Polarised Nucleon Targets for Europe, 3rd meeting, Rech 2006

Prague NMR activities H. Štěpánková, J. Englich, J. Kohout, M. Pfeffer, J. Štěpánek J. Černá, V. Chlan, K. Kouřil, V. Procházka E. Bunyatova* Faculty of Mathematics and Physics, Charles University Prague, Czech Republic *

™

Joint Institute for Nuclear Research Dubna, Russia

NMR in alcohols with TEMPO, liquid state

(analysis of 1H, 13C relaxations in ethanol +TEMPO solutions) ™

On the way to lower temperatures (solid state)

Ethanol + TEMPO, high resolution NMR in solution Interactions between electron and nuclear spins: - are known to achieve high polarization of the nuclear spin system in processes of dynamic nuclear polarization - give rise to effective relaxation mechanisms for excited nuclear spins Stable nitroxyl radicals: - spin labels for ESR experiments - paramagnetic probe in NMR Ethanol: interesting from the point of view of - molecular structure and dynamics, - forming and properties of intermolecular hydrogen bonds in polar liquids (water, simple alcohols)

Ethanol + TEMPO, high resolution NMR in solution NMR spectra and spin-lattice relaxations T1 in the liquid state - first experimental results reported previously NMR BRUKER AVANCE 500 pulse spectrometer Bexternal = 11.7 T ( 500 MHz for 1H, 125 MHz for 13C) six samples with 0 -1.5 wt% of TEMPO in CH3CH2OH temperature range 160-290 K NMR of ethanol: 1H spectra: 3 signals 13C spectra: 2 signals

Ethanol + TEMPO, high resolution NMR in solution Spectra 1H at 210K – all samples

FWHM (Hz)

Linewidth

180 CH3 160 140 CH2 120 OH 100 80 60 40 20 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 6

Shift

δ (ppm)

5 4 3

δ (CH2) - δ(CH3) δ (OH) - δ(CH3)

2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

TEMPO Conc. (wt%)

Ethanol + TEMPO, high resolution NMR in solution Spectra 1H – sample #2/2 (0.05wt%) at various temperatures Linewidth

FWHM (Hz)

200

CH3 CH2 OH

150 100 50 0 150

200

250

300

Shift

6

δ (ppm)

5 4

δ (CH2) - δ(CH3) δ (OH) - δ(CH3)

3 2 150

200

250

Temperature (K)

300

Ethanol + TEMPO, high resolution NMR in solution Spectra 13C at 210K – all samples

14 12

Linewidth CH3 CH2

10 8 6 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Shift 39.4 δ (ppm)

CH2

CH3

FWHM (Hz)

16

δ (CH2) - δ(CH3)

39.3 39.2 39.1 39.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

TEMPO Conc. (wt%)

Ethanol + TEMPO, high resolution NMR in solution Spectra 13C – sample #4/2 (1.5wt%) at various temperatures Linewidth

FWHM (Hz)

50

CH3 CH2

40 30 20 10 0 150

200

250

300

Shift δ (CH2) - δ(CH3)

δ (ppm)

39.4 39.3 39.2 39.1 39.0 150

200

250

Temperature (K)

300

Ethanol + TEMPO, high resolution NMR in solution Relaxation rate R1 = 1/T1 Strong dependence of proton and carbon relaxation rates on temperature, maximal OH-proton relaxation rate at ~200K 1H (OH ) 1H (CH 2) 1H (CH 3) 13C (CH 2) 13C (CH 3)

8

R1 (s-1)

0.05 wt% of TEMPO

6 4 2 0

160 180 200 220 240 260 280 300

Temperature (K)

Ethanol + TEMPO, high resolution NMR in solution Relaxation rate R1 = 1/T1 Strong and linear dependence of proton and carbon relaxation rates of ethanol on TEMPO concentration 1H (OH ) 1H (CH 2) 1H (CH 3) 13C (CH 2) 13C (CH 3)

40

R1 (s-1)

210 K

30 20

x 0.2

10 0 0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

TEMPO concentration (wt %)

1.6

Ethanol + TEMPO, high resolution NMR in solution Relaxation enhancement k1 ≡ dR1/d(concentration)

1

H (OH)

3500

2500

k1 (s-1M-1)

k1 (s-1M-1)

3000

2000 1500 1000

1

H (CH2)

400

1

H (CH3)

350 300 250 200 150

500 0 160

450

200

240

280

Temperature (K)

320

13

C (CH2)

100

13

C (CH3)

80 60 40 20

100 160

120

k1 (s-1M-1)

4000

200

240

280

Temperature (K)

320

0 160

200

240

280

Temperature (K)

320

The most pronounced effect of doping is seen for OH protons – a role of hydrogen bonds between OH group of ethanol and the oxygen of TEMPO

Ethanol + TEMPO, high resolution NMR in solution Mechanisms of nuclear relaxation enhancement Fluctuating magnetic interactions between nuclear (ethanol) and electron (TEMPO) spins: - Dipolar interaction modified by motion translational diffusion rotational diffusion (of complex) - Contact interaction Particular models; approximations. Concentration, temperature, field dependences. (NMRD... dispersion of nuclear magnetic relaxation rates)

Ethanol + TEMPO, high resolution NMR in solution Translational diffusion Force free (FF) model for motion (excluded volume). Long electron spin correlation time. 32π = 2γ S2 γ I2 N a S ( S + 1) (7 J (ωS ) + 3J (ω I )), k1 = 405

1000d D where the spectral density function is given by J(ω) :

1 + 5z 8 + z 2 8 J (z ) = ; 2 3 4 5 6 1 + z + z 2 + z 6 + 4 z 81 + z 81 + z 648

zn = 2 ωn τ D

translational diffusion correlation time τ D = d 2 D D = Dethanol + DTEMPO , Di = k B T 6 π ai η Di ... translation - diffusion coefficients d ... distance of the closest approach ai ... size of the i - molecule (its dynamic radius) η ... viscosity of the liquid (τ D is proportional to η/T)

Ethanol + TEMPO, high resolution NMR in solution Relaxation enhancement k1 = dR1/d(concentration) 4000

1

H (OH)

3500

k1 (s-1M-1)

k1 (s-1M-1)

2500 2000 1500

H (CH2)

1

H (CH3)

300 200

1000 500 0 160

240

280

Temperature (K)

320

160

13

C (CH2)

100

13

C (CH3)

80 60 40 20

100 200

120

k1 (s-1M-1)

400

3000

1

200

240

280

Temperature (K)

320

0 160

200

240

280

Temperature (K)

320

• We made a fit of k1 (translation diffusion) for protons except the 1H(OH) and for carbon nuclei, using common free parameters. • Reasonable agreement for relaxations of 13C, 1H(CH2) and 1H(CH3) in the region of temperatures above ~ 210K. • The optimized values of the free parameters d = 0.40 nm , ζ ≡ aethanol aTEMPO / (aethanol + aTEMPO) = 0.12 nm. • The diffusion-controlled regime could be dominant for the relaxation enhancement of carbon nuclei and protons in ethanol except the OH group.

Ethanol + TEMPO, high resolution NMR in solution Translational diffusion 8

τD (ns)

Comparison of fitted slopes k1 for 500 MHz (dashed lines) and predicted for 200 MHz (solid lines) spectrometers

correlation time of diffusion motion

10

(FF model)

6

13 C

1H - others

4 2

200

800

0 160

180

200

220

240

260

280

300 -1

TM /CTEMPO (s M )

-1

0.6

J (z)

100

400

-1

function J(z)

0.8

0.4 0.2

200

50

0

0 160 180 200 220 240 260 280 300

0.0 0

2

4

6

z

8

150

-1

600

-1

-1

TM /CTEMPO (s M )

Temperature (K)

Temperature (K)

160 180 200 220 240 260 280 300

Temperature (K)

Ethanol + TEMPO, high resolution NMR in solution Rotational diffusion 2 = 2γ S2 γ I2 n S ( S + 1) (7 J (ωS ) + 3J (ωI )), k1 = 6 15 br [ I ] where the spectral density function J(ω) is : J (ω ) =

τR ; 2 2 1+ ω τ R

4πη a 3 rotational diffusion correlation time τ R = 3kT br ... distance between the I and S spins [ I ]... molar concentration of the I spins (τ R is proportional to η/T)

Ethanol + TEMPO, high resolution NMR in solution Rotational and translation diffusion Fit, rotational + translational mechanisms of relaxation 1

13

1

H - OH

H - others

4000

350

CH2

CH2 CH3

3500

80

2000

-1

200 150

-1

1500

250

1000

60

40

-1

2500

CH3

-1

TM /CTEMPO (s M )

-1

-1

TM /CTEMPO (s M )

-1

-1

-1

TM /CTEMPO (s M )

300 3000

C

100

100 20

500

50

0

0 160 180 200 220 240 260 280 300

Temperature (K)

0 160 180 200 220 240 260 280 300

Temperature (K)

160 180 200 220 240 260 280 300

Temperature (K)

Anisotropic motion? Internal motions?

Ethanol + TEMPO, high resolution NMR in solution

Outlook: ♣ Relaxation models ♣ Dependence on frequency ♣ Chemical shifts interpretation ♣ Other alcohols/radicals ♣ Non polar solvents ♣ Adding water ♣ Changing viscosity ♣ Deuterated solvents ♣ Technical questions

Laboratory views

May/June 2005 New NMR laboratories in a new pavilion

Lower temperatures (solid state)

• 200 MHz NMR spectrometer (homemade): new hardware components and software

Lower temperatures (solid state)

• 5 T cryomagnet, cryoshimms (homogeneity ~10-5) 57 mm bore

Lower temperatures (solid state)

• 5 T cryomagnet, cryoshimms (homogeneity ~10-5) 57 mm bore

Lower temperatures (solid state)

• Helium gas continuous flow cryostat Janis, 2 - 400K

Lower temperatures (solid state)

• Nitrogen liquid cryostat (77 K) Vakuum Praha

Lower temperatures (solid state)

• NMR tunable probe for protons designed, made and tested

Lower temperatures (solid state)

• NMR tunable probe for protons designed, made and tested

Lower temperatures (solid state)

• NMR tunable probe for protons designed, made and tested

tuning

matching

saddle rf coil

Lower temperatures (solid state)

• Installation of a new cryomagnet 9.4 T (400 MHz) cryoshimms (homogeneity ~10-5) 52 mm bore

Lower temperatures (solid state) Test of the new facilities: 1H NMR spectra in ethanol

Intensity

3

Decreasing temperature

2

1

300 K, 200 MHz 0 60

40

20

0

ppm

-20

-40

-60

290 K, high resolution spectrum 500 MHz

Lower temperatures (solid state)

Outlook: ♣ Technical questions ♣ Cooling regime: complicated thermal properties of ethanol - polymorphic forms • Tmelt=159 K crystal I (monoclinic) • supercooled liquid → → Tg=97 K glassy liquid (extremely rapid chilling); • supercooled liquid → → T’melt=127.5 K metastable crystal II (cubic, ’plastic’,molecules rotate) → → T’g=97 K glassy crystal II (molecules frozen at random orientation) ♣ Relaxation models, structural and motional dependent, embedded TEMPO ♣ Deuterated ethanols

Lower temperatures (solid state)

Outlook:

T. Eguchi et al.