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Fluorescence Techniques (fluorescence + techniques)
Selected AbstractsThe effect of fungal metabolites on leaves as detected by chlorophyll fluorescenceNEW PHYTOLOGIST, Issue 2 2001Anandini Kshirsagar Summary ,,The effect is reported here of cytochalasin E isolated from the fungus Rosellinia necatrix on photosynthesis in young leaves of Malus domestica (apple). ,,Cytochalasin E was administered via the petiole to excised leaves. The chlorophyll fluorescence emission spectrum and time resolved fluorescence decay were measured up to the point where visible leaf damage was observed. ,,Within 2 h, the ratio of fluorescence emission at 730 nm decreased with respect to the peak at 690 nm. Over 6 h a small blue shift in the 690 nm emission band to 685 nm was seen. The time resolved fluorescence decay showed changes over a similar timescale after administration of cytochalasin E. The control decay could be fitted by two components, ,1, 112 ps, ,2, 402 ps, but after 6 h treatment with cytochalasin E the decay required a further component ,3, 4.25 ns for a good fit. ,,Cytochalasin E has a direct effect on photosynthesis, possibly as a result of impairment of light harvesting. This might partially account for the pathogenicity of the root infecting R. necatrix. Fluorescence techniques may therefore provide an early detection system for the fungus, a necessary prerequisite for development of a control strategy. [source] Inlaid Multi-Walled Carbon Nanotube Nanoelectrode Arrays for ElectroanalysisELECTROANALYSIS, Issue 1 2005Jun Li Abstract The rapid development in nanomaterials and nanotechnologies has provided many new opportunities for electroanalysis. We review our recent results on the fabrication and electroanalytical applications of nanoelectrode arrays based on vertically aligned multi-walled carbon nanotubes (MWCNTs). A bottom-up approach is demonstrated, which is compatible with Si microfabrication processes. MWCNTs are encapsulated in SiO2 matrix leaving only the very end exposed to form inlaid nanoelectrode arrays. The electrical and electrochemical properties have been characterized, showing well-defined quasireversible nanoelectrode behavior. Ultrasensitive detection of small redox molecules in bulk solutions as well as immobilized at the MWCNT ends is demonstrated. A label-free affinity-based DNA sensor has shown extremely high sensitivity approaching that of fluorescence techniques. This platform can be integrated with microelectronics and microfluidics for fully automated microchips. [source] Bilayer localization of membrane-active peptides studied in biomimetic vesicles by visible and fluorescence spectroscopiesFEBS JOURNAL, Issue 22 2003Tanya Sheynis Depth of bilayer penetration and effects on lipid mobility conferred by the membrane-active peptides magainin, melittin, and a hydrophobic helical sequence KKA(LA)7KK (denoted KAL), were investigated by colorimetric and time-resolved fluorescence techniques in biomimetic phospholipid/poly(diacetylene) vesicles. The experiments demonstrated that the extent of bilayer permeation and peptide localization within the membrane was dependent upon the bilayer composition, and that distinct dynamic modifications were induced by each peptide within the head-group environment of the phospholipids. Solvent relaxation, fluorescence correlation spectroscopy and fluorescence quenching analyses, employing probes at different locations within the bilayer, showed that magainin and melittin inserted close to the glycerol residues in bilayers incorporating negatively charged phospholipids, but predominant association at the lipid,water interface occurred in bilayers containing zwitterionic phospholipids. The fluorescence and colorimetric analyses also exposed the different permeation properties and distinct dynamic influence of the peptides: magainin exhibited the most pronounced interfacial attachment onto the vesicles, melittin penetrated more into the bilayers, while the KAL peptide inserted deepest into the hydrophobic core of the lipid assemblies. The solvent relaxation results suggest that decreasing the lipid fluidity might be an important initial factor contributing to the membrane activity of antimicrobial peptides. [source] Tetraalkylammonium salt as photoinitiator of vinyl polymerization in organic and aqueous media: A mechanistic and laser flash photolysis studyJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2002María L. Gómez Abstract N -Dimethyl- N -[2-(N,N -dimethylamino)ethyl]- N -(1-methylnaphthyl)ammonium tetrafluoroborate (I) was synthesized with the aim of obtaining a versatile photoinitiator for vinyl polymerization in organic solvents and water. Salt I was able to trigger the polymerization of acrylamide, 2-hydroxyethylmethacrylate and styrene even at very low concentrations of the salt (,1.0 × 10,5 M). Using laser flash photolysis and fluorescence techniques and analyzing the photoproduct distribution, we were able to postulate a mechanism for the photodecomposition of the salt. With irradiation, I undergoes an intramolecular electron-transfer reaction to form a radical ion pair (RIP). The RIP intermediate decomposes into free radicals. The RIP and the free radicals are active species for initiating the polymerization. Depending on the concentration of the vinyl monomers studied, the initiation mechanism of the polymerization reaction changes. At large monomer concentrations, the RIP state is postulated to trigger the reaction by generating the anion radical of the olefin substrate. At a low monomer concentration, the free radicals produced by the decomposition of I are believed to start the chain reaction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 901,913, 2002; DOI 10.1002/pola.10166 [source] Validation of two dual fluorescence techniques for confocal microscopic visualization of resin penetration into enamel caries lesionsMICROSCOPY RESEARCH AND TECHNIQUE, Issue 7 2009Sebastian Paris Abstract Fluorescence confocal microscopy is a useful tool to analyze the infiltration of enamel caries lesions with low-viscosity resins (infiltrants) in vitro. The conventionally used staining technique, which comprises dye labeling of the resin, has been shown to be limited by chromatographic separation of the resin-dye-mixture during penetration. The aim of this study was to develop an improved dual staining technique and to compare validity and reproducibility of both methods. Human molars with proximal white spots were cut across the demineralizations. After varnishing the cut surfaces, paired lesion halves were infiltrated with an infiltrant using either one of two different staining techniques. For the conventional direct technique (A) the infiltrant was labeled with rhodamine isothiocyanate (RITC) prior to application. Using the new indirect technique (B) lesions were stained with RITC solution and subsequently infiltrated with pure infiltrant. After light curing, unbound dye was bleached by immersion in hydrogen peroxide. Remaining lesion pores were stained with sodium fluorescein solution. Penetration depths (PD) and lesion depths (LD) were evaluated by five examiners using confocal microscopy and compared with the results of scanning electron microscopic (SEM; PD) and microradiographic (TMR; LD) analysis. The indirect technique showed better correlation (intraclass coefficients) with SEM (0.990) and TMR (0.982) compared with the direct technique (SEM: 0.513; TMR: 0.702). Inter- and intrarater reliability was higher for technique B compared with technique A. The new indirect technique yields to more valid and reliable results to visualize infiltrant penetration into natural enamel caries lesions compared with the conventional method. Microsc. Res. Tech. 2009. © 2009 Wiley-Liss, Inc. [source] Molecular Beacon Probes of Photodamage in Thymine and Uracil Oligonucleotides,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2005Soujanya Yarasi ABSTRACT Molecular beacons (MB) are becoming more common as sequence-selective detectors of nucleic acids. Although they can easily detect single-base mismatches, they have never been used to directly detect DNA or RNA damage. To measure the degree of ultraviolet (UV) light damage in oligonucleotides, we report a novel MB approach for general detection of photoproducts in UV-irradiated rU17 and dT17 oligonucleotides. With monochromatic UV light irradiation at ca 280 nm under anoxic conditions, the oligonucleotide absorption decays with a single-exponential time constant of 123 ± 1 min for rU17 and with double-exponential time constants of 78 ± 0.5 min (99%) and 180 ± 5 min (0.05%) for dT17 oligonucleotides. Under the same conditions, the MB fluorescence decays more quickly, with single-exponential time constants of 19 ± 2 and 26 ± 3 min for rU17 and dT17, respectively. Similar kinetics were observed with broadband UV light irradiation of oligonucleotides. The differences in the UV damage kinetics of dT17 and rU17 and their detection by absorption and fluorescence techniques will be discussed in the context of differential instabilities introduced in the nucleic acid-MB duplex by the different photoproducts formed. [source] Daily dynamics of photosynthesis of the freshwater red alga Sirodotia delicatula (Batrachospermales, Rhodophyta)PHYCOLOGICAL RESEARCH, Issue 4 2009Thiago Kusakariba SUMMARY The daily course of photosynthetic parameters of a population of the freshwater red alga Sirodotia delicatula from São Paulo State, Brazil (20°43,24,S, 49°18,21,W) was investigated under natural and laboratory conditions using dissolved oxygen and in vivo chlorophyll fluorescence techniques. Field specimens in laboratory conditions showed a defined daily pattern for net photosynthesis (NP) with two peaks observed in marine macroalgae and some freshwater red algae: the first (the highest) during the morning, and the second (the lowest and less evident) during the afternoon. Values of electron transport rate did not show a clear pattern of daily variation. NP results suggest the existence of an endogenous rhythm controlling photosynthesis. The study under natural conditions in two contrasting periods (autumn (June) and spring (October)) showed that the daily course of effective and potential quantum yield values was negatively correlated with irradiance and values were similar in the beginning and end of the day. These data evidenced, respectively, high excitement pressure on photosystem II and good recovery capacity (with lower values in spring) and a lack of irreversible photodamage to photosynthetic apparatus due to the prolonged exposure to high irradiances. Non-photochemical quenching values were also negatively correlated with the irradiance, suggesting a low dissipation capacity of excess energy absorbed by reaction centers. The results evidenced a typical pattern of daily variation with evident response to irradiance. [source] Binding of bioactive phytochemical piperine with human serum albumin: A spectrofluorometric studyBIOPOLYMERS, Issue 4 2007Dodda Venkatanna Suresh Abstract Piperine, the bioactive alkaloid compound of the spice black pepper (Piper nigrum) exhibits a wide range of beneficial physiological and pharmacological activities. Being essentially water-insoluble, piperine is presumed to be assisted by serum albumin for its transport in blood. In this study, the binding of piperine to serum albumin was examined by employing steady state and time resolved fluorescence techniques. Binding constant for the interaction of piperine with human serum albumin, which was invariant with temperature in the range of 17,47°C, was found to be 0.5 × 105M,1, having stoichiometry of 1:1. At 27°C, the van't Hoff enthalpy ,H° was zero; ,S° and ,G° were found to be 21.4 cal mol,1 K,1 and ,6.42 kcal mol,1. The binding constant increased with the increase of ionic strength from 0.1 to 1.0M of sodium chloride. The decrease of Stern,Volmer constant with increase of temperature suggested that the fluorescence quenching is static. Piperine fluorescence showed a blue shift upon binding to serum albumin, which reverted with the addition of ligands ,triiodobenzoic acid and hemin. The distance between piperine and tryptophan after binding was found to be 2.79 nm by Förster type resonance energy transfer calculations. The steady state and time resolved fluorescence measurements suggest the binding of piperine to the subdomain IB of serum albumin. These observations are significant in understanding the transport of piperine in blood under physiological conditions. © 2007 Wiley Periodicals, Inc. Biopolymers 86: 265,275, 2007. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] A Recombinant Glutamine-Binding Protein from Escherichia coli: Effect of Ligand-Binding on Protein Conformational DynamicsBIOTECHNOLOGY PROGRESS, Issue 6 2004Petr Herman We have investigated the effect of the binding of glutamine on the conformational dynamics of the recombinant glutamine binding protein (GlnBP) from Escherichia coli by steady-state and time-resolved fluorescence techniques. The structural stability of the protein was also studied by far-UV circular dichroism spectroscopy in the range of temperature between 25 and 80 °C. The results showed that the interaction of the protein with the ligand resulted in a marked change of the structural and conformational dynamics features of the protein. In particular, the fluorescence and circular dichroism data showed that the presence of glutamine resulted in a dramatic increase of the protein thermal stability of about 10 °C. In addition, the fluorescence time-resolved data pointed out that both in the absence and in the presence of glutamine the protein structure was highly rigid with small amplitude of segmental motion up to 65 °C and a low accessibility of the protein tryptophan residues to acrylamide. The obtained results on the structural properties of the recombinant glutamine-binding protein in the absence and in the presence of glutamine can contribute to a better understanding of the transport-related functions of the protein and structurally similar periplasmic transport proteins, as well as to the design and development of new biotechnological applications of this class of proteins. [source] Aggregation of Dodecyl 1-Pyrenylmethyl Ether and Its Application in Structure-Polarity Relations of Aggregates,CHINESE JOURNAL OF CHEMISTRY, Issue 9 2006Da-Yong Sang Abstract The aggregation behavior of dodecyl 1-pyrenylmethyl ether was studied in dioxane-water mixture solvents by fluorescence techniques. The labeled pyrenyl group was effective in monitoring the polarity change of its environment during aggregation processes. Based on the structural effects such as chain-length effect, self-coiling effect, and branch-group effect on the polarity of the probe environment, the structure features of aggregates were discussed and have been used to interpret the effect of the structural features on the aggregates formed by three cholesteryl esters and three long chain alkanes. [source] | |||||||||||||