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

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 of Chemistry, Queens College & The Graduate Center of the City University of New York Spring 2010 ACS Meeting, San Francisco March 25, 2010

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

Formation of Gas-Phase RM Approach In Nature (marine aerosols) 2. Transfer of micelle- contained droplets to 1. Formation of the gas phase, 3. RM in the gas-phase, aerosol particles at evaporation of water maintaining encapsulated the sea surface minerals and small organics C. M. Dobson, G. B. Ellison, A. F. Tuck, V. Vaida. PNAS , 97 , 11864 (2000) In Laboratory RM in vacuo , encapsulating biomolecules Reverse micelle- contained droplets Transfer to the gas phase, Nano-electrospray removal of solvent, then ionization of exposure to the vacuum micelle solution Y. Fang, A. Bennett, J. Liu, Int J Mass Spectrom . , in press (2010)

Instrument: ESI Guided-Ion-Beam Tandem Mass Spectrometer Source Hexapole Quadrupole Octapole Ion Guide 2nd Quadrupole ESI Chamber Ion Guide Mass Filter & Scattering Cell Mass Filter & Detector 9.00 " 7.00 " 12.00 " 14.00 " 16.00 " 6.00 " 6.50 "

Part I Formation of Gas-Phase AOT RM & Encapsulation of Gly m/z 1000 1500 2000 2500 3000 3500 4000 ESI solution: 3 6 8 n=2 4 5 7 z=1 4 5 6 7 8 9 10 11 12 13 14 15 16 17 5 mM NaAOT in hexane, z=2  0 ([water]/[AOT]) = 10 8 9 10 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 11 z=3 21 22 32 33 34 35 14 15 16 17 18 19 20 23 24 25 26 27 28 29 30 31 [Similar spectrum was [(NaAOT) n Na z ] z+ z=4 obtained using 5 mM 28 34 35 20 21 22 23 24 25 26 27 29 30 31 32 33 39 40 41 42 43 44 36 37 38 z=5 NAOT in methanol/water] n=3 4 5 6 7 8 9 [(NaAOT) n H] + ESI solution: 3 14+G 21+4G 15+G 18+3G 3 3 17+2G 3 13+G 3 24+5G 3 2 16+G 3 20+3G 3 Same as above, except 17+G 3 23+G 23+4G 22+G 3 3 3 3 24+4G 19+2G 21+3G 3 18+2G 3 20+G 3 into which Gly was 3 3 20+2G 19+G 22+2G 18+G 3 16+2G 17+2G 3 3 23+2G 3 2 2 3 added ([Gly] = 1 mM) 23+3G 15+G 24+3G 3 14+G 2 3 2 21+2G [(NaAOT) n Na z Gly m ] z+ = n + mG 24+G 3 24+2G 3 21+G 3 z 3 16+G 17+G 2 2 1000 1500 2000 2500 3000 3500 4000 m/z

Size Dependence of Gas-Phase RM Encapsulation Aggregation number Core diameter Max. number of Gly  Evidence that Gly molecules are confined within n (nm) encapsulated in RM  NaAOT aggregates. n < 13 0 n  13 1.4 1 n  16 1.6 2 n  17 1.7 3 n  21 1.9 4 n  24 2.1 5    D n A / Core diameter: A is the area of the AOT polar head (0.52 nm 2 ) Size of Gly: 0.6-0.7 nm 6

Collision-Induced Dissociation (CID) Cross Section As a Function of E col Empty gas-phase RM Gas-phase RM encapsulating Gly  HS  20 n m 20+G 19+G   z [( NaAOT ) Gly Na ] n 3 3 3   1000 n m z 1000 z z [( NaAOT ) n Na ] z z 500 500 0 0 0 2 4 6 8 0 2 4 6 8  HS 19+G 17+G 17 19 3 2 2 3 1000 1000 1000 1000 500 500 500 500 0 0 0 0 0 2 4 6 0 2 4 6 8 0 2 4 6 0 2 4 6 8  HS 15+G 17+G 15 17 2 3 1000 1000 2 1000 1000 3  CID (? 2 )  CID (? 2 ) At highest E col ,  cid is 500 500 500 500 approaching the hard-sphere 0 0 0 0 0 2 4 6 0 2 4 6 8 collision limit  0 2 4 6 0 2 4 6 8 13+G 16+G 13 16 3 2 1000 1000 2 3 1000 1000 Another piece of evidence 500 500 that gas-phase AOT forms 500 500 spherical reverse micellar 0 0 0 0 0 2 4 6 0 2 4 6 8 0 2 4 6 0 2 4 6 8 structure E col E col E col E col

Part II Driving Forces for Solubilization: Electrostatic vs. Hydrophobic In Solution-Phase RM Hydrophilic biomolecule (e.g. Gly, TrpH + ) located in the internal core  electrostatic interaction Hydrophobic biomolecule (e.g. neutral Trp) located at the interface  hydrophobic interaction P. L. Luisi, M. Giomini, M. P. Pileni, B. H. Robinson, Biochimica et Biophysica Acta , 947, 209(1988)

Driving Force for Solubilization in Gas-Phase RM? 1500 2000 2500 3000 3500 4000 n=4 5 6 7 8 z =1 n=7 8 9 10 11 12 13 14 15 16 17 z =2 Top: n=10 11 12 13 14 16 17 19 26 15 18 20 21 22 23 24 25 z =3 17+2WH 16+WH 13+2WH RM occupied with n + mWH 15+2WH 3 3 2 11+2WH 14+2WH = 3 19+WH 18+WH 20+2WH z 14+WH 2 2 3 4 3 3 10+WH 10+2WH protonated TrpH + 13+WH z+ 2 [(NaAOT) n Na z-m TrpH m ] 11+WH 15+WH 2 2 16+WH 2 14+WH 2 12+WH 26+WH 2 2 2 9+WH 17+WH 4 2 17+WH 25+WH 2 15+WH 12+2WH 23+2WH 21+2WH 3 2 3 3 3 3 18+WH 3 14+2WH 20+WH 13+WH 3 3 3 22+WH 21+WH 18+2WH 3 24+WH 4 3 3 23+WH 3 12+WH 3 11+WH 3 14+W 10+W 3 2 26+W 15+W 12+W 3 15+W 3 2 14+W 2 17+W 23+W 2 Bottom: 2 3 21+W 13+W 25+W 3 22+W 17+W 2 20+W 3 3 3 24+W 18+W 3 16+W RM occupied with neutral 3 3 2 n + mW 11+W Trp (hydrophobic) = 19+W 2 z 3 z+ [(NaAOT) n Na z-m Trp m ] 16+W 3 1500 2000 2500 3000 3500 4000 m/z

Probing Guest Molecule Location Using CID: Encapsulation Inside vs. Attached to the Interface 17+W * * 17+WH 2 WH = TrpH + , 2 W = Trp, 17 protonated Trp neutral Trp 16+WH 2 8 16 ( ) 2 17 1 2 2 * 15+W * 15+WH 2 2 15 7 14 ( ) 2 2 1 14+WH 15 2 2 * 21+W * 21+WH 7 14 , 21 ( ) 12+WH 3 1 2 3 3 21 2 15+WH 13+WH 3 2 2 15 5 10 6 12 ( ) ( ) 8 16 20+WH ( ) 13 2 1 1 2 2 3 1 2 2 * 20+W * 20+WH 19+WH 3 3 3 12+WH 7 14 ( ) 20 2 1 2 14+WH 8 16 3 15 ( ) 6 12 13 20 ( ) 19 2 2 1 2 1 2 2 3 3 * 18+WH * 18+W 3 3 6 12 , 18 ( ) 1 2 3 12+WH 18 17+WH 11 2 3 3 2 13 13+WH 17 2 2 3 * * 17+W 17+WH 17 3 3 3 11+WH 2 17 16+WH 3 3 6 12 ( ) 11 5 10 , 15 16 1 2 ( ) 2 1 2 3 3 * 15+WH * 15+W 14+WH 3 3 3 15 9+WH 5 10 , 15 ( ) 3 2 1 2 3 14 6 12 9 11 ( 3 ) 1 2 2 2 2000 2500 3000 3500 4000 2000 2500 3000 3500 4000 m/z m/z

Part III Selectivity Between Two AAs Case (1): Aspartic Acid vs. Tryptophan 1500 2000 2500 3000 3500 4000 n=4 5 6 7 8 z =1 ESI of AOT/Asp n=7 8 9 10 11 12 13 14 15 16 17 z =2 n=10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 z =3 19+DH n + mDH 21+DH 3 = 3 z 14+DH 17+DH 16+DH z+ 12+DH 2 [(NaAOT) n Na z-m AspH m ] 13+DH 3 3 2 2 21+2DH 17+2DH 3 3 14+2DH 25+DH 18+DH 15+DH 2 3 3 3 20+DH 14+DH 13+DH 17+DH 3 23+DH 24+DH 3 3 2 3 22+DH 3 26+DH 11+DH 3 16+DH 12+DH 10+DH 11+DH 3 18+2DH 3 15+DH 2 2 3 2 3 2 23+2DH 24+2DH 15+2DH 3 3 3 11+WH 3 ESI of AOT/Asp+Trp 12+WH 3 11+2WH 23+WH 14+2WH 3 2 3 24+WH 18+2WH 21+WH 26+WH 3 22+WH 3 3 4 4 20+WH 14+2WH 3 2 18+WH 17+WH 3 13+WH 3 3 15+WH 17+WH 3 14+WH 16+WH 12+WH 13+WH 2 3 14+WH 2 11+WH 2 2 15+WH 2 2 2 18+WH 9+WH 4 2 10+WH 16+WH 12+2WH 17+2WH 13+2WH 23+2WH 2 2 3 2 21+2WH 3 3 3 15+2WH 3 n + mWH = 19+WH z 20+2WH 3 3 z+ [(NaAOT) n Na z-m TrpH m ] 10+2WH 2 1500 2000 2500 3000 3500 4000 m/z

Case (2): Arginine vs. Tryptophan 1500 2000 2500 3000 3500 4000 n=4 5 6 7 8 z =1 n=7 8 9 10 11 12 13 14 15 16 17 z =2 ESI of AOT/Arg n=10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 z =3 17+2RH 16+RH 15+RH 3 3 20+2RH 3 19+RH 3 n + mRH 18+RH 3 15+2RH = 17+RH 19+2AH 14+AH z 10+RH 3 3 3 3 2 2 z+ [(NaAOT) n Na z-m ArgH m ] 21+RH 24+RH 12+AH 25+RH 3 20+RH 21+2RH 3 16+2RH 2 3 3 3 3 16+RH 18+2AH 22+2RH 14+RH 2 3 3 3 23+RH 24+2RH 17+RH 13+RH 3 22+RH 3 2 3 3 23+2RH 3 12+RH 3 11+RH 3 ESI of AOT/Arg+Trp No changes when mixed with Trp ! Only Arg detected, no encapsulation of Trp

Fundamentals of Selectivity Aspartic acid (D) Tryptophan (W) Proline (P) Arginine (R) pK a of  -COOH 1.9 2.8 2.0 2.2 pK a of  -NH 3 + 9.6 9.4 10.6 9.0 pK a of acidic R 3.7 - - 12.5 pI 2.8 5.9 6.3 10.8 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 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)

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.

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