Synthesis and Conformational Transition of Surface-Tethered Polypeptide:  Poly(l-lysine)

Abstract

Poly(l-lysine) (PLL) was end-grafted onto silicon oxide surfaces to study its conformational transition among α-helix, β-sheet, and random coil at the solid−water interface. Surface-grafted PLL films were prepared from surface-grafted poly(N ε -carbobenzyloxy-l-lysine) (PCBL) thin films, which were fabricated by the surface-initiated vapor-deposition polymerization (SI-VDP) of N-carboxyanhydride (NCA) of N ε -carbobenzyloxy-l-lysine. The reaction parameters during the SI-VDP process, including NCA concentration, substrate temperature, and reaction time, were optimized in order to synthesize homogeneous PCBL films with well-controlled thickness. Under the optimal conditions (substrate temperature at 105 °C, NCA evaporating temperature at 100 °C, and 8 mg of NCA at 0.1 Pa), α-helical PCBL films with thickness ranging from 4 to 120 nm can be synthesized by controlling the reaction time from 5 to 120 min. The conversion from PCBL to PLL was accomplished by removing N ε -carbobenzyloxy groups in the hydrogen bromide/benzene solution with the aid of ultrasonication for 40 min. The surface-grafted PLL films with an estimated DP of 750 exhibited versatile conformations among α-helix, β-sheet, and random coil depending on the external environments. The conformational transition from one state to another was successfully induced by external stimuli, such as pH (H+/OH-), surfactant (sodium dodecyl sulfate (SDS)), and anion (ClO4 -). In the process of the conformational transition, macroscopic properties such as thickness, refractive index, and wettability changed correspondingly. For example, a surface-grafted random-coiled PLL had a film thickness of 215 nm and a refractive index of 1.37 at pH 7, whereas it changed to a β-sheet conformation when binding with SDS, with the film thickness shrinking to 145 nm and the refractive index increasing to 1.45. Compared to the free PLL chains, the stability of the helical state increased when the PLL chains were densely immobilized on the surfaces. The transitional behaviors were characterized by Fourier transform infrared spectroscopy, circular dichroism spectroscopy, and ellipsometry.

Ionic polypeptides with unusual helical stability

“…The M n is 12,500 g mol − 1 and PDI (M w /M n ) is 1.15 as characterized by gel permeation chromatograph (GPC). The deprotection of PBLG 57 was performed at 0 °C to give PLG 57 in quantitative yield by following a slightly modified, standard procedure [36][37][38] . The resulting polymer (500 mg) was treated with 2 M NaOH (10 ml) and then with CBZ-Cl (0.1 ml) for 16 h to protect the amino terminus of PLG with CBZ.…”

Self‐Assembled Micelles Based on PEG‐Polypeptide Hybrid Copolymers for Drug Delivery

“…[14] Further verification of the secondary molecular structure of the PLL-PEG-PLL micelles was confirmed by CD. In the CD spectrum (Figure 3a), two negative bands at 208 and 220 nm can be detected, which can be assigned to p-p à and n-p à transitions, respectively, due to Cotton effects.…”

Studies on visual sensor from self-assembled polypeptides

“…CD spectra of silane terminated PBCL in TFE (dashed line) and deposited on quartz plate (solid line). cationic surface [15]. The monolayer of silane terminated PLL does not strip off from the pre-colored silica substrate against the AFM probe scratching.…”