Proton transfer and hydrogen bonding in the organic solid state: a combined XRD/XPS/ssNMR study of 17 organic acid-base complexes.

The properties of nitrogen centres acting either as hydrogen-bond or Brønsted acceptors in solid molecular acid-base complexes have been probed by N 1s X-ray photoelectron spectroscopy (XPS) as well as (15)N solid-state nuclear magnetic resonance (ssNMR) spectroscopy and are interpreted with reference to local crystallographic structure information provided by X-ray diffraction (XRD). We have previously shown that the strong chemical shift of the N 1s binding energy associated with the protonation of nitrogen centres unequivocally distinguishes protonated (salt) from hydrogen-bonded (co-crystal) nitrogen species. This result is further supported by significant ssNMR shifts to low frequency, which occur with proton transfer from the acid to the base component.

An example of how to handle amorphous fractions in API during early pharmaceutical development: SAR114137--a successful approach.

The so-called pharmaceutical solid chain, which encompasses drug substance micronisation to the final tablet production, at pilot plant scale is presented as a case study for a novel, highly potent, pharmaceutical compound: SAR114137. Various solid-state analytical methods, such as solid-state Nuclear Magnetic Resonance (ssNMR), Differential Scanning Calorimetry (DSC), Dynamic Water Vapour Sorption Gravimetry (DWVSG), hot-stage Raman spectroscopy and X-ray Powder Diffraction (XRPD) were applied and evaluated to characterise and quantify amorphous content during the course of the physical treatment of crystalline active pharmaceutical ingredient (API). DSC was successfully used to monitor the changes in amorphous content during micronisation of the API, as well as during stability studies.

Crystallography aided by atomic core-level binding energies: proton transfer versus hydrogen bonding in organic crystal structures.

Ionic bond or hydrogen bridge? Brønsted proton transfer to nitrogen acceptors in organic crystals causes strong N1s core-level binding energy shifts. A study of 15 organic cocrystal and salt systems shows that standard X-ray photoelectron spectroscopy (XPS) can be used as a complementary method to X-ray crystallography for distinguishing proton transfer from H-bonding in organic condensed matter.

Identification of protonation state by XPS, solid-state NMR, and DFT: characterization of the nature of a new theophylline complex by experimental and computational methods.

Recent studies suggested that X-ray photoelectron spectroscopy (XPS) sensitively determines the protonation state of nitrogen functional groups in the solid state, providing a means for distinguishing between co-crystals and salts of organic compounds. Here we describe how a new theophylline complex with 5-sulfosalicylic acid dihydrate was established as a salt by XPS prior to assignment with conventional methods. The presence of a C=NH(+) (N9) N1s peak in XPS allows assignment as a salt, while this peak is clearly absent for a theophylline co-crystal.

Salt or co-crystal? Determination of protonation state by X-ray photoelectron spectroscopy (XPS).

Combined (15)N ssNMR and X-ray photoelectron spectroscopy (XPS) investigations for theophylline, a theophylline co-crystal, and a theophyllinium salt demonstrate that XPS allows direct observation of the degree of proton transfer, and thus identification of whether a salt or a co-crystal has been formed. The presence of a strongly binding-energy-shifted N 1s XPS peak with protonation indicates a salt (C==NH(+)), while this peak is unmistakably absent in the co-crystal. XPS should be considered as an alternative and complementary technique to single crystal X-ray diffraction and solid-state nuclear magnetic resonance spectroscopy (ssNMR).

Detection of free base surface enrichment of a pharmaceutical salt by X-ray photoelectron spectroscopy (XPS).

Yellow discoloration was observed at the surface of normally white crystals of a development pharmaceutical fumarate salt, tentatively ascribed to the presence of trace amounts of free base. The impact of impurities on sample properties and behavior can be significant, especially if localized at the surface. No conventional bulk analytical technique could readily provide an explanation for the yellow color, so a surface-sensitive technique, X-ray photoelectron spectroscopy (XPS), was employed to characterize the salt.

Studies on the crystallinity of a pharmaceutical development drug substance.

The crystallinity and amorphous content of a micronized pharmaceutical development drug substance have been independently determined. An evaluation of different techniques for this purpose has been carried out, and it was found that solid-state nuclear magnetic resonance (ss NMR) and X-ray powder diffraction (XRPD) were suitable for the former and latter, respectively. The baseline intensities of X-ray powder diffractograms, associated with the amorphous component of the sample, have been used to detect levels of non-crystalline material greater than 5%w/w with an absolute accuracy of +/-3%.