Barbara Wandelt

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.

Steady-state and time-resolved fluorescence studies of fluorescent imprinted polymers

Abstract Molecular imprinting of synthetic polymers provides a powerful approach to control electronic and optical properties through nanoscale modification of molecular design of the material. The functional monomers were co-polymerised in the presence of a target/imprint molecule, which acts as a molecular template. Subsequent removal of the template molecules left behind functionalised cavities that are able to recognise the template molecule. The steady-state and time-resolved fluorescence spectroscopy studies are presented as methods for monitoring of the specificity and selectivity of binding of the template on the functionalised cavities.

Thin-layer Film with an Incorporated Pyrazoloquinoline Derivative as a Fluorescent Sensor for Nucleotides

A thin-layer film comprising poly(methyl methacrylate) with an incorporated pyrazolo[3,4-b]quinoline derivative was prepared. The dye was anchored onto the polymer film to form a molecular assembly at the surface. Fluorescence quenching of this thin-layer sensory system was observed when the film was incubated in the presence of the nucleotide guanosine-3′,5′-cyclic monophosphate. Steady-state and time-resolved fluorescence techniques were used to study the fluorescence quenching of this sensory system in the presence of nucleotides. The results suggest that quenching of a pyrazoloquinoline fluorosensor by nucleotide anions cannot be described simply by a collision mechanism employing the Stern-Volmer equation, but there is a possibility of the formation of a more stable association. This type of sensing polymer layer plays a role in biotechnology because it can be immobilized at the end of a fibre optic and used for measuring nucleotide concentrations within a biological system.

Polymeric sensing system molecularly imprinted towards enhanced adhesion of Saccharomyces cerevisiae.

Surface molecular imprinting of methacrylate polymers (SMIPs) was applied for obtaining sensory system that was able to selectively adsorb Saccharomyces cerevisiae cells. Molecular imprinting with a stamp prepared from particular microorganisms was applied to modify the polymeric surface during polymerisation. Polymer surface was imprinted against two microorganisms of the top-fermenting brewing yeast strains of S. cerevisiae, differing in cell flocculation behavior, in particular showed in cell wall surface proteins. Two yeast strains: K2 and LVB Gaffel from an industrial microorganism collection were used. High selectivity of the microorganism readsorption by the SMIPs was observed. The properties of surfaces of molecularly imprinted polymers were studied with the use of atomic force microscopy (AFM) working in semi-contact and force spectroscopy modes. A strong enhancement of adhesion between microorganisms and imprinted polymeric surface in comparison to non-imprinted surface was observed. This report presents the first quantification of the enhancement of adhesion forces between microorganisms and polymeric surface caused by modification of the surface with use of molecular imprinting technique. The study has proved that SMIP technology and obtained polymeric matrix can recognize microorganisms and selectively separate the cells of yeast strains of S. cerevisiae family.

Polymeric Sensory Systems Based on Molecular Imprinting for Identification and Separation of Molecules and Bigger Biological Objects

Molecular imprinting of synthetic polymers based on noncovalent interactions play an important role in producing biomimetic receptors that challenge their natural model and also in producing modern drug assays. Formation of a prearranged complex in the presence of noncovalent interactions between the template and receptor is the main idea of processing. A resulting polymer binds the template with an appreciable selectivity over structurally related compounds. A potential use of the imprinted polymers is inconceivable. A molecularly imprinted polymer can be used as polymer particles and films; as a single recognition element and as multi-binding sites and assays. Examples of molecular imprinting in a thin polymeric film and on the polymer surface are presented.

Application of a Photochromic Dye in an Automatic Welding Filter

The main purposes of this study were to select a photochromic dye and to develop an active welding filter with a photochromic layer. A series of functionalized spirobenzopyranoindolins were synthesized and their photophysical and photochemical properties were investigated in a solution using absorption and emission spectroscopy. Time-resolved fluorescence spectroscopy measurements were used to characterize the decays and rate constants of fluorescence emission. One dye was selected as a suitable photoactive compound in automatic welding filters. A model of an active welding filter with a photochromic layer based on 1’,3’,3’-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2’-indole] (6-nitroBIPS) was developed. The paper presents the results of tests of the filter conducted according to EN standards.

Molecularly Imprinted Thin Polymeric Film as a Fluorescent Sensor for Nucleotides

The technology of molecular imprinting of polymers (MIPs) was used to obtain optical sensors for nucleotides. The methacrylates were used as functional monomers and 1,3-diphenyl-6-vinyl-1H-pyrazole-[3,4-b]-quinoline (PAQ) was used as a fluorescent receptor and the nucleotides: guanosine 3′,5′-cyclic monophosphate (cGMP) and adenosine 3′,5′-cyclic monophosphate (cAMP) were a template. The optical sensor obtained as a thin-layer polymeric films was investigated by steady-state fluorescence spectroscopy. The calculated association constant of the cGMP imprinted sensor is Ka = 1.7 × 104 M−1 and of cAMP imprinted sensor Ka = 9.9 × 104 M−1.

Time-resolved excimer fluorescence studies as a probe of the coil collapse transition and phase separation in isotactic polystyrene/benzyl alcohol gel

Abstract Excimer fluorescence decays and time-resolved emission spectra are reported for isotactic polystyrene/benzyl alcohol (iPS/BA) gels stored at 283 K for extended periods of time. Characterization of the collapse of the coil structure is reported from macroscopic shrinkage measurements and microscopic observations of phase separation. A red-shifted band identified in the excimer emission spectrum is due to a long-lived (29 ns) excimer structure corresponding to a polymer-rich phase. Instability over an extended period of time of the long-lived component in the fluorescence decay of iPS gel is discussed.