Elucidating the photoprotective properties of natural UV screening agents:ZEKE-PFI spectroscopy of methyl sinapate

As a prominent derivative of a natural sunscreen, methyl sinapate is an ideal candidate to provide fundamental insight into strategies on how to come to a rational design of artificial sunscreen filters with improved photoprotective properties. Here, static and time-resolved Zero Kinetic Energy–Pulsed Field Ionization (ZEKE–PFI) photoelectron spectroscopy has been used to study the spectroscopy and decay pathways of its electronically excited states. We find that different conformers are subject to distinct structural changes upon electronic excitation, and trace the structural changes that occur upon excitation back to the character of the LUMO. Ionization efficiency spectra in combination with pump–probe ZEKE–PFI spectra are consistent with the conclusion that the long-lived electronically excited state observed in the decay of the lowest excited singlet state is the lowest excited triplet state. Concurrently with providing information on the electronically excited states, the studies allow for a detailed characterization of the spectroscopic properties of the ground state of the radical ion, which is important in the context of the use of cinnamates in nature as antioxidants. Our studies determine the adiabatic ionization energies of the syn/cis, anti/cis and anti/trans conformers as 60 291.1 ± 0.5, 60 366.9 ± 0.5 and 60 503.9 ± 1.0 cm−1, respectively, and provide accurate vibrational fequencies of low-frequency modes of the molecular ion in its electronic ground state. Finally, the studies emphasize the important role of vibrational and electronic autoionization processes that start to dominate the ionization dynamics in non-rigid molecules of the present size

Pseudo-Jahn-Teller distortion of pyridine in its lowest triplet state

Biological and Soft Matter Physic

Zero kinetic energy-pulsed field ionization and resonance enhanced multiphoton ionization photoelectron spectroscopy: Ionization dynamics of Rydberg states in HBr

The results of rotationally resolved resonance enhanced multiphoton ionization photoelectron spectroscopy and zero kinetic energy‐pulsed field ionization studies on HBr via various rotational levels of the F^ 1Δ_2 and f^ 3Δ_2 Rydberg states are reported. These studies lead to an accurate determination of the lowest ionization threshold as 94 098.9±1 cm^(−1). Observed rotational and spin–orbit branching ratios are compared to the results of ab initio calculations. The differences between theory and experiment highlight the dominant role of rotational and spin–orbit interactions for the dynamic properties of the high‐n Rydberg states involved in the pulsed field ionization process

Circular spectropolarimetric sensing of chiral photosystems in decaying leaves

Circular polarization spectroscopy has proven to be an indispensable tool in photosynthesis research and (bio)-molecular research in general. Oxygenic photosystems typically display an asymmetric Cotton effect around the chlorophyll absorbance maximum with a signal $\leq 1 \%$. In vegetation, these signals are the direct result of the chirality of the supramolecular aggregates. The circular polarization is thus directly influenced by the composition and architecture of the photosynthetic macrodomains, and is thereby linked to photosynthetic functioning. Although ordinarily measured only on a molecular level, we have developed a new spectropolarimetric instrument, TreePol, that allows for both laboratory and in-the-field measurements. Through spectral multiplexing, TreePol is capable of fast measurements with a sensitivity of $\sim 1*10^{-4}$ and is therefore suitable of non-destructively probing the molecular architecture of whole plant leaves. We have measured the chiroptical evolution of \textit{Hedera helix} leaves for a period of 22 days. Spectrally resolved circular polarization measurements (450-900 nm) on whole leaves in transmission exhibit a strong decrease in the polarization signal over time after plucking, which we accredit to the deterioration of chiral macro-aggregates. Chlorophyll \textit{a} levels measured over the same period by means of UV-Vis absorption and fluorescence spectroscopy showed a much smaller decrease. With these results we are able to distinguish healthy from deteriorating leaves. Hereby we indicate the potency of circular polarization spectroscopy on whole and intact leaves as a nondestructive tool for structural and plant stress assessment. Additionally, we underline the establishment of circular polarization signals as remotely accessible means of detecting the presence of extraterrestrial life.Comment: 29 pages, 6 figure

Mediterranean alien harmful algal blooms:Origins and impacts

Harmful algal blooms (HABs) are mostly phytoplankton blooms, which have detrimental environmental and socioeconomic impacts. The Mediterranean Sea due to its enclosed nature is of special concern since it has an enormously rich native biodiversity. Though, it is also the world's most invaded marine ecosystem and is considered at very high risk of future invasions. The aim of this review study is to explore the origins, establishment, environmental, and socioeconomic impacts of HABs caused by nonnative algal species in the Mediterranean Sea. Based on this, it is also discussed whether HABs form an increasing threat in the basin, and what could possibly be done to prevent or to minimize their impacts. The increasing rate of their introduction and the harmful impacts that they have on the environment, economy, and human health makes it important to have accurate knowledge about HABs. Anthropogenic activities and climate change are considered the main contributors of alien invasions but also the main enablers of HAB events. Mediterranean HABs are adequately studied, but there are no studies purposefully concerning invasive microalgae species in the basin. In the present study, 20 species have been identified, and an attempt has been made to collect their introduction information, as well as known or suspected impacts. Future research should be focused on data mining, current legislation updates, and monitoring of Mediterranean coastlines