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231.
Magdalena Stevanović Igor Savanović Vuk Uskoković Srečo D. Škapin Ines Bračko Uroš Jovanović Dragan Uskoković 《Colloid and polymer science》2012,290(3):221-231
A simple and green chemical method has been developed to synthesize stable bare and capped silver nanoparticles based on the
reduction of silver ions by glucose and capping by poly(α,γ,l-glutamic acid) (PGA). The use of ammonia during synthesis was avoided. PGA has had a dual role in the synthesis and was used
as a capping agent to make the silver nanoparticle more biocompatible and to protect the nanoparticles from agglomerating
in the liquid medium. The synthesized PGA-capped silver nanoparticles in the size range 5–45 nm were stable over long periods
of time, without signs of precipitation. Morphological examination has shown that the silver nanoparticles had a nearly spherical,
multiply twinned structure. The effects of the reaction temperature and the reaction time during the synthesis were investigated
too. The biocompatibility of the PGA-capped silver nanoparticles is discussed in terms of in vitro toxicity with human intestinal
Caco-2 cells. The samples were characterized by UV–Visible spectroscopy, field emission scanning electron microscopy, transmission
electron microscopy, and zeta potential measurements. 相似文献
232.
Magdalena Makarska-Bialokoz 《Journal of fluorescence》2012,22(6):1521-1530
The association between water-soluble porphyrins: 4,4′,4″,4?-(21?H,23?H-porphine-5,10,15,20-tetrayl)tetrakis-(benzoic acid) (H2TCPP), 5,10,15,20-tetrakis(4-sulfonatophenyl)-21?H,23?H-porphine (H2TPPS4), 5,10,15,20-tetrakis[4-(trimethylammonio)phenyl]-21?H,23?H-porphine tetra-p-tosylate (H2TTMePP), 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21?H,23?H-porphine tetra-p-tosylate (H2TMePyP), the Cu(II) complexes of H2TTMePP and H2TMePyP, as well as chlorophyll a with caffeine (1,3,7-trimethylxanthine) has been studied analysing their absorption and emission spectra in aqueous (or acetone in case of chlorophyll a) solution. During the titration by caffeine the porphyrins absorption spectra undergo the evolution – the bathochromic effect can be observed as well as the hypochromicity of the Soret maximum. The association constants were calculated using curve-fitting procedure (KAC of the order of magnitude of 103?mol-1). Whereas the emission spectra point at the presence of the fluorescence quenching effect testifying for the partial inactivation of the porphyrin molecule. The fluorescence quenching constants were calculated from Stern-Volmer plots. The results obtained show that caffeine can interact with water-soluble porphyrins and through formation of stacking complexes is able to quench their ability to emission. 相似文献
233.
234.
Motivated by the long-standing unresolved enigma of the relaxor ferroelectric ground state, we performed a high-resolution heat capacity and polarization study of the field-induced phase transition in the relaxor ferroelectric single crystal Pb(Mg_{1/3}Nb_{2/3})O_{3} (PMN) oriented along the [110] direction. We show that the discontinuous evolution of polarization as a function of the electric field or temperature is a consequence of a true first order transition from a glassy to ferroelectric state, which is accompanied by an excess heat capacity anomaly and released latent heat. We also find that in a zero field there is no ferroelectric phase transition in bulk PMN at any temperature, indicating that the nonergodic dipolar glass phase persists down to the lowest temperatures. 相似文献
235.
Magdalena Wilk Jan Janczak Veneta Videnova‐Adrabinska 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(9):o351-o354
The asymmetric unit of the title compound, 3C10H12N22+·2C10H11N2+·8C6H5NO5P−, contains one and a half naphthalene‐1,5‐diaminium cations, in which the half‐molecule has inversion symmetry, one 5‐aminonaphthalen‐1‐aminium cation and four hydrogen (5‐carboxypyridin‐3‐yl)phosphonate anions. The crystal structure is layered and consists of hydrogen‐bonded anionic monolayers between which the cations are arranged. The acid monoanions are organized into one‐dimensional chains along the [101] direction via hydrogen bonds established between the phosphonate sites. (C)O—H...Npy hydrogen bonds (py is pyridine) crosslink the chains to form an undulating (010) monolayer. The cations serve both to balance the charge of the anionic network and to connect neighbouring layers via multiple hydrogen bonds to form a three‐dimensional supramolecular architecture. 相似文献
236.
Magdalena A. ZaŁuska–Kotur Filip Krzyżewski StanisŁaw Krukowski 《Journal of Crystal Growth》2012,343(1):138-144
Step meandering during the growth of gallium nitride crystal is studied on using kinetic Monte Carlo method. Cause of instability is identified to be the particle advection caused by the step flow. Growth process is conducted in N-rich conditions and GaN(0001) surface kinetics is modeled by setting jump probabilities for Ga atoms adsorbed at the surface. We show that at low enough temperatures and relatively high external particle fluxes periodic regular pattern of meanders is created with its wavelength inversely proportional to the particle flux. An increase of the meander amplitude saturates after some period and further crystal grow is stationary, creating “finger-like” structure. For medium fluxes regular structure of meanders builds up for low or zero value of Schwoebel barrier. For higher fluxes wavelengths of meanders become shorter than the terrace width and they start to grow independently and finally transfer the surface to a rough structure. For very low fluxes or at relatively high temperatures steps move steadily remaining their initial shapes of straight, parallel lines. 相似文献
237.
Jeanina Pandele Cusu Adina Magdalena Musuc Mihaela Matache Dumitru Oancea 《Journal of Thermal Analysis and Calorimetry》2012,110(3):1259-1266
In this study, the thermal stability and exothermal decomposition of some ketone-2,4-dinitrophenylhydrazones have investigated using the DSC technique. The synthesized and purified crystalline solids are thermally stable and start to decompose after melting. Non-isothermal DSC curves, recorded at several heating rates, were used to evaluate the melting properties and the kinetics of thermal decomposition. The isoconversional and model-fitting methods were applied to determine the activation parameters from the common analysis of multiple curves measured at different heating rates. Based on the results of the model??free method, a kinetic model was derived, and the kinetic parameters were obtained by means of a multivariate nonlinear regression. The results are discussed in relation to the effect of the ketone structure. 相似文献
238.
The lubricants based on vegetable oils, as environmental friendly, are urgently sought. However, in addition to ecological characteristics, the lubricating properties have to be met. To meet these requirements the active additives influencing the lubricating properties and oxidation resistance are used. The useful lifetime of lubricants is determined largely by their abilities to resist oxidation. The article presented the results of new, ecological lubricants development. The oxidation performances of different developed lubricants have been tested. The experimentally determined oxidation stability of the compositions based on vegetable oils are presented. Analysed oxidation onset temperature was obtained from the differential scanning calorimetry (DSC) curves, which provides the rapid prediction of the oxidative stability of lubricants. Besides the lubricating composition based on vegetable oils, the developed greases-based mineral, or synthetic oil were investigated. The properties of these greases were evaluated using the measurement of parameters describing structure (penetration) and resistance to high temperature (dropping point). The lubricating properties of both the greases and vegetable oil compositions were tested on four-ball testing machine. In the results of the modelling of the lubricating properties the neural network models for the both types of the lubricants were developed. A discussion of the research results and analysis of models validity is given below. The experimental results are compared with the calculated using the neural models. An acceptable agreement was achieved. 相似文献
239.
Ceborska M Zimnicka M Pietrzak M Troć A Koźbiał M Lipkowski J 《Organic & biomolecular chemistry》2012,10(27):5186-5188
The formation of different complexes of folic acid depending on the size of the host cyclodextrin resulting in either an exclusion compound (with the smallest α-cyclodextrin) or 2-rotaxane, where cyclodextrin is threaded over folic acid (with β- and γ-cyclodextrins), is presented. The formation is carried out in water which allows both possible application in pharmaceutical sciences and usage of environmentally friendly "green chemistry". The obtained compounds are thoroughly characterized using one and two dimensional NMR, mass spectrometry, differential scanning calorimetry and thermogravimetric analysis. 相似文献
240.
We study a class of numerical methods for a system of second-order SDE driven by a linear fast force generating high frequency
oscillatory solutions. The proposed schemes permit the use of large step sizes, have uniform global error bounds in the position
(i.e. independent of the large frequencies present in the SDE) and offer various additional properties. This new family of
numerical integrators for SDE can be viewed as a stochastic generalisation of the trigonometric integrators for highly oscillatory
deterministic problems. 相似文献