Fluorescence Emission Measurements Research Articles

The effects of Nd2O3 concentration in the laser emission of TeO2-ZnO glasses

The present work reports the modification introduced by different Nd2O3 concentration on optical properties and the laser operation of Nd3+ doped (TeO2-ZnO) bulk tellurite glass. The spectroscopic data are analyzed within the Judd Ofelt formalism framework and the results are compared to the fluorescence lifetime and emission measurements to derive values for the quantum efficiency and the stimulated emission cross section of the considered 4F3/2 → 4I11/2 infrared laser transition around 1062.5 nm. Continuous-wave laser action is achieved with this bulk tellurite glass by pumping the sample inside a standard plan-concave mirror laser cavity with different output couplers. It is possible to observe coherent emission only for the lower concentration (0.5%(wt.) of Nd2 O3). Also laser action could only be observed for this sample with threshold pump power of 73 mW associated with a laser slope efficiency of 8% for an output coupler transmission of 4% indicating that TeO2-ZnO are potential materials for laser action. The results presented in this work together with those previously reported with higher concentration (1.0% (wt) of Nd2O3) determine the adequate Nd2O3 concentration for laser action and guide the correct experimental procedure for TeO2-ZnO glasses preparation.

Uptake of Europium(III) from Water using Magnetite Nanoparticles

It is demonstrated that colloidal magnetite nanoparticles can be used as nanosorbents for lanthanide ions dissolved in water. In particular, a series of experiments are performed for the removal of Eu(III) in distinct analytical conditions and by applying an external magnet to collect the sorbents previously dispersed in water samples. Furthermore, strategies for surface chemistry functionalization are also investigated, aiming to investigate the effect of this parameter on the removal capacity of the Fe3O4 nanoparticles. The supernatant solutions are monitored for the remaining amount of Eu(III) by fluorescence emission measurements in the presence of 2,6-pyridinedicarboxylic acid as a sensitizer. The results demonstrate that neat Fe3O4 nanoparticles are capable of capturing lanthanide ions (III) from aqueous solutions (pH 7), without need of surface modification, and for subsequent removal by magnetic separation. During the removal, efficiency is increased after modifying the particles' surfaces with silica and 3-aminopropyltrimethoxysilane; in alkaline medium (pH 10), there is complete removal regardless the type of nanosorbent used. This has been explained by the formation of insoluble Eu(III) species that adsorb strongly to the nanosorbents surfaces allowing their subsequent magnetic separation.

Synthesis and Self-Aggregation of Poly(2-ethyl-2-oxazoline)-Based Photocleavable Block Copolymer: Micelle, Compound Micelle, Reverse Micelle, and Dye Encapsulation/Release

We report on the synthesis of photocleavable poly(2-ethyl-2-oxazoline)-block-poly(2-nitrobenzyl acrylate) (PEtOx-b-PNBA) block copolymers (BCPs) with varying compositions via combination of microwave-assisted cationic ring-opening polymerization (CROP) and atom transfer radical polymerization (ATRP) using α-bromoisobutyryl bromide as an orthogonal initiator. The amphiphilic nature of this BCP causes them to self-assemble into primary micelles in THF/H2O, which further undergo secondary aggregation into nanostructured compound micelles as established through DLS, FESEM, and TEM. Upon UV irradiation (λ = 350 nm), the photocleavage of the PNBA block of the PEtOx-b-PNBA BCP takes place, and that leads to the formation of the doubly hydrophilic poly(2-ethyl-2-oxazoline)-b-poly(acrylic acid) (PEtOx-b-PAA) BCP causing the rupture of compound micelles as confirmed by spectroscopic and microscopic techniques. Encapsulation of a model hydrophobic guest molecule, nile red (NR), into the photocleavable BCP micellar core in aqueous solution and its UV-induced release is also investigated by fluorescence emission measurements. PEtOx-b-PNBA BCP amphiphiles are also shown to self-assemble into spherical nanostructures (∼90 nm) in dichloromethane as established by DLS and TEM analysis. These are referred to as reverse micelles and are able to encapsulate anionic hydrophilic dye, Eosin B, and facilitate its solubilization in organic media.

Goniometrical measurements of fluorescence quantum efficiency

Fluorescent brightening agents are widely used in various industries to enhance the appearance of materials. In order to describe the colour of a fluorescent surface, accurate measurements of fluorescence emission are needed. In this work, measurements of goniometrically resolved bispectral luminescent radiance factors are presented with improved uncertainties. In addition, a method for goniometrically determining the spectral quantum efficiencies of the fluorescent process is presented and validated. The advantage of goniometric measurements is that they avoid the need to assume a specific angular emission profile of the fluorescent sample.

Processable Amide Substituted 2,5-Bis(2-thienyl)pyrrole Based Conducting Polymer and Its Fluorescent and Electrochemical Properties

While majority of conductive polymers are insoluble and infusible, theirs solution processable derivatives are more desirable for preparing large size flat panel display and solid state applications because they are compatible with low cost, large area roll-to-roll manufacturing process. For this purpose, a solution-processable fluorescent conjugated polymer (PDOB), consisting of electron rich N-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)-4-(dodecyloxy) benzamide (DOB) and its copolymer with 3,4-ethylenedioxythiophene P(DOB-co-EDOT) were synthesized by electrochemical polymerization technique. Electrochemical and optical properties of P(DOB) and P(DOB-co-EDOT) were investigated cyclic voltammetry, UV-vis absorption and fluorescence emission measurements, respectively. The optical bandgap values of P(DOB) and P(DOB-co-EDOT) determined by spectroelectrochemical data were 1.92 eV and 1.62 eV, respectively. P(DOB) and P(DOB-co-EDOT) were exhibited favorable redox activity and electrochromic performance. Further kinetic studies demonstrated that the P(DOB) and P(DOB-co-EDOT) have high optical contrast ratios (60–25%), favorable coloration efficiencies (139.1 cm2.C−1 and 80.6 cm2.C−1), fast response time (1.5 s; 1.0 s), high stability. When compared to soluble poly (2,5-dithienyl pyrrole) derivatives in literature, P(DOB) have lowest oxidation potential and bandgap and have highest optical contrast. As a result, these materials provide more plentiful electrochromic colors which useful for display application and hold promise for other solution-processable applications.

Effects of green and red light in βL-crystallin and ovalbumin.

The effects of visible light on biological systems have been widely studied. In particular, the alterations of blue light on the ocular lens have recently attracted much attention. Here, we present a study about the effects produced by green and red light on two different proteins: βL-crystallin and ovalbumin. Based on differential scanning calorimetry (DSC), circular dichroism (CD), dynamic light scattering (DLS), and fluorescence emission measurements, we found that both wavelengths induce structural changes in these proteins. We also observed that βL-crystallin aggregates. Our work may advance our understanding about conformational and aggregation processes in proteins subjected to visible radiation and the possible relationship with cataracts. While blue light has been considered the only harmful component in the visible espectrum, our findings show the possibility that lower energy components may be also of some concern.

Measurement of the fluorescence quantum yield of bis-MSB**Supported by National Natural Science Foundation of China (11205183, 11225525, 11390381)

The fluorescence quantum yield of bis-MSB, a widely used liquid scintillator wavelength shifter, was measured to study the photon absorption and re-emission processes in a liquid scintillator. The re-emission process affects the photoelectron yield and distribution, especially in a large liquid scintillator detector, thus must be understood to optimize the liquid scintillator for good energy resolution and to precisely simulate the detector with Monte Carlo. In this study, solutions of different bis-MSB concentration were prepared for absorption and fluorescence emission measurements to cover a broad range of wavelengths. Harmane was used as a standard reference to obtain the absolution fluorescence quantum yield. For the first time we measured the fluorescence quantum yield of bis-MSB up to 430 nm as inputs required by Monte Carlo simulation, which is 0.926±0.053 at λex=350 nm.

Supramolecular coordination polymer formed from artificial light-harvesting dendrimer.

We report the formation of supramolecular coordination polymers formed from multiporphyrin dendrimers (PZnPM; M = FB or Cu), composed of the focal freebase porphyrin (PFB) or cupper porphyrin (PCu) with eight zinc porphyrin (PZn) wings, and multipyridyl porphyrins (PyPM; M = FB or Cu), PFB or PCu with eight pyridyl groups, through multiple axial coordination interactions of pyridyl groups to PZns. UV-vis absorption spectra were recorded upon titration of PyPFB to PZnPFB. Differential spectra, obtained by subtracting the absorption of PZnPFB without guest addition as well as the absorption of PyPFB, exhibited clear isosbestic points with saturation binding at 1 equiv addition of PyPFB to PZnPFB. Job's plot analysis also indicated 1:1 stoichiometry for the saturation binding. The apparent association constant between PZnPFB and PyPFB (2.91 × 10(6) M(-1)), estimated by isothermal titration calorimetry, was high enough for fibrous assemblies to form at micromolar concentrations. The formation of a fibrous assembly from PZnPFB and PyPFB was visualized by atomic force microscopy and transmission electron microscopy (TEM). When a 1:1 mixture solution of PZnPFB and PyPFB (20 μM) in toluene was cast onto mica, fibrous assemblies with regular height (ca. 2 nm) were observed. TEM images obtained from 1:1 mixture solution of PZnPFB and PyPFB (0.1 wt %) in toluene clearly showed the formation of nanofibers with a regular diameter of ca. 6 nm. Fluorescence emission measurement of PZnPM indicated efficient intramolecular energy transfer from PZn to the focal PFB or PCu. By the formation of supramolecular coordination polymers, the intramolecular energy transfer changed to intermolecular energy transfer from PZnPM to PyPM. When the nonfluorescent PyPCu was titrated to fluorescent PZnPFB, fluorescence emission from the focal PFB was gradually decreased. By the titration of fluorescent PyPFB to nonfluorescent PZnPCu, fluorescence emission from PFB in PyPFB was gradually increased due to the efficient energy transfer from PZn wings in PZnPCu to PyPFB.

A Study on Spectro-Analytical Aspects, DNA - Interaction, Photo-Cleavage, Radical Scavenging, Cytotoxic Activities, Antibacterial and Docking Properties of 3 - (1 - (6 - methoxybenzo [d] thiazol - 2 - ylimino) ethyl) - 6 - methyl - 3H - pyran - 2, 4 - dione and its Metal Complexes.

The focus of the present work is on the design, synthesis, characterization, DNA-interaction, photo-cleavage, radical scavenging, in-vitro cytotoxicity, antimicrobial, docking and kinetic studies of Cu (II), Cd (II), Ce (IV) and Zr (IV) metal complexes of an imine derivative, 3 - (1 - (6 - methoxybenzo [d] thiazol - 2 - ylimino) ethyl) - 6 - methyl - 3H - pyran - 2, 4 - dione. The investigation of metal ligand interactions for the determination of composition of metal complexes, corresponding kinetic studies and antioxidant activity in solution was carried out by spectrophotometric methods. The synthesized metal complexes were characterized by EDX analysis, Mass, IR, (1)H-NMR, (13)C-NMR and UV-Visible spectra. DNA binding studies of metal complexes with Calf thymus (CT) DNA were carried out at room temperature by employing UV-Vis electron absorption, fluorescence emission and viscosity measurement techniques. The results revealed that these complexes interact with DNA through intercalation. The results of in vitro antibacterial studies showed the enhanced activity of chelating agent in metal chelated form and thus inferring scope for further development of new therapeutic drugs. Cell viability experiments indicated that all complexes showed significant dose dependent cytotoxicity in selected cell lines. The molecular modeling and docking studies were carried out with energy minimized structures of metal complexes to identify the receptor to metal interactions.

Bio-recognizable and photo-cleavable block copolymers based on sugar and poly(4-substituted-ε-caprolactone) bearing a photo-cleavable junction

In this study, we synthesized bio-recognizable and photo-cleavable amphiphilic block copolymers containing photodegradable linkers, 5-hydroxy-2-nitrobenzyl alcohol, as junction points between bio-recognizable hydrophilic glucose (or maltose) and hydrophobic poly(4-substituted-e-caprolactone) chains, by using a combination of ring-opening polymerization and nucleophilic substitution reactions. When the polymer solutions were exposed to ultraviolet (UV) irradiation, substantial structural and morphological changes were observed in the particles. The copolymers were biodegradable and biocompatible, and they could self-assemble into spherical photo-responsive micelles. Fluorescence emission measurements indicated the release of Nile red, a hydrophobic dye, encapsulated by the Glyco-ONB-PXCL micelles, in response to irradiation caused by the disruption of the micelles. Selective lectin binding experiments confirmed that the glycosylated Glyco-ONB-PXCL could be used to bio-recognition applications. The nanoparticles were associated with negligible levels of toxicity at concentrations of less than 30 μg mL−1. The confocal microscopy and flow cytometry results showed that the uptake of doxorubicin (DOX)-loaded micelles by HeLa cells was faster than that of free DOX.

Photo‐responsive amphiphilic poly(α‐hydroxy acids) with pendent o‐nitrobenzyl ester constructed via copper‐catalyzed azide‐alkyne cycloaddition reaction

Photo‐responsive block copolymer mPEG‐b‐poly(Tyr)‐g‐NB was prepared by introduction of o‐nitrobenzyl ester group into the side chain of amphiphilic poly(ethylene glycol)‐b‐poly(α‐hydroxy acids) (mPEG‐b‐poly(Tyr)) containing pendent alkynyl group via copper‐catalyzed azide‐alkyne cycloaddition reaction. The amphiphilic mPEG‐b‐poly(Tyr) was synthesized via the ring‐opening polymerization of O‐carboxyanhydrides, with monomethoxy poly(ethylene glycol) (mPEG) as macroinitiator. The molecular structure, self‐assembly, and photo‐controlled release of the obtained mPEG‐b‐poly(Tyr)‐g‐NB were thoroughly investigated. mPEG‐b‐poly(Tyr)‐g‐NB could self‐assemble into spherical micelles in water and showed disassembly under UV light irradiation, which was demonstrated by means of UV‐vis spectroscopy, scan electron microscopes, and dynamic light scattering measurement. Fluorescence emission measurements demonstrated that Nile red, encapsulated by micelles, can be released upon UV irradiation. This study provides a convenient way to construct smart poly(α‐hydroxy acids)‐based nanocarriers for controlled release of hydrophobic drugs. Copyright © 2015 John Wiley & Sons, Ltd.

Density relaxation and particle motion characteristics in a non-ionic deep eutectic solvent (acetamide + urea): Time-resolved fluorescence measurements and all-atom molecular dynamics simulations

Temperature dependent relaxation dynamics, particle motion characteristics, and heterogeneity aspects of deep eutectic solvents (DESs) made of acetamide (CH3CONH2) and urea (NH2CONH2) have been investigated by employing time-resolved fluorescence measurements and all-atom molecular dynamics simulations. Three different compositions (f) for the mixture [fCH3CONH2 + (1 - f)NH2CONH2] have been studied in a temperature range of 328-353 K which is ∼120-145 K above the measured glass transition temperatures (∼207 K) of these DESs but much lower than the individual melting temperature of either of the constituents. Steady state fluorescence emission measurements using probe solutes with sharply different lifetimes do not indicate any dependence on excitation wavelength in these metastable molten systems. Time-resolved fluorescence anisotropy measurements reveal near-hydrodynamic coupling between medium viscosity and rotation of a dissolved dipolar solute. Stokes shift dynamics have been found to be too fast to be detected by the time-resolution (∼70 ps) employed, suggesting extremely rapid medium polarization relaxation. All-atom simulations reveal Gaussian distribution for particle displacements and van Hove correlations, and significant overlap between non-Gaussian (α2) and new non-Gaussian (γ) heterogeneity parameters. In addition, no stretched exponential relaxations have been detected in the simulated wavenumber dependent acetamide dynamic structure factors. All these results are in sharp contrast to earlier observations for ionic deep eutectics with acetamide [Guchhait et al., J. Chem. Phys. 140, 104514 (2014)] and suggest a fundamental difference in interaction and dynamics between ionic and non-ionic deep eutectic solvent systems.

Influence of chemical architecture of oils and ionic liquid on the physicochemical and thermodynamic properties and microenvironment of anionic surfactant based microemulsion

Although several studies on water-in-hydrocarbon oil microemulsions stabilized by anionic surfactant are available in literature, such study on oils possess comparable molar volumes with different chemical architectures and physicochemical properties, herein R-(+)-limonene (LIM) and isobutyl benzene (IBB) derived microemulsions in absence or presence of ionic liquid (IL) warrants uniqueness of this report. The present study delineates interfacial composition and thermodynamics properties of sodium dodecylsulfate, SDS/1-pentanol/LIM or IBB/water microemulsions in absence or presence of IL, 1-butyl-3-methylimidazolium chloride (bmimCl) as additive by the dilution method. Further, precise characterization of these systems is accomplished by conductivity and DLS studies as function of ω, [bmimCl] and temperature, which provide an insight into unique features of the oil/water interface. Finally, the influence of distinctive features of oils and the states of water organization in nanopool of these microemulsions have been explored from steady state fluorescence emission, fluorescence anisotropy and FTIR measurements. bmimCl containing microemulsions are more spontaneous than aqueous microemulsions. Addition of bmimCl yields smaller droplets compared to aqueous system. Fluorescence measurements reveal penetration of oil molecules in the surfactant palisade layer vis-a-vis interfacial micropolarity and their consequential effects in microenvironment of microemulsions in absence or presence of bmimCl, using suitable molecular probes. Apart from reciprocal variation in free and bound water with increasing water content, results exhibit mild variation in interfacial water (which is basically trapped water in the hydrophobic tail region of surfactant) by changing oil continuum. Finally, correlation of the results in terms of evaluated physicochemical and thermodynamic parameters has been presented.

Reconstitution and Topological Analysis of Caveolin-1 in Bicelles

Caveolae are 50-100 nm invaginations in the plasma membrane of many cell types that play a critical role in signal transduction. Caveolin-1 is a 21 kD integral membrane protein that is required for the formation of caveolae. Caveolin-1 is thought to adopt an unusual horseshoe topology in the membrane where the N- and C- termini are cytoplasmic. Caveolin-1 has 4 native tryptophan residues in this region (W85, W98, W115, and W128) that can be used as reporters of the micro-environment of the polypeptide chain. Caveolin-1 single tryptophan mutants were successfully reconstituted into CHAPSO/DMPC bicelles. Fluorescence emission measurements were performed on each mutant and analysis of these spectra indicated that tryptophan residues 85 and 128 are in the head group region of the lipid bilayer with λmax values of 344.4 ± 2.4 nm and 338.2 ± 0.6 nm respectively, and tryptophan residues 98 and 115 are inserted into the hydrophobic core with λmax values of 334.4 ± 0.2 nm and 330.2 ± 1.0 nm, respectively. The information gleaned from these studies was supported by MD simulations performed on caveolin-1 in a DMPC bilayer. These data together support the postulation that caveolin-1 contains a membrane embedded turn.

Spectroscopic and thermodynamic properties of recombinant heat shock protein A6 from Camelus dromedarius.

Heat shock protein A6, also known as HSP70B', is a member of the Hsp70 family of molecular chaperones. Under stressed conditions, the level of HSPA6 increases substantially, and the protein has been targeted as a biomarker of cellular stress in several studies. We report the spectroscopic and thermodynamic properties of Arabian camel species cHSPA6, determined by measurement of intrinsic and extrinsic fluorescence emission, and use of far-UV circular dichroism and dynamic multimode spectroscopy. Our results showed that cHSPA6 has similar binding affinity for both ATP and ADP (K D=~50nM). Binding of ATP and ADP reduced the surface hydrophobicity of the protein, and slightly altered its secondary structure, suggesting localized conformational rearrangement after ATP or ADP binding. Dynamic multimode spectroscopy revealed that cHSPA6 unfolds through three transitions with melting points (T m) of 42.3±0.2, 61.3±0.1, and 81.2±0.2°C. To the best of the author's knowledge, and literature search, this is the first report of the spectroscopic and thermodynamic properties of the Arabian camel heat shock protein.

Synthesis and characterization of amphiphilic photocleavable polymers based on dextran and substituted-ɛ-caprolactone

In this study, we synthesized photocleavable amphiphilic block copolymers containing photodegradable linkers, 5-hydroxy-2-nitrobenzyl alcohol, as junction points between hydrophilic dextran (or maltodextrin) and hydrophobic poly(4-substituted-ɛ-caprolactone) chains, by using a combination of ring-opening polymerization and nucleophilic substitution reactions. When the polymer solutions were exposed to ultraviolet (UV) irradiation, major structural and morphological changes were observed in the particles. The copolymers were biodegradable and biocompatible, and they can self-assemble into spherical photoresponsive micelles. Fluorescence emission measurements indicated the release of Nile red, a hydrophobic dye, encapsulated by the Dex-ONB-PXCL micelles, in response to irradiation caused by the disruption of the micelles. Light-triggered bursts were observed for indomethacin (IMC)-loaded Dex-ONB-PXCL micelles during the first 5h. The nanoparticles were associated with nonsignificant toxicity at concentrations of less than 100μgmL−1. The confocal microscopy and flow cytometry results showed that the uptake of DOX-loaded micelles by HeLa cells was slightly less than that of free DOX, and it was predominantly retained in the cytoplasm.

Proton concentration in the thylakoid membranes can regulate energy distribution between the two photosystems

The aim of our study was to investigate the role of protons in regulating energy distribution between the two photosystems in the thylakoid membranes. Low pH-induced changes were monitored in the presence of a proton blocker, N,N'-dicyclohexylcarbodiimide (DCCD). When thylakoid membranes were suspended in a low-pH reaction mixture and incubated with DCCD, then a decrease in the fluorescence intensity of photosystem II (PSII) was observed, while no change in the intensity of photosystem I (PSI) fluorescence occurred according to the measured fluorescence emission spectra at 77 K. Since low pH induced distribution of energy from PSII to PSI was inhibited in the presence of DCCD, we concluded that pH/proton concentration of the thylakoid membranes plays an important role in regulating the distribution of the absorbed excitation energy between both photosystems.

A bifunctional chromogenic and fluorogenic probe for F− and Al3+ based on azo-benzimidazole conjugate

A versatile bifunctional probe has been reported for selective individual detection of Al3+ and F− through “turn-on” chromogenic and fluorogenic dual modes. The photonic behaviors of probe upon addition of analyte have been determined using UV–vis absorption, fluorescence emission, quantum yield and fluorescence life-time measurement. Density functional theory calculations have been performed to establish the nature of interaction between probe and Al3+/F−.

Soft and hard multiway FRET-based investigation of interaction between drug and QD labeled DNA

Interaction of 7-aminoactinomycin D (7AAD) with duplex form of quantum dot (QD) conjugated DNA, is the subject of this report. Excitation emission fluorescence measurements based on FRET mechanism offer a powerful means of studying this process. During titration experiments of DNA with 7AAD, three-way data are obtained—fluorescence measurements as a function of excitation and emission wavelengths at different 7AAD concentrations. The PARAFAC algorithm is applied to resolve the recorded data array. Upon inspection of the results, however, deviation from trilinearity as an intrinsic property of FRET data is observed that results in chemically less meaningful profiles from PARAFAC. This difficulty is addressed by using the restricted Tucker3 algorithm. The restricted Tucker3 shows a better performance compared to PARAFAC in resolving the data sets. Whereas this approach is more flexible in the modeling of profiles, the non-unique resolution is the major disadvantage of the algorithm. Therefore, to assess complete analysis of the FRET data hard trilinear decomposition is tried. It is shown that HTD algorithm has succeeded in the unique calculation of concentration profiles and pure spectra of all species. Also, equilibrium constants for the hybridization (3.1×106M−1) and the intercalation equilibrium (1.4×107M−1) are estimated in a unique way using hard modeling.

Spectroscopic properties and Judd–Ofelt analysis of BaY_2F_8:Sm^3+

Optical spectroscopy and Judd–Ofelt analysis were performed on a BaY2F8:Sm3+ crystal and used to guide the potential application of BaY2F8:Sm3+ as a laser material. Crystals were characterized by polarized absorption spectroscopy, fluorescence emission, and fluorescence lifetime measurements. The H69/2 and H67/2 manifolds are of most interest for visible lasers. This investigation seeks to capture the behavior of the samarium ion in a barium–yttrium–fluoride host from the UV–vis into the near-infrared wavelength regions.