Spatial and Electronic Structures of BeB8 and MgB8: How far Does the Analogy Go?

Doping boron clusters with Be and its heavier alkaline-earth congener, Mg, usually leads to complexes of different geometry and electronic structure. In this work we show that both neutral BeB₈ and MgB₈ exhibit a singlet ground state umbrella-like form. In addition, the stability, electronic structure, and aromaticity of the target molecules are compared. The magnetically induced current densities show that BeB₈ and MgB₈ are double aromatic systems: π and σ electrons induce strong diatropic currents. The current densities induced in the studied complexes are of very similar intensity, but with a different spatial distribution. The differences in the current density patterns observed for BeB₈ and MgB₈ arise from the very nature of the bonding interactions between the M atom and B₈ fragment, as demonstrated through the energy decomposition analysis.     

Optimal strong Mal’cev conditions for congruence meet-semidistributivity in locally finite varieties

Locally finite, congruence meet-semidistributive varieties have been characterized by numerous Mal’cev conditions and, recently, by two strong Mal’cev conditions. We provide three new strong Mal’cev characterizations and a new Mal’cev characterization each of which improves the known ones in some way.     

Composition of the essential oil of Geocaryum cynapioides (Guss.) L. Engstrand

Volatile constituents from two fresh samples of the subendemic Geocaryum cynapioides (Guss.) L. Engstrand (Apiaceae) obtained by hydrodistillation were analyzed by GC and GC-MS. Forty four and one hundred-twenty three constituents identified in the oils accounted for 98.7 % and 98.4 % of the total oils, respectively. The major component of both oils was (E)-β-farnesene (73.3 % and 57.7 %) while the other major contributors were: (E,E)-α-farnesene (4.8 % and 14.6 %) and trans-sesquisabinene hydrate (12.2 % and 3.0 %). The constituents endo-fenchyl acetate, and three sesquiterpene lactones belonging to the selinane (callitrisin) and guaiane (grilactone and jalcaguaianolide) series, with a rather restricted natural occurrence, were present in only one of the samples (4.7 %, trace amount, 0.1 %, 0.5 %, respectively) and completely absent from the other distinguishing so the two samples. A chemotaxonomic discussion of the results is presented.     

Feasibility of the internal standardization in direct determination of arsenic in wine samples by inductively coupled plasma atomic emission spectrometry

In this study, a fast and simple method is proposed for determination of arsenic in wine employing inductively coupled plasma atomic emission spectroscopy and internal standard technique. First Co, Bi, V and Y were evaluated as internal standards to minimize transport interferences. All samples and reference solutions were automatically spiked by autosampler, eliminating the need for manual dilutions. The result demonstrated that vanadium can be used as an internal standard. The experimental parameters (plasma power and nebulization flow rate) were optimized. The relative standard deviations (R.S.D) of measurements varied from 1.1 to 6.0% and 3.2 to 8.7% (n = 12) with and without internal standardization, respectively. Recoveries in the 95-103% range for As spiked samples were obtained.     

Pulse perturbation technique for determination of piroxicam in pharmaceuticals using an oscillatory reaction system

A simple and reliable novel kinetic method for the determination of piroxicam (PX) was proposed and validated. For quantitative determination of PX, the Bray-Liebhafsky (BL) oscillatory reaction was used in a stable non-equilibrium stationary state close to the bifurcation point. Under the optimized reaction conditions (T = 55.0°C, [H₂SO₄]₀ = 7.60×10^?2 mol L^?1, [KIO₃]₀ = 5.90×10^?2 mol L^?1, [H₂O₂]₀ = 1.50×10^?1 mol L^?1 and j ₀ = 2.95×10^?2 min^?1), the linear relationship between maximal potential shift ΔE _m , and PX concentration was obtained in the concentration range 11.2–480.5 μg mL^?1 with a detection limit of 9.9 μg mL^?1. The method had a rather good sample throughput of 25 samples h^?1 with a precision RSD = 4.7% as well as recoveries RCV ≤ 104.4%. Applicability of the proposed method to the direct determination of piroxicam in different pharmaceutical formulations (tablets, ampoules and gel) was demonstrated.      

ICP-AES analysis of metal content in shell of mussel Mytilus galloprovincialis from Croatian coastal waters

Metal content in samples of shell of mussel Mytilus galoprovincialis was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). The efficiency of conversion of crude samples into solution by acid digestion in an open plate and in a microwave oven was examined by use of certified reference material of marine sediment and laboratory made standards of calcite and aragonite. Influence of high Ca content matrix on emission intensities of Al, Ba, Cd, Cu, Fe, Mg, Mn, Na, Ni, Pb, Sr and Zn was observed as depression of emission signal for most of the measuring elements, ranging from 0.8% to 8%. Greater values were noted at Ba and Ni emission lines. Enhancement of signals was observed for Na and Mg lines. The determination of As, Sb, Se and Sn was performed by HG/ICP-AES. The greater abundance of Sn was found in samples collected near the Al-processing industry centre. No detectable concentrations of As, Sb, and Se were found in shell samples. Results of ICP-AES metal analysis showed that samples collected near harbours, city waste or sewage outlets, and chemical industry centres indicate the certain level of contamination. It is shown that shell analysis provides useful data in determination of marine environment status.     

Unusual N,Se-heterocycles with cyclic Se–N+ bond of isoselenazolopurinium type

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Applicability of alkyl-bonded ultra-pure silica stationary phases for gradient reversed-phase HPLC of folates with conventional and volatile buffers under highly aqueous conditions

Applicability of several alkyl-bonded silica stationary phases was tested for gradient RP-HPLC of folates under highly aqueous conditions. High retention of folates was achieved on alternative phases with enhanced polarity and classical phases with higher carbon content. Phases exhibiting polar secondary interactions were found to provide better selectivity for late-eluting folates, whereas selectivity for early-eluting folates was mostly dependent on hydrophobic interactions. Best selectivity in phosphate buffered mobile phase was achieved on polar-endcapped silica phases (Aquasil C18 and HyPurity Aquastar) followed by alternative Atlantis dC18. Classical phases exhibited poorer separation of 10-formyl-folic acid and 5-formyl-tetrahydrofolate, but it could be considerably improved by increasing the buffer pH. Strong secondary interactions of ion-exchange character on polar-embedded phases resulted in marked peak deterioration, loss of recovery and dramatic changes in retention behaviour for early- and late-eluting folates when changing the mobile phase composition and pH. Therefore, polar-embedded phases such as HyPurity Advance were found to be unsuitable for separating folates. Stationary phases exhibited peak deterioration when using volatile buffer of low ionic strength. Better results were obtained with classical phases, whereas alternative phases showed not only peak deterioration but also a decrease in recovery and poorer selectivity due to increased secondary interactions in volatile buffer.     

Study of Thin Oxide Films by Electron, Ion and Synchrotron Radiation Beams

 Titanium oxide and zirconium oxide thin films deposited on silicon substrates were characterised using electron probe microanalysis (EPMA), Rutherford backscattering spectroscopy (RBS), time-of-flight elastic recoil detection analysis (TOF-ERDA) and scanning photoelectron microscopy (SPEM). The composition and mass thickness of the films were determined and the results of different methods compared. It was revealed that the synchrotron radiation used for SPEM studies caused considerable modification of zirconia films grown at low temperatures.     

Extraction of lutetium(III) from aqueous solutions by employing a single fibre‐supported liquid membrane

Transport behaviour of Lu(III) across a polypropylene hollow fibre‐supported liquid membrane containing di(2‐ethylhexyl)phosphoric acid (DEHPA) in dihexyl ether as a carrier has been studied. The donor phase was LuCl₃ in the buffer solution consisting of 0.2 M sodium acetate at pH 2.5–5.0. A miniaturised system with a single hollow fibre has been operated in a batch mode. The concentration of Lu(III) was determined by indirect voltammetric method using Zn–EDTA complex. The effect of pH and volume of the donor phase, DEHPA concentration in the organic (liquid membrane) phase, the time of extraction and the content of the acceptor phase on the Lu(III) extraction and stripping behaviour was investigated. The results were discussed in terms of the pertraction and removal efficiency, the memory effect and the mean flux of Lu(III). The optimal conditions for the removal of ¹⁷⁷Lu(III) from labelled ¹⁷⁷Lu‐radiopharmaceuticals were discussed and identified. The removal efficiency of Lu(III) greater than 99% was achieved at pH of the donor phase between 3.5 and 5.0 using DEHPA concentration in the organic phase of 0.47 M and the ratio of the donor to the acceptor phase of 182.