Zirconium-based hydrophobic-MOFs as innovative electrode modifiers for flibanserin determination: Exploring the electrooxidation mechanism using a comprehensive spectroelectrochemical study.

Three different types of Zr-based MOFs derived from benzene dicarboxylic acid (BDC) and naphthalene dicarboxylic acid as organic linkers (ZrBDC, 2,6-ZrNDC, and 1,4-ZrNDC) were synthesized. They were characterized using X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform IR spectroscopy (FT-IR), and Transmission electron microscopy (TEM). Their hydrophilic/hydrophobic nature was investigated via contact angle measurements; ZrBDC MOF was hydrophilic and the other two (ZrNDC) MOFs were hydrophobic. The three MOFs were combined with MWCNTs as electrode modifiers for the determination of a hydrophobic analyte, flibanserin (FLB), as a proof-of-concept analyte. Under the optimized experimental conditions, a significant enhancement in the oxidation peak current of FLB was observed when utilizing 2,6-ZrNDC and 1,4-ZrNDC, being the highest when using 1,4-ZrNDC. Furthermore, a thorough investigation of the complex oxidation pathway of FLB was performed by carrying out simultaneous spectroelectrochemical measurements. Based on the obtained results, it was verified that the piperazine moiety of FLB is the primary site for electrochemical oxidation. The fabricated sensor based on 1,4-ZrNDC/MW/CPE showed an oxidation peak of FLB at 0.8 V vs Ag/AgCl. Moreover, it showed excellent linearity for the determination of FLB in the range 0.05 to 0.80 µmol L-1 with a correlation coefficient (r) = 0.9973 and limit of detection of 3.0 nmol L-1. The applicability of the developed approach was demonstrated by determination of FLB in pharmaceutical tablets and human urine samples with acceptable repeatability (% RSD values were below 1.9% and 2.1%, respectively) and reasonable recovery values (ranged between 97 and 103% for pharmaceutical tablets and between 96 and 102% for human urine samples). The outcomes of the suggested methodology can be utilized for the determination of other hydrophobic compounds of pharmaceutical or biological interest with the aim of achieving low detection limits of these compounds in various matrices.

Development of an innovative turn-on fluorescent probe for targeted in-vivo detection of nitric oxide in rat brain extracts as a biomarker for migraine disease.

Nitric oxide (NO) is one of the reactive nitrogen species (RNS) that has been proposed to be a key signaling molecule in migraine. Migraine is a neurological disorder that is linked to irregular NO levels, which necessitates precise NO quantification for effective diagnosis and treatment. This work introduces a novel fluorescent probe, 2,3-diaminonaphthelene-1,4-dione (DAND), which was designed and synthesized to selectively detect NO in-vitro and in-vivo as a migraine biomarker. DAND boasts high aqueous solubility, biocompatibility, and facile synthesis, which enable highly selective and sensitive detection of NO under physiological conditions. NO reacts with diamine moieties (recognition sites) of DAND, results in the formation of a highly fluorescent product (DAND-NO) known as 1H-naphtho[2,3-d][1,2,3]triazole-4,9-dione at λem 450 nm. The fluorescence turn-on sensing mechanism operates through an intramolecular charge transfer (ICT) mechanism. To maximize fluorescence signal intensity, parameters including DAND concentration, reaction temperature, reaction time and pH were systematically optimized for sensitive and precise NO determination. The enhanced detection capability (LOD = 0.08 µmol L-1) and high selectivity of the probe make it a promising tool for NO detection in brain tissue homogenates. This demonstrates the potential diagnostic value of the probe for individuals suffering from migraine. Furthermore, this study sheds light on the potential role of zolmitriptan (ZOLM), an antimigraine medication, in modulating NO levels in the brain of rats with nitroglycerin-induced migraine, emphasizing its significant impact on reducing NO levels. The obtained results could have significant implications for understanding how ZOLM affects NO levels and may aid in the development of more targeted and effective migraine treatment strategies.

QuEChERS-assisted ion pair chromatography/fluorescence detection method for determination of antimigraine combination therapy in rabbit plasma samples: Application to a pharmacokinetic study.

Antimigraine combination therapy has shown significant effectiveness in relieving pain, as well as reducing the frequency, duration, and severity of migraine attacks if compared to a single migraine medication. This work represents the first analytical investigation for emphasizing the synergistic effect of combining ophthalmic beta blockers with triptans in migraine treatment. The presented study was conducted to investigate the pharmacokinetic profile of almotriptan (ALM), a serotonin (5-HT1B/1D) receptor agonist used to treat migraine, when coadministered with timolol (TIM) or verapamil (VER) which are considered as an adjuvant therapy in migraine prevention. Ion pair chromatography (IPC) with online fluorescence detection was applied to simultaneously detect and quantify the binary mixtures of ALM/TIM and ALM/VER in rabbit plasma samples. The separation was achieved using a Platinum C18 analytical column with a mobile phase composed of methanol: 35 mmol L-1 phosphate buffer solution containing 10 mmol L-1 SDS at pH = 6.8 (60:40 v/v). Several parameters were evaluated during the optimization of separation conditions including mobile phase composition, buffer concentration, buffer pH and concentration of ion pair reagent. A thorough investigation of the retention mechanism was performed, and the results showed that Coulomb forces were the main contributors to the overall retention mechanism, which may be hydrophobically assisted. QuEChERS extraction technique was utilized to extract the investigated drugs from plasma samples and a detailed study was carried out to optimize partition/extraction solvents, pH, extraction salts, sample volume and clean-up step. The method had a limit of detection and quantitation of 5.6 and 16.9 ng mL-1 for ALM in ALM/TIM mixture and 2.5 and 7.6 ng mL-1 for ALM in ALM/VER mixture, with an overall recovery not less than 95.22%. This newly proposed method offers a faster alternative to existing chromatographic methods for extraction and determination of ALM in binary mixtures with TIM or VER in rabbit plasma and provides a platform for studying pharmacokinetic parameters. The coadministration of either TIM or VER with ALM resulted in a notable rise in Cmax (maximum plasma concentration) and AUC (area under the plasma concentration-time curve) of ALM, implying possible alterations in the absorption and overall exposure of ALM.

A Comprehensive Review on Analytical Techniques for Determination of Sex Stimulants, PDE5 Inhibitors in Different Matrices with Special Focus on the Electroanalytical Methods.

Erectile dysfunction (ED) is one of the most common chronic diseases affecting men and its incidence increases with aging. Due to its substantial influence on the quality of life, phosphodiesterase type-5 (PDE5) inhibitors have been implemented to treat ED by increasing the penile blood flow that results in improving erection. PDE5 inhibitors is a class of drugs that affects many pharmacological sectors, and it is essential to review the different analytical methods described for their determination. Few reviews were published concerning this group of drugs. For this reason, this review article gathers the different analytical methods used to determine PDE5 inhibitors in pharmaceutical and biological samples over the past 20 years. Different analytical techniques were used to analyze these compounds in different matrices such as separation methods (capillary electrophoresis, LC-MS, UPLC-MS/MS, and GC-MS), spectroscopic methods (UV-visible methods, FT-IR spectroscopy and spectrofluorometry) and electrochemical methods (polarography, voltammetry and potentiometry). This review focuses on the different electrochemical methods and their use in analytical determination of PDE5 inhibitors in pharmaceutical dosage forms and biological samples. Moreover, it discusses the different modified electrodes used for their electroanalytical determination and the behavior of the studied drugs at different modified electrodes. Additionally, this review discusses the pharmacokinetics of the studied compounds and their interactions with other co-administered drugs especially the metabolic interactions between the studied compounds and other co-administered drugs in different matrices. This literature survey would provide a beneficial guide for future analytical investigation of PDE5 inhibitors.

Cytochrome P450 3A4-mediated pharmacokinetic interaction study between tadalafil and canagliflozin using high-performance thin-layer chromatography.

Diabetes is a known risk factor for sexual dysfunction in men; diabetic men have an increased risk of erectile dysfunction compared to non-diabetic men. Canagliflozin is one of the common antidiabetic drugs that is readily used in the treatment of type-2 diabetes. Concomitantly phosphodiesterase 5 inhibitors, such as tadalafil, can be given to the patient to alleviate erectile dysfunction. Canagliflozin is reported to be one of the cytochrome P450 3A4 enzyme inhibitors, that might seriously influence blood concentration levels of tadalafil but there is no study till now, discussing this interaction. Therefore, a fast, simple, and sensitive high-performance thin-layer chromatographic method was developed, validated, and applied for the simultaneous determination of tadalafil and canagliflozin in spiked and real human plasma. The limit of detection for tadalafil was 0.14 ng/band and for canagliflozin was 0.16 ng/band. The limit of quantitation value for tadalafil was 0.43 ng/band and for canagliflozin was 0.47 ng/band. Tadalafil and canagliflozin were determined simultaneously in real human plasma using the described procedure and the method was applied for in vivo pharmacokinetic drug interaction study between the studied drugs, which proved significant interaction between them when administered simultaneously.

Biocompatible magnetite nanoparticles coated with ionic liquid-based surfactantas a hydrophilic sorbent for dispersive solid phase microextraction of cephalosporins prior to their quantitation by HPTLC.

Extraction of highly hydrophilic compounds from biological fluids including urine or plasma samples is a dilemma due to high hydrophilicity of the matrix itself. The main aim of the current work is to explore the competence of ionic liquid (IL)-based surfactant-coated mineral oxide nanoparticles (NPs) in dispersive solid-phase microextraction (d-SPME) of highly hydrophilic analytes taking cefoperazone (CPZ) as a model analyte for the study. The IL-based surfactant coated Fe3O4 NPs is utilized as an innovative adsorbent for the separation and pre-concentration of CPZ after intramuscular injection (I.M) in rabbits. The utilized magnetite NPs were synthesized via simple and reliable co-precipitation procedure, which doesn't require any air-free environment and depends on a single iron (III) salt. Characterization of the as-synthesized NPs was achieved by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) and energy dispersive X-ray (EDX). Surface area measurements show that Fe3O4 NPs have large surface area of 75 m2 g-1. The developed approach utilizes the unique properties of the IL-based surfactant including multiple polar interaction types provided by the polar head in addition to merits of Fe3O4 nanoparticles, which include large adsorptive capacity and magnetic properties, to improve separation, save time, and achieve satisfactory recovery. Comprehensive study was developed for the factors, that affect the adsorption capacity such as pH, NPs amount, IL-based surfactant concentration, ionic strength, adsorption time, and desorption conditions. Moreover, the adsorption data was fitted to Langmuir and second-order kinetic models as reflected by the reasonable determination coefficients of 0.9319 and 0.9726, respectively. Under the optimized conditions, the developed approach achieves good correlation coefficient of 0.9975, and 0.9981 over linearity range of 0.7-12.0 and 4.0-50.0 µg mL-1 for both CPZ standard solutions and spiked rabbit plasma, respectively. It also provides good sensitivity expressed by the low values of limit of detection (LOD) of 0.2 and 1.2 µg mL-1 and limit of quantitation (LOQ) of 0.7 and 4.0 µg mL-1 for both the standard solutions and spiked plasma, respectively. The developed approach was also applied successfully for monitoring CPZ in rabbit plasma samples with satisfactory recovery % (83-110). In addition, a detailed pharmacokinetic study is performed where pharmacokinetic parameters of CPZ in rabbit plasma samples were calculated.

Vortex-assisted dispersive solid phase microextraction using Fe3O4/FeOOH magnetic nanocomposites for high-performance thin-layer chromatographic determination of zolmitriptan in rabbit plasma samples.

In this work, a fast, versatile, and convenient dispersive solid-phase micro-extraction (DSPME) method is combined with a spectro-densitometric technique for the analysis of zolmitriptan (ZOLM) in biological fluids. Fe3O4/FeOOH magnetic nanocomposites (MNCs) were prepared by a co-precipitation method in aqueous solutions and utilized subsequently as a sorbent in DSPME. By coupling DSPME with high-performance thin-layer chromatography (HPTLC) with fluorescence detection, the preconcentration and determination of (ZOLM) in presence of metoclopramide (MET) and paracetamol (PARA), which are prescribed as an adjuvant therapy with ZOLM, was accomplished. Adsorption capability was assessed using both Langmuir and Freundlich adsorption isotherm models. The adsorption data was fitted to Langmuir adsorption isotherm model as reflected by high determination coefficient (R2 = 0.9944). Moreover, adsorption kinetics was assessed by pseudo-first and pseudo-second order kinetic models. The data was fitted to pseudo-second order kinetics, which proves that ZOLM interaction with the adsorbent is a chemisorption process. Surface complexation with MNCs was suggested to explain the pH dependence of ZOLM sorption. The key parameters of extraction and desorption steps (including pH, extraction time, sample volume, magnetic adsorbent amount, and desorption circumstances) were evaluated. Optimized conditions for solid phase microextraction of ZOLM were pH 2.9, 5.0 mg Fe3O4/FeOOH MNCs, 15 min vortex-assisted extraction time and 3 × 200 µL of methanol: 33% ammonia; 4:1 as eluent. The analysis was achieved using ACN: dichloromethane: 33% ammonia (22.5: 6.0: 1.5, v/v/v) as a mobile phase and the fluorescence detection was carried out at 223 nm. The proposed DSPME method was successfully applied for trace quantification of ZOLM in rabbits' plasma (n = 6) after oral administration with a linearity range of 50.0 - 400.0 ng mL-1 (R2 = 0.9931), a detection limit of 12.0 ng mL-1 and extraction recovery of 97.27-99.89% with an RSD < 2% (n = 9). Moreover, the selectivity of the proposed approach for analysis of ZOLM in the presence of MET and PARA is demonstrated.

Optimization of a sensitive and robust strategy for micellar electrokinetic chromatographic analysis of sofosbuvir in combination with its co-formulated hepatitis C antiviral drugs.

Based on our previous work with "pseudostationary-ion exchanger sweeping", we use this strategy to develop a sensitive, reliable and robust method for the analysis of the newly-FDA approved hepatitis C antiviral drugs namely; sofosbuvir (SOV), daclatasvir (DAC), ledipasvir (LED) and velpatasvir (VEP) in their pure forms and co-formulated pharmaceutical dosage forms using micellar electrokinetic chromatography (MEKC) as a separation method. For the first time, a successful separation of all the investigated compounds was achieved in less than 8 min using a basic background electrolyte (BGE) composed of 25 mmol L-1 SDS + 20% (v/v) ACN (acetonitrile) in 10 mmol L-1 disodium tetraborate buffer (final apparent pH is 9.90). A special focus was given to optimize the composition of the sample matrix to maintain the solubility of the analytes within the sample zone while gaining additional benefits regarding analyte zone focusing. It was found that replacing phosphoric acid (as a sample matrix) with a zwitterionic/isoelectric buffering compound (L-glutamic acid) has a substantial positive impact on the obtained enrichment efficiency. The interplay of other enrichment principles such as the retention factor gradient effect (RFGE) is also discussed. A full validation study is performed based on the pharmacopeial and ICH guidelines. The obtained limits of detection and quantitation are as low as 0.63 and 1.3 µg mL-1; respectively for SOV and DAC and 1.3 and 2.5 µg mL-1; respectively for LED and VEP using UV-DAD as a detection method. The selectivity of the developed method for determination of the studied compounds in their pharmaceutical dosage forms or in the presence of ribavirin (RIB) or elbasvir (ELB), which are other prescribed medications in the treatment regimen of patients with hepatitis C virus infection, is demonstrated. It is shown that with acidic sample matrix and basic BGE, an efficient and precise approach was designed in which analyte adsorption on the capillary wall was minimized while keeping repeatable peak height, peak area and migration time together with the highest possible enrichment efficiency.

Assessment of lipophilicity of newly synthesized celecoxib analogues using reversed-phase HPLC.

BACKGROUND: Lipophilicity is a physicochemical property of an essential importance in medicinal chemistry; therefore, fast and reliable measurement of lipophilicity will affect greatly the drug discovery process. RESULTS: A series of N-benzenesulfonamide-1H-pyrazoles, oximes and hydrazones as celecoxib analogues was investigated with regard to their retention behavior using reversed-phase high performance liquid chromatography (RP-HPLC). The mobile phases employed for this study consist of a mixture of water and methanol in different proportions. In addition, the stationary phase utilized for this separation was C18 silanized silica gel and using 200 nm as a detection wavelength. The retention behavior of the investigated compounds was determined based on practical determination of log k at different concentrations of methanol (as an organic modifier) in the mobile phase ranging from 60 to 80%. It was observed that the retention of these compounds (expressed as log k) decreased in a linear manner with increasing the concentration of methanol. High correlation coefficients (more than 0.90 in most cases) were obtained for the relationship between the volume fraction of the organic solvent and the retention values represented as log k w. A comparative evaluation was carried out between chromatographically-obtained lipophilicity parameters (represented as lipophilicity chromatographic index log k w or isocratic chromatographic hydrophobicity index, φ 0) and the computationally calculated log P values (miLogP, ALOGP, ACD/Labs and ALOGPs). CONCLUSION: It was found that a good correlation exists between the experimental and computed log P values. In the future, these results can give a deep insight about the anti-inflammatory and analgesic activity of the newly synthesized compounds.

Novel sublingual tablets of Atorvastatin calcium/Trimetazidine hydrochloride combination; HPTLC quantification, in vitro formulation and characterization.

BACKGROUND: Ischemic heart disorders and accumulation of lipids in blood vessels could contribute to angina pectoris. Therefore, the aim of this study was to formulate sublingual tablets containing a novel combination of Atorvastatin calcium (ATOR) and Trimetazidine HCl (TMZ) for efficient treatment of coronary heart disorders. METHODS: The dissolution rate of water-insoluble ATOR was enhanced via complexation with sulfobutyl ether-ß-cyclodextrin (SBE-ß-CD) and addition of soluplus as a polymeric solubilizer excipient. The solubilized ATOR and TMZ were compressed into a sublingual tablets by direct compression technique and evaluated for their tableting characteristics. In addition, a new validated method based on High Performance Thin Layer Chromatography (HPTLC) was developed for simultaneous determination of both drugs in pure forms and sublingual tablets. RESULTS: The developed HPTLC method showed LODs of 0.056 and 0.013 µg/band and LOQs of 0.17, 0.040 µg/band for TMZ and ATOR, respectively and proved to be linear, accurate, precise and robust. The optimum formulation containing mixture of superdisintegrants; Ac-Di-Sol and crospovidone (4.8% w/w, each) showed the shortest disintegration time (65 s) and enhanced release profiles of both drugs. CONCLUSIONS: The prepared sublingual tablets combining ATOR and TMZ will be a promising dosage form for coronary heart disease patients with an instant action and improved patient compliance.

Highly sensitive UHPLC-DAD method for simultaneous determination of two synergistically acting antiepileptic drugs; levetiracetam and lacosamide: Application to pharmaceutical tablets and human urine.

A simple and highly sensitive ultra-high-performance liquid chromatographic-diode array (UHPLC-DAD) detection method was developed and validated for the simultaneous estimation of levetiracetam (LEV) and lacosamide (LAC). It was clinically proven that the combination of LEV and LAC exhibits a synergistic effect against refractory seizures in mice, which was the motivation for the analysis of this binary mixture both in bulk and in human urine samples. The binary mixture was resolved on a Hypersil BDS C18 analytical column, utilizing a mobile phase of 0.050 mol L-1 phosphate buffer (pH 5.60), methanol and acetonitrile in the ratio (80:10:10 v/v/v) using catechol as an internal standard. The mobile phase was pumped at a flow rate of 1.2 mL min-1 with diode array detection at 205 nm for both drugs and 270 nm for IS. Calibration curves were linear with correlation coefficient >0.9990 over the studied concentration range of 0.1-70.0 µg mL-1 for both drugs. The developed method was reproducible with low relative standard deviation values for intra- and inter-day precision (<2.0%). Both drugs were determined in bulk, pharmaceutical formulations and human urine samples without any interference from complex matrices.

Selectivity enhanced cation exchange chromatography for simultaneous determination of peptide variants.

If strong cation exchange chromatography (SCX) is combined with ion-pair chromatography, then the solute could be retained selectively with the power of mixed separation modes. This combination is termed selectivity enhanced strong cation exchange chromatography (SE-SCX). Macroporous polystyrene-divinylbenzene (PS/DVB) resin with sulfonate coating that conveys ion exchange and reversed phase characteristics was employed. Sodium dodecyl sulfate (SDS) was utilized as a selectivity modifier and an ion-pair reagent. This separation strategy is exploited for a challenging simultaneous separation of peptide variants having similar isoelectric points (pIs) and comparable retention behaviour. Insulin variants were used as a model in this study. The selective separation of insulin and five structurally-related analogues namely; ASPART, LISPRO, GLULISIN, GLARGIN, and DETEMIR was conducted using gradient elution mode. Three eluents were used for the separation of the target compounds. Eluent A was a mixture of acetonitrile and 10 mmol L-1 SDSat ratio (1:1) and was kept at 20% through the run. Eluent B was 20 mmol L-1 KH2PO4 adjusted at pH = 4.0 and eluent C was eluent B plus 1 mol L-1 NaCl that was increased linearly till 80% at 20 min. It was found that the retention of the tested variants can be modeled mainly by electrostatic interaction that might be hydrophobically-assisted. The developed method was validated in accordance with ICH guidelines and was appropriate for the intended purposes. Finally, this study introduces SE-SCX as a new selective separation strategy for peptides and proteins that may open the door for novel mixed mode perspectives in protein analysis.

Hydrophilic-interaction planar chromatography in ultra-sensitive determination of α-aminocephalosporin antibiotics. Application to analysis of cefalexin in goat milk samples using modified QuEChERS extraction technique.

A highly sensitive, selective and precise HPTLC method coupled with fluorescence detection was developed and validated for the determination of α-aminocephalosporin antibiotics; namely cefalexin, cefadroxil and cefradine in their standard solutions. The applicability of the developed methodology was demonstrated via analysis of cefalexin in goat milk samples. Full optimization of the fluorescence derivatization reaction was carried out with regard to the standard solutions of the studied compounds or after extraction of milk samples. The separation of the studied compounds was performed on HPTLC precoated silica gel plates 60 F254 using acetonitrile: water in a ratio 85:15 (v/v) as a mobile phase. The retention behavior of the formed derivatives was discussed in detail. It was found that hydrophilic interaction mode is the main interaction mechanism governing the retention of the formed derivatives. In addition, an experimental design approach was conducted for optimization of the chromatographic conditions. Modified QuEChERS was applied as an efficient extraction technique of cefalexin from both spiked and real goat milk samples. Optimization of QuEChERS extraction technique to achieve the highest extraction recovery was performed and the results indicate that this method provides a good extraction recovery (83-116%) for cefalexin from goat milk samples. Limit of detection (LOD) of the developed method was found to be 0.023, 0.005, and 0.023 ng band-1 for cefalexin, cefadroxil and cefradine, respectively in their standard solutions and 0.165 ng band-1 for cefalexin in goat milk samples. According to the achieved LOD values, the method sensitivity was quasi-equivalent to other methods based on expensive techniques such as HPLC-UV and HPLC-MS and it is sufficient to determine cefalexin below its MRL in milk samples. Moreover, the method was successfully applied to a pharmacokinetic study of cefalexin in goat milk after single intramuscular injection of 10 mg of cefalexin kg-1 per body weight.

Micelle and inclusion complex enhanced spectrofluorimetric methods for determination of Retigabine: Application in pharmaceutical and biological analysis.

Two new, simple, selective, and highly sensitive spectrofluorimetric methods were developed and validated for the determination of the antiepileptic drug; retigabine (RTG). The first method (Method-I) depends on enhancement of the weak native fluorescence of RTG via the use of an organized medium; sodium dodecyl sulphate (SDS) in acetate buffer (pH 3.74). The second method (Method-II) depends on the enhancement of RTG weak native fluorescence through complexation with a macromolecule; beta cyclodextrin (ß-CD) in phosphate buffer (pH 3.20). A full study of different experimental parameters influencing the fluorescence intensity was carried out. In addition, a thorough investigation of the fluorescence quantum yield, fluorophore brightness and mechanism of fluorescence enhancement was performed. A seven-fold improvement in the fluorescence intensity was brought by the first method, whereas a six and half-fold enhancement of the fluorescence intensity was obtained by the second one. Linearity was achieved over wide ranges (0.05-12.5 µg mL-1) and (0.05-15 µg mL-1) with low limits of detection (LOD) of 10.6 and 14.3 ng mL-1, and limits of quantification (LOQ) of 32.0 and 43.2 ng mL-1 for (Method-I) and (Method-II), respectively. The proposed methods were validated according to ICH and US-FDA guidelines. The applicability of the proposed methods was tested for determination of RTG in its pharmaceutical dosage forms, and to study the stability of RTG under different stress conditions according to ICH guidelines including alkaline, acidic, oxidative, thermal, and photolytic stress conditions. Moreover, the high sensitivity achieved by the proposed methods permitted the determination and detection of RTG in both spiked and real rabbit plasma samples utilizing a simple protein precipitation step followed by liquid-liquid extraction method. Percentage recoveries from rabbit plasma samples were within the acceptable limits; (93.47-104.74%) and (91.33-105.70%) for (Method-I) and (Method-II), respectively.

ε-MnO2-modified graphite electrode as a novel electrochemical sensor for the ultrasensitive detection of the newly FDA approved Hepatitis C antiviral drug ledipasvir.

A novel, simple and sensitive electrochemical method for the determination of ledipasvir (LED), the newly FDA approved Hepatitis C antiviral drug was developed and validated using ε-MnO2-modified graphite electrode. Two different MnO2 polymorphs (γ- and ε-MnO2 nanoparticles) were synthesized and characterized using X-ray powder diffraction (XRD), Fourier transform infrared (FTIR), energy dispersive X-ray (EDX) and thermogravimetric analysis (TGA). Surface area measurements show that ε-MnO2 NPs have large surface area of 345 m2/g, which is extremely high if compared to that of γ-MnO2 NPs (38 m2/g). In addition, a comprehensive study of the difference in the electrochemical behavior of LED while using pencil graphite electrode (PGE) modified with either γ- or ε-MnO2 NPs is carried out. It was found that surface area and percentage of surface hydroxyls of MnO2 NPs are the key factors governing the sensitivity of the fabricated electrode toward the oxidation of the positively charged LED. Scanning electron microscopy (SEM) was employed to investigate the morphological shape of MnO2 NPs and the surface of the bare and modified electrodes. Moreover, cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were used for the surface analysis of the modified electrodes. Based on the obtained results, ε-MnO2/PGE was applied as a selective and sensitive electrode for determination of LED. Under the optimized experimental conditions, ε-MnO2/PGE provides a linear response over the concentration range of 0.025-3.60 µmol L-1 LED with a low limit of detection, which was found to be 5.10 nmol L-1 (4.50 ng mL-1) for the 1st peak and 9.20 nmol L-1 (8.10 ng mL-1) for the 2nd one. In addition, the oxidation behavior of LED is discussed with a full investigation of the oxidized product using FT-IR and LC/MS. The fabricated sensor exhibits a good precision, selectivity and stability and was applied successfully for the determination of LED in its tablets and real rat plasma samples with a good recovery using a simple extraction technique.

Application of salting-out thin layer chromatography in computational prediction of minimum inhibitory concentration and blood-brain barrier penetration of some selected fluoroquinolones.

The 2017 FDA safety review regarding the CNS (central nervous system) side effects associated with the systemic use of fluoroquinolones antibacterials (FQs) was the key motivation to carry out this work. The main objective of this study is to investigate lipophilicity and retention parameters of some selected fluoroquinolones antibacterials (FQs) namely; levofloxacin (LEV), ofloxacin (OFL), gatifloxacin (GAT), norfloxacin (NOR), sparfloxacin (SPA), ciprofloxacin (CIP) and lomefloxacin (LOM) using salting-out thin layer chromatography (SOTLC). Statistically significant correlations between the chromatographically-obtained retention parameters and experimental log P values were found and expressed as quantitative structure retention relationship (QSRR) equations. Principal component analysis was carried out to explain the variation between chromatographic and both experimental and computed lipophilicity parameters. In another aspect of this study, a comparison between the chromatographically-determined retention parameters (for five of the drugs under study) obtained using SOTLC (current study) and relative lipophilicity (RM0) determined using a previously reported RP (reversed-phase)-TLC method was carried out. Statistically significant correlation between the two methods was found, although RM0 values obtained using SOTLC was lower than those reported using RP-TLC. Multiple linear regression analysis was performed to predict MIC (minimum inhibitory concentration) and blood brain barrier (BBB) penetration of the examined drugs in which efficient QSAR (quantitative structure-activity relationship) and QSPR (quantitative structure-property relationship) models were generated using the calculated chromatographic parameters (RM0 and C0). The described models can provide a useful approach to predict MIC and BBB penetration of newly synthesized FQs targeting to increase their activity against Gram-positive organisms and to minimize the associated CNS side effects.

Fabrication of novel electrochemical sensors based on modification with different polymorphs of MnO2 nanoparticles. Application to furosemide analysis in pharmaceutical and urine samples.

A novel MnO2 nanoparticles/chitosan-modified pencil graphite electrode (MnO2 NPs/CS/PGE) was constructed using two different MnO2 polymorphs (γ-MnO2 and ε-MnO2 nanoparticles). X-ray single phases of these two polymorphs were obtained by the comproportionation reaction between MnCl2 and KMnO4 (molar ratio of 5 : 1). The temperature of this reaction is the key factor governing the formation of the two polymorphs. Their structures were confirmed by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) and energy dispersive X-ray (EDX) analysis. Scanning electron microscopy (SEM) was employed to investigate the morphological shape of MnO2 NPs and the surface of the bare and modified electrodes. Moreover, cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were used for surface analysis of the modified electrodes. Compared to bare PGE, MnO2 NPs/CS/PGE shows higher effective surface area and excellent electrocatalytic activity towards the oxidation of the standard K3[Fe(CN)6]. The influence of different suspending solvents on the electrocatalytic activity of MnO2 was studied in detail. It was found that tetrahydrofuran (THF) is the optimum suspending solvent regarding the peak current signal and electrode kinetics. The results reveal that the modified γ-MnO2/CS/PGE is the most sensitive one compared to the other modified electrodes under investigation. The modified γ-MnO2/CS/PGE was applied for selective and sensitive determination of FUR. Under the optimized experimental conditions, γ-MnO2/CS/PGE provides a linear response over the concentration range of 0.05 to 4.20 µmol L-1 FUR with a low limit of detection, which was found to be 4.44 nmol L-1 (1.47 ng mL-1) for the 1st peak and 3.88 nmol L-1 (1.28 ng mL-1) for the 2nd one. The fabricated sensor exhibits a good reproducibility and selectivity and was applied successfully for the determination of FUR in its dosage forms and in spiked urine samples with good accuracy and precision.

Lipophilicity estimation of statins as a decisive physicochemical parameter for their hepato-selectivity using reversed-phase thin layer chromatography.

Lipophilicity plays a crucial role in determining the hepato-selectivity and hence, the biological activity and the associated side effects of statins. Herein, the employment of RP-TLC for estimation of lipophilicity of six statins namely; atorvastatin, simvastatin, pravastatin, lovastatin, rosuvastatin and fluvastatin is examined. A very good correlation between the chromatographically-determined retention parameters (relative lipophilicity (RM0) or lipophilic parameter (C0)) and both experimental and computed log P values were obtained. However, the results indicate that the type of organic modifier in the mobile phase system (methanol, acetonitrile and acetone) has a small influence on RM0 or C0 values. Higher values of RM0 or C0 are ascribed to lipophilic statins and lower values of RM0 or C0 are attributed to hydrophilic ones. Therefore, RM0 or C0 could be effectively used as simple practical predictors of extra-hepatic distributions of statins and thus their expected side effects. Furthermore, three QSPR (quantitative structure-property relationship) models were constructed to describe the relationship between RM0 with log P and log D of the statins under investigation. These models can be very useful to predict the lipophilicity of other members of statin drugs and might be expanded to newly synthesized compounds with the same structural features.

Boronate affinity-assisted MEKC separation of highly hydrophilic urinary nucleosides using imidazolium-based ionic liquid type surfactant as pseudostationary phase.

In this work, we extend our investigations regarding the separation of urinary nucleosides by MEKC with the ionic liquid type surfactant 1-tetradecyl-3-methylimidazolium bromide (C14MImBr). We study the impact of adding alkyl- and arylboronic acids (in the presence of C14MImBr micelles) to the separation of these highly hydrophilic metabolites and investigate the mechanism of interaction between the negatively charged nucleosides (the negative charge is acquired either due to deprotonation of the amidic group and/or complexation with boronate) and the positively charged pseudostationary phase. This interaction is not only due to electrostatic (Coulombic) forces, but also due to hydrophobic interaction of the alkyl or aryl group of the boronate that forms a complex with the cis-diol group of the nucleoside. In this case, alkylboronates can act as a cosurfactant that increases the partitioning coefficient of the analytes into the micelles. In the presence of an alkylboronate in the BGE (employing only 20 mmol/L C14MImBr), the retention factors of the studied analytes are increased considerably when compared to a BGE without this additive. It is shown that the concept of one-site hydrophobically assisted ion exchange can be applied to describe the observed retention behavior. The high selectivity of boronates toward cis-diol-containing compounds can be used to adjust selectively the migration behavior of members of this compound class. By adding alkylboronic acid to the BGE, the separation selectivity is fine-tuned so that interferences from matrix components can be avoided in real sample analysis.

Determination of urinary nucleosides via borate complexation capillary electrophoresis combined with dynamic pH junction-sweeping-large volume sample stacking as three sequential steps for their on-line enrichment.

The combination of dynamic pH junction, sweeping (using borate complexation), and large volume sample stacking (LVSS) is investigated as three consecutive steps for on-line focusing in the sensitive quantitation of urinary nucleosides by CE-UVD. A low conductivity aqueous sample matrix free from borate and a high conductivity BGE (containing borate, pH 9.25) are needed to fulfill the required conditions for dynamic pH junction, LVSS, and sweeping. Parameters affecting the separation and the enrichment efficiency are studied such as buffer concentration, separation voltage, capillary temperature, sample composition, and sample injection volume. Prerequisite for the developed strategy is the extraction of the nucleosides from urine using a phenylboronate affinity gel, which is described to be a unique means for the selective enrichment of cis-diol metabolites under alkaline conditions. The impact of ionic constituents remaining in the eluate after extraction on focusing efficiency and resolution is investigated. The developed method is applied to the analysis of blank and spiked urine samples. Fundamental aspects underlying the proposed enrichment procedure are discussed. A detection limit as low as 10 ng mL(-1) is achieved. To the best of our knowledge, this LOD represents the lowest LOD reported so far for the analysis of nucleosides using CE with UV detection and provides a comparable sensitivity to CE/MS. Because of the high sensitivity, the proposed method shows a great potential for the analysis of nucleosides in human urine and other types of biological fluids.