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Related Concept Videos

Colors and Magnetism03:02

Colors and Magnetism

Color in Coordination Complexes
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
Valence Bond Theory02:42

Valence Bond Theory

Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
Diamagnetic Shielding of Nuclei: Local Diamagnetic Current01:14

Diamagnetic Shielding of Nuclei: Local Diamagnetic Current

An applied magnetic field causes the electrons present in the molecule to circulate, setting up a local diamagnetic current within the molecule. The local diamagnetic current arising from circulating sigma-bonding electrons induces a magnetic field, Blocal that opposes the applied magnetic field, B0. The effective magnetic field experienced by these nuclei is given by the difference between the applied and local magnetic fields in a phenomenon called local diamagnetic shielding. Essentially,...
Atomic Nuclei: Magnetic Resonance01:05

Atomic Nuclei: Magnetic Resonance

The number of nuclear spins aligned in the lower energy state is slightly greater than those in the higher energy state. In the presence of an external magnetic field, as the spins precess at the Larmor frequency, the excess population results in a net magnetization oriented along the z axis. When a pulse or a short burst of radio waves at the Larmor frequency is applied along the x axis, the coupling of frequencies causes resonance and flips the nuclear spins of the excess population from the...
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Light-generated paramagnetic intermediates in BLUF domains.

Stefan Weber1, Claudia Schroeder, Sylwia Kacprzak

  • 1Albert-Ludwigs-Universität Freiburg, Institut für Physikalische Chemie, Freiburg, Germany.

Photochemistry and Photobiology
|January 5, 2011
PubMed
Summary
This summary is machine-generated.

Researchers studied blue-light photoreceptors (BLUF domains) using low-temperature electron paramagnetic resonance. They observed photoinduced states and radical pairs, linking electronic structure differences to amino acid variations in BLUF domains.

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Area of Science:

  • Biochemistry
  • Photobiology
  • Molecular Biology

Background:

  • Blue-light sensitive BLUF domains are flavoproteins regulating stress responses.
  • These domains are found in bacteria and eukaryotes, indicating conserved functions.

Purpose of the Study:

  • To investigate the photoreactivity of flavin adenine dinucleotide (FAD) cofactors in three distinct BLUF domains.
  • To correlate structural differences in BLUF domains with their photochemical properties.

Main Methods:

  • Time-resolved electron paramagnetic resonance (TREPR) spectroscopy at low temperatures.
  • Analysis of photoinduced flavin triplet states and radical-pair species on a microsecond timescale.

Main Results:

  • Photoinduced flavin triplet states and radical-pair species were detected in BLUF domains from Rhodobacter sphaeroides, Synechocystis sp. PCC 6803, and Escherichia coli.
  • Differences in zero-field splitting parameters of triplet states indicated variations in FAD cofactor electronic structures.
  • These electronic structure variations correlated with amino acid composition within the cofactor binding pockets.
  • A tyrosine residue was identified as critical for generating light-induced radical pairs in the Synechocystis BLUF domain.

Conclusions:

  • The electronic structure of FAD cofactors in BLUF domains is influenced by the surrounding amino acid environment.
  • TREPR is a valuable technique for elucidating the photochemistry and structure-function relationships of BLUF domains.
  • Specific amino acid residues, like tyrosine, play crucial roles in the photoactivation mechanisms of BLUF domains.