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PubMed2001

Structure-activity relationships for aquatic toxicity to Tetrahymena: halogen-substituted aliphatic esters.

The toxicity of a series of 21 mono- and dihalogenated aliphatic monoesters has been evaluated using a Tetrahymena pyriformis population growth impairment assay. A structure-activity model has been developed for toxicity data (log(IGC50(-1))), using the 1-octanol/water partition coefficient (logKow) and the energy of the lowest unoccupied molecular orbital (ELUMO) as descriptors. A statistically robust plane (log of the inverse of the 50% growth inhibitory concentration (IGC50(-1)) = 0.34logKow - 0.84 (ELUMO) + 0.04; n = 15, r2 = 0.85, s = 0.26, F = 33, Pr > F = 0.0001) was found for monohalogen-substituted derivatives. These substances are thought to exhibit toxicity via the soft electrophilic mode of toxic action. This toxicity is imparted by the leaving ability of the halogen, which is enhanced when it is placed in close proximity to the carbonyl group. This leaving ability allows haloesters, especially alpha-haloesters, to undergo an SN2, addition-elimination substitution electro(nucleo)philic reaction. Outliers to the above model broadly fell into two groups: small reactive molecules (e.g., propylbromoacetate) that were more toxic than predicted and molecules in which the reactive center was sterically hindered by an alkyl group (e.g., ethyl-2-bromoisovalerate), which were less toxic than predicted.

Animals↗
PubMed2002

The influence of redox potential on the degradation of halogenated methanes.

To determine the influence of redox potential on the reaction mechanism and to quantify kinetics of the dechlorination by digester sludge, the test compounds trichlorofluoromethane (CFCl3), carbon tetrachloride (CCl4), and chloroform (CHCl3) were incubated in the presence of sludge and variable concentrations of reducing agent. Different sources of dehalogenation were examined, including live sludge and heat-killed sludge, and abiotic mechanisms were quantified in the absence of sludge. Batch incubations were done under redox conditions ranging from +/-534 to -348 mV. The highest rates for the dehalogenation of the three compounds were observed at -348 mV. The dechlorination rate of all the compounds by the heat-resistant catalysts was approximately twofold higher than the live treatments. It was proposed that the higher degradation rates by heat-killed sludge were due to the absence of physical barriers such as cell wall and cell membranes. There was no abiotic dechlorination of CFCl3, whereas CCl4 and CHCl3 were both reduced in the absence of sludge catalyst by Ti (III) citrate at > or =2.5 mM. The degradation pathways of CFCl3 and CHCl3 appeared to be only partially reductive since the production of reduced metabolites was low in comparison with the total amount of original halogenated compounds degraded. For CFCl3, the partial reductive degradation implied that different intra- and extracellular pathways were concurrent. The Gibbs free energy and the redox potential for the dehalogenation reactions utilizing Ti (III) citrate and acetate as electron donors are reported here for the first time.

Carbon Tetrachloride↗
PubMed2001

[Synthesis of estrone derivatives containing different halogens and/or heterocyclic moieties].

New compounds derived from the 3-methyl and 3-benzyl ethers of a D-secoestrone aldehyde were synthesized. In the presence of different Lewis acids D-homosteroids could form. These reactions which can be explained by an intramolecular Prinstype mechanism follow high stereoselectivity and reactivity and lead to compounds containing 16 beta-oriented halogens in the sterane skeleton. The formation and reaction of the imines derived from the aldehyde and aniline as well as substituted anilines provide a highly efficient access to steroid derivatives. The steroid alkaloids are of pharmacological interest.

Estrone↗
PubMed2003

Reproductive and morphological effects of halogenated dimethyl bipyrroles on captive American kestrels (Falco sparverius).

Sixty-four adult captive American kestrels (Falco sparverius) were exposed to a dietary source of halogenated dimethyl bipyrroles (HDBPs), a group of organohalogens proposed to have a natural origin. Adult kestrels were assigned to four treatment groups that were administered a different dose of HDBPs [high, 140 microg/(bird x d); medium, 4.3 microg/(bird x d); low, 0.13 microg/(bird x d); control, 0 microg/(bird x d)]. Exposure began prior to pairing and continued during breeding until approximately 28 d after hatching of the final eggs. Juvenile and adult kestrels accumulated HDBPs in carcass tissue, plasma, and liver. In addition, HDBPs were transferred to yolks during egg development. Low dietary absorption efficiencies (0.011-0.029) indicated that HDBPs were effectively cleared from kestrels either from increased elimination, metabolism, or a combination of the two processes. Reproductive and morphological endpoints examined for HDBP-induced changes included egg volume, egg mass, eggshell thickness, egg fertility, clutch size, liver and whole body mass, antebrachium, central retrice, tarsus, ninth primary, and wing cord lengths. Few statistically significant dose-dependent effects were observed. Hepatic tissue samples from selected individuals underwent histomorphological evaluation. Although the hepatic function was not evaluated specifically in these birds, no clinical signs suggestive of liver disease or gross hepatic anomalies were observed. Only minor histomorphological changes were detected in the hepatic tissue. The lack of serious effects suggests that HDBPs are not an acute reproductive threat to avian populations.

Animals↗
PubMed2003

Effect of a LED versus halogen light cure polymerization on the curing characteristics of three composite resins.

PURPOSE: To evaluate the effect, in vitro, of a LED (GC E Light) versus an halogen (Astralis 7) polymerization on the mechanical properties of three commercially available microhybrid composite resins. METHODS: Three commercially available composite resins (Tetric Ceram, Charisma, and Z100), and six modes of polymerization were evaluated (one mode for Astralis (AST): HIP 40 seconds and five modes for the GC E Light (GCE): standard 40 seconds, fast cure 6 seconds, fast cure 12 seconds, soft cure A 39 seconds, and turbo 10 seconds) in terms of top surface and bottom surface (2 mm-depth) microhardness, and flexural strength. Five specimens of each composite resin were made for the two mechanical properties tested. Five hardness values were recorded on each side for each sample with a Vickers diamond indenter. A three point bending test was performed at a crosshead speed of 1 mm/minute. Statistical comparisons were made using a two-way ANOVA (composite resin, polymerization mode) and a Fisher's test (P < 0.05). RESULTS: Z100 presented highest properties for both tests. Top surface microhardness: for Tetric Ceram and Charisma, the longer the exposure time, the higher the results, with no difference between AST mode and the longer GCE modes. For Z100, the highest values were obtained with AST. Whichever the material, short times (fast cure 6 seconds and turbo) exhibited poor results. Bottom surface microhardness: the samples cured with AST presented higher results but quite similar mechanical properties were achieved with the fast cure 12 GCE mode of the LED LCU. Fast cure 6 seconds and turbo obtained the lowest results. Flexural strength: the results were comparable with those obtained in bottom microhardness.

Analysis of Variance↗
PubMed1992

[Halogenated organic compounds in swimming pool water].

18 different swimming pool waters in the Bonn-Rhein-Sieg area were analysed for trihalogenmethanes, halogenated acetic acids, 2,2-dichloropropionic acid, dihalogenacetonitriles and chloral hydrate. Most substances mentioned above were determined in almost every sample reaching total concentrations up to 538 micrograms/l. Considering the results one can see that some of the main pollutants are polar organic compounds like di- and trichloroacetic acid as well as chloral hydrate.

Acetonitriles↗
PubMed2004

Synthesis and odour thresholds of mixed halogenated anisoles in water.

Earthy-musty off-flavour compounds in water samples are usually associated with the presence of geosmin and 2-methylisoborneol. However, the presence of 2,3,6- and 2,4,6-trichloroanisoles or other halogenated anisoles can impart objectionable tastes and odours to the water even at very low trace levels. This paper shows the synthesis of non-commercial 2,3,6- and 2,4,6- mixed chloro/bromoanisoles which can be present in bromide rich waters and could also be suspected of imparting earthy-musty off-flavours to the water. All the synthesized compounds were subjected to the flavour profile analysis (FPA) method and their odour threshold concentrations (OTC) in water were carried out giving values in the low ng/L range.

Anisoles↗
PubMed2004

Halogen-lithium exchange reactions under in situ-quench conditions: a powerful concept for organic synthesis.

In contrast to commonly accepted routine protocols for chemical synthesis, the reactions of lithioarenes, generated either by deprotonation or halogen-lithium exchange, need not necessarily be conducted in a stepwise fashion. As this review will demonstrate, the 'in situ-quench protocol provides a powerful alternative to stepwise construction in many cases. The operational simplicity of this methodology suggests interesting applications both for library syntheses and microreactor technology.

Boron↗
PubMedDate not supplied

[Halogenated volatile organic compounds in bottled mineral water and soft drinks].

74 mineral natural water samples and 56 samples of different commercial drinks have been analysed by head-space chromatography in order to evidence the presence of volatile halogenated organic compounds (VHO). Trihalomethanes (THM) as drinking water chlorination by-products and trichloroethane, carbon tetrachloride, trichloroethylene and tetrachloroethylene as ubiquitarious substances have been investigated. The presence of VHO has been evidenced in 20,3% of mineral natural water samples and in the 58,9% of the commercial soft drinks: this latest group has usually shown higher levels of the investigated compounds. The results of the present study has been compared with a similar study performed in 1991 in the same area: the VHO values observed in the present study appear to be lower than those obtained in the previous study.

Beverages↗
PubMed2005

Efficacy of halogen photopolymerization units in private dental offices in Toronto.

PURPOSE: Light units used for polymerization of resin composites are subject to deterioration with age, and frequent maintenance is required to maintain optimal efficacy. This study examined the efficacy of quartz-tungsten-halogen light units in private dental offices in Toronto for polymerization of resin composites. MATERIALS AND METHODS: One hundred dental offices met all selection criteria and agreed to participate in the study. The light intensity was determined for a total of 214 light units. Disk-shaped specimens, 2.5 mm thick, were made from 2 resin composites (Charisma, Heraeus Kulzer; Point 4, Kerr Corp) and were subjected to photopolymerization: Charisma for 20 seconds (99 units) and Point 4 for 20 and 40 seconds (all 214 units). Knoop hardness values for the upper and lower surfaces of each specimen were determined, and relative hardness values (hardness of lower surface/hardness of upper surface x 100) were calculated. Data were analyzed using descriptive statistics, t-tests, 1-way analysis of variance, and simple and multiple linear regression (a = 0.05). RESULTS: The light intensity of the individual units varied widely, from 120 to 1,000 mW/cm2. Surface hardness and relative hardness were significantly (p < 0.05) and positively associated with light intensity, and wide ranges in surface hardness and relative hardness values were observed. Mean relative hardness ranged from 34.8% to 57.7%. CONCLUSIONS: Light polymerization units in private dental offices displayed a wide range in light intensity, and many had below-recommended levels. Of the resin composite specimens polymerized for 40 seconds with each of the 214 light units, only 10% reached the desired relative hardness of at least 80%. A positive linear relationship was found between light intensity and relative hardness. Increased exposure time resulted in a significant increase in relative hardness. Also, relative hardness was found to be dependent on the brand of composite material used. Dentists should regularly monitor the condition of light units and replace deteriorating parts.

Analysis of Variance↗
PubMedDate not supplied

The effect of composite type on microhardness when using quartz-tungsten-halogen (QTH) or LED lights.

This study evaluates the Knoop microhardness of resin composites cured with different light-emitting diode (LED) based light curing units (LCU) or with a conventional quartz-tungsten-halogen light (QTH). Ten experimental groups with 10 specimens each were used. The specimens were prepared by placing two light-cured resin composites with similar VITA shade A2-microhybrid Filtek Z250/3M ESPE and microfill Durafil VS/Heraeus Kulzer--in a 2.0 mm-thick disc shaped mold. The specimens were polymerized for 40 seconds with the use of one QTH LCU (Optilux 501/Kerr-Demetron) and four LED LCUs: Elipar FreeLight 1 Cordless LED (3M ESPE), Ultrablue II LED with cord (DMC), Ultrablue III LED cordless (DMC) and LEC 470 I (MM Optics). Knoop microhardness was determined at the top and bottom surfaces of the specimens 24 hours following curing. Microhardness values in the microhybrid resin composite group showed no statistically significant differences when cured with LED FreeLight 1 LCU and QTH LCU (p<0.05). The other LED devices evaluated in the study presented lower microhardness values in both surfaces (p<0.05) when compared to QTH. In the microfill resin composite group, no statistically significant differences were observed among all LCUs evaluated on the bottom surfaces (p<0.05). However, on the top surfaces, QTH presented the highest KHN values, and the LED devices presented similar results when compared with KHN values relative to each other (p<0.05).

Analysis of Variance↗
PubMed2005

Early surface microhardness of a resin composite exposed to a pulse-delayed curing exposure: a comparison of a tungsten halogen and a plasma arc lamp, in vitro.

Surface microhardness numbers of a commercial resin composite have been compared after exposure to a quartz tungsten halogen (QTH) and plasma arc (PAC) lamp respectively, using two exposure protocols. The effect of increased tip-to-composite distance has also been compared. Exposure with the PAC lamp tested is more appropriate to the early finishing of composite restorations after placement and curing than with the QTH. However both lamps were capable of producing comparable surface hardness, with appropriate exposure protocols. The effect of increased tip-to-composite distance was generally not significant between the lamps for continuous exposure.

Acrylic Resins↗
PubMed2006

Surface microhardness of a resin composite: a comparison of a tungsten halogen and a LED light curing unit, in vitro.

A comparison has been made between published surface microhardness numbers (VHN) of a commercial resin composite for different exposure times to a quartz tungsten halogen (QTH) and light-emitting diode (LED) light-curing unit (LCU). Both LCUs produced comparable hardness at both top and bottom surfaces, respectively, and similar bottom/top hardness ratios, for a specimen thickness of 1.5 mm, given sufficient exposure time (40 s) and an elapsed time of 24 h before measurement (for hardness numbers). However, some data are significantly different. There is no advantage in either LCU regarding optimal hardness and hardness ratios given an appropriate protocol. Immediate finishing (1 h) was more appropriate to the use of the LED LCU (with adequate exposure time). The effect of elapsed time after exposure on microhardness was more pronounced with the QTH LCU.

Analysis of Variance↗
PubMed1990

[Distribution pattern of chemical in surface waters as a reflexion of entry pattern--nonvolatile halogenated hydrocarbons].

The concentrations of some nonvolatile halogenated hydrocarbons in surface waters of an industrialized city and its surroundings are given. About 80% of the ballast isomers of hexachlorocyclohexane (alpha, beta and delta BHC) and of DDT and its metabolites are in the range of less than 5 micrograms l-1, whereas ca. 50% of lindane (gamma BHC) were found to be between 5 and 100 micrograms l-1. Starting form the remarks about the differential-diagnostic assessment of environmental concentrations conclusions as to the origin of hexachlorocyclohexane isomers are drawn with the help of their distribution pattern. A high part of the gamma isomer, compared with the ballast isomers means an application (e.g. against mosquitos). This fact may be supported if it coincides with the months typical for such an application. in contrast to this if you have high percentages of alpha, beta and delta hexachlorocyclohexane, it indicates a point source or diffuse inputs of technical BHC. If all four isomers are present on a comparable and very low level this may reflect a remobilization from the sediment.

DDT↗
PubMed1976

[Increased blood-CO-content in humans and animals by incorporated halogenated hydrocarbons (author's transl)].

Contrarily to the general opinion about the harmlessness of dichloromethane, clear functional disturbances of the central nervous system could be recorded by means of effect investigations as well in humans as in animals. The depressive effect on the REM-sleep of albino rats was especially well recognisable, similarly as with carbon monoxide exposure. Surprisingly the analytical investigations of the blood of these animals showed a clearly elevated blood-CO-content after exposure to dichloromethane. Further experiments during which albino rats were exposed three hours along to a dichloromethane-concentration equal to the TLV (1750 mg/m3!!) resulted in a blood-COHb-level of about 13%, corresponding to over 30 mug CO/ml blood. So high blood-COHb-levels are obtained after a three-hour-exposure to 120 ppm CO. Following these findings, a number of halogenated and oxygenated hydrocarbon compounds of the methane and ethane series were investigated relatively to their CO-forming capacity. Only the di- and trihalogenated methane derivatives were found leading to an increased blood-COHb-level. After a three hours-exposure to 1000 ppm respectively the jodoalkanes yielding about 23% COHb were strongestly, the bromoalkanes with about 20% COHb more strongly and the chloroalkanes with about 12% COHb strongly implicated in the endogenous CO-formation. By means of detailed experiments with human volunteers (non-smokers) it resulted that after eight-hours-exposure to 500 ppm dichloromethane (TLV) a mean value for CO-content in blood of about 30 mug/ml corresponding to 12% COHb was obtained, in one case raising as high as 60 mug CO/1 ml blood or 24% COHb. After an eight-hours-exposure to 100 ppm of the halocarbon, the blood-COHb-level reached 5%. The elimination was very slow, so that 24 to 26 hours were necessary to reestablish the original blood-COHb-level. These results show that the actually TLV for dichloromethane e.g. 1750 mg/m3 has to be revised, because a fifth of this value already leads to a blood-COHb-content equal to that produced by the TLV for carbon monoxide and that also eventually arising problems due to gas mixtures have to be considered and thoroughly investigated.

Air Pollution↗
PubMed1990

[Relationship between molecular structure of halogenated methane compounds and their hypotensive effect in rats].

In this study gases of twelve halogenated methane compounds were administered by inspiration to Wistar rats in order to elucidate the relationship between molecular structure of the compounds and their hypotensive effect, and to develop new inhalational circulatory control agents. The correlation between the hypotensive effect of the compounds evaluated from the experimental data and computed van der Waals volume as well as surface area following molecular mechanics calculations of structure and energy, was investigated. The results showed that the compounds with van der Waals volume and surface area more than 73 A3 and 100 A2, respectively, had the hypotensive effect. In conclusion, our data suggest that the hypotensive effect of inhalational agents requires greater molecular sizes than regular ones.

Administration, Inhalation↗
PubMed1990

Preparation and biokinetic evaluation of various halogenated iminodiacetic acid-type compounds labeled with technetium-99m for hepatobiliary scintigraphy in the baboon (Papio ursinus) model.

In an evaluation of various 99mTc-labeled halogenated (F, Cl, Br, I) iminodiacetic acid (IDA) derivatives for hepatobiliary scintigraphy, it was found that, in the baboon model, none of these compounds performed as well as did disida. F-IDA was least effective, with the lowest biliary excretion and highest renal participation, but multihalogen substitution as in penta-F-IDA increased the biliary specificity and reduced urinary excretion to the extent that penta-F-IDA scored second to disida and even above I-IDA, with its high molecular weight. Surprising also was the relatively good performance of Cl-IDA compared to Br-IDA and I-IDA.

Animals↗
PubMed1989

[The mutagenicity of organic microcontamination in the environment. II. The mutagenicity of volatile organic halogens in the Salmonella microsome test (Ames Test) with regard to the contamination of groundwater and drinking water].

To determine the sensitivity and specificity of microbial shortterm-tests for the registration of the mutagenic potency of halogenated hydrocarbons (OHV) 18 pure substances out of the groups of halomethanes, -ethanes and -ethylenes were examined with different laboratory methods (classical Ames-Test, Spot-Testing, Preincubation-Procedure) of the Salmonella-Microsome-Test (Ames-Test). The Salmonella typhimurium- strains TA97, TA98, TA100 und TA102 were used with and without metabolic activation of Arochlor 1254 induced rat-liver microsomes. Mutagenicity with one or several procedures shows 1,1,2,2-tetrachloroethane, hexachloroethane, trichloroethylene, bromdichloromethane and bromoform without metabolic activation and dichloromethane, tetrachloromethane, 1,1,2,2-tetrachloroethane, hexachloroethane, 1,1-dichloroethylene, trans-1,2-dichloroethylene, tetrachloroethylene and bromdichloromethane with metabolic activation. The range of sensitivity amounted from microgram to nanogram values of OHV's per plate, so that the Ames-test can be a sensitive screening method sufficient for detection of mutagenic effects by several OHV's in high contaminated environmental samples even without extraction procedures.

Fresh Water↗