Metal cross-linking of helical oligoamide nanorods serves as platform for hierarchical nanofibers

Abstract Helical $$\upbeta$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>β</mml:mi> </mml:math> -oligoamides serve as versatile molecular building blocks with the unique ability to maintain stable helical fold and be functionalized by sequence modifications without affecting the folding ability. Fibrous head-to-tail self-assembly of these building blocks provides a platform to develop complex nanomaterials. In this study, the metallosupramolecular structure formed by Cu(II) coordination of the Ac- $$\upbeta$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>β</mml:mi> </mml:math> 3 A $$\upbeta$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>β</mml:mi> </mml:math> 3 V $$\upbeta$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>β</mml:mi> </mml:math> 3 S- $$\upalpha$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>α</mml:mi> </mml:math> H- $$\upbeta$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>β</mml:mi> </mml:math> 3 A $$\upbeta$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>β</mml:mi> </mml:math> 3 V $$\upbeta$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>β</mml:mi> </mml:math> 3 A ( 1 H ) oligoamide was characterized with spectroscopic, microscopic, and computational methods. Our findings demonstrate that the hybrid sequence leads to a complex helical structure combining a 13-helix on a 14-helix template, stabilized by bifurcated hydrogen bonds. We observe that the 1 H fibers form in solution, and that copper coordination increases the size of the colloidal structures. When deposited, a homogeneous two-dimensional surface coating was produced, and based on our measurements we are able to propose a structure for the supramolecular framework. These results underline the utility of metallosupramolecular frameworks in bottom-up nanofabrication and nanostructured surface coatings. Graphical abstract Impact statement This work describes a unique concept in designing hierarchical nanostructured framework-type materials using self-assembly principles. These materials incorporate a combination of head-to-tail supramolecular self-assembly of small helical beta-oligoamide units into nanorods, such as a molecular LEGO system, that are then cross-linked in a specific and geometrically defined way with metal coordination. The resulting materials have a definite internal structure that was assessed with a combination of computer modeling and experimental methods, including atomic force microscopy (AFM), small angle x-ray scattering (SAXS), x-ray photoelectron spectroscopy (XPS), infrared (IR) spectroscopy as well as ultrahigh-resolution STM that made it possible to visualize submolecular details. The ability to form a polynuclear metal complex core in nanoscale fiber bundles in a highly regular but noncrystalline structure opens a range of possibilities for using these materials in, for example, smart fabrics, implants, and potentially molecular electronic and electrooptic applications.