Abrupt Change from Ionic to Covalent Bonding in Nickel Halides Accompanied by Ligand Field Inversion.

The electronic configuration of transition metal centers and their ligands is crucial for redox reactions in metal catalysis and electrochemistry. We characterize the electronic structure of gas-phase nickel monohalide cations via nickel L-edge X-ray absorption spectroscopy. Comparison with multiplet charge-transfer simulations and experimental spectra of selectively prepared nickel monocations in both ground- and excited-state configurations are used to facilitate our analysis.

Direct spectroscopic evidence for the high-spin state of dioxidomanganese(V).

The spin state of metal centers in many catalytic reactions has been demonstrated to be a rate limiting factor when high-valent metal centers such as manganese are involved. Although numerous manganese(V) complexes, including a few manganese(V) oxo complexes, have been identified, thus far only one of these, [MnH buea(O)], has been directly confirmed to exist in a high spin state. Such a high-spin manganese(V) center may play a crucial role in the dioxygen formation process in the elusive S state of the Kok cycle in photosystem II.

Soft X-ray absorption and fragmentation of tin-oxo cage photoresists.

"Tin-oxo cage" organometallic compounds are considered as photoresists for extreme ultraviolet (EUV) photolithography. To gain insight into their electronic structure and reactivity to ionizing radiation, we trapped bare gas-phase -butyltin-oxo cage dications [(BuSn)O(OH)] in an ion trap and investigated their fragmentation upon soft X-ray photoabsorption by means of mass spectrometry. In complementary experiments, the tin-oxo cages with hydroxide and trifluoroacetate counter-anions were cast in thin films and studied using X-ray transmission spectroscopy.

Mapping the electronic transitions of protonation sites in peptides using soft X-ray action spectroscopy.

Near-edge X-ray absorption mass spectrometry (NEXAMS) around the nitrogen and oxygen K-edges was employed on gas-phase peptides to probe the electronic transitions related to their protonation sites, namely at basic side chains, the N-terminus and the amide oxygen. The experimental results are supported by replica exchange molecular dynamics and density-functional theory and restricted open-shell configuration with single calculations to attribute the transitions responsible for the experimentally observed resonances. We studied five tailor-made glycine-based pentapeptides, where we identified the signature of the protonation site of N-terminal proline, histidine, lysine and arginine, at 406 eV, corresponding to N 1s → σ*(NH) ( = 2 or 3) transitions, depending on the peptides.

Electronic Structure of the Complete Series of Gas-Phase Manganese Acetylacetonates by X-ray Absorption Spectroscopy.

Metal centers in transition metal-ligand complexes occur in a variety of oxidation states causing their redox activity and therefore making them relevant for applications in physics and chemistry. The electronic state of these complexes can be studied by X-ray absorption spectroscopy, which is, however, due to the complex spectral signature not always straightforward. Here, we study the electronic structure of gas-phase cationic manganese acetylacetonate complexes Mn(acac) using X-ray absorption spectroscopy at the metal center and ligand constituents.

Exposing the Oxygen-Centered Radical Character of the Tetraoxido Ruthenium(VIII) Cation [RuO ].

The tetraoxido ruthenium(VIII) radical cation, [RuO ] , should be a strong oxidizing agent, but has been difficult to produce and investigate so far. In our X-ray absorption spectroscopy study, in combination with quantum-chemical calculations, we show that [RuO ] , produced via oxidation of ruthenium cations by ozone in the gas phase, forms the oxygen-centered radical ground state. The oxygen-centered radical character of [RuO ] is identified by the chemical shift at the ruthenium M edge, indicative of ruthenium(VIII), and by the presence of a characteristic low-energy transition at the oxygen K edge, involving an oxygen-centered singly-occupied molecular orbital, which is suppressed when the oxygen-centered radical is quenched by hydrogenation of [RuO ] to the closed-shell [RuO H] ion.

The association between soluble CD163, disease severity, and ursodiol treatment in patients with primary biliary cholangitis.

Introduction: The macrophage activation marker soluble (s)CD163 is associated with disease severity and prognosis in patients with primary biliary cholangitis (PBC). Ursodeoxycholic acid (UDCA) treatment attenuates fibrosis progression in PBC patients, but its effect on macrophage activation is unclear. We examined the effect of UDCA on macrophage activation, as determined by sCD163 levels.

Direct Observation of Charge, Energy, and Hydrogen Transfer between the Backbone and Nucleobases in Isolated DNA Oligonucleotides.

Understanding how charge and energy, as well as protons and hydrogen atoms, are transferred in molecular systems as a result of an electronic excitation is fundamental for understanding the interaction between ionizing radiation and biological matter on the molecular level. To localize the excitation at the atomic scale, it was chosen to target phosphorus atoms in the backbone of gas-phase oligonucleotide anions and cations, by means of resonant photoabsorption at the L- and K-edges. The ionic photoproducts of the excitation process were studied by a combination of mass spectrometry and X-ray spectroscopy.

Isolation and Characterization of the Homoleptic Nickel(I) and Nickel(II) Bis-benzene Sandwich Cations.

A stable salt of the metalloradical [Ni(C H ) ] hitherto unknown in the condensed phase was synthesized from [Ni(CO) ] [WCA] and benzene ([WCA] =[F{Al(OR ) } ] ; R =C(CF ) ). Single crystal XRD reveals a remarkable asymmetrically η ,η -slipped sandwich structure. The magnetic properties of the [Ni(C H ) ] cation were determined in solution and in the gas phase.

Association between fibrosis markers and kidney function following peptide receptor radionuclide therapy in patients with neuroendocrine tumours.

Peptide receptor radionuclide therapy (PRRT) is a treatment for neuroendocrine tumours (NET). Renal impairment is a known side effect due to kidney fibrosis. We investigated the association between novel specific fibrosis markers and kidney function following PRRT.

Iron L-edge energy shifts for the full range of possible 3d occupations within the same oxidation state of iron halides.

Oxidation states are integer in number but d configurations of transition metal centers vary continuously in polar bonds. We quantify the shifts of the iron L excitation energy, within the same formal oxidation state, in a systematic L-edge X-ray absorption spectroscopy study of diatomic gas-phase iron(II) halide cations, [FeX],where X = F, Cl, Br, I. These shifts correlate with the electronegativity of the halogen, and are attributed exclusively to a fractional increase in population of 3d-derived orbitals along the series as supported by charge transfer multiplet simulations and density functional theory calculations.

The Highest Oxidation State of Rhodium: Rhodium(VII) in [RhO ].

Although the highest possible oxidation states of all transition elements are rare, they are not only of fundamental interest but also relevant as potentially strong oxidizing agents. In general, the highest oxidation states are found in the electron-rich late transition elements of groups 7-9 of the periodic table. Rhodium is the first element of the 4d transition metal series for which the highest known oxidation state does not equal its group number of 9, but reaches only a significantly lower value of +6 in exceptional cases.

Diminished Short- and Long-Term Antibody Response after SARS-CoV-2 Vaccination in Hemodialysis Patients.

Short-term studies have shown an attenuated immune response in hemodialysis patients after COVID-19-vaccination. The present study examines how antibody response is maintained after vaccination against SARS-CoV-2 in a large population of hemodialysis patients from six outpatient dialysis centers. We retrospectively assessed serum antibody levels against SARS-CoV-2 spike protein and nucleocapsid protein (electrochemiluminescence immunoassays, Roche Diagnostics) after COVID-19-vaccination in 298 hemodialysis and 103 non-dialysis patients (controls), comparing early and late antibody response.

Intramolecular hydrogen transfer in DNA induced by site-selective resonant core excitation.

We present experimental evidence for soft X-ray induced intramolecular hydrogen transfer in the protonated synthetic tri-oligonucleotide (UAG) in the gas-phase (U: fluorouracil). The trinucleotide cations were stored in a cryogenic ion trap and exposed to monochromatic synchrotron radiation. Photoionization and photofragmentation product ion yields were recorded as a function of photon energy.

X-ray Induced Fragmentation of Protonated Cystine.

We demonstrate site-specific X-ray induced fragmentation across the sulfur L-edge of protonated cystine, the dimer of the amino acid cysteine. Ion yield NEXAFS were performed in the gas phase using electrospray ionization (ESI) in combination with an ion trap. The interpretation of the sulfur L-edge NEXAFS spectrum is supported by Restricted Open-Shell Configuration Interaction (ROCIS) calculations.

Soft X-ray signatures of cationic manganese-oxo systems, including a high-spin manganese(V) complex.

Manganese-oxo species catalyze key reactions, including C-H bond activation or dioxygen formation in natural photosynthesis. To better understand relevant reaction intermediates, we characterize electronic states and geometric structures of [MnO] manganese-oxo complexes that represent a wide range of manganese oxidation states. To this end, we apply soft X-ray spectroscopy in a cryogenic ion trap, combined with multiconfigurational wavefunction calculations.

Mn -Acetate Complexes Studied as Single Molecules.

The phenomenon of single molecule magnet (SMM) behavior of mixed valent Mn coordination clusters of general formula [Mn Mn O (RCOO) (H O) ] had been exemplified by bulk samples of the archetypal [Mn Mn O (CH COO) (H O) ] (4) molecule, and the molecular origin of the observed magnetic behavior has found support from extensive studies on the Mn system within crystalline material or on molecules attached to a variety of surfaces. Here we report the magnetic signature of the isolated cationic species [Mn O (CH COO) (CH CN)] (1) by gas phase X-ray Magnetic Circular Dichroism (XMCD) spectroscopy, and we find it closely resembling that of the corresponding bulk samples. Furthermore, we report broken symmetry DFT calculations of spin densities and single ion tensors of the isolated, optimized complexes [Mn O (CH COO) (CH CN)] (1), [Mn O (CH COO) ] (2), [Mn O (CH COO) (H O) ] (3), and the complex in bulk geometry [Mn Mn O (CH COO) (H O) ] (5).

Antibody response to mRNA SARS-CoV-2 vaccines in haemodialysis patients.

Background: Some studies have shown an attenuated immune response in haemodialysis patients after vaccination. The present study examines the humoral response after mRNA vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in a large population of haemodialysis patients from different outpatient dialysis centres.

Methods: We retrospectively assessed antibodies against SARS-CoV-2 spike protein and nucleocapsid protein (chemiluminescence immunoassays, Roche diagnostics) 3-6 weeks after the second mRNA vaccine dose in 179 maintenance haemodialysis and 70 non-dialysis patients (control cohort).

Breaking inversion symmetry by protonation: experimental and theoretical NEXAFS study of the diazynium ion, NH.

As an example of symmetry breaking in NEXAFS spectra of protonated species we present a high resolution NEXAFS spectrum of protonated dinitrogen, the diazynium ion NH. By ab initio calculations we show that the spectrum consists of a superposition of two nitrogen 1s absorption spectra, each including a π* band, and a nitrogen 1s to H charge transfer band followed by a weak irregular progression of high energy excitations. Calculations also show that, as an effect of symmetry breaking by protonation, the π* transitions are separated by 0.

The electronic structure and deexcitation pathways of an isolated metalloporphyrin ion resolved by metal L-edge spectroscopy.

The local electronic structure of the metal-active site and the deexcitation pathways of metalloporphyrins are crucial for numerous applications but difficult to access by commonly employed techniques. Here, we applied near-edge X-ray absorption mass spectrometry and quantum-mechanical restricted active space calculations to investigate the electronic structure of the metal-active site of the isolated cobalt(iii) protoporphyrin IX cation (CoPPIX) and its deexcitation pathways upon resonant absorption at the cobalt L-edge. The experiments were carried out in the gas phase, thus allowing for control over the chemical state and molecular environment of the metalloporphyrin.

Site-selective soft X-ray absorption as a tool to study protonation and electronic structure of gas-phase DNA.

The conformation and the electronic structure of gas-phase oligonucleotides depends strongly on the protonation site. 5'-d(FUAG) can either be protonated at the A-N1 or at the G-N7 position. We have stored protonated 5'-d(FUAG) cations in a cryogenic ion trap held at about 20 K.

Probing Structural Information of Gas-Phase Peptides by Near-Edge X-ray Absorption Mass Spectrometry.

Near-edge X-ray absorption mass spectrometry (NEXAMS) is an action-spectroscopy technique of growing interest for investigations into the spatial and electronic structure of biomolecules. It has been used successfully to give insights into different aspects of the photodissociation of peptides and to probe the conformation of proteins. It is a current question whether the fragmentation pathways are sensitive toward effects of conformational isomerism, tautomerism, and intramolecular interactions in gas-phase peptides.

The carbon and oxygen K-edge NEXAFS spectra of CO.

We present and analyze high resolution near edge X-ray absorption fine structure (NEXAFS) spectra of CO+ at the carbon and oxygen K-edges. The spectra show a wealth of features that appear very differently at the two K-edges. The analysis of these features can be divided into three parts; (i) repopulation transition to the open shell orbital - here the C(1s) or O(1s) to 5σ transition, where the normal core hole state is reached from a different initial state and different interaction than in X-ray photoelectron spectroscopy; (ii) spin coupled split valence bands corresponding to C(1s) or O(1s) to π* transitions; (iii) remainder weak and long progressions towards the double ionization potentials containing a manifold of peaks.

Site-Selective Dissociation upon Sulfur L-Edge X-ray Absorption in a Gas-Phase Protonated Peptide.

Site-selective dissociation induced by core photoexcitation of biomolecules is of key importance for the understanding of radiation damage processes and dynamics and for its promising use as "chemical scissors" in various applications. However, identifying products of site-selective dissociation in large molecules is challenging at the carbon, nitrogen, and oxygen edges because of the high recurrence of these atoms and related chemical groups. In this paper, we present the observation of site-selective dissociation at the sulfur L-edge in the gas-phase peptide methionine enkephalin, which contains only a single sulfur atom.