Rational design of fully synthetic platforms displaying active control over ionic transport in close resemblance to biological systems represents an ongoing challenge in molecular materials science. Here, we demonstrate that the synergism arising from the chemistries involved in mesoporous films and polymer brushes is a key enabler to next-generation "smart" nanofilters capable of mimicking the gating functions of specific biological channels. Hybrid functional assemblies constituted of mesoporous silica films modified with polyzwitterionic brushes are able to discriminate and gate the transport of cations while the passage of anionic species is precluded. The synthetic membranes behave as proton-gated cation-selective platforms mimicking the functioning of acid-sensing ion channels encountered in the neurons of the central nervous system. We believe that this experimental evidence will stimulate further multidisciplinary work across the boundaries of materials chemistry to attain new functional nanostructured interfaces with transport properties so far believed to be exclusive features of biological channels.
A first study of the behavior of amino functions in mesoporous hybrid thin films M 1-x (Si-(CH 2 ) 3 NH 2 ) x O 2-x/2 (M ) Si, Ti, Zr; 0.05 e x e 0.2) with accessible Im3 j m-or Fm3 j m-derived pore mesostructures is presented. An XPS study of surface nitrogen species shows two different sites corresponding to amino and ammonium groups. The ratio of these species changes with pH and is related to the nature of M, suggesting that the interaction between the organic functions and the surface M-OH groups can be tailored to tune the surface acid-base behavior. Density functional theory (DFT) calculations were used to rationalize the XPS observations showing that -NH 3 + functions irreversibly transfer a proton to neighboring M-Osurface groups. The acid-base surface properties can be further modified by adding a phosphonate "capping" on the M surface sites. Our findings have a series of interesting implications in surface functionalization: attachment of biomolecules to surfaces, design of perm-selective or philicity-selective membranes, or design of catalysts that show a well-defined organic reactive function near surface hydroxyl groups.
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