Many molecular crystals (approximately one third) grow as twisted helicoidal ribbons from the melt, and this preponderance is even higher in restricted classes of materials, for instance charge transfer complexes. Previously, twisted crystallites of such complexes present an increase in carrier mobilities. Here, the effect of twisting on charge mobility is better analyzed for a mono-component organic semiconductor 2 2,5-bis(3-dodecyl-2-thienyl)-thiazolo [5,4-d]thiazole (BDT) that forms twisted crystals with varied helicoidal pitches and makes a possible correlation with carrier mobility. These films were analyzed by Xray scattering and Mueller matrix polarimetry to characterize the microscale organization of the polycrystalline ensembles. Carrier mobilities of organic field effect transistors were five times higher when the crystals were grown with the smallest pitches (most twisted) compared to those with the largest pitches along the fiber elongation direction. A ten-fold increase was observed along the perpendicular direction.Simulation of electrical potential based on scanning electron micrographs and density functional theory suggests that the twisting-enhanced mobility is mainly controlled by the fiber organization in the film. A greater number of tightly packed twisted fibers separated by numerous smaller gaps permits better charge transport over the film surface compared to fewer big crystallites separated by larger gaps.
Two books that describe the forms of thin films of many molecular crystals grown from the melt in polarized light, "Gedrillte" Kristalle (1929) by Ferdinand Bernauer and Thermomicroscopy in the Analysis of Pharmaceuticals (1971) by Maria Kuhnert-Brandstaẗter, are analyzed. Their descriptions, especially of curious morphologies consistent with helicoidal twisting of crystalline fibrils or narrow lamellae, are compared in the aggregate with observations from our laboratory collected during the past 10 years. According to Bernauer, 27% of molecular crystals from the melt adopt helicoidal crystal forms under some growth conditions even though helicoids are not compatible with long-range translational symmetry, a feature that is commonly thought to be an a priori condition for crystallinity. Bernauer's figure of 27% is often met with surprise if not outright skepticism. Kuhnert-Brandstaẗter was aware of the tell-tale polarimetric signature of twisting (rhythmic interference colors) but observed this characteristic morphology in less than 0.5% of the crystals described. Here, the experience of the authors with 101 arbitrarily selected compoundsmany of which are polymorphousrepresenting 155 total crystal structures, shows an even higher percentage (ca. 31%) of twisted crystals than the value reported by Bernauer. These observations, both positive (twisting) and negative (no twisting), are tabulated. It is concluded that twisting is not associated with molecular structure or crystal structure/symmetry. Rather, these nonclassical morphologies are associated with certain habits with exaggerated aspect ratios, and their appearance is strongly controlled by the growth conditions. Comments are offered in an attempt to reconcile the observations here, and those of Bernauer, the work of seekers of twisted crystals, with those of Kuhnert-Brandstaẗter, whose foremost consideration was the characterization of polymorphs of compounds of medicinal interest.
Many crystals grow as banded spherulites from the melt with an optical rhythm indicative of helicoidal twisting. In this work, 23 of 41 charge transfer complexes (CTCs) are grown with twisted morphologies. As a group, CTCs more commonly twist (56%) than molecular crystals arbitrarily chosen in our previous research (31%). To analyze the effect of twisting on charge transport, three tetracyanoethylene-based CTCs with phenanthrene (PhT), pyrene (PyT), and perylene are characterized. PhT and PyT are subject to mobility measurements using organic field-effect transistors. The mobilities for twisted crystals are around three times higher than for crystals with no ostensible optical modulation, which are effectively straight. The differences in mobilities of straight and twisted crystals are considered computationally based on density functional theory. Straight crystal models built from crystallographic information files are calculated and present anisotropic hole and electron transport. For twisted crystal models, adjacent layers in the supercell are rotated by 0.01°around experimentally determined twisting directions. The modified transfer integrals lead to a slight increase (up to 25%) in the calculated mobilities of twisted crystals. Comparisons of model calculations on individual fibrils and measurements of ensembles of fibrils indicate that interfaces between single crystals are likely consequential.
Imidacloprid, the world’s leading insecticide, has been approved recently for controlling infectious disease vectors; yet, in agricultural settings, it has been implicated in the frightening decline of pollinators. This argues for strategies that sharply reduce the environmental impact of imidacloprid. When used as a contact insecticide, the effectiveness of imidacloprid relies on physical contact between its crystal surfaces and insect tarsi. Herein, seven new imidacloprid crystal polymorphs are reported, adding to two known forms. Anticipating that insect uptake of imidacloprid molecules would depend on the respective free energies of crystal polymorph surfaces, measurements of insect knockdown times for the metastable crystal forms were as much as nine times faster acting than the commercial form against Aedes, Anopheles, and Culex mosquitoes as well as Drosophila (fruit flies). These results suggest that replacement of commercially available imidacloprid crystals (a.k.a. Form I) in space-spraying with any one of three new polymorphs, Forms IV, VI, IX, would suppress vector-borne disease transmission while reducing environmental exposure and harm to nontarget organisms.
Long noncoding RNAs (lncRNAs) are considered a novel class of regulatory factors in many diseases, but their biological function and the signaling pathway involved in osteoarthritic (OA) remain unknown. To identify the lncRNAs specifically expressed in OA cartilage, the expression of lncRNAs in OA cartilage was measured using an illumina sequencing platform. Furthermore, differentially expressed transcripts of uncertain coding potential (TUCPs) and messenger RNAs (mRNAs) were identified. The colocated target genes and the possible role of lncRNAs as a competing endogenous RNA (ceRNA) were predicted. Based on 19 samples from osteoarthritis patients of knees, 580 significantly dysregulated lncRNAs as well as differently expressed TUCPs and mRNAs were identified. Four differently expressed lncRNAs (SNHG5, ZFAS1, GAS5, and DANCR) involved in OA cartilage were analyzed by protein-protein interactions network and ceRNA regulatory network. Part of our results were consistent with previous studies, and 96 novel differently expressed lncRNAs were identified in OA. These results could expand our knowledge of the OA mechanism.
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