Module 3 Flashcards

1
Q

Molecules “_______” or _______randomly

A

“tumble” or rotate

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2
Q

Tc

A

rotational correlation time

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3
Q

Three things that influence tumbling rates:

A

viscoscity

temperature

size of particle

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4
Q

Molecular rotations cause ____ ___-_______ _____ , B loc(t)

A

local time-dependent fields

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5
Q
NMR-active nuclei with \_\_\_\_\_ \_\_\_\_\_\_ \_\_\_\_\_\_can interact with other nuclei causing
spin relaxation (T1 and T2).
A

fluctuating local fields

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6
Q

the __ and __ time constants describe the rate (T1= 1/R1) at which longitudinal and
transverse relaxation occur, respectively.

A

T1 and T2

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7
Q

Where do molecular rotations occur from?

A

They occur from the influence of a single spin or many spins simultaneously

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8
Q

What do molecular rotations depend on?

A

gama Bloc = omega knot

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9
Q

Where does the fluctuation come from?

A
Random events ……
• Rotational diffusion
• Translational diffusion
• Vibrational / Librational motions
• Conformational sampling (conformational exchange)`
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10
Q

The behavior of the random fluctuation can be described by a _______ function.

A

correlation

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11
Q

Correlation function:

A
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).
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12
Q

The ______ ______ describes the distribution of motions (frequency of rotation) in a sample.

A

spectral density

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13
Q

Tc is directly porportional to

A

MW

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14
Q

T2 is inversely porportional to

A

MW

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15
Q

Any particular source of a local magnetization field can be considered a _______ ______.

A

relaxation mechanism

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16
Q
\_\_\_\_\_\_ mechanism (DD) :
influences of one local spin on another
A

Dipolar mechanism (DD)

17
Q

____ ___ ____ (CSA :

anisotropy of chemical shift tensor

A

Chemical shift anisotropy

18
Q

_____: non-symmetric electronic field (I>=1)

A

Quadropole

19
Q

DD > CSA > spin-rot

A

for 1/2 spin

20
Q

Quad.&raquo_space; DD > CSA > spin-rot

A

for spin > 1/2

21
Q
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
A

correlation

22
Q

In NMR, any source of a fluctuating nuclear interaction (global or local) can
lead to____ _____ (with respect to the external magnetic field).

A

spin relaxation

23
Q

A pattern or process of change, growth, or activity

24
Q

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

A

Molecular Dynamics

25
Internal motions …..
J-couplings, side-chain rotations
26
Fluorescence studies …..
quenching of aromatic residues within a protein
27
NMR …..
site-specific molecular dynamic information
28
NMR Motional Timescale for Fast (ps-ns) ``` Motions: - - - NMR parameters - - ```
Flesibility Diffusion Domain motions ``` Spin relaxation (R1,R2, and hnNOE) Residual dipolar coupling averaging ```
29
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
30
• 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
31
• 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
32
``` Longitudinal elaxation (T1) (relaxation and local magnetic fields) ```
local fields are time dependent Bloc
33
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
34
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
35
For spins to "sense the Bloc(t) of another spin they must be?
very close to eachother
36
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
37
lattice is also known as
reservoir of energy = molecular motion
38
longitudinal relaxation is also known as
spin-lattice relaxation (T1)
39
Transverse or spin-spin relaxation (time constant  T2) | - loss of phase coherence of the ____ ____ in the transverse plane (xy-plane)
nuclear dipoles