Christian Fernandez | Universidad de Buenos Aires (original) (raw)

Papers by Christian Fernandez

Research paper thumbnail of Performance of the silica aerogel cherenkov detector used in the European hybrid spectrometer

Nuclear Instruments and Methods in Physics Research, 1984

Research paper thumbnail of Performance of the silica aerogel cherenkov detector used in the European hybrid spectrometer

Nuclear Instruments and Methods in Physics Research, 1984

Research paper thumbnail of Performance of the silica aerogel cherenkov detector used in the European hybrid spectrometer

Nuclear Instruments and Methods in Physics Research, 1984

Research paper thumbnail of Engineered Nanoscaled Polyplex Gene Delivery Systems

Molecular Pharmaceutics, 2009

Improving the transfection efficiencies of nonviral gene delivery requires properly engineered na... more Improving the transfection efficiencies of nonviral gene delivery requires properly engineered nanoscaled delivery carriers that can overcome the multiple barriers associated with the delivery of oligonucleotides from the site of administration to the nucleus or cytoplasm of the target cell. This article reviews the current advantages and limitation of polyplex nonviral delivery systems, including the apparent barriers that limit gene expression efficiency compared to physical methods such as hydrodynamic dosing and electroporation. An emphasis is placed on engineered nanoscaled polyplexes (NSPs) of modular design that both self-assemble and systematically disassemble at the desired stage of delivery. It is suggested that NSPs of increasingly sophisticated designs are necessary to improve the efficiency of the rate limiting steps in gene delivery.

Research paper thumbnail of BNCT for skin melanoma in extremities: Updated Argentine clinical results

Applied Radiation and Isotopes, 2009

As part of phase I/II melanoma BNCT clinical trial conducted in Argentina in a cooperative effort... more As part of phase I/II melanoma BNCT clinical trial conducted in Argentina in a cooperative effort of the Argentine Atomic Energy Commission (CNEA) and the Oncology Institute Angel H. Roffo (IOAHR), 7 patients (6 female-1 male) received eight treatment sessions covering ten anatomical areas located in extremities. Mean age of the patients was 64 years (51-74). The treatments were performed between October 2003 and June 2007. All patients presented multiple subcutaneous skin metastases of melanoma and received an infusion containing $14 gr/m 2 of 10 borophenyl-alanine (BPA) followed by the exposition of the area to a mixed thermal-epithermal neutron beam at the RA-6 reactor. The maximum prescribed dose to normal skin ranged from 16.5 to 24 Gy-Eq and normal tissue administered dose varied from 15.8 to 27.5 Gy-Eq. Considering evaluable nodules, 69.3% of overall response and 30.7% of no changes were seen. The toxicity was acceptable, with 3 out of 10 evaluable areas showing ulceration (30% toxicity grade 3).

Research paper thumbnail of Multiplex MQMAS NMR of quadrupolar nuclei

Solid State Nuclear Magnetic Resonance, 2005

A multiplex phase cycling method (N. Ivchenko et al., J. Magn. Reson. 160 (2003) 52-58) has been ... more A multiplex phase cycling method (N. Ivchenko et al., J. Magn. Reson. 160 (2003) 52-58) has been used to record twodimensional MQMAS spectra with a very short phase cycling. A straightforward procedure has been developed to easily process the data. Combining this Multiplex approach and the new Soft-Pulse-Adding-Mixing (SPAM) method considerably increases the signal-to-noise ratio of the conventional MQMAS experiment. The Multiplex acquisition procedure is much simpler than the echo/ anti-echo method recently proposed, and has been applied with success to record 87 Rb spectra of RbNO 3 and 27 Al 3Q and 5Q MQMAS NMR of microporous aluminophosphate AlPO 4 -14. r 2005 Elsevier Inc. All rights reserved.

Research paper thumbnail of High-field 17 O NMR studies of the SiOAl bond in solids

Chemical Physics Letters, 1998

Oxygen-17 multiple-quantum magic-angle spinning and double rotation nuclear magnetic resonance st... more Oxygen-17 multiple-quantum magic-angle spinning and double rotation nuclear magnetic resonance studies were performed in the field of 17.6 T. A correlation between the isotropic value of the chemical shift and the SiOAl bond angle in zeolites was found. The correlation may be used for the determination of bond angles in SiOAl sites without long-range order. It is shown that multiple-quantum and double rotation techniques are complementary tools for getting highly-resolved 17 O NMR spectra of solids. q

Research paper thumbnail of Distribution of Tetrahedral Aluminium Sites in ZSM-5 Type Zeolites: An 27 Al (Multiquantum) Magic Angle Spinning NMR Study

The Journal of Physical Chemistry, 1996

Up to now the distribution of Al atoms in the zeolite lattice could be monitored mainly by 29 Si ... more Up to now the distribution of Al atoms in the zeolite lattice could be monitored mainly by 29 Si MAS NMR. The data about the nonequivalent aluminium T sites, present in the 27 Al MAS NMR spectra, was obscured by second-order effects of quadrupolar interaction. By applying the five-quantum 27 Al MQMAS NMR method to ZSM-5 type zeolites, we were able to distinguish at least two nonequivalent aluminium T sites in the H-ZSM-5 and establish the relation between 27 Al, 29 Si, and 1 H NMR data. Comparison with 29 Si MAS NMR spectra gives information about the distribution and siting of aluminium in the zeolite framework.

Research paper thumbnail of 2D multiquantum MAS-NMR spectroscopy of 27Al in aluminophosphate molecular sieves

Chemical Physics Letters, 1995

Two-dimensional multiquantum MAS-NMR spectroscopy (2D-MQ) has been applied to the discrimination ... more Two-dimensional multiquantum MAS-NMR spectroscopy (2D-MQ) has been applied to the discrimination of the different 27Al sites in several aluminophosphate molecular sieves. It is shown that a new quintuple-quantum MAS-NMR method (2D-5Q) gives an extraordinary improved resolution compared to the DOR or DAS technique. The pure-absorption 2D spectra allow the direct determination of the number of different species, the correct determination

Research paper thumbnail of Diffusion of alkanes in molecular sieves evidence for confinement effects

Applied Catalysis, 1988

Abstract Sorption kinetics, heats of sorption, NMR relaxation time measurements, and molecular gr... more Abstract Sorption kinetics, heats of sorption, NMR relaxation time measurements, and molecular graphics simulations support the proposal that confinement effects regulate the diffusional behavior of alkanes in zeolites (ZSM-5, ferrierite, mordenite, type Y) and other ...

Research paper thumbnail of Triple, quintuple and higher order multiple quantum MAS NMR of quadrupolar nuclei

Solid State Nuclear Magnetic Resonance, 1998

The optimization of the coherence transfers involved in five, seven and nine-quantum versions of ... more The optimization of the coherence transfers involved in five, seven and nine-quantum versions of the recently discovered MQMAS technique, is analysed numerically. Data reported in this paper may serve as starting parameters for the experiment set up. An analysis of the intensity and resolution given by each type of experiment is performed, which confirms the need to use very high rf fields for MQ transfers. It follows that five-quantum is achievable rather easily but the use of seven and nine-quantum MAS experiments becomes increasingly difficult due to the demand for high rf power and decreasing sensitivity. The advantages of using the z-filter MQMAS method with respect to a two-pulse sequence are analysed. The method for qualitatively and quantitatively interpret the MQMAS spectra is described. The nature of the spinning side bands along the multiple quantum dimension is explained. It is shown that the rotor synchronization can be conveniently used to eliminate these side bands, but only for 3QMAS experiments. The use of the multiple-quantum method in combination with static samples and VAS, DAS and DOR techniques is finally discussed. q 1998 Elsevier Science B.V.

Research paper thumbnail of Multiple-quantum magic-angle spinning NMR with cross-polarization: Spectral editing of high-resolution spectra of quadrupolar nuclei

Solid State Nuclear Magnetic Resonance, 1997

An experiment is presented that combines the multiple-quantum magic-angle spinning (MQMAS) techni... more An experiment is presented that combines the multiple-quantum magic-angle spinning (MQMAS) technique with cross-polarization (CP). As a preliminary test of this new method, we measured and compared the '7Al 3QMAS and 19 F --f *'Al CP 3QMAS spectra of a fluorinated AIPO, aluminophosphate.

Research paper thumbnail of Triple-quantum MAS-NMR of quadrupolar nuclei

Solid State Nuclear Magnetic Resonance, 1996

From two-dimensional multiquantum NMR spectra of quadrupolar nuclei, it is now possible to obtain... more From two-dimensional multiquantum NMR spectra of quadrupolar nuclei, it is now possible to obtain much greater resolution than in a classical single-quantum magic-angle spinning or variable-angle spinning spectrum. We describe here a very simple pulse scheme which efficiently excites the desired multiquantum NMR coherence and a new acquisition procedure which yields to pure-absorption mode 2D spectra. Experimental spectra for "Rb in polycrystalline rubidium nitrate illustrate the method.

Research paper thumbnail of Optimized multiple-quantum magic-angle spinning NMR experiments on half-integer quadrupoles

Chemical Physics Letters, 1996

It has been recently shown that second-order anisotropies can be removed from solid phase NMR spe... more It has been recently shown that second-order anisotropies can be removed from solid phase NMR spectra of quadrupolar nuclei via the combined use of magic-angle spinning (MAS) and bidimensional multiple-quantum (MQ) spectroscopy. The present study investigates the conditions under which the acquisition of such high-resolution MQMAS NMR spectra are optimized. The excitation and conversion pulse lengths that maximize 0 -~ _ 3(t 1) ~ -l(t 2) coherence transfer pathway signals for arbitrary spin numbers were calculated, as were the pulse lengths that provide NMR spectra free from dispersive line shape distortions. For the case of spin-5/2 nuclei, the conditions which optimize experiments involving quintuplequantum coherences were also determined.

Research paper thumbnail of Stray-field imaging and multinuclear magnetic resonance spectroscopy studies on the setting of a commercial glass-ionomer cement

Journal of Materials Science-materials in Medicine, 2004

A commercial glass-ionomer (Fuji II) was studied using different NMR techniques. 1H and 19F stray... more A commercial glass-ionomer (Fuji II) was studied using different NMR techniques. 1H and 19F stray-field imaging (STRAFI) were used to monitor the curing kinetics of the cement and two processes were distinguished: the gelation and maturation phases. Characterization of the aluminium and silicon species present in the glass component and cement was performed by conventional 27Al and 29Si MAS and two-dimensional 27Al triple quantum MAS NMR (MQMAS) techniques. Quantification of the aluminium in the glass component and in the cement indicates the leaching of about 32% of the 4-coordinate aluminium, about 100% of the 5-coordinate aluminium and about 41% of the 6-coordinate aluminium, during the setting reaction. It is also shown that the 5-coordinate aluminium is only present in the surface layer created by the acid attack during the cement formation process. In the cement, silicon maintains species with four bridging oxygens after the leaching of tetrahedral (4-coordinate) aluminium. The silicon analysis correlates well with the aluminium determinations.

Research paper thumbnail of 17O multiple-quantum and 1H MAS NMR studies of zeolite ZSM-5

Chemical Physics Letters, 1998

Oxygen-17 multiple-quantum magic-angle spinning nuclear magnetic resonance studies were performed... more Oxygen-17 multiple-quantum magic-angle spinning nuclear magnetic resonance studies were performed, for the first time, in the high field of 17.6 T. A good resolution between two oxygen signals due to SiOSi and SiOAl fragments could be obtained. From the residual linewidth of the SiOSi signal, it is concluded that a change of the bridging SiOSi angle by 13.48 gives rise to a quite large change in the isotropic chemical shift of less than 5.7 ppm. q 1998 Elsevier Science B.V.

Research paper thumbnail of ZFiltering in MQMAS NMR

Journal of Magnetic Resonance, Series A, 1996

... Multiplex MQMAS NMR of quadrupolar nuclei. Nicolas Malicki, Luís Mafra, Anne-Agathe Quoineaud... more ... Multiplex MQMAS NMR of quadrupolar nuclei. Nicolas Malicki, Luís Mafra, Anne-Agathe Quoineaud, João Rocha, Frédéric Thibault-Starzyk, Christian Fernandez in Solid State Nuclear Magnetic Resonance (2005). Save reference to library · Related research 4 readers. ...

Research paper thumbnail of Quantitative study of the short range order in B 2O 3 and B 2S 3 by MAS and two-dimensional triple-quantum MAS 11B NMR

Solid State Nuclear Magnetic Resonance, 1997

Two-dimensional multiple-quantum magic angle spinning (MQMAS) NMR and MAS NMR of "B at various ma... more Two-dimensional multiple-quantum magic angle spinning (MQMAS) NMR and MAS NMR of "B at various magnetic fields, were applied to elucidate the structure of vitreous (glassy) boron trioxide (v-B203), vitreous boron trisulfide (v-B,S,) and crystalline boron trisulfide (c-B2S3). These techniques, when combined with computer simulations of the resulting spectra, provide the isotropic chemical shifts and the quadrupole parameters, as well as a quantitative measure of the intensities of various boron resonances. The MAS NMR of v-B,O, produced overlapping anisotropic lineshapes corresponding to the -l/2 c, l/2 transition in two distinct types of BO, units with 3(_+0.08): 1 intensity ratio. A combination of MAS and the multiple-quantum method resulted in a better resolved, isotropic "B spectrum of v-B,O,. A remarkable enhancement of resolution of the MQMAS NMR proved instrumental in finding and identifying various impurities present in V-B,S, and c-B,S,. In addition to the resonances from boron in two types of BS, groups, four other structural units, BOS,, BO,S, BO, and BS,, were elucidated from the spectra of vitreous and crystalline samples. The effects of various experimental parameters, such as the magnitude of the B, and B, fields, on the resolution of the MAS and MQMAS techniques are also shown. 0 1997 Elsevier Science B.V.

Research paper thumbnail of High-Resolution Heteronuclear Correlation Spectra between 31P and 27Al in Microporous Aluminophosphates

Solid State Nuclear Magnetic Resonance, 2002

A new two-dimensional scheme is proposed for accurate measurements of high-resolution chemical sh... more A new two-dimensional scheme is proposed for accurate measurements of high-resolution chemical shifts and heteronuclear dipolar couplings in NMR of aligned samples. Both the 1 H chemical shifts and the 1 H-15 N dipolar couplings are evolved in the indirect dimension while the 15 N chemical shifts are detected. This heteronuclear correlation (HETCOR) spectroscopy yields high-resolution 1 H chemical shifts split by the 1 H-15 N dipolar couplings in the indirect dimension and the 15 N chemical shifts in the observed dimension. The advantages of the HETCOR technique are illustrated for a static 15 N-acetyl-valine crystal sample and a 15 N-labeled helical peptide sample aligned in hydrated lipid bilayers.

Research paper thumbnail of Theoretical and experimental study of quadrupolar echoes in solid state NMR

Molecular Physics, 1997

Theoretical explanations are offered for the creation of echo, anti-echo and transient signals ob... more Theoretical explanations are offered for the creation of echo, anti-echo and transient signals observed in solid state NMR of quadrupolar nuclei, based on density matrix calculations and using concepts in agreement with the definition of coherence transfer pathways. From ...

Research paper thumbnail of Performance of the silica aerogel cherenkov detector used in the European hybrid spectrometer

Nuclear Instruments and Methods in Physics Research, 1984

Research paper thumbnail of Performance of the silica aerogel cherenkov detector used in the European hybrid spectrometer

Nuclear Instruments and Methods in Physics Research, 1984

Research paper thumbnail of Performance of the silica aerogel cherenkov detector used in the European hybrid spectrometer

Nuclear Instruments and Methods in Physics Research, 1984

Research paper thumbnail of Engineered Nanoscaled Polyplex Gene Delivery Systems

Molecular Pharmaceutics, 2009

Improving the transfection efficiencies of nonviral gene delivery requires properly engineered na... more Improving the transfection efficiencies of nonviral gene delivery requires properly engineered nanoscaled delivery carriers that can overcome the multiple barriers associated with the delivery of oligonucleotides from the site of administration to the nucleus or cytoplasm of the target cell. This article reviews the current advantages and limitation of polyplex nonviral delivery systems, including the apparent barriers that limit gene expression efficiency compared to physical methods such as hydrodynamic dosing and electroporation. An emphasis is placed on engineered nanoscaled polyplexes (NSPs) of modular design that both self-assemble and systematically disassemble at the desired stage of delivery. It is suggested that NSPs of increasingly sophisticated designs are necessary to improve the efficiency of the rate limiting steps in gene delivery.

Research paper thumbnail of BNCT for skin melanoma in extremities: Updated Argentine clinical results

Applied Radiation and Isotopes, 2009

As part of phase I/II melanoma BNCT clinical trial conducted in Argentina in a cooperative effort... more As part of phase I/II melanoma BNCT clinical trial conducted in Argentina in a cooperative effort of the Argentine Atomic Energy Commission (CNEA) and the Oncology Institute Angel H. Roffo (IOAHR), 7 patients (6 female-1 male) received eight treatment sessions covering ten anatomical areas located in extremities. Mean age of the patients was 64 years (51-74). The treatments were performed between October 2003 and June 2007. All patients presented multiple subcutaneous skin metastases of melanoma and received an infusion containing $14 gr/m 2 of 10 borophenyl-alanine (BPA) followed by the exposition of the area to a mixed thermal-epithermal neutron beam at the RA-6 reactor. The maximum prescribed dose to normal skin ranged from 16.5 to 24 Gy-Eq and normal tissue administered dose varied from 15.8 to 27.5 Gy-Eq. Considering evaluable nodules, 69.3% of overall response and 30.7% of no changes were seen. The toxicity was acceptable, with 3 out of 10 evaluable areas showing ulceration (30% toxicity grade 3).

Research paper thumbnail of Multiplex MQMAS NMR of quadrupolar nuclei

Solid State Nuclear Magnetic Resonance, 2005

A multiplex phase cycling method (N. Ivchenko et al., J. Magn. Reson. 160 (2003) 52-58) has been ... more A multiplex phase cycling method (N. Ivchenko et al., J. Magn. Reson. 160 (2003) 52-58) has been used to record twodimensional MQMAS spectra with a very short phase cycling. A straightforward procedure has been developed to easily process the data. Combining this Multiplex approach and the new Soft-Pulse-Adding-Mixing (SPAM) method considerably increases the signal-to-noise ratio of the conventional MQMAS experiment. The Multiplex acquisition procedure is much simpler than the echo/ anti-echo method recently proposed, and has been applied with success to record 87 Rb spectra of RbNO 3 and 27 Al 3Q and 5Q MQMAS NMR of microporous aluminophosphate AlPO 4 -14. r 2005 Elsevier Inc. All rights reserved.

Research paper thumbnail of High-field 17 O NMR studies of the SiOAl bond in solids

Chemical Physics Letters, 1998

Oxygen-17 multiple-quantum magic-angle spinning and double rotation nuclear magnetic resonance st... more Oxygen-17 multiple-quantum magic-angle spinning and double rotation nuclear magnetic resonance studies were performed in the field of 17.6 T. A correlation between the isotropic value of the chemical shift and the SiOAl bond angle in zeolites was found. The correlation may be used for the determination of bond angles in SiOAl sites without long-range order. It is shown that multiple-quantum and double rotation techniques are complementary tools for getting highly-resolved 17 O NMR spectra of solids. q

Research paper thumbnail of Distribution of Tetrahedral Aluminium Sites in ZSM-5 Type Zeolites: An 27 Al (Multiquantum) Magic Angle Spinning NMR Study

The Journal of Physical Chemistry, 1996

Up to now the distribution of Al atoms in the zeolite lattice could be monitored mainly by 29 Si ... more Up to now the distribution of Al atoms in the zeolite lattice could be monitored mainly by 29 Si MAS NMR. The data about the nonequivalent aluminium T sites, present in the 27 Al MAS NMR spectra, was obscured by second-order effects of quadrupolar interaction. By applying the five-quantum 27 Al MQMAS NMR method to ZSM-5 type zeolites, we were able to distinguish at least two nonequivalent aluminium T sites in the H-ZSM-5 and establish the relation between 27 Al, 29 Si, and 1 H NMR data. Comparison with 29 Si MAS NMR spectra gives information about the distribution and siting of aluminium in the zeolite framework.

Research paper thumbnail of 2D multiquantum MAS-NMR spectroscopy of 27Al in aluminophosphate molecular sieves

Chemical Physics Letters, 1995

Two-dimensional multiquantum MAS-NMR spectroscopy (2D-MQ) has been applied to the discrimination ... more Two-dimensional multiquantum MAS-NMR spectroscopy (2D-MQ) has been applied to the discrimination of the different 27Al sites in several aluminophosphate molecular sieves. It is shown that a new quintuple-quantum MAS-NMR method (2D-5Q) gives an extraordinary improved resolution compared to the DOR or DAS technique. The pure-absorption 2D spectra allow the direct determination of the number of different species, the correct determination

Research paper thumbnail of Diffusion of alkanes in molecular sieves evidence for confinement effects

Applied Catalysis, 1988

Abstract Sorption kinetics, heats of sorption, NMR relaxation time measurements, and molecular gr... more Abstract Sorption kinetics, heats of sorption, NMR relaxation time measurements, and molecular graphics simulations support the proposal that confinement effects regulate the diffusional behavior of alkanes in zeolites (ZSM-5, ferrierite, mordenite, type Y) and other ...

Research paper thumbnail of Triple, quintuple and higher order multiple quantum MAS NMR of quadrupolar nuclei

Solid State Nuclear Magnetic Resonance, 1998

The optimization of the coherence transfers involved in five, seven and nine-quantum versions of ... more The optimization of the coherence transfers involved in five, seven and nine-quantum versions of the recently discovered MQMAS technique, is analysed numerically. Data reported in this paper may serve as starting parameters for the experiment set up. An analysis of the intensity and resolution given by each type of experiment is performed, which confirms the need to use very high rf fields for MQ transfers. It follows that five-quantum is achievable rather easily but the use of seven and nine-quantum MAS experiments becomes increasingly difficult due to the demand for high rf power and decreasing sensitivity. The advantages of using the z-filter MQMAS method with respect to a two-pulse sequence are analysed. The method for qualitatively and quantitatively interpret the MQMAS spectra is described. The nature of the spinning side bands along the multiple quantum dimension is explained. It is shown that the rotor synchronization can be conveniently used to eliminate these side bands, but only for 3QMAS experiments. The use of the multiple-quantum method in combination with static samples and VAS, DAS and DOR techniques is finally discussed. q 1998 Elsevier Science B.V.

Research paper thumbnail of Multiple-quantum magic-angle spinning NMR with cross-polarization: Spectral editing of high-resolution spectra of quadrupolar nuclei

Solid State Nuclear Magnetic Resonance, 1997

An experiment is presented that combines the multiple-quantum magic-angle spinning (MQMAS) techni... more An experiment is presented that combines the multiple-quantum magic-angle spinning (MQMAS) technique with cross-polarization (CP). As a preliminary test of this new method, we measured and compared the '7Al 3QMAS and 19 F --f *'Al CP 3QMAS spectra of a fluorinated AIPO, aluminophosphate.

Research paper thumbnail of Triple-quantum MAS-NMR of quadrupolar nuclei

Solid State Nuclear Magnetic Resonance, 1996

From two-dimensional multiquantum NMR spectra of quadrupolar nuclei, it is now possible to obtain... more From two-dimensional multiquantum NMR spectra of quadrupolar nuclei, it is now possible to obtain much greater resolution than in a classical single-quantum magic-angle spinning or variable-angle spinning spectrum. We describe here a very simple pulse scheme which efficiently excites the desired multiquantum NMR coherence and a new acquisition procedure which yields to pure-absorption mode 2D spectra. Experimental spectra for "Rb in polycrystalline rubidium nitrate illustrate the method.

Research paper thumbnail of Optimized multiple-quantum magic-angle spinning NMR experiments on half-integer quadrupoles

Chemical Physics Letters, 1996

It has been recently shown that second-order anisotropies can be removed from solid phase NMR spe... more It has been recently shown that second-order anisotropies can be removed from solid phase NMR spectra of quadrupolar nuclei via the combined use of magic-angle spinning (MAS) and bidimensional multiple-quantum (MQ) spectroscopy. The present study investigates the conditions under which the acquisition of such high-resolution MQMAS NMR spectra are optimized. The excitation and conversion pulse lengths that maximize 0 -~ _ 3(t 1) ~ -l(t 2) coherence transfer pathway signals for arbitrary spin numbers were calculated, as were the pulse lengths that provide NMR spectra free from dispersive line shape distortions. For the case of spin-5/2 nuclei, the conditions which optimize experiments involving quintuplequantum coherences were also determined.

Research paper thumbnail of Stray-field imaging and multinuclear magnetic resonance spectroscopy studies on the setting of a commercial glass-ionomer cement

Journal of Materials Science-materials in Medicine, 2004

A commercial glass-ionomer (Fuji II) was studied using different NMR techniques. 1H and 19F stray... more A commercial glass-ionomer (Fuji II) was studied using different NMR techniques. 1H and 19F stray-field imaging (STRAFI) were used to monitor the curing kinetics of the cement and two processes were distinguished: the gelation and maturation phases. Characterization of the aluminium and silicon species present in the glass component and cement was performed by conventional 27Al and 29Si MAS and two-dimensional 27Al triple quantum MAS NMR (MQMAS) techniques. Quantification of the aluminium in the glass component and in the cement indicates the leaching of about 32% of the 4-coordinate aluminium, about 100% of the 5-coordinate aluminium and about 41% of the 6-coordinate aluminium, during the setting reaction. It is also shown that the 5-coordinate aluminium is only present in the surface layer created by the acid attack during the cement formation process. In the cement, silicon maintains species with four bridging oxygens after the leaching of tetrahedral (4-coordinate) aluminium. The silicon analysis correlates well with the aluminium determinations.

Research paper thumbnail of 17O multiple-quantum and 1H MAS NMR studies of zeolite ZSM-5

Chemical Physics Letters, 1998

Oxygen-17 multiple-quantum magic-angle spinning nuclear magnetic resonance studies were performed... more Oxygen-17 multiple-quantum magic-angle spinning nuclear magnetic resonance studies were performed, for the first time, in the high field of 17.6 T. A good resolution between two oxygen signals due to SiOSi and SiOAl fragments could be obtained. From the residual linewidth of the SiOSi signal, it is concluded that a change of the bridging SiOSi angle by 13.48 gives rise to a quite large change in the isotropic chemical shift of less than 5.7 ppm. q 1998 Elsevier Science B.V.

Research paper thumbnail of ZFiltering in MQMAS NMR

Journal of Magnetic Resonance, Series A, 1996

... Multiplex MQMAS NMR of quadrupolar nuclei. Nicolas Malicki, Luís Mafra, Anne-Agathe Quoineaud... more ... Multiplex MQMAS NMR of quadrupolar nuclei. Nicolas Malicki, Luís Mafra, Anne-Agathe Quoineaud, João Rocha, Frédéric Thibault-Starzyk, Christian Fernandez in Solid State Nuclear Magnetic Resonance (2005). Save reference to library · Related research 4 readers. ...

Research paper thumbnail of Quantitative study of the short range order in B 2O 3 and B 2S 3 by MAS and two-dimensional triple-quantum MAS 11B NMR

Solid State Nuclear Magnetic Resonance, 1997

Two-dimensional multiple-quantum magic angle spinning (MQMAS) NMR and MAS NMR of "B at various ma... more Two-dimensional multiple-quantum magic angle spinning (MQMAS) NMR and MAS NMR of "B at various magnetic fields, were applied to elucidate the structure of vitreous (glassy) boron trioxide (v-B203), vitreous boron trisulfide (v-B,S,) and crystalline boron trisulfide (c-B2S3). These techniques, when combined with computer simulations of the resulting spectra, provide the isotropic chemical shifts and the quadrupole parameters, as well as a quantitative measure of the intensities of various boron resonances. The MAS NMR of v-B,O, produced overlapping anisotropic lineshapes corresponding to the -l/2 c, l/2 transition in two distinct types of BO, units with 3(_+0.08): 1 intensity ratio. A combination of MAS and the multiple-quantum method resulted in a better resolved, isotropic "B spectrum of v-B,O,. A remarkable enhancement of resolution of the MQMAS NMR proved instrumental in finding and identifying various impurities present in V-B,S, and c-B,S,. In addition to the resonances from boron in two types of BS, groups, four other structural units, BOS,, BO,S, BO, and BS,, were elucidated from the spectra of vitreous and crystalline samples. The effects of various experimental parameters, such as the magnitude of the B, and B, fields, on the resolution of the MAS and MQMAS techniques are also shown. 0 1997 Elsevier Science B.V.

Research paper thumbnail of High-Resolution Heteronuclear Correlation Spectra between 31P and 27Al in Microporous Aluminophosphates

Solid State Nuclear Magnetic Resonance, 2002

A new two-dimensional scheme is proposed for accurate measurements of high-resolution chemical sh... more A new two-dimensional scheme is proposed for accurate measurements of high-resolution chemical shifts and heteronuclear dipolar couplings in NMR of aligned samples. Both the 1 H chemical shifts and the 1 H-15 N dipolar couplings are evolved in the indirect dimension while the 15 N chemical shifts are detected. This heteronuclear correlation (HETCOR) spectroscopy yields high-resolution 1 H chemical shifts split by the 1 H-15 N dipolar couplings in the indirect dimension and the 15 N chemical shifts in the observed dimension. The advantages of the HETCOR technique are illustrated for a static 15 N-acetyl-valine crystal sample and a 15 N-labeled helical peptide sample aligned in hydrated lipid bilayers.

Research paper thumbnail of Theoretical and experimental study of quadrupolar echoes in solid state NMR

Molecular Physics, 1997

Theoretical explanations are offered for the creation of echo, anti-echo and transient signals ob... more Theoretical explanations are offered for the creation of echo, anti-echo and transient signals observed in solid state NMR of quadrupolar nuclei, based on density matrix calculations and using concepts in agreement with the definition of coherence transfer pathways. From ...