Medical intelligence article: assessing the impact on global climate from general anesthetic gases.

Although present in the atmosphere with a combined concentration approximately 100,000 times lower than carbon dioxide (i.e., the principal anthropogenic driver of climate change), halogenated organic compounds are responsible for a warming effect of approximately 10% to 15% of the total anthropogenic radiative forcing of climate, as measured relative to the start of the industrial era (approximately 1750). The family of anesthetic gases includes several halogenated organic compounds that are strong greenhouse gases. In this short report, we provide an overview of the state of knowledge regarding the impact of anesthetic gas release on the environment, with particular focus on its contribution to the radiative forcing of climate change.

Atmospheric chemistry of isoflurane, desflurane, and sevoflurane: kinetics and mechanisms of reactions with chlorine atoms and OH radicals and global warming potentials.

The smog chamber/Fourier-transform infrared spectroscopy (FTIR) technique was used to measure the rate coefficients k(Cl + CF(3)CHClOCHF(2), isoflurane) = (4.5 ± 0.8) × 10(-15), k(Cl + CF(3)CHFOCHF(2), desflurane) = (1.0 ± 0.3) × 10(-15), k(Cl + (CF(3))(2)CHOCH(2)F, sevoflurane) = (1.1 ± 0.1) × 10(-13), and k(OH + (CF(3))(2)CHOCH(2)F) = (3.5 ± 0.7) × 10(-14) cm(3) molecule(-1) in 700 Torr of N(2)/air diluent at 295 ± 2 K. An upper limit of 6 × 10(-17) cm(3) molecule(-1) was established for k(Cl + (CF(3))(2)CHOC(O)F). The laser photolysis/laser-induced fluorescence (LP/LIF) technique was employed to determine hydroxyl radical rate coefficients as a function of temperature (241-298 K): k(OH + CF(3)CHFOCHF(2)) = (7.05 ± 1.80) × 10(-13) exp[-(1551 ± 72)/T] cm(3) molecule(-1); k(296 ± 1 K) = (3.73 ± 0.08) × 10(-15) cm(3) molecule(-1), and k(OH + (CF(3))(2)CHOCH(2)F) = (9.98 ± 3.24) × 10(-13) exp[-(969 ± 82)/T] cm(3) molecule(-1); k(298 ± 1 K) = (3.94 ± 0.30) × 10(-14) cm(3) molecule(-1). The rate coefficient of k(OH + CF(3)CHClOCHF(2), 296 ± 1 K) = (1.45 ± 0.16) × 10(-14) cm(3) molecule(-1) was also determined. Chlorine atoms react with CF(3)CHFOCHF(2) via H-abstraction to give CF(3)CFOCHF(2) and CF(3)CHFOCF(2) radicals in yields of approximately 83% and 17%. The major atmospheric fate of the CF(3)C(O)FOCHF(2) alkoxy radical is decomposition via elimination of CF(3) to give FC(O)OCHF(2) and is unaffected by the method used to generate the CF(3)C(O)FOCHF(2) radicals. CF(3)CHFOCF(2) radicals add O(2) and are converted by subsequent reactions into CF(3)CHFOCF(2)O alkoxy radicals, which decompose to give COF(2) and CF(3)CHFO radicals. In 700 Torr of air 82% of CF(3)CHFO radicals undergo C-C scission to yield HC(O)F and CF(3) radicals with the remaining 18% reacting with O(2) to give CF(3)C(O)F. Atmospheric oxidation of (CF(3))(2)CHOCH(2)F gives (CF(3))(2)CHOC(O)F in a molar yield of 93 ± 6% with CF(3)C(O)CF(3) and HCOF as minor products. The IR spectra of (CF(3))(2)CHOC(O)F and FC(O)OCHF(2) are reported for the first time. The atmospheric lifetimes of CF(3)CHClOCHF(2), CF(3)CHFOCHF(2), and (CF(3))(2)CHOCH(2)F (sevoflurane) are estimated at 3.2, 14, and 1.1 years, respectively. The 100 year time horizon global warming potentials of isoflurane, desflurane, and sevoflurane are 510, 2540, and 130, respectively. The atmospheric degradation products of these anesthetics are not of environmental concern.

Effect of hyperconjugation on ionization energies of hydroxyalkyl radicals.

On the basis of electronic structure calculations and molecular orbital analysis, we offer a physical explanation of the observed large decrease (0.9 eV) in ionization energies (IE) in going from hydroxymethyl to hydroxyethyl radical. The effect is attributed to hyperconjugative interactions between the sigma CH orbitals of the methyl group in hydroxyethyl, the singly occupied p orbital of carbon, and the lone pair p orbital of oxygen. Analyses of vertical and adiabatic IEs and hyperconjugation energies computed by the natural bond orbital (NBO) procedure reveal that the decrease is due to the destabilization of the singly occupied molecular orbital in hydroxyethyl radical as well as structural relaxation of the cation maximizing the hyperconjugative interactions. The stabilization is achieved due to the contraction of the CO and CC bonds, whereas large changes in torsional angles bear little effect on the total hyperconjugation energies and, consequently, IEs.

Electronic spectroscopy and photodissociation dynamics of the 1-hydroxyethyl radical CH3CHOH.

The electronic spectroscopy and photodissociation dynamics of the CH3CHOH radical in the region 19,400-37,000 cm(-1) (515-270 nm) were studied in a molecular beam using resonance-enhanced multiphoton ionization (REMPI), photofragment yield spectroscopy, and time-of-flight (TOF) spectra of H and D fragments. The onset of the transition to the Rydberg 3s state, the lowest excited state, is estimated at 19,600 +/- 100 cm(-1). The 3s state dissociates fast, and no REMPI spectrum is observed. The origin band of the transition to the 3pz state, identified by 2 + 2 REMPI, lies at 32,360 +/- 70 cm(-1), and a vibrational progression in the C-O stretch is assigned. When exciting CH3CHOH near the onset of the unstructured absorption to the 3s state, only one peak is observed in the center-of-mass (c.m.) translational energy (Et) distribution obtained by monitoring H photofragments. The measured recoil anisotropy parameter beta = -0.7 +/- 0.1 is typical of a perpendicular transition. The O-H bond energy is determined to be D0 = 1.1 eV +/- 0.1 eV. At excitation energies >31,200 cm(-1) (3.87 eV) a second, low Et peak appears in the c.m. Et distribution with beta approximately 0. Its relative intensity increases with excitation energy, but its beta value does not change. In contrast, the beta value of the higher Et peak becomes monotonically less negative at higher excitation energies, decreasing to -0.2 +/- 0.1 at 35,460 cm(-1). By comparison of the TOF distributions of the isotopologs CH3CHOH, CH3CHOD, and CD3CHOH, it is concluded that two major product channels dominate the photodissociation, one leading to acetaldehyde and the other to vinyl alcohol (enol) products. There is no indication of isomerization to ethoxy. It appears that separate conical intersections lead to the observed channels, and the dynamics at the conical intersection and the exit channel deposit much of the available energy into internal energy of the products.

Unimolecular processes in CH2OH below the dissociation barrier: O-H stretch overtone excitation and dissociation.

The OH-stretch overtone spectroscopy and dynamics of the hydroxymethyl radical, CH(2)OH, are reported in the region of the second and third overtones, which is above the thermochemical threshold to dissociation to H+CH(2)O (D(0)=9600 cm(-1)). The second overtone spectrum at 10 484 cm(-1) is obtained by double resonance IR-UV resonance enhanced multiphoton ionization (REMPI) spectroscopy via the 3p(z) electronic state. It is rotationally resolved with a linewidth of 0.4 cm(-1) and displays properties of local-mode vibration. No dissociation products are observed. The third overtone spectra of CH(2)OH and CD(2)OH are observed at approximately 13 600 cm(-1) by monitoring H-atom photofragments while scanning the excitation laser frequency. No double resonance REMPI spectrum is detected, and no D fragments are produced. The spectra of both isotope analogs can be simulated with a linewidth of 1.3 cm(-1), indicating dissociation via tunneling. By treating the tunneling as one dimensional and using the calculated imaginary frequency, the barrier to dissociation is estimated at about 15 200 cm(-1), in good agreement with theoretical estimations. The Birge-Sponer plot is linear for OH-stretch vibrations 1nu(1)-4nu(1), demonstrating behavior of a one-dimensional Morse oscillator. The anharmonicity parameter derived from the plot is similar to the values obtained for other small OH containing molecules. Isomerization to methoxy does not contribute to the predissociation signal and the mechanism appears to be direct O-H fission via tunneling. CH(2)OH presents a unique example in which the reaction coordinate is excited directly and leads to predissociation via tunneling while preserving the local-mode character of the stretch vibration.