Phototoxicity of Some Bromine-Substituted Rhodamine Dyes: Synthesis, Photophysical Properties and Application as Photosensitizers

Abstract— The synthesis of some bromine-substituted rhodamine derivatives viz. , 4,5-dibromorhodamine methyl ester (dye 2) and 4,5-dibromorhodamine n -butyl ester (dye 3) are reported. These dyes were synthesized to promote a more efficient cancer cell photosensitizer for potential use in in vitro bone marrow purging in preparation for autologous bone marrow transplantation. Spectroscopic and photo-physical characterization of these dyes together with rhodamine 123 (dye 1) are reported in water, methanol, eth-anol and also in a microheterogeneous system, sodium dodecyl sulfate. The possible mechanism of photosensi-tization is characterized in terms of singlet oxygen efficiency of these dyes. Singlet oxygen quantum yields for bromine-substituted dyes are in the range of 0.3-0.5 depending on the solvent. For dye 1 no singlet oxygen production is found. The photodynamic actions of these dyes in different cell lines are tested. It was found that dye 2 and dye 3 are efficient photosensitizers and mediate eradication of K562, EM2, myeloid cell lines (CML) and the SMF-AI rhabdomyosarcoma line.     

Syntheses of Strychnos and Aspidospermatan-Type Alkaloids. 8. Selective Total Syntheses of Mossambine and 14-epi-Mossambine by a Radical Cyclization Reaction(1)

Mossambine (6) was obtained by a six-step reaction sequence from the indoloazepine ester 7. Radical cyclization of the tetracyclic vinyl iodide 12a provided a racemic pentacyclic ketone 16E, which could be converted to either enantiomer by condensation with (S or R)-N,S-dimethyl-S-phenylsulfoximine and selective pyrolysis of the resulting diastereomeric alcohols 18 and 19 or 20 and 21. Selective reductions of the resolved (or racemic) ketone 16E provided mossambine (6) and its hydroxy epimer 17.     

Matrix influence on stability constants of 15-crown-5-alkali metal complexes measured by liquid secondary ion mass spectrometry

The liquid secondary ion mass spectra of 15-crown-5 in the presence of equimolecular mixtures of three alkali metal salts show large changes in the relative abundances of the 15-crown-5-cation complexes formed, depending on the relative concentrations of ligand and salts. These variations are due either to various desorption rates of the cationized species or to different affinities of 15-crown-5 toward the alkali metal cations. An original method allowing discrimination between desorption and complexation effects on the relative abundance of ligand-metal complex ions is described and can be applied for the calculation of their stability constants. The spectral data obtained using two different matrices demonstrate that the matrix polarity has a very important effect on the two parameters considered, i.e. the stability constants of the 15-crown-5-cation complexes and their desorption rates.     

Etude des petits cycles—XXXVII: Syntheses et proprietes spectrales du tetracyclopropylidene ([4]rotane) et des composes polycyclopropylspiraniques de la serie

The syntheses of [4]rotane and polycyclopropylspiranic derivatives are reported. One route involves the formation of cyclopropane rings from C₄-acyloins; a second route uses the dimerisation of bicyclopropylidene. Spectroscopic data do not point to any particular electronic interactions between cyclopropane rings in these compounds.     

Chiral 2-Aryl-2-methyl-2H-1-benzopyrans: Synthesis,characterization of enantiomers,and barriers to thermal racemization

The ease of thermal breaking of the C(sp³)? O bond of the 2-aryl-2-methyl-2H-1-benzopyrans 1 – 9 was evaluated by measuring the free energy (ΔG) of the racemization reaction of optically active compounds. The variation of ΔG of the thermal ring opening in terms of structural modifications is discussed. The synthesis of the studied compounds, the preparative separation of enantiomers by liquid chromatography, the determination of enantiomeric purity, the circular dichroism of enriched enantiomers, and the measurement of rate constants of enantiomerization by monitoring the decrease of the polarimetric angle of rotation at suitable temperatures are described.     

Photodynamic inactivation of isolated crayfish mechanoreceptor neuron: different death modes under different photosensitizer concentrations

To study the mechanism of photodynamic nerve cell killing, isolated crayfish mechanoreceptor neurons were photosensitized by the sulfonated aluminum ophthalocyanine Photosens. Neuron activity was continuously recorded until irreversible abolition. Intense (10(-5) M Photosens) or weak (10(-7) M Photosens) photosensitization induced different bioelectric neuron responses: firing activation followed by irreversible depolarization block or gradual inhibition until firing abolition, respectively. These bioelectric responses were accompanied by different biochemical and morphological changes. In the case of intense photosensitization, neuron nuclei swelled and then shrank. Succinate dehydrogenase (SDH) was inhibited, and the plasma membrane was compromised just after firing cessation. Weak photosensitization did not induce these changes but caused swelling of the endoplasmic reticulum and destruction of the matrix, cristae and membranes in some of the mitochondria. Other mitochondria, however, retained the normal structure. Plasma membrane damage, SDH inhibition, nucleus shrinkage and impairment of the nuclear border occurred after 2-4 h. It is concluded that intense photosensitization induced necrotic processes during irradiation, whereas weaker impact caused delayed necrosis 2-4 h later. The observed electrophysiological neuron responses to photodynamic therapy may be considered as early hallmarks of different modes of forthcoming cell death.     

Electrochemically-induced spirolactonization of alpha-(methoxyphenoxy)alkanoic acids into quinone ketals

Anodic oxidation of two series of alpha-(2)- and alpha-(4-methoxyphenoxy)alkanoic acids were studied both at the analytical and preparative scales in order to delineate mechanistic aspects of electrochemically induced spirolactonization and to develop synthetically useful orthoquinone bis- and monoketals. Although alpha-monomethylated carboxylic acids and acetic acid derivatives do not undergo any spiroannulation, alpha-dimethylated carboxylic acids furnished spirolactones in high yields. A gem-dimethyl effect is invoked to explain these differences in cyclization capacity. Electrooxidation conditions can be selected to furnish either quinone spirolactone bis- or monoketals. Chemoselective monohydrolysis of bisketals can also be accomplished in a stepwise fashion to furnish the corresponding spirolactone monoketals, but the ortho compound unfortunately dimerized in situ via a Diels-Alder process. An ECEC pathway is proposed to rationalize the observed spirolactonizations on the basis of cyclic voltammetry analyses.     

Effect of Ion Energy on Structure and Composition of Cathodic Arc Deposited Alumina Thin Films

The effect of energy supplied to the growing alumina film on the composition and structure has been investigated by varying substrate temperature and substrate bias potential. The constitution and composition were studied by X-ray diffraction and elastic recoil detection analysis, respectively. Increasing the substrate bias potential from −50 to −100 V caused the amorphous or weakly crystalline films to evolve into stoichiometric, crystalline films with a mixture of the α- and γ-phase above 700 ^oC, and γ-phase dominated films at temperatures as low as 200 ^oC. All films had a grain size of <10 nm. The combined constitution and grain size data is consistent with previous work stating that γ-alumina is thermodynamically stable at grain sizes <12 nm [McHale et al., Science 277, 788 (1997)]. In order to correlate phase formation with synthesis conditions, the plasma chemistry and ion energy distributions were measured at synthesis conditions. These results indicate that for a substrate bias potential of −50 V, ion energies in excess of 100 eV are attained, both from a high energy tail and the accelerated ions with charge >1. These results are of importance for an increased understanding of the evolution of film composition and microstructure, also providing a pathway to γ-alumina growth at temperatures as low as 200 ^o C.