A novel curcumin assay with the metal ion Cu (II) as a simple probe by resonance light scattering technique

Activated Screen-Printed Boron-Doped Diamond Electrode for Rapid and Highly Sensitive Determination of Curcumin in Food Products

Due to a great interest in the beneficial properties of polyphenolic antioxidant curcumin (CCM), sensitive and accurate methods for determining CCM are needed. The purpose of our research was to develop a very simple, fast, and sensitive differential pulse adsorptive stripping voltammetric (DPAdSV) procedure using an electrochemically activated screen-printed boron-doped diamond electrode (aSPBDDE) for the determination of CCM. The activation of the SPBDDE was accomplished in a solution of 0.1 mol/L NaOH by performing five cyclic voltammetric scans in the range of 0-2 V, at ν of 100 mV/s. The changes in surface morphology and the reduction of the charge transfer resistance due to the activation of the electrode resulted in the amplification of the CCM analytical signal on the aSPBDDE. As a result, an extremely sensitive measurement tool was formed, which under optimized conditions (0.025 mol/L PBS of pH = 2.6, Eacc of 0.3 V, tacc of 90 s, ΔEA of 100 mV, ν of 150 mV/s, and tm of 10 ms) allowed us to obtain a limit of detection (LOD) of 5.0 × 10-13 mol/L. The aSPBDDE has proven to be a highly effective tool for the direct determination of CCM in food samples with high accuracy and precision. The results are in agreement with those obtained using ultra-high-performance liquid chromatography coupled with mass spectrometry and electrospray ionization (UHPLC-ESI/MS).

Synthesis and photophysical properties of ditrifluoroacetoxyboron complexes with curcumin analogues

A new class of ditrifluoroacetoxyboron complexes were designed and synthesized by chelation reaction of curcumins with boron trifluoroacetate. Their photophysical behaviors were studied in different solvents, powder state and PMMA polymer films. The results indicated that these complexes revealed a green to yellow emission at 486-595 nm in solution or PMMA films and an orange to red emission at 598-710 nm in powder state. Especially, complex 2c displayed the strongest emission intensity, the highest quantum yield in solution and the longest fluorescence lifetime in powder state in these complexes. In addtion, the emission bathochromic shifts of these complexes as a function of the solvent polarity parameter E_T(30) were investigated by Lippert-Mataga approximation. It was observed that these complexes exhibited the higher values of the dipole moment difference (Δμ) between the ground and excited states, which implied an intense intramolecular charge transfer characteristics and a noticeable emission solvatochromic effect.

Electrochemical Detection of Curcumin in Food with a Carbon Nanotube-Carboxymethylcellulose Electrode

Herein, an electrochemical method is presented for the detection of curcumin in food using a carbon nanotube (CNT)-carboxymethylcellulose (CMC) electrode. The CNT-CMC electrode exhibited ideal characteristics for curcumin detection, namely, a high response current and adequate peak separation toward curcumin oxidation. Cyclic voltammetry revealed two oxidation peaks. In the first scan, only the irreversible peak (Peak I) was observed at a higher potential. In the second scan, the reversible redox peak pairs (Peaks II and II') appeared at lower potentials, and the potential of Peak I was decreased. Peak I corresponded to oxidation of the hydroxyl groups of the benzene ring to the catechol group via a phenoxy radical, while Peaks II and II' indicated the redox loop system of the generated catechol group. The current at Peak II was used to quantify the concentration of curcumin in the linear range of 1 - 48 μM and detection limit of 0.084 μM. The concentrations of curcumin determined by the CNT-CMC electrode in real food samples were consistent with those determined by high-performance liquid chromatography.

New insights into the binding behavior of lomefloxacin and human hemoglobin using biophysical techniques: binary and ternary approaches

Demonstrates the overlap that had been induced between the fluorescence emission spectrum of Hb and the absorption spectrum of drugs, which has proved that there is a high probability to the occurrence of energy transfer from Hb and LMF in the absence and presence of NRF.

A magnetic molecularly imprinted optical chemical sensor for specific recognition of trace quantities of virus

A magnetic resonance light scattering (RLS) sensor based on the molecularly imprinted polymer (MIP) technique was developed for specific recognition of trace quantities of hepatitis A virus (HAV).

Polyhydric polymer-loaded pyrene composites as powerful adsorbents and fluorescent probes: highly efficient adsorption and test strips-based fluorimetric analysis of curcumin in urine and plant extracts

A polyhydric polymer fluorescent probe was designed for the accumulation and fluorimetric detection of curcumin (Cur).

Mn-doped ZnS quantum dots with a 3-mercaptopropionic acid assembly as a ratiometric fluorescence probe for the determination of curcumin

Mn-doped ZnS quantum dots capped with 3-mercaptopropionic acid (MPA) were synthesized by a facile method in aqueous solution as a ratiometric fluorescent (I_{590 nm}/I_{458 nm}) probe for curcumin.

Nitrogen-doped carbon dots as fluorescent probe for detection of curcumin based on the inner filter effect

A facile, economical and green one-step hydrothermal method for N-doped CDs was presented by using citric acid as carbon source and urea as nitrogen source. The fluorescence of N-doped CDs quenched dramatically from curcumin via inner filter effect.

Binding site identification of metformin to human serum albumin and glycated human serum albumin by spectroscopic and molecular modeling techniques: a comparison study

The interaction between metformin and human serum albumin (HSA), as well as its glycated form (gHSA) was investigated by multiple spectroscopic techniques, zeta potential, and molecular modeling under physiological conditions. The steady state and time-resolved fluorescence data displayed the quenching mechanism of HSA-metformin and gHSA-metformin was static. The binding information, including the binding constants, number of binding sites, effective quenching constant showed that the binding affinity of metformin to HSA was greater than to gHSA which also confirmed by anisotropy measurements. It was determined that metformin had two and one set of binding sites on HSA and gHSA, respectively. Far-UV CD spectra of proteins demonstrated that the α-helical content decreased with increasing metformin concentration. The zeta potential and resonance light scattering (RLS) diagrams provided that lower drug concentration induced metformin aggregation on gHSA surface as compare to HSA. The increase in polarizability was one of the important factors for the enhancement of RLS and the formation of drug/protein complexes. The zeta potential results suggested that both hydrophobic and electrostatic interactions played important roles in the protein-metformin complex formation. Site marker experiments and molecular modeling showed that the metformin bound to subdomain IIIA (Sudlow's site II) on HSA and gHSA.

Formation of curcumin molecular ion under electrospray ionisation conditions in the presence of metal cations

Electrospray ionisation (ESI) mass spectra obtained for solutions containing curcumin, copper cation and other metal cations, namely Co2+, Ni2+, Mn2+ and Zn2+, have shown an abundant curcumin molecular ion at m/z 368. This ion was not formed for solutions containing curcumin and copper cations or for those containing curcumin and other metal cations. To the best of our knowledge, it is the first example of a system in which copper cations and other metal cations promote formation of organic radical cation under ESI conditions.

Curcumin

Curcumin and its two related compounds, that is, demethoxycurcumin and bis-demethoxycurcumin (curcuminoids) are the main secondary metabolites of Curcuma longa and other Curcuma spp. Curcumin is commonly used as coloring agent as well as food additive; curcumin has also shown some therapeutic activities. This review summarizes stability of curcumin in solutions, spectroscopy characteristics of curcumin (UV, IR, Raman, MS, and NMR), polymorphism forms, method of analysis in both of biological and nonbiological samples, and metabolite studies of curcumin. For analysis of curcumin and its related compounds in complex matrices, application of LC-MS/MS is recommended.

Use of cetyltrimethylammonium bromide as a simple probe for rapid determination of emodin by resonance light scattering technique

A new resonance light scattering (RLS) method for emodin determination with cationic surfactant cetyltrimethylammonium bromide (CTAB) as probe has been developed. In Britton-Robinson buffer (pH 6.5) medium, emodin reacted with cationic surfactant CTAB and formed the emodin-CTAB complex. The complex aggregated together through hydrophobic forces and causing great enhancement of RLS signals with the maximum peak located at about 350 nm. The enhanced RLS intensities were found to be proportional to the concentration of emodin in the range of 0.54-9.72 μg ml(-1) with the detection limit (3σ) of 10.3 ng ml(-1). In this work, the characteristics of RLS, absorption, fluorescence spectra of the system were studied. The optimum reaction condition and the influencing factors on the RLS signal were investigated in detail. The proposed method was applied to the analysis of emodin in synthetic samples and human urine with satisfactory results. Furthermore, the forms of the substances under the experimental condition and the mechanism of the reaction were discussed in detail.

High-sensitivity determination of curcumin in human urine using gemini zwitterionic surfactant as a probe by resonance light scattering technique

INTRODUCTION

Curcumin is a popular plant medicine that is extracted from turmeric dry rhizomes of Curcuma longa Linn. The study of curcumin is well established and is currently becoming a centre of attention.

OBJECTIVE

To develop a steady and simple assay for curcumin determination at the nanogram level based on the intense resonance light scattering (RLS) enhancement due to the interaction between curcumin and phosphodiesters quaternary ammonium salt (PQAS).

METHODOLOGY

PQAS, a new kind of Gemini zwitterionic surfactant, was used as the probe for the determination of curcumin by the RLS technique. A series of validation experiments was also performed.

RESULTS

A linear relationship was constructed between the ΔI(RLS) and the concentration of curcumin. The linear regression equation was presented as ΔI(RLS)  = 8.37 + 44.92c (µg/mL) with the regression coefficient r = 0.9987 (n = 12) and the linear range was 0.08-60.0 µg/mL. The detection limit (3σ) was 2.6 ng/mL.

CONCLUSION

The proposed method can be used to detect the content of curcumin in human urine samples and this new assay using PQAS as a probe was more sensitive and displayed a wider linear range than that reported previously.

A sensitive resveratrol assay with a simple probe methylene blue by resonance light scattering technique

A novel resonance light scattering (RLS) method was developed for the determination of resveratrol based on the interaction between resveratrol and methylene blue (MB). It was found that at pH 8.69, the weak RLS intensity of MB was remarkably enhanced by the addition of trace amount of resveratrol with the maximum peak located at 385.0 nm. Under the optimum conditions, a good linear relationship between the enhanced RLS intensities and the concentrations of resveratrol was obtained over the range of 2.0-14.0 μg ml(-1) with the detection limit (3σ) of 0.63 μg ml(-1). The results of the analysis of resveratrol in synthetic samples and human urine are satisfactory, which showed it may provide a more sensitive, convenient, rapid and reproducible method for the detection of resveratrol, especially in biological and pharmaceutical field. In this work, the characteristics of RLS, absorption and fluorescence spectra of the resveratrol-MB system, the influencing factors and the optimum conditions of the reaction were investigated.

Study on the interaction between hematoporphyrin monomethyl ether and DNA and the determination of hematoporphyrin monomethyl ether using the resonance light scattering technique

The interaction between photosensitizer anticancer drug hematoporphyrin monomethyl ether (HMME) and ctDNA has been studied based on the decreased resonance light scattering (RLS) phenomenon. The RLS, UV-vis and fluorescence spectra characteristics of the HMME-ctDNA system were investigated. Besides, the phosphodiesters quaternary ammonium salt (PQAS), a kind of new gemini surfactant synthesized recently, was used to determine anticancer drug HMME based on the increasing RLS intensity. Under the optimum assay conditions, the enhanced RLS intensity was proportional to the concentration of HMME. The linear range was 0.8-8.4microgmL(-1), with correlation coefficient R(2)=0.9913. The detection limit was 0.014microgmL(-1). The human serum samples and urine samples were determined satisfactorily, which proved that this method was reliable and applicable in the determination of HMME in body fluid. The presented method was simple, sensitive and straightforward and could be a significant method in clinical analysis.

Simple and novel screening assay of natural antioxidants for Cu(II) ion/adrenaline-mediated oxidation of N-terminal amyloid beta by liquid chromatography/mass spectrometry

In the present study, a novel assay for screening inhibitors of Cu(II) ion/adrenaline-mediated oxidative modification of N-terminal amyloid beta (Abeta) peptides was developed using liquid chromatography with mass spectrometry (LC/MS). The physiological condition of Cu(II) ion/adrenaline in buffer (pH 7.4) at 37 degrees C for 90 min revealed a specific modification of N-terminal Abeta peptides, such as Abeta1-6, Abeta1-40, and Abeta1-42, using trypsin digestion and LC/MS detection of the modified Abeta peptide. When this oxidative modification of the shorter N-terminal Abeta1-6 was subjected to LC/MS, single charged ions from native peptide ([M+H]+, m/z 774) were observed at m/z 729 and 685, corresponding to a decrease in mass of 45 and 89 Da, respectively, as compared with the original peptide. To determine the effect of specific antioxidants, a screening assay to find inhibitors of Cu(II) ion/adrenaline-mediated oxidation was developed based on the response ratio of m/z 685 to 774. LC/MS detection of the modified peptides allowed us to identify antioxidants that inhibit oxidative modification of Abeta1-6 model peptide. The oxidative modification of Abeta1-6 was inhibited by curcumin but not an isoflavone or catechin mixture or saponin or capsaicin, revealing a clear difference between antioxidants that inhibit oxidative modification and other antioxidants. This novel assay may allow for the identification of antioxidants that protect against oxidative modification of Abeta and other proteins related to oxidative stress by adrenaline and Cu(II) ions under normal physiologic conditions.