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Photoirradiation of TiO2nanoparticles by visible light in the presence of the water-soluble natural polysaccharide arabinogalactan complexes of the hydrocarbon carotenoid β-carotene leads to enhanced yield of the reactive hydroxyl (OH) radicals. The electron paramagnetic resonance (EPR) spin-trapping technique using α-phenyl-N-tert-butyl nitrone (PBN) as the spin-trap has been applied to detect this intermediate by trapping the methyl and methoxy radicals generated upon reaction of the hydroxyl radical with dimethylsulfoxide (DMSO). The free radicals formed in this system proceed via oxygen reduction and not via the reaction of holes on the TiO2surface. As compared with pure carotenoids, carotenoid−arabinogalactan complexes exhibit an enhanced quantum yield of free radicals and stability toward photodegradation. The observed enhancement of the photocatalytic efficiency for carotenoid complexes, as measured by the quantum yield of the desired spin adducts, arises specifically from the decrease in the rate constant for the back electron transfer to the carotenoid radical cation. These results are important for a variety of TiO2applications, namely, in photodynamic therapy, and in the design of artificial light-harvesting, photoredox, and catalytic devices. [ABSTRACT FROM AUTHOR]

We present the first example of water soluble complexes of carotenoids. The stability and reactivity of carotenoids in the complexes with natural polysaccharide arabinogalactan were investigated by different physicochemical techniques: optical absorption, HPLC, and pulsed EPR spectroscopy. Compared to pure carotenoids, polysaccharide complexes of carotenoids showed enhanced photostability by a factor of 10 in water solutions. A significant decrease by a factor of 20 in the reactivity toward metal ions (Fe3+) and reactive oxygen species in solution was detected. On the other hand, the yield and stability of carotenoid radical cations photoproduced on titanium dioxide (TiO2) were greatly increased. EPR measurements demonstrated efficient charge separation on complex-modified TiO2nanoparticles (7 nm). Canthaxanthin radical cations are stable for ∼10 days at room temperature in this system. The results are important for a variety of carotenoid applications, in the design of artificial light-harvesting, photoredox, and catalytic devices. [ABSTRACT FROM AUTHOR]

Abstract  Anodic dissolution of ferroniobium in anhydrous methanol in the presence of sodium methylate was studied. The possibility of recovering pure hexamethoxyniobate from the electrolyzate and its conversion into niobium methylate with an iron content not exceeding 0.01% was analyzed. [ABSTRACT FROM AUTHOR]

Abstract  Anodic dissolution of niobium in anhydrous methanol in the presence of sodium methylate was studied. A method for recovery of niobium methylate from sodium hexamethoxyniobate by the reaction with ammonium chloride was developed. [ABSTRACT FROM AUTHOR]

Physicochemical methods were used to explore the regularities of complexing between the calcium channel blocker nifedipine (NF) and pharmaceutically acceptable complex-forming glycyrrhizic acid (GA) in view of the discovered influence of GA on the therapeutic activity of NF. 1H NMR (including relaxation measurements) and UV−vis spectra have produced illustrative evidence that NF forms stable complexes with GA within a wide concentration range, from 0.05 to 5 mM. At low GA concentrations, below 0.5 mM, NF forms an inclusion complex where each NF molecule is bound by two molecules of GA. Computer simulations of the NMR experimental data have shown that, in aqueous solution, the stability constant of this complex, K, is about 105M-1. At higher concentrations, GA forms large micelle-like aggregates which increase the water solubility of NF. Quenching of chemically induced dynamic nuclear polarization effects in the photoinduced interaction of the NF−GA complex with tyrosine suggests that complex formation with GA completely blocks the single electron-transfer step between NF and the amino acid. This, arguably, could explain the increased therapeutic activity of GA complexes, since GA might protect the drug molecule from the reaction with amino acid residues of the receptor binding site. [ABSTRACT FROM AUTHOR]

Abstract  The effect of the alkali metal nature on the electronic structures and chemical bonding in mixed cyanoferrates M2Cu[Fe(CN)6] (M = Na, K, Rb, and Cs) was studied by ab initio tight-binding linear muffin-tin orbital (TB-LMTO) method (in the spin-polarized implementation) and the extended H�ckel molecular orbital (EHMO) method. It was found that the X-ray photoelectron spectra of the ferrimagnetic compounds Na2Cu[Fe(CN)6] (I), K2Cu[Fe(CN)6] (II), Rb2Cu[Fe(CN)6] (III), and Cs2Cu[Fe(CN)6] (IV) are similar. The magnetic moments on Cu2+ and iron ions remain virtually constant in compounds I–IV (μ(Cu) = 0.9 μB, μ(Fe) B). Analyses of the electron density maps and the bond overlap populations showed that the cubic frameworks of cyanoferrates are built from stable fragments ⋯-Fe-C≡N-Cu-⋯. The bond strength in these fragments decreases substantially in the order C-N → Fe-C → Cu-N and only slight in the order IV → III → II → I. The calculated total energies of the cyanoferrates Cs2−x Cu[Fe(CN)6], CsHCu[Fe(CN)6], and NaHCu[Fe(CN)6] for different concentrations and configurations of defects (cesium vacanices and hydrogen substitution defects) suggest mutual repulsion of defects. This repulsion is responsible for the experimentally observed lowering of the ionic conductivity with an increase in the defect concentration in the mixed cyanoferrates. [ABSTRACT FROM AUTHOR]

The structure, stability, and reactivity of the host−guest complexes between a set of carotenoids and the triterpene glycoside, β-glycyrrhizic acid (GA), were investigated by different physicochemical techniques:  high-performance liquid chromatography, optical absorption, and fluorescence spectroscopy. It has been demonstrated recently that the molecular complexes of GA with a number of drugs are characterized by reduced toxicity and increased therapeutic activity of these drugs. In the present work it was found that carotenoids form 1:2 complexes with GA in aqueous solutions as well as in polar organic solvents, methanol, acetonitrile, and dimethylsulfoxide. We assume that the structure of the complex is a cycliclike dimer of GA encapsulating a carotenoid molecule. The stability constants in all solvents are near 104 M-1. In addition, GA forms inclusion complexes with carotenoid radical cations, which results in their stabilization. Complex formation (a) decreases the rate of electron transfer from carotenoids to electron acceptors (Fe3+ or quinone) and (b) considerably increases the lifetime of the carotenoid−quinone charge-transfer complex and the yield of the major product (a carotenoid−quinone adduct). A thermodynamic study shows that hydrophobic interactions are the main driving force of the carotenoid−GA complex formation. These results are important for understanding both the nature of GA complexes and the influence of GA on the therapeutic activity of some drugs. Furthermore, carotenoid−GA complexes could be used for the design of artificial light-harvesting, photoredox, and catalytic systems. [ABSTRACT FROM AUTHOR]

NMR and UV−vis spectroscopy have been used to study the complexation of antiarrhythmic alkaloid lappaconitine with an efficient complexing agent from licorice, glycyrrhizic acid, which is known to profoundly influence the therapeutic activity of the alkaloid in the complex. In MeOH, DMSO, or aqueous solutions, lappaconitine has been shown to form a stable complex with glycyrrhizic acid with 1:1 stoichiometry over a broad concentration range from 1 μM to 300 μM. The stability constant K11 equals 2.0 × 105 M-1 in aqueous solution. A similar complex of lappaconitine hydrobromide—the pharmaceutical formulation used in the treatment of arrhythmia—is 2 orders of magnitude less stable than pure lappaconitine. A notable decrease in the rate of the photoinduced electron-transfer reaction between lappaconitine in a complex with glycyrrhizic acid and tyrosine allows the suggestion of an explicit interrelation between the suppressed chemical reactivity of the bound alkaloid and the changes of its therapeutic efficiency. [ABSTRACT FROM AUTHOR]

Abstract  The formation of niobium(V) methylate in methanol against the background of lithium chloride is studied. It is found that, in the anodic dissolution of niobium in the diaphragmless electrolyzer, formed niobium(V) methylate is partially reduced to the four-valent state at the cathode. In order to suppress the reduction of Nb(V), an electrolyzer was designed, which enabled one to separate the anolyte from the catholyte using the difference between their densities. Niobium methylate was not found in the anolyte; however, it forms as a result of mixing the anolyte with the catholyte after completion of electrolysis. The current efficiency of niobium methylate of 96–97% was achieved. Possible mechanism of the process is discussed. [ABSTRACT FROM AUTHOR]

Interspin distances between the Ti3+ions and the carotenoid radicals produced inside TiMCM-41 pores by photoinduced electron transfer from 7′-apo-7′-(4-carboxyphenyl)-β-carotene (coordinated to Ti3+), canthaxanthin (formed as a random distribution of isomers), and β-ionone (model for a short-chain polyene) to Ti3+framework sites were determined using the pulsed EPR relaxation enhancement method. To estimate the electron transfer distances, the temperature dependence of relaxation rates was analyzed in both siliceous and metal-substituted siliceous materials. The phase memory times, TM, of the carotenoid radicals were determined from the best fits of two-pulse ESEEM curves. The spin−lattice relaxation times, T1, of the Ti3+ion were obtained from the inversion recovery experiment with echo detection on a logarithmic time scale in the temperature range of 10−150 K. The relaxation enhancement for the carotenoid radicals in TiMCM-41 as compared to that in MCM-41 is consistent with an interaction between the radical and the fast relaxing Ti3+ion. For canthaxanthin and β-ionone, a dramatic effect on the carotenoid relaxation rate, 1/TM, occurs at 125 and 40 K, respectively, whereas for carboxy-β-carotene 1/TMincreases monotonically with increasing temperature. The interspin distances for canthaxanthin and β-ionone were estimated from the 1/TM− 1/TM0difference, which corresponds to the Ti3+contribution at the temperature where the maximum enhancement in the relaxation rate occurs. Determination of the interspin distances is based on calculations of the dipolar interaction, taking into consideration the unpaired spin density distribution along the 20-carbon polyene chain, which makes it possible to obtain a fit over a wider temperature interval. A distribution of the interspin distances between the carotenoid radical and the Ti3+ion was obtained with the best fit at ∼10 Å for canthaxanthin and β-ionone and ∼9 Å for 7′-apo-7′-(4-carboxyphenyl)-β-carotene with an estimated error of ±3 Å. The interspin distances do not depend on 1/TM− 1/TM0for carboxy-β-carotene which shows no prominent peak in the relaxation rate over the temperature range measured. [ABSTRACT FROM AUTHOR]

1H NMR and CIDNP methods were used to demonstrate that triterpene glycoside (glycyrrhizic acid, GA) can substantially change the efficiency and direction of phototransformation of alkaloid lappaconitine (LA) due to both its solubilization in GA micelles and protonation of LA amine nitrogen in water−alcohol solutions. The LA solubilization in the GA micelle suppresses the process of deacylation. [ABSTRACT FROM AUTHOR]

The elementary steps of the enzymatic oxidation of nifedipine (NF) catalyzed by horseradish peroxidase (HRP) have been described based on analysis of kinetic magnetic field effects (MFEs). It has been shown that the first step of the catalytic cycle is single electron transfer resulting in formation of NF•radical cation and ferroperoxidase (Per2). As a result, comparison with an earlier studied oxidation reaction of NADH catalyzed by HRP evidenced that the enzymatic oxidations of two substratesnative, NADH, and its synthetic analogue, NFcatalyzed by HRP in the absence of H2O2follow identical mechanisms. [ABSTRACT FROM AUTHOR]

The principal possibility of using natural microorganisms for binding and subsequent precipitation of 137Cs from low-level aqueous industrial process solutions was examined. [ABSTRACT FROM AUTHOR]