Development and validation of an analytical method for detection of estrogens in water

An analytical procedure enabling routine analysis of four environmental estrogens at concentrations below 1 ng L^–1 in estuarine water samples has been developed and validated. The method includes extraction of water samples using solid-phase extraction discs and detection by gas chromatography (GC) with tandem mass spectrometry (MS–MS) in electron-impact (EI) mode. The targeted estrogens included 17- and 17-estradiol (aE2, bE2), estrone (E1), and 17-ethinylestradiol (EE2), all known environmental endocrine disruptors. Method performance characteristics, for example trueness, recovery, calibration, precision, accuracy, limit of quantification (LOQ), and the stability of the compounds are presented for each of the selected estrogens. Application of the procedure to water samples from the Scheldt estuary (Belgium – The Netherlands), a polluted estuary with reported incidences of environmental endocrine disruption, revealed that E1 was detected most frequently at concentrations up to 7 ng L^–1. aE2 was detected once only and concentrations of bE2 and EE2 were below the LOQ.Presented at the 9th FECS Conference on Chemistry and the Environment, Bordeaux, France, 29 August–1 September 2004     

Oxidation of Cyclohexane by Molecular Oxygen Photoassisted by meso-Tetraarylporphyrin Iron(III)-Hydroxo Complexes

The photochemical and photocatalytic properties of iron meso-tetraarylporphyrins bearing an OH(-) axial ligand and different substituents in the beta-positions of the porphyrin ring are reported. Irradiation (lambda = 365 nm) in the absence of dioxygen leads to the reduction of Fe(III) to Fe(II) with the formation of OH(*) radicals. Substituents at the pyrrole beta-positions are found to markedly affect the photoreduction quantum yields. Under aerobic conditions, this photoreaction can induce the subsequent oxidation of cyclohexane to cyclohexanone and cyclohexanol by O(2) itself. The process occurs under mild conditions (22 degrees C; 760 Torr of O(2)) and without the consumption of a reducing agent. The polarity of the solvent and the nature of the porphyrin ring have a remarkable effect on the selectivity of the photooxidation process, likely controlling the cleavage of O-O bonds of possible iron peroxoalkyl intermediates. In particular, in pure cyclohexane, oxidation occurs with the selective formation of cyclohexanone; in contrast, in dichloromethane/cyclohexane mixed solvent, the main oxidation product is cyclohexanol. Phenyl-tert-butylnitrone (pbn) has been found to quench the radical chain autooxidation of the substrate thus increasing the yield of cyclohexanol. This becomes the only oxidation product when iron 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin hydroxide (Fe(III)(TDCPP)(OH)) is used as photocatalyst.     

Conformational Study of Naringenin in the Isolated and Solvated States by Semiempirical and Ab Initio Methods

Naringenin is a natural widespread flavanone occurring in different foodstuffs that presents several important biological activities. Although its properties are well documented, its mechanisms of action are still controversial. The present article reports a conformational analysis of naringenin, using the semiempirical AM1 and ab initio methods, at the Hartree–Fock level of theory. The 3-21G, 3-21G*, 6-31G, and 6-31G** basis sets were used. The electron correlation effects were included through the Møller–Plesset second-order perturbation theory. The solvation of naringenin has been investigated through the standard SCRF, the supermolecule (SM), and the combined SM/SCRF models. The results have shown that there are two degenerate forms of naringenin, differing mainly by the orientation of a hydroxyl group (C4—OH). The energy barrier for the interconversion between them is ca. 6 kcal.mol^–1, suggesting some conjugation between the -system of the aromatic B ring and the hydroxyl group (C4—OH).     

Noise and correlation functions of hot carriers in semiconductors

We present a unifying theory of electronic noise appropriate to semiconductor materials in the presence of electric fields of arbitrary strength. In addition to thermal noise, a classification scheme for excess noise indicating different microscopic sources of fluctuations responsible for number and mobility fluctuations is provided. On the basis of simple two-level models, numerical calculations using a Monte Carlo technique are performed for the case of p-type Si at 77 K. The primary quantity which is evaluated by the theory is the auto-correlation function of current fluctuations which, subsequently, is analyzed in terms of correlation functions of the relevant physical variables. Accordingly, the corresponding current spectral-densities are determined and then compared with direct experimental results and/or analytical expressions. Important subjects which have been investigated are: (i) the effect of field assisted ionization on generation-recombination noise from shallow impurity levels; (ii) the contribution to the total noise spectrum of cross-correlation terms coupling fluctuations in velocity with those in energy and number; (iii) the current random telegraph signal and the corresponding spectral density associated with a mobility fluctuator. In all cases the numerical calculations are found to be in satisfactory agreement with experiments and/or analytical expressions thus fully supporting the physical reliability of the theoretical approach here proposed.List of the Symbols Used e Absolute value of the electron charge - f Frequency - f Distribution function - g ₁ Scattering strength with the scatter in state 1 - g ₂ Scattering strength with the scatter in state 2 - Reduced Planck constant - j Total current density - j _c Conduction current density - j _d Displacement current density - j _x Component along the x direction of the total current density - k Carrier wavevector - m Carrier effective mass - m ₀ Free electron mass - r Position vector - s Average sound velocity - t Time - u Fraction of ionized carriers - u _i Random telegraph signal related to carrier state - u _m Random telegraph signal related to scatterer state - v _d Ensemble average of the free carrier drift-velocity - v _i Carrier group velocity - v _t Ensemble average of the carrier velocity in the direction transverse to the applied field - v _ix Component along the x direction of the carrier group velocity - v _d ^r Ensemble average of the reduced drift-velocity - v ^r _i Reduced velocity component in the field direction of the i-th particle - v _ix ^j Reduced velocity component along the x axis of the i-th particle in band j - v ^r _ix Reduced velocity component along the x axis of the i-th particle - x _d Ensemble average of the carrier displacement along the x direction from the initial position - x _i Displacement along the x direction of the i-th carrier from the initial position - y _i i-th stochastic parameter - A Cross-sectional area of a homogeneous sample - C _I Auto-correlation function of the total current fluctuations - Auto-correlation function of the total current fluctuations due to mobility fluctuations - D Diffusion coefficient - D _t K Optical deformation potential - E Electrical field strength - E Electric field - E _x Component of the electric field along the x direction - E ₁ ⁰ Acoustic deformation potential - G Conductance - I Total current - I ₀ Total current in the voltage noise operation - I _m Total current associated with mobility fluctuations - I ^V Total current in the current noise operation - K _B Boltzmann constant - L Length of a homogeneous sample - N Number of free carriers which are instantaneously present in the device - N _A Acceptor concentration - N _I Total number of carriers inside the device participating in the transport (here assumed to be constant in time) - N _T Total number of carriers which are instantaneously present in the device - S _I Spectral density of current fluctuations - S _V Spectral density of voltage fluctuations - Spectral density of current fluctuations associated with the mobility fluctuations - Spectral density of current fluctuations due to correlations between fluctuations in number and velocity - Spectral density of current fluctuations due to generation-recombination processes - Spectral density of current fluctuations due to free carrier drift-velocity fluctuations - S _I ^l Longitudinal component with respect to the applied field of the current spectral-density - S _I ^t Transverse component with respect to the applied field of the current spectral-density - T Absolute temperature - T _e Electron temperature - V Electrical potential - V ^I Electrical potential in the voltage noise operation - W Collision rate - Z Small signal impedance - Poole-Frenkel factor - Equilibrium generation rate - _E Field dependent generation rate - Typical energy for thermally escaping from the impurity level - v _d ⁽⁰⁾ Fluctuation of the ensemble average of the driftvelocity associated with Brownian-like motion - v _d ^r(0) Fluctuation of the ensemble average of the reduced drift-velocity associated with Brownian-like motion - Carrier energy - ₀ Vacuum permittivity - _a Energy of the acceptor level - _r Relative static dielectric constant - Angle between initial and final k states - _op Optical phonon equivalent temperature - Mobility - ₀ Chemical potential - ₁ Mobility with the fluctuating scatterer in state 1 - ₂ Mobility with the fluctuating scatterer in state 2 - ₀ Crystal density - _E Field dependent volume recombination rate - _eq Equilibrium volume recombination rate - Conductivity - _g Cross-section for impact ionization - _c Average scattering time - _g Generation time - _l Carrier lifetime - _m Scatterer lifetime - _m1 Mean value of the time spent by the fluctuating scatterer in state 1 - _m2 Mean value of the time spent by the fluctuating scatterer in state 2 - _r Average recombination time - _T Transit time - Scattering rate - _AB Correlation function of the two variables A and B     

Tying together the ultrastructural modifications of wood fibre induced by pulping processes with the mechanical properties of paper

The composition and ultrastructural arrangement of cell wall polymers in wood fibres have determining influence on the properties of wood derived materials. It is therefore important to improve our understanding of the relationship between fibres organisation, the modifications induced by pulping treatments, and the resulting paper sheet mechanical properties. The different treatments to which fibres are subjected during the manufacturing of pulps and papers induce morphological and micro-structural alterations due to the removal of wall constituents and of microfibrillar elements. The impact of pulping processes on fibres was investigated at the ultrastructural scale of transmission electron microscopy. Particular attention was given to the effects of beating in refiners at various intensities on the ultrastructure of fibres. The most characteristic effects consisted of delaminations, microfibril disorganisation, and even fractures, of varying importance depending on the intensity of the mechanical refining. The consequences of internal alterations and surface modifications of the fibres were examined in relation to the paper sheet mechanical properties. Correlations between the type of alteration observed in the fibres and its possible impact on a given paper mechanical property are suggested. With similar approaches, the effects of drying and recycling were studied.     

The effect of optical substrates on micro-FTIR analysis of single mammalian cells

The study of individual cells with infrared (IR) microspectroscopy often requires living cells to be cultured directly onto a suitable substrate. The surface effect of the specific substrates on the cell growth—viability and associated biochemistry—as well as on the IR analysis—spectral interference and optical artifacts—is all too often ignored. Using the IR beamline, MIRIAM (Diamond Light Source, UK), we show the importance of the substrate used for IR absorption spectroscopy by analyzing two different cell lines cultured on a range of seven optical substrates in both transmission and reflection modes. First, cell viability measurements are made to determine the preferable substrates for normal cell growth. Successively, synchrotron radiation IR microspectroscopy is performed on the two cell lines to determine any genuine biochemically induced changes or optical effect in the spectra due to the different substrates. Multivariate analysis of spectral data is applied on each cell line to visualize the spectral changes. The results confirm the advantage of transmission measurements over reflection due to the absence of a strong optical standing wave artifact which amplifies the absorbance spectrum in the high wavenumber regions with respect to low wavenumbers in the mid-IR range. The transmission spectra reveal interference from a more subtle but significant optical artifact related to the reflection losses of the different substrate materials. This means that, for comparative studies of cell biochemistry by IR microspectroscopy, it is crucial that all samples are measured on the same substrate type.