pH-Regulated Selectivity in Supramolecular Polymerizations: Switching between Co- and Homopolymers [feedly]

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pH-Regulated Selectivity in Supramolecular Polymerizations: Switching between Co- and Homopolymers
// ChemEurJ

Abstract

A strategy is presented to regulate the selectivity in aqueous supramolecular polymerizations by changes in pH. In neutral buffered conditions, oppositely charged phenylalanine-based dendritic peptide amphiphiles self-assemble into (AB)_n alternating copolymers of low polydispersity when mixed in a 1:1 comonomer feed ratio. Via pH switch of the glutamic acid and lysine side chains, attractive Coulomb interactions in the coassembled materials are screened and selective polymerization occurs to form (A)_n homopolymers of the acidic comonomer at low pH and (B)_n homopolymers of the basic comonomer at high pH, while the complementary comonomer is released during the transition. Reversible switching is demonstrated between these three different polymeric states, which were characterized by CD and fluorescence spectroscopy, using a peptide based minimalistic fluorophore/quencher pair, and transmission electron microscopy.

Switchcraft: A strategy to regulate the selectivity in aqueous supramolecular polymerizations is presented. In neutral buffer, oppositely charged dendritic peptide amphiphiles selectively self-assemble into alternating copolymers. At high and low pH, the formation of either the basic or acidic homopolymer occurs while the complementary comonomer is released. The transition between these three different polymeric states is fully reversible and can be switched multiple times.

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B.Osmialowski

Frontispiece: Anionic CH⋅⋅⋅X− Hydrogen Bonds: Origin of Their Strength, Geometry, and Other Properties [feedly]

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Frontispiece: Anionic CH⋅⋅⋅X− Hydrogen Bonds: Origin of Their Strength, Geometry, and Other Properties
// ChemEurJ

The Power of the H-Bond Because of its importance and widespread occurrence, the phenomenon of H-bonding has motivated an enormous amount of investigative effort over the years. In their Full Paper on page 1474 ff., B. Nepal and S. Scheiner describe the various sources of binding in the CH⋅⋅⋅X⁻ⁿ H-bond between F₃CH and various anions. The top figure in the highlight graphic shows the charge transfer from a F lone pair into the σ*(CH) antibonding orbital. The Coulombic attraction between the F⁻ anion and the most positive region of F₃CH is displayed in the middle section. The lower segment illustrates the redistribution of electron density that occurs when the two subunits interact, increases in purple and losses in blue.

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Thermochromic and Mechanochromic Luminescence Umpolung in Isostructural Metal–Organic Frameworks Based on Cu6I6 Clusters [feedly]

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Thermochromic and Mechanochromic Luminescence Umpolung in Isostructural Metal–Organic Frameworks Based on Cu6I6 Clusters
// InorgChem

Inorganic Chemistry

DOI: 10.1021/ic502207f

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B.Osmialowski