Imaging the activity of nitrate reductase by means of a scanning electrochemical microscope

Scanning electrochemical microscopy (SECM) was used to characterize immobilized nitrate reductase (NaR) from Pseudonomonas stutzeri (E.C. 1.7.99.4). Nitrate reductase with membrane fragment was embedded in a polyurethane hydrogel in a capillary and solubilized NaR without membrane fragment was covalently coupled to a diaminoethyl-cellulose-carbamitate film on glass. After systematic studies of possible mediators, SECM feedback imaging of both forms of immobilized NaR was accomplished with methylviologen as redox mediator.     

The anomalous Mössbauer fraction of ferritin and polysaccharide iron complex (PIC)

Mössbauer studies of the ubiquitous protein molecule ferritin and its synthetic biomimic polysaccharide iron complex (PIC) exhibit an anomaly in the Mössbauer spectrum wherein the recoil free fraction orf-factor has a sharp drop with respect to temperature as the temperature rises above 30 K for mammalian ferritin and 60 K for PIC. The anomaly coincides with the disappearance of hyperfine splitting, which is due to superparamagnetic relaxation above the blocking temperature. Different absorbers were used to experimentally investigate the effect of absorber thickness on the Mössbauer spectrum. The anomaly persists for thin absorbers. Also, spectra treated with FFT procedures to eliminate the thickness effect still exhibit this anomaly. Motion of the core with respect to the protein shell was also eliminated as a possible source for this phenomenon, by comparing the Debye temperature obtained from the temperature dependence of thef-factor and the isomer shift. A comparison of the magnetic anisotropy constants from magnetization studies with those obtained by relating the hyperfine fieldH of the Mössbauer spectra to the fluctuations of the magnetization imply that the ferritin and PIC molecules possess magnetic anisotropy energy which may not be strictly uniaxial. This, we believe, may be intimately connected with the mechanism causing thef-factor anomaly.This work was carried out in partial fulfilment of the requirements of the PhD degree at Tufts University.     

New Entrance Optics for Solar Spectral UV Measurements

The investigation of the impact of solar UV radiation on the biosphere requires spectral measurements of solar UV radiation of high accuracy. However, the accuracy of current measurements is limited, and this can partly be attributed to the entrance optics of the instruments used for these examinations. The angular response of spectro-radiometers measuring spectral global UV irradiance should be given by the cosine of the incidence angle. In-tercomparison campaigns have shown that deviations from this ideal cosine response lead to uncertainties in solar measurements of more than 10%. Here we present recently developed entrance optics that reduce these uncertainties to ±4% in the UV. The new entrance optics have been characterized with respect to their angular response, transmission, weather durability, fluorescence and dependence of the angular response on wavelength and polarization. Solar spectroradiometric measurements carried out with the new optics were compared with simultaneously performed measurements of a second spectroradiometer that was equipped with a conventional diffuser. The deviations of up to 12% between both systems are quantitatively explained to within 3%.     

Electromagnetic wormholes and virtual magnetic monopoles from metamaterials

We describe new configurations of electromagnetic (EM) material parameters, the electric permittivity epsilon and magnetic permeability micro, which allow one to construct devices that function as invisible tunnels. These allow EM wave propagation between the regions at the two ends of a tunnel, but the tunnels themselves and the regions they enclose are not detectable to lateral EM observations. Such devices act as wormholes with respect to Maxwell's equations and effectively change the topology of space vis-à-vis EM wave propagation. We suggest several applications, including devices behaving as virtual magnetic monopoles, invisible cables, and scopes for MRI-assisted surgery.     

Pyroxene inclusions in paleo-Christian mosaic tesserae: a new tool for constraining the glass manufacturing temperature

The mineral inclusions of two orange glass tesserae from paleo-Christian mosaics were investigated in order to derive the melting temperature reached during their production (sourced from Padua and Vicenza, Veneto region, Italy). In particular, clinopyroxene crystals were studied by single-crystal X-ray diffraction and electron microprobe WDS analysis. The crystals show C2/c symmetry, typical of disordered Ca/Na and Mg/Al distributions indicating high-temperature of formation (>700°C). The cation site populations were obtained by combining results from the two experimental techniques enabled us to derive the following stoichiometric formula:

Compactness in fuzzy convergence spaces

Lowen and Lowen [Applications of category theory to fuzzy subsets (Kluwer, 1992) p. 153] and Lowen et al. [Fuzzy Sets and Systems 40 (1991) 347] recently introduced the category FCS of fuzzy convergence spaces, a topological quasitopos which is a supercategory of FTS, the category of fuzzy topological spaces. In this paper, compactness in FCS is examined. Doing so we found that to define compactness as an absolute property we had to generalize the definition of fuzzy convergence space to fuzzy subsets. All basic theorems are proved including the Tychonoff product theorem. Based on the theory developed here, in a following publication, a Richardson compactification for fuzzy convergence spaces will be given.     

Electronic Transitions in Different Redox States of Trinuclear 5,6,11,12,17,18-Hexaazatrinaphthylene-Bridged Titanium Complexes: Spectroelectrochemistry and Quantum Chemistry

Multinuclear transition metal complexes bridged by ligands with extended π-electronic systems show a variety of complex electronic transitions and electron transfer reactions. While a systematic understanding of the photochemistry and electrochemistry has been attained for binuclear complexes, much less is known about trinuclear complexes such as hexaphenyl-5,6,11,12,17,18-hexaazatrinaphthylene-tristitanocene [(Cp₂Ti)₃HATN(Ph)₆]. The voltammogram of [(Cp₂Ti)₃HATN(Ph)₆] shows six oxidation and three reduction waves. Solution spectra of [(Cp₂Ti)₃HATN(Ph)₆] and of the electrochemically formed oxidation products show electronic transitions in the UV, visible and the NIR ranges. Density functional theory (DFT) and linear response time-dependent DFT show that the three formally titanium(II) centers transfer an electron to the HATN ligand in the ground state. The optically excited transitions occur exclusively between ligand-centered orbitals. The charged titanium centers only provide an electrostatic frame to the extended π-electronic system. Complete active self-consistent field (CASSCF) calculation on a structurally simplified model compound, which considers the multi-reference character imposed by the three titanium centers, can provide an interpretation of the experimentally observed temperature-dependent magnetic behavior of the different redox states of the title compound in full consistency with the interpretation of the electronic spectra.