Studies on syntheses and self-assembly behaviour of homoseleno-peptides

The development of straightforward synthetic and characterization methods for selenopeptides is essential to discovering hierarchical structured functional materials. Here, the synthesis of a series of homo-selenopeptides 1-4, having the benzyl (Bzl) group-protected selenocysteine [(Bzl)SeCH₂CH(NH₂)COOH] monomer units in the sequence, is reported. The homo-selenopeptides 1-4 are characterized by 1D (¹H, ¹³C, and ⁷⁷Se) and 2D (¹H-¹H COSY, ¹H-¹H NOESY, and ¹H-¹H TOCSY) NMR spectroscopy, and ESI-MS spectrometry. The triselenopeptide 1 shows a propensity for self-assembly into β-sheet amyloid-like fibril structure in acetonitrile (ACN) solution at room temperature. This has systematically been analyzed and established through the spectroscopic techniques; FT-IR, CD, and ThT-based fluorescence spectroscopy for secondary bonding analyses and microscopic techniques; SEM and TEM for the amyloid-like fibril structure in ACN solution. The amide I band vibrational stretching frequencies observed in the range 1600-1700 cm⁻¹ confirm that all peptides in the homologous series have a strong propensity to form amyloid-like fibril structures.

Graphical abstract

Synthesis of a series of homo-selenopeptides 1-4 through the solid-phase peptide synthesis (SPPS), using Fmoc protected Sec(Bzl)-OH as a source of amino acid, has been described. Spectroscopic and morphological imaging studies revealed that the homo-selenopeptides have a high propensity to get self-organized into amyloid-like fibrillar structures.