INDUCTION OF DNA-PROTEIN CROSS-LINKS IN CHINESE HAMSTER CELLS BY THE PHOTODYNAMIC ACTION OF CHLOROALUMINUM PHTHALOCYANINE AND VISIBLE LIGHT

Abstract— Chloroaluminum phthalocyanine (CAPC) is an efficient photosensitizer for the inactivation of Chinese hamster V79 cells. In order to investigate possible molecular mechanisms in the photo-dynamic action of CAPC and visible light, the induction and repair rate of two classes of DNA lesions have been determined, i.e. DNA single-strand breaks and DNA-protein cross-links. In cells pretreated with 1 μ.M CAPC, a fluence of 12 kJ/m² of red light (>600 nm) kills approximately 50% of the cells and induces 3 to 3.5 Gy-equivalents of single-strand breaks. The repair of these breaks was slower than the repair of single-strand breaks induced by -irradiation. The photodynamic action of CAPC also induces a large number of DNA-protein cross-links which, in contrast to -radiation-induced DNA-protein cross-links, do not appear to be repaired during 4 h of post-treatment incubation in fresh medium. These studies suggest that DNA may be an important target for the cytotoxicity of CAPC + red light.     

Stabilising small clusters: synthesis and characterisation of thermolabile [Gd4F7(15-crown-5)4][AsF6]5.6 SO2

Addition of 15-crown-5 to [GdF(AsF6)2], both dissolved in liquid SO2, and crystallisation at -30 degrees C has led to the isolation of the tetranuclear ionic complex [Gd4F7(15-crown-5)4][AsF6]5.6 SO2 which is stable up to--10 degrees C where SO2 loss leads to loss of crystallinity.     

Orientation of nucleophilic substitution in π-cation radicals or π-dications from meso-substituted metalloporphyrins

Treatment of meso-substituted metalloporphyrins [meso -substituent = OCOCF₃, OCOCH₃, OMe, CHO, CN, Cl; metal = Zn(II) or Cd(II)] with thallium(III) trifluoroacetate, followed by an acidic work-up, gives the corresponding β-substituted α-oxophlorins which were either characterised as such or else further derivatised. In all cases the major (or only) disubstitution product has the αβ orientation at the meso positions, indicating that the existing meso substituent directs the incoming one (trifluoroacetate) into the flanking, rather than opposite, meso position of the intermediate π-cation radical or π-dication. In contradistinction, meso substituted zinc(II) porphyrins which are able to lose protons (e.g. α-oxophlorins or α-aminoporphyrins) react with thallium(III) trifluoroacetate, and after a work-up with HCl the corresponding γ-chloro-α-oxophlorin or γ-chloro-α-aminoporphyrin is obtained.     

Reactivity of "Eu(OiPr)2" with phenols: formation of linear Eu3, square pyramidal Eu5, cubic Eu8, and capped cubic Eu9 polymetallic europium complexes

The direct reaction of europium with 2-propanol and phenols has been investigated under a variety of conditions. The reaction of europium metal with 2,6-dimethylphenol and 2,6-diisopropylphenol in 2-propanol at reflux revealed that polymetallic europium complexes could be generated by this method. Hx[Eu8O6(OC6H3Me2-2,6)12(OiPr)8], 1, and H5[Eu5O5(OC6H3iPr2-2,6)6(NCCH3)8], 2, were isolated by recrystallization in the presence of hexanes and acetonitrile, respectively, and characterized by X-ray crystallography. Complex 1 has a cubic arrangement of europium ions with face-bridging mu 4-O donor atoms, edge-bridging mu-O(phenoxide/phenol) ligands, and terminal O(isopropoxide/2-propanol) ligands. Complex 2 is mixed valent and has a square pyramidal europium core with four Eu(II) ions at the basal positions and one Eu(III) ion at the apex. Since these reactions gave complicated mixtures of products from which 1 and 2 could only be obtained in low yields, direct reactions under less forcing reaction conditions were investigated. Europium reacts slowly at room temperature to form arene-soluble divalent [Eu(OiPr)2(THF)x]n, 3. Complex 3 reacts with 2,6-dimethylphenol to form the arene-insoluble complex (H[Eu(OC6H3Me2)2(OiPr)])n, 4. Recrystallization of 4 in the presence of THF results in the crystallographically characterizable divalent trimetallic complex [Eu(OC6H3Me2-2,6)2(THF)2]3, 5, which has an unusual linear metal geometry. In the presence of HOiPr at ambient conditions in the glovebox, crystals of 5 slowly convert to the mixed valent H10[Eu8O8(OC6H3Me2-2,6)10(OiPr)2(THF)6], 6, which was found to have a cubic arrangement of europium atoms similar to 1 by X-ray crystallography. Complex 4, upon heating under vacuum, followed by reaction with THF, forms the arene-soluble divalent complex H18([Eu9O8(OC6H3Me2-2,6)10(THF)7][Eu9O9(OC6H3Me2-2,6)10(THF)6]), 7, which contains two types of capped cubic arrangements of europium ions in the solid state.     

Inverse gas chromatography in the study of polymer degradation. Part 2. Oxidation of sulphurated squalene as a model for the oxidative degradation of natural rubber vulcanizates

Summary Inverse gas chromatography with sulphurated olefinic stationary phases and air as carrier gas has been found to yield characteristic shifts of retention data. The resulting plots of retention index versus reaction time obtained for a range of squalene vulcanizates have been found to be similar to those given by oxygen absorption measurements. Furthermore the chromatographic oxidation curves have been found to be consistent with the known oxidation behaviour of the various sulphur networks formed on vulcanization. This paper is dedicated to the memory of Dr.Graham Moore (1924–1968).     

Random and cooperative sequential adsorption on infinite ladders and strips

We analyze various processes where particles are added irreversibly and sequentially at the sites of infinite ladders or broader strips (i.e., on terraces) of adsorption sites. For sufficiently narrow strips or ladders, exact solution in closed form is possible for a variety of processes. Often this is most naturally achieved by mapping the process onto an equivalent one-dimensional process typically involvingcompetitive adsorption. We demonstrate this procedure for sequential adsorption with nearest-neighbor exclusion on a 2× square ladder. For other select processes on strips slightly too broad for exact solution, almost exact analysis is possible exploiting an empty-site shielding property. In this way, we determine a jamming coverage of 0.91556671 for random sequential adsorption of dimers on a 2× square ladder. For broader strips, we note that the complexity of these problems quickly approaches that for × lattices.