Electrochemical oxidation behavior of hydrochlorothiazide on a glassy carbon electrode and its voltammetric determination in pharmaceutical formulations and biological fluids

The electrochemical oxidation behavior of hydrochlorothiazide (HCT) on a glassy carbon as a working electrode was investigated in Britton–Robinson (B–R) buffer pH 3, by using anodic stripping voltammetry (ASV) and cyclic voltammetry (CV). This drug gave a well-defined voltammetric oxidation peak at + 1200 mV versus an Ag/AgCl reference electrode. The electrochemical oxidation process was shown to be irreversible and diffusion controlled, with adsorption characterized over the entire pH range. The optimized conditions, such as accumulation time and potential, scan rate, frequency, pulse amplitude, varying of working electrodes, and instrumental parameters were studied. The calibration graph for HCT was obtained from 4 × 10⁻⁶ to 4 × 10⁻⁵ M (correlation coefficient = 0.997) using the developed electroanalytical method (ASV). The detection limit of this drug was 4.3 × 10⁻⁹ M. ASV and CV techniques with adequate precision and accuracy have been developed and applied for direct determination of HCT in commercial tablets without separation or extraction procedures and biological fluids such as urine and plasma.     

Application of novel Ni(II) complex and ZrO2 nanoparticle as mediators for electrocatalytic determination of N-acetylcysteine in drug samples

The electrooxidation of N-acetylcysteine (N-AC) was studied by a novel Ni(II) complex modified ZrO₂ nanoparticle carbon paste electrode [Ni(II)/ZrO₂/NPs/CPE] using voltammetric methods. The results showed that Ni(II)/ZrO₂/NPs/CPE had high electrocatalytic activity for the electrooxidation of N-AC in aqueous buffer solution (pH = 7.0). The electrocatalytic oxidation peak currents increase linearly with N-AC concentrations over the concentration ranges of 0.05–600μM using square wave voltammetric methods. The detection limit for N-AC was equal to 0.009μM. The catalytic reaction rate constant, k_h, was calculated (7.01 × 10² M⁻¹ s⁻¹) using the chronoamperometry method. Finally, Ni(II)/ZrO₂/NPs/CPE was also examined as an ultrasensitive electrochemical sensor for the determination of N-AC in real samples such as tablet and urine.     

Novel discovery of schisandrin A regulating the interplay of autophagy and apoptosis in oligoasthenospermia by targeting SCF/c-kit and TRPV1 via biosensors

Oligoasthenospermia is the primary cause of infertility. However, there are still enormous challenges in the screening of critical candidates and targets of oligoasthenospermia owing to its complex mechanism. In this study, stem cell factor (SCF), c-kit, and transient receptor potential vanilloid 1 (TRPV1) biosensors were successfully established and applied to studying apoptosis and autophagy mechanisms. Interestingly, the detection limit reached 2.787 × 10⁻¹⁵ g/L, and the quantitative limit reached 1.0 × 10⁻¹³ g/L. Furthermore, biosensors were used to investigate the interplay between autophagy and apoptosis. Schisandrin A is an excellent candidate to form a system with c-kit similar to SCF/c-kit with a detection constant (K_D) of 5.701 × 10⁻¹¹ mol/L, whereas it had no affinity for SCF. In addition, it also inhibited autophagy in oligoasthenospermia through antagonizing TRPV1 with a K_D of up to 4.181 × 10⁻¹⁰ mol/L. In addition, in vivo and in vitro experiments were highly consistent with the biosensor. In summary, high-potency schisandrin A and two potential targets were identified, through which schisandrin A could reverse the apoptosis caused by excessive autophagy during oligoasthenospermia. Our study provides promising insights into the discovery of effective compounds and potential targets via a well-established in vitro-in vivo strategy.     

Simultaneous determination of ranitidine and metronidazole in pharmaceutical formulations at poly(chromotrope 2B) modified activated glassy carbon electrodes

A simple and sensitive electrochemical method for the simultaneous and quantitative detection of ranitidine (RT) and metronidazole (MT) was developed, based on a poly(chromotrope 2B) modified activated glassy carbon electrode (PCHAGCE). The PCHAGCE showed excellent electrocatalytic activity toward the reduction of both RT and MT in 0.1 mol/L phosphate buffer solution (pH 6.0). The peak-to-peak separations for the simultaneous detection of RT and MT between the two reduction waves in cyclic voltammetry were increased significantly from ∼0.1 V at activated GCE, to ∼0.55 V at PCHAGCE. By differential pulse voltammetry techniques, the reduction peak currents of RT and MT were both linear over the range of 1.0 × 10⁻⁵–4.0 × 10⁻⁴ mol/L. The detection limits (S/N = 3) were 5.4 × 10⁻⁷ mol/L and 3.3 × 10⁻⁷ mol/L for RT and MT, respectively. The modified electrode was successfully applied to the determination of RT and MT in pharmaceutical preparations and human serum as real samples with stable and reliable recovery data.     

Determination of urea in milk based on N-bromosuccinimide–dichlorofluorescein postchemiluminescence method

A new postchemiluminescence (PCL) reaction was observed when urea was injected into the reaction mixture after the CL reaction of N-bromosuccinimide and dichlorofluorescein. A possible reaction mechanism was proposed based on the studies of the CL kinetic characteristics, CL spectra, fluorescence spectra, and other experiments. A new flow injection CL method for the determination of urea was established based on the PCL reaction. The relative standard deviation for the determination of urea was 1.3% (n = 11, c = 5.0 × 10⁻⁸ g/mL). The CL intensity responded linearly to the concentration of urea in the range 2.0 × 10⁻⁹–1.0 × 10⁻⁶ g/mL (r = 0.9992). The detection limit was 7 × 10⁻¹⁰ g/mL. The method had been applied to the determination of urea in milk with satisfactory results.     

三丁基磷酸酯化学修饰电极伏安法测定黄嘌呤

目的：用三丁基磷酸酯化学修饰电极伏安法研究痕量黄嘌呤的测定。方法：在pH 9.5的NH₄OH—NH₄Cl缓冲溶液中,黄嘌呤在该化学修饰电极上于0.50 V(vs.SCE)左右产生一灵敏的氧化峰。结果：化学修饰膜选择性优先富集黄嘌呤,峰电流与浓度2.63×10^-7～7.89×10^-4 mol.L^-1呈线性关系,检出限为6.57×10-8 mol.L^-1 。结论：本法适用于血清、人尿中痕量黄嘌呤的测定。     

Determination of terbutaline based on oxidation by voltammetry

A voltammetric study of the oxidation of terbutaline has been carried out at an activated glassy carbon electrode. The compound was oxidized irreversibly at high positive potential. The response was evaluated with respect to pH, scan rate, nature of the buffer and other variables. The peak current, at about 0.8 V (versus a saturated calomel electrode), was proportional to the terbutaline concentration in the range of 8×10⁻⁶–8×10⁻⁴ M in phosphate buffer pH 6.0. This method was applied, without any interferences from the excipients, to determine the drug in a tablet dosage form.     

Voltammetric determination of chlorogenic acid in pharmaceutical products using poly(aminosulfonic acid) modified glassy carbon electrode

In this work, a poly(aminosulfonic acid) modified glassy carbon electrode was fabricated and the electrochemical behavior of chlorogenic acid (CGA) was studied by cyclic voltammetry. Compared with a bare glassy carbon electrode, the modified electrode exhibits excellent catalytic effect on the electrochemical redox of CGA. Utilizing this catalytic effect, a sensitive and selective electrochemical method for the determination of CGA was developed. The analytical parameters were optimized. Under the optimized conditions, the oxidation peak current is linearly proportional to the concentration of CGA in the range from 4.00 × 10⁻⁷ to 1.20 × 10⁻⁵ mol/L and the detection limit is 4.00 × 10⁻⁸ mol/L. Further, the performance of the proposed method has been validated in terms of linearity (r = 0.9995), recovery (96.3–102.8%), reproducibility (RSD ＜ 4.0%, n = 6) and robustness. The developed method has been successfully applied for the determination of CGA in a variety of pharmaceutical products.     

碳糊电极阳极伏安法测定秋水仙碱

在0.05mol·L^-1H₂SO₄介质中,用碳糊电极(石墨粉:液体石蜡油=1.5∶1)阳极扫描伏安法测定秋水仙碱,检测限1×10^-7mol·L^-1,检测线性范围4.0×10^-7～1×10^-3mol·L^-1,氧化时出现两个氧化峰,峰电位分别为1.07V和1.33VvsSCE,峰电位随pH值升高而正移。对原料和片剂进行了测定,均获得满意的结果。     

Electrochemical behavior and determination of rutin on a pyridinium-based ionic liquid modified carbon paste electrode

In this paper the electrochemical behavior of rutin on a pyridinium-typed ionic liquid modified carbon paste electrode (IL-CPE) was investigated and further used for rutin sample determination. The IL-CPE showed strong electrocatalytic effects to the oxidation of rutin. In phosphate buffer solution (PBS, pH 2.5; 0.1 M) a pair of well-defined cyclic voltammetric redox peaks of rutin appeared with the redox peak located at 512 mV (Epa) and 448 mV (Epc) (vs. SCE), respectively. The redox peak current was increased about 27.5 times more than that on traditional carbon paste electrode (CPE). The electrochemical parameters of rutin on the IL-CPE were calculated with the results of the charge transfer coefficient (α), the number of electron transfer (n) and the electrode reaction rate constant (k_s) as 0.53, 1.80 and 2.39 s⁻¹, respectively. The cathodic peak currents increased linearly with the concentration of rutin in the range from 5.0 × 10⁻⁷ to 1.0 × 10⁻⁴ M with the detection limit as 3.58 × 10⁻⁷ M (3σ). The relative standard deviation (RSD) of 10 successive detection of 5.0 × 10⁻⁵ M rutin was 4.2%. The method was successfully applied to the determination of rutin content in tablets samples with good recovery. The modified electrode showed good stability and reproducibility without the influence of the coexisting substances.     

Effects of S-adenosyl-L-methionine on platelet thromboxane and vascular prostacyclin

We therefore designed the present study to evaluate the effect of S-adenosyl-L-methionine (SAMe) on the synthesis of platelet thromboxane and vascular prostacyclin. The experimental materials were human blood and aortic rings from untreated Wistar rats; and platelets and aortic rings from Wistar rats treated for 7 days with SAMe at 5 or 10 mg/kg/day s.c. The administration of 10 mg/Kg/day of SAMe to rats significantly increased vascular production of 6-keto-PGF_1α. In vitro vascular production of 6-keto-PGF_1α increased in a concentration-dependent manner when SAMe was incubated in the range of 10⁻⁷ to 10⁻⁴ M. The greatest increase was 167 ± 15%, obtained in samples incubated with 5 × 10⁻⁵M SAMe. In aortic rings, lipid peroxidase production was inhibited in a concentration-dependent manner in the SAMe range of 10⁻⁷ to 10⁻⁵ M. Maximum inhibition (75.3 ± 6.2%) was obtained with SAMe at 1.5 × 10⁻⁵M. Vascular 6-keto-PGF_1α production showed a significant inverse linear correlation with vascular lipid peroxide production (Y = −0.04 × + 18.1, r = 0.7309, P < 0.0001).     

Determination of doxorubicin in pharmaceutical preparation and rat plasma with luminol-K3Fe(CN)6 chemiluminescence system

A novel and rapid flow injection chemiluminescence (FI-CL) method was established for the determination of doxorubicin, which was based on the phenomenon that CL intensity of the reaction between K₃Fe(CN)₆ and luminol in alkaline solution could be strongly enhanced by doxorubicin. Under optimum conditions, the relative CL intensity of the system was linear with the concentration of doxorubicin in the range from 2.0 × 10^?9 g/mL to 5.0 × 10^?7 g/mL with a correlation coefficient of 0.9993 (n = 9). The detection limit (3σ) was 4.25 × 10^?10 g/mL, and the relative standard deviation (RSD) for 1.0 × 10^?7 g/mL doxorubicin (n = 11) was 0.33%. The method was applied to the determination of doxorubicin in pharmaceutical preparation and rat plasma, and the percentage recovery of doxorubicin in rat plasma was between 89.8% and 102.2%. The possible CL mechanism was also discussed briefly.     

Lymphokines production by concanavalin A-stimulated mouse splenocytes: modulation by Met-enkephalin and a related peptide

Methionine-enkephalin (ME) and its synthetic congener Tyr-D-Ala-Gly-Me-Phe-Gly-NH.C₃H₇-iso (82/205), in a concentration-dependent biphasic manner modulated the concanavalin A (Con A)-stimulated phagocytosis-promoting (PP)-activity elaboration in the culture supernatants of mouse splenocytes in vitro. Both these peptides at 1 × 10⁻⁵ and 1 × 10⁻⁶ M inhibited the production of PP activity; conversely, at 1 × 10⁻⁷−1 × 10⁻⁹ M they augmented it. Peptide 82/205 was nearly 1.2-fold more inhibitory and approximately 1.8-fold more potent in augmenting the PP activity elaboration. The PP activity appeared to be due to lymphokines (LK) gamma interferon and interleukin-4 as the neutralizing concentrations of monoclonal antibodies against these LK significantly (p<0.05) inhibited it. Cycloheximide (50.0 μg/ml) completely inhibited the production of LK indicating their de novo synthesis. The peptides appeared to exert their inhibitory and augmenting effects via δ-and μ-opioid receptors, respectively, as pretreatment of splenocytes with 100-fold higher (1 × 10⁻³ M) concentration of naloxone was required to block their inhibitory effect; the augmenting effect was blocked by 1 × 10⁻⁵ M only. None of the peptides or naloxone could directly stimulate the splenocytes for PP-LK elaboration.     

Inhibition of voltage-dependent Ca2+ channels of porcine tracheal smooth muscle by the novel Ca2+ channel antagonist RWJ-22108

• 1.1. We compared electrophysiological effects of the bronchoselective Ca²⁺ channel antagonist RWJ-22108 on voltage-dependent Ca²⁺ channels (VDCs) of porcine tracheal smooth muscle cells to the effects of nicardipine and verapamil.
• 2.2. Each of the three Ca²⁺ channel antagonists tested inhibited inward Ca²⁺ currents (I_Ca) measured by whole-cell patch clamp techniques. Inhibition was dose-dependent with ∼50% inhibition of peak I_Ca at +20 mV obtained with 3 × 10⁻⁶M RWJ-22108, 3 × 10⁻⁷M nicardipine, or 10⁻⁵M verapamil.
• 3.3. Both RWJ-22108 (3 × 10⁻⁶M) and nicardipine (3 × 10⁻⁷M) shifted the voltage dependence of steady-state inactivation to more negative potentials; however, the change in the potential of half-maximal inactivation induced by RWJ-22108 (−18 mV) was significantly greater than that induced by nicardipine (−12 mV). Verapamil did not alter the voltage dependence of inactivation.
• 4.4. We conclude that inhibition of VDCs by RWJ-22108 is qualitatively similar to that by nicardipine but with a greater stabilizing effect on the inactivated channel state.

     

Effect of naringin and naringenin on contractions induced by noradrenaline in rat vas deferens—I. Evidence for postsynaptic alpha-2 adrenergic receptor

• 1.1. Naringin at all doses (2 × 10⁻⁶, 5 × 10⁻⁷, and 1 × 10⁻⁷ M) significantly increased contractions induced by noradrenaline in rat vas deferens but the increments of maximal contraction were not concentration-dependent.
• 2.2. In a medium containing 1 × 10⁻⁶ M yohimbine (a selective blocker of α₂-adrenoceptor) and naringin, the curve constructed with noradrenaline decreased below the control curve.
• 3.3. Naringenin (aglycone of naringin) (2 × 10⁻⁶ and 1 × 10⁻⁷ M) increased the contractile effect of noradrenaline and the maximal effect evoked was related to the maximal dose of naringenin.
• 4.4. The α₂ antagonism produced by yohimbine in the naringenin-noradrenaline association were retained at two doses of naringenin tested and we noticed a similar behaviour when we used clonidine-noradrenaline.

     

Differential pulse voltammetric determination and catalytic oxidation of sulfamethoxazole using [5,10,15,20‐ tetrakis (3‐methoxy‐4‐hydroxy phenyl) porphyrinato] Cu (II) modified carbon paste sensor

Sulfamethoxazole (SM) is a sulfonamide bacteriostatic antibiotic. Its primary activity is against susceptible forms of streptococcus, staphylococcus aureus, escherichia coli, haemophilus influenzae, and oral anaerobes. It is commonly used to treat urinary tract infections. In addition it can be used as an alternative to amoxicillin‐based antibiotics to treat sinusitis. It can also be used to treat toxoplasmosis. In the present work, a metalloporphyrin modified carbon paste sensor was fabricated and the electrochemical behaviour of SM was studied using differential pulse voltammetry (DPV). Cu (II) complex of 5,10,15,20‐ tetrakis (3‐methoxy‐4‐hydroxy phenyl) porphyrin (TMHPP Cu (II)) was used as the active material. Compared with bare carbon paste electrode (CPE), the TMHPP Cu (II) modified CPE exhibits excellent enhancement effect on the electrochemical oxidation of SM. A well‐defined oxidation peak of SM occurs at ? 140 mV in 0.1M phosphate buffer solution (PBS) of pH 6. All the experimental parameters were optimized and it was found that under optimum conditions the oxidation peak current was linear to the concentration of SM in the range of 1.0 × 10^?2–1.0 × 10^?8 M with a detection limit of 1.5 × 10^?9M. The developed sensor has been successfully applied for the determination of SM in pharmaceutical formulations and urine sample. Copyright © 2010 John Wiley & Sons, Ltd.     

M3-Type Muscarinic Receptors Predominantly Mediate Neurogenic Quick Contraction of Bovine Ciliary Muscle

• 1.The present experiments were designed to investigate which subtypes of muscarinic receptors are involved in the neurogenic quick contraction of bovine ciliary muscle in connection to quick eye focal accommodation.
• 2.Transmural electrical stimulation (TES) produced a transient contraction, which was abolished in the presence of 3×10⁻⁷ M tetrodotoxin and 10⁻⁶ M atropine, but greatly augmented by 3×10⁻⁷ M physostigmine.
• 3.The exogenously applied acetylcholine (ACh: 10⁻⁹ to 3×10⁻⁶ M) produced a concentration-dependent contraction, which was competitively antagonized by 10⁻⁶ M atropine and augmented by 3×10⁻⁷ M physostigmine, but unaffected by 3×10⁻⁷ M tetrodotoxin.
• 4.The magnitude and time to peak of the maximal contraction produced by TES were significantly greater (1267.5±86.0 mg, P<0.005) and shorter (9.0±0.2 sec, P<0.005) than corresponding values (97.0±9.9 mg and 20.3±2.1 sec, respectively) of the phasic contraction caused by exogenously applied 10⁻⁵ M ACh, at which concentration the agonist caused the maximal contraction. The velocity (140.6±7.8 mg/sec) of the transient contraction caused by TES was approximately 28-fold greater than that of the phasic contraction caused by ACh (5.1±0.9 mg/sec).
• 5.The contractions produced by TES were greatly attenuated by 4-diphenylacetoxy-N-methylpiperidine (4-DAMP) as an M₃ antagonist and slightly by pirenzepine as an M₁ antagonist (20.2±7.9% inhibition at the highest concentration), but not by methoctramine (MET) as an M₂ antagonist. The IC₅₀ value (−log M) for 4-DAMP was determined to be 7.17±0.14.
• 6.Scatchard plot analysis of [³H]-quinuclidinylbenzilate (QNB) binding revealed that the binding sites constituted a single population with a K_d of 31.2±0.8 pM and a B_max of 895.5±93.2 fmol/mg protein. The activity in inhibiting [³H]-QNB binding was most potent with 4-DAMP (-log K_i=7.98±0.02), but less potent with pirenzepine (−log K_i=6.43±0.04) and MET (−log K_i=7.32±0.16). 4-DAMP was approximately 35- and 5-fold more potent than pirenzepine and MET in terms of −log K_i values, respectively, suggesting the predominant localization of M₃ receptor subtypes in the bovine ciliary muscle membrane.
• 7.These results suggest that TES produces a neurogenic quick contraction of the bovine ciliary muscle, which would be mediated mainly by ACh released from the intramural nerve terminals and subsequent excitation of M₃ receptor subtypes localized on the ciliary muscle cells, and that neurogenic quick contraction of the ciliary muscle is possibly involved in part in eye focal accommodation.

     

Development and validation of a simple reversed-phase HPLC-UV method for determination of oleuropein in olive leaves

A simple, precise, accurate, and selective method is developed and validated for the determination of oleuropein, which is the main phenolic compound in olive leaves. Separation was achieved on a reversed-phase C₁₈ column (5 μm, 150 × 4.6 mm inner diameter) using a mobile phase consisting of acetonitrile/phosphate buffer pH 3.0 (20:80, v/v), at a flow rate of 1.0 mL/minute and UV detection at 280 nm. This method is validated according to the requirements for new methods, which include accuracy, precision, selectivity, robustness, limit of detection, limit of quantitation, linearity, and range. The current method demonstrates good linearity over the range of 3–1000 ppm of oleuropein, with r² > 0.999. The recovery of oleuropein in olive leaves ranges from 97.7% to 101.1%. The method is selective, in that oleuropein is well separated from other compounds of olive leaves with good resolution. The method is also precise—the relative standard deviation of the peak areas of replicate injections of oleuropein standard solution is <1%. The degree of reproducibility of the results obtained as a result of small deliberate variations in the method parameters and by changing analytical operators has proven that the method is robust and rugged. The low limit of detection and limit of quantitation of oleuropein when using this method enable the detection and quantitation of oleuropein at low concentrations.     

Spectrophotometric investigation on complex formation of captopril with palladium(II) and its analytical application

The formation of the complex between captopril and palladium(II) chloride in Britton-Robinson buffer solution was studied. It has been established that captopril reacts with palladium(II) chloride in the pH range 2.14–9.10 to form a yellow water — soluble 2:1 complex with maximum absorbance at 380 nm. By applying different spectrophotometric methods, the conditional stability constant of the complex at the optimum pH of 4.03 and ionic strength μ = 0.5 M was found to be 10^8.25. The molar absorptivity was 1.875 × 10³ l mol⁻¹ cm⁻¹. Beer's law was obeyed in concentrations up to 5 × 10⁻⁴ M captopril. The detection limit was 2.17 μg ml⁻¹ and the relative standard deviation varied from 1.24 to 1.68%. The proposed method was found to be suitable for the accurate and reproducible analysis of captopril in water and in tablets.     

Activity of the enzymes of the antioxidative system in cadmium-treated Oxya chinensis (Orthoptera Acridoidae)

One purpose in this research was to determine the toxic effects of Cd on antioxidant enzymes of Oxya chinensis (Orthoptera: Acridoidae). Changes in the activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and guaiacol peroxidase (GPx) were measured in O. chinensis insects injected with Cd²⁺. Fifth-nymphs of O. chinensis insects were injected with Cd²⁺ at different concentrations (0, 0.55 × 10⁻⁴, 1.10 × 10⁻⁴, 1.65 × 10⁻⁴, 2.20 × 10⁻⁴, and 2.75 × 10⁻⁴ g g⁻¹). An increase in SOD activity in O. chinensis was observed at 1.10 × 10⁻⁴ to 2.75 × 10⁻⁴ g g⁻¹ Cd²⁺. The SOD activity was lower at 2.20 × 10⁻⁴and 2.75 × 10⁻⁴ g g⁻¹ than that at 1.10 × 10⁻⁴ and 1.65 × 10⁻⁴ g g⁻¹. It appears that SOD had a positive protective effect at low Cd²⁺ concentrations, and that this effect disappeared at high Cd²⁺ concentrations. CAT activity was accelerated to varying degrees at 1.10 × 10⁻⁴ to 2.75 × 10⁻⁴ g g⁻¹ for males and at 1.10 × 10⁻⁴, 2.20 × 10⁻⁴, and 2.75 × 10⁻⁴g g⁻¹ for females. CAT showed a strong detoxification effect with all treatments. GPx activity decreased with increasing Cd²⁺ concentration with all treatments for males and at 2.20 × 10⁻⁴ and 2.65 × 10⁻⁴g g⁻¹ for females. We showed that GPx activity had a weak detoxification function with all treatments for males and at high Cd²⁺ for females. Thus, CAT had a strong detoxification effect, whereas SOD had a medium and GPx had a weak detoxification effect. Among the three enzymes, CAT played an important role in the damaging mechanisms of reactive oxygen species in O. chinensis insects. Alterations of the antioxidant enzyme level under environmental stresses are suggested as indicators of biotic and abiotic stress.