Perturbation of fluorescence by nonspecific interactions between anionic poly(phenylenevinylene)s and proteins: implications for biosensors

The use of anionic water-soluble conjugated polymers (CPs) for sensing the presence of avidin by use of a biotin-modified fluorescence quencher was studied. The molecules involved in the study included poly[2-methoxy-5-(3'-propyloxysulfonate)-1,4-phenylenevinylene] with either lithium (Li+-MPS-PPV) or sodium (Na(+)-MPS-PPV) countercations, the well-defined oligomer pentasodium 1,4-bis(4'(2",4"-bis(butoxysulfonate)-styryl)-styryl)2-butoxysulfonate-5-methoxybenzene (5R5-), the quenchers N-methyl-4,4'-pyridylpyridinium iodide (mMV+) and [N-(biotinoyl)-N'-(acetyl 4,4'-pyridylpyridinium iodide)] ethylenediamine (BPP+), which contains a molecular recognition fragment (biotin) attached to a unit that accepts an electron from a CP excited state, and the proteins avidin, tau, BSA, and pepsin A. Fluorescence quenching experiments were examined in a variety of conditions. Experiments carried out in water and in ammonium carbonate buffer (which ensures avidin/biotin complexation) reveal that nonspecific interactions between the CP and the proteins cause substantial perturbations on the CP fluorescence. The overall findings are not consistent with a simple mechanism whereby avidin complexation of BPP+ leads to encapsulation of the quencher molecule and recovery of Li+-MPS-PPV fluorescence. Instead, we propose that binding of BPP+ to avidin results in the quenching unit attaching to a positively charged macromolecule. Electrostatic attraction to the negatively charged conjugated polymer results in closer proximity to the quencher. Therefore, more enhanced fluorescence quenching is observed.     

Synthesis and properties of poly(silylenevinylene(bi)phenylenevinylene)s by hydrosilylation polymerization

Poly(silylenevinylene(bi)phenylenevinylene)s were synthesized by chloroplatinic acid-catalyzed hydrosilylation polymerization between α,ω-diethynylarenes and methylphenylsilane or diphenylsilane. The polymer structure was dependent on the substituent size of silane reagent. Poly(silylenevinylenephenylenevinylene)s showed fluorescence emission in the blue region. Optical and thermal properties of the polymers were extensively investigated. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2933–2940, 1999     

Photoinduced electron transfer of fullerenes (C60 and C70) studied by transient absorption measurements in near-IR region

Efficiencies and rates of electron transfer from various electron donors to excited fullerenes (C₆₀ and C₇₀) have been determined by observing the transient absorption bands in the near-IR region, where the anion radicals of fullerenes appear. From the rise of the absorption bands of C₆₀ ⁻⁺ and C₇₀ ⁻⁺ in the near-IR region, electron transfer takes place via the triplet states (^TC₆₀ ^* and ^TC₇₀ ^*) under appropriately low concentrations of electron donors. By analysis of the rise curves C₆₀ ⁻⁺ and C₇₀ ⁻⁺, contribution of the excited singlet states (^SC₆₀ ^* and ^SC₇₀ ^*) in addition to the route of the triplet states (^TC₆₀ ^* and ^TC₇₀ ^*) is confirmed. The quantum yield for electron transfer via the triplet states Φ_ct ^T was evaluated by the ratio of [C₆₀ ⁻⁺]/[^TC₆₀ ^*] (or [C₇₀ ⁻⁺/[^TC₇₀ ^*]). The Φ_ct ^T depends upon the donor-ability, donor concentration, and solvent polarity. The back electron-transfer process, which was evaluated by observing C₆₀ ⁻⁺, also depends upon the solvent polarity.     

Photoinitiated thermolysis of poly(phenylenevinylene) precursor and photochemical doping of poly(phenylenevinylene)

The photoinitiated elimination of methoxy groups of poly(p-phenylene-1-methoxyethylene) and the photochemical doping of the resulting poly(phenylenevinylene) (PPV) were investigated. Upon irradiation and then heat treatment at 150°C, poly(p-phenylene-1-methoxyethylene) containing triphenylsulfonium hexafluoroantimonate was converted to PPV. The resulting PPV was observed to be conductive, and its conductivity was 10⁻²–10⁻³ S/cm. By a lithographic procedure, we produced a conducting pattern doped photochemically in a nonconjugated poly(p-phenylene-1-methoxyethylene) matrix.     

Hydration of poly(ethylene oxide)s in aqueous solution as studied by dielectric relaxation measurements

The hydration state of poly(ethylene oxide)s (PEOs) in aqueous solutions was investigated using dielectric relaxation measurements at 25 degrees C over a frequency range up to 20 GHz, which is the relaxation frequency of water molecules in a bulk state. The dielectric relaxation spectra obtained indicated decomposition into two major and one minor relaxation modes with relaxation times of 8.3, 22, and 250 ps, respectively. The two major modes were attributed to rotational relaxation of water molecules belonging to the bulk state and water molecules hydrogen bonded to ethylene oxide (EO) monomer units. The number of hydration water molecules per EO unit depended on the molar mass of PEO (M) and reached a constant value of 3.7 at M > 1500, which agrees with the value obtained by other experiments.     

Synthesis of poly(Schiff-base)s by organometallic processes

Some new monomers with Schiff-base structures and bromine final atoms were obtained by combining condensation reactions of dialdehydes or diamines with p-bromoaniline or p-bromobenzaldehyde. The corresponding polymers were synthesized by Ni- or Pd-catalyzed polycondensation reactions in combination with 2,5-dihexylbenzene-1,4-diboronic acid. The new structures were characterized by spectral methods (¹H NMR, IR, UV-vis) as well as by thermal analyses (TGA, DSC).     

Cyclization reaction of polyacrylonitrile and poly(styrene-co-acrylonitrile) studied by PVT measurements

Pressure, volume, temperature (PVT) measurements reveal that during the intramolecular cyclization reaction of poly(acrylonitrile) (PAN) and poly(styrene-co-acrylonitrile) (SAN) the volume decreases. This volume contraction becomes smaller with increasing styrene content in the random copolymers and should be related to the simultaneous decrease of longer acrylonitrile homo-sequences. The onset temperature of the cyclization reaction is raised with higher styrene contents in the random copolymers. Thus, it can be excluded that the cyclization reaction has a major influence on the discoloration process of SAN samples having relatively small acrylonitrile contents (less than 50 mol-%) during thermal annealing below 300°C.     

Sodium dodecyl sulfate-poly(amidoamine) interactions studied by AFM imaging, conductivity, and Krafft temperature measurements

The conductivity, kappa, and Krafft temperature, TK, of sodium dodecyl sulfate (SDS) with poly(amidoamine) dendrimers (PAMAM) of 0.0, 0.5, and 1.0 generations (G) have been determined at different surfactant as well as PAMAM concentrations. The critical micelle concentration of SDS increases with the increase in the amount of each generation and the additive effect of 0.5G is maximum. TK of SDS shows a systematic decrease with maximum reduction in the presence of 0.5G. Atomic force microscopy (AFM) captures a layered pattern of 1.0G in the form of nanorods and no AFM images are detected for 1.0G in the presence of SDS. All results demonstrate that SDS has favorable interactions with ester-terminated 0.5G PAMAM rather than amine-terminated 0.0G and 1.0G.     

Photoinduced electron transfer and nonlinear absorption in poly(carbazole-alt-2,7-fluorene)s bearing perylene diimides as pendant acceptors

This paper reports the synthesis, photophysical behavior, and use in nanosecond optical-pulse suppression of a poly(2,7-carbazole-alt-2,7-fluorene) and a poly(3,6-carbazole-alt-2,7-fluorene) in which the carbazole N-positions are linked by an alkyl chain to one of the nitrogen atoms of a perylene-3,4,9,10-tetracarboxylic diimide (PDI) acceptor. It was found that the PDI pendants on the polymer side chain aggregated even in dilute solution, which extended the onset of PDI absorption into the near-infrared (NIR). Transient-absorption spectra of these polymers provide evidence for efficient electron transfer following either donor or acceptor photoexcitation to form long-lived charge-separated species, which exhibit strong absorption in the NIR. The spectral overlap between the transient species and the long-wavelength absorption edge of the aggregated PDI leads to reverse saturable absorption at 680 nm that can be used for optical-pulse suppression. Additionally, at high input energies, two-photon absorption mechanisms may also contribute to the suppression. PDI-grafted polymers exhibit enhanced optical-pulse suppression compared with blends of model materials composed of unfunctionalized poly(carbazole-alt-2,7-fluorene)s and PDI small molecules.     

Molecular orientation in poly(vinyl chloride) studied by Raman spectroscopy and birefringence measurements

The ratios of the intensities of Raman scattering in the C? CI stretching region for eight combinations of sample orientation and directions of polarization of incident and scattered light have been measured for 15 samples of poly(vinyl chloride) (PVC) containing 0, 5, 10, 15 or 20 pph dioctyl sebacate (DOS) plasticizer which had been drawn uniaxially at 22, 70, 75, 80, or 90°C to draw ratios in the range 1–4.5. The birefringences of the samples were also measured. The Raman data were analyzed to give 〈P₂(cosθ)〉_cryst and 〈P₄(cosθ)〉_cryst, the values of the second- and fourth-order Legendre polynomials in cosθ averaged over the distribution of orientations of the crystallites, where θ is the angle between the c axis of a typical crystallite and the draw direction. Comparison of 〈P₂(cosθ)〉_cryst with the birefrigence showed that the crystallites are more highly oriented than the noncrystalline material in samples containing the higher amounts of plasticizer drawn at the higher temperatures. A value of 13.0 × 10^?3 was deduced for the birefringence of fully oriented PVC. The values of 〈P₄(cosθ)〉_cryst for a given 〈P₂(cosθ)〉_cryst were found to be higher than predicted by calculations based on two simple models, the pseudoaffine rigid-rod rotation model and the affine rubber elasticity model.     

Synthesis,optical absorption and fluorescence of new poly(p-phenylene)-related polymers

The synthesis and properties of soluble, conjugated polymers consisting of oligo(p-phenylene) sequences linked by ethylene, vinylene, or ethylene, units are reported. Benzene-, stilbene-, diphenylacetylene- and 1,2-diphenylethane derivatives serve as monomers and are connected by the Suzuki-coupling method. A wide range of poly-(p-phenylene)-related polymers are available by the combination of different AA/BB-type monomers in various concentrations. The optical properties of the resulting polymers can therefore be tailored. Number-average degrees of polymerization of up to X̄_n = 137 were reached under optimized conditions. Photoluminescence quantum yields of these materials in solution are nearly one.     

Dynamics of poly(L-lysine) in hyaluronic acid/poly(L-lysine) multilayer films studied by fluorescence recovery after pattern photobleaching

Poly( L-lysine) (PLL)/hyaluronic acid (HA) multilayers are films whose thickness increases exponentially with the number of deposition steps. Such a growth process was attributed to the diffusion, in and out of the whole film, of at least one of the polyelectrolytes constituting the film. In the case of PLL/HA, PLL is known to be the diffusing species. In order to better understand the growth mechanism of such films, it is of primary importance to well characterize the diffusion process of the polyelectrolytes in the multilayer. This process is studied here by fluorescence recovery after pattern photobleaching. We show that the diffusion behavior is different when we consider either PLL chains that are deposited on top of the film or PLL chains embedded in the film, even below only one HA layer. For chains that are embedded, we find two populations: a mobile one with a diffusion coefficient, D, of the order of 0.1 microm(2) x s(-1) and a population that appears immobile ( D < 0.001 microm(2) x s(-1)). For chains deposited on top of the multilayer, a third population appears which is rapidly diffusing ( D congruent with 1 microm(2) x s(-1)). These results confirm the validity of the model generally accepted for the exponential growth process and in particular the existence of up to three subgroups of PLL chains from the point of view of their diffusion coefficient.     

Photoinduced charge transfer in molecular materials studied by optical absorption using photoacoustic spectroscopy

Photoacoustic spectra of molecular materials based on the assembling of the [Fe(CN)₆] molecular block were recorded and evaluated. Those compositions where the valence of the involved metals allows a charge transfer (an inner photoinduced redox reaction) through the CN ligand shown an intense photoacoustic signal around 600 nm; when this transition is unable only the signal corresponding to metal-to-ligand and d-d transitions within the metal were observed. This suggests that this technique provides a fast and reliable method to explore the existence of tunable photoinduced charge transfer in molecular materials.     

Synthesis, characterization, and optical response of dipolar and non-dipolar poly(phenylenevinylene) dendrimers

New dipolar and non-dipolar poly(phenylenevinylene) dendrimers bearing electron-donating and electron-withdrawing groups have been efficiently synthesized using Heck and Horner-Wadsworth-Emmons reactions. The photoluminescence of these systems may be tuned in the blue zone by choosing the appropriate peripheral groups. Despite the meta-substitution pattern, large Stokes shifts can be observed when pi-donor and pi-acceptor groups are connected by a m-phenylenevinylene system.     

Control of surface functionality in poly(phenylenevinylene) dendritic architectures

The efficient synthesis of new asymmetric poly(phenylenevinylene) dendritic macromolecules using a stepwise convergent-growth approach is described. By an iterative methodology that made use of the Horner-Wadsworth-Emmons (HWE) reaction, dendrons and dendrimers up to the third generation, with eight different functional groups located at the periphery, were prepared in good yields. Both the number and placement of functionalities can be accurately controlled to afford a large variety of dendritic architectures.     

Excitation and decay processes in helium clusters studied by fluorescence spectroscopy

Excitation and decay processes of helium clusters are investigated with fluorescence methods. The results differ remarkably from that obtained for the heavier rare gas clusters. They are discussed in view of the unusual structural and electronic properties of helium.     

Acid-base equilibria of dipyridylethylenes studied by absorption and fluorescence spectrometry

In connection with photochemical and fluorimetric studies and with previous pK measurements on styrylpyridines, the acid-base equilibria of the trans-1,2-dipyridylethylenes have been studied by absorption and fluorescence spectrometry. The results obtained by the two methods are compared and the pK's of first and second protonation discussed in dependence with the nitrogen positional isomerism. The measurements of the dissociation constant of the trans-3-styrylpyridinium ion is also reported as a particularly convenient application of fluorescence spectrometry.     

Interactions of cationic gemini surfactants with hydrophobically modified poly(acrylamides) studied by fluorescence and microcalorimetry

Steady-state fluorescence, time-resolved fluorescence quenching, and isothermal titration microcalorimetry have been used to study the interactions of cationic gemini surfactants alkanediyl-alpha,omega-bis(dodecyldimethylammonium bromide) (C(12)C(S)C(12)Br(2), S = 3, 6, and 12) with hydrophobically modified poly(acrylamide) (HMPAM) and unmodified poly(acrylamide) (PAM). Without addition of gemini surfactant, 0.2 wt % HMPAMs except PAM have already self-aggregated into hydrophobic aggregates. Different from single-chain surfactants, C(12)C(S)C(12)Br(2) have stronger interactions with HMPAMs to form surfactant/polymer aggregates, even with PAM. Addition of C(12)C(S)C(12)Br(2) may cause the disruption of HMPAM hydrophobic aggregates and the formation of mixed micelles. It is found that HMPAMs generate lower micropolarity of mixed micelles, larger values of enthalpy of interaction (DeltaH(ps)), and nearly constant values of Gibbs free energy of interaction (DeltaG(ps)). On the other hand, C(12)C(S)C(12)Br(2) with longer spacer brings out slightly lower micropolarity of mixed micelles, owing to the lower electrostatic repulsion between surfactant headgroups. Especially for C(12)C(12)C(12)Br(2), the values of DeltaH(ps) are much more endothermic and the values of DeltaG(ps) are much less negative. The weaker interactions of C(12)C(12)C(12)Br(2) with HMPAMs arise from the marked reduction of attraction between surfactant headgroups and polymer hydrophilic groups induced by its longer spacer.