A cryospectroscopic infrared and Raman study of the CX⋯π halogen bonding motif: complexes of the CF3Cl, CF3Br, and CF3I with ethyne, propyne and 2-butyne.

Experimental information on the C-X⋯π halogen bonding motif was obtained by studying the formation of molecular complexes of CF3Cl, CF3Br and CF3I with ethyne, propyne and 2-butyne in liquid krypton, using FTIR and Raman spectroscopy. For CF3Br, experimental evidence was found for the formation of 1:1 complexes with propyne and 2-butyne only, while for CF3I spectroscopic features confirming the existence of the halogen bonded complexes were observed for ethyne, propyne and 2-butyne. In addition, at higher concentrations of CF3I and 2-butyne, weak absorptions due to a 2:1 complex were also observed. The experimental complexation enthalpies, obtained by using spectra recorded at temperatures between 120 K and 140 K, are -5.9(3) kJ mol(-1) for CF3I.ethyne, -5.6(3) kJ mol(-1) for CF3Br.propyne, -8.1(2) kJ mol(-1) for CF3I.propyne, -7.3(2) kJ mol(-1) for CF3Br.2-butyne, -10.9(2) kJ mol(-1) for CF3I.2-butyne and -20.9(7) kJ mol(-1) for (CF3I)2.2-butyne. The experimental study is supported by theoretical data obtained from ab initio calculations at the MP2/aug-cc-pVDZ(-PP) and MP2/aug-cc-pVTZ(-PP) levels, and Monte Carlo Free Energy Perturbation (MC-FEP) simulations. The experimental and theoretical values on the C-X⋯π halogen-bonding motifs studied are compared with previously reported data for the complexes with ethene and propene and with preliminary results obtained for benzene and toluene.

Setting safe acute exposure limits for halon replacement chemicals using physiologically based pharmacokinetic modeling.

Most proposed replacements for Halon 1301 as a fire suppressant are halogenated hydrocarbons. The acute toxic endpoint of concern for these agents is cardiac sensitization. An approach is described that links the cardiac endpoint as assessed in dogs to a target arterial concentration in humans. Linkage was made using a physiologically based pharmacokinetic (PBPK) model. Monte Carlo simulations, which account for population variability, were used to establish safe exposure times at different exposure concentrations for Halon 1301 (bromotrifluoromethane), CF(3)I (trifluoroiodomethane), HFC-125 (pentafluoroethane), HFC-227ea (1,1,1,2,3,3,3-heptafluoropropane), and HFC-236fa (1,1,1,3,3,3-hexafluoropropane). Application of the modeling technique described here not only makes use of the conservative cardiac sensitization endpoint, but also uses an understanding of the pharmacokinetics of the chemical agents to better establish standards for safe exposure. The combined application of cardiac sensitization data and physiologically based modeling provides a quantitative approach, which can facilitate the selection and effective use of halon replacement candidates.

An overview of the risk assessment of hazardous materials and the role of toxicology.

The chemical risk assessment process and the need for health-based approaches to identify and characterize potential hazardous substances will be discussed. The risk assessment process can be applied to both workplace and environmental settings. Toxicology will be defined and related to the risk assessment process. A brief overview of toxicity screens and tests will be presented in order to help make toxicity data more meaningful. Toxicity data for Halon 1301 replacements and trichloroethylene (TCE) will be presented as examples. The paper will conclude with a description of tri-service toxicology; what it is and what this laboratory provides to the Department of Defense (DOD), industry, and academia.

Assessment of the reproductive toxicology of bromochlorodifluoromethane (BCF, halon 1211) in the rat.

The effect of bromochlorodifluoromethane (BCF) on reproduction in the rat has been investigated in two studies. Pregnant female rats were exposed by inhalation to 1000, 10,000, or 50,000 ppm BCF for six hours a day on days six to 15 of gestation (day of mating = day 0). Exposure to 50,000 ppm BCF caused a reduction in maternal weight gain over the exposure period but there was no evidence of either teratogenicity or embryo/fetotoxicity at any concentration. In a study designed to assess the potential effect of BCF during a complete reproductive cycle male and female rats were exposed to 5000 ppm or 25,000 ppm BCF for six hours a day for five days a week for 10 weeks (males) or three weeks (females) before mating. Exposure to BCF continued during mating and up to day 20 of gestation for half the females which were subsequently allowed to litter and the development of their offspring monitored. The remaining females were removed from exposure to BCF after mating and killed on day 20 of gestation for examination of their uterine contents. There were no effects on adult fertility, pup numbers, survival, or pup development. It was concluded that BCF had no reproductive toxicity potential in the rat.