On the equivalence of acidic centers in H-beta zeolites tested by Fries rearrangement of phenyl acetate

The heterogeneously catalyzed liquid phase Fries rearrangement reaction of phenyl acetate was carried out on Beta zeolites reexchanged with different amounts of metal cations. The aim of this work was to determine the influence of the amount of Brønsted acid sites as the catalytic active centers on the conversion. Sodium and potassium ions as well as divalent calcium and zinc ions were used in the reexchange procedure. The conversion shows a linear dependency on the degree of ion reexchange following the theoretically expected values. So the results prove that the bridged hydroxyl groups are indeed the dominating active centers and that their strength seems to be independent of the degree of reexchange; consequently, their acidic strength should be identical. A special emphasis was placed on the reexchange with divalent metal ions. It was shown that one divalent ion is not able to replace two protons as is supposed to be necessary for the charge balance—so a 1:1 stoichiometry is needed to assume to explain the catalytic results.     

Intracellular transport and localization of microsomal cytochrome P450

The cytochrome P450 (P450) enzymes are mainly localized to the endoplasmic reticulum (ER), where they function within catalytic complexes metabolizing xenobiotics and some endogenous substrates. However, certain members of families 1–3 were also found in other subcellular compartments, such as mitochondria, plasma membrane, and lysosomes. The physiological function of these enzymes in non-ER locations is not known, although plasma-membrane-associated P450s have been described to be catalytically active and to participate in immune-mediated reactions with autoantibody formation that can trigger drug-induced hepatitis. Several retention/retrieval mechanisms are active in the ER retention of the P450s and inverse integration of the translated P450 into the ER membrane appears to be responsible for transport to the plasma membrane. Furthermore, hydrophilic motifs in the NH₂-terminal part have been suggested to be important for mitochondrial import. Phosphorylation of P450s has been described to be important for increased rate of degradation as well as for targeting into mitochondria. It was also suggested that the mitochondria-targeted P450s from families 1–3 could be active in drug metabolism using an alternative electron transport chain. In this review we present an update of the field emphasizing studies concerning localization, posttranslational modification, such as phosphorylation, and intracellular transport of microsomal P450s.     

Some intriguing items in the history of scientific balances

The short survey covers the development of the balance since its invention in the Neolithic era. Scales have been used most probably first as tools in trading, but already in Old Egyptian papyrus its use in techniques is documented. Its theory was cleared by Aristotle and Archimedes and at least at that time it was used as a scientific instrument. Today the balance is still the most widely used instrument in science and there are still improvements.     

Theoretical studies on the infrared spectrum of the tetrahedral molecules R<Subscript>2</Subscript>MH<Subscript>2</Subscript> (R = D(H), CH<Subscript>3</Subscript>, OH; M = Ti,Zr, Hf)

Using Stuttgart/Dresden effective core potentials MWB28, MWB60, and GTO valence basis sets (8s7p6d)/[6s5p3d], (8s7p6d)/[6s5p3d] for Zr and Hf atoms and 6-311++G(3df,3pd) basis set for C, H, O, and Ti atoms, tight convergence criteria geometry optimizations and harmonic frequency calculations are performed at B3LYP and B3LYP/IEF-PCM levels of theory so as to model the gas phase and argon matrix infrared spectra of the tetrahedral molecules R₂MH₂ (R = D(H), CH₃, OH; M = Ti, Zr, Hf). Influence of the transition metal and/or substituent group on the symmetric and asymmetric stretching frequencies of the MH₂ fragment of the R₂MH₂ molecules is investigated at both the levels of theory. The modelling of the argon matrix effect improves the agreement between the calculated frequencies and the experimental ones. The calculated argon matrix to gas phase frequency shifts is compared reasonably to the experimental argon to neon matrix shifts.     

Thermal stability and flame resistance of polypyrrole-coated PET fibres

Electro-conducting doped polypyrrole was deposited by in situ oxidative polymerisation on PET non-wovens. Thermal properties were evaluated by means of DSC and TG in nitrogen and air. Flame resistance tests reveal that coated PET fibres resist to direct contact with fire. By thermal analysis, it was found that PPy reduces the temperature at which thermo-oxidative degradation of PET occurs. Polypyrrole-coated PET non-wovens were heated above the melting point of PET for 30 min. After the heating the fibres become brittle and frail, but SEM observations revealed that they maintained their fibrous shape. A loss of chlorine was found because of intense heating.     

Structures and thermodynamic properties of aluminum oxyhalides: a computational study

The molecular geometries and vibrational frequencies of aluminum oxyhalides, AlOX, and their dimers, (AlOX)₂, have been calculated by MP2 and density functional methods. The monomeric molecules are linear while the dimers have a D _2h -symmetry geometry with a four-membered ring, in which the oxygen atoms serve as bridging ligands. Different thermodynamic properties have been calculated; for AlOBr and AlOI for the first time.     

3,5-Bis(2-hydroxyphenyl)-1<Emphasis Type="Italic">H</Emphasis>-1,2,4-triazole based ligands — protonation and metal complex formation

3,5-Bis(2-hydroxyphenyl)-1H-1,2,4-triazole (H₂L^a) and 4-[3,5-bis(2-hydroxyphenyl)-1H-1,2,4-triazol-1-yl]benzoic acid (H₃L^b) have been prepared, and crystal structure of the intermediate 2-(2-hydroxyphenyl)-4H-1,3-benzoxazin-4-one has been determined. Temperature dependent ¹H NMR spectroscopic measurements of H₂L^a indicated dynamic behavior with the equilibrium between the two asymmetric tautomers. For H₃L^b, pD-dependent ¹H NMR spectroscopic measurements showed small but characteristic shifts in the range of 0 ≤ pD ≤ 1, indicative of a triazole nitrogen atom protonation; the corresponding pK _a of 0.98 ± 0.04 was determined by spectrophotometric titrations. (H₂O, 26°C, 1 M KCl/HCl). Formation of [Fe^III(L^a)]⁺ (pH 2.5) and [Fe^III(L^a)₂]⁻ (pH > 6) was verified by UV-Vis spectroscopy. Complex formation of H₃L^b with Al³⁺ and VO²⁺ was investigated by ¹H NMR spectroscopic titration and cyclic voltammetry, respectively. Single crystals of the phenoxo bridged [V^VO(HL^b)(EtO)]₂·2EtOH were characterized by X-ray structural analysis. Dedicated to Professor Milan Melník on the occasion of his 70th birthday     

Quantification of measurement uncertainty in the sequential determination of <Superscript>210</Superscript>Pb and <Superscript>210</Superscript>Po by liquid scintillation counting and alpha-particle spectrometry

Methodologies for the quantification of measurement uncertainties associated with the determination of ²¹⁰Pb- and ²¹⁰Po-specific activities by liquid scintillation counting (LSC) and alpha-particle spectrometry are presented, and are demonstrated using the soil reference material IAEA-326. Major contributors to the combined uncertainty associated with the measurement result of ²¹⁰Pb were the uncertainties of net count rates in the ²¹⁰Pb energy region of the sample spectrum and in the ²¹⁰Bi energy region of the blank spectrum. The predominant sources of uncertainty in the measurement of ²¹⁰Po were the uncertainties of net count rates in the regions of interest of ²⁰⁹Po and ²¹⁰Po. The relative standard uncertainty of ²¹⁰Po exponentially increases with the time interval between the sampling date and the separation date of Po, and this effect is strongly dependent on the ²¹⁰Po/²¹⁰Pb activity ratio. When the specific activity of ²¹⁰Pb is much higher than that of ²¹⁰Po in the sample, the relative standard uncertainty of the ²¹⁰Po determination increases significantly within a short time interval between the sampling date (or reference date) and the separation date of Po in samples.     

Study of a Monod–Haldene type food chain chemostat with pulsed substrate

In this paper, we introduce and study a model of a Monod–Haldene type food chain chemostat with pulsed substrate. We investigate the subsystem with substrate and prey and study the stability of the periodic solutions, which are the boundary periodic solutions of the system. The stability analysis of the boundary periodic solution yields an invasion threshold. By use of standard techniques of bifurcation theory, we prove that above this threshold there are periodic oscillations in substrate, prey, and predator. Simple cycles may give way to chaos in a cascade of period-doubling bifurcations. Furthermore, by comparing bifurcation diagrams with different bifurcation parameters, we can see that the impulsive system shows two kinds of bifurcations, whose are period-doubling and period-halfing.     

Major flavonoid components of heartsease (<Emphasis Type="Italic">Viola tricolor</Emphasis> L.) and their antioxidant activities

Sephadex LH-20 column chromatography was used to separate flavonoid components in a heartsease methanol extract. One of the main components was identified by NMR as violanthin (6-C-glucosyl-8-C-rhamnosylapigenin). As a first approximation, the other main flavonoid component was considered to be rutin (3-O-rhamnoglucosylquercetin), based on comprehensive comparison of retention times and UV spectra of reference molecules, as well as molecular mass and fragmentation patterns obtained by mass spectrometry. The minor flavonoids were separated by polyamide column and analyzed by LC-MS. The antioxidant capacity of different flavonoid fractions was determined using both Trolox equivalent antioxidant capacity (TEAC) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) in vitro antioxidant assays. The highest electron-donor capacity was found for the major flavonoid component (rutin), whereas one minor component-rich flavonoid fraction exhibited the highest hydrogen-donor activity.