Trevor A. Smith

Early infection and subsequent insulin dependent diabetes

In a study of 58 children under the age of 16 with insulin dependent diabetes (IDDM) and 172 matched non-diabetic controls, infection during the first year of life was associated with a reduction in diabetes risk (odds ratio 0.81, 95% confidence interval 0.67 to 0.98, per infective episode). Decreased exposure to common infections during infancy may be linked with subsequent IDDM.

Chemically induced phosphorescence from manganese(II) during the oxidation of various compounds by manganese(III), (IV) break and (VII) in acidic aqueous solutions

Chemiluminescence was observed during the manganese(III), (IV) and (VII) oxidations of sodium tetrahydroborate, sodium dithionite, sodium sulfite and hydrazine sulfate in acidic aqueous solution. From the corrected chemiluminescence spectra, the wavelengths of maximum emission were 689±5 and 734±5 nm when the reactions were performed in sodium hexametaphosphate and sodium dihydrogenorthophosphate/ orthophosphoric acid environments, respectively. The corrected phosphorescence spectrum of manganese(II) sulfate in a solution of sodium hexametaphosphate at 77 K exhibited two peaks with maxima at 688 and 730 nm. The chemical and spectroscopic evidence presented strongly supported the postulation that the emission was an example of solution-phase chemically induced phosphorescence of manganese(II) thereby, confirming earlier predictions that the chemiluminescence from acidic potassium permanganate reactions originated from an excited manganese(II) species.

Long-lived photoinduced charge separation in a bridged C60-porphyrin dyad

Abstract Long-range photoinduced energy and electron transfer have been investigated in a novel dyad containing a zinc tetraarylporphyrin (PZn) donor and a C60 acceptor separated by a saturated norbornylogous bridge nine sigma bonds in length (PZn-9σ-C60). In non-polar solvents singlet-singlet energy transfer from PZn to C60 is observed but in benzonitrile efficient (> 90%) charge separation occurs with a rate constant of 1 × 1010 sec−1 to yield PZn.+-9σ-C60.−. The charge separated state exhibits a remarkably long lifetime for a dyad of 420 ns. This behaviour is discussed with reference to the energetics, dynamics and orbital symmetry properties of the states involved.

Singlet oxygen quantum yields of potential porphyrin-based photosensitisers for photodynamic therapy

The singlet oxygen formation quantum yield (Phi(Delta)) for solutions of the di-cation, free-base and metallated forms of hematoporphyrin derivative (HpD), hematoporphyrin IX (Hp9) and a boronated protoporphyrin (BOPP) are reported using the method of direct detection of the characteristic phosphorescence following polychromatic excitation. Values of Phi(Delta) for the free-base form of all the porphyrins and the di-cation forms of Hp9 and HpD are in the range of 0.44 to 0.85 in the solvents investigated. Incorporation of zinc ions into the macrocycle reduces Phi(Delta) for all three porphyrins. BOPP facilitates the coordination of certain transition metals (Mn, Co and Cu) compared to Hp9 and HpD and results in a dramatic decrease in Phi(Delta). The experimental data suggest the introduction of low energy charge transfer states associated with the disruption of the planarity of the macrocyclic ring provides alternative non-radiative deactivation pathways. In BOPP, this non-planarity is augmented by the large closo-carborane peripheral substituent groups.

The Effect of pH on the Photophysics and Photochemistry of Di- sulphonated Aluminum Phthalocyanine

Abstract The results of a study of the effect of pH on the photophysics and photochemistry of di-sulphonated aluminum phthalocyanine (AlPcS2) in aqueous solution are presented. The pH dependence of the triplet quantum yield, fluorescence quantum yield, singlet-oxygen quantum yield, triplet lifetime, fluorescence lifetime and apparent dimerization constants is investigated and the results interpreted in terms of the pH dependence of the nature of the axial ligands. Evidence that the aluminum–axial ligand bond strength, rather than dimer binding energy that determines the extent of dimerization is provided by semi-empirical and ab initio calculations. Possible dimer structures obtained using ab initio calculations are discussed.

Growth and spectral analysis of ZnO nanotubes

ZnO nanotubes were fabricated by vapor-phase transport using the mixture of ZnO and graphite powders in air. A self-catalyzed growth mechanism was proposed based on microstructure analysis by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. Raman scattering, integrated photoluminescence, and time-resolved photoluminescence were employed to explore the optical properties and the dynamic process. Combing with crystal structure and the spectral characteristics of the ZnO nanotubes, the charge carrier transport process was discussed.

Tunability Limit of Photoluminescence in Colloidal Silicon Nanocrystals

Luminescent silicon nanocrystals (Si NCs) have attracted tremendous research interest. Their size dependent photoluminescence (PL) shows great promise in various optoelectronic and biomedical applications and devices. However, it remains unclear why the exciton emission is limited to energy below 2.1 eV, no matter how small the nanocrystal is. Here we interpret a nanosecond transient yellow emission band at 590 nm (2.1 eV) as a critical limit of the wavelength tunability in colloidal silicon nanocrystals. In the “large size” regime (d > ~3 nm), quantum confinement dominantly determines the PL wavelength and thus the PL peak blue shifts upon decreasing the Si NC size. In the “small size” regime (d < ~2 nm) the effect of the yellow band overwhelms the effect of quantum confinement with distinctly increased nonradiative trapping. As a consequence, the photoluminescence peak does not exhibit any additional blue shift and the quantum yield drops abruptly with further decreasing the size of the Si NCs. This finding confirms that the PL originating from the quantum confined core states can only exist in the red/near infrared with energy below 2.1 eV; while the blue/green PL originates from surface related states and exhibits nanosecond transition.

Iron(III) tartrate as a potential precursor of light-induced oxidative degradation of white wine: studies in a model wine system.

The potential for iron(III) tartrate to act as a photoactivator in light-induced oxidative degradation of white wine is described. Using a tartaric-acid-based model wine system containing 5 mg/L iron, exposure to light from a xenon arc lamp led to the oxidative degradation of tartaric acid and the production of glyoxylic acid. The critical wavelength of light for the degradation process was found to be below 520 nm. No glyoxylic acid was formed in the absence of iron and/or light. Flint glass offered little protection from the light-induced photodegradation of tartaric acid. Antique Green glass offered more protection but did not stop the photodegradation process.

Photoinduced reduction of catalytically and biologically active Ru(II)bisterpyridine-cytochrome c bioconjugates.

Ruthenium(II)bisterpyridine chromophores were covalently linked to iso-1 cytochrome c from yeast to create light-activated donor-acceptor bioconjugates.

Time-resolved evanescent wave-induced fluorescence anisotropy for the determination of molecular conformational changes of proteins at an interface

We have shown that the molecular conformation of a protein at an interface can be probed spatially using time-resolved evanescent wave-induced fluorescence spectroscopic (TREWIFS) techniques. Specifically, by varying the penetration depth of the evanescent field, variable-angle TREWIFS, coupled with variable-angle evanescent wave-induced time-resolved fluorescence anisotropy measurements, allow us to monitor how fluorescence intensity and fluorescence depolarization vary normal to an interface as a function of time after excitation. We have applied this technique to the study of bovine serum albumin (BSA) complexed noncovalently with the fluorophore 1-anilinonaphthalene-8-sulfonic acid. The fluorescence decay varies as a function of the penetration depth of the evanescent wave in a manner that indicates a gradient of hydrophobicity through the adsorbed protein, normal to the interface. Restriction of the fluorescent probe’s motion also occurs as a function of distance normal to the interface. The results are consistent with a model of partial protein denaturation: at the surface, an adsorbed BSA molecule unfolds, thus optimizing protein–silica interactions and the number of points of attachment to the surface. Further away, normal to the surface, the protein molecule maintains its coiled structure.