Laxman S. Walekar

Spectroscopic analysis on the binding interaction of biologically active pyrimidine derivative with bovine serum albumin

A biologically active antibacterial reagent, 2–amino-6-hydroxy–4–(4-N, N-dimethylaminophenyl)-pyrimidine-5-carbonitrile (AHDMAPPC), was synthesized. It was employed to investigate the binding interaction with the bovine serum albumin (BSA) in detail using different spectroscopic methods. It exhibited antibacterial activity against Escherichia coli and Staphylococcus aureus which are common food poisoning bacteria. The experimental results showed that the fluorescence quenching of model carrier protein BSA by AHDMAPPC was due to static quenching. The site binding constants and number of binding sites (n≈1) were determined at three different temperatures based on fluorescence quenching results. The thermodynamic parameters, enthalpy change (ΔH), free energy (ΔG) and entropy change (ΔS) for the reaction were calculated to be 15.15 kJ/mol, –36.11 kJ/mol and 51.26 J/mol K according to vant Hoff equation, respectively. The results indicated that the reaction was an endothermic and spontaneous process, and hydrophobic interactions played a major role in the binding between drug and BSA. The distance between donor and acceptor is 2.79 nm according to Försters theory. The alterations of the BSA secondary structure in the presence of AHDMAPPC were confirmed by UV–visible, synchronous fluorescence, circular dichroism (CD) and three-dimensional fluorescence spectra. All these results indicated that AHDMAPPC can bind to BSA and be effectively transported and eliminated in the body. It can be a useful guideline for further drug design.

A novel colorimetric probe for highly selective recognition of Hg2+ ions in aqueous media based on inducing the aggregation of CPB-capped AgNPs: accelerating direct detection for environmental analysis

In this study, we have developed a novel and highly selective naked-eye colorimetric probe for the detection of mercury ions (Hg2+) in aqueous solution, using cetylpyridinium bromide (CPB)-capped colloidal silver nanoparticles (AgNPs), based on induced aggregation. The synthesized AgNPs and their interaction with Hg2+ were characterized using UV-Vis absorption spectroscopy, Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS) measurements and zeta potential measurement techniques. The color of the AgNP solution changed from yellowish-brown to colorless within a few minutes following the addition of Hg2+, resulting in a blue shift from 408–354 nm with quenching in the absorption spectra. Under the most favorable conditions, the calibration plot of (A0−A) against concentration of Hg2+ was linear in the range of 0.5–10 μg mL−1 with a correlation coefficient of 0.9931. The concentration of Hg2+ is quantitatively determined using a UV-Vis spectrophotometer with a Limit of Detection (LOD) of 0.80 μg mL−1. In addition, this method shows an excellent selectivity towards Hg2+ over sixteen other interfering cations tested. The accuracy and reliability of the method were further ascertained for the detection of Hg2+ from water bodies via a standard addition method, with percentage recoveries in the range of 99.96–100.13%. The probable mechanism for the observed color changes was also discussed. The method is simple, rapid, specific, and highly selective with good precision.

One-pot synthesis and in vivo biological evaluation of new pyrimidine privileged scaffolds as potent anti-inflammatory agents

A simple methodology has been developed for the synthesis of diverse members of multifunctionalized 4-hydroxy-2-methyl-6-(phenyl)pyrimidine-5-carbonitrile derivatives via multicomponent reaction of aromatic aldehydes, ethyl cyanoacetate, and acetamidine hydrochloride using a quantitative amount of NaOH in dry DMF at 80xa0°C in a single procedural step. The carbon skeleton of synthesized compounds resembles the bacimethrin, an antibiotic active against several yeast and bacteria. The anti-inflammatory activities of all the synthesized compounds were assessed on Wistar rats using diclofenac sodium as a standard reference. The compound AC1, 2, 5, 9, and AC10 showed promising anti-inflammatory activity (80–83xa0%) in comparison with diclofenac sodium (85xa0%) in the carrageenan-induced rat paw edema assay, which is the key finding of this article.Graphical AbstractThe synthesized 4-hydroxy-2-methyl-6-(phenyl)pyrimidine-5-carbonitrile derivatives shown promising anti-inflammatory activity (80–83xa0%) in comparison with diclofenac sodium (85xa0%) in the carrageenan-induced rat paw edema assay.

Synthesis, anti-inflammatory, ulcerogenic and cyclooxygenase activities of indenopyrimidine derivatives.

Objective of the present work was to evaluate the anti-inflammatory, ulcerogenicity and cyclooxygenase activity of indenopyrimidine derivatives. Anti-inflammatory activity of the tested compounds is investigated by carrageenan-induced rat paw edema assay. Compounds A1, A6, A7 and A12 exhibit the comparable anti-inflammatory activity (79.33-81.33%) to the standard drug diclofenac sodium (85.33%), while A6, A7, A9, A12 and A14 show better ulcer index than the reference standard diclofenac sodium. To rationalize the anti-inflammatory activity, docking experiments are performed to study the ability of these compounds to bind into the active site of COX-2 enzyme.

A quantum dot-based dual fluorescent probe for recognition of mercuric ions and N-acetylcysteine: “On–Off–On” approach

A mercaptopropionic acid-capped cadmium sulfide quantum dot (MPA-CdS QD) based dual fluorescent “On–Off–On” probe was designed and applied for sensitive and selective monitoring of mercuric ions (Hg2+) and N-acetylcysteine (NAC) in aqueous solution. In the mercuric ion detection, the fluorescence of MPA-CdS QDs decreased with increasing amount of Hg2+. This is because of the binding of mercuric ions to mercaptopropionic on the surface of quantum dots and the electron transfer from the photoexcited MPA-CdS QDs to mercuric ions. Subsequently, upon the successive addition of NAC, the fluorescence of MPA-CdS QDs is recovered due to the high binding affinity of NAC with mercuric ions; NAC can form a more stable complex with mercuric ions in aqueous solution, and this releases the fluorescent MPA-CdS QDs. The strategy was simply achieved by measuring the changes in the fluorescence intensity of QDs. The present results suggest that the developed method has several advantages such as being simple, straightforward, and highly sensitive, ease of operation and cost effectiveness and is used for simultaneous determination of two analytes in aqueous media. The linear response range was obtained over the range of 25–225 ng mL−1 and 0.05–0.9 μg mL−1 with a low detection limit of 25.2 ng mL−1 and 0.092 μg mL−1 for Hg2+ ions and NAC, respectively. The developed probe was successfully applied for the determination of Hg2+ and NAC in real samples with satisfactory results.

Fluorescence-based sensor for selective and sensitive detection of amoxicillin (Amox) in aqueous medium: Application to pharmaceutical and biomedical analysis

We here for the first time demonstrate an analytical approach for the highly selective and sensitive detection of amoxicillin (Amox) in aqueous medium based on the fluorescence quenching of quantum dots (QDs). The change in fluorescence intensity of mercaptopropionic acid-capped cadmium sulphide (MPA-CdS) QDs is attributed to the increasing concentration of Amox. The results show that the fluorescence quenching of QDs by Amox takes place through both static and dynamic types of quenching mechanism. The fluorescence quenching of QDs with increase in concentration of Amox shows the linear range between 5xa0μgxa0ml-1 and 30xa0μgxa0ml-1 and the limit of detection (LOD) is 5.19xa0μgxa0ml-1 . There is no interference of excipients, which are commonly present in pharmaceutical formulation and urine samples. For the practical application approach, the developed method has been successfully applied for the determination of Amox in pharmaceutical formulations and urine samples with acceptable results.

Spectroscopic Investigation of Interaction Between Carbon Quantum Dots and D-Penicillamine Capped Gold Nanoparticles

This study reports the interaction and energy transfer between fluorescent carbon quantum dots (CQDs) and D-Penicillamine capped gold nanoparticles (DPA−AuNPs). The CQDs was synthesized by a simple chemical oxidation method at room temperature. The prepared CQDs shows a strong fluorescence at λemu2009=u2009430xa0nm when excited at λexu2009=u2009320xa0nm. The interaction of CQDs with DPA−AuNPs was characterized by fluorescence spectroscopy, Transmission Electron Microscopy (TEM) study and Dynamic Light Scattering (DLS) techniques. The fluorescence study shows the continuous quenching in the fluorescence intensity of CQDs in presence of increasing concentrations of DPA−AuNPs. The change in fluorescence spectra of CQDs in presence of increasing concentration of DPA−AuNPs and quenching are suggestive of a rapid adsorption of CQDs on the surface of DPA−AuNPs. The Ksv, K, Kq and n values were calculated and results indicated that the dynamic type of quenching takes place. The distance between donor and acceptor (r) is 6.07xa0nm which supports the energy transfer by Fluorescence Resonance Energy Transfer (FRET) phenomenon. The plausible mechanism for FRET is also discussed.

Ultrasensitive, highly specific, colorimetric recognition of sulfide ions [S2−] in aqueous media: applications to environmental analysis

Herein, we have demonstrated a simple, ultrasensitive and highly specific colorimetric assay for the detection of sulfide ions (S2−) based on the aggregation of nanoparticles via electrostatic interaction of a surface capped gold nanoparticles with S2− in aqueous media. Cetylpyridinium bromide capped gold nanoparticles (CPB-AuNPs) were synthesized by a borohydride chemical reduction method and further characterized using UV-visible and fluorescence spectroscopy, transmission electron microscopy (TEM), dynamic light scattering (DLS) and zeta potential measurements. The change in color from red to purple immediately after the addition of S2− in the solution of CPB-AuNPs was first monitored by the naked eye and then by UV-vis spectroscopy to construct calibration plot for practical applications. Under the optimized circumstances, a plot of [(A0 − A)/A] versus the concentrations of S2− was linear over the range of 0.01–1.0 μg mL−1 with a correlation coefficient of 0.9952. The developed method also shows excellent selectivity towards S2− by a factor of 20-fold or more relative to sixteen interfering ions that were tested. The probe offers a low limit of detection (LOD) up to 0.0013 μg mL−1 (40.6 nM), which is much lower (about 400-fold) than the maximum level (0.5 μg mL−1 or 15u2006625 nM) of S2− in drinking water permitted by the World Health Organization (WHO). Moreover, our results demonstrate the practical applicability of the probe for S2− sensing in environmental water samples without pretreatment or use of a masking agent. Therefore, the proposed scheme could be a good alternative means for onsite and real time screening of S2−.

Study of energy transfer between riboflavin (vitamin B2) and AgNPs

Here, we report the studies on the interaction and formation of nanobiocomplex between silver nanoparticle (AgNPs) and vitamin B2, i.e., riboflavin (RF). The binding study of AgNP to RF was studied by fluorescence, UV–Vis, and TEM techniques. AgNPs were prepared by reducing AgNO3 with trisodium citrate. Prepared nanoparticles size obtained at 20xa0nm having surface Plasmon resonance band at 426xa0nm. The absorbance band of RF at 264, 374, and 444xa0nm changes significantly in the presence of AgNPs suggests that there is change in the chemical environment surrounding AgNPs. A fluorescence spectral change for a solution of RF upon the addition of AgNPs and rapid quenching is suggestive of a rapid adsorption of RF on AgNPs.Graphical Abstract

CdS nanocrystals as fluorescent probe for detection of dolasetron mesylate in aqueous solution: Application to biomedical analysis

A simple and straightforward method for the determination of dolasetron mesylate (DM) in aqueous solution was developed based on the fluorescence quenching of 3-Mercaptopropionic acid (MPA) capped CdS quantum dots (QDs). The structure, morphology, and optical properties of synthesized QDs were characterized by using UV-Vis absorption spectroscopy, fluorescence spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements. Under the optimum conditions, the MPA-CdS QDs fluorescence probe offered good sensitivity and selectivity for detecting DM. The probe provided a highly specific selectivity and a linear detection of DM in the range of 2–40 µg/mL with detection limit (LOD) 1.512 µg/mL. The common excipients did not interfere in the proposed method. The fluorescence quenching mechanism of CdS QDs is also discussed. The developed sensor was applied to the quantification of DM in urine and human serum sample with satisfactory results.