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 g_eff ≅ 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.