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Practical Aspects of Solid State NMR Experiments

Denis Schneider

International School on SS NMR, Jan. 4 – 8, 2010, Ooty, India

Outline

• Practical aspects of solid state NMR experiments

• Magic angle adjustment

• Hartmann-Hahn adjustment (cross polarization)

• Decoupling

• CP throughout the periodic table

• What to consider for VT experiments

Magic Angle Adjustment

• Requirements for the set-up sample:

• Sensitive to angle setting

• large interaction to be averaged by MAS

• narrow lines achievable

• more sensitive than samples of interest

• Easy to observe

• large signal

• at desired observe frequency

54.7°


• Standard set-up sample (13C work):

• KBr with 79Br detection

• criterion: spinning side bands

• sensitive to magic angle due to approx. 100 kHzquadrupolar interaction

• narrow lines

• close to 13C frequency (75.16 MHz vs 75.43 MHz @ 300 MHz)

• good S/N on a single scan 54.7°


-200400 200 0 ppm-16-14-12-10-8-6-4-20 ppm

setting the magic angle with KBr (79Br detection)spinning speed 5 kHz

angle grossly misset (by about 1 turn)x 16 x 8


-200400 200 0 ppm-16-14-12-10-8-6-4-20 ppm


angle misset (by about 1/4 turn)x 16 x 8


-200400 200 0 ppm-16-14-12-10-8-6-4-20 ppm


angle well set x 8x 16

Outline




• Decoupling



Cross Polarization – Basic Principles

I,0ω S,0ωS,1I,1 ωω =

laboratoryframe, I spin

laboratoryframe, S spin

rotatingframe

I,1II,1

0II,0

BB

γωγω

=

=

Hartmann-Hahn match: S,1SI,1I BB γγ =

nucleus naturalabundance

max. enhancementfactor

13C 1.11 % 415N 0.37 % 1029Si 4.70 % 531P 100 % 2.5

Cross Polarization – What can beAchievedsignal enhancement by polarization transfer:

εγγ

+⋅1

1

S

I

faster repetition: recycle delay ~ 1.25 T1,1H

usually T1,1H << T1,13C (T1,15N …)

I

S

NN

=ε

13C CP/MAS Set-up Using Glycine

CP/MAS spectrum of glycine (5 kHz spinning speed)

-20240 220 200 180 160 140 120 100 80 60 40 20 0 ppm

HOOHOOCC--CCHH22--NHNH22Carboxyl 13C:• sensitive HH match• easy to decouple• sensitive to angle 13Ca:

• broad HH match• high power decoupling

Basic CP(/MAS) Pulse Sequence

90x

decoupling

contactaquire

1H

13C

contact

ν1,13-C = ν1,1-H

ν1=1/(4*τ90) is RF field

Hartmann-Hahn Matching Profiles

MAS = 12500 Hz

75 70 65 60 55 50 45 40 35 30 25 kHz75 70 65 60 55 50 45 40 35 30 25 kHz

MAS = 2500 HzCH2 CH2

COCO

Ha-Ha-match Ha-Ha-match

Glycine 13C signal amplitudes as function of 1H RF field13C RF field constant at 45 kHzusing square pulses for CP

Ramped (Variable Amplitude) Cross Polarization

90x

contactdecoupling

contactaquire

1H

13C

Hartmann-Hahn Matching Profiles

MAS = 12500 Hz

75 70 65 60 55 50 45 40 35 30 25 kHz75 70 65 60 55 50 45 40 35 30 25 kHz

MAS = 2500 HzCH2 CH2

COCO

Ha-Ha-match Ha-Ha-match

Glycine 13C signal amplitudes as function of 1H RF field13C RF field constant at 45 kHzusing ramp pulse for CP from 100 % to 50 % amplitude

Cross Polarization Dynamics

proton magnetization decays with T1ρ

cross polarization builds up with TIS

signal follows combined effect of buildup and decay

90

~ TIS

~ T1ρ

13C

1H

90° contact


best case: T1ρ >> TIS

worst case: T1ρ << TIS

1H

13C

1H

13C


• Contact time, practical considerations for 13C

• Short TIS (~500 µs): directly attached protons (-CH3, -CH2-, >CH-)

• Long TIS (>1 – 2 ms): quaternary carbons (>C<,-COO-, substituted aromatic systems, …), high mobility

• Short T1ρ: paramagnetic systems/impurities (e.g. in coal), high mobility

Outline




• Decoupling



Decoupling Methods

high power decoupling (CW)

ττdecdec

BB1,dec1,dec

TPPM decoupling (Two Pulse Phase Modulation)

ττdecdec

BB1,dec1,dec

ππ00

ππ11

55

ππ00

ππ11

55

……

and many more (XiX, SPINAL, π-pulse, etc.)

Outline




• Decoupling



Cross Polarization Throughout the Periodic Table

• Standard: I = ½ → S = ½

• Most frequent:

• I = 1H → S = 13C, 15N, 29Si, 31P

• Less common, but worthwhile:

• I = 1H → S = 77Se, 89Y, 113Cd, 119Sn, 129Xe, 195Pt, 199Hg, 207Pb

• Fluorinated materials:

• I = 19F → S = 13C, 15N, 29Si, 31P• Low γ nuclei (e.g. 15N): more X and/or less 1H power

• Quadrupolar nuclei: different story

Cross Polarization Throughout the Periodic Table

• Experiment will be simple, if

• Natural abundance is high

• Larmor frequency is high

• CP can be used in case of spin ½ nuclei

• difficult, if TIS >> T1ρ, e.g. for low γ nuclei

• Spin I must be considered

• For spin > ½ selectivity and connectivity information is more importantthan gain in sensitivity

• Consider elements with several isotopes

Cross Polarization Throughout the Periodic Table• Elements with several NMR aktive isotopes

• 6Li 7Li• 10B 11B• 14N 15N• 35Cl 37Cl• 39K 41K• 47Ti 49Ti• 50V 51V• 63Cu 65Cu• 69Ga 71Ga• 77Se 79Se• 79Br 81Br• 85Rb 87Rb• 95Mo 97Mo• 99Ru 101Ru• 101Rh 103Rh• 107Ag 109Ag• 111Cd 113Cd• 113In 115In• 115Sn 117Sn 119Sn

• 121Sb 123Sb• 123Te 125Te• 129Xe 131Xe• 135Ba 137Ba• 138La 139La• 147Sm 149Sm• 151Eu 153Eu• 155Gd 157Gd• 161Dy 163Dy• 171Yb 175Yb• 175Lu 176Lu• 177Hf 179Hf• 185Re 187Re• 187Os 189Os• 191Ir 193Ir• 199Hg 201Hg• 203Tl 205Tl

• Spin ½

• Spin n

• Spin n/2

• > 99 % natl. abundance• 9Be, 14N, 19F, 23Na• 27Al, 31P, 45Sc, 55Mn• 59Co, 75As, 89Y, 93Nb• 103Rh, 127I, 133Cs, 139La• 141Pr, 159Tb, 165Ho, 169Tm• 181Ta, 197Au, 209Bi

Chart of all 29 X Nuclei with Spin ½

57Fe 187Os 13C 15N 29Si 77Se3He 115Sn

117Sn 119Sn123Te 125Te

< 10%

183W 111Cd 113Cd 171Yb 195Pt 199Hg 207Pb

129Xe50-10%

107Ag 109Ag203Tl 205Tl70-50%

89Y 103Rh 169Tm19F 31P100-70%

γN-15 > γXγC-13 ≥ γX ≥ γN-15γX > γC-13nucl.

natl.abundance

Cross Polarization of “Standard” Nuclei

002relative attenuation 1H [dB]

656355RF field [kHz]

30-2relative attenuation X [dB]

150200500X power at CP match [≈W]

16210040Larmor frequency [MHz]

31P13C15Nnucleus

15N 13C 31Pfrequency

Cross Polarization of “Exotic” Nuclei

15N 13C 31P

57Fe 89Y 199Hg 29Si 113Cd 125Te 119Sn

frequency

002relative attenuation 1H [dB]

656355RF field [kHz]

30-2relative attenuation X [dB]

150200500X power at CP match [≈W]

16210040Larmor frequency [MHz]

31P13C15Nnucleus

Some Reference Compounds forCP Set-up

nucleus sample shift (ppm) relative to contact (ms)

recycle (s) frequency (MHz) rel. to 200

remarks

15N glycine, enriched -345 CH3NO2 5 10 20.280213 natl. abundance: visible in 1 scan

29Si Q8M8 12.4 (t) TMS 5 10 39.758361 easy but expensive

-110 (o)

31P (NH4)H2PO4 0 H3PO4 1 4 81.013812 anything will do

77Se H2SeO3 Se(Me)2 3 4 38.217585 1 scan, but poisonous easy, narrow

(NH4)2SeO4 -1040.2 38.128907

89Y Y(NO3)3*H2O -53.2 sol. in H2O 10 10 9.807451 visible after 1 scan FT

113Cd Cd(NO3)*4H2O -100 1m Cd(ClO4)2 15 8 44.381609

119Sn Sn(cyclohexyl)4 -97.35 Sn(Me)4 1 20 74.639360 easy, 1 scan

129Xe Xe at 40b in hydroquinone clathrate, 3 hours

222 Xe in air 30 5 55.333703 Xe in air is visible overnight (single pulse)

199Hg Hg(OAc)2 -2487 Hg(Me)2 5 10 35.765352 16 scans, 125 kHz, 4K points (lots of sidebands)

-2493

207Pb Pb(phe)4 41.861650 1 scan, poisonous, no good set-up

Pb(p-tol)4 -148.8 Pb(Me)4 5 12 41.863710 better, but also poisonous, 1 scan

Outline




• Decoupling



Variable temperature in MAS

• experimental aspects

• probe design

• high temperature experiments

• low temperature experiments

• rotors and caps

• temperature determination

• undesired temperature changes

• challenges and problems

Variable temperature - demands

• In general

• stable temperature (during experiment)

• small temperature gradient

• protection of probe, shim system, magnet

• temperature calibration

• MAS in particular

• stable spinning during cooling or heating

• stable spinning at high and low temperature

• temperature calibration

VT ranges of WB MAS probes

Exception: 1.3 mm and 2.5 mm probes: -30°C ↔ +70°C

VTN : Variable Temperature Normal (BN-Stator)WVT : Wide Variable Temperature (MgO-Stator)DVT : Direct Variable Temperature (BN-Stator)

VTNVTN

+150+150°°CC +300+300°°CC

WVTWVT

--140140°°CC

DVTDVT

TT

+120+120°°CC--8080°°CC--120120°°CC

2020°°CC+700+700°°CC+400+400°°CC

MASCAT (7mm)MASCAT (7mm)

LTMASLTMAS

LASERMAS (7mm)LASERMAS (7mm)

SB MASSB MAS

MAS probe design

VTN/WVT

variable temperature via bearinggas

DVT

variable temperature via separate (direct) gas

Arrangement of thermocouples

TC 2: regulation (regul)

TC 1: control (read)

PH MAS DVT 600 WB BL4 (H8724)

heaterheaterconnectorconnector

heaterheater

bearingbearing gas gas plus VT gasplus VT gas

thermocouplethermocouple((Cu/ConstCu/Const))

spinningspinning rate rate sensorsensor electronicselectronics

drivedrive gasgas

frameframe flushingflushingVTNVTN

VTN + WVTVTN + WVT

all all typestypes

Variable temperature

thermocouplethermocouple 1 (gas 1 (gas exhaustexhaust))

thermocouplethermocouple 2 (VT gas 2 (VT gas inputinput))

VT gas VT gas onlyonly

bearingbearing gasgas

drivedrive gasgas

WVTWVT

DVTDVT

DVTDVT

bearingbearing gasgasplus VT gasplus VT gas

Variable temperature

Low temperature

Moderately low: BCU-05 cooling unitHR- and MAS-Version (pressure)cools gas stream typically by 65 Ktemperature range: approx. -15°C to +50°C

Low temperature: BCU-X cooling unitHR- and MAS-Version (pressure)cools gas stream typically by 100 Ktemperature range: approx. -50°C to +50°C

Low temperature

really low: heat exchangerMAS version for VTN, WVT, DVTHR version for DVTcooling down of heat exchanger only underdry N2 gas

Low temperature

LT-MAS system: 100K

High temperature

Laser MAS system

diode Laser

7mm MAS probe

up to 700°C

Rotor caps

ZrOZrO22 MacorMacor BNBN KelKel--FF VespelVespel

Rotor caps

Kel-F (polymer): ambient temperature ± , (cold: shrinks, hot: deforms), easy pull-out

BN (ceramic): high and low temperature, mechanicallydamageable (glue in, if necessary)

Macor (ceramic): high and low temperature, mechanicallyweak (glue in, if necessary)

ZrO2 (ceramic): high and low temperature, mechanicallyrobust, easy pull-out,not cheap ...

Vespel (polymer): high speed and temperature, easypull-out

spinner diameter

-140°C ... +300°CBoron nitrid

-140°C ... +300°CZirconia, Macor

-10°C ... +50°CKel-F7 mm

-140°C ... +300°C

-140°C ... +300°C

Zirconia

Boron nitrid

-10°C ... +50°C

-30°C ... +70°C

Kel-F

Vespel4 mm

-140°C ... +300°CZirconia

-10°C ... +50°C

-30°C ... +70°C

Kel-F

Vespel3.2 mm

-30°C ... +70°CVespel1.3 mm and 2.5 mm

temperature rangematerial of rotor cap

Spinner Caps: Materials / Applic. Ranges

VT gas

N2 from boil-off device:dry, oil freelow pressure fluctuationinert

! Caution !! Look after fresh air !

! O2 warning system where required !

Compressed gas from compressor:pay attention to dew point and oil content (0.0 %)condensation of O2 at low temperaturerisc of oxidation at high temperaturepressure fluctuation

Probe and magnet protection

transfer tube

shimsystem “frame cooling“

NO ice nor heat at O-rings!

Probe and magnet protection

flush gas (ambient temperature) forshimsystemprobehead (“frame cooling“)transfertube

critical parameters:high temperature: shim coils: T ≤ 70 °Clow temperature: shim coils: T > 0 °Clow temperature: in case of icing of O-rings risc of leakage of vacuum and quench!

Undesired temperature effects

coolingJoule-Thompson-effect when bearing gas expands(depends on bearing pressure)

heatingfrictional heating in the bearingsdepends on bearing pressure and flowimportant to consider at fast spinning

Slow heating and cooling!

For heating and cooling consider thermal burdenon probe

using a ramp of 6 to 10 degrees per minute is recommended

Change temperature via ramp (1)

Change temperature via ramp (2)

Challenges and problems

rotor crashunbalance when sample meltspushing out of rotor caps due to

degassing, loss of crystal water, decompositionmoving material (plastic crystals, fatty acids)extreme thermal expansion

solution:reduce volume (insert-plugs, CRAMPS rotor)glue cap inuse top CRAMPS plug

no sample ejectreason: moist air is absorbed via the transfer tube

and condensation in low temperature experimentssolution: flush gas trough “insert“-tube

Variable temperature: literature

• Chemical shift thermometer:

• 207Pb-MAS using Pb(NO3)2:A.Bielecki and D.P. Burum: Temperature Dependence of 207Pb MAS Spectra of Solid Lead Nitrate. An Accurate, Sensitive Thermometer for Variable-Temperature MAS; J.Magn.Reson. A116, 215-220 (1995)

• 119Sn-MAS using Sm2Sn2O7:B. Langer, I. Schnell, H.W. Spiess and A.-R. Grimmer: Temperature Calibration under Ultrafast MAS Conditions, J.Magn.Reson. 138, 182-186 (1999)

• 79Br-MAS using KBr:Measurement of sample temperatures under Magic-angle spinning from the chemical shift and spin-lattice relaxation rate of 79Br in KBr powder, J.Magn.Reson. – in Press

• Fix points with liquid to solid or solid to solid phase transition:

• J.F. Haw, R.A. Crook and R.C. Crosby: Solid-Solid Phase Transition for Temperature Calibration in Magic-Angle Spinning, J.Magn.Reson. 66, 551-554 (1986)

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