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AVS 2007: selective biomolecular ion soft landing

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Biomolecular ions Soft-Landing on Surfaces with first observation of charge transfer

Biomolecular ions Soft-Landing on Surfaces with first observation of charge transfer

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  • 1. Biomolecular ions Soft-Landing on Surfaces: First Observation of Charge Loss and Desorption Kinetics Omar Hadjar J. H. Futrell, J. Laskin AVS Seattle 2007 Pacific Northwest National Laboratory, Environmental Molecular Sciences Laboratory, Richland, Washington
  • 2. Motivation mass-selected ions Soft-Landing (SL) Specific and prompt surface modification with minimum purification of amount of material material using ion deposition fundamental understanding of charge retention, charge loss, desorption kinetics
  • 3. Systems •Cyclic Gramicidin S (GS), M=1141 amu Left: view perpendicular to the plane of the ring, illustrating the peptide backbone structure. The antiparallel  -sheet region is stabilized by hydrogen bonds. Right: side-view, indicating the disposition in space of the hydrophobic Val and Leu residues (left) and the basic Orn (right) relative to the peptide ring. •Protonation state: 1, 2 •Soft Landing energy: 1 to 100 eV Terminal Group The Alkyl thiol based SAMs consist of three parts: namely, the thiol group (SH) which covalently bonds the two dimensional crystal to the Au by loss of a hydrogen atom, a spacer group (CH2)n defining the length of the molecule and (CH2)n the terminal group responsible for modified surface reactivity towards the soft landed ionic peptide. Used here are CF3 , CH3 and COOH terminal groups SH
  • 4. FT-ICR-SIMS Instrument Schematic +26V 20l/h of 0.1 +(2-3) kV C.Q. mM peptide +20V +20V Collision +15V 1 solution Electrospray energy C.L. 0V 0V 2 Ion Back -5V 10-1 Torr C.O. Funnel Trap + -30V -30V 3 surface Ring Front -45V -45V Trap Trap2 Trap1 Collision Quadrupole 1 5 2*10-2 Torr SIMS Ar Gas Conductance Limit 2 -250V Soft Landing line Ion Guide 4 5*10-5 Torr Resolving Quadrupole Back Front Trap Trap Gas cell Collision 3 6T Octopole Field 5*10-8 Torr Movable 7*10-10 Torr 8 keV Cs+ 8 Segments Ring Gun Surface for SIMS subsequent -V Soft Landing Electrostatic ICR Cell Flight Tube Ion Guide 4 40 by 40 mm cell 5
  • 5. Experiment Principles: Ion Deposition & Surface Analysis Au2SH+ Alternating exposure of the Au3+ surface to both beams Au3S+ Au2+ AuCF2+ 200 400 600 800 1000 1200 m/z real time SIMS during and after Soft-Landing (GS+2H)2+ 500 Ion Beam 400 8 keV 8 keV 300 Cs+ Cs+ 200 Surface peak: Au2SH+ ex situ 571.0 571.5 572.0 572.5 573.0 573.5 100 m/z TOF-SIMS 0 Line Scan (GS/2+H)+ (GS+H)+ 10 5 1.2 4 Au+ 1.0 10 0.8 (GS+2H)2+ TOF SIMS Signal 10 3 Peptide (GS+2H)2+ 0.6 PVO+ 0.4 10 2 (GS+Au)+ 0.2 1 Cs+ 0.0 10 200 400 600 800 1000 1200 0 50 100 150 200 250 300 350 400 450 500 550 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 m/z Time (min) Line Scan (mm)
  • 6. Kinetics of Peptide related peaks after S.L. 0.08 0.24 0.07 70 0.12 115 0.21 169 0.03 192 0.03 233 0.06 0.10 0.18 0.05 0.08 0.15 0.04 0.06 0.12 0.02 0.02 (LF-28)+ 0.03 0.09 0.04 0.01 0.01 0.02 0.06 0.02 0.01 0.00 P+ 0.00 O+ 0.03 0.00 (PV-28)+ 0.00 0.00 0 100 200 300 400 500 0 100 200 300 400 500 0 100 200 300 400 500 0 100 200 300 400 500 0 100 200 300 400 500 time (min) time (min) time (min) time (min) time (min) 0.12 0.08 0.07 261 0.8 311 0.10 429 0.04 441 0.4 457 0.06 0.08 0.03 0.6 0.3 0.05 0.04 LF+ 0.4 0.06 0.02 (FPVO-NH3)+ 0.2 0.03 0.04 0.02 0.2 0.01 0.1 0.02 0.01 0.00 0.0 PVO+ 0.00 (LFPV-28)+ 0.00 (LFPV)+ 0.0 0 100 200 300 400 500 0 100 200 300 400 500 0 100 200 300 400 500 0 100 200 300 400 500 0 100 200 300 400 500 time (min) time (min) time (min) time (min) time (min) 0.08 6 1.4 1.2 571.5 1.2 572 0.07 813 5 1142 0.30 1338 1.0 0.06 0.25 1.0 0.05 4 0.8 0.20 0.8 0.04 3 0.6 0.15 0.6 0.03 0.4 2 0.10 0.4 0.2 (0GS/2)+ 0.2 1GS2+ 0.02 0.01 1 GS+ 0.05 (GS+Au)+ 0.0 0.0 0.00 0 0.00 0 100 200 300 400 500 0 100 200 300 400 500 0 100 200 300 400 500 0 100 200 300 400 500 0 100 200 300 400 500 time (min) time (min) time (min) time (min) time (min)
  • 7. Kinetics Model during and after S.L. A* = SA A +FIB B B* = SB B + FIC C C’ = SC C A* B* C’ SIMS Fragments Population z=2 FIB z=1 FIC from neutrals k2 k4 k5 R A charge loss B charge loss C Surface z=2 k1 z=1 k3 z=0 Population S.L. induced sudden charge loss FB FC and neutralization dA/dt = -(k1+k2)A + R dB/dt = -(k3+k4)B + k1A + FBR dC/dt = -k5C + k3B + FCR
  • 8. Experimental Results & Kinetics Model Fit Charge 0.9 Best simultaneous fit Reduction: Desorption: of the three populations (min-1) (min-1) 0.6 (GS+2H)2+ k1 ~ 10-2 k2  10-4 0.3 0.0 0 100 200 300 400 500 600 3 2 FT-ICR-SIMS signal (arb. units) 1 (GS+H)+ k3 ~ 2*10-5 k4 ~ 6*10-4 0 0 100 200 300 400 500 600 0.4 End of S.L. 0.2 GS0 k5 ~ 10-3 Time (min) 0.0 0 100 200 300 400 500 600
  • 9. Surface Effect on Charge Retention PVO+ GS+ m/z=311 m/z=1141 0.30 (GS/2)+ GS+ PVO+ 100 m/z=571 m/z=1141 FT-ICR-SIMS signal m/z=311 COOHSAM GS+/PVO+ 50 4 571 572 573 574 1.0 3 2 0 0.5 300 400 500 600 700 800 900 1000 1100 1 m/z 0.0 0 (GS/2)+ 1.5 100 m/z=571 1.11 0.9 HSAM 1.0 0.6 50 571 572 573 574 0.5 0.3 0.0 0.0 0 6 0.9 300 400 500 600 700 800 900 1000 1100 m/z FSAM 4 0.6 900 (GS/2)+ m/z=571 2 0.3 GS2+ 600 0 0.0 0 100 200 300 400 500 600 571 572 573 574 300 6.26 Time (min) t0= end of 0 300 400 500 600 700 800 900 1000 1100 m/z Soft-Landing Snapshot @ t0
  • 10. Effect of the Charge State on the Kinetics 180 160 GS2+ 100 GS+ 140 80 120 100 60 80 40 60 40 20 20 200 400 600 800 1000 1200 1400 200 400 600 800 1000 1200 1400 m/z m/z 0 100 200 300 400 500 600 700 FT-ICR-SIMS (normalized GS signal) 3.0 2.5 GS2+ vs 1+ S.L. + 2.5 2.0 2.0 1.5 1.5 1.0 1.0 GS1+ SIMS 0.5 t0 end of soft 0.5 Landing 0.0 0.0 -100 0 100 200 300 400 500 600 Time (min)
  • 11. Conclusion ♣ S.L.-SIMS: New tool for fundamental understanding of ion-surface interactions ♣ First observation of charge loss & desorption of soft landed ions in real time ♣ Excellent agreement between experiments & a simple kinetic model ♣ First experimental values of rate constants produced What have we learned: ♣ Proton loss governs GS2+ signal decay ♣ Desorption governs GS+ signal decay ♣ Sudden neutralization governs GS0 formation ♣ FSAM retains more charges than H & COOH-SAM
  • 12. Thanks: Julia Laskin Peng Wang Zhibo Yang • Chemical Sciences Division (CSD) • Office of Basic Energy Sciences (BES) of the US Department of Energy. • Laboratory Directed Research and Development (LDRD) Program at PNNL.

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