10 research outputs found
Far-red fluorescence:A direct spectroscopic marker for LHCII oligomer formation in non-photochemical quenching
AbstractTime-resolved fluorescence on oligomers of the main light-harvesting complex from higher plants indicate that in vitro oligomerization leads to the formation of a weakly coupled inter-trimer chlorophyll–chlorophyll (Chl) exciton state which converts in tens of ps into a state which is spectrally broad and has a strongly far-red enhanced fluorescence spectrum. Both its lifetime and spectrum show striking similarity with a 400ps fluorescence component appearing in intact leaves of Arabidopsis when non-photochemical quenching (NPQ) is induced. The fluorescence components with high far-red/red ratio are thus a characteristic marker for NPQ conditions in vivo. The far-red emitting state is shown to be an emissive Chl–Chl charge transfer state which plays a crucial part in the quenching
Recent advances in the application of parahydrogen in catalysis and biochemistry
Nuclear Magnetic Resonance (NMR) spectroscopy and Magnetic Resonance Imaging (MRI) are analytical and diagnostic tools that are essential for a very broad field of applications, ranging from chemical analytics, to non-destructive testing of materials and the investigation of molecular dynamics, to in vivo medical diagnostics and drug research. One of the major challenges in their application to many problems is the inherent low sensitivity of magnetic resonance, which results from the small energy-differences of the nuclear spin-states. At thermal equilibrium at room temperature the normalized population difference of the spin-states, called the Boltzmann polarization, is only on the order of 10⁻⁵. Parahydrogen induced polarization (PHIP) is an efficient and cost-effective hyperpolarization method, which has widespread applications in Chemistry, Physics, Biochemistry, Biophysics, and Medical Imaging. PHIP creates its signal-enhancements by means of a reversible (SABRE) or irreversible (classic PHIP) chemical reaction between the parahydrogen, a catalyst, and a substrate. Here, we first give a short overview about parahydrogen-based hyperpolarization techniques and then review the current literature on method developments and applications of various flavors of the PHIP experiment
Excitation energy trapping and dissipation by Ni-substituted bacteriochlorophyll a in reconstituted LH1 complexes from Rhodospirillum rubrum
Bacteriochlorophyll a with Ni2+ replacing the central Mg 2+ ion was used as an ultrafast excitation energy dissipation center in reconstituted bacterial LH1 complexes. B870, a carotenoid-less LH1 complex, and B880, an LH1 complex containing spheroidene, were obtained via reconstitution from the subunits isolated from chromatophores of Rhodospirillum rubrum. Ni-substituted bacteriochlorophyll a added to the reconstitution mixture partially substituted the native pigment in both forms of LH1. The excited-state dynamics of the reconstituted LH1 complexes were probed by femtosecond pump-probe transient absorption spectroscopy in the visible and near-infrared spectral region. Spheroidene-binding B880 containing no excitation dissipation centers displayed complex dynamics in the time range of 0.1-10 ps, reflecting internal conversion and intersystem crossing in the carotenoid, exciton relaxation in BChl complement, and energy transfer from carotenoid to the latter. In B870, some aggregation-induced excitation energy quenching was present. The binding of Ni-BChl a to both B870 and B880 resulted in strong quenching of the excited states with main deexcitation lifetime of ca. 2 ps. The LH1 excited-state lifetime could be modeled with an intrinsic decay time constant in Ni-substituted bacteriochlorophyll a of 160 fs. The presence of carotenoid in LH1 did not influence the kinetics of energy trapping by Ni-BChl unless the carotenoid was directly excited, in which case the kinetics was limited by a slower carotenoid S1 to bacteriochlorophyll energy transfer. © 2013 American Chemical Society
Ultrafast fluorescence study on the location and mechanism of non-photochemical quenching in diatoms
Excitation energy trapping and dissipation by Ni-substituted bacteriochlorophyll a in reconstituted LH1 complexes from Rhodospirillum rubrum
Bacteriochlorophyll a with N
Excitation Energy Trapping and Dissipation by Ni-Substituted Bacteriochlorophyll <i>a</i> in Reconstituted LH1 Complexes from Rhodospirillum rubrum
Bacteriochlorophyll <i>a</i> with Ni<sup>2+</sup> replacing
the central Mg<sup>2+</sup> ion was used as an ultrafast excitation
energy dissipation center in reconstituted bacterial LH1 complexes.
B870, a carotenoid-less LH1 complex, and B880, an LH1 complex containing
spheroidene, were obtained via reconstitution from the subunits isolated
from chromatophores of Rhodospirillum rubrum. Ni-substituted bacteriochlorophyll <i>a</i> added to
the reconstitution mixture partially substituted the native pigment
in both forms of LH1. The excited-state dynamics of the reconstituted
LH1 complexes were probed by femtosecond pump–probe transient
absorption spectroscopy in the visible and near-infrared spectral
region. Spheroidene-binding B880 containing no excitation dissipation
centers displayed complex dynamics in the time range of 0.1–10
ps, reflecting internal conversion and intersystem crossing in the
carotenoid, exciton relaxation in BChl complement, and energy transfer
from carotenoid to the latter. In B870, some aggregation-induced excitation
energy quenching was present. The binding of Ni-BChl <i>a</i> to both B870 and B880 resulted in strong quenching of the excited
states with main deexcitation lifetime of ca. 2 ps. The LH1 excited-state
lifetime could be modeled with an intrinsic decay time constant in
Ni-substituted bacteriochlorophyll <i>a</i> of 160 fs. The
presence of carotenoid in LH1 did not influence the kinetics of energy
trapping by Ni-BChl unless the carotenoid was directly excited, in
which case the kinetics was limited by a slower carotenoid S<sub>1</sub> to bacteriochlorophyll energy transfer