A Retrospective: 10 Years of Oligo(phenylene-ethynylene) Electrolytes: Demystifying Nanomaterials

An Effective Approach to the Disinfection of Pathogens: Cationic Conjugated Polyelectrolytes and Oligomers

The synthetic cationic conjugated polyelectrolytes and oligomers have demonstrated great effectiveness and versatility as antimicrobial materials. They have the ability to eliminate or render inactive various pathogens, including viruses like SARS-CoV-2, bacteria, and fungi. These pathogens can be rapidly eradicated when the polyelectrolytes and oligomers are applied as sprays, wipes, or coatings on solid surfaces. Inactivation of the pathogens occurs through two distinct processes: a non-light-activated process similar to Quats, and a more efficient and faster process that is triggered by light. These materials possess fluorescence and photosensitizing properties, enabling prolonged protection when coated on surfaces. The level of fluorescence exhibited by samples applied to nonfluorescent surfaces serves as an indicator of the coating's integrity and viability, making it easily detectable. Importantly, these materials demonstrate low toxicity towards mammalian cells and human skin, allowing for their safe use. While they can serve as durable coatings for pathogen protection, extended exposure to visible or ultraviolet light leads to their photochemical degradation. Our research also suggests that these materials act against pathogens through nonspecific mechanisms, minimizing the likelihood of pathogens developing resistance and rendering the materials ineffective.

Controlled and Selective Photo-oxidation of Amyloid-β Fibrils by Oligomeric p-Phenylene Ethynylenes

Photodynamic therapy (PDT) has been explored as a therapeutic strategy to clear toxic amyloid aggregates involved in neurodegenerative disorders such as Alzheimer's disease. A major limitation of PDT is off-target oxidation, which can be lethal for the surrounding cells. We have shown that a novel class of oligo-p-phenylene ethynylenes (OPEs) exhibit selective binding and fluorescence turn-on in the presence of prefibrillar and fibrillar aggregates of disease-relevant proteins such as amyloid-β (Aβ) and α-synuclein. Concomitant with fluorescence turn-on, OPE also photosensitizes singlet oxygen under illumination through the generation of a triplet state, pointing to the potential application of OPEs as photosensitizers in PDT. Herein, we investigated the photosensitizing activity of an anionic OPE for the photo-oxidation of Aβ fibrils and compared its efficacy to the well-known but nonselective photosensitizer methylene blue (MB). Our results show that, while MB photo-oxidized both monomeric and fibrillar conformers of Aβ40, OPE oxidized only Aβ40 fibrils, targeting two histidine residues on the fibril surface and a methionine residue located in the fibril core. Oxidized fibrils were shorter and more dispersed but retained the characteristic β-sheet rich fibrillar structure and the ability to seed further fibril growth. Importantly, the oxidized fibrils displayed low toxicity. We have thus discovered a class of novel theranostics for the simultaneous detection and oxidization of amyloid aggregates. Importantly, the selectivity of OPE's photosensitizing activity overcomes the limitation of off-target oxidation of traditional photosensitizers and represents an advancement of PDT as a viable strategy to treat neurodegenerative disorders.

Current Progress of Interfacing Organic Semiconducting Materials with Bacteria

Microbial bioelectronics require interfacing microorganisms with electrodes. The resulting abiotic/biotic platforms provide the basis of a range of technologies, including energy conversion and diagnostic assays. Organic semiconductors (OSCs) provide a unique strategy to modulate the interfaces between microbial systems and external electrodes, thereby improving the performance of these incipient technologies. In this review, we explore recent progress in the field on how OSCs, and related materials capable of charge transport, are being used within the context of microbial systems, and more specifically bacteria. We begin by examining the electrochemical communication modes in bacteria and the biological basis for charge transport. Different types of synthetic organic materials that have been designed and synthesized for interfacing and interrogating bacteria are discussed next, followed by the most commonly used characterization techniques for evaluating transport in microbial, synthetic, and hybrid systems. A range of applications is subsequently examined, including biological sensors and energy conversion systems. The review concludes by summarizing what has been accomplished so far and suggests future design approaches for OSC bioelectronics materials and technologies that hybridize characteristic properties of microbial and OSC systems.

CO/light dual-activatable Ru(ii)-conjugated oligomer agent for lysosome-targeted multimodal cancer therapeutics

Stimuli-activatable and subcellular organelle-targeted agents with multimodal therapeutics are urgently desired for highly precise and effective cancer treatment. Herein, a CO/light dual-activatable Ru(ii)-oligo-(thiophene ethynylene) (Ru-OTE) for lysosome-targeted cancer therapy is reported. Ru-OTE is prepared via the coordination-driven self-assembly of a cationic conjugated oligomer (OTE-BN) ligand and a Ru(ii) center. Upon the dual-triggering of internal gaseous signaling molecular CO and external light, Ru-OTE undergoes ligand substitution and releases OTE-BN followed by dramatic fluorescence recovery, which could be used for monitoring drug delivery and imaging guided anticancer treatments. The released OTE-BN selectively accumulates in lysosomes, physically breaking their integrity. Then, the generated cytotoxic singlet oxygen (¹O₂) causes severe lysosome damage, thus leading to cancer cell death via photodynamic therapy (PDT). Meanwhile, the release of the Ru(ii) core also suppresses cancer cell growth as an anticancer metal drug. Its significant anticancer effect is realized via the multimodal therapeutics of physical disruption/PDT/chemotherapy. Importantly, Ru-OTE can be directly photo-activated using a two-photon laser (800 nm) for efficient drug release and near-infrared PDT. Furthermore, Ru-OTE with light irradiation inhibits tumor growth in an MDA-MB-231 breast tumor model with negligible side effects. This study demonstrates that the development of an activatable Ru(ii)-conjugated oligomer potential drug provides a new strategy for effective subcellular organelle-targeted multimodal cancer therapeutics.

The anticancer therapeutics of lysosome disruption/PDT/chemotherapy based on Ru-OTE complex was achieved, which provides a new strategy for developing multimodal and effective stimuli-activatable subcellular organelle-targeted cancer therapeutics.

Comparison and Mechanism Study of Antibacterial Activity of Cationic and Neutral Oligo-Thiophene-Ethynylene

Photodynamic therapy (PDT) is a potential approach to resolve antibiotic resistance, and phenylene/thiophene-ethynylene oligomers have been widely studied as effective antibacterial reagents. Oligomers with thiophene moieties usually exhibit good antibacterial activity under light irradiation and dark conditions. In the previous study, we verified that neutral oligo-p-phenylene-ethynylenes (OPEs) exhibit better antibacterial activity than the corresponding cationic ones; however, whether this regular pattern also operates in other kinds of oligomers such as oligo-thiophene-ethynylene (OTE) is unknown. Also, the antibacterial activity comparison of OTEs bearing cyclic and acyclic amino groups will offer useful information to further understand the role of amino groups in the antibacterial process and guide the antibacterial reagent design as amino groups affect the antibacterial activity a lot. We synthesized four OTEs bearing neutral or cationic, cyclic, or acyclic amino groups and studied their antibacterial activity in detail. The experimental results indicated that the OTEs exhibited better antibacterial activity than the OPEs, the neutral OTEs exhibited better antibacterial activity in most cases, and OTEs bearing cyclic amino groups exhibited better antibacterial activity than those bearing acyclic ones in most cases. This study provides useful guidelines for further antibacterial reagent design and investigations.

A review of oligo(arylene ethynylene) derivatives in molecular junctions

Oligo(arylene ethynylene) (OAE) derivatives are the "workhorse" molecules of molecular electronics. Their ease of synthesis and flexibility of functionalisation mean that a diverse array of OAE molecular wires have been designed, synthesised and studied theoretically and experimentally in molecular junctions using both single-molecule and ensemble methods. This review summarises the breadth of molecular designs that have been investigated with emphasis on structure-property relationships with respect to the electronic conductance of OAEs. The factors considered include molecular length, connectivity, conjugation, (anti)aromaticity, heteroatom effects and quantum interference (QI). Growing interest in the thermoelectric properties of OAE derivatives, which are expected to be at the forefront of research into organic thermoelectric devices, is also explored.

A Portrait of the OPE as a Biological Agent

Oligophenylene ethynylenes, known as OPEs, are a sequence of aromatic rings linked by triple bonds, the properties of which can be modulated by varying the length of the rigid main chain or/and the nature and position of the substituents on the aromatic units. They are luminescent molecules with high quantum yields and can be designed to enter a cell and act as antimicrobial and antiviral compounds, as biocompatible fluorescent probes directed towards target organelles in living cells, as labelling agents, as selective sensors for the detection of fibrillar and prefibrillar amyloid in the proteic field and in a fluorescence turn-on system for the detection of saccharides, as photosensitizers in photodynamic therapy (due to their capacity to highly induce toxicity after light activation), and as drug delivery systems. The antibacterial properties of OPEs have been the most studied against very popular and resistant pathogens, and in this paper the achievements of these studies are reviewed, together with almost all the other roles held by such oligomers. In the recent decade, their antifungal and antiviral effects have attracted the attention of researchers who believe OPEs to be possible biocides of the future. The review describes, for instance, the preliminary results obtained with OPEs against severe acute respiratory syndrome coronavirus 2, the virus responsible for the COVID-19 pandemic.

Understanding the role of conjugation length on the self-assembly behaviour of oligophenyleneethynylenes

Oligophenyleneethynylenes (OPEs) are prominent building blocks with exciting optical and supramolecular properties. However, their generally small spectroscopic changes upon aggregation make the analysis of their self-assembly challenging, especially in the absence of additional hydrogen bonds. Herein, by investigating a series of OPEs of increasing size, we have unravelled the role of the conjugation length on the self-assembly properties of OPEs.

A Practical and Efficient Synthesis of Uniform Conjugated Rod-Like Oligomers

Herein, a more practical and efficient synthesis protocol for the preparation of uniform rod-like oligo(1,4-phenylene ethynylene)s (OPE)s is presented. Applying an iterative reaction cycle consisting of a decarboxylative coupling reaction and a saponification of an alkynyl carboxylic ester, a uniform pentamer is obtained in ten steps with 14% overall yield. The copper-free conditions prevent homocoupling until the trimer stage, resulting in a significantly easier work-up of the products. Homocoupling is observed from the tetramer stage on, but a simple variation of the work-up procedure also yields the uniform tetramer and pentamer. A thorough comparison with the commonly used and described Sonogashira approach reveals that with the new presented strategy, OPEs can be built in similar overall yield, but easier purification and in a quarter of the time. All oligomers are fully characterized by proton and carbon nuclear magnetic resonance spectroscopy (NMR), mass spectrometry (MS), size-exclusion chromatography (SEC), and infrared spectroscopy (IR).

On-Demand Antimicrobial Agent Release from Functionalized Conjugated Oligomer-Hyaluronic Acid Nanoparticles for Tackling Antimicrobial Resistance

Controllable drug release is promising for fighting against antimicrobial resistance, which is a critical threat to human health worldwide. Herein, new hyaluronidase-responsive conjugated oligo(thiophene ethynylene) (OTE)-covalently modified hyaluronic acid (OTE-HA) nanoparticles for on-demand release of antimicrobial agents are reported. The synthesis of amphiphilic OTE-HA was carried out by esterification reaction. The resulting macromolecules were self-assembled in water to form nanoparticles, in which the hydrophobic OTE section, as bactericides, formed "cores" and the hydrophilic hyaluronic acid (HA) formed "shells". The OTE-HA nanoparticles avoid bactericide premature leakage and effectively block the dark cytotoxicity of the OTE section, possessing excellent biocompatibility. Using methicillin-resistant Staphylococcus aureus (MRSA) as an example, hyaluronidase, largely secreted by MRSA, can in situ trigger the release of OTE via hydrolyzing OTE-HA nanoparticles into fragments, even disaccharides linked with OTE. Importantly, the OTE section could effectively break cell membranes, leading to bacterial death. The half-maximal inhibitory concentration of the nanoparticles against MRSA is 3.3 μg/mL. The great antibacterial activity of OTE-HA nanoparticles against Gram-positive bacteria Streptococcus pneumoniae further confirms the controllable bactericide delivery mechanism. OTE-HA nanoparticles coated on a surface can also effectively inhibit the growth of bacteria, which holds a remarkable promise in biomedical applications. Therefore, this work provides a favorable strategy of on-demand and in situ drug release for sterilization and defeating antimicrobial resistance.

Well-Defined Conjugated Macromolecules Based on Oligo(Arylene Ethynylene)s in Sensing

Macromolecules with well-defined structures in terms of molar mass and monomer sequence became interesting building blocks for modern materials. The precision of the macromolecular structure makes fine-tuning of the properties of resulting materials possible. Conjugated macromolecules exhibit excellent optoelectronic properties that make them exceptional candidates for sensor construction. The importance of chain length and monomer sequence is particularly important in conjugated systems. The oligomer length, monomer sequence, and structural modification often influence the energy bang gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the molecules that reflect in their properties. Moreover, the supramolecular aggregation that is often observed in oligo-conjugated systems is usually strongly affected by even minor structural changes that are used for sensor designs. This review discusses the examples of well-defined conjugated macromolecules based on oligo(arylene ethynylene) skeleton used for sensor applications. Here, exclusively examples of uniform macromolecules are summarized. The sensing mechanisms and importance of uniformity of structure are deliberated.

Near-Infrared-Light-Assisted in Situ Reduction of Antimicrobial Peptide-Protected Gold Nanoclusters for Stepwise Killing of Bacteria and Cancer Cells

Biomolecule-protected gold nanostructures show good performance in biomedical applications. However, precise control over gold nanocluster (AuNC) preparation with biomolecules remains challenging. Here, we develop a simple near-infrared (NIR)-light-assisted method for in situ reduction of antimicrobial peptide (AMP)-protected AuNCs. Take advantage of the high photothermal conversion efficiency of the conjugated polymer (CP) upon NIR light irradiation, we promote the rapid reduction of AuNCs by the AMP on the surface of the CP. The fluorescent properties of the AuNCs were improved owing to the formation of a unique Au(0)NC@Au(I)AMP core-shell nanostructure. This nanostructure is attributed to the rapid reduction of Au(0) and collision and fusion of Au(0) at high temperatures. Integrating antibacterial AMPs, fluorescent AuNCs, and photothermal CPs, the composites facilitated different killing mechanisms for both bacteria and cancer cells. This material system provides an all-in-one strategy for the stepwise killing of cancer cells and bacterial infection.

Discrete boronate ester ladders from the dynamic covalent self-assembly of oligo(phenylene ethynylene) derivatives and phenylenebis(boronic acid)

Reversible boronate ester chemistry enables the controlled, dynamic self-assembly of olig(phenylene ethynylene)s into highly conjugated ladder frameworks.

Amino Acid-Modified Conjugated Oligomer Self-Assembly Hydrogel for Efficient Capture and Specific Killing of Antibiotic-Resistant Bacteria

Bacterial infection is one of main causes that threaten global human health. Especially, antibiotic-resistant bacteria like methicillin-resistant Staphylococcus aureus (MRSA) lead to high mortality rate and more expensive treatment cost. Here, a novel amino-acid-modified conjugated oligomer OTE-d-Phe was synthesized by modifying the side chain of conjugated oligo(thiophene ethynylene) with d-phenylalanine. By mixing 9-fluorenylmethyloxycarbonyl-l-phenylalanin (Fmoc-l-Phe) with OTE-d-Phe, a new and biocompatible low-molecular weight hydrogel (HG-2) was prepared through self-assembly. In solution, HG-2 can effectively capture bacteria spontaneously, such as Escherichia coli and MRSA. Most importantly, the hydrogel has specific and strong antibacterial activity against MRSA over methicillin-susceptible S. aureus, Staphylococcus epidermidis, and E. coli. Interestingly, when the hydrogel was put on a model surface, a piece of cloth, it also is able to selectively kill MRSA with low cell cytotoxicity. The antibacterial mechanism was investigated, and it demonstrated that the HG-2 interacts with and physically breaks the cell wall and membrane, which leads to MRSA death. Therefore, this new conjugated oligomer-based hydrogel provides promising applications in disinfection and therapy of MRSA in hospital and in community.

High Selectivity and Sensitivity of Oligomeric p-Phenylene Ethynylenes for Detecting Fibrillar and Prefibrillar Amyloid Protein Aggregates

Misfolding and aggregation of amyloid proteins into fibrillar aggregates is a central pathogenic event in neurodegenerative disorders such as Alzheimer's (AD) and Parkinson's diseases (PD). Currently, there is a lack of reliable sensors for detecting the range of protein aggregates involved in disease etiology, particularly the prefibrillar aggregate conformations that are more neurotoxic. In this study, the fluorescent sensing of two novel oligomeric p-phenylene ethynylenes (OPEs), anionic OPE1- and cationic OPE2+, for detecting prefibrillar and fibrillar aggregates of AD-associated amyloid-β (Aβ40 and Aβ42) and PD-associated α-synuclein proteins (wildtype, and single mutants A30P, E35K, and A53T) over their monomeric counterparts, were tested. Furthermore, the performance of OPEs was evaluated and compared to thioflavin T (ThT), the most widely used fibril dye. Our results show that OPE1- and OPE2+ exhibited aggregate-specific binding inducing large fluorescence turn-on and spectral shifts based on a combination of backbone planarization, hydrophobic unquenching, and superluminescent OPE complex formation sensing modes. OPEs exhibited higher selectivity, higher binding affinity, and comparable limits of detection for Aβ40 fibrils compared to ThT. OPE2+ exhibited the largest fluorescence turn-on and highest sensitivity. Significantly, OPEs detected prefibrillar aggregates of Aβ42 and α-synuclein that ThT failed to detect. The superior sensing performance, the nonprotein specific detection, and the ability to selectively detect fibrillar and prefibrillar amyloid protein aggregates point to the potential of OPEs to overcome the limitations of existing probes and promise significant advancement in the detection of the myriad of protein aggregates involved in the early stages of AD and PD.