Photoinduced elementary processes in chiral linked systems, consisting of drugs and tryptophan (Trp) residues, attract considerable attention due to several aspects. First of all, these are models ...that allow one to trace the full and partial charge transfer underlying the binding of drugs to enzymes and receptors. On the other hand, Trp fluorescence is widely used to establish the structure and conformational mobility of proteins due to its high sensitivity to the microenvironment. Therefore, the study of mechanisms of Trp fluorescence quenching in various systems has both fundamental and practical interest. An analysis of the photo-chemically induced dynamic nuclear polarization (CIDNP) and Trp fluorescence quenching in (
/
)-ketoprofen-(
)-tryptophan ((
/
)-KP-(
)-Trp) dyad carried out in this work allowed us to trace the intramolecular reversible electron transfer (ET) and obtain evidence in favor of the resonance energy transfer (RET). The fraction of dyad's singlet excited state, quenched via ET, was shown to be 7.5 times greater for the (
,
)-diastereomer than for the (
,
) analog. At the same time, the ratio of the fluorescence quantum yields shows that quenching effectiveness of (
,
)-diastereomer to be 5.4 times lower than for the (
,
) analog. It means that the main mechanism of Trp fluorescence quenching in (
/
)-KP-(
)-Trp dyad is RET.
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The study of the L- and D-amino acid properties in proteins and peptides has attracted considerable attention in recent years, as the replacement of even one L-amino acid by its D-analogue due to ...aging of the body is resulted in a number of pathological conditions, including Alzheimer’s and Parkinson’s diseases. A recent trend is using short model systems to study the peculiarities of proteins with D-amino acids. In this report, the comparison of the excited states quenching of L- and D-tryptophan (Trp) in a model donor–acceptor dyad with (R)- and (S)-ketoprofen (KP-Trp) was carried out by photochemically induced dynamic nuclear polarization (CIDNP) and fluorescence spectroscopy. Quenching of the Trp excited states, which occurs via two mechanisms: prevailing resonance energy transfer (RET) and electron transfer (ET), indeed demonstrates some peculiarities for all three studied configurations of the dyad: (R,S)-, (S,R)-, and (S,S)-. Thus, the ET efficiency is identical for (S,R)- and (R,S)-enantiomers, while RET differs by 1.6 times. For (S,S)-, the CIDNP coefficient is almost an order of magnitude greater than for (R,S)- and (S,R)-. To understand the source of this difference, hyperpolarization of (S,S)-and (R,S)- has been calculated using theory involving the electron dipole–dipole interaction in the secular equation.
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1.
Iodine is a broad-spectrum antimicrobial disinfectant for topical application. Recent studies have shown promising results on the applicability of an iodine-containing complex, FS-1, against ...antibiotic-resistant pathogens. It was hypothesized that the antimicrobial activity of iodine-containing complexes may be modulated by the organic moiety of the complex, i.e., amino acids. 2.
Gene regulation and metabolic alterations were studied in two model multidrug-resistant microorganisms,
ATCC BAA-39, and
ATCC BAA-196, treated with three complexes containing iodine and three different amino acids: glycine, L-alanine, and L-isoleucine. The bacterial cultures were exposed to sub-lethal concentrations of the complexes in the lagging and logarithmic growth phases. Gene regulation was studied by total RNA sequencing and differential gene expression analysis. 3.
The central metabolism of the treated bacteria was affected. An analysis of the regulation of genes involved in stress responses suggested the disruption of cell wall integrity, DNA damage, and oxidative stress in the treated bacteria. 4.
Previous studies showed that the application of iodine-containing complexes, such as FS-1, serves as a supplement to common antibiotics and can be a promising way to combat antibiotic-resistant pathogens. Current results shed light on possible mechanisms of this action by disrupting the cell wall barriers and imposing oxidative stress. It was also found that the effect of the complexes on metabolic pathways varied in the tested microorganisms depending on the organic moiety of the complexes and the growth phase when the complexes had been applied.
In this work, the effect of 10 MeV electron irradiation on the structure and electrical properties of bulk α-In2Se3 crystals is studied by X-ray diffraction, scanning electron microscopy, ...energy-dispersive X-ray microanalysis, atomic-force microscopy, and Raman spectroscopy methods. Droplets of 200–500 nm in size were detected on the bulk α-In2Se3 crystal surface. The droplets can be formations with the γ-In2Se3 crystalline phase. The current–voltage characteristics measured by conductive atomic-force microscopy are different on and outside the droplets after electron irradiation. On the droplets, slightly better conductive properties were detected after irradiation with the electron fluence of 1015 cm−2. It is found that local resistance increases significantly for both on and outside the droplets after irradiation with the electron fluence of 1017 cm−2. Our study shows that electron irradiation can contribute to the disappearance of ferroelectric domains in the bulk α-In2Se3 crystals. Also, the distribution of surface potentials measured by Kelvin probe force microscopy becomes more uniform after electron irradiation. The results obtained in the work allow us to calculate the operating time of the device containing α-In2Se3 under conditions of long-term electron irradiation with high-energy electrons. The study shows that α-In2Se3 is a very promising material for applications in the aerospace and nuclear industries.
The interatomic Auger transitions in compounds containing atomic components with core levels close in energy are studied theoretically and experimentally. The Coulomb transitions of a hole between ...such levels lead to a resonant enhancement of the Auger spectra (with respect to the energy difference between the levels). Interatomic Auger transitions involving high lying levels are formed by shaking up electrons due to the dynamic field of photo holes produced during the transition. These effects are observed experimentally in XPS and Auger spectra of CuInSe2 type materials.
The experimental XPS spectra in CuInSe2 based compounds show intense interatomic CuL3M2,3InN4,5 and CuL3InN4,5V Auger transitions. The interaction of copper 3p and indium 4p levels of similar energy gives a resonant increase in the magnitude of the first Auger transition. Shaking the In 4d electron because of the appearance of a photo hole is the mechanism of the second transition.
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Methionine γ-lyase (MGL) is a pyridoxal 5′-phosphate–dependent enzyme catalyzing γ-elimination in l-methionine. Pyridoxal 5′-phosphate–dependent enzymes have unique spectral properties that allow to ...monitor sequential formation and decomposition of various intermediates via the detection of absorbance changes. The kinetic mechanism of the γ-elimination reaction catalyzed by Citrobacter freundii MGL was elucidated here by fast stopped-flow kinetic analysis. Single-wavelength detection of characteristic absorbance changes enabled us to compare transformations of intermediates in the course of the reaction with different substrates. The influence of various γ-substituents in the substrate on the formation of key intermediates was estimated. Kinetic isotope effects of α- and β-protons were determined using deuterium-substituted l-methionine. Contributions of amino acid residues Tyr113 and Tyr58 located in the active site on the formation and decomposition of reaction intermediates were identified too. α-Aminocrotonate formation is the rate-limiting step of the enzymatic γ-elimination reaction. Kinetic isotope effects strongly support concerted reaction mechanisms of transformation between an external aldimine and a ketimine intermediate as well as a ketimine intermediate and an unsaturated ketimine.
•The kinetic mechanism of the γ-elimination reaction catalyzed by MGL was elucidated.•Process of protein-substrate interaction was analyzed by pre-steady state kinetics.•Kinetic isotope effects of α- and β-protons were determined.•Concerted reaction mechanisms of transformation between some intermediates were suggested.•Role of amino acid residues Y113 and Y58 located in the active site were specified.
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Diclofenac sodium (DS) is a widely used nonsteroidal anti-inflammatory drug (NSAIDs). NSAIDs are poorly removed during standard wastewater treatment. The consequences of the presence of NSAIDs in ...rivers and lakes at 10−11–10−8 mol/L are not yet established; therefore, ecotoxicologists have focused their efforts on studying the effect of low-concentration NSAIDs on fish and hydrobionts, and also on predicting the potential risks to humans. Literature provides some information about the bioeffects of some NSAID solutions in low concentrations but there is no physicochemical explanation for these phenomena. Studying the physicochemical patterns of DS solutions in the low range of concentrations and establishing an interconnection between the solutions' physicochemical properties and bioeffects can provide a conceptually new and important source of information regarding the unknown effects of DS. The physicochemical properties and action of DS solutions on Ceriodaphnia affinis cladocerans, Paramecium caudatum infusoria, Chlorella vulgaris unicellular green algae, as well as on the growth of the roots of Triticum vulgare wheat seeds, were studied in the calculated concentration range of 1 × 10−3–1 × 10−18 mol/L. The relationship between these phenomena was established using the certified procedures for monitoring the toxicity of natural water and wastewater. It was shown for the first time that water solutions of DS are dispersed systems in which the dispersed phase undergoes a rearrangement with dilution, accompanied by changes in its size and properties, which affects the nonmonotonic dependences of the system's physicochemical properties and could cause nonmonotonic changes in action on hydrobionts in the low concentration range.
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is a key stress-responsive regulator of the hypothalamic-pituitary-adrenal axis. To elucidate the contribution of rs1360780
C/T alleles to aging and longevity, we genotyped
in a cohort of 800 ...non-demented and Alzheimer's disease (AD) subjects of different age, taking into account the allele state of
ε4, the major risk factor for AD. Furthermore, we searched for the association of
with subcohorts of non-demented subjects evaluated for anxiety and resting-state quantitative EEG characteristics, associated with cognitive, emotional, and functional brain activities. We observed that increased state anxiety scores depend on the combination of the
and
genotypes and on the DNA methylation state of the
promoter and
genotype. We also found a significant gender-dependent correlation between
promoter methylation and alpha-, delta-, and theta-rhythms. Analysis of the
expression in an independent cohort revealed a significant upregulation of
in females versus males. Our data suggest a synergistic effect of the stress-associated (
) and neurodegeneration-associated (
) gene alleles on anxiety and the gender-dependent effect of
on neurophysiological brain activity.
Alkaline version of the single‐cell gel electrophoresis (Comet assay) is widely used in toxicological, environmental, and monitoring studies to assess the DNA damage levels in individual cells. The ...change in the temperature of the electrophoretic solution is one of the reasons leading to interlaboratory variation of Comet assay results. In this work, changes of surface temperature of the solution during electrophoresis were studied using technique of real‐time thermal imaging. It has been found that the electrophoresis is accompanied by nonuniform temperature rise in different areas of the electrophoretic chamber. The maximum of heating was observed in the central region of the chamber, where temperature increased by an average of 7°C. The minimum temperature rise in other parts of the chamber was about 5°C. After removing the solution, the temperature on the surface of slides was higher than that on the surface of the solution. We believe that (1) nonuniform heating of the electrophoretic solution and convection could be the reasons responsible for the variability of results both in inter‐ and intralaboratory studies; (2) the spatial distribution of heating of the solution depends on the size and configuration of the electrophoretic chambers used.
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Two new isomeric complexes CuBr2(R-bian) (R = 4-Me-Ph (1), 2-Me-Ph (2)) were obtained by reacting copper(II) bromide with 1,2-bis(2-methylphenyl)iminoacenaphthene ligands and characterized. The ...crystal structure of 2 was determined by X-ray diffraction analysis. The copper atom has a distorted square-planar environment; the ω angle between the CuN2 and CuBr2 planes is 37.004°. The calculated ω parameters for optimized structures 1 and 2 were 76.002° and 43.949°, indicating significant deviations from the ideal tetrahedral and square-plane geometries, respectively. Molecules 2 form dimers due to non-covalent Cu···Br contacts, which were analyzed by DFT calculations. The complexes were also characterized by cyclic voltammetry and UV-Vis spectroscopy. A quasi-reversible Cu(II)/Cu(I) redox event with E1/2 potentials of 0.81 and 0.66 V (vs. SHE) was found for 1 and 2, respectively. The electronic absorption spectra showed the presence of Cu(I) species as a result of the partial reduction of the complexes in the acetonitrile solution. Both complexes were tested as homogenous catalysts for the oxidation of isopropylbenzene (IPB) in acetonitrile at low temperatures. Differences in the mechanism of the catalytic reaction and the composition of the reaction products depending on the oxidizing ability of the catalyst were revealed.
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