Recombinant cell bioassay systems for the detection and relative quantitation of halogenated dioxins and related chemicals

Proper epidemiological, risk assessment and exposure analysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin) and related halogenated aromatic hydrocarbons (HAHs) requires accurate measurements of these chemicals both in the species of interest and in various exposure matrices (i.e. biological, environmental, food and feed). High-resolution instrumental analysis techniques are established for these chemicals, however, these procedures are very costly and time-consuming and as such, they are impractical for large scale sampling studies (i.e. for epidemiological studies and assessment of areas with widespread contamination). Accordingly, numerous bioanalytical methods have been developed for the detection of these chemicals in extracts from a variety of matrices, the majority of which take advantage of the ability of these chemicals to activate the aromatic hydrocarbon receptor (AhR) and the AhR signal transduction pathway. Here we review the currently available in vitro AhR-based cell bioassay systems with a focus on recent recombinant reporter gene cell lines that have been developed for detection and relative quantitation of TCDD and related HAHs. Comparison of the relative sensitivities of the various cell bioassays and examples of their use in screening and analysis of environmental, biological, and food and feed samples are presented. Currently available experimental results and validation studies demonstrate the utility of these cell bioassay systems to provide a relatively rapid, accurate, and cost effective screening approach for the detection of TCDD and related HAHs in a variety of environmental, biological, food and feed samples. The availability of these cell bioassay systems will not only facilitate the large scale sampling studies needed for accurate assessment of contamination and exposure to these environmental chemicals, but they provide avenues for the identification of novel classes of TCDD-like chemicals.     

Studies in heterocyclic polymers. Part VI. A weight-loss study of the formation of a polybenzoxazole

The cyclisation of an aromatic poly(o-hydroxyamide) to form polybenzoxazole has been studied by combining isothermal weight-loss and thermogravimetric analyses. The thermogravimetric data were analysed by the method of Gyulai and Greenhow [4] to derive values for the apparent activation energy of the cyclisation process which was found to double at about 50% conversion (74–155 kJ mole^?1. A similar result was observed when the process was studied in the presence of low concentrations of p-toluene sulphonic acid, which appears to have a moderate catalytic effect upon the cyclisation process. The apparent order of reaction of the process has been found to be close to 2, contrary to previous studies which have assumed it to be unimolecular.     

A novel strategy for the preparation of naturally occurring phosphocitrate and its partially esterified derivatives

A novel method for the synthesis of phosphocitrate (1, PC) starting from triethyl ester of citric acid and MeOPCl2 is described. The method is based on selective stepwise hydrolysis of ester moieties from the intermediate Me-O-P(O)(Cl)(Z) (Z = triethylcitrate), 4a, which also allows one to prepare partially esterified derivatives of PC with good yield and purity without chromatographic purifications.     

A reductive recycle strategy for the facile synthesis of molybdenum(VI) alkylidyne catalysts for alkyne metathesis

A convenient synthesis of trisamido molybdenum(VI) alkylidyne complexes has been developed, in which the key step is the addition of a geminal dichloride to a trisamido molybdenum(III) complex in the presence of magnesium to continuously recycle unwanted side product 4, selectively generating the desired alkylidyne complexes in high yield.     

Deoxygenation of polyhydroxybenzenes: an alternative strategy for the benzene-free synthesis of aromatic chemicals

New synthetic connections have been established between glucose and aromatic chemicals such as pyrogallol, hydroquinone, and resorcinol. The centerpiece of this approach is the removal of one oxygen atom from 1,2,3,4-tetrahydroxybenzene, hydroxyhydroquinone, and phloroglucinol methyl ether to form pyrogallol, hydroquinone, and resorcinol, respectively. Deoxygenations are accomplished by Rh-catalyzed hydrogenation of the starting polyhydroxybenzenes followed by acid-catalyzed dehydration of putative dihydro intermediates. Pyrogallol synthesis consists of converting glucose into myo-inositol, oxidation to myo-2-inosose, dehydration to 1,2,3,4-tetrahydroxybenzene, and deoxygenation to form pyrogallol. Synthesis of pyrogallol via myo-2-inosose requires 4 enzyme-catalyzed and 2 chemical steps. For comparison, synthesis of pyrogallol from glucose via gallic acid intermediacy and the shikimate pathway requires at least 20 enzyme-catalyzed steps. A new benzene-free synthesis of hydroquinone employs conversion of glucose into 2-deoxy-scyllo-inosose, dehydration of this inosose to hydroxyhydroquinone, and subsequent deoxygenation to form hydroquinone. Synthesis of hydroquinone via 2-deoxy-scyllo-inosose requires 2 enzyme-catalyzed and 2 chemical steps. By contrast, synthesis of hydroquinone using the shikimate pathway and intermediacy of quinic acid requires 18 enzyme-catalyzed steps and 1 chemical step. Methylation of triacetic acid lactone, cyclization, and regioselective deoxygenation of phloroglucinol methyl ether affords resorcinol. Given the ability to synthesize triacetic acid lactone from glucose, this constitutes the first benzene-free route for the synthesis of resorcinol.     

Analytical properties of the amidoxime group: Part VI. Electroanalytical behaviour of ethanediamidoxime

The electroanalytical behaviour of ethanediamidoxime (EDA) has been studied at 0.1 mol l^?1 ionic strength and several pH values (1.75–8.62), using several techniques (dc and DP polarography, chronocoulometry, dc and DP cyclic voltammetry). EDA undergoes an irreversible diffusion-controlled reduction in the entire pH range considered. The best conditions for identification and determination of EDA with the techniques mentioned are also studied.     

A theoretical examination of substituent effects on the detoxification reaction between glutathione and halogenated methanes

An important metabolic pathway for halogenated methanes is the detoxification reaction with glutathione in the cell cytosol fraction. Experimental studies have shown that the rate of this S_N2 displacement reaction is directly related to the leaving group ability of the dissociating halide; the rate increases in order of the ions F^?, Cl^?, Br^?, and I^? leaving. In this study, we examine the role of the other halomethane substituents on the rate of this reaction for compounds with a common leaving anion. To this end, reaction Cl^? + CY₃Cl → ClCY₃ + Cl^? (Y = H,F,Cl) is examined using ab initio methods. The barrier for this exchange process may arise from requiring an inversion of the CY₃ group in the transition structure, the energy required to homolytically cleave the C? Cl bond, or from unfavorable steric and electronic interactions in the five-coordinated transition structure. Of these three factors, only the third explains the calculated ordering of barrier heights. This suggests that successive halogenation of methane not only increases its activity as a substrate for anaerobic reduction, as was shown earlier, but also decreases its ability to take part in the detoxification reaction with glutathione.     

A comparison of QSARs proposed for the inhibition of dihydropteroate synthase by substituted 4-aminodiphenylsulfones

Recently DeBenedetti et al. [1] synthesized and tested some substituted 4-aminodiphenylsulfones as Escherichia coli dihydropteroate synthase inhibitors. The findings from this assay have been shown to correlate highly with the measured inhibition potencies of dihydropteroate synthase from Mycobacterium lufu by Seydel and coworkers [2]. The resulting QSARs proposed by DeBenedetti et al. and Seydel et al. are compared to one another as well as to the QSARs proposed from an analysis of the M. lufu inhibition data. Intramolecular conformational entropy, S, is found to be the key correlation property, which can also be used to construct a QSAR for the E. coli inhibition data.     

Homolytic reactions of polyfluoroaromatic compounds Part VI. The mechanism of the phenylation of hexafluorobenzene

The decomposition of phenylazotriphenylmethane in hexafluorobenzene gives very little 2,3,4,5,6-pentafluorobiphenyl, since no mechanism exists for the defluorination of the radical intermediate. The yield of biaryl is raised by added benzoic acid, although this also introduces a competition with the substrate for the radicals and their precursor. The decomposition of benzoyl peroxide in hexafluorobenzene gives pentafluorobiphenyl, the yield of which increases considerably when the reaction is caried out in the presence of p-fluorobenzoic acid; in the latter case, 2,3,4,4′,5,6-hexafluorobiphenyl is also found.A mechanism incorporating these observations is suggested.     

Ab initio computation of force constants: Part VI. Applications of the force relaxation method for geometry optimization

Techniques to improve the computational efficiency of the force relaxation method are discussed. Force constants for fragments in previously computed smaller molecules can be transferred to construct a guess force constant matrix. Additional force constants that may be needed can be computed by a procedure which uses only one additional force calculation per diagonal force constant required. A scaling technique to improve convergence on the optimized geometry is discussed.     

A theoretical study of the decomposition of halogenated alkoxy radicals. II. Fluorine extrusion

The extrusion of a fluorine atom from alkoxy radicals is analyzed theoretically and compared with experiment. Although the MNDO/CI method gives qualitatively correct information about the nature of the wavefunction, the MNDO method with or without CI is inadequate to describe the dissociation reaction path, presumably due to parameterization problems. On the contrary, ab initio SCF coupled with extended CI seems to correctly mimic the barrier for fluorine extrusion. Using modified Marcus theory in conjunction with the ab initio results for CH₂FO, we evaluate the barriers for the other radicals investigated.     

A novel degradative strategy for the synthesis of p-quinones.

p-Hydroxybenzylalcohols undergo Fremy's salt promoted degradative oxidation to give the corresponding p-benzoquinones. A novel strategy for the synthesis of p-benzoquinones based on the regioselective metalation of 2-methoxy-4-methoxymethyl phenols is presented.     

Chromatographic studies of metal complexes. Part VI. Investigation of the effect of electrolytes on thin-layer chromatography

The octahedral cationic Co^III complexes [Co(ida)(bigH)₂]⁺, [Co(glyO)(bigH)₂]²⁺, [Co(α-alanO)(bigH)₂]²⁺, [Co(β-alanO)BigH)₂]²⁺ and Co(PhbigH)₃]³⁺, where idaH₂=iminodiacetic acid, glyOH=glycine, α-alanOH=α-alanine, β-alanOH=β-alanine and PhbigH=phenylbiguanide, were studied by thin-layer chromatography on silica gel in solutions of different electrolytes (NaCl, NaBr, NaI, Na₂SO₄, Na₂S₂O₃, NaNO₂ and NaNO₃). Among other factors, the movement of the cationic complexes was found to be dependent on the surface tension and equivalent conductance of the developer electrolyte.     

Photochromism in Bianthrone and Related Compounds. Part VI. The structure of the photocromic isomers of bianthrones

The cyclic structure III is assigned to the C photochromic isomer of 1, 8′-dimethylbianthrones on the basis of spectral and chemical evidence. Similar considerations indicate that this does not apply to the B photoisomers of bianthrones.     

Mechanisms for reactions of halogenated compounds. Part 4.[1] activating influences of ring-nitrogen and trifluoromethyl in nucleophilic aromatic substitution

Rate constants have been measured for the reactions of ammonia with various fluorinated pyridines and diazines in aqueous dioxan at 25°. From the results the activating effects of ring-nitrogen (relative to CH) and of trifluoromethyl (relative to -H) have been determined. Ring-nitrogen activates the system at points $\text{ortho}$-, $\text{meta}$- and $\text{para}$- to the point of substitution, in the ratios $\text{ortho}$- 6.2 × 10⁴, $\text{meta}$- 8.5 × 10², and $\text{para}$- 2.3 × 10⁵. Similarly a trifluoromethyl substituent is activating by a factor of 2.4 × 10³$\text{ortho}$- and 4.5 × 10³$\text{para}$- to the point of substitution.