El-Zeiny M. Ebeid

Fluorescence enhancement of coumarin thiourea derivatives by Hg2+, Ag+, and silver nanoparticles.

Fluorescence enhancement by factors of 5-12 times 8-alkyl thiourido-7-ethoxy-4-methyl coumarin derivatives was observed upon complexation with Hg(2+), Ag(+), and Ag nanoparticles. The study reveals a chelation-enhanced fluorescence (CHEF) mechanism with the formation of 1:2 complexes in Hg(2+)/coumarin derivatives and 1:1 complexes in Ag(+)/coumarin derivatives. The activation parameters of the complexation processes were evaluated with energy of activation values in the case of Ag(+) being nearly twice those in the case of Hg(2+) complexation. Isokinetic studies indicate an enthalpy-controlled mechanism in the Hg(2+)/coumarin derivatives complex formation. No fluorescence enhancement was observed with Fe(3+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), La(3+), and Ce(3+), making the present coumarin thiourea derivatives selective chemosensors of both Hg(2+) and Ag(+) ions with different complexation time scales between these two ions. Fluorescence enhancement of the studied coumarin thiourea derivatives using silver nanomaterials occurs almost instantaneously and can be induced by silver nanoparticles in the picomolar (pM) concentration ranges.

Structural and fluorescence quenching characterization of hematite nanoparticles.

Nanoparticles of the dominant hematite form (α-Fe(2)O(3)) of iron oxide have been prepared by a simple route of dropping FeCl(3) solution into boiling water. The nanoparticles have been characterized by transmission electron microscopy (TEM), UV-visible electronic absorption spectroscopy, chemical stoichiometry, thermal analysis methods (TGA, DSC and DTA), XRD, FTIR and magnetic susceptibility measurements. Kinetic analysis of the DSC calorigram of thermal dehydration of the nanoparticles reveals one stage of the dehydration process of energy of activation of 29.0 kJ mol(-1). The role of iron oxide nanoparticles in fluorescence quenching of coumarin thiourea derivatives (I-IV) was investigated at room temperature (296 K) by means of steady-state fluorescence spectroscopy. The quenching process was characterized by Stern-Volmer (S-V) plots which display a positive deviation from linearity. This could be explained by static and dynamic quenching models. The positive deviation in the S-V plot is interpreted in terms of ground-state complex formation model and sphere of action static quenching model. Various rate parameters for the fluorescence quenching process were determined by using the modified Stern-Volmer equation. The sphere of action static quenching model agrees very well with experimental results. Quenching constants for iron oxide nanoparticles are about four orders of magnitudes higher than quenching by Fe(3+) ions.

Nanostructure-loaded mesoporous silica for controlled release of coumarin derivatives: A novel testing of the hyperthermia effect

The synthesis of three types of mesoporous materials is reported: pure mesoporous silica (MCM-41), a nanocomposite of mesoporous silica with hydroxyapatite (MCM-41-HA) and mesoporous silica/gold nanorods nanocomposite (MCM-41-GNRs). The mesoporous materials were characterized by X-ray diffraction, N(2) adsorption isotherms, FTIR spectroscopy, transmission electron microscopy, and scanning electron microscopy. The samples were loaded with coumarin thiourea derivatives (I-IV) having functional groups of varying sizes and the in vitro release assays were monitored, and the release behavior was investigated as a function of soaking time in simulated body fluid. Two release stages were obtained in MCM-41, MCM-41-HA and MCM-41-GNRs loaded samples with the early release stages accounting for about 30% of loaded derivatives. These early release stages are characterized by Higuchi rate constant values nearly twice the values associated with the second release stages. The influence of substituent size on the release rate constants was explained in terms of sorption sites and hydrogen bonding with silanol groups on silicates. The release of coumarin derivatives loaded on MCM-41, MCM-41-HA and MCM-41-GNRs occurs over remarkably long time of the order of about 260 h with faster release rates in loaded MCM-41 and MCM-41-GNRs samples compared with MCM-41-HA ones. The role of hyperthermia effect in enhancing release rates was investigated by subjecting loaded MCM-41-GNRs to near infrared (NIR) radiation at 800 nm. This would be of significance in targeted drug release using hyperthermia effect. Unlike hydroxyl apatite, loading MCM-41 with gold nanorods does not affect the release kinetics. Only when these samples are irradiated with NIR photons, does the release occur with enhanced rates. This property could be valuable in selected targeting of drugs.

Thermochromism in Ni(ii) complexes with schiff base derivatives of 4-aminoantipyrine

Abstract Ni(II) complexes of 2-hydroxy-1-naphthylidene-4-aminoantipyrine (I) and salicylidene-4-aminoantipyrine (II) display a change of colour upon heating. The change in II is reversible in the presence of moisture. The thermochromism in crystalline I and II has been studied using differential thermal analysis (DTA), electronic and IR spectroscopy. X-ray powder diffraction and electrical conductivity. Thermochromism in these complexes has been attributed to dehydration.

1,4-Bis (β-Pyridyl-2-Vinyl)Benzene (P2VB) and2,5-Distyryl-pyrazine (DSP) asBlue Laser Dyes

Solutions of P2VB and DSP in dimethyl-sulphoxide (DMSO) of concentration ca. 10–3 M/l act as laser dyes on pumping with nitrogen laser. P2VB and DSP are lasing in the ranges 390–440 nm (λmax = 416 nm) and 435–465 nm (λmax = 447 nm) respectively. An equimolar mixture of P2VB and DSP behaves as an energy transfer dye laser (ETDL) and is lasing in the range 429–455 nm (λmax = 438 nm). Such ETDL system obeys a long range coulombic energy transfer mechanism with a critical transfer distance R0 = 7.5 nm.

Emission characteristics and photostability of 1,4-bis[β-(2-benzoxazolyl) vinyl]benzene (BBVB) laser dye

Abstract The fluorescence efficiencies of (Φf) of 1,4-bis[β-(2-benzonazolyl) vinyl]benzene (BBVB) havebeen measured in various hydrogen bonding and non-hydrogen bonding solvents of different polarities on the π ∗ scale. In hydrogen bonding solvents Φf increases with increasing π ∗ value. The fluorescence has also been studied in other media, including micellar, microemulsion and acidic ones. BBVB solutions exhibit short excited state lifetimes in the range 0.5–0.7 ns. The second-order rate constant of oxygen and rhodamine 6G (R6G) quenching of BBVB fluorescence have been determined from Stern-Volmer relations. The critical transfer distances for the BBVB/R6G system have been determined as R 0 = 46.8 and 48.5 A in ethanol and methanol respectively. The photochemical quantum yields (Φc) have also been determined in various organic solvents.

Viscosity and medium effects on the fluorescence and photochemical behaviour of some aryl chalcones

Abstract The emission, excitation and absorption spectra toghether with the fluorescence and photochemical quantum yields of some chalcone derivatives have been studied in organic solvents and micellar and microemulsion media. Both 4-[2-(2-pyridyl)ethenyl] ( I ) and 4-[2-(4-pyridyl)ethenyl ( II ) chalcones show large positive solvatochromic effects. The fluorescence quantum yields increase substantially as the medium viscosity increases with a subsequent decrease in the photochemical quatum yield. Compounds I and II undergo excited-state molecular aggregation in concentrated solutions giving excimer-like emission that coincides with emission from crystalline samples. The enthalpies of photoassociation have been estimated. The chalcone derivative I acts as an efficient quencher of the fluorescence of the laser dye 1,4-bis (β-pyridyl-2-vinyl)benzene via a long-range mechanism. The excited-state lifetimes of both I and II are short and at 20°C their τ values are less than 800 ps.

The spectra, lifetime and laser activity of 2,5-bis-2(l-naphthyl) vinylpyrazine and 2,5-bis-2(2-naphthyl)vinylpyrazine

Both 2,5-bis-2(l-naphthyl) vinylpyrazine (BNVP) and 2,5-bis-2(2-naphthyl) vinylpyrazine (B2NVP) diolefinic dyes have relatively short excited-state lifetimes, high fluorescence efficiencies and low photochemical quantum yields. BNVP solutions in dimethyl formamide and methylene chloride give amplified spontaneous emission (ASE) with a maximum at 500 nm. The low solubility of B2NVP in organic solvents does not allow the measurement of ASE for this dye. The excited state absorption spectra (ESA) of BNVP show an absorption band around 525 nm which reduces dye laser efficiency.Energy transfer from 7-diethylamino-4-methylcoumarin to BNVP and B2NVP has been studied by applying Stern-Volmer plots. The underlying mechanism is a radiative long range energy transfer.Both BNVP and B2NVP undergo solubilization in anionic as well as cationic micelles.

Emission characteristics and micellization of cationic 1,4-bis(β-pyridyl-2-vinyl)benzene laser dye

Cationic species of the recently reported 1,4-bis(β-pyridyl-2-vinyl)benzene (P2VB) blue laser dye has been generated by direct protonation and identified analytically. The steady state emission and the emission quantum yields have been studied both in aqueous and in micellar media. The hydrochloride derivative (P2VB · HCl) shows a substantial increase in fluorescence quantum yields (ϕf) as a result of both cationic and anionic micellization. Micellization also induces weak laser action in P2VB · HCl dye upon pumping with a nitrogen laser.The photochemical quantum yield of P2VB · HCl(λex= 337 nm) has been evaluated as ϕc= 0.003 and contrasted to that of the parent V2VB dye, for which ϕc= 0.004.Both conductometric and surface tension studies reveal a ground-state aggregation of P2VB · HCl at a critical concentration of ca. 7.5 × 10–3 mol dm–3. Excited-state molecular aggregation has also been observed in concentrated P2VB · HCl solutions which show excimeric emission at 500 nm. The enthalpy of excited-state photoassociation has been evaluated as ΔHa=–11.0 kJ mol–1 indicating that P2VB · HCl molecules in the excimer configuration are bound less tightly.

New diolefinic laser dyes: 1,4-bis(β-pyrazinyl-2-vinyl)-benzene (BPVB)

1,4-Bis(β-pyrazinyl-2-vinyl)benzene (BPVB) is an efficient blue laser dye. BPVB solutions in dimethyl sulphoxide (DMSO) of concentration ca. 10–3 mol dm–3 give laser emission in the range 417–498 nm (λmax= 438 nm) upon pumping with a nitrogen laser (λex= 337.1 nm). Both fluorescence and photochemical quantum yields have been evaluated in various solvents using various excitation wavelengths. The dye displays a relatively weak excimeric emission at ca. 500 nm in the more concentration solutions (ca. 10–2 mol dm–3) in DMSO. Excimer-like emission is also obtained from BPVB crystals at 510 nm that decreases in intensity upon irradiation ageing (λex= 365 nm) owing to solid-state photopolymerization. BPVB undergoes solubilization in both cationic (cetyltrimethylammonium chloride; CTAC) and anionic (sodium dodecyl sulphate; SDS) micellar media. BPVB undergoes ground-state protonation. The hydrochloride salt of the dye has been isolated and identified by conductometric and thermoanalytical techniques.