Francoise M. Winnik

Phase transition of aqueous poly-(N-isopropylacrylamide) solutions: a study by non-radiative energy transfer

Abstract The thermoreversible phase separation of aqueous solutions of poly-(N-isopropylacrylamide) (PNIPAM) was investigated by fluorescence experiments that probe transfer of electronic excitation between donor and acceptor chromophores attached to the same polymer chain. Doubly labelled polymers were prepared by reaction of a copolymer of N-isopropylacrylamide and N-acryloxysuccinimide first with 4-(1-pyrenyl)-butylamine, then with 1-naphthylethylamine. Samples were prepared and characterized. They differ in total chromophore incorporation, on average 1 chromophore per 170 and 416 N-isopropylacrylamide units, and in pyrene to naphthalene molar ratio, 3.8 and 7.3, respectively. Non-radiative energy transfer between excited naphthalene and pyrene occurred in solutions of both polymers in water, but not in methanol. The energy transfer efficiency was monitored as a function of solution temperature for the more lightly labelled polymer. The value increased gradually from c. 15% at 15°C to c. 75% for solutions heated above their lower critical solution temperature (LCST). Results are interpreted in terms of a mechanism of phase separation initiated by a gradual shrinking of solvated polymer coils into a collapsed state, followed by aggregation of individual chains into larger particles.

Interactions of liposomes and hydrophobically-modified poly-(N-isopropylacrylamides): an attempt to model the cytoskeleton

The interactions of small unilamellar vesicles (SUV) and water-soluble copolymers were studied by fluorescence spectroscopy, differential scanning calorimetry (DSC) and quasi-elastic light scattering (QELS). The anchoring onto liposomal bilayer membranes of copolymers of N-isopropylacrylamide, N-(2-(1-naphthyl)ethyl)-N-n-octadecylacrylamide and or N-[4-(1-pyrenyl)butyl]-N-n-octadecylacrylamide (0.5 mol% of the octadecylacrylamide comonomer) was monitored by non-radiative energy transfer between excited naphthalene and pyrene. The anchoring process occurred on zwitterionic lecithin liposomes and on negatively charged phosphatidic acid liposomes, whether the bilayer was in the crystalline or the liquid-crystalline phase. Insertion of the copolymer octadecyl groups within crystalline bilayers was attributed to the presence of packing defects. Aqueous solutions of poly-(N-isopropylacrylamide) and of its hydrophobically-modified copolymers exhibit a lower critical solution temperature (LCST). The coil to globule collapse of the polymer chains which is known to occur as the aqueous solution is heated through the LCST, also took place when the copolymers were anchored onto vesicular bilayers. The copolymers remained anchored during this collapse and the liposomes were not destroyed. The process was thermo-reversible. Detailed aspects of the reversibility of the phenomenon depended on the relative values of the phase transition temperatures of the liposomes and of the polymer LCST.

Neural cell pattern formation on glass and oxidized silicon surfaces modified with poly(N-isopropylacrylamide)

Control over the adsorption of proteins and over the adsorption and spatial orientation of mammalian cells onto surfaces has been achieved by modification of glass and other silicon oxide substrates with poly(N-isopropylacrylamide) (PNIPAM). The functionalization of the substrates was achieved either by a polymer-analogous reaction of aminosilanes with reactive N-(isopropylacrylamide) (NIPAM)-copolymers and by copolymerization of NIPAM with surface-bound methacrylsilane. The obtained coatings were characterized by FT-1R, ellipsometry, and surface plasmon resonance measurements. The adsorption of two proteins-fibrinogen and ribonuclease A-on these surfaces was studied in situ by real time surface plasmon resonance measurements. The PNIPAM-grafted surfaces prepared by either chemical procedure inhibited the adsorption of both proteins. More importantly they prevented the adhesion of neuroblastomaXglioma hybrid cells cultured either in serum-free medium or in a medium containing serum proteins. Deep-UV irradiation was used to perform ablation processes and to create patterns permitting the examination of spatially controlled adhesion and growth of cells. This study showed that patterned ultrathin polymer films on glass are suitable substrates for controlling the interactions of cells with surfaces and are capable of directing the attachment and spreading of cells.

New water-dispersible silica-based pigments: synthesis and characterization

Abstract Water-dispersible pigments were prepared by grafting reactive dyes to the surface of derivatized silicas. The silica core consisted of either fumed hydrophilic silica with surface areas of 200 or 380 m2g−1 or monodisperse spherical silica ranging in diameter from 40 to 500 nm. The silica surface was derivatized with silane coupling agents, such as aminopropyltriethoxysilane (APS) and N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane (BHAPS). The coloration proceeded on suspensions of the derivatized silica in water in the presence of a soluble reactive dye. The resulting brightly colored pigments were characterized by particle size analysis and visible absorption spectroscopy.

Coloured particles by dispersion polymerization

Abstract Coloured particles have been prepared by dispersion copolymerization of colourless vinyl monomers and polymerizable anthraquinone dyes. The dyes were synthesized by condensation of methacryloyl chloride and amino- or hydroxy-substituted anthraquinones. This paper describes the formation by dispersion polymerization of coloured copolymer particles of diameter greater than 5 microns. The coloured particles were characterized by size, visible absorption spectra, and solution properties of the copolymers.

Curious new emissive complex between pyrene and N-alkylpyridinium halides in methanol

Abstract A new emissive ground state complex between pyrene and its derivatives and N-alkylpyridinium halides has been observed in methanol. The formation of this complex occurs in addition to the quenching of the pyrene fluorescence by N-alkylpyridium salts. The emission spectrum of the complex has three bands centered at 381, 404, and 424 m. The complex has a lifetime similar to that of pyrene in the presence of quencher.

FLUORESCENCE STUDIES OF HYDROPHOBIC POLYMERS IN WATER: PHASE TRANSITIONS IN AQUEOUS POLY-(N-ISOPROPYLACRYLAMIDE) SOLUTIONS

Phase transitions of dye-labeled poly-(N-isopropylacrylamides) (PNIPAM) in dilute solution have been studied by two steady-state fluorescence techniques. These probe a) the relative intensity of pyrene monomer and excimer emissions from a pyrene-labeled polymer (PNIPAM-Py/200) and b) the efficiency of Forster energy transfer between a donor (naphthalene) and an acceptor (pyrene) attached to a doubly-labeled polymer (PNIPAM-Py/366-N/50). The phase transitions were induced either by heating solutions of the polymers in water or by varying the composition of methanol/water polymer solutions. Results are interpreted in terms of a mechanism of phase separation initiated by a gradual shrinking of solvated polymer coils into a collapsed state, followed by aggregation of individual chains into larger particles.

The preparation and characterization of new thioanthraquinone dyes

Abstract A synthetic route to derivatives of 1,8-dihydroxy-2,7-diisobutyl-4-thioaryl-anthraquinones and 1,5-dihydroxy-2,6-diisobutyl-4-thioarylanthraquinones is described. The new red and purple dyes are fully characterized. The effect of the suhstituents of the thiophenoxy group on the color of the dyes is correlated to the Hammett σ values of the substituents.