- Crystal Structure of Glycine Dihydrate: Glycine, the simplest amino acid, is also the most polymorphous. Herein, we report the structure determination of a long unknown phase of glycine, which was first reported by Pyne and Suryanarayanan in 2001. To date, this phase has only been prepared at 208 K as nanocrystals within ice. Through computational crystal-structure prediction and powder X-ray diffraction methods, we identified this elusive phase as glycine dihydrate (GDH), representing the first report on the structure of a hydrated glycine structure. The structure of GDH has important implications for the state of glycine in aqueous solution and the mechanisms of glycine crystallization. GDH may also be the form of glycine that comes to Earth from extraterrestrial sources.
- Crystal Structure of New Aspirin Polymorph: Polymorphism of aspirin (acetylsalicylic acid), one of the most widely consumed medications, was equivocal until the structure of a second polymorph II, similar in structure to the original form I, was reported in 2005. Here, the third ambient polymorph of aspirin (form IV) is described. It was crystallized from the melt, and its structure was determined using a combination of X-ray powder diffraction analysis and crystal structure prediction algorithms.
- Fighting Counterfeit Drugs Using X-Ray Micro-Diffraction: Counterfeit pharmaceutical products are a global threat to public health, and they undermine the credibility and the financial success of the producers of genuine products. The escalating circulation of counterfeit drugs demands new anticounterfeit measures that permit rapid screening, are nondestructive, and cannot be circumvented easily. Herein we describe a micro-X-ray diffraction (μ-XRD) protocol for this purpose capable of reading barcodes and logos fabricated on various substrates using soft-lithography stamping of compounds that can be read by X-ray diffraction but are invisible to the naked eye or optical microscopy. This method is demonstrated with barcodes and logos of compounds, approved by the Food and Drug Administration, printed on flat substrates as well as commercial aspirin and ibuprofen tablets. The μ-XRD protocol is nondestructive, automated, and user-friendly and can be used to certify the authenticity of drug tablets by mapping hidden patterns printed under the tablet coating and on packages.
- One Stone Two Birds: The β → α and β → γ transformations in glycine can occur concurrently in single crystals in a non-topotactic manner.
- Guests are Welcome: A molecular framework based on guanidinium cations and 1,2,4,5-tetra(4-sulfonatophenyl)benzene (TSPB), an aromatic tetrasulfonate with nominal 2-fold and mirror symmetry, exhibits three crystallographically unique one-dimensional channels as a consequence of molecular symmetry and complementary hydrogen bonding between the guanidinium (G) ions and the sulfonate (S) groups of TSPB. Unlike previous GS frameworks, this new topology is sufficiently flexible to permit reversible release and adsorption of guest molecules in large single crystals through a cyclic shrinkage and expansion of the channels with retention of single crystallinity, as verified by single crystal X-ray diffraction.
- Trapped in the Cage: The sequestration of luminophores within supramolecular polyhedral compartments of a crystalline zeolite-like hydrogen-bonded framework illustrates a unique approach to limiting the self-quenching ordinarily exhibited at the high concentrations achievable in this framework. A range of differently sized luminescent guests, namely coumarin 1, coumarin 4, fluorescein, [Ru(bpy)3]Cl2, and rhodamine B, can be encapsulated in amounts of up to one molecule per cage, equivalent to a concentration of 0.175 m, which is significantly higher than the concentration at which aggregation-induced quenching occurs in other media. The luminescence spectra of the encapsulated guests are consistent with the presence of isolated monomers and the absence of self-quenching. The emission color of the single crystals can be tuned readily from blue to red through the choice of guest molecules. These observations promise an approach to organic solid-state lasing compounds if crystals of sufficient size and quality can be prepared.
