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1. Design of Chemoresponsive Soft Matter Using Hydrogen-Bonded Liquid Crystals

   https://doi.org/10.3390/ma14051055  

   Yu, Huaizhe ; Wang, Kunlun ; Szilvási, Tibor ; Nayani, Karthik ; Bao, Nanqi ; Twieg, Robert J. ; Mavrikakis, Manos ; Abbott, Nicholas L. ( March 2021 , Materials)

   null (Ed.)

   Soft matter that undergoes programmed macroscopic responses to molecular analytes has potential utility in a range of health and safety-related contexts. In this study, we report the design of a nematic liquid crystal (LC) composition that forms through dimerization of carboxylic acids and responds to the presence of vapors of organoamines by undergoing a visually distinct phase transition to an isotropic phase. Specifically, we screened mixtures of two carboxylic acids, 4-butylbenzoic acid and trans-4-pentylcyclohexanecarboxylic acid, and found select compositions that exhibited a nematic phase from 30.6 to 111.7 °C during heating and 110.6 to 3.1 °C during cooling. The metastable nematic phase formed at ambient temperatures was found to be long-lived (>5 days), thus enabling the use of the LC as a chemoresponsive optical material. By comparing experimental infrared (IR) spectra of the LC phase with vibrational frequencies calculated using density functional theory (DFT), we show that it is possible to distinguish between the presence of monomers, homodimers and heterodimers in the mixture, leading us to conclude that a one-to-one heterodimer is the dominant species within this LC composition. Further support for this conclusion is obtained by using differential scanning calorimetry. Exposure of the LC to 12 ppm triethylamine (TEA) triggers a phase transition to an isotropic phase, which we show by IR spectroscopy to be driven by an acid-base reaction, leading to the formation of ammonium carboxylate salts. We characterized the dynamics of the phase transition and found that it proceeds via a characteristic spatiotemporal pathway involving the nucleation, growth, and coalescence of isotropic domains, thus amplifying the atomic-scale acid-base reaction into an information-rich optical output. In contrast to TEA, we determined via both experiment and computation that neither hydrogen bonding donor or acceptor molecules, such as water, dimethyl methylphosphonate, ethylene oxide or formaldehyde, disrupt the heterodimers formed in the LC, hinting that the phase transition (including spatial-temporal characteristics of the pathway) induced in this class of hydrogen bonded LC may offer the basis of a facile and chemically selective way of reporting the presence of volatile amines. This proposal is supported by exploratory experiments in which we show that it is possible to trigger a phase transition in the LC by exposure to volatile amines emitted from rotting fish. Overall, these results provide new principles for the design of chemoresponsive soft matter based on hydrogen bonded LCs that may find use as the basis of low-cost visual indicators of chemical environments. 

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2. Spontaneous Transition of Spherical Coacervate to Vesicle‐Like Compartment

   https://doi.org/10.1002/advs.202305978  

   Choi, Hyunsuk ; Hong, Yuri ; Najafi, Saeed ; Kim, Sun Young ; Shea, Joan‐Emma ; Hwang, Dong Soo ; Choi, Yoo Seong ( December 2023 , Advanced Science)

   Numerous biological systems contain vesicle‐like biomolecular compartments without membranes, which contribute to diverse functions including gene regulation, stress response, signaling, and skin barrier formation. Coacervation, as a form of liquid–liquid phase separation (LLPS), is recognized as a representative precursor to the formation and assembly of membrane‐less vesicle‐like structures, although their formation mechanism remains unclear. In this study, a coacervation‐driven membrane‐less vesicle‐like structure is constructed using two proteins, GG1234 (an anionic intrinsically disordered protein) and bhBMP‐2 (a bioengineered human bone morphogenetic protein 2). GG1234 formed both simple coacervates by itself and complex coacervates with the relatively cationic bhBMP‐2 under acidic conditions. Upon addition of dissolved bhBMP‐2 to the simple coacervates of GG1234, a phase transition from spherical simple coacervates to vesicular condensates occurred via the interactions between GG1234 and bhBMP‐2 on the surface of the highly viscoelastic GG1234 simple coacervates. Furthermore, the shell structure in the outer region of the GG1234/bhBMP‐2 vesicular condensates exhibited gel‐like properties, leading to the formation of multiphasic vesicle‐like compartments. A potential mechanism is proposed for the formation of the membrane‐less GG1234/bhBMP‐2 vesicle‐like compartments. This study provides a dynamic process underlying the formation of biomolecular multiphasic condensates, thereby enhancing the understanding of these biomolecular structures.

    

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3. Simulations of the star-forming molecular gas in an interacting M51-like galaxy: cloud population statistics

   https://doi.org/10.1093/mnras/stab1683  

   Treß, Robin G ; Sormani, Mattia C ; Smith, Rowan J ; Glover, Simon C ; Klessen, Ralf S ; Mac Low, Mordecai-Mark ; Clark, Paul ; Duarte-Cabral, Ana ( July 2021 , Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT To investigate how molecular clouds react to different environmental conditions at a galactic scale, we present a catalogue of giant molecular clouds (GMCs) resolved down to masses of ∼10 M⊙ from a simulation of the entire disc of an interacting M51-like galaxy and a comparable isolated galaxy. Our model includes time-dependent gas chemistry, sink particles for star formation, and supernova feedback, meaning we are not reliant on star formation recipes based on threshold densities and can follow the physics of the cold molecular phase. We extract GMCs from the simulations and analyse their properties. In the disc of our simulated galaxies, spiral arms seem to act merely as snowplows, gathering gas, and clouds without dramatically affecting their properties. In the centre of the galaxy, on the other hand, environmental conditions lead to larger, more massive clouds. While the galaxy interaction has little effect on cloud masses and sizes, it does promote the formation of counter-rotating clouds. We find that the identified clouds seem to be largely gravitationally unbound at first glance, but a closer analysis of the hierarchical structure of the molecular interstellar medium shows that there is a large range of virial parameters with a smooth transition from unbound to mostly bound for the densest structures. The common observation that clouds appear to be virialized entities may therefore be due to CO bright emission highlighting a specific level in this hierarchical binding sequence. The small fraction of gravitationally bound structures found suggests that low galactic star formation efficiencies may be set by the process of cloud formation and initial collapse. 

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4. Collision cross‐section analysis of self‐assembled metallomacrocycle isomers and isobars via ion mobility mass spectrometry

   https://doi.org/10.1002/rcm.8717  

   Endres, Kevin J. ; Barthelmes, Kevin ; Winter, Andreas ; Antolovich, Robert ; Schubert, Ulrich S. ; Wesdemiotis, Chrys ( February 2020 , Rapid Communications in Mass Spectrometry)

   Coordinatively driven self‐assembly of transition metal ions and bidentate ligands gives rise to organometallic complexes that usually contain superimposed isobars, isomers, and conformers. In this study, the double dispersion ability of ion mobility mass spectrometry (IM‐MS) was used to provide a comprehensive structural characterization of the self‐assembled supramolecular complexes by their mass and charge, revealed by the MS event, and their shape and collision cross‐section (Ω), revealed by the IM event.

   Self‐assembled complexes were synthesized by reacting a bis(terpyridine) ligand exhibiting a 60^odihedral angle between the two ligating terpyridine sites (T) with divalent Zn, Ni, Cd, or Fe. The products were isolated as (Metal²⁺[T])_n(PF₆)_2nsalts and analyzed using IM‐MS after electrospray ionization (ESI) which produced several charge states from eachn‐mer, depending on the number of PF₆ˉ anions lost upon ESI. Experimental Ω data, derived using IM‐MS, and computational Ω predictions were used to elucidate the size and architecture of the complexes.

   Only macrocyclic dimers, trimers, and tetramers were observed with Cd²⁺, whereas Zn²⁺formed the same plus hexameric complexes. These two metals led to the simplest product distributions and no linear isomers. In sharp contrast, Ni²⁺and Fe²⁺formed all possible ring sizes from dimer to hexamer as well as various linear isomers. The experimental and theoretical Ω data indicated rather planar macrocyclic geometries for the dimers and trimers, twisted 3D architectures for the larger rings, and substantially larger sizes with spiral conformation for the linear congeners. Adding PF₆ˉ to the same complex was found to mainly cause size contraction due to new stabilizing anion–cation interactions.

   Complete structural identification could be accomplished using ESI‐IM‐MS. Our results affirm that self‐assembly with Cd²⁺and Zn²⁺proceeds through reversible equilibria that generate the thermodynamically most stable structures, encompassing exclusively macrocyclic architectures that readily accommodate the 60^oligand used. In contrast, complexation with Ni²⁺and Fe²⁺, which form stronger coordinative bonds, proceeds through kinetic control, leading to more complex mixtures and kinetically trapped less stable architectures, such as macrocyclic pentamers and linear isomers.

    

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5. Relaxational dynamics of the T -number conversion of virus capsids

   https://doi.org/10.1063/5.0160822  

   Clark, Alexander Bryan ; Safdari, Mohammadamin ; Zoorob, Selim ; Zandi, Roya ; van der Schoot, Paul ( August 2023 , The Journal of Chemical Physics)

   We extend a recently proposed kinetic theory of virus capsid assembly based on Model A kinetics and study the dynamics of the interconversion of virus capsids of different sizes triggered by a quench, that is, by sudden changes in the solution conditions. The work is inspired by in vitro experiments on functionalized coat proteins of the plant virus cowpea chlorotic mottle virus, which undergo a reversible transition between two different shell sizes (T = 1 and T = 3) upon changing the acidity and salinity of the solution. We find that the relaxation dynamics are governed by two time scales that, in almost all cases, can be identified as two distinct processes. Initially, the monomers and one of the two types of capsids respond to the quench. Subsequently, the monomer concentration remains essentially constant, and the conversion between the two capsid species completes. In the intermediate stages, a long-lived metastable steady state may present itself, where the thermodynamically less stable species predominate. We conclude that a Model A based relaxational model can reasonably describe the early and intermediate stages of the conversion experiments. However, it fails to provide a good representation of the time evolution of the state of assembly of the coat proteins in the very late stages of equilibration when one of the two species disappears from the solution. It appears that explicitly incorporating the nucleation barriers to assembly and disassembly is crucial for an accurate description of the experimental findings, at least under conditions where these barriers are sufficiently large.

    

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