Electrochemically Tunable Proton-Coupled Electron Transfer in Pd-Catalyzed Benzaldehyde Hydrogenation

Acid functionalization of a carbon support allows to enhance the electrocatalytic activity of Pd to hydrogenate benzaldehyde to benzyl alcohol proportional to the concentration of Brønsted-acid sites. In contrast, the hydrogenation rate is not affected when H₂ is used as a reduction equivalent. The different responses to the catalyst properties are shown to be caused by differences in the hydrogenation mechanism between the electrochemical and the H₂-induced hydrogenation pathways. The enhancement of electrocatalytic reduction is realized by the participation of support-generated hydronium ions in the proximity of the metal particles.     

Plasticized polylactide/clay nanocomposites. II. The effect of aging on structure and properties in relation to the filler content and the nature of its organo‐modification

Plasticized polylactide (PLA) – layered silicate nanocomposites were obtained by melt blending PLA with polyethylene glycol as plasticizer (20 wt %) and with different montmorillonite fillers: Cloisite® 20A, Cloisite® 25A, and Cloisite® 30B (from 1 to 10 wt %). Comparative samples of melt‐blended polylactide (without filler) and plasticized PLA with 20 wt % PEG were considered as well. Samples have been aged for 1 and 4 years and their chemical and physical characteristics were compared with not aged reference ones. It was found that molecular weight of the PLA decreased upon melt‐processing and aging, particularly when the Cloisite content increased, without a clear relation to the nature of the organo‐modifier. On the contrary, the PEG plasticizer was practically undegraded upon melt processing and aging. Structural studies revealed that plasticized PLA and plasticized PLA‐based nanocomposites are unstable in time of aging and undergo deplasticization. They showed, after aging, the presence of a thin PEG crystalline layer at the surface of the samples and improved the order in the PLA matrix to a higher extent in plasticized polylactide than in plasticized nanocomposite (due to clay stabilization effect). The amount of PEG diffusing toward sample surface was correlated with aging time, molecular weight of PLA matrix, and Cloisite® type, in clear relation to the extent of intercalation with PLA and PEG. Some modifications of the viscoelastic properties of PLA matrix, induced by the presence of both the nanoparticlate filler and the plasticizer, as well as a deterioration of the mechanical properties upon aging were observed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 312–325, 2006     

Nonlinear directional couplers with asymmetrical distribution of nonlinearity

An analytical solution is given for the nonlinear directional coupler with asymmetrically placed nonlinearity. It is shown that the distribution of nonlinearity influences the critical power value and changes the transmission characteristics.     

Spectroscopic properties and photodynamic effects of new lipophilic porphyrin derivatives: efficacy, localisation and cell death pathways

Photodynamic therapy (PDT) and photodynamic diagnostics (PDD) of cancer are based on the use of non-toxic dyes (photosensitisers) in combination with harmless visible light. This paper reports physicochemical properties, cell uptake, localisation as well as photodynamic efficiency of two novel lipophilic porphyrin derivatives, suitable for use as PDT sensitisers. Both compounds are characterised by high quantum yield of singlet oxygen generation which was measured by time-resolved phosphorescence. Photodynamic in vitro studies were conducted on three cancer cell lines. Results of cell survival tests showed negligible dark cytotoxicity but high phototoxicity. The results also indicate that cell death is dependent on energy dose and time following light exposure. Using confocal laser scanning microscopy both compounds were found to localise in the cytoplasm around the nucleus of the tumour cells. The mode of cell death was evaluated based on the morphological changes after differential staining. In summary, good photostability, high quantum yield of singlet oxygen and biological effectiveness indicate that the examined lipophilic porphyrin derivatives offer quite interesting prospects of photodynamic therapy application.     

Crystal structure, spectroscopy and thermodynamic properties of MVWO6(M – Li, Na)

In the present work lithium (sodium) vanadium tungsten oxides with brannerite structure is refined by the Rietveld method (space group C2/m, Z=2). IR and Raman spectroscopy was used to assign vibrational bands and determine structural particularities. The diffuse reflectance spectra allow to calculate bandgap for M^IVWO₆(M^I – Li, Na). The temperature dependences of heat capacity have been measured first in the range from 7 to 350 K for these compounds and then between 330 and 640 K, respectively, by precision adiabatic vacuum and dynamic calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity C_p^o(T), enthalpy H^o(T)−H^o(0), entropy S^o(T)−S^o(0) and Gibbs function G^o(T)−H^o(0), for the range from T→0 to 640 K. The differential scanning calorimetry was applied to measure decomposition temperature of compounds under study.     

Destruction of Freon HFC-134a Using a Nozzleless Microwave Plasma Source

In this paper, results of the pyrolysis of Freon HFC-134a (tetrafluoroethane C₂H₂F₄) in an atmospheric pressure microwave plasma are presented. A waveguide-based nozzleless cylinder-type microwave plasma source (MPS) was used to produce plasma for the destruction of Freon HFC-134a. The processed gaseous Freon HFC-134a at a flow rate of 50–212 l min⁻¹ was introduced to the plasma by four gas ducts which formed a swirl flow in the plasma reactor (a quartz cylinder). The absorbed microwave power was 0.6–3 kW. The experimental results showed that the Freon was converted into carbon black, hydrogen and fluorine. The total conversion degree of HFC-134a was up to 84% with selectivity of 100% towards H₂, F₂ and C₂, which means that there was no conversion of HFC-134a into other hydrocarbons. The Freon destruction mass rate and corresponding energetic mass yield were up to 34.5 kg h⁻¹ and 34.4 kg per kWh of microwave energy absorbed by the plasma, respectively.     

Diurnal variability of delta13C and delta18O of atmospheric CO2 in the urban atmosphere of Kraków, Poland

This article presents the results of measurements of the isotopic composition and concentration of atmospheric carbon dioxide, performed on air samples from Kraków (Southern Poland) in different seasons of the year. A simple isotope mass balance model has been applied to determine the contributions of different sources of CO2 to the urban atmosphere of Kraków city: the latitudinal/regional background, biospheric contributions and anthropogenic emissions. The calculations show that during the summer and early autumn the dominant contribution to local CO2 peaks is the biosphere, making up to 20% of atmospheric CO2 during the nocturnal temperature inversion in the lower troposphere. During early spring and winter, anthropogenic emissions are the main local source.     

Analysis of heparan sulfate oligosaccharides with ion pair-reverse phase capillary high performance liquid chromatography-microelectrospray ionization time-of-flight mass spectrometry

Heparan sulfate, a cell surface bound glycosaminoglycan polysaccharide, has been implicated in numerous biological functions. Heparan sulfate molecules are highly complex and diverse, yet deceivingly look simple and similar, rendering structure--function correlation tedious. Current chromatographic and mass spectrometric techniques have limitations for analyzing glycosaminoglycan samples that are in low abundance and that are large in size, due to their highly acidic nature arising from a large number of sulfate and of carboxylate groups. A new methodology was developed using capillary ion-paired reverse-phase C18 HPLC directly coupled to ESI-TOF-MS to address the above issues. On the basis of HS disaccharide analysis, dibutylamine was found to be the best suited for HS analysis among many ion-pairing agents investigated. Next, analysis of oligosaccharides derived from heparosan, the precursor for heparan sulfate, was undertaken to demonstrate its greater applicability in a more complex structural analysis. The established chromatographic conditions enabled the characterization of heparosan oligosaccharides of sizes up to tetracontasaccharide with high resolution in a single run and were amenable to negative ion electrospray MS in which sodium adduction and fragmentation were avoided. To date, these are the largest nonsulfated HS precursor oligosaccharides to be characterized by LC/MS. Finally, the current methodology was applied to the characterization of the biologically important ATIII binding pentasaccharide and its precursors, which differ from each other by sulfation pattern and/or degree of sulfation. All of these pentasaccharides were well-resolved and characterized by the LC/MS system with (34)SO(4) as a mass spectral probe. This newly developed methodology facilitates the purification and rapid characterization of biologically significant HS oligosaccharides, and will thus expedite their synthesis. These findings should undoubtedly pave the way in deciphering multiple functional arrangements, ascribed to many biological activities, which are predictably embedded in a single large chaotic, yet well-organized HS polysaccharide chain. Development of newer techniques for HS oligosaccharide analysis is greatly needed in the postgenome era as attention shifts to the functional implications of proteins and carbohydrates in general and HS in particular.