Biomedical subjects

Kevin J Pike

Publications and source records attributed to Kevin J Pike.

10 recordsLinked to original sources

PubMed2006

Solid-state NMR and EXAFS spectroscopic characterization of polycrystalline copper(I) O,O'-dialkyldithiophosphate cluster compounds: Formation of copper(I) O,O'-diisobutyldithiophosphate compounds on the surface of synthetic chalcocite.

A number of polycrystalline copper(I) O,O'-dialkyldithiophosphate cluster compounds with Cu4, Cu6, and Cu8 cores were synthesized and characterized by using extended X-ray absorption fine-structure (EXAFS) spectroscopy. The structural relationship of these compounds is discussed. The polycrystalline copper(I) O,O'-diisobutyldithiophosphate cluster compounds, [Cu8{S2P(OiBu)2}6(S)] and [Cu6{S2P(OiBu)2}6], were also characterized by using 31P CP/MAS NMR (CP = cross polarization, MAS = magic-angle spinning) and static 65Cu NMR spectroscopies (at different magnetic fields) and powder X-ray diffraction (XRD) analysis. Comparative analyses of the 31P chemical-shift tensor, and the 65Cu chemical shift and quadrupolar-splitting parameters, estimated from the experimental NMR spectra of the polycrystalline copper(I) cluster compounds, are presented. The adsorption mechanism of the potassium O,O'-diisobutyldithiophosphate collector, K[S2P(OiBu)2], at the surface of synthetic chalcocite (Cu2S) was studied by means of solid-state 31P CP/MAS NMR spectroscopy and scanning electron microscopy (SEM). 31P NMR resonance lines from collector-treated chalcocite surfaces were assigned to a mixture of [Cu8{S2P(OiBu)2}6(S)] and [Cu6{S2P(OiBu)2}6] compounds.

Journal Article↗

PubMed2006

New limits for solid-state 17O NMR spectroscopy: complete resolution of multiple oxygen sites in a simple biomolecule.

A solid-state 17O NMR 1H-decoupled double angle rotation (DOR) study of monosodium l-glutamate monohydrate (l-MSG) is reported. It is shown that all eight inequivalent sites can be resolved with DOR line widths ( approximately 65 Hz) approximately 120 times narrower than those in the MAS spectrum. The lines are tentatively assigned on the basis of their behavior under proton decoupling and the isotropic chemical shift and the quadrupole interaction parameter for each extracted by a combination of DOR and 3Q MAS at variable magnetic fields. With a shift range of approximately 45 ppm for these similar oxygen sites and spectral resolution under DOR comparable to that for spin-1/2 nuclei, solid-state 17O NMR should have tremendous potential in the study of biomolecules.

Binding Sites↗

PubMed2006

Experimental and theoretical 17O NMR study of the influence of hydrogen-bonding on C=O and O-H oxygens in carboxylic solids.

A systematic solid-state 17O NMR study of a series of carboxylic compounds, maleic acid, chloromaleic acid, KH maleate, KH chloromaleate, K2 chloromaleate, and LiH phthalate.MeOH, is reported. Magic-angle spinning (MAS), triple-quantum (3Q) MAS, and double angle rotation (DOR) 17O NMR spectra were recorded at high magnetic fields (14.1 and 18.8 T). 17O MAS NMR for metal-free carboxylic acids and metal-containing carboxylic salts show featured spectra and demonstrate that this combined, where necessary, with DOR and 3QMAS, can yield site-specific information for samples containing multiple oxygen sites. In addition to 17O NMR spectroscopy, extensive quantum mechanical calculations were carried out to explore the influence of hydrogen bonding at these oxygen sites. B3LYP/6-311G++(d,p) calculations of 17O NMR parameters yielded good agreement with the experimental values. Linear correlations are observed between the calculated 17O NMR parameters and the hydrogen bond strengths, suggesting the possibility of estimating H-bonding information from 17O NMR data. The calculations also revealed intermolecular H-bond effects on the 17O NMR shielding tensors. It is found that the delta11 and delta22 components of the chemical shift tensor at O-H and C=O, respectively, are aligned nearly parallel with the strong H-bond and shift away from this direction as the H-bond interaction weakens.

Carboxylic Acids↗

PubMed2005

Solid-state 31P CP/MAS and static 65Cu NMR characterization of polycrystalline copper(I) dialkyldithiophosphate clusters.

Polycrystalline tetra-nuclear Cu4[S2P(O-i-C3H7)2]4, hexa-nuclear Cu6[S2P(OC2H5)2]6, and octa-nuclear Cu8[S2P(O-i-C4H9)2]6(S) complexes were synthesized and analyzed by means of solid-state 31P CP/MAS and 65Cu static NMR spectroscopy. The symmetries of the electronic environments around each P-site were estimated from the 31P chemical shift anisotropy (CSA) parameters, Deltaaniso and eta. The 65Cu chemical shift and quadrupolar splitting parameters obtained from the experimental 65Cu NMR spectra of the polycrystalline Cu(I)-complexes are presented. A solid-state NMR approach for the elucidation of the stereochemistry of poly-nuclear Cu(I) dithiophosphate complexes, when the structural analysis of the systems by single-crystal X-ray diffraction is not readily available, is proposed.

Journal Article↗

PubMed2005

Multiple-magnetic field 139La NMR and density functional theory investigation of the solid lanthanum(III) halides.

Results from a solid-state 139La NMR spectroscopic investigation of the anhydrous lanthanum(III) halides (LaX3; X=F, Cl, Br, I) at applied magnetic fields of 7.0, 9.4, 11.7, 14.1, and 17.6 T are presented and highlight the advantages of working at high applied magnetic field strengths. The 139La quadrupolar coupling constants are found to range from 15.55 to 24.0 MHz for LaCl3 and LaI3, respectively. The lanthanum isotropic chemical shifts exhibit an inverse halogen dependence with values ranging from -135 ppm for LaF3 to 700 ppm for LaI3, which represents nearly half of the total lanthanum chemical shift range. The spans of the magnetic shielding tensors also vary widely, from 35 to 650 ppm for the solid LaF3 through LaI3. DFT calculations of the 139La electric field gradient and magnetic shielding tensors have been performed and provide a qualitative interpretation of the trends observed experimentally.

Journal Article↗

PubMed2005

Combined first-principles computational and experimental multinuclear solid-state NMR investigation of amino acids.

13C, 14N, 15N, 17O, and 35Cl NMR parameters, including chemical shift tensors and quadrupolar tensors for 14N, 17O, and 35Cl, are calculated for the crystalline forms of various amino acids under periodic boundary conditions and complemented by experiment where necessary. The 13C shift tensors and 14N electric field gradient (EFG) tensors are in excellent agreement with experiment. Similarly, static 17O NMR spectra could be precisely simulated using the calculation of the full chemical shift (CS) tensors and their relative orientation with the EFG tensors. This study allows correlations to be found between hydrogen bonding in the crystal structures and the 17O NMR shielding parameters and the 35Cl quadrupolar parameters, respectively. Calculations using the two experimental structures for L-alanine have shown that, while the calculated isotropic chemical shift values of 13C and 15N are relatively insensitive to small differences in the experimental structure, the 17O shift is markedly affected.

Amino Acids↗

PubMed2005

Formation of {Cu6[S2P(OC2H5)2]6} on Cu2S surfaces from aqueous solutions of the KS2P(OC2H5)2 collector: scanning electron microscopy and solid-state 31P cross-polarization/magic angle spinning and static 65Cu NMR studies.

The interactions of synthetic chalcocite surfaces with diethyldithiophosphate, potassium salt, K[S2P(OC2H5)2], were studied by means of 31P cross-polarization/magic angle spinning (CP/MAS) NMR spectroscopy and scanning electron microscopy (SEM). To identify the species formed on the Cu2S surfaces, a polycrystalline {CuI6[S2P(OC2H5)2]6} cluster was synthesized and analyzed by SEM, powder X-ray diffraction techniques and solid-state 31P CP/MAS NMR and static 65Cu NMR spectroscopy. 31P chemical shift anisotropy (CSA) parameters, delta(cs) and eta(cs), were estimated and used for assigning the bridging type of diethyldithiophosphate ligands in the {CuI6[S2P(OC2H5)2]6} cluster. The latter data were compared to 31P CSA parameters estimated from the spinning sideband patterns in 31P NMR spectra of the collector-treated mineral surfaces: formation of polycrystalline {CuI6[S2P(OC2H5)2]6} on the Cu2S surfaces is suggested. The second-order quadrupolar line shape of 65Cu was simulated, and the NMR interaction parameters, CQ and etaQ, for the copper(I) diethyldithiophosphate cluster were obtained.

Journal Article↗

PubMed2005

Solid state 31P and 207Pb MAS NMR studies on polycrystalline O,O'-dialkyldithiophosphate lead(II) complexes.

A number of lead(II) O,O'-dialkyldithiophosphate complexes were studied by (13)C, (31)P, and (207)Pb MAS NMR. Simulations of (31)P chemical shift anisotropy using spinning sideband analysis reveal a linear relationship between the SPS bond angle and the principal values delta(22) and delta(33) of the (31)P chemical shift tensor. The (31)P CSA data were used to assign ligands with different structural functions. In the cases of diethyldithiophosphate and di-iso-butyldithiophosphate lead(II) complexes, (2)J((31)P, (207)Pb)-couplings were resolved and used to confirm the suggested assignment of the ligands. The SIMPSON computer program was used to calculate (31)P and (207)Pb spectral sideband patterns.

Journal Article↗

PubMed2003

Efficient 5QMAS NMR of spin-5/2 nuclei: use of fast amplitude-modulated radio-frequency pulses and cogwheel phase cycling.

We report here an efficient multiple-quantum magic-angle spinning (MQMAS) pulse sequence involving fast amplitude-modulated (FAM) radio-frequency pulses for excitation and conversion of five-quantum (5Q) coherences of spin-5/2 nuclei. The use of a FAM-I type pulse train for the conversion of 5Q into 1Q coherences proves to be easier to implement experimentally than the earlier suggested use of a FAM-II type sequence [J. Magn. Reson. 154 (2002) 280], while delivering at least equal signal enhancement. Results of numerical simulations and experimental 27Al 5QMAS spectra of aluminium acetylacetonate for different excitation and conversion schemes are compared to substantiate these claims. We also demonstrate the feasibility of acquiring 5QMAS spectra of spin-5/2 systems using cogwheel phase cycling [J. Magn. Reson. 155 (2002) 300] to select the desired coherence pathways. A cogwheel phase cycle of only 57 steps is shown to be as effective as the minimum conventional nested 77-step phase cycle.

Journal Article↗

PubMed2003

Application of amplitude-modulated radiofrequency fields to the magic-angle spinning NMR of spin-7/2 nuclei.

We report pulse sequences for the sensitivity enhancement of magic-angle spinning and multiple-quantum magic-angle spinning spectra of spin-72 systems. Sensitivity enhancement is obtained with the use of fast amplitude-modulated (FAM) radiofrequency pulses. In one-dimensional magic-angle spinning experiments, signal enhancement of 3 is obtained by a FAM pulse followed by a soft 90 degrees pulse. In two-dimensional multiple-quantum magic-angle spinning experiments, FAM pulses are used for both the excitation of multiple-quantum coherences and for their conversion into observable single-quantum coherences. The observed signal enhancements are 2.2 in 3Q experiments, 3.1 in 5Q experiments, and 4.1 in 7Q experiments, compared to the conventional two-pulse scheme. The pulse schemes are demonstrated on the 45Sc NMR of Sc2(SO4)3 x 5H2O and the 139La NMR of LaAlO3. We also demonstrate the generation of FAM pulses by double-frequency irradiation.

Journal Article↗