Fluorescence Intensity Of Complex Research Articles

Determination of phenformin hydrochloride employing a sensitive fluorescent probe

A complexation of non-fluorescent phenformin hydrochloride (PFH) with cucurbit [7]uril (CB [7]) in aqueous solution was investigated using the fluorescent probe of palmatine (PAL) coupled with CB [7]. The fluorescent probe of CB [7]–PAL exhibited strong fluorescence in aqueous solution, which was quenched gradually with the increase of PFH. This effect is observed because when PFH was added to the host–guest system of CB [7]–PAL, PFH and PAL competed to occupy the CB [7] cavity. Portions of the PAL molecule were expelled from the CB [7] cavity owing to the introduction of PFH. Based on the significant quenching of the supramolecular complex fluorescence intensity, a fluorescence method of high sensitivity and selectivity was developed to determine PFH with good precision and accuracy for the first time. The linear range of the method was 0.005–1.9μgmL−1 with a detection limit of 0.003μgmL−1. In this work, association constants (K) of PFH with CB [7] were also determined. KCB [7]–PFH=(2.52±0.05)×105Lmol−1. The ability of PFH to bind with CB [7] is stronger than that of PAL. The results of a density functional theory calculation authenticated that the moiety of PFH was embedded in the hydrophobic cavity of CB [7] tightly, and the nitrogen atom is located in the vicinity of a carbonyl-laced portal in the energy-minimized structure. The molecular modelling of the interaction between PFH and CB [7] was also confirmed by 1H NMR spectra (Bruker 600MHz).

Construction of multifunctional materials based on Tb3+and croconic acid, directed by K+cations: synthesis, structures, fluorescence, magnetic and ferroelectric behaviors

In order to obtain multifunctional molecular-based materials, especially multiferroics, a polar structure is essential. In this study, we find that intelligently using the K+ cation can effectively achieve this goal in the Tb3+-croconate hybrid system. Four rationally designed complexes based on Tb3+ and croconic acid have been synthesized and structurally characterized. The complexes have the formula [Tb2(C5O5)3(H2O)12]·2H2O (1), [KTb(C5O5)2(H2O)6]·1.5H2O (2), [Tb(C5O5)(Hdpa)(H2O)5]·H2O (3) and [KTb(C5O5)2(H2O)5]·2H2O (4), (H2C5O5 = croconic acid, H2dpa = 2,5-dipicolinic acid). The structures of the complexes were remarkably different after K+ was introduced. Complex 1, constructed by eight-coordinate Tb3+ nodes connected with C5O52− and H2O, is a novel 0D metal–organic architecture with abundant O–H⋯O hydrogen bonds, whereas complex 2 is a 1D chain built by C5O52− spacers bridging five-coordinate K+ and eight-coordinate Tb3+ ions. Complex 3 has deprotonated C5O52− and Hdpa− anions connected to an eight-coordinate Tb3+ center, to give a polar 0D structure. Complex 4, constructed by nine-coordinate Tb3+ and ten-coordinate K+ nodes connected with C5O52− and H2O, is a novel, polar 3D metal–organic architecture. The fluorescence spectra of 1–4 show characteristic emission bands of Tb3+ ions. Interestingly, the fluorescence intensities of complexes 3 and 4, especially emissions at 370 nm, are significantly enhanced compared to the intensities of 1 and 2, owing to the structural differences. Magnetic susceptibility studies of complexes 1–4 show similar patterns. Furthermore, complex 4 exhibits a ferroelectric hysteresis loop at room temperature, due to its polarity. Thus, in this work, by merely adjusting the polarity of the structure, a series of different, versatile compounds were obtained as potential multifunctional materials.

Fluorescence enhancement of europium complexes by core–shell Ag@SiO2 nanoparticles

Three kinds of core–shell Ag@SiO2 nanoparticles with shell thickness of around 10, 15, and 25nm, respectively, have been prepared by modified Stöber method and used for fluorescence enhancement. Six kinds of europium complexes with halobenzoic acid have been synthesized. Elemental analysis and lanthanide coordination titration show that the complexes have the compositions of Eu(p-XBA)3·H2O and Eu(o-XBA)3·2H2O (X=F, Cl, Br). The fluorescence spectra investigation indicates that the introduction of Ag@SiO2 nanoparticles into the europium complexes’ solution can significantly enhance the fluorescence intensities of the complexes. The sequence of enhancement factors for halobenzoic acid complexes with different halogen atoms is F<Cl<Br, and the fluorescence enhancement factors increase as the excitation wavelength of complexes increase. When the thickness of the SiO2 shell is 25nm, the fluorescence intensity of the europium complexes can reach a maximum enhancement factor of 5.1. The fluorescence enhancement mechanism may be the metal-enhanced fluorescence resulting from surface plasmon resonance of nanoparticles. And the nanoparticles near the complexes can effectively prevent complexes from the interaction with the solvent molecules, leading to a decrease of nonradiative energy transfer and the suppression of luminescence quench.

Two dinuclear Ru(II) polypyridyl complexes with different photophysical and cation recognition properties

Two dinuclear Ru(II) polypyridyl complexes functionalized with vacant coordination sites have been designed and synthesized. Their photophysical properties and interactions with various metal ions have been investigated at room temperature. The two complexes exhibit different UV/Vis absorption and emission intensities. When titrated with various metal ions, complex [{Ru(bpy)2}2(μ2-L1)]4+ exhibits a notable fluorescence quenching in the presence of Cu2+ in H2O–CH3CN media (1:1, v/v); its analogous complex [{Ru(bpy)2}2(μ2-L2)]4+ exhibits no cation selectivity, the fluorescence intensity of complex [{Ru(bpy)2}2(μ2-L2)]4+ has been enhanced by several transition metal ions due to prevention of the photo-induced electron transfer process. The fluorescence titration spectra and Benesi–Hildebrand expression reveal the formation of a 1:1 bonding mode between [{Ru(bpy)2}2(μ2-L1)]4+ and Cu2+ ion with the association constant of 5.50×104M−1.

Rapid and sensitive determination of clenbuterol in porcine muscle and swine urine using a fluorescent probe

The feed additive Clenbuterol hydrochloric acid (CLB) is non-fluorescent, thus it is difficult to quantify through direct fluorescent method. Palmatine (PAL) can react with cucurbit[7]uril (CB[7]) to form stable complexes as a fluorescent probe. Significant quenching of the fluorescence intensity of the CB[7]–PAL complex was observed with the addition of CLB. Based on the significant quenching of the supramolecular complex fluorescence intensity, a novel spectrofluorimetric method with high convenience, selectivity and sensitivity was developed for the determination of CLB. The fluorescence quenching values (ΔF) showed good linear relationship with CLB concentrations from 0.011μgmL−1 to 4.2μgmL−1 with a detection limit 0.004μgmL−1. In this research, an ultrasound treatment replaced the former time-consuming shake method to form stable complexes. The proposed spectrofluorimetric method had been successfully applied to the determination of CLB in porcine muscle and swine urine with good precision and accuracy. The competing reaction and the supramolecular interaction mechanisms between the CLB and PAL as they fight for occupancy of the CB[7] cavity were studied using spectrofluorimetry, 1H NMR, and molecular modeling calculations. Interestingly, results indicate that two stable CB[7]–CLB complexes were formed.

Two novel tetranuclear zinc(II) clusters with different topological structures: Crystal structures and luminescence properties

Two novel tetranuclear zinc(II) clusters with different topological structures have been synthesized by using Zn(ClO4)2·6H2O, sodium azide and potentially multidentate Schiff base ligands containing different substituent groups. The two complexes have been characterized by elemental analysis, IR, single crystal X-ray diffraction and fluorescence studies. Structural studies reveal that [Zn4(HL1)4(μ1,1-N3)2(N3)2] (1) is a linear tetranuclear cluster whereas [Zn4(HL2)4(μ1,1-N3)4] (2) is a square-planar tetranuclear cluster. Both two complexes display intraligand (π→π*) fluorescence. Due to the heavy atom effect which increases the probability for intersystem crossing to the triplet state, the fluorescence intensity of complex 2 is much lower than that of complex 1.

Determination of paraquat in water samples using a sensitive fluorescent probe titration method

Paraquat (PQ), a nonselective herbicide, is non-fluorescent in aqueous solutions. Thus, its determination through direct fluorescent methods is not feasible. The supramolecular inclusion interaction of PQ with cucurbit[7]uril was studied by a fluorescent probe titration method. Significant quenching of the fluorescence intensity of the cucurbit[7]uril-coptisine fluorescent probe was observed with the addition of PQ. A new fluorescent probe titration method with high selectivity and sensitivity at the ng/mL level was developed to determine PQ in aqueous solutions with good precision and accuracy based on the significant quenching of the supramolecular complex fluorescence intensity. The proposed method was successfully used in the determination of PQ in lake water, tap water, well water, and ditch water in an agricultural area, with recoveries of 96.73% to 105.77%. The fluorescence quenching values (ΔF) showed a good linear relationship with PQ concentrations from 1.0 × 10−8 to 1.2× 10−5 mol/L with a detection limit of 3.35 × 10−9 mol/L. In addition, the interaction models of the supramolecular complexes formed between the host and the guest were established using theoretical calculations. The interaction mechanism between the cucurbit[7]uril and PQ was confirmed by 1H NMR spectroscopy.

Competitive supramolecular interaction of carbachol and berberine with cucurbit[7]uril and its analytical application

Carbachol (CCH) is non-fluorescent in aqueous solution. This property makes its determination through direct fluorescent method impossible. Berberine (BER) exhibits very weak fluorescence emissions in aqueous solution. However, In acidic medium and room temperature, BER can react with CB[7] to form stable complex and the fluorescence intensity of the complex was greatly enhanced. The dramatic quenching of the fluorescence intensity of CB[7]–BER complex was observed with the addition of CCH. The competitive supramolecular interaction between CCH and BER for occupancy of the cucurbit[7]uril (CB[7]) cavity was studied by spectrofluorometry, 1H NMR, and molecular modeling calculation. Based on the significant quenching of the supramolecular complex fluorescence intensity, a simple, rapid, and sensitive fluorescence probe method for the determination of CCH in pharmaceutical dosage forms and in biological fluids was developed. The linear range of the method was from 0.01 μg mL− 1 to 1.5 μg mL− 1. The limit of detection was 0.003 μg mL− 1. This shows that the proposed method has promising potential for quality control, forensic identification, drug abuse or therapeutic monitoring, pharmacokinetics, and clinical application.

Supramolecular Interaction of Gliclazide with Cucurbit[7]uril and its Analytical Application

Gliclazide (GLZ) is non-fluorescent in aqueous solution. This property makes its determination through direct fluorescent methods impossible. Palmatine (PAL) exhibits very weak fluorescence emissions in aqueous solution. However, in acidic media at room temperature, PAL can react with cucurbit[7]uril (CB[7]) to form a stable complex and the fluorescence intensity of the complex is greatly enhanced. Dramatic quenching of the fluorescence intensity of the CB[7]–PAL complex was observed with the addition of GLZ. The competing reactions and the supramolecular interaction mechanisms between GLZ and PAL as they fight for occupancy of the CB[7] cavity were studied using spectrofluorimetry, 1H NMR spectroscopy, and molecular modelling calculations. The association constants of the complexes formed between the host and the guest were determined. Based on the significant quenching of the supramolecular complex fluorescence intensity, a fluorescent probe method of high sensitivity was developed to determine GLZ in its pharmaceutical dosage forms and in human plasma with good precision and accuracy. The linear range of the method was from 0.003 to 2.100 μg mL–1. The limit of detection was 0.001 μg mL–1. This shows that the proposed method has promising potential for therapeutic monitoring and pharmacokinetics and for clinical application.

Study on the supramolecular interaction of astemizole with cucurbit[7]uril and its analytical application

Astemizole (AST) is non-fluorescent in aqueous solution. This property makes its determination through direct fluorescence methods difficult. Reaction and supramolecular interaction mechanisms, between AST and palmatine (PAL) as they compete for occupancy of the cucurbit[7]uril (CB[7]) cavity, were studied using spectrofluorimetry, 1H NMR, and molecular modeling calculations. The association constants of the complexes formed between the host and the guest were determined. Based on the significant quenching of the supramolecular complex fluorescence intensity, a fluorescent probe method of high sensitivity and selectivity was developed to determine AST in its pharmaceutical dosage forms and in urine samples with good precision and accuracy. The linear range of the method was from 0.02 μg mL−1 to 2.2 μg mL−1. The detection limit was 0.007 μg mL−1. This shows that the proposed method has promising potential for therapeutic monitoring and pharmacokinetics and for clinical application.

Elimination of autofluorescence background from fluorescence tissue images by use of time-gated detection and the AzaDiOxaTriAngulenium (ADOTA) fluorophore

Sample autofluorescence (fluorescence of inherent components of tissue and fixative-induced fluorescence) is a significant problem in direct imaging of molecular processes in biological samples. A large variety of naturally occurring fluorescent components in tissue results in broad emission that overlaps the emission of typical fluorescent dyes used for tissue labeling. In addition, autofluorescence is characterized by complex fluorescence intensity decay composed of multiple components whose lifetimes range from sub-nanoseconds to a few nanoseconds. For these reasons, the real fluorescence signal of the probe is difficult to separate from the unwanted autofluorescence. Here we present a method for reducing the autofluorescence problem by utilizing an azadioxatriangulenium (ADOTA) dye with a fluorescence lifetime of approximately 15 ns, much longer than those of most of the components of autofluorescence. A probe with such a long lifetime enables us to use time-gated intensity imaging to separate the signal of the targeting dye from the autofluorescence. We have shown experimentally that by discarding photons detected within the first 20 ns of the excitation pulse, the signal-to-background ratio is improved fivefold. This time-gating eliminates over 96 % of autofluorescence. Analysis using a variable time-gate may enable quantitative determination of the bound probe without the contributions from the background.

Determination of Pesticide Residue Cartap Using a Sensitive Fluorescent Probe

The insecticide cartap (CP) is non-fluorescent in aqueous solutions. This property makes its determination through direct fluorescent method difficult. In acidic medium and at room temperature, palmatine (PAL) can react with cucurbit[7]uril (CB[7]) to form stable complexes, and the fluorescence intensity of the complex is greatly enhanced. Significant quenching of the fluorescence intensity of the CB[7]-PAL complex was observed with the addition of cartap. Based on the significant quenching of the supramolecular complex fluorescence intensity, a new spectrofluorimetric method with high sensitivity and selectivity was developed to determine cartap in aqueous solution. The fluorescence quenching values (ΔF) showed good linear relationship with cartap concentrations from 0.009 to 2.4 μg mL−1 with a detection limit 0.0029 μg mL−1. The proposed method had been successfully applied to the determination of cartap residues in grain and vegetable with recoveries of 87.4-103%. In addition, the association constants of the complexes formed between the host and the guest were determined. The competing reaction and the supramolecular interaction mechanisms between the cartap and PAL as they fight for occupancy of the CB[7] cavity were studied using spectrofluorimetry, 1H NMR and molecular modeling calculations.

Determination of amantadine and rimantadine using a sensitive fluorescent probe

Amantadine hydrochloride (AMA) and rimantadine hydrochloride (RIM) are non-fluorescent in aqueous solutions. This property makes their determination through direct fluorescent method difficult. The competing reactions and the supramolecular interaction mechanisms between the two drugs and coptisine (COP) as they fight for occupancy of the cucurbit[7]uril (CB[7]) cavity, were studied using spectrofluorimetry, 1H NMR, and molecular modeling calculations. Based on the significant quenching of the supramolecular complex fluorescence intensity, a fluorescent probe method of high sensitivity and selectivity was developed to determine AMA or RIM in their pharmaceutical dosage forms and in urine samples with good precision and accuracy. The linear range of the method was from 0.0040 to 1.0μgmL−1 with a detection limit ranging from 0.0012 to 0.0013μgmL−1. This shows that the proposed method has promising potential for therapeutic monitoring and pharmacokinetics and for clinical application.

Crystal structures and thermodynamic properties of lanthanide complexes with 2-chloro-4,5-difluorobenzoate and 1,10-phenanthroline

A series of lanthanide complexes with the 2-chloro-4,5-difluorobenzoate (2-cl-4,5-dfba) and 1,10-phenanthroline (phen), have been synthesized with the formulae of [La(2-cl-4,5-dfba)3phen]n·nH2O (1), [Nd(2-cl-4,5-dfba)3phenH2O]2 (2), [Ln(2-cl-4,5-dfba)3phen]2 (Ln=Eu (3), Ho (4)). The complexes are characterized by elemental analysis, infrared and fluorescent spectra and X-ray single-crystal diffraction. The structures of the four complexes are very different. Complex 1 is an infinite 1D chain polymeric structure formed by the asymmetric units with the mirror growth pattern. Each La3+ ion is coordinated to four bridging carboxylic groups, two tridentate chelating–bridging carboxylic groups, simultaneous with one phen molecule, giving the coordination number of nine. In the molecular structures of complexes 2 and 3, two Ln3+ ions are linked by four carboxyl groups, forming two binuclear molecules. In addition, each Nd3+ ion in complex 2 is bonded to one H2O molecule and one carboxyl group by monodentate mode, one phen molecule by bidentate chelating, and each Eu3+ ion is also chelated to one phen molecule and one carboxyl group in complex 3. And in complex 4, the Ho3+ ion yields a eight-coordinated distorted square anti-prism coordination geometry. The three-dimensional IR accumulation spectra of gaseous products for complexes 1 to 4 are analyzed and further authenticated the thermal decomposition processes with TG-DTG curves. The heat capacities of complexes 2 to 4 are measured and fitted to a polynomial equation by the least squares method on the basis of the reduced temperature x (x=[T−(Tmax+Tmin)/2]/[(Tmax−Tmin)/2]). Then the smoothed molar heat capacities and thermodynamic functions of complexes 2 to 4 are calculated. The fluorescence intensity of complex 3 is markedly improved as well.

Facile synthesis of a water-soluble bidentate pyridine–acid ligand and its application in quantifying bovine serum albumin by fluorescence spectroscopy

A water-soluble bidentate pyridine–acid ligand (1) was synthesized. The ligand 1 had a stronger interaction with Mo6+ than with other metal ions. Subsequently, we found that a linear increase in the fluorescence intensity of complex (1-Mo) was observed upon addition of bovine serum albumin (BSA).

Copper(ii) complexes as turn on fluorescent sensors for nitric oxide

Two copper(II) complexes, 1 and 2, of two tridentate N-donor ligands, L(1) and L(2) [L(1) = dansyl derivative of bis-[3-(dimethylamino)-propyl]amine; L(2) = dansyl derivative of dipropylenetriamine] were synthesized and characterized. The quenched fluorescence intensity of complexes 1 and 2, in degassed methanol or aqueous (buffered at pH 7.2) solution, was found to reappear on exposure to nitric oxide. This is attributed to the reduction of paramagnetic Cu(II) center by nitric oxide to diamagnetic Cu(I).

Supramolecular interaction of cucurbit[n]urils and coptisine by spectrofluorimetry and its analytical application

The supramolecular interaction of a homologous series of cucurbit[n]uril (CB[n], n=5, 6, 7, 8) hosts and coptisine (COP) was studied by spectrofluorimetry. All of the CB[n]s were found to react with COP to form 1:1 host-guest stable complexes and the fluorescence intensity of the complexes was greatly enhanced. The apparent association constants of the complexes were 1.44 x 10(4), 1.28 x 10(4), 1.86 x 10(4) and 1.26 x 10(4)L mol(-1) for CB[5], CB[6], CB[7] and CB[8], respectively. In addition, CB[5] and CB[7] exhibited a higher fluorescence signal than CB[6] and CB[8]. The fluorescence intensity of the complex with CB[7] was enhanced 70-fold compared to that of the studied drug itself. Based on the significant enhancement of fluorescence intensity of supramolecular complex, a simple, rapid, highly sensitive, and selective spectrofluorimetric method was developed for the determination of COP in aqueous solution in the presence of CB[7]. At the optimum reaction conditions, a linear relationship was obtained in the range from 0.05 to 1700 ng mL(-1) with a detection limit of 0.012 ng mL(-1). The proposed method was successfully applied for the determination of the drug in urine and serum samples.

Chelation of spironaphthoxazine with zinc ions and its photochromic behavior during the sol–gel–xerogel transitions of alkyl silicon alkoxide

The isomerization and zinc-chelation of spironaphthoxazine (SNO) during the course of the sol–gel–xerogel transitions of the tetraethylorthosilicate (TEOS) system and the mixture systems of TEOS and octyltriethoxysilane (OcTES) have been investigated by measuring the fluorescence and excitation spectra as a function of time. The influence of the hydrophobic octyl groups on the spectroscopic behavior of SNO in the TEOS and TEOS–OcTES systems containing zinc ions have been discussed. A fluorescence spectrum at around 430 nm, observed just after the preparation of the TEOS system, was similar to that of SNO observed in protic highly-polar solvents due to the presence of the ethanol solvent in the system. A weak fluorescence spectrum was observed at around 400 nm just after the preparation of the TEOS–OcTES systems. This spectrum corresponded to that of SNO in low-polar solvents due to the hydrophobicity of OcTES. The fluorescence spectra in both systems were gradually red-shifted to around 450 nm along with the progress of the sol–gel transition, indicating that SNO (ring-closed form) interacts with silanol groups generated by the hydrolysis of the alkoxides. A spectrum due to the zinc complex of the SNO-derivative, merocyanine (MC, ring-open form), also appeared at around 540 nm during the initial stage of the sol–gel–xerogel transitions (around the gelation point) for both systems. SNO molecules and zinc ions were concentrated in prestructural pores and easily interacted with each other. The fluorescence intensity of the complex in the TEOS–OcTES systems, however, was remarkably lower than that in the TEOS system due to the hydrophobicity of the system. Depending on changes in the polarity and volume of the space containing the species, the complex fluorescence intensity increased and decreased. In the TEOS–OcTES systems, the non-complex band was blue-shifted around the gelation point since the polymerization of the silanol groups preferentially occurred and the polarity decreased in the system containing hydrophobic groups. In the gel of the TEOS system and the sol of the TEOS–OcTES system, a photochromic reaction was observed, i.e., SNO formed the MC–Zn complex during UV irradiation, whereas a change was hardly observed during visible irradiation. In the xerogel of the TEOS system and in the gel and xerogel of the TEOS–OcTES system, a reversible photochromic reaction was observed, i.e., the MC–Zn complex was associated and dissociated by UV and visible irradiation, respectively.

Synthesis of Eu(III) and Tb(III) complexes with novel pyridine dicarboxylic acid derivatives and their fluorescence properties

Starting from pyridine-2,6-dicarboxylic acid (DPA), a series of novel pyridine-2,6-dicarboxylic acid derivatives were synthesized. In these compounds, 4-(hydroxymethyl)pyridine-2,6-dicarboxylate (4-HMDPA) and 4-[(bis-carboxymethyl-amino)-methyl]-pyridine-2,6-dicarboxylic acid (4-BMDPA) were used as multifunctional ligands to coordinate with Tb(III) and Eu(III) and the complexes were prepared. The fluorescence properties of the solid complexes and their solutions were investigated in detail. The results indicated that the weak election-withdrawing group 4-hydroxymethyl in 4-position of pyridine in 4-HMDPA could weaken the fluorescence intensity of the lanthanide complexes. The contradistinctive experimental results showed that the fluorescence intensities of these complexes are related to pH values of the aqueous solutions and the dipole moments of solvent molecules: in the neutral aqueous solutions, the fluorescence intensities of these complexes were strongest, while the dipole moments were lower when the fluorescence intensities were stronger. 4-BMDPA is the better sensitizer and may be used as time-resolved fluoroimmunoassay.

Spectrofluorimetric determination of tin in canned foods

A simple and sensitive spectrofluorimetric method for the determination of tin as its complex with 1-(2-pyridylazo)-2-naphtol (PAN) in a mixed micellar medium was developed. The mixture of a non-ionic surfactant, Triton X-100 and an anionic surfactant, bis(2-ethylhexyl) sulfosuccinate (AOT) was used as a suitable micellar medium for solubilizing of complex and ligand and also for enhancing the fluorescence intensity of complex. In the optimum experimental conditions the maximum excitation and emission wavelengths of Sn–PAN complex were 300 and 360 nm, respectively. The calibration graph was linear in the range of 0.01–0.8 μg ml −1 with a correlation coefficient of 0.9991. The detection limit was found to be 2 ng ml −1. The relative standard deviation of the method for the determination of 0.1 μg ml −1 tin was calculated to be 0.74%. The interferences caused by the presence of a number of common cations and anions were studied. Finally, the method was successfully applied to the determination of tin in various canned products.