beta-NMR:
from nuclear physics to biology
University of Copenhagen

CERN

KU Leuven
M. Stachura, L. Hemmingsen

D. Yordanov

M. Bissell, G. Neyens

University of Mainz

MPIK Heidelberg

R. Neugart

Free University Berlin

University of Saarland

A. Gottberg

K. Johnston

K. Blaum

Magdalena Kowalska
CERN, PH-DeptOutline
NMR in nuclear physics and biology
Metal ions in biology
Ultra-sensitive beta-NMR
Methods of spin polarization
Challenge of beta-NMR in liquids
Proof-of-principle experiment
Outlook and summary

2

NMR in nuclear physics
Observable: Larmor frequency (for different nuclei in one host)
Determined properties:
 Precise values of electromagnetic moments of ground- and metastable-states of stable
nuclei and radio-nuclides (magnetic dipole and electric quadrupole moment): When combined with hyperfine structure determination =>direct measurement of nuclear spinI  gI  I  N

1
Emag  g I   N  B  Q  Vzz
2Electric field
gradient (in noncubic host lattice)(static) external
magnetic fieldB0B0Derived information: comparison to nuclear models
 I: determination on the orbits occupied by valence protons and neutrons Q: determination of nuclear deformation
3

NMR in (chemistry and) biology
Most versatile method to study structure and dynamics of molecules in solution
Observables: chemical shift (Larmor frequency) and relaxation times indifferent hosts
Determined properties
 local electronic environment (i.e. number and type of coordinating groups)
Same B, different shielding by hostDepends on environment

1
Emag  g I   N  B  Q  Vzz
2knownB0B0  B' B0  B' 'Derived information: comparison to quantum-chemical models (e.g DFT) kinetics and dynamics and ligand binding of the metal ions and biomolecules
 3D structure of proteins and protein-metal complexes
4

NMR and role of metal ions in biology
Role of metal ions in human body depends on adopted coordination
environment
Zn(II), Cu(I), Mg(II): among most abundant cations in living organisms; rightconcentration is crucial for correct functioning of cellular processes Mg: active in RNA- and DNA-processing enzymes and ribozymes Cu: present in many enzymes involved in electron transfer and activation of oxygen Zn: 2nd most abundant trace element in human body; catalytic and structural role,involved in regulation of genetic message transcription and translation

Challenges:
 closed electron shells, thus invisible in many methods;
 in NMR: almost invisible signals due to small abundance, I>1/2, and small sensitivity(due to small magnetic moment)

Common features with NMR in nuclear physics:
 Probe nuclei of interest are rare and give weak signals

Sensitivity of conventional NMR is very (or even too) low, so it has to be enhanced=> ultra-sensitive NMR approaches needed, e.g. beta-detected NMR
5

Beta-(detected) NMR
B

Weak interaction doesn’t conserve parity
 Anisotropic emission of beta particles from decay ofpolarized nuclei
 NMR resonance: destruction of asymmetry,observed as decrease in beta-decay asymmetry+b+++++++

Angular distribution of beta-radiation:
Velocity of beta-particle (v/c close to 1)

1Angle between beta-particle
emission and direction of spinpolarizationv IzD(Θ)  1  acos(Θ)
c I
Asymmetry factor (-1,1),
depends on details of beta decay

0.50°0- 0.5- 1PI (0-100%): degree of spin polarization

Measured b-decay asymmetry: A 

0N (0)  N (180)N  N2
 1
N1  N 2
N (0)  N (180)

0.5

11.5

Conventional versus beta-NMR
Conventional NMR

Beta-NMR

Polarization• << 1%: Created inside sample: • 1%-100%: Created outside sample:(thermal occupation of levels(e.g. laser excitation)
in NMR magnetic field)Detection• << 100% detection efficiency:
Change of magnetization• Up to 100% efficiency:
Anisotropy of beta decay

Probenuclei• Stable or long-lived: 1H, 13C…
• Need ~1017 in the sample• Radioactive; 8Li, 11Be, 31Mg, …
• 107 per resonanceSamplesLiquids, solids

Solids (until 2012)10 orders of magnitude higher sensitivity than conventional NMR
Dozens of different (radioactive) probe nuclei

Beta-NMR: spin polarization
Spin polarization to obtain large population differences: Production mechanism -> versatile, but only at fragmentation facilities, low polarizations
 Low temperature (subK) -> cannot perform studies on liquids
 Passage via titled foils -> versatile, but so far low polarizations, work under way Optical pumping -> dependent on laser scheme available, but high polarizations

Techniques available at ISOLDE-CERN:
Tilted-foils
behind REX-ISOLDE

VITO (inpreparation)

COLLAPSNICOLE8

Towards beta-NMR in biology: in practice
Simple idea:
Radioactive beamfacility(e.g. ISOLDE)

Ion
beam

Experimental setup forspin polarization

Polarizedbeam

NMR magnet andchamber withliquid sample

Big challenge: radioactive beams like high vacuum; most liquids – don’t
10-6 mbar

Ion
beam

10-5 – 10-6 mbar

Polarized
beam

Water: 1-10 mbar
Glycerol: 10-2mbar

Suggested solution:
Radioactive beamfacility

Optical pumping(well tested, highpolarization) 99

Differentialpumping

NMR magnet andchamber withliquid sample

Mg isotopes: good starting points
Some history: M. Kowalska, talk at ENAM 2004 on:First measurement of spins and moments of 29,31Mg - my PhD thesis:
 G. Neyens, M. Kowalska, D. Yordanov et al., Phys. Rev. Lett. 94, 022501 (2005)
 M. Kowalska, D. Yordanov et al, Phys. Rev. C 77, 034307 (2008)
10Experimental setup at the time
COLLAPS setup for collinear laser spectroscopy
at ISOLDE
Crystal host lattice

Magnet pole

HVLaser beam+++++Mg+ ions fromISOLDE+++

Optical pumping
10-6 mbar+++Rf coil+
Magnet pole

Beta-NMR

Betadetectors

crystals

Experimental procedure: Optical pumping: polarization of atomic spinswith laser light HFS interaction = polarization of nuclear spins
 Strong magnetic field: electron and nuclear spindecoupling Nuclear spin polarization observed in beta-decay
asymmetryplasticscintilators

RF-coilmagnet poles
11What did we learn?
NMR

HFSs-EHFS = -3089(7) MHz|gI(31Mg)| =1.7671(3)Doppler tuning voltage (V)E  g  ( I  1 / 2) Measured ground-state HFS and g-factor =independent determination of nuclear spin(with 25Mg as reference for A and g)
isotopespin

 (N)

29Mg

3/2 (*)+0.9780(3)31Mg

1/2-0.88355(15)33Mg (**)

3/2−0.7456(5)Arefg ref(*) confirms previous assignment from b-decay(**) PhD thesis of D. Yordanov, DY et al, Phys.
Ref. Lett. 99, 212501 (2007)

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What does it mean?
In nuclear physics:
 first spin and moment measurement for Mg isotopes around the “island of inversion”
 29Mg properties consistent with N=20 as good magic number 31,33Mg: 2 neutrons across N=20 in ground state => inside the island
 Contribution to the understanding of the “island of inversion” mechanism

Towards biology applications: 31Mg is a spin 1/2 nucleus => no additional splitting in NMR: strong and clean signals
 31Mg is well produced (1e5 ions/s at ISOLDE) and gives high beta-asymmetries => betaNMR resonances can be recorded quickly (a few min per scan) 29Mg can serve as comparison: spin 3/2 (so quadrupole interaction present), weakerasymmetries but stronger production, so comparable time to record resonances Interesting case: Mg cations play important roles in living organisms=> 29,31Mg are ideal cases to tests beta-NMR feasibility on liquid samples (towards
applications in chemistry and biology)

13

First beta-NMR in a liquid sample
Proof-of-principle experiment (at ISOLDE)

August 2012

 Magnesium-31 beam
 Spin polarization with lasers Liquid host: ionic liquid (EMIM-Ac)
 No biological hosts yet

COLLAPS setup + tailor-made chamber

Project: part of PhD thesis of M. Stachura (Copenhagen, supervisor L. Hemmingsen)
Beta-NMR spectrometer and differential pumping designed by A. Gottberg (CERN,Madrid, Copenhagen)Optical pumping, beta detection and magnet: laser-spectroscopy setup (M. Kowalska,
CERN and COLLAPS collaboration)
M. Stachura, L. Hemmingsen et al., Letter of Intent to the INTC, INTC-I-088 (2010)

Ion beam transmission
10-2 mbar just in front of liquid drop;
1-10 mbar in the last 2-3 mm to minimise beam losses

Beam below detection limit
for 1e-1mbar; no tests withwater possible at this point.
But there are other liquids
to start with

M. Stachura15

31Mg HFS in solid and liquid hosts
2004-2005,MgO host2012

Host: empty liquid capillary

Host: water drop at the tip of the capillary(V/50)

Increase in beta-asymmetry amplitude inpresence of liquid -> indirect proof that theion beam reacts to the liquid
16First beta-NMR in a liquidData: Several NMR spectrawith high frequency
modulation and 2
spectra with resonances
resolved (no resonancefrequency reference due
to end of beamtime)B-static = 0.3 T
B-rf= 0.4 G
Width = 5 kHz

Data interpretation:
 NMR: observed frequency difference (chemical shift 1300 ppm) much larger thanknown chemical shifts in liquids (ca. 200 ppm), also quantum chemical calculations
cannot find Mg binding sites producing such a shift
 2nd NMR resonance comes from metal capillary (Knight shift in metals – ca. 1000 ppm),
where about 20% of ion beam is lost: artefact, but also internal frequency reference Conventional NMR (at higher Mg concentration): also no 2nd resonance visible in liquid
A. Gottberg, M. Stachura, M. Kowalska, et. al., to be submitted to Angew. Chemie

Where do we stand?
Proof-of-principle system for beta-NMR in liquids exists
First beta-NMR signal in a liquid recorded (but not in presence of abiomolecule)beta-asymmetry and beta-NMR signals observed up to 0.1 mbar pressure(not yet compatible with water)
No detailed studies yet possible:
 Influence of rest gas (so far – He) Different liquid hosts and with biomolecules
 Change of temperature and pH

Open questions: Will aqueous hosts be possible?
 Will radionuclides host to biomolecules within their lifetime?
 Will small chemical shifts be visible in beta-NMR?

18

Where are we going?
Towards beta-NMR studies in biological hosts on Mg, Cu, and Zn cations: Better vacuum-liquid interface (stronger differential pumping, beam
reacceleration, use of foils, other means of polarization?) More efficient optical pumping and less polarization losses Stronger magnetic field

More studies – scientific proposals : ISOLDE: Further studies with Mg, Polarization tests with Cu
 TRIUMF: tests of Mg polarization

New VITO beamline at ISOLDE (M. Stachura et al):
 PAC and beta-NMR in different vacuum environments
 Devoted to material science, chemistry and biology, and nuclear structure19

Summary
NMR is a powerful method in nuclear physics and in biology

Common requirement of high sensitivity calls for methods such as beta-NMR
Recent beta-NMR studies of properties of Mg isotopes was very fruitful for
nuclear-structure studies
And it is promising for biology, but beta-NMR has never been used in liquid(body-like) hosts
Proof-of principle experiment was performed at ISOLDE in 2012:
 First liquid b-NMR signal was recorded

Many challenges and work ahead but the goal is very motivating20

Thanks to my collaborators
andthank you for your attention
M. Stachura, A. Gottberg, L. Hemmingsen, V. Arcisauskaite, M. L. Bissell, K.
Blaum, A. Helmke, K. Johnston, K. Kreim, F. H. Larsen, R. Neugart, G. Neyens, D.
Szunyogh, P. W. Thulstrup, D. T. Yordanov

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Optical pumping and atomic spin polarizationfinestructure
3p 2P3 /229

hyperfinestructure
32
10

Zeeman levels-3-2-10

12-2-10

12

F+Mg I =3/2
D2-line23s 2S

1/ 2

1s+ circularly polarized light => mF = +1(or -1 for s -) => atomic spin polarization

frequency

Mg+: 280nm, UV
223

Zn and Cu isotopes
Backup slides

Chemical shift range for different metal ions:
67Zn: 2700 ppm, from 0 to 2700 (calculations)
113Cd: 650 ppm, from -650 to 0
199Hg: 3500 ppm, from -3000 to 500

Zn candidates: (spin in brackets - not yet measured)
mass
spin
t1/2
production (ions/s)
73 gs
(1/2)
23 s
ca 1e677isomer
(1/2)
1s
3e4
77 gs
(7/2)
2s
7e6
79
(9/2)
1s
1e6

Transition:
4s4p 3PJ=0,2 ->4s6s 3S1 and 4s4d 3DJ(300-335 nm)

Cu candidates: (all spins confirmed or measured at COLLAPS setup)massspin
t1/2
production (ions/s)
58
1
3.4 s
3e5
Transition:
73
3/2
4s
4e6
2S1/2 gs -> 2P3/2
74
2
1.6 s
6e5
(324.754 nm)
75
5/2
1.2 s
1e523

Systematic approach
Observables: chemical shifts, coupling constants, relaxation times-> Metal coordination number, oxidation state, electronic configuration

Approach:
ReferencecompoundSimplemolecules

Larger, rigid
molecules

Molecules of interestin suitable liquid

Prediction and comparison to quantum-chemical calculations

Long-term – Studies on other biologically-relevant metal ionsMetal binding to proteins
Studied with Perturbed Angular Correlation method25