Biomedical subjects

Philip J Grandinetti

Publications and source records attributed to Philip J Grandinetti.

9 recordsLinked to original sources

PubMed2006

Spectral editing in solid-state MAS NMR of quadrupolar nuclei using selective satellite inversion.

A sensitivity enhancement method based on selective adiabatic inversion of a satellite transition has been employed in a (pi/2)CT-(pi)ST1-(pi/2)CT spectral editing sequence to both enhance and resolve multisite NMR spectra of quadrupolar nuclei. In addition to a total enhancement of 2.5 times for spin 3/2 nuclei, enhancements up to 2.0 times is reported for the edited sites in a mixture of rubidium salts.

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PubMed2006

Two-dimensional one pulse MAS of half-integer quadrupolar nuclei.

We show that the two-dimensional one pulse (TOP) representation of magic-angle spinning nuclear magnetic resonance data of half-integer quadrupolar nuclei has significant advantages over the conventional one-dimensional spectrum. The TOP spectrum, which correlates NMR frequency to spinning sideband order, provides a rapid determination of the number of sites as well as the size of the their quadrupolar coupling. Additionally, synchronous acquisition spectra of the central and satellite transition resonances can be separated by different projections of the TOP spectrum, with higher resolution spectra often found in the satellite transitions projection. A previously perceived problem of centerband aliasing in TOP can be eliminated with an algorithm that uses larger subspectral widths and the sideband order dimension to distinguish centerbands from sidebands.

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PubMed2006

Solid-state NMR characterization of 69Ga and 71Ga in crystalline solids.

Gallium model systems containing four- and six-coordinate gallium sites have been investigated using solid-state NMR. Measurement of the isotropic chemical shift and electric field gradient (EFG) have been performed at 9.4 T on alpha-Ga2O3, beta-Ga2O3, LiGaO2, NaGaO2, KGaO2, Ga2(SO4)3, and LaGaO3 using a variety of techniques on both NMR active nuclei (69Ga and 71Ga) including static, high speed magic-angle spinning (MAS), satellite transition (ST) spectroscopy, and rotor-assisted population transfer (RAPT). The chemical shift is found to correlate well with the coordination number, with four-coordinate gallium having values of approximately 50 ppm and six-coordinate gallium having values near 225 ppm (referenced to 1 M gallium nitrate solution). The magnitude of the EFG is found to be correlated to the distortion of the gallium polyhedra, with the strained systems having EFGs of 3 x 10(21) Vm(-2) or more, while the less strained systems have values of 1.5 x 10(21) Vm(-2) or less. A plot of chemical shift versus EFG suggests that solid-state NMR of gallium oxyanions can be more discriminating than liquid state NMR chemical shifts alone.

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PubMed2005

A combined 17O RAPT and MQ-MAS NMR study of L-leucine.

We report the application of rotor-assisted population transfer (RAPT) to measure the quadrupolar coupling constant (C(q)) for spin 5/2 nuclei. Results from numerical simulations are presented on the magnitude of enhancement factor as a function of frequency offsets, i.e. the RAPT profile. Experimental O17 RAPT profile is traced for the amino acid L-leucine. In addition, results from MQ-MAS experiments are incorporated to determine the quadrupolar asymmetry parameter (eta(q)). Unlike previous reports, the O17 NMR parameters for an amino acid, L-leucine, is reported at a relatively low field of 9.4 T.

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PubMed2005

Calculation of bridging oxygen 17O quadrupolar coupling parameters in alkali silicates: a combined ab initio investigation.

Ab initio band-structure calculations based on the density functional theory have been performed for several crystalline Li, Na, and K-silicates to obtain electric-field gradients (efg) for oxygen atoms. The efg for bridging oxygen environments in these compounds were also investigated by performing ab initio self-consistent field Hartree-Fock molecular orbital calculations on silicate clusters, and there is good agreement between these two approaches. By performing additional ab initio quantum chemistry calculations on model silicate clusters the factors influencing the 17O quadrupole coupling parameters for bridging oxygen environments in alkali silicates have been examined. The quadrupolar asymmetry parameter was found to be dependent on the Si-O-Si angle and the nature of the modifier cation, in agreement with previous studies. In contrast, the quadrupolar coupling constant was found to have a strong dependence on Si-O distance, as well as Si-O-Si angle and the nature of the modifier cation. Analytical expressions describing these dependencies are proposed, which should assist in describing the local environments of bridging oxygen in crystalline and amorphous materials.

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PubMed2003

Selective suppression and excitation of solid-state NMR resonances based on quadrupole coupling constants.

The dependence of the (Rotor Assisted Population Transfer) RAPT enhancement on offset frequency for nuclei experiencing different quadrupolar couplings has been exploited to design two new spectral editing schemes, pi/2-RAPT and RAPT-pi-RAPT, for the selective excitation or suppression, respectively, of nuclei with large quadrupolar couplings. Both approaches are demonstrated on the 87 Rb spectrum of Rb(2)SO(4), which contains two resonances with C(q) values of 2.6 and 5.3 MHz. The conditions for optimal selectivity are discussed. Combining pi/2-RAPT with the RIACT MQ-MAS experiment it is also demonstrated how a pure absorption mode triple quantum MQ-MAS spectrum devoid of narrow resonances can be obtained.

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PubMed2002

A simple technique for determining nuclear quadrupole coupling constants with RAPT solid-state NMR spectroscopy.

An enhanced Rotor Assisted Population Transfer (RAPT) experiment is presented and used as a simple and fast technique to measure the magnitude of the nuclear quadrupolar coupling constant of half-integer quadrupolar nuclei. The enhanced RAPT sequence consists of a train of Gaussian pulses with alternating off-resonant frequencies of +/-nuoff. Simulated and experimental results demonstrating the method are given in the case of 87Rb (spin 3/2) and 27Al (spin 5/2) nuclei. The RAPT sequence is also used to selectively suppress resonances based on their quadrupolar coupling constant.

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PubMedDate not supplied

Does phase cycling work for nuclei experiencing strong quadrupolar couplings?

The question of whether the phase cycling can still be used to select coherence transfer pathways in spin systems experiencing a tilting of its eigenstates away from the Zeeman eigenstates due to strong couplings was investigated theoretically. Based on the analysis presented it is concluded that conventional phase cycling is still a valid approach for selecting a coherence transfer pathway signal, although changes in pathway efficiencies can occur as the mechanisms for excitation and detection of coherences are affected by the tilting of the eigenstates.

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PubMedDate not supplied

Enhancing sensitivity of quadrupolar nuclei in solid-state NMR with multiple rotor assisted population transfers.

Rotor-assisted population transfer (RAPT) was developed as a method for enhancing MAS NMR sensitivity of quadrupolar nuclei by transferring polarization associated with satellite transitions to the central m=12-->-12 transition. After a single RAPT transfer, there still remains polarization in the satellite transitions that can be transferred to the central transition. This polarization is available without having to wait for the spin system to return to thermal equilibrium. We describe a new RAPT scheme that uses the remaining polarization of the satellites to obtain a further enhancement of the central transition by performing RAPT-enhanced experiments multiple times before waiting for re-equilibration of the spin system. For 27Al (I=5/2) in albite we obtain a multiple RAPT enhancement of 3.02, a 48% increase over single RAPT. For 93Nb (I=9/2) in NaNbO(3) we obtain a multiple RAPT enhancement of 5.76, an 89% increase over single RAPT. We also describe a data processing procedure for obtaining the maximum possible signal-to-noise ratio.

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