Harald B. Steen

Wavelength dependence of the quantum yield of fluorescence and photoionization of indoles

The fluorescence quantum yields φf (λx) of L‐tryptophan and indole were measured relative to that of Rhodamine B as functions of the excitation wavelength λx between 200 and 300 nm. Two different experimental geometries produced identical results, indicating that experimental artifacts were negligible. In aqueous solution at 296 K, φf (λx) increased by 45% for both solutes in going from 230 to 260 nm. Outside this wavelength region, φf (λx) was constant to within 2%. Similar results, although with a somewhat smaller shift in φf (λx), were obtained for tryptophan in an equivolume mixture of ethylene glycol and water EG/H2O at both 296 and at 113 K, the latter temperature being below the glass transition temperature of this medium. The emission spectra and the phosphorescence to fluorescence ratios were independent of λx, indicating that the shift in φf (λx) was not due to intersystem crossing from higher excited states. The shift in φf (λx) was accompanied by a considerable increase in the quantum yield of...

Uptake of hematoporphyrin derivative and sensitized photoinactivation of C3H cells with different oncogenic potential

Four types of mouse embryo fibroblast cells of different oncogenic potential were investigated with respect to uptake of the tumor localizing agent hematoporphyrin derivative (Hpd) and sensitized photoinactivation. Cell size and cellular content of Hpd were measured simultaneously for single cells by means of flow cytofluorimetry. The more malignant cell types had a slightly higher porphyrin uptake per unit cellular volume than the untransformed type, while the photosensitivity of cells incubated with Hpd was equal for all the cell types. Since Hpd seems to concentrate in membranes, this may be related to the fact that the membrane areas of malignant cells are relatively larger than that of untransformed cells, due to the presence of more microvilli. The present study indicates that the preferential localization of Hpd in tumors, as well as the high efficiency of phototherapy reported in the literature, are due to extracellular differences between the tumors and normal tissue.

Temperature dependence of a process competing with S/sub 2/--S/sub 1/ internal conversion in indole and phenol in aqueous solutions

The drop in phi/sub f/ with decreasing excitation wavelength, previously attributed to ionization from the S/sub 2/ state, increases substantially with increasing temperature for both indole and phenol in aqueous solution. Addition of 2-propanol to the solvent reduces the drop in phi/sub f/ but not its activation energy which on the other hand depends significantly on the solute. phi/sub eaq/-measured upon excitation of the S/sub 2/ state of indole in H/sub 2/O increases from 0.09 at 25/sup 0/C to 0.17 at 65/sup 0/C. The results are interpreted in terms of an intermediate charge transfer to solvent state (CTTS) populated from S/sub 2/. In the 2-propanol-water solvent the formation of this CTTS state appears to be governed primarily by interaction of the excited solute with water molecules. (auth)

Flow Cytometry of Bacteria: Cell Cycle Kinetics and Effects of Antibiotics

Flow cytometric determination of the DNA and protein content of E. coli has been carried out by means of a microscope-based flow cytophotometer with a high pressure arc lamp excitation ligh source. Fluorescence (DNA)/light scatter (total cell protein) dual parameter histograms with a resolution cv of 5% were obtained for cells labeled with a combination of mithramycin and ethidium bromide. Histograms of E. coli in rapid and slow exponential growth are presented to exemplify how the cell cycle kinetics of bacteria can be studied in much more detail than has been possible by other methods. Significant effects of chloramphenicol and penicillin on the cell cycle distribution and cell numbers of E. coli cultures were evident after one hour of culture. The data provided information on which parts of the cell cycle and what types of processes were affected by the drug. It appears that flow cytometry may become a valuable tool in studies of the cell cycle of bacteria as well as in clinical drug testing.

Radioluminescence of H2O and D2O ice

The luminescence emitted during x‐ray irradiation of H2O and D2O ice at 77 K exhibits an identical emission band peaked at 373 nm. D2O also exhibits a band peaked at 534 nm which is not seen for H2O. The 373 nm band appears to have a decay time in the range 10−4–10−3 sec, whereas the 534 nm band decays completely in less than 10−4 sec. The emission yield is G∼2×10−2 and G∼2×10−3 for D2O and H2O, respectively. The yield of the peak at 373 nm is significantly increased by NaCl, NaBr, NaI, and HCl in concentrations above 10−3M, whereas the 534 nm band in D2O is not affected by any of these additives. AgNO3, H2O2, and NaNO3 reduce the emission yield whereas other efficient electron and OH scavengers like CCl3COONa and acrylamide do not affect the luminescence even in concentrations of 1M. The identity of the luminescent species is obscure. The scavenger effects indicate that it has a mobile precursor which is not electrons or OH and probably not H atoms. The emission yields, as well as the decay time of the 3...

Observation of x-ray- and U.V.-induced luminescence and absorption during and after the irradiation

Abstract An apparatus is described by which the X-ray- and U.V.-induced emission and absorption of solutions and solid materials can be studied during, as well as after, irradiation at any temperature between 77 and 330 K. Fluorescence and phosphorescence spectra can be obtained separately and simultaneously. The emission spectra of phenanthrene observed during irradiation with X-rays and U.C. light at 77 K are compared, and the kinetics of the formation and decay of trapped electrons in a glycol + water glass, as observed during and after irradiation with X-rays and intense U.V. light, are demonstrated.

Electron scavenging in ethylene glycol-water glass at 4 and 77K: Scavenging of trapped vs mobile electrons

Abstract Electron scavenging efficiencies have been measured at 77 and 4 K in ethylene glycol-water glass for the following scavengers which span a 250-fold range of scavenger efficiencies at 77 K: HCl, NaNO 3 and K 2 CrO 4 . The range of scavenging efficiencies decreases to 62 at 4 K with the largest relative change occurring for the less efficient scavengers. These results are suggested to be most consistent with a model in which scavenging occurs by tunneling from shallowly and deeply trapped electrons at 4 and 77 K, respectively.

Polarity effects on wavelength dependence of the fluorescence quantum yield for indole

Abstract The change in fluorescence quantum yield for indole as a function of excitation wavelength between 250 and 220 nm is found to vary with the static dielectric constant of various alcohol—water mixtures at 296 K. The supports the intermediacy of a CTTS state in the photoionization process.

Mechanisms of x-ray-induced excitation. Effect of scavengers on the radioluminescence of glassy solutions

The luminescence of indole and tryptophan in EG/H2O glass at 77 K during irradiation with x rays and uv light has been studied with various concentrations of two electron scavengers (acrylamide and trichloroacetate). The two types of radiation gave identical emission spectra except for a considerable enhancement of the phosphorescence to fluorescence ratio with x irradiation. The effect of the scavengers on the yields of x‐ray‐induced singlet (S) and triplet (T) levels were calculated from the results. It was found that the yield versus scavenger concentration curves could be decomposed into two components, one being independent of the scavenger, the other one decreasing exponentially with increasing scavenger concentration. Associating the former component with excitation directly from the ground state and the latter with excitation resulting from recombination between solute cations and electrons, it was found that about 80% of the solute excitation is due to recombination. In the case of indole the ratio of triplets to singlets T/S formed by direct excitation was T/S=0.2, whereas for the recombination T/S=1.2. The latter value was attributed primarily to spin relaxation of the recombining ion pairs, whereas intersystem crossing between highly excited levels and recombination in spurs appeared to be of minor importance in this respect. The spin relaxation of the recombining ions, the large scavenger concentrations needed to quench recombination, and the observation that T/S was independent of the LET of the radiation indicated that the recombining ions are closely associated so that the ion pair may be comparable to the CTTS states involved in photoionization of solutes rather than to pairs of free separate ions.

The effect of čerenkov light in the radiation-induced luminescence of aqueous solutions

Abstract The yield of luminescence from indole in an equivolume mixture of glycol and water observed during irradiation with 60 Co γ-rays is found to be considerably larger than that obtained during exposure to 220 kV X-rays. The difference is attributed to the γ-induced Cerenkov light which is absorbed by the solute and thereby causes additional luminescence. Thus, about 80 percent of the singlet excitation in a 10 −2 mol dm −3 indole solution is due to this effect. The yields of the fluorescence and phosphorescence induced by Cerenkov light are determined as a function of solute concentration. The yield of Cerenkov light in water is calculated as a function of the radiation energy for various sample sizes. The results indicate that because of this effect radiations having sufficient energy to produce Cerenkov light are not suited for studies of radiation-induced solute excitation in systems where energy transfer from the solvent does not contribute to the luminescence yield.