Reaction dynamics of small bio- -molecular ions with molecular ions - PowerPoint PPT Presentation

Reaction dynamics of small bio- -molecular ions with molecular ions with Reaction dynamics of small bio electronically excited singlet molecular oxygen electronically excited singlet molecular oxygen using guided- -ion beam scattering and direct ion beam scattering and direct using guided dynamics simulations dynamics simulations Jianbo Liu Department of Chemistry & Biochemistry Queens College and the Graduate Center of The City University of New York Gordon Research Conference on Gaseous Ions Galveston, TX, 02/27/-03/042011

Significance of 1 O 2 in biological milieux & atmospheric chemistry 1 O 2  1    quenching     3   ( ) ( ) O Q O Q 2 2 g g  spin - fobidden unless Q has multiplici ty 1, thus long - lived     quenching       ( 1 ) ( 1 ) Q O Q O 2 2 g g  not spin - fobidden, 10 5 times faster tha n O ( 1 ) 2 g Biological systems : 1 O 2 -mediated Air Environment : damage and cell death 1 O 2 can be produced under sunlight and plays an important role in natural and polluted troposphere 1 O 2 -mediated oxidation is one of major sinks for amino acids loss in the troposphere, and accounts for one Calculated consumption of 1 O 2 by route of aerosol formation over remote various cellular components with a marine area. typical leukocyte cell. P.R. Ogilby, Chem. Soc. Rev. 2010 , 39, 3181. M. Davies, Biochim. Biophys. Acta , 2005 , 1703, 93

Study of 1 O 2 -mediated oxidation in solution Amino acids susceptible to 1 O 2 -oxidation: Tyr, Met, Cys, Trp and His Experimental techniques used for most 1 O 2 -oxidation studies: Photo-sensitized oxidation in the presence of light and sensitizers in solution ( since the discovery of photodynamic actions in 1900s )    * h sensitizer sensitizer  3  Energy   Transfer   (TypeII)     1 * sensitizer O sensitizer O 2 2 Other species (e.g. radicals via Type I process) may generate during photosensitization and contribute to reaction.

Reaction dynamics of bio-molecular ions with 1 O 2 in the gas phase Guided-ion beam techniques to investigate reactions of amino acid ions with an external clean source of 1 O 2 , + 1 O 2 aimed at achieving a molecular level understanding of reaction mechanisms  Reaction thermochemistry & energy dependence ( guided-ion beam scattering )  Effects of hydration and charge ( electrospray ionization )  Benchmark systems for quantum chemistry and dynamics simulations In conjunction with solution-phase study  Revealing intrinsic properties of biomolecules  Biogenesis  Better understanding of intrinsic vs. external imposed properties in biological systems 4

Experimental setup for biomolecular ions + 1 O 2 2 : Ions are passed into a quadrupole for Step 1. ESI mass selection. I k T    / product B generation of k v rel I P l tan reac t cell cell biomolecular ions Hexapole Quadrupole Octopole ion guide 2nd quadrupole ESI source ion guide mass filter & Scattering cell mass filter & Detector ESI HV 3. Mass-selected ions are guided into 4. Product ions are an octopole surrounded by a collision mass analyzed & cell, and scattered from 1 O 2 contained counted. within. Y. Fang and J. Liu, J Phys Chem A, 2009, 113 , 11250

Generation and detection of 1 O 2 Micro-wave discharge Optical TE-cooled InGaAs Chopper 3 O 2 /Ar Detector          3 arg 1 1 ( ) Microwave Disch e O O Emission Cell 2 2 g          1 3 ( ) ( ) 1270 Emission O O nm 2 2 g g Evenson 1 O 2 /Ar MW Cavity Wood’s Horn Light Trap Chemical 1 O 2 generator        21  1 3   2 2 / 2 2 C H O Cl KOH O O KCl H O 2 2 2 2 2 2 High yield, w/o O atom and O 3 contaminants A. Midey, I. Dotan, J. Seeley and A. Viggiano, IJMS , 2009, 280 , 6. Y. Fang, F. Liu, A. Bennett, S. Ara and J. Liu, J Phys Chem B , 2011, 10.1021/jp11223yy

I. Reaction of protonated tyrosine with 1 O 2 3 10 TyrH + + 1 O 2 [Tyr-H] + + H 2 O 2 Reaction Efficiency % Cross Section ( Å 2 ) 8 2 6 H2T 4 1 2 [TyrH] + 0 0 0 1 2 3 Collision Energy (eV) Only one product channel is observed, corresponding to generation of H 2 O 2 via transfer of two H atoms from TyrH + to O 2 ( H2T ). At low E col , the reaction shows strong inhibition by collision energy; At high E col , the reaction efficiency drops to 1% and starts to have contribution from a direct mechanism.

Reaction coordinate and statistical modeling at low E col Direct O H2T ransfer from HOOC O Reactants COOH H O COOH TS 5 O backbone (25%) H H TyrH + + 1 O 2 H N NH 3 + H 2 + CH 0.0 NH 3 + TyrH + = TS 6 TS 3, 4 HOOC OH C6 complex OH NH 3 + Potential energy (eV) C5 OH -0.5 C6 COOH HE3+H2O2 O O NH 2 + HE4 + complex C3,C4 H 2 O 2 1B endo- OH peroxide COOH TS1A hydro- -1.0 complex peroxide TS1B NH 3 + HOOC 1B C1 HE5 OH NH 3 + 3 TS2 C2 1A HE5 + COOH H 2 O 2 HOOC HOO O 3 4 NH 3 + O NH 3 + O 2 COOH NH 3 + HE6+ -1.5 HOOC 1A NH 3 + NH 3 + H 2 O 2 OH HOOC O O OOH 4 2 O OH Formation of endoperoxide H2O2 elimination HE6  H = -1.11  -1.47 eV HE3 HE4 CO OH CO from hydroperoxide ( E TS = -1  -1.17eV ) intermediates (75%) RRKM Intermediate complexes   10 ps, able to mediate  J  reactions at low E col .    [ ( , )] G E E E J K 0 r d    ( . ) k J k E J  RRKM predicted H2T% close to experimental values, J  h  [ ( , )] N E E J K i.e., 2-2.4% at E col = 0.1- 0.2 eV, 0.5 % at 0.5 eV. r   k J

Potential energy surface and statistical modeling at low E col O HOOC O Reactants COOH H O COOH TS 5 O H H TyrH + + 1 O 2 H N NH 3 + H 2 + CH 0.0 NH 3 +  RRKM predicted formation of TyrH + = TS 6 endoperoxides overwhelms at low TS 3, 4 HOOC OH C6 E col (> 90%). complex OH NH 3 + Potential energy (eV) C5 OH -0.5 Their fate? C6 COOH HE3+H2O2 O O NH 2 + HE4 + complex C3,C4 H 2 O 2 1B endo- OH peroxide COOH TS1A hydro- -1.0 complex        1 peroxide    1  TS1B NH 3 + [ ] HOOC 1B C1 TyrH O TyrH O HE5 OH 2 2 NH 3 + 3 TS2 C2 1A HE5 +   COOH       3 3 3 3 [ ] H 2 O 2 HOOC HOO TyrH O TyrH O O 3 4 2 2 NH 3 + O NH 3 + O 2 COOH NH 3 + HE6+ -1.5 HOOC 1A NH 3 + NH 3 + H 2 O 2 OH HOOC O O OOH 4 2 O OH Formation of endoperoxide HE6  H = -1.11  -1.47 eV HE3 HE4 CO OH CO ( E TS = -1  -1.17eV )

Direct dynamics trajectory simulations  Based on Born-Oppenheimer approach  Trajectory initial conditions generated using Hase’s Venus (representing experimental conditions) batches of trajectories (125 each) at b = 0.1, 0.5, 1.0,1.5,2.0,2.5,3.0, and 4.0 Å  Trajectory integration using G03 - B3LYP/6-21G  Linux-based computer cluster

A direct H2T trajectory two new rOH being formed 400 n e k o r b g Trajectory Time (fs) n i e 300 b H C CM distance r o w t 200 * * * 100 50 fs 0 8.0 6.0 4.0 2.0 -779.50 -779.55 -779.60 Distance ( Å ) PE (Hartree)

H2T following formation of hydroperoxide 10.0 CM distance -779.50 8.0 CM distance ( Å ) PE (Hartree) 6.0 -779.55 4.0 2.0 -779.60 0.0 0 100 200 300 400 500 Trajectory Time (fs)

Dependence on impact parameter & collision orientation H2T  b    max 2 ( ) 0.10 P b bdb Endoperoxide 0 b max         [ ( ) ( ) ] ( ) P b b P b b b b    1 1 1 i i i i i i P(b)  0 b min 0.05 Contribution of different mechanism vs. orientation dependence: 25% H2T via direct H2T 0.00  only in collisions where orientation allows 0.2 simultaneous rupture of two C-H bonds in backbone while forming two O-H bonds in H 2 O 2 . P(b) x b 0.1 8% of collisions have “O 2 in parallel to two H atoms being abstracted”, and 10% of those reactive. 0.1 75% H2T via decomposition of hydroperoxide  13% of collisions have “O 2 close to the phenolic 0.0 group”, and 30% eventually forms hydroperoxide. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Impact Parameter b ( Å )

II. Reaction of protonated methionine with 1 O 2 Summary of photo-oxidation results Biological significance of Met oxidation H COO - H 2 N C CH 2 OH - /water, pH > 9 CH 2 + H 2 O 2 Path (a) S + O - CH 3 H H + H 3 N COO - COO - + H 3 N C COO - C H C COO - H 2 N .. NH CH H + , 6< pH < 10 CH 2 CH 2 + H 2 O 2 CH 2 S + CH 2 Path (b) 1 O 2 CH 2 CH 2 H 3 C C CH 2 H 2 S + O - O S S + OOH CH 3 CH 3 CH 3 Met, pH < 6 H + H 3 N COO - C Path (c) CH 2 x 2 CH 2 S + O - CH 3

Reaction Efficiency % Reaction cross section and efficiency 100 80 60 40 20 0 1.5 MetH + + 1 O 2 [Met-H] + + H 2 O 2 Collision Energy (eV) 1.0 H2T 0.5 0.0 100 10 1 0.1 2 ) Cross Section ( Å

Potential Energy Surface TS_P12 Reactants Intermediates and TSs Products MetH + + 1 O 2 [Met-H] + + H 2 O 2 1.0 Potential Energy (eV) 0.5 0.0 TS_P13 precursor -0.5 1.50 complex P_1 TS_H2 P_2 product-like -1.0 1.64 H_1 complex 2.28 H_2 -1.5 P_3 B3LYP/6-31+G*