Tailoring the sensitivity and spectral properties of a chromoreactand for the detection of amines and alcohols

The chromoreactand N,N-dioctylamino-4′-trifluoroacetyl-2′-nitroazobenzene (CR-546) is sensitive to amines and alcohols when dissolved in plasticised PVC. The chromoreactand provides an improvement over related reactands in that a nitro group meta to the trifluoroacetyl group enhances the chemical reactivity and, consequently, the sensitivity by a factor of 20 compared to the derivative without nitro group. Furthermore, the absorbance is shifted by around 40 nm to longer wavelengths, making the sensor membranes compatible with the green LED as a light source for a miniaturised sensor device. The sensor membrane responds to aqueous 1-propylamine in the 0.5-50 mM concentration range and exhibits a detection limit of 0.1 mM. Response times are in the range of 5-15 min.A fluorescent ethanol-sensitive membrane is obtained by dissolving the inert fluorophore N,N′-bis(1-hexylheptyl)perylene-3,4:9,10-bis(dicarboximide) together with CR-546 and the catalyst tridodecylmethylammonium chloride in the polymer matrix. The trifluoroacetyl form of CR-546 with its absorbance at around 560 nm overlaps the emission of the fluorophore. Increasing ethanol concentrations cause decreasing absorbance at 560 nm and consequently, increasing luminescence of the fluorophore. The resulting layer has been evaluated for its detection of ethanol via changes in luminescence intensity. The calibration is linear in the range from 1 to 15% (v/v) ethanol with a limit of detection of 0.1% (v/v). Response times are in the range from 20 to 40 min for both forward and reverse reaction.     

Characterization of poly(acrylamide-co-acrylates) obtained by inverse microemulsion polymerization

Two series of poly(acrylamide-co-acrylates) with compositions rangingfrom 10 to 55 mol % acrylate units were prepared by radical polymerization in inverse microemulsions. The compositional analyses of the samples were performed using elemental analysis, potentiometry and¹³C NMR. The comparison between the three methods indicates that¹³C NMR is the most reliable one, avoiding errors which often arise from associated water in hydrophilic polymers. The copolymer viscosity exhibits a maximum behavior around 40 mol % acrylate content, a lower value than that already observed for co-polymers prepared in homogeneous solution. The production of copolymers presenting high intrinsic viscosities ( 3700 cm³g^–) is achieved using an inverse microemulsion as the polymerization medium operating at lower temperature.     

A simple click generated probe for highly selective sequential recognition of Cu(II) and pyrophosphate

A click generated quinoline derivative (1) has been synthesized and used as a fluorescent probe for sequential recognition of Cu²⁺ and pyrophosphate (PPi) in DMSO/H₂O (1:1, v/v, HEPES 20 mM, pH = 7.4) solution. Probe 1 displays high selectivity to Cu²⁺ ions, and the in-situ prepared probe 1-Cu²⁺ exhibits high selectivity toward pyrophosphate (PPi) with emission recovery of probe 1. Therefore, 1-Cu²⁺ complex can be applied as a fluorescence turn-on probe for PPi with high selectivity and sensitivity.     

Rapid spectrophotometric determination of thorium(IV) with 1-(2′-thiazolylazo)-2-naphthol

Thorium(IV) reacts with 1-(2-thiazolylazo)-2-naphthol (TAN) in the presence of antipyrine to form a sparingly soluble red-coloured chelate, soluble in 36% methanol (v/v). Complexation takes place instantaneously at pH 2.4–2.8, maintained by glycine buffer. Antipyrine is found to enhance sensitivity of the complex, which is stable for 19 hours. The 12 complex exhibits maximum absorbance at 555 nm, obyes Beer's law in the concentration range from 0.32 to 6.56 g of thorium(IV) per ml, has a molar absorptivity of 3.14·10⁴ dm³/mol^–1·cm^–1 and a Sandel sensitivity of 7.4 ng·cm^–2. The formation constant (log K) is found to be 8.62 and 8.45. Interference of 57 anions and cations in the determination of thorium(IV) has been studied. From ten repeated determinations, the coefficient of variation was found to be ±0.98%. The method was successfully applied for determination of thorium content in a sample of monazite.     

Fluorimetric determination of 1-naphthol and mixtures of carbaryl and 1-naphthol in micellar media

Summary The interaction of 1-naphthol with different types of anionic, cationic and non-ionic surfactants has been studied spectrofluorimetrically in order to obtain a sensitivity enhancement in the determination of this compound. At neutral pH, cetyl trimethyl ammonium bromide (CTAB) provides a 2-fold sensitivity enhancement of 1-naphthol and exhibits a weak interaction with carbaryl. In strong alkaline medium carbaryl is hydrolyzed to 1-naphthol and in the presence of CTAB micells, a 5-fold sensitivity enhancement and a limit of detection of 0.2 g·ml^–1 with a 101±3% percentage of recovery is obtained. These facts permit the development of an accurate method for the fluorimetric analysis of 1-naphthol and carbaryl mixtures, comprising the determination of the sum of both compounds (pH 12, 0.1% w/v CTAB, _em=449 nm, _ex=341 nm) and of the concentration of 1-naphthol (neutral pH, 0.4% w/v CTAB, _em=449 nm, _ex=312 nm).     

Extraction and micro-determination of vanadium(V) in the environment with α-phenylstyrylacrylo-substituted hydroxamic acid and Aliquat 336 and inductively coupled plasma atomic emission spectrometry

A selective and sensitive method for the microgram determination of vanadium(V) with -phenylstyrylacrylohydroxamic acid by selective extraction of the blueish violet vanadium-hydroxamate complex with Aliquat 336 from acidic medium is described. The effect of thiocyanate on the extraction is discussed. The vanadium-hydroxamate complex has _max 553 nm and molar absorptivity 7.8 × 10³ l mol^–1 cm^–1, while the mixed 121 complex, vanadium-hydroxamate-Aliquat 336, has _max 546 nm and molar absorptivity 8.2 × 10³ l mol^–1 cm^–1. The system obeys Beer's law in the range 0.3–10.0 mg l^–1 vanadium. Sandell's sensitivity is 0.00624 g cm². The sensitivity is increased twentyfold by inductively coupled plasma atomic emission measurements on the extract and the detection limit is more than 1 ng ml^–1. Vanadium is determined in standard alloys, rock, environmental and clinical samples.     

A new Hg-selective fluorescent sensor based on a dansyl amide-armed calix[4]-aza-crown

A new fluorescent chemosensor for Hg²⁺ based on a dansyl amide-armed calix[4]-aza-crown was reported. It exhibits high sensitivity and selectivity toward Hg²⁺ over a wide range of metal ions in MeCN-H₂O (4:1, v/v). The association constant of the 1:1 complex formation for 2-Hg²⁺ was calculated to be 1.31 × 10⁵ M⁻¹, and the detection limit for Hg²⁺ was found to be 4.1 × 10⁻⁶ mol L⁻¹.     

Quantitative determination of chloride by means of flow injection analysis with spectrophotometric detection in the UV/VIS range

Chloride is determined indirectly by Spectrophotometric flow injection analysis. Two systems are compared, both based on the principle of ion exchange of easily detectable anions versus chloride from suitable mercury salts. The first method is based on the exchange of chloride with chloranilate which is detected at 332 nm or at 306 nm in neutral or in acidic medium respectively. In the second case, chloride reacts with Hg(SCN)₂. The liberated thiocyanate forms a strongly coloured complex with Fe(III) in acidic solution with an absorption maximum at 460 nm. Both methods have a detection limit of about 5 mol Cl^–/l (175 ng/ml). In the case of the thiocyanate method, the relative standard deviation is about 2% (7 measurements) in the range of 5 to 150 mol/l and decreases significantly to a value of approximately 0.2% at higher concentrations; for the chloranilate method it is 10% for lower and about 1% for higher concentrations respectively.     

A highly selective and sensitive fluorescein-based chemodosimeter for Hg2+ ions in aqueous media

A new fluorescein-based chemodosimeter (II) for Hg²⁺ ion was designed and synthesized, and it displayed excellent selective and sensitive toward Hg²⁺ ion over other commonly metal ions in aqueous media. II was a colorless, non-fluorescent compound. Upon addition of Hg²⁺ to the solution of II, the thiosemicarbazide moiety of II would undergo an irreversible desulfurization reaction to form its corresponding oxadiazole (IV), a colorful and fluorescent product. During this process, the spirocyclic ring of II was opened, causing instantaneous development of visible color and strong fluorescence emission in the range of 500-600 nm. Based on the above mechanism, a fluorogenic Hg²⁺-selective chemodosimeter was developed. The fluorescence increase is linearly with Hg²⁺ concentration up to 1.0 μmol L⁻¹ with a detection limit of 8.5 × 10⁻¹⁰ mol L⁻¹ (3σ). Compared with the rhodamine-type chemodosimeter, II is more stable in aqueous media and exhibits higher sensitivity toward Hg²⁺. The findings suggest that II will serve as a practical chemodosimeter for rapid detection of Hg²⁺ concentrations in realistic media.     

A Test Method for the Determination of Mercury(I, II) on a Polymer Surface

It was found that mercury(I, II) reacts with 5-chloro-2-hydroxy-3-[(tetrahydro-2,4-dithioxo-1,3-thiazin-5-yl)azo]benzenesulphonic acid (tyrodine) in weakly acid solutions in the presence of acetates, formates, and some organic solvents (ethanol and acetone) to give an intensely colored insoluble compound (_max = 600 nm, > 3 × 10⁴). The composition of the solution affected the sensitivity of the color reaction between mercury and tyrodine. A test procedure was developed for the determination of mercury(I, II) on the surface of a polycaproamide membrane with a detection limit of <50 ng in the adsorbent zone. The procedure involves the quantitative and selective adsorption of the mercury complex of tyrodine on the support surface from 0.5 M acetate solutions of pH 3–4 in the dynamic mode; the sample volume was 5–25 mL. Mercury was then determined by the change in the support color using a color scale or by the change in diffuse reflectance at 600 nm. The adsorption of the mercury complex was accompanied by an abrupt change in the color of the support surface from pale crimson (reagent) to stable blue-violet. The test procedure was used in the analysis of an industrial sample of complex composition with a mercury concentration of lower than 0.05%. The determination error (relative standard deviation) was 20%.     

Jahn-Teller effect in trigonal μ-oxoclusters

A theory of the Jahn-Teller effect in trinuclear Cr^III and Fe^III -oxocomplexes based on the generalized angular overlap model is developed. The central bridging O atom is not localized at the center of the triangle formed by the metal atoms. Rather, it executes a free or hindered motion along a circular groove of radius 0.05–0.1 . The theory provides a qualitative explanation for apparent discrepancy between the X-ray structural data and the results of the heat capacity, magnetic susceptibility, and inelastic neutron scattering measurements. Namely, X-ray structural data correspond to a regular triangle symmetry while other data correspond to an equilateral or even irregular triangle symmetry.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2375–2380, November, 2004.     

Direct and Derivative Spectrophotometric Determination of Thorium with 2,4-dihydroxybenzaldehyde Isonicotinoyl Hydrazone

A simple and sensitive spectrophotometric method is developed for the determination of throium in aqueous medium. The metal ion forms yellow coloured complex with 2,4-dihydroxybenzaldehyde isonicotinoyl hydrazone (2,4-DHBINH) in the pH range 2.0–8.0. The complex shows an absorption maximum at 390 nm. The absorbance of the complex is maximum at pH 5.5 Beer's law is obeyed in the range 0.30–7.00 g/ml of thorium(IV). The molar absorptivity and the Sandell's sensitivity of the method are 2.20· 10⁴ l·mol^–1·cm^–1 and 0.0106 g/cm^–2, respectively. The interference of various ions was studied. The composition of the complex is 1:1 {Th(IV) : 2,4-DHBINH}. The first derivative spectrum of the complex shows a zero cross at 391.2 nm and maximum amplitude at 415 nm. Thus a sensitive derivative spectrophotometric method for the determination of Th(IV) is proposed.     

Fluorescence of phthalocyanines: Emission from an upper excited state

The weak (φ_f < 10³) fluorescence at around 430 nm of the S² upper excited singlet state of metal-free phthalocyanine and metallophthalocyanines is presented. Polarization measurements indicate that the emission is short-lived (< 800 ps) contrary to the intense (φ_f > 0.3) normal emission at around 700 nm originating from S¹ and having a lifetime in the 4.1 to 10.6 ns range, depending on the solvent. The short wavelength emitting S² excited state has been populated by a two photon absorption process using the excitation light at 695 nm of a pulsed ruby laser. This process is shown not to involve the triplet state but the following stepwise two photon absorption process: .     

The kinetic of the oxidation of InSn48

The oxidation of InSn48 has been investigated at partial pressures between 10^-8 Pa and 10⁺⁴ Pa over a temperature range from 22^°C to 250^°C with different analytical methods. The oxide film contains a mixture of several oxides, although indium oxide forms preferentially. Below the melting point a logarithmic growth, and above this, a parabolic growth of the oxide film has been observed. The oxide film formed in air at 250^°C does not become thicker than 50 nm in the first 5 min of oxidation.     

Extractive spectrophotometric determination of dioxouranium(VI) with the sodium salt of hexamethyleneiminecarbodithioate

The optimum conditions for the extractive spectrophotometric determination of dioxouranium(VI) with hexamethyleneiminecarbodithioate(HMICdt) have been established. Dioxouranium(VI) reacts with this ligand at pH 4.5 to form a yellowish-orange uncharged 12 metal-ligand complex which can be extracted by chloroform. The calibration graph was linear in the range of 1–20 g ml^–1 of dioxouranium(VI) at 335 nm. The molar absorptivity of the extracted species is 5.952×10³ l mol^–1 cm^–1 with Sandell's sensitivity of 0.04 g cm^–2. The average of 10 determinations of dioxouranium was 49.75 g for the samples containing 50 g of U(VI) and the variation from the mean at 95% confidence limit was 49.75±0.5955.     

Molecular model of the neural dopamine transporter

The dopamine transporter (DAT) regulates the action of dopamine by reuptake of the neurotransmitter into presynaptic neurons, and is the main molecular target of amphetamines and cocaine. DAT and the Na⁺/H⁺ antiporter (NhaA) are secondary transporter proteins that carry small molecules across a cell membrane against a concentration gradient, using ion gradients as energy source. A 3-dimensional projection map of the E. coli NhaA has confirmed a topology of 12 membrane spanning domains, and was previously used to construct a 3-dimensional NhaA model with 12 trans-membrane -helices (TMHs). The NhaA model, and site directed mutagenesis data on DAT, were used to construct a detailed 3-dimensional DAT model using interactive molecular graphics and empiric force field calculations. The model proposes a dopamine transport mechanism involving TMHs 1, 3, 4, 5, 7 and 11. Asp79, Tyr252 and Tyr274 were the primary cocaine binding residues. Binding of cocaine or its analogue, (–)-2-carbomethoxy-3-(4-fluorophenyl)tropane (CFT), seemed to lock the transporter in an inactive state, and thus inhibit dopamine transport. The present model may be used to design further experimental studies of the molecular structure and mechanisms of DAT and other secondary transporter proteins.     

A sodium-selective optrode

An ion selective optrode (ISO) for continuous determination of sodium is presented. It is based on the optical measurement of the membrane potential between an aqueous sample solution and a lipid membrane phase with the help of a potential-sensitive dye. The lipid membrane is composed of rhodamine B C-18 ester together with the sodium selective ionophore ETH 157 and either arachidic acid or 1-octadecanol, and is prepared by using the Langmuir-Blodgett (LB) technique. The fluorescence intensity of the dye reversibly responds to the sodium ion concentration. Fluorescence decreases with increasing sodium concentraction. Interferences by potassium or calcium can be compensated for by using a reference optrode. The sodium sensor works in the 1 to 100 mM sodium ion concentration range with a maximal signal change of –4.2% of the full scale signal for 100 mM. The relationship between the relative signal change (I/I) and the negative logarithm of the sodium concentration is linear over two orders of magnitude. The selectivity coefficients over potassium or calcium are better than 1 × 10⁵ when use is made of a reference optrode. The sensors can be stored under air for more than half a year without loss in fluorescence intensity or changes in response function.     

Spectrophotometric determination of hydrogen cyanide in air using phloroglucinol

Summary A spectrophotometric determination of hydrogen cyanide in air is described. Hydrogen cyanide from air is collected in dilute sodium hydroxide and then reacted with pyridine forming glutaconic aldehyde. The glutaconic aldehyde thus formed is subsequently coupled with aqueous phloroglucinol solution to form a polymethine red-violet dye having absorbance maxima at 540 nm. The colour system obeys Beer's law in the range of 0.45 to 3.6 mg/m³ of hydrogen cyanide (0.4 to 3.2 g/g). Collection efficiency of absorbing solution, molar absorptivity and Sandell's sensitivity have been evaluated. All other important analytical parameters have been studied and applied for the determination/detection of hydrogen cyanide in air samples and cigarette smoke.     

Coumarine–imino–C2-glucosyl conjugate as receptor for Cu in blood serum milieu,on silica gel sheet and in Hep G2 cells and the characterization of the species of recognition

A coumarine–imino–C2-glucosyl conjugate (L) was synthesized and characterized. The conjugate L is found to recognize Cu²⁺ in aqueous HEPES buffer by exhibiting a 95% fluorescence quenching in pH range 7–10 even in the presence of several biologically and ecologically relevant metal ions. Fluorescence on–off behavior has been clearly demonstrated on the basis of the binding variability of Cu²⁺ to L. The binding has been elicited through the changes observed in fluorescence, absorption, ESI-MS and ¹H NMR titrations. All the other thirteen metal ions studied did not show any change in the fluorescence emission. These ions do not interfere with the recognition of Cu²⁺ by L. The structural features of [CuL]₂ complex in both the isomeric forms were established by DFT computational calculations. The utility of L has been demonstrated by showing its sensitivity toward Cu²⁺ on a thin layer of silica gel. The L gives sensitive fluorescence signals for Cu²⁺ even in blood serum and exhibits appropriate fluorescence responses in living cells.     

Extraction and spectrophotometric determination of titanium(IV) withN 1-hydroxy-N 1,N 2-diphenylbenzamidine and thiocyanate

A precise, reliable, sensitive, and selective method for the determination of titanium(IV) is described. Titanium(IV) reacts withN ¹-hydroxy-N ¹,N ²-diphenylbenzamidine (HDPBA) and thiocyanate to form an orange-coloured mixed-ligand complex of stoichiometry 112 (Ti SCN^– HDPBA). The complex is quantitatively extractable into toluene from 0.05–0.15M hydrochloric acid. The spectrum of the complex exhibits an absorption maximum at 400 nm with a molar absorptivity of 20000M ^–1 cm^–1 and the coloured system obeys Beer's law in the concentration range 0.20–3.0 gml^–1 titanium. The effects of foreign ions and of various experimental parameters have been studied to establish the optimum conditions for the extraction and determination of titanium. The precision of the method has been evaluated and the relative standard deviation has been found to be 0.53%. The method has been successfully applied to the determination of titanium in synthetic matrices corresponding to titanium-containing ores, minerals, and alloys.