Conformation of poly(<Emphasis Type="SmallCaps">l</Emphasis>-glutamic acid) in bipolar amphiphiles with alkyl ammonium cations of different hydrophobicity

The conformation of the sodium salt of poly(l-glutamic acid) (P(Glu)) in solutions of the cationic bipolar amphiphile 1, 20-isosanediylbis(alkylammonium chloride) (C ₂₀(RA) ₂) with different alkyl head groups as a function of amphiphile concentration was investigated using circular dichroism (CD). RA included methylammonium (MA), ethylammonium (EA), propylammonium (PA), butylammonium (BA), and pentylammonium (PeA) cationic groups. The CD spectrum of each C ₂₀(RA) ₂ had a double minima corresponding to the a-helix of P(Glu), which was replaced by CD spectra with a single minimum at wavelengths larger than 222 nm as concentration increased. These changes in the CD spectrum were ascribed to the conformational change from random coil to a-helix and to aggregates of helices. In C ₂₀(EA) ₂ solutions, a step-like change in the CD intensity was observed at 222 nm as a function of the ratio of C ₂₀(RA) ₂ to P(Glu). At the step, the CD spectrum of the complete a-helix was observed. At 10–35 °C, an a-helix was induced in P(Glu) in the order: C ₂₀(EA) ₂>C ₂₀(MA) ₂>C ₂₀(PA) ₂>C ₂₀(BA) ₂>C ₂₀(PeA) ₂. This order was ascribed to the best fit of ethylammonium to the P(Glu) side chain.     

Kinetic study of dipivaloylmethane by ozawa method

The lanthanidic complexes of general formula Ln(C₁₁H₁₉O₂)₃ were synthesized and characterized by elementary analysis, infrared absorption espectroscopy, thermogravimetry (TG) and differential scanning calorimetry (DSC). The reaction of thermal decomposition of complexes has been studied by non-isothermal and isothermal TG. The thermal decomposition reaction of complexes began in the solid phase for Tb(thd)₃, Tm(thd)₃ and Yb(thd)₃ and in the liquid phase for Er(thd)₃ and Lu(thd)₃, as it was observed by TG/DTG/DSC superimposed curves. The kinetic model that best adjusted the experimental isothermal thermogravimetric data was the R1 model. Through the Ozawa method it was possible to find coherent results in the kinetic parameters and according to the activation energy the following stability order was obtained: Tb(thd)₃>Lu(thd)₃>Yb(thd)₃>Tm(thd)₃>Er(thd)₃ This revised version was published online in August 2006 with corrections to the Cover Date.     

Perfluoro and polyfluorosulfonic acids: XVI. Difluoromethanesulfonic acids as a precursor of CF2: In the synthesis of difluoromethyl poly- and perfluoroalkanesulfonates

Difluoromethanesulfonic acid (1) readily reacts with P₂O₅ at room temperature to give difluoromethyl difluoromethanesulfonate (2) and SO₂ in stead of the expected acid anhydride. If perfluorosulfonic acid (3) perfluorocarboxylic acid (5) or KI was added to this reaction mixture, difluoromethyl perfluorosulfonate (4), difluoromethyl perfluorocarboxylate (6) and HCF₂I (7) was formed respectively in addition to 2. A similar result was obtained using POCl₃ or SOCl₂ instead of P₂O₅ as dehydrating agent. The mechanisms of the formation of difluorocarbene were discussed.     

Synthesis and reactions of [tris(trimethylsilyl)methyl]ethyl dichlorosilane

The crowded dichlorosilane TsiSiEtCl₂, (1), (Tsi = (Me₃Si)₃C) was prepared from the reaction between EtSiCl₃ and TsiLi, then it was reduced with LiAlH₄ to give TsiSiEtH₂, (2). The hydride (2) was then treated with two equivalents of ICl/CCl₄ or Br₂/CCl₄ to produce TsiSiEtI₂, (3), and TsiSiEtBr₂, (4), respectively. The reaction of compound (2) with one equivalent of ICl/CCl₄ gives TsiSiEtHI, (5). This product reacted with H₂O/dioxane in the presence of AgClO₄ or with dry MeOH to produce TsiSiEtHOH, (6), and TsiSiEtHOMe, (7), respectively. The compound (3) reacted with H₂O in DMSO/CH₃CN to give TsiSiEt(OH)₂, (8), and the compound TsiSiEtIOMe, (9), was prepared from the reaction of the compound (7) with ICl/CCl₄. When the dichloride (1) was treated with NaOMe/MeOH it gave (Me₃Si)₂CHSiEt(OMe)₂. It is suggested that the reaction proceeds through an elimination-addition mechanism. The dichloride (1) was also treated with KSCN, NaN₃ or NaOCN in CH₃CN to give S_N2 substitution products. All the new products were characterized by FTIR, ¹H NMR, and ¹³C NMR spectroscopy, mass spectrometry and elemental analysis.     

Synthesis and X-ray Molecular Structure Analysis of Some Au-Co,Au-Mn,and Hg-Co Bonded Compounds

The reaction of NaCo(CO)_4-x (PR₃) _x (x = 0, 1) with Au(PR₃)Cl was examined in THF. The products were characterized by single crystal X-ray analysis and/or XPS spectroscopy. When the THF solution of NaCo(CO)_4-x (PR₃) _x which was in situ prepared by the reduction of the corresponding cobalt carbonyl dimer with Na amalgam was filtered, the main product was (R₃P)Au-Co(CO)₄ and (R₃P)Au-Co(CO)_4-x (PR₃) _x (x = 1,2); phosphine migration from the Au to the Co site was observed for bulky phosphines during the recrystallization process. When the THF solution of NaCo(CO)_4-x (PR₃) _x was not filtered, the main product had the composition of M[Co(CO)₃(PR₃)]₂. The element M was clearly determined to be Hg by XPS spectroscopy. The reaction of NaMn(CO)₅ with Au(PR₃)Cl, however, afforded R₃PAu-Mn(CO)₅. The bonding parameters such as Au-M and Hg-Co bond-lengths were interpreted in terms of the electronic nature of the R group of the monodentate PR₃ ligand.     

Photocatalytic activity of divalent ion (copper,zinc and magnesium) doped NiAl2O4

Nickel aluminate (NiAl₂O₄) and doped nickel aluminate (Ni_1-xM_xAl₂O₄; M = Mg, Zn, Cu; x = 0.1) were prepared by sol-gel method using citric acid. The synthesized compounds were analyzed by various techniques such as powder XRD, FTIR, SEM-EDAX and UV-DRS. The lattice parameter was found to increase with the copper, zinc and magnesium doping in nickel aluminate. The band gap was decreased from 3.0 eV (NiAl₂O₄) to 2.9 (zinc doped), 2.7 eV (magnesium doped) and increased to 3.1 eV in the case of copper doping. The catalytic study was carried out for a cationic (methylene blue) and an anionic dye (methyl orange). The percentage degradation of methyl orange using Zn_0.1Ni_0.9Al₂O₄ and Mg_0.1Ni_0.9Al₂O₄ was found to be 92% (180 min) and 96% (90 min). 93% (120 min) and 97% (120 min) degradation of methylene blue was observed using zinc doped and magnesium doped nickel aluminate respectively. These results are comparatively higher than its parent analogue (94% (180 min) degradation against methyl orange and 91% (120 min) against methylene blue). Whereas the percentage degradation was found to be less in the case of Cu_0.1Ni_0.9Al₂O₄ (83% (180 min) against methyl orange and 90% (120 min) against methylene blue).     

弱磁场下低温中和法制备亚微米非晶态δ-FeOOH的研究

利用XRD和SEM分别对在弱磁场下通过低温中和法制备的羟基铁氧化物进行相成分和颗粒形貌分析. 试验结果表明: 无磁场下, 产物是由部分球形和部分针状的α-FeOOH组成. 0.1 T磁场下, 产物是纺锤形的γ-FeOOH, 但是, 其粒度分布很不均匀. 0.3 T磁场下, 产物是球形的Fe_1.833(OH)_0.5O_0.25. 0.5 T磁场下, 产物是100 nm左右的球形的非晶态δ-FeOOH. Fe_1.833(OH)_0.5O_0.25是无磁场下制备的α-FeOOH向弱磁场下制备的δ-FeOOH转变的中间产物. 并且, 亚微米球形Fe_1.833(OH)_0.5O_0.25和亚微米非晶态球形δ-FeOOH的粒度分布都很均匀. 此外, 弱磁场影响羟基铁氧化物的结晶度.     

Light production in alkaline mixtures of reducing agents and dimethylbiacridylium nitrate.

Abstract— Kinetic studies were made of light production and 0₂ absorption elicited by treatment of dimethylbiacridylium hydroxide [D(OH)₂] with reducing agents in alkaline aqueous solutions. D(OH)2 addition stimulated O₂ uptake which proceeded with zero-order kinetics until nearly all of the O₂ or of the D(OH)₂ was converted to end products. At the termination of the reactions with fructose as reductant the D(OH)₂ was converted to methylacridone and to dimethylbiacridene each compound accounting for approximately one-half the D(OH)₂ consumed. O₂ was reduced to H₂O₂. With hydroxylamine as the reducing agent the emitted light intensity was related to the first power of the D(OH)₂ concentration and the rate of O₂ uptake to the square root of the D(OH)₂. The disappearance of D(OH)₂ in these circumstances was by a first order or pseudo-first order rate. Fructose as a reducing agent by contrast resulted in an O₂ uptake nearly independent of D(OH)₂ concentration over a range from 1 × 10^-5M-1 × 10^-4M, while the light intensity and disappearance of D(OH)₂ followed a one-half order rate. O₂ uptake was by zero order kinetics and the oxidation of fructose proceeded at the same rate as was found with ferricyanide as oxidant. The kinetics, quantum yields and temperature dependence of the fructose reactions were compared with similar reactions employing H₂O₂ as the light eliciting reagent. The results are interpreted as indicating that D(OH)₂ acts as a chain initiator in a manner analogous to better known, radical producing compounds found to accelerate hydrocarbon autooxidations.     

Ferrocenyl‐Functionalised Molybdenum Imido Complexes: An Approach to Redox‐Tunable Olefin Polymerisation Catalysts

[(FcdippN)₂MoCl₂(DME)] ( 1 ) was used as starting material for the synthesis of the novel ferrocenyl‐functionalised complexes [(FcdippN)₂Mo(CH₂CMe₂Ph)₂] ( 2 ), [(FcdippN)₂Mo(OTf)₂(DME)] ( 3 ), and [(FcdippN)Mo(CHCMe₂Ph)(O^tBu)₂] ( 4 ) (Fcdipp = 4‐ferrocenyl‐2,6‐diisopropylphenyl). The crystal structure of 2 was determined. Electrochemical investigations by cyclic voltammetry suggest a communication of the ferrocenyl unit and the molybdenum centre in these compounds. The monoalkylation of [(DippN)₂MoCl₂(DME)] ( 5 ) to [(DippN)₂Mo(CH₂CMe₂Ph)Cl] ( 6 ) (Dipp = 2,6‐diisopropylphenyl) was achieved.     

Structural evolution of a recoverable rhodium hydrogenation catalyst

A recoverable, water soluble, hydrogenation catalyst was synthesized by reacting poly-N-isopropylacrylamide containing a terminal amino group (H₂N-CH₂CH₂-S-pNIPAAm) with [Rh(CO)₂Cl]₂ in organic solvents to form the square planar rhodium complex (Rh(CO)₂Cl(H₂N-CH₂CH₂-S-pNIPAAm)). The catalyst-ligand structure was characterized using in situ multinuclear NMR, XAFS and IR spectroscopic methods. Model complexes containing glycine (H₂NCH₂COOH), cysteamine (H₂NCH₂CH₂SH) and methionine methyl ester (H₂NCH(CH₂CH₂SCH₃)COOCH₃) ligands were studied to aid in the interpretation of the coordination sphere of the rhodium catalyst. The spectroscopic data revealed a switch in ligation from the amine bound (Rh-NH₂-CH₂CH₂-S-pNIPAAm) to the thioether bound (Rh-S(-CH₂CH₂NH₂)(-pNIPAAm)) rhodium when the complex was dissolved in water. The evolution of the structure of the rhodium complex dissolved in water was followed by XAFS. The structure changed from the expected monomeric complex to form a rhodium cluster of up to four rhodium atoms containing one SRR′ ligand and one CO ligand per rhodium center. No metallic rhodium was observed during this transformation. The rhodium-rhodium interactions were disrupted when an alkene (3-butenol) was added to the aqueous solution. The kinetics of the hydrogenation reaction were measured using a novel high-pressure flow-through NMR system and the catalyst was found to have a TOF of 3000/Rh/h at 25 °C for the hydrogenation of 3-butenol in water.     

Synthesis,crystal structure,thermal decomposition,and XPS studies of homo and heterotrinuclear Cu(II)–Cu(II)–Cu(II) and Cu(II)–Ni(II)–Cu(II) complexes obtained from salpn type ligands

In this study, a mononuclear CuL complex was prepared by the use of bis-N,N′-(salicylidene)-1, 3-propanediamine (LH₂) and Cu²⁺ ion. NiCl₂ and NiBr₂ salt were treated with this complex in dioxanewater medium and two new complexes [(CuL)₂NiCl₂(H₂O)₂] and [(CuL)₂NiBr₂(H₂O)₂)] with Cu(II)–Ni(II)–Cu(II) nucleus structure were obtained. In addition to this bis-N,N′-(2-hydroxybenzyl)-1,3-diaminopropane (L^HH₂) was prepared by the reduction of LH₂ with NaBH₄ in MeOH medium. The treatment of this reduced complex with Cu²⁺ ion resulted a complex [(CuL^H)₂CuCl₂] with a structure of Cu(II)–Cu(II)–Cu(II). The complexes prepared were characterized by the use of elemental analysis, IR spectroscopy, thermogravimetric and X-ray diffraction methods. The crystal structures of [(CuL)₂NiBr₂(H₂O)₂] (СIF file CCDC 1448402) and [(CuL^H)₂CuCl₂] (СIF file CCDC 1448401) complexes were elucidated. It was found that halogen ions are coordinated to terminal Cu²⁺ ions which are in a distorted square pyramid coordination sphere. It was determined that the central Cu(II), which joins terminal square pyramidal Cu(II), was coordinated only by the phenolic oxygens of the ligand while the central Ni(II) was coordinated by two phenolic oxygens of the organic ligand and two water molecules. These complexes were investigated by XPS and it was found that the terminal and central Cu²⁺ ions were different in Cu(II)–Cu(II)–Cu(II) complex. Also, the thermal degradation of the CuLH complex unit was observed to exothermic in contrast to the expectations.

     

Coordination of neighboring C?H bond to transition metal center: III. Study on localized molecular orbitals of the binucleate ion [Fe2(CH3)(CO)(Ph2PCH2PPh2)Cp2]+

A localized INDO method was used to calculate the ion [Fe₂ (CH₃) (CO) (Ph₂PCH₂PPh₂)-Cp₂]⁺. Based on the analysis of the localized molecular orbitals (LMO), bond orders and contour maps, it was pointed out that the LMO no. 20 corresponds to the coordination of C(1)—H(1) σ bond to Fe(2) atom. Non occurrence of metal-metal bond between Fe(1) and Fe(2) atoms was found and the covalence of irons was numerated, which coincides with the value in ref 17.     

Investigation of Novel Organometallics by Thermal Spectroscopic Methods

The photolysis of W(CO)₆in CH₂Cl₂ produces (CO)₅WCH₂Cl₂. The high reactivity of (CO)₅WCH₂Cl₂ (1) was exploited to synthesize a vinylidene complexes via the acetylene-vinylidene rearrangement. The addition of a terminal acetylene (H-C≡C-COOCH₃) to a solution of (1) produced the η²-acetylene-pentacarbonyltungsten complex (CO)₅W(η²-HC≡C-COOCH₃) in good yield. The production of the vinylidene complex (CO)₅W=C=CH-COOCH₃in equilibrium with the acetylene complex in the reaction medium was verified experimentally by reaction with excess imine. The heterocyclic organometallic compound of tungsten obtained was separated and purified and its structure was studied by IR, ¹H NMR, ¹³C NMR and mass spectrometry in comparison with the thermal analysis and elemental analysis data. The final aim of this investigation is the development of a new alternative route to a β-lactame with antibacterial activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

A new method for preparation of silica potassium cobalt hexacyanoferrate composite ion exchanger from silica sol

A new method for the preparation of porous silicapotassium cobalt hexacyanoferrate (SiO₂ ^.KCoFC) composite from silica sol is described. Silica sol was first gelled with K₄Fe(CN)₆ solution. Then the resulting hydrogel, SiO₂ ^.K₄Fe(CN)₆ was reacted with Co(NO₃)₂ solution in acetone to give the composite SiO₂ ^.KCoFC hydrogel. The empirical formula of KCoFC in the composite was found to be K₁.₆₉Co _0.93Fe(CN)₆. The removal efficiency of the composite for Cs was judged by measuring its distribution coefficient, K _d in 1M HCl solution containing 10 ppm Cs. The K _d of Cs was found to be 5.73^.10⁵ ml/g-composite.     

Characterization and TG-MS studies of lactato and bipyridine-lactato complexes of Co(II) and Ni(II)

Two lactates and four new mixed ligand complexes with formulae Co(lact)₂·2H₂O, Ni(lact)₂·3H₂O, Co(4-bpy)(lact)₂, Co(2,4'-bpy)₂(lact)₂, Ni(4-bpy)(lact)₂·2H₂O and Ni(2,4'-bpy)₂(lact)₂ (where 4-bpy=4,4'-bipyridine, 2,4'-bpy=2,4'-bipyridine, lact=CH₃CH(OH)COO^-) were isolated and investigated. The thermal behaviour of compounds was studied by thermal analysis (TG, DTG, DTA). In the case of hydrated complexes thermal decomposition starts with the release of water molecules. The compounds decompose at high temperature to metal(II) oxides in air. A coupled TG-MS system was used to analyse the principal volatile products of thermolysis and fragmentation processes of obtained complexes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preparation and luminescence properties of tris(bipyridine) ruthenium(II)-containing vinyl polymers: Ru(bpy)2 (poly-6-vinyl-2,2′-bipyridine)Cl2 and Ru(bpy)2(poly-4-methyl-4′-vinyl-,2,2′-bipyridine)Cl2

Ruthenium (II) complex-containing polymers were prepared and characterized by absorption and luminescence spectra, luminescence quantum yield, and luminescence lifetime. The polymers are Ru(bpy)₂(poly-6-vinyl-2,′2-bipyridine)CI₂ ( 1 ) and Ru(bpy)₂(poly-4-methyl-4′-methyl-4′ -vinyl-2,2′-bipyridine)CI₂ ( 2 ). The absorption spectra and luminescence spectra of polymers 1 and 2 were substantially the same as that of Ru(bpy)₃CI₂. The lifetime of polymers 1 and 2 was similar to that of the respective monomer model compounds. The lifetime of polymer 1 was very short (ca. 13 ns) in comparison to Ru(bpy)₃CI₂ (660 ns), whereas the lifetime of polymer 2 (660 ns) was similar to that of Ru(bpy)₃CI₂. The temperature-dependency of the lifetime was discussed in terms of Watts' model.     

Effect of different Fe(III) compounds on photosynthetic electron transport in spinach chloroplasts and on iron accumulation in maize plants

Synthesis and spectral characteristics of [Fe(nia)₃Cl₃] and [Fe(nia)₃(H₂O)₂](ClO₄)₃ are described. The effect of these compounds as well as of FeCl₃·6H₂O on photosynthetic electron transport in spinach chloroplasts was investigated using EPR spectroscopy. It was found that due to the interaction of these compounds with tyrosine radicals situated at the 161^st position in D₁ (Tyr_Z) and D₂ (Tyr_D) proteins located at the donor side of photosystem (PS) II, electron transport between the photosynthetic centres PS II and PS I was interrupted. In addition, the treatment with [Fe(nia)₃(H₂O)₂](ClO₄)₃ resulted in a release of Mn(II) from the oxygen evolving complex situated on the donor side of PS II. Moreover, the effect of the Fe(III) compounds studied on some production characteristics of hydroponically cultivated maize plants and on Fe accumulation in plant organs was investigated. In general, the production characteristic most inhibited by the presence of Fe(III) compounds was the leaf dry mass and [Fe(nia)₃(H₂O)₂](ClO₄)₃ was found to be the most effective compound. The highest Fe amount was accumulated in the roots, and the leaves treated with Fe(III) compounds contained more Fe than the stems. The treatment with FeCl₃·6H₂O caused the most effective translocation of Fe into the shoots. Comparing the effect of nicotinamide complexes, [Fe(nia)₃(H₂O)₂](ClO₄)₃ was found to facilitate the translocation of Fe into the shoots more effectively than [Fe(nia)₃Cl₃]. This could be connected with the different structure of these complexes. [Fe(nia)₃(H₂O)₂](ClO₄)₃ has ionic structure and, in addition, coordinated H₂O molecules can be easily substituted by other ligands. Dedicated to Professor Milan Melník on the occasion of his 70th birthday.     

A study of the thermal behavior of the system of zirconium and neodymium dipyvaloylmethanates

TG-DTA method was used to study the thermal behavior of the Zr(thd)₄/[Nd(thd)₃]₂ system (thd = 2,2,6.6-tetramethylheptane-3,5-dionato) in the condensed phase. Data were obtained on the kinetics of vaporization of individual beta-diketonate precursors and variously prepared mixtures. A mass-spectrometric monitoring of the gas-phase composition was employed to examine the thermal stability of vapors and to study in situ how individual dipyvaloylmethanates Zr(thd)₄ and Nd(thd)₃ and the two-component system Zr(thd)₄–Nd(thd)₃ are thermally decomposed in a vacuum and in the presence of oxygen. It was found that there is no chemical interaction between the precursors in the whole temperature range under study, but rather pronounced effects of nonadditivity of the thermal parameters are observed for the mixtures examined.     

Determination of Riboflavin Using Flow Injection Inhibitory Chemiluminescence

ABSTRACT

A new flow injection method for the determination of riboflavin based on the inhibition of the intensity of chemiluminescence (CL) from the luminol-K₃Fe(CN)₆ system is described. While riboflavin mixed with K₃Fe(CN)₆, by the fast oxidation reaction between riboflavin and K₃Fe(CN)₆, K₄Fe(CN)₆ was generated, which then inhibited the CL reaction of K₃Fe(CN)₆ and luminol in alkaline aqueous solution. The CL emission was correlated with the riboflavin concentration in the range from 0.032 to 100 μg·ml?¹, and the detection limit was 0.01 μg·ml?¹ (3σ). A complete analysis could be performed in 2 min with a relative standard deviation of less than 2.2%. The influence of foreign species was studied and the method has been applied successfully to the determination of riboflavin in pharmaceutical samples, the recovery was from 98.0% to 102%.     

Synthesis and Reactivity of Molybdenum and Tungsten Alkyne Complexes Containing 6-Methylpyridine-2-thiolate Ligands

A series of M(II) and M(IV) (M=Mo, W) alkyne adducts employing two 6-methylpyridine-2-thiolate (6-MePyS) ligands was synthesized and investigated towards the nucleophilic attack of PMe₃ on the coordinated alkynes. For this approach, 2-butyne (C₂Me₂), phenylacetylene (HC₂Ph), and diphenylacetylene (C₂Ph₂) were used. For the exploration of an intramolecular attack, but-3-yn-1-ol (HCCCH₂CH₂OH) was coordinated to the metal centers. A nucleophilic attack of PMe₃ was observed in [W(CO)(HC₂Ph)(6-MePyS)₂] yielding an η²-vinyl compound. Reaction of [W(CO)(C₂Ph₂)(6-MePyS)₂] with excess PMe₃ resulted in the selective coordination of one molecule of PMe₃ concomitant with decoordination of the nitrogen atom of one 6-MePyS ligand. In contrast, the W(IV) complexes did not react with PMe₃. While no selectivity was observed in the reaction of the Mo(II) compounds with PMe₃, alkynes in the Mo(IV) compounds were replaced by PMe₃. Addition of Et₃N to the but-3-yn-1-ol complexes did not lead to the anticipated formation of 2,3-dihydrofuran.