Biomedical subjects

P J Grandinetti

Publications and source records attributed to P J Grandinetti.

8 recordsLinked to original sources

PubMed2001

Enhanced sensitivity in RIACT/MQ-MAS NMR experiments using rotor assisted population transfer.

The rotor assisted population transfer (RAPT) sequence is used to enhance the sensitivity of the RIACT(II) experiment for spin-3/2 quadrupolar nuclei. A detailed theoretical analysis of the polarizations that contribute to different types of MQ-MAS experiments is provided. In particular, two polarization pathways are distinguished for the creation of triple-quantum coherence. The existence of these pathways is experimentally demonstrated by comparing the sensitivities of different sequences with and without RAPT preparation.

Journal Article↗

PubMed2000

Pure absorption-mode spectra using a modulated RF mixing period in MQMAS experiments.

Different approaches to obtain pure absorption-mode lineshapes in MQMAS experiments employing a train of 180 degrees phase-alternating pulses for the multiple-quantum to single-quantum mixing period are investigated. Four pulse sequences, which achieve this by using either the shifted-echo approach or the hypercomplex approach with symmetric coherence transfer pathways, are presented and their improved lineshape- and sensitivity-performance is experimentally demonstrated by (87)Rb MQMAS of RbNO(3). Compared to the original modulated-rf mixing sequence, sensitivity enhancements by factors up to 1.3 are obtained with the sequences described here.

Magnetic Resonance Spectroscopy↗

PubMed2000

Factors influencing the 17O quadrupole coupling constant in bridging oxygen environments.

Ab initio calculations were performed on the series of clusters [(OH)3M-O-M(OH)3](-2) where M = B, Al, and Ga, (OH)3M-O-M(OH)3 where M = C, Si, and Ge, (OH)2OM-O-MO(OH)2 where M = P and As, and (OH)O2M-O-MO2(OH) where M = S and Se. These clusters were constructed to model the effect of changing the coordinating cation and coordinating cation-oxygen distances on the bridging oxygen 17O quadrupole coupling constant. For all clusters studied, we observed a general trend that the magnitude of Cq increases linearly with increasing cation-oxygen bond distance and cation group number, suggesting that group number and cation-bridging oxygen distance can serve as a better predictor of the bridging oxygen quadrupole coupling constant than electronegativity differences.

Electrochemistry↗

PubMed1998

Solid-state 13C NMR investigations of the glycosidic linkage in alpha-alpha' trehalose.

The sugar trehalose is known to play a central role in the desiccation tolerance of many organisms. Essential to trehalose's role are its glass forming abilities and ability to directly interact with lipid molecules. Detailed information on the structure and dynamics of glassy trehalose and its interactions with lipids, however, have been elusive. We have used solid-state NMR and ab initio quantum mechanical methods (Gaussian 94) in order to characterize the possible molecular conformations of trehalose. Using a simplified structure (2-(tetrahydropyran-2-yloxy) tetrahydropyran) as a model we have calculated the energy and 13C magnetic shielding parameters as a function of the two glycosidic torsion angles. Combining ab initio derived maps and using the 13C lineshape as constraints we were able to construct the torsion angle distribution map for alpha-alpha' trehalose. We believe measurements of 13C isotropic chemical shift and other solid-state NMR tensor parameter distributions in combination with ab initio methods can prove useful in identifying sources of structural disorder in glassy trehalose. By monitoring these structural distributions new information about the membrane surface associative properties of trehalose and other sugars should be accessible.

Carbohydrate Conformation↗

PubMed1996

Two-dimensional magic-angle spinning isotropic reconstruction sequences for quadrupolar nuclei.

Two-dimensional magic-angle spinning (triple quantum, single quantum) correlation pulse sequences and phase cycles based on the technique of Frydman and Harwood for the reconstruction of the isotropic spectrum of half-integer spin quadrupolar nuclei broadened to second-order are described. These sequences provide pure absorption mode two-dimensional lineshapes and increased sensitivity. Experimental examples on spin I = 3/2 (87Rb in RbNO3) and I = 5/2 (27Al in NaSi3AlO8) are presented. The isotropic chemical shift and quadrupolar coupling parameters could be obtained from a simple analysis of the triple quantum filtered single quantum magic-angle spinning cross-sections.

Absorption↗

PubMed1992

Quantification of the disorder in network-modified silicate glasses.

Local order in silicate glasses has been observed by many experimental techniques to be similar to that in crystalline materials. Details of the intermediate-range order are more elusive, but essential for understanding the lack of long-range symmetry in glasses and the effect of composition on glass structure. Two-dimensional 17O dynamic-angle-spinning nuclear magnetic resonance experiments reveal intermediate-range order in the distribution of inter-tetrahedral (Si-O-Si) bond angles and a high degree of order in the disposition of oxygen atoms around the network-modifying cations.

Glass↗

PubMed1990

Simultaneous contact allergy to neomycin, bacitracin, and polymyxin.

Simultaneous contact allergy to neomycin, bacitracin, and polymyxin was seen in two patients. Although neomycin sensitivity is common, bacitracin and polymyxin are less frequently considered as causes of allergic contact dermatitis. Allergy to all three items simultaneously has not been previously reported.

Adult↗

PubMed1988

High-resolution 13C NMR study of pressure effects on the main phase transition in L-alpha-dipalmitoyl phosphatidylcholine vesicles.

The effects of pressure on the liquid-crystalline to gel transition in vesicles of L-alpha-dipalmitoyl phosphatidylcholine were investigated by high-resolution proton-decoupled natural-abundance 13C NMR spectroscopy. The linewidths of several 13C resonances, including the choline methyl groups, carbonyl carbons, and choline methylene groups and the palmitoyl methyl groups are reported as a function of pressure at 52.7 degrees C. These preliminary NMR experiments clearly demonstrate that high-pressure, high-resolution proton-decoupled natural-abundance 13C NMR spectra are a promising tool to study the phase-transition behavior and the dynamics of model membrane systems.

1,2-Dipalmitoylphosphatidylcholine↗