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

Reaction dynamics of small bio Reaction dynamics of small bio-

• molecular ions with

molecular ions with electronically excited singlet molecular oxygen electronically excited singlet molecular oxygen using guided using guided-

• ion beam scattering and direct

ion beam scattering and direct 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 1O2 in biological milieux & atmospheric chemistry

) ( O n faster tha times 10 fobidden,

• spin

not Q ) ( ) ( lived

• long

thus 1, ty multiplici has Q unless fobidden

• spin

) ( ) (

g 1 2 5 1 2 quenching 1 2 3 2 quenching 1 2

                   

  g g g g

O Q O Q O Q O

1O2

Air Environment:

1O2 can be produced under sunlight

and plays an important role in natural and polluted troposphere

1O2-mediated oxidation is one of major

sinks for amino acids loss in the troposphere, and accounts for one route of aerosol formation over remote marine area.

P.R. Ogilby, Chem. Soc. Rev. 2010, 39, 3181.

Biological systems: 1O2-mediated damage and cell death Calculated consumption of 1O2 by various cellular components with a typical leukocyte cell.

• M. Davies, Biochim. Biophys. Acta, 2005, 1703, 93

Study of 1O2-mediated oxidation in solution

Amino acids susceptible to 1O2-oxidation: Tyr, Met, Cys, Trp and His Experimental techniques used for most 1O2-oxidation studies:

Photo-sensitized oxidation in the presence of light and sensitizers in solution (since the discovery of photodynamic actions in 1900s) Other species (e.g. radicals via Type I process) may generate during photosensitization and contribute to reaction.

2 1 (TypeII) Transfer Energy 2 3

* * O sensitizer O sensitizer sensitizer sensitizer

h

            

4

Reaction dynamics of bio-molecular ions with 1O2 in the gas phase

Guided-ion beam techniques to investigate reactions of amino acid ions with an external clean source of 1O2, 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

+ 1O2

Experimental setup for biomolecular ions + 1O2

ESI source Hexapole ion guide Quadrupole mass filter Octopole ion guide & Scattering cell 2nd quadrupole mass filter & Detector

HV cell cell t reac B product rel

l P I T k I v k

tan

/   

ESI

Step 1. ESI generation of biomolecular ions

• 3. Mass-selected ions are guided into

an octopole surrounded by a collision cell, and scattered from 1O2 contained within.

• 4. Product ions are

mass analyzed & counted. 2: Ions are passed into a quadrupole for mass selection.

• Y. Fang and J. Liu, J Phys Chem A, 2009, 113, 11250

Micro-wave discharge Chemical 1O2 generator High yield, w/o O atom and O3 contaminants

• A. Midey, I. Dotan, J. Seeley and A. Viggiano, IJMS, 2009, 280, 6.

nm O O O O

g Emission g g e Disch Microwave

1270 ) ( ) ( ) (

3 2 1 2 1 2 1 arg 2 3

                



3O2/Ar

Evenson MW Cavity

1O2/Ar

Wood’s Horn Light Trap Emission Cell Optical Chopper TE-cooled InGaAs Detector

Generation and detection of 1O2

O H KCl O O KOH Cl O H

C 2 2 3 2 1 21 2 2 2

2 2 / 2 2        

 

• Y. Fang, F. Liu, A. Bennett, S. Ara and J. Liu, J Phys Chem B, 2011, 10.1021/jp11223yy

Collision Energy (eV)

1 2 3 1 2 3

Reaction Efficiency %

2 4 6 8 10

Cross Section (Å2)

TyrH+ + 1O2 [Tyr-H]+ + H2O2

• I. Reaction of protonated tyrosine with 1O2

Only one product channel is observed, corresponding to generation of H2O2 via transfer of two H atoms from TyrH+ to O2 (H2T). At low Ecol, the reaction shows strong inhibition by collision energy; At high Ecol, the reaction efficiency drops to 1% and starts to have contribution from a direct mechanism.

[TyrH]+ H2T

Potential energy (eV)

• 1.5
• 1.0
• 0.5

0.0

Reactants TyrH+ + 1O2 C1

TS1A TS2 TS1B

1A 2

HE6+ H2O2 HE5 + H2O2

C2

hydro- peroxide

TS 6 C6 TS 5 complex C5

HE3+H2O2

4

complex C3,C4 TS 3, 4

HE4 + H2O2

endo- peroxide 3

1B TyrH+ = complex C6

OH NH3+ COOH OH NH3+ HOOC O O

OH NH3+ HOOC O O OH NH3+ HOOC O O O NH3+ COOH OOH

O NH3+ COOH HOO OH N H2+ HOOC H H

O O OH NH3+ COOH OH NH2+ COOH

HE4 HE5 HE6 3 4 2 1A 1B HE3

OH CH NH3+ COOH H H O O NH3+ HOOC CO NH3+ HOOC CO

H2O2 elimination from hydroperoxide intermediates (75%)

Reaction coordinate and statistical modeling at low Ecol

Direct H2Transfer from backbone (25%) Formation of endoperoxide H = -1.11  -1.47 eV ( ETS = -1  -1.17eV )

• Intermediate complexes   10 ps, able to mediate

reactions at low Ecol.

• RRKM predicted H2T% close to experimental values,

i.e., 2-2.4% at Ecol = 0.1- 0.2 eV, 0.5 % at 0.5 eV.

 

    

   

J J k r J J k r

K J E E N K J E E E G h d J E k RRKM )] , ( [ )] , ( [ ) . (

Potential energy surface and statistical modeling at low Ecol

Potential energy (eV)

• 1.5
• 1.0
• 0.5

0.0

Reactants TyrH+ + 1O2 C1

TS1A TS2 TS1B

1A 2

HE6+ H2O2 HE5 + H2O2

C2

hydro- peroxide

TS 6 C6 TS 5 complex C5

HE3+H2O2

4

complex C3,C4 TS 3, 4

HE4 + H2O2

endo- peroxide 3

1B TyrH+ = complex C6

OH NH3+ COOH OH NH3+ HOOC O O

OH NH3+ HOOC O O OH NH3+ HOOC O O O NH3+ COOH OOH

O NH3+ COOH HOO OH N H2+ HOOC H H

O O OH NH3+ COOH OH NH2+ COOH

HE4 HE5 HE6 3 4 2 1A 1B HE3

OH CH NH3+ COOH H H O O NH3+ HOOC CO NH3+ HOOC CO

Formation of endoperoxide H = -1.11  -1.47 eV ( ETS = -1  -1.17eV )

• RRKM predicted formation of

endoperoxides overwhelms at low Ecol (> 90%). Their fate?

2 3 3 2 3 3 2 1 2 1

] [ ] [ O TyrH O TyrH O TyrH O TyrH         

         

 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

Direct dynamics trajectory simulations

A direct H2T trajectory

Trajectory Time (fs)

100 200 300 400

PE (Hartree)

• 779.60
• 779.55
• 779.50

*

Distance (Å)

2.0 4.0 6.0 8.0

t w

• r

C H b e i n g b r

• k

e n two new rOH being formed CM distance

* *

50 fs

H2T following formation of hydroperoxide

Trajectory Time (fs)

100 200 300 400 500

PE (Hartree)

• 779.60
• 779.55
• 779.50

CM distance (Å)

0.0 2.0 4.0 6.0 8.0 10.0

CM distance

Dependence on impact parameter & collision orientation

) ( ] ) ( ) ( [ ) ( 2

1 1 1

max min max

i i i b b i i i b

b b b b P b b P bdb b P       

   

 

  

Impact Parameter b (Å)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

P(b) x b

0.0 0.1 0.1 0.2

P(b)

0.00 0.05 0.10

H2T Endoperoxide Contribution of different mechanism vs. orientation dependence: 25% H2T via direct H2T  only in collisions where orientation allows simultaneous rupture of two C-H bonds in backbone while forming two O-H bonds in H2O2. 8% of collisions have “O2 in parallel to two H atoms being abstracted”, and 10% of those reactive. 75% H2T via decomposition of hydroperoxide  13% of collisions have “O2 close to the phenolic group”, and 30% eventually forms hydroperoxide.

• II. Reaction of protonated methionine with 1O2

Summary of photo-oxidation results Biological significance of Met oxidation

H C COO- CH2

+H3N 1O2

CH2 S CH3 H C COO- CH2

+H3N

CH2 S+ CH3 O O-

Path (a)

H C COO- CH2 H2N CH2 S+ CH3 O- + H2O2 H C COO- CH2 H2N CH2 S+ CH3 OOH .. + H2O2 CH NH S+ C H2 CH2 COO- H3C

OH-/water, pH > 9 Path (b) H+, 6< pH < 10 Path (c) Met, pH < 6

H C COO- CH2

+H3N

CH2 S+ CH3 O- x 2

Reaction cross section and efficiency

Collision Energy (eV)

0.0 0.5 1.0 1.5 0.1 1 10 100

Reaction Efficiency %

20 40 60 80 100

Cross Section (Å

2)

MetH+ + 1O2 [Met-H]+ + H2O2

H2T

Potential Energy Surface

Potential Energy (eV)

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 Reactants H_1 [Met-H]+ + H2O2 TS_H2

B3LYP/6-31+G*

precursor complex H_2 P_3 P_1 product-like complex P_2 TS_P12 TS_P13 MetH+ +1O2 Intermediates and TSs Products

2.28

1.64 1.50

Trajectory results for MetH+ + 1O2

At Ecol = 1.0 eV traj = 2.0 Å2 vs. exp =1.5 Å2

Impact Parameter b (Å)

1 2 3 4 5

P(b) x b

0.00 0.05 0.10 0.15

P(b)

0.00 0.05 0.10

Nature of dynamical bottleneck at Ecol = 1.0 eV Strong orientation-dependence:

20% collisions have favorable orientation at the time of collision, and less than half eventually lead to reaction.

33% 47% 20%

TyrH+ + 1O2 vs. MetH+ + 1O2

• Reaction efficiency of TyrH+ is significantly lower than that of MetH+, presumably due

to the formation of endoperoxides which eventually leads to physical quenching of

1O2.

• vs.
• Biological implication: locally produced 1O2 with a short lifetime converts to H2O2

that has a much longer lifetime and can diffuse to distant targets in biological systems.

Potential energy (eV)

• 1.5
• 1.0
• 0.5

0.0

Reactants TyrH+ + 1O2 C1

TS1A TS2 TS1B

1A 2 C2 complex

endo- peroxide

1B TyrH+ = complex

OH NH3+ COOH OH NH3+ HOOC O O OH NH3+ HOOC O O OH NH3+ HOOC O O O NH3+ COOH OOH

4 2 1A 1B

Potential Energy (eV)

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5 Reactants H_1 [Met-H]+ + H2O2 TS_H2

B3LYP/6-31+G*

precursor complex H_2 P_3 P_1 product-like complex P_2 TS_P12 TS_P13 MetH+ +1O2 Intermediates and TSs Products

2.28

1.64 1.50

• III. Reaction of protonated cysteine with 1O2
• Exothermic
• No activation barriers

above the reactants

Collision Energy (eV)

0.0 0.1 0.2 0.3 0.4 0.5 0.01 0.1 1 10

Reaction Efficiency %

0.01 0.1 1 10 100

Cross Section (Å

2)

CysH+ (m/z, 122) + 1O2 [H2NCHCOOH]+(m/z, 74) + ?

NO H2 elimination (m/z 120) was observed for CysH+ (m/z 122) + 1O2

Potential Energy (eV)

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5

Reactants

[Cys-H]+ + H2O2

B3LYP/6-31+G*

CysH++1O2

TS1 TS2

C

-C  bond breakage

H2O2 elimination

Hydroperoxide_2 P_2 P_1 Hydroperoxide_1 Weak complex TS3

[H2NCHCOOH]

+ m/z74

+ CH3SH +

1O2

Dissociative excitation transfer in CysH+ + 1O2

+

m/z 74

Potential Energy (eV)

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5

Reactants

[Cys-H]+ + H2O2

B3LYP/6-31+G*

CysH++1O2

TS1 TS2

C

-C  bond breakage

H2O2 elimination

Hydroperoxide_2 P_2 P_1 Hydroperoxide_1 Weak complex TS3

[H2NCHCOOH]

+ m/z74

+ CH3SH +

1O2

Dissociative excitation transfer in CysH+ + 1O2

[H2NCHCOOH]+ + CH3SH+ 3O2 Dissociative excitation transfer

+

0.98 eV

m/z 74

Previous report on dissociative excitation transfer: OH-(H2O) + 1O2 OH- + H2O+O2(X3g

• )
• A. Viggiano, et al. JCP, 2009, 131, 094303

Collision Energy (eV)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 10 20 30 40

Reaction Efficiency %

10 20 30 40

Cross Section (Å2)

TrpH

+ + 1O2

Side chain cation (m/z130) + H2NCH2COOH

Another example of dissociative excitation transfer: TrpH+ + 1O2 TrpH+

Potential Energy (eV)

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0

Reactants B3LYP/6-31+G* Dissociation w/o decay of 1O2

+ 3O2 + 1O2

Dissociative excitation transfer in TrpH+ + 1O2

0.98 eV C-C bond breakage

H(c-c  E*(1O2)

Conclusions

Protonated amino acids TyrH+ MetH+ CysH+ TrpH+ Most probable Intermediate complexes (L) Hydroperoxide (R) endoperoxide Hydroperoxide Hydroperoxide endoperoxide Reaction mechanisms, product ions and reaction efficiencies H2O2 eli. from hydro- peroxide < 3% H2O2 eli. from hydroperoxide > 84% Dissociative excitation transfer < 15% (spin-forbidden process) Dissociative excitation transfer < 25% (spin-forbidden process Other paths Endo- peroxides decay to reactants, quench 1O2 No physical quenching at low Ecol No H2O2 elimination or

• ther oxidation reactions
• bserved, due to high

TSs. No H2O2 elimination or

• ther oxidation reactions
• bserved.

25

Creating a biologically relevant gas-phase environment for bio-molecules

Gas-phase reverse micelles

Approach

• 1. Formation of

aerosol particles at the sea surface

• 3. RM in the gas-phase,

maintaining encapsulated minerals and small

• rganics
• 2. Transfer of micelle-

contained droplets to the gas phase, evaporation of water

In Nature

(marine aerosols)

• C. M. Dobson, G. B. Ellison, A. F. Tuck, V. Vaida. PNAS, 97, 11864 (2000)

In Laboratory

Nano-electrospray ionization of micelle solution

Reverse micelle- contained droplets

RM in vacuo, encapsulating biomolecules Transfer to the gas phase, removal of solvent, then exposure to the vacuum

m/z

1000 1500 2000 2500 3000 3500 4000

[(NaAOT)nNaz]Z+ z=2 z=3

4 6 5 7 8 9 10 11 13 12 14 15 16 17

z=4

n=2 3 4 5 6 8 7

z=5

4 5 6 7 8 9 8 9 10 11 12 13 14 15 16 17 23 18 19 21 24 25 26 22 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 20

14 15 16 17 18 19 21 20 22 23 24 25 26 27 28 29 30 31 32 33 34 35

z=1

[(NaAOT)nH]+

n=3

water attached to small aggregates

Multiply charged, gas- phase AOT reverse micelles, obtained by ESI of AOT solution. NaAOT:

bis(2-ethylhexyl) sulfosuccinate

Formation of gas-phase AOT reverse micelles, and encapsulation of biomolecules

• Y. Fang, A. Bennett and J. Liu, IJMS, 2010, 293,12;

PCCP, 2011, 13, 1466

m/z

1000 1500 2000 2500 3000 3500 4000

[(NaAOT)nNaz]Z+ z=2 z=3

4 6 5 7 8 9 10 11 13 12 14 15 16 17

z=4

n=2 3 4 5 6 8 7

z=5

4 5 6 7 8 9 8 9 10 11 12 13 14 15 16 17 23 18 19 21 24 25 26 22 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 20

14 15 16 17 18 19 21 20 22 23 24 25 26 27 28 29 30 31 32 33 34 35

z=1

[(NaAOT)nH]+

n=3

water attached to small aggregates

= 0, [(AOT)nNaz]z+ m/z

1000 1500 2000 2500 3000 3500 4000

26+P 3 26+2P 3 26+3P 3 17+P 2 25+P 3 24+P 3 24+2P 3 16+P 2 23+P 3 23+3P 3 23+2P 3 15+P 2 22+P 3 14+P 2 21+P 3 21+2P 3 20+P 3 20+2P 3 13+P 2 19+P 3 18+P 3 18+2P 3 12+P 2 17+2P 3 17+P 3 11+P 2 16+P 3 15+P 3 10+P 2 15+2P 3 18+P 4 18+2P 4 13+P 3 12+P 3 8+P 2 4+P 2 4+2P 2 5+P 2 5+2P 2 9+P 3 19+P 4 19+2P 4

small aggregates could be frgaments

• f large micelles

Multiply charged, gas- phase AOT reverse micelles, obtained by ESI of AOT solution. NaAOT:

bis(2-ethylhexyl) sulfosuccinate n + mP

z

= [(NaAOT)n Naz (Proline)m]z+

Proline:

Formation of gas-phase AOT reverse micelles, and encapsulation of biomolecules

Encapsulation of proline into the micellar internal core, indicated in shaded peaks as

• Y. Fang, A. Bennett and J. Liu, IJMS, 2010, 293,12;

PCCP, 2011, 13, 1466

29

Driving force for solubilization in gas-Phase RM?

1500 2000 2500 3000 3500 4000

z =2 n=7 8 9 10 11 13 12 14 15 16 17 n=4 5 6 8 7 n=10 11 12 13 14 15 16 17 23 18 19 21 24 25 26 22 20 z =1

14+WH 3 18+WH 3 12+WH 2 18+2WH 3

[(NaAOT)nNaz-mTrpHm]

z+

n + mWH z =

z =3

17+2WH 3 21+WH 3 14+WH 2 14+2WH 2 15+WH 2 23+WH 3 24+WH 3 16+WH 2 25+WH 3 17+WH 2 19+WH 3 11+WH 2 11+WH 3 12+WH 3 13+WH 3 18+WH 4 9+WH 2 14+2WH 3 15+WH 3 10+WH 2 15+2WH 3 16+WH 3 10+2WH 2 22+WH 4 17+WH 3 11+2WH 2 13+WH 2 13+2WH 2 20+2WH 3 21+2WH 3 23+2WH 3

m/z

1500 2000 2500 3000 3500 4000 [(NaAOT)nNaz-mTrpm]

z+

n + mW z =

14+W 3 17+W 3 12+W 2 18+W 3 15+W 3 10+W 2 11+W 2 20+W 3 13+W 2 21+W 3 14+W 2 22+W 3 15+W 2 23+W 3 24+W 3 16+W 2 25+W 3 17+W 2 26+W 3 19+W 3 16+W 3

20+WH 3 26+WH 4 12+2WH 2

Top: RM occupied with protonated TrpH+ (hydrophilic) Bottom: RM occupied with neutral Trp (hydrophilic)

Hydrophobic biomolecule (e.g. neutral Trp) located at the interface  hydrophobic interaction

In Solution-Phase RM

Hydrophilic biomolecule (e.g. Gly, TrpH+) located in the internal core  electrostatic interaction

• P. L. Luisi, M. Giomini, M. P. Pileni, B. H. Robinson, Biochimica et Biophysica Acta, 947, 209(1988)

Encapsulation in solution-phase reverse micelles

m/z

2000 2500 3000 3500 4000

17+WH 2 18+WH 3 15+WH 2 17+WH 3 15+WH 3

*

21+WH 3

* * * * *

20+WH 3

*

14+WH 2 14 2 7 1 14 2

( )

15 2 15+WH 2 8 1 5 1 10 2 ( ) 6 1 12 2 ( ) 12+WH 2 13 2 13+WH 2

20+WH 3

8 1 15 2 14+WH 2 7 1 14 2 ( ) 20 3 6 1 12 2 ( ) 12+WH 2 19 3 19+WH 3 17 2 16+WH 2 8 1 16 2 ( ) 12+WH 2 6 1 12 2 ( ) 17 3 17+WH 3 11 2 13 2 13+WH 2 6 1 12 2 ( ) 17 3 11+WH

2 11 2

16+WH 3 16 3 5 1 6 1 12 2 ( ) 11 2 5 1 10 2 ( ) 14+WH 3 14 3 9 2

m/z

2500 3000 3500 4000

17+W 2 18+W 3 17 2 15 2 15+W 2 17+W 3 15+W 3 15 3

*

21+W 3

* * * * *

20+W 3 20 3

*

18 3 21 3 17 3

a) b)

* precursor ions

15 3 ,

n+mWH z [(NaAOT)nNaz-mTrpHm]z+ n+mW z =[(NaAOT)nNazTrpm]z+ =

Structures of gas-phase reverse micelles

1500 2000 2500 3000 3500 4000

z =2 n=7 8 9 10 11 13 12 14 15 16 17 n=4 5 6 8 7 n=10 11 12 13 14 15 16 17 23 18 19 21 24 25 26 22 20 z =1

14+DH 3 18+DH 3 12+DH 2 18+2DH 3

[(NaAOT)nNaz-mAspHm]

z+

n + mDH z =

z =3

17+2DH 3 20+DH 3 21+DH 3 14+DH 2 21+2DH 3 23+DH 3 24+DH 3 16+DH 2 25+DH 3 17+DH 2 19+DH 3 11+DH 3 12+DH 3 13+DH 3 15+DH 3 10+DH 2 16+DH 3 11+DH 2 17+DH 3 13+DH 2 22+DH 3 23+2DH 3 15+2DH 3 14+2DH 2 15+DH 2 24+2DH 3 26+DH 3

ESI of AOT/Asp

m/z

1500 2000 2500 3000 3500 4000

14+WH 3 18+WH 3 12+WH 2 18+2WH 3

[(NaAOT)nNaz-mTrpHm]

z+

n + mWH z =

17+2WH 3 20+WH 3 21+WH 3

14+WH

2 14+2WH 2 15+WH 2 23+WH 3 24+WH 3 16+WH 2 17+WH 2 19+WH 3 11+WH 2 11+WH 3 12+WH 3 13+WH 3 18+WH

4

9+WH 2 14+2WH 3 15+WH 3 10+WH 2 15+2WH 3 16+WH 3 10+2WH 2 22+WH 4 17+WH 3 12+2WH 2 26+WH 4 13+WH 2 13+2WH 2 20+2WH 3 21+2WH 3 23+2WH 3 11+2WH 2

ESI of AOT/Asp+Trp

Selectivity between different amino acids

No changes when mixed with Trp ! Only Arg detected, no encapsulation of Trp

1500 2000 2500 3000 3500 4000

z =2 n=7 8 9 10 11 13 12 14 15 16 17 n=4 5 6 8 7 n=10 11 12 13 14 15 16 17 23 18 19 21 24 25 26 22 20 z =1

14+RH 3 18+RH 3 12+AH 2 18+2AH 3

[(NaAOT)nNaz-mArgHm]

z+

n + mRH z =

z =3

17+2RH 3 20+RH 3 21+RH 3 14+AH 2 19+RH 3 17+RH 3 11+RH 3 12+RH 3 13+RH 3 15+RH 3 15+2RH 3 16+RH 3 10+RH 2 16+2RH 3 19+2AH 3 21+2RH 3 20+2RH 3 22+RH 3 22+2RH 3 23+2RH 3 23+RH 3 24+RH 3 24+2RH 3 16+RH 2 17+RH 2 25+RH 3

ESI of AOT/Arg ESI of AOT/Arg+Trp

Selectivity between different amino acids

pH of ESI solution of AOT/(Trp+Asp) in methanol/water = 5.1 pH of ESI solution of AOT/(Trp+Arg) in methanol/water = 7.4 Aspartic acid (D) Tryptophan (W) Proline (P) Arginine (R) pKa of -COOH 1.9 2.8 2.0 2.2 pKa of -NH3

+

9.6 9.4 10.6 9.0 pKa of acidic R 3.7

• 12.5

pI 2.8 5.9 6.3 10.8

Transport selectivity between different AAs?

• Selectivity reflects a competition between electrostatic & hydrophobic forces, which can be

tuned up by changing the pH of ESI solution.

• Amino acid with a higher pI exists in protonated form and has a larger affinity with AOT-.

(i.e., Arg > Trp > Asp)

Fundamentals of selectivity

35

Conclusions

• Gas-phase NaAOT reverse micelles can act as nanometer-

sized vehicle for the selective transport of non-volatile biomolecules into the gas phase.

• Site locations and driving forces for solubilization in gas-

phase reverse micelles (.. more in Yigang Fang’s poster). Future Directions

• 1O2-mediated oxidation of bio-molecule encapsulated in gas-

phase gas phase

• Modeling of bio-molecule encapsulating gas-phase reverse

micellar structure and reactivity

36 36

Graduate Students Undergraduate Students

Yigang Fang Andrew Bennett Fangwei Liu William Pineros Fang He Kallol Mitra Shamim Ara Huixi Zhu Stacy Lindsay Yun Chen

Funding

Acknowledgements

CHE CAREER-0954507 48208-G6