Regulation of Self-assembling Process of a Cationic β-Sheet Peptide by Photoisomerization of an Anionic Azobenzene Derivative

Abstract

Advances in molecular self-assembly are essential to establish practical guidelines to fabricate novel nanostructured materials. Our focus has been on artificial peptides as building blocks for the design of functional materials. 1 The interest in peptides is based on their ability to hierarchically self-organize into well-defined three-dimensional architectures than those which can be generated from conventional synthetic block polymers. In particular, much attention has been focused on the biological -sheet motif because of their association with neurodegenerative diseases like Alzheimer's, and as a building unit in the design of supramolecular nanofibers.2-7 Recently, we have reported that the triblock-type amphiphilic peptide, L 4 K 8 L 4 (LKL16), is an excellent -sheet foldamer and can be hierarchically self-assembled into amyloid-like nanofibers upon partial neutralization of the Lys residues at around pH 9.6,7 However, it is still difficult to control the spontaneous aggregation processes of peptides. Creating novel and facile methodology to regulate the self-assembling processes by external signals, such as light, 8 is therefore valuable to facilitate a bottom-up nanotechnology.Here we report a photo-responsive molecular system, in which self-assembling process of the cationic peptide intosheet nanofibers is regulated by photoisomerism of the exogenous anionic azobenzene derivative. Azobenzene is well known to change the overall geometry from planar to non-planar and the polarity of azo-linkage by trans-cis photoisomerization. In previous studies concerning azobenzene-conjugated peptide molecular systems, such changes in physical properties of azobenzenes have been utilized as a photosensitive switch to regulate conformation, 9 high-order structure, 10 and hydrogen-bonding pattern 11 of peptides. To our knowledge, however, it is the first report that the process of nanofiber formation is controlled by using a polarity change of photochromic additive, which causes slight change of total hydrophobicity of the target peptide.An azobenzene derivative with two carboxylate anions, azo(COO À ) 2 , was employed as a control agent for self-assembly of the cationic LKL16. The preparation of LKL16 and its self-assembling properties in water have been described elsewhere. 7 The azo(COO À ) 2 was synthesized by reacting the 4,4 0 -azodianiline with succinic anhydride. Photoisomerization of the azo(COO À ) 2 was first of all investigated in the presence of LKL16 at pH 9.2. In this condition, the azo(COO À ) 2 couples with the peptide, which is supported by FT-IR study (described later). The azo(COO À ) 2 existed in trans-form with an absorption at 370 nm upon dark adaptation. In contrast, UV irradiation of trans-azo(COO À ) 2 at 365 nm (4W UV lamp) caused a rapid conversion to the cisisomer within 1 min, as evidenced by a ca. 60% reduction in the peak intensity at 370 nm and an increase in the absorbance at 270 and 500 nm. Such photoisomerism of the azo(COO À ) 2 affected the conformational properties of LKL16. Figure...

Injectable Hydrogel: Amplifying the pH Sensitivity of a Triblock Copolypeptide by Conjugating the N-Termini via Dynamic Covalent Bonding

“…In fact, it has been previously reported that the changes in total hydrophobicity of artificial and amphiphilic peptides by guest additives, such as cyclodextrin 52 and azobenzene derivatives, 53 affect the self-assembling process of the amphiphilic peptides. In particular, it was reported that the hydrophobicity enhancement of the peptides promotes the structural transition into β-sheet drastically.…”

Functional Nano-Objects by Electrostatic Self-Assembly: Structure, Switching, and Photocatalysis

“…In nano-assemblies azo benzenes were first used to change vesicles into elongated structures upon irradiation ( Sakai et al, 1999 ). The first light-responsive electrostatically self-assembled nanostructures based on azobenzenes were formed by Higashi et al ( Koga et al, 2007 ). They assembled an anionic azobenzenes derivate with a cationic β-sheet peptide into nanofibers.…”

Recent Progress in Ionic Coassembly of Cationic Peptides and Anionic Species

“…This size-dependence implied that the counterions were adsorbed on the inner face of the lanreotide nanotube walls. Recently, an ionic coassembly system based on cationic triblock-type peptide (L 4 K 8 L 4 , P2) and azobenzene derivative with two carboxylate anions (azo(COO − ) 2 ) has been reported by Koga et al [87] The photoresponsive azobenzene anion with switchable geometry could be employed to regulate the coassembling kinetic process. Yang et al investigated the effect of charges of anions on the assembled nanostructures of cationic peptide EAK 16 (II)GGH (P3).…”

“…Recently, an ionic coassembly system based on cationic triblock‐type peptide (L 4 K 8 L 4 , P2 ) and azobenzene derivative with two carboxylate anions (azo(COO − ) 2 ) has been reported by Koga et al. [ 87 ] The photoresponsive azobenzene anion with switchable geometry could be employed to regulate the coassembling kinetic process. Yang et al.…”