How phenol and alpha-tocopherol react with ambient ozone at gas/liquid interfaces.
The exceptional ability of alpha-tocopherol (alpha-TOH) for scavenging free radicals is believed to also underlie its protective functions in respiratory epithelia. Phenols, however, can scavenge other reactive species. Herein, we report that alpha-TOH/alpha-TO(-) reacts with closed-shell O(3)(g) on the surface of inert solvent microdroplets in < 1 ms to produce persistent alpha-TO-O(n)(-)(n = 1-4) adducts detectable by online thermospray ionization mass spectrometry. The prototype phenolate PhO(-), in contrast, undergoes electron transfer under identical conditions. These reactions are deemed to occur at the gas/liquid interface because their rates: (1) depend on pH, (2) are several orders of magnitude faster than within microdroplets saturated with O(3)(g). They also fail to incorporate solvent into the products: the same alpha-TO-O(n)(-) species are formed on acetonitrile or nucleophilic methanol microdroplets. alpha-TO-O(n = 1-3)(-) signals initially evolve with [O(3)(g)] as expected from first-generation species, but alpha-TO-O(-) reacts further with O(3)(g) and undergoes collisionally induced dissociation into a C(19)H(40) fragment (vs C(19)H(38) from alpha-TO(-)) carrying the phytyl side chain, whereas the higher alpha-TO-O(n > or = 2)(-) homologues are unreactive toward O(3)(g) and split CO(2) instead. On this basis, alpha-TO-O(-) is assigned to a chroman-6-ol (4a, 8a)-ene oxide, alpha-TO-O(2)(-) to an endoperoxide, and alpha-TO-O(3)(-) to a secondary ozonide. The atmospheric degradation of the substituted phenols detected in combustion emissions is therefore expected to produce related oxidants on the aerosol particles present in the air we breathe.
Enami
Shinichi
S
W. M. Keck Laboratories, California Institute of Technology, Pasadena, California 91125, USA.
Hoffmann
Michael R
MR
Colussi
A J
AJ
D002245:Carbon Dioxide / Q000737:chemistry; D005740:Gases / Q000737:chemistry*; D006571:Heterocyclic Compounds / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D000432:Methanol / Q000737:chemistry; D010126:Ozone / Q000737:chemistry*; D010545:Peroxides / Q000737:chemistry; D010636:Phenols / Q000737:chemistry*; D013499:Surface Properties; D024502:alpha-Tocopherol / Q000737:chemistry*
C503429:1,2,4-trioxane; D005740:Gases; D006571:Heterocyclic Compounds; D010545:Peroxides; D010636:Phenols; D002245:Carbon Dioxide; D010126:Ozone; D024502:alpha-Tocopherol; D000432:Methanol