Pyrene Fluorescence Research Articles

Steric hindrance regulated supramolecular assembly between β-cyclodextrin polymer and pyrene for alkaline phosphatase fluorescent sensing

We herein report a strategy for sensitive alkaline phosphatase (ALP) fluorescent sensing based on steric hindrance regulated supramolecular assembly between β-cyclodextrin polymer (polyβ-CD) and pyrene. The fluorescence of pyrene was enhanced more than 10 times through supramolecular assembly with polyβ-CD. The 5′-phosphorylated dsDNA probe with pyrene attached on the 3′-terminal could be cleaved by λ exonuclease (λ exo), yielding pyrene attached on mononucleotides. Pyrene attached on mononucleotides could easily enter the cavity of polyβ-CD, resulting in fluorescence enhancement. When ALP was introduced, it could remove 5′-phosphate groups from dsDNA and then prevented the cleavage of dsDNA. Pyrene attached on dsDNA was difficult to enter the cavity of polyβ-CD because of steric hindrance, resulting in an inconspicuous fluorescence enhancement. Owing to the excellent fluorescence enhancement during steric hindrance regulated supramolecular assembly, excellent performance of the assay method was achieved for ALP with a detection limit of 0.04UmL−1. The detection limit was superior or comparable with the reported methods. Besides, this method was simple in design, avoiding double-labeling of probe.

Binding of a novel 12-E2-12 gemini surfactant to xanthine oxidase: Analysis involving tensiometric, spectroscopic, microscopic and molecular docking approach

Binding interaction of a synthesized biodegradable gemini surfactant, ethane-1, 2-diyl bis(N, N-dimethyl-N-dodecylammoniumacetoxy) dichloride (12-E2-12), with bovine milk xanthine oxidase (XO) was studied using tensiometry, fluorescence spectroscopy, UV, CD, FT-IR, TEM and molecular docking. Tensiometry revealed lowering in surface tension (γ) and critical micelle concentration (CMC) of 12-E2-12 upon XO combination, suggesting a significant interaction between XO and 12-E2-12 (both in the bulk as well as at interface). Intrinsic fluorescence studies depict that 12-E2-12 quenches XO fluorescence intensity through static mechanism. The magnitude of binding parameters infers substantial and effective binding of 12-E2-12 to (XO). ANS and pyrene fluorescence demonstrate the exposure of aromatic residues (tyrosine/tryptophan) to a non-polar environment. UV, circular dichroism (CD) and FT-IR results delineate change in the secondary structure of the enzyme XO. Microscopic TEM micrographs confirm the disrupture of enzyme structure at higher concentrations of 12-E2-12. Molecular docking results show that 12-E2-12 binds to XO in the vicinity of both hydrophobic and hydrophilic residues, inferring that binding is governed by both hydrophilic and hydrophobic forces. This study may be of significance in biomedical world to further interpret mechanistic treatment modes of diseases like gout and hyperuricemia. Moreover, this study provides deeper biophysical insight into surfactant–protein interactions.

Aggregation and microenvironmental properties of gemini and conventional mixed surfactants systems: A fluorometric study

Aggregation behavior of cationic gemini (hexanediyl-1,5-bis(dimethylcettylammonium bromide) (16-5-16)) surfactant with conventional single chain surfactants cetyltrimethylammonium bromide (CTAB) and tetradecyltrimethylammonium bromide (TTAB) were studied with the help of fluorescence measurements. Fluorescence probe is a proficient technique for examining the surfactant-surfactant interaction and aggregation. The micelle aggregation number (Nagg) was measured using steady-state fluorescence quenching method. The micelle aggregation numbers of binary combinations fall between those of constituent surfactants. The micropolarity (I1/I3), binding constant (Ksv) and dielectric constant (Dexp) of mixed systems were determined from the ratio of peaks intensity in the pyrene fluorescence spectrum. The I1/I3 values were found to be more than >1, showing more polar environment around pyrene in the mixed micelle as compared to the pure micelles.

Water soluble, biodegradable amphiphilic polymeric nanoparticles and the molecular environment of hydrophobic encapsulates: Consistency between simulation and experiment

Star polymers with a crosslinked nanogel core constitute an unusual class of polymers with many arms emanating from the functionalized core. Although the core is usually hydrophobic, the arms can be hydrophobic, hydrophilic or amphiphilic. We describe the synthesis of biodegradable nanogel core stars which are largely water soluble and use encapsulated pyrene fluorescence to probe the environment both in aqueous solution and in solid thin films. In spite of the expected hydrophobic nature of the inner portions, the encapsulated pyrene environment seems quite polar. Although the molecular environment based on the pyrene fluorescent probe of the inner aliphatic polyester regions is more polar than expected for an aliphatic polyester, the molecular environment of the encapsulated probe in aqueous solution is influenced by the proximity of water even though simulations suggest that water excursions into the inner regions of the hydrophobic core area are rare and transient. NMR studies in water show the disappearance of the arm polyester signals. This and the pyrene environmental probe studies are consistent with collapse of the inner polyester regions and localization of the probe at or near the hydrophobic/hydrophilic interface as suggested in the simulations. This study has implications for the encapsulation of strongly hydrophobic cargos barring some loosening of the collapsed core by sterically-demanding substituents, increased hydrophobicity and/or some optimized specific interactions of the cargo with the core.

Fluorescence study on the aggregation of collagen molecules in acid solution influenced by hydroxypropyl methylcellulose

The effect of hydroxypropyl methylcellulose (HPMC) on the aggregation of collagen molecules with collagen concentrations of 0.25, 0.5 and 1.0mg/mL was studied by fluorescence techniques. On one hand, both the synchronous fluorescence spectra and fluorescence emission spectra showed that there was no change in the fluorescence intensity of collagen intrinsic fluorescence when 30% HPMC was added, while it decreased obviously when HPMC content ≥50%. From the two-dimensional fluorescence correlation analysis, it was indicated that collagen molecules in 0.25 and 0.5mg/mL collagen solutions were more sensitive to HPMC than those in 1.0mg/mL collagen solution. On the other hand, the pyrene fluorescence and the fluorescence anisotropy measurements indicated that HPMC inhibited the collagen aggregation for 0.25 and 0.5mg/mL collagen, but promoted it for 1.0mg/mL collagen. The atomic force microscopy images further confirmed the effect of HPMC on collagen with different initial states.

NaCl-triggered self-assembly of hydrophilic poloxamine block copolymers

Tetronic 1307 (T1307) is a hydrophilic poloxamine (HLB>24) with a high molecular mass owing to its long PEO and PPO blocks. In spite of good biocompatibility, its use as a component of drug delivery systems is limited by its high critical micelle concentration (CMC) and temperature (CMT). The aim of this work was to elucidate whether the addition of NaCl or the combination of salts and temperature may bring T1307 micellization and gelling features into more practically useful values. Increasing NaCl concentration in the 0.154M (isotonic) to 2M (hypertonic) range made the copolymer more hydrophobic and more prone to self-assemble into unimodal micelles, as observed by means of π–A isotherms, 1H NMR, dynamic light scattering (DLS), small-angle neutron scattering (SANS), and pyrene fluorescence. The decrease in CMC and CMT observed for T1307 in 0.5M NaCl medium (tolerable hypertonic solution), compared to water, notably favored the solubility of hydrophobic drugs such as curcumin and quercetin. Moreover, phase diagram, intrinsic viscosity and sol-to-gel transition were markedly affected by NaCl concentration. Overall, the strong dependence of T1307 self-assembly features on NaCl opens interesting possibilities for tuning the performance of T1307 as a component of nanocarriers and in situ gelling systems.

Synthesis of water‐soluble zwitterionic polysiloxanes

ABSTRACTA series of water‐soluble siloxane polymers with pendent phosphorylcholine (PC) and sulfobetaine (SB) zwitterions was prepared using thiol‐ene “click” chemistry. Specifically, well‐defined vinyl‐substituted siloxane homopolymers and block copolymers were functionalized with small molecule zwitterionic thiols at room temperature. Rapid and quantitative substitution of the pendent vinyl groups was achieved, and zwitterionic polysiloxanes of narrow molecular weight distribution were obtained. The PC‐ and SB‐substituted polymers were found to be readily soluble in pure, salt‐free water. Critical micelle concentrations (CMCs) of these polymers in water were measured using a pyrene fluorescence probe, with CMC values estimated to be <0.01 g/L. Polymer aggregates were studied by dynamic light scattering, and the micelles generated from the PC block copolymers were visualized, after drying, by transmission electron microscopy. Aqueous solutions of these zwitterionic polysiloxanes significantly reduced the oil‐water interfacial surface tension, functioning as polymer amphiphiles that lend stability to oil‐in‐water emulsions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 127–134

Synthesis and characterization of oligodeoxyribonucleotides modified with 2'-thio-2'-deoxy-2'-S-(pyren-1-yl)methyluridine.

Pyrene-functionalized oligonucleotides are intensively explored for applications in materials science and diagnostics. Here, we describe a short synthetic route to 2'-S-(pyren-1-yl)methyl-2'-thiouridine monomer S, its incorporation into oligodeoxyribonucleotides (ONs), and biophysical characterization thereof. Pseudorotational analysis reveals that the furanose ring of this monomer has a slight preference for South-type conformations. ONs modified with monomer S display high cDNA affinity but decreased binding specificity. Hybridization is associated with bathochromic shifts of pyrene absorption bands and quenching of pyrene fluorescence consistent with an intercalative binding mode of the pyrene moiety. Monomer S was also evaluated as a building block for mixed-sequence recognition of double-stranded DNA via the Invader strategy. However, probes with +1 interstrand arrangements of monomer S were found to be less efficient than Invader probes based on 2'-O-(pyren-1-yl)methyluridine or 2'-N-(pyren-1-yl)methyl-2'-N-methyl-2'-aminouridine.

Investigation of bovine serum albumin-surfactant aggregation and its physicochemical characteristics

Abstract The mechanism of the formation of aggregates between a protein, bovine serum albumin (BSA), and alkyltrimethylammonium bromides of varied hydrocarbon chain lengths, namely, cetyltrimethylammonium bromide (CTAB), tetradecyltrimethylammonium bromide (TTAB), and dodecyltrimethylammonium bromide (DTAB) in an aqueous solution and the physicochemical characteristics of the aggregates were systematically investigated by surface tensiometry, fluorimetry, UV–vis spectrometry, dynamic light scattering, zeta potential, and differential scanning calorimetry (DSC). The surface tension and fluorimetry data indicate a steady decrease in the critical micelle concentrations of the surfactants with an increase in the amount of BSA in the mixture. The evolution of an additional nonpolar segment in the backbone of BSA was indicated by the fluorescence of pyrene and the intrinsic fluorescence of BSA as well. The decrease in the aggregation number, increase in the area per molecule of the surfactant at the interface with a concomitant increase in the hydrodynamic radius of the aggregate were attributed to the formation of BSA–surfactant mixed aggregate and the induction of the unfolding of BSA by the surfactants. The DSC study and nature of the denaturation curves of BSA indicate that the stability of the BSA–surfactant complex follows the order: CTAB > TTAB > DTAB. The neutralization of the negatively charged surface of BSA by the positively charged surfactants is evident from the zeta potential measurements. Both the head group and nonpolar moiety of the surfactants affected the surface charge of the aggregates and the studied surfactants denature and unfold BSA; the extent of denaturation is predominately decided by the hydrocarbon chain length of the former. The in situ unfolding of the protein and the subsequent formation of the aggregates are proposed. The characteristic parameters of the aggregates were determined.

RAFT made methacrylate copolymers for reversible pH‐responsive nanoparticles

ABSTRACTIn this study, we designed and investigated pH‐responsive nanoparticles based on different ratios of monomers with primary, secondary or tertiary amino groups. For this purpose, copolymers of methyl methacrylate (MMA) with different compositions of amino methacrylates (2‐(dimethylamino)ethyl methacrylate (DMAEMA), 2‐(tert‐butylamino)ethyl methacrylate (tBAEMA) and 2‐aminoethyl methacrylate hydrochloride (AEMA·HCI)) were synthesized using the reversible addition‐fragmentation chain transfer (RAFT) polymerization process. The controlled nature of the radical polymerization was demonstrated by kinetic studies. All copolymers show low dispersities (ĐM < 1.2) with amino contents between 9 and 21 mol %. For the nanoparticle formation, nanoprecipitation with subsequent solvent evaporation was used. All suspensions were characterized by dynamic light scattering (DLS) and scanning electron microscopy (SEM). Different initial conditions of the formulations resulted in differently sized nanoparticles that have monomodal size distributions, relatively narrow polydispersity index (PDI) values and positive zeta potential values. The pH‐stability test results demonstrated that, depending on the structure and amount of the amino content, the obtained nanoparticles reveal a reversible pH‐response, such as dissolution at acidic pH values. The ability of the nanoparticles to encapsulate guest molecules was confirmed by pyrene fluorescence studies. The cytotoxicity assay results showed that the nanoparticles did not have any significant cytotoxic effect. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2711–2721

Apparent molar volume, conductivity, and fluorescence studies of ternary systems of dipeptides + ionic liquids ([Cnmim]Br, n = 10, 14) + water at different temperatures

Densities, conductivities, and fluorescence spectra of two imidazolium ionic liquids ([Cnmim]Br, n = 10, 14)-glycyl dipeptide-water mixtures were measured as a function of temperature. The density data have been utilized to calculate the apparent molar volumes, standard partial molar volumes (V 2,φ 0 ), standard partial molar volumes of transfer from water to aqueous ionic liquids solutions (Δt V°), the hydration number (N H), partial molar expansibility (E φ 0 ), and Hepler’s constant of glycyl dipeptides. Through the electrical conductivity measurements, the c cmc values at different temperatures and a series of thermodynamic parameters (ΔG , ΔH , and ΔS ) of micellization of [Cnmim]Br (n = 10, 14) in aqueous glycyl dipeptides solutions are evaluated. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interaction of [Cnmim]Br with glycyl dipeptide, and the aggregation behavior of [Cnmim]Br (n = 10, 14). The results shown above have been explained in terms of solute–solvent interactions and structural changes in the mixed solutions. The interaction between [Cnmim]Br (n = 10, 14) and glycyl dipeptide is affected by temperature and hydrocarbon chain length of the dipeptides.

Usage of cellulose acetate membranes for the sorption-luminescence determination of pyrene in aqueous media

The applicability of cellulose acetate membranes (CAMs) as a solid matrix for the luminescence determination of pyrene in aqueous micellar solutions is shown. The effect of the concentrations of various surfactants, namely, anionic sodium dodecyl sulfate (SDS), cationic cetyltrimethylammonium bromide (CTAB), and nonionic polyoxyethylene (10) mono-4-isooctyl phenyl ether (TX-100), on the fluorescence of pyrene in aqueous micellar solutions before and after sorption preconcentration and in an adsorbed state on a CAM has been studied. It has been found that the fluorescence intensity of pyrene on the solid-phase matrix increases as a result of pyrene solubilization in surfactant hemimiceles formed on the sorbent surface. The highest degree of pyrene extraction on CAMs has been achieved in the presence of cationic CTAB micelles. The CAM has a negative surface potential (−31.5 ± 2.5 mV), which affects the hydrocarbon recovery. The degree of extractlion and the polarity index of a microenvironment of pyrene molecules in solutions decrease in the order CTAB → SDS → TX-100.

Synthesis of 2,3-O-dibenzyl-6-O-sulfobutyl-α and β cyclodextrins: new chiral surfactants for capillary electrophoresis

Amphiphilic sodium hexakis(2,3-O-dibenzyl-6-O-sulfobutyl)cyclomaltohexaose and sodium heptakis(2,3-O-dibenzyl-6-O-sulfobutyl)cyclomaltoheptaose were synthesized in four steps. Pyrene fluorescence studies indicate micelle formation at 90μM in water for both modified cyclodextrins (CDs). Both CDs offer potential as chiral micellar selectors for enantiomeric separations using capillary electrophoresis. Sodium heptakis(2,3-O-dibenzyl-6-O-sulfobutyl)cyclomaltoheptaose baseline resolved fluorescent cyanobenzylindole (CBI) derivatives of d/l-serine at concentrations of 50–200μM.

Membrane perturbations induced by the interactions of zinc ions with band 3 in human erythrocytes

Of group 12 metals, zinc is an essential element to maintain our life, but other metals such as cadmium and mercury are toxic in cellular activities. Interactions of these metals with biomembranes are important to understand their effects on our living cells. Here, we describe the membrane perturbations induced by these metals in human erythrocytes. Of these metals, Zn2+ ions only induced the erythrocyte agglutination. Histidine residues in extracellular domains of band 3 participated in Zn2+-induced agglutination. Interestingly, it was found that band 3-cytoskeleton interactions play an important role in Zn2+-induced agglutination. In contrast with Hg2+ and Cd2+ ions, Zn2+ ions greatly suppressed pressure-induced hemolysis by cell agglutination. Such a suppression was removed upon dissociation of agglutinated erythrocytes by washing, indicating the reversible interactions of Zn2+ ions with erythrocyte membranes. Excimer fluorescence of pyrene indicated that spectrin is denatured by a pressure of 200MPa irrespective of hemolysis suppression. Taken together, these results suggest that the agglutination of erythrocytes due to the interactions of Zn2+ ions with band 3 is stable under pressure, but spectrin, cytoskeletal protein, is denatured by pressure

Covalently Functionalized Graphene Composites: Mechanistic Study of Interfacial Fluorescence Quenching and Recovery Processes

Functionalized graphene oxide nanosheets (GONs) have received much attention in a broad range of applications from light harvesting devices to biological sensors. Owing to their implications in devices and sensors, the interactions between graphene and organic molecules, especially π–π interactions, have also been extensively investigated. Herein we present a mechanistic study of the interfacial fluorescence quenching and its recovery processes between a pyrene derivative, 1-(aminohexyl)-1-pyrenebutyricamide (4) as a fluorophore and nanometer-sized GO sheets. Owing to strong π–π interactions with 4, GON quenches the photoluminescence from pyrene in “folded” conformation of 4-GON. On the other hand, the treatment of 4-GON with sodium dodecyl sulfate (SDS) helps 4 overcome this strong pyrene/GON interactions and causes 4-GON to be in “unfolded” conformation where the fluorescence of pyrene is recovered. By time-resolved spectroscopy, the ultrafast energy and charge transfer behavior (<1 ps) is observed espe...

Self-Assembly and Collagen-Stimulating Activity of a Peptide Amphiphile Incorporating a Peptide Sequence from Lumican.

The self-assembly and bioactivity of a peptide amphiphile (PA) incorporating a 13-residue sequence derived from the last 13 amino acids of the C-terminus of lumican, C16-YEALRVANEVTLN, attached to a hexadecyl (C16) lipid chain have been examined. Lumican is a proteoglycan found in many types of tissue and is involved in collagen fibril organization. A critical aggregation concentration (cac) for the PA was determined through pyrene fluorescence measurements. The structure of the aggregates was imaged using electron microscopy, and twisted and curved nanotapes were observed. In situ small-angle X-ray scattering and fiber X-ray diffraction reveal that these tapes contain interdigitated bilayers of the PA molecules. FTIR and circular dichroism spectroscopy and fiber X-ray diffraction indicate that the lumican sequence in the PA adopts a β-sheet secondary structure. Cell assays using human dermal fibroblasts show that below the cac the PA displays good biocompatibility and also stimulates collagen production over a period of 3 weeks, exceeding a 2-fold enhancement for several concentrations. Thus, this PA has promise in future biological applications, in particular, in tissue engineering.

Effect of [C n mim][Br] Based Ionic Liquids on the Aggregation Behavior of Tetradecyltrimethylammonium Bromide in Aqueous Medium

In order to gain insight into the role of environmentally benign imidazolium based ionic liquids (ILs) to alter the physicochemical properties of single chain cationic surfactants, we have investigated the effect of 1-hexyl-3-methylimidazolium bromide ([C6mim][Br]) and 1-octyl-3-methylimidazolium bromide ([C8mim][Br]) on the aggregation behavior of aqueous tetradecyltrimethylammonium bromide (TTAB). The critical micelle concentration (CMC) of TTAB at different concentrations of ILs was determined through conductance, surface tension, spectral change of a dye by UV–Vis measurement, and the pyrene fluorescence probe measurement techniques at 298.15 K. Decreasing of the CMC of aqueous TTAB with increasing ILs concentration proves the micellization is favorable. The effect of ILs on the properties of TTAB was verified by using NaBr. Surface tension measurements complimented by dynamic light scattering (DLS) data revealed the packing density of TTAB aggregates at different concentrations of ILs. The effective area of TTAB molecules at the air/water interface was calculated by the Gibbs adsorption isotherm and found to decrease up to 0.6 wt% of ILs followed by an increase at higher concentration. DLS data revealed an increase in micellar size of TTAB at higher concentration of IL with decrease in the aggregation number (N agg), determined by the fluorescence quenching method.

Pyrene fluorescence quenching in supramolecular systems based on dimethylaminomethylated resorcinarene

The aim of this work is the development of stable fluorophore-quencher pairs with a controlled response for bioassay in the laboratory. The widely used in bioanalysis pyrene and its water-soluble derivative were selected as organic fluorophores. Water-soluble aminomethylated calixarene with sulfonatoethyl groups at the “lower rim” was chosen as a stabilizer. We have established a strong fluorescence quenching in the solution of resorcinarene even at low premicellar concentrations which indicates the pyrene transition into a non-polar microenvironment. The data on the influence of pH, buffer composition, and the macrocyclic platform on the fluorescence quenching of pyrene in the presence of resorcinarene were obtained. The temperature dependence of the fluorescence quenching of pyrene was obtained with the aim of establishing the mechanism of the formation of complex fluorophore-resorcinarene (static versus dynamic quenching).

Water-soluble complexes of hydrophobically modified polymer and surface active imidazolium-based ionic liquids for enhancing oil recovery

The current study introduces the water-soluble complexes containing hydrophobically associating copolymer and a series of surface activity imidazolium-based ionic liquids (CnmimBr, n = 6, 8, 10, 12, 14 and 16). The polymer, denoted as PAAD, was prepared with acrylamide (AM), acrylic acid (AA) and N,N-diallyl-2-dodecylbenzenesulfonamide (DBDAP). And the hydrophobic associative behavior of PAAD was studied by a combination of the pyrene fluorescence probe and viscosimetry. Incorporation of CnmimBr (n = 10, 12, 14 and 16) in PAAD leaded to the white thick gel, while the pellucid solutions were obtained in complexes of PAAD and CnmimBr (n = 6 and 8); addition of C6mimBr around critical micelle concentration resulted in a large decrease in viscosity of solution. Therefore, we particularly investigated the performance of PAAD/C8mimBr complex. The interfacial tension of PAAD/C8mimBr complex solution and crude oil under different conditions was examined. Moreover, PAAD/C8mimBr complex exhibited superior temperature resistance and shear reversible performance for enhancing oil recovery (EOR) by rheological test. The promising EOR of 21.65% can be obtained by PAAD/C8mimBr complex showing high potential to utilize this kind of new complex in EOR processes.

Cellulose diacetate films as a solid-phase matrix for fluorescence analysis of pyrene traces in aqueous media

We report on the possibility of using cellulose diacetate (CDA) films as a solid-phase matrix for the fluorescence analysis of pyrene in aqueous micellar media. We examined the effect of the concentration of three surfactants—the anionic sodium dodecyl sulfate (SDS), the cationic cetyltrimethylammonium bromide (CTAB), and the nonionic polyoxyethylene (10) mono-4-isooctylphenyl ether (TX-100)—on the fluorescence of pyrene in aqueous micellar solutions before and after sorptional concentration and as adsorbed on CDA films. The increased fluorescence intensity of pyrene on the solid-phase matrix was due to pyrene solubilization in the surfactant hemimicelles formed on the sorbent surface. The highest degree of pyrene recovery on CDA was achieved in the presence of micelles of the cationic CTAB. The surface electric potential of the CDA films was negative (−31.5 ± 2.5 mV), affecting the hydrocarbon recovery degree. The recovery degree and the polarity index of the pyrene molecules’ microenvironment in solution decreased in the sequence CTAB > SDS > TX-100.