A new NMR crystallographic approach to reveal the calcium local structure of atorvastatin calcium.

We combine experimental and computational determination of 43Ca solid-state NMR parameters (chemical shift tensors, quadrupolar coupling tensors, and Euler angles) to constrain the structure of the local calcium-ligand coordination environment. A new 43Ca NMR crystallographic approach which includes an extensive survey of the Cambridge Structural Database and a new symmetry benchmark is developed to enhance the selectivity of structural screening. The application of this method to quadrupolar NMR crystallographic investigations is demonstrated by unearthing the calcium local structure of the active pharmaceutical ingredient atorvastatin calcium trihydrate, the active ingredient in Lipitor®, in the absence of diffraction data. This method has been tested by applying it to calcium acetate monohydrate which has a known structure.

Application of Solid-State NMR to Reveal Structural Differences in Cefazolin Sodium Pentahydrate From Different Manufacturing Processes.

Solid-state Nuclear magnetic resonance, thermogravimetric analysis, X-ray diffraction, and Fourier-transform infrared spectroscopy were combined with theoretical calculation to investigate different crystal packings of α-cefazolin sodium obtained from three different vendors and conformational polymorphism was identified to exist in α-cefazolin sodium. Marginal differences observed among cefazolin sodium pentahydrate 1, 2, and 3 were speculated as being caused by the proportion of conformation 2.

Characterization of partially reduced graphene oxide as room temperature sensor for H2.

Reduced graphene oxide (RGO) was synthesized under H(2)/Ar treatment from 100 °C to 900 °C. RGO-300 shows excellent sensitivity to H(2) and a dual sensing mode was observed. The balance between the chemical adsorption capacity and electronic conductivity, and the dominance of either electrons or holes are the key factors.

Measurement of the principal values of the chemical-shift tensors of overlapping protonated and unprotonated carbons with the 2D-SUPER technique and dipolar dephasing (DD-SUPER).

A modified 2D-SUPER technique is demonstrated to allow independent measurement of the principal values of the chemical-shift tensors of overlapping protonated and unprotonated carbons. The insertion of a dipolar-dephasing period into the sequence causes loss of signal from protonated carbons. The spectrum obtained with this modification allows one to determine the principal values of the unprotonated carbons with high precision. Subsequent fitting of the usual 2D-SUPER spectrum, with the chemical-shift parameters of the unprotonated carbons fixed, gives the parameters of the overlapped resonances of the protonated carbons. As an example, we report the determination of the (13)C chemical-shift parameters of the carbons of form II of piroxicam. The experimental results are compared with those obtained from calculations using the DFT/GIAO method. Potential applications of this method are discussed.