A liquid flatjet system for solution phase soft-x-ray spectroscopy

We present a liquid flatjet system for solution phase soft-x-ray spectroscopy. The flatjet set-up utilises the phenomenon of formation of stable liquid sheets upon collision of two identical laminar jets. Colliding the two single water jets, coming out of the nozzles with 50 μm orifices, under an impact angle of 48° leads to double sheet formation, of which the first sheet is 4.6 mm long and 1.0 mm wide. The liquid flatjet operates fully functional under vacuum conditions (<10(-3) mbar), allowing soft-x-ray spectroscopy of aqueous solutions in transmission mode. We analyse the liquid water flatjet thickness under atmospheric pressure using interferomeric or mid-infrared transmission measurements and under vacuum conditions by measuring the absorbance of the O K-edge of water in transmission, and comparing our results with previously published data obtained with standing cells with Si3N4 membrane windows. The thickness of the first liquid sheet is found to vary between 1.4-3 μm, depending on the transverse and longitudinal position in the liquid sheet. We observe that the derived thickness is of similar magnitude under 1 bar and under vacuum conditions. A catcher unit facilitates the recycling of the solutions, allowing measurements on small sample volumes (∼10 ml). We demonstrate the applicability of this approach by presenting measurements on the N K-edge of aqueous NH4 (+). Our results suggest the high potential of using liquid flatjets in steady-state and time-resolved studies in the soft-x-ray regime

Ultrafast photoinduced relaxation dynamics of the indoline dye D149 in organic solvents

The relaxation dynamics of the indoline dye D149, a well-known sensitizer for photoelectrochemical solar cells, have been extensively characterized in various organic solvents by combining results from ultrafast pump–supercontinuum probe (PSCP) spectroscopy, transient UV-pump VIS-probe spectroscopy, time-correlated single-photon counting (TCSPC) measurements as well as steady-state absorption and fluorescence. In the steady-state spectra, the position of the absorption maximum shows only a weak solvent dependence, whereas the fluorescence Stokes shift Δ[small nu, Greek, tilde]F correlates with solvent polarity. Photoexcitation at around 480 nm provides access to the S1 state of D149 which exhibits solvation dynamics on characteristic timescales, as monitored by a red-shift of the stimulated emission and spectral development of the excited-state absorption in the transient PSCP spectra. In all cases, the spectral dynamics can be modeled by a global kinetic analysis using a time-dependent S1spectrum. The lifetime τ1 of the S1 state roughly correlates with polarity [acetonitrile (280 ps) < acetone (540 ps) < THF (720 ps) < chloroform (800 ps)], yet in alcohols it is much shorter [methanol (99 ps) < ethanol (178 ps) < acetonitrile (280 ps)], suggesting an appreciable influence of hydrogen bonding on the dynamics. A minor component with a characteristic time constant in the range 19–30 ps, readily observed in the PSCP spectra of D149 in acetonitrile and THF, is likely due to removal of vibrational excess energy from the S1 state by collisions with solvent molecules. Additional weak fluorescence in the range 390–500 nm is observed upon excitation in the S0 → S2 band, which contains short-lived S2 → S0 emission of D149. Transient absorption signals after excitation at 377.5 nm yield an additional time constant in the subpicosecond range, representing the lifetime of the S2 state. S2 excitation also produces photoproducts

Highly efficient soft x-ray spectrometer for transient absorption spectroscopy with broadband table-top high harmonic sources

We present a novel soft x-ray spectrometer for ultrafast absorption spectroscopy utilizing table-top femtosecond high-order harmonic sources. Where most commercially available spectrometers rely on spherical variable line space gratings with a typical efficiency on the order of 3% in the first diffractive order, this spectrometer, based on a Hettrick–Underwood design, includes a reflective zone plate as a dispersive element. An improved efficiency of 12% at the N K-edge is achieved, accompanied by a resolving power of 890. The high performance of the soft x-ray spectrometer is further demonstrated by comparing nitrogen K-edge absorption spectra from calcium nitrate in aqueous solution obtained with our high-order harmonic source to previous measurements performed at the electron storage ring facility BESSY II

Integrative Analysis of <i>Retusa pertenuis</i> (Heterobranchia: Cephalaspidea) from Arctic and Russian Far East Seas with Discussion of Its Morphology, Validity and Population Structure

Retusa pertenuis is still formally considered a junior subjective synonym of Retusa obtusa, despite previous data indicating R. pertenuis and R. obtusa differ significantly in copulatory system morphology. In this paper, we study the species identity and population structure of R. pertenuis with an integrative approach combining morphological and molecular data. The external morphology, head copulatory system and gizzard plates were studied using light microscopy and scanning electron microscopy. We also obtained two mitochondrial (COI and 16S) and two nuclear (H3 and 28S) markers to test the monophyly of R. pertenuis and R. obtusa. Populations from the White Sea, Sea of Okhotsk and Sea of Japan were studied using COI and 18S molecular markers. Our results show that Retusa obtusa sensu lato represents a species complex of at least four species: the nominative species occurring in the North Atlantic, the widely distributed R. pertenuis and two additional species whose identities should be clarified in further studies. Retusa pertenuis geographic range encompasses the North Atlantic, Eurasia’s northern seas, the Canadian Arctic, the Bering Sea, the Sea of Okhotsk and the Sea of Japan. Within R. pertenuis’s range, this species demonstrates a wide variability in shell morphology

Cr L Edge X ray Absorption Spectroscopy of CrIII acac 3 in Solution with Measured and Calculated Absolute Absorption Cross Sections

X ray absorption spectroscopy at the L edge of 3d transition metals is widely used for probing the valence electronic structure at the metal site via 2p 3d transitions. Assessing the information contained in L edge absorption spectra requires systematic comparison of experiment and theory. We here investigate the Cr L edge absorption spectrum of high spin chromium acetylacetonate CrIII acac 3 in solution. Using a transmission flatjet enables determining absolute absorption cross sections and spectra free from x ray induced sample damage. We address the challenges of measuring Cr L absorption edges spectrally close to the O K absorption edge of the solvent. We critically assess how experimental absorption cross sections can be used to extract information on the electronic structure of the studied system by comparing our results of this CrIII 3d3 complex to our previous work on L edge absorption cross sections of MnIII acac 3 3d4 and MnII acac 2 3d5 . Considering our experimental uncertainties, the most insightful experimental observable for this d3 Cr III d4 Mn III d5 Mn II series is the L edge branching ratio and we discuss it in comparison to semi empirical multiplet theory and ab initio restricted active space calculations. We further discuss and analyze trends in integrated absorption cross sections and correlate the spectral shapes with the local electronic structure at the metal site

A liquid flatjet system for solution phase soft-x-ray spectroscopy

We present a liquid flatjet system for solution phase soft-x-ray spectroscopy. The flatjet set-up utilises the phenomenon of formation of stable liquid sheets upon collision of two identical laminar jets. Colliding the two single water jets, coming out of the nozzles with 50 μm orifices, under an impact angle of 48° leads to double sheet formation, of which the first sheet is 4.6 mm long and 1.0 mm wide. The liquid flatjet operates fully functional under vacuum conditions (<10−3 mbar), allowing soft-x-ray spectroscopy of aqueous solutions in transmission mode. We analyse the liquid water flatjet thickness under atmospheric pressure using interferomeric or mid-infrared transmission measurements and under vacuum conditions by measuring the absorbance of the O K-edge of water in transmission, and comparing our results with previously published data obtained with standing cells with Si3N4 membrane windows. The thickness of the first liquid sheet is found to vary between 1.4–3 μm, depending on the transverse and longitudinal position in the liquid sheet. We observe that the derived thickness is of similar magnitude under 1 bar and under vacuum conditions. A catcher unit facilitates the recycling of the solutions, allowing measurements on small sample volumes (∼10 ml). We demonstrate the applicability of this approach by presenting measurements on the N K-edge of aqueous NH4+. Our results suggest the high potential of using liquid flatjets in steady-state and time-resolved studies in the soft-x-ray regime

Ultrafast proton transport in water-methanol mixtures

Femtosecond UV/IR pump-probe experiments and ab initio molecular dynamics simulations of 7-hydroxyquinoline in water-methanol mixtures demonstrate an unexpectedly dominant OH-/CH3O- transport pathway but consistent with a solvent-dependent photoacidity free energy-reactivity correlation behaviour

Aqueous Solvation of Ammonia and Ammonium: Probing Hydrogen Bond Motifs with FT-IR and Soft X-ray Spectroscopy

In a multifaceted investigation combining local soft X-ray and vibrational spectroscopic probes with ab initio molecular dynamics simulations, hydrogen-bonding interactions of two key principal amine compounds in aqueous solution, ammonia (NH3) and ammonium ion (NH4+), are quantitatively assessed in terms of electronic structure, solvation structure, and dynamics. From the X-ray measurements and complementary determination of the IR-active hydrogen stretching and bending modes of NH3 and NH4+ in aqueous solution, the picture emerges of a comparatively strongly hydrogen-bonded NH4+ ion via N–H donating interactions, whereas NH3 has a strongly accepting hydrogen bond with one water molecule at the nitrogen lone pair but only weakly N–H donating hydrogen bonds. In contrast to the case of hydrogen bonding among solvent water molecules, we find that energy mismatch between occupied orbitals of both the solutes NH3 and NH4+ and the surrounding water prevents strong mixing between orbitals upon hydrogen bonding and, thus, inhibits substantial charge transfer between solute and solvent. A close inspection of the calculated unoccupied molecular orbitals, in conjunction with experimentally measured N K-edge absorption spectra, reveals the different nature of the electronic structural effects of these two key principal amine compounds imposed by hydrogen bonding to water, where a pH-dependent excitation energy appears to be an intrinsic property. These results provide a benchmark for hydrogen bonding of other nitrogen-containing acids and bases

Fab Fragment of V_HH-Based Antibody Netakimab: Crystal Structure and Modeling Interaction with Cytokine IL-17A

Interleukin 17A (IL-17A) is a proinflammatory cytokine produced by Th17 cells. Antibody BCD-085 (netakimab) against human IL-17A is one of the new inhibitors of this cytokine. In netakimab, the VH domain is replaced by the VHH domain of Lama glama possessing a long complementarity determining region (CDR-H3) in its heavy chain. Here we demonstrate the high affinity of IL-17A to the Fab fragment of netakimab and to its integral part, the VHH domain. We have determined the crystal structure of the Fab fragment of netakimab at 1.9 &#197; resolution. High variability in the orientation of light and heavy chains of the Fab fragment of netakimab was shown, which is determined by the peculiarity of the structural organization of the CDR-H3. As the high conformational plasticity of the molecule hampers modeling the Fab fragment of netakimab complexed to IL-17A, we have carried out modeling the complex between the antigen and the integral part of the Fab fragment, the VHH domain. We explain the high netakimab Fab fragment affinity for IL-17A by a large number of protein&#8211;protein contacts due to additional interactions between CDR-H3 and the cytokine dimer

Still Many to Be Named: An Integrative Analysis of the Genus <i>Dendronotus</i> (Gastropoda: Nudibranchia) in the North Pacific Revealed Seven New Species

In this paper, we report on the discovery of the hidden biodiversity of the genus Dendronotus (Gastropoda: Nudibranchia) in bathyal areas of the North Pacific (the Sea of Okhotsk and the Kuril Islands). We also test different scenarios of Dendronotus expansion to deeper waters. An integrative analysis was implemented based on morphological data (light microscopy and SEM) and molecular data, which included molecular phylogenetic analysis of four markers (COI, 16S, H3, and 28S), molecular species delimitation analyses, and ancestral area reconstruction. Our results indicated the presence of seven species new to science, five of which are described herein. The phylogenetic reconstructions show that these new species are members of different Dendronotus lineages. Ancestral area reconstruction indicates the shallow-water origin of the genus, while the invasion of deep waters occurs independently multiple times