Fluorescence Spectra Of Pyrene Research Articles

Two-Level Self-Thickening Mechanism of a Novel Acid Thickener with a Hydrophobic-Associated Structure during High-Temperature Acidification Processes.

Two acid thickeners, ADMC and ADOM, were prepared by aqueous solution polymerization using acrylamide (AM) and methacryloyloxyethyl trimethyl ammonium chloride (DMC) as raw materials, with or without the introduction of octadecyl polyoxyethylene ether methacrylate (OEMA). It was characterized by FTIR, 1H NMR, and the fluorescence spectra of pyrene. The double-layer thickening mechanism of ADOM was proved by comparing the thickening and rheological properties of ADMC and ADOM tested by a six-speed rotary viscometer and a HAKKE MARSIV rheometer during the acidification process. The results showed that the synthetic product was the target product; the first stage of the self-thickening ADOM fresh acid solution during high-temperature acidification was mainly affected by Ca2+ concentration, and the second stage of self-thickening was mainly affected by temperature. The residual viscosity of the 0.8 wt% ADOM residual acid solution was 250, 201.5, and 61.3 mPa·s, respectively, after shearing at 90, 120, and 150 °C for 60 min at a shear rate of 170 s-1. The thickening acid ADOM with a hydrophobic association structure has good temperature resistance and shear resistance, which can be used for high-temperature deep-well acid fracturing. In addition, no metal crosslinking agent was introduced in the system to avoid damage to its formation, and ADOM exhibited good resistance to Ca2+, which could provide ideas for the reinjection of the acidizing flowback fluid. It also has certain advantages for environmental protection.

Synergistic effect and co-adsorption mechanism of a mixed collector on the flotation separation of spodumene from feldspar

In this study, the flotation separation of spodumene from feldspar was achieved using mixed collector of sodium oleate (NaOL)/cetyl trimethylammonium bromide (CTAB). Micro-flotation experiments show that the selective flotation separation of the two minerals could not be achieved in the presence of single collector under the pH range of 2–12, but the they could be effectively separated using mixed collector at the NaOL-to-CTAB molar ratio (MR) of 7:1 at pH 6.0 Artificial mixed minerals tests prove the effective flotation separation effect of the mixed NaOL/CTAB at pH 6.0. Analyses of bubble collision-attachment show that when using mixed NaOL/CTAB as the collector, the bubble could quickly form a three-phase contact (TPC) line on spodumene surface (tTPC=396 ms), but the bubble did not form TPC line on feldspar surface (tTPC＞2000 ms), suggesting a much stronger hydrophobic surface of spodumene. Adsorption amount tests show the much higher adsorption density of mixed NaOL/CTAB on spodumene surface than feldspar, moreover, CTAB promoted the NaOL adsorption on spodumene surface, but it hindered the NaOL adsorption on feldspar surface. The surface and thermodynamic parameters (CMC, γcmc, ∆Gm0, Γmax, Amin) obtained from surface analyses demonstrate higher surface activity and denser molecular arrangement in mixed NaOL/CTAB system than that in the individual system, indicating a positive synergistic effect of mixed collector. Pyrene fluorescence spectrum analyses present the lower critical micelle concentration (CMC) value and polarity of the mixed NaOL/CTAB than their individual components, suggesting that the mixture had much stronger hydrophobicity and was more likely to form micelles than single collector. All the tests were conducted at temperature of 25 ℃.

Conductometric and Fluorescence Probe Analysis to Investigate the Interaction between Bioactive Peptide and Bile Salts: A Micellar State Study.

The present work deals with the micellar state study of sodium cholate and sodium deoxycholate in the aqueous solution of a bioactive peptide, namely glycyl dipeptide, having different concentrations through conductivity and fluorescence methods at different temperatures. The data obtained from conductivity is plotted against the concentration of Bile salts, and CMC (critical micelle concentration) values are calculated. The results realized have been elucidated with reference to Glycyl dipeptide-bile salts hydrophobic/hydrophilic interactions existing in solution. In addition, the CMC values converted to mole fraction (Xcmc) values have been used to evaluate the standard thermodynamic factors of micellization viz., enthalpy H, free energy ΔGm0, and entropy (ΔSm0) which extract information regarding thermodynamic feasibility of micellar state, energy alteration, and the assorted interactions established in the existing (bile salts-water-glycyl dipeptide) system. Furthermore, the pyrene fluorescence spectrum has also been utilized to study the change in micro polarity induced by the interactions of bile salts with glycyl dipeptide and the aggregation action of bile salts. The decrease in modification in the ratio of intensities of first and third peaks i.e., (I1/I3) for the pyrene molecules in aqueous bile salts solution by the addition of dipeptide, demonstrates that the micelle polarity is affected by glycyl dipeptide. This ratio has also been utilized to determine CMC values for the studied system, and the results have been found to be in good correlation with observations made in conductivity studies.

Polyelectrolyte complexes of hyaluronic acid and diethylaminoethyl dextran: Formation, stability and hydrophobicity

Polyelectrolyte complexes (PECs) of hyaluronic acid (HA) and diethylaminoethyl dextran (DEAE-D), promising for biomedical applications, have been investigated with respect to physicochemical properties, mainly in terms of particle size and relative hydrophobicity as well as storage stability. Influences of charge ratio, polymer concentration, molar masses of HA, ionic strength and mixing methods have been particularly investigated. The complexation between HA and DEAED generally resulted in colloidal particles having mean hydrodynamic diameter of 150–350 nm, with larger particle size observed at negative to positive charge ratio (n-/n+) further from the unity. Higher polymer concentration or higher molar mass of HA also led to higher particle size of the PECs, whereas the increasing ionic strength led to a non-monotonic evolution in particle size. The effects of mixing mode and mixing order on particle size were interdependent and depended also on n-/n+. PECs at n-/n+ ≤ 0.4 showed lack of stability, which seemed not to be sensitive to storage temperature but significantly improved at higher salt concentration or lower polymer concentration. The relative hydrophobicity of such PECs was also confirmed by the fluorescence spectra of pyrene incorporated in PEC particles. Such results gave a better insight to polysaccharides-based PECs, especially as a potential system to encapsulate hydrophobic active molecules for drug delivery purposes.

Local chemical environment in hexane-methylethylketone solutions as a model of polyethylene degradation investigated by fluorescence spectroscopy

The fluorescence spectra of pyrene and Prodan in hexane-methylethylketone solutions, which are models of polyethylene degradation, were investigated to develop a method for understanding the degradation of polymer materials. The fluorescence properties of pyrene and Prodan were highly sensitive to the polarity of the solutions. The fluorescence intensity ratios, I384/I373 for pyrene and I380/I420 for Prodan, were useful indexes for investigating the local chemical environment. These fluorescence indexes may be more than 10 times sensitive to the conventional carbonyl index by infrared absorption. This fluorescence probe method will find further application in the evaluation of polymer degradation.

Cholesterol-pyrene as a probe for cholesterol distribution on ordered and disordered membranes: Determination of spectral wavelengths.

Biological membranes contain a large variety of lipids species compartmentalized in different domains heterogeneous in size, composition and dynamics. Cholesterol induces membrane ordered domains thanks to its affinity for saturated lipids. Membrane domains had been studied with fluorescent probes either linked to phospholipids and proteins or as individual fluorophore. However, no efficient formulation of a cholesterol probe has been available so far. Herein, we described a cholesterol-pyrene probe behaviour in heterogeneous membranes. We characterised the pyrene fluorescence spectra in liquid-ordered (Lo) and liquid-disordered (Ld) membranes. Using statistical multivariate analysis, we found out the most appropriate wavelengths for membrane domains studies. 373 nm and 379 nm were the most discriminant wavelengths to follow the liquid-ordered and the liquid-disordered environments. Cholesterol clustering behaviour was quantified by the modulation of the cholesterol-pyrene excimers peak (474 nm). In liquid-ordered membranes at low temperature, cholesterol-pyrene was found as multimers and as monomers. At high temperature, the liquid-ordered status of the membrane decreases and cholesterol-pyrene tends to cluster. In liquid-disordered membranes, cholesterol-pyrene was present mostly as monomers and the small quantity of excimers increased with temperature. Cholesterol-pyrene was used to test the ceramide effect on membranes, and presented a behaviour in agreement with the cholesterol behaviour reported in the literature. Overall, the presented data show that cholesterol-pyrene is an efficient sensor to study liquid ordered and liquid disordered organisation in membranes.

Enhanced Exciplex Emission of Pyrene Thin Films Doped by Perylene: Structural, Photophysical and Morphological Investigation.

The present work reports on the preparation of thin films of pyrene luminophors doped by varying amounts of perylene by spin coating technique. The structural, morphological, and photophysical properties of pyrene thin films have been investigated as a function of perylene contents. X-ray diffraction studies of doped thin films show well-defined peaks, and estimated crystallite size decreases with increasing perylene content, due to the formation of closed packed crystal structure. SEM images of pure pyrene revealed smooth, and compact and separated crystals with amounts of perylene. The result of absorption spectra showed decrease in intensity with perylene content. However, the fluorescence spectra of pyrene containing higher amounts of perylene showed broad and structureless exciplex emission at 510nm. The emission colour of pyrene luminophors tuned from blue to green by controlling the concentration of perylene. The phenomenon of change in colour was seen due to efficient excitation energy transfer from pyrene to perylene in thin films. It also found that the intensity of exciplex emission increases with increasing concentration of perylene is of high demand in fluorescent lamp as well as green organic light emitting diodes.

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.

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.

Vibronic structure of electronic absorption and fluorescence spectra of pyrene in the complex with β-cyclodextrin in the presence of nonpolar and polar solvents

The feasibility of using pyrene as a fluorescent probe in complexes cyclodextrin-pyrene-analyte in aqueous solutions was studied for several analytes (A) of different polarity. Bands that prove the formation of the complex Py2βCD were found for the first time in the UV-VIS spectrum of an aqueous solution of pyrene in the presence of β-cyclodextrin. A characteristic of a fluorescent probe is the ratio I3/I1 in the fluorescence spectrum, where I3 is the intensity of the third vibronic line at ∼800 cm−1, and I1 is the intensity of the 0-0 transition. The value of I3/I1 for Py2βCD is highly sensitive to the addition of an analyte with a concentration of several μM/L to the aqueous solution. Dependences of (I3/I1)/C on the function of the dielectric constant ɛ of the analyte fɛ= (ɛ − 1)/(2ɛ + 1) are divided into two straight lines with different slopes for nonpolar and polar solvents. Energies of insertion of analytes into Py2βCD were calculated by the quantumchemical PM3 method. An increase in (I3/I1)/C corresponds to the more thermodynamically stable complex 2APy2βCD.

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.

Densities, electrical conductances, and spectroscopic properties of glycyl dipeptide + ionic liquid ([C12mim]Br) + water mixtures at different temperatures

Densities, conductivity, fluorescence and UV–vis absorption spectroscopy of glycyl dipeptide+ionic liquid (1-dodecyl-3-methylimidazolium bromide ([C12mim]Br))+water mixtures have been measured at different temperatures. From density data, the standard partial molar volume (V2,ϕ0), standard partial molar volume of transfer for three glycyl dipeptides from water to aqueous [C12mim]Br solutions (ΔtVo), partial molar expansibility (Eϕ°) and Hepler's constant have been calculated. Through the electrical conductivity measurements, the critical micellar concentration (ccmc) and a series of thermodynamic parameters of micellization of [C12mim]Br in aqueous glycyl dipeptide solutions are evaluated. Effects of temperature and hydrocarbon chain length of the glycyl dipeptides on the volumetric properties of dipeptides and critical micelle concentration (ccmc) of [C12mim]Br were examined. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interactions of [C12mim]Br with glycyl dipeptides, and the aggregation behavior of [C12mim]Br. From the results of UV–vis absorption spectra, the binding constant between dipeptide and [C12mim]Br above the ccmc was determined.

N-trimethyl chitosan (TMC)-modified microemulsions for improved oral bioavailability of puerarin: preparation and evaluation

The aim of this research was to increase the oral bioavailability of puerarin by N-trimethyl chitosan-modified microemulsions (TMC-MEs) loaded with puerarin. Different concentrations of TMC-modified microemulsions were prepared in our study, and then evaluated for particle size, zeta potential, morphological observation and changes of the microenvironment polarity of inner oil core. It was shown that the zeta potential of the microemulsion was increased with the increasing concentration of TMC, and the peak value was achieved when the concentration of TMC was 3.0 mg/mL. The enhancement of the ratio of I1/I3 (the ratio between the first band and the third band of the emission fluorescence spectrum of pyrene, I1 = 373 nm, I3 = 384 nm) indicated that polarity of the inner core of TMC-MEs was increased with the addition of the modifier. Pharmacokinetic studies demonstrated that after oral administration of puerarin N-trimethyl chitosan (TMC)-modified microemulsions (PUE-TMEs) and puerarin microemulsions (PUE-MEs) to rats at a dose of 100 mg/kg, relative bioavailability was enhanced about 6.8- and 1.2-fold, respectively, compared to puerarin suspension (PUE-SUS) as control. It indicated that the TMC-MEs could be used as an effective formulation for enhancing the oral bioavailability of puerarin.

Interactions of dipeptides with Triton X-100 in aqueous solution: A volumetric and spectroscopic study

The interactions of dipeptides with Triton X-100 in aqueous solution have been investigated by means of density, fluorescence spectroscopy and UV–vis spectroscopy. The standard partial molar volume (V2,ϕo), standard partial molar volume of transfer for dipeptide from water to aqueous Triton X-100 solution (ΔtVo) and partial molar expansibility (Eϕo) have been calculated from density data. Fluorescence spectroscopy was used to estimate the critical micellar concentration (ccmc) and micelle aggregation number of Triton X-100 in aqueous dipeptide solutions. Effects of temperature and hydrocarbon chain length of dipeptides on the volumetric properties of dipeptide and critical micelle concentration (ccmc) of Triton X-100 were examined. The pyrene fluorescence spectra were also used to study the change of micropolarity produced by the interactions of Triton X-100 with dipeptides. From the results of UV–vis absorption spectra, the binding constant between dipeptide and Triton X-100 above the ccmc was determined. The results have been interpreted in terms of solute–solvent interactions and structural changes in the mixed solutions.

Modulation of the Photophysical Properties of Pyrene by the Microstructures of Five Poly(alkyl methacrylate)s Over a Broad Temperature Range

Pyrene fluorescence spectra have been recorded in five poly(alkyl methacrylate)s (where alkyl is ethyl butyl, isobutyl, cyclohexyl and hexadecyl) over a 20-400 K temperature range. The changes in the position and the full width at half maximum (FWHM) of the 0-0 emission band (peak I) have been correlated with the structural characteristics of the alkyl groups in the different relaxation regimes of the polymers to assess the degree of coupling of the excited singlet states with the polymer cybotactic regions. Data treatment of the peak I positions using an electron-phonon model indicates that longitudinal optical modes are involved, and that the magnitude of coupling depends on the polymer structure and follows the same trend as the glass transition temperatures. The same spectral parameters have been correlated also with "hole" free volumes from positron annihilation spectroscopy over temperature ranges which span the glass or melting transitions of the polymers. Reasons why free volume and FWHM measurements follow the same trends, and other aspects of the systems, are discussed.

Study of mixed micellar aqueous solutions of sodium dodecyl sulfate and amino acids

Thermodynamic properties of sodium dodecyl sulfate (SDS) in micellar aqueous solutions of L-serine and L-threonine were determined by fluorescence spectroscopy and dynamic light scattering techniques. The values of Gibbs free energy, enthalpy and entropy of the process of micelle formation were calculated using the critical micelle concentration and degree of dissociation. Changes in critical micelle concentration of SDS with the addition of amino acids were examined by both conductivity and pyrene I 1/I 3 ratio methods at different temperatures. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interaction of SDS with amino acids. The aggregation behavior of SDS was explained in terms of structural changes in mixed solutions. The data on dynamic light scattering suggest that size of SDS micelles was influenced by the presence of amino acids.

External Electric Field Effect on Fluorescence Spectra of Pyrene in Solution

Electrophotoluminescence (E-PL) spectra, i.e., plots of the electric-field-induced change in photoluminescence intensity as a function of wavenumber, have been measured for pyrene solution. At high concentrations of pyrene where excimer fluorescence is observed along with the monomer fluorescence emitted from the locally excited state, both excimer fluorescence and monomer fluorescence are enhanced by application of electric fields. The results show that the nonradiative decay process at the excimer emitting state is decelerated by application of electric fields. It is also found that molecular polarizability of pyrene excimer is larger than that of pyrene monomer in the ground state by ~270 ± 90 Å(3), based on the analysis of the Stark shift of the excimer fluorescence.

Effects of the nanoassociation of hexadecyltrimethoxysilane precursors on the sol–gel process

Modifications to the refractive indices of meso-structured organic–inorganic films caused by variations in the mole fraction of precursors in ethanolic solutions were investigated. The refractive indices were dependent on the mole fraction of C16TMS (hexadecyltrimethoxysilane) and of the C16TMS/TMOS (tetramethoxysilane) (1/1) mixture in ethanol. The dependency was determined to be nonlinear, and the phenomenon was attributed to self-assembly caused by the long alkyl groups (C16) on the C16TMS. Changes in the maximum decreasing rate of dn/dx values [(dn/dx)max—for dn/dx estimation, the curves from Fig. 1 were associated with a polynomial; using a dedicated program, dn/dx was calculated; maximum values of dn/dx were taken into account and were included in Table 1)] were used to distinguish the behavior of alcoholic precursor mixtures. In the case of using pyrene as a fluorescent probe, the ratio between two peaks from the pyrene emission spectra (I1/I3) strongly decreased as hydrophobic micro-surroundings formed due to the self-assembly process. The UV–VIS spectra of a cationic dye solution, R6G, was studied because dilute solutions of the dye in equilibrium form measurable ratios of dimers and monomers. The absorbance was modified as micro-surroundings with different polarities were formed. These three methods demonstrated that nano-structuration was present prior to the occurrence of the sol–gel process. The combination of C16TMS with other alkyltrialkoxysilane precursors having hydrocarbon chain lengths between C1 and C8 provided further evidence for a nonlinear dependence of the refractive indice and fluorescence spectra of pyrene. The properties of the final hybrids obtained by the sol–gel process were significantly affected by the precursor hydrocarbon chain lengths. DSC, XRD and FTIR measurements were used to show the plasticizing phenomena of C16 as other alkyltrialkoxysilanes (i.e., C1–C8) were added.

Effect of dipeptides on the micellization and thermodynamic parameters of sodium dodecyl sulfonate: Conductometric and fluorimetric studies

Micellization and related thermodynamic parameters of a conventional anionic surfactant sodium dodecyl sulfonate (C12SO3Na) in various compositions of water–dipeptide mixed media have been studied by means of conductivity and fluorescence spectroscopy at five temperatures ranging between 298.15K and 318.15K. The electrical conductivity data have been utilized to calculate the values of critical micelle concentration (ccmc) and the counterion binding constant (β) of C12SO3Na. From ccmc values, it is observed that the micellization tendency of the surfactant increases in the presence of dipeptides. Thermodynamic parameters (ΔGmo, ΔHmo and ΔSmo) of micellization of C12SO3Na in aqueous dipeptide solutions have been obtained by applying the mass action model and an enthalpy–entropy compensation effect was observed. The effect of dipeptides on the micellar properties of C12SO3Na depends upon their nature and concentration, as well as the temperature. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interaction of C12SO3Na with dipeptides, and the aggregation behavior of C12SO3Na. The results have been interpreted in terms of solute–solvent interactions and structural changes in the mixed solutions. The interaction difference of C12H25SO3Na/C12H25SO4Na with dipeptides was also studied and it was found that C12H25SO3Na were seen to interact more weakly than their sulfate analogues.

Effect of temperature on the interactions of glycyl dipeptides with sodium perfluorooctanoate in aqueous solution: Volumetric, conductometric, and spectroscopic study

The interactions of glycyl dipeptides (glyglycine, glycyl-l-valine and glycyl-l-leucine) with sodium perfluorooctanoate (SPFO) in aqueous solutions have been investigated by means of density, conductivity, fluorescence spectroscopy, and UV–vis spectroscopy. The standard partial molar volume (V2,ϕ∘), standard partial molar volume of transfer for dipeptide from water to aqueous SPFO solutions (ΔtVo), partial molar expansibility (Eϕ∘) and Hepler’s constant have been calculated from density data. Electrical conductivity was used to estimate the critical micellar concentration (ccmc) and the thermodynamic parameters of micellization of SPFO in aqueous glycyl dipeptide solutions. Effects of temperature and hydrocarbon chain length of the glycyl dipeptides on the volumetric properties of dipeptides and critical micelle concentration (ccmc) of SPFO were examined. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interactions of SPFO with glycyl dipeptides, and the aggregation behaviour of SPFO. From the results of UV-vis absorption spectra, the binding constant between dipeptide and SPFO above the ccmc was determined.