Solid State NMR experimental

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1

Solid‐state NMR Training Course

Experimental Basics

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2

The Building Blocks

High‐resolution solid‐state NMR

Magic‐angle spinning

Direct‐polarisation (DP)

[aka SPE and pulse‐acquire]

Cross‐polarisation (CP)

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Direct‐polarisation

recycle delay

free induction decay

recycle delay

relaxation delay

pulse delay

recycle

free induction decay

FID

signal

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4

When to use DP

Quantitative measurements –

spin‐½ nuclei (

31

P (100%), 

29

Si(4.7%))

Soft solids

Heterogeneous materials

Quadrupoles (

27

Al, 

11

B, 

23

Na)

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5

When to use DP

Quantitative measurements (

31

P, 

29

Si)

Soft solids (high molecular mobility)

Heterogeneous materials
(containing “soft” and “hard” phases)

Quadrupoles (

27

Al, 

11

B, 

23

Na)

Deliberately selective conditions

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6

When to use DP

Quantitative measurements (

31

P, 

29

Si)

Soft solids

Heterogeneous materials

Quadrupoles (

27

Al, 

11

B, 

23

Na)

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7

Optimising a DP experiment

t

time constant T

1

(spin‐lattice 
relaxation time)

90

o

90

o

Recovery of 
equilibrium 
magnetisation 
after a pulse

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8

Optimising a DP experiment

repetitions 

(constant 

experiment time)

recycle / T

1

relative 

S/N

8

5

1.00

12

3.33

1.19

32

1.2

1.41

80

0.5

1.25

400

0.1

0.68

tip‐angle = cos

‐1

(e

‐t/T

1

)

“Ernst” angle

tip‐angle < 90/(I+½)

quadrupoles

t

90

o

90

o

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9

Cross‐polarisation

…. for sensitivity enhancement

requires:

an abundant nucleus – usually 

1

H

coupled network of abundant nuclei (ideally)

coupling between the abundant spin and 

n

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10

Cross‐polarisation – the pulse sequence

B

0

z

y

x

90

x

1

H

90

x

1

H

spin-lock

y

n

X

spin-lock

y

contact

90

x

1

H

γ

H

B

1

H

= γ

X

B

1

X

Hartmann‐
Hahn match 
condition

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11

90

x

1

H

flip-back

-x

decouple

y

FID

contact time

acquisition time

n

X

spin-lock

y

contact

Cross‐polarisation – the pulse sequence

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12

The advantages and disadvantages of CP

9 Recycle T

1

H

(not T

1

X

) and T

1

H

<< T

1

X

9 Signal enhancement (potentially γ

H

/γ

X

)

9 Fewer problems with background signals

9 Can probe relationship between nuclei

8 Loss of quantitivity

8 Potentially selective

Advantages

Disadvantages

9 Potentially selective

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13

90

1

H

decouple

n

X

spin-lock

y

-y

-y

x

x

y

-y

y

-y

y
y
x
x

y

-y

x

-x

Receiver

Cross‐polarisation – the phase cycling

• A full phase‐cycle removes the signal generated directly from the contact pulse

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14

The advantages of cross‐polarisation ‐ illustrated

recycle 3 s, 448 repetitions
experiment time 22 minutes

DP

CP

DP

recycle 120 s, 448 repetitions
experiment time 15 hours
(T

1

(C) >> T

1

(H))

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15

Why CP is not (necessarily) quantitative

n

X

spin-lock

y

contact

Energy transfer 
depends on 
relationship of X
and H

COOH

H

3

C

H

2

N

CH

3

H

H

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16

How to make CP quantitative

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17

How to make CP quantitative

COOH

H

3

C

H

2

N

CH

3

H

H

COOH
Rise: 

0.2 and

1.1 ms 

Decay: 

2.2

ms

Absolute intensity: 23.4
CH
Rise: 32 μs 

and 0.33 ms

Decay: 

2.1

ms

Absolute intensity: 30.5 

• Dilute H or high spin‐rate introduces extra complexity

T

1ρ

(H)

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18

Decoupling

phase

continuous wave (cw)

phase

p

180

two‐pulse phase‐modulated (tppm)

p

180

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19

Matching

low spin‐rate

2 kHz

high spin‐rate

22 kHz

‐1 0 +1 +2

centreband

sideband

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20

Matching (fast MAS)

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21

1

H

n

X

spin-lock

contact

dephasing
delay

180

1/spin-rate

1/spin-rate

Spectral editing (dipolar dephasing)

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22

Spectral editing (dipolar dephasing)

Difference (CH)

Quaternaries (and anything mobile)

All carbons

(two molecules in the crystallographic asymmetric unit)

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23

H

X

1

H ‐

n

X WIdeline SEparation (WISE)

rigid

mobile

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24

1

H ‐

13

C (wideline) correlation

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25

Chemical shifts: solid vs solution

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26

Instrument (probe) issues

7.5 mm

4 mm

S/N on HMB

350:1

80:1

Time

1 hour

19 hours

Decoupling

60 kHz

125 kHz

Spin‐rate

7 kHz

18 kHz

Sample volume

450 μl

52 μl

13

C (1.11%)

13

C minor component

15

N (0.37%)

29

Si (4.70%)

27

Al (100%)

119

Sn (8.58%)

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27

Li

Be

B

C

N

O

F

Na

Mg

Al

Si

P

S

Cl

Xe

K

Ca

Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn

Ga

Ge

As

Se

Br

Rb

Sr

Y

Zr

Nb

Mo

Tc

Ru

Rh

Pd

Ag

Cd

In

Sn

Sb

Te

I

Cs

Ba

La

Hf

Ta

W

Re

Os

Ir

Pt

Au

Hg

Tl

Pb

Bi

Accessible elements

Easy!

Feasible with varying degrees of difficulty

Special


Document Outline


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