“Blue silver”: transformation of clusters and metal coagulation

The formation and transformations of blue silver ( _max 700 nm) during -irradiation of a weakly alkaline (pH 9) aqueous solution containing AgClO₄, polyacrylic acid (PAA), and isopropanol were studied. We believe that blue silver is a linear silver cluster stabilized on a polymeric molecule. During radiation-chemical reduction the cluster is transformed into new clusters ( _max = 365 and 460 nm). When all of the Ag⁺ ions present in the solution have been reduced, clusters coalesce and a new phase,i.e., colloidal silver particles, forms. The mechanism of the radiation-chemical transformations is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 35–37, January, 1995.     

Colorimetric determination of copper ions based on the catalytic leaching of silver from the shell of silver-coated gold nanorods

We have developed a method for the colorimetric determination of copper ions (Cu²⁺) that is based on the use of silver-coated gold nanorods (Au@Ag NRs). Its outstanding selectivity and sensitivity result from the catalytic leaching process that occurs between Cu²⁺, thiosulfate (S₂O₃ ^2?), and the surface of the Au@Ag NRs. The intrinsic color of the Au@Ag NRs changes from bright red to bluish green with decreasing thickness of the silver coating. The addition of Cu²⁺ accelerates the leaching of silver from the shell caused in the presence of S₂O₃ ^2?. This result in a decrease in the thickness of the silver shell which is accompanied a change in color and absorption spectra of the colloidal solution. The shifts in the absorption maxima are linearly related to the concentrations of Cu²⁺ over the 3–1,000 nM concentration range (R?=?0.996). The method is cost effective and was applied to the determination of Cu²⁺ in real water samples.

XPS characterization ofγ-zirconium phosphate and of some of its intercalation compounds. A comparison with the α-zirconium phosphate analogues

An X-ray photoelectron spectroscopic investigation of-Zr (HP0₄)₂·2 H₂O and its intercalation compounds with 1,10-phenanthroline, Co²⁺-phenanthroline and Cu²⁺-phenanthroline is described. The analysis of theNls spectra of the compound containing only phenanthroline clearly shows that, on average, more than one nitrogen atom of the diamine interacts with the acid groups of the host, giving protonated species. XPS also provides evidence of the coordination of Co²⁺ and Cu²⁺ ions after their diffusion in the phenanthroline--zirconium phosphate intercalation compound. They form mixed N-and O-coordinated species with the diamine and the oxygens of the interlayer region, but the presence of the characteristic peaks of uncoordinated phenanthroline, even at low intensity, shows that the diamine molecules anchored to the host are still present.A comparison is made with the analogous derivatives of -Zr (HPO₄)₂·H₂O and the differences between the two series of compounds are discussed.     

The electrochemistry of the inclusion complex of anthraquinone withβ-Cyclodextrin studied by means of OSWV

The reduction of anthraquinone (AQ) in the presence of -Cyclodextrin (-CD) has been investigated by Osteryoung square wave voltammetry (OSWV) in phosphate buffer (pH = 7.0). -CD forms a 1 : 1 inclusion complex with AQ. The experimental results show that -CD causes a decrease in the peak current (I _p) and a negative shift in the peak potential (E _p) for AQ reduction. The relationship betweenI _p (andE _p) and the concentration of -CD has been studied. The dissociation constant of the inclusion complex,K _d = 3.5 × 10^–3 mol/L, was obtained from the plot ofI _p ^/2 vs. (I _p ^(AQ)/2 –I _p ^/2 ) [CD]. The diffusion coefficients of free AQ and in the presence of -CD have been determined by means of chronocoulometry (CC). The adsorption properties of -CD on glassy carbon and gold electrodes was investigated. UV vis spectra gave further evidence for complexation and the dissociation constant determined spectroscopically,K _d ^/ = 4.5 × 10^–3 mol/L, was in agreement with that obtained electrochemically.     

Colloidal copper and peculiarities of its reaction with silver ions in aqueous solution

Interactions between colloidal copper and silver ions lead to the formation of silver nanoparticles. The reaction proceeds through the intermediate stage of the formation of a copper-silver contact pair. The formation of bimetallic Ag_coreCu_shell nanoparticles is observed in the presence of the “seeding” silver nanoparticles and upon the simultaneous radiochemical reduction of Ag⁺ and Cu²⁺ ions.     

Directly Linked and Fused Oligoporphyrin Arrays from Oxidation of Metalloporphyrins

The Ag^I-promoted oxidative meso-meso coupling reaction of 5,15-diaryl Zn^II-porphyrins is advantageous in light of its high regioselectivity as well as its easy extension to large porphyrin arrays. Linear meso-meso linked porphyrin 128-mer and three-dimensionally arranged grid porphyrin 48-mer were isolated in a discrete form by repetitive oxidation reaction and subsequent gel-permeation chromatography (GPC)-HPLC. 5,15-Diaryl Cu^II-, Ni^II-, and Pd^II-porphyrins were converted to meso- doubly-linked diporphyrins by oxidation with(p-BrC₆H₄)₃NSbCl₆. End-aryl-capped meso-meso linked Cu^II-, Ni^II-, and Pd^II- diporphyrins were converted to completely fused meso-meso - -triply-linked diporphyrins through the oxidative ring closure (ODRC) reaction with (p-BrC₆H₄)₃NSbCl₆. Finally, we found that Sc^III-catalyzed oxidation with DDQ gave a very efficient ODRC reaction and hence allowed the synthesis of triply-linked oligoporphyrins up to 12-mer.     

Synthesis and crystal structure of copper halide complexes with triethylallylammonium (teaa) chloride: [(teaa)Cu3ICl4], [(teaa)Cu3IBr3.86Cl0.14], and (teaa)2CuIICl4

The results of X-ray diffraction analysis of novel triethylallylammonium chloride compounds with copper(I) chloride, copper(I) bromide, and copper(II) chloride are reported. The [(CH₃CH₂)₃(CH₂=CHCH₂xN]Cu ₃ ^I Cl₄ and [(CH₃CH₂)₃(CH₂=CHCH₂Cu ₃ ^I Br_3.86)Cl_0.14 -complexes are isostructural: space group P2₁/a; a= 17.58(1) Å, b = 12.059(8)Å, c = 7.184(4) Å, = 98.37(5)° and a = 17.972(9) Å, b=12.479(8) Å, c = 7.290(5) Å, = 98.81(5)°, respectively. ²-Coordination of the copper atom by the olefinic bond plays a key role in the structural ordering of the tetraalkylammonium cation. In contrast, the structure of {(CH₃CH₂)₃x(CH₂=CHCH₂)N}₂Cu^IICl₄ (P4₂/nmc; a = 8.839(3) Å, c =15.660(9) Å) follows the ionic salt pattern.Original Russian Text Copyright © 2004 by L. M. Babkov, I. I. Gnatyuk, G. A. Puchkovskaya, and S. V. TrukhachevTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 398–405, May–June, 2004.     

ESR study of weak exchange interactions in binuclear copper(ii) complexes with acyldihydrazones of fluorinated β-diketones

A series of binuclear copper(ii) complexes with acyldihydrazones of aliphatic dicarboxylic acids (from malonic to adipic) and fluorinated -diketones (trifluoro- and hexafluoroacetylacetone) of composition Cu₂L·2Py (H₄L is acyldihydrazone) were studied by ESR spectroscopy. The ESR spectra of solutions of complexes with trifluoroacetylacetone acyldihydrazones have an isotropic signal with a seven-line hyperfine structure from two equivalent copper nuclei (g = 2.112, a _Cu = (39—40)·10^–4 cm^–1), which is indicative of weak exchange interactions between the paramagnetic centers due to spin density delocalization through a chain of the -bonds of the polymethylene bridge. On going to hexafluoroacetylacetone derivatives, the coupling is suppressed and the ESR spectra of solutions of such complexes show a signal with a four-line hyperfine structure (g = 2.121—2.131, a _Cu = (55—63)·10^–4 cm^–1) typical of mononuclear copper complexes.     

Influence of the Molecular Mass of Poly(<Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone) on Formation of Cu<Subscript>2</Subscript>O Nanoparticles During Reduction of Divalent Copper Ions with <Emphasis Type="Italic">tert</Emphasis>-Butylamine Borane in Polymer Solution

The process of reduction of divalent copper ions with tert-butylamine borane in dilute aqueous solutions of poly(N-vinylpyrrolidone) is investigated. The influence of polymer molecular mass on properties of the resultant Cu₂O sols is studied. It is shown that Cu₂O nanoparticles with an average diameter of 6–8 nm independent of polymer molecular mass and a relatively narrow size distribution of particles are formed in the systems under study. The contour length of macromolecules and the hydrodynamic diameter of a poly(N-vinylpyrrolidone) macromolecular coil are compared with the diameter of Cu₂O particles. Poly(N-vinylpyrrolidone) with M ≥ 1 × 10⁴ can be used to produce Cu₂O nanoparticles. Poly(N-vinylpyrrolidone) with M > 4 × 10⁴ should be used for the formation of long-living Cu₂O sols.     

Charge-transfer complexes betweenp-toluidine and iodine in solution: A kinetic study

The kinetics of charge-transfer interaction betweenp-toluidine and iodine in methylene chloride was investigated in depth. Thethermal process of formation of theinner complex was found to proceed to an equilibrium. Thephotochemical process follows a different reaction coordinate, going through the formation of an exciplex between the excitedouter complex and the amine ground state. In both cases the same ionic complex (Am ₂I⁺I ₃ ^– , whereAm stands forp-toluidine) was detected as the final product.

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Kinetische Untersuchung der Charge-Transfer-Komplexe zwischenp-Toluidin und Jod

Zusammenfassung Die Kinetik der Charge-Transfer-Wechselwirkung zwischenp-Toluidin und Jod in Methylenchlorid wurde ausführlich untersucht. Derthermische Prozeß, der zur Bildung desinner-Komplexes führt, geht bis zu einem Gleichgewicht. Derphotochemische Prozeß folgt einer unterschiedlichen Reaktionskoordinate und verläuft über die Bildung eines Exziplexes zwischen dem angeregtenouter-Komplex und dem Amin im Grundzustand. In beiden Fällen wurde derselbe ionische Komplex (Am ₂I⁺I ₃ ^– , wobeiAm fürp-Toluidin steht) als Endprodukt festgestellt.

     

Relative susceptibility of the Iα and Iβ phases of cellulose towards acetylation

The relative reactivity of the I and I phases of Valonia cellulose toward partial homogeneous acetylation was investigated by FT-IR and CP/MAS ¹³C-NMR spectroscopy. At the beginning of the acetylation and when only partial reaction was achieved, it was found that the reactivity of the I phase was substantially higher than that of the corresponding I component. At a later stage of acetylation, the difference in reactivity between the two phases was less pronounced. In correlation with previous ultrastructural observations (Sassi and Chanzy, 1995), it can be concluded that at equivalent accessibility, the I phase of cellulose is indeed more reactive toward acetylation than the I phase. The homogeneous acetylation of cellulose is essentially a surface reaction that affects only the accessible parts located at the surface of the microfibrils. The decrease in the rate of I phase disappearance with acetylation time confirms therefore that the microstructure of Valonia is made of domains that are distributed throughout the thickness of its microfibrils.     

Electrochemical reduction of cobalt and nickel complexes with ligands stabilizing metal in low oxidation state

Electrochemical reduction of cobalt(ii) complexes containing -acceptor ligands (L = bpy, Ph₂Ppy) proceeds through three consecutive reversible steps: one-electron transfer to form a more stable Co^IL complex, transfer of two electrons at more negative potentials to form an anionic [NiL]^– complex, and reduction of the ligand to the radical anion. The stability of the cobalt complexes with different ligands decreases in the series Ph₂Ppy > Ph₃P > bpy.     

Effect of ionizing radiaton on the stability of colloidal silver and other metals in aqueous solutions

The effect of ionizing radiation (accelerated electrons and γ-rays of⁶⁰Co) on the stability of aqueous solutions of colloidal silver was studied. The threshold of absorbed dose, at which the stability dramatically decreases and coagulation of the metal occurs, was found. This critical dose corresponds to the reduction of silver ions that determine the electrical potential of the sols. “Radiation” neutralization was also found for cadmium sols and was not observed in the case of thallium, copper, or platinum. A mechanism of the effect of radiation, taking into account the electrostatic factor in the stability of metal sols, was considered. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 259–264, February, 1997.     

Structural Dynamics of Isomorphic Substitution in N,N′-Diallylbenzimidazolium Copper Halide π-Complexes [C7H5N2(C3H5)2]+[Cu2Cl3?xBrx]? (x=0, 1.60, 2.33, 3)

Two new -complexes of copper(I) halides with the 1,3-diallylbenzimidazolium cation, [C₇H₅N₂(C₃H₅)₂]⁺[Cu₂Cl_1.40Br_1.60]^– and [C₇H₅N₂(C₃H₅)₂]⁺[Cu₂Br₃]^–, have been synthesized and structurally defined (space group P2 ₁/c for both; a = 22.094(6), b = 9.272(8), c = 9.22(1) , = 118.26(4)° and a = 22.267(5), b = 9.311(3), c = 9.263(2) , = 117.51(2)°). The mutual effects of chlorine–bromine substitution and the efficiency of -interactions are discussed based on XRD data for these two compounds and for the compounds [C₇H₅N₂(C₃H₅)₂]⁺[Cu₂Cl₃]^– and [C₇H₅N₂(C₃H₅)₂]⁺[Cu₂Cl_0.67Br_2.33]^– studied previously.     

Spin-transition behaviour of transition metal complexes with 2,6-bis-(benzimidazol-2′-yl)-pyridine induced by deprotonation of the complex

Summary 2,6-bis-(Benzimidazol-2-yl)-pyridine (bzimpy = H₂ L) acts as a bidentate ligand when combining with transition metal ions. The complexes [M(bzimpy)₂](ClO₄)₂ (M = Fe²⁺, Mn²⁺, Zn²⁺, Co²⁺, and Ni²⁺) were obtained as solids. The protonation constants (logK) for the ligand and the complexes were evaluated in 30:70 (v/v) H₂O:EtOH at 293 K and at constant ionic strength of 0.12M KCl. Coordination of the ligand to the metal ions leads to an increase of acidity of the imino-hydrogen of the benzimidazole group of the ligand as a function of the complex stability. Deprotonation leads to a spin-state transition (intermediate spin-state low-spin) of the iron(II)-complex, followed by a shift of the metal-to-ligandcharge transfer band (MLCT) to lower energies (_max=563 to 580 nm). The d-d absorption bands are found to shift to higher energies and the low-spin isomer is favoured at room temperature. An opposite shift of theMLCT band (_max=563 to 557 nm) is observed when HClO₄ is added to the complex solution, rendering the high-spin state of the complex more favourable.On leave from the Chemistry Department, Jahangirnagar University, Dhaka, Bangladesh     

Copper(I) complexes with fluorinated hydrotris(pyrazolyl)borate: Influence of electronic effects on their structure,physicochemical properties,and reactivity

Copper(I) coordination complexes of the anionic fluorinated ligand, hydrotris(3-trifluoromethyl-5-methyl-1-pyrazolyl)borate (L0f⁻), i.e. the copper(I) carbonyl complex, [Cu^I(L0f)(CO)] (1), the copper(I) triphenylphosphine complex, [Cu^I(L0f)(PPh₃)] (2), the copper(I) acetonitrile complex, [Cu^I(L0f)(NCMe)] (3), and the corresponding copper(I) triphenylphosphine complex with hydrotris(3,5-diisopropyl-1-pyrazolyl)-borate anion (L1⁻), i.e. [Cu^I(L1)(PPh₃)] (4), were synthesized in order to investigate the influence of the electron-withdrawing groups on the pyrazolyl rings. The structures of complexes 1, 2, and 4 were determined by X-ray crystallography. While X-ray crystallography did not show definitive trends in terms of copper(I) atom geometry, the clear influence of the electronic structure of the pyrazolyl rings is observed by spectroscopic techniques, namely, IR and multinuclear NMR spectroscopy. Finally, the relative stability of the copper(I) complexes is discussed.     

X-ray spectroscopic characterization of Cu2+-phenanthroline complexes intercalated in α-zirconium phosphate

X-ray photoelectron spectroscopy provides evidence that when [Cu(phen)₂]²⁺(phen = 1,10-phenanthroline) is diffused between the layers of -zirconium phosphate, the complex species does not remain intact after intercalation, but some Cu-N bonds are broken, replaced with Cu-O bonds and the released nitrogen atoms can now interact with the PO₃-OH groups of the host. XPS also provides evidence for coordination of the Cu²⁺ ions when they are diffused by ion exchange in the phenanthroline--zirconium phosphate intercalation compound. Although Cu²⁺ and phen are in a 1 : 1 molar ratio in the interlayer region of the host, so that a 1 : 1 coordination could be expected between the two species, the characteristic peaks of the uncoordinated phenanthroline, even though at a low intensity, are still present. The differences between the two Cu(II)-intercalation compounds are discussed.     

Synthesis,structure, and fungicidal activity of mono- and binuclear mixed-ligand copper complex with <Emphasis Type="Italic">p</Emphasis>-nitrobenzoic acid and monoethanolamine

Mixed-ligand metal complexes based on ethanolamines and simple monosubstituted benzoic acids, in particular, mono- and binuclear copper complexes with monoethanolamine (MEA) and p-nitrobenzoic acid (PNBA), [Cu²⁺((PNBA)₂ ^-(MEA)₂)] (I) and [2Cu²⁺((PNBA)₄ ^-(MEA)₂(H₂O)₂)] (II), were prepared for the first time. The structures of the complexes were characterized by FT IR spectroscopy and X-ray diffraction (CIF files CCDC no. 1497849 (I) and no. 1497848 (II)). The doubly charged copper ions are coordinated at the vertices of octahedra, which are highly distorted due to the Jahn–Teller effect. In the crystals of the mononuclear complex I, the molecules are joined into columns, whereas in the binuclear compound II, a three-dimensional framework is formed owing to intermolecular H-bonds involving the nitro group. Fungicidal activities were found for compounds I, II, MEA, PNBA, previously obtained single-ligand copper complexes with MEA and PNBA, and MEA- and PNBA-based organic salt. The biological activity gradually increases in the series: ligand, single-ligand metal complex, organic salt, mono- and binuclear mixed-ligand complex, i.e., some ligands and copper ions show a synergistic effect.     

Properties of aqueous salt solutions of poly(ethylene oxide). Cloud points, θ temperatures

The determination of the properties of aqueous salt solutions of poly(ethylene oxide) has been extended to the cloud point, and temperature measurements have been made at several concentrations for various salts (flourides, iodides, acetates, formates, phosphates, bromides, thiosulfates and perchlorates). The resulting dependency of the critical temperatures (mostly between 290–350 K) on the molar concentration can be expressed as sequences showing the decreasing effect of anion species or cation species in salting out the polymer. The decreasing order of effectiveness of the anions in reducing the temperature is PO ₄ > HPO ₄ > S₂O ₃ > H₂PO ₄ ^– >F^– > HCOO^– > CH₃COO^– > Br^– > I^–. The order for cations is K⁺ Rb⁺ Na⁺ Cs⁺ > Sr⁺⁺ > Ba⁺⁺ Ca⁺⁺ > NH ₄ ⁺ > Li⁺. The changes brought about in temperatures by the salts were found to be the results of the changes taking place in the hydrophilic and hydrophobic interactions among polymer, solvent and additive salts and of the change of water structure by structure making or structure breaking ions, and of the influence of salts on the hydration sheath of the polymer.     

Kinetics and mechanism of the hydrolysis of sodium carboxymethylcellulose (Na-CMC) by a cellulase complex

TheSomogyi-Nelson colorimetric method is applied in a new manner more suitable for evaluating the kinetics of the enzyme hydrolysis of sodium carboxymethylcellulose (Na-CMC) catalyzed by the cellulase complex. By means of selective inhibition of a chosen enzyme from the cellulase complex it became possible to trace the effect of the other enzymes included in its composition.

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Kinetik und Mechanismus der Hydrolyse von Natriumcarboxymethylcellulose (Na-CMC) durch einen Cellulase-Komplex

Zusammenfassung Die kolorimetrische Methode nachSomogyi undNelson wird nach einem neuen Verfahren zur Verfolgung der Kinetik der hydrolytischen Spaltung von Natriumcarboxymethylcellulose (Na-CMC), katalysiert durch den Cellulase-Komplex, angewandt. Durch selektive Inhibierung eines bestimmten Enzyms des Cellulase-Komplexes kann man die Wirkung der anderen zu seiner gesamten Zusammensetzung gehörenden Enzyme verfolgen.

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Symbols Used E enzyme (E—cellulase;E—exo-cellobiohydrolase;E—-glucosidase) - [E] _w weight concentration of enzymeE - S substrate (Na-CMC—sodium carboxymethylcellulose) - [S]₀ weight concentration of substrateS - I inhibitor (I—lactose;I—calcium chloride;I—condurrite-B-epoxide) - P product (P—oligosaccharides;P—cellobiose;P—D-glucose) - P end product (K , K , K ) - DP degree of polymerization - DS degree of substitution - ES enzyme-substrate complex (E S, E S, E S) - EP enzyme-product complex (E P, E P) - EI enzyme-inhibitor complex (E I, E I, E I) - M _s molecular mass of substrateS - K _s substrate constant (K _s , K _s , K _s ) - K _I inhibitor constant (K _I , K _I , K _I ) - K _m Michaelis-Menten constant - k ₊₁,k ₊₂ (k ₊₂ ,k ₊₂ ,k ₊₂ ) forward rate constants - k _–1 reverse rate constant - ₀ initial rate of reaction - V maximal reaction rate - A change in absorbance - molar absorption coefficient - wavelength Herrn Prof. Dr.Hans Tuppy zum 60. Geburtstag herzlichst gewidmet.