Preparative isolation of (+)-beta-eudesmol fromAmyris balsamifera

Summary Optically pure (+)-beta-eudesmol is a possible starting material for the synthesis of several termite defense compounds. A two step procedure for the isolation of gram quantities of (+)-beta-eudesmol from commercially availableAmyris balsamifera oil (syn. West Indian sandalwood oil), containing 8% beta-eudesmol, was developed. Step one consisted of an efficient vacuum distillation of the total oil. Step two was a medium pressure LC separation with an AgNO₃ impregnated silica gel stationary phase. Several other separation procedures failed due to the presence of many closely related sesquiterpene alcohols (75% of the oil).     

Excitation-energy dependence of the mechanism for two-photon ionization of liquid H(2)O and D(2)O from 8.3 to 12.4 eV

Transient absorption measurements monitor the geminate recombination kinetics of solvated electrons following two-photon ionization of liquid water at several excitation energies in the range from 8.3 to 12.4 eV. Modeling the kinetics of the electron reveals its average ejection length from the hydronium ion and hydroxyl radical counterparts and thus provides insight into the ionization mechanism. The electron ejection length increases monotonically from roughly 0.9 nm at 8.3 eV to nearly 4 nm at 12.4 eV, with the increase taking place most rapidly above 9.5 eV. We connect our results with recent advances in the understanding of the electronic structure of liquid water and discuss the nature of the ionization mechanism as a function of excitation energy. The isotope dependence of the electron ejection length provides additional information about the ionization mechanism. The electron ejection length has a similar energy dependence for two-photon ionization of liquid D(2)O, but is consistently shorter than in H(2)O by about 0.3 nm across the wide range of excitation energies studied.     

Subpicosecond Excited-State Proton Transfer Preceding Isomerization During the Photorecovery of Photoactive Yellow Protein

The ultrafast excited-state dynamics underlying the receptor state photorecovery is resolved in the M100A mutant of the photoactive yellow protein (PYP) from Halorhodospira halophila. The M100A PYP mutant, with its distinctly slower photocycle than wt PYP, allows isolation of the pB signaling state for study of the photodynamics of the protonated chromophore cis-p-coumaric acid. Transient absorption signals indicate a subpicosecond excited-state proton-transfer reaction in the pB state that results in chromophore deprotonation prior to the cis-trans isomerization required in the photorecovery dynamics of the pG state. Two terminal photoproducts are observed, a blue-absorbing species presumed to be deprotonated trans-p-coumaric acid and an ultraviolet-absorbing protonated photoproduct. These two photoproducts are hypothesized to originate from an equilibrium of open and closed folded forms of the signaling state, I(2) and I(2)'.     

Investigations into beam monitors at the AEg ̄ IS experiment

Detailed diagnostic of antiproton beams at low energies is required for essentially all experiments at the Antiproton Decelerator (AD), but will be particularly important for the future Extra Low ENergy Antiproton ring (ELENA) and its keV beam lines to the different experiments. Many monitors have been successfully developed and operated at the AD, but in particular beam profile monitoring remains a challenge. A dedicated beam instrumentation and detector test stand has recently been setup at the AE \(\bar {g}\) IS experiment (Antimatter Experiment: Gravity, Interferometry, Spectroscopy). Located behind the actual experiment, it allows for parasitic use of the antiproton beam at different energies for testing and calibration. With the aim to explore and validate different candidate technologies for future low energy beam lines, as well as the downstream antihydrogen detector in AE \(\bar {g}\) IS, measurements have been carried out using Silicon strip and pixel detectors, a purpose-built secondary emission monitor and emulsions. Here, results from measurements and characterization of the different detector types with regard to their future use at the AD complex are presented.     

Deconstructing the excited-state dynamics of β-carotene in solution

The femtosecond to nanosecond dynamics of the all-trans β-carotene carotenoid dissolved in 3-methylpentane is characterized and dissected with excitation-wavelength and temperature-dependent ultrafast dispersed transient absorption signals. The kinetics measured after red-edge (490 nm) and blue-edge (400 nm) excitation were contrasted under fluid solvent (298 K) and rigid glass (77 K) conditions. In all four measured data sets, the S* population kinetics was resolved prompting the development of a modified multicompartment model. The temperature-dependent and excitation wavelength-dependent S* quantum yield is ascribed to a competition of population surmounting a weak (55 cm(-1)) energy barrier on the S(2) state to favor S(1) generation and rapid internal conversion that favors S* generation. When cooled from room temperature to 77 K, the S* decay time scale shifted significantly from 30 to 400 ps, which is ascribed to small-scale structural relaxation with a 115 cm(-1) energy barrier. For the first time under low-energy excitation conditions, the triplet state is observed and confirmed to not originate from S* or S(1), but from S(2). The interconnectivity of the S* and S(1) populations is discussed, and no observed population flow is resolved between S* and S(1). Comparison of samples obtained from different laboratories with different purity levels demonstrates that sample contamination is not the primary origin of the S* state.