Mueller matrix analysis of infrared ellipsometry.

A Mueller analysis has been done of IR ellipsometry performed with imperfect optical components. Equations linking experimental and calculated Fourier coefficients have been derived and consistently solved. Correction routines for permittivity measurements are demonstrated and discussed with gold and SrTiO(3) as examples. It is shown that such effects as interferometer polarization, detector dichroism, transmission, and phase changes in polarizers can be calculated and effectively removed from the spectra. The problems of calibration and multiple reflections between IR polarizers are discussed, and error propagation in permittivity measurements is analyzed.

Infrared ellipsometer for the study of surfaces, thin films, and superlattices.

An automatic infrared ellipsometer for the study of surface and interface phenomena has been constructed. The system is based on a Fourier transform spectrometer that we equipped with an ellipsometer unit. Polarizers and analyzers are of the ion-etched wire-grid type. Their rotation is governed by means of a computer-controlled stepping-motor system. A discussion of calibration procedures for the infrared range is given, and special attention is given to the problem of selecting the best measurement strategy. The polarization state of the reflected beam is determined by measuring the intensity at 72 regularly spaced polarizer/analyzer settings. It is found that the effects of interferometric polarization, beam wandering, and detector dichroism cannot be neglected. However, these error sources have been eliminated by analyzing the zeroth, second, and fourth harmonic components of the azimuthally recorded intensity. Both the multiplex advantage of Fourier transform spectroscopy and the phase sensitivity ofellipsometry are combined in this instrument. Measurements on superconducting films, superlattices, and doped GaAs films are reported.

Light-Harvesting Function in the Diatom Phaeodactylum tricornutum: I. Isolation and Characterization of Pigment-Protein Complexes.

Three pigment-protein complexes were isolated from the marine diatom Phaeodactylum tricornutum (Bohlin) by treatment of thylakoid membrane fragments with 1% Triton X-100 at 4 degrees C followed by centrifugation on sucrose density gradients. The major complex contains chlorophyll a, c(1), c(2), and the carotenoid fucoxanthin (chlorophyll a: c(1): c(2): fucoxanthin = 1.0: 0.09: 0.28: 2.22) bound to an apoprotein doublet of 16.4 and 16.9 kilodaltons. This complex accounts for >70% of the total pigment and 20 to 40% of the protein in the thylakoid membranes. Efficient coupling of chlorophyll c and fucoxanthin absorption to chlorophyll a fluorescence supports a light-harvesting function for the complex. A minor light-harvesting complex containing chlorophyll a, c(1), and c(2) but no fucoxanthin (chlorophyll a: c(1): c(2) = 1.0: 0.23: 0.26) was also isolated at Triton: chlorophyll a ratios between 20 and 40. These pigments are bound to a similar molecular weight apoprotein doublet. The third complex isolated was the P700-chlorophyll a protein, the reaction center of photosystem I, which showed characteristics similar to those isolated from other plant sources. The yield of the chlorophyll a/c-fucoxanthin complex was shown to respond strongly to changes in light intensity during growth, accounting for most of the changes in cellular pigmentation.

Combined electron radiation and hyperthermia. Repair of DNA strand breaks in NHIK 3025 cells irradiated and incubated at 37, 42.5, or 45 degrees C.

Induction of DNA strand breaks by a short electron pulse (18.5 Gy) and the subsequent strand-break rejoining were investigated at hyperthermia (42.5 and 45 degrees C) and at 37 degrees C during irradiation and repair. The cells were irradiated immediately after 2.5 min equilibration (i.e., from 37 to 42.5 or 45 degrees C) to investigate the effect of short-duration hyperthermia on radiation damage and subsequent repair. Due to a high radiation dose rate and a rapid lysis technique, the cells could be kept at the actual temperature during irradiation and repair, and the strand-break frequency could be measured only seconds after irradiation. At all temperatures, a constant or possible increase in the initial number of breaks was observed during the first 7 sec after the electron pulse. At 37 degrees C, strand-break rejoining was nearly complete within 1 hr. Hyperthermia at 42.5 degrees C had only minor influence on the net rate of strand-break rejoining. At 45 degrees C, 50% of the breaks remained after 1 hr. Subsequent incubation for 23 hr at 37 degrees C reduced by half the number of breaks remaining at 1 hr in irradiated samples. Unirradiated samples exposed to the same heat treatment showed a significant increase in the number of DNA strand breaks. Thus, heat treatment at 45 degrees C may lead to a combined effect of reduced rejoining capacity and formation of breaks after the electron pulse which in turn may be responsible for increased cell death when both modalities are employed.

The electron affinity of some radiotherapeutic agents used in cancer therapy.

In order to evaluate whether chemotherapeutic compounds applied in cancer treatment might interact with radiation as anoxic cell sensitizers, the electron-affinic properties of DTIC, AIC, hydroxyurea, busulfan and cyclophosphamide were studied by pulse radiolysis. Reaction rates with hydrated electrons were determined for all these compounds. With the exception of DTIC, they all reacted much more slowly with electrons than do most electron-affinic sensitizers. One-electron reduction potentials were determined for DTIC, AIC and hydroxyurea. The values were all in the region for the onset of sensitization, with hydroxyurea as the most promising (E71 =- 0.0552V). For busulfan and cyclophosphamide no value could be determined, but these compounds are probably less electron-affinic than hydroxyurea. A possible application of chemotherapeutic agents as radiosensitizers is discussed.

Cavernous haemangioma of the retina.

Seven cases of retinal cavernous haemangioma are presented. Three cases have been followed for more than 6 years, and three cases between 1 and 2 years. Six cases had no eye symptoms related to the vascular tumour, while in one case vitreous haemorrhage occurred on two occasions. On both these occasions full vision was regained. None of the vascular tumours were treated. Two patients had grand mal seizures. They also had convulsive disease in the family history. In three cases family members of two generations were found to have normal eyes on examination.

Detection of singlet oxygen production by ESR.

SINGLET molecular oxygen is a very powerful oxidant. Its action is important in a variety of chemical and biological processes(1-4), for examples dye-sensitised photooxidation of lipids, proteins and nucleic acids(4), photodynamic inactivation of viruses(5) and cells(4), phototherapy of cancer(6,7), carcinogenesis(8), haemolysis of erythocytes(9), sensitisation of the human skin(4) and degradation of food(4). The methods used to detect singlet oxygen are unspecific, of low sensitivity or laborious. Photooxidation of 1,3-diphenylisobenzofuran seems to be the most widely used diagnostic test for (1)O(2). However, in the absence of additional control experiments this test does not prove the intermediacy of (1)O(2) (ref. 4) and 1,3-diphenylisobenzofuran has very low solubility and dimerises in aqueous solutions. Lion et al.(10) have proposed a new method to detect (1)O(2) involving the generation of stable nitroxide radicals when (1)O(2) reacts with the sterically hindered amine 2,2,6,6,-tetramethylpiperidin. When using this method to detect (1)O(2) in neutral aqueous solutions, we found no radical production. We report here our investigation of this problem, as it is biologically important to be able to detect (1)O(2) production in such solutions.

Binding of a nitroxyl to radiation-induced DNA transients in repair and repair deficient of E. coli K-12.

Binding of tritiated 2,2,6,6-tetramethyl-4-piperidone-N-oxyl (3H-TAN) to radiation-induced DNA-transients in E. coli K-12 strains AB 1157 and JO 307 rec A uvr A has been studied under in vivo conditions. After irradiation the cells were washed and resuspended in growth medium and left overnight at 37 degrees C. Within an uncertainty of about 10%, no effect of repair could be detected on the yield of TAN bound to DNA for any of the strains. During the period after resuspension. TAN or fragments of TAN leaked out of the irradiated cell samples. This leakage may be attributed to semi-permanant association between TAN and radiation-induced radicals within the cell. The relevance of different interactions between TAN and transients in DNA is discussed.