Issue 56, 2016

Hydrogen bonding interactions affect the hierarchical self-assembly and secondary structures of comb-like polypeptide supramolecular complexes displaying photoresponsive behavior

Abstract

In this study we blended 4-(4-hexadecylphenylazo)pyridine (AzoPy-C16), synthesized through facile diazonium and monoetherification reactions, with polytyrosine (PTyr) to form comb-like polypeptide supramolecular complexes stabilized through hydrogen bonding between the pyridyl ring of each AzoPy-C16 unit and the OH groups of PTyr. The secondary structure of PTyr transformed from an α-helical to a β-sheet conformation upon the addition of AzoPy-C16, because the long alkyl chains of the AzoPy-C16 units disrupted the weak intramolecular hydrogen bonds between the C[double bond, length as m-dash]O and NH groups in the α-helical conformation, as determined using Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopy. Small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) suggested a hierarchical lamellae-within-lamellae structure for the PTyr/AzoPy-C16 supramolecular complex, featuring long-range-ordered lamellae arising from the antiparallel β-pleated sheet conformation of PTyr (d = 1.15 nm) within long-range-ordered lamellae arising from the alkyl groups of AzoPy-C16 units (d = 5.94 nm), oriented in a perpendicular manner. The d-spacing and long-range order of the lamellar structure formed from the alkyl groups decreased upon UV irradiation as the rod-like trans isomers of the AzoPy-C16 units transformed into V-shaped cis counterparts. This phenomenon also led to a change in the water contact angle of the supramolecular material, with the hydrophobic surface of PTyr/trans-AzoPy-C16 (94.2°) transforming to a hydrophilic surface for PTyr/cis-AzoPy-C16 (61.3°).

Graphical abstract: Hydrogen bonding interactions affect the hierarchical self-assembly and secondary structures of comb-like polypeptide supramolecular complexes displaying photoresponsive behavior

Supplementary files

Article information

Article type
Paper
Submitted
27 Mar 2016
Accepted
16 May 2016
First published
18 May 2016

RSC Adv., 2016,6, 51456-51469

Hydrogen bonding interactions affect the hierarchical self-assembly and secondary structures of comb-like polypeptide supramolecular complexes displaying photoresponsive behavior

M. G. Mohamed, J. Tu, S. Huang, Y. Chiang and S. Kuo, RSC Adv., 2016, 6, 51456 DOI: 10.1039/C6RA07907E

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