TY - JOUR
T1 - Freezing Conformers for Gas-Phase Förster Resonance Energy Transfer
AU - Toft Lindkvist, Thomas
AU - Djavani-Tabrizi, Iden
AU - Chen, Li
AU - Brøndsted Nielsen, Steen
PY - 2024/12
Y1 - 2024/12
N2 - Various techniques are available to illuminate geometric structures of molecular ions in gas phase, such as Förster Resonance Energy Transfer (FRET) informing on distances between two dyes covalently attached to a molecule. Typically, cationic rhodamines, which absorb and emit visible light, are used for labeling. Extensive work has revealed that the transition energy of a rhodamine is intricately linked to its nearby microenvironment, with nearby charges causing Stark-shifted emission. This occurs because the inter-dye Coulomb interaction is weaker in the excited state (S1) than in the ground state (S0) due to the increase in polarizability upon excitation. Therefore, absorption and emission spectra, along with FRET efficiencies, provide insights into structural motifs. At room temperature, multiple conformers often co-exist, leading to overlapping absorption bands among different conformers and broad spectra. To study specific conformers, it is necessary to isolate them, for example, using ion-mobility spectrometry. Another approach is to reduce temperature, which results in spectral narrowing and distinct absorption bands, allowing for the selection of specific conformers through selective excitation. Here, we describe the instrumentation used for cryogenically cold FRET experiments and discuss recent results for small model systems, as well as future directions for a technique still in its infancy.
AB - Various techniques are available to illuminate geometric structures of molecular ions in gas phase, such as Förster Resonance Energy Transfer (FRET) informing on distances between two dyes covalently attached to a molecule. Typically, cationic rhodamines, which absorb and emit visible light, are used for labeling. Extensive work has revealed that the transition energy of a rhodamine is intricately linked to its nearby microenvironment, with nearby charges causing Stark-shifted emission. This occurs because the inter-dye Coulomb interaction is weaker in the excited state (S1) than in the ground state (S0) due to the increase in polarizability upon excitation. Therefore, absorption and emission spectra, along with FRET efficiencies, provide insights into structural motifs. At room temperature, multiple conformers often co-exist, leading to overlapping absorption bands among different conformers and broad spectra. To study specific conformers, it is necessary to isolate them, for example, using ion-mobility spectrometry. Another approach is to reduce temperature, which results in spectral narrowing and distinct absorption bands, allowing for the selection of specific conformers through selective excitation. Here, we describe the instrumentation used for cryogenically cold FRET experiments and discuss recent results for small model systems, as well as future directions for a technique still in its infancy.
KW - Cryogenic temperatures
KW - FRET
KW - Gas phase
KW - Mass spectroscopy
KW - Rhodamine
UR - http://www.scopus.com/inward/record.url?scp=85207002643&partnerID=8YFLogxK
U2 - 10.1002/cplu.202400448
DO - 10.1002/cplu.202400448
M3 - Journal article
C2 - 39190502
AN - SCOPUS:85207002643
SN - 2192-6506
VL - 89
JO - ChemPlusChem
JF - ChemPlusChem
IS - 12
M1 - e202400448
ER -