Max Maier

The role of singlet oxygen and oxygen concentration in photodynamic inactivation of bacteria

New antibacterial strategies are required in view of the increasing resistance of bacteria to antibiotics. One promising technique involves the photodynamic inactivation of bacteria. Upon exposure to light, a photosensitizer in bacteria can generate singlet oxygen, which oxidizes proteins or lipids, leading to bacteria death. To elucidate the oxidative processes that occur during killing of bacteria, Staphylococcus aureus was incubated with a standard photosensitizer, and the generation and decay of singlet oxygen was detected directly by its luminescence at 1,270 nm. At low bacterial concentrations, the time-resolved luminescence of singlet oxygen showed a decay time of 6 ± 2 μs, which is an intermediate time for singlet oxygen decay in phospholipids of membranes (14 ± 2 μs) and in the surrounding water (3.5 ± 0.5 μs). Obviously, at low bacterial concentrations, singlet oxygen had sufficient access to water outside of S. aureus by diffusion. Thus, singlet oxygen seems to be generated in the outer cell wall areas or in adjacent cytoplasmic membranes of S. aureus. In addition, the detection of singlet oxygen luminescence can be used as a sensor of intracellular oxygen concentration. When singlet oxygen luminescence was measured at higher bacterial concentrations, the decay time increased significantly, up to ≈40 μs, because of oxygen depletion at these concentrations. This observation is an important indicator that oxygen supply is a crucial factor in the efficacy of photodynamic inactivation of bacteria, and will be of particular significance should this approach be used against multiresistant bacteria.

Electric-field-induced level shifts of perylene in amorphous solids determined by persistent hole-burning spectroscopy

Abstract Small shifts of the electronic levels of perylene in polyvinylbutyral by an electric field are probed by measuring the reversible filling of the center of a persistent spectral hole. The experimental results are explained by a linear electric-field dependence of the level shifts which is ascribed to the interaction of the perylene molecules with the amorphous matrix.

Concentration and temperature dependence of electronic and vibrational energy relaxation of O2 in liquid mixtures

Abstract The energy relaxation of the vibrational 3Σg−(ν = 1) state and the electronic 1Δg(ν′ = 0) state of oxygen in liquid mixtures with Ar and N2 was investigated. The normalized electronic relaxation rate shows the same nonlinear concentration dependence as the normalized vibrational relaxation rate. The temperature dependence of the vibrational relaxation in the mixtures is essentially determined by O2O2 interactions. The experimental results are compared with calculations of the energy relaxation, where the liquid mixtures are described in two different ways: by a cell model and by pair distribution functions.

Stokes parameters in the unfolding of an optical vortex through a birefringent crystal.

Following our earlier work [F. Flossmann et al., Phys. Rev. Lett. 95 253901 (2005)], we describe the fine polarization structure of a beam containing optical vortices propagating through a birefringent crystal, both experimentally and theoretically.We emphasize here the zero surfaces of the Stokes parameters in three-dimensional space, two transverse dimensions and the third corresponding to optical path length in the crystal. We find that the complicated network of polarization singularities reported earlier -lines of circular polarization (C lines) and surfaces of linear polarization (L surfaces) - can be understood naturally in terms of the zeros of the Stokes parameters.

Vibrational energy relaxation of O2 in liquid mixtures with Ar and N2

Abstract The relaxation rate of the first vibrational level of O 2 in the electronic ground state was determined in liquid O 2 /Ar and O 2 /N 2 mixtures. Ar and N 2 were found to be inefficient in de-exciting O 2 . The oxygen relaxation rate decreases non-linearly with decreasing O 2 concentration. The experimental results are discussed in terms of a model using the pair distribution functions of liquid mixtures.

Electric field selective optical data storage using persistent spectral hole burning

The electric field domain is used as a storage dimension in optical data storage by persistent spectral hole burning. The memory locations in the electric field domain are addressed with the voltage applied to the sample consisting of the amorphous polymer polyvinyl‐butyral doped with the dye 9‐amino acridine. The information is written by burning spectral holes at different electric field strengths with a HeCd laser and read by detecting the presence or absence of holes with weak laser intensity.

Temperature dependence of vibrational energy relaxation in liquid oxygen

Abstract The energy relaxation of the lowest vibrational level (υ = 1) of liquid oxygen in the electronic ground state was investigated within a wide temperature range (53.4 K ⩽ T ⩽ 96 K). The relaxation time exhibits a peak value of τ′ ≈ 3.1 ms around 65 K and is shorter at lower and higher temperatures. The observed temperature behavior is discussed in view of theoretical models of energy relaxation in liquids.

Propagation dynamics of phase dislocations embedded in a Bessel light beam

Abstract The evolution of an off-axis optical vortex inserted in a propagation invariant J 0 Bessel background beam is studied in a linear medium. Good coincidence of the measured intensity distributions with simulations allows us to derive the phase distribution and topology of the beam. The initial vortex interacts with the edge dislocations of the background beam to form a propagating mixed edge-screw dislocation. Finally we observe the trapping of a stable vortex in the center of the beam. The simple wave vector distribution of the Bessel background beam allows for an interpretation of the propagation dynamics of the dislocations.

Electric-field-induced spectral matrix-shift variations of perylene in non-polar matrices

We determined the electronic level shifts and the effective electric dipole moment differences of perylene in non-polar and polar matrices from the changes of spectral holes in an external electric field. The effective dipole moment differences of perylene in the non-polar matrices polyethylene, solid paraffin oil and n-octodecane are about one order of magnitude smaller than in the polar matrices polyvinylbutyral and butanol. The observed frequency shifts in the non-polar matrices, which depend linearly on the electric field strength, are attributed to electric-field-induced variations of the gas-to-matrix shift of the electronic levels of perylene.

Temperature dependence of the relaxation rate constants of the a 1Δg and b 1Σ +g states of oxygen isotopes

The relaxation rate constants of the low-lying electronic singlet states, a 1Δg and b 1Σ+g , of gaseous natural O2 and of the isotope 18O2 were investigated as a function of temperature from 100 to 295 K. The measured increase of the rate constants with temperature is in good agreement with a theory of electronic-to-vibrational-translational energy transfer. The significant effects of the different electronic states and of the isotope masses on the absolute values of the relaxation rate constants, which range from 1.0× 10−20 to 3.9× 10−17 s−1 molecule−1 cm3 at 295 K, are discussed.