JRA3: Cold and Complex (Biomolecular) Targets

Why study interaction of HCI with biomolecular targets?

• Basic physics: large energy transfer in a single collision!

• Applied physics: HCI as secondary products, e.g. in radiation therapy

Why “cold” targets?

• All molecules in one electronic (ground-) state

• Possibility of recoil momentum spectroscopy

Co-ordinators:

Thomas Schlathölter and Reinhard Morgenstern

Tasks and Volunteers

A. Solid biomolecular targets, CEA/Caen (Huber, Lebius)

B. Ionic biomolecular targets NUI/Maynoth (O’Neill, v.d. Burgt) QUB/Belfast

(Greenwood, Williams, McCullough, OUL/London (Mason),

KVI/Groningen (Schlathölter, Morgenstern)

C. Neutral gasphase biomolecular targets CUB/ Bratislava (Matejcik), OUL/London (Mason), UIBK/Innsbruck (Scheier, Märk), LCAR/Toulouse (Moretto

Capelle)

D. Ultracold neutral targets (nanodroplets, MOT’s) UBI/Bielefeld (Stienkemeier, Werner), OUL/London (Mason), KVI/Groningen (Schlathölter, Morgenstern)

E. Datareduction and analysis UBI/Bielefeld (Werner),

A. Solid biomolecular targets

In the case of a nucleic bases, a compressed powder is used as a 'solid' target, which can be bombarded with ions of different charges and energies, and at different incidence angles. Fragmentation spectra are analysed with mass-spectrometric methods.

DeOxyAdenosine

0

1000

2000

3000

0 40 80 120

= 5°

*10

cou

nts

0

100

200

300

0 40 80 120

= 0°

*10

mass/charge (a.u.)

50

100

150

0 40 80 120

= 10°

O2+

(40 keV) + thymidine

inset part magnified by a factor 10

Huber et al, Caen

Dependence of the fragmentation of thymidine on the incidence angle

(m=241)

B. Ionic biomolecular targets

Adaption of MALDI techniques

Desorption laser Desorption of

ions and neutrals

Laser

QUB arrangement to study neutral targets

Pulsed ion beam

the principle to get an ionic target

MALDIsample

(located in a trap endcap)

laser pulse

matrixbio

molecules

3rd or 4th harmonic of our Nd:YAG-laser (355 or 266 nm)

Quantel Brilliant

pulse length: ~5 ns frequency: 50 Hz

fluence: up to 200 mJ/cm2 @ 1064 nm.

MALDI and an electrostatic trap

trapping and cooling of desorbed ions

expandingplume

(neutrals and ions)

trapped ions as target for HCI/fs-laser pulses

ECRISor

fs-laser

YAG laser

trap Einzellens

MALDIsample

reflectron

detector

electrostatic analyzer

ions

TOF analysis by means of a FAST P7888 TDC (1ns resolution, 1ns deadtime, 1 GHz)

Several events per sweep: possibility of coincidence experiments

fields are switched off for MCI bunch passage!

measurement cycle1) laser desorbed ionic biomolecules are introduced from one electrode of the trap

trap/TOF tandem leads to high mass resolution which can be extended to high m/q values allowing for the study of

large biomolecules.

1) reflectron2,3)

3) the trapping potentials are switched of

2) ions are accumulated and cooled

4)

4) a pulse of MCI passes the trapping region through the ring electrode

6) ions pass a reflectron TOF spectrometer

5)

5) a dc pulse applied to the second end cap extracts molecular ions and fragments

C. Neutral gasphase bio-molecular targets

Target production via evaporation possible for DNA or RNA building bloks like thymine or uracil

Problem: Are the molecules in their electronic groundstate?

Approach for a solution: Check via reactions which are sensitive for electronic state

Example: H-loss or fragmentation in low energy attachment reactions

Electron attachment (Scheier, Märk)

Thymine

Uracil

0 1 2 3 40

1

2

3

4

Electron energy (eV)

Cro

ss s

ectio

n (1

0-20 m

2)

(×0.33)

Glycine

M + e‾ → (M-H)‾ + H

P. Scheier, T. Märk

D. Production and manipulation of ultracold targets

• Capture in magneto-optical traps (MOT’s)

• sympathetic cooling of molecules in a MOT

• Capture of biomolecules in He nano droplets

Ultra cold Na target in a Magneto Optical Trap (MOT)

near resonance laser light to trap and cool Na atoms:

•Load from background vapor•106 –107 Sodium atoms•sub mm size cloud•200-300 K (<30 neV!)

laser light + magnetic quadrupole field = MOT

P P-hn

red detuned light

Spontaneous emission

TOF and recoilspectroscopy of O6+ + Na collisions

-12 -10 -8 -6 -4 -2 0 2 40

10

20

30

40

50

60

70

80

90

100

110

tra

nsve

rsal

mo

me

ntu

m

longitudinal momentum-12 -10 -8 -6 -4 -2 0 2 40

10

20

30

40

50

60

70

80

90

100

110

tra

nsve

rsal

mo

me

ntu

m

longitudinal momentum

Na4+

-12 -10 -8 -6 -4 -2 0 2 40

10

20

30

40

50

60

70

80

90

100

110

tra

nsve

rsal

mo

me

ntu

m

longitudinal momentum

Na3+ Na2+

Apparatus for He nanodroplet studiesToennies et al , Physics Today, Feb. 2001, 31-37

Helium droplet beam Helium droplet beam machinemachine

Fakultät für PhysikFakultät für Physik

Formation of large molecular complexes in helium Formation of large molecular complexes in helium dropletsdroplets

0.00.20.40.60.81.0 (PTCDA)

n in helium droplets

Rel

. Fl

uore

scen

ce

0.0

0.2

0.4

0.6

0.8

1.0

Abs

orpt

ion

PTCDA on quartz

17000 19000 21000 23000 250000.0

0.2

0.4

0.6

0.8

1.0 PTCDA monomer spectrum

Rel

. Fl

uore

scen

ce

Wavenumber [cm-1]

Formation of large molecular complexes in helium Formation of large molecular complexes in helium dropletsdroplets

M. Wewer and F. Stienkemeier, Phys. Rev. A 37, 2002

Spectroscopy of excitonic transitions in PTCDA nanostructures at 380 Spectroscopy of excitonic transitions in PTCDA nanostructures at 380 mKmK

Laser induced fluorescence

spectrum of PTCDA

(a) in a nanodroplet (b) in the gasphase

F. Stienkemeier and A.F. VilesovJ. Chem. Phys.115 (2001) 10119

E. Data reduction and analysis

A non-trivial task!

High-dimensional parameter space! (up to 30-40 parameters per collision event)

Pattern recognition

Fitting procedures based on e.g. maximum entropy methods

2000

4000

6000

0 40 80 120

Xe20+ (400 keV)

Aq+

+ thymidine ( = 0°)

0

100

200

300

0 40 80 120

O2+ (40 keV)

mass/charge (a.u.)

cou

nts

Xe20+, 400 keV

O2+, 40 keV

Huber et al, Caen

NIM B 205 (2003) 666–670

Fragmentation of thymidine by ions with high and low

charge