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Quenching Method (quenching + method)

Distribution by Scientific Domains
Chemistry33%

Kinds of Quenching Method

  • fluorescence quenching method
    		•

    Selected Abstracts

    Factors controlling the partitioning of pyrene to dissolved organic matter extracted from different soils

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2005
    B. Marschner
    Summary The mobility of hydrophobic organic compounds (HOCs) in soils can be influenced by the presence of dissolved organic matter (DOM). While numerous studies have determined interactions of HOCs with humic and fulvic acids, only few data exist on the partitioning of HOCs to natural, non-fractionated DOM as it occurs in soil solutions. In this study, DOM was extracted from 17 soil samples with a broad range of chemical and physical properties, originating from different land uses. The partition coefficients of pyrene to DOM were determined in all soil extracts and for two commercial humic acids using the fluorescence quenching method. For the soil extracts, log KDOC values ranged from 3.2 to 4.5 litres kg,1. For the Aldrich and Fluka humic acids, log KDOC was 4.98 and 4.96 litres kg,1, respectively, thus indicating that they are not representative for soil DOM. After excluding these two values, the statistical analysis of the data showed a significant negative correlation between log KDOC and pH. This was also shown for one sample where the pH was adjusted to values ranging from 3 to 9. A multiple regression analysis suggested that ultraviolet absorbance at 280 nm (an indicator for aromaticity) and the E4:E6 ratio (an indicator for molecular weight) had additional effects on log KDOC. The results indicate that the partitioning of pyrene to DOM is reduced at alkaline pH, probably due to the increased polarity of the organic macromolecules resulting from the deprotonation of functional groups. Only within a narrow pH range was the KDOC of pyrene mainly related to the aromaticity of DOM. [source]

    Film boiling heat transfer around a vertical finite-length cylinder with a convex hemispherical bottom

    HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2010
    Takashi Yamada
    Abstract The film boiling heat transfer around a vertical silver cylinder with a convex hemispherical bottom was investigated experimentally in quiescent water at atmospheric pressure. The experiments have been carried out using a quenching method. The diameter and length of the test cylinder are 32 mm and 48 mm, respectively. The test cylinder was heated to about 600 °C in an electric furnace and then cooled in saturated or subcooled water with an immersion depth of about 100 mm. The degree of liquid subcooling was varied from 0 K to 30 K. The analytical solutions for saturated and subcooled boiling are obtained by applying a two-phase boundary layer theory for vapor film with a smooth interface. The experimental data correlates within ±15% based on the proposed prediction method. Also, the lower limit of film boiling was examined in terms of wall heat flux and degree of superheating. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20289 [source]

    Binding of cationic porphyrin to human serum albumin studied using comprehensive spectroscopic methods

    JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 1 2009
    Bo Zhou
    Abstract The interaction between cationic porphyrin, a potential valuable anti-tumor and antibiotic drug, and human serum albumin (HSA) was investigated using spectroscopy methods. The binding constants were obtained using fluorescence quenching method (KSV,=,(3.24,±,0.29),×,104 M,1) and surface plasmon resonance (SPR) spectroscopy (KA,=,(6.287,±,0.407),×,104 M,1). The association rate constant (ka,=,1622,±,72.9 M,1,s,1) and dissociation rate constant (Kd,=,0.02589,±,0.0024 s,1) of the binding process were also calculated. Compared with the two results, it was known that one of the binding sites was near the tryptophan residue and also there existed other binding sites. The Fourier transform infrared (FT-IR) spectroscopy and circular dichroism (CD) spectroscopy indicated that the confirmation of HSA was nearly not affected with the addition of porphyrin. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:105,113, 2009 [source]

    Ziegler-Natta/Metallocene Hybrid Catalyst for Ethylene Polymerization

    MACROMOLECULAR REACTION ENGINEERING, Issue 6 2007
    Mostafa Ahmadi
    Abstract A Ziegler-Natta/metallocene hybrid catalyst was produced and utilized in the polymerization of ethylene with the aim of producing bimodal polyethylene. The MgCl2 adduct was prepared by a melt quenching method and Cp2ZrCl2 and TiCl4 catalysts were loaded, respectively, after treating the surface with TiBAl. The polymerization kinetics involved an induction period, followed by fragmentation and expansion of particles. SEM micrographs revealed that the spherical morphology was retained through the initial mild reaction conditions of induction period. The polymers produced showed bimodal molecular weight distribution patterns, suggesting that both components of the hybrid catalyst were active over the support. [source]

    Pharmacokinetic study on the mechanism of interaction of sulfacetamide sodium with bovine serum albumin: a spectroscopic method

    BIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 2-3 2010
    Praveen N. Naik
    Abstract The binding of sulfacetamide sodium (SAS) to bovine serum albumin (BSA) was investigated by spectroscopic methods, namely fluorescence, FT-IR and UV-vis absorption spectral studies. The binding parameters were evaluated by a fluorescence quenching method. The thermodynamic parameters, ,H0, ,S0and ,G0 were observed to be ,49.03,k,J,mol,1, ,99.9,J,K,1,mol,1 and ,18.96,k,J,mol,1, respectively. These indicated that the hydrogen bonding and weak van der Waals forces played major roles in the interaction. Based on Förster's theory of non-radiation energy transfer, the binding average distance, r, between the donor (BSA) and acceptor (SAS) was evaluated and found to be 3.72,nm. The spectral results showed that binding of SAS to BSA induced conformational changes in BSA. The effect of common ions and some of the polymers used in drug delivery for controlled release were also tested on the binding of SAS to BSA. Copyright © 2010 John Wiley & Sons, Ltd. [source]

    Conformational Stability of Bovine Serum Albumin in Aqueous Amides: A Further Insight into the Mechanism of Urea Acting on the Protein

    CHINESE JOURNAL OF CHEMISTRY, Issue 6 2010
    Lin Ma
    Abstract The binding distances of fluorescein to bovine serum albumin (BSA) in formamide-water and N,N -dimethyl- formamide-water mixtures were determined by fluorescence quenching method and compared with the values in urea-water mixtures in our previous work. The results, together with the analysis of fluorescence spectra, were utilized to probe the conformational stability of protein in aqueous amides, providing a further insight into the mechanism of urea acting on protein. The spectral properties of BSA showed significant difference in the aqueous solutions of the three kinds of amide and indicated that both NH2 group and C=O group could form hydrogen bond with the protein, serving as donor and acceptor, respectively. However, the results revealed that the multiple hydrogen bonds of NH2 group with back bond and hydrophilic side chains of the protein played a key role in the nonspecific urea-mediated network of intramolecular interaction due to its higher hydrogen bonding capability compared to C=O group. [source]