Concentration of hydroxyl groups in dental apatites: a solid-state 1H MAS NMR study using inverse 31P -->1H cross-polarization

The concentration of structural hydroxyl groups in the apatite mineral of enamel, dentin and cementum of healthy human teeth was estimated by reference to stoichiometric hydroxyapatite to be 73 +/- 3, 18 +/- 2 and 18 +/- 1%, respectively.     

Periodic segment implies infinitely many periodic solutions

In this note we show that the existence of a periodic segment for a non-autonomous ODE with periodic coefficients implies the existence of infinitely many periodic solutions inside this segment provided that a sequence of Lefschetz numbers of iterations of an associated map is not constant. In the case when this sequence is bounded we have to impose a geometric condition on the segment to get solutions by use of symbolic dynamics.

     

Identification of degradation products of indigoids by tandem mass spectrometry

The study concerns identification of photodegradation products of indigotin, indirubin and isoindigo. Experimental methodology consists of degradation of standard solutions of indigoids in a solar box and analysis of samples taken at different aging time by using capillary high‐performance liquid chromatography coupled with electrospray ionization tandem mass spectrometric and spectrophotometric detectors. Identification of the formed compounds was based on careful interpretation of the electrospray ionization MS/MS spectra. Apart from the well‐known degradation products of indigoids: isatin, isatoic anhydride and anthranilic acid, another seven species were also identified, and their proposed structures were confirmed by high‐resolution molecular masses measurements; according to the best knowledge of authors, they have not been reported so far. The obtained results formed the basis for postulating mechanism of the process. Moreover, the MRM (Multiple Reaction Monitoring) method was developed for the identification of natural dyes and their degradation products in textiles of historical value. Apart from such colorants as indigotin and flavonoids, also presence of degradation products of indigoids was confirmed. Copyright © 2015 John Wiley & Sons, Ltd.     

11th Conference on Solid and Liquid Crystals—Material Science and Applications

Abstract

The eleventh conference in a series of biennial meetings was organized by Professor Jozef Zmija group from the Institute of Technical Physics WAT, Warsaw, Poland. It was supported by the State Committee of Scientific Research (KBN), the Polish chapter of the International Society for Optical Engineering (SPIE) and the Committee of Crystallography, Polish Academy of Sciences. These conferences have become more international, and this meeting, organized just outside Zakopana, in the Tatra mountains attracted more than 210 scientists, 51 from abroad.     

Dynamical phase transition in a model for evolution with migration

We study a simple quasispecies model for evolution in two different habitats, with different fitness landscapes, coupled through one-way migration. Our key finding is a dynamical phase transition at a critical value of the migration rate, at which the time to reach the steady state diverges. The genetic composition of the population is qualitatively different above and below the transition. Using results from localization theory, we show that the critical migration rate may be very small-demonstrating that evolutionary outcomes can be very sensitive to even a small amount of migration.     

Efficiency of 1H --> 31P NMR cross-polarization in bone apatite and its mineral standards

Human bone mineral was studied using solid-state ³¹P NMR with cross-polarization (CP) from protons. The CP efficiency was determined for trabecular and cortical bone tissue from human adults and compared with synthetic mineral standards. The study shows the similarity between carbonatoapatite of type B and bone mineral as shown by their CP behaviour. The method can be used for the characterization of synthetic apatite-based implant materials.     

Stimulated Brillouin scattering in highly birefringent microstructure fiber: experimental analysis

We report on an experimental analysis of stimulated Brillouin scattering (SBS) in a 20-m-long highly birefringent microstructure fiber for sensing applications. In particular, an experimental setup based on Brillouin optical frequency-domain analysis, operating at a wavelength of 1550 nm, has been employed in order to analyze the distribution of Brillouin frequency shift along the fiber, as well as to study the dependence of Brillouin frequency shift on optical polarization, temperature, and strain. Our results indicate that, for any fixed polarization, the fiber has a dual-peaked Brillouin spectrum. A study about the origin of these two peaks is presented.     

New concepts in bonded functions theory II. Canonical set of high internal symmetry

A new definition of a canonical set of bonded functions has been introduced. For a given configuration with r singly occupied orbitals and given multiplicity, the set exhibits symmetry properties of a group of order r. It simplifies the evaluation of the energy matrix H as well as the orthogonalization procedure.     

Oxygen vacancies at oxide surfaces: ab initio density functional theory studies on vanadium pentoxide

The local electronic structure at the V₂O₅ (010) surface is studied by ab initio density functional theory (DFT) methods using gradient-corrected functionals (RPBE) where embedded clusters as large as V₂₀O₆₂H₂₄, representing one or two crystal layers of the substrate, are used as models. Results of local binding and charging of differently coordinated surface-oxygen sites as well as densities of states allow a characterization of the detailed electronic structure of the surface. Electronic and geometric details of surface-oxygen vacancies as well as hydrogen adsorption are studied by appropriate clusters. A comparison of the data, concerning vacancy energies, charging, geometric relaxation, and diffusion, shows sizeable variations between different oxygen sites and can give further insight into possible mechanisms of surface relaxation and reconstruction. Hydrogen is found to stabilize at all surface-oxygen sites forming surface-OH and H₂O species. As a result, the binding of surface oxygen with its vanadium neighbors is weakened. Therefore, the presence of hydrogen at the oxide surface facilitates oxygen removal and can contribute to the enhanced yield of oxygenated products near vanadia-based surfaces. Received: 10 April 2000 / Accepted: 25 July 2000 / Published online: 7 March 2001     

Mechanistic Insight into Peroxo‐Shunt Formation of Biomimetic Models for Compound II,Their Reactivity toward Organic Substrates,and the Influence of N‐Methylimidazole Axial Ligation

High‐valent iron‐oxo species have been invoked as reactive intermediates in catalytic cycles of heme and nonheme enzymes. The studies presented herein are devoted to the formation of compound II model complexes, with the application of a water soluble (TMPS)Fe^III(OH) porphyrin ([meso‐tetrakis(2,4,6‐trimethyl‐3‐sulfonatophenyl)porphinato]iron(III) hydroxide) and hydrogen peroxide as oxidant, and their reactivity toward selected organic substrates. The kinetics of the reaction of H₂O₂ with (TMPS)Fe^III(OH) was studied as a function of temperature and pressure. The negative values of the activation entropy and activation volume for the formation of (TMPS)Fe^IV?O(OH) point to the overall associative nature of the process. A pH‐dependence study on the formation of (TMPS)Fe^IV?O(OH) revealed a very high reactivity of OOH^? toward (TMPS)Fe^III(OH) in comparison to H₂O₂. The influence of N‐methylimidazole (N‐MeIm) ligation on both the formation of iron(IV)‐oxo species and their oxidising properties in the reactions with 4‐methoxybenzyl alcohol or 4‐methoxybenzaldehyde, was investigated in detail. Combined experimental and theoretical studies revealed that among the studied complexes, (TMPS)Fe^III(H₂O)(N‐MeIm) is highly reactive toward H₂O₂ to form the iron(IV)‐oxo species, (TMPS)Fe^IV?O(N‐MeIm). The latter species can also be formed in the reaction of (TMPS)Fe^III(N‐MeIm)₂ with H₂O₂ or in the direct reaction of (TMPS)Fe^IV?O(OH) with N‐MeIm. Interestingly, the kinetic studies involving substrate oxidation by (TMPS)Fe^IV?O(OH) and (TMPS)Fe^IV?O(N‐MeIm) do not display a pronounced effect of the N‐MeIm axial ligand on the reactivity of the compound II mimic in comparison to the OH^? substituted analogue. Similarly, DFT computations revealed that the presence of an axial ligand (OH^? or N‐MeIm) in the trans position to the oxo group in the iron(IV)‐oxo species does not significantly affect the activation barriers calculated for C?H dehydrogenation of the selected organic substrates.