“Matrix effects” in the activation of compounds with a system of conjugation in the inhibition of oxidative processes

Russian Chemical Bulletin -     

Effect of the State of a Surface Layer on the Properties of Pd–P Catalysts in the Hydrogenation of Alkylanthraquinones

Kinetics and Catalysis - X-ray photoelectron spectroscopy (XPS) was used to study the state of the surface layer of a Pd–P catalyst, which exhibits high selectivity in the hydrogenation of...     

The Effect of a Covalent and a Noncovalent Small-Molecule Inhibitor on the Structure of Abg β-Glucosidase in the Gas-Phase

The effects of binding two small-molecule inhibitors to Agrobacterium sp. strain ATCC 21400 (Abg) β-glucosidase on the conformations and stability of gas-phase ions of Abg have been investigated. Biotin-iminosugar conjugate (BIC) binds noncovalently to Abg while 2,4-dinitro-2-deoxy-2-fluoro-β-d-glucopyranoside (2FG-DNP) binds covalently with loss of DNP. In solution, Abg is a dimer. Mass spectra show predominantly dimer ions, provided care is taken to avoid dissociation of dimers in solution and dimer ions in the ion sampling interface. When excess inhibitor, either covalent or noncovalent, is added to solutions of Abg, mass spectra show peaks almost entirely from 2:2 inhibitor-enzyme dimer complexes. Tandem mass spectrometry experiments show similar dissociation channels for the apo-enzyme and 2FG-enzyme dimers. The +21 dimer produces +10 and +11 monomers. The internal energy required to dissociate the +21 2FG-enzyme to its monomers (767?±?30 eV) is about 36 eV higher than that for the apo-enzyme dimer (731?±?6 eV), reflecting the stabilization of the free enzyme dimer by the 2FG inhibitor. The primary dissociation channels for the noncovalent BIC-enzyme dimer are loss of neutral and charged BIC. The internal energy required to induce loss of BIC is 482?±?8 eV, considerably less than that required to dissociate the dimers. For a given charge state, ions of the covalent and noncovalent complexes have about 15 % and 25 % lower cross sections, respectively, compared with the apo-enzyme. Thus, binding the inhibitors causes the gas-phase protein to adopt more compact conformations. Noncovalent binding surprisingly produces the greatest change in protein ion conformation, despite the weaker inhibitor binding.

Deracemization of α-monosubstituted cyclopentanones in the presence of a TADDOL-type host molecule

Racemic α-monosubstituted cyclopentanones were converted to optically active forms by a thermodynamically controlled deracemization using TADDOL-type host molecule 1 in alkaline aqueous MeOH. The efficiency of this conversion was strongly influenced by the ratio of the solvent components (H₂O/MeOH) and the functionality and architecture of the α-side-chain on the cyclopentanones. For example, (R)-2-(2-benzyloxyethyl)cyclopentanone (9) was obtained in 89% yield with 97% ee using a 7:3 mixture of H₂O/MeOH as the solvent. X-ray analytical studies were also carried out and disclosed the nature of this chiral molecular recognition process in the solid phase.     

Trace elements in a profile of the unsaturated zone of the São Paulo Basin

This study comprises Tertiary sediments (clays, silts, and fine clayey sands) from the unsaturated zone of the Experimental Station in the University of São Paulo, taken from a nine meters depth profile; ten samples were separated in bulk and <53 m fractions. Chemical composition was determined by INAA to ascertain the distribution of trace elements throughout the sediment deposition, and to establish the background parameters, useful for mobilization studies of such elements after industrial waste disposal.     

Synthesis and Characterization of Ti-ZSM-5 in a Non-alkaline Medium in the Presence of Fluoride Ions

Ti-ZSM-5 was synthesized by hydro thermal crystallization in the presence of fluoride via using a non-alkaline medium. pH values were 5~7. SEM showed perfect Ti-ZSM-5 crystals and a large single crystal growing from the favourable medium. Substitution of titanium for silicon in the ZSM-5 framework led to a decrease of crystal size and of the length/width ratio. Electron microprobe analysis indicated a homogeneous distribution of titanium in the ZSM-5 framework. The unit cell parameters of the Ti-ZSM-5 determined by XRD increased with an increase in titanium content in the framework. TiO4tetrahedron vibrations were found in the IR spectrum. Si(1Ti) peakwas seen in the 29Si MAS NMR spectrum at -1O1ppm(from TMS) and 13CMAS NMR analysis verified the effect of (C3H7)4N F- occluded in thechannels. XPS study on the precursors, calcined and H2O2 adsorbed Ti-ZSM-5 was performed and some interesting results were observed.     

Transformations of α- and β-ionones in the presence of Al2O3 in a supercritical solvent in a flow reactor

The reactivity of α- and β-ionones under the supercritical conditions in a flow type reactor in the presence of Al₂O₃ at 200–230°C was studied. α-Ionone was reduced to α-ionol, while β-ionol was unstable already at 200°C and underwent dehydration. The secondary reaction products were the corresponding megastigmatrienes.     

Conformational Heterogeneity of a Tripeptide in the Solid State and in Solution: Characterization of a γ-Turn Containing Incipient Hairpin in Solution

A terminally blocked tripeptide Boc--Ala-Aib--Ala-OMe 1 with noncoded amino acids forms a novel type of hairpin structure containing a -turn instead of a conventional -turn in the central loop region in solution. This new type structural motif was characterized by NMR and restraint molecular dynamics simulation study. In the solid state peptide 1 adopts an extended backbone conformation and self-assembles to form supramolecular -sheet.     

Diastereotopos-Differentiation in the Rh-Catalyzed Amination of Benzylic Methylene Groups in the α-Position to a Stereogenic Center

The diastereoselectivity of the Rh-catalyzed C-H amination was examined with 18 chiral open-chain substrates, which bear a benzylic methylene group in the α-position to a stereogenic center (-CHMeX), and with four chiral cyclic tetralins, in which the stereogenic center was positioned at carbon atom C2. The C-H amination was performed using trichloroethoxysulfonyl-substituted amine (H(2)NTces) as the nitrogen source, a diacyloxyiodobenzene as the oxidant, and bis[rhodium(α,α,α',α'-tetramethyl-1,3-benzenedipropionate)] [Rh(2)(esp)(2)] as the catalyst. For acyclic substrates a high syn diastereoselectivity (dr > 95/5) was found if the substituent X was Br, PO(OEt)(2), SO(2)Ph, or OOCCF(3) (eight examples). Moderate to good syn selectivities (dr = 80/20 to 91/9) were found for X = NO(2), OAc, COOMe, and CN (eight examples). Only two substrates gave a low diastereoselectivity. Kinetic isotope effect (KIE) experiments revealed that there is no secondary KIE when replacing -CHMeCOOMe by -CDMeCOOMe, but there is a significant primary KIE at the benzylic methylene position (4.8 ± 0.7). Deuteration experiments provided evidence that the reaction proceeds stereospecifically with retention of configuration. A preferred conformation is proposed, which explains the outcome of the reaction. In this conformation the X substituent is antiperiplanar to the C-H bond, which is diastereoselectively attacked, and steric strain between the remaining substituents at the stereogenic and the prostereogenic center is minimized. DFT calculations support this model. They suggest, however, that the reaction is not concerted but occurs via hydrogen atom abstraction and subsequent radical rebound. Further support for an antiperiplanar attack relative to a given substituent X = Br, COOMe, or CN was obtained with the respective 2-substituted tetralins. Attack at C1 provides almost exclusively the trans-amination product. If the size of the X substituent increases [Br < CN < COOMe < PO(OEt)(2)], attack at the carbon atom C4 prevails, delivering the respective trans-amination products at this position.     

Shift of the nematic–isotropic phase transition temperature in a thin layer of a metallomesogenic complex

The effect of boundaries on the nematic–isotropic phase transition temperature in a melt of a metallomesogenic complex was studied for the first time. This was done by comparison of the electro-optical constant of the isotropic phase with the dielectric and optical anisotropy of the nematic phase on the basis of the Landau–de Gennes theory. In a real experiment, the two liquid phases (nematic and isotropic ones) coexist in a range of several degrees around the transition. According to polarization microscopy data, the phase transition temperature decreases by more than 10°C as the metallomesogen layer thickness is reduced from 200 to 5 μm.     

α-Effect of hydroxylamine in the transfer of a toluenesulfonyl group in water—Dimethyl sulfoxide mixtures

A kinetic and thermodynamic analysis of the reactions of hydroxylamine with aryltoluenesulfonates in H₂O-DMSO mixtures (0–90 vol.% DMSO) indicated that the neutral and anionic forms of hydroxylamine are strong α-nucleophiles, and the magnitude of the α-effect shows an asymmetric bell shape depending on the DMSO content. This phenomenon is interpreted. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 2, pp. 83–88, March–April, 1999.     

Experiments of the secondary ignition of gasoline–air mixture in a confined tunnel

In this article, a special phenomenon of secondary ignition, which is caused when a gasoline–air mixture comes in contact with a local heat source after the first explosion or fire in a confined tunnel, is studied through experiments carried out in a cylinder tunnel with a solid heating device. Based on the analysis of the experimental results of secondary thermal ignition in the confined tunnel, the mode, critical ignition temperature, and critical concentration of the secondary thermal ignition’s occurrence of the gasoline–air mixture in the confined tunnel are discussed. The results indicate that the mode of secondary thermal ignition of gasoline–air mixture in the confined tunnel includes burning, slow deflagration, and rapid deflagration. Compared to the first thermal ignition, the burning intensity of the secondary thermal ignition is stronger and the ignition delay is much shorter. The relationship between critical ignition temperature and gas mixture temperature follows a cubic polynomial. Experiments also indicate that whether the secondary thermal ignition occur or not is determined by critical gasoline vapor and oxygen concentration even if the temperature is maintained in a reasonable scope. When the concentration of the gas vapor is as low as 0.45 % and the oxygen as low as 10.4 %, the secondary thermal ignition still can be triggered.     

Voltammetric Investigation of Host–Guest Systems in the Absence of a Supporting Electrolyte

Journal of Inclusion Phenomena and Macrocyclic Chemistry - In the classic voltammetric approach to host--guest systems the investigations are carried out in excess of a supporting electrolyte,...     

Alteration of the Conformational Dynamics of a DNA Hairpin by α-Synuclein in the Presence of Aqueous Two-Phase Systems

The effect of an amyloidogenic intrinsically disordered protein, α-synuclein, which is associated with Parkinson's disease (PD), on the conformational dynamics of a DNA hairpin (DNA-HP) was studied by employing the single-molecule Förster resonance energy transfer method. The open-to-closed conformational equilibrium of the DNA-HP is drastically affected by binding of monomeric α-synuclein to the loop region of the DNA-HP. Formation of a protein-bound intermediate conformation is fostered in the presence of an aqueous two-phase system mimicking intracellular liquid-liquid phase separation. Using pressure modulation, additional mechanistic information about the binding complex could be retrieved. Hence, in addition to toxic amyloid formation, α-synuclein may alter expression profiles of disease-modifying genes in PD. Furthermore, these findings might also have significant bearings on the understanding of the physiology of organisms thriving at high pressures in the deep sea.