جستجوی مقالات مرتبط با کلیدواژه "fluorescence spectroscopy" در نشریات گروه "شیمی"

A novel, fast, highly sensitive, and selective non-enzymatic label-free method was developed based on the fluorescence emission activity of surface-modified cerium oxide nanoparticles (CeO2 NPs) for morphine (MP) detection. The fluorescence intensity of CeO2 NPs increased following the adsorption of double-stranded DNA (dsDNA) onto its surface. Upon the addition of MP, the fluorescence intensity of the dsDNA-CeO2 NPs probe switched to a “turn-off” state and was quenched. This was attributed to the binding of MP to dsDNA and displacement of dsDNA with MP from the NPs. Under optimized conditions (pH 7.4; dsDNA concentration 1.1×10-6 M and a time of 30 and 10 min for incubation of dsDNA with CeO2 NPs and for MP and dsDNA-CeO2 NPs incubation, respectively), the fluorescent sensor was able to detect MP with high sensitivity. A linear relationship was obtained in the range of [(3.5–35)×10-6 M] with a limit of detection (LOD) of 1.8×10-6 M and the relative standard deviation (RSD)% 1.5-2.3%. The proposed system was successfully applied to determine MP levels in human urine samples from spiked patients and healthy individuals after deproteinization with acetonitrile. The analytical recoveries for treated biological samples ranged from 99.1 to 103.1%. The excellent selectivity for MP compared to other substances (The common interfering species, such as codeine, amphetamine, and methamphetamine) with concentrations 10-fold higher than MP. In addition, the newly proposed method was based on an optical biosensor, as compared to most existing methods, providing advantages such as rapidity, simplicity, low cost, and high sensitivity, thus, making it a promising method for rapid and direct determination of MP in clinical samples.

Acrylamide is one of the potential environmental public health problems, resulting from its increased accumulation in the process of cooking foods containing high levels of carbohydrates that are fried or cooked at high temperatures. So, developing a precise and sensitive analytical method for detecting and determining acrylamide in foods is absolutely necessary and inevitable. Gas Chromatography (GC) and Liquid Chromatography (LC) are two main laboratory techniques for acrylamide determination. In this study, we tried to use a cheaper, faster, accurate method for measuring acrylamide in real food samples. P540 and P503 were used as fluorescent reagents to detect the concentration of acrylamide in potato chips samples from 4 companies. Fluorescence spectroscopy was used in this work. The results obtained for the detection of acrylamide in comparison with the HPLC-MS method showed that there is an acceptable overlap between the fluorescence spectroscopy and HPLC method. The amount of acrylamide in four potato chips samples, obtained from the market in Tehran city, was determined using the proposed method. The optimum values of different parameters were determined. Comparisons between two methods, HPLC-MS and fluorescence spectroscopy were also described. The figures of merit for the proposed method were in the ideal range. The developed methods showed a high correlation coefficient (R2= 0.991). According to the results of the fluorescence emission spectroscopy and its comparison with HPLC-MS, the performance and reliability of the proposed method as a simple, efficient, and rapid method with reduction of cost and time for determining acrylamide in potato chip samples were demonstrated.

In this work, the interaction of two synthesized complexes [Tb(phen)2Cl3.OH2] and [Yb(phen)2Cl3.OH2] (phen is 1,10-phenanthroline) with bovine serum albumin (BSA) were studied by UV-Vis, fluorescence, and molecular docking examinations. The experimental data indicated that these lanthanide complexes have a high binding affinity with BSA by effectively quenching the fluorescence of BSA via the static mechanism. The binding parameters, the type of interaction, the value of resonance energy transfer, and the binding distance between complexes and BSA were estimated from the analysis of fluorescence measurements and Förster theory. The thermodynamic parameters suggested that van der Waals interactions and hydrogen bonds play an important role in the binding mechanism. While the energy transfer from BSA molecules to these complexes occurs with high probability, the binding constants showed that the binding affinity ranked in the order Tb-complex > Yb-complex, which has been related to the radius of Ln3+ ion. Also, the results of competitive experiments and molecular docking calculations assessed the microenvironment residues around the bound mentioned complexes and represent site 3 of BSA, located in subdomain IB, as the most probable binding site for these complexes. The computational results kept in good agreement with experimental data.

Nasunin is the main phenol-based constituent of eggplant peels, be famed for its multiple advantages and antioxidant activity. α-lactalbumin (α-lac) is a milk protein with a great nutritional worthiness due to its necessary amino acids. Mechanism of interaction of α-lac with nasunin were investigated by in silico and spectroscopy studies. The results of the fluorescence quenching experiments demonstrated a reduction in the fluorescence parts by cause of bonding approach with fluorescing residues. The particle size of α-lac and nasunin complex is considerably more than the native protein. Far ultraviolet circular dichroism outcomes indicated that the second construction of the protein was rearranged in attending nasunin. Molecular docking pointed out that hydrogen binding has a significant influence on the constitution of nasunin-α-lac complex. The results suggested that α-lac could be a perfect carrier to nasunin loading for additional uses in nutrition field.

Mutual interactions of human serum albumin (HSA) with the two binuclear platinum complexes, containing [(bhq)Pt(dppm)2(Cl)Pt(bhq)(Cl)] (1) and [(bhq)Pt(dppm)2(PhMe)Pt(bhq)(CO2CF3)] (2), in which bhq=benzo[h]quinoline, and dppm=bis(diphenylphosphino) methane, were thoroughly investigated using spectroscopic and molecular modeling techniques. In this respect, fluorescence, Ultraviolet-Visible (UV-Vis) and circular dichroism (CD) spectroscopies, along with the docking and molecular dynamics simulations (MD) were utilized. Analysis of spectroscopic and MD simulation results revealed the structural alterations of HSA, upon binding to the binuclear platinum complexes, while the hydrogen bonding and van der Waals forces were found to mainly contribute to the protein-ligand intermolecular interactions. Results of far-UV CD measurements showed the strong ability of platinum complexes, in reducing the α-helical content of HSA, while other secondary structural features were increased. Due to their different chemical natures, these complexes bind to HSA in different manners. Binding constants and thermodynamic binding parameters between these complexes and HSA were calculated using the Stern−Volmer and van’t Hoff equations. Calculated thermodynamic binding parameters indicated that the interaction is spontaneous and enthalpy driven, through the static and dynamic quenching mechanisms, for complexes 1 and 2, respectively.

This study presents an overview on the recent advances in fluorescence methods for detection of catecholamines. In the past few decades, development of fluorescence probe has appeared as an important research area, which attracted a remarkable amount of attention due to its considerable sensitivity, simplicity, and selectivity. In this study, detection of catecholamines based on fluorescent metal nanoparticles, fluorescent semiconductor nanoparticles, fluorescent dyes, conjugated polymers, graphene, carbon nanotube sensors, biosensors, chemiluminescence as well as combination of Fluorescence methods with electrophorese, chromatography, electrochemical techniques, and Raman spectroscopy were evaluated.

A novel polyfunctional dipodal ligand, L = N,N'-bis[2-[(2-hydroxy-1-naphthyl)methyleneamino]ethyl]propanediamide (DOTA2HNAP) was developed and characterized through elemental and spectral analyses. The complexation behavior of the ligand was investigated with Co2+, Cu2+, and Zn2+ metal ions by potentiometric and spectrophotometric methods in the H2O-DMSO mixture (99:1) at µ = 0.1M KCl and 25 ± 1 °C. Four protonation constants for –OH of naphtholate groups and –N of imine were determined for the ligand. The ligand forms monomeric complexes of ML type with the metal ions, where coordination occurs through N-imine and O-naphtholate donors (N2O2). In the case of a complex of copper, an additional species, MLH-2, was formed due to ionization of the amide groups in a higher pH. The minimum energy structures of the metal complexes in solution have been obtained through molecular modeling studies by using the semi-empirical/ PM3 method. The photophysical properties of DOTA2HNAP were investigated in the presence of a wide range of biologically relevant metal ions. The fluorescence emission of the ligand at 450 nm (λex = 361 nm) exhibited a remarkable enhancement with Zn2+ ions (1 equivalent) at physiological pH amongst all metal ions. Such behavior enables the ligand to be considered as a suitable model for the detection of Zn2+ towards environmental applications.

UV-visible and Fluorescence spectroscopic methods were employed to study the interaction of human serum albumin (HSA) with Valacyclovir Hydrochloride. Additionally, molecular dynamics and molecular docking simulations were used to visualize and specify the binding site of Valacyclovir Hydrochloride. The Stern-Volmer and van't Hoff equations along with spectroscopic observations, were used to determine the binding and thermodynamic parameters. Overall obtained results revealed the presence of dynamic type of quenching mechanism in binding of Valacyclovir Hydrochloride to HSA, while the interaction was found to be entropy driven at domain III of HSA. Analyzing the protein ligand interactions with LIGPLOT, confirmed the dominance of hydrophobic interactions, while the hydrogen bonding interactions play the minor role.

In this research, the interaction of [CuL(DMF)], [NiL(DMF)] and [VOL(DMF)] (where L = ((E)-4-((2-amino-5-nitrophenylimino)methyl)benzene-1,3-diol)) complexes derived from tridentate Schiff base ligand with bovine serum albumin (BSA) and DNA was investigated via electronic absorption and fluorescence spectroscopy. The Ultraviolet-Visible (UV-Vis) spectra exhibited an isosbestic point for the complexes through titration with DNA. The experimental results showed the presence of intercalation interaction between the complexes and calf-thymus DNA (CT-DNA). The interaction of BSA protein and complexes was significant. The recorded florescence spectra of complexes interacting with DNA and BSA revealed the static quenching manner. The free binding energies of complexes and their interaction modes with DNA and BSA were determined by the molecular docking. MTT-dye reduction technique was applied to define cytotoxicity of [NiL(DMF)], [CuL(DMF)] and [VOL(DMF)] complexes against breast cancer 4T1 and colon carcinoma C26 cell lines. The [VOL(DMF)] complex had cytotoxic activity against 4T1 and C26 cell lines.

This paper is designed to examine the binding behavior of Coumarin with bovine -casein (βCN) through fluorescence spectroscopy and molecular modeling techniques. The data analysis on fluorescence titration experiments at various temperatures represents the enthalpy driven nature for the formation of Coumarin–βCN complex and the prevailed role of hydrogen bonds and van der Waals interactions in the binding process. The results also represent the static quenching of tryptophan and dynamics quenching of tyrosine and phenylalanine residues due to the binding of Coumarin. It can be concluded from molecular docking studies that Coumarin binds to several polar and non-polar residues in the hydrophobic core of βCN with the binding energy of -6.96 kcal mol-1. Finally, analysis of molecular dynamics (MD) simulation results suggested that the interactions between βCN and Coumarin are very stable and the binding of Coumarin restricted the flexibility of important residues in the binding site of this protein.

Several heterocyclic bioactive fluorescent 3-alkyl-3H-pyrazolo[4,3-a]acridin-11-carbonitriles were conveniently synthesized from the reaction of 1-alkyl-1H-indazoles with different aryl acetonitrile in basic methanol solution in good yields. The interactions of 3H-pyrazolo[4,3-a]acridin-11-carbonitriles with Human Serum Albumin (HSA) were studied by fluorescence spectroscopy. The binding of 3-alkyl-3H-pyrazolo[4,3-a]acridin-11-carbonitriles quenches the HSA fluorescence, revealing a 1:1 interaction with a binding constant of about 1.28 × 103 – 1.85 × 103 M-1.A decrease in fluorescence intensity at 339 nm, when excited at 295 nm, is attributed to changes in the environment of the protein fluorophores caused by the presence of the ligand. The results show that pyrazolo[4,3-a]acridines with R=propyl, butyl, isobutyl and R'=chlorine substituents have suitable thermodynamic and binding parameters with HSA.

In this work, interaction study of metal ions with quercetin, the secondary metabolite of plants was investigated by conductometric method and fluorescence spectroscopy. The conductometric study was done in acetonitrile solution. The conductance of the solution is measured after each addition of the quercetin to the cation solution. The fluorescence spectrum of quercetin was recorded in presence and absence of metal ions at maximum wave length (481 nm) upon excitation at 425 nm. Among the many cations titrated with quercetin, Mg2+, Al3+, Pb2+ and Zn2+ enhanced the intrinsic fluorescence of the quercetin while Cu2+, Ni2+ and Co2+ ions quench the intrinsic fluorescence emission of the quercetin solution. These different phenomena are observed due to the different release of absorbed energy in formed complex. The ability of quercetin molecule to form a complex with metal ions may be has an effect in quercetin anti-oxidative properties.