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At least 19 recordsLinked to original sources
PubMed1979

Potential halogenated industrial carcinogenic and mutagenic chemicals. II. Halogenated saturated hydrocarbons.

The halogenated saturated hydrocarbons analogously to the previously considered halogenated unsaturated hydrocarbons (Part I) possess considerable utility in a broad spectrum of applications including; solvents, dry-cleaning fluids, refrigerants, fumigants, degreasing agents, propellants and intermediates in the production of other chemicals, textiles and plastics. Methyl chloride, methylene chloride, chloroform, carbon tetrachloride, methyl chloroform, 1,1,2-trichloroethane, hexachloroethane, ethyl chloride and fluorocarbons were reviewed principally in terms of their synthesis (or occurrence), areas of application, stability, distribution, reactivity, levels of exposure, populations at risk, carcinogenicity, mutagenicity and metabolism.

Animals↗
PubMed1979

Potential halogenated industrial carcinogenic and mutagenic chemicals. I. Halogenated unsaturated hydrocarbons.

The halogenated aliphatic hydrocarbons represent one of the most important categories of industrial chemicals from a consideration of use categories, production volume, environmental and toxicological considerations, and hence most importantly, potential population risk. The major unsaturated hydrocarbons reviewed, primarily in terms of their synthesis, utility, stability, distribution and levels of exposure as well as their reactivity, carcinogenicity, mutagenicity and metabolism, include: vinyl chloride, vinylidene chloride, trichloroethylene, perchloroethylene, chloroprene, trans-1,4-dichlorobutene, hexachlorobutadiene and allyl chloride.

Adult↗
PubMed1979

Potential halogenated industrial carcinogenic and mutagenic chemicals. IV. Halogenated aryl derivatives.

A variety of halogenated aryl derivatives possess significant activity as solvents for pesticides, heat transfer agents, pesticide intermediates, additives for rubber products, intermediates in organic synthesis and as insect repellants and deodorants. Ortho- and para-dichlorobenzenes; 1,2,4-trichloro- and hexachlorobenzene, as well as bromobenzenes and benzylchloride were reviewed principally in terms of their synthesis, areas of utility, stability, distribution, reactivity, levels of exposure, populations at risk, metabolism, carcinogenicity and mutagenicity.

Animals↗
PubMed1978

[Studies on halogen quenching through the Stern-Volmer plot (author's transl)].

The quenching effect for halogenated benzenes, methanes and ethanes have been investigated. The halogen quenching was accurately measured using the internal conversion electrons emitted from 113Sn-113mIn. From the quenching constants determined by the Stern-Volmer plots with respect to various halogen quenchers, the following results have been obtained. (1) The quenching constants increase with the number of halogen substituents, so as linearly in halogenated benzenes and exponentially in halogenated methanes and ehtanes. Even the isomers of halogenides have different quenching constants. (2) There is a linearity between logarithm of the quenching constant and a polarographic half-wave reduction potential. (3) Electron excitation provides larger quenching constants than UV excitation for halogenated methames. Based on these results, the mechanism of halogen quenching have been discussed in connection with the exciplex formation.

Benzene↗
PubMed1992

Microbial breakdown of halogenated aromatic pesticides and related compounds.

Considerable progress has been made in the last few years in understanding the mechanisms of microbial degradation of halogenated aromatic compounds. Much is already known about the degradation mechanisms under aerobic conditions, and metabolism under anaerobiosis has lately received increasing attention. The removal of the halogen substituent is a key step in degradation of halogenated aromatics. This may occur as an initial step via reductive, hydrolytic or oxygenolytic mechanisms, or after cleavage of the aromatic ring at a later stage of metabolism. In addition to degradation, several biotransformation reactions, such as methylation and polymerization, may take place and produce more toxic or recalcitrant metabolites. Studies with pure bacterial and fungal cultures have given detailed information on the biodegradation pathways of several halogenated aromatic compounds. Several of the key enzymes have been purified or studied in cell extracts, and there is an increasing understanding of the organization and regulation of the genes involved in haloaromatic degradation. This review will focus on the biodegradation and biotransformation pathways that have been established for halogenated phenols, phenoxyalkanoic acids, benzoic acids, benzenes, anilines and structurally related halogenated aromatic pesticides. There is a growing interest in developing microbiological methods for clean-up of soil and water contaminated with halogenated aromatic compounds.

Bacteria↗
PubMed1976

[On the mechanism of the biological persistence of halogenated and sulfonated aromatic hydrocarbons (author's transl)].

Aromatic compounds with unphysiological substituents like halogen or SO2H-groups are mainly degraded by cometabolism. Investigations with model compounds show, that the negative inductive effect (-I-effect) of the halogen substituents impede the electrophilic attack of the oxygenases, particularly the pyrocatechases. Although the "affinity" of the enzyme for the substrate increases with the number of halogen substituents, the rate of ring cleavage decreases by the presence of halogen substituents. Benzoate oxygenation shows that in certain positions of substitution the -I-effect can be weakened by the + M-effect of the halogen. As soon as aromaticity is lost by the action of dioxygenases, halide can be eliminated with greater ease and total mineralization is possible. When naphthalene-2-sulfonic acid is degraded by a naphthalene utilizing Pseudomonas strain the sulfonic acid group appears to be eliminated oxygenolytically and the carbon skeleton is channelled into the naphthalene pathway.

Alcaligenes↗
PubMed1975

Relationship between the mutagenic and base-stacking properties of halogenated uracil derivatives. The crystal structures of 5-chloro- and 5-bromouracil.

Three-dimensional X-ray diffraction data were used to determine the crystal structures of 5-chlorouracil and 5-bromouracil, two mutagenic pyrimidine analogs that can substitute for thymine in DNA. Crystals of the two compounds are nearly isostructural. The space group is P21/c, with a equals 8.450(6), b equals 6.842(3), c equals 11.072(16) angstrom, beta equals 123.53(19) degrees for 5-chlorouracil, and a equals 8.598(3), b equals 6.886(1), c equals 11.417(5) angstrom, beta equals 123.93(3) degrees for 5-bromouracil. Intensity data were collected with an automated diffractometer. The structures were refined by full-matrix least-squares to R equals 0.058 for 5-chlorouracil and R equals 0.027 for 5-bromouracil. The analogs from planar, hydrogen-bonded ribbons that are nearly identical to those found in the crystal structure of thymine monohydrate. As in many other structures of 5-halogenated uracil derivatives, the bases assume a stacking pattern that permits intimate contacts between the halogen substituents and the pyrimidine rings of adjacent bases. This stacking pattern involves halogen contacts that are significantly shorter than normal van der Waals interactions. The crystallographic results provide additional evidence that halogen substituents influence the stacking patterns of uracil derivatives, while exerting little direct effect on the hydrogen-bonding properties. The observed stacking patterns are consistent with the hypothesis that altered stacking interactions may account for the mis-pairing between 5-halogenated uracil bases and guanine residues within double-helical nucleic acids.

Bromouracil↗
PubMed1979

The mutagenicity of halogenated alkanols and their phosphoric acid esters for Salmonella typhimurium.

9 halogenated alkanols, 9 corresponding tris (haloalkyl)phosphates, and 2 bis-(2,3-dibromopropyl)phosphate salts were evaluated for mutagenicity against Salmonella typhimurium TA98, TA100, TA1535, TA1537 and TA1538, with and without rat liver in vitro metabolic activation system (S9 mix). Most of the test samples showed mutagenic activity in the strains TA100 and TA1535, but not in the strains TA98, TA1537 and TA1538. In general, the mutagenic activities of the phosphates obtained with S9 mix were greater than the activities obtained without S9 mix. Among the phosphates, several structure--activity relationships were found; i.e., (i) the bromoalkyl derivatives were more mutagenic than the corresponding chloroalkyl derivatives, (ii) the beta-haloethyl derivatives were more mutagenic than the gamma-halopropyl derivatives, (iii) the phosphates having adjacent beta and gamma halogen atoms in the alkyl moiety, e.g., tris-(2,3-dibromopropyl)phosphate, were particularly potent mutagens, (iv) the branched carbon chain reduced the mutagenic activities in spite of the presence of beta-halogen atoms, e.g., tris(1-bromomethyl-2-bromoethyl)phosphate. However, such relations did not necessarily apply to the halogenated alkanols. It is concluded that the metabolic activation pathway via haloalkanols to mutagens must not be in common with all tris-BP-like phosphates.

Alcohols↗
PubMed1992

Para-substituted Phe3 deltorphin analogues: enhanced selectivity of halogenated derivatives for delta opioid receptor sites.

The delta-selective opioid peptide deltorphin C(H-Tyr-D-Ala-Phe-Asp-Val-Val-Gly-NH2) (DEL C) was modified by para-substitution of Phe3 with halogens (F, Cl, Br, I), amino, or nitro groups. The bioactive potencies in peripheral tissues and brain receptor selectivities of these analogues depended upon the particular substituent; peptides containing halogen substituents exhibited the least disruptive effect. In the mouse vas deferens (MVD) bioassay, [p-ClPhe3]DEL C displayed equivalent bioactivities to DEL C; in combination with the guinea pig ileum (GPI) bioassay, [p-ClPhe3]DEL C and [p-BrPhe3]DEL C exhibited marked preference for delta sites (IC50GPI/IC50MVD = 11,250 and 6,363, respectively), which are approximately 4- and 2-fold greater than DEL C. In a receptor binding assay, none of the halogenated analogues had delta affinities (Ki) exceeding that of DEL C; however, in terms of delta selectivity (Ki mu/Ki delta), [p-BrPhe3]DEL C was nearly twice as selective as DEL C, while [p-FPhe3]DEL C was equivalent, and [p-IPhe3]DEL C only 25% less selective. The only correlation evident with the halogenated derivatives occurred between IC50GPI and Ki mu (r = 0.814) rather than between delta receptor studies (MVD or Ki delta); interestingly, IC50GPI also correlated with K' (r = 0.982). The p-amino or p-nitro substituents of Phe3 in DEL C and DEL B (= [Glu4]DEL C) were deleterious for bioactivity (MVD) (losses ranged from 400- to approximately 8,000-fold) and in receptor binding assays, where delta affinities decreased 140- to 840-fold and delta selectivities by 34- to 380-fold. p-Nitro-Phe3 was the most detrimental substitution for all the parameters measured for both deltorphins: the loss in MVD activity, however, was less with DEL B than with DEL C, which was the opposite for delta receptor affinity.

Amino Acid Sequence↗
PubMed1976

Peroxidase-catalyzed halogenation.

Peroxidase-catalyzed halogenation reactions have been established as being important in the biosynthesis of the hormone thyroxine and in biological defense mechanisms. Recently these reactions have been recognized as valuable tools for the study of proteins as well as their arrangement in macromolecular structures. The pathways of peroxidase catalyses can be accommodated within the framework of the classical Chance-George mechanism. This implies that the initial steps of the reaction invariably involve oxidation of peroxidases by peroxides--and that the resulting derivative, compound I, is the oxidant of the halide ions. Such reactions may result either in the formation of hypohalous acids, or in halogenation of the enzyme apoprotein, followed by transhalogenation to substrate for halogenation. Chloro- and myeloperoxidases catalyze oxidation of all halide ions, except F-; oxidation of bromide and iodide is mediated by lactoperoxidase, but horseradish peroxidase only oxidizes iodide. All of the above enzymes except horseradish will oxidize the pseudo halide thiocyanate. The origins of this differentiation remain to be defined, but they presumably reflect significant variation in oxidation potential of different peroxidase-peroxide derivatives, rather than constraints on the peroxidase-donor interactions. As pointed out above, halogenation of the amino acids tyrosine and histidine or these residues in proteins can take place on the enzyme. This makes lactoperoxidase-catalyzed iodination selective. The amino acid residues in proteins that are iodinated depend not only on reactivity of the amino acid residue but also on its geometric location. Thus lactoperoxidase-catalyzed iodination can be a useful tool in the study of protein structure and function. It is also useful in establishing the geometric position of proteins within macromolecular structures. Thyroid peroxidase catalyzes iodination of thyroglobulin and is involved in a second important step, the coupling of the iodotyrosines to form thyroxine or triiodothyronine. A proposed mechanism for this reaction suggests that the oxidation is mediated by the iodoenzyme derivative mentioned above followed by a prototropic rearrangement and scission to form the ether bound of thyronine and a serine residue on thyroglobulin.

Amino Acids↗
PubMed1975

Exposure to halogenated hydrocarbons in the indoor environment.

The indoor environment has frequently been ignored as a significant source of exposure to air pollutants. To date there are a number of documented examples of levels of indoor air pollutants greatly exceeding those levels which commonly occur in the outdoor environment. Among these instances are airborne buildup of polynuclear aromatics and cadmium from cigarette smoke, lead from burning candles, and vinyl chloride from use of aerosols containing this substance as a propellant. These examples suggest that there may be additional sources of indoor air pollutants, particularly halogenated hydrocarbons from aerosol products, which have heretofore not been generally recognized as important. The present paper endeavors to review those instances where halogenated hydrocarbons in the indoor air environment may build up to concentrations of potential public health concern. These considerations may be especially relevant in future years as increasing efforts are being made to insulate buildings more efficiently as a means to conserve energy. The available data strongly suggest that halogenated hydrocarbons are an important class of air pollutants in the indoor environment and that their presence in the outdoor environment should also be carefully examined. In this regard, halogenated hydrocarbons in the outdoor environment may also contaminate indoor air spaces.

Aerosol Propellants↗
PubMed1976

The binding of lac repressor and the catabolite gene activator protein to halogen-substituted analogues of poly[d(A-T)].

We have measured the binding of two regulatory proteins to the complete halogen-substituted series of poly[d(A-T)] analogues. Both the lac repressor and the catabolite gene activator protein were found to bind more strongly to all of the halogen-substituted DNAs than they do to poly[d(A-T)]. For both proteins, the order of binding preference is poly[d(A-ioU)] is greater than poly[d(A-brU)] is greater than or equal to poly[d(A-clU)] is greater than poly[d(A-flU)] is greater than poly[d(A-T)]. Quantitative data on the binding of these proteins to poly[d(A-U)] is also given. The significance of these results for the mechanism of protein-DNA interaction is discussed. This is the first report that an activator protein binds more strongly to a halogen-substituted DNA; we discuss this result with regard to the mechanism of action of bromodeoxyruidine and other halogen-substituted base analogues on the inhibition and induction of differentiation in eucaryotic cells.

Bacterial Proteins↗
PubMed1978

Sites of direct and indirect halogenation of albumin.

The sites of radiohalogenation in proteins vary with the labeling method and the pH of the labeling reaciton. We have directly halogenated albumin with carrier-free radioiodide by three methods (pH range 2.2--9.3), and with carrier-free radiobromide by the chloroperoxidase method (pH range 2.2--4.6). Albumin was also indirectly halogenated by attaching a radioiodinated acylating agent, N-succinimidyl-3-(4-hydroxyphenyl) propionate (SHPP). The labeled proteins were proteolyzed enzymatically at neutral pH and the labeled amino acids produced were analyzed by liquid chromatography. Iodination at pH 7 yielded predominantly monoiodotyrosine, but at lower pH, fewer tyrosyl residues are labeled and a greater number of unstable sulfur-iodine bonds are formed at cysteinyl residues. Bromination with chloroperoxidase resulted in a high degree of labeling of cysteinyl residues at pH 2.8, the condition for optimum activity of this halogenating enzyme. Indirect halogenation with SHPP resulted in labeling of mid-chain lysyl, histidyl and tyrosyl residues.

Bromine↗
PubMed1978

The specificity of the interaction of bovine pancreatic ribonuclease A with natural and halogenated purine nucleotides.

The interaction between bovine pancreatic ribonuclease A (EC 3.1.4.22) and the purine nucleotides AMP, GMP, 6-chloropurine 5'-ribonucleotide and 8-bromoadenosine 5'-monophosphate was studied by u.v. difference spectroscopy. The stoicheiometry of the binding of the halogenated nucleotides to the enzyme shows a 1:1 ratio, as for the natural ones. The binding constants, Ka, for all four nucleotides at pH 5.5 were determined. They are within the same order of magnitude, though the nucleotides with a 6-amino group show a stronger interaction. The magnitude of the binding shows a reciprocal dependence on the ionic strength, which indicates an electrostatic interaction between ligand and enzyme. Finally, solvent-perturbation experiments show that all four nucleotides bind to the enzyme in a partially hydrophobic region. It is concluded that both halogenated and natural purine ribonucleotides interact in a similar manner with the enzyme molecule. The special synthesis and identification of 6-chloropurine 5'-ribonucleotide are discussed extensively. It is concluded that both halogenated and natural purine ribonucleotides interact in a similar manner with the enzyme molecule and thus the halogenated analogues are potential reagents for the affinity labelling of the purine-binding site.

Binding Sites↗
PubMed1975

E.s.r. studies of halogenated pyrimidines in gamma-irradiated alkaline glasses.

The reactions of mobile electrons (em-) and oxygen radical anions (O--) with halogenated bases and nucleosides have been studies in gamma-irradiated alkaline glasses by e.s.r. and specific halogen-ion electrode techniques. It is shown that electrons react with halogenated uracil bases (XUr where X = Cl, Br. I but not F) by dissociative electron attachment to form uracil-5-yl radicals (U-) and halogen anions. The relative rates of reaction of em- with XUr decrease in the sequence BrUr greater than ClUr greater than FUr greater than IUr. Thermal annealing studies carried out on U- in H2O and D2O matrices support the hypothesis that U- in H2O hydrates across the 5-6 double bond in the temperature region 135 degrees-155 degrees K, and deuterates to a much smaller extent in D2O at temperatures above 155 degrees K. Studies on bromouridine and bromodeoxyurinde suggest that em- reacts with the base moieties to form U- type radicals which abstract H- from the sugar moieties of adjacent nucleosides.

Bromouracil↗
PubMed1992

Rat liver microsomal metabolism of 2-halogenated 4-methylanilines.

1. Rat liver microsomal metabolism of 2-fluoro-, 2-chloro- and 2-bromo-4-methylaniline was investigated using h.p.l.c. Metabolites identified include products from side-chain C-hydroxylation (benzyl alcohols and benzaldehydes) and N-hydroxylation (hydroxylamines and nitroso derivatives). Aromatic ring hydroxylation was not a major reaction pathway. 2. A new type of microsomal metabolite was detected which was identified as a secondary amine, i.e. a halogenated N-(4'-aminobenzyl)-4-methylaniline. 3. In addition to these products azoxy, azo and hydrazo derivatives were formed. 4. Benzyl alcohols and halogenated N-(4'-aminobenzyl)-4-methylanilines were the major microsomal metabolites for all three 2-halogenated 4-methylanilines. 5. Quantification of the metabolite patterns demonstrated an influence of the type of halogen substituent on the rate of microsomal metabolism. The rate of side-chain C-hydroxylation increases in the order 2-fluoro-4-methylaniline < 2-chloro-4-methylaniline < 2-bromo-4-methylaniline. 6. The rate of N-hydroxylation increases from 2-bromo-4-methylaniline < 2-fluoro-4-methylaniline < 2-chloro-4-methylaniline. That 2-chloro-4-methylaniline is N-hydroxylated to a larger extent is in accordance with its greater mutagenicity, twice that of 2-bromo-4-methylaniline.

Animals↗
PubMed1976

Compound X. An intermediate in enzymatic halogenation.

Previous studies have shown that chlorite serves as a halogenation substrate for horseradish peroxidase. In its substrate role, chlorite serves both as a halogen donor and as a source of oxidizing equivalents in the chlorination reaction. We now show that a new spectral intermediate, which we have termed Compound X, can be detected as the initial product of the reaction of chlorite with horseradish peroxidase. The reaction of chlorite with horseradish peroxidase to form Compound X is a relatively fast reaction especially at acidic pH values. The second order rate constant (Kf) for the formation of Compound X at pH 4.5 (optimum pH) is 0.9 X 10(6) M-1 S-1. Compound X, in the absence of a halogen acceptor, decomposes to Compound I and chloride ion. The first order rate constant (Kd) for the decay of Compound X to Compound I is 0.2 s-1 at pH 4.5. The pH optimum for enzymatic chlorination with chlorite compares favorably with the pH profile for the lifetime of Compound X (Kf/Kd). These observations indicate that Compound X is the halogenating intermediate in the chlorite reaction and that the rate of enzymatic chlorination is directly related to the stability of Compound X. We propose an -OCl ligand on a ferric heme as the most likely structure for Compound X.

Binding Sites↗