ABSTRACT
Helical structures are ubiquitous in biological materials and often serve a structural purpose. Bioinspired helical materials can be challenging to synthesize and rarely reach the degree of hierarchy of their natural counterparts. Here we report the first example of particles synthesized by direct emulsification of polypeptides found to display spiral morphologies in the dry state. The polypeptides were α-helical homo- and copolypeptides of γ-benzyl glutamate and allylglycine. The chirality of the spirals was controlled by the chirality of the α-helices. Notably, right-handed α-helical polypeptides (rich in l residues) produced clockwise spirals, whereas left-handed α-helical polypeptides (rich in d residues) produced the enantiomorphs, i.e., counterclockwise spirals. The disruption of the α-helical conformation by the introduction of chiral defects led to less regular spirals and in some cases their suppression. A hypothesis for the transmission of helicity and chirality from a molecular to a higher hierarchical level, involving fibril bundling of coiled α-helices, is proposed.
Subject(s)
Peptides/chemical synthesis , Particle Size , Peptides/chemistry , Protein Conformation, alpha-Helical , Stereoisomerism , Surface PropertiesABSTRACT
Owing to its rod-like α-helical secondary structure, the synthetic polypeptide poly(γ-benzyl-l-glutamate) (PBlG) can form physical and thermoreversible gels in helicogenic solvents such as toluene. The versatility of PBlG can be increased by introducing functionalizable comonomers, such as allylglycine (AG). In this work we examined the secondary structure of PBlG and a series of statistical poly(γ-benzyl-l-glutamate-co-allylglycine) copolypeptides, varying in composition and chain length, by circular dichroism (CD), Fourier-transform infrared (FTIR) and Raman spectroscopy, and wide-angle X-ray scattering (WAXS). The secondary structure of PBlG and the copolypeptides presented dissimilarities that increased with increasing AG molar fraction, especially when racemic AG units were incorporated. The physical gelation behavior of these copolypeptides was analyzed by temperature-sweep (1)H NMR and rheological measurements. The study revealed that both copolypeptide composition and chain length affected secondary structure, gelation temperature, and gel stiffness.
Subject(s)
Gels/chemistry , Peptides/chemistry , Polyglutamic Acid/chemistry , Polymers/chemistry , Circular Dichroism , Hydrogen-Ion Concentration , Magnetic Resonance Spectroscopy , Protein Conformation, alpha-HelicalABSTRACT
Stable commercial primary ammonium chlorides were combined with tertiary amines to initiate the controlled ring opening polymerisation of amino acid N-carboxyanhydrides to yield polypeptides with defined end group structure, predetermined molar mass and narrow molar mass distribution.