Photodissociation of p-xylene in polar and nonpolar solutions

The photodissociation of p-xylene at 266 nm in n-heptane and acetonitrile has been studied with use of nanosecond fluorescence and absorption spectroscopy. The p-methylbenzyl radical was identified in n-heptane and acetonitrile by its fluorescence, which was induced by excitation at 308 nm. The p-xylene radical cation was observed in acetonitrile by its absorption. In n-heptane, the decay rate of the S(1) state of p-xylene ((3.2 +/- 0.2) x 10(7) s(-1)) is equal to the growth rate of the p-methylbenzyl radical ((2.7 +/- 0.4) x 10(7) s(-1)), showing that the molecule dissociates via the S(1) state into the radical by C-H bond homolysis (quantum efficiency approximately 5.0 x 10(-3)). In acetonitrile, the formation of the p-xylene radical cation requires two 266 nm photons, and the decay rate of the radical cation ((1.6 +/- 0.2) x 10(6) s(-1)) equals the growth rate of the p-methylbenzyl radical ((2.0 +/- 0.2) x 10(6) s(-1)). This shows that the radical cation dissociates into the radical by deprotonation (quantum efficiency approximately 8.9 x 10(-2)).     

Rapid quantitative determination of hydrogen peroxide by oxidation decolorization of methyl orange using a Fenton reaction system

In this study, a sensitive and rapid method for hydrogen peroxide (H(2)O(2)) determination has been developed with the aid of oxidation decolorization of methyl orange (MO) by using Fenton reactions, because the decolorization extent of MO solution (at the maximum absorption wavelength of 507 nm) is proportion to the concentration of H(2)O(2). Under optimum conditions, this spectrophotometric method for the H(2)O(2) analysis yields a dynamic range of H(2)O(2) concentration from 5.0 x 10(-7) to 1.0 x 10(-4) mol L(-1) (r=0.997) and a detection limit (3 sigma/k) of 2.0 x 10(-7) mol L(-1). This method for the determination of H(2)O(2) (0.04 mmol L(-1)) is able to tolerate the interference from NaCl (0-5.0 mmol L(-1)), Na(2)SO(4) (0-5.0 mmol L(-1)), MgCl(2) (0-5.0 mmol L(-1)), sodium humate (0-0.1 mmol L(-1)), benzene (0-0.2 mmol L(-1)), toluene (0-0.2 mmol L(-1)), chlorobenzene (0-0.2 mmol L(-1)) and chloroform (0-0.2 mmol L(-1)). The analysis results for practical rainwater samples are in good agreement with the classical N,N-diethyl-p-phenylenediamine (DPD) method for H(2)O(2) determination.     

Synthesis,structure, and second-order nonlinear optical properties of copper(II) and palladium(II) acentric complexes with N-salicylidene-N'-aroylhydrazine tridentate ligands

Two new N-salicylidene-N'-aroylhydrazines ligands have been prepared: N-4-diethylaminosalicylidene-N'-4-nitrobenzoyl-hydrazine (L(1)) and N-4-diethylaminosalicylidene-N'-4-(4-nitrophenylethylidene)-benzoyl-hydrazine (L(2)). The ligands are properly functionalized with strong electron donor-acceptor groups and are of potential interest in second-order nonlinear optics (NLO). Dimeric copper(II) and palladium(II) complexes with L(1) and L(2) have been prepared, and, starting from these, mononuclear acentric adducts with pyridine as a further ligand have been prepared and characterized. The X-ray structures of three adducts are also reported. The NLO activity of the adducts has been determined by EFISH measurements giving mubeta values up to 1500 x 10(-48) esu for an incident wavelength of 1.907 microm.     

Fluorimetric study of the interaction between human serum albumin and quinolones-terbium complex and its application

A highly sensitive spectrofluorimetric method is proposed for determination of human serum albumin (HSA) and some quinolone drugs. Using quinolones-terbium (Tb3+) complex as a fluorescent probe, in the buffer solution of pH 7.8, HSA can remarkably enhance the fluorescence intensity of the quinolones-Tb3+ complex at 545 nm and the enhanced fluorescence intensity of Tb3+ ion is in proportion to the concentration of HSA and quinolone drugs. Optimum conditions for the determination of HSA were also investigated. The linear ranges and limits of detection are 8.0 x 10(-9) to 8.0 x 10(-8) mol L(-1), 4.20 x 10(-9) mol L(-1) (for HSA); 1.0 x 10(-6) to 4.0 x 10(-6) mol L(-1), 1.87 x 10(-8) mol L(-1) (for norfloxacin) and 1.0 x 10(-7) to 1.0 x 10(-6) mol L(-1), 4.82 x 10(-8) mol L(-1) (for enoxacine), respectively. This method is simple, practical and relatively free interference from coexisting substances, as well as much more sensitive than most of the existing assays.     

Degradation of ampicillin in the presence of cadmium (II) ions

Cadmium (II) ion-catalyzed degradation of ampicillin in methanol at 20 degrees C has been studied. It has been observed that the rate values tend to saturate when the concentration of ampicillin or the metal ion is increased. The results obtained in the present study suggest that ampicillin degradation occurs through the formation of a 1:1 (SM) and 2:1 (S(2)M) ampicillin-metal complexes. These complexes decompose giving a single product (absorption maximum at 285 nm; ((p)=1.82x10(4) l mol(-1) cm(-1)) that has been isolated and identified (Cd(II) (L(2-))(2) (H(2)O)(4) Na(2)). The appearance of this product reflects a first order reaction with respect to the 1:1 complex, with a rate constant of 3.87x10(-2) min(-1) and the existence of an equilibrium between the 1:1 and 2:1 initial complexes. The equilibrium constant value, calculated from kinetic data, is 1.7x10(3) l mol(-1).     

Unraveling the photochemistry of Fe(CO)5 in solution: observation of Fe(CO)3 and the conversion between 3Fe(CO)4 and 1Fe(CO)4(Solvent)

The photochemistry of Fe(CO)5 (5) has been studied in heptane, supercritical (sc) Ar, scXe, and scCH4 using time-resolved infrared spectroscopy (TRIR). 3Fe(CO)4 ((3)4) and Fe(CO)3(solvent) (3) are formed as primary photoproducts within the first few picoseconds. Complex 3 is formed via a single-photon process. In heptane, scCH4, and scXe, (3)4 decays to form (1)4 x L (L = heptane, CH4, or Xe) as well as reacting with 5 to form Fe2(CO)9. In heptane, 3 reacts with CO to form (1)4 x L. The conversion of (3)4 to (1)4 x L has been monitored directly for the first time (L = heptane, kobs = 7.8(+/- 0.3) x 10(7) s(-1); scCH4, 5(+/- 1) x 10(6) s(-1); scXe, 2.1(+/- 0.1) x 10(7) s(-1)). In scAr, (3)4 and 3 react with CO to form 5 and (3)4, respectively. We have determined the rate constant (kCO = 1.2 x 10(7) dm3 mol(-1) s(-1)) for the reaction of (3)4 with CO in scAr, and this is very similar to the value obtained previously in the gas phase. Doping the scAr with either Xe or CH4 resulted in (3)4 reacting with Xe or CH4 to form (1)4 x Xe or (1)4 x CH4. The relative yield, [(3)4]:[3] decreases in the order heptane > scXe > scCH4 > scAr, and pressure-dependent measurements in scAr and scCH4 indicate an influence of the solvent density on this ratio.     

Investigation of the extraction equilibria in the system hexachloridorhenate(IV)-neotetrazolium chloride-dichloroethane-water

The neotetrazolium hexachloridorhenate(IV) (NTReCl(6)) has been synthesized and its composition checked. The optimum conditions for the extraction of NTReCl(6) with dichloroethane have been established. The recovery factor for one-fold extraction is R = 74%. The distribution constant, K(D), extraction constant, K(ex), and ion-association constant, beta, have been determined. Neotetrazolium chloride was found to be suitable reagent for extraction-spectrophotometric determination of rhenium(IV) ((NTReCl(6)) = 3.42 +/- 0.20 x 10(4)M(-1) cm(-1)).     

Synthesis, spectroscopic characterization, photochemical and photophysical properties and biological activities of ruthenium complexes with mono- and bi-dentate histamine ligand

The monodentate cis-[Ru(phen)(2)(hist)(2)](2+)1R and the bidentate cis-[Ru(phen)(2)(hist)](2+)2A complexes were prepared and characterized using spectroscopic ((1)H, ((1)H-(1)H)COSY and ((1)H-(13)C)HSQC NMR, UV-vis, luminescence) techniques. The complexes presented absorption and emission in the visible region, as well as a tri-exponential emission decay. The complexes are soluble in aqueous and non-aqueous solution with solubility in a buffer solution of pH 7.4 of 1.14 × 10(-3) mol L(-1) for (1R + 2A) and 6.43 × 10(-4) mol L(-1) for 2A and lipophilicity measured in an aqueous-octanol solution of -1.14 and -0.96, respectively. Photolysis in the visible region in CH(3)CN converted the starting complexes into cis-[Ru(phen)(2)(CH(3)CN)(2)](2+). Histamine photorelease was also observed in pure water and in the presence of BSA (1.0 × 10(-6) mol L(-1)). The bidentate coordination of the histamine to the ruthenium center in relation to the monodentate coordination increased the photosubstitution quantum yield by a factor of 3. Pharmacological studies showed that the complexes present a moderate inhibition of AChE with an IC(50) of 21 μmol L(-1) (referred to risvagtini, IC(50) 181 μmol L(-1) and galantamine IC(50) 0.006 μmol L(-1)) with no appreciable cytotoxicity toward to the HeLa cells (50% cell viability at 925 μmol L(-1)). Cell uptake of the complexes into HeLa cells was detected by fluorescence confocal microscopy. Overall, the observation of a luminescent complex that penetrates the cell wall and has low cytotoxicity, but is reactive photochemically, releasing histamine when irradiated with visible light, are interesting features for application of these complexes as phototherapeutic agents.     

Lysozyme-enhanced europium(III)-metacycline luminescence and its application to the determination of metacycline.

A new spectrofluorometric method is described for the determination of metacycline (MC), based on modified enzyme-amplified lanthanide luminescence. Under the optimum conditions, Eu3+-MC forms a ternary complex with lysozyme in close proximity. Then lysozyme can remarkably enhance the characteristic fluorescence intensity of Eu3+ at 612 nm in metacycline-Eu3+ binary complex. The enhanced fluorescence intensity is in proportion to the concentration of MC. The limit of detection is 1.6 x 10(-8) mol L(-1), with a linear range from 6.2 x 10(-6) to 1.7 x 10(-5) mol L(-1). Interferences of other coexisting substances were studied. The developed method was successfully applied to the determination of MC in serum and urine samples. The mechanism of fluorescence enhancement was also studied.     

Fluorescence studies on native and bound to trifluraline soy bean Lb"a" in the enhanced N2 fixation.

The differences in the tryptophan (Trp) fluorescence of native (control) Lb"a" and experimental substance isolated from nodules of the Williams' soy beans variety treated with trifluraline at a concentration of 2.1 x 10(-10) M have been studied. A positively charged environment has been proved for the tryptophans of the native Lb"a" and a negative one for the tryptophans of the experimental Lb"a". The difference in the tryptophan emission spectra at lambdaex = 280 and 300 nm may be assigned to conformational alterations occurring in the experimental Lb"a". This is also confirmed by the greater energy transfer from tyrosine to tryptophan in the experimental Lb"a"--30% compared to the 10% in the native Lb"a". The value of the constant of acrylamide quenching (Ksv = 2.77 M(-1)) shows that the tryptophans are buried more deeply in the experimental Lb"a" than in the native Lb"a" (Ksv = 4 M(-1)). They are substantially lower than Ksv of the standard compound N-Ac-Trp-NH2 (16.30 M(-1)). The activation energy (Ea) of the thermal quenching of tryptophan fluorescence is higher for the experimental Lb"a" (37 kJ mol(-1)) as compared to the standard compound N-Ac-Trp-NH2 (24 kJ mol(-1)) and the native Lb "a" (32 kJ mol(-1)). The dissociation constant of the complex of trifluraline with Lb "a" (6.32 x 10(-11) M) has been determined as well as the stoichiometric ratio trifluraline/Lb"a" (1:1). The estimated nitrogenase activity (microM/gfrw h) and the total Lb (mg/gfrw) for trifluraline are higher as compared to those for the control.     

Determination of adenosine disodium triphosphate (ATP) using oxytetracycline-Eu3+ as a fluorescence probe by spectrofluorimetry

A new spectrofluorimetric method was developed for determination of adenosine disodium triphosphate (ATP). We studied the interactions between oxytetracycline (OTC)-Eu3+ complex and adenosine disodium triphosphate (ATP) by using UV-vis absorption and fluorescence spectra. Using oxytetracycline (OTC)-Eu3+ as a fluorescence probe, under the optimum conditions, ATP can remarkably enhance the fluorescence intensity of the OTC-Eu3+ complex at lambda = 612 nm and the enhanced fluorescence intensity of Eu3+ ion is in proportion to the concentration of ATP. Optimum conditions for the determination of ATP were also investigated. The linear ranges for ATP are 8.00 x 10(-8)-1.50 x 10(-6) mol L(-1) with detection limits of 2.67 x 10(-9) mol L(-1). This method is simple, practical and relatively free interference from coexisting substances and can be successfully applied to determination of ATP in samples. The mechanism of fluorescence enhancement between oxytetracycline (OTC)-Eu3+ complex and ATP was also studied.     

Resonance light-scattering spectrometric study of interaction between enzyme and MPA-modified CdTe nanoparticles

This paper described a novel assay of enzyme based on the measurement of enhanced resonance light-scattering (RLS) signals resulting from the electrostatic and coordination interaction of functionalized CdTe nanoparticles with enzyme. The CdTe nanoparticles which were modified with 3-mercaptocarboxylic acid (MPA) have abundant carboxylic groups (COOH). So the nanoparticles are water-soluble, stable and biocompatible. At pH 8.3 phosphate buffered saline (PBS), the RLS signals of functionalized nano-CdTe are greatly enhanced by bromelain and papain in the region of 220-800 nm characterized by the peak around 318-314 nm, respectively. The optimization conditions of the reaction were also examined and selected. Under the selected conditions, the enhanced RLS intensity is linearly proportional to the concentration of bromelain and papain. The liner range is (0.09-0.9) x 10(-6)mol/L for bromelain and (0.048-0.702) x 10(-6)mol/L for papain. The influences of some foreign substances were also examined. This method can be applied to the determination of enzyme.     

Protective effect of total flavonoids from Spirodela polyrrhiza (L.) Schleid on human umbilical vein endothelial cell damage induced by hydrogen peroxide

In this study, we determined the protective effect of total flavonoids from Spirodela polyrrhiza (L.) Schleid (STF), which is a kind of traditional Chinese medicine, on human umbilical vein endothelial cells (ECV-304) damage induced by hydrogen peroxide (H(2)O(2)). Treated with 1mmol/L H(2)O(2) for 1h, the viability of ECV-304 cells markedly decreased. However, pretreatment with 10-50mug/mL STF resulted in a significant recovery. The survival rate of ECV-304 increased from 21.98% (only treated with 1mmol/L H(2)O(2)) to 64.74% (pretreated with 50microg/mL STF), which accompanied with the amounts of malondialdenhyde (MDA) decreasing from 1.6883nmol/L to 0.9628nmol/L. Furthermore, compared with control group, the 50mumol/L STF pretreatment enhanced the total antioxidant capacity (T-AOC) by 4.49 times, increased the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) by 85.12%, 158.94% and 94.5%,respectively, and increased the content of nitric oxide (NO) by 116.55%.Taken together, STF protect ECV-304 cells against H(2)O(2) damage by enhancing the antioxidant ability and increasing NO production.     

Synthesis, thermodynamics stability constant and relaxation properties of neutral Gd(III) complex with derivative from diethylene triamine pentaacetic acid and p-hydroxybenzoyl hydrazine

A novel ligand, diethylenetriamine-N,N'-bis(acetyl-p-hydroxybenzoyl hydrazine)-N,N',N'-triacetic acid (H3L) was synthesized and characterized on the basis of elemental analysis, molar conductivity, 1H-NMR spectrum, FAB-MS, TG-DTA analysis and IR spectrum. Its complex of Gd(III) holding promise of magnetic resonance imaging (MRI) was synthesized, and relaxivity (R1) of complex and Gd(DTPA)2- used as a control was determined in water solution, respectively. The relaxivity of GdL (R1 = 6.39 l.mmol(-1).s(-1)) was larger than that of Gd(DTPA)2- (R1 = 4.34 l.mmol(-1).s(-1)). The relaxivity of GdL has also been investigated in human serum albumin (HSA) solution, the relaxivity of GdL was enhanced from 6.39 l.mmol(-1).s(-1) in water solution to 7.69 l.mmol(-1).s(-1) in HSA solution. In addition, thermodynamics stability constant of GdL was determined. The results showed that complex of GdL is a prospective MRI contrast agent, although the thermodynamic stability constant of GdL complex (K(GdL) = 10(19.56)) was a little less than that of Gd(DTPA)2- (K(Gd-DTPA) = 10(20.73)).     

A novel micellar PEGylated hyperbranched polyester as a prospective drug delivery system for paclitaxel

A hyperbranched aliphatic polyester has been functionalized with PEG chains to afford a novel water-soluble BH40-PEG polymer which exhibits unimolecular micellar properties, and is therefore appropriate for application as a drug-delivery system. The solubility of the anticancer drug paclitaxel was enhanced by a factor of 35, 110, 230, and 355 in aqueous solutions of BH40-PEG of 10, 30, 60, and 90 mg x mL(-1), respectively. More than 50% of the drug is released at a steady rate and release is almost complete within 10 h. The toxicity of BH40-PEG was assessed in vitro with A549 human lung carcinoma cells and found to be nontoxic for 3 h incubation up to a 1.75 mg x mL(-1) concentration while LD50 was 3.5 mg x mL(-1). Finally, it was efficiently internalized in cells, primarily in the absence of foetal bovine serum, while confocal microscopy revealed the preferential localization of the compound in cell nuclei. [Figure: see text].     

Ionic liquids as mobile phase additives for the high-performance liquid chromatographic analysis of fluoroquinolone antibiotics in water samples

In this work, four ionic liquids differing in the length of the alkyl chain on the imidazolium cation and one ionic liquid containing tetraethylammonium, all with the same counterion, (i.e. 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIm-BF(4)), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF(4)), 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIm-BF(4)), 1-methyl-3-octylimidazolium tetrafluoroborate (MOIm-BF(4)), and tetraethylammonium tetrafluroborate (Et(4)N-BF(4))) were tested as mobile phase additives for HPLC separation of a group of seven basic fluoroquinolone (FQ) antibiotics for human and veterinary use (i.e. fleroxacin, ciprofloxacin, lomefloxacin, danofloxacin, enrofloxacin, sarafloxacin, and difloxacin) using a conventional reversed-phase Nova-Pak C(18) column. Fluorescence detection was used. Among the ionic liquids selected, use of BMIm-BF(4) enabled effective separation of these compounds with relatively low analysis time (14 min). The best separation was achieved by isocratic elution at 1 mL min(-1) with 5 mmol L(-1) BMIm-BF(4) and 10 mmol L(-1) ammonium acetate at pH 3.0 with 13% (v/v) acetonitrile. Limits of detection (LODs) for fluorescence detection were in the range 0.5-11 microg L(-1). The method was tested by analyzing several water samples after the optimization of a suitable solid-phase extraction (SPE) procedure using Oasis HLB cartridges. Mean recovery values were above 84% for all analytes with LODs in the range 1-29 ng L(-1).     

Permanently oriented antibody immobilization for digoxin determination with a flow-through fluoroimmunosensor

This paper reports a new flow-through fluoroimmunosensor, the function of which is based on antibodies immobilized on an inmunoreactor of controlled-pore glass (CPG), for determination of digoxin, used in the treatment of congestive heart failure and artery disease. The immunosensor has a detection limit of 1.20 microg L(-1) and provides high reproducibility (RSD=4.5% for a concentration of 0.0025 mg L(-1), and RSD=6.7% for 0.01 mg L(-1)). The optimum working concentration range was found to be 1.2 x 10(-3)-4.0 x 10(-2) mg L(-1). The lifetime of the immunosensor was about 50 immunoassays; if stored unused its lifetime can be extended to three months. A sample speed of about 10-12 samples per hour can be attained. Possible interference from substances with structures similar to digoxin (morphine, heroin, tebaine, codeine, pentazocine and narcotine) was investigated. No cross-reactivity was seen at the highest digoxin: interferent ratio studied (1:100). The proposed fluoroimmunosensor was successfully used to determine digoxin concentrations in human serum samples.     

Determination of some antirheumatics by capillary isotachophoresis

Isotachophoresis (ITP) was applied for the determination of some antirheumatic drugs (fenoprofen, naproxen, ibuprofen, and ketoprofen) in human serum. The leading electrolyte contained hydrochloric acid (10 mmol x L(-1)), creatinine (pH 4.5) and methylhydroxyethyl cellulose (0.1%). The terminating electrolyte was 2-(N-morpholino)ethanesulfonic acid (10 mmol x L(-1)) adjusted with tris(hydroxymethyl)aminomethane to pH 6.9. The ITP separations were carried out in column-coupling configuration of the separation unit provided with a preseparation column of 160 x 0.8 mm inner diameter (ID) and analytical column of 160 x 0.3 mm ID. The limit of detection for ibuprofen, fenoprofen, and naproxen in serum by direct sampling was 0.008, 0.005 and 0.004 mmol x L(-1). The limit of detection for ketoprofen in serum after ethanol precipitation was 0.001 mmol x L(-1).     

A New Class of Aluminum Cations Based upon Tetradentate (N(2)O(2)) Chelating Ligands

Herein are described the synthesis and characterization of the complexes of formula LAlR (where R = Cl and L = Salen (1), SalenCl (2), Acen (3) and where R = Me and L = Salen (4), SalenCl (5), Acen (6); Salen = N,N'-ethylenebis((2-hydroxyphenyl)methylimine), SalenCl = N,N'-ethylenebis((2-hydroxy-5-chlorophenyl)methylimine), Acen = N,N'-ethylenebis((2-hydroxyphenyl)-1-ethylimine)). The LAlCl derivatives dissolve in water and MeOH to yield the cationic complexes [LAl(H(2)O)(2)](+)Cl(-) (L = Salen (7), SalenCl (8), Acen (9)) and [LAl(MeOH)(2)](+)Cl(-) (L = Salen (10), SalenCl (11), Acen (12)), respectively. An alternative preparation of the cationic species involves the reaction of the LAlCl derivative with NaBPh(4). This leads to complexes of formula [LAl(MeOH)(2)](+)BPh(4)(-) (L = Salen (13), SalenCl (14), Acen (15)). Complexes 4-6 can be reacted with either MeOH or 4-chloro-3,5-dimethylphenol (Ph') to form complexes of general formula LAlOR (R = Me, L = Salen (16), SalenCl (17), Acen (18); R = Ph', L = Salen (19), SalenCl (20), Acen (21)). All of the compounds were characterized by IR, melting points, elemental analyses, and, when soluble, NMR. Additionally, the crystal structures of 7, 13, 15, and 18 were obtained.     

Determination of ATP as a fluorescence probe with europium(III)-doxycycline.

A new spectrofluorimetric method has been developed for the determination of adenosine disodium triphosphate (ATP). We studied the interactions between the doxycycline (DC)-Eu3+ complex and adenosine disodium triphosphate (ATP) by using UV-visible absorption and fluorescence spectra. Using doxycycline (DC)-Eu3+ as a fluorescence probe, under the optimum conditions, ATP could remarkably enhance the fluorescence intensity of the DC-Eu3+ complex at lambda = 612 nm. The enhanced fluorescence intensity of the Eu3+ ion was in proportion to the concentration of ATP. The optimum conditions for the determination of ATP were also investigated. The linear ranges for ATP were 1.00 x 10(-7) - 2.00 x 10(-6) mol L(-1) with detection limits of 4.07 x 10(-8) mol L(-1). This method is simple, practical and relatively free of interference from coexisting substances, and can be successfully applied to the determination of ATP in samples. The mechanism of fluorescence enhancement between the doxycycline (DC)-Eu3+ complex and ATP was also studied.