Informed Molecular Design of Conjugated Oligoelectrolytes To Increase Cell Affinity and Antimicrobial Activity

Membrane‐intercalating conjugated oligoelectrolytes (COEs) are emerging as potential alternatives to conventional, yet increasingly ineffective, antibiotics. Three readily accessible COEs, belonging to an unreported series containing a stilbene core, namely D4 , D6 , and D8 , were designed and synthesized so that the hydrophobicity increases with increasing side‐chain length. Decreased aqueous solubility correlates with increased uptake by E. coli. The minimum inhibitory concentration (MIC) of D8 is 4 μg mL^?1 against both E. coli and E. faecalis, with an effective uptake of 72 %. In contrast, the MIC value of the shortest COE, D4 , is 128 μg mL^?1 owing to the low cellular uptake of 3 %. These findings demonstrate the application of rational design to generate efficacious antimicrobial COEs that have potential as low‐cost antimicrobial agents.     

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.     

Guanidinylated Amphiphilic Polycarbonates with Enhanced Antimicrobial Activity by Extending the Length of the Spacer Arm and Micelle Self‐Assembly

Nine guanidinylated amphiphilic polycarbonates are rationally designed and synthesized. Each polymer has the same biodegradable backbone but different side groups. The influence of the hydrophobic/hydrophilic effect on antimicrobial activities and cytotoxicity is systematically investigated. The results verify that tuning the length of the spacer arm between the cationic guanidine group and the polycarbonate backbone is an efficient design strategy to alter the hydrophobic/hydrophilic balance without changing the cationic charge density. A spacer arm of six methylene units (CH₂)₆ shows the best antimicrobial activity (minimum inhibitory concentration, MIC = 40 µg mL^?1 against Escherichia coli, MIC = 20 µg mL^?1 against Staphylococcus aureus, MIC = 40 µg mL^?1 against Candida albicans) with low hemolytic activity (HC₅₀ > 2560 µg mL^?1). Furthermore, the guanidinylated polycarbonates exhibit the ability to self‐assemble and present micelle‐like nanostructure due to their intrinsic amphiphilic macromolecular structure. Transmission electron microscopy and dynamic light scattering measurements confirm polymer micelle formation in aqueous solution with sizes ranging from 82 to 288 nm.     

Synthesis and discovery of N-(1-methyl-4-oxo-4,5-dihydro-1H-imidazol-2-yl)-[1,1′-biphenyl]-2-carboxamide derivatives as antimicrobial agents

Novel dihydro-1H-imidazole-2-yl)-[1,1′-biphenyl]-2-carboxamides ( 4a-l ) was achieved using a three-step synthesis process and evaluated as antimicrobial agents. These compounds were characterized through FTIR, NMR, LCMS and evaluated for DNA gyrase inhibition potentials and antimicrobial properties against Gram-negative bacteria Escherichia coli (MTCC 443), Pseudomonas aeruginosa (MTCC 424), Klebsiella pneumoniae MTCC 530 and Gram-positive bacteria Staphylococcus aureus (MTCC 3160), Corynebacterium diphtheriae (MTCC 116) and Streptococcus pyogenes (MTCC 442). Excellent DNA gyrase inhibition exhibited by compound 4f (IC₅₀ 0.2 μM and relative percentage activity 96.24%). A broad spectrum of antimicrobial activity showed by compounds 4d , 4f and 4 k with a Minimal Inhibitory Constant (MIC) of 1.05, 1.35 and 1.25 μg mL⁻¹, respectively.     

Turning on the Antimicrobial Activity of Gold Nanoclusters Against Multidrug-Resistant Bacteria**

In this work, we show that the addition of thiourea (TU) initiated broad-spectrum antimicrobial activity of otherwise inactive D-maltose-capped gold nanoclusters (AuNC-Mal). For example, AuNC-Mal/TU was effective against multidrug-resistant Pseudomonas aeruginosa with a minimum inhibitory concentration (MIC) of 1 μg mL⁻¹ (2.5 μM [Au]) while having 30–60 times lower in vitro cytotoxicity against mammalian cells. The reaction of AuNC-Mal and TU generated the antimicrobial species of [Au(TU)₂]⁺ and smaller AuNCs. TU increased the accumulation of Au in bacteria and helped maintain the oxidation state as Au^I (vs. Au^III). The modes of action included the inhibition of thioredoxin reductase, interference with the Cu^I regulation and depletion of ATP. Moreover, the antimicrobial activity did not change in the presence of colistin or carbonyl cyanide 3-chlorophenylhydrazone, suggesting that AuNC-Mal/TU was indifferent to the outer membrane barrier and to bacterial efflux pumps.     

Discovery of 4,6-bis(2-((E)-benzylidene)hydrazinyl)pyrimidin-2-Amine with Antibiotic Activity

Robenidine (E)-N′-((E)-1-(4-chlorophenyl)ethylidene)-2-(1-(4-chlorophenyl)ethylidene)hydrazine-1-carboximidhydrazide displays methicillin-resistant Staphyoccoccus aureus (MRSA) and vancomycin-resistant Enterococci (VRE) MICs of 2 μg mL⁻¹. Herein we describe the structure-activity relationship development of a novel series of guanidine to 2-aminopyrimidine isosteres that ameliorate the low levels of mammalian cytotoxicity in the lead compound while retaining good antibiotic activity. Removal of the 2-NH₂ pyrimidine moiety renders these analogues inactive. Introduction of a central 2-NH₂ triazine moiety saw a 10-fold activity reduction. Phenyl to cyclohexyl isosteres were inactive. The 4-BrPh and 4-CH₃Ph with MIC values of 2 and 4 μg mL⁻¹, against MRSA and VRE respectively, are promising candidates for future development.     

Antimicrobial anilinium polymers: The properties of poly(N,N‐dimethylaminophenylene methacrylamide) in solution and as coatings

Antimicrobial polymers have been widely reported to exert strong biocidal effects against bacteria. In contrast with antimicrobial polymers with aliphatic ammonium groups, polymers with anilinium groups have been rarely studied and applied as biocidal materials. In this study, a representative polymer with aniline side functional groups, poly(N,N‐dimethylaminophenylene methacrylamide) (PDMAPMA), was explored as a novel antimicrobial polymer. PDMAPMA was synthesized and its physicochemical properties evaluated. The methyl iodide‐quaternized polymer was tested against the Gram‐positive Staphylococcus aureus, with a minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 16–32 and 64–128 μg mL^?1, respectively. Against the Gram‐negative Escherichia coli, the MIC and MBC were both 64–128 μg mL^?1. To broaden the range of applications, PDMAPMA was coated on substrates via crosslinking to endow the surface with contact‐kill functionality. The effect of charge density of the coatings on the antimicrobial behavior was then investigated, and stronger biocidal performance was observed for films with higher charge density. This study of the biocidal behavior of PDMAPMA both in solution and as coatings is expected to broaden the application of polymers containing aniline side groups and provide more information on the antimicrobial behavior of such materials. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1908–1921     

Inspiration from Old Dyes: Tris(stilbene) Compounds as Potent Gram‐Positive Antibacterial Agents

Herein we describe the preparation and structure‐activity relationship studies on range of stilbene based compounds and their antibacterial activity. Two related compounds, each bearing carboxylic acid moieties, exhibit good activity against several bacterial strains, including methicillin‐resistant Staphylococcus aureus MRSA (ATCC 33592 and NCTC 10442). Compound 10 was most active against Moraxella catarrhalis with minimum inhibitory concentrations (MICs) of 0.12–0.25 μg mL^?1 and against Staphylococcus spp. with MICs ranging from 2–4 μg mL^?1. The derivative 17 showed increased activity with MICs of 0.06–0.25 μg mL^?1 against M. catarrhalis and 0.12–1 against Staphylococcus spp. This level of activity is similar to that reported for S. aureus for antibiotics, such as vancomycin, with MICs of ≤2.0 μg mL^?1 and clindamycin with MICs of ≤0.5 μg mL^?1. As an indicator of toxicity, 17 was tested for its ability to lyse sheep erythrocytes, and showed low haemolytic activity. Such results highlight the value of tris(stilbene) compounds as antibacterial agents providing suitable properties for further development.     

Effect of the topology on the antibacterial activity of cationic polythioether synthesized by all-click chemistry

Cationic compounds often serve as antibacterial materials for a wide range of applications. However, the relationship of topology−antibacterial activity has been rarely revealed. Herein, three cationic polythioethers (CPTEs) with hyperbranched topologies are well designed and facilely synthesized via an all-click chemistry strategy (including thiol-ene and epoxy-amine additions). These as-prepared CPTEs were found to exhibited outstanding antibacterial activity against Escherichia coli and Staphylococcus aureus with minimum inhibitory concentrations against E. coli of 7.3, 14.6, and 14.6 μg ml⁻¹, and against S. aureus of 14.6, 29.2, and 29.2 μg ml⁻¹, respectively. The antibacterial activity is coincident with their degree of branching (DB, their DB values of 0.81, 0.48, and 0.27), which is mainly attributed to the inherent three-dimensional structure. The present strategy reveals the relationship of polymer topology and antibacterial activity, providing a novel possibility for designing and/or synthesis of high-efficiency antibacterial agents.     

A New Nonconjugated Naphthalene Derivative of Meso-tetra-(3-hydroxy)-phenyl-porphyrin as a Potential Sensitizer for Photodynamic Therapy

A new 5,10,15,20-tetra-(phenoxy-3-carbonyl-1-amino-naphthyl)-porphyrin was prepared by an isocyanate condensation reaction and its photophysical properties fully evaluated, both in terms of photostability and singlet oxygen production. It shows considerably enhanced photostability when compared with the parent 5,10,15,20-tetra-(3-hydroxy-phenyl)-porphyrin, with the photodegradation quantum yields for T(NAF)PP and T(OH)PP being 4.65 × 10⁻⁴ and 5.19 × 10⁻³, respectively. Its photodynamic effect in human carcinoma HT-29 cells was evaluated. The new porphyrin showed good properties as a sensitizer in photodynamic therapy with an in vitro cytotoxicity IC₅₀ value of 6.80 μg mL⁻¹ for a 24 h incubation. In addition to the potential of this compound, the synthetic route used provides possibilities of extension to a wide range of new sensitizers.     

A Versatile Boc Solid Phase Synthesis of Daptomycin and Analogues Using Site Specific,On-Resin Ozonolysis to Install the Kynurenine Residue

A de novo solid-phase synthesis of the cyclic lipodepsipeptide daptomycin via Boc chemistry was achieved. The challenging ester bond formation between the nonproteinogenic amino acid kynurenine was achieved by esterification of a threonine residue with a protected tryptophan. Subsequent late-stage on-resin ozonolysis, inspired by the biomimetic pathway, afforded the kynurenine residue directly. Synthetic daptomycin possessed potent antimicrobial activity (MIC₁₀₀=1.0 μg mL⁻¹) against S. aureus, while five other daptomycin analogues containing (2R,3R)-3-methylglutamic acid, (2S,4S)-4-methylglutamic acid or canonical glutamic acid at position twelve prepared using this new methodology were all inactive, clearly establishing that the (2S,3R)-3-methylglutamic acid plays a key role in the antimicrobial activity of daptomycin.     

A Flexible Energy Harvester from an Organic Ferroelectric Ammonium Salt

Organic ferroelectrics due to their low cost, easy preparation, light weight, high flexibility and phase stability are gaining tremendous attention in the field of portable electronics. In this work, we report the synthesis, structure and ferroelectric behavior of a two-component ammonium salt 2 , containing a bulky [Bn(4-BrBn)NMe₂]⁺ (Bn=benzyl and 4-BrBn=4-bromobenzyl) cation and tetrahedral (BF₄)⁻ anion. The structural analysis revealed the presence of rich non-classical C−H⋅⋅⋅F and C−H⋅⋅⋅Br interactions in this molecule that were quantified by Hirshfeld surface analysis. The polarization (P) vs. electric field (E) hysteresis loop measurements on 2 gave a remnant polarization (P_r) of 14.4 μC cm⁻² at room temperature. Flexible polymer composites with various (5, 10, 15 and 20) weight percentages (wt%) of 2 in thermoplastic polyurethane (TPU) were prepared and tested for mechanical energy harvesting applications. A notable peak-to-peak output voltage of 20 V, maximum current density of 1.1 μA cm⁻² and power density of 21.1 μW cm⁻² were recorded for the 15 wt% 2 -TPU composite device. Furthermore, the voltage output generated from this device was utilized to rapidly charge a 100 μF capacitor, with stored energies and measured charges of 156 μJ and 121.6 μC, respectively.     

Isoxazole derivatives of silatrane: synthesis,characterization, in silico ADME profile,prediction of potential pharmacological activity and evaluation of antimicrobial action

A new family of mono- ( 3a-h ) and bis- ( 4a-g ) isoxazole-bridged silatranes has been synthesized by the reaction of 3-aminopropylsilatrane ( 1 ) and 3-substituted 5-chloro-methylisoxazoles ( 2a-h ). The structure of the isoxazole-silatrane hybrids is characterized by elemental analysis, FT-IR, UV, NMR (¹H, ¹³C,²⁹Si and ¹⁵N) spectroscopy, high-resolution mass spectrometry, and X-ray diffraction analysis. The in silico ADME (absorption, distribution, metabolism, excretion) assessment reveals that properties of mono-adducts ( 3a-h ) are similar to those of drugs obeyed to the Lipinski's rule. The calculated screening of potential pharmacological activity profiles (in silico PASS program) of isoxazole-silatranes shows that all synthesized compounds (both mono- and bis-substituted) may have high antitumor action, unlike starting isoxazoles. The preliminary screening of the synthesized silatranes for antimicrobial activity against Enterococcus durans, Bacillus subtilis, Escherichia coli, and Pseudomonas aeruginosa indicates that all test samples are active only against gram-positive microorganisms. Silatrane 3f displays minimal inhibitory concentration (MIC 12.5 and 6.2 μg ml⁻¹) against E. durans and B. subtilis as compared with standard drug gentamicin (MIC 25 and 50 μg ml⁻¹).     

Phenolic glucosides and chromane analogs from the insect fungus Conoideocrella krungchingensis BCC53666

Six new compounds, named conoideoglucosides A − C and conoideochromanes A − C, together with eight known compounds, including eutypinic acid, 2,2-dimethyl-2H-1-chromene-6-carboxylic acid, (−)-luteoskyrin, (−)-4a-oxyluteoskyrin, chrysophanol, islandicin, catenarin, and (22E)-5α,8α-epidioxyergosta-6,22-dien-3β-ol were isolated from the insect fungus Conoideocrella krungchingensis BCC53666. (−)-Luteoskyrin exhibited a broad range of antimicrobial activity such as antimalarial (IC₅₀ 0.51 μg/mL), antitubercular (MIC 6.25 μg/mL), antibacterial (both Gram positive; MIC 0.39–1.56 μg/mL and Gram negative; MIC 3.13–12.50 μg/mL), and antifungal (against various plant pathogens; MIC 3.13–50.00 μg/mL) activities, while (−)-4a-oxyluteoskyrin and catenarin showed weaker antibacterial activity. Moreover, eutypinic acid, (−)-luteoskyrin, (−)-4a-oxyluteoskyrin, and catenarin showed cytotoxicity against NCI-H187 cells with IC₅₀ in a range of 0.16–17.99 μg/mL, while eutypinic acid and catenarin had no cytotoxicity against non-cancerous (Vero) cells at maximum tested concentration (50 μg/mL). The complete NMR spectral data and biological activity of the known (−)-4a-oxyluteoskyrin was also reported for the first time.     

Magnetic Nanohybrids Loaded with Bimetal Core–Shell–Shell Nanorods for Bacteria Capture,Separation, and Near‐Infrared Photothermal Treatment

A novel antimicrobial nanohybrid based on near‐infrared (NIR) photothermal conversion is designed for bacteria capture, separation, and sterilization (killing). Positively charged magnetic reduced graphene oxide with modification by polyethylenimine (rGO–Fe₃O₄–PEI) is prepared and then loaded with core–shell–shell Au–Ag–Au nanorods to construct the nanohybrid rGO–Fe₃O₄–Au–Ag–Au. NIR laser irradiation melts the outer Au shell and exposes the inner Ag shell, which facilitates controlled release of the silver shell. The nanohybrids combine physical photothermal sterilization as a result of the outer Au shell with the antibacterial effect of the inner Ag shell. In addition, the nanohybrid exhibits high heat conductivity because of the rGO and rapid magnetic‐separation capability that is attributable to Fe₃O₄. The nanohybrid provides a significant improvement of bactericidal efficiency with respect to bare Au–Ag–Au nanorods and facilitates the isolation of bacteria from sample matrixes. A concentration of 25 μg mL^?1 of nanohybrid causes 100 % capture and separation of Escherichia coli O157:H7 (1×10⁸ cfu mL^?1) from an aqueous medium in 10 min. In addition, it causes a 22 °C temperature rise for the surrounding solution under NIR irradiation (785 nm, 50 mW cm^?2) for 10 min. With magnetic separation, 30 μg mL^?1 of nanohybrid results in a 100 % killing rate for E. coli O157:H7 cells. The facile bacteria separation and photothermal sterilization is potentially feasible for environmental and/or clinical treatment.     

Interfacial Capacitance of Graphene Oxide Films Electrodes: Fundamental Studies on Electrolytes Interface Aiming (Bio)Sensing Applications

The understanding of bidimensional materials dynamics and its electrolyte interface equilibrium, such as graphene oxide (GO), is critical for the development of a capacitive biosensing platform. The interfacial capacitance (C_i) of graphene-based materials may be tuned by experimental conditions such as pH optimization and cation size playing key roles at the enhancement of their capacitive properties allowing their application as novel capacitive biosensors. Here we reported a systematic study of C_i of multilayer GO films in different aqueous electrolytes employing electrochemical impedance spectroscopy for the application in a capacitive detection system. We demonstrated that the presence of ionizable oxygen-containing functional groups within multilayer GO film favors the interactions and the accumulation of cations in the structure of the electrodes enhancing the GO C_i in aqueous solutions, where at pH 7.0 (the best condition) the C_i was 340 μF mg⁻¹ at −0.01 V vs Ag/AgCl. We also established that the hydrated cation radius affects the mobility and interaction with GO functional groups and it plays a critical role in the Ci, as demonstrated in the presence of different cations Na⁺=640 μF mg⁻¹, Li⁺=575 μF mg⁻¹ and TMA⁺=477 μF mg⁻¹. As a proof-of-concept, the capacitive behaviour of GO was explored as biosensing platform for standard streptavidin-biotin systems. For this system, the C_i varied linearly with the log of the concentration of the targeting analyte in the range from 10 pg mL⁻¹ to 100 ng mL⁻¹, showing the promising applicability of capacitive GO based sensors for label-free biosensing.     

Microwave assisted synthesis,docking and antimalarial evaluation of hybrid PABA-substituted 1,3,5-triazine derivatives

A series of novel PABA-substituted 1,3,5-triazine derivatives were developed via microwave assisted synthesis and subsequently tested for antimalarial activity against chloroquine sensitive 3D7 strain of Plasmodium falciparum using chloroquine as standard. Antimalarial screening result showed that synthesized compounds exhibited IC₅₀ in the range of 4.46 to 79.72 μg mL⁻¹. Among the tested compounds, 4c and 4f showed significant antimalarial activity with low binding energies (BE) -172.32 and 160.41 kcal mol⁻¹ via interacting with Arg122 through the involvement of COOH of the phenyl linked to 1,3,5-triazine. In conclusion, these core scaffolds can be used for future antimalarial drug development.     

Preparation,spectroscopic, X-ray crystallographic,DFT, antimicrobial and ADMET studies of N-[(4-flourophenyl)sulfanyl]phthalimide

N-[(4-Fluorophenyl)sulfanyl]phthalimide (C₁₄H₈FNO₂S, FP ) was synthesized and characterized using X-ray crystallography. It was then investigated via quantum chemical analysis using the density functional theory (DFT) approach, as well as spectrochemically using FT–IR and ¹H and ¹³C NMR spectroscopy, and elemental analysis. The observed and stimulated spectra are in very good agreement for the DFT method. The in vitro antimicrobial activity of FP against three Gram-positive bacteria, three Gram-negative bacteria and two fungi were determined using the serial dilution method, and FP showed the highest antibacterial activity against E. coli, with a MIC of 128 µg ml⁻¹. Druglikeness, ADME (absorption, distribution, metabolism and excretion) and toxicology studies were carried out to theoretically examine the drug properties of FP .     

Development of Bio-inspired Composite Materials for the Detection of Traces of Silver Present in Water: Use of Taguchi Methodology to Design Low-cost Carbon Paste Electrodes

Carbon Paste Electrodes (CPE) modified with Grapefruit-Peels (GP) functionalized with Urea (GPU) and, Melamine (GPM) were designed for the detection of Ag⁺ in water. Taguchi L₉ methodology was used to determine the optimal graphite-Active material ratio. The best electrochemical response was for CPE-GPU with an 80 : 20 ratio. The results obtained showed a linear detection range between 0.5 to 28 μg L⁻¹, with a detection limit of 0.73 μg L⁻¹ and a limit of quantification of 1.04 μg L⁻¹. Attributable to CPE-GPU characteristics: electroactive surface area 0.175 cm², roughness factor 3.87, resistance 0.09 Ω and, mostly −NH₂ groups on its surface. The composite material offers a viable option to be used for the determination of silver traces in situ in industrial processes.     

Antimicrobial Polymers Prepared by Ring‐Opening Metathesis Polymerization: Manipulating Antimicrobial Properties by Organic Counterion and Charge Density Variation

The synthesis and characterization of a series of poly(oxanorbornene)‐based synthetic mimics of antimicrobial peptides (SMAMPs) is presented. In the first part, the effect of different organic counterions on the antimicrobial properties of the SMAMPs was investigated. Unexpectedly, adding hydrophobicity by complete anion exchange did not increase the SMAMPs’ antimicrobial activity. It was found by dye‐leakage studies that this was due to the loss of membrane activity of these polymers caused by the formation of tight ion pairs between the organic counterions and the polymer backbone. In the second part, the effect of molecular charge density on the biological properties of a SMAMP was investigated. The results suggest that, above a certain charge threshold, neither minimum inhibitory concentration (MIC₉₀) nor hemolytic activity (HC₅₀) is greatly affected by adding more cationic groups to the molecule. A SMAMP with an MIC₉₀ of 4 μg mL^?1 against Staphylococcus aureus and a selectivity (=HC₅₀/MIC₉₀) of 650 was discovered, the most selective SMAMP to date.