Article pubs.acs.org/JPCB
Thermodynamic Factors Impacting the Peptide-Driven Self-Assembly of Perylene Diimide Nanofibers Galen L. Eakins,†,‡ Joseph K. Gallaher,†,‡ Robert A. Keyzers,‡ Alexander Falber,⊥,∥ James E. A. Webb,⊥ Alistair Laos,⊥ Yaron Tidhar,§ Haim Weissman,§ Boris Rybtchinski,§ Pall Thordarson,⊥ and Justin M. Hodgkiss*,†,‡ †
MacDiarmid Institute for Advanced Materials and Nanotechnology, ‡School of Chemical and Physical Sciences, Victoria University of Wellington, P.O. Box 600, Wellington 6012, New Zealand ⊥ School of Chemistry and the Australian Centre for Nanomedicine, The University of New South Wales, Sydney, NSW 2052, Australia ∥ Flurosol Industries Pty. Ltd., Level 5, 574 St. Kilda Road, Melbourne, VIC 3004, Australia § Department of Organic Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel S Supporting Information *
ABSTRACT: Synthetic peptides offer enormous potential to encode the assembly of molecular electronic components, provided that the complex range of interactions is distilled into simple design rules. Here, we report a spectroscopic investigation of aggregation in an extensive series of peptide-perylene diiimide conjugates designed to interrogate the effect of structural variations. By fitting different contributions to temperature dependent optical absorption spectra, we quantify both the thermodynamics and the nature of aggregation for peptides by incrementally varying hydrophobicity, charge density, length, as well as asymmetric substitution with a hexyl chain, and stereocenter inversion. We find that coarse effects like hydrophobicity and hexyl substitution have the greatest impact on aggregation thermodynamics, which are separated into enthalpic and entropic contributions. Moreover, significant peptide packing effects are resolved via stereocenter inversion studies, particularly when examining the nature of aggregates formed and the coupling between π electronic orbitals. Our results develop a quantitative framework for establishing structure−function relationships that will underpin the design of self-assembling peptide electronic materials.
■
INTRODUCTION Nature has evolved an exquisite self-assembly toolbox, which is illustrated in proteins whose precise three-dimensional folding and interaction with other elements is encoded by the sequence of amino acids.1−3 Protein subunits can be bound in specific configurations via relatively short (
Thermodynamic Factors Impacting the Peptide-Driven Self-Assembly of Perylene Diimide Nanofibers Galen L. Eakins,†,‡ Joseph K. Gallaher,†,‡ Robert A. Keyzers,‡ Alexander Falber,⊥,∥ James E. A. Webb,⊥ Alistair Laos,⊥ Yaron Tidhar,§ Haim Weissman,§ Boris Rybtchinski,§ Pall Thordarson,⊥ and Justin M. Hodgkiss*,†,‡ †
MacDiarmid Institute for Advanced Materials and Nanotechnology, ‡School of Chemical and Physical Sciences, Victoria University of Wellington, P.O. Box 600, Wellington 6012, New Zealand ⊥ School of Chemistry and the Australian Centre for Nanomedicine, The University of New South Wales, Sydney, NSW 2052, Australia ∥ Flurosol Industries Pty. Ltd., Level 5, 574 St. Kilda Road, Melbourne, VIC 3004, Australia § Department of Organic Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel S Supporting Information *
ABSTRACT: Synthetic peptides offer enormous potential to encode the assembly of molecular electronic components, provided that the complex range of interactions is distilled into simple design rules. Here, we report a spectroscopic investigation of aggregation in an extensive series of peptide-perylene diiimide conjugates designed to interrogate the effect of structural variations. By fitting different contributions to temperature dependent optical absorption spectra, we quantify both the thermodynamics and the nature of aggregation for peptides by incrementally varying hydrophobicity, charge density, length, as well as asymmetric substitution with a hexyl chain, and stereocenter inversion. We find that coarse effects like hydrophobicity and hexyl substitution have the greatest impact on aggregation thermodynamics, which are separated into enthalpic and entropic contributions. Moreover, significant peptide packing effects are resolved via stereocenter inversion studies, particularly when examining the nature of aggregates formed and the coupling between π electronic orbitals. Our results develop a quantitative framework for establishing structure−function relationships that will underpin the design of self-assembling peptide electronic materials.
■
INTRODUCTION Nature has evolved an exquisite self-assembly toolbox, which is illustrated in proteins whose precise three-dimensional folding and interaction with other elements is encoded by the sequence of amino acids.1−3 Protein subunits can be bound in specific configurations via relatively short (
