Tuning underwater adhesion with cation–π interactions

Journal name:
Nature Chemistry
Year published:
Published online
Corrected online


Cation–π interactions drive the self-assembly and cohesion of many biological molecules, including the adhesion proteins of several marine organisms. Although the origin of cation–π bonds in isolated pairs has been extensively studied, the energetics of cation–π-driven self-assembly in molecular films remains uncharted. Here we use nanoscale force measurements in combination with solid-state NMR spectroscopy to show that the cohesive properties of simple aromatic- and lysine-rich peptides rival those of the strong reversible intermolecular cohesion exhibited by adhesion proteins of marine mussel. In particular, we show that peptides incorporating the amino acid phenylalanine, a functional group that is conspicuously sparing in the sequences of mussel proteins, exhibit reversible adhesion interactions significantly exceeding that of analogous mussel-mimetic peptides. More broadly, we demonstrate that interfacial confinement fundamentally alters the energetics of cation–π-mediated assembly: an insight that should prove relevant for diverse areas, which range from rationalizing biological assembly to engineering peptide-based biomaterials.

At a glance


  1. Sequences and molecular structures of the peptides studied.
    Figure 1: Sequences and molecular structures of the peptides studied.

    a,b, Each of the four peptides included one of the amino acids illustrated in b, incorporated in the sequence locations marked by a purple ‘X’ in a. The Lys residues are conserved in each peptide sequence and are marked in blue to emphasize the positive charge of Lys at a pH of 2.5.

  2. Schematic of the SFA set-up and illustration of the surface–peptide–surface interface studied.
    Figure 2: Schematic of the SFA set-up and illustration of the surface–peptide–surface interface studied.

    a, SFA experimental set-up. The peptide was solution deposited onto mica surfaces before placing it into the SFA, and all the experiments were performed in a pH 2.5 buffer solution of 100 mM acetic acid and 250 mM KNO3, without additional dissolved peptide. b, When the two surfaces are compressed into hard contact, a multilayer peptide film is confined between the two surfaces. When the surfaces are separated, failure occurs within the peptide film, which means that the measured work of adhesion is proportional to the intermolecular interactions between peptide molecules.

  3. Representative force–distance data measured for peptides between mica surfaces.
    Figure 3: Representative force–distance data measured for peptides between mica surfaces.

    a, Representative force–distance profiles measured when two mica surfaces are brought together in 100 mM acetic acid and 250 mM KNO3. Measurements were also performed under variable solution salinities and are presented in Supplementary Figs 4 and  5. Positive forces are repulsive and negative forces are attractive. The black data were measured in the absence of adsorbed peptide, and each of the coloured curves corresponds to an experiment in which the peptide was adsorbed onto a single mica surface. b, Representative profiles measured when mica surfaces are separated in 100 mM acetic acid and 250 mM KNO3. The black force–distance profile measured in the absence of peptide exhibits repulsive behaviour, which supports that the adhesion measured in the presence of peptide films results from peptide intermolecular cohesion. The average work of adhesion and associated uncertainty quoted on the plot was obtained from at least ten different force–distance profiles for each peptide. Small variations in peptide-film thicknesses were measured between different experiments, and these variations exhibited no dependence on the peptide molecular structure. Importantly, the work of adhesion does not exhibit a systematic dependence on the film thickness, which implies that the cohesion interactions are independent of minor variations in the film thickness.

  4. Solid-state 2D 13C{1H} HETCOR MAS NMR spectrum acquired from bulk Tyr peptide with a 1D 13C{1H} CP MAS NMR spectrum along the top horizontal axis and a single-pulse 1H MAS NMR spectrum along the left vertical axis.
    Figure 4: Solid-state 2D 13C{1H} HETCOR MAS NMR spectrum acquired from bulk Tyr peptide with a 1D 13C{1H} CP MAS NMR spectrum along the top horizontal axis and a single-pulse 1H MAS NMR spectrum along the left vertical axis.

    Red arrows indicate the intensity correlations that result from the close proximities (<1 nm) of the aromatic b–e 1H moieties of the tyrosine residues (purple letters) and alkyl l and m 13C moieties of the lysine side chains (blue letters). The superscript ‘+’ denotes chemical shifts associated with protonated (positive) lysine residues, whereas the superscript ‘neut.’ denotes chemical shifts associated with neutral lysine residues. The intersection of the shaded red bands indicates a correlated intensity that arises from the proximate alkyl j 13C moieties and protonated amide ε+ 1H moieties of lysine residues, which resonate approximately 0.6 ppm to a lower frequency in the 1H dimension compared with a Leu sample measured under otherwise identical conditions (Supplementary Fig. 5). Such a displacement is consistent with ring-current effects that would result from a configuration of the lysine and tyrosine side chains shown schematically in the inset, associated with inter-residue contact through cation–π electron interactions. All the NMR measurements were conducted at 11.74 T under 10 kHz MAS conditions at 0 °C.

  5. Schematic that depicts the proposed mechanism of cation–π binding in aromatic- and Lys-rich peptide films, with many cation–aromatic binding pairs forming in close proximity.
    Figure 5: Schematic that depicts the proposed mechanism of cation–π binding in aromatic- and Lys-rich peptide films, with many cation–aromatic binding pairs forming in close proximity.

    Each cation–π pair is positively charged, and anion complexation is required to avoid strongly repulsive electrostatic interactions. The most favourable configuration for the anions is within the plane of the aromatic rings, as illustrated by the shaded pink areas that surround the aromatic groups. Aromatic hydroxylation reduces the total volume of favourable anion-interaction sites that are in direct molecular contact with the aromatic ring, illustrated by the reduced pink area in the Dopa panel relative to the Phe panel. Aromatic hydroxylation may also provide a second type of anion interaction site that could be important for anions that form strong hydrogen bonds, illustrated by the green area. The potential importance of hydrogen bonding between ions and aromatic substituents awaits future studies. We propose that an increased configurational entropy within the Phe films is the molecular origin of the increased cohesion present in the Phe peptide relative to the Dopa and Tyr peptides.

Change history

Corrected online 08 June 2017
In the version of this Article originally published, the accept date was incorrect and should have read ‘9 December 2016’. This has now been corrected in the online versions of the Article.


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Author information


  1. Materials Department, University of California, Santa Barbara, California 93106, USA

    • Matthew A. Gebbie,
    • Thomas R. Cristiani &
    • Jacob N. Israelachvili
  2. Materials Research Laboratory, University of California, Santa Barbara, California 93106, USA

    • Matthew A. Gebbie,
    • Wei Wei,
    • Alex M. Schrader,
    • J. Herbert Waite &
    • Jacob N. Israelachvili
  3. Department of Molecular, Cell and Developmental Biology, University of California, Santa Barbara, California 93106, USA

    • Alex M. Schrader &
    • J. Herbert Waite
  4. Department of Chemical Engineering, University of California, Santa Barbara, California 93106, USA

    • Howard A. Dobbs,
    • Matthew Idso,
    • Bradley F. Chmelka &
    • Jacob N. Israelachvili


M.A.G. and W.W. contributed equally to this work. M.A.G., W.W., J.H.W. and J.N.I. conceived the research. M.A.G., A.M.S. and T.R.C. performed and analysed the force–distance measurements, W.W. synthesized and purified the peptides, M.A.G., H.A.D. and M.I. performed the NMR measurements, H.A.D., M.I. and B.F.C. analysed the NMR results, M.A.G. wrote the paper. All of the authors interpreted the data, discussed the results and commented on the manuscript.

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