Biomedical subjects

Sam Motherwell

Publications and source records attributed to Sam Motherwell.

3 recordsLinked to original sources

PubMed2005

Searching the Cambridge Structural Database for polymorphs.

In order to identify all pairs of polymorphs in the Cambridge Structural Database (CSD), a method was devised to automatically compare two crystal structures. The comparison is based on simulated powder diffraction patterns, but with special provisions to deal with differences in unit-cell volumes caused by temperature or pressure. Among the 325,000 crystal structures in the Cambridge Structural Database, 35,000 pairs of crystal structures of the same chemical compound were identified and compared. A total of 7300 pairs of polymorphs were identified, of which 154 previously were unknown.

Algorithms↗

PubMed2004

A molecular dynamics simulation of the melting points and glass transition temperatures of myo- and neo-inositol.

The heat of sublimation, density, melting point, and glass transition temperature are calculated for myo- and neo-inositol, using the condensed-phase optimized molecular potentials for atomistic simulation studies (COMPASS) force field and molecular dynamics techniques. Our results show that the calculated heats of sublimation and density are very close to the experimental values for both compounds. Furthermore, our simulated melting temperatures for myo- and neo-inositol also compare very well to the experimentally obtained data. The glass transition temperatures for myo- and neo-inositol have been calculated to be ca. 494 K and ca. 518 K, respectively, and the shape of the volume versus temperature plots produced are typical for a glass transition. As a result, it is our view that the COMPASS force field suitably describes these two compounds in molecular simulations and that molecular dynamics techniques, combined with this force field, can be used to simulate the melt and glass transitions for such molecules.

Journal Article↗

PubMed2003

Structure of a 4-nitroso-5-aminopyrazole and its salts: tautomerism, protonation, and E/Z isomerism.

The structures of 1-benzyl-4-nitroso-5-aminopyrazole (1) and its hydrochloride (1H+) have been determined in the solid state and in solution in DMSO, methanol, and ethanol. The free base exists in solution as a mixture of amino/nitroso tautomers 2a and 2b rather than in the imino/oxime tautomers 3. The conjugated cation 1H+ results from the protonation of the nitroso group. X-ray crystallography showed that both amino hydrogen atoms of 2a form NH...O=N hydrogen bonds: one is intramolecular, the other links adjacent molecules in an infinite chain.

Journal Article↗