Intramolecular Dynamics and Molecular Structure of Europium(III) Chelate Complexes with Crown Ethers as Studied by NMR Spectroscopy

Earlier the intramolecular inversion of the 18-crown-6 molecules was found in the complex ion pairs [Ln(ptfa)₂ (18-crown-6)]⁺ [Ln(ptfa)₄]⁻ (H₂O)₄ where Ln = La(1), Ce (2), Pr (3), Nd (4), and ptfa is 1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedione. In this work the peculiarities of the molecular structure and dynamics were studied for [Eu(ptfa)₂ (18-crown-6)]⁺ [Eu(ptfa)₄]⁻ (H₂O)₄ (5) by NMR spectroscopy techniques. Through VT-NMR spectra analysis the temperature dependence was obtained for the rate constant. The free energy ΔG^‡(320) of 18-crown-6 ring inversion activation was found to be 65 ± 5 kJ mol⁻¹ for 5 in CDCl₃. This result is comparable with the earlier data [S.P. Babailov and D.A. Mainichev: J. Inclusion Phenom. Macrocyclic Chem. 43, 187–193 (2002)] for complexes 2, 3, 4 in deuterated toluene (ΔG^‡(320)=65 ± 9, 64 ± 9, 64 ± 9 kJ mol⁻¹ respectively). It was found by relaxation NMR spectroscopy that the effective distance between Ln and protons of the crown molecule is 4.5 ± 0.2 Å. The analysis of structural parameters testifies that the crown ether and chelated anions are in the first coordination sphere of a Ln cation. Obtained geometrical parameters show that the complex cations of Eu, Ce and Pr have similar spatial structures.     

Synthesis and psychotropic properties of 1-triorganylsiloxy- and 1-triorganylgermoxy-germatranes

Triorganylsiloxy- and triorganylgermoxy-germatranes have been prepared by the interaction of the easily available 1-hydroxygermatrane with various hetaryl-silanes and -germanes. The compounds were of the general structure:

• M = Si; X = S, CH = CH (viz. phenyl); n = 0,1,2
• M = Ge; X = CH = CH (viz. phenyl); n = 0

All siloxy- and germoxy-germatranes obtained were subjected to psychotropic assays. Some of phenylsiloxygermatranes are effective for memory enhancement (inhibition of retrogradal amnesia by triphenylsiloxygermatrane was 80%).     

Data Interpretation in Mass Spectrometry

An algorithm was proposed for interpreting mass spectra. It allows sufficiently reliable determination of some individual components and improves the resolution of the procedure. The algorithm can be recommended for use with commercial instruments based on time-of-flight mass analyzers and mirror electro energy analyzers and is characterized by low resolution (today no more than 500, e.g. LAMMA-500 and LAMMA-1000).__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 8, 2005, pp. 790–793.Original Russian Text Copyright © 2005 by Burlaka, Maiboroda, Startseva.     

Structure-activity studies of irumamycin type macrolides from Streptomyces sp. INA-Ac-5812

Three natural glycosylated macrolide compounds, known irumamycin 1 and X-14952B 2, as well as new isoirumamycin 3, were isolated from ethyl acetate mycelium extract of Streptomyces sp. INA-Ac-5812. Structures of the compounds were elucidated using 1D and 2D NMR. Isoirumamycin 3 was found to be an isomer of irumamycin with an 18-membered macrolactone ring instead of 20-membered macrolide in irumamycin. A previously unknown stereo configuration of irumamycin epoxide (C23, C24) and hemiketal (C3, C7) fragments was deduced from NMR data (ROESY/NOESY and HSQMBC). Cytotoxic, antifungal and antibacterial activities were studied for all isolated compounds. Comparison of the collected data showed crucial importance of 20-membered macrolactone ring for antimicrobial properties of this antibiotic family.     

Nonlinear continual growth model of nonuniformly scaled reliefs as applied to the rigorous analysis of the X-ray scattering intensity of multilayer mirrors and gratings

It is revealed that certain terms entering into the nonlinear continual equation describing thin-film growth enable its application to the simulation of the surfaces of multilayer mirrors and gratings with a large height and/or jumps of boundary-profile gradients. The proposed model characterizes both variations in the power spectral-density function of the surface of Al/Zr multilayer mirrors and the smoothing and shift of the boundaries of Mo/Si and Al/Zr gratings grown on Si substrates with triangular groove profiles by means of magnetron and ion-beam deposition. Rigorous calculations indicate that the intensities of diffuse X-ray scattering by Au mirrors, which have similar boundary profiles with Gaussian and exponential autocorrelation functions, differ substantially from each other. Computer simulation of the growth of Mo/Si and Al/Zr multilayer gratings is performed. On the basis of the calculated boundary profiles, the absolute diffraction efficiencies of the Mo/Si and Al/Zr gratings are found via the integral equation method in the extreme UV region. It is demonstrated that the proposed comprehensive approach to calculations of the boundary profiles and the intensities of short-wavelength scattering from multilayer mirrors and gratings makes it possible to carry out studies comparable in accuracy to measurements based on synchrotron radiation.     

Superoxide- and NO-Dependent Mechanisms of the Reprogramming of Bone Marrow Cells by Tumor Cells

Electron paramagnetic resonance (EPR) experiments in vitro; spin trapping of the reactive oxygen/nitrogen species (superoxide radicals and nitric oxide, NO); gel zymography measurements in the tumor tissues, in the healthy and tumor-affected bone marrow (BM) samples of rats are carried out. The superoxide and NO generation rates are derived; matrix metalloproteinases (MMP-2 and MMP-9) concentrations are measured. Their changes after the incubation of BM samples with Guérin carcinoma cells at 37 °C are defined. It is shown that the impact of tumor cells on BM manifests in the metabolic disorder, increased concentrations of active forms of MMP-2 and MMP-9, increased production of superoxide and NO radicals. Correlation between the appearance and intensity of the broad EPR signal at g = 2.2–2.4 with the concentrations of active forms of MMP-2 and MMP-9, NO and superoxide radicals’ rates is observed. The obtained spatial and temporal changes of the measured parameters demonstrate the usefulness of the potential application of EPR imaging to study the mechanisms of tumor invasion. The EPR signal may indicate the presence of distant metastases, may become a part of diagnostics and used for the estimation of the therapeutic treatments in the pre-clinical studies. It is proposed that labile iron pool is responsible for the appearance of the EPR signal in tumor and BM samples.     

General route to symmetric and asymmetric meso-CF3-3(5)-aryl(hetaryl)- and 3,5-diaryl(dihetaryl)-BODIPY dyes

A general efficient route to hitherto inaccessible symmetric and asymmetric meso-CF(3)-BODIPY dyes has been developed. The key stages include the reduction of available 2-trifluoroacetylpyrroles to the corresponding alcohols which are further condensed with pyrroles. The method allows the BODIPY with 3(5)aryl(hetaryl) and 3,5-diaryl(hetaryl) substituents to be readily assembled. The BODIPY dyes synthesized fluoresce (Φ(f) = 0.56-1.00) in the 560-680 nm region.     

Kinetic model of growth of GaAs nanowires

A kinetic model of growth and formation of the crystal structure of gallium arsenide nanowires by molecular beam epitaxy on surfaces activated by Au drops is developed. The thicknesses of alternating layers of cubic and hexagonal phases formed due to fluctuations of the solution composition in the drop are calculated and compared with experimental data.     

Reaction of propionitrile with methylidyne: A theoretical study

The results of a CCSD(T)-F12/cc-pVTZ-f12//ωB97XD/cc-pVTZ quantum-chemical study of the potential energy surface (PES) for the reaction of propionitrile with methylidyne are combined with Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of the reaction rate constants and product branching ratios in the deep space conditions corresponding to the zero-pressure limit at various collision energies. The most energetically favorable reaction pathways have been identified. The reaction outcome has been shown to strongly depend on the branching in the entrance reaction channel, between CH additions and insertions into various C-H and C-C bonds. For instance, CH addition to the N atom predominantly leads to 3H-pyrrole + H (p9), with CH₂NC + C₂H₄ (p2) also being a significant product. CH addition to the triple C≡N bond mostly results in 2-methylene-2H-azirine + CH₃ (p13), whereas CH insertions into C-H bonds in the CH₃ and CH₂ groups of propionitrile form CH₂CN + C₂H₄ (p1) and CH₂CHCN + CH₃ (p7) respectively. Less likely CH insertions into single C-C bonds yield CH₃CHCHCN + H (p5) and CH₂CHCH₂CN + H (p8). The results indicate that the methylidyne + propionitrile reaction may represent a critical step toward the formation of heterocyclic N-containing molecules in the interstellar medium and in planetary atmospheres.