Study of Water Adsorption on Organics Crystal Surfaces Using a Modified X-ray Photoelectron Spectroscopy Instrument

Abstract

The coupling of a high partial pressure water vapor system to a conventional X-ray photoelectron spectroscopy instrument for use with both organic powders and single crystals is described. The modified chamber serves a dual purpose as both a treatment and sample preparation apparatus. The design utilizes the high- and cryo-temperature capabilities of the existing system to allow investigation of various states of surface water, as well as the interplay between temperature, water, and surface structure of the substrate. Sample handling and methods for compatibility testing are detailed, and data illustrating the application of the modified and integrated capabilities are summarized, detailing novel studies on the state of water on the surface of model organic pharmaceutical salts. In addition to facilitating investigation of the presence of various states of water at the surface of organic material, namely, dissociated versus molecular water, the setup allows the investigation of structural effects of the surface on the state of water.

Spectroscopic Study of Water Adsorption and Desorption on/from Oligo(ethylene glycol)-Substituted Alkanethiolate Self-Assembled Monolayers

“…On the side of experiment, a variety of different tools are used, including surface force apparatus, , optical methods (infrared and Raman spectroscopy, ellipsometry, etc. ), − classical methods of surface science such as temperature-programmed desorption (TPD), and so forth, − X-ray scattering, ,, neutron scattering, X-ray spectroscopy, − and so forth. As far as well-defined organic or biology-relevant surface is required, it is frequently mimicked by molecular self-assembly on a solid support.…”

Acid–Base Interactions of Polystyrene Sulfonic Acid in Amorphous Solid Dispersions Using a Combined UV/FTIR/XPS/ssNMR Study

“…Thus, the XPS technique has not been widely applied to drug analysis. However, XPS was successfully used to show the susceptibility of hydrochloride pharmaceutical salts to water-induced dissociation at the surface. , XPS was also critical to characterize the surface chemistry of peptide modified sol–gel thin films. − Recently, several studies have indicated the potential of XPS for exploring intermolecular drug–polymer interactions . Of particular interest is the high sensitivity of XPS for the detection of the degree of proton transfer in acid–base systems by measuring the BE shift of the involved atoms. , For example, a strong N 1s shift of +2 eV toward higher BEs has been observed for both the protonation of an aromatic nitrogen in theophylline as well as the protonation of the aliphatic nitrogen in piperidine groups …”

“…However, XPS was successfully used to show the susceptibility of hydrochloride pharmaceutical salts to water-induced dissociation at the surface. 22,23 XPS was also critical to characterize the surface chemistry of peptide modified sol−gel thin films. 24−26 Recently, several studies have indicated the potential of XPS for exploring intermolecular drug−polymer interactions.…”