Inversion of Polymeric Micelles Probed by Spin Labeled Peptide Incorporation and Electron Paramagnetic Resonance

Abstract

As the concentration of amphiphilic invertible polymers (AIPs) in both polar and nonpolar solvents increases, the AIP macromolecules self-assemble into polymeric micelles. The resulting invertible micellar assemblies (IMAs) have a controlled size and morphology determined by macromolecular composition and hydrophilic lipophilic balance (HLB) of the AIPs. It has been demonstrated that AIPs can rapidly switch the conformation in response to changes in the environmental polarity, thus facilitating, micellar inversion. In combination with IMAs’ ability to solubilize otherwise insoluble substances, inversion can be promising for rapid and controlled cargo delivery and release in applications that require simultaneous utility in polar and nonpolar media. While IMAs have been demonstrated to interact with peptides, fundamental pictures of micellar inversion remain elusive and became the focus of this work, including the behavior of the incorporated peptide in IMAs at the molecular level at different polarities of the environment and how polymer composition impacts such behavior. To trigger conformational changes of the micelle-forming AIPs, acetone (no self-assembly occurs in acetone) was added into the peptide-loaded IMAs aqueous solutions. Electron Paramagnetic Resonance (EPR) in combination with peptide spin labeling was used to probe the local environment of an antigenic peptide at various acetone concentrations. The obtained results are consistent with the previously revealed micellar structure. Increasing acetone percentage clearly impacts the extent of IMA inversion as reported by the labeled peptide and quantified by semiquantitative spectral analysis. The conformational changes are different for the two AIPs differing in the macromolecular composition. Conformational changes clearly relate to the HLB of the AIPs macromolecules and can certainly be meaningful in controlling the IMAs-mediated peptide release.

Improving Antioxidant Activity of β-Lactoglobulin by Nature-Inspired Conjugation with Gentisic Acid

“…In other words, we could increase the GA-grafted amount by increasing the GA addition amount considering protein self-crossing and the cost of catalysts (i.e., EDC and sNHS). Therefore, an EDC/GA ratio of 10:1 was maintained while the addition of GA was tuned (5,30,75,150, and 300 times of βLG protein) upon optimizing the catalytic reaction conditions. Consequentially, the conjugate design can balance the adverse effect of protein conformation disruption and the beneficial effect of GA attachment on the antioxidant capability of the conjugates.…”

“…A protective effect stemming from the moieties to which the phenolic compounds were conjugated was speculated for the enhanced antioxidant activity of phenolic compounds. Inspired by such naturally existing soluble-bound phenolics, we chemically conjugate GA onto βLG using the N -(3-(dimethylamino)­propyl)- N ′-ethylcarbodiimide hydrochloride (EDC)/ N -hydroxysuccinimide (NHS)-catalyzed reaction under a mild condition. − In comparison to other antioxidant phenolics, GA has high water solubility and antioxidant capability . We selected the EDC/NHS-catalyzed conjugation because of the ease of controlling the degree of conjugation as well as the mild reaction conditions.…”

Dynamics in Controllable Stimuli-Responsive Self-Assembly of Polymer Vesicles with Stable Radical Functionality

“…Redox-responsive polymer assemblies are of great interest due to their potential applications in different industries from the biomedical fields to electronic devices. , Figure A shows the UV–vis absorbance against time representing a quantitative evaluation of redox-responsiveness. We added different molar equivalents of ascorbic acid (Asc), as a reducing agent, to observe the dissolution.…”

“…However, due to the low selectivity and sensitivity of most mainstream analytical techniques, there are some limitations in understanding the molecular-level interactions . To study the molecular interactions and dynamics in nanostructured materials’ interfaces, we used a highly selective and sensitive electron paramagnetic resonance (EPR) spectroscopy. , EPR spectroscopy is a promising and tailor-made technique for the study of microenvironments and dynamic phenomena of colloidal systems. − Various studies were reported on the internal dynamics and local structure of radical-associated nanostructures using EPR spectroscopy by investigating the line shape changes. − The rotational dynamics of the radical-containing covalent linkage position and the side groups in the polymer chain significantly reflect the local dynamics of polymer assembly. − For example, by considering the hydrogen bonding tendencies, Ortony et al used EPR spectroscopy to report the local dynamics of supramolecular nanofibers in the assembly structure . EPR spectroscopy provides quantitative evidence of the rotational dynamics, inter and/or intramolecular distance between the radicals, solvent accessibility, and micropolarity of the immediate environment.…”

Investigation of segmental reorganization within amphiphilic block polymer nanoparticles derived from shell crosslinked micelle templates: Shell crosslinked knedel‐like inversion

“…32,36,40,[47][48][49][50][51] Rather than being limited to the thermodynamically favored morphology created initially from aqueous solution-state assembly, in which a hydrophobic core is surrounded by a crosslinked hydrophilic shell, the robust character and structural versatility of shell crosslinked knedel-like (SCK) polymer micelle nanoparticles raise several questions regarding their morphological flexibility. Unlike their supramolecular micellar precursors, which undergo morphological changes, including inversion, 52,53 under environmental variations, such as changes in pH, 17 ionic strength, 19 and solvent system, 18,54,55 SCKs are essentially single molecules of nanometer-scale dimensions. Of particular interest is the question of whether the polymer chain segments that constitute the core domain, which are covalently attached to the inner surface of the crosslinked shell, are capable of being extracted through an inversion of the SCK core-shell morphology.…”