News & Events

In a special issue dedicated to Martin Pope, a pioneer of organic electronics, graduate studnets Anna Yusov and Alexandra Dillon report that guanidinium organosulfonate (GS) hydrogen-bonded frameworks (HBFs) constructed from three different naphthalenesulfonates incorporate the electron acceptor tetracyanoquinodimethane (TCNQ) as a guest molecule, with framework architectures that reflect synergy between the persistent 2D hydrogen-bonded GS network and donor-acceptor interactions. The spectroscopic and computational results confirm weak charge-transfer interactions associated with the formation of mixed stacks containing naphthalene donors and TCNQ acceptors that are enforced by the GS framework, suggesting opportunities for the synthesis of new optoelectronic materials through a combination of molecular and crystal design. Find the article here.

Crystallization from the melt can allow the achievement of high driving force for crystallization accompanied by relatively slow growth, nucleation, and transformation rates, features that favor its use as an efficient polymorph screening method. Surprisingly, even though melt crystallization has a long history, it has been employed less often in the search for new polymorphs than solution crystallization. In a study of 21 well-characterized compounds with at least five ambient polymorphs, MDI investigators found that melt crystallization afforded more than half of the known polymorphs and in many cases revealed new polymorphs not detected by other screening methods. A statistical analysis revealed that polymorphs grown from the melt have a greater propensity for high Z′ values, which are not easily accessible by other crystallization protocols and are often not detectable by crystal structure prediction methods. Melt crystallization within nanopores (8–100 nm) performed for 19 of the 21 compounds mostly resulted in polymorphs that dominated crystallization from the bulk melt at similar temperatures. The total number of polymorphs observed in nanopores was less than that observed during crystallization from the bulk melt, however, and melt crystallization under confinement revealed new polymorphs not detected by other crystallization methods. Find the article here.

MDI investigators, including graduate students Fangyuan Dong, Samira Munkaila and Veronica Grebe, devised a synthetic strategy for fabricating colloidal particles with spatially segregated amine-functionalized lobes enables regioselective coating with gold to afford metallodielectric particles with a variety of shapes and lobe sizes. This approach can produce either dissymmetric dumbbell-shaped two-lobed Au-TPM particles (Au-T) or dissymmetric or symmetric three-lobed particles with gold coating on one (Au-T-T and T-Au-T) or two lobes (Au-T-Au). Dielectrophoretic (DEP) forces exerted by an AC field confined between two opposing electrodes generate aggregates ranging from 1D chains to 2D close-packed lattices, depending on the particle shape and lobe arrangement. The aggregate structures reflect the lowest energy configurations resulting from the induced dipole moments created in particle lobes within the confined electric field. Find the article here.

MDI investigators previously discovered that the efficacy of crystalline contact insecticides depends on the crystalline form (a.k.a. polymorphs). Polymorphism in contact insecticides, however, and its importance to efficacy, was largely unknown to the vector control community. Crystallographic characterization of contact insecticide solids needs to be systematic to identify more active solid forms. Here, the investigators report seven new crystal structures, mostly pyrethroid insecticides recommended by the WHO for indoor residual spraying, as well as a new form of a neonicotinoid insecticide. These results further highlight polymorphism in contact insecticides.

Impurities and intentionally introduced additives can exert significant influence on crystal growth, and they can play a critical role in crystallization processes. Additives can inhibit growth by binding to the edge of advancing steps. So-called “stopper” mechanisms, described by Cabrera-Vermilyea and Bliznakov, are regarded as the most effective mode of inhibition. Growth inhibition kinetic data, however, often do not fit these models, prompting the use of various corrections and numerical simulations. In a recently published article, MDI investigators describe approaches to more accurate modeling of kinetic data that reveal the limits of accurate and quantitative agreement with the aforementioned models. Kinetic data for crystal growth on the {0001} faces of L-cystine single crystals in the presence of the dimethylester of L-cystine, a proven growth inhibitor described as a “molecular imposter” or “tailor-made additive,” is simulated using a numerical model that incorporates chaotic distribution of stoppers over the crystal surface. A related analysis is included for potassium dihydrogen phosphate. Find the article here.