Use of an electrostatic preconcentration system to identify interferences in atomic-absorption spectrometry

Interference effects can be identified by deviations from ideality of the slopes of the concentration curves generated with an electrostatic trapping system. The technique is employed to detect spectral interferences in atomic-absorption measurements, due to the presence of sodium chloride, and caused by imperfect background correction. The electrostatic trap is found to be a particularly convenient means of obtaining the required concentration curves because the device gives a ready control of the concentration factor, reliable performance for a range of different solutions, and ease of use in dealing with the necessary number of samples.     

Structure and dynamics of radicals in zeolite matrices: ESR and theoretical studies

Amine radical cations of the type R₃N^·+ and [R₃NCH₂]^·+, R=CH₃, C₃H₇, and nitric oxide, NO, have been used to probe the bonding to the surface and the dynamics of the radicals trapped in the confined space of cages or channels in the zeolite. Regular continuous-wave electron spin resonance (ESR) was employed to study the internal motion of the cation radicals formed by γ-irradiation of amines and related ammonium ions, introduced during the synthesis of the zeolites Al-offretite, SAPO-37, SAPO-42 and AlPO₄-5. The ESR spectra of [(CH₃)₃NCH₂]^·+ radical cation in several studied systems changed reversibly with temperature, indicating dynamical effects. Free rotation about the >N?CH₂ bond of the [(CH₃)₃NCH₂]^·+ species was found to occur in the temperature range of 110 to 300 K, while the rotation about the >N?CH₃ bonds was hindered. The observations confirm the theoretical prediction on the basis of density functional theory calculations, which indicate that the corresponding barriers are of the order of 0.3 and 7 kJ/mol, respectively. The radical cations of the type R₃N^·+ with R=C₂H₅, C₃H₇ were found to undergo a different type of dynamics, involving a two-jump process of the methylene hydrogens next to the nitrogen. A cage or channel size effect on the stability and molecular dynamics was inferred in some cases. Pulsed ESR was employed to study the (NO)₂ triplet-state dimers in Na-A type zeolite, with the purpose to resolve the interaction with surface groups, and to elucidate the role of the zeolite on stabilizing the triplet rather than the usual singlet state. Measurements performed at 5 K gave rise to Fourier transform spectra that were assigned to the dimer species interacting with one or more²³Na nuclei, with approximative parameters A(²³Na)=(4.6, 4.6, 8.2) MHz and Q(²³Na)=(?0.3, ?0.3, 0.6) MHz for the hyperfine and nuclear quadrupole coupling tensors, respectively. The values are of similar magnitude as those determined for the NO?Na⁺ complex. The stability of the triplet-state structure was attributed to unusual geometric structure imposed by the zeolite matrix, with the N?O bonds along a line as in [O?N?Na⁺?N?O], which according to UHF ab initio calculations has a triplet ground     

A Taxicab geometry quantification system to evaluate the performance of in silico methods: a case study on adenosine receptors ligands

Journal of Computer-Aided Molecular Design - Among still comparatively few G protein-coupled receptors, the adenosine A2A receptor has been co-crystallized with several ligands, agonists as well as...     

Experimental and computational investigations of cadmium(II) complexes incorporating 2-benzoylpyridine

Three novel cadmium(II) complexes of 2-benzoylpyridine [Cd(bopy)₂Cl₂] (1), {[Cd(bopy)(μ_1,1-N₃)₂]·bopy}_n (2) and [Cd(bopy)₂(SCN)₂] (3) were synthesized and characterized by spectroscopic and crystallographic methods. Azide ions of 2 act as bridging ligands generating a 1D chain running along [0 1 0]. The zig-zag chains consisting of {Cd(bopy)(N₃)₂} units are separated by 2-benzoylpyridine molecules. The fluorescence properties of the complexes 1, 2 and 3 were examined both in solid state and solution, and compared with the free ligand. Additionally, the electronic spectrum of 3 were investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ.     

Anwendung radioaktiver Indikatoren zur quantitativen Bestimmung nichtmetallischer Einschlüsse in Stahl

Es werden Methoden zur Bestimmung und zur Untersuchung der Quellen von nichtmetallischen Einschlüssen im Stahl sowie einige Ergebnisse der radiometrischen Untersuchungen dargestellt.

Die Erfahrungen mehrjähriger eigener Forschungen in der Industrie und ein ausführliches Studium der Weltliteratur wurden zu einer Systematik und kritischen Diskussion der angewandten Methoden herangezogen. Es wurden optimale Verfahren zur quantitativen Bestimmung der Oxideinschlüsse sowie zur Feststellung ihrer Herkunft (z. B. aus der feuerfesten Ofenauskleidung, dem Stichloch, der Rinne, der Gießpfanne oder der Kokillenschlacke) ausgewählt.

Besprochen werden Probleme des Tracers (Art, Menge, Zustand, Aktivität), der jeder Einschlußquelle entsprechenden Markierungsmethode, der Probennahme, der chemischen Verarbeitung des Probenmaterials und des radiometrischen Meßverfahrens (einschließlich einer evtl. Aktivierung).

Abschließend wird eine Methode zur Bestimmung von bei der Desoxydation des Stahls entstehenden Einschlüssen kurz dargestellt.     

Optical and X-ray Fluorescence Spectroscopy Studies of Bone and Teeth in Newborn Rats After Maternal Treatment with Indinavir

An experiment estimating influence of antiviral drug indinavir treatment during pregnancy on bones and teeth development in newborn rats was performed. Two different fluorescence noninvasive spectroscopy techniques, i.e . laser (407 nm)-induced fluorescence method to characterize the organic fluorescent molecules and X-ray fluorescence analysis to determine mineral components were used to study the surface response of femur, mandible and incisor during their formation in the first month of a rat's life. Differences in autofluorescence depending on the form of the bone were observed on the basis of the emission from enamel in 7-, 14- and 28-day-old newborn rats. The dependence between decrease in intensity of fluorescence and increase in mineralization with age in newborn rats was observed. An enhancement of the autofluorescence and a decrease in the concentration of Ca as a main element, as well as disturbances in the concentration of Zn as trace element were observed for bone as well as teeth in newborns during the first month of their life after maternal administration of indinavir (500 mg kg⁻¹ P.O.) in comparison with the control group. The results indicate that indinavir causes a delay in development of the skeleton and teeth in newborn rats.     

Calorimetric and spectroscopic studies characterization of newborn rat’ blood serum after maternal administration of cyclophosphamide

Differential scanning microcalorimetry (DSC) and UV–VIS absorption spectroscopy were used to obtain the characteristics of blood serum from newborn rat’ after maternal treatment with cyclophosphamide in comparison with control. The obtained DSC curves reveal a complex endothermic peak due to the unfolding process of various serum proteins. Thermal profiles and absorption spectra of blood serum are sensitive to the age of newborns as well as to effect of maternal administration of cyclophosphamide. The most significant disturbances in serum proteome were observed for 14-day old newborns. The thermodynamic parameters: enthalpy change (∆H), the normalized first moment (M₁) of the thermal transition with respect to the temperature axis and the ratio of C _p^ex at 70 and 60 °C describing denaturation contributions of globulin forms in respect to unliganded albumin with haptoglobin was estimated. Moreover, the second derivative spectroscopy in the UV region was used to resolve the complex protein spectrum. The differences in blood serum detected by DSC and UV–VIS confirm a potential usefulness of these methods for diagnostic and monitoring changes with age as well as the pathological state of blood serum.     

X-Ray Crystal Structure of Betulin–DMSO Solvate

Abstract  

Betulin is a lupane triterpenoid [lup-20(29)-ene-3β,28-diol, C₃₀H₅₀O₂] showing high biological activity. This activity is supposed to be strongly affected by the molecular structure of its polymorphic forms. Different solvate polymorphic forms of betulin have aroused increasing interest as the possible anticancer agents of natural origin. X-ray diffraction was used to investigate crystal structure of (1:1) betulin–DMSO solvate. Title compound crystallizes in the orthorhombic P2₁2₁2₁ space group. Unit cell parameters are as follows: a = 7.0006(2) ?, b = 12.1623(3) ?, c = 33.6991(8) ?, Z = 4. Crystal packing and selected geometric parameters are described. It has been found that the hydrogen bonding and the dipole–dipole interaction between DMSO molecules play the major role in the formation of the crystal structure.