecificity of the catalysts is consistent for a wide range of reaction conditions, except temperature. The electronic influence of ligand structure towards metal center is investigated by using cyclic voltammetric analysis and the generation of cationic active centers is identified via UV-vis spectroscopic analysis of the catalyst system.     

Living polymerization of 1,3-butadiene by a Ziegler-Natta type catalyst composed of iron(III) 2-ethylhexanoate, triisobutylaluminum and diethyl phosphite

Living characteristics of facilely prepared Ziegler-Natta type catalyst system consisting of iron(III) 2-ethylhexanoate, triisobutylaluminum and diethyl phosphite have been found in the polymerization of 1,3-butadiene in hexane at 40 °C. The characteristics have been well demonstrated by: a first-order kinetics with respect to monomer conversion, a narrow molecular weight distribution (M_w/M_n = 1.48-1.52) of polybutadiene in the entire range of polymerization conversion and a good linearity between M_n and the yield of polymer. Feasible post-polymerization of 1,3-butadiene and block co-polymerization of 1,3-butadiene and isoprene further support the living natures of the catalyst bestowed with. The current catalyst system is highly active (yield > 80%, 35 min), providing polybutadiene with 1,2, cis-1,4 and trans-1,4 units about 44.0%, 51.0% and 5.0%, respectively.     

A novel polycondensate containing cyclodextrin and lactose: Synthesis, metal-complexing properties, and degradation

The synthesis and characterization of the novel water-soluble polycondensate from β-cyclodextrin triazine and d-lactose are described, which represents the first copolymer containing cyclodextrin and lactose in the main-chain. In addition, the metal complex forming properties of the novel polymer for different metal ions such as Cr(III), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Sr(II), Cd(II), Pb(II), and Al(III) were studied using the liquid-phase polymer-based retention (LPR) method and compared with those of β-cyclodextrin. According to the retention profiles obtained by the LPR method, all 10 metal ions investigated showed a strong interaction with this polymer. Finally, this polycondensate was shown to be microbiologically degradable with exponential microbial growth of 45 CFU (10⁸ mL⁻¹) by using conventional microbiological methods.     

Sequence analysis of poly(ethylene/1,4-cyclohexanedimethylene terephthalate) copolymer using H and C NMR

The triad-level sequence analysis of poly(ethylene/1,4-cyclohexanedimethylene terephthalate) copolymer was reported in a solvent system of o-chlorophenol/deuterated chloroform mixture (50/50 v/v) at 80 °C using 600 MHz ¹H NMR. The well-resolved alcoholic CH₂ proton peak of the glycol units was observed, which made the detailed sequence analysis possible. The peaks of the cis- and trans-forms of the 1,4-cyclohexanedimethylene glycol units were split into the triad sequence in the chain and could be assigned by a comparison of the spectra with those of homopolymers and by an additional two-dimensional heteronuclear multiple bond correlation observation. The triad sequence distributions centered on 1,4-cyclohexanedimethylene glycol units were determined, which was independent of the cis- and trans-forms of the units and controlled according to Bernoullian statistics.     

Detection of trivalent-iron based on low-dimensional semiconductor metal oxide nanostructures for environmental remediation by ICP-OES technique

A large-scale synthesis of undoped low-dimensional semiconductor metal oxide nanostructures (ZnO nanoparticles, NPs) by simple wet-chemical method was performed using reducing agents at low temperature. The NPs were characterized in terms of their morphological, structural, and optical properties, and efficiently applied for the metal ions uptake. The detailed structural, compositional, and optical characterizations of the NPs were evaluated by powder X-ray diffraction pattern (XRD), Fourier-transform infra-red spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Electron dispersion spectroscopy (EDS), and UV–vis. spectroscopy, respectively which confirmed that the obtained NPs are well-crystalline undoped ZnO and possessed good optical properties. The ZnO NSs morphology was investigated by FESEM, which confirmed that the calcined materials were spherical shape in nano-level and growth in huge-quantity. The analytical efficiency of newly synthesized ZnO NPs was also investigated for a selective separation of trivalent iron [Fe(III)] prior to its determination by inductively coupled plasma-optical emission spectrometry (ICP-OES). The selectivity of ZnO NPs towards different metal ions, including Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Ni(II), Zn(II), and Zr(IV), was studied. Data obtained from the selectivity study suggested that that ZnO NPs phase was the most selective towards Fe(III). The static uptake capacity of Fe(III) was found to be ~79.80 mg g⁻¹. Moreover, adsorption isotherm data also provided that the adsorption process was mainly monolayer on a homogeneous adsorbent surface.     

Highly active and trans-1,4 specific polymerization of 1,3-butadiene catalyzed by 2-pyrazolyl substituted 1,10-phenanthroline ligated iron (II) complexes

A new family of iron (II) complexes (2a–h) bearing tridentate 2-pyrazolyl substituted 1,10-phenanthroline ligands were successfully prepared and characterized by IR spectroscopy, elemental analysis, and mass spectra. Complexes 2a–f and 2h were further confirmed by the X-ray crystallographic analysis. 2a, 2b, 2e, and 2f adopted distorted trigonal bipyramidal configuration. 2c displayed a distorted octahedron formed by six coordinated nitrogen atoms of the two ligands. Linked by two bridged chloride atoms, complex 2d was a centrosymmetric dimmer, and complex 2h adopted a six-coordinate distorted octahedral geometry due to the coordination of two solvent molecules. These complexes activated by alkylaluminum were examined in butadiene polymerization. In combination with AlⁱBu₃, complexes 2a–c exhibited high catalytic activity (73.5%–94.3%) at 20 °C, whereas other complexes exhibited much lower activity. Interestingly, the activity and selectivity of the complexes increased as increasing polymerization temperature. In particular, 2b and 2c displayed both high activity (99% and 80%, respectively) and trans-1,4 selectivity (95.6% and 96.2%, respectively) at 60 °C. The trans-1,4 selectivity of 2b varied as alkylaluminum used as a cocatalyst, in the following order: AlⁱBu₃ > AlOct₃ > AlEt₃ > AlMe₃, whereas much lower trans-1,4 selectivity was observed in the cases of using MAO and MMAO.     

Ferrous and cobaltous chloride complexes bearing 2-(1-(arylimino)methyl)-8-(1H-benzimidazol-2-yl)quinolines: Synthesis, characterization and catalytic behavior in ethylene polymerization

The series of ligands 2-(1-(arylimino)methyl)-8-(1H-benzimidazol-2-yl)quinolines was synthesized and used to prepare new iron(II) and cobalt(II) dichloride complexes. X-ray diffraction studies revealed that the coordination geometry around the metal center can best be described as distorted square-based pyramidal. Upon activation with methylaluminoxane (MAO), both families (Fe and Co) of complexes showed good activities in ethylene polymerization, affording highly linear polyethylenes. Enhanced activities were observed on increasing the reaction temperature to 100 °C. The optimization of the reaction parameters and the influence of the substituents on the imino-bound aryl group of the chelate ligands were investigated.     

Molecular dynamics simulation of cis-1,4-polybutadiene. 2. Chain motion and origin of the fast process

Molecular dynamics (MD) simulations of cis-1,4-polybutadiene in bulk amorphous state were performed to elucidate the origin of a fast relaxation process observed by quasielastic neutron scattering (QENS) measurements. The details of the torsional motion for each dihedral angle were investigated with the torsional auto- and cross-correlation functions for several temperatures in this study. Temperature dependence of the correlation between the torsional autocorrelation and cross-correlation functions is also evaluated. The origin of the fast process of cis-1,4-polybutadiene is found to be mainly the cooperative conformational transitions of two dihedral angles located at both sides of the CH₂-CH₂ bond when the bond is in the trans conformation. The cooperative conformational transitions exhibit even below the glass transition temperature of cis-1,4-polybutadiene. The cooperative motion appears at about 50 K below the glass transition temperature, corresponding to the Vogel-Fulcher temperature.     

Hydrothermal synthesis and structural characterization of one-dimensional coordination polymers of cobalt(II) and nickel(II) with 1,3,5-benzenetriacetic acid

Transition metal complexes [M(Hbta)(H₂O)₄] [M=Co(II) (1), Ni(II) (2), H₃bta=1,3,5-benzenetriacetic acid] have been prepared by reaction of H₃bta with the M(OH)₂ in water by hydrothermal method. The complexes were characterized by X-ray crystallography and electrospray mass spectrometry. The coordination geometries around Co(II) and Ni(II) atoms are both distorted octahedral with O₆ donor set. And the conformation of flexible triacid is cis, trans, trans in the title complexes.     

Complexes with biologically active ligands. Part 9 metal complexes of 5-benzoylamino- and 5-(3-nitrobenzoyl-amino)-1,3,4-thiadiazole-2-sulfonamide as carbonic anhydrase inhibitors

Complexes containing the anions of 5-benzoylamido-1,3,4-thiadiazole-2-sulfonamide and 5-(3-nitro-benzoylamido)-1,3,4-thiadiazole-2-sulfonamid as ligands, and V(IV); Cr(III); Fe(III); Co(II); Ni(II); Cu(II) and Ag(I) were synthesized and characterized by standard procedures (elemental analysis; IR, electronic, and EPR spectroscopy; TG, magnetic and conductimetric measurements). The original sulfonamides and their metal complexes are strong inhibitors of two carbonic anhydrase (CA) isozymes, CA I and II.     

Linear and nonlinear optical properties of trans- and cis-poly(1-ethynylpyrene) based sonogel hybrid materials

The synthesis of sol-gel materials induced by ultrasonic action (sonolysis) is implemented as an alternative method for the fabrication of highly pure organic-inorganic composites with good monolithic and optical properties. The resulting SiO₂ glass exhibits high porosity and allows the inclusion of organic compounds in the colloidal sol-state. In this work, optical properties of trans-poly(1-ethynylpyrene) (trans-PEP) and cis-poly(1-ethynylpyrene) (cis-PEP) (M_w=24,000 g/mol) incorporated in this kind of gels were studied by absorption and fluorescence spectroscopies. Absorption spectra of the polymers showed that trans-PEP possesses a higher degree of conjugation than its homologue cis-PEP in sol-gel. Intramolecular interactions occur between adjacent pendant pyrene units (associated pyrenes) present in each polymer, giving rise to static excimer emissions, strongest in cis-PEP because of the shorter distances between aromatic rings. The results were compared to those previously reported for these polymers in solution. Besides, trans- and cis-PEP exhibited nonlinear optical properties like third harmonic generation (THG), which were measured in sol-gel phase for spin-coated film samples.     

Synthesis and properties of polyimides derived from cis- and trans-1,2,3,4-cyclohexanetetracarboxylic dianhydrides

Cis-1,2,3,4-cyclohexanetetracarboxylic dianhydride (cis-1,2,3,4-CHDA) was synthesized. It was found that under such conditions as heating or boiling in acetic anhydride, cis-1,2,3,4-CHDA could be converted to its trans-isomer. The process of thermal isomerization was monitored by ¹H NMR spectra and the mechanism of conversion was proposed. Their absolute structures of cis- and trans-1,2,3,4-CHDAs were elucidated by single crystal X-ray diffraction. The polycondensations of cis- and trans-1,2,3,4-CHDAs with aromatic diamines such as 4,4′-oxydianiline (ODA), 4,4′-methylenedianiline (MDA), 4,4′-diamino-3,3′-dimethyldiphenylmethane (DMMDA), 4,4′-bis(4-aminophenoxy)benzene (TPEQ), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) were studied. It is easy to obtain higher molecular weight polyimides from trans-1,2,3,4-CHDA using conventional one-step or two-step methods. However, higher molecular weight polyimides derived from cis-1,2,3,4-CHDA could not be prepared by the usual methods (solid content ca. 10%) owing to the trend of forming cyclic oligomers. Increasing the concentration of monomers could give higher molecular weight cis-polymers. All of the cis-polyimides were soluble at room temperature in aprotic polar solvents and phenolic solvents and some of them even soluble in chloroform and tetrahydrofuran, while the corresponding trans-polymers showed poor solubility as compared to cis-polymers. All of the polyimides showed good thermal stability with the 5% weight loss temperatures in air over 415 °C. Furthermore, polyimides derived from cis-1,2,3,4-CHDA have higher glass transition temperatures (T_gs) than corresponding trans-polyimides. The flexible polyimide films possessed a tensile modulus range of 2.1-3.6 GPa, a tensile strength range of 42-116 MPa, an elongation at break of 4-18%. These polyimides exhibited cutoffs at wavelengths around 270 nm and were entirely colorless. All the polyimides showed amorphous pattern according to Wide angle X-ray diffraction measurements. The differences of polymerization and properties were explained by the structural changes resulted from isomerism.     

Water-soluble oxidized starch in complexation of Fe(III), Cu(II), Ni(II) and Zn(II) ions

The structure of the bromate-oxidized wheat starch (OS) contains partly opened glucose units with carbonyl and carboxyl groups at C2-, C3- or C6-positions. OS with a variable degree of oxidation (DO) was studied in alkaline conditions as a water-soluble complexing agent for Fe(III), Cu(II), Ni(II) and Zn(II) ions, which are common in various wastewaters. Complexation was studied by inductively coupled plasma-optical emission spectrometry (ICP–OES) in a single metal ion or multi-metal ion solutions. The DO affected the efficiency of the complexation with metal ions. OS with the high DO (carboxyl and carbonyl DO of 0.72 and 0.23, respectively) complexed and held Fe(III) or Zn(II) ions in a soluble form effectively in 0.5 mM single ion alkaline solution with the molar ratio of 0.65:1 of oxidized starch-to-metal ion (OS-to-M). The OS-to-M molar ratio of 1.3:1 was required to form a soluble complex with Cu(II) or Ni(II) ions. These complexes were thermally stable at the temperature range of 20–60 °C. OS with the low DO (carboxyl and carbonyl DO 0.47 and 0.17, respectively) complexed Zn(II) ions highly, Cu(II) and Ni(II) ions poorly and Fe(III) ions only partly. In the multi-metal ion solution of OS the solubility of these metal ions improved with the increasing DO of starch, which followed the same tendency as was observed in the single metal ion systems. The increased molar ratio of OS-to-M improved the complexation and solubility of the metal ions in all multi-metal ion series. As the soluble multi-metal ion complexes were reanalyzed after 7 days, all solutions had kept the high complexation and solubility of metal ions (ca. 90%). Complexation by OS did not show a selective binding of the ions in the multi-metal ion solution. It was concluded that the flexible, opened ring structure units of OS prevented the selective binding to metal ions but made the complexes highly stable. Titrimetric studies of OS–Fe(III) complexation showed that each anhydroglucose unit of OS had more than one coordination site and as the content of OS increased, the free sites coordinated to Fe(III) ions and formed cross-linked starch structures.     

Carbon nanotube filter for heavy metal ion adsorption

This study investigated carbon nanotube filtration technology using catalyst particles supported on silicalite-1–biomorphic carbon materials (BCMs). Aqueous solutions of Mn(II), Cu(II), Cr(III), Cd(II), and Pb(II) were used to test the efficiency of heavy metal ions removal. Carbon nanotubes (CNTs) were synthesized and grown on BCMs by the chemical vapor deposition method catalyzed with the catalyst (Co, Fe, and Ni). The synthesized CNTs with Co– and Fe– nanoparticles were typically multi-walled carbon nanotubes, and they showed good crystallinity (I_D/I_G = 1.05) and yield of (11.10 and 8.86) %. The removal efficiency of Mn(II), Cu(II), Cr(III), Cd(II), and Pb(II) ions using Co-catalyzed CNT filter was 97.57%, 98.01%, 97.89%, 97.42%, and 99.99%, respectively.     

Magnetic interactions as a stabilizing factor of semiquinone species of lawsone by metal complexation

Changes in electrochemical reactivity for lawsone anions (lawsone, 2-hydroxy-1,4-naphthoquinone, HLw) being coordinated to a series of metallic ions in dimethylsulfoxide solution were evaluated. Upon performing cyclic voltammetry experiments for metal complexes of this quinone with pyridine (Py) - structural formula M(II)(Lw⁻)₂(Py)₂; M: Co(II), Ni(II), Zn(II) - it was found that the reduction of coordinated Lw⁻ units occurs during the first and second electron uptake in the analyzed compounds. The stability of the electrogenerated intermediates for each complex depends on the d electron configuration in each metal center and is determined by magnetic interactions with the available spins considering an octahedral conformation for all the compounds. This was evidenced by in situ spectroelectrochemical-ESR measurements in the Zn(II) complex in which due to the lack of magnetic interaction owing to its electron configuration, the structure of the coordinated anion radical species was determined. Successive reduction of the associated Lw⁻ units leads to partial dissociation of the complex, determined by the identification of free radical dianion structures in solution. These results show some insights on how metal-lawsone complexation can modify the solution reactivity and stability of the electrogenerated radical species.     

Electrolyte solutions in liquid ammonia—IX. Electrodeposition and electrodissolution of metals from their salts

Anodic dissolution and cathodic deposition of 20 transition metals in acidic solutions in liquid ammonia has been surveyed. The early transition metal elements Ti, Zr, V Nb, Mo and W form high oxidation-state insoluble amido complexes during anodic oxidation. Soluble ammines of normal metal oxidation states are produced with Cr(III), Mn(II), Fe(II), Co(III), Ni(II), Cu(II), Ag(I), Zn(II), Cd(II) and Hg(II) (Mn dissolves spontaneously). The metals Ru, Pd, Pt and Au only dissolve slightly after prolonged electrolysis. Anodic enrichment of Au in its alloys is unlike that in aqueous solution; in ammonia both Cu and Ag can be simultaneously depleted from a 9 carat gold alloy. Cathodic reduction of metal-bearing solutions follows wide variations of behaviour. Fe and Ru ammines reduce to amido-complexes with concomittant hydrogen evolution, but Cr is not reduced. Solutions of Mn, Co, Ni, Pd, Pt, Ag, Au, Zn, Cd and Hg give metallic cathode deposits under differing conditions. Electrodeposition is potential dependent for Ni, Cu and Ag; metal plate at low potentials, and powders at high potentials. The two different products are the result of reduction of species with different degrees of solvation.     

Study on Synthesis, Characterization, Thermal Stability and Conductivity Properties of a New Conjugated Oligoazomethine and some of its Metal Complexes

A novel azomethine oligomer of 2,3-bis[(2-hydroxyphenyl)methylene]diaminopyridine (HPMDAP) was first synthesized by oxidative polycondensation reaction using air and NaOCl as oxidative agents. Optimum reaction conditions for the oxidative polycondensation and the main parameters of the process were established. At optimum reaction conditions, the yield of the product was found to be 69%. Oligomeric complexes of 2,3-bis[(2-hydroxyphenyl)methylene]diaminopyridine with Cd(II), Co(II), Cu(II), Ni(II), Fe(II), Pb(II), Cr(III) and Zn(II) were successfully prepared. Structures of monomer, oligomer and some oligomer metal complexes obtained were confirmed by FT-IR, UV–vis, ¹H- and ¹³C-NMR and elemental analysis. Characterization was carried out by TG-DTA, size exclusion chromatography (SEC), magnetic moment and solubility tests. The ¹H- and ¹³C-NMR data showed that polymerization proceed by C–C coupling of ortho and para positions according to –OH group of HPMDAP. Elemental analysis of chelates suggests that the metal ligand ratio is about 1:2. Molecular weight distribution values of the products were determined by size exclusion chromatography (SEC). According to TG analyses, the carbonaceous residues of HPMDAP and OHPMDAP were found to be 34.94 and 29.36% at 1000 °C, respectively. Thermal analyses of Cd, Co, Cu, Ni, Fe, Pb, Cr and Zn oligomer–metal complexes were also investigated under N₂ atmosphere between 15 and 1000 °C. Electrical conductivities of OHPMDAP and its metal complexes were also measured with four probe technique.