Spectrofluorimetric Assessment of Metoclopramide Hydrochloride Using Terbium Doped in PMMA Matrix Optical Sensor

A new, simple and accurate spectrofluorimetric method for the determination of metoclopramide hydrochloride was developed. The metoclopramide hydrochloride can remarkably enhance the luminescence intensity of the Tb³⁺ ion doped in PMMA matrix at λ_ex = 360 nm in methanol at pH 6.9. The intensity of the emission band at 545 nm of Tb³⁺ ion doped in PMMA matrix is increased due to the energy transfer from metoclopramide hydrochloride to Tb³⁺ in the excited stated. The effect of different parameters, e.g., pH, temperature, Tb³⁺ concentration, foreign ions that control the fluorescence intensity of the produced ion associate was critically investigated. The calibration curve of the emission intensity at 545 nm shows linear response of metoclopramide over a concentration range of 5 × 10⁻⁵–5.0 × 10⁻⁸ M with detection limit of 8.7 × 10⁻¹⁰ M. The method was used successfully for the determination of metoclopramide in pharmaceutical preparations and human serum. The average recovery of 99.48% with standard deviation of 0.32% and 96.98% with standard deviation of 0.4%, of pharmaceutical preparations and human serum respectively, were obtained which compared will with the results obtained from standard LC method of average recovery 99.04% and standard deviation of 0.6% and average recovery of 98.19% with standard deviation of 0.6% of pharmaceutical preparations and human serum, respectively.     

Determination of Paracetamol Based on its Quenching Effect on the Photoluminescence of CdTe Fluorescence Probes

L-Cysteine capped CdTe nanoparticles (NPs) were synthesized in aqueous medium, and their application as fluorescence probes in the determination of paracetamol was studied. The L-cysteine capped CdTe NPs were characterized by transmission electron microscopy, X-ray diffraction spectrometry, spectrofluorometry, ultraviolet-visible and Fourier transform infrared spectrometry. Based on the distinct fluorescence quenching of CdTe fluorescence probes in the presence of paracetamol, a simple, rapid and specific method for paracetamol determination was presented. Under optimum conditions, the relative fluorescence intensity of CdTe NPs was linearly proportional to paracetamol concentration from 1.0 × 10⁻⁸ mol/L to 1.6 × 10⁻⁷ mol/L with a detection limit of 4.2 × 10⁻⁹ mol/L. The proposed method was applied to detect paracetamol in commercial tablets with satisfactory results.     

Determination of Enoxacin Using Tb Composite Nanoparticles Sensitized Luminescence Method

In our study, terbium-acetylacetone (Tb-acac) composite nanoparticles have been prepared under vigorous ultrasonic irradiation. The nanoparticles are water soluble, stable and have extremely narrow emission bands and high internal quantum efficiencies. They were used as fluorescence probes in the determination of enoxacin (Enox) based on the fluorescence enhancement of nanoparticles through fluorescence resonance energy transfer (FRET). The influence of buffer solution on the fluorescence intensity was investigated. Under the optimum conditions, the fluorescence intensity of the Tb-acac-Enox system is linearly proportional to the Enox concentration in the Enox concentration range of 2 × 10⁻⁷–1 × 10⁻⁴ M. The correlation coefficient for the calibration curve was 0.9976. The limit of detection as defined by IUPAC, C _LOD = 3S _b/m (where S _b is the standard deviation of the blank signals and m is the slope of the calibration graph) was found to be 3 × 10⁻⁸ M. The relative standard deviation (RSD) for six repeated measurements of 1 × 10⁻⁴ M Enox was 1.35%. The method was applied to the determination of Enox in pharmaceutical formulation and recovery results were obtained from urine samples.     

Fluorescence Enhancement Effect for the Determination of Polychlorinated Biphenyls with Bovine Serum Albumin

A sensitive and selective method for the trace determination of 3, 3’, 4, 4’-tetrachlorobiphenyl (PCB77) by using bovine serum albumin (BSA) as a fluorescence probe was introduced. Under optimum conditions, the enhanced fluorescence intensity was proportional to the concentration of polychlorinated biphenyls in the range of 8.9 × 10⁻⁸–5.0 × 10⁻⁶ mol L⁻¹ for PCB77, and 5.0 × 10⁻⁷–5.0 × 10⁻⁶ mol L⁻¹ for 2, 2’, 5, 5’-tetrachlorbiphenyl (PCB52). The detection limits (S/N = 3) of PCB77 and PCB52 were 2.6 × 10⁻⁸ mol L⁻¹ and 2.9 × 10⁻⁷ mol L⁻¹, respectively. Furthermore, the fluorescence enhancement mechanism was discussed in detail. Results indicated that fluorescence enhancement of the system originated from the formation of BSA-PCBs complexes. In addition, PCBs were mainly bound to the tyrosine residues in BSA molecules.     

Impedance and FTIR studies on plasticized PMMA–LiN(CF<Subscript>3</Subscript>SO<Subscript>2</Subscript>)<Subscript>2</Subscript> nanocomposite polymer electrolytes

Plasticized polymer electrolytes composed of poly(methyl methacrylate) (PMMA) as the host polymer and lithium bis(trifluoromethanesulfonyl)imide LiN(CF₃SO₂)₂ as a salt were prepared by solution casting technique at different ratios. The ionic conductivity varied slightly and exhibited a maximum value of 3.65 × 10⁻⁵ S cm⁻¹ at 85% PMMA and 15% LiN(CF₃SO₂)₂. The complexation effect of salt was investigated using FTIR. It showed some simple overlapping and shift in peaks between PMMA and LiN(CF₃SO₂)₂ salt in the polymer electrolyte. Ethylene carbonate (EC) and propylene carbonate (PC) were added to the PMMA–LiN(CF₃SO₂)₂ polymer electrolyte as plasticizer to enhance the conductivity. The highest conductivities obtained were 1.28 × 10⁻⁴ S cm⁻¹ and 2.00 × 10⁻⁴ S cm⁻¹ for EC and PC mixture system, respectively. In addition, to improve the handling of films, 1% to 5% fumed silica was added to the PMMA–LiN(CF₃SO₂)₂–EC–PC solid polymer electrolyte which showed a maximum value at 6.11 × 10⁻⁵ S cm⁻¹ for 2% SiO₂.     

Fluorescence Enhancement of the Silver Nanoparticales – Curcumin - Cetyltrimethylammonium Bromide-nucleic Acids System and its Analytical Application

It is found that silver nanoparticles (AgNPs) can further enhance the fluorescence intensity of curcumin (CU) - cetyltrimethylammonium bromide (CTAB) – nucleic acids and improve its anti-photobleaching activity. Under optimum conditions, the enhanced fluorescence intensity is proportion to the concentration of nucleic acids in the range of 2.0 × 10⁻⁸–1.0 × 10⁻⁶ g mL⁻¹ for fish sperm DNA (fsDNA), 2.0 × 10⁻⁸–1.0 × 10⁻⁶ g mL⁻¹ for calf thymus DNA (ctDNA), 1.0 × 10⁻⁸–1.0 × 10⁻⁶ g mL⁻¹ for yeast RNA (yRNA), and their detection limits (S/N = 3) are 8.0 ng mL⁻¹, 10.5 ng mL⁻¹ and 5.8 ng mL⁻¹, respectively. This method is used for determining the concentration of DNA in actual sample with satisfactory results. The interaction mechanism is also studied.     

A Long Wavelength Excitable Fluorophore; Chloro Phenyl Imino Propenyl Aniline (CPIPA) for Selective Sensing of Hg (II)

In this study, a very sensitive and highly selective irreversible optical chemical sensor (optode) for mercury ions was described. The sensing scheme was based on the interaction of Hg (II) with a newly synthesized fluoroionophore; chloro phenyl imino propenyl aniline (CPIPA) in plasticized PVC membrane. The sensor membranes were tested for the determination of mercury ion in aqueous solutions by batch and flow-through methods. The optodes allow determination of Hg (II) in the working range of 1.0 × 10⁻⁹–1.0 × 10⁻⁵ M with a detection limit of 4.3 ppb. The sensor exhibited excellent selectivity for Hg (II) with respect to several common alkali, alkaline earth and transition metal ions. The association constant of the 1:1 complex formation for Hg (II) was found to be K_a = 1.86 × 10⁵ M⁻¹. The CPIPA exhibited high fluorescence quantum yield, long excitation and emission wavelength and high Stokes’ shift values in the solid matrix which makes it compatible with solid state optics.     

Preparation and Characterization of CdHgTe Nanoparticles and Their Application on the Determination of Proteins

CdHgTe nanoparticles (NPs) with the emission in the near-infrared regions were prepared in aqueous solution, and were characterized by transmission electron microscopy, X-ray diffraction spectrometry, spectrofluorometry and ultraviolet-visible spectrometry. Based on the fluorescence quenching of CdHgTe NPs in the presence of proteins, a novel method for the determination of proteins with CdHgTe NPs as a near-infrared fluorescence probe was developed. Maximum fluorescence quenching was observed with the excitation and emission wavelengths of 500 and 693 nm, respectively. Under the optimal conditions, the calibration graphs were linear in the range of 0.04 × 10⁻⁶–5.6 × 10⁻⁶ g ml⁻¹ for lysozyme (Lyz) and 0.06 × 10⁻⁶–6.1 × 10⁻⁶ g ml⁻¹ for bovine hemoglobin (BHb), respectively. The limits of detection were 13 ng ml⁻¹ for Lyz and 27 ng ml⁻¹ for BHb, respectively. Four synthetic samples were determined and the results were satisfied.     

Conductivity, dielectric behaviour and thermal stability studies of lithium ion dissociation in poly(methyl methacrylate)-based gel polymer electrolytes

Thin films of poly(methyl methacrylate) (PMMA) with lithium triflate (LiCF₃SO₃) were prepared by using the solution-casting method with PMMA as the host polymer. Ionic conductivity and dielectric measurements were carried out on these films. The highest conductivity for polymer electrolyte with a ratio of 65:35 was found to be 9.88 × 10⁻⁵ S cm⁻¹, which is suitable for the production of mobile phone battery. Thermal gravimetric analysis was carried out to evaluate the thermal stability of the polymer electrolyte. The addition of salts will increase thermal stability of the polymer electrolyte.     

Interaction of Thyroxine with 7 Hydroxycoumarin: A Fluorescence Quenching Study

The interaction between thyroxine hormone and 7 hydroxycoumarin (7HC) was investigated using fluorescence quenching method. The experimental results showed that thyroxine could quench the fluorescence of 7HC by forming the 7HC–thyroxine complex with static quenching. The apparent binding constants (K) between 7HC and thyroxine were determined to be 1.51 × 10⁴ (297 K) and 9.06 × 10³ (310 K). The binding sites (n) 0.98 ± 0.1. The thermodynamic parameters showed that the interaction between 7HC and thyroxine was driven mainly by hydrogen bonding interactions and van der Waals force. Calibration for thyroxine, based on quenching titration data, was linear in the concentration range 2.0 × 10⁻⁸ to 3.0 × 10⁻⁷ mol/l. The relative standard deviation was 2.58% for 2.0 × 10⁻⁷ mol/l thyroxine (n = 4) and the 3σ limit of detection was 3.42 × 10⁻⁸ mol/l in cationic surfactant CTAB medium.     

Influence of temperature and ethanol content on aggregation of rhodamine 6G molecules in aqueous ethanol solutions

The effect of temperature on absorption spectra of Rhodamine 6G at concentrations of 10⁻⁶ and 10⁻³ M in water:ethanol solutions of various ethanol content was studied. The dimeric molecular fraction of Rhodamine 6G (10⁻³ M) was found as a function of temperature and ethanol content in the aqueous solution. It was shown that the absorption spectrum of Rhodamine 6G dimers (10⁻³ M) is dependent on temperature and ethanol content in the aqueous solution. Based on the relationship between J-and H-bands in the absorption spectrum of Rhodamine 6G dimers, both the angle between planes of associated Rhodamine 6G dye molecules and the free enthalpy of association were calculated. The structure of Rhodamine 6G dimers depends essentially on the ethanol content and aqueous ethanol solution temperature while experiencing the most temperature changes at an ethanol concentration of 25%. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 640–645, September–October, 2008.     

Spectrofluorimetric Determination of Coumarin in Commercial Tablets

A simple, rapid and effective analytical method based on fluorescence spectroscopy for the determination of coumarin in pharmaceutical formulations without pre-treatment or pre-concentration step was development. Coumarin had maximum excitation and emission at 310 nm and 390 nm, respectively. Optimum conditions for the detection of coumarin were investigated. Under optimized conditions, we observed a linear behavior for the sign of coumarin in the concentration range of 2.5 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹, with linearity of 0.998 and sensitivity of 2.9 × 10¹⁰ u.a/mol L⁻¹. The proposed method was validated in terms of accuracy, precision and specificity of coumarin using the standard addition and external calibration. It was noted that the results support (P < 0.05), indicating that the matrices were not an interference in the determination of coumarin by fluorescence spectroscopy. The results were favorable compared with those obtained by reference chromatographic methods.     

Oxygen-dependent Oxidation of Fe(II) to Fe(III) and Interaction of Fe(III) with Bovine Serum Albumin, Leading to a Hysteretic Effect on the Fluorescence of Bovine Serum Albumin

The serum albumin is the most abundant protein in blood plasma and the iron is essential for many cellular processes. However, the interaction between Fe³⁺ and haem-free serum albumin remains unclear. Here we provide evidence for the fact that haem-free BSA possesses one specific Fe³⁺-binding site. The binding of Fe³⁺ to BSA results in a significant quenching of the Trp fluorescence of BSA. The average apparent dissociation constant value for the interaction of Fe³⁺ and BSA is 3.46 × 10⁻⁸ ± 3 × 10⁻¹⁰ M at 37 °C and 3.30 × 10⁻⁸ ± 5 × 10⁻¹⁰ M at 25 °C, respectively, as determined by fluorescence titration. Addition of 50 μM Fe²⁺ to 1 μM BSA results in an obvious hysteretic effect on the fluorescence of BSA. The time-dependent fluorescence quenching of BSA by Fe²⁺ is not caused by the Fe²⁺-induced conformational change of BSA, but the oxygen-dependent oxidation of Fe²⁺ to Fe³⁺. Fe²⁺ undergoes an oxygen-dependent oxidation to Fe³⁺ under aerobic conditions, which is accelerated by the interaction of BSA with Fe³⁺ and extensively inhibited under anaerobic conditions. The results suggest that BSA may take part in non-transferrin bound iron transfer.     

Pyrophosphate Selective Recognition in Aqueous Solution Based on Fluorescence Enhancement of a New Aluminium Complex

A novel and simple fluorescence enhancement method for selective pyrophosphate(PPi) sensing was proposed based on a 1:1 metal complex formation between bis(8-hydroxy quinoline-5-solphonat) chloride aluminum(III) (Al(QS)₂Cl), (L) and PPi in aqueous solution. The linear response range covers a concentration range of 1.6 × 10⁻⁷ to 1.0 × 10⁻⁵ mol/L of PPi and the detection limit of 2.3 × 10⁻⁸ mol/L. The association constant of L-PPi complex was calculated 2.6 × 10⁵ L/mol. L was found to show selectively and sensitively fluorescence enhancement toward PPi over than I₃^-, NO₃^-, CN⁻, CO₃²⁻, Br⁻, Cl⁻, F⁻, H₂PO4⁻ and SO₄²⁻, which was attributed to higher stability of inorganic complex between pyrophosphate and L.     

Fluorescent Method for the Determination of Sulfide Anion with ZnS:Mn Quantum Dots

Water-soluble Mn²⁺-doped ZnS quantum dots (QDs) were prepared using mercaptoacetic acid as the stabilizer. The optical properties and structure features were characterized by X-Ray, absorption spectrum, IR spectrum and fluorescence spectrum. In pH 7.8 Tris-HCl buffer, the QDs emitted strong fluorescence peaked at 590 nm with excitation wavelength at 300 nm. The presence of sulfide anion resulted in the quenching of fluorescence and the intensity decrease was proportional to the S²⁻ concentration. The linear range was from 2.5 × 10⁻⁶ to 3.8 × 10⁻⁵ mol L⁻¹ with detection limit as 1.5 × 10⁻⁷ mol L⁻¹. Most anions such as F⁻, Cl⁻, Br⁻, I⁻, CH₃CO₂ ⁻, ClO₄ ⁻, CO₃ ²⁻, NO₂ ⁻, NO₃ ⁻, S₂O₃ ²⁻, SO₃ ²⁻ and SO₄ ²⁻ did not interfere with the determination. Thus a highly selective assay was proposed and applied to the determination of S²⁻ in discharged water with the recovery of ca. 103%.     

Determination of Total Antioxidant Capacity by a New Spectrofluorometric Method Based on Ce(IV) Reduction: Ce(III) Fluorescence Probe for CERAC Assay

A Ce(IV)-based reducing capacity (CERAC) assay was developed to measure the total antioxidant capacity (TAC) of foods, in which Ce(IV) would selectively oxidize antioxidant compounds but not citric acid and reducing sugars which are not classified as antioxidants. The method is based on the electron-transfer (ET) reaction between Ce(IV) ion and antioxidants in optimized acidic sulphate medium (i.e., 0.3 M H₂SO₄ and 0.7 M Na₂SO₄) and subsequent determination of the produced Ce(III) ions by a fluorometric method. The fluorescent product, Ce(III), exhibited strong fluorescence at 360 nm with an excitation wavelength of 256 nm, the fluorescence intensity being correlated to antioxidant power of the original sample. The linear concentration range for most antioxidants was quite wide, e.g., 5.0 × 10⁻⁷–1.0 × 10⁻⁵ M for quercetin. The developed procedure was successfully applied to the TAC assay of antioxidant compounds such as trolox, quercetin, gallic acid, ascorbic acid, catechin, naringin, naringenin, caffeic acid, ferulic acid, glutathione, and cysteine. The proposed method was reproducible, additive in terms of TAC values of constituents of complex mixtures, and the trolox equivalent antioxidant capacities (TEAC coefficients) of the tested antioxidant compounds gave good correlations with those found by reference methods such as ABTS and CUPRAC.     

Binding of Quercetin to Lysozyme as Probed by Spectroscopic Analysis and Molecular Simulation

The binding of quercetin to lysozyme (LYSO) in aqueous solution was investigated by fluorescence spectroscopy, UV-vis absorption spectroscopy and molecular simulation at pH 7.4. The fluorescence quenching of LYSO by addition of quercetin is due to static quenching, the binding constants, K _a , were 3.63 × 10⁴, 3.31 × 10⁴ and 2.85 × 10⁴ L·mol⁻¹ at 288, 298 and 308 K, respectively. The thermodynamic parameters, enthalpy change, ∆H, and entropy change, ∆S, were noted to be −7.56 kJ·mol⁻¹ and 61.07 J·mol⁻¹·K⁻¹. The results indicated that hydrophobic interaction may play a major role in the binding process. The distance r between the donor (LYSO) and acceptor (quercetin) was determined as 3.34 nm by the fluorescence resonance energy transfer. The synchronous fluorescence spectroscopy showed the polarity around the tryptophan residues increased and the hydrophobicity decreased. Furthermore, the study of molecular simulation indicated that quercetin could bind to the active site (a pocket made up of 24 amino-acid residues) of LYSO mainly via hydrophobic interactions and that there were hydrogen interactions between the residues (Gln 57, Ile 98) of LYSO and quercetin. The accessible surface area (ASA) calculation verified the important roles of tryptophan (Trp) residues during the binding process.     

New Fluorescent Antitumour Cisplatin Analogue Complexes. Study of the Characteristics of their Binding to DNA by Flow Injection Analysis

The flow injection technique is applied to study the binding to DNA of new platinum complexes—E₁: ethylenediaminechlorocholylglycinateplatinum(II): [PtCl(CG)(en)], C₅₄H₉₂O₁₂Pt and E₂: ethylenediaminebischolylglycinateplatinum(II): [Pt(CG)₂(en)], C₂₈H₅₀ClN₃O₆Pt—derived from cisplatin in which the exchangeable ligands were replaced by bile acids, such that these anticancer drugs have less toxicity and less resistance is developed towards them. Both compounds are fluorescent and their fluorescence is enhanced when they form adducts with DNA, a property that is extremely useful for monitoring the cytotoxic activity and their mechanisms of action. The binding parameters to DNA of E₁ [apparent intrinsic binding constant K_E1: (11.2 ± 0.4) × 10³ M⁻¹ and maximum number of binding sites per nucleotide, n _E1: 0.121 ± 2 × 10⁻³) and E₂ (K_E2: 9.2 ± 0.7) × 10³ M⁻¹ and n _E2 0.098 ± 2 × 10⁻³] were determined following the Scatchard method and the type of binding was studied experimentally through the modifications introduced by each of the compounds into the ethidium bromide–DNA bond.     

Spectrofluorimetric Assessment of Hydrochlorothiazide Using Optical Sensor Nano-Composite Terbium Ion Doped in Sol-Gel Matrix

A new, simple, sensitive and selective spectrofluorimetric method for the determination of Hydrochlorothiazide was developed in acetonitrile at pH 6.2. The Hydrochlorothiazide can remarkably enhance the luminescence intensity of the Tb³⁺ ion doped in sol–gel matrix at λ_ex = 370 nm. The intensity of the emission band of Tb³⁺ ion doped in sol–gel matrix was increased due to the energy transfer from the triplet excited state of Hydrochlorothiazide to (⁵D₄) excited energy state of Tb³ ion. The enhancement of the emission band of Tb³⁺ ion doped in sol–gel matrix at (⁵D₄→⁷ F₅) 545 nm was directly proportion to the concentration of Hydrochlorothiazide with a dynamic ranges of 5.0 × 10⁻¹⁰—5.0 × 10⁻⁶ mol L⁻¹ and detection limit of 2.2 × 10⁻¹¹ mol L⁻¹.