16.Photochemistry.11

16.Photochemistry.11 - ETX 1 02A 11 February 2011 Dr Crosby...

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Unformatted text preview: ETX 1 02A 11 February 2011 Dr. Crosby Shedding Light on Toxicity I. Introduction A, Light—what is it? Energy, absorption, spectra B. Light—What does it do? Photochemical reactions, phototoxicity C. Sunlight D. Examples: UV effects in the atmosphere, in water, and on surfaces ll. Atmosphere A. Atmospheric oxidants: generation, concentrations, hydroxyl B. Atmospheric reactions of oxidants C. Toxic consequences from the atmosphere lll. Water A. Properties of water; light penetration vs depth B. UV absorption by chemicals in aqueous solution C. Photolysis in water (direct and indirect): oxidation, reduction, hydrolysis D. Toxic consequences from natural waters lV. Surfaces A. Light penetration of surfaces (e.g., soil, skin) B. UV absorption by skin C. Phototoxicity: fish vs humans; singlet oxygen D. Toxic consequences from skin exposure V. Light and Toxicity (Summary) Shedding Light on Toxicity A Light Absorption—To cause chemical change, energy must be absorbed (Principle #1). 438nm l Absorption Spectrum of Dexon 1000 (C H3)2N"< >— NZN803N3 E E = Energy = 28500 kcanole *3 x .Q < 100 >. Example: 438 nm = 28’600 kcallmole g: 438 65 = 65.3 kcallmole 2 :5; 5% 1o Ultraviolet Violet Blue reen Yellow i 250 300 350 400 450 500 550 <— X-ray Wavelength, nm \fisible ——> B Photolysis of Dexon: Absorbed energy must be released as heat, light, or bond rupture (Principle #2). (—OH— (CH3)2N—©—N=N—803Nalfl”—»(CH3)2N—©—on + N2 + HSOgNa Dexon Energy, kcallmole C Sunlightenergy atthe 120 110 100 90 80 _ 7o Earth's surface Source doesnt matter—only wavelength distribution and light intensity (Principle #3). 1 . Solar energy causes chemical change; 2. Change in chemistry causes change in toxicity; 3. Each reaction product has its own toxicity. 0.. E g E :2 290 g Q) o 250 300 350 400 Wavelength, nm <— X—ray Ultraviolet Visible ——-> ATMOSPHERE Typical diurnal variation of atmospheric NOx and ozone in Los Angeles smog. Relative Concentration AM 4 8 12 4 8 PM E Generation of atmospheric oxidants 1000°C 02 UV, 02 uv _____> . —> - —————> 2 O 4 ' N2 + 02 1 2 NO 2 2 N02 _ 2N0 3 3 2 H20 4 HO Result: 02 + 2H20fl+4-0H Q —Q- Triplet oxygen 2.7x10a pg/m3 Q —Q —Q- Ozone 400900 pig/m3 ~NO Nitric oxide 1200 pig/m3 Q =Q Singlet oxygen o_03 ilg/ma -N02 Nitrogen dioxide 400—900 rig/m3 _ _ - QzH Hydroxyl 3x104 pig/m3 F Key atmospheric processes” A. Alkanes OO- OCH 0 . . - H O NO ll RCHZCH3 fl» RCHCH3 92-» RQHCHafl» RQHCH3 H—ZOI» RCCH3 .373» RCO-ON02 PAN (R : CH3) _ Fuel oxidation Pero acet B. Aromatics HO ("smog") ngate yl ', Phenol O - H20 Q—OH formation C. Alkenes (EH3 CH3 CH3 CH2=CCH=CH2-%QL> CH2=(’:CH-CH20H —»CH2=(IJCH=O Blue haze lsoprene 2 -O‘ + CH 2:0 D. lnorganics: H28 H—O'>802 419;» [H0302] —02—> soy—fl» H2804 UV R—Br—-—> Fi~ + Bri» ~OBr + 02 Ozone destruction a See Finlayson-Pitts and Pitts, Atmospheric Chemistry, 1986 Note: Products can be toxic to eyes, lungs, and skin, to crops and habitat; and via rain to aquatic life. G Properties of Water Universal solvent for chemicals; Transparent to UV radiation; --------- pH of fresh water 6-8, pH of seawater 7.9-8.2; Oxygen concentration in fresh water 1.5 mmol/L, in seawater 1.3 mmol/L Baker & Smith, in The Role of Solar Ultraviolet Radiation in Man‘ine Ecosystems (J Calkins, ed),1982, p 333. H UV Absorption by Solutions 150 2,40 Na salt 1.4x10“1 M :5 «i 8 1.00 C en E 8 Solar cutoff .0 <12 00 250 300 Wavelength, nm UV Depth 100 Penetration into Water 0+ m - - -> N g 10 E w" 1 250 300 350 400 Wavelength, nm | Photolysis of 2,4-D (Direct) OCHZCOOH OH 0' Oxidation 0' _ ulez 2,4~D Cl Reduction Cl w OCH2000H Hydrolysis gm uv/H 0 2 H W102 ule2 OCH2000H _ 0H Inorganic uv102 (002, Cl , H20) —-—-—-—-——-> "Minerlization" Cl J Photooxidation of 2-Methylnaphthalene in Water (Indirect) H202 ——U-\L—> 2 HO- N03' %> HO- + N02' CU“ + H20 —-—->UV HO~ + Cu+ _H+ CH=0 HO- COOH ---> 00 Sidechain Oxidation Ring Oxidation COOH H3 H0- (:1: Oxygen ’ COOH Addition L UV absorption by NH2 - - l skin constituents CHZCHCOOH K UV penetration into skin UV Wavelengh 250 300 350 400nm DNA T . yrosme Solar cutoff OH (in protein) N IH2 H Tryptophan (in protein) Tryptophan my Oak Skin: Epidermis UV Absorption —> Dermis Subcutaneoustissue 240 260 280 300 320 340 H Wavelength, nm Thymine (in DNA) M Phototoxicity / | \ UV 5. \ o o 02 _ o Psoralen O (Limes, celery) (IDOH 1 1. FiCH=CHCHgCOOFi' ————>FiCHCH=CHCOOFi' Lipid THQ 1 ? NH2 2, CHsscHzCHchCOOH —->CH380HQCH2&HCOOH Methionine 3. 1 - 3% ——>°* ““ if —>W ft fl 0 N O NHCHO Thymine See: DG Crosby, The Poisoned Weed: Plants Toxic to Skin, Oxford Univ. Press, 2004. N Consequences of Sunlight Beneficial: Adverse: Selfcleaning—purification of water and air Adverse health effects of smog Plant photosynthesis Toxicity to plants, especially crops Vitamin D generation in skin Phototoxicity Melanin and other natural sunscreens Sunburn and skin cancer Destruction of the ozone layer Understanding the relation of light to toxicity can help control adverse effects ...
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