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The multiple-readout capability of multimodal detection enhances the flexibility, reliability, and accuracy of lateral flow immunoassay (LFIA). The conjugation of two different metal-organic frameworks (MOFs) as a new-generation composite material offers extraordinary opportunities for developing multimodal LFIA. It is anticipated to compensate limitations of traditional single colorimetric signal LFIA and improve the analysis performance. Herein, an ultra-bright fluorescent AIE-MOF was proposed and coupled with an in-situ growth of Prussian blue (PB) nanoparticles strategy to obtain a novel multimodal signal tracer (AIE-MOF@PB). Thereafter, it was successfully applied to develop the multimodal LFIA platform for the detection of nitrofurazone metabolites. The synergy of AIE-MOF and PB endows AIE-MOF@PB with superb water dispersibility, robust fluorescence emission, brilliant colorimetric signal, marvelous photothermal conversion, and enhanced antibody coupling efficiency, all of which facilitate a highly sensitive triple-readout LFIA platform. The detection sensitivity improved by at least 5-fold compared with the colloidal gold-based LFIA. This work not only inspires the rational design of aggregation-induced emission luminogens (AIEgen)-based complex materials but also highlights the promising potential in flexible point-of-care applications., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The study presents the successful development of a new electrochemical sensor with low cost and disposability for application in nitrofurazone detection in environmental and pharmaceutical samples. The sensors were fabricated using materials obtained from local storage and conductive carbon ink. The modification of the screen-printed electrodes with the hybrid nanomaterial based on silver nanoparticles, carbon quantum dots, and carbon nanotubes showed synergistic contributions in the nitrofurazone electrooxidation, as observed in the wide linear range (0.008 at 15.051 μM), with a sensitivity of 0.650 μA/μM. The limit of detection obtained was 4.6 nM. Differential pulse voltammetry, cyclic voltammetry, X-ray photoelectron spectroscopy, X-ray diffraction analysis, and high-resolution transmission electron microscopy were used to evaluate the electrochemical and structural characteristics. Studies of possible interferences were considered with nitrofurazone in the presence of the ions and organic molecules. The results were satisfactory, with a variation of 93.3% ± 4.39% at 100% ± 2.40%. The low volume used in the analyses (50 μL), disposability, high sensibility, selectivity, and low limit of detection are advantages that make the proposed sensor an electrochemical tool of high viability for the NFZ detection in environmental matrices and pharmaceutical formulations., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The synthesis of three-dimensional silver nanopopcorns (Ag NPCs) onto a flexible polycarbonate membrane (PCM) for the detection of nitrofurazone (NFZ) on the fish surface by surface-enhanced Raman spectroscopy (SERS) is presented. The proposed flexible Ag-NPCs/PCM SERS substrate exhibits significant Raman signal intensity enhancement with the measured enhancement factor of 2.36 × 10 6 . This is primarily attributed to the hotspots created on Ag NPCs, including numerous nanoscale protrusions and internal crevices distributed across the surface of Ag NPCs. The detection of NFZ by this flexible SERS substrate demonstrates a low limit of detection (LOD) of 3.7 × 10 -9  M and uniform and reproducible Raman signal intensities with a relative standard deviation below 8.34%. It also exhibits excellent stability, retaining 70% of its efficacy even after 10 days of storage. Notably, the practical detection of NFZ in tap water, honey water, and fish surfaces achieves LOD values of 1.35 × 10 -8  M, 5.76 × 10 -7  M, and 3.61 × 10 -8  M, respectively,  which highlights its effectiveness across different sample types. The developed Ag-NPCs/PCM SERS substrate presents promising potential for sensitive SERS detection of toxic substances in real-world samples., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Four new quinofuracins F - I were isolated from the culture broth of Staphylotrichum boninense PF1444. The structures of quinofuracins F - I were elucidated by extensive spectroscopic analysis. These quinofuracins induced tumor suppressor protein p53-dependent cell death in human glioblastoma LNZTA3 cells., (© 2021. The Author(s), under exclusive licence to the Japan Antibiotics Research Association.)

Drug repurposing has gained much attention as a cost-effective strategy that plays an exquisite role in identifying undescribed biological activities in clinical drugs. In the present work, we report the repurposing of the antibacterial drug nitrofurazone (NFZ) as a potential anticancer agent against CaCo-2, MDA-MB 231 and HepG-2 cancer cell lines. Novel series of nitrofurazone analogs were then designed considering the important pharmacologic features present in NFZ. Synthesis and biological evaluation of the target compounds revealed their promising anticancer activities endowed with antimicrobial potential and possessing better lipophilicity than NFZ. Compound 7, exclusively, inhibited the growth of all tested cancer cells more potently than NFZ with the least cytotoxicity against normal cells, displaying anti Gram-positive bacterial activities and antifungal potential. Analysis of the stereo-electronic properties of compound 7 via investigating the energies of HOMO, LUMO, HOMO-LUMO energy gap and MEP maps demonstrated its high reactivity and the expected molecular mechanism of action through reduction of the 5-nitrofuryl moiety. Data of the bioactivity studies indicated that the potent anticancer activity of 7 is mainly through increasing intracellular ROS levels and induction of apoptosis via significantly down-regulating the expression of Bcl-2 while up-regulating BAX, p53 and caspase 3 expression levels. Compound 7 potently inhibited the cellular expression levels of antioxidant enzymes GPx1 and GR compared to NFZ. Antioxidant enzymes kinetic studies and blind molecular docking simulations disclosed the mechanistic and structural aspects of the interaction between 7 and both GR and GPx1. Thus, the successful discovery of 7 as a potential dual anticancer-antimicrobial nitrofurazone analog might validate the applicability of drug repurposing strategy in unravelling the unrecognized bioactivity of the present conventional drugs, besides furnishing the way towards more optimization and development studies., (Copyright © 2021 Elsevier Inc. All rights reserved.)

(1) Background: Environmental contamination with antibiotics is particularly serious because the usual methods used in wastewater treatment plants turn out to be insufficient or ineffective. An interesting idea is to support natural biodegradation processes with physicochemical methods as well as with bioaugmentation with efficient microbial degraders. Hence, the aim of our study is evaluation of the effectiveness of different methods of nitrofurazone (NFZ) degradation: photolysis and photodegradation in the presence of two photocatalysts, the commercial TiO 2 -P25 and a self-obtained Fe 3 O 4 @SiO 2 /TiO 2 magnetic photocatalyst. (2) Methods: The chemical nature of the photocatalysis products was investigated using a spectrometric method, and then, they were subjected to biodegradation using the strain Achromobacter xylosoxidans NFZ2. Additionally, the effects of the photodegradation products on bacterial cell surface properties and membranes were studied. (3) Results: Photocatalysis with TiO 2 -P25 allowed reduction of NFZ by over 90%, demonstrating that this method is twice as effective as photolysis alone. Moreover, the bacterial strain used proved to be effective in the removal of NFZ, as well as its intermediates. (4) Conclusions: The results indicated that photocatalysis alone or coupled with biodegradation with the strain A. xylosoxidans NFZ2 leads to efficient degradation and almost complete mineralization of NFZ.

The interaction between DNA and furazolidone/furacillin was investigated using various analytical techniques including spectroscopy and electroanalysis and molecular modelling. With the aid of acridine orange (AO), the fluorescence lifetimes of DNA-AO, DNA-furazolidone/furacillin-AO remained almost the same, which proved that the ground state complex was formed due to furazolidone/furacillin binding with DNA. Circular dichroism spectra and Fourier transform infrared spectroscopy showed that the second structure of DNA changed. Viscosity experiments presented that relative viscosity of DNA was increased with the increasing concentrations of furazolidone and almost unchanged for furacilin. In addition, the results of melting temperature (T m ), ionic strength, site competition experiments, cyclic voltammetry, and molecular docking all proved the intercalation binding mode for furazolidone and groove binding mode for furacilin. The binding constants (K a ) obtained from Wolfe-Shimmer equation were calculated as 3.66 × 10 4 L mol -1 and 3.95 × 10 4 L mol -1 for furazolidone-DNA and furacilin-DNA, respectively., (© 2019 John Wiley & Sons, Ltd.)

In this study, a self-biased bio-photoelectrochemical system (SB-BPES) was constructed using a bioanode and the g-C 3 N 4 /CdS heterojunction photocathode for nitrofurazone (NFZ) degradation under solar irradiation. The physio-chemical properties and optical performance of photocatalysts were characterized, and photo-electrochemical properties of various photocathodes were analyzed. Results showed that g-C 3 N 4 /CdS exhibited the broadest visible light absorption range (to 594 nm) and the most efficient e - -h + separation; and its corresponding photocathode showed the highest photocurrent (9.8 μA), and the lowest charge transfer resistance (5.43 ☓ 10 3  Ω). In the solar-illuminated SB-BPES with g-C 3 N 4 /CdS photocathode, about 80% of NFZ removal rate was achieved within 10 h. More importantly, TOC removal of 62.6% was achieved in 24 h, which was 1.8 times of that from the open circuit SB-BPES, and 4.3 folds of that from microbial degradation; also, about 1.5 times of those from SB-BPES with g-C 3 N 4 and CdS photocathodes. Besides, reproducible current generations (∼1.0 mA) were produced. These verified that it was a self-sustained system for spontaneously pollutants degradation and electricity generation. Moreover, possible degradation mechanism and pathways were proposed according to the identified intermediates. This study provides inspiration for synchronic improving refractory organics degradation and net energy recovery., (Copyright © 2019 Elsevier B.V. All rights reserved.)

A computational strategy in consideration of attachment energy, temperature, solubility and supersaturation unravels details of the solvent effect on the crystal morphology. The crystal morphologies were predicted by the advanced screw dislocation growth model. This research sheds much light on the crystal growth mechanisms with the example of 3,4-bis(3-nitrofurazan-4-yl)furoxan (DNTF) in ethanol. The solvation model based on the experiment situation was established into periodic supercell. Molecular dynamics simulation was performed for obtaining the adsorption energy at the equilibrium state of the interface layer. The growth characteristics of relevant growth faces are introduced. At the same time, a periodic bond chains analysis can be applied to the existence and evolution of crystal growth units. The prediction results are in remarkable agreement with the experimental results. We found that crystal morphology of DNTF is composed of (002), (111), (111¯) and (101) faces in ethanol. As the saturation temperature rises, the (101) face becomes smaller and eventually disappears., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The global spread of multidrug-resistant enterobacteria warrants new strategies to combat these pathogens. One possible approach is the reconsideration of "old" antimicrobials, which remain effective after decades of use. Synthetic 5-nitrofurans such as furazolidone, nitrofurantoin, and nitrofurazone are such a class of antimicrobial drugs. Recent epidemiological data showed a very low prevalence of resistance to this antimicrobial class among clinical Escherichia coli isolates in various parts of the world, forecasting the increasing importance of its uses to battle antibiotic-resistant enterobacteria. However, although they have had a long history of clinical use, a detailed understanding of the 5-nitrofurans' mechanisms of action remains limited. Nitrofurans are known as prodrugs that are activated in E. coli by reduction catalyzed by two redundant nitroreductases, NfsA and NfsB. Furazolidone, nevertheless, retains relatively significant antibacterial activity in the nitroreductase-deficient Δ nfsA Δ nfsB E. coli strain, indicating the presence of additional activating enzymes and/or antibacterial activity of the unreduced form. Using genome sequencing, genetic, biochemical, and bioinformatic approaches, we discovered a novel 5-nitrofuran-activating enzyme, AhpF, in E. coli The discovery of a new nitrofuran-reducing enzyme opens new avenues for overcoming 5-nitrofuran resistance, such as designing nitrofuran analogues with higher affinity for AhpF or screening for adjuvants that enhance AhpF expression., (Copyright © 2019 American Society for Microbiology.)

The failures of glutaraldehyde (GLUT) cross-linked bioprosthetic heart valves (BHVs) are mainly due to degeneration and calcification. In this study, we developed a new preparation strategy for BHVs named as "HPA/EDC/EGCG" that utilized 3,4-hydroxyphenylpropionic acid (HPA)-conjugated pericardium, epigallocatechin gallate (EGCG), and horseradish peroxidase (HRP)/hydrogen peroxide (H 2 O 2 ) enzymatic cross-linking. HPA-pericardium conjugation was done by carbodiimide coupling reaction using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS). Then HPA-conjugated pericardium was cross-linked by HRP/H 2 O 2 enzyme-catalyzed oxidation. The feeding ratios of HPA and EGCG were optimized. The consumption of amino groups, collagenase and elastase degradation in vitro, biomechanics, extracellular matrix stability, and calcification of HPA-/EDC-/EGCG-treated pericardiums were characterized. We demonstrated that HPA-/EDC-/EGCG-treated pericardiums had better elastin stabilization and less calcification. EGCG and enzymatic cross-linking treated pericardiums showed improved mechanical properties. This new EGCG and enzymatic cross-linking strategy would be a promising method to make BHVs with better elastin stability and anti-calcification property. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1551-1559, 2019., (© 2018 Wiley Periodicals, Inc.)

Hydroxymethylnitrofurazone (NFOH) is a nitrofurazone prodrug effective in vivo during acute infections, and it has less hepatotoxicity effect than the standard drug benznidazole (BZN) which has been used during short- and long-term treatment. In the present study, we induced the indeterminate form of Chagas disease in mice with a Y strain of Trypanosoma cruzi and analysed the histopathological data about the effects of NFOH and BZN on different tissues, including the heart, skeletal muscle, liver, kidney, colon, spleen and brain. After infection, BALB/c mice were treated with NFOH (150 mg/kg) and BZN (60 mg/kg) for 60 days and then submitted to immunosuppression using dexamethasone (5 mg/kg) for 14 days. Two trained analysts, as part of a blind evaluation, examined the results using serial sections of 3 mm diameter in two different moments. The results showed reactivation of the disease only in the infected nontreated group (POS). After treatment, amastigote nests were found in the heart, colon, liver and skeletal muscle in the POS group and in the heart and liver of the BZN group. Interestingly, amastigote nests were not found in the NFOH and NEG groups. The histopathological analysis showed fewer tissue lesions and parasite infiltrates in the NFOH group when compared with the BZN and POS groups. We have not observed any increase in the levels of hepatocellular injury biomarkers (AST/ALT) in the NFOH group. These in vivo studies show the potential for NFOH as an effective and safe compound useful as an anti-T. cruzi agent., (© 2018 The Authors. International Journal of Experimental Pathology © 2018 International Journal of Experimental Pathology.)

Chagas disease, caused by Trypanosoma cruzi, is a parasitosis that predominates in Latin America. It is estimated that 25 million people are under the risk of infection and, in 2008, more than 10 thousand deaths were registered. The only two drugs available in the therapeutics, nifurtimox and benznidazole, showed to be more effective in the acute phase of the disease. However, there is no standard treatment protocol effective for the chronic phase. Nitrofurazone (NF), an antimicrobial drug, has activity against T. cruzi, although being toxic. Considering the need for new antichagasic drugs, the existence of promising new therapeutic targets, as 14α-sterol demethylase and cruzain, and employing the bioisosterism and molecular hybridization approaches, four novel compounds were synthesized, characterized by melting point range, elemental analysis, IR and NMR spectroscopy. The compounds were tested against T. cruzi amastigotes in infected U2OS cells. All compounds showed selectivity towards T. cruzi and showed trypanomicidal activity in low micromolar range. The compound 3 showed potency similar to benznidazole, but lower efficacy. These results highlight the importance of the 1,2,4-triazole, thiosemicarbazonic and nitro group moieties for designing new efficient compounds, potentially for the chronic phase of Chagas disease., (Copyright © 2016 Elsevier Masson SAS. All rights reserved.)

Two new polymorphic forms of 5-nitrofurazone (5-nitro-2-furaldehyde semicarbazone) have been synthesized and structurally characterized by single-crystal and powder X-ray diffraction methods, vibrational spectroscopy (FT-IR and temperature Raman), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Hirshfeld surface analysis. The compound crystallizes in three different polymorphic forms P21/a (polymorph α), P21 (polymorph β) and P21/c (polymorph γ), the crystal structures of two of which (polymorphs β and γ) represent new structure determinations. The solid-state molecular organization in the three crystal forms is analyzed and discussed in terms of molecular conformation, crystal packing and hydrogen-bonded networks. All three crystals are formed from trans geometrical isomers, but the molecular conformation of the α-polymorph is syn-anti-anti-anti, while that of β- and γ-polymorphs is syn-anti-syn-syn. As a consequence of this the hydrogen-bond donor and acceptor sites of the molecules are oriented differently, which in turn results in different hydrogen-bond connectivity and packing patterns.

A newly developed modified coacervation method is utilized to synthesize gelatin nano/submicron particles (GN/SPs) as a drug carrier. Binary nonsolvent aided coacervation (BNAC) method is a modified single step coacervation method, which has yielded approximately a threefold lower particle size and higher average yield in terms of weight percentage of around 94% in comparison to the conventional phase separation methods. In this study 0.5% (w/v) gelatin aqueous solution with a binary nonsolvent system of acetone and ethanol was used. Nanoparticle synthesis was optimized with respect to nonsolvent system type and pH. pH7 has resulted a minimum particle size of 55.67 (±43.74) nm in anhydrous medium along with a swollen particle size of 776nm (±38.57) in aqueous medium with a zeta potential of (-16.3±3.51) mV in aqueous medium. Swelling ratio of 13.95 confirms the crosslinked hydrogel nature of the particles. Furthermore, drug loading efficiency of the gelatin particles prepared at 7pH was observed with nitrofurazone as the model drug. Results of drug release study indicate the potential use of GN/SPs as drug loading matrix for wound management such as burn wound management., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Traditional methods for regulating oxygen concentration ([O2]) in in vitro experiments over the range found in normal and tumor tissues require the use of expensive equipment to generate controlled gas atmospheres or the purchase of a range of gas cylinders with certified O2 percentages. Here we describe a simple and inexpensive enzymatic method for generating low, precise steady-state [O2] levels that are stable for several hours. This method is particularly applicable to the in vitro study of some classes of hypoxia-targeted antitumor prodrugs and bioreductively activated agents., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Reliably detecting nitrofurazone (NFZ) residues in farmed crab and shrimp was previously hindered by lack of appropriately specific analytical methodology. Parent NFZ rapidly breaks down in meat, and the commonly used side-chain metabolite, semicarbazide (SEM), is non-specific as it occurs naturally in crustacean shell often leading to 'false positive' detections in meat. Using 5-nitro-2-furaldehyde (NF) as marker metabolite, following pre-column derivatization with 2,4-dinitrophenylhydrazine (DNPH), ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis in negative electrospray ionization mode enabled confirmation of NFZ residues in deliberately treated whole crab, crab meat and shrimp meat, with a limit of detection (LOD) and limit of quantification (LOQ) below 1 ng g(-1). Meanwhile, the derivatives of DNPH-NF were synthesized for the first time, purified by preparative liquid chromatography and structure characterized with nuclear magnetic resonance spectroscopy ((1)H-NMR). The purity of derivative was checked by ultra-performance liquid chromatography-tunable ultraviolet (UPLC-TUV), and the contents were beyond 99.9%. For comparison purposes, crustacean samples were analysed using both NF and SEM marker metabolites. NFZ treatment was revealed by both NF and SEM marker metabolites, but untreated crab also showed measurable levels of SEM which could potentially be misinterpreted as evidence of illegal NFZ use.

Antibiotics in wastewaters must be degraded to eliminate their antibacterial activity before discharging into the environment. A cathode can provide continuous electrons for the degradation of refractory pollutants, however the cathodic degradation feasibility, efficiency and pathway for different kinds of antibiotics is poorly understood. Here, we investigated the degradation of four antibiotics, namely nitrofurazone (NFZ), metronidazole (MNZ), chloramphenicol (CAP), and florfenicol (FLO) by a poised cathode in a dual chamber electrochemical reactor. The cyclic voltammetry preliminarily proved the feasibility of the cathodic degradation of these antibiotics. The cathodic reducibility of these antibiotics followed the order of NFZ > MNZ > CAP > FLO. A decreased phosphate buffered solution (PBS) concentration as low as 2 mM or utilization of NaCl buffer solution as catholyte had significant influence on antibiotics degradation rate and efficiency for CAP and FLO but not for NFZ and MNZ. PBS could be replaced by Na2CO3-NaHCO3 buffer solution as catholyte for the degradation of these antibiotics. Reductive dechlorination of CAP proceeded only after the reduction of the nitro group to aromatic amine. The composition of the degradation products depended on the cathode potential except for MNZ. The cathodic degradation process could eliminate the antibacterial activity of these antibiotics. The current study suggests that the electrochemical reduction could serve as a potential pretreatment or advanced treatment unit for the treatment of antibiotics containing wastewaters., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Nitrofurazone (NTZ) is usually employed in the topical treatment of infected wounds and lesions of both skin and mucosa. Microencapsulation is a process utilized in the incorporation of active ingredients within polymers aiming at, among other objectives, the prolonged release of pharmaceutical compounds and protection from atmospheric agents (viz. moisture, light, heat and/or oxidation). With the goal of utilizing the microparticles containing encapsulated NTZ in pharmaceutical formulations, one prepared microparticles containing NTZ via ionotropic gelation of sodium alginate. The microparticles were characterized via scanning electron microscopy analyses, Fourier transform infrared spectroscopy (FTIR) analyses, via determination of encapsulation efficiency, and via thermal analyses (both TGA and DSC). The final gel formulation was also characterized rheologically. The extrusion/solidification technique employed to obtain the calcium alginate microparticles with encapsulated NTZ was found to be adequate, and produced an NTZ encapsulation efficiency of ca. 97.8% ± 1.1%. The calcium alginate microparticles thus obtained, with encapsulated NTZ, exhibited an oval shape and hydrodynamic diameters between 500 μm and 800 μm. From the thermal analyses performed, together with information from the infrared spectra, one may conclude that NTZ did not strongly bind to the polymer, which may be favorable for the release of the active ingredient. From the results obtained in the present research effort, one may conclude that the microparticles produced possess the potential to be utilized as carriers for NTZ in pharmaceutical formulations such as gels, ointments, and solutions.

The goal of the research work entertained herein was the development and characterization of a poly-(vinyl alcohol) (PVA) hydrogel cross-linked with glutaraldehyde and impregnated with 0.2% (w/w) nitrofurazone (NTZ), for topical applications. To verify the active principle release capability, one has determined (i) swelling profile, (ii) in vitro release of NTZ via UV-VIS spectrophotometry, and (iii) antimicrobial activity via exposure to the hydrogel of ATCC strains of Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. The optimized hydrogel was further characterized via scanning electron microscopy (SEM), infrared spectroscopy with Fourier transform, moisture content determinations and thermal analyses via thermal gravimetry (TGA). Swelling tests revealed a mass increase from 100±5% up to 350±11%. Incorporated NTZ displayed bactericidal activity, as expected, being released in a linearly controlled fashion above 6 µg/mL during experiment timeframes of 14 h. SEM analyses allowed verification of a homogeneous surface morphology, while infrared spectra showed that NTZ did not bind strongly to the cross-linked polymer. Furthermore, results from thermal analyses suggested a loss of thermal stability arising from incorporation of NTZ in the hydrogel. The optimized hydrogel exhibited characteristics with high potential for (antimicrobial) treatment of skin lesions.

Hydroxymethylnitrofurazone (NFOH) is a trypanocidal prodrug of nitrofurazone (NF), devoid of mutagenic toxicity. The purpose of this work was to study the chemical conversion of NFOH into NF in sodium acetate buffer (pH 1.2 and 7.4) and in human plasma and to determine preclinical pharmacokinetic parameters in rats. At pH 1.2, the NFOH was totally transformed into NF, the parent drug, after 48 h, while at pH 7.4, after the same period, the hydrolysis rate was 20%. In human plasma, 50% of NFOH was hydrolyzed after 24 h. In the investigation of kinetic disposition, the concentration of drug in serum versus time curve was used to calculate the pharmacokinetic parameters after a single-dose regimen. NFOH showed a time to maximum concentration of drug in serum (Tmax) as 1 h, suggesting faster absorption than NF (4 h). The most important results observed were the volume of distribution (V) of NFOH through the tissues, which showed a rate that is 20-fold higher (337.5 liters/kg of body weight) than that of NF (17.64 liters/kg), and the concentration of NF obtained by in vivo metabolism of NFOH, which was about four times lower (maximum concentration of drug in serum [Cmax] = 0.83 μg/ml; area under the concentration-time curve from 0 to 12 h [AUC0-12] = 5.683 μg/ml · h) than observed for administered NF (Cmax = 2.78 μg/ml; AUC0-12 = 54.49 μg/ml · h). These findings can explain the superior activity and lower toxicity of the prodrug NFOH in relation to its parent drug and confirm NFOH as a promising anti-Chagas' disease drug candidate.

A reliable, selective and sensitive LC-MS/MS assay has been proposed for the determination of nitrofurantoin in human plasma. The analyte and nitrofurazone were extracted from 100 μL of human plasma via SPE on Strata-X 33 μm extraction cartridges. Chromatography was done on a BDS Hypersil C18 (100 mm × 4.6 mm, 5 μm) column under isocratic conditions. Quantitation was done using the multiple reaction monitoring (MRM) mode for deprotonated precursor to product ion transitions of nitrofurantoin (m/z 237.0 → 151.8) and nitrofurazone (m/z 197.0 → 123.9). The limit of detection and the lowest limit of quantitation of the method were 0.25 ng mL-1 and 5.00 ng mL-1, respectively, with a linear dynamic range of 5.00-1500 ng mL-1 for nitrofurantoin. The intra- -batch and inter-batch precision (RSD, %) was ≤ 5.8 %, while the mean extraction recovery was > 92 %. The method was successfully applied to a bioequivalence study of a 100 mg nitrofurantoin capsule formulation in 36 healthy subjects.

Electrochemical behavior of nitrofurazone (NFZ) was investigated with the use of cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. The pH-dependence of NFZ was studied at a glassy carbon electrode (GCE) in ethanol/Britton-Robinson buffer (30:70), and short-lived nitro-radicals were generated by the reduction of NFZ at high pHs (>7.0). In the presence of DNA, the DPV peak current of NFZ decreased and the peak potential shifted negatively, which indicated that there was an electrostatic interaction between NFZ and DNA. An electrochemical dsDNA/GCE biosensor was prepared to study the DNA damage produced in the presence NFZ; this process was followed with the use of the Co(phen)(3)(2+) electroactive probe. Also, the oxidation peaks of guanosine (750 mV) and adenosine (980 mV) indicated that DNA damage was related directly to the nitro-radicals. Experiments demonstrated that DNA damage occurred via two different steps while NFZ was metabolized and nitro-radicals were produced. Novel work with AFM on the NFZ/DNA interaction supported the suggestion that in vivo, the nitro-radicals were more cytotoxic than the NFZ molecules. A linear DPV calibration plot was obtained for NFZ analysis at a modified dsDNA/GCE (concentration range: 2.50 × 10(-6)-3.75 × 10(-5) mol L(-1); limit of detection: 8.0 × 10(-7) mol L(-1)), and NFZ was determined successfully in pharmaceutical samples., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Two nanoparticle based adjuvants were assessed for their ability to produce polyclonal antibodies in rabbits to low molecular weight target analytes, i.e. veterinary drugs banned from use in food producing animals. The nanoparticles, Montanide IMS 251 and amphiphilic poly (γ-glutamic acid) were compared against a mineral oil adjuvant, Montanide ISA 50, which had previously been shown to be successful in producing antibodies to haptens whilst being safe to use with respect to the welfare of the host animals. The adjuvants were assessed for their tendency to cause adverse effects to the host animals and by the quality of the antibodies generated in terms of assay sensitivity. None of the three adjuvants employed in the trial generated any measurable adverse effects in the host animals. While the mineral oil adjuvant produced higher titres of antibodies the nanoparticle adjuvants were found to produce antibodies of statistically comparable sensitivity. Based on IC(50) values, six antisera displayed potential to detect the required level of the target compounds; five of these were produced by rabbits immunised with the two different nanoparticle adjuvants. As antibody sensitivity is the main performance criteria of an analytical immunoassay, it can be concluded that the nanoparticle adjuvants under evaluation are fit for the purpose described in this study., (Copyright © 2012 Elsevier B.V. All rights reserved.)

A molecular modeling study was carried out to investigate the most likely enzymatic disassembly mechanism of dendrimers that were designed as potential antichagasic and antileishmanial prodrugs. The models contained myo-inositol (core), L-malic acid (spacer), and active agents such as 3-hydroxyflavone, quercetin, and hydroxymethylnitrofurazone (NFOH). A theoretical approach that considered one, two, or three branches has already been performed and reported by our research group; the work described herein focused on four (models A and B), five, or six branches, and considered their physicochemical properties, such as spatial hindrance, electrostatic potential mapping, and the lowest unoccupied molecular orbital energy (E(LUMO)). The findings suggest that the carbonyl group next to the myo-inositol is the most promising ester breaking point.

The interaction of nitrofurazone (NF) and human serum albumin (HSA) has been studied by fluorescence spectroscopy, FT-IR spectroscopy and molecular modeling methods. The results showed that the fluorescence of HSA was quenched by NF in a static quenching mechanism. Thermodynamic parameters revealed that hydrogen bonds and van der Waals force played the major role during the interaction. The calculated binding distance (r) indicated that the non-radioactive energy transfer came into being in the interaction between NF and HSA. HSA had a single class of binding site at Sudlow' site I in subdomain IIA for NF, which was verified by the displacement experiment. The molecular modeling study further confirmed the specific binding sites of NF on HSA, such as the interaction between N11 and N14 of NF with Lue 283 and Ser 287 predominately through hydrogen bonds. Three-dimensional fluorescence spectra indicated that the polarity around the tryptophan residues decreased and the conformation of HSA changed after adding NF. FT-IR spectra showed that NF could induce the polypeptides of HSA unfolding because it changed α-helix and β-sheet into β-turn and random structure of HSA.

In therapeutics research, the nitro compounds are part of an important group of drugs with multiple pharmacological activities. However, in drug design, the inclusion of a nitro group in a molecule changes the physico-chemical and electronic properties and is associated with increased mutagenicity and carcinogenicity. In addition, several studies have related the relationship between the antimicrobial and/or anti-protozoal activity and the mutagenic effect to reduction of the nitro group. This work reviews the toxicity of nitro compounds and shows how the use of prodrugs can increase the biological activity and decrease the genotoxicity of nitro compounds, without any modification in nitro reduction behavior, but rather by physico-chemical improvement. Examples are given of metronidazole and nitrofurazone prodrugs.

Azoreductases are well known for azo pro-drug activation by gut flora. We show that azoreductases have a wider role in drug metabolism than previously thought as they can also reduce and hence activate nitrofurazone. Nitrofurazone, a nitroaromatic drug, is a broad spectrum antibiotic which has until now been considered as activated in bacteria by nitroreductases. The structure of the azoreductase with nitrofurazone bound was solved at 2.08 Å and shows nitrofurazone in an active conformation. Based on the structural information, the kinetics and stoichiometry of nitrofurazone reduction by azoreductase from P. aeruginosa, we propose a mechanism of activation which accounts for the ability of azoreductases to reduce both azo and nitroaromatic drugs. This mode of activation can explain the cytotoxic side-effects of nitrofurazone through human azoreductase homologues.

The addition of a hydroxymethyl group to the antimicrobial drug nitrofurazone generated hydroxymethylnitrofurazone (NFOH), which had reduced toxicity when its activity against Trypanosoma cruzi was tested in a murine model of Chagas' disease. Four groups of 12 Swiss female mice each received 150 mg of body weight/kg/day of NFOH, 150 mg/kg/day of nitrofurazone (parental compound), 60 mg/kg/day of benznidazole (BZL), or the solvent as a placebo. Treatments were administered orally once a day 6 days a week until the completion of 60 doses. NFOH was as effective as BZL in keeping direct parasitemia at undetectable levels, and PCR results were negative. No histopathological lesions were seen 180 days after completion of the treatments, a time when the levels of anti-T. cruzi antibodies were very low in mice treated with either NFOH or BZL. Nitrofurazone was highly toxic, which led to an overall rate of mortality of 75% and necessitated interruption of the treatment. In contrast, the group treated with its hydroxymethyl derivative, NFOH, displayed the lowest mortality (16%), followed by the BZL (33%) and placebo (66%) groups. The findings of histopathological studies were consistent with these results, with the placebo group showing the most severe parasite infiltrates in skeletal muscle and heart tissue and the NFOH group showing the lowest. The present evidence suggests that NFOH is a promising anti-T. cruzi agent.

In this work, a simple, rapid, and selective high-performance liquid chromatography (HPLC) method with diode array detection was developed for the simultaneous determination of nitrofurazone (NZ) and lidocaine hydrochloride (LD). The chromatographic separation was achieved by using Zorbax Eclipse XDB-C(18) (4.6 x 150 mm, 5 mum p.s.) analytical column and a mobile phase composed of 0.025 M disodium hydrogen phosphate-methanol-triethylamine (70:30:0.1, v/v/v) (pH 4.0) at a flow rate of 1 mL/min. The detector was set at wavelengths 374 and 220 nm for NZ and LD, respectively, and quantification of the analytes was based on measuring their peak areas. The retention times for NZ and LD were approximately 4.5 and 5.7 min, respectively. The reliability and analytical performance of the proposed HPLC procedure were statistically validated with respect to system suitability, linearity, ranges, precision, accuracy, selectivity, robustness, and detection and quantification limits. The linear dynamic ranges were 0.5-25 and 2.5-100 mug/mL for NZ and LD, respectively, with correlation coefficients > 0.999. The stability-indicating aspects of the proposed method were demonstrated by the resolution of the two analytes from the related substance and potential impurity (2,6-dimethylaniline) as well as from forced-degradation products. The validated HPLC method was successfully extended to the analysis of the combined topical dosage form (soluble dressing) where no interfering peaks were encountered from the dosage form matrix or the inactive ingredients.

This work aims at describing the kinetic model of nitrofurazone photodegradation by a novel chemometric technique, hybrid hard-soft multivariate curve resolution (HS-MCR). The study was applied to UV-spectral data from the photolysis of nitrofurazone solutions at different concentrations and exposed under varying illuminance power. The HS-MCR method was able to elucidate the kinetics of the photodegradation process and to determine the rate constants, and estimating at the same time the pure spectra of the degradation products. Exposure to light of the drug gave a first rapid isomerization to the syn-form that in turn underwent degradation furnishing a mixture of yellow-red products. The photodegradation process could be explained with a kinetic model based on three consecutive first-order reactions (A>B, B>C and C>D). These results were confirmed by application of the MCR procedure to the analysis of the data obtained from HPLC-DAD analysis of the nitrofurazone samples at different reaction times. The kinetic model was observed to be dependent on experimental conditions. The samples at higher concentrations showed rate constants lower than the diluted samples, whereas an increase of the rate of all degradation processes was observed when the light power also increased. This work shows the power of the hybrid hard- and soft-multivariate curve resolution as a method to deeply study degradation processes of photolabile drugs., (Copyright 2009 Elsevier B.V. All rights reserved.)

Nitrofurazone (NF) and its derivative, hydroxymethylnitrofurazone (NFOH), have presented antichagasic activity. NFOH has higher activity and lower mutagenicity. The aim of this work was to assess whether NF and its derivative NFOH would also be inhibitors of cruzain, besides their trypanothione reductase inhibitory activity. In vitro cruzain inhibition tests were performed for both compounds, and the 50% inhibitory concentration (IC50) for NF and NFOH presented values of 22.83 +/- 1.2 microM and 10.55 +/- 0.81 microM, respectively. AM1 semi-empirical molecular modeling studies were performed to understand the activity of the compounds, corroborating the observed cruzain inhibitory activity.

The enzyme nitroreductase, NfsB, from Escherichia coli has entered clinical trials for cancer gene therapy with the prodrug CB1954 [5-(aziridin-1-yl)-2,4-dinitrobenzamide]. However, CB1954 is a poor substrate for the enzyme. Previously we made several NfsB mutants that show better activity with CB1954 in a cell-killing assay in E. coli. Here we compare the kinetic parameters of wild-type NfsB with CB1954 to those of the most active single, double, and triple mutants isolated to date. For wild-type NfsB the global kinetic parameters for both k(cat) and K(m) for CB1954 are about 20-fold higher than previously estimated; however, the measured specificity constant, k(cat)/K(m) is the same. All of the mutants are more active with CB1954 than the wild-type enzyme, the most active mutant showing about 100-fold improved specificity constant with CB1954 over the wild-type protein with little effect on k(cat). This enhancement in specificity constants for the mutants is not seen with the antibiotic nitrofurazone as substrate, leading to reversed nitroaromatic substrate selectivity for the double and triple mutants. However, similar enhancements in specificity constants are found with the quinone menadione. Stopped-flow kinetic studies suggest that the rate-determining step of the reaction is likely to be the release of products. The most active mutant is also selective for the 4-nitro group of CB1954, rather than the 2-nitro group, giving the more cytotoxic reduction product. The double and triple mutants should be much more effective enzymes for use with CB1954 in prodrug-activation gene therapy.

Reactions of nitrofuran antibiotics (nitrofurazone (NFZ) and frazolidone (FZD)) with hypochlorite in aqueous solution were investigated under the conditions that simulate wastewater disinfection. The chlorination byproducts were determined by high performance liquid chromatography. At the levels of 5 microM, NFZ reacted rapidly with free chlorine in neutral pH (7.0), while the FZD-hypochlorite reaction was reasonably slow under the same pH. Nevertheless, the strong mutagenic parents disappeared completely after the hypochlorite reactions, and the chlorination byproducts were observed to exert a weak mutagenic effect on Salmonella typhimurium TA100 without S9-mix. The extent of the reactions depended on the chlorine dose, solution pH and compound structures.

The N-alkylated derivatives from nitrofurazone were synthesised and evaluated in vitro for their efficacy as antimicrobial agents against representative strains, including methicillin-resistant Staphylococcus aureus (MRSA). The derivative 2a demonstrated greater activity than the prototype and was comparable to currently used antimicrobial drugs.

A simple, rapid, selective and sensitive spectrofluorimetric method was described for the analysis of three nitrofuran drugs, namely, nifuroxazide (NX), nitrofurantoin (NT) and nitrofurazone (NZ). The method involved the alkaline hydrolysis of the studied drugs by warming with 0.1 M sodium hydroxide solution then dilution with distilled water for NX or 2-propanol for NT and NZ. The formed fluorophores were measured at 465 nm (lambda (Ex) 265 nm), 458 nm (lambda (Ex) 245 nm) and 445 nm (lambda (Ex) 245 nm) for NX, NT and NZ, respectively. The reaction pathway was discussed and the structures of the fluorescent products were proposed. The different experimental parameters were studied and optimized. Regression analysis showed good correlation between fluorescence intensity and concentration over the ranges 0.08-1.00, 0.02-0.24 and 0.004-0.050 microg ml(-1) for NX, NT and NZ, respectively. The limits of detection of the method were 8.0, 1.9 and 0.3 ng ml(-1) for NX, NT and NZ, respectively. The proposed method was validated in terms of accuracy, precision and specificity, and it was successfully applied for the assay of the three nitrofurans in their different dosage forms. No interference was observed from common pharmaceutical adjuvants. The results were favorably compared with those obtained by reference spectrophotometric methods.

Chagas disease is a serious health problem for Latin America. Nitrofurazone (NF) and Hidroxymethylnitrofurazone (NFOH) are active against Trypanosoma cruzi. The effect of beta-cyclodextrin (beta-CD) and dimethyl-beta-cyclodextrin (DM-beta-CD) complexation on the UV absorption and retention time of nitrofurazone (NF) and its hydroxymethylated analog (NFOH) were studied in solution. The retention behavior was analyzed on a reversed phase C18 column and the mobile phase used was acetonitrile-water (20/80 v/v), in which cyclodextrins (beta-CD or DM-beta-CD) were incorporated as a mobile phase additive. The decrease in the retention times of NF (or NFOH) with increasing concentration of HP-beta-CD enables the determination of the complex stability constants by HPLC. A phase-solubility study was performed, according to the method reported by Higuchi and Connors, to evaluate the changes of NF/NFOH in the complexation state, and the diagrams obtained suggested that it forms complexes with a stoichiometry of 1:1. This is an important study for the characterization of potential formulations to be used as therapeutic options for the treatment of Chagas disease.

Chagas disease is a serious health problem in Latin America. Hidroxymethylnitrofurazone (NFOH) is a nitrofurazone prodrug more active than nitrofurazone against Trypanosoma cruzi. However, NFOH presents low aqueous solubility, high photodecomposition and high toxicity. The present work is focused on the characterization of an inclusion complex of NFOH in 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD). The complexation with HP-beta-CD was investigated using reversed-phase liquid chromatography, solubility isotherms and nuclear magnetic resonance. The retention behavior was analyzed on a reversed-phase C(18) column, using acetonitrile-water (20/80, v/v) as the mobile phase, in which HP-beta-CD was incorporated as a mobile phase additive. The decrease in the retention times with increasing concentrations of HP-beta-CD enables the determination of the apparent stability constant of the complex (K=6.2+/-0.3M(-1)) by HPLC. The solubility isotherm was studied and the value for the apparent stability constant (K=7.9+/-0.2M(-1)) was calculated. The application of continuous variation method indicated the presence of a complex with 1:1 NFOH:HP-beta-CD stoichiometry. The photostability study showed that the formation of an inclusion complex had a destabilizing effect on the photodecomposition of NFOH when compared to that of the "free" molecule in solution. The mobility investigation (by NMR longitudinal relaxation time) gives information about the complexation of NFOH with HP-beta-CD. In preliminary toxicity studies, cell viability tests revealed that inclusion complexes were able to decrease the toxic effect (p<0.01) caused by NFOH.

We made fusion protein of fastatin and FIII 9-10, termed tetra-cell adhesion molecule (T-CAM) that can interact simultaneously with alphavbeta3 and alpha5beta1 integrins, both playing important roles in tumor angiogenesis. T-CAM can serve as a cell adhesion substrate mediating adhesion and migration of endothelial cells in alphavbeta3 and alpha5beta1 integrin-dependent manner. T-CAM showed pronounced anti-angiogenic activities such as inhibition of endothelial cell tube formation, endothelial cell proliferation, and induction of endothelial cell apoptosis. T-CAM also inhibited angiogenesis and tumor growth in mouse xenograft model. The anti-angiogenic and anti-tumoral activity of molecule like fastatin could be improved by fusing it with integrin-recognizing cell adhesion domain from other distinct proteins. The strategy of combining two distinct anti-angiogenic molecules or cell adhesion domains could facilitate designing improved anticancer agent of therapeutic value.

The antibiotics nitrofurazone and nitrofurantoin are used in the treatment of genitourinary infections and as topical antibacterial agents. Their action is dependent upon activation by bacterial nitroreductase flavoproteins, including the Escherichia coli nitroreductase (NTR). Here we show that the products of reduction of these antibiotics by NTR are the hydroxylamine derivatives. We show that the reduction of nitrosoaromatics is enzyme-catalyzed, with a specificity constant approximately 10,000-fold greater than that of the starting nitro compounds. This suggests that the reduction of nitro groups proceeds through two successive, enzyme-mediated reactions and explains why the nitroso intermediates are not observed. The global reaction rate for nitrofurazone determined in this study is over 10-fold higher than that previously reported, suggesting that the enzyme is much more active toward nitroaromatics than previously estimated. Surprisingly, in the crystal structure of the oxidized NTR-nitrofurazone complex, nitrofurazone is oriented with its amide group, rather than the nitro group to be reduced, positioned over the reactive N5 of the FMN cofactor. Free acetate, which acts as a competitive inhibitor with respect to NADH, binds in a similar orientation. We infer that the orientation of bound nitrofurazone depends upon the redox state of the enzyme. We propose that the charge distribution on the FMN rings, which alters upon reduction, is an important determinant of substrate binding and reactivity in flavoproteins with broad substrate specificity.

The constant-volume combustion energy, DeltacU (DNTF, s, 298.15K) and kinetic behavior of the exothermic decomposition reaction of the title compound (DNTF) are determined by a precise rotating bomb calorimeter and DSC, respectively. Its standard enthalpy of combustion, DeltacHmtheta (DNTF, s, 298.15K), standard enthalpy of formation, DeltacHmtheta (DNTF, s, 298.15K) and kinetic parameters of the major exothermic decomposition reaction in a temperature-programmed mode [the apparent activation energy (Ea) and pre-exponential factor (A)] are calculated. The values of DeltacU (DNTF, s, 298.15K), DeltacHmtheta (DNTF, s, 298.15K), and DeltacHmtheta (DNTF, s, 298.15K) of DNTF are -9733.96 +/- 8.59 Jg(-1), -3018.29 +/- 2.68 kJ mol(-1), and 657.23 +/- 2.70 kJ mol(-1), respectively. The kinetic model function in integral form and the value of E(a) and A of the major exothermic decomposition reaction of DNTF are 1-(1-alpha)1/3, 177.03 kJ mol(-1) and 10(13.68)s(-1), respectively. The critical temperature of thermal explosion of DNTF is 240.6 degrees C.

Objective: To explore the relationship between the illuminance and the observed order of reaction of photodegradation of nitrofurazone solution., Methods: Studying the observed order of reaction of photodegradation of nitrofurazone solution exposed to light with three illuminance values at three concentration values respectively., Results: The observed order of reaction of photodegradation increased with the decrease of concentration when the illuminance kept constant and, on the other hand, the observed order increased with the increase of illuminance when the concentration kept constant., Conclusion: The observed order of reaction of photodegradation of nitrofurazone solution depends on both the concentration of the drug and the illuminance of the incident light.

A coumarin derivative 4-methyl-8-methylacrylamide-2H, 5H-pyrano [3, 2-C] benzpyran 2, 5-dione (MMPBD) has been synthesized as a fluorescent carrier for preparing an optical chemical sensor. The carrier is immobilized on a quartz glass plate surface treated with a silanizing agent to prevent the leakage of the dye. This MMPBD sensor can be utilized for a nitrofurazone (NF) assay based on fluorescence quenching. The sensor shows good repeatability, a long lifetime and a fast response of less then 50 s. NF can be determined in the range between 1.0x10(-6)-1.0x10(-3 )mol L(-1) with a detection limit of 8.0x10(-7) mol L(-1 )at pH 7.0.

Aim: To study the effect of both light and heat on the stability of furacilin aqueous solution and the probability of substituting for isothermal accelerated tests by nonisothermal accelerated tests upon exposure to light at high temperatures., Methods: The isothermal and nonisothermal accelerated tests were employed. The accelerated tests were proceeded in the dark and exposed to light at high temperature. Tungsten, ultraviolet and fluorescent lamps were employed in exposure tests., Results: The degradation of furacilin aqueous solution in isothermal heating experiments or the exposure experiments to light at high temperatures obeys zero-order kinetics. The total degradation rate constant k caused by both light and heat can be divided into two parts: k = kdark + klight, where kdark and klight are the degradation rate constant caused by heat and light, respectively. The klight can be expressed as klight = Alight.exp(-Ea,light/RT).E, where E is the illuminance of light; Alight and Ea,light are both experimental constants. The parameters obtained in nonisothermal accelerated tests were comparable to those obtained in classic isothermal accelerated tests., Conclusion: Nonisothermal accelerated tests may substitute for isothermal accelerated tests during the study of the effects of both light and heat on the stability of drugs, in order to save time, labor and drugs.

The physico-chemical properties of some 5-nitro-2-furaldehyde semicarbazones (nitrofurazones) and thiophene analogues were compared with their in vitro and in vivo trypanocidal activity against Trypanosoma cruzi (Tulahuen strain). 3D-QSAR models were obtained by applying the SIMCA methodology to the electrostatic and steric fields (CoMFA fields) of the molecules. Nitrofurazones bearing N4 substituents. which cover a range of 14-17 A from the nitro group with a thickness of about 6 A when considering the extended conformer. produced complete survival in infected mice. The in vitro model allows larger N4 substituents than the SURVival model, but they must not bear positive centres in the region 15-16 A from the nitro group. Moreover, the in vitro model is in agreement with the active site of trypanothione reductase (TR). Both models can be of use in the design of novel drugs bearing an amide-like group at a distance of 7-9 A from an easily reducible group.

The effect of cysteamine and glutathione addition on the redox behaviour of metronidazole, chloramphenicol, M&B 4998, nitrofurazone, and nifuroxime has been studied by electrochemical techniques. The presence of thiol influences the redox behaviour of the nitro compound in a number of ways. In aqueous media, the single-step nitro/hydroxylamine reduction shows a decrease in current and a shift to more positive potentials, which is assigned to the thiol acting as the reducing agent, but only after the formation of the nitro radical anion. In addition, the reversible RNO/RNHOH couple is greatly diminished or removed. In a dimethylformamide/H2O solvent, the nitro radical anion can be selectively generated. The effect of thiol addition on the stability of the radical anion is strongly dependent on the drug, the identity of the thiol, and the concentration of the supporting electrolyte. The presence of thiol can result in an increase or a decrease in the lifetime of the radical with no apparent correlation with the redox couple of the nitro compound, or can act as an oxidizing agent and regenerate the original nitro compound. These disparate routes by which thiol can modify the redox characteristics of nitro compounds suggest that the traditional role of thiol as a radical scavenger needs to be extended.

The stability of the one electron addition product of four biologically important nitroheterocyclic compounds has been examined electrochemically. Using cyclic voltammetry the tendency of the nitro radical anion to undergo disproportionation was studied by two methods of analysis. The first was based on determining the voltammetric time-constant required for half of the reduction product, RNO2-., to react further. The second concerned the minimum volume of dimethylformamide which had to be added to the aqueous electrolytic medium to give a specific cyclic voltammetric response. Both methods were found to compare well with the results obtained for RNO2-. stabilities using a theoretically derived procedure for a second order reaction following a charge-transfer step. The use of these alternative approaches for quantifying the reactivity of reduction products is discussed. The time-constant method in particular may be useful in studying complex reaction pathways.

The electrochemical behaviour of three nitrofuran compounds, nitrofurazone, nitrofurantoin and furazolidone, has been studied in three solvent types; aprotic, aqueous and mixed, and at four working electrodes. Particular attention has focused on the 1-electron RNO2/RNO2.- couple as measured by the cyclic voltammetric mode. Using Hg in aqueous buffer, reduction of the NO2 group proceeds directly to the hydroxylamine with no intermediate stages being identified. Addition of an aprotic solvent gave a 2-stage reduction, initially forming the RNO2.- species. At all solid electrodes, however, the RNO2/RNO2.- couple was identified under simple aqueous conditions. The switch to a mixed aqueous/aprotic solvent medium produced only minor changes in the response compared with the situation on Hg. This presents the opportunity of using nitrofuran complexes as model systems for the redox behaviour of nitro aromatic compounds in general at solid electrode surfaces where the latters' more negative reduction potentials makes direct study difficult. The conditions have been defined whereby we can examine pH effects and RNO2.- biological target interactions in simple aqueous media to allow the further refinement of the electrolytic model system for studying bio-reducible drug action.