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M. Pecul and W. Dzwolak
ECd brings information on the structure of the ground state of a chiral molecule,
CPL is a source of information on the geometry of the excited state, which may differ significantly from the ground-state one. (CPL is not to be confused with fluorescence-detected Cd, which still probes the structure of the ground state.) unlike Cd,
for which several commercial instruments have been distributed for over 40 years,
CPL measurements have been made up to date mainly on custom-built instruments.
however, with the method becoming more popular, first commercial spectropolarimeters/fluorometers emerged (the first one has been CPL-200 by JASCo).
Even though CPL is far less widespread than Cd, CPL spectra of numerous systems of biological significance have been measured, and it seems this field of application is growing. there are several early works (reviewed in Ref. 89 and 90)
concerning CPL as a probe of NAdh-dehydrogenase complexes [91, 92], conformational changes in tRNA [93], and bilirubin bound to albumin [94–96], as well
as several studies involving time-resolved CPL applied to probe fast processes in
biomolecules and their metal complexes (as reviewed for example in Ref. 97). more
recently, CPL has also been observed for example in green fluorescent protein [98].
there have been also several studies utilizing strong CPL signal of lanthanide(III)
complexes as a structural probe, including the biological applications [99]. more examples of the recent applications of CPL for solving structural problems concerning
proteins and their complexes can be found in a specialized review on this subject by
gussakovsky [100] and in a more general review on CPL by Riehl and muller [101].
Recently, first quantum chemical calculations of CPL have been performed,
which is likely to give impulse to more experimental studies. From theoretical point
of view, the nature of CPL is very similar to ECd, with the only difference that
while ECd intensity needs to be evaluated at the equilibrium structure of the ground
state, to calculate CPL intensity one needs to know geometry of the energy minimum on the excited state potential energy surface. this requirement was impossible
to fulfill for all but the smallest molecules before developement of analytical excitation energy gradient in time-dependent density functional theory formalism. CPL
spectra are being calculated since 2010 [102, 103], and it is likely their calculations
will be soon extended to the systems of biological significance.
6.7 SUMMARY
In this brief chapter, we have ventured to outline the most important fields of application of circular dichroism spectroscopy (and related circularly polarized luminescence spectroscopy) in bioscience. While vibrational chiroptical spectroscopies
are successful competitors of electronic Cd in structural analysis (in particular determination of absolute configuration) of small molecules, ECd is, and is likely to
remain, a method of choice in obtaining information on global (and in some cases
local, when prosthetic group chromophores are involved) structure of proteins and
nucleic acids. unlike vCd, ECd does not require dissolving biopolymers in d 2 o,
and, unline in RoA, the samples are not subjected to prolonged laser irradiation.
M. Pecul and W. Dzwolak
ECd brings information on the structure of the ground state of a chiral molecule,
CPL is a source of information on the geometry of the excited state, which may differ significantly from the ground-state one. (CPL is not to be confused with fluorescence-detected Cd, which still probes the structure of the ground state.) unlike Cd,
for which several commercial instruments have been distributed for over 40 years,
CPL measurements have been made up to date mainly on custom-built instruments.
however, with the method becoming more popular, first commercial spectropolarimeters/fluorometers emerged (the first one has been CPL-200 by JASCo).
Even though CPL is far less widespread than Cd, CPL spectra of numerous systems of biological significance have been measured, and it seems this field of application is growing. there are several early works (reviewed in Ref. 89 and 90)
concerning CPL as a probe of NAdh-dehydrogenase complexes [91, 92], conformational changes in tRNA [93], and bilirubin bound to albumin [94–96], as well
as several studies involving time-resolved CPL applied to probe fast processes in
biomolecules and their metal complexes (as reviewed for example in Ref. 97). more
recently, CPL has also been observed for example in green fluorescent protein [98].
there have been also several studies utilizing strong CPL signal of lanthanide(III)
complexes as a structural probe, including the biological applications [99]. more examples of the recent applications of CPL for solving structural problems concerning
proteins and their complexes can be found in a specialized review on this subject by
gussakovsky [100] and in a more general review on CPL by Riehl and muller [101].
Recently, first quantum chemical calculations of CPL have been performed,
which is likely to give impulse to more experimental studies. From theoretical point
of view, the nature of CPL is very similar to ECd, with the only difference that
while ECd intensity needs to be evaluated at the equilibrium structure of the ground
state, to calculate CPL intensity one needs to know geometry of the energy minimum on the excited state potential energy surface. this requirement was impossible
to fulfill for all but the smallest molecules before developement of analytical excitation energy gradient in time-dependent density functional theory formalism. CPL
spectra are being calculated since 2010 [102, 103], and it is likely their calculations
will be soon extended to the systems of biological significance.
6.7 SUMMARY
In this brief chapter, we have ventured to outline the most important fields of application of circular dichroism spectroscopy (and related circularly polarized luminescence spectroscopy) in bioscience. While vibrational chiroptical spectroscopies
are successful competitors of electronic Cd in structural analysis (in particular determination of absolute configuration) of small molecules, ECd is, and is likely to
remain, a method of choice in obtaining information on global (and in some cases
local, when prosthetic group chromophores are involved) structure of proteins and
nucleic acids. unlike vCd, ECd does not require dissolving biopolymers in d 2 o,
and, unline in RoA, the samples are not subjected to prolonged laser irradiation.