Stabilities and coordination modes of histidine in copper(II) mixed-ligand complexes with ethylenediamine,diethylenetriamine or N,N,N′,N″,N″-pentamethyldiethylenetriamine in aqueous solution

Solution equilibrium studies on the Cu(II)–polyamine–histidine ternary systems (polyamine: ethylenediamine (en), diethylenetriamine (dien), N,N,N′,N″,N″-pentamethyldiethylenetriamine (Me₅dien)) have been performed by pH-potentiometry, UV–Vis spectrophotometry and EPR methods. The obtained results suggest the formation of the mixed-ligand complexes with [Cu(A)(His)]⁺ stoichiometry in all studied systems. Additionally, in the systems with dien and Me₅dien protonated [Cu(A)(H–His)]²⁺ species also exists in acid solution. Our spectroscopic results indicate the tetragonal geometry for the [Cu(en)(His)]⁺, the geometry slightly deviated from square pyramidal for the [Cu(dien)(His)]⁺ and strongly deviated from square pyramidal towards trigonal bipyramidal for the [Cu(Me₅dien)(His)]⁺ species. The coordination modes in these mixed-ligand complexes are discussed.     

Identification of volatiles from pineapple (Ananas comosus L.) pulp by comprehensive two-dimensional gas chromatography and gas chromatography/mass spectrometry

Combining qualitative data from the chromatographic structure of 2-D gas chromatography with flame ionization detection (GC×GC-FID) and that from gas chromatography-mass spectrometry (GC/MS) should result in a more accurate assignment of the peak identities than the simple analysis by GC/MS, where coelution of analytes is unavoidable in highly complex samples (rendering spectra unsuitable for qualitative purposes) or for compounds in very low concentrations. Using data from GC×GC-FID combined with GC/MS can reveal coelutions that were not detected by mass spectra deconvolution software. In addition, some compounds can be identified according to the structure of the GC×GC-FID chromatogram. In this article, the volatile fractions of fresh and dehydrated pineapple pulp were evaluated. The extraction of the volatiles was performed by dynamic headspace extraction coupled to solid-phase microextraction (DHS-SPME), a technique appropriate for slurries or solid matrices. Extracted analytes were then analyzed by GC×GC-FID and GC/MS. The results obtained using both techniques were combined to improve compound identifications.     

Improved standardization in reversed-phase high-performance liquid chromatography using 1-nitroalkanes as a retention index scale

A retention index scale based on 1-nitroalkanes was introduced for reversed-phase high-performance liquid chromatography. The retention behaviour of nitroalkanes was examined using two different ODS-silica columns. The nitroalkanes are stable compounds having high UV absorbances at 200-220 nm. The correlation between the logarithm of the capacity factor and the carbon number was linear from the second homologue. The compounds up to 1-nitrohexane are easily available commercially, and they cover the retention range for the majority of toxicologically relevant substances. The retention indices of several test compounds showed that the scale based on 1-nitroalkanes is comparable to that based on alkyl aryl ketones, and additionally may cover the early eluted compounds, for which reference compounds on the alkyl aryl ketone scale are not available.     

XPS and ionic conductivity studies on Li1.3Al0.15Y0.15Ti1.7(PO4)3 ceramics

Li_1.3Al_0.15Y_0.15Ti_1.7(PO₄)₃ compound was synthesized by solid-state reaction, and ceramics were sintered. The surfaces of the ceramics were investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. Li_1.3Al_0.15Y_0.15Ti_1.7(PO₄)₃ samples were tested in solid galvanic cells Ag|O₂+CO₂|Li₂CO₃|Li_1.3Al_0.15Y_0.15Ti_1.7(PO₄)₃|LiMnO₂+Mn₂O₃|O₂|Ag. The electromotive force measurements of this cell indicated that investigated samples are practically pure Li-ion conductors. Impedance spectroscopy studies have been performed in the frequency range 10^?2–3·10⁹ Hz and temperatures from ?57 °C to 334 °C. Three dispersion regions related to Li⁺ ionic transport in bulk, grain boundaries of the ceramics and to polarization of electrodes have been found. Total conductivity changes according to Arrhenius law in the studied temperature range, but an anomalous behavior was observed for the bulk conductivity of the ceramics.     

On the Existence of a Classical Optimal Solution and of an Almost Strongly Optimal Solution for an Infinite-Horizon Control Problem

We consider an infinite-horizon optimal control problem with the cost functional described either by an integral over an unbounded interval (a Lebesgue integral) or by a limit of integrals (an improper Lebesgue integral). We prove some theorems on the existence of solutions to such problems. The proofs are based on appropriate lower closure theorems and some extensions of Olech’s theorem on the lower semicontinuity of an integral functional; these extensions cover the cases of functionals described by an integral over an unbounded interval and by a limit of integrals.     

Thermal stability and impedance spectroscopy studies of (Cu, Ni) substituted Bi4V2O11 ceramics

Polycrystalline samples of the oxygen ion conductor Bi₂V_0.9Cu_0.1−xNi_xO_5.35 with various contents of nickel (0 ≤ × ≤ 0.1) were investigated. The X-ray powder diffraction revealed the tetragonal structure of all compositions. DTA curves exhibit effects due to phase transition, one endothermic effect during heating and one exothermic one during cooling. The impedance of the ceramics with Pt electrodes was measured in the frequency range 10⁻¹–10⁷ Hz at constant temperatures between 350 and 920 K. The conductivity was determined by nonlinear least-squares analysis of the impedance spectra. Separation of the total resistance into grain interior and grain boundary components was feasible at temperatures below 580 K. The transition temperatures observed in DTA coincide with those observed in conductivity measurements. A phase transition, involving a reordering process of the oxygen ions is considered to be responsible for this phenomenon. The frequency dependent part of the intragrain conductivity was modeled by a constant phase admittance. The effective hopping rate was estimated by comparing the frequency dependent part and the dc limit of the intragrain conductivity. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997.     

Poor reproducibility of in-source collisional atmospheric pressure ionization mass spectra of toxicologically relevant drugs

The purpose of the study was to examine the intra- and interlaboratory reproducibility of mass spectra obtained with liquid chromatography-atmospheric pressure ionization mass spectrometry (LC--API-MS) both in electrospray (ESI) and atmospheric pressure chemical ionization (APCI) modes. Toxicologically relevant drugs of different polarity were selected as test substances: morphine-6-glucuronide, 6-monoacetylmorphine, codeine, lysergic acid diethylamide, methylenedioxymethamphetamine. The study was performed in two laboratories using identical instruments and in one using a slightly different instrument. Basic instrument settings and mobile phase were identical in all laboratories. Mass spectra of drugs were taken at four collision energy voltages and using mobile phase of different composition (four concentration levels of acetonitrile and of ammonium formate buffer). The experiments demonstrated that mass spectra of given drugs, obtained in identical conditions with identical instruments, may show very different degrees of fragmentation. Mass spectra obtained with different instruments differed profoundly not only in the degree of fragmentation, but also different fragments and adducts were observed. Short-term intralaboratory reproducibility of mass spectra was satisfactory. On the other hand, the long-term experiments showed different degrees of fragmentation of APCI-generated mass spectra at nominally identical fragmentation energy. The changes in the composition of the mobile phase (concentration of organic modifier or buffer molarity) did not affect the reproducibility of fragmentation to any relevant degree. The study showed that the interlaboratory exchange and use of mass spectrum library, generated by single-quadrupole (LC--API-MS instruments, is hardly feasible at the moment, even under very carefully standardized conditions.