Ciprofloxacin-nitroxide hybrids with potential for biofilm control

Photodynamic antimicrobial chemotherapy activities of phthalocyanine-antibiotic conjugates against bacterial biofilms and interactions with extracellular polymeric substances

This study sheds light on how to rationally design efficient photodynamic antimicrobial chemotherapy (PACT) agents by covalently linking phthalocyanines (Pcs) as photosensitizers with an antibiotic: Ciprofloxacin (CIP). Pcs used are zinc (II) 3-(4-((3,17,23-tris(4-(Benzo(d)thiazol-2-yl] thiol) phthalocyanine-9-yl) oxy) phenyl) propanoic acid (1) and zinc (II) 3-(4-(3,17,23-tris(3-(4-(triphenylphosphine) butyl) benzo[d]thiazol-3-ium bromide phthalocyanine-9-yl) oxy) phenyl) propanoic acid (2). High singlet oxygen quantum yields are observed in the presence of CIP. Square wave voltammetry was used to analyse the Pc-CIP uptake by bacteria biofilms of Streptococcus pneumoniae (S. pneumonia) and Escherichia coli (E. coli). Electrochemical impedance spectroscopy and scanning electron spectroscopy were used to study the stability of the biofilms in the presence Pc-CIP complexes and when exposed to light. Raman and time of flight-secondary ion mass spectrometry (TOF-SIMS) are used to identify the breakdown of cellular components of the biofilm and penetration of the Pc-CIP into the biofilms, respectively.

Preclinical Evaluation of Nitroxide-Functionalised Ciprofloxacin as a Novel Antibiofilm Drug Hybrid for Urinary Tract Infections

Urinary tract infections (UTIs) are the second most common bacterial infection with high recurrence rates and can involve biofilm formation on patient catheters. Biofilms are inherently tolerant to antimicrobials, making them difficult to eradicate. Many antibiofilm agents alone do not have bactericidal activity; therefore, linking them to antibiotics is a promising antibiofilm strategy. However, many of these hybrid agents have not been tested in relevant preclinical settings, limiting their potential for clinical translation. Here, we evaluate a ciprofloxacin di-nitroxide hybrid (CDN11), previously reported to have antibiofilm activity against uropathogenic Escherichia coli (UPEC) strain UTI89 in vitro, as a potential UTI therapeutic using multiple preclinical models that reflect various aspects of UTI pathogenesis. We report improved in vitro activity over the parent drug ciprofloxacin against mature UTI89 biofilms formed inside polyethylene catheters. In bladder cell monolayers infected with UTI89, treatment with CDN11 afforded significant reduction in bacterial titers, including intracellular UPEC. Infected mouse bladders containing biofilm-like intracellular reservoirs of UPEC UTI89 showed decreased bacterial loads after ex vivo bladder treatment with CDN11. Activity for CDN11 was reported across different models of UTI, showcasing nitroxide-antibiotic hybridization as a promising antibiofilm approach. The pipeline we described here could be readily used in testing other new therapeutic compounds, fast-tracking the development of novel antibiofilm therapeutics.

Evaluation of Antimicrobial Resistance Profiles of Bacteria Isolated from Biofilm in Meat Processing Units

The aim of this study was to assess the hygiene of pork, beef, and poultry carcasses and to determine the phenotypic antibiotic susceptibility of the bacteria embedded in the biofilm formed on the carcasses kept in cooling chambers for at least three days. The level of hygiene was assessed by determining the total aerobic colony count (TACC) and the Enterobacteriaceae level in different sampling points of the carcasses, along with the detection of E. coli and Pseudomonas spp. embedded in the biofilm. Furthermore, the E. coli and Pseudomonas spp. isolates were tested for antimicrobial resistance profiles. A total of 130 samples collected from pork, beef, and poultry from processing units were analyzed to determine the total aerobic colony count as well as to measure the level of Enterobacteriaceae found on the carcasses. The antimicrobial susceptibility of 44 Escherichia coli and eight Pseudomonas spp. strains isolated from the carcasses were assessed using the Vitek 2 system using two different cards. Overall, the regulatory limits for the TACC were exceeded in 7.6% of the samples, and 65% of the samples exceeded the regulatory limits for Enterobacteriaceae levels. The antimicrobial susceptibility tests of the E. coli isolates analyzed with the AST-GN27 card revealed the highest resistance to be that towards ampicillin (76.1%), followed by cefazolin (71.4%), amoxicillin/clavulanic acid (61.9%), nitrofurantoin (52.3%), cefoxitin (47.6%), tetracycline (38.1%), piperacillin, norfloxacin (19%), trimethoprim-sulfamethoxazole (11.9%), cefotaxime (9.5%), ceftazidime, cefazolin, amikacin, gentamicin, and ciprofloxacin (4.7%). However, all of the isolates were sensitive to piperacillin-tazobactam and imipenem. Thirty-two (61.5%; 95% CI 47.9-73.5) out of fifty-two isolates exhibited multidrug resistance, resulting in the expression of 10 resistance profiles. The findings of this study highlight serious hygienic and sanitary deficiencies within the meat processing units and demonstrate that the resulting meat can harbor Multidrug-resistant Escherichia coli and Pseudomonas spp., both of which pose a serious public health risk. However, further research with a larger number of samples is required to reach thorough results.

Synergistic or antagonistic antioxidant combinations - a case study exploring flavonoid-nitroxide hybrids

Neurodegenerative diseases impose a considerable medical and public health burden on populations throughout the world. Oxidative stress, an imbalance in pro-oxidant/antioxidant homeostasis that leads to the generation of reactive oxygen species (ROS), has been implicated in the progression of a number of neurodegenerative diseases. The manipulation of ROS levels may represent a promising treatment option to slow down neurodegeneration, although adequate potency of treatments has not yet been achieved. Using a hybrid pharmacology approach, free radical nitroxide antioxidants were hybridised with a class of natural antioxidants, flavonoids, to form a potential multitargeted antioxidant. Modification of the Baker-Venkataraman reaction achieved the flavonoid-nitroxide hybrids (6-9) in modest yields. Antioxidant evaluation of the hybrids by cyclic voltammetry showed both redox functionalities were still active, with little influence on oxidation potential. Assessment of the peroxyl radical scavenging ability through an ORAC assay showed reduced antioxidant activity of the hybrids compared to their individual components. It was hypothesized that the presence of the phenol in the hybrids creates a more acidic medium which does not favour regeneration of the nitroxide from the corresponding oxammonium cation, disturbing the typical catalytic cycle of peroxyl radical scavenging by nitroxides. This work highlights the potential intricacies involved with drug hybridization as a strategy for new therapeutic development.

The resistance mechanisms of bacteria against ciprofloxacin and new approaches for enhancing the efficacy of this antibiotic

For around three decades, the fluoroquinolone (FQ) antibiotic ciprofloxacin has been used to treat a range of diseases, including chronic otorrhea, endocarditis, lower respiratory tract, gastrointestinal, skin and soft tissue, and urinary tract infections. Ciprofloxacin's main mode of action is to stop DNA replication by blocking the A subunit of DNA gyrase and having an extra impact on the substances in cell walls. Available in intravenous and oral formulations, ciprofloxacin reaches therapeutic concentrations in the majority of tissues and bodily fluids with a low possibility for side effects. Despite the outstanding qualities of this antibiotic, Salmonella typhi, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa have all shown an increase in ciprofloxacin resistance over time. The rise of infections that are resistant to ciprofloxacin shows that new pharmacological synergisms and derivatives are required. To this end, ciprofloxacin may be more effective against the biofilm community of microorganisms and multi-drug resistant isolates when combined with a variety of antibacterial agents, such as antibiotics from various classes, nanoparticles, natural products, bacteriophages, and photodynamic therapy. This review focuses on the resistance mechanisms of bacteria against ciprofloxacin and new approaches for enhancing its efficacy.

Formulation of ciprofloxacin-loaded oral self-emulsifying drug delivery system to improve the pharmacokinetics and antibacterial activity

This study aims to increase the aqueous solubility of ciprofloxacin (CPN) to improve oral bioavailability. This was carried out by formulating a stable formulation of the Self-Emulsifying Drug Delivery System (SEDDS) using various ratios of lipid/oil, surfactant, and co-surfactant. A pseudo-ternary phase diagram was designed to find an area of emulsification. Eight formulations (F1-CPN–F8-CPN) containing oleic acid oil, silicone oil, olive oil, castor oil, sunflower oil, myglol oil, polysorbate-80, polysorbate-20, PEO-200, PEO-400, PEO-600, and PG were formulated. The resultant SEDDS were subjected to thermodynamic study, size, and surface charge studies to improve preparation. Improved composition of SEDDS F5-CPN containing 40% oil, 60% polysorbate-80, and propylene glycol (Smix ratio 6: 1) were thermodynamically stable emulsions having droplet size 202.6 nm, charge surface -13.9 mV, and 0.226 polydispersity index (PDI). Fourier transform infra-red (FT-IR) studies revealed that the optimized formulation and drug showed no interactions. Scanning electron microscope tests showed the droplets have an even surface and spherical shape. It was observed that within 5 h, the concentration of released CPN from optimized formulations F5-CPN was 93%. F5-CPN also showed a higher antibacterial action against S. aurous than free CPN. It shows that F5-CPN is a better formulation with a good release and high antibacterial activity.

Fluoroquinolones Hybrid Molecules as Promising Antibacterial Agents in the Fight against Antibacterial Resistance

The emergence of bacterial resistance has motivated researchers to discover new antibacterial agents. Nowadays, fluoroquinolones keep their status as one of the essential classes of antibacterial agents. The new generations of fluoroquinolones are valuable therapeutic tools with a spectrum of activity, including Gram-positive, Gram-negative, and atypical bacteria. This review article surveys the design of fluoroquinolone hybrids with other antibacterial agents or active compounds and underlines the new hybrids' antibacterial properties. Antibiotic fluoroquinolone hybrids have several advantages over combined antibiotic therapy. Thus, some challenges related to joining two different molecules are under study. Structurally, the obtained hybrids may contain a cleavable or non-cleavable linker, an essential element for their pharmacokinetic properties and mechanism of action. The design of hybrids seems to provide promising antibacterial agents helpful in the fight against more virulent and resistant strains. These hybrid structures have proven superior antibacterial activity and less susceptibility to bacterial resistance than the component molecules. In addition, fluoroquinolone hybrids have demonstrated other biological effects such as anti-HIV, antifungal, antiplasmodic/antimalarial, and antitumor activity. Many fluoroquinolone hybrids are in various phases of clinical trials, raising hopes that new antibacterial agents will be approved shortly.

Strategies to improve the potency of oxazolidinones towards bacterial biofilms

Biofilms are part of the natural lifecycle of bacteria and are known to cause chronic infections that are difficult to treat. Most antibiotics are developed and tested against bacteria in the planktonic state and are ineffective against bacterial biofilms. The oxazolidinones, including the last resort drug linezolid, are one of the main classes of synthetic antibiotics progressed to clinical use in the last 50 years. They have a unique mechanism of action and only develop low levels of resistance in the clinical setting. With the aim of providing insight into strategies to design more potent antibiotic compounds with activity against bacterial biofilms, we review the biofilm activity of clinically approved oxazolidinones and report on structural modifications to oxazolidinones and their delivery systems which lead to enhanced anti‐biofilm activity.

Combination Therapies for Biofilm Inhibition and Eradication: A Comparative Review of Laboratory and Preclinical Studies

Microbial biofilms are becoming increasingly difficult to treat in the medical setting due to their intrinsic resistance to antibiotics. To combat this, several biofilm dispersal agents are currently being developed as treatments for biofilm infections. Combining biofilm dispersal agents with antibiotics is emerging as a promising strategy to simultaneously disperse and eradicate biofilms or, in some cases, even inhibit biofilm formation. Here we review studies that have investigated the anti-biofilm activity of some well-studied biofilm dispersal agents (e.g., quorum sensing inhibitors, nitric oxide/nitroxides, antimicrobial peptides/amino acids) in combination with antibiotics from various classes. This review aims to directly compare the efficacy of different combination strategies against microbial biofilms and highlight synergistic treatments that warrant further investigation. By comparing across studies that use different measures of efficacy, we can conclude that treating biofilms in vitro and, in some limited cases in vivo, with a combination of an anti-biofilm agent and an antibiotic, appears overall more effective than treating with either compound alone. The review identifies the most promising combination therapies currently under development as biofilm inhibition and eradication therapies.

Isothiazolone-Nitroxide Hybrids with Activity against Antibiotic-Resistant Staphylococcus aureus Biofilms

Isothiazolones are widely used as biocides in industrial processing systems and personal care products, but their use to treat infections in humans has been hampered by their inherent cytotoxicity. Herein, we report a strategy to alleviate isothiazolone toxicity and improve antibacterial and antibiofilm potency by functionalization with a nitroxide moiety. Isothiazolone-nitroxide hybrids 6 and 22 were prepared over three steps in moderate yields (58 and 36%, respectively) from (Z)-3-(benzylsulfanyl)-propenoic acid. Hybrid 22 displayed better activity (minimum inhibitory concentration (MIC) = 35 μM) than the widely used methylisothiazolinone (MIT 1, MIC = 280 μM) against methicillin-susceptible Staphylococcus aureus (MSSA). Hybrid 22 was even more active against drug-resistant strains, such as vancomycin-resistant Staphylococcus aureus (VRSA, MIC = 8.75 μM) over MIT 1 (MIC = 280 μM). The enhanced antibacterial activity of hybrid 22 over MIT 1 was retained against established MSSA and VRSA biofilms, with minimum biofilm eradication concentration (MBEC) values of 35 and 70 μM, respectively, for 22 (the MBEC value for MIT 1 against both strains was ≥280 μM). No toxicity was observed in human epithelial T24 cells treated with hybrid 22 in concentrations up to 560 μM using a lactate dehydrogenase assay.

Identification of ruthenium (II) complexes with furan-substituted ligands as possible antibacterial agents against Staphylococcus aureus

The growing burden of antibiotic resistance worldwide calls for developing new classes of antimicrobial strategy. Recently years, the use of adjuvants that rescue antibiotics identified as a promising strategy for overcoming bacterial resistance. In this study, three ruthenium complexes functionalized with furan-substituted ligands([Ru(phen)₂ (CAPIP)](ClO₄ )₂ (Ru(Ⅱ)-1), [Ru(dmp)₂ (CAPIP)](ClO₄ )₂ (Ru(Ⅱ)-2) and [Ru(dmb)₂ (CAPIP)](ClO₄ )₂ (Ru(Ⅱ)-3) (dmb=4,4'-dimethyl-2,2'-bipyridine, phen=1,10-phenanthroline, dmp=2,9-dimethyl-1,10-phenanthroline, CAPIP=(E)-2- (2-(furan-2-yl)vinyl)-1H-imidazo[4,5-f][1,10]phenanthroline)) were designed and synthesized. The antimicrobial activities of all compounds against S. aureus were assessed by growth inhibition assays. The MIC values of three complexes range from 0.015 to 0.050 mg/ml. Subsequently, the Ru(II)-2 complexes which exhibited strongest antibacterial activity were further tested against bacteria biofilms formation and toxin secretion. In addition, aimed to test whether ruthenium complexes have potential value as antimicrobial adjuvants, the synergism between Ru(Ⅱ)-2 and some antibiotics against S. aureus were examined through checkerboard method. Interestingly, Ru(Ⅱ)-2 could not only effectively inhibit biofilms formation of S. aureus and inhibit the hemolysin toxin secretion, but also selectivity show synergism with two common antibiotics. More importantly, mouse infection study also verified Ru(Ⅱ)-2 were highly effective against S. aureus in vivo.

Polyradical PROXYL/TEMPO Conjugates Connected by Ester/Amide Bridges: Synthesis, Physicochemical Studies, and DFT Calculations

A series of di-/trinitroxide esters and amides featuring PROXYL and/or TEMPO radicals connected with alicyclic bridges were prepared in 61-92 % yields and their properties were analysed by using multiple experimental techniques. The examination of EPR spectra of radicals in organic solvents augmented with DFT calculations brought valuable information on the conformational dynamics and spin exchange mechanisms. Cyclic voltammetry investigations revealed (quasi)reversible electrochemical behaviour of studied nitroxides with their half-wave potentials ranging from -51 to -17 mV. SQUID measurements of selected radicals revealed that the magnetism of di- and trinitroxides is significantly different, since antiferromagnetic coupling in biradicals is notably larger than in triradicals. The single-crystal X-ray analysis of selected biradicals revealed the existence of 3D supramolecular networks of molecules linked through hydrogen-bonding interactions. These polynitroxide radicals can serve as promising bridging or chelating ligands in the synthesis of transition-metal-based molecular magnets.

Nitric oxide-releasing compounds for the treatment of lung infections

The spread of acquired drug resistance and of microorganisms naturally resistant to antibiotics is a major threat to global health, leading to an urgent need for novel antimicrobial compounds. Exogenous nitric oxide (NO) represents an attractive and promising antimicrobial approach, showing both bactericidal and biofilm dispersal activities. Numerous studies have been performed to develop NO donor scaffolds, including small molecules, macromolecular compounds, nanoparticles (NPs), and polymeric materials. This approach has resulted in successful outcomes, with some NO-releasing compounds entering clinical practice. In this review, we highlight the importance of this strategy, with a focus on lung infections.

It takes two for chronic wounds to heal: dispersing bacterial biofilm and modulating inflammation with dual action plasma coatings

Chronic wounds are affecting increasingly larger portions of the general population and their treatment has essentially remained unchanged for the past century. This lack of progress is due to the complex problem that chronic wounds are simultaneously infected and inflamed. Both aspects need to be addressed together to achieve a better healing outcome. Hence, we hereby demonstrate that the stable nitroxide radical (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) can be plasma polymerized into smooth coatings (TEMPOpp), as seen via atomic force microscopy, X-ray photoelectron spectroscopy and ellipsometry. Upon contact with water, these coatings leach nitroxides into aqueous supernatant, as measured via EPR. We then exploited the known cell-signalling qualities of TEMPO to change the cellular behaviour of bacteria and human cells that come into contact with the surfaces. Specifically, the TEMPOpp coatings not only suppressed biofilm formation of the opportunistic bacterium Staphylococcus epidermidis but also dispersed already formed biofilm in a dose-dependent manner; a crucial aspect in treating chronic wounds that contain bacterial biofilm. Thus the coatings' microbiological efficacy correlated with their thickness and the thickest coating was the most efficient. Furthermore, this dose-dependent effect was mirrored in significant cytokine reduction of activated THP-1 macrophages for the four cytokines TNF-α, IL-1β, IL-6 and IP-10. At the same time, the THP-1 cells retained their ability to adhere and colonize the surfaces, as verified via SEM imaging. Thus, summarily, we have exploited the unique qualities of plasma polymerized TEMPO coatings in targeting both infection and inflammation simultaneously; demonstrating a novel alternative to how chronic wounds could be treated in the future.

We plasma polymerized the stable nitroxide radical TEMPO into thin coatings and exploited the coatings' unique qualities in targeting both infection and inflammation simultaneously; demonstrating a novel alternative as to how chronic wounds could be treated in the future.

Nitroxide Functionalized Antibiotics Are Promising Eradication Agents against Staphylococcus aureus Biofilms

Treatment of biofilm-related Staphylococcus aureus infections represents an important medical challenge worldwide, as biofilms, even those involving drug-susceptible S. aureus strains, are highly refractory to conventional antibiotic therapy. Nitroxides were recently shown to induce the dispersal of Gram-negative biofilms in vitro, but their action against Gram-positive bacterial biofilms remains unknown. Here, we demonstrate that the biofilm dispersal activity of nitroxides extends to S. aureus, a clinically important Gram-positive pathogen. Coadministration of the nitroxide CTEMPO (4-carboxy-2,2,6,6-tetramethylpiperidin-1-yloxyl) with ciprofloxacin significantly improved the biofilm eradication activity of the antibiotic against S. aureus Moreover, covalently linking the nitroxide to the antibiotic moiety further reduced the ciprofloxacin minimal biofilm eradication concentration. Microscopy analysis revealed that fluorescent nitroxide-antibiotic hybrids could penetrate S. aureus biofilms and enter cells localized at the surface and base of the biofilm structure. No toxicity to human cells was observed for the nitroxide CTEMPO or the nitroxide-antibiotic hybrids. Taken together, our results show that nitroxides can mediate the dispersal of Gram-positive biofilms and that dual-acting biofilm eradication antibiotics may provide broad-spectrum therapies for the treatment of biofilm-related infections.

Bacterial Biofilm Eradication Agents: A Current Review

Most free-living bacteria can attach to surfaces and aggregate to grow into multicellular communities encased in extracellular polymeric substances called biofilms. Biofilms are recalcitrant to antibiotic therapy and a major cause of persistent and recurrent infections by clinically important pathogens worldwide (e.g., Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus). Currently, most biofilm remediation strategies involve the development of biofilm-inhibition agents, aimed at preventing the early stages of biofilm formation, or biofilm-dispersal agents, aimed at disrupting the biofilm cell community. While both strategies offer some clinical promise, neither represents a direct treatment and eradication strategy for established biofilms. Consequently, the discovery and development of biofilm eradication agents as comprehensive, stand-alone biofilm treatment options has become a fundamental area of research. Here we review our current understanding of biofilm antibiotic tolerance mechanisms and provide an overview of biofilm remediation strategies, focusing primarily on the most promising biofilm eradication agents and approaches. Many of these offer exciting prospects for the future of biofilm therapeutics for a large number of infections that are currently refractory to conventional antibiotics.

Profluorescent Fluoroquinolone-Nitroxides for Investigating Antibiotic⁻Bacterial Interactions

Fluorescent probes are widely used for imaging and measuring dynamic processes in living cells. Fluorescent antibiotics are valuable tools for examining antibiotic⁻bacterial interactions, antimicrobial resistance and elucidating antibiotic modes of action. Profluorescent nitroxides are 'switch on' fluorescent probes used to visualize and monitor intracellular free radical and redox processes in biological systems. Here, we have combined the inherent fluorescent and antimicrobial properties of the fluoroquinolone core structure with the fluorescence suppression capabilities of a nitroxide to produce the first example of a profluorescent fluoroquinolone-nitroxide probe. Fluoroquinolone-nitroxide (FN) 14 exhibited significant suppression of fluorescence (>36-fold), which could be restored via radical trapping (fluoroquinolone-methoxyamine 17) or reduction to the corresponding hydroxylamine 20. Importantly, FN 14 was able to enter both Gram-positive and Gram-negative bacterial cells, emitted a measurable fluorescence signal upon cell entry (switch on), and retained antibacterial activity. In conclusion, profluorescent nitroxide antibiotics offer a new powerful tool for visualizing antibiotic⁻bacterial interactions and researching intracellular chemical processes.

Eradicating uropathogenic Escherichia coli biofilms with a ciprofloxacin-dinitroxide conjugate

Urinary tract infections (UTIs) are amongst the most common and prevalent infectious diseases worldwide, with uropathogenic Escherichia coli (UPEC) reported as the main causative pathogen. Fluoroquinolone antibiotics are commonly used to treat UTIs but for infections involving UPEC biofilms, which are commonly associated with catheter use and recurrent episodes, ciprofloxacin is often ineffective. Here we report the development of a ciprofloxacin-dinitroxide (CDN) conjugate with potent UPEC biofilm-eradication activity. CDN 11 exhibited a 2-fold increase in potency over the parent antibiotic ciprofloxacin against UPEC biofilms. Moreover, CDN 11 resulted in almost complete UPEC biofilm cell eradication (99.7%) at concentrations as low as 12.5 μM, and significantly potentiated ciprofloxacin's biofilm-eradication activity against UPEC upon co-administration. The biofilm-eradication activity of CDN 11 highlights the potential of nitroxide functionalized antibiotics as a promising strategy for the treatment of biofilm-related UTIs.

Controlling biofilm formation with nitroxide functional surfaces

Nitroxide functional polymer coatings with inherent antibiofilm activity are introduced as an avenue to combat bacterial biofilm contamination of medical devices.

Modifications of quinolones and fluoroquinolones: hybrid compounds and dual-action molecules

ABSTRACT

This review is aimed to provide extensive survey of quinolones and fluoroquinolones for a variety of applications ranging from metal complexes and nanoparticle development to hybrid conjugates with therapeutic uses. The review covers the literature from the past 10 years with emphasis placed on new applications and mechanisms of pharmacological action of quinolone derivatives. The following are considered: metal complexes, nanoparticles and nanodrugs, polymers, proteins and peptides, NO donors and analogs, anionic compounds, siderophores, phosphonates, and prodrugs with enhanced lipophilicity, phototherapeutics, fluorescent compounds, triazoles, hybrid drugs, bis-quinolones, and other modifications. This review provides a comprehensive resource, summarizing a broad range of important quinolone applications with great utility as a resource concerning both chemical modifications and also novel hybrid bifunctional therapeutic agents.

GRAPHICAL ABSTRACT

Ciprofloxacin derivatives and their antibacterial activities

Bacterial infections represent a significant health threat globally, and are responsible for the majority of hospital-acquired infections, leading to extensive mortality and burden on global healthcare systems. The second generation fluoroquinolone ciprofloxacin which exhibits excellent antimicrobial activity and pharmacokinetic properties as well as few side effects is introduced into clinical practice for the treatment of various bacterial infections for around 3 decades. The emergency and widely spread of drug-resistant pathogens making ciprofloxacin more and more ineffective, so it's imperative to develop novel antibacterials. Numerous of ciprofloxacin derivatives have been synthesized for seeking for new antibacterials, and some of them exhibited promising potency. This review aims to summarize the recent advances made towards the discovery of ciprofloxacin derivatives as antibacterial agents and the structure-activity relationship of these derivatives was also discussed.

Polynitroxide copolymers to reduce biofilm fouling on surfaces

Polynitroxide films – the first example of surface tethered nitroxides reducing biofilm fouling.

Nitroxide radical polymers – a versatile material class for high-tech applications

A comprehensive summary of synthetic strategies for the preparation of nitroxide radical polymer materials and a state-of-the-art perspective on their latest and most exciting applications.

Polyradical PROXYL/TEMPO-Derived Amides: Synthesis, Physicochemical Studies, DFT Calculations, and Antimicrobial Activity

A series of polynitroxide amides possessing 2,2,5,5-tetramethyl-1-pyrrolidinyloxy (PROXYL) and/or 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) units connected through various bridges were synthesized and their properties were analyzed. EPR spectroscopy provided detailed insight into their paramagnetic character and related properties. A thorough examination of the EPR spectra of dinitroxides in organic solvents provided valuable information on the intramolecular motions, thermodynamics, and spin-exchange mechanisms. Analysis of low-temperature X- and Q-band EPR spectra of the dissolved dinitroxides provided spin-spin distances that were comparable with the theoretical values obtained by DFT. Cyclic voltammetry investigations revealed (quasi)reversible electrochemical behavior for PROXYL-derived biradicals, whereas significant loss of the reversibility was found for TEMPO-containing bi- and polyradicals. The inhibitory activities of the nitroxides against model bacteria, yeasts, and filamentous fungi were assessed.