Membrane-intercalating conjugated oligoelectrolytes: impact on bioelectrochemical systems

Conjugated Oligoelectrolyte with DNA Affinity for Enhanced Nuclear Imaging and Precise DNA Quantification

Precise DNA quantification and nuclear imaging are pivotal for clinical testing, pathological diagnosis, and drug development. The detection and localization of mitochondrial DNA serve as crucial indicators of cellular health. We introduce a novel conjugated oligoelectrolyte (COE) molecule, COE-S3, featuring a planar backbone composed of three benzene rings and terminal side chains. This unique amphiphilic structure endows COE-S3 with exceptional water solubility, a high quantum yield of 0.79, and a significant fluorescence Stokes shift (λex = 366 nm, λem = 476 nm), alongside a specific fluorescence response to DNA. The fluorescence intensity correlates proportionally with DNA concentration. COE-S3 interacts with double-stranded DNA (dsDNA) through an intercalation binding mode, exhibiting a binding constant (K) of 1.32 × 106 M-1. Its amphiphilic nature and strong DNA affinity facilitate its localization within mitochondria in living cells and nuclei in apoptotic cells. Remarkably, within 30 min of COE-S3 staining, cell vitality can be discerned through real-time nuclear fluorescence imaging of apoptotic cells. COE-S3's high DNA selectivity enables quantitative intracellular DNA analysis, providing insights into cell proliferation, differentiation, and growth. Our findings underscore COE-S3, with its strategically designed, shortened planar backbone, as a promising intercalative probe for DNA quantification and nuclear imaging.

Controlled electron transfer by molecular wires embedded in ultrathin insulating membranes for driving redox catalysis

Organic bilayers or amorphous silica films of a few nanometer thickness featuring embedded molecular wires offer opportunities for chemically separating while at the same time electronically connecting photo- or electrocatalytic components. Such ultrathin membranes enable the integration of components for which direct coupling is not sufficiently efficient or stable. Photoelectrocatalytic systems for the generation or utilization of renewable energy are among the most prominent ones for which ultrathin separation layers open up new approaches for component integration for improving efficiency. Recent advances in the assembly and spectroscopic, microscopic, and photoelectrochemical characterization have enabled the systematic optimization of the structure, energetics, and density of embedded molecular wires for maximum charge transfer efficiency. The progress enables interfacial designs for the nanoscale integration of the incompatible oxidation and reduction catalysis environments of artificial photosystems and of microbial (or biomolecular)-abiotic systems for renewable energy.

A Broad Light-Harvesting Conjugated Oligoelectrolyte Enables Photocatalytic Nitrogen Fixation in a Bacterial Biohybrid

We report a rationally designed membrane-intercalating conjugated oligoelectrolyte (COE), namely COE-IC, which endows aerobic N2 -fixing bacteria Azotobacter vinelandii with a light-harvesting ability that enables photosynthetic ammonia production. COE-IC possesses an acceptor-donor-acceptor (A-D-A) type conjugated core, which promotes visible light absorption with a high molar extinction coefficient. Furthermore, COE-IC spontaneously associates with A. vinelandii to form a biohybrid in which the COE is intercalated within the lipid bilayer membrane. In the presence of L-ascorbate as a sacrificial electron donor, the resulting COE-IC/A. vinelandii biohybrid showed a 2.4-fold increase in light-driven ammonia production, as compared to the control. Photoinduced enhancement of bacterial biomass and production of L-amino acids is also observed. Introduction of isotopically enriched 15 N2 atmosphere led to the enrichment of 15 N-containing intracellular metabolites, consistent with the products being generated from atmospheric N2 .

A broad-spectrum synthetic antibiotic that does not evoke bacterial resistance

BACKGROUND

Antimicrobial resistance (AMR) poses a critical threat to public health and disproportionately affects the health and well-being of persons in low-income and middle-income countries. Our aim was to identify synthetic antimicrobials termed conjugated oligoelectrolytes (COEs) that effectively treated AMR infections and whose structures could be readily modified to address current and anticipated patient needs.

METHODS

Fifteen chemical variants were synthesized that contain specific alterations to the COE modular structure, and each variant was evaluated for broad-spectrum antibacterial activity and for in vitro cytotoxicity in cultured mammalian cells. Antibiotic efficacy was analyzed in murine models of sepsis; in vivo toxicity was evaluated via a blinded study of mouse clinical signs as an outcome of drug treatment.

FINDINGS

We identified a compound, COE2-2hexyl, that displayed broad-spectrum antibacterial activity. This compound cured mice infected with clinical bacterial isolates derived from patients with refractory bacteremia and did not evoke bacterial resistance. COE2-2hexyl has specific effects on multiple membrane-associated functions (e.g., septation, motility, ATP synthesis, respiration, membrane permeability to small molecules) that may act together to negate bacterial cell viability and the evolution of drug-resistance. Disruption of these bacterial properties may occur through alteration of critical protein-protein or protein-lipid membrane interfaces-a mechanism of action distinct from many membrane disrupting antimicrobials or detergents that destabilize membranes to induce bacterial cell lysis.

INTERPRETATION

The ease of molecular design, synthesis and modular nature of COEs offer many advantages over conventional antimicrobials, making synthesis simple, scalable and affordable. These COE features enable the construction of a spectrum of compounds with the potential for development as a new versatile therapy for an imminent global health crisis.

FUNDING

U.S. Army Research Office, National Institute of Allergy and Infectious Diseases, and National Heart, Lung, and Blood Institute.

Membrane-intercalating conjugated oligoelectrolytes

By acting as effective biomimetics of the lipid bilayers, membrane-intercalating conjugated oligoelectrolytes (MICOEs) can spontaneously insert themselves into both synthetic lipid bilayers and biological membranes. The modular and intentional molecular design of MICOEs enable a range of applications, such as bioproduction, biocatalysis, biosensing, and therapeutics. This tutorial review provides a structural evolution of MICOEs, which originated from the broader class of conjugated molecules, and analyses the drivers behind this evolutionary process. Various representative applications of MICOEs, accompanied by insights into their molecular design principles, will be reviewed separately. Perspectives on the current challenges and opportunities in research on MICOEs will be discussed at the end of the review to highlight their potential as unconventional and value-added materials for biological systems.

Predicting Antimicrobial Activity of Conjugated Oligoelectrolyte Molecules via Machine Learning

New antibiotics are needed to battle growing antibiotic resistance, but the development process from hit, to lead, and ultimately to a useful drug takes decades. Although progress in molecular property prediction using machine-learning methods has opened up new pathways for aiding the antibiotics development process, many existing solutions rely on large data sets and finding structural similarities to existing antibiotics. Challenges remain in modeling unconventional antibiotic classes that are drawing increasing research attention. In response, we developed an antimicrobial activity prediction model for conjugated oligoelectrolyte molecules, a new class of antibiotics that lacks extensive prior structure-activity relationship studies. Our approach enables us to predict the minimum inhibitory concentration for E. coli K12, with 21 molecular descriptors selected by recursive elimination from a set of 5305 descriptors. This predictive model achieves an R² of 0.65 with no prior knowledge of the underlying mechanism. We find the molecular representation optimum for the domain is the key to good predictions of antimicrobial activity. In the case of conjugated oligoelectrolytes, a representation reflecting the three-dimensional shape of the molecules is most critical. Although it is demonstrated with a specific example of conjugated oligoelectrolytes, our proposed approach for creating the predictive model can be readily adapted to other novel antibiotic candidate domains.

Photoswitchable Conjugated Oligoelectrolytes for a Light-Induced Change of Membrane Morphology

The synthesis of a new conjugated oligoelectrolyte (COE), namely DSAzB, is described, which contains a conjugated core bearing a diazene moiety in the center of its electronically delocalized structure. Similar to structurally related phenylenevinylene-based COEs, DSAzB readily intercalates into model and natural lipid bilayer membranes. Photoinduced isomerization transforms the linear trans COE into a bent or C-shape form. It is thereby possible to introduce DSAzB into the bilayer of a cell and disrupt its integrity by irradiation with light. This leads to controlled permeabilization of membranes, as demonstrated by the release of calcein from DMPG/DMPC vesicles and by propidium iodide influx experiments on S. epidermidis. Both experiments support that the permeabilization is selective for the light stimulus, highly efficient, and repeatable. Target-selective and photoinduced actions demonstrated by DSAzB may have broad applications in biocatalysis and related biotechnologies.

A Comprehensive Understanding of Electro-Fermentation

Electro-fermentation (EF) is an upcoming technology that can control the metabolism of exoelectrogenic bacteria (i.e., bacteria that transfer electrons using an extracellular mechanism). The fermenter consists of electrodes that act as sink and source for the production and movement of electrons and protons, thus generating electricity and producing valuable products. The conventional process of fermentation has several drawbacks that restrict their application and economic viability. Additionally, metabolic reactions taking place in traditional fermenters are often redox imbalanced. Almost all metabolic pathways and microbial strains have been studied, and EF can electrochemically control this. The process of EF can be used to optimize metabolic processes taking place in the fermenter by controlling the redox and pH imbalances and by stimulating carbon chain elongation or breakdown to improve the overall biomass yield and support the production of a specific product. This review briefly discusses microbe-electrode interactions, electro-fermenter designs, mixed-culture EF, and pure culture EF in industrial applications, electro methanogenesis, and the various products that could be hence generated using this process.

Molecular design of antimicrobial conjugated oligoelectrolytes with enhanced selectivity toward bacterial cells

A series of cationic conjugated oligoelectrolytes (COEs) was designed to understand how variations in molecular dimensions impact the relative activity against bacteria and mammalian cells. These COEs kept a consistent distyrylbenzene framework but differed in the length of linker between the core and the cationic site and the length of substitute on the quaternary ammonium functioned group. Their antimicrobial efficacy, mammalian cell cytotoxicity, hemolytic activity, and cell association were determined. We find that hydrophobicity is a factor that controls the degree of COE association to cells, but in vitro efficacy and cytotoxicity depend on more subtle structural features. COE2-3C-C4butyl was found to be the optimal structure with a minimum inhibitory concentration (MIC) of 4 μg mL⁻¹ against E. coli K12, low cytotoxicity against HepG2 cells and negligible hemolysis of red blood cells, even at 1024 μg mL⁻¹. A time-kill kinetics study of COE2-3C-C4butyl against E. coli K12 demonstrates bactericidal activity. These findings provide the first systematic investigation of how COEs may be modulated to achieve low mammalian cell cytotoxicity with the long-range perspective of finding candidates suitable for developing a broad-spectrum antimicrobial agent.

A series of cationic conjugated oligoelectrolytes (COEs) was designed to understand how variations in molecular dimensions impact the relative activity against bacteria and mammalian cells.

Membrane Environment Enables Ultrafast Isomerization of Amphiphilic Azobenzene

The non-covalent affinity of photoresponsive molecules to biotargets represents an attractive tool for achieving effective cell photo-stimulation. Here, an amphiphilic azobenzene that preferentially dwells within the plasma membrane is studied. In particular, its isomerization dynamics in different media is investigated. It is found that in molecular aggregates formed in water, the isomerization reaction is hindered, while radiative deactivation is favored. However, once protected by a lipid shell, the photochromic molecule reacquires its ultrafast photoisomerization capacity. This behavior is explained considering collective excited states that may form in aggregates, locking the conformational dynamics and redistributing the oscillator strength. By applying the pump probe technique in different media, an isomerization time in the order of 10 ps is identified and the deactivation in the aggregate in water is also characterized. Finally, it is demonstrated that the reversible modulation of membrane potential of HEK293 cells via illumination with visible light can be indeed related to the recovered trans→cis photoreaction in lipid membrane. These data fully account for the recently reported experiments in neurons, showing that the amphiphilic azobenzenes, once partitioned in the cell membrane, are effective light actuators for the modification of the electrical state of the membrane.

Highly Fluorescent Distyrylnaphthalene Derivatives as a Tool for Visualization of Cellular Membranes

Fluorescent imaging, which is an important interdisciplinary field bridging research from organic chemistry, biochemistry and cell biology has been applied for multi-dimensional detection, visualization and characterization of biological structures and processes. Especially valuable is the possibility to monitor cellular processes in real time using fluorescent probes. In this work, conjugated oligoelectrolytes and neutral derivatives with the distyrylnaphthalene core (SN-COEs) were designed, synthetized and tested for biological properties as membrane-specific fluorescent dyes for the visualization of membrane-dependent cellular processes. The group of tested compounds includes newly synthesized distyrylnaphthalene derivatives (DSNNs): a trimethylammonium derivative (DSNN-NMe3+), a phosphonate derivative (DSNN-P), a morpholine derivative (DSNN-Mor), a dihydroxyethylamine derivative (DSNN-DEA), a phosphonate potassium salt (DSNN-POK), an amino derivative (DSNN-NH2) and pyridinium derivative (DSNN-Py+). All compounds were tested for their biological properties, including cytotoxicity and staining efficiency towards mammalian cells. The fluorescence intensity of SN-COEs incorporated into cellular structures was analyzed by fluorescence activated cell sorting (FACS) and photoluminescence spectroscopy. The cytotoxicity results have shown that all tested SN-COEs can be safely used in the human and animal cell studies. Fluorescence and confocal microscopy observations confirm that tested COEs can be applied as fluorescent probes for the visualization of intracellular membrane components in a wide range of different cell types, including adherent and suspension cells. The staining procedure may be performed under both serum free and complete medium conditions. The presented studies have revealed the interesting biological properties of SN-COEs and confirmed their applicability as dyes for staining the membranous structures of eukaryotic cells, which may be useful for visualization of wide range of biological processes dependent of the extra-/intracellular communications and/or based on the remodeling of cellular membranes.

Enterococcus faecalis Adapts to Antimicrobial Conjugated Oligoelectrolytes by Lipid Rearrangement and Differential Expression of Membrane Stress Response Genes

Conjugated oligoelectrolytes (COEs) are emerging antimicrobials with broad spectrum activity against Gram positive and Gram negative bacteria as well as fungi. Our previous in vitro evolution studies using Enterococcus faecalis grown in the presence of two related COEs (COE1-3C and COE1-3Py) led to the emergence of mutants (changes in liaF and liaR) with a moderate 4- to16-fold increased resistance to COEs. The contribution of liaF and liaR mutations to COE resistance was confirmed by complementation of the mutants, which restored sensitivity to COEs. To better understand the cellular target of COEs, and the mechanism of resistance to COEs, transcriptional changes associated with resistance in the evolved mutants were investigated in this study. The differentially transcribed genes encoded membrane transporters, in addition to proteins associated with cell envelope synthesis and stress responses. Genes encoding membrane transport proteins from the ATP binding cassette superfamily were the most significantly induced or repressed in COE tolerant mutants compared to the wild type when exposed to COEs. Additionally, differences in the membrane localization of a lipophilic dye in E. faecalis exposed to COEs suggested that resistance was associated with lipid rearrangement in the cell membrane. The membrane adaptation to COEs in EFC3C and EFC3Py resulted in an improved tolerance to bile salt and sodium chloride stress. Overall, this study showed that bacterial cell membranes are the primary target of COEs and that E. faecalis adapts to membrane interacting COE molecules by both lipid rearrangement and changes in membrane transporter activity. The level of resistance to COEs suggests that E. faecalis does not have a specific response pathway to elicit resistance against these molecules and this is supported by the rather broad and diverse suite of genes that are induced upon COE exposure as well as cross-resistance to membrane perturbing stressors.

Mechanistic Understanding of the Interactions of Cationic Conjugated Oligo- and Polyelectrolytes with Wild-type and Ampicillin-resistant Escherichia coli

An in-depth understanding of cell-drug binding modes and action mechanisms can potentially guide the future design of novel drugs and antimicrobial materials and help to combat antibiotic resistance. Light-harvesting π-conjugated molecules have been demonstrated for their antimicrobial effects, but their impact on bacterial outer cell envelope needs to be studied in detail. Here, we synthesized poly(phenylene) based model cationic conjugated oligo- (2QA-CCOE, 4QA-CCOE) and polyelectrolytes (CCPE), and systematically explored their interactions with the outer cell membrane of wild-type and ampicillin (amp)-resistant Gram-negative bacteria, Escherichia coli (E. coli). Incubation of the E. coli cells in CCOE/CCPE solution inhibited the subsequent bacterial growth in LB media. About 99% growth inhibition was achieved if amp-resistant E. coli was treated for ~3-5 min, 1 h and 6 h with 100 μM of CCPE, 4QA-CCOE, and 2QA-CCOE solutions, respectively. Interestingly, these CCPE and CCOEs inhibited the growth of both wild-type and amp-resistant E. coli to a similar extent. A large surface charge reversal of bacteria upon treatment with CCPE suggested the formation of a coating of CCPE on the outer surface of bacteria; while a low reversal of bacterial surface charge suggested intercalation of CCOEs within the lipid bilayer of bacteria.

Direct microbial transformation of carbon dioxide to value-added chemicals: A comprehensive analysis and application potentials

Carbon dioxide storage in petroleum and other geological reservoirs is an economical option for long-term separation of this gas from the atmosphere. Other options include applications through conversion to valuable chemicals. Microalgae and plants perform direct fixation of carbon dioxide to biomass, which is then used as raw material for further microbial transformation (MT). The approach by microbial transformation can achieve reduction of carbon dioxide and production of biofuels. This review addresses the research and technological processes related to direct MT of carbon dioxide, factors affecting their efficiency in operation and the review of economic feasibility. Additionally, some commercial plants making utilization of CO₂ around the globe are also summarized along with different value-added chemicals (methane, acetate, fatty acids and alcohols) as reported in literature. Further information is also provided for a better understanding of direct CO₂ MT and its future prospects leading to a sustainable and clean environment.

Conjugated Polymers for Assessing and Controlling Biological Functions

The field of organic bioelectronics is advancing rapidly in the development of materials and devices to precisely monitor and control biological signals. Electronics and biology can interact on multiple levels: organs, complex tissues, cells, cell membranes, proteins, and even small molecules. Compared to traditional electronic materials such as metals and inorganic semiconductors, conjugated polymers (CPs) have several key advantages for biological interactions: tunable physiochemical properties, adjustable form factors, and mixed conductivity (ionic and electronic). Herein, the use of CPs in five biologically oriented research topics, electrophysiology, tissue engineering, drug release, biosensing, and molecular bioelectronics, is discussed. In electrophysiology, implantable devices with CP coating or CP-only electrodes are showing improvements in signal performance and tissue interfaces. CP-based scaffolds supply highly favorable static or even dynamic interfaces for tissue engineering. CPs also enable delivery of drugs through a variety of mechanisms and form factors. For biosensing, CPs offer new possibilities to incorporate biological sensing elements in a conducting matrix. Molecular bioelectronics is today used to incorporate (opto)electronic functions in living tissue. Under each topic, the limits of the utility of CPs are discussed and, overall, the major challenges toward implementation of CPs and their devices to real-world applications are highlighted.

Precisely Defined Conjugated Oligoelectrolytes for Biosensing and Therapeutics

Conjugated oligoelectrolytes (COEs) are a relatively new class of synthetic organic molecules with, as of yet, untapped potential for use in organic optoelectronic devices and bioelectronic systems. COEs also offer a novel molecular approach to biosensing, bioimaging, and disease therapy. Substantial progress has been made in the past decade at the intersection of chemistry, materials science, and the biological sciences developing COEs and their polymer analogues, namely, conjugated polyelectrolytes (CPEs), into synthetic systems with biological and biomedical utility. CPEs have traditionally attracted more attention in arenas of sensing, imaging, and therapy. However, the precisely defined molecular structures and interactions of COEs offer potential key advantages over CPEs, including higher reliability and fluorescence quantum efficiency, larger diversity of subcellular targeting strategies, and improved selectivity to biomolecules. Here, the unique-and sometimes overlooked-properties of COEs are discussed and the noticeable progress in their use for biological sensing, imaging, and therapy is reviewed.

From Single Molecules to Thin Film Electronics, Nanofibers, e-Textiles and Power Cables: Bridging Length Scales with Organic Semiconductors

Organic semiconductors are the centerpiece of several vibrant research fields from single-molecule to organic electronics, and they are finding increasing use in bioelectronics and even classical polymer technology. The versatile chemistry and broad range of electronic functionalities of conjugated materials enable the bridging of length scales 15 orders of magnitude apart, ranging from a single nanometer (10^-9 m) to the size of continents (10⁶ m). This work provides a taste of the diverse applications that can be realized with organic semiconductors. The reader will embark on a journey from single molecular junctions to thin film organic electronics, supramolecular assemblies, biomaterials such as amyloid fibrils and nanofibrillated cellulose, conducting fibers and yarns for e-textiles, and finally to power cables that shuffle power across thousands of kilometers.

A Chain-Elongated Oligophenylenevinylene Electrolyte Increases Microbial Membrane Stability

A novel conjugated oligoelectrolyte (COE) material, named S6, is designed to have a lipid-bilayer stabilizing topology afforded by an extended oligophenylenevinylene backbone. S6 intercalates biological membranes acting as a hydrophobic support for glycerophospholipid acyl chains. Indeed, Escherichia coli treated with S6 exhibits a twofold improvement in butanol tolerance, a relevant feature to achieve within the general context of modifying microorganisms used in biofuel production. Filamentous growth, a morphological stress response to butanol toxicity in E. coli, is observed in untreated cells after incubation with 0.9% butanol (v/v), but is mitigated by S6 treatment. Real-time fluorescence imaging using giant unilamellar vesicles reveals the extent to which S6 counters membrane instability. Moreover, S6 also reduces butanol-induced lipopolysaccharide release from the outer membrane to further maintain cell integrity. These findings highlight a deliberate effort in the molecular design of a chain-elongated COE to stabilize microbial membranes against environmental challenges.

Addressable Peptide Self-Assembly on the Cancer Cell Membrane for Sensitizing Chemotherapy of Renal Cell Carcinoma

Chemotherapy has been validated unavailable for treatment of renal cell carcinoma (RCC) in clinic due to its intrinsic drug resistance. Sensitization of chemo-drug response plays a crucial role in RCC treatment and increase of patient survival. Herein, a recognition-reaction-aggregation (RRA) cascaded strategy is utilized to in situ construct peptide-based superstructures on the renal cancer cell membrane, enabling specifically perturbing the permeability of cell membranes and enhancing chemo-drug sensitivity in vitro and in vivo. First, P1-DBCO can specifically recognize renal cancer cells by targeting carbonic anhydrase IX. Subsequently, P2-N₃ is introduced and efficiently reacts with P1-DBCO to form a peptide P3, which exhibits enhanced hydrophobicity and simultaneously aggregates into a superstructure. Interestingly, the superstructure retains on the cell membrane and perturbs its integrity/permeability, allowing more doxorubicin (DOX) uptaken by renal cancer cells. Owing to this increased influx, the IC₅₀ is significantly reduced by nearly 3.5-fold compared with that treated with free DOX. Finally, RRA strategy significantly inhibits the tumor growth of xenografted mice with a 3.2-fold enhanced inhibition rate compared with that treated with free DOX. In summary, this newly developed RRA strategy will open a new avenue for chemically engineering cell membranes with diverse biomedical applications.

Matrine inhibits prostate cancer via activation of the unfolded protein response/endoplasmic reticulum stress signaling and reversal of epithelial to mesenchymal transition

Prostate cancer is the second most commonly diagnosed malignancy and the sixth global primary cause of malignancy-associated fatality. Increased invasiveness and motility in prostate cancer cells are associated with ubiquitin proteasome system-regulated epithelial to mesenchymal transition (EMT). Impairment of the endoplasmic reticulum (ER) causes ER stress due to the accumulation of unfolded proteins and altered cell survival. In the current study, the effect and mechanism of matrine on cell apoptosis, viability, migration and invasion of human prostate cancer cells in vivo and in vitro through the unfolded protein response (UPR)/ER stress pathway were investigated. Matrine inhibited proteasomal chymotrypsin-like (CT-like) activity in the prostate carcinoma cellular proteasome. Upregulated vimentin and N-cadherin and downregulated E-cadherin were also observed in vitro and in vivo. In vitro analyses showed that matrine repressed cell motility, viability and invasion, arrested the cell cycle at the G₀/G₁ phase and induced prostate cancer cell apoptosis. Furthermore, matrine activated the UPR/ER stress signaling cascade in prostate cancer cells and tumor tissues of xenograft-bearing nude mice. Results also demonstrated that the anti-apoptotic protein Bcl-2 was downregulated, the pro-apoptotic protein Bak was upregulated and the cell growth and cell cycle-related proteins c-Myc, Cyclin B1, Cyclin D1 and CDK1 were downregulated. Moreover, matrine inhibited tumor growth and Ki-67 expression in xenograft-bearing nude mice. To the best of our knowledge, the present study indicated for the first time that matrine exerted marked anticancer functions in human prostate carcinoma in vivo and in vitro through activation of the proteasomal CT-like activity inhibition mediated by the UPR/ER stress signaling pathway.

Membrane adaptation limitations inEnterococcus faecalisunderlie sensitivity and the inability to develop significant resistance to conjugated oligoelectrolytes

COEs are emerging antimicrobials to combat drug resistant infections and to which bacteria develop only limited resistance.

Interactions of a paracyclophane-based conjugated oligoelectrolyte with biological membranes

We report a non-planar conjugated oligoelectrolyte as a membrane permeabilizing material and its membrane interactions compared to the linear analog.

Salt-induced thermochromism of a conjugated polyelectrolyte

We report here the photophysical properties of a water-soluble polythiophene with cationic side-chains in PBS buffer solution.

Influence of molecular structure on the antimicrobial function of phenylenevinylene conjugated oligoelectrolytes

Structure/property relationships were obtained to understand the antimicrobial function of conjugated oligoelectrolytes toward Gram-negative and Gram-positive bacteria.

Conjugated oligoelectrolytes (COEs) with phenylenevinylene (PV) repeat units are known to spontaneously intercalate into cell membranes. Twelve COEs, including seven structures reported here for the first time, were investigated for the relationship between their membrane disrupting properties and structural modifications, including the length of the PV backbone and the presence of either a tetraalkylammonium or a pyridinium ionic pendant group. Optical characteristics and interactions with cell membranes were determined using UV-Vis absorption and photoluminescence spectroscopies, and confocal microscopy. Toxicity tests on representative Gram-positive (Enterococcus faecalis) and Gram-negative (Escherichia coli) bacteria reveal generally greater toxicity to E. faecalis than to E. coli and indicate that shorter molecules have superior antimicrobial activity. Increased antimicrobial potency was observed in three-ring COEs appended with pyridinium ionic groups but not with COEs with four or five PV repeat units. Studies with mutants having cell envelope modifications indicate a possible charge based interaction with pyridinium-appended compounds. Fluorine substitutions on COE backbones result in structures that are less toxic to E. coli, while the addition of benzothiadiazole to COE backbones has no effect on increasing antimicrobial function. A weakly membrane-intercalating COE with only two PV repeat units allowed us to determine the synthetic limitations as a result of competition between solubility in aqueous media and association with cell membranes. We describe, for the first time, the most membrane disrupting structure achievable within two homologous series of COEs and that around a critical three-ring backbone length, structural modifications have the most effect on antimicrobial activity.

Extracellular electron transfer from cathode to microbes: application for biofuel production

Extracellular electron transfer in microorganisms has been applied for bioelectrochemical synthesis utilizing microbes to catalyze anodic and/or cathodic biochemical reactions. Anodic reactions (electron transfer from microbe to anode) are used for current production and cathodic reactions (electron transfer from cathode to microbe) have recently been applied for current consumption for valuable biochemical production. The extensively studied exoelectrogenic bacteria Shewanella and Geobacter showed that both directions for electron transfer would be possible. It was proposed that gram-positive bacteria, in the absence of cytochrome C, would accept electrons using a cascade of membrane-bound complexes such as membrane-bound Fe-S proteins, oxidoreductase, and periplasmic enzymes. Modification of the cathode with the addition of positive charged species such as chitosan or with an increase of the interfacial area using a porous three-dimensional scaffold electrode led to increased current consumption. The extracellular electron transfer from the cathode to the microbe could catalyze various bioelectrochemical reductions. Electrofermentation used electrons from the cathode as reducing power to produce more reduced compounds such as alcohols than acids, shifting the metabolic pathway. Electrofuel could be generated through artificial photosynthesis using electrical energy instead of solar energy in the process of carbon fixation.

Membrane permeabilization by conjugated oligoelectrolytes accelerates whole-cell catalysis

Conjugated oligoelectrolytes (COE) increase outer membrane permeability inEscherichia coli,improve transport of small molecules through the cell envelope and thus accelerate whole-cell catalysis.

Tuning cell surface charge in E. coli with conjugated oligoelectrolytes

Conjugated oligoelectrolytes intercalate into and associate with membranes, thereby changing the surface charge of microbes, as determined by zeta potential measurements.

Cationic conjugated oligoelectrolytes (COEs) varying in length and structural features are compared with respect to their association with E. coli and their effect on cell surface charge as determined by zeta potential measurements. Regardless of structural features, at high staining concentrations COEs with longer molecular dimensions associate less, but neutralize the negative surface charge of E. coli to a greater degree than shorter COEs.