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W D Samuel Motherwell

Publications and source records attributed to W D Samuel Motherwell.

15 recordsLinked to original sources
PubMed2006

Prediction and observation of isostructurality induced by solvent incorporation in multicomponent crystals.

The crystal structures of two pharmaceutical molecules-carbamazepine and its 10,11-dihydro derivative-with acetic acid have been successfully predicted by computational methods. While the crystalline structure of the former was known a priori, no structural information was available for the latter. Possible crystal structures were generated in silico before any experimental work was performed. Although the crystal structures of the pure drug molecules are very different, incorporation of acetic acid in their crystal lattices results in isomorphic products.

Crystallization↗
PubMed2006

Glass transition temperature of glucose, sucrose, and trehalose: an experimental and in silico study.

Isothermal-isobaric molecular dynamics simulations are used to calculate the specific volume of models of different amorphous carbohydrates (glucose, sucrose, and trehalose) as a function of temperature. Plots of specific volume vs temperature exhibit a characteristic change in slope when the amorphous systems change from the glassy to the rubbery state. The intersection of the regression lines of data below (glassy state) and above (rubbery state) the change in slope provides the glass transition temperature (T(g)). These predicted glass transition temperatures are compared to experimental T(g) values as obtained from differential scanning calorimetry measurements. As expected, the predicted values are systematically higher than the experimental ones (about 12-34 K) as the cooling rates of the modeling methods are about a factor of 10(12) faster. Nevertheless, the calculated trend of T(g) values agrees exactly with the experimental trend: T(g)(glucose) < T(g)(sucrose) < T(g)(trehalose). Furthermore, the relative differences between the glass transition temperatures were also computed precisely, implying that atomistic molecular dynamics simulations can reproduce trends of T(g) values in amorphous carbohydrates with high quality.

Biophysics↗
PubMed2005

Screening for crystalline salts via mechanochemistry.

Neat grinding and solvent-drop grinding methods are found to be effective screening tools for indicating the potential for crystalline salt formation involving a given acid-base pair, as demonstrated with two model pharmaceuticals.

Journal Article↗
PubMed2005

Selective polymorph transformation via solvent-drop grinding.

A method of inducing specific polymorph transformations is exemplified with two single-component systems, whereby a given crystal form undergoes conversion when subjected to solid state grinding in the presence of a minor quantity of a certain solvent.

Combinatorial Chemistry Techniques↗
PubMed2005

Formation of quinol co-crystals with hydrogen-bond acceptors.

The crystal structures of eight new co-crystals of quinol with pyrazine, piperazine, morpholine, pyridine, piperidine, 4,4'-bipyridine, N-methylmorpholine and N,N'-dimethylpiperazine are reported. Quinol forms 1:1 co-crystals with pyrazine, piperazine and N,N'-dimethylpiperazine, but 1:2 co-crystals with morpholine, 4,4'-bipyridine, N-methylmorpholine, pyridine and piperidine. This difference can be rationalized in most cases by the presence of, respectively, two or one strong hydrogen-bond acceptor(s) in the guest molecule. The exception to this generalization is 4,4'-bipyridine, which forms a 1:2 co-crystal, possibly to optimize crystal packing. All structures are dominated by hydrogen bonding between quinol and the guest molecules. A doubly bridging motif, which connects pairs of quinol and guest molecules via NH...O or CH...O interactions, is present in all but the sterically hindered N,N'-dimethylpiperazine and N-methylmorpholine co-crystals.

Crystallization↗
PubMed2005

Structures of the monofluoro- and monochlorophenols at low temperature and high pressure.

2-Fluorophenol, 3-fluorophenol and 3-chlorophenol were recrystallized from frozen solids at 260, 263 and 283 K. All compounds were also crystallized by the application of high pressure (0.36, 0.12 and 0.10 GPa). While 3-fluorophenol and 3-chlorophenol yielded the same phases under both conditions, different polymorphs were obtained for 2-fluorophenol. 4-Chlorophenol was crystallized both from the melt and from benzene to yield two different ambient-pressure polymorphs; crystallization from the melt at 0.02 GPa yielded the same phase as from benzene at ambient pressure. 3-Fluorophenol is unusual in forming a hydrogen-bonded chain along a 2(1) screw axis. Such behaviour is usually only observed for small alcohols, but here it appears to be stabilized by intermolecular C-H...F hydrogen-bond formation. 3-Chlorophenol is a more typical large alcohol and emulates a fourfold screw axis with two independent molecules positioned about a 2(1) axis, although there are significant distortions from this ideal geometry. The two phases of 4-chlorophenol consist of chains or rings connected by C-Cl...H interactions. The low-temperature and high-pressure polymorphs of 2-fluorophenol consist of chains of molecules connected through OH...OH hydrogen bonds; while inter-chain C-H...F interactions are significant at high pressure, there are none in the low-temperature form.

Chlorophenols↗
PubMed2005

Occurrence of pharmaceutically acceptable anions and cations in the Cambridge Structural Database.

The occurrence of a number of pharmaceutically acceptable counterions in the Cambridge Structural Database (CSD) has been investigated. The results have been compared to the occurrence of the same counterions in a list of known pharmaceutical salts. Chloride salts are by far the highest occurring in both groups. The occurrence of hydrates in the structures of salts of pharmaceutically acceptable counterions in the CSD has also been investigated. It was found that salts of these counterions show an increased tendency to hydrate when compared to the database average. The CSD was also searched for co-crystals of the list of pharmaceutically acceptable acids and bases corresponding to the list of counterions used for the salt investigation.

Acids↗
PubMed2003

A database survey of molecular and crystallographic symmetry.

The point of contact between molecular and crystallographic symmetries is that of the Wyckoff position, the position at which a molecule resides in a crystal structure. These Wyckoff positions may have the same symmetry as the molecules, some symmetry in common with the molecules or no symmetry at all. Using CSDSymmetry [Yao et al. (2002). Acta Cryst. B58, 640-646], a relational database containing information pertaining to the symmetry of molecules and the crystal structures that play host to them, the distribution of molecules over Wyckoff positions and the occupancy of Wyckoff positions in crystal structures is presented. Analysis of these data has led to the characterization of some relationships between molecular and crystallographic symmetry.

Journal Article↗
PubMed2002

The formation of paracetamol (acetaminophen) adducts with hydrogen-bond acceptors.

The crystal structures of five hemiadducts of paracetamol with 1,4-dioxane, N-methylmorpholine, morpholine, N,N-dimethylpiperazine and piperazine and a related 1:1 adduct of paracetamol with 4,4'-bipyridine are described. All structures are characterized by the formation of chains of paracetamol molecules, which are linked via either OHtriplebondO=C interactions [C(9) chains in graph-set notation] or NHtriplebondO=C interactions [C(4) chains], depending on the presence or absence of substituent groups on the guest molecule. In all cases except for the morpholine and bipyridine adducts these chains are connected by hydrogen-bond interactions with the guest molecules, which reside on crystallographic inversion centres. In the bipyridine adduct this linkage also involves a pi-stacking interaction; in the morpholine adduct it is formed between the OH groups of two opposed paracetamol molecules. Most adducts (that with 4,4'-bipyridine is an exception) decompose on heating to give monoclinic paracetamol. This is the first systematic study of a series of co-crystals containing paracetamol.

Acetaminophen↗
PubMed2002

CSDSymmetry: the definitive database of point-group and space-group symmetry relationships in small-molecule crystal structures.

An algorithm that perceives molecular symmetry has been applied to ca. 200,000 entries from the Cambridge Structural Database (CSD). For each molecule, the perceived point group, together with crystallographic properties such as space group, occupied Wyckoff positions and number of residues in the asymmetric unit, have been placed in a relational database, CSDSymmetry, using Microsoft Access software. Database queries can be constructed easily to find occurrences of any combination of molecular or crystallographic attributes, and thereby to answer questions on relative distributions. Some typical example queries are given. The inclusion of CSD reference codes enables direct visualization of search results using the Cambridge Crystallographic Data Centre's three-dimensional structure visualizer, Mercury.

Journal Article↗
PubMed2002

Applications of the Cambridge Structural Database in organic chemistry and crystal chemistry.

The Cambridge Structural Database (CSD) and its associated software systems have formed the basis for more than 800 research applications in structural chemistry, crystallography and the life sciences. Relevant references, dating from the mid-1970s, and brief synopses of these papers are collected in a database, DBUse, which is freely available via the CCDC website. This database has been used to review research applications of the CSD in organic chemistry, including supramolecular applications, and in organic crystal chemistry. The review concentrates on applications that have been published since 1990 and covers a wide range of topics, including structure correlation, conformational analysis, hydrogen bonding and other intermolecular interactions, studies of crystal packing, extended structural motifs, crystal engineering and polymorphism, and crystal structure prediction. Applications of CSD information in studies of crystal structure precision, the determination of crystal structures from powder diffraction data, together with applications in chemical informatics, are also discussed.

Journal Article↗