QUANTUM YIELD OF SINGLET OXYGEN PRODUCTION BY XANTHENE DERIVATIVES

The singlet oxygen quantum yield (φ₁o₂) of 11 purified fluorescein derivatives was determined by reaction with singlet oxygen acceptors in aqueous and ethanolic solutions; in both solvents φ₁o₂ was enhanced with increasing halogenation. Tryptophan and 2,2,6,6-tetramethylpiperidone were found to be unadapted for the determination of φ₁o₂, in our systems; however, the use of 9.10-dipropionic anthracene acid andp-nitrosodimethylaniline in conjunction with imidazole derivatives was suitable for ¹O₂ detection in water. Both methods lead to results in excellent agreement. As in ethanol. φ₁o₂, was equal to the triplet state quantum yield (φ_T), the comparison between the two solvents showed that φ_T in water was greater than in ethanol. The comparison between our values obtained with polychromatic light with published data obtained with monochromatic light suggests that the triplet quantum yield of fluorescein derivatives is wavelength independent.     

Generalized Rouse model for a dilute solution of clustered polymers

A theory analogue to tha of Rouse is given, to describe the rheological behavior of dilute solutions consisting of clusters of crosslinked polymers. The frequency-dependent behavior of the dynamic moduli of these fluids differs substantially from that of the well-known Rouse-like fluid (GG^1/2). In our case the storage modulus becomes proportional to ^3/2, while the loss modulus is proportional to . The loss modulus dominates the dynamic behavior for frequencies smaller than the largest normal frequency of the clusters.     

Steady-state behaviour of flexible rotordynamic systems with oil journal bearings

This paper deals with the long term behaviour of flexible rotor systems, which are supported by nonlinear bearings. A system consisting of a rotor and a shaft which is supported by one oil journal bearing is investigated numerically. The shaft is modelled using finite elements and reduced using a component mode synthesis method. The bearings are modelled using the finite-length bearing theory. Branches of periodic solutions are calculated for three models of the system with an unbalance at the rotor. Also self-excited oscillations are calculated for the three models if no mass unbalance is present. The results show that a mass unbalance can stabilize rotor oscillations.     

TARGETED MUTAGENESIS OF M13 DNA INDUCED BY PHOTOSENSITIZED REACTION

Abstract— Photoacoustic spectroscopy has been used to observe a qualitative depth profile in vitro in mouse skin. Because the photoacoustic response is a vector quantity, it can be used to qualitatively determine the depth of a chromophore in skin. The spectrum of an induced layer of β-carotene in albino mouse skin was separated from the spectrum of hemoglobin. Dyes were then used to determine more precisely the position of the β-carotene in the epidermis. The spectrum of melanin was also separated from that of the underlying hemoglobin in pigmented mouse skin.     

EPR STUDIES ON SINGLET OXYGEN PRODUCTION BY PORPHYRINS

Abstract— EPR studies of the porphyrin-sensitized photooxidation of 2, 2, 6,6-tetramethyl-piperidine to the nitroxide demonstrate that all the porphyrins examined are able to generate ¹O₂, although the efficiency of the photoprocess is dependent on the nature of the side chains. Incorporation of metal ions into the porphyrin molecule depresses or even inhibits the formation of ¹O₂. Comparison of these results with previously obtained kinetic data points out that the efficiency of porphyrins as photosensitizes is controlled by the lifetime of their lowest triplet state.     

PHOTOSENSITIZATION OF AMINO ACIDS BY DI-CYAN-HEMIN: KINETIC AND EPR STUDIES

Abstract— The low spin hemin derivative di-cyan-hemin can sensitize the photooxidation of amino acids. The efficiency of this dye as a photosensitizer is generally lower than that of other porphyrins such as hematoporphyrin in aqueous solution, but it is significantly enhanced by addition of ethanol. On the basis of the identified photooxidation end-products of some amino acids, photooxidation kinetic data and EPR measurements, it appears that methionine is quantitatively converted to methionine sulfoxide by a pure Type II (singlet oxygen) mechanism, whereas in the case of cysteine and tryptophan a mixed Type ILType II mechanism is probably operative.     

EVIDENCE FOR THE PRODUCTION OF SINGLET OXYGEN BY PHOTOEXCITED ACRIDINE ORANGE

Abstract In contrast to previous results obtained with the nitroxide radical detection technique, generation of the specific ¹O₂ oxidation product of cholesterol shows that photoexcited acridine orange produces singlet oxygen.     

Calculation of polarization energies in some III–VII and IV–VI compounds with stereochemically active (ns)2-ions

The polarization energies of AB compounds, with A a monovalent or divalent cation with an (ns)²-lone pair and B an anion with a noble gas electronic configuration, have been calculated to investigate whether the stereochemical activity of the (ns)²-ion can be understood in an ionic picture. Computations have been performed applying the computer program EWALD. Formal ionic charges and partly estimated polarizabilities have been used. The polarization energy is shown to be predominantly due to cation polarization and may constitute an appreciable fraction of the total lattice energy. Hence, it can play a crucial role in the formation of structures, in which the (ns)²-ion is in a noncentrosymmetrical environment.     

PHOTOTOXIC POTENTIALITIES OF TARTRAZINE: SCREENING TESTS

Abstract Tartrazine (TRT) a cosmetics, food and drug additive, was tested with respect to phototoxic potentialities. Although, using the cholesterol technique, TRT did not appear to produce any ¹O₂ upon visible light irradiation, the EPR spin trapping experiments with 5,5-dimethyl-1-pyrroline-N-oxide, as spin trap, were in favour of activated oxygen species (O₂^˙, OH^˙) and hydrated electron production by photoexcited TRT.
Irradiation of TRT with complementary biological systems (nucleic acids, bacteria, biological membranes) showed that few of them can be damaged by this photosensitizer. Tartrazine could induce a weak deoxyribose degradation but did not produce any DNA strand breaks on isolated φXRFI DNA. Tartrazine was detected as mutagen in the Salmonella microsome (Ames) assay, only in conjunction with visible light. In the presence of photoexcited TRT, erythrocyte membranes were damaged by covalently cross-linking proteins.
The tests developed here seem thus to be suitable for detecting any unwanted phototoxic activity associated with potential photosensitizers.     

A multipath model for atmospheric scintillations at microwaves and millimeter waves

The paper describes a deterministic model for the effects of atmospheric turbulences on satellite-earth links from 1 to 100 GHz. Turbulent cells are considered as dielectric volumes crossing the Fresnel's zones of the link. The transmission coefficients are calculated for point receivers as well as for actual aperture antennas. The model yields a transfer function submitted to the influence of the equivalent dielectric constant, the thickness, size, and geometry of the cells, the size of the antenna, and the operating frequency. The resulting group delay is also evaluated, as well as the impulse and step-responses.