Nagappa L. Teradal

Interactions of polyphenols with plasma proteins: insights from analytical techniques.

Phenolic compounds are commonly found in natural sources like plant-based foods and beverages. These compounds have received much attention due to their unique biological properties. Polyphenols possess a significant binding affinity for serum albumins which are known to be principal extracellular proteins with a high concentration in blood plasma. They act as carriers of several drugs to different molecular targets. This review summarizes the salient features of the reported work on polyphenol-protein interactions by analytical methods viz., chromatography, circular dichroism, fluorescence spectroscopy (steady state and time resolved), light scattering, equilibrium dialysis, differential scanning calorimetry, UV-vis spectroscopy, isothermal calorimetry, MALDI-TOF mass spectrometry, size exclusion chromatography, capillary electrophoresis, electrospray ionization mass spectrometry, FT-IR, molecular modelling, HPLC, NMR, cyclic voltammetry etc. Polyphenol-serum albumin interaction studies assume significance from the view point of pharmacokinetics and pharmacodynamics.

A novel electrochemical sensor for non-ergoline dopamine agonist pramipexole based on electrochemically reduced graphene oxide nanoribbons

A facile and feasible electrochemical sensing platform based on electrochemically reduced graphene oxide nanoribbons (ERGONRs) was designed for electrochemical investigations and determination of a non-ergoline dopamine agonist, pramipexole dihydrochloride monohydrate (PPX), in pharmaceutical formulations and biological fluids. Newly synthesized graphene oxide nanoribbons were characterized by SEM, AFM, XRD and EDX. The solution of graphene oxide nanoribbons (GONRs) was placed on a glassy carbon electrode (GCE) and reduced electrochemically in phosphate buffer solution of pH 6 to obtain the electrochemically reduced graphene oxide nanoribbon modified glassy carbon electrode (ERGONR-GCE). Significant electrooxidation of PPX was observed at the ERGONR-GCE in phosphate buffer of pH 6.0 compared to that at the bare GCE. The effect of accumulation time, pH and scan rate was studied and various electrochemical parameters were evaluated. The plot of pH versus Ep yielded a slope of 57.65 mV per pH in the pH range of 3.0–8.0 indicating the participation of an equal number of electrons and protons in the electrode process. A differential pulse voltammetric method was developed for the determination of PPX in bulk, pharmaceutical formulations and urine samples. PPX showed a linear relationship between the peak current and the concentration in the range of 0.01–15 μM with a LOD of 2.8 nM and a LOQ of 9.4 nM. The fabricated electrode also showed good selectivity and excellent sensitivity. The proposed method is simple, rapid and inexpensive and hence could be readily adopted for the analysis of PPX. The results were subjected to statistical analysis.

Unzipped carbon nanotubes: analytical and binding applications of semisynthetic phlebotropic flavonoid, diosmin

The present study describes the utility of unzipped carbon nanotubes as electrochemical sensing platforms for the determination of diosmin (DIO) in pharmaceutical formulations and for the investigation of its binding to the drug transport protein, human serum albumin (HSA). Graphene oxide nanoribbons (GONRs) were prepared by unzipping of multiwalled carbon nanotubes and characterized by employing powder XRD, FTIR, absorption, Raman, AFM, SEM and electrochemical impedance spectroscopic methods. The suspension of GONRs was drop cast onto a glassy carbon electrode (GCE) and then was subjected to electrochemical reduction (Er) in the potential range of 0.8 to −1.6 V to obtain ErGONRs/GCE. DIO showed a redox peak (Epa = 0.587 V and Epc = 0.548 V) and an irreversible oxidation peak at 0.845 V on ErGONRs/GCE in a phosphate buffer of pH 3. DIO exhibited an enhanced electrochemical response (∼39-fold increment in the peak current) at ErGONRs/GCE when compared to that at bare GCE. Linearity between the peak current and concentration of DIO was noticed in the range of 51.01–39.21 μM and 25–3.48 μM for differential pulse and square wave voltammetric methods, respectively. The practical utility of the proposed sensor was established by determining DIO in pharmaceutical formulations. Furthermore, the sensor was used for understanding the binding mechanism of the DIO–HSA system. The binding constant and binding ratio between HSA and DIO were calculated to be 2.58 × 104 M−1 and 1 : 1, respectively.

Electrosensing of an alpha-adrenergic agonist psychoactive methyldopa using a sodium bentonite–graphene oxide nanocomposite

In the present report, we describe the preparation of a sodium bentonite–graphene oxide nanocomposite for the electrosensing of methyldopa (MD). The fabricated electrode materials viz., graphene oxide (GO), sodium bentonite–graphene oxide (Bent–GO) and Bent–electroreduced graphene oxide (Bent–ErGO) were characterized using XRD, FTIR, absorption, Raman spectroscopy, FESEM and AFM methods. Bent–GO suspension was prepared by the exfoliation of GO and Bent in water. Bent–GO suspension was drop casted on GCE followed by electrochemical reduction to obtain Bent–ErGO/GCE. The electronic properties of the modified GCEs were evaluated employing CV and electrochemical impedance measurements. The redox response of MD increased significantly with the negative shift in peak potentials with Bent–ErGO/GCE compared to that with bare GCE. Based on the enhanced electrochemical response, chronoamperometric and differential pulse voltammetric (DPV) methods were developed as alternative analytical methods for the assay of MD. Under the optimized conditions, a linear relationship was observed between the peak current and concentration of MD in the range of 1.13–40.6 μM and 0.1–60 μM for chronoamperometric and DPV methods, respectively. Furthermore, the proposed electrochemical sensor was successfully employed for the determination of MD in pharmaceutical formulations.

Electro-reduced graphene oxide film modified glassy carbon electrode as an electrochemical sensor for sibutramine

In the present study, the electrochemical behavior of an anorexiant drug, sibutramine (SHM), was studied at an electro-reduced graphene oxide film modified glassy carbon electrode (ERGO-GCE) for the first time. SHM exhibited two irreversible oxidation peaks at 0.620 V and 0.835 V in Britton–Robinson buffer in the pH range 3–10. The first peak and second peak were found to result from adsorption and diffusion controlled processes, respectively. ERGO-GCE exhibited excellent electrocatalytic activity for the oxidation of SHM. Under optimized experimental conditions, the oxidation peak (a2) current was observed to be proportional to the concentration of SHM up to 2.00 × 10−5 mol L−1 with a limit of detection of 4.80 × 10−8 mol L−1. The proposed sensor was successfully applied for the assay of SHM in analyte fortified human serum and urine samples. No interference was evident from endogenous substances present in biological fluids.

Eco-friendly reduced graphene oxide for the determination of mycophenolate mofetil in pharmaceutical formulations

Graphene oxide (GO) was synthesized and characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). GO was then electrochemically reduced and used for electrochemical study of mycophenolate mofetil (MMF). The electrochemically reduced graphene oxide (ERGO) film on glassy carbon electrode (GCE) showed enhanced peak current for electrooxidation of MMF. MMF exhibited two irreversible oxidation peaks at 0.84 V (peak a1) and 1.1 V (peak a2). Effects of accumulation time, pH and scan rate were studied and various electrochemical parameters were calculated. A differential pulse voltammetric method was developed for the determination of MMF in bulk samples and pharmaceutical formulations. Linear relationship was observed between the peak current and concentration of MMF in the range of 40 nM–15 μM with a limit of detection of 11.3 nM. The proposed method is simple, sensitive and inexpensive and, hence, could be readily adopted in clinical and quality control laboratories.

Surface-Enhanced Oxidation and Determination of Isothipendyl Hydrochloride at an Electrochemical Sensing Film Constructed by Multiwalled Carbon Nanotubes

The electrochemical behavior of isothipendyl hydrochloride (IPH) was investigated at bare and multiwalled-carbon-nanotube modified glassy carbon electrode (MWCNT-GCE). IPH (55 μM) showed two oxidation peaks in Britton-Robinson (BR) buffer of pH 7.0. The oxidation process of IPH was observed to be irreversible over the pH range of 2.5–9.0. The influence of pH, scan rate, and concentration of the drug on anodic peak was studied. A differential pulse voltammetric method with good precision and accuracy was developed for the determination of IPH in pure and biological fluids. The peak current was found to be linearly dependent on the concentration of IPH in the range of 1.25–55 μM. The values of limit of detection and limit of quantification were noticed to be 0.284 and 0.949 μM, respectively.