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Formation, Characterization, and Application Formation, - - PowerPoint PPT Presentation

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Formation, Characterization, and Application Formation, Characterization, and Application of Gas- -Phase, Multiply Charged Reverse Phase, Multiply Charged Reverse of Gas Micelles Micelles Jianbo Liu*, Yigang Fang, William Pineors Department

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SLIDE 1

Formation, Characterization, and Application Formation, Characterization, and Application

  • f Gas
  • f Gas-
  • Phase, Multiply Charged Reverse

Phase, Multiply Charged Reverse Micelles Micelles

Jianbo Liu*, Yigang Fang, William Pineors

Department of Chemistry, Queens College & The Graduate Center of the City University of New York

Spring 2010 ACS Meeting, San Francisco March 25, 2010

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SLIDE 2

Reverse Micelles (RMs)

One of the most interesting nanometer- sized structures  selective encapsulation/solubilization  catalysis  membrane-mimetic system NaAOT, sodium bis(2-ethylhexyl) sulfosuccinate, a surfactant molecule commonly used for making RMs

Na+

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SLIDE 3

Formation of Gas-Phase RM

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

  • Y. Fang, A. Bennett, J. Liu, Int J Mass Spectrom. , in press (2010)
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SLIDE 4

Instrument: ESI Guided-Ion-Beam Tandem Mass Spectrometer

Source Chamber 9.00 " Hexapole Ion Guide 7.00 " Quadrupole Mass Filter 12.00 " Octapole Ion Guide & Scattering Cell 14.00 " 2nd Quadrupole Mass Filter & Detector 16.00 " 6.00 " 6.50 " ESI

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SLIDE 5

m/z

1000 1500 2000 2500 3000 3500 4000

ESI solution: Same as above, except into which Gly was added ([Gly] = 1 mM)

14+G 3 15+G 3

16+G 3

17+G 3

17+2G 3

18+G 3

18+2G 3 19+G 3

19+2G 3

13+G 2 20+G 3 20+2G

3

20+3G 3

21+G 3 14+G 2 21+2G 3

21+3G 3

21+4G 3

15+G 2

23+G 3 23+2G 3 23+3G 3 23+4G 3

16+G 2 16+2G 2

24+4G 3 24+5G 3

24+3G 3

24+G 3

24+2G 3

17+G 2 17+2G 2

22+G 3 22+2G 3

3 18+3G 3

[(NaAOT)nNazGlym]z+ = n + mG z

Part I Formation of Gas-Phase AOT RM & Encapsulation of Gly

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

ESI solution: 5 mM NaAOT in hexane, 0 ([water]/[AOT]) = 10 [Similar spectrum was

  • btained using 5 mM

NAOT in methanol/water]

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SLIDE 6

Size Dependence of Gas-Phase RM Encapsulation

6

 Evidence that Gly molecules are confined within

NaAOT aggregates.

2.1 1.9 1.7 1.6 1.4  Core diameter (nm) Aggregation number n

  • Max. number of Gly

encapsulated in RM n < 13 n  13 1 n  16 2 n  17 3 n  21 4 n  24 5 Core diameter: A is the area of the AOT polar head (0.52 nm2) Size of Gly: 0.6-0.7 nm

 / A n D  

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SLIDE 7

2 4 6 500 1000 2 4 6

CID (? 2)

500 1000

Ecol

2 4 6 500 1000 2 4 6 8 500 1000 2 4 6 8 500 1000

Ecol

2 4 6 8 500 1000

19+G 3 19+G 3 15+G 2 16+G 3 17+G 2

2 4 6 8 500 1000

17+G 3 20+G 3 13+G 2

2 4 6 500 1000 2 4 6

CID (? 2)

500 1000

Ecol

2 4 6 500 1000 2 4 6 8 500 1000 2 4 6 8 500 1000

Ecol

2 4 6 8 500 1000

19 3 17 3 13 2 16 3 17 2 15 2

2 4 6 8 500 1000

20 3

Collision-Induced Dissociation (CID) Cross Section As a Function of Ecol

Empty gas-phase RM

z z n Na

NaAOT z n ] ) [(

Gas-phase RM encapsulating Gly

 

z z m n

Na Gly NaAOT z m n ] ) [(

At highest Ecol, cid is approaching the hard-sphere collision limit  Another piece of evidence that gas-phase AOT forms spherical reverse micellar structure

HS HS HS

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SLIDE 8

Part II Driving Forces for Solubilization: Electrostatic vs. Hydrophobic

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)
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SLIDE 9

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+ Bottom: RM occupied with neutral Trp (hydrophobic)

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SLIDE 10

Probing Guest Molecule Location Using CID: Encapsulation Inside vs. Attached to the Interface

m/z

2000 2500 3000 3500 4000

17+WH 2 18+WH 3

15 2

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

*

21+WH 3

* * * * *

20+WH 3

*

14+WH 2 7 1 14 2

( )

7 1 14 2

( ) ,21

3 15 2 15+WH 2 8 1 16 2

( )

5 1 10 2

( )

6 1 12 2

( )

12+WH 2

13 2 13+WH 2 20+WH 3 8 1 16 2

( )

15 2 14+WH 2 7 1 14 2

( )

20 3 13 2 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

( )

,18

3 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 10 2

( )

,15

3 6 1 12 2

( )

11 2 5 1 10 2

( )

,15

3 14+WH 3 14 3 9 2 9+WH 2

m/z

2000 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

WH = TrpH+, protonated Trp W = Trp, neutral Trp

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SLIDE 11

Part III Selectivity Between Two AAs Case (1): Aspartic Acid vs. Tryptophan

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

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 ESI of AOT/Asp

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SLIDE 12

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

Case (2): Arginine vs. Tryptophan

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

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SLIDE 13

Fundamentals of Selectivity

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 6.3

  • 10.6

2.0 Proline (P) 2.8 3.7 9.6 1.9 Aspartic acid (D) 12.5

  • pKa of acidic R

5.9 9.4 2.8 Tryptophan (W) 9.0 pKa of -NH3

+

10.8 pI 2.2 pKa of -COOH Arginine (R)

Selectivity between different AAs?

  • Selectivity reflects a competition between electrostatic and 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)

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SLIDE 14

Conclusions

 NaAOT surfactants are able to form RM in the gas phase.  Gas-phase RM can act as nanometer-sized vehicle for selective transport of non-volatile biomolecules into the gas phase.  Driving force for solubilization: electrostatic & hydrophobic interactions. Application in Analytical Chemistry: Separation and Direct Determination of ionic and neutral amino acids in solution.

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SLIDE 15

Acknowledgements Acknowledgements

$$ ACS-PRF Grant CUNY Collaboration Grant QC Research Enhancement Funds