Light-induced electron spin polarization in the ground state of water-soluble copper porphyrins

Light-induced spin-polarized transient EPR spectra are reported for several water-soluble copper porphyrins. The spectra are assigned to the doublet ground state, with emissive spin polarization resulting from photoexcitation and subsequent electronic relaxation. In contrast to other systems for which polarization of a doublet ground state has been observed, the exchange interactions in the copper porphyrins are strong and the geometry is fixed. It is proposed that intersystem crossing from the photoexcited trip-doublet to the trip-quartet state can lead to net polarization of the spin system and that this polarization is maintained during electronic decay, possibly via charge-transfer and exciplex states. The intensity of the observed spin polarization is essentially independent of the molecular orientation in the external field, but is strongly dependent on the nature of the charged peripheral groups. Possible reasons for this behavior are discussed.     

Effect of oxidants on microalgal flocculation

The effects of chlorine, ozone and chlorine dioxide on Scenedesmus sp. cultures were studied. Algal cell viability and chlorophyll concentration decreased, and the concentration of dissolved organic substances increased with increasing applied oxidant concentration. Pretreatment with chlorine dioxide (1, 3 or 5 mg l⁻¹) or ozone (2.6, 4.6 or 8.1 mg l⁻¹) on algal cultures enhanced algal flocculation with alum, while prechlorination with 10 or 20 mg l⁻¹ increased the required dosage of alum by 15%. Scanning electron micrographs of oxidized cells revealed drastically adverse effects upon the cell surface architecture: in addition to the oxidation of noncellular organic materials, the oxidants damaged both cell surface structures and intracellular components. A model explaining the effects of the different oxidants on microalgal flocculation is suggested.     

New waveform design for magnetron-based marine radar

At their long-range mode, conventional magnetron-based marine radar use low pulse repetition frequency (PRF) to extend the unambiguous range, and increase the pulse-width to regain the average power. The proposed new waveform maintains narrow pulses and high PRF even at the long-range mode. Range ambiguity is mitigated by periodic `yes`no` coding of the transmitted pulse train. Using narrow pulses improves the range resolution and reduces the radial dimension of the illuminated clutter.     

Kinetic Study of the Photoexcited Triplet State of Free Base Porphyrins by EPR

An electron paramagnetic resonance (EPR) study of the photoexcited triplet state of four free base porphyrins is presented. The zero field splitting parameters (ZFS) |D| and |E| were calculated from the EPR spectra of the porphyrins dissolved in n-octane matrices at 80°K. |D| = 0.0359 cm^?1, |E| = 0.0079 cm^?1 for tetra phenyl porphyrin (H₂ TPP), |D| = 0.0432 cm^?1, |E| = 0.0037 cm^?1 for tetra (per-fluoro) phenyl porphyrin H₂T (per-F) PP, |D| = 0.0366 cm^?1, |E| = 0.0078 cm^?1 for tetra (para-chloro) phenyl porphyrin H₂T(P-Cl)PP, |D| = 0.0369 cm^?1, |E| = 0.0076 cm^?1 for tetra (para-methyl) phenyl porphyrin H₂T(P-Me)PP. The transient behavior of the EPR signal intensities in the last two porphyrins is discussed. The depopulation rate constants of the triplet sublevels k_p, the ratio between the population rate constants A_p (at zero field, p = x,y,z), and the spin lattice relaxation rate W within the triplet manifold, were calculated. k_x = (12 ± 2) × 10² sec^?1, k_y = (0.5 ± 0.1) × 10² sec^?1, k_z = (1.2 ± 0.4) × 10² sec^?1, A_x:A_y:A_z ? 0.63:0.01:0.33, W = (0.4 ± 0.1) × 10⁴ sec^?1 for H₂T(P-Cl)PP, k_x = (7 ± 2) × 10² sec^?1, k_y = (4 ± 1) × 10² sec^?1, k_z = (1.5 ± 0.5) × 10² sec^?1, A_x:A_y:A_z ? 0.56:0.31:0.13, W = (1.7 ± 0.4) × 10³ sec^?1 for H₂T(P-Me)PP.     

Evaluation of the use of tannic acid in preparation of the rabbit knee meniscus for scanning electron microscopy

The femoral faces of medial and lateral menisci of the rabbit knee were structurally reinforced with tannic acid and studied using the scanning electron microscope. Significant improvement in preservation of the meniscal surfaces, as compared to previous studies, was brought about by the structural reinforcement technique. Menisci, although detacted from tibial plateaux, retained well their shape, dimensions, and microarchitecture. Differences in surface morphology between medial and lateral menisci and between longitudinal sectors on menisci were recorded. Appearances of surface irregulatities were reduced to a very low level, and the possibility that this minimum exists in situ is forwarded.     

ESR Studies of Uncomplexed and Complexed HO2 Radical Formed in the Reaction of H2O2 with Ce4+, Fe2+ and Ti3+ Ions

Excess of H₂O₂ reacting in 0.5N HClO₄ with Ce⁴⁺, Ti³⁺ and Fe²⁺ yields the uncomplexed HO₂ radical. This radical gives a broad ESR signal with a line width of 27±1 gauss and a g-value of 2.0140±0.0015. The HO₂ radical forms a complex with excess of Ce³⁺ which gives an ESR spectrum with a linewidth of 1.3±0.1 gauss and a g-value of 2.0180±0.0005. The equilibrium between complexed [Ce³⁺‥HO₂] and uncomplexed HO₂ was studied. Two complexes are formed between HO₂ and [Ti⁴⁺…H₂O₂]. These complexes give two ESR signals with a linewidth of 0.7 ± 0.1 and 0.5± 0.1 gauss and g-value of 2.0140± ± 0.0005 and 2.0120± 0.0005 respectively.     

Efficiency and efficacy of the electrogastrogram

The efficiency and efficacy of the electrogastrogram (EGG) involve a few practical factors, including recording length, sample size, and the characteristics of subjects. The aim of this study was to investigate the effect of these factors on the accuracy of EGG analysis. Gastric myoelectrical activity was recorded using electrogastrography in 24 subjects (ages 22-91 years) for 1 hr in the fasting state and 2 hr after a test meal. Computerized spectral analysis was performed to compute EGG parameters, including dominant frequency, dominant power, and the percentage of 2-4 cycles per minute (cpm) slow waves. A parameter called misinterpretation was defined to investigate the effect of recording length. The results were as follows: (1) Using the recording length of 1 hr in each state as a gold standard, the misinterpretation for the recording length of 30 min was 27% for the dominant frequency and 17% for the dominant power. When the recording length was reduced to 15 min, the misinterpretation increased to 61% for the dominant frequency and 38% for the dominant power. (2) With a sample size of 10 subjects and a recording length of 60 min, a statistically significant postprandial increase was observed in the dominant frequency and power, and a trend in the postprandial increase of the regularity of the EGG was noted. When the sample size increased to 24 subjects, a significant postprandial increase was found in all these parameters. (3) None of the EGG parameters exhibited any significant difference between the younger and older subjects or between men and women. In conclusion, a recording length of 30-60 min seems to be appropriate and produces reliable and predictable results. Age and gender do not affect any of the EGG parameters.     

Triplet EPR Dynamics of Randomly Oriented Dications and Dianions of Tetraoxaporphyrinoids

This paper deals with the photoexcited triplet state of several tetraoxaporphyrinoids studied by time-resolved electron paramagnetic resonance (EPR). The porphyrinoids studied are tetraoxa[18]porphyrin ( 1a ⁺⁺), octaethyl-tetraoxa[18]porphyrin ( 1b ⁺⁺), tetra-n-butyl tetraoxa[18]porphyrin ( 1c ⁺⁺), octaethyl-tetraoxa[26]porphyrin ( 2 ⁺⁺), and tetraoxa[18]porphycene ( 3 ⁺⁺), all of them as per-chlorate salts. To qualify as stable aromatic 18π- (or 26π-) electron systems, they must exist as dications. Analysis of the triplet EPR spectra is characterized by unique features not found in their parent porphyrins and porphycenes. While in the case of the axially-symmetric tetraphenylporphyrin, the triplet EPR spectra indicate deviation from axial symmetry, the tetraoxaporphyrin 1a ⁺⁺ exhibits, as expected, a vanishing E-term of the zero-field splitting (ZFS) tensor. A conspicuous difference is found between the triplet EPR spectra of the dications and the dianions of all tetraoxa compounds. The results are discussed in terms of the electronic structures of the porphyrinoids.     

Range sidelobes blanking by comparing outputs of contrasting mismatched filters

Range sidelobes, a major shortcoming of radar pulse compression, are often reduced through the use of mismatched filters. The authors propose to blank the remaining sidelobes by using two or more mismatched filters, whose sidelobes are designed to peak at different delays. The authors show how to design such filters and present promising simulation results with two or more mismatched filters.