Acrylic Polymer Radicals: Structural Characterization and Dynamics

Forbes, Malcolm D D. E.; Лебедева, Н. В.

doi:10.1002/9780470584118.ch14

Cited by 3 publications

(5 citation statements)

References 111 publications

(92 reference statements)

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“…In contrast to these ionic or concerted reactions, radical cascade reactions proceed through two or more consecutive steps, mediated by the radical’s unpaired electron. Radical cascades provide a complementary and scientifically appealing strategy, due to their undeniable benefits, − including extraordinarily high atom economy, enabling time-, labor-, and resource-efficient management, and reduced waste generation. Thus, radical cascade reactions are a promising route toward “green chemistry” .…”

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confidence: 99%

On-Surface Site-Selective Cyclization of Corrole Radicals

Tebi¹,

Paszkiewicz

Aldahhak

et al. 2017

ACS Nano

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Radical cyclization is among the most powerful and versatile reactions for constructing mono- and polycyclic systems, but has, to date, remained unexplored in the context of on-surface synthesis. We report the controlled on-surface synthesis of stable corrole radicals on Ag(111) via site-specific dehydrogenation of a pyrrole N-H bond in the 5,10,15-tris(pentafluoro-phenyl)-corrole triggered by annealing at 330 K under ultrahigh-vacuum conditions. We reveal a thermally induced regioselective cyclization reaction mediated by a radical cascade and resolve the reaction mechanism of the pertaining cyclodefluorination reaction at the single-molecule level. Via intramolecularly resolved probing of the radical-related Kondo signature, we achieve real space visualization of the distribution of the unpaired electron density over specific sites within the corrole radical. Annealing to 550 K initiates intermolecular coupling reactions, producing an extended π-conjugated corrole system.

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confidence: 99%

On-Surface Site-Selective Cyclization of Corrole Radicals

Tebi¹,

Paszkiewicz

Aldahhak

et al. 2017

ACS Nano

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“…The ester side chain excited molecular triplet state is itself EPR silent in liquid solution due to fast spin relaxation caused by modulation of its electron dipole–dipole interaction. The stable nitroxide radical has a Boltzmann population of spin states in the dark, but this is not observed in the TREPR experiment (the experiment is not, except in rare cases of very high radical concentrations, sensitive to Boltzmann levelsCIDEP is essentially required for observation of direct detection TREPR signals). , If nitroxide radicals and photoexcited triplet states are the only paramagnetic species that exist in a particular solution, and the triplet state does not react to make radicals, no TREPR signal is observed unless they make collisional encounters within the excited triplet state lifetime. The results in Figure are intriguing with regard to polymer chain dynamics on the time scale of 1–100 ns, and thus, other parameters that might affect polymer chain mobility were also investigated.…”

Section: Resultsmentioning

confidence: 99%

“…Continuous wave TREPR experiments were performed as previously described. , All experiments were performed on a JEOL USA Inc. JES-RE1X X-band EPR spectrometer equipped with a wide bandwidth preamplifier and a low-noise GaAsFET microwave amplifier. Samples were typically prepared as solutions of nitroxide-containing polymer (0.5–1.2 g) in propylene carbonate or dimethyl ethyl ether (diglyme) (20–35 mL) and circulated through a quartz flat cell (0.4 mm path length) positioned in the center of a Varian TE 103 optical transmission cavity.…”

Section: Methodsmentioning

confidence: 99%

Radical–Triplet Pair Interactions as Probes of Long-Range Polymer Motion in Solution

Sim

Forbes

2014

J. Phys. Chem. B

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Radical-triplet pair interactions are used to investigate the dynamics of acrylic polymers in dilute solution. Methyl methacrylate was randomly copolymerized with a small amount of an amine-containing monomer to create the polymers. The amine subunits were then oxidized to nitroxide moieties (stable free radicals). Using time-resolved electron paramagnetic resonance (TREPR) spectroscopy on the sub-microsecond time scale, competition is observed between two deactivation processes of the ester side chain photoexcited triplet state: (1) Norrish I α-cleavage, leading to a 21-line main chain polymeric free radical TREPR spectrum with emissive triplet mechanism spin polarization, and (2) spin polarization transfer or quenching by a nearby stable nitroxide radical, which gives a 3-line spectrum exhibiting emissive radical-triplet pair spin polarization. The main chain polymer radical signal dominates the TREPR spectrum if the probability of radical-triplet pair encounters is low. These competing reactions show a strong dependence on nitroxide incorporation (mol %), temperature, solvent, and acrylic polymer ester side chain structure. A comparison of steady state EPR and TREPR signals from inter- vs intramolecular processes clearly demonstrates the influence of polymer chain dynamics on the observed phenomena.

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“…One of the degradation products is an acyl radical, which can recombine to form the parent polymer. 58 PCA1 has the lowest v/v ratio of AA to PAA-Cys in the hydrogel precursor and as such exhibits less cross-linking and PAA branching. The low levels of crosslinking and PAA branching ensure mechanical properties of PCA1 are impacted by β-scission degradation induced by increased UV exposure.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…This degradation affects the PAA molecules involved in covalent cross-linking of the thiol groups and PAA branching, the two critical factors influencing hydrogel mechanical strength. One of the degradation products is an acyl radical, which can recombine to form the parent polymer . PCA1 has the lowest v/v ratio of AA to PAA-Cys in the hydrogel precursor and as such exhibits less cross-linking and PAA branching.…”

Section: Resultsmentioning

confidence: 99%

Synthesis of Poly(acrylic acid)-Cysteine-Based Hydrogels with Highly Customizable Mechanical Properties for Advanced Cell Culture Applications

et al. 2022

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The fabrication of highly customizable scaffolds is a key enabling technology in the development of predictive in vitro cell models for applications in drug discovery, cancer research, and regenerative medicine. Naturally derived and synthetic hydrogels are good candidates for in vitro cell growth studies, owing to their soft and biocompatible nature; however, they are often hindered by limited ranges of stiffness and the requirement to modify the gel with additional extracellular matrix (ECM) proteins for cell adherence. Here, we report on the synthesis of a printable synthetic hydrogel based on cysteine-modified poly(acrylic acid) (PAA-Cys) with tuneable mechanical and swelling properties by incorporating acrylic acid into the PAA-Cys network and subsequent photoinitiated thiol-acrylate cross-linking. Control of the acrylic acid concentration and UV curing time produces a series of hydrogels with swelling ratios in excess of 100% and Young’s modulus values ranging from ∼2 to ∼35 kPa, of which most soft tissues fall within. Biocompatibility studies with RPE1 cells showed excellent cell adhesion and cell viability without the need for further modification with ECM proteins, but still can be modified as needed. The versatility of the hydrogel tuneable properties is demonstrated by culturing with RPE1 cells, which in vivo perform an important function in the visual process and the dysfunction of which may lead to various retinal abnormalities, such as glaucoma.

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Acrylic Polymer Radicals: Structural Characterization and Dynamics

Cited by 3 publications

References 111 publications

On-Surface Site-Selective Cyclization of Corrole Radicals

On-Surface Site-Selective Cyclization of Corrole Radicals

Radical–Triplet Pair Interactions as Probes of Long-Range Polymer Motion in Solution

Synthesis of Poly(acrylic acid)-Cysteine-Based Hydrogels with Highly Customizable Mechanical Properties for Advanced Cell Culture Applications

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