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Transcript
GSU Chem 4050/6050
Lecture 1
Feb 28,2017
PSC 311
Zhenming (Jimmy) Du
Round Robin
Instructor: Dr. Zhenming (Jimmy) Du
NSC 134A
Email: [email protected]
Phone: 404-413-5538
Web: sites.gsu.edu/zdu
Students:
Scope of Chem 4050/6050: Level I
Chem 4050/6050.
Introduction to Fourier-Transform NMR
Spectroscopy. Prerequisites: demonstrated
research need and approval of the
departmental chair. Introduction to
techniques of Fourier-Transform Nuclear
Magnetic Resonance Spectroscopy
Next step: Level II
Fall Semester
Chem 8450, NMR Spectroscopy (4) Prerequisite: Chem
6050 or consent of the instructor. Theory and application
of NMR spectroscopy for the characterization and
elucidation of organic and biological molecules.
Next step: Level III
Spring semester:
Chem 8540. Biomolecular Nuclear Magnetic Resonance.
(3) Prerequisite: Introductory courses in spectroscopy,
such as Chem 4050/6050 and Chem 4190/6190 or
equivalent. Some experience in the application of
quantum mechanics in spectroscopy is useful, but not
essential. Experimental design and interpretation of
nuclear magnet resonance data, particulary with respect
to applications in structural biology.
Textbook required
Edition: 2nd
ISBN-13: 978-0198703419
ISBN-10: 0198703414
Helpful Books
This text is aimed at people who have
some familiarity with high-resolution NMR
and who wish to deepen their
understanding of how NMR experiments
actually ‘work’. This revised and updated
edition takes the same approach as the
highly-acclaimed first edition. The text
concentrates on the description of
commonly-used experiments and explains
in detail the theory behind how such
experiments work. The quantum
mechanical tools needed to analyse pulse
sequences are introduced set by step, but
the approach is relatively informal with the
emphasis on obtaining a good
understanding of how the experiments
actually work. The use of two-colour
printing and a new larger format improves
the readability of the text.
Helpful Books
This work-book will guide you safely, in
step-by-step descriptions, through every
detail of the NMR experiments within,
beginning with 1D routine experiments and
ending with a series of advanced 3D
experiments on a protein:
Topics today
NMR Basics:
Theory for NMR detection;
Concerns during NMR detection.
Reading assignment:
1. Lecture 1 notes;
2. Chapter 1 & 2;
3. Read gsuNMR guide before lab 1;
4. Reading NMR operation procedures.
1. What is NMR?
NMR =
Nuclear
Magnetic
Resonance
About MRI
(N)MRI =
(Nuclear)
Magnetic
Resonance
Imaging
NMR Applications
NMR Applications
Organic Structure Illustration:Heparin
Protein Structure Illustration
2LCJ
CFPGDTRILVQIDGVPQKITLRELYELFED
ERYENMVYVRKKPKREIKVYSIDLETGKV
VLTDIEDVIKAPATDHLIRFELEDGRSFETT
VDHPVLVYENGRFIEKRAFEVKEGDKVL
VSELELVEQSSSSQDNPKNENLGSPEHD
QLLEIKNIKYVRANDDFVFSLNAKKYHNV
IINENIVTHQ
Du, Z., Liu, J., Albracht, C.D., Hsu, A., Chen,
W., Marieni, M.D., Colelli, K.M., Williams,
J.E., Reitter, J.N., Mills, K.V., Wang, C.
Journal: (2011) J.Biol.Chem. 286: 38638-38648
Nuclear=?
Atoms are made of electrons and nuclei.
Each atomic nucleus has four important physical properties: mass,
electric charge, magnetism, and spin.
Mass, electric charge: more sensible
Nuclear magnetism and spin: less tangible ( but need to understand
here)
Quantum mechanics treatment
Nucleus
have
numbers(n,l,ms,s)
four
quantum
n: Principle quantum number(n): the size
of the orbital (1,2,3,…,n)
l: Angular quantum number (l): the shape
of the orbital (0, 1, …, n-1)(s,p,d,f,…)
ms: Magnetic quantum
number(m):orientation in space of a
particular orbital [-l, …,-2,-1,0,1,2,…,l]
s: Nucleus has an intrinsic spin angular
momentum ( hence spin quantum
number, I).
Nuclear Spin
 Some nuclei possess an intrinsic angular momentum
 Nuclear spin angular momentum is quantized in integer multiples
of h/2π(or h is Planck’s constant)
 Maximum observable component p of nuclear spin angular
momentum is p= I * h/2 π
 I = nuclear spin quantum number
 I varies as a result of the interactions between protons and
neutrons
Nuclear spin differs from electron spin
both quantized, I ≠ 0: Nmrable
Nuclear spin differs from electron spin
both quantized, I ≠ 0: Nmrable
I
Nuclide
0
12C
16O
1/2
1H
13C
1
2H
14N
3/2
11B
23Na
5/2
17O
27Al
3
10B
15N
19F
35Cl
37Cl
29Si,
31P
Example:
ν = γ * B0/ 2π
For proton , γ = 26.7519 * 107 rad T-1 S-1
For carbon, γ = 6.73 * 107 rad T-1 S-1
T: Telsa = 10,000 Gauss
B0= 9.40T, corresponds to 400MHz NMR for proton.
corresponds to
NMR for carbon.
B0= 11.45T, corresponds to
Bo =
NMR;
, corresponds to 600 MHz NMR;
Commercially available magnetic field 1.4T------22.31
60MHz-950 MHz
This lies on the radiofrequency range (RF) of the
electromagnetic spectrum.
Resonance along is not enough
Detecting the resonance is the key!
Low energy range!
Radio frequency range!
At room temp, the number of spins in the
lower energy level (N+)is slightly greater than
the number in the upper level (N-).
The Boltzmann Factor and Partition Functions
The Boltzmann factor tells us that if a system has states with energies
E1, E2, E3,. …, the probability Pj that the system will be in the state
with energy Ej depends exponentially on the energy of that state, or
Pj ∝ 𝑒 −𝐸𝑖/𝐾𝑏𝑡
At room temp, the number of spins in the
lower energy level (N+)is slightly greater than
the number in the upper level (N-).
NMR Detection Key Elements
1. A strong magnetic field;
2. RF pulse to excite nuclei in the sample;
3. Detection of the feedback (NMR signal).
1. A strong
magnetic
field;
Superconduc
ting
solenoid;
2. RF pulse
Δ𝐸 = ℎ𝑣 = γℏ𝐵0
Twist between 𝑣 and 𝐵0 to achieve
balance;
For protons, if you supply a magnetic field
B0, then all protons will appear in the same
frequency 𝑣 as
γ 𝑎𝑛𝑑 ℏ 𝑎𝑟𝑒 𝑎𝑙𝑙 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡𝑠? .
• 1926 Pauli’s prediction of nuclear spin!
• 1932 Detection of nuclear magnetic
moment by Stern using molecular
beam!
– 1936 First theoretical prediction of NMR
by Gorter; his attempt to detect the
first NMR did not work (LiF
&K[Al(SO4)2]12H2O) at low temp.
• 1945 First NMR of solution (Bloch et al
for H2O) and solids (Purcell et al for
parafin)!
• 1949 Discovery of chemical shifts!
NMR Sensitivity.
Relative sensitivity S/N ∝ γ3
Absolute Sensitivity S/N ∝ γ3 * C
C stands for natural abundance.
Pulse NMR is fast
20ppm at 400MHz= 8000Hz, 125us for 360 pulse
20ppm at 800MHz=16000Hz, 62.5 us for 360 pulse
Exercises
Now you are running NMR on 500Mhz NMR, and you found your 90 pulse
for proton is 12 μs long. Your lab mate told you he has peaks that
appears between 5 ppm and 0 ppm. Is the pulse strong enough to cover
that range?
What about a spectrum between 40ppm and -10 ppm?
RF Pulses
3. Chemical Shift
Earth’s magnetic field
Refrigerator magnet
MRI medical scanners
High field NMR magnet
200 MHz
400 MHz
500 MHz
800 MHz
0.6 Gauss at equator
100 - 150 Gauss
0.3 - 1.5 Tesla (3 - 15,000 G)
4.7 Tesla (47,000 G)
9.4 Tesla (94,000 G)
11.7 Tesla (117,000 G)
18.8 Tesla (181,000 G)
Proton peaks are isolated
Chemical Shift
𝐵𝑙𝑜𝑐 =𝐵0 (1-σ)
Chemical Shift
Chemical Shift
Chemical Shift
CH4
CH3Cl
CH2Cl2
CHCl3
δ=0.23
δ=3.05
δ=5.33
δ=7.26
CH3I
CH3Br
CH3Cl
CH3F
δ=2.16
δ=2.68
3.05
4.26
Chemical Shift
Chemical Shift
Chemical Shift
Advantage of FT-NMR vs. CW
• Faster speed. No sweeping
needed. 1 s/ scan vs. 4500s /
scan
• Multiple scan to improve S/N;
• Spin Manipulation for
complicated NMR
experiments, such as water
suppression, NOESY, and
HMBC.