Fluorescence decay and quenching of pyrene labeled on sulfonate polyelectrolytes in salt-free aqueous solutions

Fluorescence decay and quenching of pyrene labels on copolymers of 2-acrylamido-2-methylpropanesulphonic acid (AMPS) and N,N-dimethylacrylamide were observed in dilute salt-free aqueous solutions as a function of the mole fraction F_AMPS of AMPS from 0 to 0.896. Monoexponential decay was found for the samples of F_AMPS<0.35 and biexponential decay for the samples of F_AMPS>0.35. The fast decay component is 80%, and the averaged lifetime 〈τ〉 and lifetime τ₁ of the fast decay is decreased with increasing F_AMPS. Quenching efficiency of Cu²⁺, I⁻, CH₃NO₂, and dinitrobenzene to the pyrene label was investigated in the framework of Stern-Volmer plot. With increasing F_AMPS the quenching efficiency of Cu²⁺ is increased while that of I⁻ decreased. For the neutral quenchers, the quenching rate constant k_q increases when F_AMPS<0.449 then decreases, showing a decline of accessibility to the pyrene label. These results were interpreted consistently with the counterion condensation concept, where condensed counterions caused the polyelectrolyte chains to aggregate. The existence of less-polar “temporal aggregated domain” in highly charged polyelectrolytes appears to lead to the slower decay and lower accessibility of the pyrene labels.     

Photophysical investigations of interpolymer interactions in solutions of a pyrene substituted poly(acrylic acid), poly(vinyl amine), poly(1-aminoacrylic acid), and poly(1-acetylaminoacrylic acid)

Photophysical properties of the pyrene chromophore covalently bound to poly(acrylic acid) were used to investigate the interactions of a pyrene substituted poly(acrylic acid) (1) with poly(vinyl amine hydrochloride) (PVAm), poly(1-aminoacrylic acid) (PDA), and poly(1-acetylaminoacrylic acid) (PADA) in aqueous solutions. A number of photophysical parameters were obtained from fluorescence emission and excitation spectra, the deconvolution of decay curves for pyrene monomer, and excited state complex fluorescence and the quenching of pyrene monomer fluorescence by nitromethane in polymer solutions. These photophysical parameters were considered to reflect the inter- and intrapolymer interactions in solutions of 1 , PVAm, PDA, and PADA. The formation of interpolymer complexes between 1 and PVAm was noticed at low (< 4) as well as high (> 8) values, whereas PDA and 1 formed interpolymer complexes at low pH only. No interpolymer complex formation was detected in solutions of 1 and PADA under low or high pH conditions. The structures of interpolymer complexes formed between 1 and PVAm under low and high pH conditions were found to be determined by the conformation of 1 . There were significant differences in the interpolymer interactions of 1 and PDA in comparison to those of 1 and PVAm; in particular, the fluorescence from the excited state complex was enhanced in solutions of 1 and PVAm but quenched in solutions of 1 and PDA. The investigations of terpolymer solutions of 1 , PVAm, and PADA indicated that the nature of interpolymer complexes formed in terpolymer solutions was determined by Coulombic interactions of the amino and carboxylic group containing polymers.     

Influence of the conformational state of polymethacrylic acid on the photophysical properties of pyrene in aqueous solution: A fluorescent probe and laser photolysis study

The excited state of pyrene observed in fluorescence and pulsed laser techniques is used to show that pyrene is solubilized in the polymer coil of aqueous solution of polymethacrylic acid (PMA) at pH < 4–5. This leads to a decreased access of molecules such as I^?, Tl⁺, CH₃NO₂, and O₂ to excited pyrene in the polymer coil. The protection of the excited state by solubilization in the polymer is sufficient to enable 3-bromopyrene phosphorescence to be observed at room temperature in these systems. Increasing the pH of the system uncoils the polymer and leads to increased accessibility of excited pyrene to CH₃NO₂; eventually, at pH >5, the pyrene is ejected into the aqueous phase of the system. In the presence of micellar solutions of surfactants increasing pH transports the pyrene from the polymer to the micellar aggregates. These fluorescence techniques are used to investigate the kinetics of expansion of the polymer coil. The system is suggested as a suitable model for the interaction of pyrene with biopolymers such as DNA.     

Pyrene Fluorescence in the Presence of Acrylic Acid-Ethyl Methacrylate Copolymers: Effect of the Copolymer Composition in the Formation of Microdomains*

The properties of aqueous solutions of acrylic acid-ethyl methacrylate (EMA) copolymers have been investigated using pyrene and pyrene pyrenebutyltrimethylammonium (PBTA) as probes. Static and dynamic fluorescence have been used to obtain information about the microenviron-ments formed. Micropolarity studies using the I₁/I₃ ratio of the vibronic bands of pyrene show the formation of hydrophobic domains. At low pH the increase of the amount of ethyl methacrylate in the copolymers shows that aqueous microdomains are excluded from the core of the polymer, for the copolymers with high content of EMA low polarity microdomains are still present on the mac-romolecular chain even at higher pH. The pH-induced conformational transition indicates that the more hydro-phobic copolymers adopt a more tightly coiled conformation. Compared to PAA, the decay times for both probes are increased twice for the polymer with 25% molar proportion of EMA. The fluorescence quenching of the probes by nitromethane depends on pH, copolymer composition and probe structure. The efficiency of quenching decreases with increase of the EMA proportion in the copolymers. Pyrene is more efficiently quenched than PBTA as a consequence of the latter being located in more internal (less accessible) sites of the polymer structure.     

Open-chain polyazaalkanes functionalised with pyrene groups as sensing fluorogenic receptors for metal ions

The new open-chain polyazaalkanes ligands L¹, L², L³ and L⁴ functionalised with one or two pyrene groups were synthesised and characterised and their potential use as selective cation and anion sensing chemosensors studied. Solution studies by potentiometric methods were carried out in the presence of the metal cations Cu²⁺ and Zn²⁺ in acetonitrile–water (70:30 v/v, 0.1 mol dm⁻³ tetrabutylammonium perchlorate, 25 °C) The results are compared with those reported for the analogous non-functionalised ligand triethylentetraamine (tta). The fluorescence behaviour of the ligands L¹–L⁴ has been studied as a function of the pH in the presence of the metal cations Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺ and Pb²⁺ in acetonitrile–water 70:30 v/v mixtures. The Zn²⁺ and Cd²⁺ cations enhance the fluorescence emission of the L¹–L⁴ chemosensors at basic pH, whereas Cu²⁺ induce quenching of the fluorescence emission at acid pH. The fluorescence behaviour of L¹–L⁴ receptors was also studied as a function of the pH in acetonitrile–water 70:30 v/v in the presence of anions.     

新型经由三氮唑连接的含芘基团的杯[4]芳烃：对锌离子的比率荧光识别及其在组合逻辑门中的应用

通过“click”反应合成了两个新的由三氮唑连接的含芘的杯[4]芳烃。 化合物1含有两个芘单元,对Zn2+表现出比率荧光响应,且对Cu2+, Hg2+ 和 Pb2+表现出选择性的荧光淬灭;而化合物2只含一个芘单元,对铜离子有显著的荧光淬灭,对汞离子有中等程度的荧光淬灭。利用化合物1对锌离子和铜离子不同的荧光响应,设计了INH和NOR逻辑门。     

Hg-selective fluoroionophoric behavior of pyrene appended diazatetrathia-crown ether

Bis(pyrene) derivative of diazatetrathia-crown ether has been prepared and its Hg²⁺-selective fluoroionophoric properties were investigated. The compound showed a pronounced Hg²⁺-selectivity and other metal ions except for Cu²⁺ showed almost no discernible responses. The Hg²⁺-selectivity of the compound was also confirmed by the competitive experiments performed in the presence of physiologically important metal ions and the detection limit was found to be 1.6 × 10⁻⁶ M. The prominent selective and efficient fluorescence quenching behavior could be utilized as a new chemosensing system for the analysis of toxic Hg²⁺ ions in aqueous environment.     

Probing solubilization sites in block copolymer micelles using fluorescence quenching

The solubilization sites provided by micelles formed by a diblock copolymer with one neutral hydrophobic block, polystyrene, and one charged hydrophilic block, poly(acrylic acid) or poly(methacrylic acid), have been studied by fluorescence quenching of pyrene by polar and nonpolar quenchers. Pyrene solubilized into these micelles is distributed between the inner corona and the micelle core. The fraction of pyrene residing in the inner corona is almost unity for star micelles, where the corona-forming blocks are larger than the core-forming blocks, and around 0.5 for crew-cut micelles where the opposite situation prevails. The kinetics of the quenching process depends on the pyrene location, i.e. is static in the micelle core, and largely dynamic in the inner corona at low quencher concentration. The rate constants for fluorescence quenching by nitromethane are shown to increase with increasing pH.     

MECHANISMS OF QUENCHING OF THE FLUORESCENCE OF A BENZO[a]PYRENE TETRAOL METABOLITE MODEL COMPOUND BY 2'-DEOXYNUCLEOSIDES

Abstract— The hydrophobic interactions of bulky polycyclic aromatic hydrocarbons with nucleic acid bases and the formation of noncovalent complexes with DNA are important in the expressions of the mutagenic and carcinogenic potentials of this class of compounds. The fluorescence of the polycyclic aromatic residues can be employed as a probe of these interactions. In this work, the interactions of the (+)-trans stereoisomer of the tetraol 7,8,9,10-tetrahydroxytetrahydrobenzo[a]pyrene (BPT), a hydrolysis product of a highly mutagenic and carcinogenic diol epoxide derivative of benzo[a]pyrene, were studied with 2′-deoxynucleosides in aqueous solution by fluorescence and UV spectroscopic techniques. Ground-state complexes between BPT and the purine derivatives 2′-deoxyguanosine (dG), 2′-deoxyadenosine (dA), and 2′-deoxyinosine (dI) are formed with association constants in the range of ～40–130 M^?1 Complex formation with the pyrimidine derivatives 2′-deoxythymidine (dT), 2′-deoxycytidine (dC), and 2′-deoxyuridine (dU) is significantly weaker. Whereas dG is a strong quencher of the fluorescence of BPT by both static and dynamic mechanisms (dynamic quenching rate constant k_dyn= [2.5 ± 0.41 × 10⁹M¹ s ¹, which is close to the estimated diffusion-controlled value of ～ 5 × 10⁹M^{? 1} s^?1), both dA and dI are weak quenchers and form fluorescenceemitting complexes with BPT. The pyrimidine derivatives dC, dU, and dT are efficient dynamic fluorescence quenchers (K_dyn～ [1.5–3.0] × 10⁹M^?1 s^?1), with a small static quenching component due to complex formation evident only in the case of dT. None of the four nucleosidcs dG, dA, dC and dT are dynamic quenchers of BPT in the triplet excited state; the observed lower yields of triplets are attributed to the quenching of single excited states of BPT by 2′-deoxynucleosides without passing through the triplet manifold of BPT. Possible fluorescence quenching mechanisms involving photoinduced electron transfer are discussed. The strong quenching of the fluorescence of BPT by dG, dC and dT accounts for the low fluorescence yields of BPT-native DNA and of pyrene-DNA complexes.     

Fluorescence study for the electrostatic interaction and aggregation in dilute polar solution of polyelectrolytes

Fluorescence decay and quenching of pyrene labels on copolymers of 2-acrylamido-2-methylpropanesulphonic acid (AMPS) and N,N-dimethylacryl-amide (DMAA) were observed in dilute salt-free aqueous solutions as a function of the mole fraction F_AMPS of AMPS from 0 to 0.896. Monoexponential and biexponential decays were found for the samples of F_AMPS < 0.35 and samples of FAMPS > 0.35, respectively. The fast decay component is 80% and the averaged lifetime <τ> and lifetime τ₁ of the fast decay decreased with increasing F_AMPS. Quenching efficiency of Cu²⁺, CH₃NO₂, and dinitrobenzene to the pyrene label was investigated in the framework of Stern-Volmer plot. The quenching effects of Cu²⁺ included both of dynamic and static ones, the latter was due to the condensed Cu²⁺. For the neutral quenchers, the quenching rate constant k_q increased when F_AMPS < 0.449 then decreased, showing a decline of accessibility to the pyrene label. I₁/I₃ value in salt-free dilute aqueous solution and in DMSO solution decreased obviously with an increase in F_AMPS, indicating that the labeled fluorophore experienced a decrease in polarity of its microenvironment with increasing charge density of the polymer. This I₁/I₃ decrease was enhanced with increasing the polymer concentration and adding salt NaCl up to 0.75 mol/L showed no effect on the appearance of this decrease. These results were interpreted consistently with the counterion condensation concept, where condensed counterions induced the “temporal” aggregation of less-polar in the polyelectrolyte solutions surrounding the pyrene labels.     

Photochemistry of iminium salts in the presence of N-electron donating alcohols and ethers

Irradiation of 2-phenyl and 2-isobutenyl-1-pyrrolinium salts in solutions of alcohols and ethers containing α-hydrogens leads to production of addition products. In addition, alcohols and ethers having low ionization potentials and α-hydrogens serve as efficient quenchers of fluorescence from 2-phenyl-1-pyrrolinium salts. Deuterium isotope effects on fluorescence quenching rate constants appear to implicate electron transfer mechanisms in photoaddition and quenching pathways.     

Quenching of excited states of pyrene sulfonate solutions and their metal complexes by molecular oxygen

The results of study of fluorescence quenching, by molecular oxygen, of unsubstituted pyrene solutions within the framework of exchange complex are generalized. The oxygen quenching rate constants of the fluorescence and triplet state of pyrene monosulfonate and pyrene tetrasulfonate solutions and their aggregates and complexes (second and first coordination spheres) with REE ions in H₂O, DMSO, and DMFA are measured. The effect of the number of substituting sulfo groups, aggregates, complex formation, and the nature of the solvent on the efficiency of this quenching is investigated. It is shown that, in contrast to metalloporphyrins with the paramagnetic Cu(II) ion, the formation of pyrenesulfonates complexes with REE paramagnetic ions does not lead to an increase in oxygen quenching efficiency of the triplet state of organic ligands.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 23, No. 3, pp. 302–311, May–June, 1987.The authors express their deep gratitude to Prof. V. L. Ermmolaev for a fruitful discussion of the results.     

Synthesis and Characterization of a Water‐Soluble Carboxylated Polyfluorene and Its Fluorescence Quenching by Cationic Quenchers and Proteins

We have developed a new intermediate monomer, 2,7‐[bis(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)‐9,9‐bis(3‐(tert‐butyl propanoate))]fluorene, that allows the easy synthesis of water‐soluble carboxylated polyfluorenes. As an example, poly[9,9′‐bis(3′′‐propanoate)fluoren‐2,7‐yl] sodium salt was synthesized by the Suzuki coupling reaction, and the properties of the polymer were studied in aqueous solutions of different pH. Fluorescence quenching of the polymer by different cationic quenchers (MV²⁺, MV⁴⁺, and NO₂MV²⁺; MV=methyl viologen) was studied, and the quenching constants were found to be dependent on the charge and electron affinity of the quencher molecule and the pH of the medium. The largest quenching constant was observed to be 1.39×10⁸ M ^?1 for NO₂MV²⁺ at pH 7. The change in polymer fluorescence upon interaction with different proteins was also studied. Strong fluorescence quenching of the polymer was observed in the presence of cytochrome c, whereas weak quenching was observed in the presence of myoglobin and bovine serum albumin. Lysozyme quenched the polymer emission at low protein concentrations, and the quenching became saturated at high protein concentrations. Under similar experimental conditions, the polymer showed improved quenching efficiencies toward cationic quenchers and a more selective response to proteins relative to other carboxylated conjugated polymers.     

Nitroanilines as Quenchers of Pyrene Fluorescence

The quenching of pyrene and 1‐methylpyrene fluorescence by nitroanilines (NAs), such as 2‐, 3‐, and 4‐nitroaniline (2‐NA, 3‐NA, and 4‐NA, respectively), 4‐methyl‐3‐nitroaniline (4‐M ‐3‐NA), 2‐methyl‐4‐nitroaniline (2‐M‐4‐NA), and 4‐methyl‐3,5‐dinitroaniline (4‐M‐3,5‐DNA), are studied in toluene and 1,4‐dioxane. Steady‐state fluorescence data show the higher efficiency of the 4‐NAs as quenchers and fit with a sphere‐of‐action model. This suggests a 4‐NA tendency of being in close proximity to the fluorophore, which could be connected with their high polarity/hyperpolarizability. In addition, emission and excitation spectra evidence the formation of emissive pyrene—NA ground‐state complexes in the case of the 4‐NAs and, in a minor degree, in the 2‐NA. Moreover, time‐resolved fluorescence experiments show that increasing amounts of NA decrease the pyrene fluorescence lifetime to a degree that depends on the NA nature and is larger in the less viscous solvent (toluene). Although the NA absorption and the pyrene (Py) emission overlap, we found no evidence of dipole–dipole energy transfer from the pyrene singlet excited state (¹Py) to the NAs; this could be due to the low NA concentration used in these experiments. Transient absorption spectra show that the formation of the pyrene triplet excited state (³Py) is barely affected by the presence of the NAs in spite of their efficiency in ¹Py quenching, suggesting the involvement of ¹Py—NA exciplexes which—after intersystem crossing—decay efficiently into ³Py.     

Proton-transfer mediated quenching of pyrene/indole charge-transfer states in isooctane solutions

The fluorescence quenching of pyrene (Py) by a series of N-methyl and N-H substituted indoles was studied in isooctane at 298 K. The fluorescence quenching rate constants were evaluated by mean of steady-state and time-resolved measurements. In all cases, the quenching process involves a charge-transfer (CT) mechanism. The I(o)/I and tau(o)/tau Stern-Volmer plots obtained for the N-H indoles show a very unusual upward deviation with increasing concentration of the quenchers. This behavior is attributed to the self-quenching of the CT intermediates by the free indoles in solution. The efficiency of quenching of the polyaromatic by the N-H indoles increases abruptly in the presence of small amount of added pyridine (or propanol). A detailed analysis of the experimental data obtained in the presence of pyridine provides unambiguous evidence that the self-quenching process involves proton transfer from the CT states to indoles.     

Self-assembly of pyrene boronic acid-based chemodosimeters for highly efficient mercury(II) ion detection

A new chemodosimeter consisting of pyrene and boronic acid (1) for the detection of Hg²⁺ ions is described. The amphiphilic nature of 1 leads to self-assembly in aqueous solution and the high electron density throughout the aggregated pyrene units provides an outstanding platform for energy and electron transport. Self-assembled 1 exhibits a selective and sensitive fluorescence response to Hg²⁺ ions, where the Hg²⁺ ion allows a fast transmetallation of 1, which drastically reduces its fluorescence. The Stern-Volmer (SV) quenching constant for the fluorescence quenching of self-assembled 1 by Hg²⁺ ions is approximately 1.8 × 10⁶ M^?1, and Hg²⁺ ions can be sensed with a detection limit of 6.6 × 10^?9 M. In addition, self-assembled 1 exhibits excellent sensing performance at nano-molar concentration levels for Hg²⁺ ion contamination of tap water, fresh water, and seawater.     

A novel intramolecular charge transfer fluorescent chemosensor highly selective for Cu<Superscript>2+</Superscript> in neutral aqueous solutions

A selective and sensitive intramolecular charge transfer (ICT) fluorescent chemosensor was designed for Cu²⁺ in neutral aqueous solutions of pH 7.0. The design of this totally water-soluble fluorescent chemosensor was based on the binding motif of Cu²⁺ to aminoacid, which is coupled to an ICT fluorophore bearing a 1,3,4-thiodiazole moiety in the electron acceptor. The formation of a 1:1 complex of Cu²⁺ to 2 was suggested to lead to fluorescence quenching. The quenching obeyed Stern-Volmer theory in neutral aqueous solution of pH 7.0 for Cu²⁺ over 5.0 × 10⁻⁷ to 3.0 × 10⁻⁵ mol·L⁻¹, with a quenching constant of 1.8 × 10⁵ L·mol⁻¹ and a detection limit of 2.0 × 10⁻⁷ mol·L⁻¹. The binding of Cu²⁺ to 2 can be fully reversed by addition of chelator EDTA, affording a reversible sensing performance.     

Pyrene fluorescence quenching and triplet-state formation in the presence of DABCO (1,4-Diazabicyclo[2-2-2]octane): A laser photolysis study

In this paper, we present a study of fluorescence quenching of pyrene by DABCO in cyclohexane solutions. The absorption spectra of pyrene singlet state ¹S-ⁿS have been measured in the presence and in the absence of DABCO; the spectra are practically identical. The de-excitation of singlet pyrene by DABCO seems to be a non-reversible process leading to the triplet state, the probability of formation of this triplet state being near unity in the quenching process.     

Distribution of fluorocarbon quencher among micelles via pyrene fluorescence probe method

 Fluorescence-quenching of pyrene in micellar system has been investigated using 1,1,2,2-tetrahydroheptadecafluorodecylpyridinium chloride (HFDePC). The new fluorocarbon quencher has a similar quenching ability as hexadecyl-pyridinium chloride (CPC) towards pyrene in hydrocarbon micelles if only a quencher molecule is solubilized in a micelle. The fluorocarbon quencher randomly distributed among micelles if the average occupancy number of probes per a micelle was small enough. The fluorescence behavior of pyrene was examined for hexadecyl-trimethylammonium chloride (CTAC) and HFDePC mixtures. The variation of fluorescence intensity gave second cmc, reflecting the micellar immiscibility of fluorocarbon and hydrocarbon surfactants. The second cmc can be simulated by material balances of both surfactants supposing the coexistence of two kinds of mixed micelles. The fluorescence-quenching behavior suggested the enhanced micellar immiscibility probably due to nonrandom distribution of fluorocarbon quenchers among micelles. Received: 13 March 1997 Accepted: 24 May 1997