Gilles Durocher

Steady state and time-resolved fluorescence properties of metastatic and non-metastatic malignant cells from different species

Steady state and time-resolved fluorescence spectroscopy were employed to study the fluorescence from non-metastatic, metastatic and non-tumorigenic cell lines from different species. Excitations at 310 nm and 350 nm were used to monitor tryptophan and reduced nicotinamide adenine dinucleotide (NADH) fluorescence respectively. Subtle and consistent differences were observed between different categories of cell lines. It was found that the tryptophan to NADH fluorescence intensity ratio is higher in metastatic cell lines than in non-metastatic and normal cell lines. The fluorescence decay of the tryptophan residue in different cell lines was best described by triple exponential kinetics, whereas the NADH fluorescence decay was best described by mainly double and, in some cases, triple exponential kinetics. The average fluorescence lifetimes for tryptophan were in the range 2.5-3.7 ns. The average lifetime of NADH was lower (by a factor of approximately three) in metastatic cells than in non-metastatic cells and this finding is consistent for cell lines from different origins (rat or human). Correcting the fluorescence intensity for the average fluorescence lifetime of each species and for the volume of each cell line, it was shown that the concentrations of tryptophan and NADH are consistently higher in malignant metastatic cancer cells than in non-metastatic cells.

Analysis of fluorescence quenching in some antioxidants from non-linear Stern—Volmer plots

Abstract The fluorescence quenching of 6-hydroxy-1,4-dimethylcarbazole (HDC) and α-tocopherol or vitamin E (α-toc) by methylene bromide (CH 2 Br 2 ) in n-butanol was investigated by both stationary and time-dependence measurements. Nonlinear Stern-Volmer behavior was observed in both cases at higher quencher concentrations for these highly exothermic electron transfer (ET) intermolecular reactions. Both static and dynamic quenching models can fit the experimental data, but only the finite sink approximation model was able to recover both the mutual diffusion coefficient and the distance-averaged ‘activation energy controlled’ rate constant ( K a ). The two ET reactions investigated are diffusion-controlled (α-toc) ( K a ⪢ K d ) and diffusion-influenced (HDC) ( k a

Steady-state and time-resolved studies of 2,7-carbazole-based conjugated polymers in solution and as thin films: determination of their solid state fluorescence quantum efficiencies

k d ) respectively.

Spectroscopic and photophysical properties of some new rhodamine derivatives in cationic, anionic and neutral micelles

The UV–Vis absorption spectra and the luminescence properties of poly(N-octyl-2,7-carbazole) (POC) and poly(N-octyl-2,7-carbazole-alt-9,9-dioctyl-2,7-fluorene) PCF have been investigated in solution and in the solid state (thin films). No aggregate and/or excimer formation has been detected in these polymeric systems. From time-resolved fluorescence measurements in solution and in the solid state, the fluorescence efficiencies of the thin films have been estimated. It is found that the fluorescence efficiencies of these polycarbazoles in the solid state are quenched, as compared to those measured in fluid solutions, but remain relatively high (φF≅0.40), making them promising materials for electroluminescent devices.

Novel polyacetylenes containing pendant 1-pyrenyl groups: synthesis, characterization, and thermal and optical properties

Abstract The spectroscopic and photophysical characterization of rhodamine 123 (dye 1 ), 4,5-dibromorhodamine methyl ester (dye 2 ) and 4,5-dibromorhodamine n-butyl ester (dye 3 ) are reported in homogeneous media like water and some alcohols and also in microheterogeneous media; anionic sodium dodecylsulfate (SDS), cationic cetyltrimethylammonium bromide (CTAB) and neutral triton X-100 (TX) micelles. The selective biodistribution of these ionic drugs in tissues and membranes strongly influence their photosentisizing properties which have been part of our earlier studies. Results suggest that the hydrogen bonding capability of the amino end group lone pair of these dyes dominates in water. All these dyes interact with anionic SDS micelles. The interaction is mainly electrostatic in nature. At low SDs concentrations (below c.m.c.), dye-SDS aggregate formation takes place. But above c.m.c. only the monomeric dye form is observed. The penetration of dye 3 in SDS is a little less compared to dyes 1 and 2 . Dyes 2 and 3 show a finite interaction with CTAB micelle unlike dye 1 . With neutral TX micelles all the dyes form strong complexes. The fluorescence quantum yield ( Φ F ) of these three dyes in TX is lower. In time-resolved fluorescence experiments, two lifetimes are observed. The effects of the TX concentration on the fluorescence decay are measured. The decay associated spectra of dye 2 in TX are obtained by global compartmental analysis. The dye-surfactant interaction mechanisms are also discussed.

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

Abstract We report the synthesis as well as the thermal, optical and photophysical properties of four different polyacetylenes with pendant 1-pyrenyl groups: poly(1-ethynylpyrene) (PEP), poly(1-(trimethylsilanylethynyl)pyrene) (PTMSEP), poly(1-(4-(trimethylsilanyl-buta-1,3-diynyl)pyrene) (PTMSBDP) and poly(1-buta-1,3-diynylpyrene) (PBDP). Polymerizations were carried out with W and Ta catalysts, respectively, for mono- and disubstituted monomers. Soluble poly(1-ethynylpyrene) with high molecular weights (up to 4×10 5 ) and extended conjugation of the main chain was obtained with good yields. Lower molecular weights (up to 6×10 3 ) were obtained with the other polymers. Oligomers and polymers displayed high thermal stability. From the absorption spectra of the various polymers, it is found that PEP possesses a higher degree of conjugation than the other polyacetylenes. Molecular interactions occur between pyrene units present in each polymer giving rise to an emission due to associated pyrenes. These interactions are affected by the steric hindrance present in the polymer backbone. Excitation spectra combined with fluorescence decay profiles show that these interactions occur in the ground state (excited complex).

TOWARDS A THEORETICAL DESIGN OF THERMOCHROMIC POLYTHIOPHENES

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.

Conformational analysis and electronic properties of bithiophene and terthiophene in their ground state as well as in their first excited singlet and triplet states

Abstract Ab initio calculations have been performed on several bithiophene derivatives which are the building blocks of substituted polythiophenes in order to correlate their torsional potential energy curves with the thermochromic properties of the parent polymers. It is found that the occurrence of thermochromism in polythiophenes can be related to the values of the energy barrier calculated for the dimer models. Moreover, trends in the thermally induced blue-shift observed with some polythiophene derivatives can be related to the difference in the torsional angles between a co-planar conformation and the more stable conformation of the corresponding bithiophene moieties.

Study of the interactions between substituted 2,2′-bithiophenes and cyclodextrins

Abstract For the first time a joint theoretical and experimental method is proposed that allows one to elucidate the conformations of oligothiophenes in their respective ground and first excited singlet and triplet states. Semiempirical calculations (AM1 and ZINDO/S) are used to obtain the ground state conformation (S0) of bithiophene and terthiophene. Similar potential energy curves are obtained for both molecules. A higher rotational barrier between adjacent rings is calculated for terthiophene suggesting that a higher conjugation length is effective for this molecule. This is confirmed by comparison with experiments. ZINDO/S is used to calculate the energy of the S1 ← S0 electronic transitions as well as the S1 and Tn excited state energies. These calculations suggest that, after excitation, both molecules relax to a planar S1 conformation. The geometry of the molecules in their T1 states is also predicted to be planar. From the S1−Tn energy gaps and the reported values of the intersystem crossing rate constants (kisc) of bithiophene and terthiophene, it is suggested that the Franck-Condon factors are not playing an important role in the intersystem crossing probability of these thiophene oligomers.

Conformational, optical and photophysical properties of a substituted terfluorene isolated and incorporated in a polyester

Abstract The interactions of 4,4′-dimethoxy-2,2′-bithiophene (DMO44BT), 4,4′-dibutoxy-2,2′-bithiophene (DBO44BT), and 2,2′-bithiophene (BT) with α- and/or β-cyclodextrins (CD) were investigated by absorption and steady-state fluorescence spectroscopy. The absorption spectra in all cases are only slightly shifted going from water to the CD cavity showing that the ground state conformations of the bithiophenes in the CD cavity remain similar to that found in water. From fluorescence measurements, it was found that DMO44BT and DBO44BT form 1:2 (guest:host) complexes with α-CD, while DMO44BT and BT form 1:1 complexes with β-CD. The nature of the interactions involved in the inclusion complexes are discussed.