Solvent dependence of the photophysical properties of 2-chlorothioxanthone, the principal photoproduct of chlorprothixene

2‐chlorothioxanthone (CTX) is used as photoinitiator for the reticulation of synthetic resins and for the preparation of pharmaceuticals. It was previously determined that CTX is the primary photoproduct of z‐chlorprothixene (CPTX) when irradiated at 313 nm and is formed in an autocatalyzed reaction through an energy‐transfer mechanism (Piñero et al. [2009] Photochem. Photobiol., 85 , 895–900). In this work, the photophysical properties of CTX were measured in acetonitrile/water solutions to determine if their magnitude can affect the side effects of CPTX. The results show that CTX has higher absorption coefficients in the visible region (400–420 nm) and higher triplet quantum yields than its parent compound. Similar to TX, both properties strongly depend on the solvent polarity/hydroxylicity. The quantum yield of the triplet intermediate is very close to the value of the phenothiazine triplets. The phenothiazines are the most phototoxic antidepressants. Therefore, given the appropriate microenvironment, the photosensitization side effects of CPTX can be intensified on the production of CTX.     

Multinuclear cytotoxic metallodrugs: physicochemical characterization and biological properties of novel heteronuclear gold-titanium complexes

An unprecedented series of titanocene-gold bi- and trimetallic complexes of the general formula [[(η(5)-C(5)H(5))(μ-η(5):κ(1)-C(5)H(4)(CH(2))(n)PPh(2))TiCl(2)](m)AuCl(x)](q+) (n = 0, 2, or 4; m = 1, x = 1, q = 0 or m = 2, x = 0, q = 1) have been prepared and characterized spectroscopically. The luminescence spectroscopy and photophysics of one of the compounds, [[(η(5)-C(5)H(5))(μ-η(5):κ(1)-C(5)H(4)PPh(2))TiCl(2)](2)Au]PF(6), have been investigated in 2MeTHF solution and in the solid state at 77 and 298 K. Evidence for interfragment interactions based on the comparison of electronic band positions and emission lifetimes, namely, triplet energy transfer (ET) from the Au- to the Ti-containing chromophores, is provided. The cytotoxicity of the complexes was evaluated on A2780 ovarian cancer cells and on their cisplatin-resistant cell line A2780cisR; the compounds showed activity in the low micromolar range that was markedly more active than the corresponding titanocene-phosphine precursors [(η(5)-C(5)H(5))(η(5)-C(5)H(4)(CH(2))(n)PPh(2))TiCl(2)], cisplatin, and, for some of them, the gold analogue [(PPh(3))AuCl]. In an attempt to draw preliminary structure-activity relationships, cell uptake measurements and interaction studies with plasmid DNA and the model protein ubiquitin (Ub) have been undertaken on some of the compounds.     

In situ study of electrochromic properties of self-assembled TiO2 nanotubes

Electrochromical properties of anodic self-assembled nanotubes were investigated. It was found that amorphous titania nanotubes were able to insert H⁺ ions in a highly reversible manner. Coloration of the TiO₂ nanotubes occurred at potentials below ?0.5 V vs. Ag/AgCl in 1M (NH₄)₂SO₄ aqueous solution. The proton insertion reaction probably leads to the formation of a Ti³⁺/Ti⁴⁺ solid solution in the amorphous titania electrode, as was shown by the analysis of the derivative curve. The nanotubular titania electrode shows reasonable color efficiency when compared with other electrochromic materials and it is a promising candidate for the fabrication of low-cost interdigitated electrochromic devices.     

New Bimetallics of Mo and W with Metallocene,Metal Carbonyl and Bridging PPh2 or ‘Cp’PPh2 Units

Ring substituted (R=^tBu, SiMe₃) metallocene dichlorides undergo a nucleophilic substitution on one of the two rings upon the action of LiPPh₂M'(CO)_x salts with the formation of chloro-hydrido complexes [C₅H₃(R)PPh₂M'(CO)_x](C₅H₄R)M(H)Cl. Their UV irradiation leads to the chloro-bridged M(μ-Cl)M' separable diastereoisomers. Use of the ansa-metal-locene dichlorides [Me₂X(C₅H₄)₂MCl₂] (X=Si or C) allowed the access to the new bridging system [M(μ-PPh₂, μ-Cl)M′] (M=Mo, W ; M'=W).     

CeCl3.7H2O: an effective additive in Ru-catalyzed enantioselective hydrogenation of aromatic alpha-ketoesters

In the presence of catalytic amounts of CeCl 3.7H 2O, [RuCl(benzene)(S)-SunPhos]Cl is a highly effective catalyst for the asymmetric hydrogenation of aromatic alpha-ketoesters. A variety of ethyl alpha-hydroxy-alpha-arylacetates have been prepared in up to 98.3% ee with a TON up to 10,000. Challenging aromatic alpha-ketoesters with ortho substituents are also hydrogenated with high enantioselectivities. The addition of CeCl 3.7H 2O not only improves the enantioselectivity but also enhances the stability of the catalyst. The ratio of CeCl 3.7H 2O to [RuCl(benzene)(S)-SunPhos]Cl plays an important role in the hydrogenation reaction with a large substrate/catalyst ratio.     

Exfoliated nanoplatelets of an Aurivillius phase, Bi3.25La0.75Ti3O12: Characterisation by X-ray diffraction and by high-resolution electron microscopy

Nanoparticles of the Aurivillius phase La-substituted BTO (Bi_4−xLa_xTi₃O₁₂, with x=0.75) were obtained through a chemical lithiation process. They have been characterised by X-ray diffraction and transmission electron microscopy (diffraction and imaging at high resolution). The defect-free particles are platelet-shaped with the c large axis perpendicular to the plane. From high-resolution images, it is clear that the delamination process occurs at the level of the (Bi₂O₂)²⁺ intermediate layer and is destructive for this layer. The smallest thickness measured corresponds to one cell parameter (3.3 nm) but a large range of thicknesses have been observed: this suggests that the lithium insertion does not take place in all (Bi₂O₂)²⁺ layers, despite a large excess of lithium and a long reaction time. This is confirmed by ICP analysis, which leads to a formula Li_0.99Bi_3.25La_0.77Ti_3.00O₁₂ for the lithiated compound. This behaviour towards lithium intercalation differs from those observed with BTO in literature, where lithium insertion is reported as occurring in every (Bi₂O₂)²⁺ layer. Possible explanations for this difference are advanced based on microstructural and structural considerations.     

Isoelectric focusing in an ordered micropillar array

An original micropillar array dedicated to electrophoretic separations has been developed. It consists of a rectangular zone of PDMS micropillars protruding on a PDMS block. This area has been chosen to mimic a diluted gel structure and remains uncovered to keep the ability to perform an immunoblot after the protein separation for further applications in the field of allergy diagnosis. The micropillar array geometry has been optimized by evaluating the influence of pillar shape, pillar size and interpillar distance on evaporation and IEF separation. The separation conditions namely electrolyte composition, temperature and sample loading have been studied. Finally a protein mixture with pI ranging from 4.7 to 10.6 has been successfully separated within this microdevice by IEF without decreasing the resolving power obtained with conventional minigel. The micropillar array developed for electrophoretic separations leads to much shorter analysis times and can be reused several times while gels are disposable.     

Characterization, reactivity and photosensitizing properties of the triplet excited state of alpha-lapachone

alpha-Lapachone is a natural 1,4-naphthoquinone with promising biological activity. The fused dihydropyran ring present in its structure, acting as formal 2-alkoxy and 3-alkyl substituents to the quinone moiety, endows this compound with milder redox properties and lower toxicity, when compared with other bioactive 1,4-quinones. Its photochemistry, here reported, seems to originate from the triplet state, which shows pipi* character. Triplet quenching in acetonitrile solution with added hydrogen-atom donors such as 1,4-cyclohexadiene or 2-propanol is inefficient, independent of solvent polarity, and leads to formation of the semiquinone radical. With phenol and indole, quenching rate constants are two orders of magnitude higher, but smaller than the value for triethylamine. In the first two cases the semiquinone radical can be detected by laser flash photolysis and in the last case, the anion radical derived from alpha-lapachone is readily detected. The semiquinone radical can also be observed in the quenching of triplet alpha-lapachone by 2'-deoxyguanosine and by the methyl esters of L-tryptophan and L-tyrosine, whereas for L-cysteine methyl ester the quenching rate constant is very slow. Triplet alpha-lapachone is not quenched by thymine, thymidine, 2'-deoxycytosine or 2'-deoxyadenosine; this is probably due to its pipi* character and low energy, which prevents oxetane formation and triplet-triplet energy transfer, respectively. Steady-state photolysis of aerated solutions of these compounds in the presence of alpha-lapachone does not show evidence of decomposition, whereas similar experiments with 2'-deoxyguanosine result in efficient consumption of the nucleoside. Singlet oxygen is formed from triplet alpha-lapachone, and a quantum yield of 0.68 is measured.