An EPR study on cytosine irradiated

In this study, paramagnetic centers over the cytosine were formed by photolysis then these centers were investigated using EPR method. EPR signals were not recorded from non‐irradiated the cytosine, but irradiated polycrystalline exhibited complex EPR spectra. For obtaining of cytosine polycrystalline, novel crystallization method was performed on powder cytosine. Effective crystallization conditions were achieved by adjustment of the concentration of the metal ions, chemical solutions, NaCl, KCl, glacial asetic acid, nitric oxide, percloric acid, glutamic acid, and pH of buffer. Cytosine (C₄H₅N₂O) polycrystalline obtained were irradiated with ⁶⁰Co – rays at room temperature for 24 and 72 h. At the sample irradiated for 72 h, the paramagnetic centers were determined between 120 and 450 K by X‐band EPR spectrometer. The spectra were found to be dependent slightly on temperature. Two cation radicals were determined in the structure and these were called Radicals I and II. The g and hyperfine constants were found to be a_H2a = 61 G, a_N2 = 9.39 G, a_N1 = 7.15 G, and g₁=2.0026 for the Radical I; a_H3 = 10.57 G, a_H1 = 3 G, a_N3 = 6.72 G, a_N1 = 5.36 G for, and g₂=2.0034 the Radical II. Copyright © 2010 John Wiley & Sons, Ltd.     

Developing teachers' models for assessing students' competence in mathematical modelling through lesson study

Applications and modelling have gained a prominent role in mathematics education reform documents and curricula. Thus, there is a growing need for studies focusing on the effective use of mathematical modelling in classrooms. Assessment is an integral part of using modelling activities in classrooms, since it allows teachers to identify and manage problems that arise in various stages of the modelling process. However, teachers’ difficulties in assessing student modelling work are a challenge to be considered when implementing modelling in the classroom. Thus, the purpose of this study was to investigate how teachers’ knowledge on generating assessment criteria for assessing student competence in mathematical modelling evolved through a professional development programme, which is based on a lesson study approach and modelling perspective. The data was collected with four teachers from two public high schools over a five-month period. The professional development programme included a cyclical process, with each cycle consisting of an introductory meeting, the implementation of a model-eliciting activity with students, and a follow-up meeting. The results showed that the professional development programme contributed to teachers’ knowledge for generating assessment criteria on the products, and the observable actions that affect the modelling cycle.     

Bodipy–C60 triple hydrogen bonding assemblies as heavy atom-free triplet photosensitizers: preparation and study of the singlet/triplet energy transfer

Supramolecular triplet photosensitizers based on hydrogen bonding-mediated molecular assemblies were prepared. Three thymine-containing visible light-harvesting Bodipy derivatives (B-1, B-2 and B-3, which show absorption at 505 nm, 630 nm and 593 nm, respectively) were used as H-bonding modules, and 1,6-diaminopyridine-appended C₆₀ was used as the complementary hydrogen bonding module (C-1), in which the C₆₀ part acts as a spin converter for triplet formation. Visible light-harvesting antennae with methylated thymine were prepared as references (B-1-Me, B-2-Me and B-3-Me), which are unable to form strong H-bonds with C-1. Triple H-bonds are formed between each Bodipy antenna (B-1, B-2 and B-3) and the C₆₀ module (C-1). The photophysical properties of the H-bonding assemblies and the reference non-hydrogen bond-forming mixtures were studied using steady state UV/vis absorption spectroscopy, fluorescence emission spectroscopy, electrochemical characterization, and nanosecond transient absorption spectroscopy. Singlet energy transfer from the Bodipy antenna to the C₆₀ module was confirmed by fluorescence quenching studies. The intersystem crossing of the latter produced the triplet excited state. The nanosecond transient absorption spectroscopy showed that the triplet state is either localized on the C₆₀ module (for assembly B-1·C-1), or on the styryl-Bodipy antenna (for assemblies B-2·C-1 and B-3·C-1). Intra-assembly forward–backward (ping-pong) singlet/triplet energy transfer was proposed. In contrast to the H-bonding assemblies, slow triplet energy transfer was observed for the non-hydrogen bonding mixtures. As a proof of concept, these supramolecular assemblies were used as triplet photosensitizers for triplet–triplet annihilation upconversion.     

X-band EPR study on benzo[c]cinnoline single crystals

The benzo[c]cinnoline compound has been crystallized in ethanol solution. These crystals have been irradiated with ⁶⁰Coγ-rays at room temperature. The crystals have been investigated by an X-band electron spin resonance (ESR) spectrometer two days after irradiation. Very strong ESR peaks have been observed at the temperatures between 130 and 430 K. However, a line broadening has been observed at 130 K. Also analyses found that EPR specra are temperature-dependent and show anisotropic behaviour.     

Clean and efficient microwave-solvent-free conversion of homochiral amines, α-amino alcohols and α-amino acids to their chiral 2-substituted pyrrole derivatives

Efficient synthesis of 1,2-disubstituted homochiral pyrroles has been achieved by a two-component coupling of chloroenones and amine compounds on the surface of silica gel without any solvent under microwave irradiation.     

On Weighted Estimates of High-Order Riesz-Bessel Transformations Generated by the Generalized Shift Operator

In this paper, we establish sufficient conditions on weights which ensure that high-order Riesz-Bessel transformations generated by the generalized shift operator act boundedly from one weighted Lp-space into another.     

Synthesis and Optical Characterization of Red-Emitting BaTa<Subscript>2</Subscript>O<Subscript>6</Subscript>:Eu<Superscript>3+</Superscript> Phosphors

Undoped and Eu³⁺ doped BaTa₂O₆ phosphors were synthesized via solid state reaction method and characterized by using XRD, SEM-EDS and photoluminescence (PL) analyses. The XRD results revealed that the crystal structure of BaTa₂O₆ allowed up to 10 mol% levels of Eu³⁺ ions due to the TTB characteristic network of adjacent octahedrals. SEM-EDS analyses confirmed the formation of BaTa₂O₆ structure and EuTaO₄ secondary phase. BaTa₂O_6:Eu³⁺ phosphors exhibited orange and red emissions at 592.2 nm and 615.7 nm in the visible region respectively. The Commission Internationale d’Eclairage (CIE) chromaticity coordinates of the BaTa₂O_6:Eu³⁺ phosphors that excited at λ _ex = 400 nm ranged from orangish-red to pinkish-red depending on increasing Eu³⁺ concentration.