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At least 1,027 records · Page 57Linked to original sources
PubMed2002

Organochlorine concentrations in the Saimaa ringed seal (Phoca hispida saimensis) from Lake Haukivesi, Finland, 1981 to 2000, and in its diet today.

Organochlorine and mercury (Hg) pollution has been one possible reason for a decline in the size of the population of the Saimaa ringed seal (Phoca hispida saimensis) in Lake Haukivesi, Finland. In this study, we analyzed changes in the concentrations of organochlorine compounds (OCls) and extractable organic halogen (EOX) in the blubber of Saimaa ringed seals that died from 1981 to 2000. In addition, the present concentrations and biomagnification factors of OCls and Hg from the main prey fish of ringed seal and pike (Esox lucius) were determined. Concentrations of pollutants in bream (Abramis brama) also were analyzed. The decline in the OCl concentrations in blubber was, on average, 25% during the two decades since polychlorinated biphenyls and DDT compounds were banned. Today, concentrations in blubber of Saimaa ringed seals are similar of those in ringed seals from the Arctic. Correspondingly in fish, the OCl and Hg concentrations were, on average, similar to those found in other studies on Finnish and Arctic areas. The low diet concentrations and metabolism of OCls also reflect the lower age correlation of OCls in the male ringed seals in the 1990s than in the 1980s. Biomagnification was considerably higher from fish to the ringed seal than from prey fish to pike because of higher feeding rate of ringed seals and differences in the metabolisms of these animals.

Adipose Tissue↗
PubMed2003

ortho-Halogen naphthaleins as specific inhibitors of Lactobacillus casei thymidylate synthase. Conformational properties and biological activity.

Thymidylate synthase (TS) (EC 2.1.1.45), an enzyme involved in the DNA synthesis of both prokaryotic and eukaryotic cells, is a potential target for the development of anticancer and antinfective agents. Recently, we described a series of phthalein and naphthalein derivatives as TS inhibitors. These compounds have structures unrelated to the folate (Non-Analogue Antifolate Inhibitors, NAAIs) and were selective for the bacterial versus the human TS (hTS). In particular, halogen-substituted molecules were the most interesting. In the present paper the halogen derivatives of variously substituted 3,3-bis(4-hydroxyphenyl)-1H,3H-naphtho[2,3-c]furan-1-one (1-5) and 3,3-bis(4-hydroxyphenyl)-1H,3H-naphtho[1,8-c,d]pyran-1-one (6-14) were synthesized to investigate the biological effect of halogen substitution on the inhibition and selectivity for the TS enzymes. Conformational properties of the naphthalein series were explored in order to highlight possible differences between molecules that show species-specific biological profile with respect to non species-specific ones. With this aim, the conformational properties of the synthesized compounds were investigated by NMR, in various solvents and at different temperatures, and by computational analysis. The apparent inhibition constants (K(i)) for Lactobacillus casei TS (LcTS) were found to range from 0.7 to 7.0 microM, with the exception of the weakly active iodo-derivatives (4, 10, 13); all] the compounds were poorly active against hTS. The di-halogenated compounds 7, 8, 14 showed the highest specificity towards LcTS, their specificity index (SI) ranging between 40 and >558. The di-halogenated 1,8-naphthalein derivatives (7-10) exhibited different conformational properties with respect to the tetra-haloderivatives. Though a clear explanation for the observed specificity by means of conformational analysis is difficult to find, some interesting conformational effects are discussed in the context of selective recognition of the compounds investigated by the LcTS enzyme.

Crystallography, X-Ray↗
PubMed2006

Roof-shaped halide-bridged bimetallic complexes via ring expansion reaction.

Binucleating behavior of rigid triptycene-based ligands has been studied. It has been demonstrated that trans-spanned transition-metal mononuclear complexes bearing 1,8-bis(diisopropylphosphino)triptycene (L1) and 1-diisopropylphosphino-8-diphenylphosphinotriptycene (L2) react with an appropriate transition-metal precursor via a ring-expansion pathway to form unusual bimetallic quasi-closed structures. New palladium and rhodium complexes featuring strongly bent (ca. 115 degrees ) M2(mu-Cl2) cores with very closely spanned metal centers (less than 3 A) have been prepared using the described ring-expansion reaction and have been fully characterized. Despite a constrained arrangement of the binuclear system, halogen bridges in all new compounds were stable in both the solid state and solution showing no tendency for dissociation even in the presence of added Lewis bases. Spontaneous resolution of the dissymmetric Pd2(mu-Cl)2Cl2(1-diisopropylphosphino-8-diphenylphosphinotriptycene) (2) into enantiopure antipodes is discussed as well.

Crystallography, X-Ray↗
PubMed2004

An investigation of halogens in Izmit hazardous and clinical waste incinerator.

In the combustion facilities, halogens (Cl, F, Br, I) should be considered with regard to the control of the compounds such as polychlorinated dibenzodioxins (PCDD), polychlorinated dibenzofurans (PCDF), halogenated polyaromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB) and volatile heavy metals formed as a result of incomplete combustion and caused adverse environmental effects. In this study halogens were observed in Izmit Hazardous and Clinical Waste Incinerator (IZAYDAS). Halogen contents of the combustion menu, flue gas, fly ash, bottom ash and filter cake were measured and their distributions in these exit streams were determined. Results showed that the major part of the halogens was partitioned to solid residues, i.e., bottom ash and filter cake which represents the removal by wet scrubbers. Fly ash and flue gas fractions of halogens were much lower due to the reduced formation of volatile compounds.

Air Pollutants↗
PubMed2005

Dichroic, dinuclear mu2-(eta2-NO)-nitrosoaniline-bridged complexes of rhenium of the type [[(CO)3Re(mu-X)]2ONC6H4NR2] (X = Cl, Br, I; R = Me, Et).

A series of unusual dinuclear mu2-(eta2-NO)-nitrosoaniline-bridged complexes [[(CO)3Re(mu-X)]2ONC6H4NR2] (X = Cl, Br, I; R = Me, Et) with dichroic properties have been synthesised by reaction of pentacarbonylhalogenorhenium(I) [(CO)5ReX] (X = Cl, Br, I) with the corresponding nitrosoaniline derivatives R2NC6H4NO (R = Me, Et). The deeply coloured solutions in CH2Cl2 show broad UV/Vis absorptions from 595 to 620 nm depending on the halogen bridges and N substituents. Single crystals of all six compounds exhibit a pronounced linear dichroism. The molecular structures have been determined by single-crystal X-ray analyses. All the compounds contain two face-shared octahedra, with two halogens and one NO ligand as bridges. The NO ligand coordinates in a nonsymmetrical eta2-like fashion with N or O coordination to each Re centre. Therefore, the C-nitroso group and the planar NC2 moiety of NR2 both lie almost exactly within the symmetry plane of the dinuclear complexes. These complexes belong to the novel and simple class of neutral dinuclear C-nitroso complexes that include the rare, non-assisted mu2-(eta2-NO) ligand function and have only single halogen atoms in bridging positions.

Journal Article↗
PubMed1994

Hemoglobin binding of arylamines and nitroarenes: molecular dosimetry and quantitative structure-activity relationships.

N-Oxidation and nitroreduction to yield N-hydroxyarylamines are metabolic steps that are crucial for the genotoxic properties of aromatic amines and nitroarenes, respectively. N-Hydroxyarylamines can form adducts with DNA, tissue proteins, and the blood proteins albumin and hemoglobin in a dose-dependent manner. The determination of hemoglobin adducts is a useful tool for biomonitoring exposed populations. We have established the hemoglobin binding index (HBI) [(mmole compound/mole Hb)/(mmole compound/kg body weight)] of several aromatic amines and nitroarenes in female Wistar rats. Incorporating values obtained by other researchers in the same rat strain, the logarithm of hemoglobin binding (log HBI) was plotted against several physicochemical parameters and against calculated electronic descriptors of nitroarenes and arylamines. Most arylamines and nitroarenes form hydrolyzable (e.g., sulfinamide) adducts with hemoglobin in rats. The amount of hemoglobin binding decreases with the oxidizability of the arylamines, except for compounds that are substituted with halogens in ortho or meta position. For halogen-substituted arylamines, the amount of hemoglobin binding is directly proportional to the pKa. Hemoglobin binding of nitroarenes increases with the reducibility of the nitro group. The structure activity relationships (SAR) for hemoglobin binding of nitroarenes and arylamines are comparable. The SAR found for hemoglobin binding were compared with the SAR found in the literature for mutagenicity, carcinogenicity, and cytotoxicity of arylamines and nitroarenes. In general, the mutagenicity or carcinogenicity of arylamines increases with their oxidizability. This first set of data suggests that the levels of hemoglobin binding, mutagenicity, and carcinogenicity of arylamines are not determined by the same electronic properties of the compounds, or not by these properties alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Amines↗
PubMed1975

[Lacrimators as acceptors for NADH].

Lachrymators of varied structure are reduced either by hydrogen addition or halogen substitution using NADH model compounds as donors. Similar compounds without lachrymatory activity were reduced either very slowly or not at all. CS (o-Chlorobenzalmalonitril) is reduced by NADH, the reaction being catalyzed by an enzyme present in erythrocytes. Thus the lachrymatory action follows a general scheme for the activity of sensory transduction. This scheme consists of a reception in the nerve cell membrane and a fast or simultaneous chemical transformation in an enzymic reaction.

Acetophenones↗
PubMed1985

Biochemical studies on the metabolic activation of halogenated alkanes.

This paper reviews recent investigations by Slater and colleagues into the metabolic activation of halogenated alkanes in general and carbon tetrachloride in particular. It is becoming increasingly accepted that free radical intermediates are involved in the toxicity of many such compounds through mechanisms including lipid peroxidation, covalent binding, and cofactor depletion. Here we describe the experimental approaches that are used to establish that halogenated alkanes are metabolized in animal tissues to reactive free radicals. Electron spin resonance spectroscopy is used to identify free-radical products, often using spin-trapping compounds. The generation of specific free radicals by radiolytic methods is useful in the determination of the precise reactivity of radical intermediates postulated to be injurious to the cell. The enzymic mechanism of the production of such free radicals and their subsequent reactions with biological molecules is studied with specific metabolic inhibitors and free-radical scavengers. These combined techniques provide considerable insight into the process of metabolic activation of halogenated compounds. It is readily apparent, for instance, that the local oxygen concentration at the site of activation is of crucial importance to the subsequent reactions; the formation of peroxy radical derivatives from the primary free-radical product is shown to be of great significance in relation to carbon tetrachloride and may be of general importance. However, while these studies have provided much information on the biochemical mechanisms of halogenated alkane toxicity, it is clear that many problems remain to be solved.

Aerobiosis↗
PubMed1994

Nucleic acid related compounds. 84. Synthesis of 6'-(E and Z)-halohomovinyl derivatives of adenosine, inactivation of S-adenosyl-L-homocysteine hydrolase, and correlation of anticancer and antiviral potencies with enzyme inhibition.

Treatment of 9-[6-(E)-(tributylstannyl)-5,6-dideoxy-2,3-O-isopropylidene- beta-D-ribo-hex-5-enofuranosyl]adenine [2b(E)] or the 6-N-benzoyl derivative 2a(E) with iodine (or N-iodosuccinimide) or bromine (or N-bromosuccinimide) gave virtually quantitative and stereospecific conversions to the 6'-(E)-(halohomovinyl)nucleoside analogues. Analogous treatment of the 6'-(Z)-vinyl-stannanes gave the 6'-(Z)-halo compounds. Treatment of 2a or 2b with chlorine or xenon difluoride/silver triflate gave E and Z mixtures of the respective 6'-chloro- or 6'-fluorohomovinyl products. Deprotection gave the 9-[6-(E and Z)-halo-5,6-dideoxy-beta-D-ribo- hex-5-enofuranosyl]-adenines [(E and Z)-5',6'-didehydro-6'-deoxy-6'-halohomoadenosines, EDDHHAs and ZDDHHAs, 4c-7c(E and Z)]. The acetylenic 5',5',6',6'-tetradehydro-6'- deoxyhomoadenosine (3c) and the 5'-bromo-5'-deoxy-5'-methyleneadenosine (10c) regioisomer of EDDBHA [5c(E)] also were obtained from 2. Concentration- and time-dependent inactivations of S-adenosyl-L-homocysteine (AdoHcy) hydrolase were observed with 3c and the 6'-(halohomovinyl)adenosine analogues. The order of inhibitory potency was I > Br > Cl > F and E > Z for the geometric isomers. AdoHcy hydrolase effected "hydrolysis" of the 6'-halogen from the (halohomovinyl)Ado compounds (to give the putative 6'-carboxaldehyde which underwent spontaneous decomposition) independently of its oxidative activity. Partition ratios for these hydrolytic turnovers/lethal inhibitory events were in the order F > Cl > Br > I. Biological activities were evaluated with several viruses and cancer cell lines, and potencies were generally in the order I > Br > Cl > F and E > Z isomers. This represents the first observation of a direct correlation of cytostatic activity with inhibition of AdoHcy hydrolase and highlights the potential of this enzyme as a viable target for chemotherapeutic intervention in anticancer as well as antiviral drug design.

Adenosine↗
PubMed2001

2- and 3-haloalkoxy fischer carbene complexes of chromium as synthons for either hydroxycyclopropanation or oxaspirocyclopropanation of alkenes.

The thermal reaction of 2-haloethoxy- and 3-chloropropoxy(alkenyl)carbene complexes of chromium with electronically neutral alkenes furnished diastereoselectively the corresponding 1-haloalkoxy-l-vinylcyclopropanes that, subjected to subsequent halogen-lithium exchange reactions, provided vinylcyclopropanols or compounds containing the spiro[cyclopropane-tetrahydrofuran/tetrahydropyran] structure, depending on the nature of both the halogen atom and the lithiating reagent. The hydroxycyclopropanation reaction can be efficiently achieved in a one-pot fashion.

Journal Article↗
PubMed1978

Effects of some pyrazinecarboxamides on sodium transport in frog skin.

1 The inhibitory effect of amiloride (N-amidino-3,5-diamino-6-chloropyrazinecarboxamide) on sodium transport in isolated skin of frog has been compared with 17 of its analogues. The dissociation constant of amiloride for passive sodium channels was 181.9 +/- 8.9 nM, and the maximal percentage inhibition of sodium transport was 101.3 +/- 0.4% (means of 123 measurements) when measured at a sodium concentration of 111 mM. 2 The N-benzylamidino and N-o-chlorobenzylamidino compounds had affinities approximately 20 times larger than those for amiloride, and produced maximal inhibition of transport. 3 Substitution of chlorine in the 6-position by other halogens showed that the bromo-compound was equally active to amiloride, whereas the iodo derivative had an affinity equal to 15% of that for amiloride. 4 Substitution in the 5-amino group in 10 compounds reduced the affinities to less than 1% of that of amiloride, without affecting their ability to produce complete inhibition of transport. 5 N-Amidino-3,5-diaminopyrazinecarboxamide was unique in that it produced an unusual concentration-response relationship.

Amiloride↗