Module 3 Flashcards
Molecules “_______” or _______randomly
“tumble” or rotate
Tc
rotational correlation time
Three things that influence tumbling rates:
viscoscity
temperature
size of particle
Molecular rotations cause ____ ___-_______ _____ , B loc(t)
local time-dependent fields
NMR-active nuclei with \_\_\_\_\_ \_\_\_\_\_\_ \_\_\_\_\_\_can interact with other nuclei causing spin relaxation (T1 and T2).
fluctuating local fields
the __ and __ time constants describe the rate (T1= 1/R1) at which longitudinal and
transverse relaxation occur, respectively.
T1 and T2
Where do molecular rotations occur from?
They occur from the influence of a single spin or many spins simultaneously
What do molecular rotations depend on?
gama Bloc = omega knot
Where does the fluctuation come from?
Random events …… • Rotational diffusion • Translational diffusion • Vibrational / Librational motions • Conformational sampling (conformational exchange)`
The behavior of the random fluctuation can be described by a _______ function.
correlation
Correlation function:
the measure of how quickly two variables change as a function of time.
Or, how quickly the NH dipole (or other vector dipole) changes as a function of time with respect to the external magnetic field (autocorrelation function).
The ______ ______ describes the distribution of motions (frequency of rotation) in a sample.
spectral density
Tc is directly porportional to
MW
T2 is inversely porportional to
MW
Any particular source of a local magnetization field can be considered a _______ ______.
relaxation mechanism
\_\_\_\_\_\_ mechanism (DD) : influences of one local spin on another
Dipolar mechanism (DD)
____ ___ ____ (CSA :
anisotropy of chemical shift tensor
Chemical shift anisotropy
_____: non-symmetric electronic field (I>=1)
Quadropole
DD > CSA > spin-rot
for 1/2 spin
Quad.»_space; DD > CSA > spin-rot
for spin > 1/2
Since all these result from molecular rotations, this implies that there may be a degree of \_\_\_\_\_\_\_ between mechanisms. Cross-correlation. TROSY-type experiments rely on this phenomena (DD and CSA). TROSY Transverse Optimized SpectroscopY
correlation
In NMR, any source of a fluctuating nuclear interaction (global or local) can
lead to____ _____ (with respect to the external magnetic field).
spin relaxation
A pattern or process of change, growth, or activity
Dynamics
Molecules are not static!
Brownian motion……molecular tumbling
Internal motions ….. J-couplings, side-chain rotations
Fluorescence studies ….. quenching of aromatic residues within a protein
NMR ….. site-specific molecular dynamic information
Molecular Dynamics
Internal motions …..
J-couplings, side-chain rotations
Fluorescence studies …..
quenching of aromatic residues within a protein
NMR …..
site-specific molecular dynamic information
NMR Motional Timescale for Fast (ps-ns)
Motions: - - - NMR parameters - -
Flesibility
Diffusion
Domain motions
Spin relaxation (R1,R2, and hnNOE) Residual dipolar coupling averaging
NMR Motional Timescale for Slow (us-ms)
Motions: - - - NMR parameters - - - -
Protein folding
Enzyme catalysis
Domain motions
Line shape R1p dispersion
Longitudinal magnetization exchange
Hydrogen exchange
Residual dipolar coupling averaging
• Dipolar, CSA, Spin rotation, Quadropole (all result from a fluctuating Bloc)
• Dipolar couplings are the origin of distance (NOE) and orientation (RDC) information
and also provide a mechanism for transitions to occur that contribute to relaxation
• Internal motions within a protein can be an additional source of relaxation in addition
to overall tumbling
Mechanisms of spin relaxation
• Keep track of random motions (rotations) [and Bloc(t)]
• The FT of the auto-correlation function yields the spectral density function, J()
• The spectral density function tells us about the probability of having a spin with the
frequency appropriate to cause relaxation – this explains spin relaxation !!
• Both T1 and T2 (and heteronuclear NOE) are proportional to the spectral density, J()
(because of molecular tumbling)
The auto-correlation and spectral density functions
Longitudinal elaxation (T1) (relaxation and local magnetic fields)
local fields are time dependent Bloc
Due to molecular motions (rotations), ____-_________ _____ ___________ ________ ______
[Bloc(t), transverse components (x-y)] occur within the sample and interact with individual
magnetic moments to rotate them into new positions– like an RF pulse! These transitions
occur only at Bloc =
◦
time-dependent local oscillating magnetic fields
Bloc(t) fields vary in magnitude due to _____ __ _______ ____ ______ ________ _______
(orientations are relative to Bo). The spins are in “contact” with the thermal motions.
changes in orientation from random thermal motions
For spins to “sense the Bloc(t) of another spin they must be?
very close to eachother
Since these local fields effect the orientation of individual magnetic moments, both the
magnitude and orientation of the ____ _________ can be affected leading to spin
relaxation and re-establishment of equilibrium magnetization along the z-axis.
BULK magnetization
lattice is also known as
reservoir of energy = molecular motion
longitudinal relaxation is also known as
spin-lattice relaxation (T1)
Transverse or spin-spin relaxation (time constant T2)
- loss of phase coherence of the ____ ____ in the transverse plane (xy-plane)
nuclear dipoles
