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.