Graham D. Darling

Effect of temperature and viscosity on intramolecular charge-transfer fluorescence of a 4-p-dimethylaminostyrylpyridinium salt in protic solvents

The steady-state fluorescence of a 4-p-dimethylaminostyrylpyridinium salt (1) has been studied in aqueous solutions. An orange emission band close to 600 nm arose from two excitation bands, at 360 and 469 nm. Possible origins of species responsible for the red-side emission are discussed: (i) excitation at 360 nm, followed by twisted intramolecular charge transfer (TICT) and (ii) excitation at 469 nm of a different ground state with intramolecular charge transfer (ICT).The effect of temperature and solvent viscosity on the fluorescence quantum yield of both charge transfer (CT) bands of 1 has been investigated. The Debye–Stokes–Einstein hydrodynamic model gave an accurate description of the reorientation dynamics of the fluorescent probe. At low viscosities, the quantum yield of the charge transfer fluorescence was linear with solvent viscosity. The activation energy of the thermally activated reorientation relaxation for both CT bands corresponds to the viscosity energy of activation of the medium. Nearly identical activation energies for both CT bands suggest that the corresponding emitting species have the same origin.

Substituted 4-[4-(dimethylamino)styryl]pyridinium salt as a fluorescent probe for cell microviscosity

In aqueous solution, 4-[4-(dimethylamino)styryl]pyridine (DMASP) derivatives displayed dual fluorescence, in which excitation at either 469 or 360 nm produced an emission band near 600 nm. Increasing the viscosity of the environment intensified the fluorescence emission obtained at the longer wavelength of excitation, whereas the emission at the lower wavelength of excitation showed little change in intensity. Thus, using the ratio of the 600 nm emission obtained by exciting at 469 nm to that obtained with 360 nm excitation, it is possible to obtain a value related to the local viscosity that does not depend on the system parameters. The fluorescence emission of the dye in aqueous solution, as well as in living cells, is well suited for use with visible fluorescence spectroscopy. The N-carboxymethyl butyl ester DMASP derivative (1) was found to be irreversibly loaded into living smooth muscle cells, presumably because it is hydrolyzed by cellular esterases, transforming it into a membrane-impermeable fluorescent carboxylate DMASP derivative. (2) After calibrating 2 against glycerol/water and sucrose/water mixtures of known viscosity, the fluorescence ratio generated from cultured smooth muscle cells in dual-excitation mode gave an average intracellular viscosity of 4.5 cP. This value corresponds to those reported in the literature.

Fluorescent molecularly imprinted polymer studied by time-resolved fluorescence spectroscopy

Abstract Molecularly imprinted polymers (MIPs) with template-selective recognition sites and incorporated fluorosensor were prepared against adenosine 3′,5′-cyclic monophosphate (cAMP). The time-resolved fluorescence decay analysis was used to investigate the specificity and affinity of the binding of template molecules to the MIP. The fluorescence decays were modelled in terms of lifetime distributions and two fluorescence lifetimes were observed for the MIPs. The lifetime distributions are interpreted in terms of the heterogeneity of the functionalised imprinted cavities. Quenching of fluorescence of the imprinted polymer with increasing concentration of aqueous cAMP was observed from the fluorescence lifetime parameters data. The mechanisms of interactions between the cAMP and fluorosensor molecules inside the imprinted cavity in comparison with the interactions in solution are discussed.

Enhanced fluorescence of 4-(p-dimethylaminostyryl)pyridinium salts in the presence of biological macromolecules

The fluorescence quantum yields of two cationic styrylpyridinium dyes, trans-4-(p-N,N-dimethylaminostyryl)-N-vinylbenzylpyridinium chloride (1) and trans-4-(p-N,N-dimethylaminostyryl)-N-phenethylpyridinium bromide (2), increase dramatically in the presence of low concentrations of DNA with slight blue shifts (4 and 8 nm, respectively) of the emission maxima. These spectral changes suggest that the dyes are interacting with double helical DNA. Dyes 1 and 2 display similar enhancements in fluorescence in the presence of proteins, such as bovine serum albumin, with blue shifts in the emission maxima of 28 and 33 nm, respectively, suggesting that they also interact with proteins. Equilibrium association constants in the order of 104 l mol−1 were determined for the binding of 1 and 2 to bovine serum albumin. This family of dyes may be useful for the fluorescence detection of very low concentrations of DNA and proteins, and for the fluorescence staining of DNA and proteins in electrophoresis gels.

Completely water-processable and other chemically amplified resists from maleic anhydride copolymers

A new family of resists is presented that makes possible an all-water (sub)micron scale lithography. It was found by infrared (IR) and thermo-gravimetric analysis (TGA) studies, that polymers with vicinal carboxylic acid moieties undergo thermo-acid-catalyzed dehydration and anhydride formation at a lower temperature, than upon simple uncatalyzed thermolysis. Carboxylic acid moieties allow the use of water for spin-coating, developing, and stripping. For example, ethylene- or methyl vinyl ether-alt-maleic anhydride copolymers with a photo- acid generator can be spin-coated from water to form clear films. Mild heating at 110 - 10 degrees Celsius for 20 - 60 s before and after greater than or equal to 25 mJ/cm2 of UV irradiation, produces a latent image that is developable in water within seconds. Similar acid- catalyzable alcohol elimination was observed with some monoesters, for example poly(styrene- alt-maleic acid monoethyl ester). The difference in reactivity and hydrophobicity between exposed and non-exposed areas also follows functional developing, e.g., the introduction of polyamino compounds or metal ions selectively into non-exposed resist areas.

Functional polymers from (vinyl)polystyrene. Enzyme immobilization through a cysteinyl-S-ethyl spacer

By radical-catalyzed addition to residual vinyl groups, cysteine was S-linked to porous beads of divinylbenzene/ethylstyrene copolymer. Subsequent treatment with acetic anhydride gave polystyrene-supported azlactone groups able to covalently bind enzymes out of aqueous solution under mild conditions. Pseudomonas cepacia lipase thus immobilized remained active for the hydrolysis of esters, even after storage and/or several cycles of use and recovery.

Dialkyl fumarate copolymers: new photoresist materials for deep- and mid-UV microlithography

Photopatterning is described using chemically amplified resists formulated from the copolymer of di-t-butyl fumarate and styrene with various acid-photogenerators. Exposure of the materials to deep- and mid-UV light followed by postbaking results in significant changes in solubility and polarity due to carboxylic functions produced on the polymer chain through the action of photogenerated acid catalyst (chemical amplification). As resists, they possess good sensitivity (14-40 mJ/cm2), contrast ((gamma) >4) and thermostability (up to 300 degree(s) C). Relief images with good resolution can be readily obtained with either aqueous base (positive-tone) or organic (negative-tone) solvents as developer. Such photoinduced changes of the functional groups in the exposed areas were also used to pattern molecules on the surface at micron-scale, thus generating functional images, as illustrated by the selective binding of fluorescent dyes in either exposed (positive-tone) or unexposed (negative-tone) areas.

Synthesis of Hydrogenated Oligo(isoprene)carboxylic Acid N-Alkanolamides: A New Group of Nonionic Surfactants

Abstract Uniform hydrogenated oligo(isopcene)carboKylic acid N-alkanolamides were prepared in high yields by living anionic oligomerizalion of isoprene, followed by carboxylaliou with dry ice, hydrogcnaiion, then amidauon with several commercial alkanolamincs.