Guest Molecule-Mediated Energy Harvesting in a Conformationally Sensitive Peptide-Metal Organic Framework

Abstract

The apparent piezoelectricity of biological materials is not yet fully understood at the molecular level. In particular, dynamic noncovalent interactions, such as host-guest binding, are not included in the classical piezoelectric model, which limits the rational design of eco-friendly piezoelectric supramolecular materials. Here, inspired by the conformation-dependent mechanoresponse of the Piezo channel proteins, we show that guest-host interactions can amplify the electromechanical response of a conformationally mobile peptide metal-organic framework (MOF) based on the endogenous carnosine dipeptide, demonstrating a new type of adaptive piezoelectric supramolecular material. Density functional theory (DFT) predictions validated by piezoresponse force microscopy (PFM) measurements show that directional alignment of the guest molecules in the host carnosine-zinc peptide MOF channel determines the macroscopic electromechanical properties. We produce stable, robust 1.4 V open-circuit voltage under applied force of 25 N with a frequency of 0.1 Hz. Our findings demonstrate that the regulation of host-guest interactions could serve as an efficient method for engineering sustainable peptide-based power generators.

Figure 1

(a) Schematic illustration of the combination of methods used to decipher and optimize the guest molecule-mediated electromechanical properties of bio-inspired peptide-MOFs. Modeling-guided statistical PFM measures the piezoelectric tensor of peptide-MOF crystals, allowing us to map the relationship between microstructure and electromechanical behavior. (b) Powder X-ray diffraction (XRD) patterns of Car_Zn MOF incubated with five different guest molecules. (c–g) Scanning electron microscopy (SEM) images of neat prismatic morphologies of all assembled crystalline architectures (scale bar: 2, 3, 1, 10, and 3 μm, respectively), namely, the triangular prism morphology for Car_Zn with guest IPA or EtOH, rectangular prism morphology with acetone or DMF, and representative hexagonal prism morphology observed in Car_Zn·(MeCN).

Figure 2

Structural analysis of Car_Zn MOFs. (a) The carnosine molecule links four tetrahedral Zn cations. (b) The unit cell parameters of Car_Zn·(IPA) (left panel) and Car_Zn·(MeCN) (right panel) and their prismatic morphologies predicted by the Bravais, Friedel, Donnay, and Harker (BFDH) method. (c) Reverse-interdigitated arrangement of the “T” shape of carnosine facilitates the formation of lozenge-shaped channels. Color code: green, Zn; gray, C; blue, N; and red, O. (d, e) View down the one-dimensional channels of (d) Car_Zn·(IPA) and (e) Car_Zn·(MeCN) shows the change in channel shape and orientation caused by the guest molecule. (f, g) Hydrogen-bonding pattern of (f) Car_Zn·(IPA) and (g) Car_Zn·(MeCN) illustrates how the nature of the guest molecule in the channel affects the conformation of the peptide linker through hydrogen bonds.

Figure 3

Mechanical and piezoelectric properties of the Car_Zn·(MeCN) crystal. (a) Directional guest solvent MeCN molecule alignment (circled in red) in the Car_Zn framework channel and molecular dipole sum to a spontaneous crystal polarization (green arrow in right panel) along the a-axis. (b) Molecule dipole of MeCN. (c) Young’s modulus and (d) point stiffness statistical distributions of the Car_Zn·(MeCN) crystal. (e) Calculated piezoelectric strain constants for the Car_Zn·(MeCN) crystal. (f, g) Experimental measurement of piezoelectric coefficients using PFM. (f) Statistical distribution of the vertical d_L^eff coefficients. (g) Statistical distribution of the shear d_S^eff coefficients. The mean and median values for each distribution are shown alongside the theoretical maximum DFT value to demonstrate the good correspondence between DFT predictions and experimental measurements.

Figure 4

Characterization of the peptide-MOF-based generator. (a) Schematic configuration of the generator using the Car_Zn·(MeCN) crystal as the active component. (b) Open-circuit voltage and (c) short-circuit current obtained from the generator with an applied periodic compressive force of 25 N. (d) Open-circuit voltage and (e) short-circuit current of the generator as a function of the applied force. (f) Stability measurement of the peptide-MOF-based generator. The open-circuit voltage was recorded continually under ∼19 N applied force at a frequency of 0.1 Hz.