Lecture 11 Photochemistry PDF

BIOL 439 ENVIRONMENTAL PHOTOCHEMISTRY 11/14/24 Okechukwu Igboeli, Department of Biology https://www.scienceboard.net/index.aspx?sec=ser&sub=def&pag=dis&ItemID=2390  Environmental Photochemistry ▪ Light processes are crucial to the biosphere Photosynthesis...

BIOL 439 ENVIRONMENTAL PHOTOCHEMISTRY 11/14/24 Okechukwu Igboeli, Department of Biology https://www.scienceboard.net/index.aspx?sec=ser&sub=def&pag=dis&ItemID=2390  Environmental Photochemistry ▪ Light processes are crucial to the biosphere Photosynthesis nothing can survive without life Vision heat and photosynthesis sight ▪ Not surprising there are photoactive allelopathic compounds and environmental photochemical processes ▪ Many xenobiotics are also photoactive ▪ Many activated by UV radiation, but visible radiation also important ▪ UV (290 to 400 nm) and visible radiation (400 to 700 nm) drive these processes, because they cause electronic transitions in molecules; infrared (> 800 nm) causes vibrational transitions (heat); < 290 nm does not reach the earth ▪ Electronic transitions are required for photochemistry Environmental Photochemistry PAGE 1  Environmental Photochemistry ▪ Energy of photons is quantized, as is absorption of photons by a chemical ▪ Energy = h = hc/; = frequency and  = wavelength ▪ E is photon energy (joules) ▪ h is the Planck constant - 6.62607015 × 10−34 (m2kgs−1) ▪ ν (nu) is the photon's frequency ▪ c is the speed of light Environmental Photochemistry PAGE 2  Environmental Photochemistry ▪ Energy of photons is quantized, as is absorption of photons by a chemical ▪ Energy = h = hc/; = frequency; c = speed of light; and  = wavelength ▪ Thus, energy is inversely proportional to  ▪ For an organic molecule to absorb light it must have conjugated double bonds (or a conjugated -orbital system) ▪ We will look at: Examples of environmental and biological photoactive chemicals Why UV or visible radiation is required can be very toxic Why conjugated -orbitals are required How light energy can result in chemical (often damaging) reactions Environmental Photochemistry PAGE 3  ay Question Examples of Engetic compounds altered or made toxic by impacts UV light at use ice Twitan Paha If in Effivated Larson & Berenbaum 1998 Environmental Photochemistry psyfisible destinentsianets F inacteria Iii comma Filian toblast  cliproblast s yg Basic Photochemical Processes ▪ Begins with absorption of a photon ▪ Absorbance of a photon results in elevation of an electron from a ground state to an excited state ▪ The photons energy must match the difference in energy between the ground and excited states of the molecule ▪ Because most organic molecules have all electrons in covalent bonds, all electrons are paired (with opposite spin; Pauli exclusion principle) ▪ Therefore, the net electron spin in organic molecules is 0 and they exist as singlet state molecules zero ▪ When the molecule absorbs, spin must be conserved, therefore excitation is always from the ground singlet state to the excited singlet state There is a tripletstate Environmental Photochemistry PAGE 5 Wallet.fi  ng Id se Lowest Unoccupied Molecular Orbital 3options generateheat generatehigh transferenery heat heat acrossstates tripletstate light Highest Occupied Molecular Orbital light Larson & Berenbaum 1998 Environmental Photochemistry PAGE 6  How it changes as result of absorbance of a photon ground to excited state H H Ethylene H H Environmental Photochemistry  doublebonds wavelengthrequired depending on amount ofphotonabsorbed Fitts Inside excited at absorbat diff Once light is absorbed: the energy in the molecule must be dissipated guff Flip igggtsg.ae refinotosynthesizer Uquenched bymolecule  que tinasEugen ng E ate itousen to p duce ROS Environmental Photochemistry  Further Reactions of H2O2 canhappenat any time happy H2O2 + Fe2+ HO + OH- + Fe3+ gn Hydroxyl radical can attack any biomolecule For example, lipid cross-linking via a chain reaction RR R excited singletoxygenmostreactive R R inprocess of reducing can form peroxide and lipidperoxides HO  Etc. Environmental Photochemistry  Cellular defenses against ROS or H2o EEE Emea hotharmful Larson & Berenbaum 1998 Wcreaten Is reagentattte Environmental Photochemistry  g Photosensitizers of possible environmental importance psoralin Larson & Berenbaum 1998 Environmental Photochemistry  Plant-derived phototoxic compounds with insecticidal properties parent compoundnot insecticidal but is When exposed to light selectwhicharephototoxic with insecticidalproperties Larson & Berenbaum 1998 Environmental Photochemistry Psoralen: Inhibits cell division and sterilizes blood Photodynamic therapy based on direct photochemical reaction Psoralen-DNA adducts: formed via the Diels-Alder reaction: h + For psoralen and 2 Thymines: O O N N + + O O O N O N O h O N O O N usedto sterilize N O blood N O O zap it nothing O If two T’s are in opposite strands of a DNA (or RNA) initiatethat molecule, the DNA strands can be covalently crosslinked. needsDNA  Photodynamic therapy: Based on triplet state mechanism formation ForBPDnot fullyunderstood leadto oxidative exposureto light causeschange in energy state damage and cell death tape I photosensitivity could also be Type II TPPusedas aplasticizerand fire retardant I  Photochemistry of Beer ▪ Products in beer formed during malting and fermentation ▪ Heating of grain in a concerted way, results in very specific compounds ▪ Composition of beer (from barley and Hops): H2O 91% iso α acid uponexposureto EtOH 5% light forms compound that Carbs/Malt 3% picks up sulfur antjyig.royia CO2 0.5% skunkyflavour aa’s 0.1% Salts 0.1% Hop acids 0.0035% FOCKS inverylowconc will affecttaste Riboflavin (vitB) 0.001% Environmental Photochemistry PAGE 17  Malt Volatiles Quiz slide 4 categories Whatareathesories 1. Lipid oxidation products 2 I 2. Maillard reaction products 3. Aliphatic sulfur compounds 4. Phenols Lipid oxidation products Short chain aldehydes and shortchain enols (low conc) Maillard products – Flavor and color From sugar oxidation and modification Pyrazines, furans, pyrroles, thiophenes (and their polymers) get IIe Pigment (yellow, brown to black) – Melanoidins or colour Caramelization in many foods from heating  Melanoidins (colour) polymerise Reducing sugars - H 2O O R Furans reductones NH3 -amino acids amino acid H 2S N R H IFlavour Pyrroles -aminoketones  / O2 S R Thiophenes N R Pyrazines N Maillard (browning) reaction scheme.  Malt Volatiles Sulfur volatiles ▪ Dimethyl sulfide - MeSMe ▪ From degradation of methionine and Cysteine EE 1 n ▪ Must be controlled for flavor quality skunkyflavour Phenols ▪ From ferulic and coumaric acid during malting ▪ Consumed by yeast during fermentation ▪ In low content  Hops ▪ Source of distinctive bitter taste of beer ▪ Source of skunky flavor in light struck beer ▪ From the plant Humulus lupulus onlyhappenswhen you usehops https://www.gardenia.net/plant/humulus-lupulus-nugget  Hops ▪ Source of distinctive bitter taste of beer ▪ Source of skunky flavor in light struck beer ▪ From the plant Humulus lupulus ▪ In the Cannabaceae family ▪ Been used in brewing for > 1000 years (in ancient Egypt ~ 3000 yrs) ▪ Leafy vine plant – leaves shaped like maple leaves (eh) ▪ Unseeded flowers used - only female plants used – male plants highly regulated ▪ Originally used in brewing as a preservative whytheythought it wassaferthanwater ▪ Hop acids allelopathic – kill most fungi, except yeast  Hops ▪ Flavor from hop oil - over 300 products – 300 of the 400 compounds in beer (most in low concentration) O Thioesters – Off cheesy flavor R-C-S-R' Characteristic odor – Terpenes – Hoppy smell but not flavor Flavor – Hop acids ▪ Terpenoid alcohols, epoxides ketones and esters if youmust use hops ▪ Stabilize the foam howdo youprevent ▪ Spicy citrus flavor of hoppy beers lightstruckbeer brownbottles ▪ Most important: -acids, -acids and iso--acids not ▪ Also, what will cause light struck beer  OH O OH O OH O a b HO O HO O HO OH OH 2a 3 1a a: h (350 – 366 nm), MeOH; b: O2, Pb(OAc)2, MeOH, then H2SO4 Howlight will leadtodiffere transformatio b an I Till OH O O O O O movefrom 5 5 one HO 6 O a HO 4 HO 4 OH OH OH O + O another 1a 4a 4b haispens a: t, wort; b: h (350 – 366 nm), MeOHdon't Ted Hop acids interconverted provide by heat and light  s q yy Most important flavor constituent Iso--acids Present at 20 to 25 ppm skunkflavour Flavor threshold: 5.6 ppm O O Skunky flavor at < 1ppb (< 1 % of iso O O acid) IV HO OH O a HO SH IE OH III O 6 a: h (UV or visible), beer; b: NaBH4 I II b O O ISOHUMULONES 4a + 4b HO I: bitter taste OH HO II: Light struck flavour III: foam stabilization, water 7 solubility Can’t go light struck (reduced) IV: bacteriostatic action Miller beer does this Light struck reaction of Iso--acids O O O O Skunky flavor at < 1ppb (< 1 % of iso acid) IV HO OH HO OH OH O O SH 6 From SH sulfur volatiles Can occur in UV alone C=O + In visible with riboflavin (abs at 450 nm) OH Riboflavin (R) light can attackthe Iso α acid h (Visible) 1R* 3R* + 3O2 R + 1O2 H2O2 ISC QuizQuestions Twodiff dishinfridge 2weeksold spoiled 4weeks notspoiled 4weekold is plantbased 2 Bestdescribesalleopathic Communication 3 Mechanismsof Algicide all arecorrect 3 Characteristics ofJubilone Pecanstrees inhibitsphotosystemI coenzymeQ reductioninhibited 4 most toxictype of fungicide andleast least terpenoid most polyphenolics 5 select alsacide that is not polyphenolic orderivative acetic acid 6 Capsacinfoundin St Johnswort causesphotosenzatization ofskin uponexposure FALSE 7 StJonas wort is toxic to Livestock 8 All alleochemicalsenter cellthroughdiffusion FALSE 9 In constitutiveresistance are and onsiteand slow 10 inducedplantvolatiles directlyaffect HIP favore 11 Specialtyherbavorearenotaffected defensemechanismsofhostplants by False 12 Catpillarspreferto feedon because of_ I herglucosenoidconcentrations 13 D Limone myacinLinalool Mono terpenoidssuchas FALSE 14 Leavesof C locdom C and harmful to mosquitos TRUE  15 Whichprecursor to all Flavanoids chalcones 16 Chalconesconversion is the comital step TRUE 17 Flavanoids have 10 classes 20skeletons FALSE 18 chavaracteriad by link of Bringat pos 4 ofCring neoflavanoids flavanoid it p iii an 20 whichare charactericsofflavonal 21 Colours of anticyansdependsonPH True 22 Whichar characterics of chalcones notfoundin III is is Cringabsent phiorative 3 aggregate will havedifferentcolour TRUE 4 tanninscausedamage toinsectsby grindingdowntheirmandible