Jennifer A. Swift

Bio: Jennifer A. Swift is an academic researcher from Georgetown University. The author has contributed to research in topics: Crystallization & Nucleation. The author has an hindex of 22, co-authored 67 publications receiving 2439 citations. Previous affiliations of Jennifer A. Swift include Johns Hopkins University & Curtin University.

Polymorphs, Salts, and Cocrystals: What’s in a Name?

Abstract: The December 2011 release of a draft United States Food and Drug Administration (FDA) guidance concerning regulatory classification of pharmaceutical cocrystals of active pharmaceutical ingredients (APIs) addressed two matters of topical interest to the crystal engineering and pharmaceutical science communities: (1) a proposed definition of cocrystals; (2) a proposed classification of pharmaceutical cocrystals as dissociable “API-excipient” molecular complexes. The Indo–U.S. Bilateral Meeting sponsored by the Indo–U.S. Science and Technology Forum titled The Evolving Role of Solid State Chemistry in Pharmaceutical Science was held in Manesar near Delhi, India, from February 2–4, 2012. A session of the meeting was devoted to discussion of the FDA guidance draft. The debate generated strong consensus on the need to define cocrystals more broadly and to classify them like salts. It was also concluded that the diversity of API crystal forms makes it difficult to classify solid forms into three categories that...

Metric Engineering of Soft Molecular Host Frameworks

Abstract: The self-assembly and solid-state structures of host-guest inclusion compounds with lamellar architectures based on a common building block, a resilient hydrogen-bonded sheet consisting of guanidinium ions and sulfonate moieties of organodisulfonate "pillars", are described. The pillars connect adjacent sheets to generate galleries with molecular-scale cavities occupied by guest molecules. The size, shape, and physicochemical character of the inclusion cavities can be systematically adjusted by interchanging framework components while maintaining the lamellar architecture, enabling prediction and control of crystal lattice metrics with a precision that is unusual for "crystal engineering". The reliability of the lamellar architecture is a direct consequence of conformational flexibility exhibited by these hosts that, unlike rigid systems, enables them to achieve optimal packing with guest molecules. The adaptability of these hosts is further reflected by an architectural isomerism that is driven by guest templating during assembly of the inclusion compounds. Host frameworks constructed with various pillars display metric interdependences among specific structural features that reveal a common mechanism by which these soft frameworks adapt to different guests. This unique feature facilitates structure prediction and provides guidance for the design of inclusion compounds based on these hosts.

Template-Directed Architectural Isomerism of Open Molecular Frameworks: Engineering of Crystalline Clathrates

Abstract: Crystalline clathrates formed from two-dimensional guanidinium sulfonate hydrogen-bonded networks connected by 4,4‘-biphenyldisulfonate “pillars” in the third dimension exhibit a “brick-like” molecular framework that is a predictable architectural isomer of a previously observed bilayer architecture based on the same pillars. The amount of void space in the brick framework is nominally twice that of the bilayer form, with the framework occupying only 30% of the total volume. The formation of the brick architecture can be attributed to steric templating by the included molecular guests and host−guest interactions that favor assembly of this framework over its bilayer counterpart. The brick framework conforms to the different steric demands and occupancies of various aromatic guests (1,4-dibromobenzene, 1-nitronaphthalene, nitrobenzene, and 1,4-divinylbenzene) by puckering of the flexible, yet resilient, hydrogen-bonded network and by rotation of the pillars about their long axes, the latter also governing ...

Controlling molecular crystal polymorphism with self-assembled monolayer templates.

Abstract: The control of crystal polymorphism is a long-standing issue in solid-state chemistry, which has many practical implications for a variety of commercial applications. At least four different crystalline forms of 1,3-bis(m-nitrophenyl) urea (MNPU), a classic molecular crystal system, are known to crystallize from solution in various concomitant combinations. Herein we demonstrate that the introduction of gold-thiol self-assembled monolayers (SAMs) of substituted 4'-X-mercaptobiphenyls (X = H, I, and Br) into the crystallization solution can serve as an effective means to selectively template the nucleation and growth of alpha-, beta-, and gamma-MNPU phases, respectively. Polymorph control in the presence of SAM surfaces persists under a variety of solution conditions and consistently results in crystalline materials with high phase purity. The observed selectivity is rationalized on the basis of long-range two-dimensional geometric lattice matching and local complementary chemical interactions at the SAM/crystal interfaces.

Solvent Effects on the Growth Morphology and Phase Purity of CL-20

Abstract: The performance and stability of the high energy secondary explosive 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (HNIW, also known as CL-20) can be affected by factors including the phase purity of the bulk material, as well as the particle size, morphology, and defect density of the individual crystallites. Slow evaporation crystallization of CL-20 from 16 different single solvent and co-solvent systems was performed. The phase purity of the bulk material obtained was analyzed by powder X-ray diffraction, optical microscopy, and differential scanning calorimetry. These complementary methods confirmed that under most of the slow evaporation conditions examined, a concomitant mixture of two or more crystalline phases was usually obtained. Numerous individual crystal morphologies were determined using single crystal X-ray goniometry and compared against calculated BFDH morphologies. Examination of the packing interactions in the different CL-20 phases via Hirshfeld surface analysis provides some insight int...

Reticular synthesis and the design of new materials

Abstract: The long-standing challenge of designing and constructing new crystalline solid-state materials from molecular building blocks is just beginning to be addressed with success. A conceptual approach that requires the use of secondary building units to direct the assembly of ordered frameworks epitomizes this process: we call this approach reticular synthesis. This chemistry has yielded materials designed to have predetermined structures, compositions and properties. In particular, highly porous frameworks held together by strong metal-oxygen-carbon bonds and with exceptionally large surface area and capacity for gas storage have been prepared and their pore metrics systematically varied and functionalized.