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PubMed1999

Comamonas acidovorans strain MC1: a new isolate capable of degrading the chiral herbicides dichlorprop and mecoprop and the herbicides 2,4-D and MCPA.

A gram-negative prototrophic bacterial species, strain MC1, was isolated from the vicinity of herbicide-contaminated building rubble and identified by 16S rDNA sequence analysis, its physiological properties, GC content, and fatty acid composition as Comamonas acidovorans. This strain displays activity for the productive degradation of the two enantiomers of dichlorprop [(RS)-2-(2,4-dichlorophenoxy-)propionate; (RS)-2,4-DP] and mecoprop [(RS)-2-(4-chloro-2-methyl-) phenoxypropionate; (RS)-MCPP] in addition phenoxyacetate herbicides, i.e. 2,4-dichlorophenoxyacetate (2,4-D) and 4-chloro-2-methylphenoxyacetate (MCPA), and various chlorophenols were utilized. Rates amounted to 1.2 mmoles/h g dry mass (2,4-D) and 2.7 mmoles/h g dry mass [(RS)-2,4-DP]. Degradation of (RS)-2,4-DP was not inhibited up to concentrations of 500 mg/l, nor of 2,4-D up to 200 mg/l. The optimum pH value of (RS)-2,4-DP degradation was around 8. The application of respective primers for PCR amplification revealed the presence of tfdB and tfdC genes.

2,4-Dichlorophenoxyacetic Acid↗

PubMed2002

A novel ISFET-type biosensor based on P450 monooxygenases.

We made a biosensor based on ion-sensitive field effect transistor (ISFET) using P450 monooxygenase. ISFETs are electrical devices and have been used as pH sensors. We used genetically engineered P450 monooxygenase for our research because of its high enzymatic activity. The fusion enzyme between rat CYP1A1P450 monooxygenase and yeast NADPH-cytochrome P450 oxidoreductase was expressed in yeast Saccharomyces cerevisiae strain AH22. Yeast microsomal membranes were immobilized in an agarose layer on the ISFET. o-Deethylation of 7-ethoxycoumarin to 7-hydroxycoumarin was catalyzed by the enzyme in the presence of nicotinamide adenine dinucleotide phosphate reduced form (NADPH). Formation of 7-hydroxycoumarin from 7-ethoxycoumarin was also measured by fluorescence. The difference of the voltage between the ISFET device and control device without enzymes showed a voltage increase along with the enzymatic reaction of P450 monooxygenases, and this voltage increase in the device was inhibited by addition of MnCl(2), an inhibitor of P450 monooxygenase. There was a positive correlation between the voltage increase in the ISFET device and the fluorescence intensity. This is the first electrochemical biosensing using P450 monooxygenases immobilized on the ISFET, and is applicable to the sensing of chlorophenol compounds.

Biosensing Techniques↗

PubMed2001

Sonochemical degradation for toxic halogenated organic compounds.

This paper describes the degradation of p-chlorophenol using three different ultrasonic devices. The dissipated power in the reaction matrix was measured based on calorimetric method. The study showed that hydrogen peroxide can improve the sonochemical reaction and gases dissolved in reaction matrix can affect the process to a small extent. The reaction mechanism and kinetics of degradation were also investigated.

Calorimetry↗

PubMed2002

Sonolysis of chlorobenzene in Fenton-type aqueous systems.

The influence of ultrasounds (200 kHz frequency) on the decomposition of chlorobenzene (CB) in a water solution (around 100 ppm concentration) containing iron or palladium sulfates was investigated. The intermediates of the sonolysis were identified, thus allowing a deeper insight into the degradation mechanism. It was established that CB degradation starts by pyrolysis inside the cavitation bubbles. The initial sonolysis product is benzene, formed in a reaction occurring outside the cavitation from phenyl radicals and the hydrogen atoms sonolytically generated from the water. Polyphenols as products of the CB sonochemical degradation are reported for the first time. The palladium salt was found to be a useful and sensitive indicator for differentiating the sites and mechanisms of the product formation. An alternative mechanism for the CB sonolysis is advanced, explaining the formation of phenols, polyphenols, chlorophenols and benzene.

Benzene↗

PubMed2000

Surface-enhanced Raman scattering: a structure-specific detection method for capillary electrophoresis.

A new approach to detecting capillary electrophoresis (CE) eluent components by interfacing CE with a surface-enhanced Raman scattering (SERS) system is described. In this approach, CE-based separation of a mixture of trans-1,2-bis(4-pyridyl)ethylene and N,N-dimethyl-4-nitrosoaniline has been detected by SERS in a postcolumn geometry. The retention time obtained from SERS corresponds well with that from conventional UV-visible detection. Meanwhile, CE eluants are identified by their characteristic vibrational spectra, demonstrating the validity of SERS as a structure-specific detection method for CE. In addition, the ability to monitor SERS intensity changes at molecule-specific frequencies makes selective detection of individual analytes possible, even when separation is incomplete. Finally, CE-SERS is evaluated for separation of amino acids (tyrosine and tryptophan) and environmental pollutants (chlorophenol mixtures).

Aniline Compounds↗

PubMed1995

Multicomponent kinetic determinations using artificial neural networks.

Neural networks were successfully used for multicomponent kinetic determinations of species with rate constant ratios approaching unity without the aid of spectral discrimination. The ensuing method relies on two inputs describing the profile of the kinetic curve for each mixture, which is obtained by preprocessing kinetic data using nonlinear least-squares regression. A straightforward network architecture (2:4s:21) was used to resolve mixtures of 2- and 3-chlorophenol; the trained network estimated the concentrations of both components in the mixture with a relative standard error of prediction of approximately 5%, which is much lower than that obtained with Kalman filtering. The effect of some variables such as the rate constant and analyte concentration ratios on the proposed multicomponent determination is discussed.

Chlorophenols↗

PubMed1997

Evaluation of temperature effects on selectivity in RPLC separations using polybutadiene-coated zirconia.

The effect of temperature on selectivity in RPLC method development has been evaluated on polybutadiene-coated zirconia. We find that the influence of temperature on selectivity depends strongly on solute type. For solutes of similar structure such as polyaromatic hydrocarbons, temperature has almost no effect on selectivity; however, for solutes with very different functional groups such as chlorophenols, temperature changes did significantly affect selectivity. We feel that simple mixtures with one dominant retention mechanism-e.g., solvophobic retention-will not be helped appreciably by adjusting temperature. However, in complex mixtures with polar and ionizable solutes, optimization by varying the temperature may well be fruitful.

Acrylonitrile↗

PubMed1994

X-ray absorption studies on catechol 2,3-dioxygenase from Pseudomonas putida mt2.

X-ray absorption spectroscopy has been utilized to investigate the structure of the active site of iron(II) catechol 2,3-dioxygenase from Pseudomonas putida mt2 both in the native and the 2-chlorophenol inhibited forms. XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) results allow us to discuss the coordination number and geometry of the ferrous ion in the native enzyme. The metal geometry is not significantly affected by the binding of the inhibitor. The EXAFS spectrum is consistent with an iron(II) bound to six N/O atoms at an average distance of 2.05 A or to five N/O at an average distance of 2.04 A. The stimulation of the experimental data is greatly enhanced by considering the iron ligands divided in two different shells. Analysis of the outer shells performed using multiple scattering theory shows that there are histidines in the coordination sphere. The best fitting is obtained assuming the presence of two of them. Similar results are obtained for the inhibited enzyme, which, however, are indicative of a slight shortening of the average metal-donor bond distances. The direct binding of inhibitors to the metal center is confirmed by 1H NMR data.

Bacterial Proteins↗

PubMed2003

Measurement of the electronic properties of the flavoprotein old yellow enzyme (OYE) and the OYE:p-Cl phenol charge-transfer complex using Stark spectroscopy.

Low-temperature absorption and Stark spectroscopy have been used to study the electronic properties of oxidized flavin mononucleotide (FMN) in old yellow enzyme (OYE) and OYE complexed with p-chlorophenol (p-Cl phenol). The low-temperature absorbance spectrum of OYE showed splittings of the blue and near-UV vibronic bands, which appears to be due to hydrogen bonding between the isoalloxazine moiety and the protein. A Stark spectroscopic analysis showed that the electronic structure of the FMN cofactor in OYE is not significantly perturbed relative to flavins in simple solvents. However, the charge-transfer band in the OYE:p-Cl phenol complex showed a large Stark effect indicative of substantial charge displacement. The magnitude and direction of this charge displacement are consistent with significant charge transfer along the charge-transfer transition dipole moment direction. In addition, the Stark spectrum of the CT band showed unexpected fine structure that could correlate with vibrational progressions in either the p-Cl phenol donor or the flavin acceptor.

Chlorophenols↗

PubMed2003

Sorption and manganese-induced oxidative coupling of hydroxylated aromatic compounds by natural geosorbents.

The sorption/desorption equilibria and solvent extractabilities of phenol, o-cresol, and p-chlorophenol with respect to natural sorbents having different types of soil organic matter were investigated. Parallel tests in systems amended with birnessite (delta-MnO2), a solid-phase oxidative coupling catalyst, were also conducted. Sorption/desorption isotherms and solvent extraction data reveal that the relative isotherm linearities, desorption hysteresis, and extractabilities of these compounds are related to the geochemical nature of the sorbent organic matter and to the existence of system conditions that promote oxidative coupling reactions. When suitable coupling catalysts are present, soils containing primarily diagenetically "young" and highly amorphous organic matter (e.g., humic materials) are more likely to retain those solutes than are those containing primarily diagenetically "old" and more condensed organic matter (e.g., kerogens). The sorption/desorption properties of the solutes were significantly altered in the presence of birnessite as a result of both cross-coupling reactions with reactive soil organic matter components and self-coupling reactions with each other to form polymeric species. Under appropriate conditions, mineral-catalyzed oxidative coupling may exert a dominant influence on the sorption and transport of hydroxylated aromatic compounds in soil and sediment systems.

Adsorption↗

PubMed2004

Can degradation products be used as documentation for natural attenuation of phenoxy acids in groundwater?

In situ indicators of degradation are important tools in the demonstration of natural attenuation. A literature survey on the production history of phenoxy acids and degradation pathways has shown that metabolites of phenoxy acid herbicides also are impurities in the herbicide products, making the bare presence of these compounds useless as in situ indicators. These impurities can make up more than 30% of the herbicides. Degradation of phenoxy acids was demonstrated in microcosm experiments using groundwater and sediment contaminated with MCPP, dichlorprop, and related compounds such as other phenoxypropionic acids and chlorophenols. Field observations at two phenoxy acid-contaminated sites showed the occurrence of several impurities including metabolites in the groundwater. Neither the microcosm experiments nor the field observations verified that metabolites were actually produced or accumulated in situ. However, it was demonstrated that the impurity/parent herbicide ratios can be useful in situ indicators of degradation.

Acids↗

PubMed2004

Photocatalysis by titanium dioxide and polyoxometalate/TiO2 cocatalysts. Intermediates and mechanistic study.

A representative polyoxometalate, alpha-12-tungstophosphatic acid (PW12(3-), POM), is loaded on the surface of TiO2 particles used as a cocatalyst to gain further insights into the underlying reaction mechanism and to estimate the feasibility of using the new POM/TiO2 cocatalyst in the photocatalytic degradation of 2,4-dichlorophenol (DCP) in aqueous media. Loading the PW12(3-) species on the surface of TiO2 enhances charge separation in the UV-illuminated TiO2, thereby accelerating the hydroxylation of the initial DCP substrate but not the mineralization of DCP, which is somewhat suppressed in the presence of the polyoxometalate. An increase in the load of POM increases the concentration of aromatic intermediates, and more toxic intermediates, such as 2,6-dichlorodibenzo-p-dioxin, 2,4,6-trichlorophenol, are detected in the PW12(3-)/TiO2 system. By contrast, cleavage of the whole conjugated structure of DCP predominates in TiO2 only dispersions. Strong ESR signals for the superoxide radical anionic species, O2*- (HO2* radicals in acidic media; pH < 5), are detected in TiO2 only dispersions; signals of O2*- are much weaker in the TiO2/ POM composite system under otherwise identical conditions. Experimental results infers that enhancement of charge separation in TiO2 photocatalysis does not always result in improvement of the efficiency of mineralization of organic substrates, and the reaction between organic radical cations and the formed superoxide radical anions may be responsible forthe mineralization of the chlorophenol.

Anthelmintics↗

PubMed2005

Visible light Cr(VI) reduction and organic chemical oxidation by TiO2 photocatalysis.

Here we report the simultaneous Cr(VI) reduction and 4-chlorophenol (4-CP) oxidation in water under visible light (wavelength > 400 nm) using commercial Degussa P25 TiO2. This remarkable observation was attributed to a synergistic effect among TiO2, Cr(VI), and 4-CP. It is well known that TiO2 alone cannot remove either 4-CP or Cr(VI) efficiently under visible light. Moreover, the interaction between Cr(VI) and 4-CP is minimal if not negligible. However, we found that the combination of TiO2, Cr(VI), and 4-CP together can enable efficient Cr(VI) reduction and 4-CP oxidation under visible light. The specific roles of the three ingredients in the synergistic system were studied parametrically. It was found that optimal concentrations of Cr(VI) and TiO2 exist for the Cr(VI) reduction and 4-CP oxidation. Cr(VI) was compared experimentally with other metals such as Cu(ll), Fe(lll), Mn(IV), Ce(IV), and V(V). Among all these metal ions, only Cr(VI) promotes the photocatalytic oxidation of 4-CP. The amount of 4-CP removed was directly related to the initial concentration of Cr(VI). The system was also tested with four other chemicals (aniline, salicylic acid, formic acid, and diethyl phosphoramidate). We found that the same phenomenon occurred for organics containing acid and/or phenolic groups. Cr(VI) was reduced at the same time as the organic chemicals being oxidized during photoreaction under visible light. The synergistic effect was also found with pure anatase TiO2 and rutile TiO2. This study demonstrates a possible economical way for environmental cleanup under visible light.

Carcinogens, Environmental↗

PubMed2005

Mineralization of aromatics in water by sunlight-assisted electro-fenton technology in a pilot reactor.

The viability of the degradation of aqueous solutions of aniline, nitrobenzene, and 4-chlorophenol by the so-called Photoelectro-Fenton process in a pilot reactor is reported. The Electro-Fenton process stage, based on the flow of oxygen through a gas diffusion cathode to produce H2O2, allows mineralization of about a half of the TOC content in ca. 1 h, because anodic oxidation is coupled with Fenton reaction in the presence of Fe2+ catalyst. An intensity of 20 A was applied in a flow cell comprising a Ti/Pt anode and a carbon-PTFE cathode. After electrolysis, samples of the effluent were exposed to sunlight, and almost complete mineralization was reached after ca. 50 min. Effect of parameters such as electrolysis time, pH, initial concentration, and solar or UVA irradiation on the process efficiencies and the running costs are studied. The Photoelectro-Fenton process using sunlight effectively diminishes these costs. The analogous behavior of the three aromatics suggests similar degradation pathways, regardless of the different groups attached to the ring.

Aniline Compounds↗

PubMed2001

Microstructure determination of AOT + phenol organogels utilizing small-angle X-ray scattering and atomic force microscopy.

Dry reverse micelles of the anionic twin-tailed surfactant bis(2-ethylhexyl) sulfosuccinate (AOT) dissolved in nonpolar solvents spontaneously form an organogel when p-chlorophenol is added in a 1:1 AOT:phenol molar ratio. The solvents used were benzene, toluene, m-xylene, 2,2,4-trimethylpentane (isooctane), decane, dodecane, tetradecane, hexadecane, and 2,6,10,14-tetramethylpentadecane (TMPD). The proposed microstructure of the gel is based on strands of stacked phenols linked to AOT through hydrogen bonding. Small-angle X-ray scattering (SAXS) spectra of the organogels suggest a characteristic length scale for these phenol-AOT strands that is independent of concentration but dependent on the chemical nature of the nonpolar solvent used. Correlation lengths determined from the SAXS spectra indicate that the strands self-assemble into fibers. Direct visualization of the gel in its native state is accomplished by using tapping mode atomic force microscopy (AFM). It is shown that these organogels consist of fiber bundle assemblies. The SAXS and AFM data reinforce the theory of a molecular architecture consisting of three length scales-AOT/phenolic strands (ca. 2 nm in diameter) that self-assemble into fibers (ca. 10 nm in diameter), which then aggregate into fiber bundles (ca. 20-100 nm in diameter) and form the organogel.

Chlorophenols↗

PubMed2005

Use of a self-assembling organogel as a reverse template in the preparation of imprinted porous polymer films.

The concept of reverse templating of an organogel to form imprinted porous divinylbenzene polymer films with submicrometer channels is demonstrated. The organogel comprising a 1:1 molar ratio of two organogelators, that is, bis(2-ethylhexyl) sodium sulfosuccinate and 4-chlorophenol, was formed in divinylbenzene. The gel was cast as a thin film before UV polymerization of the solvent, and the organogelators were later removed by simple washing with water and isooctane. The integrity of the fiber bundles of the organogel was preserved during polymerization, and an exact hollow replica was obtained after the organogelators were leached away. It is easily possible to imprint gel fiber bundle structures into polymeric films through this technique. The gel can also be formed on macroporous substrates to yield supported thin porous polymeric films. With the incorporation of functional nanoparticles in AOT inverse micelles and hence the organogel, nanoparticle-containing porous polymer films exhibiting luminescence or magnetic properties are envisioned.

Chlorophenols↗

PubMed2002

Biological monitoring of 2,4,5-trichlorophenol (I): preparation of antibodies and development of an immunoassay using theoretical models.

Antibodies against 2,4,5-trichlorophenol have been prepared after theoretical and molecular modeling chemical studies of three potential immunizing haptens with the aim to find out the one mimicking best the target analyte. Competitive direct and indirect ELISAs have been developed after screening a battery of haptenized enzyme tracers and coating antigens, respectively. The relation between the degree of heterology of the competitor and the resulting immunoassay detectability has been investigated according to the electronic similarities of the competitor haptens with the target analyte taking in consideration their pK(a) values. These studies have been performed using theoretical and molecular modeling tools to find out their electronic distribution at their minimum energetic levels. The results suggest that the competitors should have a high homology to produced assays with good detectability values. On the other hand detectability improves when lowering the hapten density of the competitors. An indirect competitive ELISA has been finally selected for further investigation. The immunoassay has an IC(50) value of 0.6 microg L(-)(1) and a limit of detection of 0.084 microg L(-)(1). The selectivity of the assay is high in relation to other chlorophenols frequently present in real samples. In contrast, the brominated analogues may also be recognized with this assay.

Antibodies↗

PubMed2003

Aerobic secondary utilization of a non-growth and inhibitory substrate 2,4,6-trichlorophenol by Sphingopyxis chilensis S37 and sphingopyxis-like strain S32.

This paper reports 2,4,6-trichlorophenol (246TCP) degradation by Sphingopyxis chilensis S37 and Sphingopyxis chilensis-like strain S32, which were unable to use 246TCP as the sole carbon and energy source. In R2A broth, the strains degraded 246TCP up to 0.5 mM. Results with mixtures of different 246TCP and glucose concentrations in mineral salt media demonstrated dependence on glucose to allow bacterial growth and degradation of 246TCP. Strain S32 degraded halophenol up to 0.2 mM when 5.33 mM glucose was simultaneously added, while strain S37 degraded the compound up to 0.1 mM when 1.33 mM glucose was added. These 246TCP concentrations were lethal for inocula in absence of glucose. Stoichiometric releases of chloride and analysis by HPLC, GC-ECD and GC-MS indicated 246TCP mineralisation by both strains. To our knowledge, this is the first report of bacteria able to mineralize a chlorophenol as a non-growth and inhibitory substrate. The concept of secondary utilization instead of cometabolism is proposed for this activity.

Aerobiosis↗