Preferred Label : Förster-resonance-energy transfer;
Detailed label : Förster-resonance-energy transfer FRET;
IUPAC acronym : FRET;
IUPAC definition : Non-radiative excitation transfer between two molecular entities separated by distances
considerably exceeding the sum of their van der Waals radii. It describes the transfer
in terms of the interaction between the transition (dipole) moments of the entities
in the very weak dipole-dipole coupling limit. It is a Coulombic interaction frequently
called a dipole-dipole coupling. The transfer rate constant from donor to acceptor,
kT, is given by \[k_{{T}} k_{{D}}\left ( \frac{R_{0}}{r} \right ) {6} \frac{1}{\tau
_{D} {0}}\left ( \frac{R_{0}}{r}\right ) {6}\] where kD and τD0 are the emission rate
constant and the lifetime of the excited donor in the absence of transfer, respectively,
r is the distance between the donor and the acceptor and R0 is the critical quenching
radius or Förster radius, i.e., the distance at which transfer and spontaneous decay
of the excited donor are equally probable (kT kD) (see Note 3). R0 is given by \[R_{0}
Const.\left ( \frac{\kappa {2}\mathit{\Phi}_{D} {0}J }{n {4}} \right ) {1/6}\] where
κ is the orientation factor, ΦD0 is the fluorescence quantum yield of the donor in
the absence of transfer, n is the average refractive index of the medium in the wavelength
range where spectral overlap is significant, J is the spectral overlap integral reflecting
the degree of overlap of the donor emission spectrum with the acceptor absorption
spectrum and given by \[J \int _{\lambda }I_{\lambda} {D}(\lambda)\epsilon _{A}\left
( \lambda \right )\lambda {4}{d}\lambda\] where IλD(λ) is the normalized spectral
radiant intensity of the donor so that (λ)IλD(λ)dλ 1. ɛA(λ) is the molar decadic
absorption coefficient of the acceptor. See Note 3 for the value of Const..;
Scope note : a practical expression for r0 is: r0nm 2.108 10-2
¿2 fd0 n-4 ¿ ¿ i¿d ¿
¿a ¿ dm3 mol-1 cm-1
¿ nm 4 1/6 the orientation factor ¿ is given
by ¿ ¿da 3 ¿d ¿a ¿d ¿a f
2 ¿d ¿a where¿da is the angle between the donor and acceptor moments, and
¿dand ¿aare the angles between these, respectively, and the separation vector;f is
the angle between the projections of the transition moments on a plane perpendicular
to the line through the centres.¿2 can in principle take values from 0 (perpendicular
transition moments) to 4 (collinear transition moments). when the transition moments
are parallel and perpendicular to the separation vector, ¿2 1 . when
they are in line (i.e., their moments are strictly along the separation vector),
¿2 4 . for randomly oriented transition (dipole) moments, e.g., in fluid solutions,
¿2 23 .; fret is sometimes inappropriately called fluorescence-resonance energy transfer. this
is not correct because there is no fluorescence involved in fret.; in practical terms, the integral ¿ ¿ i¿d ¿ is the
area under the plot of the donor emission intensity versus the emission wavelength.; the bandpass d¿is a constant in spectrophotometers and spectrofluorometers using
gratings. thus, the scale is linear in wavelength and it is convenient to express
and calculate the integrals in wavelengths instead of wavenumbers in order to avoid
confusion.; the transfer quantum efficiency is defined as ft kt
kd kt and can be related to the ratio r r0 as follows:
ft 1 1 r r0 6 or written
in the following form : ft 1 td td0 where
td is the donor excited-state lifetime in the presence of acceptor, and td0 in the
absence of acceptor.; foerster is an alternative and acceptable spelling for förster.;
Origin ID : FT07381;
See also
Non-radiative excitation transfer between two molecular entities separated by distances
considerably exceeding the sum of their van der Waals radii. It describes the transfer
in terms of the interaction between the transition (dipole) moments of the entities
in the very weak dipole-dipole coupling limit. It is a Coulombic interaction frequently
called a dipole-dipole coupling. The transfer rate constant from donor to acceptor,
kT, is given by \[k_{{T}} k_{{D}}\left ( \frac{R_{0}}{r} \right ) {6} \frac{1}{\tau
_{D} {0}}\left ( \frac{R_{0}}{r}\right ) {6}\] where kD and τD0 are the emission rate
constant and the lifetime of the excited donor in the absence of transfer, respectively,
r is the distance between the donor and the acceptor and R0 is the critical quenching
radius or Förster radius, i.e., the distance at which transfer and spontaneous decay
of the excited donor are equally probable (kT kD) (see Note 3). R0 is given by \[R_{0}
Const.\left ( \frac{\kappa {2}\mathit{\Phi}_{D} {0}J }{n {4}} \right ) {1/6}\] where
κ is the orientation factor, ΦD0 is the fluorescence quantum yield of the donor in
the absence of transfer, n is the average refractive index of the medium in the wavelength
range where spectral overlap is significant, J is the spectral overlap integral reflecting
the degree of overlap of the donor emission spectrum with the acceptor absorption
spectrum and given by \[J \int _{\lambda }I_{\lambda} {D}(\lambda)\epsilon _{A}\left
( \lambda \right )\lambda {4}{d}\lambda\] where IλD(λ) is the normalized spectral
radiant intensity of the donor so that (λ)IλD(λ)dλ 1. ɛA(λ) is the molar decadic
absorption coefficient of the acceptor. See Note 3 for the value of Const..
