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.     

Sequential transduction of light into redox and acid—base energy in photosynthesis

Photosynthesis consists essentially in the conversion, by the plant kingdom, of sunlight energy into chemical energy (cell material and molecular oxygen). From a physicochemical point of view, photosynthesis is intrinsically a light-driven oxidation—reduction/acid—base process. In the course of photosynthesis, water is oxidized to molecular oxygen, whereas carbon dioxide, nitrate or dinitrogen, and sulfate are respectively reduced to carbohydrate, ammonia and sulfide; water is moreover ionized, in similar amounts, into protons and hydroxide anions. Phosphorus does not change its oxidation state, but orthophosphate becomes energized to metaphosphate, at the expense of the ionization products of water, in a peculiar acid—base process. Metaphosphate is mostly used as an energy shuttle in many cell processes, among them in the reduction and assimilation of the primordial bioelements, as well as in the polymerization of the resulting monomers — sugars, lipid components, amino acids, nucleotides — and deenergizes itself back to orthophosphate, again in acid—base reactions. The role of the oxide anion, that is, an oxygen atom with two additional electrons, O²⁻ , in these bioenergetic processes is especially discussed.     

The role of pyridine derivatives in living carbocationic polymerization: Lewis base or nucleophile?

The living cationic polymerization of isobutylene induced by the 2-chloro-2,4,4-trimethylpentane/TiCl₄/hexane:methyl chloride (60:40, v:v)/-80°C system was studied in the presence of pyridine derivatives. Protic initiation, substantial in the absence of these additives, was virtually eliminated in their presence, and polyisobutylenes with controlled molecular weight and narrow molecular weight distribution were obtained. With some additives, however, proton elimination occurs, resulting in the exclusive formation of the exo olefin. The rate of elimination is independent of monomer concentration, i.e., it occurs during and after the polymerization. Results suggest that the proton elimination is due to the presence of an uncomplexed base, especially when complex formation with TiCl₄ is hindered by steric compression, but its approach of the polymer cation is not fully blocked.     

Vinyl polymerization with metal ion redox systems as initiators,manganic laurate—thiol system

Polymerization of methyl methacrylate was studied using manganic laurate in the presence of organic thiols as initiators. The thiols used were 1-propane thiol and 2-propane thiol and the solvent was carbon tetrachloride. The rate of polymerization satisfied the expression R_P = k₁ [manganic laurate]^1/2 [thiol]^1/2 [monomer]^3/2 where k₁ is a constant. Spectroscopic investigations indicated complex formation between the monomer and manganic laurate. A reaction scheme is suggested.     

The influence of surfactants on the acid—base and redox properties of reagents of the diphenylamine series

The influence of aqueous solutions of surfactants on the redox and acid—base properties of diphenylamine redox reagents was studied by potentiometric titration and UV spectroscopy. The formal redox potentials, the pK _a values of the reagents in aqueous solutions and in the presence of surfactants, and the constants of binding of the reagents by micellar solutions of surfactants were estimated. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1386–1388, August. 2000.     

Discovery of redox system enabling C–N–C bonds formation: Unprecedented Aza-Cannizzaro reaction

A novel reaction involving in situ redox conversion of glyoxylate esters to glycine is described. Simple starting materials and mild conditions for the synthesis of glycine derivatives probably indicate a pathway towards prebiotic chemistry. This proceeds analogous to Cannizzaro reaction involving ammonia therefore it can be termed as intramolecular Aza-Cannizzaro type reaction. This reaction is examined in detail with an aid of computational analysis to corroborate the proposed mechanism.     

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.     

The complex reaction kinetics of neptunium including redox and extraction process in 30% TBP—nitric acid system

In order to understand the complex and dynamic neptunium process chemistry in the TBP-HNO₃ system, the kinetics involved reversible redox reaction and extraction mass transfer was investigated. The results indicates that the mass transfer rate of Np(VI) is much faster than the redox reaction in aqueous solution. The concentrations of nitric acid and nitrous acid not only can change the Np(V) oxidation reaction and Np(VI) reduction reaction rate, but also can ultimately determine the distribution of neptunium extraction equilibrium. The variety of temperature can only influence the extraction equilibrium time, but cannot alter the equilibrium state of neptunium.     

New chiral molecular tweezers with a bis-Tröger's base skeleton

A convenient synthesis of 5alpha,8alpha,14alpha,17alpha-5,17:8,14-dimethano-5,8,14,17-tetraaza-5,6,7,8,13,14,17,18-octahydrodibenzo[e,e']benzo[1,2-a:3,4-a']dicyclooctene derivatives is described, and the compounds have been fully characterized by NMR; in some cases, the molecular structure has been determined by X-ray crystallography. These compounds represent the first examples of a new class of molecular tweezers.     

Lithium–sulfur redox: challenges and opportunities

Mechanistic and kinetic insights into the lithium–sulfur (Li–S) redox processes are essential to fundamentally increase the utilization of active material and further realize the practical applications of Li–S batteries. In this article, recent advances of in situ/operando characterizations of Li–S reaction processes and mechanism are presented, revealing the multistep transformations of S species. Interfacial visualization, from the whole interface to nanometer scale, provides specific evidence of sulfur distribution, polysulfide diffusion, and lithium sulfide precipitation. Moreover, the development of efficient electrocatalysts to improve the reaction kinetics are additionally presented and discussed. Although the understanding of the mechanism of the Li–S redox processes has improved in recent times, additional efforts are required for the scale-up production and practical applications of Li–S batteries.     

Synthesis of polydentate chalcogen-containing ligands using the system hydrazine hydrate–base

The reaction of dichlorodiethyl ether or dichlorodiethylamine hydrochloride with potassium or ethanolammonium dichalcogenides prepared in situ from elemental sulfur or selenium in the system hydrazine hydrate–alkali results in oligomeric dichalcogenides, whose further splitting at the chalcogen–chalcogen bond in the same system and subsequent alkylation affords bis(organylsulfanyl)- or bis(organylselanyl)-substituted derivatives of diethyl ether or diethylamine. Ligands with aryl substituents at the chalcogens have been prepared in 48-59% yield by splitting of diaryldichalcogenides in the system hydrazine hydrate–alkali and subsequent reaction with dichlorodiethyl ether or dichlorodiethylamine. A ditopic tetradentate ligand has been synthesized by the use of dichlorodiethylformal.     

Metal ion function in alcohol dehydrogenases—III: The enzymic reduction of pyridine carbaldehydes

The enzymic reduction of 2,3 and 4-PCA has been investigated using YADH with NADH as cofactor. All three aldehydes are effective substrates, with the V_max ratio for the 2:3:4 being 10:1:3, and the K_m ratio 1:4:2. This is interpreted in terms of substrate-metal ion interaction via the pyridine nitrogen, with no direct metal ion-NADH interaction.     

New intermetallic compounds in the Ce–Pt system

The Ce-rich part of Ce–Pt phase diagram has been investigated by means of differential thermal analysis (DTA), X-ray diffraction (XRD), optical and electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Two new intermediate phases, Ce₅Pt₃ and Ce₅Pt₄, have been discovered and found to crystallize with tetragonal Pu₅Pd₃-type structure and orthorhombic Ge₄Sm₅-type structure, respectively. All the Ce-rich compounds of the system were found to crystallize with a peritectic type formation. We have determined the temperatures of the peritectic plateaus and established the liquidus curves up to 1500 °C.     

Structure and reaction pathway of TMP-Zincate: amido base or alkyl base?

The novel directed ortho metalation (DoM) reagents for functionalized aromatic rings, TMP-Zn-ates (R2Zn(TMP)Li (R = Me, 1; tBu, 2)), have been reported to be synthetically useful for the chemo- and regioselective construction of multi-functionalized aromatic compounds. Here, we present the first comprehensive structural and mechanistic investigation by means of X-ray, NMR, and DFT studies on the DoM reaction employing our original TMP-Zn-ate base. The structures of TMP-Zn-ates in solution and in the solid state were determined. The DFT study strongly suggested that the deprotonation involving the TMP ligand on the TMP-Zn-ate is kinetically more favorable than that involving the alkyl ligand, and this view was supported by monitoring of the 13C NMR spectrum of the reaction mixture.     

Phase equilibria and critical phenomena in the cesium nitrate–water–pyridine ternary system

The solubilities of components, phase equilibria, and critical phenomena in the cesium nitrate–water–pyridine ternary system are studied in the 5–100°C temperature range by the visual–polythermal method. Cesium nitrate is found to exhibit a salting-out effect at temperatures above 79.9°C causing phase separation in homogeneous water–pyridine solutions. The temperature of formation of the critical monotectic tie line (79.9°C) and the compositions of solutions corresponding to the liquid–liquid critical points at three temperatures are determined. The pyridine distribution coefficients between the aqueous and organic phases of the monotectic state at 85.0, 90.0, and 100.0°C are calculated. Their values demonstrate that salting-out of pyridine from aqueous solutions by cesium nitrate increases at higher temperatures. The plotted isotherms of phase diagrams confirm the fragment of the scheme of topological transformation of the phase diagrams of salt–binary solvent ternary systems with salting-in and salting-out phenomena.     

New mesogenic Schiff base esters comprising benzothiazole moiety： Synthesis and mesomorphic properties

A homologous series of Schiff base esters,6-methoxy-2-(2-hydroxy-4-alkanoyloxybenzylidenamino)benzothiazoles,comprising a benzothiazole moiety as the core was synthesized.All the members of this series exhibited an enantiotropic nematic phase. The azomethine linkage along with the lateral hydroxyl and terminal methoxyl groups were found to exert an effect on the mesomorphic properties.     

Chalcogenation of 1,3-dichloropropene with elemental chalcogens in the system hydrazine hydrate–base

Sulfur reacts with 1,3-dichloropropene in the system hydrazine hydrate–KOH to form bis(1-chloroprop-1-en-3-yl) sulfide, and in the system hydrazine hydrate–monoethanolamine, bis(1-chloroprop-1-en- 3-yl) disulfide. The reaction of tellurium in the system hydrazine hydrate–KOH leads to diallyl telluride, the product of nucleophilic substitution of the allylic chlorine atom and reductive cleavage of the С_sp2–Cl bond. The reaction of selenium with 1,3-dichloropropene gives a complex mixture of products. At excess KOH (Se: KOH = 1: 5) bis(1-chloroprop-1-en-3-yl) selenide was isolated.     

Review: Single-molecule magnets based on pyridine alcohol ligands

Single-molecule magnets (SMMs) have attracted attention due to their potential applications in quantum computation and information storage, and many SMMs have been reported in the past two decades. In this review, we summarize the structures and the magnetic exchange interactions of pyridine alcohol-based SMMs to give a possible relationship between structure and magnetic property, providing information to generate new molecule-based magnetic materials. According to the correlated metal centers, these SMMs are separated into three segments to discuss.     

New approach in the treatment of data from an acid–base potentiometric titration

Based on precise analysis of the acid-base equilibrium, a new approach in the treatment of experimental data from a potentiometric titration is proposed. A new general formula giving explicitly the relation V=f([H(+)]) is derived, valid for every acid-base titration, which includes mono- and polyfunctional protolytes and their mixtures. The present study is the first practical application of this formula for the simplest case, the analysis of one monofunctional protolyte. The collected mV data during the titration are converted into pH-values by means of an auto pH-calibration procedure, thus avoiding preliminary preparation of the measuring system. The mentioned pH-calibration method is applicable also in water-organic mixtures and allows the quantitative determination of sparingly soluble substances (particularly pharmaceuticals). The treatment of the data is performed by means of ready-to-use software products, which makes the proposed approach accessible for a wide range of applications.