The Role of Side Chains in the Fine-Tuning of the Metal-Binding Ability of Multihistidine Peptides

The systematic studies of copper(II), nickel(II) and zinc(II) ion complexes of protected multihistidine peptides containing amino acids with different side chains (Ac-SarHAH-NH₂, Ac-HADH-NH₂, Ac-HDAH-NH₂, Ac-HXHYH-NH₂ X, Y = A, F, D or K, Ac-HXHAHXH-NH₂, X = F or D) have provided information about the metal ion and protein interaction and have made it possible to draw conclusions regarding general trends in the coordination of metal complexes of multihistidine peptides. The stability of the metal complexes significantly depends on the position of the histidines and amino acids, which are present in the neighbourhood of the histidine amino acids as well. The most significant effect was observed on peptides containing aspartic acid or phenylalanine. The redox parameters of complexes, however, depend on the number and position of histidines, and the other side chain donor atoms have practically no effect on the electrochemical properties of imidazole-coordinated species. However, the presence of aspartic acid side chains results in a more distorted geometry of amide-coordinated species and increases the reducibility of these complexes.     

Towards the Efficiency of Pharmacologically Active Quinoid Compounds: Electron Transfer and Formation of Reactive Oxygen Species

In this review article, the structure, properties, stability and biological application of redox-active quinones are presented. A series of quinoid molecules is evaluated in terms of their ability to act as electron-transfer active compounds using cyclovoltammetric, electron paramagnetic resonance (EPR) and spin-trapping techniques. Redox potentials and electron distribution of the intermediate radical anions are shown to be decisive factors for the generation of reactive oxygen species (ROS). Mechanisms of ROS generation in dark by biological electron-transfer reaction or under photoexcitation have been proposed and experimentally verified. For site-specific damage of tumors, some quinone derivatives were covalently bound with the luteinizing hormone-releasing hormone (LH–RH or GnRH) that produces specific complexes with receptors on the surface of cancer cells. The properties of obtained conjugates to be bound with the different lines of cancer cells (αT3-1, M2R, LNCaP) were tested. EPR was used for the estimation of efficacy of ROS production by the conjugates in solution and in the complex with cancer cells. The toxicity of these conjugates as well as their stability in the stimulated oxidative stress were tested. The proposed approach could be useful in creating a new family of addressed anticancer drugs, including compounds for the treatment of tumors by photodynamic therapy.     

Reactivity of per-O-acetylated 1-thioglycosides and glycosyl sulfones towards chromium(II) complexes in aqueous medium

Anomeric carbon-sulfur bonds in 1-thioglycosides and glycosyl sulfones can be cleaved by chromium(II) complexes in water-DMF medium. Anomeric radicals as well as sugar-chromium(III) complex intermediates can be generated in these reactions, leading in some cases, to the exclusive formation of the corresponding glycals.     

Enantioselective Michael addition of diethyl cyanomethylphosphonate to chalcones using bifunctional cinchona-derived organocatalysts: synthesis of chiral precursors of α-substituted β-aminophosphonates

An enantioselective Michael addition of diethyl cyanomethyl phosphonate to chalcones catalysed by bifunctional catalysts based on cinchona alkaloids has been developed, producing enantiomerically enriched cyanophosphonate precursors of α-substituted β-aminophosphonates.     

Surface modification of mechanochemically activated kaolinites by selective leaching

Low- and high-defect kaolinites mechanochemically activated for different periods of time have been treated with sulfuric acid solution. These modified materials were analyzed using a combination of X-ray diffraction, thermogravimetry, chemical analysis, diffuse reflectance Fourier transform infrared spectroscopy, as well as specific surface area and pore size distribution measurements. In addition to the mechanochemically amorphized part, the disordered and the adequately distorted phases also reacted with sulfuric acid. The specific surface areas of the leached samples of the partially or the completely amorphized materials were found to be greater than those of the thermally amorphized ones. The acid treatment results in a greater total pore volume for the partially amorphized materials than for the totally amorphized mineral. The partially amorphized high-defect kaolinite was proved to be more soluble than the low-defect kaolinite under similar conditions.     

Nanosphere dispersed liquid crystals for tunable negative-zero-positive index of refraction in the optical and terahertz regimes

An analysis of aligned nematic liquid crystal cells containing core-shell nanospheres shows that it is possible to devise a new type of metamaterial whose index of refraction is tunable from negative, through zero, to positive values. The design parameters for the constituents can be scaled for application in the optical as well as very long wavelength (e.g., terahertz and microwave) regions.