Quantitative determination of saquinavir from Caco-2 cell monolayers by HPLC-UV. High performance liquid chromatography

The validation and quantitative determination of the protease inhibitor, saquinavir, from confluent Caco-2 monolayers and from aqueous solution is reported. The high performance liquid chromatographic method consisted of an Ultramex 5 C(8) reverse-phase column (250 x 4.6 mm i.d.) and a mobile phase of acetonitrile:water:triethylamine (55:44:1, v/v/v, pH 6.5). Samples were analyzed using an ultraviolet detector at 238 nm, and diltiazem hydrochloride (66 micro g/mL) was used as an internal standard. A linear response over a broad concentration range (0.4-8.0 micro g/mL, r(2) = 0.997) was obtained. The limit of detection and quantitation was set at 0.14 and 0.4 micro g/mL, respectively. Over a 4 day period, the intra-day and inter-day precision ranged from 1 to 7% with a mean of 4%, and from 1 to 2% with a mean of 1.5%, respectively. Bench-top and storage stability of saquinavir was found to be satisfactory. The permeability of saquinavir through Caco-2 monolayers was estimated using this assay.     

Optical solitons to the fractional perturbed Radhakrishnan–Kundu–Lakshmanan model

This study reaches the dark, bright, mixed dark-bright, singular, mixed singular optical solitons and singular periodic wave solutions to the time-fractional Radhakrishnan–Kundu–Lakshmanan equation. The parametric conditions that guarantee the existence of valid solitons and other solutions are stated. By choosing some suitable values of parameters, the 2- and 3-dimensional surfaces to some of the reported solutions are plotted. The reported solutions may be useful in expalining the physical meaning of the Radhakrishnan–Kundu–Lakshmanan equation and other related nonlinear models arising in nonlinear sciences.     

Synthesis and Antibacterial and Antifungal Properties of Novel S-, N-, N,S-, and S,O-Substituted 1,4-Naphthoquinone Derivatives

Abstract

A novel series of substituted 1,4-naphthoquinone derivatives were synthesized and evaluated for their antibacterial and antifungal activity. The structures of the novel products were characterized by spectroscopic methods. Among the tested compounds, 2,2′,3,3′-alkoxy substituted naphthoquinones, S,O-substituted naphthoquinone, and N,S-substituted naphthoquinone derivatives are the most potent antifungals against C. tenuis. 2,3-Thio-2′,3′-alkoxy substituted naphthoquinones are the most effective antifungal compounds against A. niger.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

A Novel RP-LC Method for Determination of pK a Values of Some Anticancer Agents and Their Assay

A simple, reliable, and rapid RP-LC method has been developed for the determination of some anticancer drugs (daunorubicin, doxorubicin and vincristine sulfate) in their dosage forms and human urine. These compounds are well separated on a C18 column using the mobile phase consisting of a mixture of acetonitrile (50:50; v/v) at a flow rate of 1.5 mL min⁻¹. The analyte peaks were detected at 235 nm for doxorubicin and daunorubicin, and 220 nm for vincristine. Linearity was obtained in different concentration ranges between 0.10 and 12 μg mL⁻¹ for all compounds. Good sensitivity for all analytes was observed with DAD detection. LOD and LOQ of the method were found satisfying. The proposed method has been extensively validated in accordance with ICH guidelines and obtained results proved that the proposed method was precise, accurate, selective, and sensitive for simultaneous analysis of studied compounds. All analytical procedures including sample preparation, flow rate, and run time were at low levels. Also, pK _a values were determined using the dependence of the retention factor on the pH of the mobile phase. The effect of the mobile phase composition on the ionization constant was studied by measuring the pK _a at different methanol–water mixtures, ranging between 45 and 60 % (v/v).

     

A Novel RP-LC Method for Determination of pK a Values of Some Anticancer Agents and Their Assay

A simple, reliable, and rapid RP-LC method has been developed for the determination of some anticancer drugs (daunorubicin, doxorubicin and vincristine sulfate) in their dosage forms and human urine. These compounds are well separated on a C18 column using the mobile phase consisting of a mixture of acetonitrile (50:50; v/v) at a flow rate of 1.5 mL min^?1. The analyte peaks were detected at 235 nm for doxorubicin and daunorubicin, and 220 nm for vincristine. Linearity was obtained in different concentration ranges between 0.10 and 12 μg mL^?1 for all compounds. Good sensitivity for all analytes was observed with DAD detection. LOD and LOQ of the method were found satisfying. The proposed method has been extensively validated in accordance with ICH guidelines and obtained results proved that the proposed method was precise, accurate, selective, and sensitive for simultaneous analysis of studied compounds. All analytical procedures including sample preparation, flow rate, and run time were at low levels. Also, pK _a values were determined using the dependence of the retention factor on the pH of the mobile phase. The effect of the mobile phase composition on the ionization constant was studied by measuring the pK _a at different methanol–water mixtures, ranging between 45 and 60 % (v/v).     

A Sensitive and Selective RP-LC Method for the Simultaneous Determination of the Antihypertensive Drugs, Enalapril, Lercanidipine, Nitrendipine and Their Validation

A RP-LC method is presented, which is sensitive and selective for the simultaneous determination of enalapril–lercanidipine and enalapril–nitrendipine binary mixtures in their pharmaceutical dosage forms. The analyte peaks were detected using the LC method with the mobile phase ratio of methanol: water (70:30 v/v, pH 3.0) and a 1.0 mL min^?1 flow rate. The detection wavelength was selected at 210 nm using photo diode array detector and column temperature was optimized to 30 °C. Linearity was obtained at different concentration ranges for all working pharmaceutically active compounds between 0.5 and 25 μg mL^?1. The proposed methods were extensively validated according to USP 27 requirements and ICH guidelines. The methods were applied to the analysis of pharmaceutical dosage forms containing binary mixtures of enalapril–lercanidipine and enalapril–nitrendipine. Moreover, the proposed methods were applied for the degradation studies of the selected compounds. Degradation studies were conducted using stress conditions such as UV light, acidic and alkaline hydrolysis, oxidation and heat in oven, to evaluate the ability of the separation of the response of standard compounds from their degradation products.     

Preparation, characterization and thermal dehydration kinetics of titanate nanotubes

Titanate nanotubes were synthesized utilizing the hydrothermal method using titanium dioxide nanoparticles. The experiments were carried out considering the process as a function of reaction temperature, time, NaOH concentration and the acidity of the washing solution. The formation of titanate nanotubes was shown to be affected strongly by variations in any parameter. The optimum conditions for the synthesis of titanate nanotubes were determined to be a reaction temperature of 190 °C, and a reaction time of 12 h, using 10 M NaOH concentration and the washing solution to have a pH of 5.5. In addition, thermogravimetric analysis (TG/DTG) was used to investigate the thermal behaviour and dehydration kinetics of titanate nanotubes. In order to better understand their thermal behaviour, the thermal analysis of bulk hydrogen trititanate was performed. The values of the apparent activation energies of the first and second dehydration stages for titanate nanotubes were 81.44 ± 15.85 and 82.69 ± 7.46 kJ mol^?1, respectively. The values of the apparent activation energies of the first, second and third dehydration stages for bulk hydrogen trititanate were 115.93 ± 5.40, 137.58 ± 6.47 and 138.97 ± 8.47 kJ mol^?1, respectively.     

Spectrophotometric studies on the interactions of C.I. Basic Red 9 and C.I. Acid Blue 25 with hexadecyltrimethylammonium bromide in cationic surfactant micelles

Interactions between cationic dye-cationic surfactant and anionic dye-cationic surfactant systems were investigated in aqueous solutions using spectrophotometric method at 288.15, 298.15, 308.15 and 318.15 K. C.I. Basic Red 9 (BR9) and C.I. Acid Blue 25 (AB25) were used as cationic and anionic dyes, respectively, and hexadecyltrimethylammonium bromide (HDTMABr) was selected as cationic surfactant in this study. Although there was an interaction between the AB25 and the HDTMABr molecules, an interaction between the BR9 and HDTMABr did not occur due to the electrostatic repulsion forces. Binding constants and partition coefficients between the micellar and the bulk water phases for the AB25-HDTMABr system were calculated from the changes in absorbance values and the critical micelle concentrations at different temperatures. It was found that the values of binding constant and partition coefficient decreased with increasing temperature. Thermodynamic parameters (ΔG⁰, ΔH⁰ and ΔS⁰) were determined for the binding and partition processes of AB25-HDTMABr system. It was concluded from ΔG⁰ values that the binding of AB25 to HDTMABr occurred spontaneously. In addition, the binding and partition processes were exothermic.