Dewey H. Barich

Fitting of low-intensity wide-line spectra dominated by chemical shift anisotropy

How experimental parameters affect the appearance, and consequently the fitting, of signals having very wide lines is discussed. As these spectra usually have very low intensities, pulse sequences that remove acoustic ringing and other experimental artefacts have to be used. These pulse sequences introduce further spectral distortions. A FORTRAN 77 program was developed that accounts for these effects. The fitting of these broad spectra is demonstrated by application to 207Pb solid-state nuclear magnetic resonance (NMR) spectra.

Probing acid sites in MAPO-36 by solid state NMR

An ordering of magnesium is observed in the as-synthesized MAPO-36 molecular sieve. Upon calcination, part of the magnesium is removed from the sample and part occupies extraframework positions thus rendering a random distribution of magnesium in the lattice. The shoulder observed in the31P spectrum of the calcined sample is assigned to P(3Al, 1Mg) sites in conflict with the earlier assignment to P-OH groups. The bridging hydroxyl groups located at these sites are detected in the1H MAS spectrum at 3.6 ppm. Further, MAPO-36 catalyzed acetone conversion to mesityloxide that cracked at elevated temperature to yield acetic acid and aliphatics.

Modeling of Benzene Adsorption in Metal‐Exchanged Zeolites by Calculation of 7Li Chemical Shifts

A 1:1 complex between Li+ and benzene is formed when benzene is adsorbed into a Li-exchanged zeolite. This was the result of calculations of the 7 Li chemical shifts for several model complexes, including Li+ ⋅2 H2 O⋅C6 H6 (depicted). After 13 C and 2 H, 7 Li is a further nucleus that can be studied to determine the structure and dynamics of complexes formed between organic species and metal cations in zeolites.

Erratum to: The Stabilizing Effect of Moisture on the Solid-State Degradation of Gabapentin

Erratum to: AAPS PharmSciTech DOI 10.1208/s12249-011-9652-8 ACKNOWLEDGEMENTS We are grateful to the National Institute for Pharmaceutical Technology and Education (NIPTE) and the U.S. Food and Drug Administration (FDA) for providing funds for this research. This study was funded by the FDA-sponsored contract “Development of Quality by Design (QbD) Guidance Elements on Design Specifications across Scales with Stability Considerations” (contract number HHSF223200819929C).

2,4-dimethoxybenzoic acid and 2,5-dimethoxybenzoic acid.

The title compounds (both C(9)H(10)O(4)) have nearly planar structures, and the methyl and/or carboxylic acid groups lie out of the molecular plane, as dictated by steric interactions. 2,5-Dimethoxybenzoic acid (2,5-DMBA) forms an unusual intramolecular hydrogen bond between the carboxylic acid group and the O atom of the methoxy group in the 2-position [O.O = 2.547 (2) A and O-H.O = 154 (3) degrees ]. 2,4-DMBA forms a typical hydrogen-bond dimer with a neighboring molecule.