Raoul Peltier

Mimicking nature’s ability to orchestrate molecular self-assembly in living cells is important yet challenging. Molecular self-assembly has found wide applications in cellular activity control, drug delivery, biomarker imaging, etc. Nonetheless, examples of suborganelle-confined supramolecular self-assembly are quite rare and research in this area remains challenging. Herein, we have presented a new strategy to program supramolecular self-assembly specifically in mitochondria by leveraging on a unique enzyme SIRT5. SIRT5 is a mitochondria-localized enzyme belonging to a family of NAD⁺-dependent histone deacetylases. Accumulating studies suggest that SIRT5 is involved in regulating diverse biological processes, such as reactive oxygen defense, fatty acid metabolism, and apoptosis. In this study, we designed a novel class of succinylated peptide precursors that can be transformed into self-assembling building blocks through SIRT5 catalysis, leading to the formation of supramolecular nanofibers in vitro and in living cells. The increased hydrophobicity arising from self-assembly remarkably enhanced the fluorescence of nitrobenzoxadiazole (NBD) in the nanofibers. With this approach, we have enabled activity-based imaging of SIRT5 in living cells for the first time. Moreover, SIRT5-mediated peptide self-assembly was found to depolarize mitochondria membrane potential and promote ROS formation. Coincubation of the peptide with three different chemotherapeutic agents significantly boosted the anticancer activities of these drugs. Our work has thus illustrated a new way of mitochondria-confined peptide self-assembly for SIRT5 imaging and potential anticancer treatment.

Cyclic peptide nanotubes were coupled to poly(oxazoline)s using a cleavable connection. Upon stimuli responsive detachment of the polymer an on-demand membrane activity could be achieved.

Synthesis of long-chain hyperbranched poly(ethylenimine-co-oxazoline)s by AB₂thiol–yne chemistry is reported, and their application as pDNA transfection agents studied.

Breaking away from the linear structure of previously reported peptide‐based gelators, this study reports the first example of gel formation based on the use of cyclic peptides made of alternating d‐ and l‐amino acids, known to self‐assemble in solution to form long nanotubes. Herein, a library of cyclic peptides was systemically studied for their gelation properties in various solvents, uncovering key parameters driving both organogel and hydrogel formation. The hierarchical nature of the self‐assembly process in water was characterised by a combination of electron microscopy imaging and small‐angle X‐ray scattering, revealing a porous network of entangled nanofibres composed by the aggregation of several cyclic peptide nanotubes. Rheology measurements then confirmed the formation of soft hydrogels.

Recent progress in modern polymer synthesis techniques has led to the design of complex functional materials, which can be difficult to analyse accurately. While size-exclusion chromatography (SEC) or mass spectrometry (MS) is typically used to gain information about molecular weight distribution, chemical structure and molecular architecture, there is a lack of available methods for characterising compositional heterogeneity (i.e. monomer distribution). In contrast to SEC in which separation occurs by hydrodynamic volume, interaction-based chromatography (IC) separates compounds according to their affinity for a stationary phase, which has proven useful in gaining information about the general chemical structure of copolymers in the past. Here, we explore the potential of reverse-phase high performance liquid chromatography (RP-HPLC) as a tool for the characterisation of monomer segmentation in charged water-soluble copolymers. A library of acrylamide copolymeric systems, prepared via reversible addition–fragmentation chain transfer (RAFT) polymerisation, is used to demonstrate the influence of monomer distribution (diblock, multiblock and statistical) on the elution time. The robustness of the method is tested by studying a range of copolymers with varying charges, charge contents and hydrophobicities, as well as by using various solvent systems or column lengths. Results highlight the efficiency of RP-HPLC to separate copolymers with varying segmentations, with a limitation observed for branched architectures.

The controlled release of nucleic acids from cationic polymers is an important criteria for the design of gene delivery systems, and can be difficult to achieve due to the persistent positive charges required to initially complex the nucleic acids. Here, we report the use of highly branched tertiary amine-rich polymers for the complexation and release of dsRNA over a prolonged period of time. Controlled release of dsRNA is obtained via self-catalysed hydrolysis of the polymer side chains and associated change in electrostatic charge. Reversible addition–fragmentation chain transfer (RAFT) polymerization was utilised to synthesise a series of branched polymers of 2-(dimethylamino)ethyl acrylate (DMAEA), 3-(dimethylamino)propyl acrylate (DMAPA), and 2-(dimethylamino)ethyl methacrylate (DMAEMA) (MW ∼60 000–200 000 g mol⁻¹) and copolymers thereof. The hydrolysis kinetics of all synthesised polymer materials were followed by ¹H NMR spectroscopy. Complexation with dsRNA resulted in the formation of polyplex nanoparticles (N/P ratio of 5) with sizes of approximately 400 nm and surface charges of +15 mV. An agarose gel retardation assay showed sustained release of dsRNA from p(DMAEA-co-DMAEMA) for a period of more than 2 weeks. Unlike branched PEI commonly used for gene delivery, the majority of these systems showed little toxicity to cells (NIH3T3 fibroblasts). The results point towards pDMAPA and p(DMAEA-co-DMAEMA) being promising polymers for the controlled release of nucleic acids over prolonged periods.

A range of well-defined guanidinium-rich linear polymers with demonstrable efficiency for cellular internalisation were developed. A protected guanidinium-functional acrylamide monomer (di-Boc-guanidinium ethyl acrylamide, GEAdiBoc) was synthesised and then polymerised via RAFT polymerisation to yield well-defined homopolymers, which were then deprotected and functionalised with a fluorescein dye to observe and quantify their cellular uptake. The cellular uptake of these homopolymers was first compared to polyArginine analogues, which are commonly used in modern drug delivery. Following this, a range of well-defined guanidinium-rich copolymers were prepared in which the monomer distribution was varied using a convenient one-pot sequential RAFT polymerisation approach. Systematic quantification of the cell uptake of these compounds, supported by fluorescent confocal microscopy data, revealed that while the overall hydrophobicity of the resulting copolymers has a direct impact on the amount of copolymer taken up by cells, the distribution of monomers has an influence on both the extent of uptake and the relative extent to which each route of internalisation (endocytosis vs direct translocation) is exploited.

Block copolymers containing an organic arsenical (AsAm) have been synthesised by aqueous SET-LRP.

Self‐assembling cyclic peptide–polymer nanotubes have emerged as a fascinating supramolecular system, well suited for a diverse range of biomedical applications. Due to their well‐defined diameter, tunable peptide anatomy, and ability to disassemble in situ, they have been investigated as promising materials for numerous applications including biosensors, antimicrobials, and drug delivery. Despite this continuous effort, the underlying mechanisms of assembly and disassembly are still not fully understood. In particular, the exchange of units between individual assembled nanotubes has been overlooked so far, despite its knowledge being essential for understanding their behavior in different environments. To investigate the dynamic nature of these systems, cyclic peptide–polymer nanotubes are synthesized, conjugated with complementary dyes, which undergo a Förster resonance energy transfer (FRET) in close proximity. Model conjugates enable to demonstrate not only that their self‐assembly is highly dynamic and not kinetically trapped, but also that the self‐assembly of the conjugates is strongly influenced by both solvent and concentration. Additionally, the versatility of the FRET system allows studying the dynamic exchange of these systems in mammalian cells in vitro using confocal microscopy, demonstrating the exchange of subunits between assembled nanotubes in the highly complex environment of a cell.

Poly(2-acrylamido-2-methylpropane sulfonic acid) is a polyelectrolyte currently used in numerous industrial applications. Herein, we report the use of reversible addition fragmentation chain transfer (RAFT) polymerization to prepare a range of well-defined homopolymers and block copolymers of 2-acrylamido-2-methylpropane sulfonic acid (AMPS®) and either N-hydroxyethyl acrylamide (HEAm) or 4-acryloylmorpholine (NAM) as a comonomer. We also describe the one-pot synthesis of multiblock core cross-linked star copolymers of AMPS® and HEAm with low dispersities (<1.3). The influence of several parameters such as the cross-linker type, cross-linker to chain transfer agent (CTA) ratio, arm length and composition on the polymerization efficiency are investigated.