Energy transfer in inverse micelles

Luminescent and time-resolved determination of gemifloxacin mesylate in pharmaceutical formulations and spiked blood plasma samples using a lanthanide complex as a probe

A novel luminescence-based analytical methodology was established employing a europium(III) complex with 3-allyl-2-hydroxybenzohydrazide (HAZ) as the coordinating ligand for the quantification of gemifloxacin mesylate (GMF) in pharmaceutical preparations and human plasma samples spiked with the compound. The stoichiometry of the europium complex with HAZ was determined via the Job plot and exhibited a metal-to-ligand ratio of 1 : 2. The analytical procedure relies on a rapid and significant enhancement of luminescence by the Eu(AZ)2 complex when it interacts with gemifloxacin mesylate, which allowed for the rapid detection of 96 samples within approximately 2 minutes. The thermodynamic parameters of the complexation of GMF with Eu(AZ)2 were evaluated and showed that the complexation of GMF was spontaneous with a negative ΔG. The binding constant K was 4.27 × 105 L mol-1 and DFT calculations supported GMF binding and the formation of Eu(AZ)2-GMF without further ligand exchange. The calibration graph for the luminescence quantitation of GMF was linear over a wide concentration range of 0.11-16 μg mL-1 (2.26 × 10-7 to 3.30 × 10-5 mol L-1), with a limit of quantification (LOQ) of 110 ng mL-1 (230 nmol L-1) and a detection limit (LOD) of 40 ng mL-1 (82 nmol L-1). The proposed method showed good accuracy with an average recovery of 99% with relative standard deviations of less than 5% in spiking experiments, even in complex pharmaceutical dosage forms such as tablets and in human blood plasma. Herein, the ability of the suppression of the luminescence background by using the long lag times of the lanthanide probe in a time-resolved detection scheme provided reliable and precise results, which suggests its potential for use in further real or patient samples.

Sensitive ratiometric sensor for Al(III) detection in water samples using luminescence or eye-vision

A facile, quick, and sensitive ratiometric luminescence sensor is designed for detection aluminum ions in water samples using luminescence or eye-vision. This approach relies on the emission change of the europium(III) complex with 3-(2-naphthoyl)-1,1,1,-trifluoro acetone (3-NTA) after interaction with various concentration of aluminum ions. The addition of aluminum ions suppressed the Eu(III) emission at 615 nm under 333 nm excitation, while simultaneously enhancing the ligand emission at 480 nm. Optimum detection was obtained in methanol. The quantification of aluminum ions using ratiometric method was determined by plotting the luminescence ratio (F_480nm/F_615nm) versus aluminum ions concentration. The calibration plot was obtained within the range 0.1-100 µM with LOD = 0.27 µM. Additionally, the concentration of aluminum ions can be estimated semi-quantitatively by visually observing the luminescence colour change of the probe from red to light green and then to dark green after being excited by a UV lamp with 365 nm. As far as we are aware, this is the first luminescent lanthanide complex-based ratiometric probe for the detection of aluminum ions. The probe showed remarkable aluminum ions selectivity relative to that of other metal ions. The suggested sensor was used effectively to identify aluminum ions in water samples with good results.

Detection of Ciprofloxacin in Urine through Sensitized Lanthanide Luminescence

Ciprofloxacin, a fluoroquinolone antibiotic, is widely used for the treatment of bacterial infection in humans due to its broad antibacterial spectrum. An excessive use or overdose of ciprofloxacin on the other hand can cause several adverse effects not only to humans but also to microorganisms. Unabsorbed ciprofloxacin in the body is mostly excreted through urine and finally goes to the environment, providing a drug resistance pressure on bacteria. Hence a simple and efficient detection method of ciprofloxacin is necessary, which, for example, can be used to analyze ciprofloxacin content in urine. Although ciprofloxacin itself shows inherent fluorescence, direct fluorescent detection of ciprofloxacin in raw urine sample is difficult due to autofluorescence of urine by other components. Herein we report that a Tb(III) complex of DO3A (1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid) can be efficiently sensitized by ciprofloxacin to emit luminescence separately from the urine autofluorescence wavelength region. Tb-DO3A shows excellent sensitivity with a detection limit of three parts per billion in aqueous buffer solution. Further, Tb-DO3A is used to detect ciprofloxacin with high sensitivity and selectivity in a raw urine sample without any purification or separation procedures in the concentrations ranging from 1 µg·mL⁻¹ to 50 µg·mL⁻¹. The direct measurement of ciprofloxacin excreted in urine may be used to control overdose of the drug.

Applications and limitations of uranyl ion as a photophysical probe

Uranyl ion has a long-lived luminescent excited state, which can be used as a probe for the aggregation behaviour in a variety of surfactant and polymeric systems. The general spectroscopy and photophysics of this species are discussed, and the applications to specific micellar, microemulsion, vesicular and liquid crystalline systems presented. It is shown that both dynamic and structural information can be obtained from spectral and kinetic data. Examples of applications of uranyl probe studies to technologically important mesoscopic and mesoporous systems involving metal oxides, or their salts, and to humic acids and soils will also be reviewed. Emphasis will be given to both the advantages and restrictions on the use of this useful photophysical probe.

Association of surfactants and polymers studied by luminescence techniques

Light emission spectroscopy has unique possibilities for the study of central issues of surfactants and associating polymers. With the help of luminescent probes, information may be obtained on matters such as molecular association, microstructure, and molecular dynamics; this constitutes an important contribution to the understanding and control of macroscopic properties, as well as biological function and technical applications. Important aspects of these systems considered in this review are: formation of micelles and hydrophobic microdomains; aggregation numbers of surfactants; shape of molecular aggregates; size of droplets in water or in oil in microemulsions; formation and stability of vesicles; intra- vs. intermolecular association in polymers; conformational changes in polymers; polymer-surfactant association; surfactant organization in adsorbed layers; kinetic aspects regarding the formation and disintegration of self-assembly structures; residence times of molecules in microdomains and migration of active molecules.

Influence of Polarity and Viscosity of the Micellar Interface on the Fluorescence Quenching of Pyrenic Compounds by Indole Derivatives in AOT Reverse Micelles Solutions

The fluorescence quenching of the pyrene derivatives (4-(1-pyrenyl)butyl) trimethylammonium bromide (PBTMA), (1-(1-pyrenyl)methyl) trimethylammonium iodide (PMTMA), and 1-pyrene sulfonic acid (PSA) by indole methyl substituted in positions 1 and 2, tryptophan and tryptamine, was studied in AOT/heptane reverse micelles as a function of R = [water]/[AOT]. In these systems the pyrenic probes are associated to the micellar interface. Bulk and intramicellar quenching rate constants were determined for neutral indoles. The quenching rate constants of PBTMA by indole or 1,2-dimethylindole increase with R, whereas for those for PMTMA or PSA by indole the increment is much smaller. For the quenchers, tryptophan and tryptamine, that are bound to the interface of the reverse micelle, the bimolecular intramicellar quenching rate constant is much lower than in water. The results can be explained by a high microviscosity of the interface, and a micropolarity similar to that sensed by other probes. Moreover, the observed trend in the rate constants when R is varied is in line with the reported changes in micropolarity and microviscosity. Laser flash photolysis experiments show that in these systems the main result of the quenching process is the formation of the excited triplet of the probe. Copyright 1998 Academic Press.

Determination of catecholamines and related compounds by capillary electrophoresis with postcolumn terbium complexation and sensitized luminescence detection

A method has been developed for the determination of catecholamines and related compounds (DA, E, NE, DOPA, DOPAC, DOPAG) in urine samples. The compounds of interest were separated by capillary electrophoresis with a borate buffer as background electrolyte. Detection was based on the sensitized luminescence of terbium ions. Using a homemade postcolumn reactor, a basic solution containing a stoichiometric mixture of terbium(III) chloride and EDTA was added postcolumn to the separation buffer. The ternary catechol-EDTA-terbium complexes formed in the reaction mixture showed a strong luminescence with excitation and emission maxima at 300 and 545 nm, respectively. By optimization of the experimental conditions, zone broadening could be restrained and plate numbers up to 130,000 appeared to be possible. Detection limits found were in the order of 10(-7) mol L-1. The catecholic compounds could be determined in urine samples after a standard cleanup and preconcentration procedure.

Fluorescence lifetime distribution of 1,8-anilinonaphthalenesulfonate (ANS) in reversed micelles detected by frequency domain fluorometry

The fluorescence emission decay of ANS (1,8-anilinonaphthalenesulfonate) in reversed AOT (sodium bis-(2-ethyl-1-hexy)sulfosuccinate) micelles at different water contents was investigated by frequency domain fluorometry. The whole ANS emission decay in reversed AOT micelles could not be fitted in terms of discrete lifetime values, i.e., mono-exponential and bi-exponential models. Better fits were obtained when using continuous unimodal Lorentzian lifetime distributions. This was interpreted as arising from the reorientation processes of water molecules around the excited state of ANS or probe exchange among different probe locations, occurring on a time scale longer than fluorophore lifetime. The dependence of ANS fluorescence anisotropy on the emission wavelength was consistent with the existence of a great emission heterogeneity especially for inverted micelles having reduced H2O/AOT molar ratio. Finally, the observation that the distribution width decreases with increasing temperature and/or micelle size suggested that fast processes of water dipolar reorganization around the fluorophore are facilitated under these conditions.

Ion-induced DNA structure change in nucleosomes

Physical methods have been used to study calcium binding to the nucleosome core particle. Equilibrium dialysis of Ca2+ and spectroscopic analysis of a Ca2+ analogue show that the ion binds tightly to the particles, resulting in a significant change of DNA circular dichroism. This suggests that base stacking may be altered as a result of Ca2+ binding. In the presence of Ca2+, the absorbance and fluorescence properties of methylene blue (MB), a DNA-specific intercalator, confirm that the dye binds tightly to nucleosomes by intercalation. However, secondary changes occur which suggest that the MB binding site is altered as a result of Ca2+ binding. Triplet state anisotropy decay and triplet lifetime quenching both show that in the Ca2+-nucleosome complex, methylene blue is capable of wobbling over a substantial angular range at its binding site. To explain these data, it is proposed that Ca2+ binding to nucleosomes causes DNA to fold by means of a series of sharp bends (kinks). The properties of bound MB are best explained if it is presumed that the intercalator binds tightly to such kinked sites in the nucleosome. On the basis of these observations, we discuss the possibility that multivalent ion concentration in the nucleus is high enough that the smooth to kinked helix equilibrium may be near to its midpoint. Near such a midpoint, the secondary structure of DNA in the nucleosome might prove to be sensitive to effector molecule binding and to site-specific variation of DNA or histone composition within genes.