Benzoyl peroxide-cobalt(II) vinyl-β-diketonate systems as initiators of styrene and methyl methacrylate polymerization

New cobalt(II) vinyl-β-diketone-benzoyl peroxide [or azobis(isobutyronitrile)] binary systems were studied as initiators of polymerization of styrene and methyl methacrylate.     

Bimetallic aluminum alkyl complexes as highly active initiators for the polymerization of ε-caprolactone

Two dinuclear aluminum alkyl complexes supported by a piperazidine-bridged bis(phenolato) group were prepared, and both complexes exhibited extremely high activity for the ring-opening polymerization of ε-caprolactone. In the presence of benzyl alcohol (BnOH), the polymerization accelerated dramatically.     

New redox system: Trichloromethylarene —pyridine base

A redox reaction of trichloromethylarenes with pyridines results in respective N-(-chloroarylmethyl)substituted pyridiniurn chlorides which give, on hydrolysis, aromatic aidehydes and 4-chloropyridines or 1, 4-bipyridiniurn salts.N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow, Russia. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1373–1375, October, 1995. Original article submitted September 5, 1995.     

IMAC—Immobilized metal ion affinity based chromatography

Immobilized metal ion affinity chromatography (IMAC) is a highly versatile separation method based on interfacial interactions between biopolymers in solution and metal ions fixed to a solid support, which is usually a hydrophilic cross-linked polymer.Polymer-fixed Zn(II), Ni(II), Co(II) and Cu(II) are particularly well suited for fractionation of proteins primarily on the basis of their relative content of surface-located imidazole residues but also of Trp and Cys residues as well as terminal amino groups.IMA methods can also be devised for purification of phosphoproteins and calcium-binding proteins. In some instances, the performance of IMA gels is comparable to that of biospecific affinity-based adsorbents. In fact IMA gels may, by sandwich techniques, occasionally be converted to biospecific adsorbents.Selectivity can be varied by choice of type of ligand and metal ion as well as by varying the modes of elution, including affinity desorption.     

A macrokinetic model of redox sorption on metal–ion exchanger nanocomposites at electrochemical polarization

A conceptual macrokinetic model of redox sorption on metal–ion exchanger nanocomposites upon electrochemical polarization is formulated and a corresponding mathematical model is constructed. The solution to a multi-point boundary value problem for the concentration of a sorbed substance (oxygen) is given. The concentration front of the sorbed substance is characterized by a concentration gradient in the near-surface layer of the solution, by layers of the products of metal oxidation in the composite forming due to both external and internal diffusion transfer, and by chemical and electrochemical reactions at the interphase boundaries. A considerable reduction in the concentration gradient of the sorbate in layers of the products of oxidation of metal and the growth of the diffusion layer of the solution with polarizing currents weaker than the limiting diffusion current are noted.     

Aluminum complexes based on 1,10-phenanthroline-containing diols: synthesis and application as initiators of polymerization of ε-caprolactone

Russian Chemical Bulletin - The reaction of the O,N,N,O-type ligands, namely, 4,7-bis(4-R-phenyloxy)-2,9-(HOCR′2-CH2)2-1,10-phenanthrolines, LH2 (R = But (1–4), Me (5–8), R′...     

2,6-Di-tert-butylphenols and phenoxyl radicals with metal—metal bonds

-Aryl trans-bistriphenylphosphine complexes based on 2,6-di-tert-butylphenol containing Pt—SnCl₃, Pt—GeCl₃ groups were synthesized. Oxidation of these compounds gives the corresponding phenoxyl radicals, which were studied by ESR spectroscopy. The transformation of the diamagnetic complexes to the paramagnetic state is accompanied by cleavage of the Pt—Sn, Pt—Ge bonds and by elimination of SnCl₂, GeCl₂.     

Crystalline cerium(IV) phosphates—II: The ion exchange characteristics with alkali metal ions

The ion exchange behavior of seven crystalline cerium(IV) phosphates towards some of the alkali metal cations is described. Only two of the compounds (A and C) possess ion exchange properties in acidic solutions. Four others show some ion exchange characteristics in basic media with some of the alkali cations. Compound G does not behave as an ion exchanger in solutions of pH < 12. Compounds B, D and F exchange Li⁺, but show very little Na⁺ uptake. Compound E undergoes ion exchange with Na⁺ and Cs⁺, but not with Li⁺. Both Li⁺ and Na⁺ are sorbed by compounds A and C. The results are indicative of structures which show steric exclusion phenomena.     

Synthesis and characterization of ferrocenylgalvinol, a novel d-π redox system

A novel d-π redox molecule bearing ferrocene (Fc) and galvinoxyl (GalO) units as reversible redox active sites has been synthesized and characterized. The molecule shows solvatochromic behavior and changes from a red color in n-hexane (λ_max = 388, 541 nm) to a greenish brown (λ_max = 413, 582 nm) in MeOH. A cyclic voltammogram of 1 under neutral conditions shows a redox process corresponding to Fc/Fc⁺ but not one for GalOH (or GalO⁻)/GalO. Under basic conditions the latter process was observed and it occurred at a lower oxidative potential ( vs Ag/AgCl) than the former process . Thus 1 shows potential as a bilateral multi-redox molecule with pH dependence. Chemical oxidation of 1 under basic conditions (aq KOH, K₃Fe(CN)₆) gives an EPR spectrum with an hfc of 1.2 G attributable to Fc-GalO.     

Reaction of N(2-hydroxyethyl)ethylenediaminetriacetatocobaltate(II) with hydrogen peroxide—A base catalyzed redox system

The kinetics of the reaction of N(2-hydroxyethyl)ethylenediaminetriacetatocobaltate(II) with hydrogen peroxide have been studied in the pH range 3.6–4.8 and a possible mechanism of electron transfer is discussed.     

Enthalpy—entropy compensation upon metal ion coordination with porphyrins: generalization for the free bases and doubly deprotonated macrocycles

Russian Chemical Bulletin - Enthalpy—entropy compensation upon the coordination of zinc ions by porphyrins with various structural organizations of peripheral substitution in solutions at 298...     

Deuterium–hydrogen exchange reactions in peptides and polyatomic organic compounds,as studied on an ion cyclotron resonance mass spectrometer equipped with an ion trap with dynamic harmonization

The ultrahigh-resolution mass spectra of a substance P peptide labeled with deuterium have been obtained. The use of an ion trap with dynamic harmonization has made it possible to resolve the hyperfine isotopic structure of peaks and to reliably distinguish the hydrogen isotopes from the isotopes of carbon in the composition of the test molecules. The deuterium–hydrogen exchange reaction of humic acids has been performed in a gas phase, and it has been shown that the resolving power attained is sufficient for reliable interpretation of the results.     

Alloying of electrodeposited silicon with lithium—a principal study of applicability as anode material for lithium ion batteries

The possibility to electrodeposit silicon directly on a copper current collector out of organic electrolyte and ionic liquid was investigated with the aim to alloy the deposited silicon with lithium to prove the possible use as negative electrode in lithium ion batteries. Cyclovoltammetric analyses have shown in comparison to electrodes containing high crystalline silicon similar behaviour during the electrochemical alloying and dealloying process. SEM analyses have shown a particle size of the deposited silicon in submicron range.     

Solution properties of iron(III) complexes with 5-fluorosalicylic acid — spectra,speciation, and redox stability

Iron(III)-5-fluorosalicylic acid systems were investigated in water by pH potentiometry combined with UV-VIS spectrophotometry. The data revealed that stable aquated mono-, bis-, and tris(5-fluorosalicylato) iron(III) complexes are formed together with their monohydroxo and dihydroxo analogues. The stability constants of all present iron(III) species were calculated. Based on pH and the metal: ligand ratio dependent distribution of the species, electronic absorption spectra of the complexes in the visible region were obtained. Redox stability was monitored as an ability to undergo both spontaneous and photoinduced reduction of iron(III) to iron(II). Complexes do not undergo any redox changes when in dark neither in methanol nor in water. While aqueous solutions of complexes are stable under the influence of incident visible radiation, steady-state irradiation of the methanolic systems by visible light led to photoreduction of iron(III) to iron(II), the quantum yield of iron(II) photoformation was determined. Dedicated to Professor Milan Melník on the occasion of his 70th birthday     

Synthesis, structure and α-olefin polymerization activity of group 4 metal complexes with [OSSO]-type bis(phenolate) ligands

The tetradentate [OSSO]-type bis(phenol) ligands, [{2,2′-(HOC₆H₂-4,6-R₂)₂CH₂SCH₂CH₂SCH₂}] (R = ^tBu, 2; Br, 3) react with MBz₄ (M = Zr, Hf) to yield the corresponding dibenzyl complexes, [M{2,2′-(OC₆H₂-4,6-R₂)₂CH₂SCH₂CH₂SCH₂}Bz₂] (R = Br, M = Zr, 4^Br; Hf, 5^Br; R = ^tBu, M = Hf, 5) in a good to very good yield. Zirconium diamido complexes, [Zr{2,2′-(OC₆H₂-4,6-R₂)₂CH₂SCH₂CH₂SCH₂}(NMe₂)₂] (R = ^tBu, 6; Br, 6^Br) were prepared in a reaction of the corresponding disodium salt of 2 or 3 generated in situ with ZrCl₂(NMe₂)₂(THF)₂. Heating of 6 with TMSCl at 35 °C afforded zirconium dichloro complex, [Zr{2,2′-(OC₆H₂-4,6-^tBu₂)₂CH₂SCH₂CH₂SCH₂}Cl₂] (7), whereas the titanium analog 8 was prepared in a direct reaction with TiCl₄. While for complexes 4^Br, 5, 5^Br, 6, 6^Br and 7 single C₂-symmetric isomers were observed in solution at room temperature, as revealed by the NMR spectroscopic data, titanium complex 8 formed as a mixture of cis-α (8a) and cis-β (8b) isomers in a ratio of approx. 20:80% (measured in CD₂Cl₂). The VT NMR studies revealed a reversible conversion of 8a into 8b above 60 °C. The X-ray crystal structure determination of complexes 4^Br, 5^Br and 7 confirmed their C₂-symmetrical configuration in the solid state with cis-arranged benzyl/chloro groups and the trans-coordination of two bulky phenolato moieties. The zirconium dibenzyl complexes exhibit good catalytic activities in homopolymerization of 1-hexene (atactic poly(1-hexene), PDI = 1.5-1.7) and vinylcyclohexane (isotactic poly(vinylcyclohexane), PDI = 1.2-1.8) upon activation with a co-catalyst. In both polymerizations no increase of activity was observed for the complex 4^Br with electron-withdrawing substituents on phenolate rings. Moreover, polymerization of liquid propylene catalyzed by the titanium dichloro isomeric mixture 8 afforded at 5 °C ultrahigh molecular weight atactic/isotactic polypropylene mixtures.     

Sorption—spectrophotometric and visual test determination of trace silicon as an ion associate of 12-molybdosilicate with crystal violet

The adsorption of the ion associate (IA) of the heteropoly anion (HPA) of β-SiMo₁₂O₄₀⁴ with Crystal Violet (CV) on polyurethane foams (PUF) was studied; the conditions of HPA formation and adsorption as an IA with CV were optimised. The calculated adsorption capacity of PUF toward IA and the constant of adsorption, 0.77 μmol/g and 1.3 × 10⁶ L/mol, respectively, were determined from the linearized Lang-muirs’s adsorption isotherm. A procedure was developed for the sorption-spectrophotometric and visual test determination of silicon; C_min = 2 × 10^-8 M. The procedures were validated on examples of drinking, distilled, and mineral waters.     

Immobilized complexes of the salen Schiff’s base with metal as oxidation catalysts

The immobilized metal complexes with the Schiff’s base of salen have shown high catalytic activity in oxidation of alkenes, cycloalkenes, and alcohols as compared with their unsupported analogs. Due to the heterogeneous nature of such catalysts, their separation and recycling is rather simple.     

Surface‐initiated atom transfer radical polymerization from porous poly(tetrafluoroethylene) membranes using the C?F groups as initiators

This work reports the surface‐initiated atom transfer radical polymerization (ATRP) from hydrogen plasma‐treated porous poly(tetrafluoroethylene) (PTFE) membranes using the C? F groups as initiators. Hydrogen plasma treatment on PTFE membrane surfaces changes their chemical environment through defluorination and hydrogenation reactions. With the hydrogen plasma treatment, the C? F groups of the modified PTFE membrane surface become effective initiators of ATRP. Surface‐initiated ATRP of poly(ethylene glycol) methacrylate (PEGMA) is carried out to graft PPEGMA chains to PTFE membrane surfaces. The chain lengths of poly(PEGMA) (PPEGMA) grafted on PTFE surfaces increase with increasing the reaction time of ATRP. Furthermore, the chain ends of PPEGMA grown on PTFE membrane surfaces then serve as macroinitiators for the ATRP of N‐isopropylacrylamide (NIPAAm) to build up the PPEGMA‐b‐PNIPAAm block copolymer chains on the PTFE membrane surfaces. The chemical structures of the modified PTFE membranes are characterized using X‐ray photoelectron spectroscopy. The modification increases the surface hydrophilicity of the PTFE membranes with reductions in their water‐contact angles from 120° to 60°. The modified PTFE membranes also show temperature‐responsive properties and protein repulsion features owing to the presence of PNIPAAM and PPEGMA chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2076–2083, 2010     

Poly(4-vinylpyridine-co-aniline)-modified electrode—synthesis, characterization, and application as cadmium(II) ion sensor

A poly(4-vinylpyridine-co-aniline) (poly(4VP-co-Ani))-based solid-state ion sensor for cadmium (Cd) was developed. This was obtained from studies done on a number of selected monomers electropolymerized onto a poly(4vinylpyridine) (P4VP)-modified graphite pencil rod, surface characterizing them and then analyzing their performances as a Cd(II) ion sensor. Among them, the membrane of poly(4VP-co-Ani) at a mole ratio of 0.05:0.15 was found to be the best. The fabricated poly(4VP-co-Ani) solid-state electrode had a linear response of 1?×?10^?6 to 1?×?10^?2?M Cd²⁺, slope of 29.4?±?0.5 mV decade^?1, detection limit of 7.94?×?10^?7?M Cd²⁺, and response time of 15 s at pH 4.5–8.5 with excellent selectivity. The sensor was operationally stable within a period of 3 months. The proposed sensor was tested for determination of Cd²⁺ in environmental, plant, and pharmaceutical samples. The analyses were comparable to the standard atomic absorption spectrophotometric method.     

Contribution to the thermodynamics of complexes of alkali metal cations with 18-crown-6 in the water—nitrobenzene extraction system

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M⁺(aq)+NaL⁺(nb)⇄ML⁺(nb)+Na⁺(aq) taking place in the two-phase water-nitrobenzene system (M⁺=Li⁺, K⁺, Rb⁺, Cs⁺; L=18-crown-6; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. The stability constants of the ML⁺ complexes in nitrobenzene saturated with water were calculated; they are found to increase in the cation order Cs⁺Li⁺Na⁺Rb⁺K⁺. Further, the individual extraction constants for the NaL⁺, KL⁺, RbL⁺ and CsL⁺ complex species in the wate-nitrobenzene system were determined; their values increase in the series Na⁺Rb⁺Cs⁺K⁺.