Showing papers on "Fluorescence spectrometry published in 1987"

Preparation and characterization of quantum size zinc oxide: a detailed spectroscopic study

Abstract: We report the synthesis of transparent colloidal suspensions of small zinc oxide particles in water, 2-propano1, and acetonitrile. Quantum (Q)-size effects are observed during particle growth and qualitatively interpreted by using a simple molecular orbital (MO) picture. The particles at the final stage of growth are approximately spherical in shape and consist of 2000-3000 ZnO molecules. They exhibit many of the photophysical properties of bulk zinc oxide. However, pronounced shifts in the absorption spectrum during the illumination of anoxic suspensions of ZnO reveal a distinctively different behavior of these small particles. Fluorescence spectra of the ZnO sols suggest that adsorbed electron relays are necessary to shuttle electrons from the conduction band into lower lying traps. Two fluorescence maxima are observed at the final growth stage of the ZnO particles. The bandgap fluorescence at 365 nm has an extremely short lifetime (τ < 100 ps), while the visible luminescence at 520 nm exhibits a slower biexponential decay (i.e., τ = 14 and 190 ns). The latter fluorescence is attributed to photogenerated electrons tunneling to preexisting, trapped holes. The low overall fluorescence quantum yield of Ф = 0.03 measured in these zinc oxide suspensions is indicative of radiationless transitions accompanying the emissions. A pronounced pH dependence of the Stern-Volmer constants obtained with various ionic substances, that effectively quench the 520-nm emission, is explained by specific adsorption to the charged particle surface. The zero point of charge (pH_(zpc)) of the aqueous colloidal suspension was determined to be 9.3 ± 0.2 by several independent methods.

Parallax method for direct measurement of membrane penetration depth utilizing fluorescence quenching by spin-labeled phospholipids.

Abstract: This report describes a method suitable for determining the depth of a wide variety of fluorescent molecules embedded in membranes. The method involves determination of the parallax in the apparent location of fluorophores detected when quenching by phospholipids spin-labeled at two different depths is compared. By use of straightforward algebraic expressions, the method allows calculation of depth in angstroms. Furthermore, the analysis can be extended to quenching by energy-transfer acceptors or brominated probes under appropriate conditions. Application of the method to quenching of 7-nitro-2,1,3-benzoxadiazol-4-yl (NBD)-labeled lipids by spin-labeled lipids located at three different depths is demonstrated in model membranes. It is shown that the calculated depths of the NBD groups are self-consistent to the extent that they are the same no matter which two spin-labels have been used in a particular experiment. In addition, the calculated depth is independent of spin-label concentration in the membrane within +/- 1 A, ruling out major effects due to spin-label perturbation. The quenching experiments show that the location of the NBD group in head-group-labeled phosphatidylethanolamine is at the polar/hydrocarbon interface and that of an NBD label on the "tail" of cholesterol is deeply buried, as expected. Unexpectedly, NBD labels placed at the end of fatty acyl chains of phosphatidylcholines are also near the polar/hydrocarbon interface. Presumably, the polarity of the NBD group results in "looping" back to the surface of the NBD groups attached to flexible acyl chains.

Fetal Methylmercury Poisoning: Relationship Between Concentration in Single Strands of Maternal Hair and Child Effects

Abstract: • Pregnant women consumed bread that was prepared from methylmercurytreated wheat. Single strands of maternal head hair were analyzed by x-ray fluorescence spectrometry. The index of fetal exposure was the maximum hair mercury concentration during gestation. Effects were measured by the frequency of psychomotor retardation, seizures, and neurological signs in the children. A dose-response relationship was demonstrated for fetal effects of methylmercury. Analysis of single hair strands provides a better index of acute or subacute fetal exposure than analysis of bundles of hair; the duration and degree of exposure are more accurately defined. A sex difference in response is discussed.

Photobleaching of porphyrins used in photodynamic therapy and implications for therapy.

Abstract: — The development of an extraction procedure to quantitate dihematoporphyrin ether (DHE) concentration in tissues correlated to fluorescence measurements from instrumentation developed for in vivo fluorimetry was examined. In vivo fluorometric results from mouse mammary carcinoma (SMT-F) were calibrated against results of the chemical extraction assay quantitated spectrophotometrically. Fluorescence and drug extractable levels increase in a linear fashion with injected dose. Loss of porphyrin fluorescence (photobleaching) and intra-tumoral porphyrin level has been demonstrated both in vitro (NHIK cells) and in vivo (SMT-F tumor) during illumination with light following exposure to Hpd or DHE. This process is essentially independent of porphyrin tumor level in vivo and could lead to tumor protection at very low porphyrin levels. On the other hand, this photobleaching process which occurs concurrent with cellular inactivation and tissue damage due to the photodynamic process can be exploited to protect normal tissue during photodynamic therapy (PDT) and thus greatly enhance the therapeutic ratio. This has been demonstrated in patients undergoing PDT.

Toxic trace elements associated with airborne particulate matter: a review

Abstract: This article provides a concise review of published literature pertaining to sampling and analytical methodologies, aerometric studies, source identification techniques and modeling activities for the elements arsenic, cadmium, nickel, lead, vanadium, zinc, cobalt, chromium, copper, iron, mercury, manganese, selenium and antimony, and their compounds, associated with airborne particulate matter. Sampling techniques discussed include filtration and inertial separation. Analytical methodologies such as atomic absorption and atomic emission spectrometry, neutron activation analysis, and X-ray fluorescence spectrometry are summarized. Data on atmospheric levels of 14 trace elements are presented in summary form from numerous studies in remote, rural and urban areas, and generally indicate that concentrations measured at rural locations are several orders of magnitude lower than those measured for urban areas. Source identification methodologies are discussed in terms of advantages and disadvantages, and vario...

Membrane chloride transport measured using a chloride-sensitive fluorescent probe.

Abstract: Transport of chloride across cell membranes through exchange, cotransport, or conductive pathways is a subject of great biological importance. Current methods of measurement are restricted in their sensitivity, time resolution, and applicability. A new transport measurement technique has been developed on the basis of the fluorescence quenching by chloride of the dye 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ). SPQ fluorescence quenching by chloride is rapid (less than 1 ms) and sensitive, with a greater than 50% decrease in fluorescence at 10 mM chloride. SPQ fluorescence is not altered by other physiological anions or by pH and can be used to measure both neutral and conductive transport processes. The high water solubility and membrane permeability properties of SPQ make it ideal for use in both membrane vesicles and cells. Chloride transport determined with SPQ was validated by measurement of erythrocyte chloride/anion exchange and membrane vesicle chloride conductance.

Spectrophotometry and spectrofluorimetry : a practical approach

Abstract: Abbreviations An introduction to spectrophotometry and fluorescence spectrometry Spectra Spectrophotometric assays Measurement of ligand binding to proteins Spectrophotometry Stopped-flow spectrophotometric techniques The determination of photochemical action spectra Index

Quantitative contributions of cholesterol and the individual classes of phospholipids and their degree of fatty acyl (un)saturation to membrane fluidity measured by fluorescence polarization.

Abstract: Steady-state fluorescence polarization (P) measurements, using the probe 1,6-diphenyl-1,3,5-hexatriene, in a large variety of well-defined liposomes at 25 degrees C allowed a quantitative description of the contributions of cholesterol, sphingomyelin, and (un)saturation of fatty acyl groups in the various phospholipids to the structural order (or the mutual affinity) of membrane lipids The P values for liposomes prepared from lipid extracts of natural (purified) membranes of various origins could be more or less predicted (calculated) from the relative contributions of the individual lipid components In all cases, the polarization varied with the cholesterol/phospholipid molar ratio (C/PL) according to the equation P = Pplat -(Pplat -Pzero) exp(-alpha C/PL), in which Pzero refers to the polarization without cholesterol and Pplat is a maximal plateau value, reached at a high C/PL (greater than 1) The "cholesterol-ordering coefficient" alpha of the phospholipids was found to increase with the fraction of sphingomyelin or dipalmitoylphosphatidylcholine molecules, indicating that the susceptibility of phospholipids to be ordered by cholesterol is increased by these compounds Pzero increases curvilinearly with the fraction of either of these molecules Pplat increases linearly with the fraction of saturated acyl chains for most phospholipids Highly unsaturated fatty acyl chains (eg, 20:4 and 22:6) strongly depress Pplat but not Pzero The results suggest that such phospholipids are unlikely to associate with cholesterol and may thus create extremely fluid membrane domains The disproportionation of cholesterol in the cell can be understood by the differing composition of the phospholipids in plasma membranes and endomembranes and their ordering susceptibility (affinity) toward cholesterol

A fluorescence technique for measurement of concentration in mixing liquids

Abstract: Previous researchers have observed turbulent transport of scalars in liquid jets by fluorescence. However, the technique has not been thoroughly investigated. This work examines a fluorescence technique in detail. Fluorescein sodium in a buffer solution was used in bench tests and in an experimental jet flow. Instrumentation and properties of the dye were considered. The author measured the variation of fluorescence intensity with temperature, pH, concentration and laser intensity. Concentration of reaction product in an acid-base reaction by laser-induced fluorescence is also discussed. The distinction between requirements for qualitative flow visualisation and for quantitative concentration measurements was clarified.

Simultaneous determination of linear alkylbenzenesulfonates, alkylphenol polyethoxylates, and nonylphenol by high-performance liquid chromatography.

Abstract: Linear 4-alkylbenzenesulfonates (LAS), 4-alkylphenol polyethoxylates (APEO) (i.e., 4-octylphenol polyethoxylates (OPEO) and 4-nonylphenol polyethoxylates (NPEO), and 4-nonylphenol (NP) are simultaneously determined by reversed-phase high-performance liquid chromatography (HPLC) using octylsilica columns and water/acetonitrile gradient elution. LAS are separated according to their alkyl chain lengths and coelution of NPEO and NP is observed in contrast to the separation of OPEO and NPEO. The determination of oligomer distributions of APEO and quantitation of NP,NP1EO, and NP2EO require additional information attainable by normal-phase HPLC. Recoveries of 85-100% were found for LAS, APEO, and NP isolated by Soxhlet extraction under basic conditions from laundry detergent powders, sewage sludges, sludge-amended soils, and river sediments. Relative standard deviations for all analytes in the different matrices did not exceed 6%. Detection limits with UV fluorescence detection are 95 ng for NP, 80 ng for LAS, and 65 ng for NPEO with respect to injected amounts.

Atomic Spectrometry Update. Clinical and biological materials, foods and beverages

Abstract: This update is a little shorter than in recent years, reflecting the fewer original papers published. However, the trend for a large number of review articles has continued and these cover a wide range of important topics. In the 2012 update, a noticeable increase in work involving very small samples was evident. These observations continue through into the current review. This was particularly seen with sample introduction systems used for ICP-MS. A microflow device for aerosol generation, based on thermal inkjet technology, provided for analysis of highly dissolved solids at a flow rate of 1 μL min−1 while other high performance arrangements were described which operated at slightly larger delivery rates. As in previous years, major topics include investigations of the metabolism of As and Se. We have also previously reported on the techniques to measure Pt–DNA adducts, developed in the last few years. It is encouraging to see that these are now being applied to studies of platinum anti-cancer treatments in cell cultures and in patients. There are some interesting new methodologies. Quantum dots appeared for the first time in this review with an indirect assay for measuring very low concentrations of protein in urine. A protein conjugate formed with CdTe quantum dots was isolated and the Cd measured by ICP-MS. XRF has poor sensitivity for low atomic number elements but in another indirect assay, Li in mineral water was determined by forming a potassium lithium periodatoferrate complex and measuring the Fe. Magnetic particles are used in some immunoassays to effect separation of reagents and a similar approach was developed using Fe3O4 magnetite nanoparticles modified with 1-(p-acetyl)phenyl)-3-(o-ethoxyphenyl)triazene to extract and preconcentrate Hg from water and fish samples. Concern over the amount of As in fish and rice and the potential for this element to appear in other food products is evident from studies involving fish oils and organic brown rice syrup. Anyone tempted to eat alligator meat can be reassured that concentrations of Cd, and Pb are very low. We are pleased to have a new contributor to this review; Sarah Hill has considerable experience with ICP-MS techniques including the use of this technique for imaging.

Antenna organization in green photosynthetic bacteria. 1. Oligomeric bacteriochlorophyll c as a model for the 740 nm absorbing bacteriochlorophyll c in Chloroflexus aurantiacus chlorosomes.

Abstract: Bacteriochlorophyll (BChl) c was extracted from Chloroflexus aurantiacus and purified by reverse-phase high-pressure liquid chromatography. This pigment consists of a complex mixture of homologues, the major component of which is 4-ethyl-5-methylbacteriochlorophyll c stearyl ester. Unlike previously characterized BChls c, the pigment from C. aurantiacus is a racemic mixture of diastereoisomers with different configurations at the 2a chiral center. Diluting a concentrated methylene chloride solution of BChl c with hexane produces an oligomer with absorption maxima at 740-742 and at 460-462 nm. Both the absorption spectrum and the fluorescence emission spectrum (maximum at 750 nm) of this oligomer closely match those of BChl c in chlorosomes. Further support for this model comes from the ability of alcohols, which disrupt BChl c oligomers by ligating the central Mg atom, to convert BChl c in chlorosomes to a monomeric form when added in low concentrations. The lifetime of fluorescence from the 740 nm absorbing BChl c oligomer is about 80 ps. Although exciton quenching might be unusually fast in the in vitro BChl c oligomer because of its large size and/or the presence of minor impurities, this result suggests that energy transfer from the BChl c antenna in chlorosomes must be very fast if it is to be efficient.

Single fibre optic fluorescence pH probe

Abstract: Fibre optic sensing is a growing technology in analytical chemistry. Scattering, absorbance, reflectance and luminescence spectroscopic measurements have been made using fibre waveguides. Fluorescence is particularly suited for use in fibre sensing because of its sensitivity and versatility, and the ease with which this type of measurement may be implemented with a single fibre optic.The probe configuration used in this study for pH measurement consists of fluorescein isothiocyanate (FITC) covalently bonded to a porous glass bead. This bead is attached to a single, multi-mode optical fibre, which conducts both the excitation and emission radiations. The increase in fluorescence intensity, as the acid form of the immobilised FITC is converted to its basic form, is related to the pH. The dynamic range of this miniature probe is pH 3–7 and this can be extended by decreasing the dye loading. The response time is between 20 and 35 s, depending on the capacity.

Contribution of 3-O- and 6-O-sulfated glucosamine residues in the heparin-induced conformational change in antithrombin III.

Abstract: The role of 3-O- and 6-O-sulfated glucosamine residues within the heparin octasaccharide critical for biological activity, iduronic acid----N-acetylglucosamine 6-O-sulfate----glucuronic acid----N-sulfated glucosamine 3,6-di-O-sulfate----iduronic acid 2-O-sulfate----N-sulfated glucosamine 6-O-sulfate----iduronic acid 2-O-sulfate----anhydromannitol 6-O-sulfate, was determined by comparing its ability to bind antithrombin, induce a conformational change in this protease inhibitor as monitored by the enhancement of intrinsic fluorescence, and accelerate (at saturation) the interaction of this protein with human factor Xa. The octasaccharide produced a maximum 48% increase in intrinsic fluorescence at 37 degrees C and a rate of factor Xa inhibition of 6 X 10(5) M-1 s-1 as measured by stopped-flow fluorometry at 25 degrees C. The basal rate of the antithrombin-factor Xa interaction observed in the absence of oligosaccharide was 2 X 10(3) M-1 s-1. The synthetic pentasaccharide, consisting of residues 2-6, produced fluorescence enhancement and rate of inhibition equal to those of the octasaccharide. However, a similar pentasaccharide, identical in all respects except that it lacked the 3-O-sulfate on residue 4, produced less than a 5% fluorescence enhancement and a rate of factor Xa inhibition of 8 X 10(3) M-1 s-1. The tetrasaccharide consisting of residues 2-5 produced a 35% fluorescence enhancement and a rate of factor Xa inhibition of 3 X 10(5) M-1 s-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Calculation for fluorescence modulation by absorbing species and its application to measurements using optical fibers

Abstract: Les calculs montrent l'importance de deux parametres: la distance intermoleculaire (liee a la concentration de l'espece absorbante) et le libre parcours moyen effectif

Iron-mediated oxidative stress in erythrocytes.

Abstract: Iron in its labile, chelatable form has been implicated in the generation of radical species such as the hydroxyl radical, ferryl species [an Fe(IV)-oxygen complex], perferryl (Fe2+ −O2 ↔ Fe3+ −O 2 − ∙), and Fe2+ /Fe3+ /O2 complexes (for reviews see Halliwell and Gutteridge, 1986; Czapski and Goldstein, 1986; Aust and White, 1986; Aust and Minotti, 1987; Gutteridge and Halliwell, 1989) and in the propagation of oxidative events.

Fluorescence Properties of Calmodulin-Binding Peptides Reflect Alpha-Helical Periodicity

Abstract: A basic amphiphilic alpha-helix is a structural feature common to many calmodulin-binding peptides and proteins. A set of fluorescent analogues of a very tight binding inhibitor (dissociation constant of 200 picomolar) of calmodulin has been synthesized. The fluorescent amino acid tryptophan has been systematically moved throughout the sequence of this peptide. The fluorescence properties for the peptides repeat every three to four residues and are consistent with the periodicity observed for an alpha-helix.

Picosecond fluorescence spectroscopy on excimer formation and excitation energy transfer of pyrene in Langmuir-Blodgett monolayer films

Abstract: Molecular association of pyrene chromophores has been studied with Langmuir-Blodgett (LB) monolayer films consisting of stearic acid and small amounts of 16-( 1-pyreny1)hexadecanoic acid. Picosecond time-resolved fluorescence spectra have shown four fluorescence bands originating from (1 ) a ground-state dimer (band D with vibrational peaks at 381, 401, and 422 nm), (2) a monomer (band M with vibrational peaks at 377, 397, and 421 mm), ( 3 ) an excimer (a structureless band El with a peak at 420 nm), and (4) another type of excimer (a structureless band E2 with a peak at 470 nm). E, was assigned as a fluorescence from a two-center, sandwich-type excimer which corresponds to the well-known pyrene excimer in solution, while E, was assigned as a fluorescence from a one-center type excimer. In the initial time region (0-200 ps), the D band is dominant, and its decay is associated with a rise of the E2 band. The excimer band El forms much faster than band E,. The fluorescence decay curves of the isolated monomer (band M) are interpreted in terms of two-dimensional energy transfer and trapping, leading to the conclusion that the LB monolayer film exhibits an island structure, Le., a nonuniform distribution of guest molecules.

Quantitative two-photon LIF imaging of carbon monoxide in combustion gases

Abstract: Two-dimensional imaging of CO concentration in combustion gases is demonstrated using two-photon-excited planar laser-induced fluorescence. A quantitative model is presented for the simultaneous two-photon excitation of several rotational transitions of the B1∑+ ← X1∑+ system and the subsequent visible fluorescence (B1∑+ → A1Π). The model is verified by comparison of predicted and measured excitation spectra and of temperature-corrected relative fluorescence measurements to standard probe measurements of the center line CO distribution in a CO–air diffusion flame. In addition, CO imaging experiments in a premixed methane–air flame indicate the production of C2 by laser photodissociation of acetylene.

Determination of uranium in environmental samples using inductively coupled plasma mass spectrometry.

Abstract: An analytical technique using inductively coupled plasma mass spectrometry has been developed to estimate the concentration of uranium in a variety of environmental samples. The lower limit for quantitation is 0.1 ng/mL. Calibration is linear from the low limit to 1000 ng/mL. Precision, accuracy, and a quality control protocol have been established. A comparison with the conventional fluorometric method has been performed.

Quantitative imaging of temperature fields in air using planar laser-induced fluorescence of O(2).

Abstract: Planar laser-induced fluorescence of O2 has been used to acquire quantitative, instantaneous two-dimensional images of temperature in heated air flows. O2 is excited by using a broadband ArF excimer laser at 193 nm, and the resultant fluorescence signal is converted to temperature by using a theoretical calculation of the dependence of the fluorescence on temperature. This calculation has been confirmed experimentally, and validating data are presented.

Fluorometric determination of hydrogen peroxide in groundwater

Abstract: The fluorometric scopoletin-horseradish peroxidase method has been modified for field determinations of hydrogen peroxide concentrations in groundwaters. Standard additions calibration compensates for background fluorescence and inconsistent stoichiometry of the fluorescence quenching reaction due to interferences by the matrix. The detection limit, defined as the blank plus three standard deviations, ranged from 3.6 to 44.6 nM. However, this limit was more an indication of the difficulty of preparing peroxide-free water than the actual limit imposed by the sensitivity of the method for the peroxide contamination introduced with the reagents. For 111 field determinations the weighted average (uncorrected) hydrogen peroxide concentration was 20.2 nM and the pooled standard deviation was 7.7 nM. The average of 45 field blanks was 7.8 nM with a pooled standard deviation of 5.2 nM. At nanomolar concentration levels, it is essential that samples are analyzed for H/sub 2/O/sub 2/ in the field. Storage periods exceeding 1 h caused serious errors and irreproducible results.