Insulin-induced conformational transition of fluorescent copolymers: a perspective of self-assembly between protein and micellar solutions of smart copolymers

• Published in: Physical chemistry chemical physics : PCCP 2020-05, Vol.22 (17), p.9573-9586
• Main Authors: Kumar, Krishan, Mogha, Navin Kumar, Yadav, Ritu, Venkatesu, Pannuru
• Format: Article
• Language: English
• Subjects: Aqueous solutions; Assembling; Atomic beam spectroscopy; Atomic force microscopy; Biomimetics; Block copolymers; Body temperature; Caprolactam; Copolymers; Decay rate; Diffraction patterns; Emission spectra; Fluorescence; Fourier transforms; Insulin; Medical materials; Micelles; NMR; Nuclear magnetic resonance; Phase transitions; Proteins; Self-assembly; Smart materials; Spectrum analysis
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d0cp00645a

Synthesizing and understanding phase transition behavior of novel block copolymers is very crucial for fabricating next generation of smart materials with foreseeable applications. In this regard, we synthesized three random (r) copolymers of poly( N -vinyl-caprolactam) (PVCL) and poly(2-dimethyl amino ethyl methacrylate) (PDMAEMA) with varying percentages of each block and characterized them using nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) patterns, time-resolved fluorescence spectroscopy, and atomic force microscopy (AFM). Synthesized copolymers i.e. PVCL 30 -PDMAEMA 70 , PVCL 50 -PDMAEMA 50 and PVCL 70 -PDMAEMA 30 have fluorescence properties, which were confirmed by time-resolved fluorescence spectra and emission spectra, and emission bands were observed at ∼310, ∼435 and ∼424 nm, respectively. The fluorescence lifetime for PVCL 50 -PDMAEMA 50 is larger than those of the other two copolymers suggesting a slow decay of the excited state. The copolymers have spherical geometry as micelles, which were confirmed by TEM. We observed patterned arrangement of micelles and the arranged micelles appear to be pentagon in shape, creating space in between the arranged micelles; however, for PVCL 50 -PDMAEMA 50 , the arranged micelles do not form any particular shape. The thermal phase transition of PVCL- r -PDMAEMA in aqueous solution was studied by differential scanning calorimetry and thermal fluorescence spectroscopy. In order to design a biomimetic polymer for bio-specific applications and to understand novel concepts towards polymer-protein interactions, we studied the effect of insulin on lower critical solution temperature (LCST) of PVCL- r -PDMAEMA using multiple sophisticated techniques. The LCST is finely tuned by incorporation of two blocks with various block compositions and the value falls within the range of human body temperature, making PVCL 50 -PDMAEMA 50 a highly compatible material for bio-medical and bio-material applications. Insulin forms a self-assembly with the monomers of PVCL- r -PDMAEMA, which leads to enhancing the micellar aggregates and the eventual decrease in the LCST of the diblock copolymer aqueous solution. The present study provides new insights into insulin-copolymer interactions and can be used for self-assembling nanocarriers and designing protein resistance surfaces. Synthesizing and understanding phase transition behavior of novel block copolymers is very crucia