James S. Frye

Setting the magic angle using a quadrupolar nuclide

Quadrupolar nuclei yield Fourier transform magic-angle spinning NMR spectra exhibiting many spinning sidebands. The widths and the intensities of the sidebands are very sensitive functions of the angle the spinning axis makes with the magnetic field. This dependence can be used in adjusting the spinning angle at least to within ± 0.1° of the magic angle. In particular, the 79Br signal from powdered KBr is especially convenient for monitoring the angle in 13C MAS experiments. Large (approximately 3 mm) crystals of KBr offer greater sensitivity to angle, but are less convenient to use than powder. NaBr, KBrO3, and K55MnO4 were also tested and found to be less suitable as angle markers than is KBr.

13C NMR spectroscopy of the insoluble carbon of carbonaceous chondrites

13C NMR spectra have been obtained of the insoluble carbon residues resulting from HF-digestion of three carbonaceous chondrites, Orgueil (C1), Murchison (CM2), and Allende (CV3). Spectra obtained using the cross polarization magic-angle spinning technique show two major features attributable respectively to carbon in aliphatic/olefinic structures. The spectrum obtained from the Allende sample was weak, presumably as a consequence of its low hydrogen content. Single pulse excitation spectra, which do not depend on 1H-13C polarization transfer for signal enhancement were also obtained. These spectra, which may be more representative of the total carbon in the meteorite samples, indicate a greater content of carbon in aromatic/olefinic structures. These results suggest that extensive polycyclic aromatic sheets are important structural features of the insoluble carbon of all three meteorites. The Orgueil and Murchison materials contain additional hydrogenated aromatic/olefinic and aliphatic groups.

Carbon functionalities in amber.

High-resolution nuclear magnetic resonance spectra of the carbon nuclei in powdered amber, obtained by using the techniques of magic angle spinning and cross polarization, provide detailed information about the types of carbon functionalities. The entire spectrum of Baltic amber (succinite) is identical for several samples. Baltic amber shows minor differences from Sicilian amber and drastic differences from Burmese, Romanian, and Bohemian ambers.

The structure of coprecipitated aluminophosphate catalyst supports

Porous aluminophosphates, which are useful as catalyst supports for polymerization, isomerization, or other hydrocarbon conversions, can be made by coprecipitation when an acidic solution of A13+ and PO43− ions is neutralized. When the PAl ratio in solution is equal to or greater than one, A1PO4 is obtained often as a crystalline material, leaving the excess phosphate in solution. However, when excess Al3+ is present in solution (PAl < 1) then it also precipitates and the resulting support retains a similar PAl ratio to that in solution. In this study the structure of such aluminophosphates has been examined by means of X-ray diffraction and high resolution solid state NMR spectroscopy using both 27Al and 31P nuclei. These materials are not simple coprecipitated mixtures of A12O3 and A1PO4. In fact, no evidence for the presence of either species was detected. Instead they appear to be amorphous structures in which the phosphate is randomly dispersed, and the aluminum exists in one octahedral and several different tetrahedral environments. Results from ethylene polymerization over these catalysts also support this view.

Organic geochemical analysis of sedimentary organic matter associated with uranium

Abstract Samples of sedimentary organic matter from several geologic environments and ages which are enriched in uranium (56 ppm to 12%) have been characterized. The three analytical techniqyes used to study the samples were Rock-Eval pyrolysis, pyrolysis-gas chromatography-mass spectrometry, and solid-state C-13 nuclear magnetic resonance (NMR) spectroscopy. In samples with low uranium content, the pyrolysis-gas chromatography products contain oxygenated functional groups (as hydroxyl) and molecules with both aliphatic and aromatic carbon atoms. These samples with low uranium content give measurable Rock-Eval hydrocarbon and organic-CO 2 yields, and C-13 NMR values of > 30% aliphatic carbon. In contrast, uranium-rich samples have few hydrocarbon pyrolysis products, increased Rock-Eval organic-CO 2 contents and > 70% aromatic carbon contents from C-13 NMR. The increase in aromaticity and decrease in hydrocarbon pyrolysis yield are related to the amount of uranium and the age of the uranium minerals, which correspond to the degree of radiation damage. The three analytical techniques give complementary results. Increase in Rock-Eval organic-CO 2 yield correlates with uranium content for samples from the Grants uranium region. Calculations show that the amount of organic-CO 2 corresponds to the quantity of uranium chemically reduced by the organic matter for the Grants uranium region samples.

31P solid-state nuclear magnetic resonance spectroscopy of aluminum phosphate minerals

This study examines the links between 31P solidstate NMR studies of aluminum phosphate minerals and their crystallographic structures. We found that 31P isotropic chemical shift values, δiso, carry little information about mineral structures. There seems to be no relation between the chemical shift anisotropy, Δδ=δ33−δ11 (δ33>δ22> δ11), and indicies of phosphate-tetrahedra distortion. 31P1H heteronuclear magnetic dipole interactions, on the other hand, carry important information about hydrous phosphate mineral structures, information that should prove to be quite valuable in studies of phosphate adsorbed on mineral surfaces. This interaction can be measured through a variety of qualitative and quantitative experiments. It appears that spin diffusion is so rapid that subtle differences in hydrogen-bonding environments cannot be resolved.

Crystal structures vibrational 31p NMR studies of complexes of tertiary phosphine ligands with mercury(II) halides

Abstract The mercury(II) phosphine complexes (R 3 P) 2 HgX 2 (R 3 P = PPh 3 , PEt 3 , 1-phenyldibenzophosphole (DBP), 1-phenyl-3, 4-dimethylphosphole (DMPP); X = Cl, Br, I and PBu 3 ; X = Cl) have been prepared and their solution and solid state structures determined by a combination of elemental analyses, IR, Raman NMR spectroscopy. The structures of (DBP) 2 HgBr 2 ( 1 ), (PPh 3 ) 2 Hg 2 Br 4 ( 2 ), (DMPP) 2 Hg 2 I 4 ( 3 ) and (Bu 3 P) 2 Hg 2 I 4 ( 4 ) have been determined from three-dimensional X-ray data collected by counter methods. Compound 1 crystallizes in space group P 1 with a = 10.568(6), b = 17.390(6), c = 9.610(3) A, α = 106.02(4), β = 100.62(4), γ = 101.41(5)° and Z = 2. Compound 2 crystallizes in space group P 2 1 / a with a = 18.619(7), b = 10.938(4), c = 18.762(5) A, β = 90.36(2)° and Z = 4. Compound 3 crystallizes in space group Pbc 2 1 with a = 8.516(4), b = 19.404(7), c = 19.545(6) A and Z = 4. Compound 4 crystallizes in space group P 2 1 / c with a = 16.450(16), b = 20.609(21), c = 24.263(31) A, β = 109.38(8)° and Z = 8. Compound 1 deviates from ideal C 2 symmetry having slightly different HgBr (2.618(2), 2.604(2) A) and HgP (2.513(3), 2.490(3) A bond distances. The inequivalence of the phosphines is manifested as a second order ABX CP/MAS 31 P{ 1 H} NMR spectrum for 1 . Compound 2 is a symmetric doubly bromide bridged dimer with essentially equivalent HgP (2.40(2), 2.44(2) A) bond distances but its CP/MAS 31 P{ 1 H} NMR spectrum displays two AX resonances, showing that the phosphines are not magnetically equivalent. Compound 3 is a symmetric, doubly iodide bridged dimer having slightly different HgP (2.437(7), 2.470(7) A) bond distances displays three AX resonances in its CP/MAS 31 P{ 1 H} NMR spectrum. Compound 4 is an unsymmetrical doubly iodide bridged dimer [(Bu 3 P) 2 HgI 2 HgI 2 ] having equivalent HgP (2.393(21), 2.391(22) A bond lengths but its CP/MAS 31 P{ 1 H} NMR spectrum shows two ABX resonances arising from the two different molecules in the unit cell with the phosphines being magnetically inequivalent in each molecule. Variable temperature 31 P NMR spectroscopy shows that equilibria between monomeric (R 3 P) 2 HgX 2 and dimeric [R 3 PHgX 2 ] 2 occur in solution for R 3 P = DMPP and Bu 3 P the dimers are very easily formed from the monomers.

31P and 27Al solid-state nuclear magnetic resonance study of taranakite

High-resolution 27Al solid-state nuclear magnetic resonance (NMR) spectroscopy indicates that aluminum in taranakite is probably restricted to six-coordinate sites. High-resolution 31P solid-state NMR spectroscopy reveals that phosphate groups exist in two environments in taranakite. The rate of 1H-induced dipolar dephasing of the 31P signals in cross-polarization, magic-angle-spinning NMR spectra of taranakite suggests that one or more oxygens of one of two phosphates are directly protonated. The same experiments suggests that the oxygens of the second form of phosphate are not directly protonated but may be hydrogen-bond receptors. The ratio of protonated phosphate to non-protonated phosphate, as measured from 31P single-pulse excitation, magic-angle-spinning spectra, is approximately one to three.

Effects of unsaturation on 2H-NMR quadrupole splittings and 13C-NMR relaxation in phospholipid bilayers

Motional order and motional rates in unsonicated phospholipid bilayers were assessed as a function of unsaturation of the phospholipid. A measurement sensitive to motional order was obtained using 2H-NMR of 18:1, 18:1-phosphatidylcholine labelled at positions 9 and 10 with deuterium and included as a probe in phospholipid bilayers of interest at 10 mole percent. Spin lattice relaxation times from magic angle spinning 13C-NMR spectra of phospholipid dispersions of interest were used as a measure of motional rates. Measurements were made of phospholipid bilayers containing from 0 to 8 double bonds per molecule. No large effect of an increase in unsaturation was noted for the 2H-NMR quadrupole splittings or for the 13C-NMR spin lattice relaxation rate.

27Al Solid-state nuclear magnetic resonance study of five-coordinate aluminum in augelite and senegalite

This is a report of 27Al magic-angle spinning, nuclear magnetic resonance spectroscopy of 5- and 6-coordinate aluminum in the aluminophosphate minerals augelite and senegalite. We have determined the quadrupolar coupling constants, asymmetry parameters and chemical shifts corrected for quadrupolar-induced shift for both aluminum coordination sites in each mineral. The quadrupolar coupling constants are significantly less in senegalite than in augelite. Structural analysis (viz., longitudinal- and shear-strain of the aluminum coordination polyhedra; coefficient-of-variation for both Al-O bond lengths and <O-Al-O bond angles) shows that both 5- and 6-coordinate aluminum sites in senegalite are less distorted than in augelite.