The new technique of pulsed electron−electron double resonance in electron spin−echo (PELDOR) in combination with the CW-ESR method has been used to investigate the secondary structure of a double ...spin-labeled peptide (the TOAC-1,8-analogue of the peptaibol antibiotic trichogin GA IV) that is hidden into a tetrameric supramolecular assembly of unlabeled peptide molecules. The magnetic dipole−dipole relaxation of spin labels has been experimentally studied in glassy solutions of the double-labeled peptide frozen to 77 K in a mixture of chloroform−toluene with an excess of unlabeled peptide. The PELDOR signal oscillations have been observed at high degrees of dilution with unlabeled peptide. The intramolecular distance between the spin labels of the peptide molecule in the aggregate has been determined from the oscillation frequency to be 15.7 Å which is close to the value of ≅14 Å calculated for a 310-helical structure. Estimation of the fraction of this ordered secondary structure shows that about 19% of the peptide molecules in aggregates are folded in the 310-helical conformation. The present experimental results are consistent with our molecular model presented in J. Am. Chem. Soc. 2000, 122, 3843−3848, wherein four amphiphilic 310-helical peptide molecules form a vesicular system with the polar amino acid side chains pointing to the interior, and the apolar side chains, to the exterior of the cluster. The experimental data were compared with the results obtained with other techniques.
The method of pulsed electron-electron double resonance (PELDOR) is exploited to study intra- and intermolecular dipole-dipole interactions between the spin labels of trichogin GA IV analogues. This ...lipopeptaibol antibiotic was studied in multilamellar membranes of dipalmitoylphosphatidylcholine frozen to 77 K. For mono-labelled trichogin analogues, the molecules are shown not to form aggregates in the lipid membranes studied. For the double-labelled trichogin analogues, a function of the distance distribution between the spin labels has been obtained. We determined that the distribution function has two main maxima located at distances of 1.25 nm and 1.75 nm. The value of 1.25 nm is close to the distance between labels of a alpha-helical structure. On the other hand, a distance of 1.75 nm corresponds to a mixed 3D-structure in which a 3(10)-helix is combined with a more elongated conformation.
The strongest nitrogen base is 1,8‐bis(dimethylamino)naphthalene‐2,7‐diolate according to experimental data and DFT calculations. Its proton affinity (PA) is comparable to those of simple ions such ...as OH−, NH2−, and H−. The diaminonaphthalene diolate 2 is protonated at the neutral amino groups with extremely high gas‐phase and solution proton affinity to form highly stable H‐bonded conjugate acid 1. DMSO=dimethyl sulfoxide.
We report on first measurements of low-mass electron-positron pairs in Pb-Au collisions at the CERN SPS beam energy of 40 AGeV. The observed pair yield integrated over the range of invariant masses ...0.2<m</=1 GeV/c(2) is enhanced over the expectation from neutral meson decays by a factor of 5.9+/-1.5(stat)+/-1.2(syst data)+/-1.8(syst meson decays), somewhat larger than previously observed at the higher energy of 158 AGeV. The results are discussed with reference to model calculations based on pi(+)pi(-)-->e(+)e(-) annihilation with a modified rho propagator. They may be linked to chiral symmetry restoration and support the notion that the in-medium modifications of the rho are more driven by baryon density than by temperature.
The papers related to the theoretical background and experimental investigations by pulsed electron double resonance (PELDOR) are reviewed. The main aim of this pulsed ESR application is to study the ...dipole-dipole spin interaction. In PELDOR the ESR spectrum is excited by two ESE pulses at frequencyωa and additional pumping pulse atωb. Decay functionV(T) of the ESE signal, when the time intervalT between the first ESE pulse and pumping pulse is varied, contains the information on dipole-dipole couplings in the spin system. The kinetics ofV(T) decay strongly depends upon distance, mutual orientation inside interacting spin pairs and space distribution of radicals throughout the sample. The distances between spins which were measured or estimated using PELDOR in the papers reviewed are in the range of 15 ÷ 130 Å. This pulsed ESR technique turns now to be a powerful supplement to conventional ESE in studying the free radicals space distribution..
Data analysis of an experiment in which photon splitting in atomic fields was observed is presented. The experiment was performed at the tagged photon beam of the ROKK-1M facility at the VEPP-4M ...collider. In the energy region of 120-450 MeV, statistics of 1.6x10(9) photons incident on the BGO target was collected. About 400 candidate photon-splitting events were reconstructed. Within the attained experimental accuracy, the experimental results are consistent with the calculated exact atomic-field cross section. The predictions obtained in the Born approximation differ significantly from the experimental results.
Pulsed electron−electron double-resonance (PELDOR) and CW-ESR spectroscopies were used to study the dipole−dipole interaction of spin labels in frozen glassy solutions of mono- and double-labeled ...analogues of the 22-residue, the head-to-tail covalent dimer of the peptaibol antibiotic trichogin GA IV. The TOAC-1 and TOAC-1,19 dimers were studied in methanol and in a chloroform−toluene mixture. It was shown these dimer molecules do not form aggregates in methanol. However, in chloroform−toluene, the PELDOR signal of the mono-labeled dimer shows oscillations, due to the dipole−dipole interaction of the nitroxide spin labels. From the signal decay, the number of molecules per aggregate was estimated to be ∼2−3, depending on the concentration used. The contributions of inter- and intra-aggregate interactions of spin labels to the PELDOR signal decay were separated. The distance distribution functions of the intra-aggregate interactions range from 3.0 to 4.5 nm. The maxima are observed at 3.4 nm. From the PELDOR data, we obtained the functions of distance distributions of labels for the monomeric double-labeled peptide in methanol as well as for the same peptide isolated within aggregates of nonlabeled peptide molecules in chloroform−toluene. In the latter case, the distribution function is the most narrow with a maximum at a distance between the nitroxide spin labels of 2.8 nm, which is in agreeement with the theoretical distance between labels at corresponding residue positions of an α-helical structure.
Nanotribology of copper clusters Kuzharov, A. A.; Milov, A. A.; Gerasina, U. S. ...
Nanotechnologies in Russia,
09/2016, Letnik:
11, Številka:
9-10
Journal Article
Recenzirano
The use of nanotechnologies in tribology has led to a large number of marketable lubricants containing nanoparticles with unproven efficiency. Tribological and physicochemical studies of some ...lubricant additives aimed at determining the tribological characteristics are presented in this work. It is found that applying metal particles (copper, above all) may lead to increased tribotechnical characteristics of lubricants. The quantum chemical calculations with the full optimization of all parameters by the method of the density functional theory (DFT) PBEPBE/Lanl2DZ were carried out in order to identify the mechanism of formation and growth of copper nanoclusters as a modeling basis of the metal-clad component of the tribosystems. It is shown that the formation of Cu nanoparticles and their shape are related with the growth of nanoclusters, their stabilization by ligands, and their aggregation, as well as agglomeration and coalescence, which results in nanoparticles of sizes ranging from a few to tens and hundreds of nanometers of different shapes. The synthesis of copper nanoclusters aimed at studying physical and chemical characteristics and their application as functional tribological nanomaterials is carried out. The efficiency of such lubricant compositions is determined.
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