Plot Of Fluorescence Intensity Research Articles

A novel turn-on fluorescent probe for cyanide detection in aqueous media based on a BODIPY-hemicyanine conjugate

Abstract A novel BODIPY-hemicyanine based fluorescent probe 1 for cyanide (CN − ) detection was designed and synthesized. Among the tested anions, the probe showed high selectivity towards CN − . Only addition of CN − to probe 1 in aqueous solution (V H2O /V EtOH = 1/1) could result in a remarkable blue shift of the absorption band from 385 nm to 265 nm and induce 20-fold fluorescence enhancement at 515 nm. The sensing mechanism was based on nucleophilic addition between CN − and indolium group, which was confirmed by 1 H NMR and mass spectrum analysis. Plot of fluorescence intensity as a function of CN − concentrations exhibited a good linear relationship in the range of 0–10 μM, with a detection limit to be 1.53 ppb. Moreover, the proposed sensing approach could work in a wide pH range from 5.0–9.0 and reach an equilibrium instantaneously. Finally, probe 1 was successfully applied in detection of CN − in natural water samples and on test paper strips with satisfactory results.

Development of Stability Indicating Densitometric and Enhanced sensitivity Spectrofluorimetric Methods for Determination of Zaleplon in Presence of its Acidic Degradation Products

Zaleplon is easily degradable into its acidic degradation products, so two stability- indicating methods were developed for determination of zaleplon in the presence of these degradation products and are successfully applied to quantify zaleplon in pharmaceutical preparations. The first was a densitometric evaluation of thin-layer chromatograms of the drug using a mobile phase of ethyl acetate – ammonia (33%) - methanol (8.5:0.5:1, v/v/v). The chromatograms were scanned at 338 nm, a wavelength at which zaleplon can be readily separated from its degradation products and determined in the range of 0.5-2.5 μg/spot with mean percentage recovery of 100.79 ± 0.65%. The second method was based on measuring the fluorescence intensity of zaleplon at λex/λem =350 nm/460 nm. The effect of micelle medium on the fluorescence emission was studied which revealed that the anionic surfactant of sodium lauryl sulphate has strong sensitizing effect for the fluorescence. The fluorescence intensity plot was linear over the range of 0.1-3.6 μg/ml with mean percentage recovery of 100.39 ± 1.12%. Determination was also successful when analyzing zaleplon in a formulation in the form of Siesta capsules. Results were statistically analyzed and found to be in accordance with those given by a reported method.

Spectrofluorimetric and Spectrophotometric Stability‐Indicating Methods for the Analysis of Veralipride in Presence of Its Degradants and in Spiked Human Plasma

AbstractSpectrofluorimetric and spectrophotometric stability‐indicating methods were developed and validated for analysis of veralipride (Ver) in presence of its hydrolytic and oxidative degradants. The spectrofluorimetric method was based on direct measurement of the intrinsic fluorescence of Ver at 366 nm after excitation at 299 nm using sodium lauryl sulfate (SLS) as micelle enhancer. The fluorescence intensity plot was linear over the concentration range 1.0–10.0 µg·mL−1. The high sensitivity of the method allowed its successful application to the analysis of Ver in spiked human plasma. Two other methods were developed. They are based on the oxidative coupling reaction of Ver with 3‐methyl benzothiazolin‐2‐one hydrazone (MBTH) hydrochloride in presence of ceric ammonium sulphate in an acidic medium. The first method depends on spectrophotometric measurement of the stable green colored oxidative coupling product at 660 nm. The different experimental parameters affecting the reaction were optimized. Linearity range is 10.0–100.0 µg·mL−1. The second method depends on a fluorescence quenching effect of Ver on the fluorescence of Ce3+. The difference in fluorescence intensity was measured at 380 nm after excitation at 300 nm. This method is applicable over the concentration ranges 0.25–2.50 µg·mL−1. The methods were validated according to the ICH guidelines. They were successfully applied for the analysis of Ver in drug substance, drug product and in laboratory prepared mixtures containing different percentages of hydrolytic and oxidative degradants.

Stability-indicating methods for the determination of sertaconazole nitrate by micelle-enhanced spectrofluorimetry and TLC-densitometry

Two sensitive and selective stability-indicating methods were developed for the determination of sertaconazole nitrate (Ser-NO3), in the presence of its acid, alkaline and oxidative degradation products. The first method was based on measuring the fluorescence intensity of the drug at λex/λem = 231 nm/312 nm. The influence of micelle medium on the fluorescence emission was studied. The nonionic surfactant of Triton® X-100 showedstrong sensitizing effect for the fluorescence. The fluorescence intensity plot was linear over concentrations 0.5–5 μg mL-1 with mean percentage recoveries 100.59 ± 1.49 %. The second method was based on TLC separation of the drug from its degradation products followed by densitometric measurement of the intact drug spot at 302 nm. The developing system used for separation was chloroform-acetone-33 % ammonia (14:2:0.1 v/v/v). The linear range was 1–8 μg/spot with mean percentage recoveries 100.07 ± 1.97 %. The methods were validated according to ICH guidelines. Statistical analysis of the results revealed high accuracy and good precision. The suggested procedures could be used for the determination of sertaconazole nitrate in drug substance and drug products as well as in presence of its degradation products.

Novel saccharide-induced conformational changes in a boronic acid-appended poly(L-lysine) as detected by circular dichroism and fluorescence

Poly(L-lysine) has been modified with a 4-phenylboronic acid derivative which acts as a sugar-binding site and a dansyl group which acts as a fluorescence probing site. The helix content of this poly(L-lysine) derivative as estimated by CD spectroscopy became maximum at pH 10.3. The helix content was increased from 51 to 79% by complexation of D-fructose with the pendant boronic acid group and the maximum pH shifted from 10.3 to 7.9. Examination of the CD spectra revealed that the conformation changes in the order of β-sheet → α-helix → random coil with increasing medium pH. The D-glucose addition induced a similar increase in the helix content and a similar low pH shift of the helix content maximum but the mechanism was somewhat different: one D-glucose was bound to two boronic acid groups to form an intrapolymeric bridge and the resultant CD spectrum was similar to that of the β-turn structure. These saccharide-induced conformational changes were well reflected by plots of fluorescence intensity vs. pH. The decrease in the fluorescence intensity in the high pH region (random coil region) was confirmed by fluorescence polarization to be due to the increase in the molecular motion. This is a novel system to control the poly(amino acid) conformation by saccharides and to detect the conformational changes by convenient spectroscopic methods.

Polymerization of styrenes with pendant aminophosphazenes and fluorescence behaviors of their Eu 3+ complexes

Radical polymerizations of novel styrenes with pendant penta(3-dimethylaminopropylamino)-(SPDAP) and penta(2-dimethyl aminoethoxy)cyclotriphosphazene (SEAP) in various solvents and the fluorescence behavior of complexes of Eu 3+ with these cascade materials were studied. The conversion of SEAP increased on going from THF to ethanol, whereas the conversion of SPDAP in ethanol showed the lowest value. The application of the Kamlet-Taft equation to the conversion suggested that the polymerization of SPDAP and SEAP is primarily affected by the hydrogen bond interaction. 13C NMR spectra of SEAP showed that the peak of the β-carbon in the vinyl group shifted downfield as the conversion increased. This suggests that the interaction between the monomer and solvents brings about a change of polymerizability of SEAP. A similar downfield shift was observed for SPDAP in ethanol, suggesting that SPDAP also has a high polymerizability. The inherent viscosities of poly(SEAP) and poly(SPDAP) in ethanol were found to be considerably higher than those in THF. This result and the kinetic treatment of polymerization suggest that the side arms on the phosphazene ring in ethanol are expanded due to the hydrogen bond interactions with the solvent, and that the propagation is sterically hindered, especially for the polymerization of SPDAP with relatively long side arms. This might be responsible for the low conversion observed for the polymerization of SPDAP in ethanol. When Eu 31 ions were added to SPDAP, a significant increase in fluorescence intensity of Eu 3+ was observed. The plot of fluorescence intensity vs the concentration of SPDAP suggests the formation of a 2:1 SPDAP-Eu 3+ complex. For the polymer-Eu 3+ complex, a similar increment of the intensity was observed. From the chemical shifts of side arms in the monomer-Eu 3+ complex, the structure of the complex is discussed.

Fluorescence Measurement of Tetracycline in Model Fermentation Media Samples Containing Streptomyces Aureofaciens Cell Mass

This study describes fluorescence measurements made with a fiber-optic probe on model fermentation media samples containing natural media components, high densities of Streptomyces aureofaciens cell mass, and varying concentrations of tetracycline. Tetracycline, produced commercially from S. aureofaciens, is a highly fluorescent antibiotic, and these measurements were conducted to determine the correlation between the tetracycline content in the media and the observed fluorescence of the samples. Seven separate types of media samples were examined for this study. Each medium contained a nonfluorescent base of nutrients and salts along with one of seven different natural feedstocks at a concentration of 50 g/L. In addition, the samples contained S. aureofaciens cell mass densities of 50 g/L (based on dry cell mass). Excitation wavelengths of 290 nm, 390 nm, and 413 nm were used to probe the fluorescence of the samples, and emission spectra were obtained over the wavelength ranges of 320–360 nm, 420–600 nm, and 440–600 nm, respectively. Background fluorescence observed in the region of 320–360 nm upon 290-nm excitation in the samples was due to tryptophan fluorescence contained in the S. aureofaciens cell mass and was found to decrease dramatically as tetracycline levels increased from 0 to 8000 μg/mL. Plots of fluorescence intensity at a number of emission wavelengths versus tetracycline concentration in the samples clearly revealed strong correlations.

Damage to the vascular endothelium of diabetic patients can be assessed by analysing blood samples for the number of circulating endothelial cells with mitochondrial DNA deletions

Damage to the vascular endothelium of diabetic patients can be assessed by analysing blood samples for the number of circulating endothelial cells with mitochondrial DNA deletions

Spectroscopic studies of the tyrosine residues of human plasma apolipoprotein A-II

Human apolipoprotein A-II (apo A-II) in solution and associated with 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) was investigated by a combination of absorbance and fluorescence methods. Each apo A-II polypeptide chain contains four tyrosine residues but no tryptophan residues. Two and three tyrosine residues, respectively, appear to be buried for apo A-II in aqueous solution and in the lipid-associated protein. The spectroscopic properties of the tyrosine residues of lipid-associated apo A-II were also investigated. Plots of fluorescence intensity against temperature revealed a discontinuity in the region of the phase transition; however, over the same temperature range, there was no change in the exposure of tyrosine residues to the aqueous environment or in their mobility as measured by fluorescence polarization. Near-ultraviolet circular dichroic measurements demonstrated that the environments of the tyrosine residues of lipid-associated apo A-II and nitrated apo A-II were different from that of the apo A-II in solution or in a denatured state. Similar measurements also revealed that the microenvironments around tyrosines of apo A-II bound to DMPC in the gel phase are different from those observed in the liquid crystalline phase. Using environmentally sensitive fluorescence lipid probes, we have previously demonstrated that the polarity of the lipid/water interface of DMPC changes through a phase transition. The observations presented here indicate that these environmental changes also occur at the lipid/protein interface.

Characterization of microscopic laser beams by 2-D scanning of fluorescence emission

We describe a fast, accurate, and reproducible method for calibrating microscopic laser beams. Fundamental mode (TEM(00)) output from an argon-ion laser is focused on a thin (<0.5-microm) aqueous fluorescein solution located at the sample plane of a fluorescence microscope. The fluorescent image of the focused beam is scanned in two dimensions at the emission diaphragm of the microscope by a computer-controlled X-Y scanning mirror. Plots of fluorescence intensity vs position demonstrate that the beam profile is Gaussian in two dimensions. Both the 1/e(2) beam radius and the coordinates of peak intensity are obtained by nonlinear least-squares analysis. An adaptation of this method is used to characterize microscopic elliptical Gaussian beams. We present experimental and theoretical evidence, the latter based on the optical transfer function of an objective lens, that Gaussian beams used in fluorescence photobleaching recovery experiments are not significantly distorted by diffraction or defocusing effects.

Electron-Impact Induced Molecular Fluoresence Spectroscopy

Abstract By the bombardment of gaseous molecules with monoenergetic electrons the molecules can be electronically excited and/or fragmented, depending upon the energy supplied by the electrons. Any fragments which may be produced also have the possibility of being produced in electronically (as well as vibrationally and rotationally) excited states. The electronically excited molecules and fragments both possess the possibility of radiative decay (fluorescence). The measurement of this fluorescence as a function of both electron energy and photon wavelength is termed “electron-impact induced fluorescence spectroscopy.” A plot of fluorescence intensity as a function of the electron energy at a given photon wavelength is generally referred to as an “excitation function,” which is exactly analogous to the excitation spectrum which can be obtained in conventional (optically excited) fluorescence spectrometry. A plot of the fluorescence intensity as a function of photon wavelength at a given electron energy is...

Fluorimetric assay of ergotamine

Studies on the fluorescence properties of ergotamine in water at various pH values, and in several organic solvents are described. An assay procedure for ergotamine, based on its intense fluorescence in ethanol, is presented. Extraction of ergotamine into benzene from basic aqueous solution is followed by transfer of the extract to ethanol for fluorescence determination. The plot of fluorescence intensity vs. concentration is linear up to 5 μg ml −1, and the assay has a limit of detection of 0.002 μg ml −1. Reproducibility data at the 2.5-μg ml −1 level are given.

Use of 8-anilino-1-naphthalene sulfonate as a fluorescent indicator in colloid titration

The use of 8-anilino-1-naphthalene sulfonate (ANS) is recommended as the fluorescent indicator in the titration of dilute colloid. Potassium polyvinylsulfate (PVSK) and methylglycolchitosan (MGch) are used for the standard substances of the negatively and positively charged colloid, respectively.The fluorescence intensity was measured with the spectrofluorophotometer Hitachi 204 equipped with magnetic stirrer in cell compartment. Titrations were carried out in a 300 ml beaker using a megnetic stirrer. ANS is practically nonfluorescent in water but becomes strongly fluorescent when it is bound to cationic colloid such as MGch (λex=374 nm, λem=480 nm).The fluorescence of ANS-MGch complex is diminished by the titration with PVSK standard solution. The end point of the fluorometric titration was determined from a plot of fluorescence intensity against the volume of the titrant added.A typical example is shown in Fig. 1 where 40 ml of aqueous MGch solution (5.5×10-5 M) was titrated with 2.5×10-4 M aqueous PVSK standard solution. A clear equivalence point was obtained by this method. Transition metals, especially, iron(III), quench the fluorescence of ANS-MGch complex and must be removed by dialysis or masked with proper reagents.