Photis Dais - Profile on Academia.edu (original) (raw)
Papers by Photis Dais
Chemischer Informationsdienst, Oct 4, 1977
ChemInform Abstract W ässrige Ascorbins äure (I) reduziert die Nitroxyl-Radikale (II) zu den Hydr... more ChemInform Abstract W ässrige Ascorbins äure (I) reduziert die Nitroxyl-Radikale (II) zu den Hydroxylaminen (IV). Auf diese Weise lassen sich N-Oxyle quantitativ bestimmen, wenn man die nicht verbrauchte Ascorbins äure mit eingestellter Jodl ösung zur ücktitriert.
Detection and Quantification of Phenolic Compounds in Olive Oil, Olives, and Biological Fluids
CRC Press eBooks, Jul 18, 2008
Carbohydrate Research, 1982
13C-N.m.r. spectra of several D-@cans, recorded at 100 MHz, have afforded information about struc... more 13C-N.m.r. spectra of several D-@cans, recorded at 100 MHz, have afforded information about structural detail not previously accessible at lower frequencies. Spectra of (l-+4)-and (l-3)-linked &D&cans of oats, barley, and lichenan of Iceland moss demonstrate the presence, in each, of three, non-equivalent, 4-0substituted residues, that the ratio of these to 3-O-substituted residues averages 2.4-2.5, and hence that the patterns of repeatin g sequences in the three polymers are essentially the same. A comparison of wheat amylopectin with a minor, amylopectin-like fraction of wheat starch indicates that they are strictly analogous in basic structure, and differ only in that the average length of branches in the minor fraction is 20-25 o/0 shorter. By combining the advantages of high-field operation with the use of dimethyl sulfoxide as solvent, a large number of distinctive resonances have been observed, representing end-units, branch-points, and residues adjacent to branchpoints. Accordingly, these signals are even more prominent in the spectrum of glycogen, reflecting the higher incidence of branching in this polymer. At 100 MHz, the excellent resolution and sensitivity afforded constitute a potent basis for assessing the purity of polysaccharide preparations, as illustrated with wheat amylose and barley fi-D-@cans. '3C-~.~.~.
Magnetic Resonance in Chemistry, Sep 23, 2012
A novel magnetic carboxylated multi-walled carbon nanotubes (c-MWCNT-MNPs) was proposed for magne... more A novel magnetic carboxylated multi-walled carbon nanotubes (c-MWCNT-MNPs) was proposed for magnetic solid-phase extraction coupled with liquid chromatography-tandem mass spectrometry to determine phenolic compounds in sesame oil. In this study, c-MWCNT-MNPs were acquired by simply dispersing Fe 3 O 4 magnetic nanoparticles into carboxylated multi-walled carbon nanotubes. The major parameters affecting extraction efficiency were optimized, including the type and volume of desorption solvents, extraction and desorption time, washing solution, and sorbent amount. The limit of quantifications and limit of detections were from 0.03 µ g/kg to 43.00 µg/kg and from 0.01 µ g/kg to 13.60 µg/kg and respectively. The recoveries of phenolic compounds in vegetable oils were in the range of 83.8-125.9% with inter-day and intra-day precisions of less than 13.2%. It was confirmed that this method was simple, rapid and reliable with an excellent potential for routine analysis of phenolic compounds in oil samples.
Chemischer Informationsdienst, May 24, 1983
13C Nuclear Magnetic Relaxation and Motional Behavior of Polysaccharides in Solution
Springer eBooks, 1993
Interest in the motional behavior of polysaccharide molecules in solution has grown in recent yea... more Interest in the motional behavior of polysaccharide molecules in solution has grown in recent years. In particular, measurements of 13C relaxation parameters (T1, T2, and NOE) have been carried out in several instances1,2 for linear polysaccharides in order to probe variations in segmental motion of terminal groups, and for branched polysaccharides, to investigate differences in mobility between side-chain residues and those incorporated in the backbone. Experiments such as these have facilitated the assignment of 13C-resonance signals that were difficult to identify on the basis of chemical shifts, and have provided a qualitative description of mobility as reflected in the 13C relaxation parameters. Although qualitative analysis of 13C relaxation data appears to be useful in describing gross features of the mobility of carbohydrate chains, it is less valuable than quantitative information inherent in the measured 13C relaxation parameters.
Conformational Properties of para Monosubstituted Benzophenones. 13C NMR and Molecular Modeling Studies
Zeitschrift für Physikalische Chemie, 1990
Tetrahedron Letters, 1974
Liquid-Crystalline Character of Novel Main-Chain Oligophosphates Bearing Lipophilic and/or Mesogenic Moieties
ACS Symposium Series, 1990
Carbohydrate Research, 1999
Variable temperature and magnetic field dependent 13 C NMR relaxation measurements (T 1 , T 2 , a... more Variable temperature and magnetic field dependent 13 C NMR relaxation measurements (T 1 , T 2 , and NOE) were carried out on a series of linear homopolysaccharides: a-(1 3)-D-glucan, b-( )-D-glucan in Me 2 SO-d 6 , and a-(1 6)-D-glucan in D 2 O and Me 2 SO-d 6 dilute solutions. The relaxation data of the backbone carbons were analyzed quantitatively by using a variety of theoretical unimodal and bimodal time-correlation functions in an attempt to describe the main carbohydrate chain dynamics as a function of linkage position and stereochemistry. Among these, the time-correlation function developed by Dejean, Laupretre, and Monnerie (DLM) offered the best quantitative description of the segmental motion of the carbohydrate chains. The internal rotation of the hydroxymethyl groups about the exocyclic C-5 -C-6 bonds superimposed on segmental motion has been described as a diffusion process of restricted amplitude. Comparison of the dynamics of polysaccharides has been extended to include amylose and inulin studied previously. On the basis of the calculated correlation times for segmental motion, the flexibility of the carbohydrate chains decreases from inulin and dextran following the order; inulin\ dextran\a-(1 3)-D-glucan\ b-(1 3)-D-glucan amylose, whereas the rate and the amplitude of the internal rotation of the hydroxymethyl groups about the exocyclic C-5 -C-6 bonds showed that the restriction of the hydroxymethyl internal rotation decreases from inulin to amylose following the order; inulin\ a-(1 3)-D-glucan b-(1 3)-D-glucan\ amylose. Solvent effects on segmental dynamics and the temperature-frequency superposition of the relaxation data of the three polysaccharides have been discussed as well.
Macromolecules, Aug 1, 1991
The longitudinal NMR relaxation time for I3C is determined at three different magnetic fields in ... more The longitudinal NMR relaxation time for I3C is determined at three different magnetic fields in the extensive solution phase (L, region) of the system sodium octanoate-octanoic acid-water. This phase serves as a suitable simple model for microemulsions. The data are analyzed by using a model that emphasizes the separation of the fast internal motions within the aggregates and slow motions on a time scale characteristic of the aggregate dimensions. Three important parameters are derived from the relaxation data: a correlation time characteristic of the fast motion, an order parameter, and, finally, a correlation time for the slow motions. These three parameters show that the internal motion is fast (time scale, 2 X lo-" s), that the packing is insensitive to water content, and, finally, that the aggregates grow in size up to a certain water content. At higher contents, the simple model with closed water domains does not apply.
Progress in Nuclear Magnetic Resonance Spectroscopy, Nov 1, 1995
![Research paper thumbnail of Assignment of the 1H and 13C NMR spectra and stereochemical analysis of radical-initiated poly(1-naphthylmethyl acrylate) and poly[2-(1-naphthyl)ethyl acrylate]](https://attachments.academia-assets.com/122159955/thumbnails/1.jpg)
](Macromolecular Chemistry and Physics, Sep 1, 1994
Resonances in the 'H and l3C NMR spectra of free-radical polymerised poly(1-naphthylmethyl acryla... more Resonances in the 'H and l3C NMR spectra of free-radical polymerised poly(1-naphthylmethyl acrylate) (PNMA) and poly[2-( 1 -naphthyl)ethyl acrylate] (PNEA) have been assigned using two-dimensional techniques. The stereosequence distribution in both polymers obeyed Bernoullian statistics with probabilities of an isotactic diad of 0,43 in PNMA and 0,39 in PNEA.
Polymer, 1992
13C spin-lattice relaxation times and nuclear Overhauser effect factors were measured as a functi... more 13C spin-lattice relaxation times and nuclear Overhauser effect factors were measured as a function of temperature in two magnetic fields for poly(/&hydroxybutyrate) (PHB) in chloroform-d. The relaxation data were interpreted in terms of chain segmental motion and methyl internal rotation by using various dynamic models. Among these, the Dejean-LauprCtre-Monnerie model offered the best description of the segmental motion along the PHB chain. However, all models used in this study resulted in similar activation energy (17 kJ mol-' ) for cooperative segmental motion. An activation energy of 1 l-12 kJ mol-' was found for methyl internal rotation. Further relaxation experiments on PHB in chloroform-d as a function of concentration and molecular weights were carried out as well.
Macromolecules, Feb 1, 1992
Carbon-13 spin-lattice relaxation times and NOE factors were measured as a function of temperatur... more Carbon-13 spin-lattice relaxation times and NOE factors were measured as a function of temperature in two magnetic fields for poly(1-naphthyl acrylate) (PNA) in 1,1,2,2-tetrachloroethane-d~. The relaxation data were interpreted in terms of chain segmental motion and naphthyl internal rotation by using the sharp cutoff model of Jones and Stockmayer (JS) and the Hall-Weber-Helfand (HWH) correlation function. Both models describe in a satisfactory and comparable manner the chain local motions of PNA resulting in approximately similar correlation times (6 X lo+' s at 20 OC) and activation energy (19 kJ/mol) for cooperative segmental motions of the chain. Naphthyl internal rotation is described by a hindered rotation about the C(1)-0 bond superimposed on segmental motions described by both models. They differ, however, in the time scale and angular amplitude of the naphthyl motion, which was found to be faster and less restricted with the JS description as compared to that using the HWH model, although both models give the same activation energy (ca. 13 kJ/mol) for the naphthyl rotation. Finally, the microtacticity of PNA is examined by 13C NMR spectroscopy, and it is concluded that the stereochemistry of the propagation step conforms with Bernoullian statistics.
The Royal Society of Chemistry eBooks, Oct 23, 2012
Macromolecules, Nov 1, 1995
Journal of Polymer Science Part B, Feb 1, 1995
Variable-temperature 13C NMR spin-lattice relaxation times ( T I ) and Nuclear Overhauser Enhance... more Variable-temperature 13C NMR spin-lattice relaxation times ( T I ) and Nuclear Overhauser Enhancements (NOE) a t two magnetic fields have been used to study the dynamics of the amorphous part of a semicrystalline sample (33% of crystallinity) of poly(P-hydroxyoctanoate) (PHO). The interpretation of the relaxation data of the backbone carbons was made by employing a number of motional models. Among these, the DLM model offered the best interpretation of the relaxation data in terms of conformational transitions and librational motions of the backbone C -H vectors, and proved to be superior to unimodal distribution functions. The interpretation of temperature-and frequency-dependent TI and NOE data of the carbon nuclei in the n-pentyl side chain was made by employing a newly developed composite spectral density function for multiple internal C -C bond rotations of restricted amplitude and chain segmental motion. The temperature dependence of the linewidths of the various protonated carbon resonances of PHO has been discussed in terms of the semicrystalline character of this polymer.
Complete1H and13C NMR assignment and31P NMR determination of pentacyclic triterpenic acids
Analytical Methods, 2017
In this study we report the complete and unambiguous1H and13C NMR assignment of betulinic, maslin... more In this study we report the complete and unambiguous1H and13C NMR assignment of betulinic, maslinic, oleanolic and ursolic acids by utilizing high-resolution multidimensional NMR spectroscopy.
Nuclear magnetic resonance
Elsevier eBooks, 2020
Chemischer Informationsdienst, Oct 4, 1977
ChemInform Abstract W ässrige Ascorbins äure (I) reduziert die Nitroxyl-Radikale (II) zu den Hydr... more ChemInform Abstract W ässrige Ascorbins äure (I) reduziert die Nitroxyl-Radikale (II) zu den Hydroxylaminen (IV). Auf diese Weise lassen sich N-Oxyle quantitativ bestimmen, wenn man die nicht verbrauchte Ascorbins äure mit eingestellter Jodl ösung zur ücktitriert.
Detection and Quantification of Phenolic Compounds in Olive Oil, Olives, and Biological Fluids
CRC Press eBooks, Jul 18, 2008
Carbohydrate Research, 1982
13C-N.m.r. spectra of several D-@cans, recorded at 100 MHz, have afforded information about struc... more 13C-N.m.r. spectra of several D-@cans, recorded at 100 MHz, have afforded information about structural detail not previously accessible at lower frequencies. Spectra of (l-+4)-and (l-3)-linked &D&cans of oats, barley, and lichenan of Iceland moss demonstrate the presence, in each, of three, non-equivalent, 4-0substituted residues, that the ratio of these to 3-O-substituted residues averages 2.4-2.5, and hence that the patterns of repeatin g sequences in the three polymers are essentially the same. A comparison of wheat amylopectin with a minor, amylopectin-like fraction of wheat starch indicates that they are strictly analogous in basic structure, and differ only in that the average length of branches in the minor fraction is 20-25 o/0 shorter. By combining the advantages of high-field operation with the use of dimethyl sulfoxide as solvent, a large number of distinctive resonances have been observed, representing end-units, branch-points, and residues adjacent to branchpoints. Accordingly, these signals are even more prominent in the spectrum of glycogen, reflecting the higher incidence of branching in this polymer. At 100 MHz, the excellent resolution and sensitivity afforded constitute a potent basis for assessing the purity of polysaccharide preparations, as illustrated with wheat amylose and barley fi-D-@cans. '3C-~.~.~.
Magnetic Resonance in Chemistry, Sep 23, 2012
A novel magnetic carboxylated multi-walled carbon nanotubes (c-MWCNT-MNPs) was proposed for magne... more A novel magnetic carboxylated multi-walled carbon nanotubes (c-MWCNT-MNPs) was proposed for magnetic solid-phase extraction coupled with liquid chromatography-tandem mass spectrometry to determine phenolic compounds in sesame oil. In this study, c-MWCNT-MNPs were acquired by simply dispersing Fe 3 O 4 magnetic nanoparticles into carboxylated multi-walled carbon nanotubes. The major parameters affecting extraction efficiency were optimized, including the type and volume of desorption solvents, extraction and desorption time, washing solution, and sorbent amount. The limit of quantifications and limit of detections were from 0.03 µ g/kg to 43.00 µg/kg and from 0.01 µ g/kg to 13.60 µg/kg and respectively. The recoveries of phenolic compounds in vegetable oils were in the range of 83.8-125.9% with inter-day and intra-day precisions of less than 13.2%. It was confirmed that this method was simple, rapid and reliable with an excellent potential for routine analysis of phenolic compounds in oil samples.
Chemischer Informationsdienst, May 24, 1983
13C Nuclear Magnetic Relaxation and Motional Behavior of Polysaccharides in Solution
Springer eBooks, 1993
Interest in the motional behavior of polysaccharide molecules in solution has grown in recent yea... more Interest in the motional behavior of polysaccharide molecules in solution has grown in recent years. In particular, measurements of 13C relaxation parameters (T1, T2, and NOE) have been carried out in several instances1,2 for linear polysaccharides in order to probe variations in segmental motion of terminal groups, and for branched polysaccharides, to investigate differences in mobility between side-chain residues and those incorporated in the backbone. Experiments such as these have facilitated the assignment of 13C-resonance signals that were difficult to identify on the basis of chemical shifts, and have provided a qualitative description of mobility as reflected in the 13C relaxation parameters. Although qualitative analysis of 13C relaxation data appears to be useful in describing gross features of the mobility of carbohydrate chains, it is less valuable than quantitative information inherent in the measured 13C relaxation parameters.
Conformational Properties of para Monosubstituted Benzophenones. 13C NMR and Molecular Modeling Studies
Zeitschrift für Physikalische Chemie, 1990
Tetrahedron Letters, 1974
Liquid-Crystalline Character of Novel Main-Chain Oligophosphates Bearing Lipophilic and/or Mesogenic Moieties
ACS Symposium Series, 1990
Carbohydrate Research, 1999
Variable temperature and magnetic field dependent 13 C NMR relaxation measurements (T 1 , T 2 , a... more Variable temperature and magnetic field dependent 13 C NMR relaxation measurements (T 1 , T 2 , and NOE) were carried out on a series of linear homopolysaccharides: a-(1 3)-D-glucan, b-( )-D-glucan in Me 2 SO-d 6 , and a-(1 6)-D-glucan in D 2 O and Me 2 SO-d 6 dilute solutions. The relaxation data of the backbone carbons were analyzed quantitatively by using a variety of theoretical unimodal and bimodal time-correlation functions in an attempt to describe the main carbohydrate chain dynamics as a function of linkage position and stereochemistry. Among these, the time-correlation function developed by Dejean, Laupretre, and Monnerie (DLM) offered the best quantitative description of the segmental motion of the carbohydrate chains. The internal rotation of the hydroxymethyl groups about the exocyclic C-5 -C-6 bonds superimposed on segmental motion has been described as a diffusion process of restricted amplitude. Comparison of the dynamics of polysaccharides has been extended to include amylose and inulin studied previously. On the basis of the calculated correlation times for segmental motion, the flexibility of the carbohydrate chains decreases from inulin and dextran following the order; inulin\ dextran\a-(1 3)-D-glucan\ b-(1 3)-D-glucan amylose, whereas the rate and the amplitude of the internal rotation of the hydroxymethyl groups about the exocyclic C-5 -C-6 bonds showed that the restriction of the hydroxymethyl internal rotation decreases from inulin to amylose following the order; inulin\ a-(1 3)-D-glucan b-(1 3)-D-glucan\ amylose. Solvent effects on segmental dynamics and the temperature-frequency superposition of the relaxation data of the three polysaccharides have been discussed as well.
Macromolecules, Aug 1, 1991
The longitudinal NMR relaxation time for I3C is determined at three different magnetic fields in ... more The longitudinal NMR relaxation time for I3C is determined at three different magnetic fields in the extensive solution phase (L, region) of the system sodium octanoate-octanoic acid-water. This phase serves as a suitable simple model for microemulsions. The data are analyzed by using a model that emphasizes the separation of the fast internal motions within the aggregates and slow motions on a time scale characteristic of the aggregate dimensions. Three important parameters are derived from the relaxation data: a correlation time characteristic of the fast motion, an order parameter, and, finally, a correlation time for the slow motions. These three parameters show that the internal motion is fast (time scale, 2 X lo-" s), that the packing is insensitive to water content, and, finally, that the aggregates grow in size up to a certain water content. At higher contents, the simple model with closed water domains does not apply.
Progress in Nuclear Magnetic Resonance Spectroscopy, Nov 1, 1995
Macromolecular Chemistry and Physics, Sep 1, 1994
Resonances in the 'H and l3C NMR spectra of free-radical polymerised poly(1-naphthylmethyl acryla... more Resonances in the 'H and l3C NMR spectra of free-radical polymerised poly(1-naphthylmethyl acrylate) (PNMA) and poly[2-( 1 -naphthyl)ethyl acrylate] (PNEA) have been assigned using two-dimensional techniques. The stereosequence distribution in both polymers obeyed Bernoullian statistics with probabilities of an isotactic diad of 0,43 in PNMA and 0,39 in PNEA.
Polymer, 1992
13C spin-lattice relaxation times and nuclear Overhauser effect factors were measured as a functi... more 13C spin-lattice relaxation times and nuclear Overhauser effect factors were measured as a function of temperature in two magnetic fields for poly(/&hydroxybutyrate) (PHB) in chloroform-d. The relaxation data were interpreted in terms of chain segmental motion and methyl internal rotation by using various dynamic models. Among these, the Dejean-LauprCtre-Monnerie model offered the best description of the segmental motion along the PHB chain. However, all models used in this study resulted in similar activation energy (17 kJ mol-' ) for cooperative segmental motion. An activation energy of 1 l-12 kJ mol-' was found for methyl internal rotation. Further relaxation experiments on PHB in chloroform-d as a function of concentration and molecular weights were carried out as well.
Macromolecules, Feb 1, 1992
Carbon-13 spin-lattice relaxation times and NOE factors were measured as a function of temperatur... more Carbon-13 spin-lattice relaxation times and NOE factors were measured as a function of temperature in two magnetic fields for poly(1-naphthyl acrylate) (PNA) in 1,1,2,2-tetrachloroethane-d~. The relaxation data were interpreted in terms of chain segmental motion and naphthyl internal rotation by using the sharp cutoff model of Jones and Stockmayer (JS) and the Hall-Weber-Helfand (HWH) correlation function. Both models describe in a satisfactory and comparable manner the chain local motions of PNA resulting in approximately similar correlation times (6 X lo+' s at 20 OC) and activation energy (19 kJ/mol) for cooperative segmental motions of the chain. Naphthyl internal rotation is described by a hindered rotation about the C(1)-0 bond superimposed on segmental motions described by both models. They differ, however, in the time scale and angular amplitude of the naphthyl motion, which was found to be faster and less restricted with the JS description as compared to that using the HWH model, although both models give the same activation energy (ca. 13 kJ/mol) for the naphthyl rotation. Finally, the microtacticity of PNA is examined by 13C NMR spectroscopy, and it is concluded that the stereochemistry of the propagation step conforms with Bernoullian statistics.
The Royal Society of Chemistry eBooks, Oct 23, 2012
Macromolecules, Nov 1, 1995
Journal of Polymer Science Part B, Feb 1, 1995
Variable-temperature 13C NMR spin-lattice relaxation times ( T I ) and Nuclear Overhauser Enhance... more Variable-temperature 13C NMR spin-lattice relaxation times ( T I ) and Nuclear Overhauser Enhancements (NOE) a t two magnetic fields have been used to study the dynamics of the amorphous part of a semicrystalline sample (33% of crystallinity) of poly(P-hydroxyoctanoate) (PHO). The interpretation of the relaxation data of the backbone carbons was made by employing a number of motional models. Among these, the DLM model offered the best interpretation of the relaxation data in terms of conformational transitions and librational motions of the backbone C -H vectors, and proved to be superior to unimodal distribution functions. The interpretation of temperature-and frequency-dependent TI and NOE data of the carbon nuclei in the n-pentyl side chain was made by employing a newly developed composite spectral density function for multiple internal C -C bond rotations of restricted amplitude and chain segmental motion. The temperature dependence of the linewidths of the various protonated carbon resonances of PHO has been discussed in terms of the semicrystalline character of this polymer.
Complete1H and13C NMR assignment and31P NMR determination of pentacyclic triterpenic acids
Analytical Methods, 2017
In this study we report the complete and unambiguous1H and13C NMR assignment of betulinic, maslin... more In this study we report the complete and unambiguous1H and13C NMR assignment of betulinic, maslinic, oleanolic and ursolic acids by utilizing high-resolution multidimensional NMR spectroscopy.
Nuclear magnetic resonance
Elsevier eBooks, 2020