Solubility, lipophilicity and membrane permeability of some fluoroquinolone antimicrobials

Together or Apart? Revealing the Impact of Dietary Interventions on Bioavailability of Quinolones: A Systematic Review with Meta-analyses

BACKGROUND AND OBJECTIVE

Managing drug-food interactions is essential for optimizing the effectiveness and safety profile of quinolones. Following PRISMA guidelines, we systematically reviewed the influence of dietary interventions on the bioavailability of 22 quinolones.

METHODS

All studies describing or investigating the impact of food, beverages, antacids, and mineral supplements on pharmacokinetic parameters or pharmacokinetic/pharmacodynamic indices of orally taken quinolones were considered for inclusion. We excluded reviews, in vitro and in silico studies, studies performed on animals, and those involving alcohol. We performed the search in Medline (via PubMed), Embase, and Cochrane Library, covering reports from database inception to December 2022. We used the following tools to assess the risk of bias: version 2 of the Cochrane risk-of-bias tool for parallel trials, the Cochrane risk-of-bias tool for cross-over studies, and the NIH quality assessment tool for before-after studies. We performed quantitative analyses for each quinolone if two or more food-effect studies with specified and comparable study designs were available. If meta-analyses were not applicable, we qualitatively summarized the results.

RESULTS

We included 109 studies from 101 reports. Meta-analyses were conducted for 12 antibiotics and qualitative synthesis was employed for the remaining drugs. Of the studies, 60.5% were open-label, cross-over, as recommended by FDA. We judged 46% of studies as having a high risk of bias and only 4% of having a low risk of bias. Among 19 quinolones with available food impact data, 14 (74%) had potentially clinically important interactions. For nalidixic acid, oxolinic acid, and tosufloxacin, food exerted a high positive impact on bioavailability (AUC or Cmax increased by > 45%), whereas, for all the remaining drugs, postprandial absorption was lower. The most significant negative influence of food (AUC or Cmax decreased by > 40%) occurred for delafloxacin capsules and norfloxacin, whereas the moderate influence (AUC or Cmax decreased by 30-40%) occurred for nemonoxacin and rufloxacin. All 14 analysed quinolones showed a substantial reduction in bioavailability when co-administered with antacids and mineral supplements, except for calcium preparations. The impact of beverages was evaluated for 10 quinolones, with 50% experiencing significantly reduced absorption in the presence of milk (the highest negative impact for ciprofloxacin). Moreover, both ciprofloxacin and levofloxacin demonstrated compromised bioavailability when consumed with orange juice, particularly calcium-fortified.

DISCUSSION

Several factors may influence interactions, including the physicochemical characteristics of quinolones, the type of intervention, drug formulation, and the patient's health status. We assessed the quality of evidence as low due to the poor actuality of included studies, their methodological diversity, and uneven data availability for individual drugs.

Pharmacokinetics of Enrofloxacin in Plasma, Urine, and Feces of Donkey (Equus asinus) after a Single Intragastric Administration

Enrofloxacin is a broad-spectrum antimicrobial agent, but the study of its pharmacokinetics/pharmacodynamics (PKs/PDs) in donkeys is rarely reported. The present study aimed to investigate the pharmacokinetics of enrofloxacin administered intragastrically, and to study the pharmacokinetics of enrofloxacin and its metabolite ciprofloxacin in plasma, urine, and feces, and the PK/PD parameters were investigated to provide a rationale for enrofloxacin treatment in donkeys. A total of five healthy donkeys were selected for intragastric administration of 7.5 mg·kg-1 BW of enrofloxacin by gavage, and blood, urine, and fecal samples were collected. The results showed that the elimination half-life of plasma enrofloxacin was 11.40 ± 6.40 h, Tmax was 0.55 ± 0.12 h, Cmax was 2.46 ± 0.14 mg·L-1, AUC0-∞ was 10.30 ± 3.37 mg·L-1·h, and mean residence time (MRT) was 7.88 ± 1.26 h. The Tmax of plasma ciprofloxacin was 0.52 ± 0.08 h, Cmax was 0.14 ± 0.03 mg·L-1, and AUC0-∞ was 0.24 ± 0.16 mg·L-1·h. Urinary Cmax was 38.18 ± 8.56 mg·L-1 for enrofloxacin and 15.94 ± 4.15 mg·L-1 for ciprofloxacin. The total enrofloxacin and ciprofloxacin recovered amount in urine was 7.09 ± 2.55% of the dose for 144 h after dosing. The total enrofloxacin and ciprofloxacin recovered amount in feces was 25.73 ± 10.34% of the dose for 144 h after dosing. PK/PD parameters were also examined in this study, based on published MICs. In conclusion, 7.5 mg/kg BW of enrofloxacin administered intragastrically to donkeys was rapidly absorbed, widely distributed, and slowly eliminated in their bodies, and was predicted to be effective against bacteria with MICs < 0.25 mg·L-1.

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.

4D printing of biodegradable elastomers with tailorable thermal response at physiological temperature

4D printing has a great potential for the manufacturing of soft robotics and medical devices. The alliance of digital light processing (DLP) 3D printing and novel shape-memory photopolymers allows for the fabrication of smart 4D-printed medical devices in high resolution and with tailorable functionalities. However, most of the reported 4D-printed materials are nondegradable, which limits their clinical applications. On the other hand, 4D printing of biodegradable shape-memory elastomers is highly challenging, especially when transition points close to physiological temperature and shape fixation under ambient conditions are required. Here, we report the 4D printing of biodegradable shape-memory elastomers with tailorable transition points covering physiological temperature, by using poly(D,L-lactide-co-trimethylene carbonate) methacrylates at various monomer feed ratios. After the programming step, the high-resolution DLP printed stents preserved their folded shape at room temperature, and showed efficient shape recovery at 37 °C. The materials were cytocompatible and readily degradable under physiological conditions. Furthermore, drug-loaded devices with tuneable release kinetics were realized by DLP-printing with resins containing polymers and levofloxacin or nintedanib. This study offers a new perspective for the development of next-generation 4D-printed medical devices.

Design and synthesis of high performance magnetically separable exfoliated g-C3N4/γ-Fe2O3/ZnO yolk-shell nanoparticles: a novel and eco-friendly photocatalyst toward removal of organic pollutants from water

Herein, a new visible-light active exfoliated g-C3N4/γ-Fe2O3/ZnO yolk-shell nanoparticles (NPs) was synthesized as a magnetically separable photocatalyst. For an in-depth understanding of the magnetic photocatalyst's structural, morphological, and optical properties, the products were extensively characterized with FT-IR, XRD, TEM, HRTEM, FESEM, EDS, EDS-mapping, VSM, DRS, EIS, and photocurrent. The photocatalyst was then utilized to degrade Levofloxacin (LEVO) and Indigo Carmine (IC) by visible light at room temperature. The exfoliated g-C3N4/γ-Fe2O3/ZnO yolk-shell NPs photocatalyst revealed 80% and 95.6% degradation efficiency for Levofloxacin and Indigo Carmine within 25 and 15 min, respectively. In addition, the optimal factors such as concentration, loading of photocatalyst, and pH were also assessed. Levofloxacin degradation mechanistic studies showed that electrons and holes significantly contribute to the photocatalytic process of photocatalyst degradation. In addition, after 5 times regeneration, exfoliated g-C3N4/γ-Fe2O3/ZnO yolk-shell NPs remained as an excellent magnetic photocatalyst for the eco-friendly degradation of Levofloxacin and Indigo Carmine (76% and 90%), respectively. The superior photocatalytic performance of exfoliated g-C3N4/γ-Fe2O3/ZnO yolk-shell nanoparticles (NPs) was mostly ascribed to the synergistic advantages of stronger visible light response, larger specific surface area, and the more effective separation and transfer of photogenerated charge carriers. Based on these results, the highly effective magnetic photocatalyst achieved better results than numerous studied catalysts in the literature. The degradation of Levofloxacin and Indigo Carmine under environmentally friendly conditions can be achieved using exfoliated g-C3N4/γ-Fe2O3/ZnO yolk-shell NPs (V) as an efficient and green photocatalyst. The magnetic photocatalyst was characterized by spectroscopic and microscopic methods, revealing a spherical shape and particle size of 23 nm. Additionally, the magnetic photocatalyst could be separated from the reaction mixture by a magnet without significantly reducing its catalytic activity.

The Chemometric Evaluation of the Factors Influencing Cloud Point Extraction for Fluoroquinolones

This study aimed to analyze the factors that impact the cloud point extraction of ciprofloxacin, levofloxacin, and moxifloxacin. The following independent variables were analyzed: Triton X-114 concentration, NaCl concentration, pH, and incubation temperature. The dependent variable studied was recovery. A central composite design model was used. The applied quantitation method was HPLC. The method was validated for linearity, precision, and accuracy. The results underwent ANOVA^® analysis. The polynomial equations were generated for each analyte. The response surface methodology graphs visualized them. The analysis showed that the factor most affecting the recovery of levofloxacin is the concentration of Triton X-114, while the recovery of ciprofloxacin and moxifloxacin is most affected by pH value. However, the concentration of Triton X-114 also plays an important role. The optimization resulted in the following recoveries: for ciprofloxacin, 60%; for levofloxacin, 75%; and for moxifloxacin, 84%, which are identical to those estimated with regression equations-59%, 74% and 81% for ciprofloxacin, levofloxacin, and moxifloxacin, respectively. The research confirms the validity of using the model to analyze factors affecting the recovery of the analyzed compounds. The model allows for a thorough analysis of variables and their optimization.

Glucose-decorated engineering platelets for active and precise tumor-targeted drug delivery

Precise targeted delivery of therapeutic agents is crucial for tumor therapy. As an emerging fashion, cell-based delivery provides better biocompatibility and lower immunogenicity and enables a more precise accumulation of drugs in tumor cells. In this study, a novel engineering platelet was constructed through cell membrane fusion with a synthesized glycolipid molecule, DSPE-PEG-Glucose (DPG). The obtained glucose-decorated platelets (DPG-PLs) maintained their resting state with structural and functional integrities, while they would be activated and triggered to release their payloads once they arrive at the tumor microenvironment. Glucose decoration was verified to impart the DPG-PLs with stronger binding effects toward tumor cells that overexpress GLUT1 on their surfaces. Together with the natural homing property toward tumor sites and bleeding injury, doxorubicin (DOX)-loaded platelets (DPG-PL@DOX) exhibited the strongest antitumor effects on a mouse melanoma model, and the antitumor effect was significantly enhanced in the tumor bleeding model. DPG-PL@DOX provides an active and precise solution for tumor-targeted drug delivery, especially for postoperative treatments.

Antibacterial and antibiofilm activity of permanently ionized quaternary ammonium fluoroquinolones

A series of quaternary ammonium fluoroquinolones was obtained by exhaustive methylation of the amine groups present at the 7-position of fluoroquinolones, including ciprofloxacin, enoxacin, gatifloxacin, lomefloxacin, and norfloxacin. The synthesized molecules were tested for their antibacterial and antibiofilm activities against Gram-positive and Gram-negative human pathogens, i.e. Staphylococcus aureus and Pseudomonas aeruginosa. The study showed that the synthesized compounds are potent antibacterial agents (MIC values at the lowest 6.25 μM) with low cytotoxicity in vitro as assessed on the BALB 3T3 mouse embryo cell line. Further experiments proved that the tested derivatives are able to bind to the DNA gyrase and topoisomerase IV active sites in a fluoroquinolone-characteristic manner. The most active quaternary ammonium fluoroquinolones, in contrast to ciprofloxacin, reduce the total biomass of P. aeruginosa ATCC 15442 biofilm in post-exposure experiments. The latter effect may be due to the dual mechanism of action of the quaternary fluoroquinolones, which also involves disruption of bacterial cell membranes. IAM-HPLC chromatographic experiments with immobilized artificial membranes (phospholipids) showed that the most active compounds were those with moderate lipophilicity and containing a cyclopropyl group at the N1 nitrogen atom in the fluoroquinolone core.

The Discovery of the Role of Outer Membrane Vesicles against Bacteria

Gram-negative bacteria are intrinsically resistant to many commercialized antibiotics. The outer membrane (OM) of Gram-negative bacteria prevents the entry of such antibiotics. Outer membrane vesicles (OMV) are naturally released from the OM of Gram-negative bacteria for a range of purposes, including competition with other bacteria. OMV may carry, as part of the membrane or lumen, molecules with antibacterial activity. Such OMV can be exposed to and can fuse with the cell surface of different bacterial species. In this review we consider how OMV can be used as tools to deliver antimicrobial agents. This includes the characteristics of OMV production and how this process can be used to create the desired antibacterial activity of OMV.

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.

AB-DB: Force-Field parameters, MD trajectories, QM-based data, and Descriptors of Antimicrobials

Antibiotic resistance is a major threat to public health. The development of chemo-informatic tools to guide medicinal chemistry campaigns in the efficint design of antibacterial libraries is urgently needed. We present AB-DB, an open database of all-atom force-field parameters, molecular dynamics trajectories, quantum-mechanical properties, and curated physico-chemical descriptors of antimicrobial compounds. We considered more than 300 molecules belonging to 25 families that include the most relevant antibiotic classes in clinical use, such as β-lactams and (fluoro)quinolones, as well as inhibitors of key bacterial proteins. We provide traditional descriptors together with properties obtained with Density Functional Theory calculations. Noteworthy, AB-DB contains less conventional descriptors extracted from μs-long molecular dynamics simulations in explicit solvent. In addition, for each compound we make available force-field parameters for the major micro-species at physiological pH. With the rise of multi-drug-resistant pathogens and the consequent need for novel antibiotics, inhibitors, and drug re-purposing strategies, curated databases containing reliable and not straightforward properties facilitate the integration of data mining and statistics into the discovery of new antimicrobials.

Measurement(s)	molecular physical property analysis objective
Technology Type(s)	Computer Modeling

Effect of Methyl-β-Cyclodextrin on the Interaction of Fluoroquinolones with Human Serum Albumin

Abstract—

The influence of the structure of fluoroquinolones (on the example of ciprofloxacin and levofloxacin) and their complexation with methyl-β-cyclodextrin on the interaction of the drug with human serum albumin was studied. It was found that the binding of the drug molecule with albumin is significantly affected by the structure of fluoroquinolone, as well as the presence of methyl-β-cyclodextrin. It was discovered that of the two fluoroquinolones, the more hydrophobic ciprofloxacin molecule interacts more strongly with the protein, using circular dichroism and fluorescence spectroscopy methods. It has also been shown that binding of albumin to the drug causes quenching of protein fluorescence, and this effect is more pronounced for ciprofloxacin. The complexation of fluoroquinolones with methyl-β-cyclodextrin leads to a change in the interaction of fluoroquinolones with the protein: in the case of complexes, more pronounced interactions are observed for levofloxacin. The results obtained will help to bring the use of fluoroquinolones to a new level in clinical practice, by creating new highly effective drugs with improved properties.

The EDA deficient mouse has Zymbal's gland hypoplasia and acute otitis externa

In mice, rats, dogs and humans, the growth and function of sebaceous glands and eyelid Meibomian glands depend on the ectodysplasin signalling pathway. Mutation of genes encoding the ligand EDA, its transmembrane receptor EDAR and the intracellular signal transducer EDARADD leads to hypohidrotic ectodermal dysplasia, characterised by impaired development of teeth and hair, as well as cutaneous glands. The rodent ear canal has a large auditory sebaceous gland, the Zymbal’s gland, the function of which in the health of the ear canal has not been determined. We report that EDA-deficient mice, EDAR-deficient mice and EDARADD-deficient rats have Zymbal’s gland hypoplasia. Eda^Ta mice have 25% prevalence of otitis externa at postnatal day 21 and treatment with agonist anti-EDAR antibodies rescues Zymbal’s glands. The aetiopathogenesis of otitis externa involves infection with Gram-positive cocci, and dosing pregnant and lactating Eda^Ta females and pups with enrofloxacin reduces the prevalence of otitis externa. We infer that the deficit of sebum is the principal factor in predisposition to bacterial infection, and the Eda^Ta mouse is a potentially useful microbial challenge model for human acute otitis externa.

Summary: Ectodysplasin-deficient mice have growth retardation of the auditory sebaceous Zymbal's gland and are predisposed to spontaneous bacterial infection of the outer ear canal by opportunistic pathogens.

Lyophilized ophthalmologic patches as novel corneal drug formulations using a semi-solid extrusion 3D printer

3D printing technology is a novel and practical approach for producing unique and complex industrial and medical objects. In the pharmaceutical field, the approval of 3D printed tablets by the US Food and Drug Administration has led to other 3D printed drug formulations and dosage forms being proposed and investigated. Here, we report novel ophthalmologic patches for controlled drug release fabricated using a semi-solid material extrusion-type 3D printer. The patch-shaped objects were 3D printed using hydrogel-based printer inks composed of hypromellose (HPMC), sugar alcohols (mannitol, xylitol), and drugs, then freeze-dried. The viscous properties of the printer inks and patches were dependent on the HPMC and sugar alcohol concentrations. Then, the physical properties, surface structure, water uptake, antimicrobial activity, and drug release profile of lyophilized patches were characterized. Lyophilized ophthalmologic patches with different dosages and patterns were fabricated as models of personalized treatments prepared in hospitals. Then, ophthalmologic patches containing multiple drugs were fabricated using commercially available eye drop formulations. The current study indicates that 3D printing is applicable to producing novel dosage forms because its high flexibility allows the preparation of patient-tailored dosages in a clinical setting.

The spectrophotometric determination of lipophilicity and dissociation constants of ciprofloxacin and levofloxacin

Lipophilicity plays a significant role in the permeability of the drugs through cell membranes and impacts the drug activity in the human body. In this paper, the spectrophotometric method was used to determine the apparent partition coefficients of two amphoteric drugs: ciprofloxacin and levofloxacin. The apparent partition coefficient was determined with the classic shake-flask method with n-octanol according to OECD guidelines. The lipophilicity profiles in a wide range of pH were determined and described quantitatively with the quadratic function. Basing on the macro- and microdissociation constants, the true partition coefficient for both drugs was calculated. Both levofloxacin and ciprofloxacin were lipophilic. The neutral forms, i.e., zwitterionic and uncharged, dominate in the pH relevant to the one in the intestines, the place from which they are absorbed.

Delayed toxicity of three fluoroquinolones and their mixtures after neonatal or embryonic exposure, in Daphnia magna

Fluoroquinolones (FQs) are antibacterial drugs, used both in human and veterinary medicine, that are currently considered as emerging micropollutants. This study investigated the delayed toxic effects of enrofloxacin (ENR), flumequine (FLU), levofloxacin (LEV) and their binary mixtures in D. magna. For this purpose, a 10-day follow-up in pure medium was added to the standard D. magna immobilization test. During this follow-up, phenotypic alterations were evidenced, which were related to scarce or zeroed egg production and early mortality. Consequently, the EC_50 s recalculated at the end of the follow-up were always remarkably lower than those obtained after the 48 h immobilization test: ENR 3.13 vs. 16.72 mg L^-1; FLU 7.18 vs. 25.35 mg L^-1; LEV 15.11 vs. > 40 mg L^-1. To analyse the possible interactions within the binary mixtures, the method of nonlinear additive isoboles was applied. The three compounds showed invariably to follow the principle of concentration addition. Furthermore, as previous experiments showed toxicity of FLU and ENR after embryonic exposure of D. magna at a concentration of 2 mg L^-1, an additional two embryonic tests were conducted with identical design: one with 2 mg L^-1 LEV and the other with a ternary mixture containing 0.66 mg L^-1 of each of the three FQs. The embryos were exposed for three days in vitro to the drug solutions and were then reconducted to pure medium for 21 days observation. Both the tests ended-up with only non-significant effects on growth and reproduction, confirming the lower toxicity of LEV, when compared to ENR and FLU, and the absence of any evident synergistic interaction among the three FQs. Overall, these studies have shown two relevant features related to the toxicity of the three FQs: (1) they give rise to delayed toxic effects in D. magna that are undetectable by the standard immobilization test; (2) their interaction in mixtures follow the principle of Concentration Addition. Both these indications concern the Environmental Risk Assessment of FQs and may be of interest to regulatory authorities.

Photoelectrocatalytic treatment of levofloxacin using Ti/MMO/ZnO electrode

Here, the antibiotic levofloxacin (LFX) widely used and detected in the environment was degraded by photoelectrolysis using a new electrode based on zinc oxide (ZnO) and a mixture of mixed oxides of ruthenium and titanium (MMO). The influence of the potential and irradiation of UV light was investigated in the photostability of the Ti/MMO/ZnO electrode and in the degradation of the antibiotic. The experiments were conducted at different pH values (5.0, 7.0 and 9.0) in sodium sulfate solution in a glass reactor with central lighting. It was observed that the new Ti/MMO/ZnO electrode has good stability under light irradiation and potential, presenting excellent photocurrent and high photoactivity in LFX photoelectrolysis. The removal efficiency of the compound was directly related to the formation of oxidizing species in solution, the photo-generated charges on the electrode and the electrostatic characteristics of the molecule. The mineralization rate, the formation of reaction intermediates and short chain carboxylic acids (acetic, maleic, oxalic and oxamic acid), in addition to the formation of N-mineral species (NO₃^- and NH₄⁺) was dependent on the pH of the solution and the investigated processes: photoelectrolysis was more efficient than photolysis, which, in turn, was more efficient than electrolysis. The synergistic effect and the high rate of degradation of LFX after 4.0 h of treatment (100%) observed in photoelectrolysis at alkaline pH, was associated with the high stability of the Ti/MMO/ZnO electrode at this pH, the photoactivation of sulfate ions and the ease generation of oxidizing radicals, such as OH.

Bivalent Ni(II), Co(II) and Cu(II) complexes of [(E)-[(2-methyl-1,3-thiazol-5-yl)methylidene]amino]thiourea: synthesis, spectral characterization, DNA and in-vitro anti-bacterial studies

The present work describes the preparation of bivalent Ni(II), Co(II) and Cu(II) complexes of [(E)-[(2-methyl-1,3-thiazol-5-yl)methylidene]amino]thiourea (MTHC) by mixing in 1:2 ratio of corresponding metal salt and Schiff base ligand in ethanolic medium. The prepared ligand and its complexes are confirmed using elemental analysis, magnetic moments, FT-IR, NMR, electronic and ESR spectroscopy techniques. The spectroscopic data reveals that metal complexes are in square planar in nature. In DNA binding studies, the higher intrinsic binding constants (K_b) of Ni(II), Co(II) and Cu(II) complexes are 2.713 × 10⁶ M⁻¹, 5.529 × 10⁶ M⁻¹ and 2.950 × 10⁶ M⁻¹ respectively, evident that complexes are avid binder with DNA base pairs. The moderate anti-bacterial activity (in-vitro) against staphylococcus epidermidis, Bacillus subtilis, Pseudomonas aeruginosa and Escherichia coli bacterial culture may be due to the high electron density of ligand which prevents the charge reduction of metal ion. In the presence and absence of H₂O_2, it is notified that there is no appreciable DNA cleavage activity of Ni(II) and Co(II) complexes except Cu(II) complex which is due to aprotonation in the medium.

Batch injection analysis with amperometric detection for fluoroquinolone determination in urine, pharmaceutical formulations, and milk samples using a reduced graphene oxide-modified glassy carbon electrode

In this work, the batch injection analysis system with amperometric detection using reduced graphene oxide as a modifier of glassy carbon electrode (GCE) was investigated for the simple, fast, and sensitive monitoring of levofloxacin (LEVO) and ciprofloxacin (CIPRO) in samples of pharmaceutical formulations, synthetic urine, and milk (low- and high-fat content). LEVO and CIPRO were quantified in seven samples using amperometric measurements at +1.10 V vs Ag/AgCl, KCl(sat). The developed methods showed excellent analytical performance with limits of detection of 0.30 and 0.16 μmol L^-1, linear range from 3.0 to 50 μmol L^-1 and 1.0 to 50 μmol L^-1, relative standard deviation below 9.7 and 3.1%, and recovery ranges ranging from 80 to 107% and from 78 to 109% for LEVO and CIPRO, respectively. In addition, the minimum sample preparation (simple dilution) combined with a high analytical frequency (130 to 180 analyses per hour) can be highlighted. Thus, the methods are promising for implementation in routine analysis and quality control to different samples.

Application of a Physiologically Based Pharmacokinetic Model to Develop a Veterinary Amorphous Enrofloxacin Solid Dispersion

Zoonotic intestinal pathogens threaten human health and cause huge economic losses in farming. Enrofloxacin (ENR) shows high antibacterial activity against common intestinal bacteria. However, its poor palatability and low aqueous solubility limit the clinical application of ENR. To obtain an ENR oral preparation with good palatability and high solubility, a granule containing an amorphous ENR solid dispersion (ENR-SD) was prepared. Meanwhile, a PBPK model of ENR in pigs was built based on the physiological parameters of pigs and the chemical-specific parameters of ENR to simulate the pharmacokinetics (PK) of ENR-SD granules in the intestinal contents. According to the results of parameter sensitivity analysis (PSA) and the predicted PK parameters at different doses of the model, formulation strategies and potential dose regimens against common intestinal infections were provided. The DSC and XRD results showed that no specific interactions existed between the excipients and ENR during the compatibility tests, and ENR presented as an amorphous form in ENR-SD. Based on the similar PK performance of ENR-SD granules and the commercial ENR soluble powder suggesting continued enhancement of the solubility of ENR, a higher drug concentration in intestinal contents could not be obtained. Therefore, a 1:5 ratio of ENR and stearic acid possessing a saturated aqueous solubility of 1190 ± 7.71 µg/mL was selected. The predictive AUC24h/MIC90 ratios against Campylobacter jejuni, Salmonella, and Escherichia coli were 133, 266 and 8520 (>100), respectively, suggesting that satisfactory efficacy against common intestinal infections would be achieved at a dose of 10 mg/kg b.w. once daily. The PSA results indicated that the intestinal absorption rate constant (Ka) was negatively correlated with the Cmax of ENR in the intestine, suggesting that we could obtain higher intestinal Cmax using P-gp inducers to reduce Ka, thus obtaining a higher Cmax. Our studies suggested that the PBPK model is an excellent tool for formulation and dose design.

Comparing the interaction of the antibiotic levofloxacin with zwitterionic and anionic membranes: Calorimetry, fluorescence, and spin label studies

The present work compares the interaction of the antibiotic levofloxacin (LVX) with zwitterionic and anionic liposomes composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG), respectively. By using differential scanning calorimetry (DSC), and with spin labels incorporated into liposomes at two different depths of the bilayers, we investigated the changes induced on the membrane by increasing concentrations of LVX. Further information was obtained using intrinsic LVX fluorescence. Under the conditions used here, all techniques evinced that LVX has little affinity for DPPC zwitterionic membrane. Opposite to that, LVX exhibits a considerable affinity for anionic bilayers, with membrane partition constants K_p = (3.3 ± 0.5) × 10² and (4.5 ± 0.3) × 10², for gel and fluid DPPG membranes, respectively. On binding to DPPG, LVX seems to give rise to the coexistence of LVX -rich and -poor domains on DPPG membranes, as detected by DSC. At the highest LVX concentration used (20 mol%), DSC trace shows an increase in the cooperativity of DPPG gel-fluid transition, also detected by spin labels as an increase in the bilayer packing. Moreover, LVX does not induce pore formation in either DPPG or POPG vesicles. Considering the possible relevance of LVX-membrane interaction for the biological and toxicological action of the antibiotic, the findings discussed here certainly contribute to a better understanding of its action, and the planning of new drugs.

Evolution of Antibiotic Tolerance Shapes Resistance Development in Chronic Pseudomonas aeruginosa Infections

Over the past decades, pan-resistant strains of major bacterial pathogens have emerged and have rendered clinically available antibiotics ineffective, putting at risk many of the major achievements of modern medicine, including surgery, cancer therapy, and organ transplantation. A thorough understanding of processes leading to the development of antibiotic resistance in human patients is thus urgently needed.

The widespread use of antibiotics promotes the evolution and dissemination of resistance and tolerance mechanisms. To assess the relevance of tolerance and its implications for resistance development, we used in vitro evolution and analyzed the inpatient microevolution of Pseudomonas aeruginosa, an important human pathogen causing acute and chronic infections. We show that the development of tolerance precedes and promotes the acquisition of resistance in vitro, and we present evidence that similar processes shape antibiotic exposure in human patients. Our data suggest that during chronic infections, P. aeruginosa first acquires moderate drug tolerance before following distinct evolutionary trajectories that lead to high-level multidrug tolerance or to antibiotic resistance. Our studies propose that the development of antibiotic tolerance predisposes bacteria for the acquisition of resistance at early stages of infection and that both mechanisms independently promote bacterial survival during antibiotic treatment at later stages of chronic infections.

Enhanced bioaccumulation of fluorinated antibiotics in crucian carp (Carassius carassius): Influence of fluorine substituent

The negative impact of residual fluorinated antibiotics on the ecosystem and human health are of great concern. However, only a few studies have been conducted on the factors that influence the bioaccumulation of fluorinated antibiotics in aquatic organisms. To investigate the effects of fluorine substituent, environmental concentration of antibiotics, and temperature on the bioaccumulation of florfenicol (FLO), thiamphenicol (TAP), ofloxacin (OFX), and pipemidic acid (PPA), crucian carp (Carassius carassius) were exposed to different concentrations of antibiotics and different temperatures for 21 days. The liver exhibited the highest antibiotic concentrations, with 315.4 ± 13.6 ng g^-1 wet weight (ww), followed by the bile (279.4 ± 12.4 ng mL^-1), muscle (53.1 ± 4.3 ng g^-1 ww), and gills (37.1 ± 2.6 ng g^-1 ww). The FLO and OFX containing the fluorine substituent were much easier to accumulate in crucian carp compared with their isonomic TAP and PPA, respectively. The fluorine substituent increased the bioaccumulation of the targeted antibiotics in crucian carp. In addition, the lower levels of antibiotics presented higher bioaccumulation potential, but the temperature had little effect on the bioaccumulation. These findings in the present study can provide further insight into the environmental behaviors and ecological risks of fluorinated antibiotics in the aquatic environment.

Optimizing Pharmacokinetic Property Prediction Based on Integrated Datasets and a Deep Learning Approach

Oral bioavailability (OBA)-related pharmacokinetic properties, such as aqueous solubility, lipophilicity, and intestinal membrane permeability, play a significant role in drug discovery. However, their measurement is usually costly and time-consuming. Therefore, prediction models based on diverse approaches have been established in recent decades. Computational prediction of molecular properties has become an important step in drug discovery, aiming to identify potential drug-like candidates and reduce costs. However, limitations related to dataset capacity and algorithm adaptation still place restrictions on the applicability of the related models. In this study, we considered both dataset and algorithm optimization to address the challenge of predicting OBA-related molecular properties. Benchmark datasets of aqueous solubility (log S), lipophilicity (log D), and membrane permeability measured using the Caco-2 cell line (log P_app) were constructed by merging and calibrating experimental data from diverse articles and databases. Then, a novel molecular property prediction model, called a multiembedding-based synthetic network (MESN), was generated by applying a deep learning algorithm based on the synthesis of multiple types of molecular embeddings. MESN achieves performance improvements over other state-of-the-art methods for the prediction of aqueous solubility, lipophilicity, and membrane permeability. Results were also obtained using several other algorithms and independent validation datasets as a control study. Moreover, a dimension reduction analysis (based on t-distributed stochastic neighbor embedding, t-SNE) and an atomic feature similarity analysis showed that the molecular embeddings extracted from the MESN model exhibit good clustering and diversity. Overall, considering the fundamental role of the data and the superior prediction performance of the model, we highlight the applicability of MESN on benchmark datasets for further utility in drug discovery-related molecular property prediction.

Enzyme-powered Janus platelet cell robots for active and targeted drug delivery

Transforming natural cells into functional biocompatible robots capable of active movement is expected to enhance the functions of the cells and revolutionize the development of synthetic micromotors. However, present cell-based micromotor systems commonly require the propulsion capabilities of rigid motors, external fields, or harsh conditions, which may compromise biocompatibility and require complex actuation equipment. Here, we report on an endogenous enzyme-powered Janus platelet micromotor (JPL-motor) system prepared by immobilizing urease asymmetrically onto the surface of natural platelet cells. This Janus distribution of urease on platelet cells enables uneven decomposition of urea in biofluids to generate enhanced chemophoretic motion. The cell surface engineering with urease has negligible impact on the functional surface proteins of platelets, and hence, the resulting JPL-motors preserve the intrinsic biofunctionalities of platelets, including effective targeting of cancer cells and bacteria. The efficient propulsion of JPL-motors in the presence of the urea fuel greatly enhances their binding efficiency with these biological targets and improves their therapeutic efficacy when loaded with model anticancer or antibiotic drugs. Overall, asymmetric enzyme immobilization on the platelet surface leads to a biogenic microrobotic system capable of autonomous movement using biological fuel. The ability to impart self-propulsion onto biological cells, such as platelets, and to load these cellular robots with a variety of functional components holds considerable promise for developing multifunctional cell-based micromotors for a variety of biomedical applications.

Control of the Lung Residence Time of Highly Permeable Molecules after Nebulization: Example of the Fluoroquinolones

Pulmonary drug delivery is a promising strategy to treat lung infectious disease as it allows for a high local drug concentration and low systemic side effects. This is particularly true for low-permeability drugs, such as tobramycin or colistin, that penetrate the lung at a low rate after systemic administration and greatly benefit from lung administration in terms of the local drug concentration. However, for relatively high-permeable drugs, such as fluoroquinolones (FQs), the rate of absorption is so high that the pulmonary administration has no therapeutic advantage compared to systemic or oral administration. Formulation strategies have thus been developed to decrease the absorption rate and increase FQs’ residence time in the lung after inhalation. In the present review, some of these strategies, which generally consist of either decreasing the lung epithelium permeability or decreasing the release rate of FQs into the epithelial lining fluid after lung deposition, are presented in regards to their clinical aspects.

Residues of Fluoroquinolone Antibiotics Induce Carbonylation and Reduce In Vitro Digestion of Sarcoplasmic and Myofibrillar Beef Proteins

Although the impact of oxidation on human health has been of growing interest, the oxidation of proteins, major component of meat, has received little attention. This paper describes the in vitro effect of five fluoroquinolones (FQs) on carbonylation of sarcoplasmic and myofibrillar proteins of beef when found at concentrations close to the maximum residue limit (MRL). Samples were treated individually with the FQs, determining in each protein fraction the carbonyl index, protein content and oxidized proteins identification, using 2,4-dinitrophenyhydrazine (DNPH) alkaline assay, Western blot and Bradford methods, and mass spectrometry, respectively. Besides, the in vitro effect of these residues on gastric and duodenal digestion of proteins was evaluated. The carbonylation induced by FQs affected both protein fractions being significant with respect to the blank in 73.3% of cases. This damage was correlated with loss of solubility and digestibility, with sarcoplasmic proteins the most affected. Danofloxacin and enrofloxacin were the FQs with greatest oxidant effects, especially affecting glycolysis and glycogen proteins. Our results suggest that these residues induce irreversible oxidative damage on the main beef proteins and could affect their nutritional value.

Development of novel nanoantibiotics using an outer membrane vesicle-based drug efflux mechanism

Conventionally used antibiotics are present in low concentrations at the infection site and require multiple administrations to sustain a continuous bactericidal effect, which not only increases their systemic toxicity but also results in bacterial drug resistance. In this study, we first identified an interesting drug resistance mechanism mediated by bacterial outer membrane vesicles (OMVs) and then designed novel antibiotic-loaded OMVs using this mechanism. We show that these antibiotic-loaded OMVs can effectively enter and kill pathogenic bacteria in vitro. In a mouse model of intestinal bacterial infection, one low-dose oral administration of antibiotic-loaded OMVs showed that the drug was retained in the intestine for 36 h, and no systemic spread was detected 12 h after drug administration. The antibiotic-loaded OMVs significantly reduced the bacterial load in the small intestine and feces of infected mice. Safety experiments confirmed that the antibiotic-loaded OMVs had excellent biocompatibility. This study extends the application range of OMVs and provides new ideas for the development of antibacterial drugs.

Study of release kinetics and degradation thermodynamics of ferric citrate liposomes

Ferric citrate liposome (FAC-Lip) with good sustained-released property was prepared by the rotary-evaporated film-ultrasonic method, and characterized by TEM, DLS, zeta potential and encapsulation efficiency (EE%). The effects of membrane material ratios (m_PC: m_chol = 8:1, 10:1 and 12:1) and drug lipid ratios (m_FAC: m_PC = 1:4, 1:6.5 and 1:8) on the release of FAC-Lip were examined. The in vitro release kinetic models and mechanisms of FAC-Lip in artificial gastric juice (SGF) and artificial intestinal juice (SIF) compared with free-FAC were determined. The thermal degradation in PBS was also determined. The results showed that FAC-Lip with membrane material ratio (10:1) and drug lipid ratio (1:6.5) had the optimal sustained-released property, unilamellar vesicles with uniform size (178 ± 2.12 nm), negative charge (-56 ± 3.51 mV) and high encapsulation efficiency (72.77 ± 0.42%). The in vitro release kinetic models of FAC-Lip were two-phase kinetics model and the release mechanisms were non-Fick diffusion both in SGF and SIF. The thermal degradation of FAC-Lip was an endothermic and spontaneous reaction. The results may be helpful in optimizing drug-liposome design, application in food and medicine industries, and furthermore, predicting and guiding medication in vivo.

Synthesis and biological evaluation of hybrid quinolone-based quaternary ammonium antibacterial agents

A series of novel fluoroquinolone-Safirinium dye hybrids was synthesized by means of tandem Mannich-electrophilic amination reactions from profluorophoric isoxazolones and antibiotics bearing a secondary amino group at position 7 of the quinoline ring. The obtained fluorescent spiro fused conjugates incorporating quaternary nitrogen atoms were characterized by ¹H NMR, IR, MS, and elemental analysis. All the synthetic analogues (3a-h and 4a-h) were evaluated for their in vitro antimicrobial, bactericidal, and antibiofilm activities against a panel of Gram positive and Gram-negative pathogenic bacteria. The most active Safirinium Q derivatives of lomefloxacin (4d) and ciprofloxacin (4e) exhibited molar-based antibacterial activities comparable to the unmodified drugs and displayed considerable inhibitory potencies in E. coli DNA gyrase supercoiling assays with IC₅₀ values in the low micromolar range. Zwiterionic hybrids were noticeably less lipophilic than the parent quinolones in micellar electrokinetic chromatography (MECK) experiments. The tests performed in the presence of phenylalanine-arginine β-naphthylamide (PAβN) or carbonyl cyanide m-chlorophenylhydrazone (CCCP) revealed that the conjugates are to some extent subject to bacterial efflux and cellular accumulation, respectively. Moreover, the hybrids did not exhibit notable cytotoxicity towards the HEK 293 control cell line and demonstrated low propensity for resistance development, as exemplified for compounds 3g and 4b. Finally, molecular docking experiments revealed that the synthesized compounds were able to bind in the fluoroquinolone-binding mode at S. aureus DNA gyrase and S. pneumoniae topoisomerase IV active sites.

Microcavity-Supported Lipid Bilayers; Evaluation of Drug-Lipid Membrane Interactions by Electrochemical Impedance and Fluorescence Correlation Spectroscopy

Many drugs have intracellular or membrane-associated targets, thus understanding their interaction with the cell membrane is of value in drug development. Cell-free tools used to predict membrane interactions should replicate the molecular organization of the membrane. Microcavity array-supported lipid bilayer (MSLB) platforms are versatile biophysical models of the cell membrane that combine liposome-like membrane fluidity with stability and addressability. We used an MSLB herein to interrogate drug-membrane interactions across seven drugs from different classes, including nonsteroidal anti-inflammatories: ibuprofen (Ibu) and diclofenac (Dic); antibiotics: rifampicin (Rif), levofloxacin (Levo), and pefloxacin (Pef); and bisphosphonates: alendronate (Ale) and clodronate (Clo). Fluorescence lifetime correlation spectroscopy (FLCS) and electrochemical impedance spectroscopy (EIS) were used to evaluate the impact of drug on 1,2-dioleyl- sn-glycerophosphocholine and binary bilayers over physiologically relevant drug concentrations. Although FLCS data revealed Ibu, Levo, Pef, Ale, and Clo had no impact on lipid lateral mobility, EIS, which is more sensitive to membrane structural change, indicated modest but significant decreases to membrane resistivity consistent with adsorption but weak penetration of drugs at the membrane. Ale and Clo, evaluated at pH 5.25, did not impact the impedance of the membrane except at concentrations exceeding 4 mM. Conversely, Dic and Rif dramatically altered bilayer fluidity, suggesting their translocation through the bilayer, and EIS data showed that resistivity of the membrane decreased substantially with increasing drug concentration. Capacitance changes to the bilayer in most cases were insignificant. Using a Langmuir-Freundlich model to fit the EIS data, we propose R_sat as an empirical value that reflects permeation. Overall, the data indicate that Ibu, Levo, and Pef adsorb at the interface of the lipid membrane but Dic and Rif interact strongly, permeating the membrane core modifying the water/ion permeability of the bilayer structure. These observations are discussed in the context of previously reported data on drug permeability and log P.

The Pore-Lipid Interface: Role of Amino-Acid Determinants of Lipophilic Access by Ivabradine to the hERG1 Pore Domain

Abnormal cardiac electrical activity is a common side effect caused by unintended block of the promiscuous drug target human ether-à-go-go-related gene (hERG1), the pore-forming domain of the delayed rectifier K⁺ channel in the heart. hERG1 block leads to a prolongation of the QT interval, a phase of the cardiac cycle that underlies myocyte repolarization detectable on the electrocardiogram. Even newly released drugs such as heart-rate lowering agent ivabradine block the rapid delayed rectifier current I_Kr, prolong action potential duration, and induce potentially lethal arrhythmia known as torsades de pointes. In this study, we describe a critical drug-binding pocket located at the lateral pore surface facing the cellular membrane. Mutations of the conserved M651 residue alter ivabradine-induced block but not by the common hERG1 blocker dofetilide. As revealed by molecular dynamics simulations, binding of ivabradine to a lipophilic pore access site is coupled to a state-dependent reorientation of aromatic residues F557 and F656 in the S5 and S6 helices. We show that the M651 mutation impedes state-dependent dynamics of F557 and F656 aromatic cassettes at the protein-lipid interface, which has a potential to disrupt drug-induced block of the channel. This fundamentally new mechanism coupling the channel dynamics and small-molecule access from the membrane into the hERG1 intracavitary site provides a simple rationale for the well established state-dependence of drug blockade. SIGNIFICANCE STATEMENT: The drug interference with the function of the cardiac hERG channels represents one of the major sources of drug-induced heart disturbances. We found a novel and a critical drug-binding pocket adjacent to a lipid-facing surface of the hERG1 channel, which furthers our molecular understanding of drug-induced QT syndrome.

Fluoroquinolone Amorphous Polymeric Salts and Dispersions for Veterinary Uses

Enrofloxacin (ENRO) is a poorly soluble drug used in veterinary medicine. It differs from the more widely used fluoroquinolone ciprofloxacin (CIP) by the presence of an ethyl substituent on its piperazine amino group. While a number of recent studies have examined amorphous composite formulations of CIP, little research has been conducted with ENRO in this area. Therefore, the main purpose of this work was to produce amorphous solid dispersions (ASDs) of ENRO. The solid-state properties of these samples were investigated and compared to those of the equivalent CIP ASDs, and their water uptake behavior, solubility, dissolution, and antibacterial activity were assessed. Like CIP, X-ray amorphous solid dispersions were obtained when ENRO was ball milled with acidic polymers, whereas the use of neutral polymers resulted in semi-crystalline products. Proton transfer from the carboxylic acids of the polymers to the tertiary amine of ENRO’s piperazine group appears to occur in the ASDs, resulting in an ionic bond between the two components. Therefore, these ASDs can be referred to as amorphous polymeric salts (APSs). The glass transition temperatures of the APSs were significantly higher than that of ENRO, and they were also resistant to crystallization when exposed to high humidity levels. Greater concentrations were achieved with the APSs than the pure drug during solubility and dissolution studies, and this enhancement was sustained for the duration of the experiments. In addition, the antimicrobial activity of ENRO was not affected by APS formation, while the minimum inhibitory concentrations and minimum bactericidal concentrations obtained with the APS containing hydroxypropyl methylcellulose acetate succinate grade MG (HPMCAS-MG) were significantly lower than those of the pure drug. Therefore, APS formation is one method of improving the pharmaceutical properties of this drug.

Antimicrobial molecules in the lung: formulation challenges and future directions for innovation

Inhaled antimicrobials have been extremely beneficial in treating respiratory infections, particularly chronic infections in a lung with cystic fibrosis. The pulmonary delivery of antibiotics has been demonstrated to improve treatment efficacy, reduce systemic side effects and, critically, reduce drug exposure to commensal bacteria compared with systemic administration, reducing selective pressure for antimicrobial resistance. This review will explore the specific challenges of pulmonary delivery of a number of differing antimicrobial molecules, and the formulation and technological approaches that have been used to overcome these difficulties. It will also explore the future challenges being faced in the development of inhaled products and respiratory infection treatment, and identify future directions of innovation, with a particular focus on respiratory infections caused by multiple drug-resistant pathogens.

Fluorescence and electron paramagnetic resonance studies of norfloxacin and N-donor mixed-ligand ternary copper(II) complexes: Stability and interaction with SDS micelles

The stability of ternary copper(II) complexes of a heterocyclic ligand, L (L being 2,2'-bipyridine (bipy) or 1,10-phenanthroline (phen)) and the fluorescent antibacterial agent norfloxacin (NFX) as the second ligand was studied at pH7.4 and different ionic strengths. Fluorescence quenching upon titration of NFX with the binary complexes allowed to obtain stability constants for NFX binding, K_b, as a function of ionic strength. The K_b values vary by more than two orders of magnitude when buffer concentration varies from 0.5 to 100mM. It was observed that previously synthesized ternary complexes dissociate in buffer according with the obtained stability constants. This shows that equimolar solutions of NFX and binary complexes are equivalent to solutions of synthesized ternary complexes. The interaction of the ternary copper complexes with anionic SDS (sodium dodecyl sulfate) micelles was studied by fluorescence and electron paramagnetic resonance (EPR). Titration of NFX-loaded SDS micelles with the complexes Cu:L allowed to determine the stability constants inside the micelles. Fluorescence quenching demonstrated that SDS micelles increase the stability constants by factors around 50. EPR spectra gave details of the copper(II) local environment, and demonstrated that the structure of the ternary complexes inside SDS micelles is different from that in buffer. Mononuclear ternary complexes formed inside the micelles, while in buffer most ternary complexes are binuclear. The results show that anionic membrane interfaces increase formation of copper fluoroquinolone complexes, which can influence bioavailability, membrane diffusion, and mechanism of action of the antibiotics.

Analyses of Levofloxacin Adsorption on Pretreated Barley Straw with Respect to Temperature: Kinetics, π-π Electron-Donor-Acceptor Interaction and Site Energy Distribution

Levofloxacin, representative of an important class of fluoroquinolone antibiotics, has been considered to be one of the emerging pollutants in various water sources. In this paper, adsorption of levofloxacin from artificial contaminated water was done by pretreated barley straw adsorbent obtained from raw barley straw after modification by H₃PO₄ impregnation and microwave heating. The adsorption kinetics was investigated at various temperatures and levofloxacin concentrations, and the activation energy was determined. In addition, site energy distribution of the pretreated barley straw for levofloxacin adsorption was estimated based on the equilibrium adsorption data. The average site energy and standard deviation of the distribution were determined and applied to analyze the interaction strength between the adsorbent and adsorbate, and adsorption site heterogeneity. The π-π electron-donor-acceptor interactions between the π* aromatic C═C of pretreated barley straw adsorbent and π* carbon atom in benzene ring attached to fluorine of levofloxacin was investigated by C K-edge X-ray absorption near-edge structure spectroscopy. The results and methodologies in this work could be transferrable to investigate extended systems of water treatment.