Effects of tunable excitation in carotenoids explained by the vibrational energy relaxation approach

Carotenoids are fundamental building blocks of natural light harvesters with convoluted and ultrafast energy deactivation networks. In order to disentangle such complex relaxation dynamics, several studies focused on transient absorption measurements and their dependence on the pump wavelength. However, such findings are inconclusive and sometimes contradictory. In this study, we compare internal conversion dynamics in \(\beta\)-carotene, pumped at the first, second, and third vibronic progression peak. Instead of employing data fitting algorithms based on global analysis of the transient absorption spectra, we apply a fully quantum mechanical model to treat the high-frequency symmetric carbon–carbon (C=C and C–C) stretching modes explicitly. This model successfully describes observed population dynamics as well as spectral line shapes in their time-dependence and allows us to reach two conclusions: Firstly, the broadening of the induced absorption upon excess excitation is an effect of vibrational cooling in the first excited state (\(S_{1}\)). Secondly, the internal conversion rate between the second excited state (\(S_{2}\)) and \(S_{1}\) crucially depends on the relative curve displacement. The latter point serves as a new perspective on solvent- and excitation wavelength-dependent experiments and lifts contradictions between several studies found in literature.     

Chirality-based signatures of local protein environments in two-dimensional optical spectroscopy of two species photosynthetic complexes of green sulfur bacteria: simulation study

Two-dimensional electronic chirality-induced signals of excitons in the photosynthetic Fenna-Matthews-Olson complex from two species of green sulfur bacteria (Chlorobium tepidum and Prosthecochloris aestuarii) are compared. The spectra are predicted to provide sensitive probes of local protein environment of the constituent bacteriochlorophyll a chromophores and reflect electronic structure variations (site energies and couplings) of the two complexes. Pulse polarization configurations are designed that can separate the coherent and incoherent exciton dynamics contributions to the two-dimensional spectra.     

Safflower (Carthamus Tinctorius L.) a Potential Source of Drugs against Cryptococcal Infections,Malaria and Leishmaniasis

In this research we present that Carthamus Tinctorius L. (gen. Asteraceae, otherwise known as Safflower) (Fig. 1) may contain agents active in Cryptococcal infections, malaria and Leishmaniasis, as treatment options are becoming scarce due to drug resistance development. Phytochemistry and pharmacological activities (antimicrobial, antimalarial, antileishmanial) of C. tinctorius L. were analyzed. The composition of volatile oil of safflower dried flowers was analyzed by gas chromatography-mass spectrophotometry with flame ionization detector (GC-FID) and in vitro sensitivity assays were performed to assess biological activity. 8 known and 3 unknown compounds were detected in the extract (Fig. 1). Then the Safflower ointment was manufactured and its acute toxicity study on rats was tested. The volatile oil of C. tinctorius L exhibited activity against Cryptococcus neoformans, Plasmodium falciparum and Leishmania donovani. Safflower volatile oil has anticryptococcal, antimalarial and antileishmanial effects. The prepared ointment had an excellent acute toxicity safety profile.     

Unravelling coherent dynamics and energy dissipation in photosynthetic complexes by 2D spectroscopy

Spectroscopic studies of light harvesting and the subsequent energy conversion in photosynthesis can track quantum dynamics happening on the microscopic level. The Fenna-Matthews-Olson complex of the photosynthetic green sulfur bacteria Chlorobium tepidum is a prototype efficient light-harvesting antenna: it stores the captured photon energy in the form of excitons (collective excitations), which are subsequently converted to chemical energy with almost 100% efficiency. These excitons show an elaborate relaxation pattern involving coherent and incoherent pathways. We make use of the complex chirality and fundamental symmetries of multidimensional optical signals to design new sequences of ultrashort laser pulses that can distinguish between coherent quantum oscillations and incoherent energy dissipation during the exciton relaxation. The cooperative dynamical features, which reflect the coherent nature of excitations, are amplified. The extent of quantum oscillations and their timescales in photosynthesis can be readily extracted from the designed signals, showing that cooperativity is maintained during energy transport in the Fenna-Matthews-Olson complex. The proposed pulse sequences may also be applied to reveal information on the robustness of quantum states in the presence of fluctuating environments in other nanoscopic complexes and devices.