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1. Hydrogen Bonding Sequence Directed Coil-Globule Transition in Water Soluble Thermoresponsive Polymers

   https://doi.org/10.1103/PhysRevLett.127.167801  

   Dahanayake, Rasika; Dormidontova, Elena E. (October 2021, Physical Review Letters)
2. Worm-globule transition of amphiphilic pH-responsive heterografted bottlebrushes at air–water interface

   https://doi.org/10.1039/D3SM01635H  

   Kelly, Michael T; Zhao, Bin (February 2024, Soft Matter)

   Heterografted molecular bottlebrushes (MBBs) with side chains composed of poly(n-butyl acrylate) (PnBA) and pH-responsive poly(2-(N,N-diethylamino)ethyl methacrylate) (PDEAEMA, pKa = 7.4) have been shown to be efficient, robust, and responsive emulsifiers. However, it remains unknown how they respond to external stimuli at interfaces. In this work, the shape-changing behavior of six hetero- and homografted MBBs at air–water interfaces in response to pH changes and lateral compression was investigated using a Langmuir–Blodgett trough and atomic force microscopy. At a surface pressure of 0.5 mN m−1, PDEAEMA-containing MBBs showed no worm-globule transitions when the pH was increased from 4.0 to 10.0, at which PDEAEMA becomes insoluble in water. Upon lateral compression at pH 4.0, MBBs with a mole fraction of PDEAEMA side chains (xPDEAEMA) < 0.50 underwent pronounced worm-globule shape transitions; there was an increasing tendency for bottlebrushes to become connected with increasing xPDEAEMA. At xPDEAEMA = 0.76, the molecules remained wormlike even at high compression. These observations were presumably caused by the increased electrostatic repulsion between protonated PDEAEMA side chains in the subphase with increasing xPDEAEMA, hindering the shape change. At pH 10.0, MBBs with xPDEAEMA < 0.50 showed a lower tendency to change their wormlike morphologies upon compression than at pH 4.0. No shape transition was observed when xPDEAEMA > 0.50, attributed to the relatively high affinity toward water and the rigidity of PDEAEMA. This study revealed the shape-changing behavior of amphiphilic pH-responsive MBBs at air–water interfaces, which could be useful for future design of multicomponent MBBs for potential applications. 

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3. Connecting Coil-to-Globule Transitions to Full Phase Diagrams for Intrinsically Disordered Proteins

   https://doi.org/10.1016/j.bpj.2020.06.014  

   Zeng, Xiangze; Holehouse, Alex S.; Chilkoti, Ashutosh; Mittag, Tanja; Pappu, Rohit V. (July 2020, Biophysical Journal)

   null (Ed.)
4. VLA and NOEMA Views of Bok Globule CB 17: The Starless Nature of a Proposed First Hydrostatic Core Candidate

   https://doi.org/10.3847/1538-4357/ac3083  

   Spear, Stephanie; José Maureira, María; Arce, Héctor G.; Pineda, Jaime E.; Dunham, Michael; Caselli, Paola; Segura-Cox, Dominique (December 2021, The Astrophysical Journal)

   Abstract We use 3 mm continuum NOrthern Extended Millimeter Array and NH 3 Very Large Array observations toward the First Hydrostatic Core (FHSC) candidate CB 17 MMS in order to reveal the dust structure and gas properties to 600–1100 au scales and to constrain its evolutionary stage. We do not detect any compact source at the previously identified 1.3 mm point source, despite expecting a minimum signal-to-noise ratio of 9. The gas traced by NH 3 exhibits subsonic motions, with an average temperature of 10.4 K. A fit of the radial column density profile derived from the ammonia emission finds a flat inner region of radius ∼1800 au and a central density of ∼6 × 10 5 cm −3 . Virial and density structure analysis reveals the core is marginally bound ( α vir = 0.73). The region is entirely consistent with that of a young starless core, hence ruling out CB 17 MMS as an FHSC candidate. Additionally, the core exhibits a velocity gradient aligned with the major axis, showing an arc-like structure in the position–velocity diagram and an off-center region with high velocity dispersion, caused by two distinct velocity peaks. These features could be due to interactions with the nearby outflow, which appears to deflect due to the dense gas near the NH 3 column density peak. We investigate the specific angular momentum profile of the starless core, finding that it aligns closely with previous studies of similar radial profiles in Class 0 sources. This similarity to more evolved objects suggests that motions at 1000 au scales are determined by large-scale dense cloud motions, and may be preserved throughout the early stages of star formation. 

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