Synthesis of 2-fluoro-6-O-propargyl-11,12-carbamate ketolides. A novel class of antibiotics

A novel class of 2-fluoro-6-O-propargyl-11,12-carbamate ketolide derivatives of erythromycin has been synthesized for antibacterial SAR studies. Replacement of the C2-hydrogen by a fluorine atom allows the synthesis of 6-O-propargylic ketones and electron-deficient 6-O-propargylic aromatic derivatives by preventing intramolecular C2-enolate Michael cyclization.     

Lateral diffusion studied by pulsed field gradient NMR on oriented lipid membranes

This mini-review focuses on the utilization of pulsed magnetic field gradients to measure diffusional motion in systems of macroscopically oriented lipid bilayers. The NMR diffusion technique is proposed to have appreciable potential for future biophysical investigations in the field of membrane biology. Topics such as transport of molecules both across and in the plane of the membrane can be successfully studied, and the formation of lipid domains and their intrinsic dynamics can also be scrutinized. First, a short introduction to the NMR technique is given together with a brief discussion on methods of obtaining a good bilayer orientation. Then, a number of recent results on biophysical/biological membrane systems of great interest is presented, in which some unique conclusions on so-called 'raft membranes' are reached. It is shown for systems with large two-phase areas of liquid disordered and liquid ordered phases that lipid lateral diffusion is faster in the former phase and has a smaller apparent activation energy. Further, on the time-scale of the experiments (50-250 ms), exchange between the two phases is fast in the phospholipid-cholesterol-water ternary system, whereas it is slow in the sphingomyelin-dioleoylphosphatidylcholine-cholesterol-water quaternary system.     

Counter-flow liquid injection plasma synthesis of spinel powders

A novel counter-flow liquid injection plasma synthesis (CF-LIPS) reactor has been developed to produce ceramic powders. By using a counter-flow plasma configuration, entrainment of reactant particles into the plasma is improved compared to conventional injection methods. The counter-flow process also creates large recirculation zones which increase the residence time to more than 100 ms as predicted by modeling results [1]. The long residence time ensures complete evaporation and decomposition of precursor particles and complete reactions to the desirable products. Also, the process employs liquid precursors rather than solids, resulting in less contamination of products from unevaporated reactants. Results show that CF LIPS is an excellent method for producing single-phase and spherical spinel powders with a narrow particle size distribution. Particle size increases with increasing precursor concentration based on the synthesis of magnesium aluminate powders. Characterization techniques include X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), X-ray mapping, centrifugal sedimentation particle size distribution analysis, and vibrating sample magnetometer (VSM) measurements. In addition, crystallographic studies are conducted to determine the bond lengths, bond angles, and stoichiometries of the as-produced spinels.     

Use of spin-labelling techniques to probe the dynamics of He(23 S) deexcitation at solid surfaces

Spin labelling techniques, specifically the use of electron-spin-polarized He(2³ S) metastable atoms coupled with energy-resolved spin analysis of the ejected electrons, are used to investigate the dynamics of He(2³ S) deexcitation at solid surfaces. Data for a clean Au(100) surface are presented that show that deexcitation occurs exclusively through resonance ionization followed by Auger neutralization. The electrons involved in Auger neutralization are observed to be correlated in spin and possible reasons for this are discussed. Results obtained at Xe and NO films adsorbed on cooled Au(100) and Cu(100) substrates, respectively, show that He(2³ S) metastable atom deexcitation is analogous to gas-phase Penning ionization. Detailed differences are apparent that can be attributed to effects associated with the underlying substrate and interactions involving neighboring atoms in the film.     

Effect of Cl substituent in the aromatic tetracycline ring on its reactivity with solvated electrons

Decomposition yields of tetracycline hydrochloride /TC.HCl/ and chlorotetracycline hydrochloride /ClTC?HCl/ in methanol solution saturated with Ar or N₂O were determined. Rate constants of the reaction e_s with some antibiotics were obtained: $$\begin{gathered} k/e_s^ - + ClTC \cdot HCl/ = 2 \cdot 49 \times 10^8 dm^3 \cdot mole^{ - 1} \cdot s^{ - 1} ; \hfill \\ k/e_s^ - + TC \cdot HCl/ = 2 \cdot 86 \times 10^8 dm^3 \cdot mole^{ - 1} \cdot s^{ - 1} \cdot \hfill \\ \end{gathered} $$ On the basis of the diffence between decomposition yields: ΔG=G_?TC.HCl^?G?ClTC.HCl′ 7-C?Cl group decomposition yield and the rate constant $$k/e_s^ - + Cl - C - 7/ = 7 \cdot 94 \times 10^8 dm^3 \cdot mole^{ - 1} \cdot s^{ - 1} $$ were determined. It was demonstrated by¹H NMR that the radical formed by degradation of 7-C?Cl group is recombined with the H atoms leading to ClTC.HCl being converted into tetracycline hydrochloride /TC.HCl/.     

Infrared luminescence and vibronic coupling in ZnTe:Fe2+

Samples of crystalline ZnTe with different concentrations of iron were prepared by the vertical high-pressure Bridgman method. Absorption and emission spectra were recorded at liquid-helium temperature in the region of the⁵ T ₂(D)⁵ E(D) infrared transitions of substitutional Fe²⁺(d ⁶) ions. In the range between 2400 and 2520 cm^–1 a rich structure is observed showing more lines than predicted by plain crystal-field theory. The explanation of all these lines is found after introducing a vibronic Jahn-Teller term to the Hamiltonian. A linear coupling between the doubly degenerate vibrational mode to the electronic orbitals of the ionic multiplet⁵ D is added to the electronic and vibrational terms of the Hamiltonian. A diagonalization follows using just one free parameter: the Jahn-Teller energy representing the strength of the coupling. The corresponding value is 3 cm^–1, which is identical to the one already reported for CdTe Fe²⁺. The calculated spectrum is in good agreement with the one determined experimentally. Measurements of the absorption spectra support conclusions drawn earlier about a Jahn-Teller coupling also for the excited multiplet. Finally a prediction of how the far-infrared would look like is also given.     

Analysis and control of maritime transit traffic through the İstanbul Channel: a simulation approach

This study involves a functional simulation model for the maritime transit traffic in the İstanbul Channel that investigates the Channel Traffic Rules and Regulations, vessel types, cargo characteristics, meteorological and geographical conditions, pilotage and tugboat services. The simulation model mainly focuses on the transit traffic in the Channel. This study provides a platform to analyze the effects of factors such as Rules and Regulations, number of tugboats and pilots, vessel type, traffic density and meteorological conditions on the maritime traffic in the Channels. Results obtained and reported in the study clearly indicate some interesting relationships among these factors. As the effect of five factors on eight responses are examined, the most significant factor is determined as number of pilots and tugboats in the service, while the second effective factor is the arrival rate of vessels.     

Visible‐Light‐Driven Water Oxidation with a Polyoxometalate‐Complexed Hematite Core of 275 Iron Atoms

Although metal oxide nanocrystals are often highly active, rapid aggregation (particularly in water) generally precludes detailed solution‐state investigations of their catalytic reactions. This is equally true for visible‐light‐driven water oxidation with hematite α‐Fe₂O₃ nanocrystals, which bridge a conceptual divide between molecular complexes of iron and solid‐state hematite photoanodes. We herein report that the aqueous solubility and remarkable stability of polyoxometalate (POM)‐complexed hematite cores with 275 iron atoms enable investigations of visible‐light‐driven water oxidation at this frontier using the versatile toolbox of solution‐state methods typically reserved for molecular catalysis. The use of these methods revealed a unique mechanism, understood as a general consequence of fundamental differences between reactions of solid‐state metal oxides and freely diffusing “fragments” of the same material.