Jean-Philippe Soumillion

Anticancer drugs, ionophoric peptides, and steroids as substrates of the yeast multidrug transporter Pdr5p.

Pdr5p is the yeast Saccharomyces cerevisiae ATP-binding cassette transporter conferring resistance to several unrelated drugs. Its high overproduction in Pdr1p transcription factor mutants allows us to study the molecular mechanism of multidrug transport and substrate specificity. We have developed new in vivo and in vitro assays of Pdr5p-mediated drug transport. We show that in spite of little sequence homology, and inverted topology in respect to that of mammalian P-glycoproteins, Pdr5p shares with them common substrates. Pdr5p extrudes rhodamines 6G and 123, from intact yeast cells in an energy-dependent manner. Plasma membrane preparations from a Pdr5p-overproducing strain exhibit ATP hydrolysis-dependent, osmotically sensitive rhodamine 6G fluorescence quenching. The quenching is competitively inhibited by micromolar concentrations of many anticancer drugs, such as vinblastine, vincristine, taxol, and verapamil, and of ionophoric peptides as well as steroids. In contrast, other anticancer drugs, like colchicine and some multidrug resistance modifiers, such as quinidine, exert noncompetitive inhibition. Our experimental system opens new possibilities for the analysis of structure-function relationship of multidrug transporter substrates and inhibitors.

Luminescence and charge transfer. II: Aminomethyl anthracene derivatives as fluorescent PET (photoinduced electron transfer) sensors for protons

The importance of the modular structure ‘fluor-spacer-amine ’is pointed out for the design of fluorescent molecular sensors for pH according to the principle of photoinduced electron transfer (PET). Anthracen-9-yl methylamines (24) and some azacrown ether analogues (15 and 23) are examined in this context. They show pH-dependent fluorescence quantum yields describable by eqn. (5) while all other electronic spectral parameters remain essentially pH-invariant. The range of pKa values of these sensors are understandable in terms of macrocyclic effects and the transmission of electric fields across the anthracene short axis. Phase-shift fluorometric determination of the fluorescence lifetimes of these sensors allows the calculation of the rate constant of PET in their proton-free form to be 1010–1011 s–1, with the diamines 23 and 24b exhibiting the faster rates.

Photosensing by a fluorescing probe covalently attached to the silica

Starting from aminopropyl silicagel, an anthracene fluorophore has been covalently grafted on the surface of silica, the secondary amino group being left in the linking arm. When one fifth of the initial amino functions are grafted, the silica behaves as a pH probe, the fluorescence of which switches on when the amino groups are protonated. On the contrary, if the silica loading is almost complete, the pH probing is no longer possible. In this case, an excimeric versus monomeric emission can be used in sensing the solvent water content. Copyright (C) 1996 Elsevier Science Ltd

Ion-responsive fluorescent compounds V. Photophysical and complexing properties of coumarin 343 linked to monoaza-15-crown-5

The photophysical and complexing properties of a fluoroionophore consisting of coumarin 343 linked to monoaza-15-crown-5 are reported in acetonitrile and ethanol. The amide link between the coumarin and the crown precludes pH sensitivity of the tertiary amine bridging group. Upon complexation by calcium and magnesium cations, the photophysical properties undergo marked changes, whereas the effects are insignificant or very weak with alkali metal ions. I.R. spectra were recorded in deuterated acetonitrile in order to unravel the participation of the carbonyl groups in the complexation. The stoichiometry of the complexes is 1:1 apart from the case of complexation with calcium in acetonitrile where two complexes can be formed. The stability constants of the complexes were determined in acetonitrile and ethanol.

Poly(amidoamine) dendrimer peripherally modified with 4-N,N-dimethylaminoethyleneamino-1,8-naphthalimide as a sensor of metal cations and protons.

A new poly(amidoamine) dendrimer from second generation whose periphery comprises sixteen fluorescent 4-N,N-dimethylaminoethylamino-1,8-naphthalimide units has been synthesized and characterized. In DMF, the dendrimer shows sensitivity to the presence of Cu(2+), Fe(3+) and protons. The changes in the fluorescence intensity of the material are in opposite directions if acids or metals are present. Fluorescence enhancements (FE from 5 to 9 depending on solvent) are recorded when the photoinduced electron transfer (PET) originating from the donating amine to the electron accepting naphthalimide is inhibited by the protonation of the N,N-dimethylamino groups. In the case of Cu(2+) cations, a fluorescence quenching (FQ of 6) is first observed, followed by fluorescence partial restoration. In the Fe(3+) case, the same behaviour is observed with a final FE of 2. The successive complexations of these cations by the dendrimer core and by the external rim of the dendrimer may explain the results.

Oxidation of sulfides and disulfides under electron transfer or singlet oxygen photosensitization using soluble or grafted sensitizers

Two different photosensitizers, 9,10-dicyanoanthracene (DCA) and benzophenone (BzO) or a silica bound derivative (BzO-Si) have been compared for the photooxidation of di-n-butyl sulfide and di-n-butyl disulfide. With either photosensitizer, sulfide photooxidation in acetonitrile leads very efficiently to sulfoxide, with sulfone and disulfides as by-products. Although an electron transfer mechanism has previously been established starting with DCA, our results are indicative of two competitive mechanisms using BzO as the photosensitizer, instead of singlet oxygen addition and electron transfer. The more sluggish photooxidation of disulfides leads to a complex mixture of products, among which n-butyl butanethiosulfonate and strong acids (alkylsulfonic and sulfuric) are the major ones. The relative ratio thiosulfonate: acids depends, among other factors, on the medium polarity with acid formation favored starting with BzO or BzO-Si in a methanol-water mixture. An electron transfer mechanism only can account for the observed products Superoxide anion, the formation of which is much easier starting from BzO than from DCA, is suggested to play a crucial role in this oxidative radical pathway. Starting from disulfides, grafted benzophenone is more efficient for acid formation than its soluble counterpart. As this photosensitizer can easily be recycled, an easy and smooth way to acid formation is thus available, provided that the reaction solvent is properly chosen.

Organic sulfides photooxidation using sensitizers covalently grafted on silica : towards a more efficient and selective solar photochemistry

A visible light sensitized oxidation of organic sulfides using a derivative of 9,10 dicyanonoanthracene (DCA) covalently grafted on silica (DCAC-Si) is studied. The reaction is more efficient than the corresponding homogeneous reaction and some improvement in the rate of product formation is noticed. These observations are discussed. In the case of di n-butylsulfide, the sulfoxide/(sulfone + disulfide) selectivity is increased. Diphenyl sulfide leads selectively and efficiently to diphenylsulfoxide. Advantages of the process, using reusable sensitizer and solar light are emphasized

Ion-responsive fluorescent compounds: VI. Coumarin 153 linked to rigid crowns for improvement of selectivity

The photophysical and complexing properties of fluoroionophores consisting of the coumarin C153 linked to dibenzo-16-crown-5 (C153-DBC) and tribenzo-19-crown-6 (C153-TBC) are described in acetonitrile and ethanol. The carbonyl group of the coumarin moiety is in direct interaction with a bound cation. The selectivity of these compounds for a given alkali or alkaline earth metal ion was found to be better than that of previously reported crowned coumarins owing to the rigidity of dibenzo- and tribenzocrowns. In acetonitrile, a very high selectivity for Ca2+ versus Mg2+ has been found. In ethanol, C153-DBC is selective for Na+ and C153-TBC is selective for K+, as expected from the relative size of the crown cavity

Solvent-Free Production of Singlet Oxygen at the Gas-Solid Interface: Visible Light Activated Organic-Inorganic Hybrid Microreactors Including New Cyanoaromatic Photosensitizers

We synthesized new cyanoaromatics, benzo[b]triphenylene-9,14-dicarbonitrile (DBTP) 1a and a graftable derivative, 9,14-dicyanobenzo[b]triphenylene-3-carboxylic acid (DBTP-COOH) 1b, easily prepared from commercial reagents. Their photosensitizing properties were investigated. Hybrid porous silica monoliths loaded with encapsulated 1a or grafted 1b were prepared, and their adsorption, spectroscopic and photosensitizing properties, as well as stability, were compared. Solvent-free, efficient oxidation of dimethylsulfide (DMS) was observed at the gas-solid interface under visible light irradiation. Quantum yields of formation of 1O2 inside the porous monoliths are comparable to those of phenalenone. Singlet oxygen lifetimes (approximately 25 micros) were found to be longer in silica monoliths than in usual polar solvents such as methanol or ethanol. This new class of hybrid materials work as porous, transparent, and highly efficient microreactors for oxidation reactions under visible light.

A halogen anion sensor based on the hydrophobic entrapment of a fluorescent probe in silica sol-gel thin films

A halogen anion (Cl−, Br−, I−) sensor has been designed, based on the entrapment of a fluorescent molecule in a sol-gel silica film deposited on a glass substrate. A key factor is the use of the newly synthesized hydrophobic fluorophore, N-dodecyl-6-methoxyquinolinium, so as to avoid the problem of leaching. This probe allows detection and measurement of chloride concentrations in the physiological range (100 mM) coupled with a response time less than 1 s. The fluorescence quenching data are fitted to a model which assumes two quenching sites.