The Experts below are selected from a list of 204 Experts worldwide ranked by ideXlab platform
Photis Dais - One of the best experts on this subject based on the ideXlab platform.
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Detection and Quantification of Free Glycerol in Virgin Olive Oil by ^31P-NMR Spectroscopy
Journal of the American Oil Chemists' Society, 2010Co-Authors: Emanuel Hatzakis, Alexia Agiomyrgianaki, Photis DaisAbstract:^31P-Nuclear magnetic resonance (NMR) spectroscopy was employed to detect and quantify free glycerol in virgin olive oils originating from various regions of Greece. This analytical method was based on the derivatization of the hydroxyl groups of glycerol with the tagging reagent 2-chloro-4,4,5,5-tetramethyldioxaphospholane, and identification of the phosphitylated compound on the basis of ^31P chemical shifts. Quantification of glycerol in olive oils was accomplished by integration of the appropriate signals in the ^31P NMR Spectrum and the use of the phosphitylated cyclohexanol as internal standard. A linear correlation was observed between the glycerol content and 1,3-diacylglycerols and free acidity indicating that glycerol is the final product of the partial hydrolysis of triacylglycerols.
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Detection and Quantification of Free Glycerol in Virgin Olive Oil by 31P‐NMR Spectroscopy
Journal of the American Oil Chemists' Society, 2009Co-Authors: Emanuel Hatzakis, Alexia Agiomyrgianaki, Photis DaisAbstract:31P-Nuclear magnetic resonance (NMR) spectroscopy was employed to detect and quantify free glycerol in virgin olive oils originating from various regions of Greece. This analytical method was based on the derivatization of the hydroxyl groups of glycerol with the tagging reagent 2-chloro-4,4,5,5-tetramethyldioxaphospholane, and identification of the phosphitylated compound on the basis of 31P chemical shifts. Quantification of glycerol in olive oils was accomplished by integration of the appropriate signals in the 31P NMR Spectrum and the use of the phosphitylated cyclohexanol as internal standard. A linear correlation was observed between the glycerol content and 1,3-diacylglycerols and free acidity indicating that glycerol is the final product of the partial hydrolysis of triacylglycerols.
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Determination of Glycerol in Wines Using ^31P-NMR Spectroscopy
Journal of the American Oil Chemists' Society, 2007Co-Authors: Emanuel Hatzakis, Eleftherios Archavlis, Photis DaisAbstract:^31P-NMR spectroscopy was employed to detect and quantify glycerol in red wines from various regions of Greece. This novel analytical method was based on the derivatization of the hydroxyl groups of glycerol with 2-chloro-4,4,5,5-tetramethyl dioxaphospholane, and identification of the phosphitylated compound on the basis of ^31P chemical shifts. Quantification of glycerol in wines was accomplished by integration of appropriate signals in the ^31P-NMR Spectrum and the use of the phosphitylated cyclohexanol as the internal standard. The method was reproducible (CV (%) = 2.35) and accurate (CV (%) = 1.34). Its applicability to glycerol quantification in wines was tested against a weighted amount of a glycerol-model compound by linear regression analysis ( R = 0.999; intercept = 0.074 ± 0.078; slope = 0.998 ± 0.003; p = 0.000). Furthermore, the NMR method was compared to the AOAC official method (HPLC) using the Bland and Altman statistical analysis. The distribution of the data points in the bias plot showed that 100% of the measurements of glycerol in 16 wine samples from various regions of Greece were within the limits of agreement of the two methods.
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Novel Approach to the Detection and Quantification of Phenolic Compounds in Olive Oil Based on 31P Nuclear Magnetic Resonance Spectroscopy
Journal of Agricultural and Food Chemistry, 2006Co-Authors: Stella Christophoridou, Photis DaisAbstract:31P NMR spectroscopy has been employed to detect and quantify phenolic compounds in the polar fraction of virgin olive oil. This novel analytical method is based on the derivatization of the hydroxyl and carboxyl groups of phenolic compounds with 2-chloro-4,4,5,5-tetramethyldioxaphospholane and the identification of the phosphitylated compounds on the basis of the 31P chemical shifts. Quantification of a large number of phenolic compounds in virgin olive oil can be accomplished by integration of the appropriate signals in the 31P NMR Spectrum and the use of the phosphitylated cyclohexanol as internal standard. Finally, the validity of this technique for quantitative measurements was thoroughly examined. Keywords: Olive oil; phenolic compounds; 31P NMR spectroscopy
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Application of 31P NMR Spectroscopy in Food Analysis. 1. Quantitative Determination of the Mono- and Diglyceride Composition of Olive Oils
Journal of Agricultural and Food Chemistry, 2000Co-Authors: Apostolos Spyros, Photis DaisAbstract:This paper introduces a facile method to determine the amount of mono- and diglycerides in virgin olive oils. This method is based on the phosphorylation of the free hydroxyls of the mono- and diglycerides with 2-chloro-4,4,5,5-tetramethyldioxaphospholane and the integration of the appropriate peaks in the 31P NMR Spectrum. Quantitative 31P NMR spectroscopy can be extended to the quantification of other constituents of olive oils bearing functional groups with labile protons. Keywords: Olive oil; 31P NMR; monoglycerides; diglycerides
Claude Lecomte - One of the best experts on this subject based on the ideXlab platform.
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Crystal structure and solid state 31P NMR spectroscopy of triphenylphosphine oxide complex of zinc(II) tetrafluoroborate
Polyhedron, 1992Co-Authors: H. El Alaoui El Abdallaoui, Patrice Rubini, P. Tekely, D. Bayeul, Claude LecomteAbstract:Abstract The crystal structure of Zn(TPPO)·2BF4 (TPPO = triphenyl phosphine oxide) has been determined by single-crystal X-ray diffraction: the zinc atom coordination polyhedron is a slightly distorted tetrahedron (Zn O) 12 = 1.905A, (O Zn O) = 109.5°); three Zn O P angles are equal (Zn O P) = 150.3°), whereas due to steric constraints the fourth angle equals 170.1°. The observation of four signals in the 31P NMR Spectrum of the complex in the solid state is in agreement with this crystal structure.
H. El Alaoui El Abdallaoui - One of the best experts on this subject based on the ideXlab platform.
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Crystal structure and solid state 31P NMR spectroscopy of triphenylphosphine oxide complex of zinc(II) tetrafluoroborate
Polyhedron, 1992Co-Authors: H. El Alaoui El Abdallaoui, Patrice Rubini, P. Tekely, D. Bayeul, Claude LecomteAbstract:Abstract The crystal structure of Zn(TPPO)·2BF4 (TPPO = triphenyl phosphine oxide) has been determined by single-crystal X-ray diffraction: the zinc atom coordination polyhedron is a slightly distorted tetrahedron (Zn O) 12 = 1.905A, (O Zn O) = 109.5°); three Zn O P angles are equal (Zn O P) = 150.3°), whereas due to steric constraints the fourth angle equals 170.1°. The observation of four signals in the 31P NMR Spectrum of the complex in the solid state is in agreement with this crystal structure.
Françoise M. Winnik - One of the best experts on this subject based on the ideXlab platform.
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Destabilization of cationic lipid vesicles by an anionic hydrophobically modified poly(N-isopropylacrylamide) copolymer: a solid-state 31P NMR and 2H NMR study
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1998Co-Authors: Carla M. Franzin, Peter M. Macdonald, Alla Polozova, Françoise M. WinnikAbstract:The effect of binding PNIPAM-Py-Gly, a copolymer of N-isopropylacrylamide, N-[4-(1-pyrenyl)butyl]-N-n-octadecylacrylamide and N-glycydyl-acrylamide, on membrane stability in cationic multilamellar vesicles (MLVs) was examined using solid-state phosphorus (31P) and deuterium (2H) nuclear magnetic resonance (NMR) spectroscopy. For MLVs of composition n-octadecyldiethylene oxide (ODEO)+cholesterol (CHOL)+1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)+dimethyldioctadecylammonium bromide (DODAB) (molar ratios 75:10.5:10.5:4), PNIPAM-Py-Gly induced a complete conversion from a bilayer-type 31P NMR Spectrum to one characteristic of lipids undergoing isotropic motional averaging, indicating the existence of regions of high local membrane curvature. This response was sustained even at elevated temperatures. For MLVs of composition POPC+1,2-dioleoyloxy-3-(trimethylammonio)-propane (DOTAP), only at high levels of DOTAP and ionic strength did PNIPAM-Py-Gly induce even a partial conversion to an isotropic-type 31P NMR Spectrum. At lower pH this effect was diminished. Raising the temperature eliminated the isotropic 31P NMR spectral component, and this effect was not reversible upon returning to room temperature. 2H NMR spectroscopy of headgroup-deuterated DOTAP and POPC confirmed the 31P NMR results, but did not provide specific surface electrostatic information. We conclude that the binding of PNIPAM-Py-Gly to phospholipid-based vesicles is dominated by electrostatic attraction between cationic lipids and the polymer's glycine residues. At high binding levels, the polymer assumes a collapsed conformation at the surface, resulting in regions of high local curvature of the lipid assembly. For ODEO-based liposomes, these effects are magnified by the additional contribution of hydrogen bonding to the strength of polymer binding.
B. D. Nageswara Rao - One of the best experts on this subject based on the ideXlab platform.
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Changes in the 31P NMR Spectrum of rabbit muscle myosin subfragment 1. MgADP with temperature.
Archives of Biochemistry and Biophysics, 2002Co-Authors: Bruce D. Ray, Mikhail I. Khoroshev, Manuel F. Morales, B. D. Nageswara RaoAbstract:In pioneering studies on the 31P NMR spectra of MgADP bound to the "molecular motor" myosin subfragment 1 (S1) in the temperature range of 0 to 25 degrees C, Shriver and Sykes [Biochemistry 20 (1981) 2004-2012/6357-6362; Biochemistry 21 (1982) 3022-3028], proposed that MgADP binds to myosin S1 as a mixture of two interconvertible conformers with different chemical shifts for the beta-P resonance of the S1-bound MgADP and that the concentrations of these conformers are related by an equilibrium constant K(T). Their model implied that the weighted average of the chemical shifts of the beta-P(MgADP) for S1-bound MgADP asymptotically approaches a high temperature limit. Here, and in our earlier paper [K. Konno, K. Ue, M. Khoroshev, H., Martinez, B.D. Ray, M.F. Morales, Proc. Natl. Acad. Sci. USA 97 (2000) 1461-1466], we report experimental similarities to Shriver and Sykes, but diverge from them (especially at 0 degrees C) in not finding two distinct peaks and in finding that the average chemical shift does not change with temperature. Our observations can be explained by chemical exchange of beta-P(MgADP) of S1-bound MgADP between two nearly energetically equivalent environments.
