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The absence of an extensive series of Sc K-edge X-ray absorption near-edge structure spectroscopy (XANES) reference spectra and the scarcity of direct structural data on Sc are major hurdles to develop our understanding of Sc chemistry. However, this first step is essential to develop new Sc-based applications and to better understand the formation of Sc deposits. Here, we present a detailed comparative study of Sc K-edge XANES spectra of three Sc-bearing compounds: a garnet (Ca 3 Sc 2 Si 3 O 12 ), an oxide (Sc 2 O 3 ) and a phosphate (ScPO 4 ·2H 2 O). First-principles calculations have been performed to interpret the origin of the K pre-edge spectral features. We demonstrate the validity of our approach by reproducing satisfyingly the experimental spectra. The densities of states projected on the absorbing Sc atom and its first neighbours give the possibility to interpret the position and intensity of the pre-edge XANES features in terms of Sc local environment. The pre-edge features provide information on p-d mixing of the absorber orbitals giving clues on the centrosymmetry of the site and on the mixing of the empty 4p orbitals of the absorber with empty 3d orbitals of the neighbours via the empty p orbitals of the ligands. We also show that these features give a first estimate of the crystal-field splitting energy (ca. 1.5 eV), inaccessible using other spectroscopic methods. Comparisons with K-edge spectra of other 3d 0 ions from the literature reveal the specificities of the Sc pre-edge, indicating that core-hole screening is weaker than for Ti 4+ -bearing compounds. This study provides a dataset of spectral signatures and a theoretical basis for their interpretation, a requirement for future studies on Sc chemical form in synthetic and natural systems.

A combined experimental-theoretical study on the temperature dependence of the X-ray absorption near-edge structure (XANES) and nuclear magnetic resonance (NMR) spectra of periclase (MgO), spinel (MgAl 2 O 4 ), corundum (α-Al 2 O 3 ), berlinite (α-AlPO 4 ), stishovite and α-quartz (SiO 2 ) is reported. Predictive calculations are presented when experimental data are not available. For these light-element oxides, both experimental techniques detect systematic effects related to quantum thermal vibrations which are well reproduced by density-functional theory simulations. In calculations, thermal fluctuations of the nuclei are included by considering nonequilibrium configurations according to finite-temperature quantum statistics at the quasiharmonic level. The influence of nuclear quantum fluctuations on XANES and NMR spectroscopies is particularly sensitive to the coordination number of the probed cation. Furthermore, the relative importance of nuclear dynamics and thermal expansion is quantified over a large range of temperatures.

Theoretical predictions show that depending on the populations of the Fe 3d xy , 3d xz , and 3d yz orbitals two possible quintet states can exist for the high-spin state of the photoswitchable model system [Fe(terpy) 2 ] 2+ . The differences in the structure and molecular properties of these 5 B 2 and 5 E quintets are very small and pose a substantial challenge for experiments to resolve them. Yet for a better understanding of the physics of this system, which can lead to the design of novel molecules with enhanced photoswitching performance, it is vital to determine which high-spin state is reached in the transitions that follow the light excitation. The quintet state can be prepared with a short laser pulse and can be studied with cutting-edge time-resolved X-ray techniques. Here we report on the application of an extended set of X-ray spectroscopy and scattering techniques applied to investigate the quintet state of [Fe(terpy) 2 ] 2+ 80 ps after light excitation. High-quality X-ray absorption, nonresonant emission, and resonant emission spectra as well as X-ray diffuse scattering data clearly reflect the formation of the high-spin state of the [Fe(terpy) 2 ] 2+ molecule; moreover, extended X-ray absorption fine structure spectroscopy resolves the Fe-ligand bond-length variations with unprecedented bond-length accuracy in time-resolved experiments. With ab initio calculations we determine why, in contrast to most related systems, one configurational mode is insufficient for the description of the low-spin (LS)-high-spin (HS) transition. We identify the electronic structure origin of the differences between the two possible quintet modes, and finally, we unambiguously identify the formed quintet state as 5 E, in agreement with our theoretical expectations.

Probing the local environment of low-Z elements, such as oxygen, is of great interest for understanding the atomic-scale behavior in materials, but it requires experimental techniques allowing it to work with versatile sample environments. In this paper, the local environment of lithium borate crystals is investigated using non-resonant inelastic X-ray scattering (NRIXS) at energy losses corresponding to the oxygen K-edge. Large variations of the spectral features are observed close to the edge onset in the 535-540 eV energy range when varying the Li2O content. Calculations allow identification of contributions associated with bridging oxygen (BO) and non-bridging oxygen (NBO) atoms. The main result resides in the observed core-level shift of about 1.7 eV in the spectral signatures of the BO and NBO. The clear signature at 535 eV in the O K-edge NRXIS spectrum is thus an original way to probe the presence of NBOs in borates, with the great advantage of making possible the use of complex environments such as a high-pressure cell or high-temperature device for in situ measurements.

The structural environment of Mg in a K-bearing silicate glass of composition K(2)MgSi(3)O(8) is investigated by x-ray absorption near-edge structure (XANES) spectroscopy at the Mg K-edge. XANES calculations are performed using a plane-wave electronic structure code, and a structural model obtained by classical molecular dynamics coupled to ab initio relaxation. Bond valence theory is used to validate plausible environments within the structural models. Comparison between the experimental and calculated spectra enables us to conclude that the Mg atoms are located in distorted tetrahedral sites. Site distortions are found to be correlated to the theoretical shift of the XANES edge position.

We first present an extended introduction of the various methods used to extract electronic and structural information from the K pre-edge X-ray absorption spectra of 3d transition metal ions. The K pre-edge structure is then modelled for a selection of 3d transition metal compounds and analyzed using first-principles calculations based on the density functional theory (DFT) in the local density approximation (LDA). The selected compounds under study are presented in an ascending order of electronic structure complexity, starting with the Ti K-edge of rutile and anatase, and finishing with the Fe K-edge of the cyanomet-myoglobin. In most cases, the calculations are compared to polarized experimental spectra. It is shown that DFT-LDA methods enable us to reproduce satisfactorily the experimental features and to understand the nature of the electronic transitions involved in the pre-edge region. The limiting aspects of such methods in modelling the core-hole electron interaction and the 3d electron-electron repulsion are also pointed out.

The monobactam sodium 3-benzylcarbamoyl-2-oxo-1-azetidinesulfonate, bearing a retro (vs classical beta-lactam)-amide side chain, has been synthesized and the kinetics of its reaction with typical beta-lactamases studied. The new compound is generally a poorer substrate than the analogous compound with a normal side chain but its formation of a transiently stable complex with a class C beta-lactamase sustains the retro-amide side-chain concept.

3-(N-Benzylcarbamoyl)-7-carboxy-3, 4-dihydro-2H-1-benzo-pyran-2-one and its 8-carboxy analogue have been synthesized and evaluated as potential (inhibitory) substrates of beta-lactam-recognizing enzymes. These compounds are bicyclic delta-lactones with retro-amide (with respect to classical beta-lactams) side chains. They were found to be comparably effective as substrates of typical class A, C and D beta-lactamases as analogous benzopyranones bearing 'normal' amide side chains. The new 8-carboxy derivative, however, formed a much more (1000-fold) tightly-bound acyl-enzyme with a class C beta-lactamase than did its 'normal' analogue, and thus provides a structural lead to new inhibitors of this class of beta-lactamase.

Electric quadrupole transitions are revealed through the angular dependence of X-ray absorption spectra in a cubic crytal. Data collection was achieved at the iron K-edge in pyrite (FeS2) by using the angular moment method developed for X-ray Natural Circular Dichoism (XNCD) measurements. The natural linear dichroism (XNLD) was found to be around 0.5% of the edge jump. Experimental results are compared with monelectronic and multilectronic calculations. Calculations allow to quantitatively determine the proportion of quadrupolar transitions in the pre-edge structure and the anisotropy is explained in terms of structural and electronic parameters.

A series of derivatives of phenyl phenylacetylglycinates (aryl phenaceturates) with a carboxylate substituent meta to the oxygen of the phenoxide leaving group and a functionalized methylene group in the ortho- or para-position have been synthesized. These molecules possess a latent o- or p-quinone methide electrophile which could be unmasked during enzymic turnover and could react with an active site nucleophile. This chemistry does seem to occur in solution where a common hydrolysis product, independent of the benzylic leaving group, presumably o- or p-hydroxymethylphenol, was observed. These depsipeptides are substrates of class A and C beta-lactamases, particularly of the latter, comparable with the parent m-carboxyphenyl phenaceturate. They also have modest inhibitory activity against these enzymes and against the serine DD-peptidase of Streptomyces R61. The inhibition of a class C beta-lactamase was turnover dependent, as expected of mechanism-based inhibitor, but the small leaving group dependence of the inhibition suggested that the quinone methide, if it was in fact responsible for the inhibition, was generated in solution subsequent to release of the product phenol from the active site.