Self-assembly of Boc-p-nitro-l-phenylalanyl-p-nitro-l-phenylalanine and Boc-l-phenylalanyl-l-tyrosine in solution and into piezoelectric electrospun fibers

Abstract

Self-assembly of two N-tert-butoxycarbonyl (Boc) protected analogues of diphenylalanine dipeptide, Boc-p-nitro-l-phenylalanyl-p-nitro-l-phenylalanine and Boc-l-phenylalanyl-l-tyrosine, respectively, Boc-pNPhepNPhe and Boc-PheTyr, in 1,1,1,3,3,3-hexafluoro-2-propanol/ethanol(water) solvents and into electrospun fibers is studied. Uncommon dual self-assembly is found for Boc-pNPhepNPhe, with the formation of nanotubes which in turn self-assemble themselves into microtapes. Boc-PheTyr self-assembles into microspheres or microtapes depending on the solvent. Optical absorption and photoluminescence exhibit step-like peaks in the spectral region of 240-290 nm indicating quantum confinement due to nanostructure formation. The dipeptides were further embedded into electrospun fibers, generating high output voltages through the piezoelectric effect. For Boc-pNPhepNPhe a maximum output voltage of 58 V, a power density of 9 μW cm−2 and effective piezoelectric voltage coefficients geff ≅ 0.6 Vm N−1 were measured under a 1.5 N applied periodical force. Its estimated effective piezoelectric coefficient is twice that of diphenylalanine dipeptide.