Isometries of a generalized numerical radius

For 0<q<1, the q-numerical range is defined on the algebra M_n of all n×n complex matrices by

W_q(A)={x^∗Ay:x,y∈Cⁿ,∥x∥=∥y∥=1,〈y,x〉=q}.     

Nickel electrodes as a cheap and versatile platform for studying structure and function of immobilized redox proteins

Practical use of many bioelectronic and bioanalytical devices is limited by the need of expensive materials and time consuming fabrication. Here we demonstrate the use of nickel electrodes as a simple and cheap solid support material for bioelectronic applications. The naturally nanostructured electrodes showed a surprisingly high electromagnetic surface enhancement upon light illumination such that immobilization and electron transfer reactions of the model redox proteins cytochrome b₅ (Cyt b₅) and cytochrome c (Cyt c) could be followed via surface enhanced resonance Raman spectroscopy. It could be shown that the nickel surface, when used as received, promotes a very efficient binding of the proteins upon preservation of their native structure. The immobilized redox proteins could efficiently exchange electrons with the electrode and could even act as an electron relay between the electrode and solubilized myoglobin. Our results open up new possibility for nickel electrodes as an exceptional good support for bioelectronic devices and biosensors on the one hand and for surface enhanced spectroscopic investigations on the other hand.     

Fluorescence spectroscopy and thermal relaxation processes of anthracenyl‐labeled polysiloxanes

A fluorescent silicone network was prepared by a hydrosilylation reaction using poly(dimethylsiloxane‐co‐methylhydrogensiloxane) terminated by dimethylhydrogensilyloxy groups, poly(dimethylsiloxane‐co‐methylvinylsiloxane) terminated by dimethylvinylsilyloxy groups and 9‐vinylanthracene, as the fluorescent group. These silicone‐based materials were strongly fluorescent. Steady state emission was a convenient technique to prove that reaction occurred, based on the blue‐shift of the emission from anthracenyl moieties compared with the 9‐vinylanthracene. Thermal transitions were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and by fluorescence spectroscopy, indicating that networks with and without lumophores had similar thermal properties. Networks with and without lumophores had the same swelling capability in toluene. Fluorescence spectroscopy was a more sensitive technique to the onset of the glass transition temperature (T = 145 K) than DSC or DMA. Nevertheless, the crystallization temperature at 192 K was determined more precisely by DSC, and the melting point at 237 K was indentified more clearly by both DSC and DMA. These three techniques provided complementary information about transitions in silicone networks. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 74–81, 2010     

Structural and photophysical properties of anthracenyl and carbazolyl groups in silicone-based polymers

This paper describes a simple methodology to attach luminescent groups (anthracenyl and carbazolyl) to polysiloxanes (silicone), using hydrosilylation reactions between the Si–H groups from the silicone precursor to vinyl derivatives of the lumophores. The photophysical properties of these luminescent silicones were studied using both steady-state and dynamical photoluminescence spectroscopy. A strong correlation was obtained between the structural characteristics of the anthracenyl- and carbazolyl-based polysiloxanes, depending on the amount and the position of the Si–H bonds in the silicone precursors. For sparsely distributed Si–H groups, both the anthracenyl-labeled and carbazolyl-labeled polysiloxanes showed photophysical properties (fluorescence spectrum and fluorescence decays) similar to those of 1-alkyl anthracenyl and 1-alkyl carbazolyl derivatives, respectively. Nevertheless, for closely spaced Si–H groups, emission and decay are different. The presence of excimers was observed for anthracenyl but not for carbazolyl polysiloxanes. This latter observation is quite different from that observed for carbon-based polymers for which the carbazolyl excimer formation is a very common process probably due to the differences in the silicone structure.     

Redox processes of cytochrome c immobilized on solid supported polyelectrolyte multilayers

The heme protein cytochrome c (Cyt-c), immobilized on polyelectrolyte multilayers on a silver electrode, was studied by stationary and time-resolved surface-enhanced resonance Raman (SERR) spectroscopy to probe the redox site structure and the mechanism and dynamics of the potential-dependent interfacial processes. The layers were built up by sequential adsorption of polycations (poly[ethylene imine] (PEI); polyallylamine hydrochloride (PAH)) and polyanions (poly[styrene sulfonate] (PSS)). All multilayers terminated by PSS electrostatically bind Cyt-c. On PEI/PSS coatings, Cyt-c is peripherally bound and fully redox-active. Due to the interfacial potential drop, the apparent redox potential is lowered by 40 mV compared to that in solution. The rate constant for the heterogeneous electron transfer (ET) of ca. 0.1 s(-1) is consistent with electron tunneling through largely ordered PEI/PSS layers. ET is coupled to a reversible conformational transition of Cyt-c that involves a change of the coordination pattern of the heme. Additional (PAH/PSS) double layers cause a broadening of the redox transition and a drastic negative shift of the redox potential, which is attributed to the formation of PSS/Cyt-c complexes. It is concluded that Cyt-c can effectively compete with PAH for binding of PSS, resulting in a rearrangement of the layered structure and a penetration of the PSS-bound Cyt-c into the PAH/PSS double layers. This conclusion is consistent with SERR intensity and quartz microbalance measurements. ET was found to be overpotential-independent and faster than that for PEI/PSS coatings, which is interpreted in terms of specific PSS/Cyt-c complexes serving as gates for the heterogeneous ET.     

Partially pyrolyzed poly(dimethylsiloxane)‐based networks: Thermal characterization and evaluation of the gas permeability

In this investigation, the preparation and characterization of partially pyrolyzed membranes based on poly(dimethylsiloxane) (PDMS) are described. These membranes were obtained by the crosslinking of silanol‐terminated PDMS with multifunctional nanoclusters derived from the reaction of pentaerythritoltriacrylate with 2‐aminoethyl‐3‐aminopropyltrimethoxysilane and the in situ polycondensation of tetraethylortosilicate, followed by the thermal treatment of the resulting membranes at different temperatures. The partially pyrolyzed membranes were characterized with infrared spectroscopy, thermogravimetry, elemental analyses, dynamic mechanical analysis, small‐angle X‐ray scattering, and scanning electron microscopy. The membranes exhibited improvements in the thermal stability and mechanical strength. Even with distinct compositions with respect to the Si/O and Si/C ratios, the flexibility of these materials was maintained. The flux rates of the gases through the membranes were measured for N₂, H₂, O₂, CH₄, and CO₂, at 25 °C. The permeability of the membranes changed with increases in the pyrolysis and oxidation temperatures. These membranes could be described as PDMS chains separated by inorganic clusters. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 299–309, 2007.     

Characterisation of permanent markers by pyrolysis gas chromatography–mass spectrometry

Pyrolysis gas chromatography–mass spectrometry (PyGC-MS) was used as a rapid method for the characterization of permanent marker ink. Twenty-four samples of various colours purchased from different manufacturers were characterised. Four main typologies of polymer-binding medium could be distinguished on the basis of the pyrolysis products, and differentiation between permanent markers of different manufacturers could be accomplished. For some permanent marker samples, PyGC-MS analysis allowed pigment identification as well.     

Studies on the structural heterogeneities of poly(dimethylsiloxane) networks modified with poly(phenylsilsesquioxane)s using small-angle X-ray scattering and dynamical mechanical analysis

In the present investigation the morphological study of self-supported translucent films, constituted of semi-inorganic polymeric materials prepared by sol–gel process from poly(phenylsilsesquioxane) (PPSQ) and poly(dimethylsiloxane) (PDMS), modified by diphenylsilanediol (DPS), phenyltriethoxysilane (PTES) and/or tetraethoxysilane (TEOS), is reported. Small-angle X-ray scattering evidenced phase segregation between PPSQ and PDMS in the PPSQ/PDMS film (M1). The addition of TEOS to the sol, constituted by PPSQ and PDMS, led to morphological changes, characterized by nanoparticles of PPSQ and/or SiO₂ embedded in the PDMS-rich matrix. On its course, the use of diphenylsilanediol and phenyltriethoxysilane mixture, as an additive, led to more homogeneous films in comparison to PPSQ/PDMS.     

A Phthalocyanine‐Based Layered Two‐Dimensional Conjugated Metal–Organic Framework as a Highly Efficient Electrocatalyst for the Oxygen Reduction Reaction

Layered two‐dimensional (2D) conjugated metal–organic frameworks (MOFs) represent a family of rising electrocatalysts for the oxygen reduction reaction (ORR), due to the controllable architectures, excellent electrical conductivity, and highly exposed well‐defined molecular active sites. Herein, we report a copper phthalocyanine based 2D conjugated MOF with square‐planar cobalt bis(dihydroxy) complexes (Co‐O₄) as linkages (PcCu‐O₈‐Co) and layer‐stacked structures prepared via solvothermal synthesis. PcCu‐O₈‐Co 2D MOF mixed with carbon nanotubes exhibits excellent electrocatalytic ORR activity (E_1/2=0.83 V vs. RHE, n=3.93, and j_L=5.3 mA cm^?2) in alkaline media, which is the record value among the reported intrinsic MOF electrocatalysts. Supported by in situ Raman spectro‐electrochemistry and theoretical modeling as well as contrast catalytic tests, we identified the cobalt nodes as ORR active sites. Furthermore, when employed as a cathode electrocatalyst for zinc–air batteries, PcCu‐O₈‐Co delivers a maximum power density of 94 mW cm^?2, outperforming the state‐of‐the‐art Pt/C electrocatalysts (78.3 mW cm^?2).     

Human Nails Permeation of an Antifungal Candidate Hydroalcoholic Extract from the Plant Sapindus saponaria L. Rich in Saponins

We evaluated a hydroalcoholic extract of Sapindus saponaria L. pericarps (ETHOSS), as a candidate to a topical antifungal medicine for onychomycosis. ETHOSS was produced by extracting the crushed fruits in ethanol. The saponin contents were identified and characterized by electrospray ionization mass spectrometry. We measured the in vitro antifungal activity against three dermatophyte fungi, isolated from onychomycosis: Trichophyton rubrum, T. mentagrophytes, and T. interdigitale, using broth microdilution tests. The minimum fungicide concentration of ETHOSS ranged from 195.31 to 781.25 μg/mL. The cytotoxicity of the crude extract was tested on the HeLa cell line, and its ability to permeate into healthy human nails by photoacoustic spectroscopy and Fourier transformation infrared spectrometer (FTIR) spectroscopy by attenuated total reflection. Besides its strong antifungal activity, ETHOSS showed low cytotoxicity in human cells. It was able to permeate and reach the full thickness of the nail in one hour, without the aid of facilitating vehicles, and remained there for at least 24 h. These results suggest that ETHOSS has great potential for treating onychomycosis.