DIFFERENTIAL EFFECTS OF TRYPTOPHAN PHOTOPRODUCTS AND H2O2 ON THE GROWTH OF MOUSE EMBRYONIC FIBROBLASTS*

Abstract. Exposure of dilute solutions of L-tryptophan in balanced salt mixtures to near-ultraviolet light (ca. 320–390nm) yield several photoproducts capable of inhibiting the growth of cultured mouse embryonic fibroblasts. Recent literature suggested a need to test the possibility that the major toxic photoproduct is hydrogen peroxide, and therefore several lines of experimentation were pursued. On the basis of chemical and morphological studies and an analysis of the uptake of ³H-thymidine by these cells and its incorporation into their DNA, it is concluded that sufficient hydrogen peroxide could not be generated without the addition of high concentrations of oxygen to influence the growth or DNA synthesis of mouse embryonic fibroblasts.     

Singularity of orbital measures in SU(n)

We show that the minimalk such that μ^κ ∈L ¹(SU(n)) for all central, continuous measures μ on SU(n) isk=n. We do this by exhibiting an elementg∈SU(n) for which the (n−1)-fold product of its conjugacy class has zero Haar measure. This ensures that if μ _g is the corresponding orbital measure supported on the conjugacy class, then μ _g ^n-1 is singular toL ¹. This research is supported in part by NSERC. The hospitality of the University of Waterloo is gratefully acknowledged.     

A study of some parameters relevant to the response of harwell PMMA dosimeters to gamma and electron irradiation

The effects on the radiation response of Harwell polymethylmethacrylate (PMMA) dosimeters of dose-rate, radiation type, temperature during irradiation and post-irradiation storage, and post-irradiation stability, are of importance to the operators of commercial irradiation facilities.

This paper describes recent studies of the effects of some of these parameters on the radiation response of Harwell Red 4034, Amber 3042, and Gammachrome YR Perspex dosimeters, and provides data on batch to batch variation and shelf-life.     

Simultaneous structural and elemental nano-imaging of human brain tissue

Examining chemical and structural characteristics of micro-features in complex tissue matrices is essential for understanding biological systems. Advances in multimodal chemical and structural imaging using synchrotron radiation have overcome many issues in correlative imaging, enabling the characterization of distinct microfeatures at nanoscale resolution in ex vivo tissues. We present a nanoscale imaging method that pairs X-ray ptychography and X-ray fluorescence microscopy (XFM) to simultaneously examine structural features and quantify elemental content of microfeatures in complex ex vivo tissues. We examined the neuropathological microfeatures Lewy bodies, aggregations of superoxide dismutase 1 (SOD1) and neuromelanin in human post-mortem Parkinson''s disease tissue. Although biometals play essential roles in normal neuronal biochemistry, their dyshomeostasis is implicated in Parkinson''s disease aetiology. Here we show that Lewy bodies and SOD1 aggregates have distinct elemental fingerprints yet are similar in structure, whilst neuromelanin exhibits different elemental composition and a distinct, disordered structure. The unique approach we describe is applicable to the structural and chemical characterization of a wide range of complex biological tissues at previously unprecedented levels of detail.

Structural and chemical characterisation of microfeatures in unadulterated Parkinson''s disease brain tissue using synchrotron nanoscale XFM and ptychography.     

Time-resolved infrared spectroscopy of the lowest triplet state of thymine and thymidine

Vibrational spectra of the lowest energy triplet states of thymine and its 2′-deoxyribonucleoside, thymidine, are reported for the first time. Time-resolved infrared (TRIR) difference spectra were recorded over seven decades of time from 300 fs to 3 μs using femtosecond and nanosecond pump-probe techniques. The carbonyl stretch bands in the triplet state are seen at 1603 and 1700 cm⁻¹ in room-temperature acetonitrile-d₃ solution. These bands and additional ones observed between 1300 and 1450 cm⁻¹ are quenched by dissolved oxygen on a nanosecond time scale. Density-functional calculations accurately predict the difference spectrum between triplet and singlet IR absorption cross sections, confirming the peak assignments and elucidating the nature of the vibrational modes. In the triplet state, the C4O carbonyl exhibits substantial single-bond character, explaining the large (70 cm⁻¹) red shift in this vibration, relative to the singlet ground state. Femtosecond TRIR measurements unambiguously demonstrate that the triplet state is fully formed within the first 10 ps after excitation, ruling out a relaxed ¹nπ^* state as the triplet precursor.     

Solvent effects on the steady state photophysics of estrone and 17β-estradiol

Absorption and emission yields for estrone and 17β-estradiol were measured in a variety of room temperature solvents. Molar extinction coefficients were found to not vary as a function of solvent, while fluorescence yields were found to be significantly affected by the polarity and hydrogen-bond accepting ability of the solvent, with the yield for 17β-estradiol being highest in nonpolar, hydrogen-bond donating solvents, and lowest in the nonpolar, hydrogen-bond accepting solvent ethyl acetate. Estrone's emission yield was found to be a factor of ten smaller than 17β-estradiol's. Strong solvent and excitation wavelength dependences were found for the relative amounts of emission between estrone's two emission bands, with increased relative emission occurring in nonpolar aprotic solvents, and under higher excitation energies. These results are interpreted with the aid of vertical excitation energies from time-dependent density functional calculations using both explicit and implicit solvation models.