Pyrene Fluorescence Research Articles

Probing the sources of the apparent irreproducibility of amyloid formation: drastic changes in kinetics and a switch in mechanism due to micellelike oligomer formation at critical concentrations of IAPP.

The aggregation of amyloidogenic proteins is infamous for being highly chaotic, with small variations in conditions sometimes leading to large changes in aggregation rates. Using the amyloidogenic protein IAPP (islet amyloid polypeptide protein, also known as amylin) as an example, we show that a part of this phenomenon may be related to the formation of micellelike oligomers at specific critical concentrations and temperatures. We show that pyrene fluorescence can sensitively detect micellelike oligomer formation by IAPP and discriminate between micellelike oligomers from fibers and monomers, making pyrene one of the few chemical probes specific to a prefibrillar oligomer. We further show that oligomers of this type reversibly form at critical concentrations in the low micromolar range and at specific critical temperatures. Micellelike oligomer formation has several consequences for amyloid formation by IAPP. First, the kinetics of fiber formation increase substantially as the critical concentration is approached but are nearly independent of concentration below it, suggesting a direct role for the oligomers in fiber formation. Second, the critical concentration is strongly correlated with the propensity to form amyloid: higher critical concentrations are observed for both IAPP variants with lower amyloidogenicity and for native IAPP at acidic pH in which aggregation is greatly slowed. Furthermore, using the DEST NMR technique, we show that the pathway of amyloid formation switches as the critical point is approached, with self-interactions primarily near the N-terminus below the critical temperature and near the central region above the critical temperature, reconciling two apparently conflicting views of the initiation of IAPP aggregation.

Liquid–liquid interfacial behavior of dopamine modified poly(γ-glutamic acid) polymer

Dopamine (DA) was frequently used as a versatile platform to prepare functional coatings for diverse uses due to the excellent surface adhesion property. Our previous research work revealed that the dopamine moieties could enhance the amphiphilicity of polymer and increased the adsorption of polymer at the oil–water interface. This work reported the liquid–liquid interfacial behavior of dopamine modified poly(γ-glutamic acid) polymer (γ-PGA-g-DA) and how the structural transformation of polymer varied with pH value in turn to affect its emulsifying property. The conformation of the γ-PGA-g-DA in aqueous solution was confirmed by means of aqueous electrophoresis techniques, ultraviolet–visible spectrophotometry (UV–vis), dynamic light scattering (DLS), pyrene fluorescence probe and transmission electron microscopy (TEM) methods. The liquid–liquid interfacial behavior was investigated through emulsification experiment. The results revealed that γ-PGA-g-DA had no emulsification below pH 5.0 with a self-assembled aggregate structure. However, γ-PGA-g-DA exhibited excellent emulsifying property above pH 5.0 with a random chain structure. The added tension-activity will offer γ-PGA-g-DA wide applications in the cosmetic, medicine, and food industries due to the biocompatibility and moisture retention of γ-PGA.

A highly specific pyrene-based fluorescent probe for hypochlorite and its application in cell imaging

A fluorescent probe, 1-pyrenecarboxaldehyde, 2-phenylhydrazone (1), has been successfully developed for the detection of hypochlorite on the basis of a specific reaction with phenylhydrazone. The design strategy for the probe is based on the strong quenching effect of electron-donor phenylhydrazone on pyrene fluorescence via the photoinduced electron transfer process, and is accomplished through constructing the conjugated molecule by using a cleavable CN bond as a linker. This probe reacts selectively with hypochlorite over other ions and reactive oxygen species (ROS), accompanied by 42.6-fold fluorescence enhancement. Biological imaging studies using living cells (HeLa cells) to detect hypochlorite are successfully demonstrated.

New insights into binding interaction of novel ester-functionalized m-E2-m gemini surfactants with lysozyme: a detailed multidimensional study

Different binding patterns of m-E2-m (12-E2-12 and 14-E2-14) surfactants to HEWL.

ASSOCIATION OF BRANCHED POLYETHYLENE IMINE WITH SURFACTANTS IN AQUEOUS SOLUTION

Three polymer-surfactant systems comprised of branched polyethylene imine (PEI) with an anionic surfactant (sodium dodecylsulfate; SDS), a cationic surfactant (tetradecyltrimethylammonium bromide; TTAB), and a zwitterionic surfactant (N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate; SB3-14) were studied based on the properties of surface tension, pyrene fluorescence emission, dynamic light scattering, pH, and zeta potential measurements. The critical aggregation concentration (cac) and polymer saturation point (psp) were determined for all three systems. The effect of these surfactants on the physico-chemical characteristics (diameter and surface charge) of the complexes formed was determined. Polymer-surfactant interactions occurred in all of the systems studied, with the strongest interactions, electrostatic in nature, occurring in the SDS-PEI system. After the neutralization of the polymer charges with the addition of the surfactant, the hydrophobic effect started to control the interlacing of the polymer chains. For the PEI-TTAB system, a very dense film was formed at surfactant concentrations above 2.0 mmol L-1. In this case, the bromide counter-ion interacted with both the positively-charged PEI and the head of the surfactant, which is responsible for the formation of double layer coordination complexes. For the system composed of PEI and the zwitterionic surfactant, less cooperative associations occurred in comparison with the other systems.

Micelle-Vesicle Transition by Cleavage of Disulfide Spacer Chain for Gemini Surfactant in Didodecyldimethylammonium Chloride Aqueous Solutions.

We examined the "micelle-vesicle transition" through the mixing effect of single-tailed thiol surfactants produced by the cleavage of gemini surfactants, [C12H25N(CH3)2CH2CH2SSCH2CH2N(CH3)2C12H25] 2Cl (C12SSC12), which have a disulfide bond in the spacer chain. Phase diagrams of C12H25N(CH3)2CH2CH2SHCl-didodecyldimethylammonium chloride (C12SH-DDAC) and C12SSC12-DDAC were determined by conductivity and pyrene fluorescence probe methods. The aggregate diameters were evaluated by dynamic light scattering (DLS). The critical vesicle concentration (CVC) was confirmed by the abrupt increase in the intensity of light scattering with excitation at 335 nm. Vesicle formation was confined to the DDAC-rich region of the C12SSC12-DDAC system, while the vesicle formation region for the C12SH-DDAC system spread out with the addition of dithiothreitol (DTT) to C12SSC12-DDAC. This implies that single-tailed surfactants can induce a more favorable environment for molecular packing of the vesicular surface. The micelle-vesicle transition occurs with disulfide spacer chain cleavage of gemini surfactants at a particular specific concentration range.

Self‐Assembly of Amphiphilic Block Copolypeptoids with C2‐C5 Side Chains in Aqueous Solution

Nowadays, amphiphilic molecules play an important role in our life. In medical applications, amphiphilic block copolymers have attracted much attention as excipients in drug delivery systems. Here, the polymers are used as emulsifiers, micelles, or polymersomes with a hydrophilic corona block and a hydrophobic core or membrane. The aggregation behavior in aqueous solutions of a series of different amphiphilic block copolypeptoids comprising polysarcosine as a hydrophilic part is here reported. The formation of aggregates is investigated with 1H NMR spectroscopy and dynamic light scattering, and the determination of the critical micelle concentration (cmc) is performed using pyrene fluorescence spectroscopy. For the different block copolypeptoids cmc values ranging from 0.6 × 10−6m to 0.1 × 10−3m are found. The tendency to form micelles increases with increasing hydrophobicity at the nitrogen side chain in the hydrophobic moiety. Furthermore, in the case of the same hydrophobic side chain, a decreasing hydrophilic/lipophilic balance leads to the formation of larger aggregates. The aggregates formed in the buffer are able to solubilize the hydrophobic model compounds Reichardt's dye and pyrene, and exhibit versatile microenvironments. Final investigations about the cytotoxicity reveal that the block copolypeptoids are well tolerated by mammalian cells up to high concentrations. image

Pyrene Fluorescence in Nanoaggregates Irradiated by IR Photons

Abstract Pyrene fluorescence of a molecular donor-acceptor nanoaggregate induced by infrared (IR) radiation with λ =16 - 18 μm considered.We assume that this nanoaggregate consists of two molecules, exchanging energy by dipole-dipole interaction. The energy acceptor is an aromatic molecule. The other molecule, the energy donor, is assumed to contain a substructure CnH2n which serves as antenna for IR radiation. The antenna can accumulate collective vibrational excitations and transmit them to the acceptor molecule. Acceptor fluorescence is possible if the amount of transmitted energy is equal to the energy of its excited state in the visible part of the absorption spectrum. We analyse the fluorescence of a nanoaggregate consisting of a donor with a C5H10 substructure and pyrene molecules or pyrene dimers as acceptors. A method is proposed for determination of the ‘critical micelle concentration’ (CMC), i. e. concentration of a dissolved polymer, for which the polymer molecules are beginning to aggregate.

Complexation (cucurbit[6]uril-pyrene): Thermodynamic and spectroscopic properties

The influence of the macrocyclic compound cucurbit[6]uril (CB6) on the photophysical properties of the fluorophore pyrene (PYR) has been studied. Guest–host interaction was observed by UV–visible spectroscopy and spectrofluorimetry. The fluorescence of PYR was significantly increased in the presence of CB6. The binding equilibrium constants for the complex with 1:1 stoichiometry were determined in HCOOH 55% w/v. The values of the association constants, KA, and the fluorescence quantum yield ratios between complexed and free substrate, ϕPYR–CB6/ϕPYR, at different temperatures were (3.1±0.9)×102M−1 and (5.1±0.2), (3.6±0.5)×102M−1 and (5.9±0.1), (4.8±0.7)×102M−1 and (5.5±0.1) at 15.0°C, 25.0°C and 40.0°C, respectively.The enthalpic and entropic contributions to the complexation process were determined, yielding ΔS=(92±3) Jmol−1K−1 and ΔH=(13±1) kJmol−1. From these results it can be concluded that the complex formation is mainly driven by the entropic term. The forces involved in the complexation are interpreted from the sign and magnitude of the thermodynamic parameters obtained.The partial inclusion of PYR or the formation of a suspended complex is proposed in base of all the data. The interaction is also demonstrated in the solid state by differential scanning calorimetric (DSC) measurements.

Noncovalent Interaction between Single-Walled Carbon Nanotubes and Pyrene-Functionalized Gold Nanoparticles in Water-Soluble Nanohybrids

The combination of different nanostructures in a multifunctional nanostructured hybrid is expected to improve their functionalities and lead to synergistic effects. In these regards, carbon nanotubes and gold colloids are well-studied building blocks with unique optical and electronic properties, which could be combined in a variety of optoelectronic applications. In this framework, we herein present an innovative approach to the preparation of water-soluble nanohybrids by noncovalent interaction between single-walled carbon nanotubes (SWCNTs) and gold nanoparticles (AuNPs) cofunctionalized with pyrenyl and choline residues. To this aim, we developed a procedure based on consecutive centrifugation steps, which allows straightforward isolation of the conjugates in their water-soluble form. Each step of the process was monitored by TEM and by UV–vis–NIR absorption spectroscopy to characterize the obtained nanohybrids and to confirm that the interaction of the pyrene residues of the cofunctionalized AuNPs with the nanotube walls is the only one responsible for the formation of the water-soluble nanohybrids. Further investigations including Raman spectroscopy and photoluminescence mapping confirm that the interaction between the AuNPs and the SWCNTs is arguably noncovalent and thus assures that the emission in the NIR region by the nanotubes is preserved. Measurements of the quenching of the fluorescence of pyrene by carbon nanotubes provide the association constants for complex formation between the cofunctionalized AuNPs and SWCNTs. The results reported herein provide the basis to novel strategies for the preparation of water-soluble nanohybrids between AuNPs and SWCNTs based on noncovalent interactions.

On the Application of the Pseudophase Model to Excited State Processes: Quenching of Pyrene by the Iodide Ion in β‐Cyclodextrin and Micellar (SDS) Solutions

ABSTRACTThe pseudophase model, a two‐state model, is based on the assumption of the existence of an equilibrium between these two states (free and bound), which is not perturbed in the case of a reactive event. This implies that the processes in which these two states participate must be slow, in relation to the exchange processes between these states. This condition does not hold in the case of very rapid photochemical quenching processes. However, for these processes the pseudophase model is formally applicable. In this paper, a treatment that quantitatively explains this formal applicability is presented. This treatment is checked through the study of the quenching of pyrene fluorescence by the iodide ion in solutions containing β‐cyclodextrin and sodium dodecyl sulfate (SDS) micelles.

Star-shaped polycaprolactone-polyethyleneglycol copolymer micelle-like nanoparticles for picropodophyllin delivery.

The purpose of this work was to develop a novel picropodophyllin-loaded micelle-like nanoparticle with a biodegradable amphiphilic star-shaped polycaprolactone-polyethyleneglycol copolymer (S-PCL-PEG). S-PCL-PEG was synthesized using star-shaped polycaprolactone (S-PCL) as a hydrophobic block and monomethoxy polyethyleneglycol (PEG) as a hydrophilic block and characterized by 1H-NMR. It was confirmed by the pyrene fluorescence probe method that the obtained S-PCL-PEG could form micelles through self-assembly in aqueous media. In addition, picropodophyllin (PPP), a hydrophobic anticancer drug, could be entrapped in the hydrophobic inner core of the micelles using the thin film hydration method, forming PPP-loaded micelle-like nanoparticles (PPP-NPs). PPP-NPs had a high encapsulation efficiency of greater than 90%, an average size of 90-110 nm with a symmetrical monodisperse distribution and a zeta potential of -18 mV. Additionally, in vitro release tests showed that approximately 70% of the drug was released from PPP-NPs into PBS (pH 7.4) containing 0.2% Tween 80 at 37 degrees C for 96 h, and the drug release data fit well to the Higuchi equation. Furthermore, an in vitro tumor cell growth inhibition assay showed that the IC50 values of the PPP solution and PPP-NPs against SMMC7721 liver cancer cell lines were 0.4 microg/ml and 0.2 microg/ml respectively, which indicated that the cytotoxicity of PPP-NPs against tumor cells was greater than that of the PPP solution. In conclusion, S-PCL-PEG micelle-like nanoparticles loaded with PPP have a promising future for administration by injection.

Glossoscolex paulistus extracellular hemoglobin (HbGp) oligomeric dissociation upon interaction with sodium dodecyl sulfate: Isothermal titration calorimetry (ITC).

Annelid erythrocruorins are respiratory proteins with high cooperativity and low autoxidation rates. The giant extracellular hemoglobin of the earthworm, Glossoscolex paulistus (HbGp), has a molecular mass of 3.6 MDa. In this work, isothermal titration calorimetry (ITC), together with DLS and fluorescence emission have been used to investigate the interaction of SDS with the HbGp in the oxy-form, at pH 7.0. Our ITC and DLS results show that addition of SDS induces oxy-HbGp oligomeric dissociation, while a small amount of protein aggregation is observed only by DLS. Moreover, the oligomeric dissociation process is favored at lower protein concentrations. The temperature effect does not influence significantly the interaction of SDS with the hemoglobin, due to the similarities presented by the critical aggregation concentration (cac) and critical micelle concentration (cmc') for the mixtures. The increase of oxy-HbGp concentration leads to a slight variation of the cac values for the SDS-oxy-HbGp mixture, attributed mainly to the noncooperative electrostatic binding of surfactant to protein. However, the cmc' values increase considerably, associated to a more cooperative hydrophobic binding. Complementary pyrene fluorescence emission studies show formation of pre-micellar structures of the mixture already at lower SDS concentrations. This study opens the possibility of the evaluation of the surfactant effect on the hemoglobin stability by ITC, which is made for the first time with this extracellular hemoglobin.

Conductometric and fluorescence probe investigations of molecular interactions between dodecyltrimethylammonium bromide and dipeptides

The effect of five dipeptides (glycylglycine, glycyl-l-valine, glycyl-l-leucine, glycyl-l-glutamine, and l-alanyl-l-glutamine) on the micellar properties of catonic surfactant dodecyltrimethylammonium bromide (DTAB) has been investigated by electrical conductivity and fluorescence spectroscopy. From the conductivity data, the critical micellar concentration (c cmc), counterion binding constant (β), and thermodynamic parameters of micellization (ΔG m o , ΔH m o and ΔS m o ) have been calculated. The effect of dipeptides on the micellar properties of DTAB depends upon their nature and concentration as well as on temperature and has been used to study the interactions present in the micellar systems. Enthalpy–entropy compensation effect has also been observed. The pyrene fluorescence spectra were used as an index for the estimation of micropolarity of micellar produced by the interaction of DTAB with dipeptides and the aggregation behavior of DTAB. Comparison on the interactions between different types of surfactants and dipeptide showed that the order of the strength for these interactions is TX-100 < DTAB < SAS < SDS.

Study of the interactions in dicationic gemini–anionic conventional mixed surfactant systems in the viewpoint of regular solution theory

In the present study, the influence of the hydrocarbon chain length of gemini surfactants on the process of micellization in mixed surfactant systems was investigated. Experiments were carried out with alkyldiyl-α, ω-bis(tetradecyldimethylammonium bromide) (m-4-m) dicationic gemini (m=14, 16)/anionic sodium dodecylbenzene sulfonate (SDBS) mixed surfactant systems in different ratios. The critical micelle concentration (cmc) values of binary mixtures of surfactants were evaluated using surface tension measurements. Results showed that mixtures of the SDBS with gemini surfactants possessed significant deviations from ideal behavior (attractive interactions). The application of the regular solution theory (RST) to experimental data yielded the interaction parameter at mixed micelles (β) and air–water interface (βσ), indicating an attractive interaction and reflecting the synergistic behavior in both the systems. The experimental mole fraction (X1) was found to be lower than the ideal mole fraction (X1ideal), the mole fractions of SDBS for both systems, provided that mixed micelles were more occupied by SDBS. In addition, the micelle aggregation number (Nagg) increased with an increase in the length of the hydrophobic tail. The micropolarity and binding constant (Ksv) values of various combinations were determined from the ratio of intensity (I1/I3) of peaks of pyrene fluorescence emission spectrum and its quenching.

Doubly-grafted copolymers with hydrophilic and thermosensitive side chains: Thermosensitivity and complexation with surfactants

The behavior in aqueous solution of the doubly-grafted anionic polyelectrolyte poly(sodium 2-acrylamido-2-methylpropanesulfonate-co-sodium acrylate-)-g-poly(N-isopropylacry-lamide)-g-poly(N,N-dimethylacrylamide), P(AMPSNa-co-ANa)-g-PNIPAM-g-PDMAM, was compared to that of the single-grafted anionic polyelectrolyte poly(sodium 2-acrylamido-2-methylpropanesulfonate-co-sodium acrylate)-g-poly(N-isopropylacrylamide), P(AMPSNa-co-ANa)-g-PNIPAM. The investigation through turbidimetry, pyrene fluorescence probing, viscometry and dynamic light scattering revealed that the existence of the hydrophilic poly(N,N-dimethylacrylamide), PDMAM, side chains in the doubly-grafted copolymer P(AMPSNa-co-ANa)-g-PNIPAM-g-PDMAM did not perturb the thermoresponsiveness of the poly(N-isopropylacrylamide), PNIPAM, side chains, but favoured the stabilization in water of the core-corona nanoparticles, formed upon heating the aqueous solution above the Lower Critical Solution Temperature (LCST) of PNIPAM chains. In a similar manner, the complexes formed between the cationic surfactant N,N,N,N-dodecyltrimethylammonium chloride, DTAC, and the oppositely charged backbone of the doubly-grafted copolymer P(AMPSNa-co-ANa)-g-PNIPAM-g-PDMAM were stabilized in water by the PDMAM side chains. Thus, phase separation was prevented upon heating the aqueous solution above LCST. Moreover, the 1H NMR study revealed that the fraction of PNIPAM chains forming solid-like aggregates at high temperature increased substantially in the presence of DTAC, as a consequence of the net charge decrease of the backbone due to the polymer/DTAC complexation.

PH-responsive star-shaped functionalized poly(ethylene glycol)-b-poly(ε-caprolactone) with amino groups

Functional star-shaped 4-arm poly(ethylene glycol)-b-poly[(e-caprolactone-co-γ-amino-e-caprolactone)] (4-arm PEG-b-P(CL-co-ACL) was synthesized through ring-opening polymerization. The structure of the copolymer was confirmed by 1H NMR, Fourier transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC). To further understand the copolymers, the difference of the conversion rate between e-caprolactone (CL) and γ-(carbamic acid benzyl ester)-e-caprolactone (CABCL) and the detailed deprotection condition were studied. The thermal property of the copolymer was analyzed by WAXR and differential scanning calorimetry (DSC), which demonstrated that the thermal property could be well adjusted. The pH-responsive behavior of the copolymers was studied in detail by dynamic light scattering (DLS), pH titration, and pyrene fluorescence methods, which indicated that it could form micelles and exhibit pH responsibility. Moreover, the copolymer was nontoxic and had good biocompatibility according to the results by 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide (MTT) assay.

Hexadecyltrimethylammonium bromide micellization in glycine, diglycine, and triglycine aqueous solutions as a function of surfactant concentration and temperatures

Micellization behavior of hexadecyltrimethylammonium bromide (HTAB) was investigated conductometrically in aqueous solutions containing 0.02 mol kg−1glycine (Gly), diglycine (Gly-Gly), and triglycine (Gly-Gly-Gly) as a function of surfactant concentration at different temperatures. The critical micelle concentration (CMC) of HTAB exhibits a decreasing trend as the number of carbon atoms increases from Gly to Gly-Gly-Gly, favoring the micelle formation. The values of CMC and the degree of counterion dissociation of the micelles were utilized to evaluate the standard free energy for transferring the surfactant hydrophobic chain out of the solvent to the interior of the micelle, ΔGHP○, free energy associated with the surface contributions, ΔGS○, standard free energy, ΔGm○, enthalpy, ΔHm○, and entropy, ΔSm○ of micellization were also calculated. The results show that the micellization of HTAB in aqueous solutions as well as in aqueous Gly/Gly-Gly/Gly-Gly-Gly solutions is primarily governed by the entropy gain due to the transfer of the hydrophobic groups of the surfactant from the solvent to the interior part of the micelle. The CMC obtained by fluorometric method is in close agreement with those obtained conductometrically. Furthermore, decrease in the I1/I3 ratio of pyrene fluorescence intensity suggests the solubilization of the additives by the surfactant micelles and that this solubilization increases as the hydrophobicity increases from Gly to Gly-Gly-Gly.

Design and synthesis of fluorescent galactolipid probes

Fluorescent galactolipid analogues (1, 1a, and 2) have been synthesized with a pyrene group attached to the amino-terminal of a hexanoyl chain bound to an otherwise normal galactolipid structure. The synthetic lipids are obtained from peracetyl galactose by a general and versatile procedure based on the trichloroacetimidate methodology. The intense violet fluorescence (376 and 395nm) and good photostability of pyrene make these compounds highly suitable as probes to study galactolipid metabolism. As proof of concept, we report that compound 2 is a valid tool to detect galactolipase activity in enzymatic preparations of potato tubers.

Fluorescence Resonance Energy Transfer in Partially and Fully Labeled Pyrene Dendronized Porphyrins Studied with Model Free Analysis

A series of dendronized porphyrins were synthesized and their photophysical properties were determined by UV–vis absorption, steady-state fluorescence, and time-resolved fluorescence. The constructs contained a porphyrin core connected to a first generation Frechet-type dendron (Py2G1) with or without a C4-butanoate linker, and to a second generation dendron (Py4G2) with a C4-linker. Pyrene and porphyrin were selected as donor and acceptor, respectively, for fluorescence resonance energy transfer or FRET. FRET occurred efficiently within the dendronized porphyrins as determined from the extremely weak fluorescence of pyrene. The number of pyrene groups present in the constructs was varied from two to eight, but was found to have little effect on FRET as FRET took place efficiently from an excited pyrene to a ground-state porphyrin. The parameter that was found to affect FRET the most was the distance separating pyrene from porphyrin within a construct. This effect was probed successfully by fitting the py...