Directing the Assembly of Multicomponent Organic Crystals. Synthesis, characterisation and structural analysis of multicomponent organic systems formed from dynamic processes.
AuthorAlomar, Taghrid S.
SupervisorScowen, Ian J.
KeywordMulticomponent systems, Organic, PXRD, Crystal engineering, X-ray crystallography, Vibrational spectroscopy, Dynamic covalent chemistry, Multicomponent systems, organic, PXRD, crystal engineering, x-ray crystallography, vibrational spectroscopy, dynamic covalent chemistry.Multicomponent systems, organic, PXRD, crystal engineering, x-ray crystallography, vibrational spectroscopy, dynamic covalent chemistry, Multicomponent organic systems, Cogent assembly
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InstitutionUniversity of Bradford
DepartmentSchool of Life Sciences
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AbstractDirected assembly of molecular solids continues to attract widespread interest with its fundamental application in a wide range of commercial settings where control of the crystalline state of materials corresponds with product performance. These arenas include pharmaceuticals, personal care formulations, foods, paints and pigments and explosives. In recent times, the assembly of multicomponent organic systems has achieved considerable impetus with the widespread interest in co-crystal systems. However, cogent assembly (or engineering) of multicomponent materials is still in its infancy. Considerable advances in crystal design have been made through consideration of intermolecular ‘synthons’ – identifiable motifs utilising hydrogen bonds – but the translation of other molecular information (conformation, chirality, etc.) into solid state properties (e.g. long-range (translational) symmetry, crystal chirality) remains poorly understood. In this study, we have attempted to evaluate the influence of a chiral centre adjacent to molecular synthons to identify potential translation of information into the solid form. We have compared the co-crystallisation of nicotinamide with both the racemic mixture of malic acid against that with an enantiomerically pure form of the acid (L-malic acid). As well as DL-phenyllactic acid and L-phenyllactic acid. iii It is apparent that recognition between enantiomeric molecular forms play a significant role in the assembly of these systems. This mechanism can be considered independently from the H-bonding networks supporting the hetero-molecular interactions (e.g. acid-amide recognition). Discrimination and control of such interactions may play a role in transmitting chiral molecular information into solid state multi-component assemblies. In order to develop an understanding of co-crystal formation in chiral and achiral forms with intermolecular interactions, the CSD and crystal structures were obtained to do the analysis of how co-crystals pack. This study has also investigated the use of boronic acids. The aim of this study was to investigate the modification of the hydrogen bonding environment within the hydrogen bonded multi-component systems of boroxines. The study also attempted to determine how the starting materials drive the systems between the boronic acid co-crystal and the boroxine adduct.
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Multi-component crystals of 4-phenylpyridine: challenging the boundaries between co-crystal and organic salt formation with insight into solid-state proton transferSeaton, Colin C.; Munshi, Tasnim; Williams, Sara E.; Scowen, Ian J. (2013)Six new multi-component crystals between 4-phenylpyridine and substituted benzoic acids (3-nitrobenzoic acid, 3,5-dinitrobenzoic acid, gallic acid, 4-aminobenozic acid, salicylic acid and 2-aminobenzoic acid) were created and characterized crystallographically to investigate the influence of chemical and structural factors on the hydrogen location between the two components. While the expected intermolecular interactions are formed between the acid and pyridine group in most cases, the gallic acid structure is anomalous forming an unexpected salt with pyridine to hydroxyl interactions. Calculations of the hydrogen bonding motifs indicate that the level of proton transfer (e.g. salt versus co-crystal formation) is not solely a function of the dimer geometry but influenced by the local crystallographic environment. Analysis of the crystal structures indicates the strength of the hydrogen bonding into this motif alters the expected protonation state from chemical considerations.
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Analytical method development for structural studies of pharmaceutical and related materials in solution and solid state. An investigation of the solid forms and mechanisms of formation of cocrystal systems using vibrational spectroscopic and X-ray diffraction techniquesEdwards, Howell G.M.; Scowen, Ian J.; Elbagerma, Mohamed A. (University of BradfordDivision of Chemical and Forensic Sciences, 2010-11-11)Analysis of the molecular speciation of organic compounds in solution is essential for the understanding of ionic complexation. The Raman spectroscopic technique was chosen for this purpose because it allows the identification of compounds in different states and it can give information about the molecular geometry from the analysis of the vibrational spectra. In this research the ionisation steps of relevant pharmaceutical material have been studied by means of potentiometry coupled with Raman spectroscopy; the protonation and deprotonation behaviour of the molecules were studied in different pH regions. The abundance of the different species in the Raman spectra of aqueous salicylic acid, paracetamol, citric acid and salicylaldoxime have been identified, characterised and confirmed by numerical treatment of the observed spectral data using a multiwavelength curve-fitting program. The non-destructive nature of the Raman spectroscopic technique and the success of the application of the multiwavelength curve-fitting program demonstrated in this work have offered a new dimension for the rapid identification and characterisation of pharmaceuticals in solution and have indicated the direction of further research. The work also covers the formation of novel cocrystal systems with pharmaceutically relevant materials. The existence of new cocrystals of salicylic acid-nicotinic acid, DLphenylalanine , 6-hydroxynicotinic acid, and 3,4-dihydroxybenzoic acid with oxalic acid have been identified from stoichiometric mixtures using combined techniques of Raman spectroscopy (dispersive and transmission TRS), X-ray powder diffraction and thermal analysis. Raman spectroscopy has been used to demonstrate a number of important aspects regarding the nature of the molecular interactions in the cocrystal. Cocrystals of II salicylic acid ¿ benzamide, citric acid-paracetamol and citric acid -benzamide have been identified with similar analytical approaches and structurally characterised in detail with single crystal X-ray diffraction. From these studies the high selectivity and direct micro sampling of Raman spectroscopy make it possible to identify spectral contributions from each chemical constituent by a peak wavenumber comparison of single-component spectra (API and guest individually) and the two- component sample material (API/guest), thus allowing a direct assessment of cocrystal formation to be made. Correlation of information from Raman spectra have been made to the X-ray diffraction and thermal analysis results. Transmission Raman Spectroscopy has been applied to the study cocrystals for the first time. Identification of new phases of analysis of the low wavenumber Raman bands is demonstrated to be a key advantage of the TRS technique.