Strahlenchemie von alkoholen—IX Die UV-photolyse (λ = 185 nm) von methanol in flüssiger phase

The UV photolysis (λ = 185 nm) of liquid methanol yields hydrogen, glycol, formaldehyde, methane and traces of ethane in quantum yields of 0·83, 0·78, 0·058, 0·05 and 0·002 resp. (related to φ(H₂) = 0·4 of the ethanol-actinometer (5 mole/1 in water)). The isotopic distribution of the hydrogen (85% HD) formed in the photolysis of CH₃OD shows, that as in the gasphase² the scission of the O---H-bond (1) is the major process. CH₃OH + hv (λ = 185 nm) → CH₃O^• + H^• (1)

In methanoi-water mixtures (nearly all the light of the wavelength λ = 185 nm is absorbed by methanol) the quantum yields of hydrogen, glycol, methane and ethane are greatly reduced, while the formaldehyde yield remains unaffected. In 1 molar solution φ(H₂) = 0·42, φ(glycol) = 0·32 and φ(CH₄) = 6 x 10⁻⁴ is obtained. Ethane cannot be detected.     

The direct synthesis of dimethyl ether from syngas over hybrid catalysts with sulfate-modified γ-alumina as methanol dehydration components

A series of γ-Al₂O₃ samples modified with various contents of sulfate (0–15 wt.%) and calcined at different temperatures (350–750 °C) were prepared by an impregnation method and physically admixed with CuO–ZnO–Al₂O₃ methanol synthesis catalyst to form hybrid catalysts. The direct synthesis of dimethyl ether (DME) from syngas was carried out over the prepared hybrid catalysts under pressurized fixed-bed continuous flow conditions. The results revealed that the catalytic activity of SO₄²⁻/γ-Al₂O₃ for methanol dehydration increased significantly when the content of sulfate increased to 10 wt.%, resulting in the increase in both DME selectivity and CO conversion. However, when the content of sulfate of SO₄²⁻/γ-Al₂O₃ was further increased to 15 wt.%, the activity for methanol dehydration was increased, and the selectivity for DME decreased slightly as reflected in the increased formation of byproducts like hydrocarbons and CO₂. On the other hand, when the calcination temperature of SO₄²⁻/γ-Al₂O₃ increased from 350 °C to 550 °C, both the CO conversion and the DME selectivity increased gradually, accompanied with the decreased formation of CO₂. Nevertheless, a further increase in calcination temperature to 750 °C remarkably decreased the catalytic activity of SO₄²⁻/γ-Al₂O₃ for methanol dehydration, resulting in the significant decline in both DME selectivity and CO conversion. The hybrid catalyst containing the SO₄²⁻/γ-Al₂O₃ with 10 wt.% sulfate and calcined at 550 °C exhibited the highest selectivity and yield for the synthesis of DME.     

The luminescent properties of divalent europium complexes of crown ethers and cryptands

The luminescent properties of divalent europium complexes with crown ether, azacrown ether, N-pivot-azacrown ether, and cryptand in methanol or water have been systematically investigated under UV irradiation. These divalent europium complexes show greatly enhanced emission from 417 nm to 488 nm in the visible blue region in comparison with that of the methanol solution of EuCl₂. The aqueous solution of EuCl₂ is non-luminescent. This obvious distinction in luminescent properties between the macrocyclic ligand-coordinated divalent europium and uncoordinated divalent europium is attributed to the “insulation effect” of Eu²⁺ ion from the solvent molecules of CH₃OH and H₂O by the macrocyclic crown ether or cryptand encapsulation to divalent europium. Moreover, these macrocyclic ligands provide an additional restriction to the electronic charge expansion of the excited Eu²⁺. This also contributes to the enhancement of the Eu²⁺ luminescence. Among all the investigated macrocyclic ligands, 15-crown-5 (15C5) affords the largest enhancement to the Eu²⁺ emission. The intensity of the Eu²⁺–15C5 complex is 690 times that of the EuCl₂ methanol solution with the same Eu²⁺ concentration. This special emission enhancement effect is related to the particular complex composition of 1:3 (Eu²⁺:15C5) and corresponding configuration of Eu²⁺–15C5 complex in methanol. Concerning the mechanism, the luminescence enhancement of divalent europium by complexation with these macrocyclic crown ether or cryptand ligands is found to be initiated from the decrease in non-radiative rate constant rather than from the increase in radiative one.

The divalent europium complexes of methacrylate polymeric polyether derivatives such as 15C5-, 18-crown-6- (18C6), and cryptand [2.2.1]- or [2.2.2]-containing polymer and copolymer have also been prepared. Their luminescent properties in solid state have been studied to aim for practical application. As a similar situation to the simple polyether complexes, the divalent europium complex with 15C5-containing polymer or copolymer shows the largest luminescent enhancement effect. Its emission intensity reaches about 20% that of the commercial inorganic luminescence product CaWO₄:Pb (NBS 1026). In addition, the doping effect of several divalent ions, namely Mg, Sr, Ba and Zn in polymeric complexes, has also been investigated according to the luminescence concentration quenching mechanism in solid state luminescence materials. The emission intensity of 15C5-containing polymer europium(II) complex is raised to twice stronger by doping of Zn²⁺ ion.     

Far-UV laser flash photolysis in solution. A study of the chemistry of 1,1-dimethylsilene in hydrocarbon solvents

The far-UV (193 nm) laser flash photolysis of nitrogen-saturated isooctane solutions of 1,1-dimethylsiletane allows the direct detection of 1,1-dimethylsilene as a transient species, which (at low laser intensities) decays with pseudo-first-order kinetics (τ 10 μs) and exhibits a UV absorption spectrum with λ_max 255 nm. Characteristic rapid quenching is observed for the silene with methanol (k_McOH = (4.9 ± 0.2) × 10⁹ M⁻¹ s⁻¹), tert-butanol (k_BuOH = (1.8 ± 0.1) × 10⁹ M⁻¹ s⁻¹) and oxygen (k_O2 = (2.0 ± 0.5) × 10⁸ M⁻¹ s⁻¹). The Arrhenius activation parameters for the reaction with methanol have been determined to be E_a = −2.6 ± 0.6 kcal mol⁻¹ and log A = 7.7 ± 0.3.     

Determination of boron in water and pharmaceuticals by sequential-injection analysis and fluorimetric detection

This work reports the application of a sequential-injection analysis (SIA) method for the determination of boron. The method relies on the enhancement of the fluorescence (λ_ex=313 nm, λ_em=360 nm) of chromotropic acid (4,5-dihydroxynaphthalene-2,7-disulphonic acid-CA) as a result of its complexation with boric acid (BA). Individual zones of the sample, the CA solution in a suitable buffer and a NaOH solution were aspirated in the holding coil of the SIA apparatus. As the zones were propelled towards the detector, zone penetration in the sample–CA interfaces occurred resulting in the formation of the strongly fluorescent BA–CA complex. The native fluorescence of the CA was quenched by the alkaline environment established as a result of the mixing at the CA–NaOH interface. The chemical and instrumental parameters affecting the fluorescence intensity were investigated and the influence of potential interferents was investigated. After selecting the most suitable conditions, the calibration plot for boron was linear in the range of 8–350 μg l⁻¹ with a 3σ limit of detection of 3 μg l⁻¹ and a relative standard deviation of 2.7% at the 90 μg l⁻¹ boron level (n=8). Finally, the method was applied to the determination of boron in natural waters and pharmaceutical products with revoveries in the range of 96–106%.     

Structural and spectroscopic investigations of europium(III) entrapped by the ethylenediaminetetra(methylenephosphonate) ligand in K12H8[Eu4(EDTMP)4] · 45H2O crystal

The X-ray crystal structure of an anionic octacoordinate Eu³⁺ complex of the formula K₁₂H₈[Eu₄(EDTMP)₄] · 45H₂O, where EDTMP is the ethylenediaminetetra(methylenephosphonate) anion, hereinafter referred to as I, has been determined. The crystal consists of cyclic tetrameric complex anions, in which the surrounding of each Eu³⁺ ion is composed of two nitrogen atoms and six oxygen atoms from phosphonate groups. One of the phosphonate groups in the ligand molecule is tridentate (O:O′,O″), thus giving rise to the formation of the tetramers. The compound was characterized by UV–Vis electronic spectroscopy. At room and liquid nitrogen temperatures the complex shows luminescence from both ⁵D₀ and ⁵D₁ states, the latter one, which is very rare in Eu³⁺ compounds with organic ligands, is probably brought about by the saturation of the coordination sphere with the phosphonate groups.     

Fluorimetric determination of aminoglycoside antibiotics using lanthanide probe ion spectroscopy

The application of probe ion fluorimetry has succeeded in the microdetermination of six aminoglycoside antibiotics: neomycin, streptomycin, gentamicin, tobramycin, amikacin and kanamycin as sulfate salts in pure form and in some pharmaceutical preparations. The method is based on the reaction of Eu³⁺ ions with aminoglycosides through amino and hydroxy groups. Such interactions enhance the intensity of the 616 nm fluorescence emission of the Eu³⁺ ion. The fluorescence at 592 nm comes from a non-hypersensitive transition and is not affected by the ligand which is bound to the probe ions. The intensity ratio R, defined as I₅₉₂/I₆₁₆ was used to determine the amount of free and bound europium ions. A linear relationship between bound europium ions and aminoglycoside was found within the concentration ranges 20–100 ppm for neomycin, 5–60 ppm for streptomycin, and 10–70 ppm for gentamicin, tobramycin, amikacin, and kanamycin as sulfate salts. The percentage recoveries ranged from 99.22 to 101.07, with standard deviations ranging from ± 1.5 to ± 4.38. The relative stability constants ranged from 5 × 10³ to 2 × 10⁴. The optimum reaction conditions were studied and the results obtained compared favourably with the fluorimetric method using fluorescmine reagent.     

Luminescent properties of carbon-rich starburst gold(I) acetylide complexes. Crystal structure of [TEE][Au(PCy3)]4 ([TEE]H4=tetraethynylethene)

Two carbon-rich starburst gold(I) acetylide complexes [TEE][Au(PCy₃)]₄ (3, [TEE]H₄=tetraethynylethene) and [TEB][Au(PCy₃)]₃ (6, [TEB]H₃=1,3,5-triethynylbenzene) were prepared and their UV–vis absorption, emission and excitation spectra have been recorded. In fluid CH₂Cl₂ solutions, 3 exhibits prompt ¹(ππ*) fluorescence with λ_0–0 and λ_max at 413 and 428 nm, respectively, while 6 displays ³(ππ*) phosphorescence with λ_0–0 and λ_max at 446 and 479 nm, respectively. The crystal structure of 3·CH₂Cl₂ has been determined.     

Structure and conformational properties of carbonylbisimidosulfuryl fluoride, O=C(N=S(O)F2)2

The molecular structure and conformational properties of O=C(N=S(O)F₂)₂ (carbonylbisimidosulfuryl fluoride) were determined by gas electron diffraction (GED) and quantumchemical calculations (HF/3-21G* and B3LYP/6-31G*). The analysis of the GED intensities resulted in a mixture of 76(12)% syn–syn and 24(12)% syn–anti conformer (ΔH⁰=H⁰(syn–anti)−H⁰(syn–syn)=1.11(32) kcal mol⁻¹) which is in agreement with the interpretation of the IR spectra (68(5)% syn–syn and 32(5)% syn–anti, ΔH⁰=0.87(11) kcal mol⁻¹). syn and anti describe the orientation of the S=N bonds relative to the C=O bond. In both conformers the S=O bonds of the two N=S(O)F₂ groups are trans to the C–N bonds. According to the theoretical calculations, structures with cis orientation of an S=O bond with respect to a C–N bond do not correspond to minima on the energy hyperface. The HF/3-21G* approximation predicts preference of the syn–anti structure (ΔE=−0.11 kcal mol⁻¹) and the B3LYP/6-31G* method results in an energy difference (ΔE=1.85 kcal mol⁻¹) which is slightly larger than the experimental values. The following geometric parameters for the O=C(N=S)₂ skeleton were derived (r_a values with 3σ uncertainties): C=O 1.193 (9) Å, C–N 1.365 (9) Å, S=N 1.466 (5) Å, O=C–N 125.1 (6)° and C–N=S 125.3 (10)°. The geometric parameters are reproduced satisfactorily by the HF/3-21G* approximation, except for the C–N=S angle which is too large by ca. 6°. The B3LYP method predicts all bonds to be too long by 0.02–0.05 Å and the C–N=S angle to be too small by ca. 4°.     

Optical spectra of Yb and Yb–Nd interaction in Cs2NaNd0,4Yb0,6Cl6

Interaction between octahedrally coordinated Nd³⁺ and Yd³⁺ in Cs₂NaNd_0,4Yb_0,6Cl₆ reduces the Nd³⁺ luminescence lifetime by roughly two orders of magnitude with respect to that found in Cs₂NaNdCl_{6– · –} Analysis of low temperature absorption and emission spectra reveals that the nonradiative Nd³⁺–Yb³⁺ energy transfer has to be assisted by lattice phonon emission, nevertheless the rate of the transfer is high in the 4–300 K temperature region and attains 5.8×10⁵s^-1 at room temperature. A phase transition of Cs₂NaNd_0,4Yb_0,6Cl₆ between 12 and 13 K is evidenced by abrupt change of both the spectra and lifetimes of Yb³⁺. Reduction of Yb³⁺ lifetime from 5.3 ms to 150 μs is at the transition from low symmetry phase to high symmetry phase is supposed to be associated with a three ion interaction which occurs in ordered lattice and disappears in low temperature disordered structure.     

Chains, ladders and sheets of d metal–organic polymers generated from the flexible bipyridyl ligands

By use of the three-layer diffusion method, reactions of flexible bipyridyl ligands (4,4′-bpp or 3,3′-bpp) with M(II) salts (M = Zn, Cd) and multi-carboxylate ligands resulted in the formation of four interesting d¹⁰ metal–organic coordination polymers: [Zn(μ-4,4′-bpp)Br₂]_n (1), [Zn(μ-4,4′-bpp)(1,2-bdc)]_n · nH₂O (2), [Zn(μ-3,3′-bpp)(1,3-bdc)]_n · nCH₃OH · 2nH₂O (3) and [Cd(μ-3,3′-bpp)(C₄H₂O₄)]_n · 3nH₂O (4) (4,4′-bpp = 2,2′-bis(4-pyridylmethyleneoxy)-1,1′-biphenylene; 3,3′-bpp = 2,2 ′-bis(3-pyridylmethyleneoxy)-1,1′-biphenylene; bdc=benzenedicarboxylate, C₄H₄O₄ = fumaric acid). Complex 1 has a 2D sheet structure consisting of two unusual zigzag Zn(II) chains which are nearly perpendicular to each other. Complex 2 is comprised of two-leg ladders, in which [Zn(4,4′-bpp)] chains serve as the side rails and 1,2-bdc ligands serve as the cross rungs. In complex 3, every two 1,3-bdc ligands connect the neighbouring Zn(II)-3,3′-bpp dimetallic rings in η¹ coordination modes into an interesting chain structure. Complex 4 consists of an anionic macrocycle-containing cadmium dicarboxylate sheets that are separated by 3,3′-bpp. These d¹⁰ metal complexes exhibit high thermal stabilities and strong luminescence efficiencies.     

Heat capacity, enthalpy and entropy of strontium bismuth niobate and strontium bismuth tantalate

The heat capacities and enthalpy increments of strontium bismuth niobate SrBi₂Nb₂O₉ (SBN) and strontium bismuth tantalate SrBi₂Ta₂O₉ (SBT) were measured by the relaxation method (2–150 K), Calvet-type heat-conduction calorimetry (305–570 K) and drop calorimetry (773–1373 K). The temperature dependences of non-transition heat capacities in the form C_pm = 324.47 + 0.06371T − 5.0755 × 10⁶/T² J K⁻¹ mol⁻¹ (298–1400 K) and C_pm = 320.22 + 0.06451T − 4.7001 × 10⁶/T² J K⁻¹ mol⁻¹ (298–1400 K) were derived for SBN and SBT, respectively, by the least-squares method from the experimental data. Furthermore, the standard molar entropies at 298.15 K S_m°(SBN)=327.15±0.80 and S_m°(SBT)=339.23±0.72 J K⁻¹ mol⁻¹ were evaluated from the low-temperature heat capacity measurements.     

Redox reactions of 2-hydroxy-3-methoxybenzaldehyde (o-vanillin) in aqueous solution

Pulse radiolysis technique has been employed to study the reactions of oxidizing (^√OH, N₃^√) and reducing radicals (e⁻_aq, CO₂^√−, acetone ketyl radical) with 2-hydroxy-3-methoxybenzaldehyde (o-vanillin) at different pH. Hydroxyl radicals react mostly by addition reaction forming radical adducts (λ_max=420 nm) and the oxidation is only a minor process even in the alkaline region. The reaction with azide radicals produced phenoxyl radicals (λ_max=340 nm), which are formed on fast deprotonation of solute radical cation. Using PMZ^√+/PMZ and ABTS^√−/ABTS²⁻ as the reference couple, different methods are employed to determine the one-electron reduction potential of o-vanillin and the average value is estimated to be 1.076±0.004 V vs. NHE at pH 6. The phenoxyl radicals of o-vanillin were able to oxidize ABTS²⁻ quantitatively. The e_aq⁻ is observed to react with o-vanillin with rate constant value of 2×10¹⁰ dm³ mol⁻¹ s⁻¹. CO₂^√− and acetone ketyl radical are also observed to react with o-vanillin by electron transfer mechanism and showed the formation of transient absorption bands with λ_max at 350 and 390 nm at pH 4.5 and 9.7, respectively. The pK_a of the one-electron reduced species was determined to be 8.1. The results indicate that the aldehydic group is the most preferred site for electron addition.     

HPLC determination of Vitamin D(3) and its metabolite in human plasma with on-line sample cleanup

A HPLC method with automated column switching and UV-diode array detection is described for the simultaneous determination of Vitamin D₃ and 25-hydroxyvitamin D₃ (25-OH-D₃) in a sample of human plasma. The system uses a BioTrap precolumn for the on-line sample cleanup. A sample of 1 ml of human plasma was treated with 2 ml of a mixture of ethanol–acetonitrile (2:1 (v/v)). Following centrifugation, the supernatant was evaporated to dryness under a stream of dry and pure nitrogen. The residue was reconstituted in 250 μL of a solution of methanol 5 mmol l⁻¹ phosphate buffer, pH 6.5 (4:1 (v/v)), and a 200 μl aliquot of this solution was injected onto the BioTrap precolumn. After washing during 5 min with a mobile phase constituted by a solution of 6% acetonitrile in 5 mmol l⁻¹ phosphate buffer, pH 6.5 (extraction mobile phase), the retained analytes were then transferred to the analytical column in the backflush mode. The analytical separation was then performed by reverse-phase chromatography in the gradient elution mode with the solvents A and B (Solvent A: acetonitrile–phosphate buffer 5 mmol l⁻¹, pH 6.5; 20:80 (v/v); solvent B: methanol–acetonitrile–tetrahydrofuran, 65:20:15 (v/v)). The compounds of interest were detected at 265 nm. The method was linear in the range 3.0–32.0 ng ml⁻¹ with a limit of quantification of 3.0 ng ml⁻¹. Quantitative recoveries from spiked plasma samples were between 91.0 and 98.0%. In all cases, the coefficient of variation (CV) of the intra-day and inter-day-assay precision was ≤2.80%. The proposed method permitted the simultaneous determination of Vitamin D₃ and 25-OH-D₃ in 16 min, with an adequate precision and sensitivity. However, the overlap of the sample cleanup step with the analysis increases the sampling frequency to five samples h⁻¹. The method was successfully applied for the determination of Vitamin D₃ and 25-OH-D₃ in plasma from 46 female volunteers, ranging from 50 to 94 years old. Vitamin D₃ and 25-OH-D₃ concentrations in plasma were found from 4.30–40.70 ng ml⁻¹ (19.74 ± 9.48 ng ml⁻¹) and 3.1–36.52 ng ml⁻¹ (7.13 ± 7.80 ng ml⁻¹), respectively. These results were in good agreement with data published by other authors.     

Kinetic investigation of electronic energy transfer processes following the pulsed dye-laser generation of excited atomic barium, Ba[6s6p(P1)], in the presence of atomic strontium

The collisional behaviour of Ba[6s5d(³D_J)], 1.151 eV above the 6s²(¹S₀) electronic ground state, in the presence of atomic strontium, has been investigated in the ‘long-time domain' (ca. 100 μs–1 ms) following the pulsed dye-laser excitation of barium vapour at elevated temperature at λ = 553.5 nm (Ba[6s6p(¹P₁)] ← Ba[6s²(¹S₀)]. Ba(³D_J) is subsequently produced from the short-lived ¹P₁ state (τ_e = 8.37 ± 0.38 ns) by a number of radiative and collisional processes. It may then be monitored in the ‘long-time domain' by atomic spectroscopic marker methods involving either collisional activation of Ba(³D_J) by Ba(¹S₀) and He buffer gas to yield Ba[6s6p(³P_J)] with subsequent emission from the ³P₁ state (τ_e = 1.2 ± 0.1 μs): Ba[6s6p(³P₁)] → Ba[6s²(¹S₀)] + hv (λ = 791.1 nm). Alternatively, emission from Ba(¹P₁) may be monitored at long times following the generation of this short-lived state by energy pooling following self-annihilation of Ba(³D_J) + Ba(³D_J) from Ba[6s6p(¹P₁)] → Ba[6s²(¹S₀)] + hv (λ = 553.5 nm). The generation of Ba(³D_J) in the presence of atomic strontium yields emission in the long-time domain from Sr[5s5p(³P₁)] (τ_e = 19.6 μs): Sr[5s5p(³P₁)] → Sr[5s²(¹S₀)]  + hv (λ = 689.3 nm). Whilst the decay profiles at short times are complex in form, at long times all these atomic profiles show first-order kinetic removal with the decay coefficients for λ = 791.1 nm, 689.3 nm and 553.5 nm emissions in the ratio 1 : 2 : 2, consistent with overall third-order activation of the form: Ba(³D_J) + Ba(³D_J) + Sr(¹S₀) → Sr(³P_J) + 2Ba(¹S₀). The mechanism is modelled in detail, including measurement of integrated emission intensities, yielding kinetic data for fundamental collisional processes. The overall rate constant for the third-order collisional activation of Sr[5s5p(³P_J])from 2Ba[6s5d(³D_J)] + Sr[5s²(¹S₀)] takes the upper limit of 5.8 × 10⁻²⁷ cm⁶ atom⁻² s⁻¹ (T = 900 K). The rate constant for the two body collisional quenching of Ba[6s5d(³D_J)] by ground state atomic strontium, Sr[5s²(¹S₀)], is found to be (2.0 ± 0.1) × 10⁻¹² cm³ atom⁻¹ s⁻¹ (T = 900 K).     

Structure of liquid 1-chloronaphthalene at 293 K

The structure of 1-chloronaphthalene, C₁₀H₇–Cl, at 293 K was investigated using the X-ray diffraction method. Monochromatic radiation MoK (λ=0.71069 Å) enabled the determination of the scattered radiation intensity between S₀=4πsin ₀/λ=0.430 Å⁻¹ and S_max=14.311 Å⁻¹. The interpretation of the results was carried out using the reduction method of Blum and Narten. Experimental distributions of X-ray scattered intensity were compared with theoretical results predicted for a proposed model of 1-chloronaphthalene molecule. The electron-density radial-distribution function was calculated and some intra- and intermolecular distances in liquid 1-chloronaphthalene were determined. X-ray structural analysis was applied to determine the packing coefficient of 1-chloronaphthalene molecules.     

Determination of pentoxifylline in pharmaceutical formulations using iodine as oxidizing agent

Simple, selective and sensitive spectrophotometric methods are described for the determination of pentoxifylline, based on the haloform reaction with a known and excess of standard iodine solution under alkaline conditions. The excess of iodine is determined at pH 3.0 with metol–isoniazid (λ_max=620 nm; method A) or wool fast blue BL (λ_max=540 nm, method B). All the variables have been optimised and the reaction mechanisms presented. Regression analysis of Beer's law plots showed good correlation in the concentration ranges 4.0–24.0 and 0.4–2.4 mg ml⁻¹ for methods A and B respectively. No interferences were observed from excipients and the validity of the methods was tested by analysing pharmaceutical formulations. Recoveries were 99.0–100.0%. The concentration measurements were reproducible within a relative standard deviation of 1.0%.     

TEMPO-initiated oxidation of 2-aminophenol to 2-aminophenoxazin-3-one

The oxidation reaction of 2-aminophenol (OAP) to 2-aminophenoxazin-3-one (APX) initiated by 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) has been investigated in methanol at ambient temperature. The oxidation of OAP was followed by electronic spectroscopy and the rate constants were determined according to the rate law −d[OAP]/dt=k_obs[OAP][TEMPO]. The rate constant, activation enthalpy and entropy at 298 K are as follows: k_obs (dm³ mol⁻¹ s⁻¹)=(1.49±0.02)×10⁻⁴, E_a=18±5 kJ mol⁻¹, ΔH^‡=15±4 kJ mol⁻¹, ΔS^‡=−82±17 J mol⁻¹ K⁻¹. The results of oxidation of OAP show that the formation of 2-aminophenoxyl radical is the key step in the activation process of the substrate.     

Synthesis and crystal structure of two novel nickel (imidazole) complexes having hydrogen-bonded networks

Two nickel (imidazole) complexes, Ni(im)₆Cl₂·4H₂O (1) and Ni(im)₆(NO₃)₂ (2) (im=imidazole) have been synthesized and characterized by elemental analysis, IR, UV, TG and single crystal X-ray diffraction. 1 crystallizes in the triclinic space group P-1 with a=8.800(6) Å, b=9.081(6) Å, c=10.565(7) Å, =75.058(9)°, β=83.143(8)°, γ=61.722(8)°, V=718.3(8) Å³, Z=1 and R₁ (wR₂)=0.0469 (0.1497). 2 crystallizes in the trigonal space group R-3 with a=12.370(6) Å, b=12.370(6) Å, c=14.782(14) Å, =90.00°, β=90.00°, γ=120.00°, V=1959(2) Å³, Z=3 and R₁ (wR₂)=0.0358 (0.0955). 1 and 2 exhibit different supramolecular network due to their different counter anions and different hydrogen bonding connection. In compound 1, [Ni(im)₆]²⁺ cation and counter anions Cl⁻ alternatively array in an ABAB fashion via N–HCl hydrogen bonding. In compound 2, the plane of each NO₃²⁻ is almost parallel and each NO₃²⁻ connect three different [Ni(im)₆]²⁺ cations via N–HO hydrogen bonding.     

Immobilization enzyme fluorescence capillary analysis for determination of lactic acid

A new method for the determination of lactic acid based on the immobilization enzyme fluorescence capillary analysis (IE-FCA) was proposed. Lactic dehydrogenase (LDH) was immobilized on inner surface of a capillary with glutaraldehyde, and an immobilized enzyme lactate capillary bioreactor (IE-LCBR) was formed for the determination of lactic acid. After nicotinamide adenine dinucleotide (NAD⁺) is mixed with lactic acid solution, it was sucked into the IE-LCBR and was detected at λ_ex 353 nm/λ_em 466 nm. Optimized conditions are as follows: the temperature is 38 °C; the reaction time is 15 min; the concentrations of Tris buffer (pH 8.8) and NAD⁺ are 0.1 mol L⁻¹ and 4 mmol L⁻¹, respectively; the concentration of LDH used for immobilization is 15 kU L⁻¹. The concentration of lactic acid is directly proportional to the fluorescence intensity measured from 0.50 to 2.0 mmol L⁻¹; and the analytical recovery of added lactic acid was 99–105%. The minimum detection limit of the method is 0.40 mmol L⁻¹ and sensitivity of the IE-CBR is 4.6 F mmol⁻¹ L⁻¹ lactate. Its relative standard deviation (R.S.D.) is ≤2.0%. This IE-FCA method was employed for determination of lactate in milk drink.