Fourier Transform in Ultrafast Spectroscopy

Laser technology allows to generate femtoseconds-long pulses of light. These light pulses can be used to learn about the molecules with which they interact. Consequently, pulsed laser spectroscopy has become an important tool for investigating and characterizing electronic and nuclear structure of protein complexes. These spectroscopic techniques can either be performed in the time or frequency domain. Both the time and frequency domain are linked by Fourier Transform (FT) and thus, FT plays a central role in optical spectroscopy. Ultimately, FT is used to explain how light behaves. It is used to explain spectroscopic techniques and enables the development of new techniques. Finally, FT is used to process and analyze data. This chapter thus illustrates the centrality of FT in ultrafast optical spectroscopy

Hospitalizations for Anorexia Nervosa during the COVID-19 Pandemic in France: A Nationwide Population-Based Study

The COVID-19 pandemic has had a detrimental impact on mental health, including on food-related behaviors. However, little is known about the effect of the pandemic on anorexia nervosa (AN). We sought to assess an association between the COVID-19 pandemic and a potential increase in hospitalizations for AN in France. We compared the number of hospitalizations with a diagnosis of AN during the 21-month period following the onset of the pandemic with the 21-month period before the pandemic using Poisson regression models. We identified a significant increase in hospitalizations for girls aged 10 to 19 years (+45.9%, RR = 1.46[1.43–1.49]; p < 0.0001), and for young women aged 20 to 29 (+7.0%; RR = 1.07[1.04–1.11]; p < 0.0001). Regarding markers of severity, there was an increase in hospitalizations for AN associated with a self-harm diagnosis between the two periods. Multivariate analysis revealed that the risk of being admitted for self-harm with AN increased significantly during the pandemic period among patients aged 20–29 years (aOR = 1.39[1.06–1.81]; p < 0.05 vs. aOR = 1.15[0.87–1.53]; NS), whereas it remained high in patients aged 10 to 19 years (aOR = 2.40[1.89–3.05]; p < 0.0001 vs. aOR = 3.12[2.48–3.98]; p < 0.0001). Furthermore, our results suggest that the pandemic may have had a particular effect on the mental health of young women with AN, with both a sharp increase in hospitalizations and a high risk of self-harming behaviors

A microfluidic flow-cell for the study of the ultrafast dynamics of biological systems

The study of biochemical dynamics by ultrafast spectroscopic methods is often restricted by the limited amount of liquid sample available, while the high repetition rate of light sources can induce photodamage. In order to overcome these limitations, we designed a high flux, sub-ml, capillary flow-cell. While the 0.1 mm thin window of the 0.5 mm cross-section capillary ensures an optimal temporal resolution and a steady beam deviation, the cell-pump generates flows up to ∼0.35 ml/s that are suitable to pump laser repetition rates up to ∼14 kHz, assuming a focal spot-diameter of 100 μm. In addition, a decantation chamber efficiently removes bubbles and allows, via septum, for the addition of chemicals while preserving the closed atmosphere. The minimal useable amount of sample is ∼250 μl

Ultrafast Dynamics of the Photo-Excited Hemes b and cn in the Cytochrome b6f Complex

The dynamics of the heme b and cn within the cytochrome b6f complex are investigated by means of ultrafast broad-band transient absorption spectroscopy. On one hand, the data reveals that, subsequent to visible light excitation, part of the b hemes undergo a pulse limited photo-oxidation, with the liberated electron supposedly being admited in one of the adjacent aromatic amino acid. The photo-oxidation is followed by a charge recombination in about 8.2 ps. Subsequent to the charge recombination, the heme is promoted to an vibrationally excited ground state that relaxes in about 4.6 ps. On the other hand, the heme cn undergoes an ultrafast ground state recovery in about 140 fs. Interestingly, the data also shows that, contrarely to previous beliefs, Chl a is involved in the hemes photochemistry. Indeed, subsequently to the hemes excitation, the Chl a bleaches and recovers its ground state in 90 fs and 650 fs, respectively. The Chl a bleaching allegedly corresponds to the formation of a short lived Chl a anion. Beyond the previously suggested structural role, this study gives unique evidences that Chl a is directly involved in the photochemistry of the hemes

A Map of Dielectric Heterogeneity in a Membrane Protein: the Hetero-Oligomeric Cytochrome b 6 f Complex

The cytochrome b6f complex, a member of the cytochrome bc family that mediates energy transduction in photosynthetic and respiratory membranes, is a hetero-oligomeric complex that utilizes two pairs of b-hemes in a symmetric dimer to accomplish trans-membrane electron transfer, quinone oxidation–reduction, and generation of a proton electrochemical potential. Analysis of electron storage in this pathway, utilizing simultaneous measurement of heme reduction, and of circular dichroism (CD) spectra, to assay heme–heme interactions, implies a heterogeneous distribution of the dielectric constants that mediate electrostatic interactions between the four hemes in the complex. Crystallographic information was used to determine the identity of the interacting hemes. The Soret band CD signal is dominated by excitonic interaction between the intramonomer b-hemes, bn and bp, on the electrochemically negative and positive sides of the complex. Kinetic data imply that the most probable pathway for transfer of the two electrons needed for quinone oxidation–reduction utilizes this intramonomer heme pair, contradicting the expectation based on heme redox potentials and thermodynamics, that the two higher potential hemes bn on different monomers would be preferentially reduced. Energetically preferred intramonomer electron storage of electrons on the intramonomer b-hemes is found to require heterogeneity of interheme dielectric constants. Relative to the medium separating the two higher potential hemes bn, a relatively large dielectric constant must exist between the intramonomer b-hemes, allowing a smaller electrostatic repulsion between the reduced hemes. Heterogeneity of dielectric constants is an additional structure–function parameter of membrane protein complexes

Energy and electron transfer in photosynthetic proteins

We spectroscopically resolved the reduced state of the primary electron acceptor of Photosystem I, A0, in its lowest energy Qy region for the first time without the addition of chemical reducing agents and without extensive data manipulation. To carry this out, we used the menB mutant of Synechocystis sp. PCC 6803 in which phylloquinone is partially replaced by plastoquinone-9 in the A1 sites of Photosystem I. The subsequent long lived A0- state is most probably due to dysfunctional A1 sites. This conclusion is inferred based on the monitored A0- lifetime of ∼22 ns that is typical of charge recombination between A0 - and P700+. The maximum bleaching (A 0- - A0) was found to occur at 684 nm with a corresponding extinction coefficient of 43 mM-1 cm -1. The data show evidence of an electrochromic shift of an accessory chlorophyll pigment, suggesting that the latter Qy absorption band is centered around 682 nm. The study of electrochromic shift in the P798+ of Heliobacterium modesticaldum also shed lights on its RC core composition: we propose the first spectral evidence that, while the A 0 pigment is Chl a, the accessory pigment is BChl g. Femtosecond spectroscopy reveals that energy equilibration within the BChl g antenna pigments occurs in 0.67 ps, trapping of the energy by the special pair takes place in ∼5 and ∼20 ps and that the resulting A0- has a lifetime of ∼450 ps. With similar kinetics for energy and electron transfers, the green sulfur bacteria Chlorobium tepidum has the advantage that its special pair, P840, can be clearly differentiated from the main antenna absorption band at low temperature. Such unique feature permitted us to observe for the first time the rapid electron transfer from the directly excited special pair (BChl a) to the primary electron acceptor (Chl a) and infer that the intrinsic charge separation in the RC occurs in \u3c200 fs. We also confirm that the slow heme reduction in the dimeric cytochrome b6f complex, occurring in ∼150 s, involves both, the heme bn and bp, simultaneously. Under complete reduction of the hemes, the b6f complex most probably undergoes conformational changes. This conclusion is supported by the consequent electrochromic shift of the embedded Chl a that is opposite, in direction, to the predictions based on the current oxidized b6f complex structure

Deciphering the Mechanisms of Bacterial Inactivation on HiPIMS Sputtered CuxO-FeOx-PET Surfaces: From Light Absorption to Catalytic Bacterial Death

The production of nontoxic, affordable, and efficient antibacterial surfaces is key to the well-being of our societies. In this aim, antibacterial thin films have been prepared using earth-abundant metals deposited using high-power impulse magnetron sputtering (HiPIMS). The sputtered FeOx, CuxO, and mixed CuxO-FeOx films exhibited fast bacterial inactivation properties under exposure to indoor light (340-720 nm) showing total bacterial inactivation within 180, 120, and 60 min, respectively. The photocatalytic mechanisms of these films were investigated, from the absorption of photoOns up to the bacteria's fate, by means of ultrafast transient spectroscopy, flow cytometry, and malondialdehyde (MDA) quantification justifying the cell wall disruption. The primary driving force leading to bacterial inactivation was found to be the oxidative stress at the interface between the sputtered thin films and the microorganism. This was justified by using engineered porinless bacteria disabling the possible ion diffusion leading to internal bacterial inactivation. Such stress is a direct consequence of the photogenerated electron-hole pairs at the interface of the sputtered layers. By diffuse reflectance spectroscopy, we found that both FeOx and CuxO present a band gap of similar to 2.9 eV (>425 nm), while the mixed CuxO-FeOx, thin film has a band gap below 2.3 eV (>540 nm). The structure and atomic composition of the films were characterized by energy-dispersive X-ray, X-ray photoelectron, and optical spectroscopy. While the composition and metal oxidation states are distinct in all three films, the difference in photocatalytic efficiency can, at first sight, be explained as the direct consequence of their absorbance and the unique interaction between Fe and Cu oxides in the composite film