Behavior Of Pyrene Research Articles

Corrigendum to “Investigation on the gelatin-surfactant interaction and physiochemical characteristics of the mixture” [Journal of Molecular Liquids, 224 (2016) 900–908/MOLLIQ_2015_362

Abstract The effect of gelatin, a denatured protein on the micellization of a series of polyoxyethylated hexadecyl ethers (BC-X) were investigated through several physicochemical techniques such as surface tensiometry, contact angle measurement, fluorimetry, cyclic voltametry, zeta potential measurement, dynamic light scattering studies. The critical micellar concentrations (cmc) of BC-X increased with increase in gelatin concentration in the mixture which was also corroborated by other techniques performed. This increase in cmc was attributed to the decrease of monomeric surfactant concentration as a result of the formation of gelatin-BC-X complex. The surface excess concentration, minimum area per molecule, and surface pressure at the cmc were estimated from surface tension data. The free energies of adsorption and micellization indicated the micellization and adsorption at air/water interface to be spontaneous phenomena. Micropolarity and the aggregation numbers of the mixed systems were determined using the fluorescence behaviour of pyrene. The slanting nature of curve of polarity parameters-surfactant concentration in conjunction with appearance of pyrene excimer peak at the lower BC-X concentrations supported the stepwise growth of the micelles through the formation of pre-micellar aggregates. The entwining of the protruded chains of the surfactants around the gelatin moiety through polar and hydrophobic interactions was endorsed to be the main reason behind the formation of small sized mixed micelles. The zeta potential studies envisaged the surface of both gelatin and BC-X to have negative electrostatic potential independently. The decrease in the zeta potential of the gelatin-surfactant mixtures was attributed to the removal of fraction of the negatively charged BC-X surface as a result of casing by the hydrophobic and neutral segments of gelatin.

Thermal stimuli‐responsive behavior of pyrene end‐functionalized PDMS through tunable Π–Π interactions

ABSTRACTPyrene end‐functionalized, telechelic poly(dimethyl siloxane) (PDMS) materials were synthesized and their response to different thermal stimuli was evaluated. The incorporation of pyrene end groups introduces strong π–π interactions that facilitated a broad range of thermally responsive properties, in some circumstances forming pyrene nanocrystals that serve as physical crosslinks leading to elastic materials. By synthesizing different chain lengths, samples exhibiting a 7 orders of magnitude change in storage modulus in response to thermal stimuli were produced by modifying only the end‐groups (0.6 wt % of all polymer segments). Repeated thermal cycling during rheological experiments revealed that π–π interaction and crystallization/melting kinetics of pyrene chain‐ends plays a key role in their thermal responsiveness. The properties of these materials were tuned by adding free pyrene, neat PDMS, or graphene oxide (GO) nanoparticles, making them attractive for many applications (e.g., tunable damping materials, heat/light sensors, conductive gels, or light repositionable adhesives). For example, nanocomposites containing 1 wt % GO caused the melting temperature for pyrene crystal domains to more than double, and even induced pyrene end‐group crystallization in samples that did not exhibit crystals in neat form. It is hypothesized that these features originate from π–π interactions between pyrene ends and GO surfaces. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 159–168

Sorption of Pyrene by Clay Minerals Coated with Dissolved Organic Matter (DOM) from Landfill Leachate

Interactions of dissolved organic matter (DOM) from landfill leachate with clays could affect significantly the fate of hydrophobic organic compounds (HOCs) in soils. The complexes of montmorillonite (MT) and kaolinite (KL) with DOM extracted from landfill leachate were prepared under controlled conditions, termed CMT and CKL, respectively. The bare clays and their complexes were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), thermogravimetry (TG), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Batch experiments were designed to investigate the sorption behavior of pyrene onto the clays in the presence of DOM. The maximum sorption capacities of pyrene on MT, CMT, KL, and CKL were 22.18, 38.96, 42.00, and 44.99 μg·g−1, respectively, at the initial concentration of 1000 ± 150 μg·L−1. The sorption isotherms of pyrene by the bare clays followed the Henry model well, whereas the Freundlich sorption isotherm provided a better fit to the equilibrium data of the sorption by the complexes. The role of montmorillonite and kaolinite complexes with DOM in the retention of pyrene in soils was different. This may be due to the different crystal structures between montmorillonite and kaolinite.

Fluorescence study of film formation from PS/Al2O3 nanocomposites

Abstract Steady state fluorescence (SSF) and UV–vis (UVV) techniques were used to study the film formation behavior of pyrene (P) labeled polystyrene (PS) latex and Al 2 O 3 (PS/Al 2 O 3 ) composites depending on PS particles size and Al 2 O 3 content. The close-packed arrays of PS spheres (SmPS: 203 nm; LgPS: 382 nm) templates on clean glass substrates were covered with various layers of Al 2 O 3 by dip-coating method. Two different film series (SmPS/Al 2 O 3 and LgPS/Al 2 O 3 ) were prepared in various Al 2 O 3 layer content. The film formation behavior of these composites were studied by annealing them at a temperature range of 100–250 °C and monitoring the scattered light intensity ( I sc ), fluorescence intensity ( I P ) from P and transmitted light intensity ( I tr ) through the films after each annealing step. Optical results indicate that classical latex film formation was occurred for all Al 2 O 3 content films and film formation process was unaffected by the Al 2 O 3 content for both film series. Extraction of PS template produced highly ordered porous structures for high Al 2 O 3 content in both film series. SEM images showed that the pore size and porosity could be easily tailored by varying the PS particle size and the Al 2 O 3 content.

Sensing hydration and behavior of pyrene in POPC and POPC/cholesterol bilayers: A molecular dynamics study

Molecular dynamics (MD) simulations of bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) with varying amounts of cholesterol (0, 5, 20, and 40mol%) were carried out in the absence and presence of inserted pyrene molecules. Both fluorophore and bilayer parameters were computed, for characterization of probe location and dynamics, as well as its effects on the host bilayer. In agreement with previous studies in fluid disordered bilayers, pyrene prefers to be located in the hydrophobic acyl chain region of POPC bilayers, close to the glycerol group of lipid molecules and causes ordering of the lipid acyl chains. However, incorporation of pyrene in binary POPC/cholesterol bilayers decreases the acyl chain order parameter (especially near the end of the chains), opposing the ordering effect of cholesterol. These effects are modest and mainly felt locally. Significantly, as the bilayer is enriched with cholesterol, the relative position of pyrene and the POPC carbonyl and phosphocholine groups is invariant, and the local water density around the probe decreases. This work clarifies and supports the cautious use of pyrene Ham effect to effectively measure equivalent polarity in lipid bilayers. Within the time scale of the MD simulations, which is of the magnitude of the fluorescence lifetime of pyrene, the thermally averaged polarity of lipid bilayers is nearly out of influence of spurious uncertainty in the transverse location of pyrene in the bilayers. This renders the values of equivalent polarity measurements through the pyrene Ham effect more reliable and reproducible than previously expected.

Substrate effects in the photoenhanced ozonation of pyrene

Abstract. We report the effects of actinic illumination on the heterogeneous ozonation kinetics of solid pyrene films and pyrene adsorbed at air-octanol and air-aqueous interfaces. Upon illumination, the ozonation of solid pyrene films and pyrene at the air-aqueous interface proceeds more quickly than in darkness; no such enhancement is observed for pyrene at the air-octanol interface. Under dark conditions, the reaction of pyrene at all three interfaces proceeds via a Langmuir-Hinshelwood-type surface mechanism. In the presence of light, Langmuir-Hinshelwood kinetics are observed for solid pyrene films but a linear dependence upon gas-phase ozone concentration is observed at the air-aqueous interface. We interpret these results as evidence of the importance of charge-transfer pathways for the ozonation of excited-state pyrene. The dramatically different behaviour of pyrene at the surface of these three simple reaction environments highlights the difficulties inherent in representing complex reactive surfaces in the laboratory, and suggests caution in extrapolating laboratory results to environmental surfaces.

Behaviour of pyrene and its decomposition by-products in chlorination

The behaviour of pyrene and its decomposition by-products in chlorination and their aryl hydrocarbon receptor (AhR) ligand activities were investigated. In the study on pyrene behaviour in chlorination, the pyrene and chlorine concentrations and the pH range were 0.82–21 μg l −1 , 2.0–2.1 mg l −1 and 3.2–10, respectively. In the pH range of 3.2–5.1, pyrene was decomposed faster in the order of pH 3.2, 3.7 and 5.1. However, when the pH ranged from 5.1 to 10, pyrene was decomposed faster in a pH range of approximately 7.8–8.8. When the effects of the initial pyrene concentration were investigated, a lower pyrene concentration was decomposed faster. Pyrene decomposition in chlorination was inhibited by the presence of 30 mM ethanol, but was enhanced by the presence of 3.0 and 6.0 mgC l −1 humic acid. Pyrene decomposition by-products in chlorination were also characterized (pyrene, 92 μg l −1 ; chlorine, 7.9 mg l −1 ; pH, 7.1). 1-Chloropyrene, 1,6- and 1,8-dichloropyrenes, and pyrene-4,5-dione were identified as pyrene decomposition by-products. 1-Chloropyrene and pyrene-4,5-dione in chlorination were found to be major by-products at pH 3.2, but minor by-products at pH 7.1 (pyrene, 56–67 μg l −1 ; chlorine, 3.9–4.0 mg l −1 ). The yeast assay revealed that pyrene-4,5-dione was an AhR agonist.

Effects of Poly(ethylene glycol) Doping on the Behavior of Pyrene, Rhodamine 6G, and Acrylodan-Labeled Bovine Serum Albumin Sequestered within Tetramethylorthosilane-Derived Sol-Gel-Processed Composites

We investigate the effects of controlled poly(ethylene glycol) (PEG) doping on the behavior of pyrene, rhodamine 6G (R6G), and acrylodan-labeled bovine serum albumin (BSA-Ac) sequestered within tetramethylorthosilicate (TMOS)-derived sol-gel-processed materials. To probe the dipolarity of the local environment within the composite we performed static fluorescence measurements on pyrene as the composites aged. We found that small levels of PEG loading effected significant enhancements in the local dipolarity surrounding the average pyrene molecule. Time-resolved fluorescence anisotropy measurements were used to follow the rotational reorientation dynamics of R6G as the composites aged. As the PEG loading increased, the R6G reorientational mobility increased. Nitrogen adsorption techniques were used to quantify the effects of PEG doping level on the surface area and final xerogel pore features. A large reduction in surface area was observed with PEG doping, but no detectable change in pore size was noted. The effects of PEG doping on a biomolecule were probed by following the time-resolved fluorescence anisotropy decay of BSA-Ac. These results showed that PEG doping resulted in increased biomolecule dynamics relative to that found for a neat, undoped TMOS-derived composites. Together these results show that PEG doping can be used to tune the sol-gel-processed composite dipolarity, alter the mobility of dopants sequestered within the composite, control analyte acessibility to the sensing chemistry, and modulate the internal dynamics within a biodopant.

Behavior of pyrene in air/water monolayers of eicosanoic acid

Behavior of pyrene in air/water monolayers of eicosanoic acid

FLUORESCENCE SPECTROSCOPY OF BENZO[a]PYRENE DIOL EPOXIDE‐DNA ADDUCTS. CONFORMATION‐SPECIFIC EMISSION SPECTRA

The fluorescence characteristics of adducts derived from the covalent binding of the highly tumorigenic (+) and the non-tumorigenic (-) enantiomers of trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) to native calf thymus DNA are significantly different from one another both at room temperature and at 77 K. The ratio R of fluorescence intensities of the (0,0) band I (situated near 380 nm) and vibronic band V (near 400 nm) of the pyrene ring system in the BPDE-DNA adducts and of the tetraol (BPT) hydrolysis product of BPDE is very sensitive to the polarity of the solvent, thus mimicking the well known behavior of pyrene itself (A. Nakajima, 1971, Bull. Chem. Soc. Jpn. 44, 3272). The fluorescence excitation and emission spectra of the (+)-BPDE-DNA adducts are relatively sharp and only slightly red-shifted (2-3 nm) with respect to those of BPT in aqueous buffer solution, and R = 1.07 when the fluorescence is excited at the maximum of the absorption spectrum; this compares with R = 1.17 for BPT in water, R = 0.75 in ether, and R = 0.84 for noncovalently intercalated BPT. These results suggest that the pyrene ring system in the covalent (+)-BPDE-DNA adducts is located in an environment which is relatively exposed to the aqueous environment, while physically intercalated BPT molecules are located at hydrophobic binding sites. The fluorescence characteristics of the (-)-BPDE-DNA adducts are more heterogeneous and thus more complex than those of the (+)-adducts. The R ratio depends rather strongly on the wavelength of excitation; a minor, more highly fluorescent and relatively solvent-accessible form of adducts exhibits an R ratio of 1.01. The major, less solvent accessible form is characterized by a larger red shift in the absorption spectrum (approximately 10 nm) and emission spectrum (approximately 6 nm for the (0,0) band) relative to BPT, and an R ratio of 1.07. These characteristics suggest that the local environments of the pyrenyl residues in the (-)-BPDE-DNA adducts are significantly different from those of BPT bound noncovalently to DNA by the intercalation mechanism. Fluorescence methods, particularly at low temperatures where the bands are better resolved and the fluorescence yields are significantly greater than at room temperature, can also be used to distinguish covalent DNA adducts derived from the binding of (+)-BPDE and (-)-BPDE to native double-stranded DNA.