Abstract
Synthesized polypeptide is attracting an increased interests due to its excellent biological characteristic and adjustable chemical properties in bio-related fields. But polypeptide itself has no switching properties, which is harmful to the development of its application as a control component. Herein, light-responsive poly(γ-benzyl-L-glutamate)s (PBLGs) is synthesized by a one-step NCA method using p-aminoazobenzene (m-AZO) and p-diaminoazobenzene (m-DAZO) as initiators. PBLGs exhibit amorphous characteristics with obvious Tg transition, which are 14°C for PBLG1 and 21°C for PBLG2. In order to forecast the structure-property information of PBLGs, theoretical UV-vis spectra as well as the energy gap between HOMO and LUMO is calculated by DFT calculation. Experimental results of UV-vis spectra exhibit similar characteristics to those of theorical UV-vis spectra except for the 40–50 nm red-shifting of absorbance peak. Furthermore, the absorbance intensities of PBLGs have a good linear relationship with their concentration, but their linearity range depending on concentration is completely different. Then, trans–cis transition under a different excitation source and cis–trans recovery in a dark environment are tracked in real-time by UV-vis spectra to evaluate the light response performances. It is found that UV light is the only effective excitation source for PBLG1, and blue light is another effective excitation source for PBLG2 besides UV light. Furthermore, the addition of alcohol and water as cosolvents has little effect on trans→cis transition in UV-light-excited systems, but it shortens recovery time of the cis→trans process in a dark environment. By contrast, the detectable isomerization process becomes unclear with the addition of alcohol in blue-light-excited system. Furthermore, either alcohol or water in solvents accelerate both the trans→cis and cis→trans process in a blue-light-excited system.
Highlights
Polypeptide has a similar chemical component and secondary structure to a natural protein, which plays an essential role in biological activities (Li et al, 2017; Skoulas et al, 2017; Zhou et al, 2017; Editors, 2019; Duan and Li, 2020; Duong et al, 2020)
Before synthesis of PBLGs, a BLG monomer was synthesized by elimination reaction with participation of triphosgene
Since areas of resonance peaks are proportional to the number of protons, the ratio of different peak area is equal to ratio of proton number at different positions
Summary
Polypeptide has a similar chemical component and secondary structure to a natural protein, which plays an essential role in biological activities (Li et al, 2017; Skoulas et al, 2017; Zhou et al, 2017; Editors, 2019; Duan and Li, 2020; Duong et al, 2020). Light-responsive PBLGs as Photo Switches polypeptides, synthesized polypeptides are the main focus due to their flexible and controllable molecular structure and are usually realized by biological synthesis, solid phase peptide synthesis (SPPS), and ring-open polymerization (ROP) based on the αamino acid N-carboxyanhydrides (NCA method) (Wibowo et al, 2014; Shen et al, 2015; Zhou and Li, 2018). Γ-benzyl-L-glutamate (BLG) is a kind of readily available and low-cost amino acid with good performance (Cauchois et al, 2013; de Miguel et al, 2014; Sun et al, 2015) It can be polymerized into poly(γ-benzylL-glutamate) (PBLG) by the NCA method through two steps, namely, synthesis of γ-benzyl-L-glutamate-N-carboxyanhydride (BLG-NCA) and ROP of NCA. Light density was set at 1000 Lux, and temperature was set at room temperature
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