LIGHT-INDUCED LEAKAGE OF SPIN LABEL MARKER FROM LIPOSOMES IN THE PRESENCE OF PHOTOTOXIC PHENOTHIAZINES

Abstract— Liposomes prepared from dipalmitoyl lecithin, cholesterol and dicetyl phosphate and containing a trapped spin label marker were exposed to long wavelength UV light in the presence of a series of phenothiazine tranquilizers. EPR spectroscopy was used to detect spin label marker released from liposomes, taking advantage of the disappearance of line broadening from electron spin exchange which occurred on spin label release. The minimum effective phototoxic dose in mice of these phenothiazines was also determined. Kinetic studies of light-induced spin label release from phenothiazine-sensitized liposomes showed that membrane damage was rapidly induced and that the damaging species were short-lived. The damage process was oxygen dependent and could be temporarily prevented by cysteamine or α-tocopherol added immediately before irradiation. Only those phenothiazines which mediated light-dependent liposomal membrane damage had phototoxic activity in mice and the degree of photosensitization was parallel in the two systems. In both photosensitization phenomena, the nature of the substituent at the phenothiazine 2-position was more important than the phenothiazine side chain.     

Measurement of the rate coefficient for collisional removal of O2(X3Sigma- g, upsilon=1) by O(3P)

We report a laboratory measurement of the rate coefficient for the collisional removal of O(2)(X(3)Sigma(g) (-),upsilon=1) by O((3)P) atoms. In the experiments, 266-nm laser light photodissociates ozone in a mixture of molecular oxygen and ozone. The photolysis step produces vibrationally excited O(2)(a(1)Delta(g)) that is rapidly converted to O(2)(X(3)Sigma(g) (-),upsilon=1-3) in a near-resonant electronic energy-transfer process with ground-state O(2). In parallel, a large amount of O((1)D) atoms is generated that promptly relaxes to O((3)P). Under the conditions of the experiments, only collisions with the photolytically produced O((3)P) atoms control the lifetime of O(2)(X(3)Sigma(g) (-),upsilon=1), because its removal by molecular oxygen at room temperature is extremely slow. Tunable 193-nm laser light monitors the temporal evolution of the O(2)(X(3)Sigma(g) (-),upsilon=1) population by detection of laser-induced fluorescence near 360 nm. The removal rate coefficient for O(2)(X(3)Sigma(g) (-),upsilon=1) by O((3)P) atoms is (3.2+/-1.0)x10(-12) cm(3) s(-1) (2sigma) at a temperature of 315+/-15 K (2sigma). This result is essential for the analysis and correct interpretation of the 6.3-mum H(2)O(nu(2)) band emission in the Earth's mesosphere and indicates that the deactivation of O(2)(X (3)Sigma(g) (-),upsilon=1) by O((3)P) atoms is significantly faster than the nominal values recently used in atmospheric models.     

Synthetic magnetic opals

We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there exists no report in literature on any BiNi compound which is magnetic.     

Determination of the electron temperature of the tenuous pulsed argon ion laser plasma by means of the line intensity ratio technique

The validity of the diagnostic line-intensity ratio method for determination of the electron temperature was examined for a tenuous, NLTE pulsed argon ion laser plasma. Recently measured cross sections for simultaneous excitation and ionization of the upper levels of the argon ion laser were used and averaged over the velocity distribution, assumed Maxwellian. The electron temperature was determined by observing the sidelight intensity ratio of doublet 4765 Å and quartet 4806 Å transitions, and it was found to be 1.65 eV. This result is in agreement with electron temperature values obtained by the time resolved measurement and the double probe method, respectively. The theory of the positive column, where wall effects are not considered, gives somewhat larger values as an upper bound.     

Optical activity in mixed-ligand terbium complexes containing 1,2-Benzenedicarboxylic acid and chiral carboxylic acids

The optical activity of Tb(PHT)(L) complexes has been studied by means of circularly polarized luminescence (CPL) spectroscopy, where PHT=1,2-benzenedicarboxylic acid (phthalic acid) and L=L-mandelic, L-aspartic, and L-malic acids. The CPL spectra were characteristic of multidentate bonding, and close examination of the spectra revealed the nature of the metal-ligand bonding. The results obtained have demonstrated that the optical activity experienced by the Tb(III) ion is primarily determined by the nature of the chiral ligand, and that this chirality can be affected by the achiral ligands also bound in the metal coordination sphere.     

Strontium isotope ratios (87Sr/86Sr) of tooth enamel: a comparison of solution and laser ablation multicollector inductively coupled plasma mass spectrometry methods

Strontium isotope ratios (87Sr/86Sr) in tooth enamel provide a means to investigate migration and landscape use in humans and other animals. Established methods for measuring (87)Sr/(86)Sr in teeth use bulk sampling (5-20 mg) and labor-intensive elemental purification procedures before analysis by either thermal ionization mass spectrometry (TIMS) or multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). Another method for measuring 87Sr/86Sr is laser ablation MC-ICP-MS, but concerns have been expressed about its accuracy for measuring tooth enamel. In this study we test the precision and accuracy of the technique by analyzing 30 modern rodent teeth from the Sterkfontein Valley, South Africa by laser ablation MC-ICP-MS and solution MC-ICP-MS. The results show a mean difference in 87Sr/86Sr measured by laser ablation and by solution of 0.0003 +/- 0.0002. This degree of precision is well within the margin necessary for investigating the potential geographic origins of humans or animals in many areas of the world. Because laser ablation is faster, less expensive, and less destructive than bulk sampling solution methods, it opens the possibility for conducting 87Sr/86Sr analyses of intra-tooth samples and small and/or rare specimens such as micromammal and fossil teeth.     

Probing phenylalanine/adenine pi-stacking interactions in protein complexes with explicitly correlated and CCSD(T) computations

To examine the effects of pi-stacking interactions between aromatic amino acid side chains and adenine bearing ligands in crystalline protein structures, 26 toluene/(N9-methyl)adenine model configurations have been constructed from protein/ligand crystal structures. Full geometry optimizations with the MP2 method cause the 26 crystal structures to collapse to six unique structures. The complete basis set (CBS) limit of the CCSD(T) interaction energies has been determined for all 32 structures by combining explicitly correlated MP2-R12 computations with a correction for higher-order correlation effects from CCSD(T) calculations. The CCSD(T) CBS limit interaction energies of the 26 crystal structures range from -3.19 to -6.77 kcal mol (-1) and average -5.01 kcal mol (-1). The CCSD(T) CBS limit interaction energies of the optimized complexes increase by roughly 1.5 kcal mol (-1) on average to -6.54 kcal mol (-1) (ranging from -5.93 to -7.05 kcal mol (-1)). Corrections for higher-order correlation effects are extremely important for both sets of structures and are responsible for the modest increase in the interaction energy after optimization. The MP2 method overbinds the crystal structures by 2.31 kcal mol (-1) on average compared to 4.50 kcal mol (-1) for the optimized structures.