Determination of picomole amounts of formaldehyde in air and bio-fluids based on its enhanced myoglobin-luminol chemiluminescence reaction

Abstract

The aim of this study was to assess the performance of selected destruction methods for the determination of heavy metals (Cd, Cu, Pb and Zn) in woodlouse (Oniscus asellus). A vigorous total analysis involving microwave destruction with HF, HCl and HNO₃ (method 1) was used as a reference method. Consistently low values for the dry ashing method may indicate incomplete dissolution of the elements and/or losses through volatilisation. Method 3 (concentrated HNO₃) that frequently is used in literature, produced erroneous values for Cd, Cu and Pb. Results were consistent with the microwave digestion, provided H₂O₂ was used during digestion (method 4, HNO₃/H₂O₂). Method 5 (HNO₃/HCIO₄, one destruction step) yielded low recoveries when only one destruction step was applied. Applying two destruction steps (method 6) resulted in values consistent with the microwave method, but was at the expense of reproducibility and rendered the method more lengthy and laborious. Because of the very good performance combined with speed and simplicity, destruction with HNO₃/H₂O₂ (method 4) emerged as the most convenient method.     

Barriers to the internal rotation and observables of the ground state for hydrogen peroxyde

SCF energy and one electron properties of the H₂O₂ molecule have been calculated by using a basis of 52 STO's. The minimum total energy reached is –150.83188 a.u. By carrying out the calculation for three different geometrical configurations a reasonable agreement with experimental values of the barriers to the internal rotation is obtained.

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Zusammenfassung Die SCF-Energie und die Einelektroneneigenschaften des H₂O₂-Moleküls werden mit einer Basis von 52 Slaterorbitalen berechnet. Als minimale Gesamtenergie werden der Wert von –150,83188 a.E. erreicht. Die Ergebnisse für 3 verschiedene Geometrien liefern eine befriedigende Übereinstimmung mit dem experimentellen Wert der Barriere für die innere Rotation.

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Résumé L'énergie SCF et les propriétés monoélectroniques de la molécule H₂O₂ ont été calculées en utilisant une base de 52 orbitales de Slater. L'énergie minimum totale atteinte est –150.83188 u.a. Un accord raisonnable avec les valeurs expérimentales des barrières de rotation est obtenu en effectuant les calculs pour trois configurations géométriques différentes.

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Note. When this paper was completed, we have received the work of Dunning and Winter. Their main results are quoted in Table 4. The agreement of the result for the trans barrier is very good. As in the case of Ref. [4] and [8] the geometry optimization contributes heavily (75% of the total value) to the result for the trans barrier.     

Effect of Radiation Defects on the Electronic Structure of Zircon by X-Ray Photoelectron Spectroscopy Data

X-Ray photoelectron spectroscopy (XPS) is used to study the electronic structure of radiation damaged samples of ZrSiO₄ zircon mineral at early and middle stages of its radiation destruction. The effects of radiation induced atomic disordering are found to be most distinctly manifested in the spectra of O1s states and to a smaller extent in the spectra of Si2p states, and also in the zircon valence band. Based on the quantum chemical calculation results the conclusion is drawn that the observed changes in XPS lines are caused by the formation of oxygen vacancy defects and an increase in the covalency of interatomic bonds near oxygen vacancies. For zircon samples with a low/moderate degree of radiation damage these changes reflect the initial stage of the polymerization of the ZrSiO₄ structure due to the formation of Si—O—Si chain fragments.     

Kinetic features of cationic oligomerization of epoxides

The kinetic features of the cationic oligormerization of epoxides of various structures influenced by Lewis acids (BF₃OEt₂, SnCl₄) were investigated. It was shown that the systems studied could he divided into three groups, based on the nature of conversion-time kinetic curves of oligomerization: (1) (Epoxypropane-BF₃OEt₂, 3,4-epoxybutene-1-BF₃OEt₂) oligomerization stops before the monomer is exhausted completely. (2) (1-Chloro-2,3-epoxypropane-BF₃OEt₂ or SnCl₄, 2-methyl-2,3-epoxybutane-BF₃OEt₂) oligomerization can be carried out almost up to complete conversion of the monomer. The reaction rate, however, decreases more rapidly than that expected from the kinetics of monomer consumption. (3) (1-tert-Butylperoxy-2,3-epoxypropane-SnCI₄) oligomerization kinetics are described by a simple exponential function with regard to monomer concentration. Determination of the propagating species concentration in the systems studied suggests that the initiation of cationic oligornerization of epoxides with Lewis acids is an instantaneous process and the discrepancy observed is a result of the different nature of kinetics of the active site destruction. In the first group of systems the rapid destruction of the propagating species prevents the oligomerization to complete conversion. In the second group a somewhat lower rate of decrease in concentration of the propagating species with time is explained by their regeneration during the process. In the third system, which is a unique case, the concentration of the propagating species remains constant with time. It is assumed that these features are the result of the stability or pseudostability of the active sites which depends on the nature of the epoxide and initiator.     

Calculation of molecular crystals within the PCILOCC framework

Stabilization energies and equilibrium distances of one-dimensional (HF)_n and (H₂O)_n chains have been calculated by means of the PCILO method for finite chain length and by the PCILOCC method for infinite chain length. Both types of calculation are compared with corresponding CNDO /2-MO and CNDO /2-CO calculations. Further we have performed an analysis of the individual contributions of the stabilization energies per monomer of the PCILO and PCILOCC calculations. The results show that the PCILOCC method is well suited for the calculation of molecular associations with translational symmetry.     

Ozonation of deciduous wood in the presence of hydrogen peroxide

The kinetic curves of the dependence of ozone specific absorption (Q _{r, sp} ) upon aspen wood ozonation in the presence and absence of hydrogen peroxide are obtained. It is established that the rate of ozone and Q _{r, sp} absorption increase in the O₃/H₂O₂ system. It is demonstrated by ESR, IR, and UV spectroscopy of diffuse reflection that wood ozonation in the O₃/H₂O₂ system results in the destruction of lignin aromatic and quinoid structures. The ozonation process in the presence of H₂O₂ is accompanied by destruction of the carbohydrate component of the lignocarbohydrate complex. We conclude that O₃/H₂O₂ can be used in the deep delignification of wood. It is shown that the presence of hydrogen peroxide upon ozonation increases the efficiency of the process, allowing its duration and total ozone consumption to be reduced.     

PHOTOCONTROL OF PHYTOCHROME DESTRUCTION IN GRASS SEEDLINGS. THE INFLUENCE OF WAVELENGTH AND IRRADIANCE

Abstract— –The kinetics of phytochrome destruction in vivo of coleoptiles and mesocotyls of etiolated grass seedlings (Avena sativa L., Zea mays L.) in continuous light were investigated using wavelength and irradiance as experimental variables. In contrast to dicotyledonous seedlings, the destruction reaction of these monocotyledons is saturated at very low levels of the far-red absorbing form of phytochrome, P_fr (e.g. at 1% of total phytochrome, corresponding to the photostationary state established by 727 nm light, in 2.5-day-old dark-grown Avena). On the other hand, the first-order rate constant of monocotyledon destruction may be at least one order of magnitude larger than in dicots, as indicated by the zero-order rate measured in the presence of saturating amounts of P_fr (τ_l/2 1.5 min in Avena). At sub-saturation P_fr levels, the destruction rate was found to be determined by the rate constants of the photoreactions over a wide range of wavelengths and irradiances. These results can be interpreted in terms of a destruction enzyme with high catalytic efficiency but limited availability. Analysis of in vivo binding of phytochrome to a pelletable cell structure during destruction revealed that both the pelletable and the non-pelletable fraction lose photoreversiblility with similar rates and thus provide no useful information with respect to a causal relationship between the two processes. However, due to the short half-life of P_fr at sub-saturation levels (which make the photoreactions and intermediary processes rate-limiting for destruction even at relatively high irradiances) the existence of a similarly rapid dark-reaction between the photoreactions producing P_fr and the destruction reaction could be demonstrated. This dark reaction displays the properties of P_fr binding to a receptor site.     

On the Nature of the 7-Norbornadienyllithiums. Preliminary Communication

Lithium reductions of 7-chloronorbornadiene and of bis(7-norbornadienyl)mercury both provide (C₇H₇)₂Li₂ ( 5a ). This product is accompanied by C₇H₇Li₂Cl ( 5c ) in the first case, and by C₇H₇Li ( 5b ) in the second. The theoretically anticipated properties of all three organolithiums are apparent in the consistent C_s symmetry of their hydrocarbon ligands, their protolytic destruction by 12-crown-4, and their significant J(C(7), Li) ( 5a , 7.6; 5b , 16.0; 5c 8.9 Hz).     

Studies on the Metal Amide Bond 21. Metal Complexes of Chiral Phenyl-Substituted Bis-Picolinamide Tetradentates

Abstract

Two new C-phenyl bis-picolinamide tetradentates, N', N,'-bis(2-pyridinecarboxamide)-1,2-diphenyIethane (bpstienH₂) and N,N'-bis(2-pyridinecarboxamide)phenylethane (bpstyenH₂) together with their deproto-nated complexes of bivalent Cu, Ni and Pd have been prepared and characterised. A crystallographic analysis of the two copper(II) complexes is reported, with the S-bpstyenH₂ ligand found to be susceptible to racemisation under the warm basic conditions used in the syntheses.

{[N,N'-Bis(2-pyridinecarboxamido)-S',S-1,2-diphenylethane]copper(II)}, C₂₆H₂₀N₄O₂Cu is mono-clinic, spacegroup P2₁ (No. 4), with a = 11.170(3), b = 10.853(4), c = 18.570(7) Å, β = 103.74(3)°, Z = 4, with two molecules in the asymmetric unit. The structure was refined to R = 0.039 for 2519 reflexions. Each molecule is five coordinate with the fifth position occupied by an amide oxygen atom of a neighbouring molecule. These Cu-O(amide) distances are 2.554(7) and 2.757(6) Å. The stereochemistry of molecule 1 closely resembles a square-based pyramid, whereas that for molecule 2 approximates a distorted trigonal bipyramid. In each case the central five-membered chelate ring has a γ conformation with the two phenyl substituents occupying the axial positions in a rare configuration.

{Aqua[N,N'-bis(2-pyridinecarboxamido)phenylethane]-copper(II)}-sesquihydrate, C₂₀H₂₁N₄O₄₅Cu, is monoclinic, space group P2₁/c (No. 14), with a= 12.122(4), b= 10.691(2), c= 15.952(4)Å, β = 110.76(2)°, Z = 4. The structure was refined to R = 0.046 for 1939 reflexions. The stereochemistry of the five-coordinate copper atom approximates a square pyramid with the copper atom displaced 0.26 Å towards the apical water molecule (Cu-O 2.251(5) Å). In the enantiomer containing S-bpstyen the central five-membered chelate ring has a Δ conformation with the phenyl substituent occupying an equatorial position.

In solution the palladium(II) and nickel(II) deprotonated metal complexes of the S,S- and S- ligand forms are shown by ¹H NMR analysis, in conjunction with their chiroptical properties, to each have a X gauche central chelate ring conformation with the phenyl substituent(s) occupying axial positions.     

Crystal structures and luminescent properties of a cadmium(II) metal-organic framework based on tri(4-pyridylphenyl)amine

Abstract

A luminescent cadmium(II) metal-organic framework, [Cd(tppa)₂ (bpdc)₂]_n (1) (tppa?=?tri(4-pyridylphenyl)amine, bpdc =4,4′-biphenyldicarboxylic acid), has been solvothermally synthesized by using Cd(NO₃)₂·4H₂O and a mixture of tppa and bpdc. Single crystal X-ray analysis reveals that 1 crystallizes in the orthorhombic system and Pbcn space group. Its overall structure is a twofold interpenetrated framework, and it shows a porosity of 31.8% based on a calculation by PLATON and a 4-c type topological network with the point symbol of {6^5.8}. In addition, 1 may be exploited as WLED due to its ability to give off yellow light under ultraviolet excitation.     

Oxidation of Aqueous Unsymmetrical Dimethylhydrazine by Calcium Hypochlorite or Hydrogen Peroxide/ Copper Sulfate

Abstract

The oxidative destruction of unsymmetrical dimethylhydrazine (UDMH) by a molar excess of Ca(OCl)₂ leads mainly to formaldehyde dimethylhydrazone and tetramethyl tetrazene, but not to N-nitrosodi-methylamine (NDMA). An alternate method using H₂O₂/CuSO₄ leads to ca. 25% NDMA. The amount of UDMH destroyed is affected by the order of addition of the H₂O₂, and CuSO₄: when the CuSO₄ is added first, only ca. 65% of the UDMH is destroyed, while the reverse order of addition leads to 100% destruction of UDMH.     

n-Alkane isomerization on heteropolyacids

Acid-base properties of bulk 12-tungstophosphoric heteropolyacid (HPWA) and HPWA supported on alumina and fluorinated alumina were studied by DRIFT spectroscopy using adsorption of probe molecules. Catalytic properties of Pt-containing catalysts carried by these supports were studied inn-pentane isomerization. It was shown that the Pt/HPWA/Al₂O₃ system is almost inactive in isomerization as a result of the interaction of HPWA with basic sites of the alumina support. On the contrary, the presence of acidic sites in fluorinated alumina prevents HPWA destruction and favors the uniform distribution of HPWA on the support surface. As a result, enhancement of the activity and selectivity of the Pt/HPWA/Al₂O₃-F catalyst inn-pentane isomerization is observed. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1744–1750, October, 2000.     

Theoretical Investigation on the Topochemical Polymerization of Diacetylenes

Abstract

The solid-state polymerization of diacetylenes (MDA-PBT-PDA) is studied with a concerted reaction model and the calculation method of EHMO-ASED and EHCO-ASED, where MDA = crystalline molecular diacetylenes, PBT = polybutatrienes, and PDA = polydiacetylenes. As the reaction goes on, the symmetry of frontier orbitals inverts at state PBT, HOCO from C ₂-antisymmetry to C ₂-symmetry and LUCO from C ₂-symmetry to C ₂-antisymmetry, which means completion of the 1,4-addition. Two necessary conditions must be satisfied for the reaction to take place: 1) the geometric parameters must undergo a series of concerted changes to make the conformation suitable for the intermolecular 1,4-addition, which should overcome an energy barrier E_b ; 2) the symmetry match between the frontier crystal orbitals of the reactant and the product must be satisfied-electrons of the reactant should be excited from HOCO (C ₂-antisymmetry) into LUCO (C ₂-symmetry), which faces an energy gap E _g. At state MDA, there is E _g(MDA) ≈ 5.6 eV. If MDA and PDA are analyzed according to Woodward-Hoffmann's rules, this reaction would be considered photochemically allowed but thermochemically forbidden. It has been shown that the E _g gradually decreases along the reaction coordinate from state MDA to PBT. At state PBT there is E _g(PBT) ≤ 0.1 eV, and the electrons of the reactant can be easily excited there. Since E_b ≤ 1.0 eV is not very large and E_g (PBT) ≤ 0.1 eV is very small, the two necessary conditions mentioned above can be satisfied thermally. Therefore, thermal polymerization can take place smoothly. By this pathway the apparent activation energy of the reaction will be E_a ≤ 1.0 eV, which is consistent with the activation energies of the polymerizations of diacetylenes in the literature.     

Kinetics of destruction of diisopropyl methylphosphonate in corona discharge

The kinetics of the destruction of diisopropyl methylphosphonate (DIMP) in corona discharge has been studied using a flow tubular coaxial wire dielectric barrier corona discharge reactor. The identification and quantitative determination of DIMP, its destruction intermediates, and phosphorus‐containing destruction products were performed using molecular beam mass spectrometry and gas chromatography/mass spectrometry. Active discharge power was varied in the range 0.01–5 W. The destruction products such as isopropyl methylphosphonate, methylphosphonic acid, and orthophosphoric acid were found on the reactor walls. The dependence of the extent of the destruction, D (D = 1 ? X / X₀, where X and X₀ are DIMP mole fractions at the outlet and the inlet of the reactor), on the specific energy deposition E_x (E_x = PF^?1 X₀^?1, where F is the carrier gas flow and P is the power dissipated in discharge reactor) was measured over the DIMP mole fraction range 60–500 ppm at the pressure of 1 bar and the temperature of 340 K. Over the range of the experimental conditions studied the destruction obeys the “pseudo‐first‐order” kinetic law: ln(1 ? D) = ?KE_x. Plausible mechanisms of the destruction are discussed. It was concluded that ion mechanism is the major one responsible for the destruction process. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 331–337, 2002     

Hydrogen Ion Affinity in Humic Acids: A Coordination Approach

Potentiometric titrations of humic acids (HA) with 0.250 M Ba(OH)₂/BaCl₂ titrant (0.750 M constant ionic strength), have been performed at 25 ± 0.1°C with a calibrated glass electrode for measuring p[H⁺]. The pK′_w for water in this BaCl₂ medium is 12.899 ± 0.006 and 13.712 ± 0.006 in 0.500 M NaCl. Divalent Ba²⁺ cations force the ionization of the acid groups and improve solubility. Under such conditions derivative potentiometric curves show diverse equivalent peaks of the acidic sites of HA. The presence of 0.05% of a neutral detergent such as Triton X-100 is essential for effective dispersion of HA in the working solutions and to obtain very stable potentiometric measurements. Computer programs were used in the treatment of the potentiometric data in order to solve a number of simultaneous equations to obtain overall conditional β _{i H} formation constants, which come from a coordination model of hydrogen ions to the organic matrix and permit calculation of conditional pK data. Conductimetric titrations with Ba(OH)₂ or NaOH give the total acidity. A typical result in BaCl₂ medium for a peat HA presents seven acid groups with the following pK data: pK ₁ = 3.80 ± 0.3, pK ₂ = 4.67 ± 0.02, pK ₃ = 7.57 ± 0.01, pK ₄ = 8.190 ± 0.005, pK ₅ = 8.80 ± 0.01, pK ₆ = 8.91 ± 0.02, and pK ₇ = 8.93 ± 0.01.     

Structure of zinc-5,15-di(o-methoxyphenyl)octaalkylporphyrines and their reaction with organic peroxides in the presence of pyridine

By combined spectral and calculation methods the structure of zinc 5,15-di(o-methoxyphenyl)-2,8,12,18 3,7,13,17-octaalkylporphyrinates (I, II) and their properties in the reaction with organic peroxides with addition of different amounts of pyridine were studied. The reaction of zinc porphyrinates with peroxides in the presence of pyridine leads to destruction of the complex chromophore. Kinetic parameters of the investigated reaction (effective k _ef and true k _V rate constants) are obtained. The presence of base in the reaction medium is found to lead to a change in the structure of the zinc porphyrinates and affects the rate of oxidation. By quantum-chemical method PM3 the geometry of the reagents was calculated and the deformation distortions of the reactants molecules and intermediates in the course of the oxidation reaction was demonstrated. The influence of electronic effects of substituents and the degree of deformation of the zinc porphyrinate macrocycle on their redox properties is revealed.     

Enhancement of the bimolecular reaction of hydrogen iodide by vibrational excitation

The bimolecular reaction of HI in CO₂, which was excited vibrationally by irradiation of a continuous-wave CO₂ laser light, was investigated in the temperature range of 721–980 K. An enhancement of the reaction rate by a factor of about 2.5 was observed in the 1:1 HI? CO₂ mixture in comparison with the rate in pure HI when both sample gases were irradiated by a CO₂ laser (50 W) at 1 torr. However, in the HI-SF₆ mixtures the decomposition rate of HI was not accelerated by irradiation of the CO₂ laser. Thus the enhancement is attributed to vibrational excitation of HI through collisional energy transfers from laser-excited CO₂ (00°1). At lower total pressures or at lower partial pressures of HI in HI-CO₂ mixtures the enhancement was more significant because of inefficient vibrational deactivation of excited HI. A model calculation gave the result in agreement with the experimental one if the effective activation energy is assumed as E_a? = E_a - αE_vib, where E_a is the activation energy for the thermal reaction, E_vib is the vibrational energy of two colliding HI molecules, and α is estimated to be about 0.7. This means that a part of the vibrational energy of reacting HI is employed to reduce the activation energy for the translational or rotational degree of freedom.