Magnetic properties of Fe−Mn−Al alloy system in the FCC disordered phase

In this work we report the experimental studies of Fe?Mn?Al alloys in the FCC disordered phase at room temperature by Mössbauer spectroscopy and X-ray diffraction. In this phase the alloys are antiferromagnetic with a constant mean hyperfine field ( \(\bar H\) ) near 26 kOe in the composition range from 0 to 7.5 at.% Al and 50 to 65 at.% Fe. When the Al or Fe concentration increases, the \(\bar H\) value gradually decreases to zero and the alloy becomes paramagnetic. In the same way when the Al concentration increases the lattice parameter increases linearly but when the Fe concentration increases the lattice parameter remains nearly constant for alloys with 5 at.% Al and decreases for alloys with 10 at.% Al.     

A combination chemical and enzymatic approach for the preparation of azole carboxamide nucleoside triphosphate

Alternative substrates for DNA and RNA polymerases offer an important set of biochemical tools. Many of the standard methods for nucleoside triphosphate synthesis fail in the cases of nonpurine and nonpyrimidine nucleosides. An efficient preparation of the 5'-O-tosylates for both the deoxy- and ribonucleosides enabled preparation of the diphosphate esters by displacement with tris(tetra-n-butylammonium) pyrophosphate. Enzymatic synthesis of the azole carboxamide deoxyribonucleoside triphosphate was based on ATP as the phosphate donor, nucleoside diphosphate kinase as the catalyst, coupled with phosphoenol pyruvate (PEP) and pyruvate kinase as an ATP regeneration system. Ribonucleoside triphosphate synthesis required PEP as the phosphate donor and pyruvate kinase as the catalyst. An optimized purification procedure based upon boronate affinity gel was developed to yield highly purified nucleoside triphosphates. The strategy outlined here provides a new and efficient method for preparation of nucleoside 5'-triphosphate and is likely applicable to a broad variety of base and sugar modified nucleoside analogues.     

Counterion exchange selectivity coefficients at water-in-oil microemulsion interface

The counterion binding at a water/Aerosol-OT (AOT)/heptane microemulsion interface was treated in the context of the pseudo-phase ion exchange formalism. Two approaches were used to determine the selectivity coefficient for copper/sodium counterion binding at the AOT microemulsion interface: measurements of the Cu(II) concentration taken up by the reverse micelle in a Winsor II microemulsion system and steady-state emission quenching measurements of an anionic water-solubilized probe, the tris-(4,4'-dicarboxy-2,2'-bipyridine) ruthenium (II) ion. In addition, the selectivity coefficient for methyl viologen/sodium at the microemulsion surface was determined by the same photophysical technique. The value for copper (II)/sodium exchange (K(Cu/Na)) is 1.1+/-0.3 and that for methyl viologen/sodium (K(MV/Na)) is 0.9+/-0.3. The results show that the pseudo-phase ion exchange model can be used to obtain the selectivity coefficient in a microemulsion system.     

Translational to vibrational energy conversion during surface-induced dissociation of n-butylbenzene molecular ions colliding at self-assembled monolayer surfaces

Translational to vibrational (T-->V) energy conversion in the course of inelastic collisions of n-butylbenzene molecular ions with thiolate self-assembled monolayer (SAM) gold surfaces is studied to better understand internal energy uptake by the hyperthermal projectile ions. The projectile ion is selected by a mass spectrometer of BE configuration and product ions are analyzed using a quadrupole mass analyzer after kinetic energy selection with an electric sector. The branching ratio for formation of the fragment ions m/z 91 and m/z 92, measured over a range of collision energies, is used to estimate the average internal energy with the aid of calculations based on unimolecular dissociation kinetics [Rice-Ramsperger-Kassel-Marcus (RRKM) theory]. The measured T-->V conversion efficiencies (the fraction of the laboratory kinetic energy converted into internal energy) are 11 approximately 12% for dodecanethiolate SAM (H-SAM) and 19 approximately 20% for 2-perfluorooctylethanethiolate SAM (F-SAM), respectively, over ranges of a few 10s of eV. The values are similar to those reported earlier for other thermometer molecules undergoing surface collisions. Chemical sputtering leading to ionization of the surface is a prominent feature of the surface-induced dissociation (SID) spectra of n-butylbenzene acquired using the H-SAM surface but not the F-SAM surface because of the lower ionization energy of the former.     

Fluorescence study of the interaction between metal ions and methyl methacrylate–methacrylic acid copolymers in aqueous solutions: thallium(I), calcium(II), and terbium(III)

 The binding of the cations thallium(I), calcium(II) and terbium(III) to methyl methacrylate– methacrylic acid copolymers with different fractions of acid groups (x) has been studied in aqueous solution at various pH values using the fluorescence of covalently bonded 9-vinyl anthracene as a probe. In all cases, the extent of binding increases as a function of the charge of the polymer with either increasing fraction of carboxylic acids or of pH. However, differences are observed in the behavior of the three cations. With Tl(I), quenching of the anthracene group fluorescence is observed, indicating that the thallium(I) approaches the probe and suggesting that the alkylanthracene is probably in a relatively polar region. Binding constants have been determined from anthracene quenching data and from studies with the fluo-rescent-probe sodium pyrenetetra-sulfonate. Good agreement is obtained between the two methods, and values for the binding constants increase from 250 to 950 M^-1 as x increases from 0.39 to 1. It is suggested that the cation is held in the polyelectrolyte domain, partly by Debye–Hückel effects and partly by more specific interactions. Stronger binding is found with calcium(II) and terbium(III), and in this case increases in fluorescence intensity are observed on complexation due to the anthracene group being in a more hydrophobic region, probably as a result of conformational changes in the polymer chain. In the former case the stoichiometry of the interaction was determined from the fluorescence data to involve two carboxylate groups bound per calcium. Association constants were found using murexide as an indicator of free calcium to vary from 8400 to 37 000 M^-1 as x increases from 0.39 to 1. It is suggested that in this case specific calcium(II)–carboxylate interactions contribute to the binding. With terbium(III), a greater increase in the probe fluorescence intensity was observed than with calcium, and it is suggested that the interaction with the polymer is even stronger, leading to a more pronounced conformational change in the polymer. It is proposed that the terbium(III) interacts with six carboxylic groups on the polymer chain, with three being coordinated and three attracted by electrostatic interactions. Received: 10 June 1997 Accepted: 24 October 1997     

An insight into the mechanisms of the phototoxic response induced by cyamemazine in cultured fibroblasts and keratinocytes

The phototoxicity of cyamemazine (CMZ, Tercian), a neuroleptic of the phenothiazine family, has recently been reported in humans. CMZ has an absorbance maximum at 267 nm (molar absorptivity, 25,800 M(-1) cm(-1)) but a weaker molar absorptivity in the ultraviolet A (UV-A) region. CMZ exhibits a fluorescence with maximum emission at 535 nm and a quantum yield of 0.11. CMZ is a powerful photosensitizing agent toward HS 68 human skin fibroblasts and NCTC 2544 keratinocytes. At a UV-A radiation dose of 10 J/cm2, innocuous to cells in the absence of CMZ, the LD50 (lethal dose corresponding to 50% killing) are 0.5 and 1 microM for the fibroblasts and the keratinocytes, respectively, after overnight incubation with the drug. Short incubation times do not significantly alter the LD50. The CMZ-induced phototoxicity is accompanied by lipid membrane peroxidation consistent with the amphiphilic character of this photosensitizer. Keratinocytes are an order of magnitude less sensitive to the photosensitized lipid peroxidation than fibroblasts. Microspectrofluorometry reveals that lysosomal membranes are major sites of CMZ incorporation into the two cell lines because a Forster-type resonance energy transfer process occurs from CMZ to LysoTracker Red DND99 (LTR), a specific fluorescent probe of lysosomal membranes. The CMZ-photosensitized destruction of LTR demonstrates that CMZ retains its photosensitizing capacity after its lysosomal uptake.