Klaus Eichele:
Publication Abstracts 1993

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[UP] K. Eichele, M. D. Lumsden, R. E. Wasylishen:
Nitrogen-14 Coupled Dipolar-Chemical Shift 13C NMR Spectra of the Amide Fragment of Peptides in the Solid State.
J. Phys. Chem. 1993, 97, 8909-8916.

Carbon-13 NMR spectra of solid samples of acetanilide-13C(CO) have been examined under conditions of cross-polarization (CP) with and without magic-angle spinning (MAS). The 13C NMR line shapes are perturbed by direct dipolar coupling to the adjacent quadrupolar 14N nucleus. The 13C NMR spectra have been fully analyzed employing first-order perturbation theory for 14N. Residual 13C,14N splittings observed in the 13C CP/MAS NMR spectra of the carbonyl and Ca region of acetanilide indicate an upper limit of the 14N nuclear quadrupolar coupling constant of -3.2 MHz. The largest component of the electric field gradient (EFG) tensor at 14N is oriented perpendicular to the amide plane, while the smallest component lies in the amide plane about 20 deg off the N-H bond axis toward Ca. This orientation of the EFG tensor at nitrogen is in excellent agreement with that calculated using MO theory. Carbon-13 NMR spectra of static samples of acetanilide-13C(CO) exhibit typical 14N dipolar coupled chemical shift powder line shapes similar to those observed for the amide fragment in peptides. Asymmetric 14N,13C dipolar splittings are apparent in the d11 region of the powder pattern, but symmetrical splittings are observed at d33, while the splittings at d22 are not resolved. Analysis of the static 13C NMR spectrum yields the magnitudes and orientations of the principal components of the carbonyl carbon chemical shift tensor. The most shielded component, d33, is perpendicular to the amide plane, while the least shielded component is oriented 30 deg off the C-N bond vector toward Ca. In contrast to the MAS spectra, the static spectrum is found to be insensitive to the magnitude and orientation of the 14N EFG tensor, contrary to previous reports. The origin of the asymmetric 14N,13C dipolar splittings observed in the 13C NMR spectra of static samples of acetanilide and the amide fragment of peptides is discussed in detail.

 
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[UP] K. L. Moran, T. E. Gier, W. T. A. Harrison, G. D. Stucky, H. Eckert, K. Eichele, R. E. Wasylishen:
Synthesis and Characterization of Mixed ZnSe/GaP Semiconductor Species Included in the Sodalite Structure.
J. Am. Chem. Soc. 1993, 115, 10553-10558.

The synthesis of the solid solution series GaxZn8-xPxSe(2-x)[BO2]12 (x = 0, 0.5, 1, 2) is reported and the local and average long-range structure are discussed based on X-ray diffraction data, UV/visible spectroscopic measurements, and a variety of field-dependent static and magic-angle spinning solid-state NMR experiments. Inclusion of GaP within the borate sodalite analogue results in the formation of an isolated P-31,Ga-69/71 spin pair that exhibits resolved scalar coupling in the P-31 MAS NMR spectra. The analysis reveals that there are four different intracage structures distributed in small domains throughout the powdered materials and these are identified as [Zn4Se]6+, [GaZn3P]6+, [Zn4P]5+ and, by inference, [Ga2Zn2P]7+. P-31 spin diffusion experiments suggest that the materials are single phase solid solutions, and powder X-ray diffraction data, which do not reveal more than one phase for any composition, support this conclusion.


[UP] K. Eichele, R. E. Wasylishen, J. F. Corrigan, S. Doherty, Y. Sun, A. J. Carty:
Observations of 1J(P,Ru) in 31P CP/MAS NMR Spectra of Solid Ruthenium Compounds.
Inorg. Chem. 1993, 32, 121-123.

Values for the indirect, one-bond spin-spin coupling constants J (Ru-101,99, P-31) involving the quadrupolar ruthenium nuclei Ru-101,99 (S = 5/2) and P-31 have been measured for the first time via analysis of the satellite structure in the P-31 CP/MAS spectra of the solid complexes all-trans-Ru(PEt3)2(CO)2(CC-Ph)2 (1) and (m-H)Ru4(CO)10(m-PPh2)[m4-PPh(C6H4)] (2). The P-31 CP/MAS spectrum of 1 with satellites expanded is illustrated. Values of J(Ru-99,P-31) lie in the range 105-159 Hz for 1 and 2, and J(Ru-101,P-31) lies in the range 145-174 Hz for 2. The parameters J and d (the residual dipolar coupling) are potentially useful probes of structure and bonding in solid ruthenium complexes.


[UP] K. Eichele, G. Wu, R. E. Wasylishen:
Unusual "AB" Spectra in High-Resolution Magic-Angle Spinning NMR Studies of Solids.
J. Magn. Reson. 1993, A101, 157-161.

Phosphorus-31 CP-MAS spectra of Cd(NO3)2(PPh3)2 have been obtained as a function of spinning frequency. Although the two P-31 nuclei are crystallographically equivalent and have the same isotropic chemical shifts in the solid state, they exhibit spinning-rate-dependent MAS spectra which have been analyzed to obtain the value of 2J(P,P). At high spinning rates, the spectra are analogous to "A2" spectra in isotropic solutions, while at slower spinning rates, the spectra are more characteristic of strongly coupled "AB" solution spectra. The AB spectra are unusual in that d(A) = d(B) and J(A,B) is given by the splitting between the alternate peaks in the four-peak multiplet as opposed to the splitting between the outer and adjacent inner lines. This assignment was confirmed by a 2D CP-MAS J-resolved experiment. The unusual spinning-rate-dependent MAS line shapes result from recoupling of the J interaction between the two crystallographically equivalent nuclei via anisotropic interactions, i.e., weak homonuclear dipolar coupling and differences in the orientation dependence of the chemical-shift tensors. Such spinning-rate-dependent MAS line shapes are predicted to be a more frequent observation at higher applied magnetic fields.


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