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1. Chiral emergence in multistep hierarchical assembly of achiral conjugated polymers

   https://doi.org/10.1038/s41467-022-30420-6  

   Park, Kyung Sun ; Xue, Zhengyuan ; Patel, Bijal B. ; An, Hyosung ; Kwok, Justin J. ; Kafle, Prapti ; Chen, Qian ; Shukla, Diwakar ; Diao, Ying ( December 2022 , Nature Communications)

   Abstract Intimately connected to the rule of life, chirality remains a long-time fascination in biology, chemistry, physics and materials science. Chiral structures, e.g., nucleic acid and cholesteric phase developed from chiral molecules are common in nature and synthetic soft materials. While it was recently discovered that achiral but bent-core mesogens can also form chiral helices, the assembly of chiral microstructures from achiral polymers has rarely been explored. Here, we reveal chiral emergence from achiral conjugated polymers, in which hierarchical helical structures are developed through a multistep assembly pathway. Upon increasing concentration beyond a threshold volume fraction, dispersed polymer nanofibers form lyotropic liquid crystalline (LC) mesophases with complex, chiral morphologies. Combining imaging, X-ray and spectroscopy techniques with molecular simulations, we demonstrate that this structural evolution arises from torsional polymer molecules which induce multiscale helical assembly, progressing from nano- to micron scale helical structures as the solution concentration increases. This study unveils a previously unknown complex state of matter for conjugated polymers that can pave way to a field of chiral (opto)electronics. We anticipate that hierarchical chiral helical structures can profoundly impact how conjugated polymers interact with light, transport charges, and transduce signals from biomolecular interactions and even give rise to propertiesmore »unimagined before.« less
2. Nanoscale Structure of Langmuir–Blodgett Film of Bent-Core Molecules

   https://doi.org/10.3390/nano12132285  

   Adamo, Fabrizio Corrado ; Ciuchi, Federica ; De Santo, Maria Penelope ; Astolfi, Paola ; Warner, Isabelle ; Scharrer, Eric ; Pisani, Michela ; Vita, Francesco ; Francescangeli, Oriano ( July 2022 , Nanomaterials)

   Bent-core mesogens (BCMs) are a class of thermotropic liquid crystals featuring several unconventional properties. However, the interpretation and technological exploitation of their unique behavior have been hampered by the difficulty of controlling their anchoring at surfaces. To tackle this issue, we report the nanoscale structural characterization of BCM films prepared using the Langmuir–Blodgett technique. Even though BCMs are quite different from typical amphiphilic molecules, we demonstrate that stable molecular films form over water, which can then be transferred onto silicon substrates. The combination of Brewster angle microscopy, atomic force microscopy, and X-ray reflectivity measurements shows that the molecules, once transferred onto a solid substrate, form a bilayer structure with a bottom layer of flat molecules and an upper layer of upright molecules. These results suggest that Langmuir–Blodgett films of BCMs can provide a useful means to control the alignment of this class of liquid crystals.
3. RNA multimerization as an organizing force for liquid–liquid phase separation

   https://doi.org/10.1261/rna.078999.121  

   Bevilacqua, Philip C. ; Williams, Allison M. ; Chou, Hong-Li ; Assmann, Sarah M. ( December 2021 , RNA)

   RNA interactions are exceptionally strong and highly redundant. As such, nearly any two RNAs have the potential to interact with one another over relatively short stretches, especially at high RNA concentrations. This is especially true for pairs of RNAs that do not form strong self-structure. Such phenomena can drive liquid–liquid phase separation, either solely from RNA–RNA interactions in the presence of divalent or organic cations, or in concert with proteins. RNA interactions can drive multimerization of RNA strands via both base-pairing and tertiary interactions. In this article, we explore the tendency of RNA to form stable monomers, dimers, and higher order structures as a function of RNA length and sequence through a focus on the intrinsic thermodynamic, kinetic, and structural properties of RNA. The principles we discuss are independent of any specific type of biomolecular condensate, and thus widely applicable. We also speculate how external conditions experienced by living organisms can influence the formation of nonmembranous compartments, again focusing on the physical and structural properties of RNA. Plants, in particular, are subject to diverse abiotic stresses including extreme temperatures, drought, and salinity. These stresses and the cellular responses to them, including changes in the concentrations of small molecules such asmore »polyamines, salts, and compatible solutes, have the potential to regulate condensate formation by melting or strengthening base-pairing. Reversible condensate formation, perhaps including regulation by circadian rhythms, could impact biological processes in plants, and other organisms.« less
4. Using peptide substrate analogs to characterize a radical intermediate in NosN catalysis

   Wang, Bo ; Silakov, Alexey ; Booker, Squire J. ( April 2022 , Methods in enzymology)

   Britt, David R. (Ed.)

   Nosiheptide is a ribosomally produced and post-translationally modified thiopeptide antibiotic that displays potent antibacterial activity in vitro, especially against Grampositive pathogens. It comprises a core peptide macrocycle that contains multiple thiazole rings, dehydrated serine and threonine residues, a tri-substituted 3-hydroxypyridine ring and several other modifications. Among these additional modifications includes a 3,4-dimethyl-2-indolic acid (DMIA) moiety that bridges Glu6 and Cys8 of the core peptide to form a second smaller ring system. This side-ring system is formed by the action of NosN, a radical S-adenosylmethionine (SAM) enzyme that falls within the class C radical SAM methylase (RSMT) family. However, the true function of NosN is to transfer a methylene group from the methylmoiety of SAM to C4 of 3-methylindolic acid (MIA) attached in a thioester linkage to Cys8 of the core peptide to set up a highly electrophilic species. This species is then trapped by the side chain of Glu6, resulting in formation of a lactone and the side-ring system. The NosN reaction requires two simultaneously bound molecules of SAM. The first, SAMI, is cleaved to generate a 50-deoxyadenosyl 50-radical, which abstracts a hydrogen atom from the methyl group of the second molecule of SAM. The resulting SAM radical is believedmore »to add to C4 of MIA, affording a radical intermediate on the MIA substrate. Herein we describe synthetic approaches that allow detection of this radical by electron paramagnetic resonance (EPR) spectroscopy.« less
5. Aqueous Self-Assembly of Peptide–Diketopyrrolopyrrole Conjugates with Variation of N-Alkyl Side Chain and π-Core Lengths

   https://doi.org/10.1055/a-1503-5912  

   Panda, Sayak Subhra ; Tovar, John D. ( April 2021 , Organic Materials)

   Peptidic sequences when conjugated to π-electronic groups form self-assembled networks of π-electron pathways. These materials hold promise for bio-interfacing charge transporting applications because of their aqueous processability and compatibility. In this work, we incorporated diketopyrrolopyrrole (DPP), a well-established π-core for organic electronic applications, within the peptidic sequence. We embedded different numbers of thiophene rings (2 and 3) on both sides of the DPP to alter the length of the π-cores. We also varied the length of the N-alkyl side chains (methyl, butyl, hexyl) attached to the DPP core. These variations allowed us to explicitly study the effect of π-core and N-alkyl side-chain length on photophysical properties and morphology of the resulting nanomaterials. All of these molecules formed H-type aggregates in the assembled state. Longer π-cores have relatively red-shifted absorption maxima, whereas the N-alkyl variation did not present significant photophysical changes.