252Cf plasma desorption mass spectrometric study of interactions of steroid glycosides with amino acids

252Cf Plasma desorption with time-of-flight mass spectrometry (TOF-PDMS) has been applied to comparative studies of the interactions of steroid glycosides (SGs) of the spirostan series with amino acids. SGs can interact with amino acids to form heteroclusters of the type [SG + aminoacid + H](+) and [SG + aminoacid + K](+). It is shown how the affinity of SGs for amino acids depends on the structures of both the SG carbohydrate chain and the SG aglycone, and on the nature of the amino acid side chain. Copyright 2000 John Wiley & Sons, Ltd.     

Determination of the content and localization of magnesium in bioapatite of bone

Using x-ray diffraction, electrothermal atomization atomic absorption spectroscopy, and scanning electron microscopy with an x-ray microanalysis, we have studied the phase decomposition of biogenic and synthetic Mg-containing apatite at 900°C with formation of β-tricalcium-magnesium phosphate (β-TCMP). Employing simplified model representations, we obtained a relation that couples the initial Mg concentration with the degree of transformation of apatite into β-TCMP. It is shown that for the β-TCMP contents measured in bioapatite samples and on replacement of calcium by magnesium to about 8% in this phase the calculated range of Mg concentrations coincides with that available in literature sources (0.2–0.6 wt. %). A comparative investigation of the products of decomposition of biogenic and synthetic apatite by the methods of analysis of the composition and structure has established that the formation of β-TCMP is limited by both the insufficient concentration of magnesium and the small sizes of the crystals. The results of the investigations carried out together with the experimental data known from the literature are indicative of the nonuniform distribution of magnesium in the bulk of crystals of biogenic and synthetic apatite, with its predominant localization at the surface sites of the lattice. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 821–826, November–December, 2005.     

Observation of an interedge magnetoplasmon mode in a degenerate two-dimensional electron gas

We study the propagation of edge magnetoplasmons by time-resolved current measurements in a sample which allows for selective detection of edge states in the quantum Hall regime. At filling factors close to nu=3 we observe two decoupled modes of edge excitations, one of which is related to the innermost compressible strip and is identified as an interedge magnetoplasmon mode. From the analysis of the propagation velocities of each mode the internal spatial parameters of the edge structure are derived.     

Dynamics of Si-H vibrations in an amorphous environment

We present results of the first vibrational photon-echo, transient-grating, and temperature dependent transient-bleaching experiments on a-Si:H. Using these techniques, and the infrared light of a free electron laser, the vibrational population decay and phase relaxation of the Si-H stretching mode were investigated. Careful analysis of the data indicates that the vibrational energy relaxes directly into Si-H bending modes and Si phonons, with a distribution of rates determined by the amorphous host. Conversely, the pure dephasing appears to be single exponential, and can be modeled by dephasing via two-phonon interactions.     

Fast electrostatic sweep of a mass spectrum in permanent-magnet mass spectrometers

As was shown earlier [1], in a permanent-magnet mass spectrometer, one can record mass spectra in a considerably wide range of mass numbers by using several specially arranged collectors. This scheme is easy to implement in magnetic mass analyzers with an angle of rotation other than 180°.     

X‐ray diffraction studies of bone apatite under acid demineralization

The analysis of the X‐ray diffraction line broadening used to determine bone apatite crystallite size and lattice microstrain can provide information about the substructure of the bone mineral under differing real or simulated conditions. The paper discusses modifications in the bioapatite crystals observed in the bone subjected to demineralization in a 0.1 N HCl solution. Planar oriented specimens of mature bone with the analyzed surface normal to the longer bone axis were treated for varied immersion times. The crystallite size and the lattice microstrain were determined simultaneously by Fourier analysis of the X‐ray diffraction line profiles. Both were observed to decrease during the acid demineralization. These findings support the idea that the distribution of lattice imperfections in the bulk of bioapatite crystals is highly nonuniform, with crystallite surface regions richer in imperfections dissolving more readily. In addition, an approach is proposed suitable for rough estimation of the reaction front advancement by demineralization‐induced variations in the integrated intensity or shift in the position of the (002) and (004) diffraction lines. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermal behavior of biogenic apatite crystals in bone: An X‐ray diffraction study

The thermal behavior of the bovine bone mineral and synthetic stoichiometric hydroxyapatite was investigated by X‐ray diffraction. The bone samples in solid (planar oriented pieces) and in powder form were examined to elucidate how the microstructural and textural properties of bone mineral are modified under heating. As could be expected, the thermal behavior of the bone mineral depends not only on the structural distortions, but also on the crystal habit, texture and ordering of biocrystals in tissue. The temperature growth of biogenic apatite crystals, unlike synthetic hydroxyapatite, is seen to be nonmonotonic and multi‐staged. At 600 to 700°C the biomineral crystallites grow rapidly due to disappearance of the mosaic structure as the lattice imperfections are annealed. After heating between 700°C and 900°C the bone mineral appears to be composed of roughly equidimensional ≥200 nm crystals. The further growth of the crystals in the range from 900 to 1300°C occurs by the mass transport mechanism, supporting the idea that the bone mineral is not a discrete aggregation of crystals, but rather a continuous mineral phase with direct crystal‐crystal bonding. Estimates are presented to show the important role of the surface mass transport mechanism in the growth of apatite crystals. The material obtained by heating a cortical bone fragment between 900°C and 1300°C turns out to be composed of two crystal types: crystals oriented along the bone axis (major morphology) and those of differing shape and orientation (minor morphology). The heating‐induced variations in the longitudinal and transverse dimensions of differing‐morphology crystals are found to be coherent. Small amounts of CaO, MgO and other crystalline phases are seen to be formed in the bone mineral under heating. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Thermodynamic characteristics of small water clusters

Physicotechnical Institute of Low Temperatures, Academy of Sciences of the Ukrainian SSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 29, No. 5, pp. 89–94, September–October, 1988.