			Home About us Contact

Quenching Process (quenching + process)

Distribution by Scientific Domains

Chemistry	60%
Polymers and Materials Science	20%

Selected Abstracts

The Coupling Effect of Small Nanocrystals and Free Volume on the Ductility of Cu46Zr47Al7 Bulk Metallic Glass Alloy,

ADVANCED ENGINEERING MATERIALS, Issue 5 2009
Feng Jiang
Cu46Zr47Al7 bulk metallic glass (BMG) and its composite containing small in situ precipitated nanocrystals were prepared through copper mold casting. Different free volume states of these Cu46Zr47Al7 alloys were obtained through thermal treatment such as annealing and quenching. Three-point bending tests for these alloys were undertaken to evaluate their plastic deformation ability. Free volume changes were measured indirectly but quantitatively with differential scanning calorimetry (DSC) method. The results show that, the ductility of Cu46Zr47Al7 alloys is closely related with the free volume states and the ductility of thermally embrittled Cu46Zr47Al7 alloys samples can be partially recovered by restoring free volume through quenching process. The presence of small nanocrystals is more efficient than free volume to enhance the ductility. However, only with the concurrence of the small nanocrystals and the free volume, the Cu46Zr47Al7 BMG alloys will present excellent ductility. [source]

Synthesis, Electrochemical and Photophysical Properties, and Electroluminescent Performance of the Octa- and Deca(aryl)[60]fullerene Derivatives

ADVANCED FUNCTIONAL MATERIALS, Issue 14 2009
Yutaka Matsuo
Abstract Three multifunctionalized organo[60]fullerene derivatives, C60Ph5(C6H4 - tBu-4)5Me2 (cyclophenacene, 1), C60Ph5(C6H4 - tBu-4)5Me2 (fused corannulene, 2), and C60Ph5(C6H4 - tBu-4)3Me2 (phenylene-bridged fused corannulene, 3) are synthesized by the reaction of C60Ph5Me with 4- tert -butylphenylcopper reagent in the presence of pyridine, followed by treatment with MeI. Compounds 1,3 undergo reduction in the range from ,1.8 to ,2.5,V versus Fc/Fc+ and exhibit photoluminescence behavior with fluorescent quantum yields of 18.5%, 2.5%, and 3.2% with fluorescent lifetimes of 67, 1.1, and 27,ns (1,3, respectively). Organic electroluminescent diode devices using 1,3 are fabricated with ,-conjugated polymers and show external electroluminescent efficiencies of 0.04%, 0.07%, and 0.03% emitting yellow, green, and red light, respectively. The device containing all three compounds emits white light. This result indicates that the bulky addends in 1,3 can effectively isolate the ,-conjugated systems of the molecules in the solid state and retard the intermolecular excited-state quenching process. [source]

Inverse optimal design of cooling conditions for continuous quenching processes

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2001
Yimin Ruan
Abstract This paper presents an inverse design methodology to obtain a required yield strength with an optimal cooling condition for the continuous quenching of precipitation hardenable sheet alloys. The yield strength of a precipitation hardenable alloy can be obtained by allowing solute to enter into solid solution at a proper temperature and rapidly cooling the alloy to hold the solute in the solid solution. An aging process may be needed for the alloy to develop the final mechanical property. The objective of the design is to optimize the quenching process so that the required yield strength can be achieved. With the inverse design method, the required yield strength is specified and the sheet thermal profile at the exit of the quenching chamber can also be specified. The conjugate gradient method is used to optimize the cooling boundary condition during quenching. The adjoint system is developed to compute the gradient of the objective functional. An aluminium sheet quenching problem is presented to demonstrate the inverse design method. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Quenching with fluid jets

MATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 5-6 2009
S. Schuettenberg
Verzugskompensation; Distortion Engineering; Jetabschreckung; Flüssigkeitsabschreckung Abstract The quenching process within the heat treatment of workpieces can be optimized by applying locally adapted quenching conditions. Locally variable heat transfer conditions at the workpiece surface are realizable by impressing and regulation of adjustable flexible flow fields on the basis of arrays for jet flow impingings on surfaces inside the quenching media. With use of these adapted jet fields it is possible to generate spatially and or timewise varying quenching conditions with high cooling intensities for a systematic locally heat transfer during the quenching process. For the analysis of workpiece distortion activated by heat treatment, the heat transfer and hardening process by quenching in adapted flexible flow fields is modelwise described. By controlled quenching with liquid media, the quenching intensities can be increased for specific local hardening results on massive workpieces. By that, the heat treatment process and the quenching result can be affected and optimized by controlling the boiling process and the establishing of the rewetting front on the workpiece surface. Abschrecken mit Flüssigkeitsjets Der Abschreckprozess bei der Wärmebehandlung von Werkstücken kann durch die Aufprägung lokaler Abschreckbedingungen optimiert werden. Lokal variable Wärmeübergangsbedingungen an der Werkstückoberfläche sind hier innerhalb des Abschreckmediums durch die Aufprägung und Regelung flexibler Strömungsfelder auf der Grundlage von Jetfeldern mit Prallströmungen auf die Oberflächen möglich. Mit der Anwendung dieser angepassten Jetfelder ist es möglich, räumlich und zeitlich variable Abschreckbedingungen mit hohen Kühlintensitäten für einen gezielten, lokalen Wärmeübergang während des Abschreckprozesses zu generieren. Zur Analyse des durch die Wärmebehandlung aktivierten Bauteilverzugs wird der Härteprozess durch Abschreckung in angepassten, flexiblen Strömungsfeldern modellmäßig beschrieben. Durch gesteuertes Abschrecken mit flüssigen Medien können die Abschreckintensitäten für bestimmte lokale Härteergebnisse an massiven Werkstücken erhöht werden. Damit kann das Abschreckergebnis durch die Steuerung des Siedeprozesses und des Verlaufs der Wiederbenetzungsfront an der Werkstückoberfläche beeinflusst und optimiert werden. [source]

Photosensitizing Properties of Triplet ,-Lapachones in Acetonitrile Solution

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2009
José Carlos Netto-Ferreira
The photochemical reactivity of ,-lapachone (1), nor -,-lapachone (2) and 1,2-naphthoquinone (3) towards amino acids and nucleobases or nucleosides has been examined employing the nanosecond laser flash photolysis technique. Excitation (, = 355 nm) of degassed solutions of 1,3, in acetonitrile, resulted in the formation of their corresponding triplet excited states. These transients were efficiently quenched by l -tryptophan, l -tryptophan methyl ester, l -tyrosine, l -tyrosine methyl ester and l -cysteine (kq , 109 L mol,1 s,1). For l -tryptophan, l -tyrosine and their methyl esters new transients were formed in the quenching process, which were assigned to the corresponding radical pair resulting from an initial electron transfer from the amino acids or their esters to the excited quinone, followed by a fast proton transfer. No measurable quenching rate constants could be observed in the presence of thymine and thymidine. On the other hand, efficient rate constants were obtained when 1,3 were quenched by 2,-deoxyguanosine (kq , 109 L mol,1 s,1). The quantum efficiency of singlet oxygen (1O2) formation from 1 to 3 was determined employing time-resolved near-IR emission studies upon laser excitation and showed considerably high values in all cases (,, = 0.6), which are fully in accord with the ,,* character of these triplets in acetonitrile. [source]

False labelling due to quenching failure of N -hydroxy-succinimide,ester-coupled dyes

PROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 7 2010
Weiqun Wang
Abstract In comparative fluorescence gel electrophoresis experiments, cross-talk was detected. It was traced back to a failure in the quenching process in typical labelling protocols. Despite a huge excess of potential reaction sites for the N -hydroxy-succinimide,ester-coupled dye, sufficient active dye molecules were available after the quenching step to label protein molecules un-specifically. It could be shown that only a 100-fold increase in the amount of quencher will silence residual dye to such an extent that no artificial signals are detected. [source]

Molecular interactions of isoxazolcurcumin with human serum albumin: Spectroscopic and molecular modeling studies

BIOPOLYMERS, Issue 2 2009
Bijaya Ketan Sahoo
Abstract Curcumin is a nontoxic natural product with diverse pharmacological potencies. We report the interaction of a potent synthetic derivative of curcumin, isoxazolcurcumin (IOC) with human serum albumin (HSA) using various biophysical methods. The observed fluorescence quenching of HSA by IOC is due to a complex formation by a static quenching process with a quenching constant of the order of 105M,1. The binding affinity and the number of binding sites were obtained from a Scatchard analysis. Thermodynamics reveals that the interaction is entropy driven with predominantly hydrophobic forces. From the observed Förster-type fluorescence resonance energy transfer (FRET), the donor (Trp 214 in HSA) to acceptor (IOC) distance is calculated to be 3.2 nm. The conformational changes of HSA due to the interaction were investigated qualitatively from synchronous fluorescence spectra along with a quantitative estimation of the secondary structure from Fourier Transform Infrared (FTIR) and circular dichroism (CD) spectroscopies. Molecular docking studies were performed to obtain information on the possible residues involved in the interaction process, and changes in accessible surface area of the interacting residues were calculated. The preferred binding site of IOC was analyzed by ligand displacement experiments with 1-anilino-8-naphthalenesulfonate (ANS) and warfarin-bound HSA. © 2008 Wiley Periodicals, Inc. Biopolymers 91: 108,119, 2009. 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]

Spectroscopic studies of interaction of chlorobenzylidine with DNA

BIOPOLYMERS, Issue 6 2001
Wenying Zhong
Abstract Electronic absorbance and fluorescence titrations are used to probe the interaction of chlorobenzylidine with DNA. The binding of chlorobenzylidine to DNA results in hypochromism, a small shift to a longer wavelength in the absorption spectra, and emission quenching in the fluorescence spectra. These spectral characteristics suggest that chlorobenzylidine binds to DNA by an intercalative mode. This conclusion is reinforced by fluorescence polarization measurements. Scatchard plots constructed from fluorescence titration data give a binding constant of 1.3 × 105M,1 and a binding site size of 10 base pairs. This indicates that chlorobenzylidine has a high affinity with DNA. The intercalative interaction is exothermic with a Van't Hoff enthalpy of ,143 kJ/mol. This result is obtained from the temperature dependence of the binding constant. The interaction of chlorobenzylidine with DNA is affected by the pH value of the solution. The binding constant has its maximum at pH 3.0. Upon binding to DNA, the fluorescence from chlorobenzylidine is quenched efficiently by the DNA bases and the fluorescence intensity tends to be constant at high concentrations of DNA when the binding is saturated. The Stern,Volmer quenching constant obtained from the linear quenching plot is 1.6 × 104M,1 at 25°C. The measurements of the fluorescence lifetime and the dependence of the quenching constant on the temperature indicate that the fluorescence quenching process is static. The fluorescence lifetime of chlorobenzylidine is 1.9 ± 0.4 ns. © 2001 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 62: 315,323, 2001 [source]

Photoluminescence of Uranium(VI): Quenching Mechanism and Role of Uranium(V)

CHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2010
Satoru Tsushima Dr.
Abstract The photoluminescence of uranium(VI) is observed typically in the wavelength range 400,650,nm with the lifetime of several hundreds ,s and is known to be quenched in the presence of various halide ions (case,A) or alcohols (case,B). Here, we show by density functional theory (DFT) calculations that the quenching involves an intermediate triplet excited state that exhibits uranium(V) character. The DFT results are consistent with previous experimental findings suggesting the presence of photoexcited uranium(V) radical pair during the quenching process. In the ground state of uranyl(VI) halides, the ligand contributions to the highest occupied molecular orbitals increase with the atomic number (Z) of halide ion allowing larger ligand-to-metal charge transfer (LMCT) between uranium and the halide ion. Consequently, a larger quenching effect is expected as Z increases. The quenching mechanism is essentially the same in cases,A and B, and is driven by an electron transfer from the quencher to the UO22+ entity. The relative energetic stabilities of the triplet excited state define the "fate" of uranium, so that in case,A uranium(V) is oxidized back to uranium(VI), while in case,B uranium remains as pentavalent. [source]

Properties of Excited Ketyl Radicals of Benzophenone Analogues Affected by the Size and Electronic Character of the Aromatic Ring Systems

CHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2006
Masanori Sakamoto
Abstract The properties of benzophenone ketyl radical analogues with large aromatic ring systems, such as naphthylphenylketone (2), 4-benzoylbiphenyl (3), and bis(biphenyl-4-yl)methanone (4), were investigated in the excited state by using nanosecond,picosecond two-color two-laser flash photolysis. Fluorescence and transient absorption spectra of ketyl radicals of 2,4 in the excited state were observed for the first time. The fluorescence and properties of the excited ketyl radicals were significantly affected by the size and electronic properties of the aromatic ring systems. The reactivity of the ketyl radicals in the excited state with several quenchers was examined and they were found to show reactivity toward N,N -diethylaniline. In addition, for the benzophenone ketyl radical, a unique quenching process of the radical in the excited state by the ground-state parent molecule was found. The factors regulating the fluorescence lifetime of the ketyl radicals in the excited state are discussed quantitatively. [source]

Singlet Energy Dissipation in the Photosystem II Light-Harvesting Complex Does Not Involve Energy Transfer to Carotenoids

CHEMPHYSCHEM, Issue 6 2010
Marc G. Müller Dr.
Abstract The energy dissipation mechanism in oligomers of the major light-harvesting complex II (LHC II) from Arabidopsis thaliana mutants npq1 and npq2, zeaxanthin-deficient and zeaxanthin-enriched, respectively, has been studied by femtosecond transient absorption. The kinetics obtained at different excitation intensities are compared and the implications of singlet,singlet annihilation are discussed. Under conditions where annihilation is absent, the two types of LHC II oligomers show distributive biexponential (bimodal) kinetics with lifetimes of ,5,20 ps and ,200,400 ps having transient spectra typical for chlorophyll excited states. The data can be described kinetically by a two-state compartment model involving only chlorophyll excited states. Evidence is provided that neither carotenoid excited nor carotenoid radical states are involved in the quenching mechanism at variance with earlier proposals. We propose instead that a chlorophyll,chlorophyll charge-transfer state is formed in LHC II oligomers which is an intermediate in the quenching process. The relevance to non-photochemical quenching in vivo is discussed. [source]

Inverse optimal design of cooling conditions for continuous quenching processes

Tryptophanyl fluorescence lifetime distribution of hyperthermophilic ,-glycosidase from molecular dynamics simulation: A comparison with the experimental data

PROTEIN SCIENCE, Issue 9 2000
Ettore Bismuto
Abstract A molecular dynamics simulation approach has been utilized to understand the unusual fluorescence emission decay observed for ,-glycosidase from the hyperthermophilic bacterium Solfolobus sulfataricus (S,gly), a tetrameric enzyme containing 17 tryptophanyl residues for each subunit. The tryptophanyl emission decay of (S,gly) results from a bimodal distribution of fluorescence lifetimes with a short-lived component centered at 2.5 ns and a long-lived one at 7.4 ns Bismuto E, Nucci R, Rossi M, Irace G, 1999, Proteins 27:71,79). From the examination of the trajectories of the side chains capable of causing intramolecular quenching for each tryptophan microenvironment and using a modified Stern,Volmer model for the emission quenching processes, we calculated the fluorescence lifetime for each tryptophanyl residue of S,gly at two different temperatures, i.e., 300 and 365 K. The highest temperature was chosen because in this condition S,lgy evidences a maximum in its catalytic activity and is stable for a very long time. The calculated lifetime distributions overlap those experimentally determined. Moreover, the majority of trytptophanyl residues having longer lifetimes correspond to those originally identified by inspection of the crystallographic structure. The tryptophanyl lifetimes appear to be a complex function of several variables, such as microenvironment viscosity, solvent accessibility, the chemical structure of quencher side chains, and side-chain dynamics. The lifetime calculation by MD simulation can be used to validate a predicted structure by comparing the theoretical data with the experimental fluorescence decay results. [source]

Shape-Persistent Macrocycles Functionalised with Coumarin Dyes: Acid-Controlled Energy- and Electron-Transfer Processes

CHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2008
Carlo Giansante Dr.
Abstract We have investigated the spectroscopic properties (absorption spectra, emission spectra, emission lifetimes) of three triads in CH2Cl2: C2-M-C2, C343-M-C343, and C2-M-C343, in which M is a shape-persistent macrocyclic hexagonal backbone composed of two 2,2,-bipyridine (bpy) units embedded in opposing sides, and C2 and C343 are coumarin,2 and coumarin,343, respectively. All the components are strongly fluorescent species (,=0.90, 0.79, and 0.93 for M, C2, and C343, respectively, as established by investigating suitable model compounds). In each triad excitation of M leads to almost quantitative energy transfer to the lowest coumarin-localised excited state. Upon addition of acid, the two bpy units of the M component undergo independent protonation leading to monoprotonated (e.g., C2-M,H+ -C2) and diprotonated (e.g., C2-M,2,H+ -C2) species. Further addition of acid leads to protonation of the coumarin component so that each triad is involved in four protonation equilibria. Protonation causes strong (and reversible, upon addition of base) changes in the absorption and fluorescence properties of the triads because of inversion of the excited-state order and/or the occurrence of electron-transfer quenching processes. Il presente lavoro riporta lo studio effettuato in CH2Cl2 delle proprietà spettroscopiche (spettri di assorbimento ed emissione, tempi di vita degli stati eccitati) di tre triadi: C2-M-C2, C343-M-C343 e C2-M-C343. M rappresenta un macrociclo rigido a struttura esagonale in cui sono incorporate in posizioni diametralmente opposte due unità 2,2,-dipiridina (bpy), mentre C2 e C343 indicano, rispettivamente, la cumarina,2 e la cumarina,343. Tutte le unità componenti le triadi sono fortemente luminescenti (,=0.90, 0.79 e 0.93 per M, C2 e C343, rispettivamente, come stabilito studiando opportuni composti modello). In ciascuna triade l'eccitazione selettiva di M porta ad un trasferimento di energia al più basso stato eccitato localizzato sulle cumarine con un'efficienza praticamente unitaria. Aggiunte crescenti di acido inducono, dapprima, l'indipendente protonazione delle due unità bpy del componente M con formazione delle specie monoprotonate (per esempio, C2-M,H+ -C2) e diprotonate (per esempio, C2-M,2,H+ -C2) e, successivamente la protonazione delle cumarine. Ciascuna triade è quindi coinvolta in quattro equilibri di protonazione che, invertendo l'ordine energetico degli stati eccitati e/o favorendo l'insorgere di processi di trasferimento elettronico che spengono le emissioni, sono accompagnati da modifiche consistenti (e reversibili per aggiunta di base) delle proprietà spettroscopiche (assorbimento ed emissione) delle triadi esaminate. [source]

A Close Look at Fluorescence Quenching of Organic Dyes by Tryptophan

CHEMPHYSCHEM, Issue 11 2005
Sören Doose Dr.
Abstract Understanding fluorescence quenching processes of organic dyes by biomolecular compounds is of fundamental importance for in-vitro and in-vivo fluorescence studies. It has been reported that the excited singlet state of some oxazine and rhodamine derivatives is efficiently and almost exclusively quenched by the amino acid tryptophan (Trp) and the DNA base guanine via photoinduced electron transfer (PET). We present a detailed analysis of the quenching interactions between the oxazine dye MR121 and Trp in aqueous buffer. Steady-state and time-resolved fluorescence spectroscopy, together with fluorescence correlation spectroscopy (FCS), reveal three contributing quenching mechanisms: 1) diffusion-limited dynamic quenching with a bimolecular quenching rate constant kdof 4.0×109s,1,M,1, 2) static quenching with a bimolecular association constant Ksof 61,M,1, and 3) a sphere-of-action contribution to static quenching described by an exponential factor with a quenching constant , of 22,M,1. The latter two are characterized as nonfluorescent complexes, formed with ,30,% efficiency upon encounter, that are stable for tens of nanoseconds. The measured binding energy of 20,30 kJmol,1is consistent with previous estimates from molecular dynamics simulations that proposed stacked complexes due to hydrophobic forces. We further evaluate the influence of glycerol and denaturant (guanidine hydrochloride) on the formation and stability of quenched complexes. Comparative measurements performed with two other dyes, ATTO 655 and Rhodamine 6G show similar results and thus demonstrate the general applicability of utilizing PET between organic dyes and Trp for the study of conformational dynamics of biopolymers on sub-nanometer length and nanosecond time-scales. [source]