Self-assembling catalytic systems based on new amphiphile containing purine fragment,exhibiting substrate specificity in hydrolysis of phosphorus acids esters

Micellar catalytic systems based on new purine-containing amphiphile for hydrolytic decomposition of organophosphorus toxicants have been prepared. The aggregation threshold of the system has been estimated by means of tensiometry, conductometry, spectrophotometry, and dynamic light scattering. The solubilizing action of the amphiphile towards the hydrophobic dye has been demonstrated. Kinetic studies of hydrolysis of phosphonates differing in the hydrophobicity have disclosed the substrate specificity of the micellar catalysts; inhibition instead of catalysis has been observed in the case of the less hydrophobic substrate.     

Polynucleating open-chain systems with imidazole and proton-ionizable 1,2,4-triazole structural motifs

A multistep route for obtaining the polynucleating open-chain systems 3-5 is reported. These advanced intermediates required elaborate processes that proceeded for the pentanuclear protophanes 3 in seven steps, whereas the trinuclear compounds 4 and 5 were obtained in six steps     

EPR‐Based Approach for the Localization of Paramagnetic Metal Ions in Biomolecules

Metal ions play an important role in the catalysis and folding of proteins and oligonucleotides. Their localization within the three‐dimensional fold of such biomolecules is therefore an important goal in understanding structure–function relationships. A trilateration approach for the localization of metal ions by means of long‐range distance measurements based on electron paramagnetic resonance (EPR) is introduced. The approach is tested on the Cu²⁺ center of azurin, and factors affecting the precision of the method are discussed.     

Synthesis of zeolites in the presence of radioisotopes: a novel approach to aqueous nuclear waste treatment

Zeolites A (LTA), gismondine (GIS) and the zeotype CoAPO₄-34 (CHA) were synthesised. During the syntheses, additions of Cs-137, Sr/Y-90, U and Th were made. Measurements of residual activities at the conclusion of the syntheses enabled the estimation of the zeolite efficiency to scavenge the isotopes from the initial solution. The majority of systems examined showed excellent radioisotope uptakes. PXRD was used to characterise the synthesis products.     

Enhanced generalised beam theory buckling formulation to handle transverse load application effects

This work deals with the development, finite element implementation and application of a generalised beam theory (GBT) formulation intended to analyse the localised, local, distortional and global buckling behaviour of thin-walled steel beams and frames subjected to transverse loads applied at various member cross-section points (away from its shear centre). In order to take into account the effects stemming from the transverse load position, the GBT buckling formulation must incorporate geometrical stiffness terms stemming from either (i) the internal work of the pre-buckling transversal normal stresses (“exact” formulation) or (ii) the external work of the applied transverse loads (approximate/simplified formulation). After presenting the main concepts and procedures involved in the development of the above “exact” and simplified formulations, the paper addresses the corresponding numerical implementations. Then, in order to illustrate their application and capabilities, as well as the limitations of the simplified formulation, various numerical result sets are presented and discussed. The accuracy of the GBT-based results is assessed through the comparison with “exact” values, yielded by rigorous shell finite element analyses carried out in the code Ansys.     

Pulsed EPR Dipolar Spectroscopy under the Breakdown of the High-Field Approximation: The High-Spin Iron(III) Case

Pulsed EPR dipolar spectroscopy (PDS) offers several methods for measuring dipolar coupling and thus the distance between electron-spin centers. To date, PDS measurements to metal centers were limited to ions that adhere to the high-field approximation. Here, the PDS methodology is extended to cases where the high-field approximation breaks down on the example of the high-spin Fe³⁺/nitroxide spin-pair. First, the theory developed by Maryasov et al. (Appl. Magn. Reson. 2006 , 30, 683–702) was adapted to derive equations for the dipolar coupling constant, which revealed that the dipolar spectrum does not only depend on the length and orientation of the interspin distance vector with respect to the applied magnetic field but also on its orientation to the effective g-tensor of the Fe³⁺ ion. Then, it is shown on a model system and a heme protein that a PDS method called relaxation-induced dipolar modulation enhancement (RIDME) is well-suited to measuring such spectra and that the experimentally obtained dipolar spectra are in full agreement with the derived equations. Finally, a RIDME data analysis procedure was developed, which facilitates the determination of distance and angular distributions from the RIDME data. Thus, this study enables the application of PDS to for example, the highly relevant class of high-spin Fe³⁺ heme proteins.     

Synthesis of μ2-Oxo-Bridged Iron(III) Tetraphenylporphyrin–Spacer–Nitroxide Dimers and their Structural and Dynamics Characterization by using EPR and MD Simulations

Iron(III) porphyrins have the propensity to form μ₂-oxo-dimers, the structures of which resemble two wheels on an axle. Whereas their crystal structure is known, their solution structure and internal dynamics is not. In the present work, the structure and dynamics of such dimers were studied by means of electron paramagnetic resonance (EPR) spectroscopy and quantum chemistry based molecular dynamics (MD) simulations by using the semiempirical tight-binding method (GFN-xTB). To enable EPR investigation of the dimers, a nitroxide was attached to each of the tetraphenylporphyrin cores through a linear and a bent linker. The inter-nitroxide distance distributions within the dimers were determined by continuous-wave (cw)-EPR and pulsed electron–electron double resonance (PELDOR or DEER) experiments and, with the help of MD, interpreted in terms of the rotation of the porphyrin planes with respect to each other around the Fe–O–Fe axis. It was found that such rotation is restricted to the four registers defined by the phenyl substituents. Within the registers, the rotation angle swings between 30° and 60° in the proximal and between 125° and 145° in the distal register. With EPR, all four angles were found to be equally populated, whereas the 30° and 145° angles are strongly favored to the expense of the 60° and 125° angles in the MD simulation. In either case, the internal dynamics of these dimers thus resemble the motion of a step motor.     

Self-assembly of frame structures. 10. Stereochemistry of 2,5-dioxabicyclo [2.2.1]heptane-3,6-digne

By optimization of the geometry of 2, 5-dioxabicyclo[2. 2.1]heptane-3.6-dione (1) with an ab initio (RHF/6-31 G') calculation, we have found that a single synchro(+, +)-twist form (A) corresponds to the (1 R,4R)-enantiomer (the dihedral angles of the lactone bridges are ₀ = 2.6°). According to MM2(91) and MM3(92) calculations, (1R,4R)-1 exists as the s-ynchro(+, +)-A-twist ( ₀ = 3.9°) and the synchro(-, -)-B-twist ( = -3.8°) forms, respectively. Investigating the torsional energy surface of the dilactone 1 (MM2(91)), we found only the (1R,4R,P)-diastereomeric form (A), which is stabilized compared with the (1R,4P,M) form (B) (probably as a result of the more preferred dipole-dipole interaction of the carbonyl groups). According to the calculated puckering coordinates, the five-membered and six-membered moieties of the bicycle 1 are flattened compared with norbornane.Institute of Chemical Physics at Chernogolovka. Russian Academy of Sciences, Chernogolovka, Moscow Oblast 142432. Department of Chemistry, University of Calgary, Alberta, Canada T2N 1N4. Department of Chemistry, College of Sciences, Autonomous University of Barcelona, Bellaterra 08193, Spain. Laboratory of Organic Chemistry, College of Pharmacy, University of Barcelona, Barcelona 08028, Spain. N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow 117977. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1479-1488, November, 1995.     

Polymer–Colloid Complexes Based on Cationic Imidazolium Amphiphile,Polyacrylic Acid and DNA Decamer

The solution behavior and physicochemical characteristics of polymer–colloid complexes based on cationic imidazolium amphiphile with a dodecyl tail (IA-12) and polyacrylic acid (PAA) or DNA decamer (oligonucleotide) were evaluated using tensiometry, conductometry, dynamic and electrophoretic light scattering and fluorescent spectroscopy and microscopy. It has been established that PAA addition to the surfactant system resulted in a ca. 200-fold decrease in the aggregation threshold of IA-12, with the hydrodynamic diameter of complexes ranging within 100–150 nm. Electrostatic forces are assumed to be the main driving force in the formation of IA-12/PAA complexes. Factors influencing the efficacy of the complexation of IA-12 with oligonucleotide were determined. The nonconventional mode of binding with the involvement of hydrophobic interactions and the intercalation mechanism is probably responsible for the IA-12/oligonucleotide complexation, and a minor contribution of electrostatic forces occurred. The latter was supported by zeta potential measurements and the gel electrophoresis technique, which demonstrated the low degree of charge neutralization of the complexes. Importantly, cellular uptake of the IA-12/oligonucleotide complex was confirmed by fluorescence microscopy and flow cytometry data on the example of M-HeLa cells. While single IA-12 samples exhibit roughly similar cytotoxicity, IA-12–oligonucleotide complexes show a selective effect toward M-HeLa cells (IC₅₀ 1.1 µM) compared to Chang liver cells (IC₅₀ 23.1 µM).