Near Matches
Ignore Exact
Full Text
nuclear overhauser effect
created by
overhauser
(
thing
) by
overhauser
(2.9 mon)
(
print
)
?
(
I like it!
)
1
C!
Sun Mar 04 2001 at 2:50:08
The nuclear
overhauser
effect (or NOE) is a special case of
nuclear
relaxation
in
nuclear magnetic resonance
(NMR) spectroscopy and
magnetic resonance imaging
(MRI). In a typical NMR or MRI experiment, a nucleus in a
magnetic field
absorbs
photons
of a
frequency
mostly determined by the
elemental
identity of the nucleus (e.g.
hydrogen
,
carbon
etc.) and the strength of the applied magnetic field (see
Zeeman effect
.) Nuclei so treated are said to be in an
excited
nuclear spin state, and they literally spin like a
top
in said magnetic field. They can be observed by the
current
their spinning generates in wire coils looped around the sample compartment, be it an
NMR
tube or the huge cavernous opening in an
MRI
device.
But they don't spin forever. One nucleus in an excited spin state can transfer its magnetization to another nucleus in a process called dipolar coupling. The rate at which this happens between a given pair of nuclei is
inversely
proportional
to the cube of the distance between. It's also a complicated
function
of the
angle
between the line formed by the two atoms and the external magnetic field. Since most NMR experiments are performed in solution, and most MRI experiments involve observation of the protons on water molecules in a solution-like environment, this angle varies considerably during the time course of the experiment, as the
molecules
being observed are moving and spinning all over the place. This is called
isotropic
rotational averaging, and under these conditions the rate of magnetization transfer is independent of the angle between the magnetic field and the internuclear vector, but inversely proportional to the
sixth
power of the distance between them. Magnetization transfer by dipolar coupling under the conditions of isotropic rotational averaging is called the
nuclear overhauser effect.
This is the principal pathway by which any nucleus being observed in solution loses its magnetization, thus it is the main factor contributing to nuclear relaxation. Note that the magnitude of both the NOE and dipolar coupling are independent of the nature of the intervening
medium
, they are
through-space
interactions, as opposed to through-bond interactions like
J-coupling
.
This may seem pretty esoteric but in fact it forms the basis, along with J-coupling, for the determination of
protein
,
DNA
and
RNA
structures and their interactions with other molecules. One merely excites some particular nucleus, waits a period of time, and observes where the magnetization has been transferred. Because of the aforementioned distance dependence of the magnetization transfer, this allows the 3-dimensional
mapping
of the molecule when the experiment is repeated for a sufficient percentage of the nuclei in a molecule. The method of NMR has overtaken that of
x-ray crystallography
as the method of choice for
rational drug design
not because of its ability to determine structures, but because the nuclear overhauser effect allows one to quickly and easily observe the interaction of these
biomolecules
with small molecule drug candidates.
printable version
chaos
proteomics
i only knew when silence screamed
chemical shift
J-coupling
rational drug design
biophysics
Zeeman effect
magnetic field
biomolecules
atomic radius
ripple effect
dead hand
power plant
Entertainment Lasers
HTML symbol reference
Psychedelic Trance
Autumn Leaves
relaxation
X-Ray crystallography
magnetic resonance imaging
NMR
excited state
Isotropic
Y'know, if you
log in
, you can write something here, or contact authors directly on the site.
Create a New User
if you don't already have an account.
Login
Password
remember me
password reminder
register
Everything2 Help
The best nodes of all time:
citizen's arrest
How to smuggle a snake onto an airplane
spleen
A Prayer for Mr. Leary
Don't be smart too, I couldn't stand it
Is being domesticated an evolutionary advantage?
woodchipper
Fine paintbrush, light strokes, special paint
Bunyip
The UK's farmers, or How to reap a profit without worrying about pesky scruples
County Lines
The biggest dose of LSD ever
Paolo Soleri
antigravpussy
One fly amongst many
(
person
)
sam512
Moon Base Shackleton, 1978
(
fiction
)
Pavlovna
toy boy
(
person
)
XWiz
tear jerker
(
review
)
Heitah
Anarchy is Order
(
idea
)
jessicaj
July 26, 2008
(
dream
)
Berek
ABBA
(
person
)
devolution
k-hole
(
place
)
Nadine_2
The Sound Of Madness
(
review
)
SwimmingMonkey
Conversations with Fo Fo, the Loneliest dog in Purgatory
(
fiction
)
locke baron
lynx
(
thing
)
Simulacron3
Reality, Dimensions and the Natural Ontology
(
essay
)
SubSane
Making Love to a 9-Foot Woman
(
person
)
Ouzo
Thoughts
(
idea
)
antigravpussy
I fall silent, listening. The breadcrumbs are talking about us
(
person
)
Everything 2 is brought to you by the letter C and
The Everything Development Company
