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. 2016 Apr 28;7(16):2836-2846.
doi: 10.1039/c6py00263c. Epub 2016 Apr 6.

Use of complementary nucleobase-containing synthetic polymers to prepare complex self-assembled morphologies in water

Yan Kang  1 , Anaïs Pitto-Barry  1 , Marianne S Rolph  1 , Zan Hua  1 , Ian Hands-Portman  2 , Nigel Kirby  3 , Rachel K O'Reilly  1
Affiliations

Use of complementary nucleobase-containing synthetic polymers to prepare complex self-assembled morphologies in water

Yan Kang et al. Polym Chem. .

Abstract

Amphiphilic nucleobase-containing block copolymers with poly(oligo(ethylene glycol) methyl ether methacrylate) as the hydrophilic block and nucleobase-containing blocks as the hydrophobic segments were successfully synthesized using RAFT polymerization and then self-assembled via solvent switch in aqueous solutions. Effects of the common solvent on the resultant morphologies of the adenine (A) and thymine (T) homopolymers, and A/T copolymer blocks and blends were investigated. These studies highlighted that depending on the identity of the common solvent, DMF or DMSO, spherical micelles or bicontinuous micelles were obtained. We propose that this is due to the presence of A-T interactions playing a key role in the morphology and stability of the resultant nanoparticles, which resulted in a distinct system compared to individual adenine or thymine polymers. Finally, the effects of annealing on the self-assemblies were explored. It was found that annealing could lead to better-defined spherical micelles and induce a morphology transition from bicontinuous micelles to onion-like vesicles, which was considered to occur due to a structural rearrangement of complementary nucleobase interactions resulting from the annealing process.

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Figures

Scheme 1
Scheme 1. Synthetic route for the preparation of POEGMA70 and the nucleobase-containing block copolymers, 1–3.
Fig. 1
Fig. 1. Representative dry-state unstained TEM images on GO grids of self-assemblies 1 -DMF, 2 -DMF, 3 -DMF and 1 + 2 -DMF. Scale bar: 100 nm.
Fig. 2
Fig. 2. Representative cryo-TEM images of self-assemblies 3 -DMSO with a concentration of 1 mg mL–1 and its annealed sample 3 -DMSO′ at 0.2 mg mL–1; 1 + 2 -DMSO at a concentration of 1 mg mL–1 and its annealed sample 1 + 2 -DMSO′ at 0.2 mg mL–1. Scale bar: 100 nm.
Fig. 3
Fig. 3. SAXS profiles of self-assemblies 3 -DMSO, 1 + 2 -DMSO, 3 -DMSO′, and 1 + 2 -DMSO′. The vertical black lines indicate the major peaks, indicative of the internal structure of the assemblies. The 1 + 2 -DMSO and 1 + 2 -DMSO′ curves have been shifted by a factor 10 to improve clarity. Cryo-TEM images of 3 -DMSO and 3 -DMSO′ and the corresponding intensity profile along the white line on the TEM images.
Fig. 4
Fig. 4. Representative unstained dry-state TEM images on GO grids of 3 -DMSO annealed by different methods: (a) sample was heated at 60 °C for 45 min and then cooled down in an oil bath; (b) sample was heated from 15 °C to 60 °C and then cooled down from 60 °C to 15 °C at a rate of 1 °C min–1 and repeated 3 times in total. Scale bar: 100 nm.
Fig. 5
Fig. 5. Evolution of self-assembly from 3 -DMSO to 3 -DMSO′ with 6 annealing cycles characterized by cryo-TEM analysis (scale bar = 50 nm) and the number-average diameter and size distributions determined by DLS analysis.
Fig. 6
Fig. 6. Cryo-TEM images of self-assemblies 3 -DMSO-2a and 1 + 2 -DMSO-2a and their annealed samples 3 -DMSO-2a′ and 1 + 2 -DMSO-2a′. Scale bar: 50 nm.
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