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It is important to be able to identify the precise position of H-atoms in hydrogen bonding interactions to fully understand the effects on the structure and properties of organic crystals. Using a combination of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and density functional theory (DFT) quantum chemistry calculations, we demonstrate the sensitivity of core-level X-ray spectroscopy to the precise H-atom position within a donor-proton-acceptor system. Exploiting this sensitivity, we then combine the predictive power of DFT with the experimental NEXAFS, confirming the H-atom position identified using single-crystal X-ray diffraction (XRD) techniques more easily than using other H-atom sensitive techniques, such as neutron diffraction. This proof of principle experiment confirms the H-atom positions in structures obtained from XRD, providing evidence for the potential use of NEXAFS as a more accurate and easier method of locating H-atoms within organic crystals.

X-ray photoelectron spectroscopy (XPS) has emerged as a technique that allows for characterization and classification of hydrogen bonding and proton transfer interactions in organic crystal structures, in a way that is complementary to crystallography by X-ray or neutron diffraction. Here, we analyze the nitrogen 1s core-level binding energies (BEs) of isonicotinamide (IN) systems with proton transfer between donor and acceptor groups at short distances. We show how a careful calibration of the BE scale places these salt systems correctly on the edge of the so-called salt–cocrystal continuum. We show how performing a fitting analysis of the data that is consistent with elemental analysis, expected stoichiometry, and quantification of adventitious carbon contamination facilitates the determination of absolute BEs with accuracy and reproducibility within ±0.1 eV. The determined N 1s core-level BEs of the protonated IN acceptors suggest that the local geometric arrangements of the donor, acceptor, and proton can influence the N 1s core-level BE significantly.

The influence of milling diaqua-bis(omeprazolate)-magnesium dihydrate (DABOMD), an active pharmaceutical ingredient (API), was investigated. DABOMD was processed in a planetary ball mill at different milling times, from 1 to 300 min. The milling process resulted in a prominent comminution (size reduction) and amorphization of the API. DABOMD amorphization was identified with various characterization techniques including thermogravimetric analysis, differential scanning calorimetry, powder X-ray diffraction, and attenuated total reflection-Fourier transform infrared spectroscopy. The solid–solid crystalline to amorphous phase transformation is driven by compression, shear stresses, and heat generated in the planetary ball mill. This leads to distortion and breakage of hydrogen bonds, release of water molecules from the crystalline lattice of DABOMD and the accumulation of defects, and eventually a collapse of the crystalline order. Model fitting of the kinetics of comminution and the amorphization of DABOMD revealed a series of events: a rapid comminution at the start of milling driven by crystal cleavage of DABOMD, followed by partial amorphization, which is driven by rapid water diffusion, and subsequently, a slow steady comminution and amorphization.

We present the most recent advances in fast X-ray grating interferometer and their applications. A dedicated setup for rapid scanning with a single grating and using filtered broadband illumination of an undulator source has been implemented. With this setup tomographic scans can be achieved within minutes. Larger number of samples can be measured and chemical processes can be studied. Improvements in the data processing technique will be presented. We will also describe the new capabilities and applications.

The intermolecular interactions in concentrated (5 M) aqueous imidazole solutions have been investigated by combining neutron diffraction with isotopic substitution, total X-ray scattering and empirical potential structure refinement (EPSR) simulations using a box containing 5530 water and 500 imidazole molecules. The structural model with the best fit was used to generate radial distribution functions and spatial density functions. The local volume surrounding imidazole molecules is dominated by water, due to strong hydrogen-bonding between the nitrogen moieties of imidazole and water molecules; within a radius of 6.4 Å from the central imidazole molecule there are, on average, 17 water and only 3 imidazole molecules. Even though imidazole interacts with water it appears to disrupt hydrogen bonding in the surrounding water network only minimally. Hydrogen-bonding between imidazole molecules is negligible. The most probable positions of imidazole nearest-neighbours are above and below the plane of the aromatic ring. At low distances (up to ∼3.5-3.8 Å) these nearest neighbours were found to prefer parallel orientation of the molecular planes, indicating hydrophobic (π-π) stacking. At longer distances (up to ∼5 Å), imidazole neighbours assume both parallel and edge-to-face orientations. Overall, hydrated imidazole molecules are the most probable structural motif in aqueous solutions, with very few direct imidazole-imidazole interactions.

Conformational flexibility in molecules can give rise to a range of functional group terminations at crystal surfaces and dynamic disorder in the bulk. In this work, we explore the conformational behavior of the drug molecule lovastatin in the crystallographically disordered solid and at crystal surfaces through a combination of computational modeling and spectroscopy. Gas-phase and periodic quantum-chemical calculations are used to study the potential energy surface associated with rotatable bonds to examine the disorder in bulk. These calculations are combined with vibrational and X-ray photoelectron spectroscopy measurements to obtain insight into the conformations in bulk and at the surface. Our MD simulations show that the bulk disorder is driven by cooperative motion of the butyl group on the S-butanoate moiety along one crystallographic direction beyond a unit cell. The calculations show that the O-H group can rotate relatively freely between two low-energy conformers in the gas phase but is locked in position by intermolecular H-bonding interactions in the bulk crystal, and we find tentative spectroscopic evidence for the second conformer being present at the surface. We also comment on the relative utility of these different techniques for studying molecular conformation in bulk and at surfaces and highlight possible areas for future developments.

X-ray phase contrast imaging (XPCI) of anti-solvent crystallization of lovastatin from an acetone/water solution was carried out in a concentric flow mixing device, using water as the anti-solvent. Spinodal decomposition of the solution is observed to give rise to ‘oiled out’ phases that undergo heterogeneous nucleation at the interface with the flowing solution. Heterogeneous nucleation is also observed on the walls of the reactor walls in the form of what appears to be Stranski–Krastanov growth of plate-like crystals. XPCI together with Eulerian video magnification forms a powerful tool for the spatio-temporal analysis, revealing mechanistic details of a non-equilibrium process such as anti-solvent crystallization.

X-ray Raman scattering (XRS) has been used for in situ probing of solute molecule speciation in solution during cooling crystallization. The C and N K-edges of aqueous imidazole were measured as a function of temperature to monitor the transition from the undersaturated state through supersaturation to crystallization. A new jacketed-vessel crystallizer with internal flow was used, which enables thermal control and minimizes radiation damage. We have demonstrated that the C and N K-edges of imidazole are sensitive to changes in local bonding. In line with this, an abrupt change in the N K-edge fine structure indicates the onset of desolvation and crystallization from the supersaturated solution. In contrast, negligible changes are observed in the C and N K-edge spectra acquired during cooling, indicating that the average solvation structure around imidazole molecules does not change significantly while traversing the thermodynamically metastable supersaturated zone. To the best of our knowledge this is the first time X-ray Raman scattering has been used for studying molecular speciation in organic aqueous solutions during crystallization. Time-dependent density functional theory (TD-DFT) calculations of the near-edge spectra were performed using implicit, explicit and combined solvation models to elucidate the likely binding sites of the water molecules. An explicit solvation model with one water molecule coordinating each nitrogen moiety in the imidazole ring accurately reproduces the peak positions and intensities of the XRS spectra of aqueous imidazole solution.

The composition and speciation of the organic and third phases in the system HNO3/TBP (tri-n-butyl phosphate)/n-dodecane have been examined by a combination of gravimetric, Karl Fischer analysis, chemical analysis, FTIR, and 31P NMR spectroscopy, with particular emphasis on the transition from the two-phase to the three-phase region. Phase densities indicate that third-phase formation takes place for initial aqueous HNO3 concentrations above 15 M, while the results from the stoichiometric analysis imply that the organic and third phases are characterized by two distinct species, namely the mono-solvate TBP⋅HNO3 and the hemi-solvate TBP⋅2HNO3, respectively. Furthermore, the 31P NMR spectra of organic and third phase show no significant chemical differences at the phosphorus centers, suggesting that the second HNO3 molecule in the third phase is bound to HNO3 rather than TBP. The third-phase FTIR spectra reveal stronger vibrational absorption bands at 1028, 1310, 1653, and 3200–3500 cm−1, reflecting...

We report the use of XAFS (X-ray absorption fine structure) as an in situ method to follow the electrochemically driven deposition of palladium nanoparticles at a liquid/liquid interface. A novel glass/plastic hybrid electrochemical cell was used to enable control of the potential applied to the liquid/liquid interface. In situ measurements indicate that the nucleation of metallic nanoparticles can be triggered through chronoamperometry or cyclic voltammetry. In contrast to spontaneous nucleation at the liquid/liquid interface, whereby fluctuations in Pd oxidation state and concentration are observed, under a fixed interfacial potential the growth process occurs at a steady rate leading to a build-up of palladium at the interface. Raman spectroscopy of the deposit suggests that the organic electrolyte binds directly to the surface of the deposited nanoparticles. It was found that the introduction of citric acid results in the formation of spherical nanoparticles at the interface.

Short, strong hydrogen bonds (SSHBs) have been a source of interest and considerable speculation over recent years, culminating with those where hydrogen resides around the midpoint between the donor and acceptor atoms, leading to quasi-covalent nature. We demonstrate that X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy provide deep insight into the electronic structure of the short OHN hydrogen bond of 3,5-pyridinedicarboxylic acid, revealing for the first time distinctive spectroscopic identifiers for these quasi-symmetrical hydrogen bonds. An intermediate nitrogen (core level) chemical shift occurs for the almost centrally located hydrogen compared to protonated (ionic) and non-ionic analogues, and it reveals the absence of two-site disorder. This type of bonding is also evident through broadening of the nitrogen 1s photoemission and 1s → 1π* peaks in XPS and NEXAFS, respectively, arising from the femtosecond lifetimes of hydrogen in the potential wells slightly offset to either side of the centre. The line-shape of the core level excitations are thus related to the population occupancies, reflecting the temperature-dependent shape of the hydrogen potential energy well. Both XPS and NEXAFS provide a distinctive identifier for these quasi-symmetrical hydrogen bonds, paving the way for detailed studies into their prevalence and potentially unique physical and chemical properties.

X-ray Grating Talbot Interferometer (XGTI) is already routinely used for quantitative phase contrast imaging of soft tissue samples. XGTI can be realized using various measurement techniques, depending on the X-ray source used, the required spatial resolution and the speed of acquisition. The phase-stepping measurement technique, which is commonly used for XGTI data acquisition, needs multiple acquisitions for a single projection. For fast imaging the Moire technique, a single-shot technique, is often preferred. However, it requires two gratings which increases the dose on the sample. We have therefore examined the Spatial Harmonic Imaging (SHI) technique which is low-dose and single-shot, using the I13-2 Diamond-Manchester Beamline at Diamond Light Source (DLS). The DLS I13-2 beamline is equipped with a Double Crystal Monochromator (DCM) and a Multi-Layer Monochromator (MLM) to deliver monochromatic beam, which work at the energy bandwidths (ΔE/E) of 10-4 and 10-2, respectively. However, the disadvantage of using these monochromators, especially for fast imaging, is loss of X-ray flux. It has already been shown that XGTI can work with an energy bandwidth (ΔE/E) of 10-1. Our aim is to develop a single phase grating interferometer with pink beam from an undulator source, with X-ray mirror optics and multiple absorption filters, to obtain maximum possible flux with sufficient coherence and monochromaticity. We demonstrate performance with optimized beamline parameters for a photon energy of 15 keV with some demonstrative image reconstructions.

Herein, we designed a versatile cell for operando X-ray absorption spectroscopy (XAS) monitoring of chemical and physical transformations in liquid solutions and dispersions by fluorescence-yield detection. The cell operates under atmospheric pressure, and the composition of the gas phase can be varied, allowing monitoring of gas–liquid reactions. Samples can be examined as a flowing liquid-jet or as a sessile droplet. Both liquid-jet and droplet operations of the cell were demonstrated at the Ca K-edge through time-resolved studies of CaCO3 formation from CO2 and solid Ca(OH)2 in an aqueous suspension. The liquid-jet reaction was performed at 28 °C, and the droplet reaction was performed at ambient temperature, but both configurations had the scope to be modified for operations at higher temperatures. The liquid-jet volumes were recycled, permitting the use of the cell in a continuous sampling loop for process studies in larger reactor vessels. The jet supply tube was interchangeable, permitting adjustment of the jet size through the tubing bore size. Larger bore sizes minimized the pressure drop at the nozzle and thereby the risk of blockage of the liquid supply by the suspended particulates or growth of solid deposits. Sessile droplet operation enabled studies with minimal sample volumes and mechanical disturbances under controlled environmental conditions. The cell is portable and modular and is based on readily available standard vacuum equipment parts. Furthermore, the operation under a He atmosphere allows measurements above 4 keV, covering part of the tender X-ray range, and it is also applicable to the hard X-ray range.

The lead authors failed to name two collaborators as co-authors. The authors listed should include: Miss Claudia L. Compean-Gonzalez (ORCID: 0000-0002-2367-8450) and Dr. Giacomo Ceccone (ORCID: 0000-0003-4637-0771). These co-authors participated in VAMAS project A27, provided data that were analyzed and presented in this publication (and supporting information), and reviewed the manuscript before submission.

The mechanism of the two-phase Brust-Schiffrin synthesis of alkane thiol protected metal nanoparticles is known to be highly sensitive to the precursor species and reactant conditions. In this work X-ray absorption spectroscopy is used in conjunction with liquid/liquid electrochemistry to highlight the significance of Brˉ in the reaction mechanism. The species [AuBr4]ˉ is shown to be a preferable precursor in the Brust-Schiffrin method as it is more resistant to the formation of Au(I) thiolate species than [AuCl4]ˉ. Previous literature has demonstrated that avoidance of the Au(I) thiolate is critical to achieving a good yield of nanoparticles, as [Au(I)X2]ˉ species are more readily reduced by NaBH4. We propose that the observed behavior of [AuBr4]ˉ species described herein explains the discrepancies in reported behavior present in the literature to date. This new mechanistic understanding should enable nanoparticle synthesis with a higher yield and reduce particle size polydispersity.

The mechanism of the Brust-Schiffrin gold nanoparticle synthesis has been investigated through the use of ion transfer voltammetry at the water/1,2-dichloroethane (DCE) solution interface, combined with X-ray absorption fine structure (XAFS) of the reaction between [AuCl4](-) and thiol (RSH) in homogeneous toluene (TL) solution. Ion transfer calculations indicate the formation of [AuCl2](-) at RSH/Au ratios from 0.2-2 with a time-dependent variation observed over several days. At RSH/Au ratios above 2 and after time periods greater than 24 h, the formation of Au(I)SR is also observed. The relative concentrations of reaction products observed at the liquid/liquid interface are in excellent agreement with those observed by XAFS for the corresponding reaction in a single homogeneous phase. BH4(-) ion transfer reactions between water and DCE indicate that the reduction of [AuCl4](-) or [AuCl2](-) to Au nanoparticles by BH4(-) proceeds in the bulk organic phase. On the other hand, BH4(-) was unable to reduce the insoluble [Au(I)SR]n species to Au nanoparticles. The number and size of the nanoparticles formed was dependent on the concentration ratio of RSH/Au, as well as the experimental duration because of the competing formation of the [Au(I)SR]n precipitate. Higher concentrations of nanoparticles, with diameters of 1.0-1.5 nm, were formed at RSH/Au ratios from 1 to 2.

Heterogeneous Fenton-like catalysts have received considerable research attention because they could potentially be attractive for oxidative removal of organic contaminants from tertiary wastewater. However, process design is still hampered by insufficient understanding of the chemical pathways involved, and especially whether oxidation activity stems from heterogeneous surface chemistry or minute concentrations of dissolved metal ions in the homogeneous phase. Using inductively coupled plasma-optical emission spectroscopy (ICP-OES) in combination with pH monitoring and ultraviolet–visible spectroscopy (UV–vis) we have monitored the degradation of 4-chlorophenol (4-CP) over two Fenton-like heterogeneous systems, namely FeOx supported on TiO2 and CuFe2O4. We show conclusively that these systems proceed predominantly through a homogeneous route via dissolved metal ions from the solid phase catalysts. Control experiments with homogeneous Fe3+ or Cu2+ systems reveal that even minute concentrations (μM/subppm)...

Through X-ray absorption and emission spectroscopies, the chemical, electronic and structural properties of organic species in solution can be observed. Near-edge X-ray absorption fine structure (NEXAFS) and resonant inelastic X-ray scattering (RIXS) measurements at the nitrogen K-edge of para- aminobenzoic acid reveal both pH- and solvent-dependent variations in the ionisation potential (IP), 1s→π* resonances and HOMO–LUMO gap. These changes unequivocally identify the chemical species (neutral, cationic or anionic) present in solution. It is shown how this incisive chemical state sensitivity is further enhanced by the possibility of quantitative bond length determination, based on the analysis of chemical shifts in IPs and σ* shape resonances in the NEXAFS spectra. This provides experimental access to detecting even minor variations in the molecular structure of solutes in solution, thereby providing an avenue to examining computational predictions of solute properties and solute–solvent interactions.

We describe here a novel synthetic route for the preparation of polyurea–polyether nanoparticles (PNPs) that can be performed in a single solvent and which does not require the use of a preformed polymer. First a low molecular weight polyether-monoamine (poly(PO/EO)) is added drop wise to a solution of 4,4′-methylene-diphenylene isocyanate (4,4′-MDI). This leads to a solution of free 4,4′-MDI and low molecular weight 4,4′-MDI-functionalized poly(PO/EO). In a second stage a short diamine chain extender and additional 4,4′-MDI are added drop wise to the solution. This results in the formation of an ABA polyether–polyurea–polyether block copolymer that spontaneously precipitates forming nanoparticles (PNPs). The PNPs were characterized using a variety of techniques including transmission electron microscopy (TEM), photon correlation spectroscopy (PCS) and X-ray photoelectron spectroscopy (XPS). The combined analysis suggests that the polyether-monoamine resides preferentially on the surface of the PNPs and has a role in their stabilization as well as in the stabilization of the resulting colloidal suspensions. The nature of the diamine chain extender was varied in order to explore its effect on the formation, properties and morphology of the nanoparticles. PNPs in the size range from 20 to 100 nm were obtained depending on the diamine used and the stability of the colloidal solution obtained was also found to be dependent on the diamine used.

Tributyl phosphate (TBP) is used as a complexing agent in the Plutonium Uranium Extraction (PUREX) liquid–liquid phase extraction process for recovering uranium and plutonium from spent nuclear reactor fuel. Here, we address the molecular and microstructure of the organic phases involved in the extraction process, using molecular dynamics to show that when TBP is mixed with a paraffinic diluent, the TBP self-assembles into a bi-continuous phase. The underlying self-association of TBP is driven by intermolecular interaction between its polar groups, resulting in butyl moieties radiating out into the organic solvent. Simulation predicts a TBP diffusion constant that is anomalously low compared to what might normally be expected for its size; experimental nuclear magnetic resonance (NMR) studies also indicate an extremely low diffusion constant, consistent with a molecular aggregation model. Simulation of TBP at an oil/water interface shows the formation of a bilayer system at low TBP concentrations. At high...

Works of art prepared with acrylic emulsion paints became commercially available in the 1960s. It is increasingly necessary to undertake and optimise cleaning and preventative conservation treatments to ensure their longevity. Model artists' acrylic paint films covered with artificial soiling were thus prepared on a canvas support and exposed to a variety of wet cleaning treatments based on aqueous or hydrocarbon solvent systems. This included some with additives such as chelating agents and/or surfactants, and microemulsion systems made specifically for conservation practice. The impact of cleaning (soiling removal) on the paint film surface was examined visually and correlated with results of attenuated total reflection Fourier transform infrared, XPS and near-edge X-ray absorption fine structure analyses – three spectroscopic techniques with increasing surface sensitivity ranging from approximately − 1000, 10 and 5 nm, respectively. Visual analysis established the relative cleaning efficacy of the wet cleaning treatments in line with previous results. X-ray spectroscopy analysis provided significant additional findings, including evidence for (i) surfactant extraction following aqueous swabbing, (ii) modifications to pigment following cleaning and (iii) cleaning system residues. © 2014 The Authors. Surface and Interface Analysis published by John Wiley & Sons, Ltd.

Successful interaction between cells and biomaterial surfaces is crucial for biomedical devices, and incorporation of peptides such as RGD (Arg-Gly-Asp) at the polymer interface can substantially promote cell adhesion and proliferation. X-ray photoelectron spectroscopy (XPS) has been used to characterise poly-e-caprolactone (PCL) films modified by aminolysis and the introduction of RGD peptides via carbodiimide (CDI) and thiol-halogen ‘click’ chemistry. The nitrogen signal acts as an elemental indicator for successful attachment, and changes in the chemical environment are reflected in the carbon and oxygen spectra. Chlorine and sulfur provide additional chemical indicators of reaction progress in the thiol method, with the selective nature of the Cl–S reaction reflected in the complete loss of Cl signal and appearance of S, avoiding potential amine-peptide side-reactions. Comparison of the XPS elemental concentrations indicated an estimate of 2–3% peptide functionalisation on the PCL surface for both methods, correlating with the improvement in Schwann cell response observed after peptide immobilisation. The enhanced selectivity of peptide attachment to the polymer surface demonstrated with XPS for the novel method based on thiol chemistry shows its potential for development as a biomimetic scaffold for peripheral nerve injury. Copyright © 2014 John Wiley & Sons, Ltd.

The C 1 s, N 1 s, and O 1 s core level binding energies (BEs) of the functional groups in amino acids (glycine, aspartic acid, glutamic acid, arginine, and histidine) with varied side-chains and cell-binding RGD-based peptides have been determined and characterized by X-ray photoelectron spectroscopy with a monochromatic Al Kα source. The zwitterionic nature of the amino acids in the solid state is unequivocally evident from the N 1 s signals of the protonated amine groups and the C 1 s signature of carboxylate groups. Significant adventitious carbon contamination is evident for all samples but can be quantitatively accounted for. No intrinsic differences in the XP spectra are evident between two polymorphs (α and γ) of glycine, indicating that the crystallographic differences have a minor influence on the core level BEs for this system. The two nitrogen centers in the imidazole group of histidine exhibit an N 1 s BE shift that is in line with previously reported data for theophylline and aqueous imidazole solutions, while the nitrogen and carbon chemical shifts reflect the unusual guanidinium chemical environment in arginine. It is shown that the complex envelopes of C 1 s and O 1 s photoemission spectra for short-chain peptides can be analyzed quantitatively by reference to the less complex XP spectra of the constituent amino acids, provided the peptides are of high enough purity. The distinctive N 1 s photoemission from the amide linkages provides an indicator of peptide formation even in the presence of common impurities, and variations in the relative intensities of N 1 s were found to be diagnostic for each of the three peptides investigated (RGD, RGDS, and RGDSC).

Das Produkt der Synthese kristalliner organischer Materialien hangt stark von den ersten Schritten des molekularen Selbstorganisationswegs ab, ein Vorgang, den wir als Keimbildung von Kristallen kennen. Die Entwicklung neuer experimenteller und rechnerischer Verfahren hat zu verstarktem Interesse an der Aufklarung der molekularen Mechanismen gefuhrt, durch die Keime entstehen und sich zu makroskopischen Kristallen entwickeln. Die Kinetik der beteiligten Vorgange wird gut von der klassischen Keimbildungstheorie (“classical nucleation theory”, CNT) beschrieben, neu vorgeschlagene Keimbildungstheorien betrachten zusatzlich die Entwicklung der Struktur und die Konkurrenzsituation bei der Kristallisation polymorpher Systeme. Dieser Aufsatz diskutiert, wie weit die CNT und Messungen der Keimbildungsrate Informationen uber diese Vorgange auf molekularer Ebene liefern konnen, und fasst das aktuelle Wissen uber die molekulare Selbstorganisation in keimbildenden Systemen zusammen.

The outcome of synthetic procedures for crystalline organic materials strongly depends on the first steps along the molecular self-assembly pathway, a process we know as crystal nucleation. New experimental techniques and computational methodologies have spurred significant interest in understanding the detailed molecular mechanisms by which nuclei form and develop into macroscopic crystals. Although classical nucleation theory (CNT) has served well in describing the kinetics of the processes involved, new proposed nucleation mechanisms are additionally concerned with the evolution of structure and the competing nature of crystallization in polymorphic systems. In this Review, we explore the extent to which CNT and nucleation rate measurements can yield molecular-scale information on this process and summarize current knowledge relating to molecular self-assembly in nucleating systems.

NEXAFS-RIXS and home laboratory-based UV-Vis absorption spectroscopy are combined to examine the speciation and electronic structure of para- aminobenzoic acid (PABA) in aqueous solution as a function of pH. DFT and TD- DFT electronic structure calculations reproduce the experimental trends and provide a correlation between the experimental HOMO↔LUMO gap as well as the electronic transitions between molecular orbitals in the non-ionic, anionic and cationic forms of PABA.

Nitrogen K-edge XPS and NEXAFS of the two polymorphic forms of para- aminobenzoic acid (PABA) are significantly different reflecting variation in hydrogen bonding. Alteration in hydrogen bonding at the amino group leads to a shift to high energy for both the XPS N 1s core level and the 3π* NEXAFS resonance with β-PABA. Participation of the amine group in the aromatic system causes the 1π* resonance to be sensitive to the nature of the intermolecular bonding at the para-carboxylic acid group, and a shift to low energy for α- PABA is observed due to hydrogen-bonded carboxylic acid dimer formation. FEFF calculations also successfully reproduce both the energy and intensity variations observed for the σ* shape resonance associated with the C-N bond, with the majority of the decrease in energy observed for b-PABA arising from the longer C-N bond.

Decomposition of hydrazinium pentafluoroaluminate under oxidative (F 2 ) conditions leads to aluminium(III) fluoride whose properties are highly dependent on the conditions used for synthesis. In the presence of anhydrous HF, which probably acts as a heat exchange agent, samples have high BET areas, whereas BET areas of samples prepared under gas–solid conditions are small. XPS data are consistent with the presence of Lewis acid centres but, more importantly, emphasise the importance of surface hydroxyl groups, particularly in high surface area compounds. Catalytic behaviour towards isomerisation of 1,1,2-trichlorotrifluoroethane and subsequent dismutations at moderate temperatures and towards room temperature dehydrochlorination of tert -butyl chloride has been demonstrated for some high BET samples; both reactions indicate that surface Lewis sites exist. Catalytic ability is inhibited by surface hydroxyl groups but is improved by prior fluorination of the surface with CCl 2 F 2 . Catalysis is inhibited also by the presence of ammonium fluoroaluminate, a by-product of the decomposition process. The [NH 4 ] + salt level can be reduced by washing with anhydrous HF.

Yellow discoloration was observed at the surface of normally white crystals of a development pharmaceutical fumarate salt, tentatively ascribed to the presence of trace amounts of free base. The impact of impurities on sample properties and behavior can be significant, especially if localized at the surface. No conventional bulk analytical technique could readily provide an explanation for the yellow color, so a surface-sensitive technique, X-ray photoelectron spectroscopy (XPS), was employed to characterize the salt. XPS reveals the presence of free base at the surface through the HN + /N ratio. A free radical decarboxylation mechanism is proposed to account for the alterations observed with extended irradiation. The lower intensity carboxyl signal and significantly lower HN + /N ratio for the yellow surface samples reveal a higher level of free base at the surface than the white samples. The samples with yellow surfaces could not be successfully milled, which was an important part of the production process for providing material of the required physical quality for product formulation. Identification of residual free base at the surface of the crystalline material, by XPS, was significant for optimization of the crystallization process to yield material of required quality for successful milling at plant scale.

Recent studies suggested that X-ray photoelectron spectroscopy (XPS) sensitively determines the protonation state of nitrogen functional groups in the solid state, providing a means for distinguishing between co-crystals and salts of organic compounds. Here we describe how a new theophylline complex with 5-sulfosalicylic acid dihydrate was established as a salt by XPS prior to assignment with conventional methods. The presence of a C=NH(+) (N9) N1s peak in XPS allows assignment as a salt, while this peak is clearly absent for a theophylline co-crystal. The large low frequency shift for N9 observed by (15)N solid-state nuclear magnetic resonance spectroscopy (ssNMR) and corresponding density functional theory (DFT) calculations confirm that protonation has occurred. The crystal structure and further analytical studies confirm the conclusions reached with XPS and ssNMR. This study demonstrates XPS as an alternative technique for determining whether proton transfer has occurred in acid-base complexes.

The thermal treatment of sol−gel derived aluminum hydroxide fluorides leads to new, X-ray amorphous, macroporous aluminum oxide-hydroxide fluorides. Followed by EA, DTA-TG, XPS, FT-IR, NH3-TPD, BET, XRD, and MAS NMR, it can be shown that the simplified composition of these compounds is “AlFO” and “AlF2O1/2”, respectively. These aluminum oxide-hydroxide fluorides exhibit a large number of acid centers. The local structure consists of AlFxOcn-x units (cn, coordination numbers 6, 5, 4), and all sites are partially fluorinated. It can be shown that bridged and terminal F-sites are related to 5- and 6-fold coordinated Al sites.

Characterization at the molecular level establishes X-ray photoelectron spectroscopy (XPS) as a useful technique for determining the extent of proton transfer in molecular crystals by studying theophylline-citric acid co-crystals alongside solid-state nuclear magnetic resonance (ssNMR) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). A complex has been formed by milling theophylline with either anhydrous or monohydrate citric acid and established as a 1:1 co-crystal by a combination of both conventional and novel analytical methods. The absence of peaks from the starting materials in the X-ray diffraction powder pattern indicates that the product was formed quantitatively, with elemental analysis and XPS revealing a 1:1 stoichiometry. Thermogravimetric analysis demonstrated the complex was anhydrous, with differential scanning calorimetry showing a melting temperature different from that of the starting materials. The absence of a C═NH+ N1s peak in XPS and the small mag...

The morphology and composition of uranium alpha sources with co-deposited platinum have been investigated by scanning electron microscopy (SEM) with energy dispersive X-ray fluorescence analysis (EDX), X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) studies. Combined SEM and EDX measurements reveal the effect of porous platinum on the morphology of the sources which in turn affects their alpha-spectral resolution. The XPS analysis suggests that the presence of platinum initially increases the concentration of hydroxyl species in the deposits, which then act as centres for subsequent preferential uranium precipitation. XPS and XAFS analysis also provide for first time an indication of oxidation states of uranium present in the sources prepared by the Hallstadius method. These results are in line with Hansen's theory of electrodeposition of actinides.

The formation of gold (Au) nanocrystalline films by reduction at the liquid/liquid interface has been investigated: three product fractions have been characterized, via electron and atomic force microscopy, X-ray photoelectron and UV−vis absorption spectroscopy, and X-ray diffraction. The mechanism suggested is deposition and self-assembly of the Au nanoparticles (NPs) at the liquid/liquid interface occurring in close association with the adsorption of capping ligands obtained from the starting materials and the cleavage of the reducing agent, tetrakis(hydroxymethyl)phosphonium chloride (THPC). NPs can also be assembled at the liquid/liquid interface by adsorption from one of the adjacent solution phases. This parallel route is also followed here to demonstrate that particle formation can occur either via route (i) interfacial reaction or (ii) bulk reaction followed by self-assembly.

A series of saccharides, including several monohydrates and one amorphous phase, has been investigated by XPS, providing the first database of survey and high-resolution spectra for this class of compounds. Known stoichiometries and XPS-determined elemental compositions agree well. XPS has sufficient precision for distinguishing the stoichiometries of mono-, di-, and polysaccharides. The C 1 s chemical shifts of the acetal and alcohol groups are similar for all samples, albeit with slight binding energy increases in the series from mono- to di- and polysaccharides. Increasing X-ray exposure causes a radiation-induced increase of the aliphatic hydrocarbon emission at 285 eV, concomitant with the appearance of a high binding energy C 1s emission peak at 289.1 eV and a decrease in the 0 1 s/C 1 s emission intensity ratio. Formation of aliphatic hydrocarbon groups is proposed to arise from dehydroxylation, while the increase in the 289.1 eV peak can be attributed to double dehydroxylation at the C 1 position or partial oxidation of an alcohol or acetal group. The rate of radiation damage correlates with previously reported rates of thermally induced caramelization.

Nitrogen K-edge XPS and NEXAFS of the two polymorphic forms of para- aminobenzoic acid (PABA) are significantly different reflecting variation in hydrogen bonding. Alteration in hydrogen bonding at the amino group leads to a shift to high energy for both the XPS N 1s core level and the 3 p * NEXAFS resonance with b -PABA. Participation of the amine group in the aromatic system causes the 1 p * resonance to be sensitive to the nature of the intermolecular bonding at the para -carboxylic acid group, and a shift to low energy for a - PABA is observed due to hydrogen-bonded carboxylic acid dimer formation. FEFF calculations also successfully reproduce both the energy and intensity variations observed for the s * shape resonance associated with the C - N bond, with the majority of the decrease in energy observed for b -PABA arising from the longer C - N bond.

Thermodynamic calculations based on hybrid-exchange density functional theory are used to predict the surface structure and stability of α-AlF3 ( 0 1 1 ¯ 2 ) in the presence of gaseous HF and H2O environments. The clean stoichiometric α-AlF3 ( 0 1 1 ¯ 2 ) is predicted to be Lewis acidic. However, under most reaction conditions this surface is unstable with respect to the adsorption of hydroxyl ions. This is consistent with experimental observations. It is predicted that the surface containing no hydroxyl ions could only be realised at high temperatures and under unrealistically dry conditions.

The origin of CO oxidation performance variations between three different supported Au catalysts (Au/CeO2, Au/Al2O3, Au/TiO2) was examined by in situ XAFS and DRIFTS measurements. All samples were prepared identically, by deposition-precipitation of an aqueous Au(III) complex with urea, and contained the same gold loading (~1 wt %). The as-prepared supported Au(III) precursors exhibited different reduction behaviour during exposure to the CO/O2/He reaction mixture at 298 K. The reducibility of the Au(III) precursor was found to decrease as a function of the support material in the order: titania > ceria > alumina. The as-prepared samples were inactive catalysts, but Au/TiO2 and Au/CeO2 developed catalytic activity as the reduction of Au(III) to metallic Au proceeded. Au/Al2O3 remained inactive. The developed catalytic CO oxidation activity at 298 K varied as a function of the support as follows: titania > ceria > alumina ~ 0. The EXAFS of samples pretreated in air at 773 K and in H2 at 573 K reveals the presence of only metallic particles for Au/TiO2 and Au/Al2O3. Au(III) supported on CeO2 remains unreduced after calcination, but reduces during the treatment with H2. CO oxidation experiments performed at 298 K with the activated samples show that the presence of metallic gold is necessary to obtain active catalysts (Au/CeO2 is not active after calcination) and that the reducible supports facilitate the genesis of active catalysts, while metallic gold particles on alumina are not active.

Detailed analysis of the C K near-edge X-ray absorption fine structure (NEXAFS) spectra of a series of saccharides (fructose, xylose, glucose, galactose, maltose monohydrate, α-lactose monohydrate, anhydrous β-lactose, cellulose) indicates that the precise determination of IPs and σ* shape resonance energies is sensitive enough to distinguish different crystalline saccharides through the variations in their average C-OH bond lengths. Experimental data as well as FEFF8 calculations confirm that bond length variations in the organic solid state of 10(-2) Å can be experimentally detected, opening up the possibility to use NEXAFS for obtaining incisive structural information for molecular materials, including noncrystalline systems without long-range order such as dissolved species in solutions, colloids, melts, and similar amorphous phases. The observed bond length sensitivity is as good as that originally reported for gas-phase and adsorbed molecular species. NEXAFS-derived molecular structure data for the condensed phase may therefore be used to guide molecular modeling as well as to validate computationally derived structure models for such systems. Some results indicate further analytical value in that the σ* shape resonance analysis may distinguish hemiketals from hemiacetals (i.e., derived from ketoses and aldoses) as well as α from β forms of otherwise identical saccharides.

Sarah Price opened a general discussion of the paper by Sven Schroeder: I have been generating the thermodynamically plausible crystal structures of organic molecules for many years, and back in 2004 we did a crystal structure prediction (CSP) study on imidazole1 and found that it was relatively straightforward. Following your paper, we have reclassified the low energy structures according to the tilt within the hydrogen-bonded chain and the relative direction of the chains. Although the observed structure was the global minimum, two other structures with a displacement of otherwise identical layers are very close in energy. Do you think that if imidazole had crystallised in one of these alternative structures it would be distinguishable by NEXAFS? This would be a very sensitive test of whether NEXAFS combined with CSP could be used in characterising crystal structures.