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1. Minimalist columnar liquid crystals: influence of fluorination on the mesogenic behavior of tetramethoxytriphenylene derivatives

   https://doi.org/10.1039/d4ma00933a  

   Guragain, Parikshit; Powers, Mitchell; Ellman, Brett; Twieg, Robert J (November 2024, Materials Advances)

   A set of short-tailed discotic liquid crystals are presented which feature a mesophase despite having methoxy units as tails. Their unusual properties are a result of strategic fluorination, with more fluorination leading to broader mesophase ranges. 

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2. Structure and dynamics of tail-free discotic liquid crystals: Simulations of fluorinated triphenylene

   https://doi.org/10.1063/5.0106722  

   Powers, M.; Twieg, R. J.; Portman, J.; Ellman, B. (October 2022, The Journal of Chemical Physics)

   Recently, a large family of at least 14 discotic liquid crystals was discovered that are exceptions to the conventional paradigm that discotic mesogens tend to feature long, flexible tails on their periphery. To understand why these materials are liquid crystals, as well as the structural determinants of discotic phase behavior, we studied a group of closely related small tail-free disk-like molecules, including both mesogenic and non-mesogenic compounds differing only in the position of a single fluorine substituent. The rigidity and structural simplicity of these molecules make them well suited to for study by large, fully all-atom simulations. Using a combination of static and dynamic metrics, we were able to identify several key features of the columnar mesophase and, thereby, conclusively identify a columnar liquid crystalline mesophase present in a subset of our systems. Our simulations feature molecules hopping between columns in the columnar mesophase and distinctive molecular rotations in 60° steps about the columnar axis. The ability to create and characterize columnar mesophases in silico provides a potent tool for untangling the structural determinants of liquid crystalline behavior in these and other tail-free discotic liquid crystals. 

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3. Fluorinated triphenylenes and a path to short tailed discotic liquid crystals: synthesis, structure and transport properties

   https://doi.org/10.1039/d1ma00606a  

   Li, Zhe; Powers, Mitchell; Ivey, Kayla; Adas, Sonya; Ellman, Brett; Bunge, Scott D.; Twieg, Robert J. (January 2022, Materials Advances)

   A new synthetic approach for fluorinated alkoxytriphenylene discotic liquid crystals is presented. This methodology exploits the previously described photocyclodehydrofluorination (PCDHF) reaction for the preparation of fluorinated triphenylene derivatives coupled with a variety of nucleophilic aromatic substitution (S N Ar) reactions. This particular combination of reactions provides a versatile route to discotic materials with carefully controlled core fluorine and alkoxy tail content. In the course of these studies, new discotic materials with minimal tail content have been revealed. The mesogenic properties of these materials are reported, and their charge transport properties are measured using the time of flight technique. 

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4. Histone H4 Tails in Nucleosomes: a Fuzzy Interaction with DNA

   https://doi.org/10.1002/anie.202012046  

   Rabdano, Sevastyan O.; Shannon, Matthew D.; Izmailov, Sergei A.; Gonzalez Salguero, Nicole; Zandian, Mohamad; Purusottam, Rudra N.; Poirier, Michael G.; Skrynnikov, Nikolai R.; Jaroniec, Christopher P. (February 2021, Angewandte Chemie International Edition)

   Abstract The interaction of positively charged N‐terminal histone tails with nucleosomal DNA plays an important role in chromatin assembly and regulation, modulating their susceptibility to post‐translational modifications and recognition by chromatin‐binding proteins. Here, we report residue‐specific¹⁵N NMR relaxation rates for histone H4 tails in reconstituted nucleosomes. These data indicate that H4 tails are strongly dynamically disordered, albeit with reduced conformational flexibility compared to a free peptide with the same sequence. Remarkably, the NMR observables were successfully reproduced in a 2‐μs MD trajectory of the nucleosome. This is an important step toward resolving an apparent inconsistency where prior simulations were generally at odds with experimental evidence on conformational dynamics of histone tails. Our findings indicate that histone H4 tails engage in afuzzy interactionwith nucleosomal DNA, underpinned by a variable pattern of short‐lived salt bridges and hydrogen bonds, which persists at low ionic strength (0–100 mM NaCl). 

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5. Robots with Tails

   https://doi.org/10.1115/1.2021-NOV2  

   Ben-Tzvi, Pinhas; Liu, Yujiong (November 2021, Mechanical Engineering)

   Abstract Until recently, most four-legged robots have lacked a feature that is found again and again in nature—a tail. Studies of animal locomotion and robots in the laboratory indicate that leaving out tails has been a design drawback. In fact, research conducted by our lab at Virginia Tech has shown that an articulated robotic tail can effectively maneuver and stabilize a quadruped both for static and dynamic locomotion. 

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