Formaldehyde in Super Acids: A Succession of Products from Carbenium through Oxonium Ion to Hydroxymethyl(methylidene)oxonium Salts

An oxonium ion with hydroxymethyl and methylidene substituents is found in the salts 1 -MF₆ (M=As, Sb), which can be isolated from solutions of formaldehyde in superacids HF/MF₅. Their formation was at first surprising, since NMR spectroscopy indicates that protonated monofluoromethanol is present in solution.     

A new criterion to assess distributional homogeneity in hyperspectral images of solid pharmaceutical dosage forms

During galenic formulation development, homogeneity of distribution is a critical parameter to check since it may influence activity and safety of the drug. Raman hyperspectral imaging is a technique of choice for assessing the distributional homogeneity of compounds of interest. Indeed, the combination of both spectroscopic and spatial information provides a detailed knowledge of chemical composition and component distribution.     

A Response Surface Model to Predict and Experimentally Tune the Chemical,Magnetic and Optoelectronic Properties of Oxygen-Doped Boron Nitride**

Porous boron nitride (BN), a combination of hexagonal, turbostratic and amorphous BN, has emerged as a new platform photocatalyst. Yet, this material lacks photoactivity under visible light. Theoretical studies predict that tuning the oxygen content in oxygen-doped BN (BNO) could lower the band gap. This is yet to be verified experimentally. We present herein a systematic experimental route to simultaneously tune BNO's chemical, magnetic and optoelectronic properties using a multivariate synthesis parameter space. We report deep visible range band gaps (1.50–2.90 eV) and tuning of the oxygen (2–14 at.%) and specific paramagnetic OB₃ contents (7–294 a.u. g⁻¹). Through designing a response surface via a design of experiments (DOE) process, we have identified synthesis parameters influencing BNO's chemical, magnetic and optoelectronic properties. We also present model prediction equations relating these properties to the synthesis parameter space that we have validated experimentally. This methodology can help tailor and optimise BN materials for heterogeneous photocatalysis.     

A General Route to Construct Diverse Multifunctional Fe3O4/Metal Hybrid Nanostructures

Multifunctional nanostructures : By using 3‐aminopropyltrimethoxysilane as a linker, Au nanoparticles (NPs), Au shells, flowerlike Au/Pt hybrid NPs, and Ag or Au/Ag core/shell NPs could be supported on the surface of superparamagnetic Fe₃O₄ spheres to construct hybrid nanostructures that display near‐IR absorption, high catalytic activity towards an electron‐transfer reaction, or excellent surface‐enhanced Raman scattering activity. The picture shows SEM images of Fe₃O₄ spheres coated with Au shells (top) and with Au/Pt hybrid NPs (bottom).

     

一种经氟化和热处理在双壁碳纳米管上生成缺陷的方法(英文)

Nanoscale defects in the outer tube to preserve the electrical and optical features of the inner tube can be engineered to exploit the intrinsic properties of double walled carbon nanotubes (DWCNTs) for various promising applications. We demonstrated a selective way to make defects in the outer tube by the fluorination of DWCNTs followed by the thermal detachment of the F atoms at 1000 °C in argon. Fluorinated DWCNTs with different amounts of F atoms were prepared by reacting with fluorine gas at 25, 200, and 400 °C that gave the stoichiometry of CF0.20, CF0.30, and CF0.43, respectively. At the three different temperatures used, we observed preservation of the coaxial morphology in the fluorinated DWCNTs. For the DWCNTs fluorinated at 25 and 200 °C, the strong radial breathing modes (RBMs) of the inner tube and weakened RBMs of the outer tube indicated selective fluorine attachment onto the outer tube. However, the disappearance of the RBMs in the Raman spectrum of the DWCNTs fluorinated at 400 °C showed the introduction of F atoms onto both inner and outer tubes. There was no significant change in the morphology and optical properties when the DWCNTs fluorinated at 25 and 200 °C were thermally treated at 1000 °C in argon. However, in the case of the DWCNTs fluorinated at 400 °C, the recovery of strong RBMs from the inner tube and weakened RBMs from the outer tube indicated the selective introduction of substantial defects on the outer tube while preserving the original tubular shape. The thermal detachment of F atoms from fluorinated DWCNTs is an efficient way to make highly defective outer tubes for preserving the electrical conduction and optical activity of the inner tubes.     

From Molecular Fragments to Crystals: A UV Raman Spectroscopic Study on the Mechanism of Fe‐ZSM‐5 Synthesis

The nucleation process of iron‐exchanged zeolite Fe‐ZSM‐5, from the assembly of distorted tetrahedrally coordinated iron species and silicate rings in the precursor to the final Fe‐ZSM‐5 crystals, as well as variations in the coordination environment of iron, were studied by UV resonance Raman spectroscopy and complementary techniques.

     

Surface Dynamics of A Vanadyl Pyrophosphate Catalyst for n‐Butane Oxidation to Maleic Anhydride: An In Situ Raman and Reactivity Study of the Effect of the P/V Atomic Ratio

This work focused on investigating the effect of the P/V atomic ratio in vanadyl pyrophosphate, catalyst for n‐butane oxidation to maleic anhydride, on the nature of the catalytically active phase. Structural transformations occurring on the catalyst surface were investigated by means of in situ Raman spectroscopy in a non‐reactive atmosphere, as well as by means of steady‐state and non‐steady‐state reactivity tests, in response to changes in the reaction temperature. It was found that the nature of the catalyst surface is affected by the P/V atomic ratio even in the case of small changes in this parameter. With the catalyst having P/V equal to the stoichiometric value, a surface layer made of α_I‐VOPO₄ developed in the temperature interval 340–400 °C in the presence of air; this catalyst gave a very low selectivity to maleic anhydride in the intermediate T range (340–400 °C). However, at 400–440 °C δ‐VOPO₄ overlayers formed; at these conditions, the catalyst was moderately active but selective to maleic anhydride. With the catalyst containing a slight excess of P, the ratio offering the optimal catalytic performance, δ‐VOPO₄ was the prevailing species over the entire temperature range investigated (340–440 °C). Analogies and differences between the two samples were also confirmed by reactivity tests carried out after in situ removal and reintegration of P. These facts explain why the industrial catalyst for n‐butane oxidation holds a slight excess of P; they also explain discrepancies registered in the literature about the nature of the active layer in vanadyl pyrophosphate.     

Gold bromide complexes in acidic aqueous solutions from 25° to 300°C. A laser raman spectroscopic study

Raman spectra of gold bromide complexes in acidic solutions (pH=–0.3–3) have been recorded at 25° to 300°C and at pressures on the liquid vapor curve for the system. At 25°C, only the square planar Au(III) bromide complex, AuBr ₄ ^– , is present in solution with bands at approximately 105, 197 and 215 cm^–1. However, in these acidic solutions, when the temperature is 50°C or higher, the square planar Au(III) bromide complex is partially transformed into the linear Au(I) bromide complex, AuBr ₂ ^– , with a single band near 208 cm^–1. The transformation of the Au(III) square planar tetrabromo complex into the Au(I) linear dibromo complex is also favored by a reduction of the oxygen fugacity and an increase in pH.     

Application of surface science techniques to study a gilded Egyptian funerary mask: A multi-analytical approach

A wide range of analytical techniques has been used to study an Egyptian funerary mask of the Ptolemaic period (305-30 bc ). Secondary electron (SE) and back-scattering (BS) images, recorded by a scanning electron microscope (SEM), provided a detailed representation of the metallurgical techniques used to construct the gilded mask. It is confirmed, that the golden leaf used to cover the mask is the product of an antique refinery practice, so called, cementation process of naturally occurring alloy of gold and silver, namely electrum. Complementary results of SEM-electron dispersion spectroscopy (EDS) and electron probe microanalysis (EPMA)–wavelength dispersion spectroscopy (WDS) provided chemical compositions of the golden leaf as well as in the plaster base of the mask. X-ray photoemission spectroscopy (XPS) revealed the presence of Au, Ag, Si, S, Cl, Ca, and N, in addition to O and C. Relative concentration of Au/Ag at the surface has been measured by XPS to be 70% to 30%. XPS depth profiling verified silver-enrichment at the surface, as ratio of gold to silver is measured to be 80% to 20% at the depth of 15 nm. XPS chemical mapping images of gold and silver confirmed a rather inhomogeneous character of Au/Ag relative concentration at the surface. The main diffraction peaks in the X-ray diffraction (XRD) spectrum coincide with diffraction peaks of pure gold, silver metals, and magnesium calcite Mg_0.03Ca_0.97CO₃. Whereas, Raman spectroscopy results implied the existence of Ag₂S, a tarnishing compound, on the golden area of the mask.     

Polychloride Monoanions from [Cl3]− to [Cl9]−: A Raman Spectroscopic and Quantum Chemical Investigation

Polychloride monoanions stabilized by quaternary ammonium salts are investigated using Raman spectroscopy and state‐of‐the‐art quantum‐chemical calculations. A regular V‐shaped pentachloride is characterized for the [N(Me)₄][Cl₅] salt, whereas a hockey‐stick‐like structure is tentatively assigned for [N(Et)₄][Cl₂???Cl₃^?]. Increasing the size of the cation to the quaternary ammonium salts [NPr₄]⁺ and [NBu₄]⁺ leads to the formation of the [Cl₃]^? anion. The latter is found to be a pale yellow liquid at about 40 °C, whereas all the other compounds exist as powders. Further to these observations, the novel [Cl₉]^? anion is characterized by low‐temperature Raman spectroscopy in conjunction with quantum‐chemical calculations.     

A novel approach to investigate vascular wall in 3D: Combined Raman spectroscopy and atomic force microscopy for aorta en face imaging

A novel approach based on the combination of Raman confocal 3D imaging with atomic force microscopy (AFM) for analysis of the murine vessel wall en face is described. The approach is based on subsequent Raman and AFM imaging of the same areas of the sample. This methodology allows for direct correlation of the chemical structure (Raman data) with morphology of the surface (AFM). The sub-cellular structures of the tissue e.g., cell nuclei, heme, or lipid-rich species are visualized and localized by the application of Raman imaging, while AFM complements these data with high-resolution information about the surface topography and size of lipid-rich structures. Overall, the applied approach enables detailed characterization of the inner layer of the vessel wall.     

A new instrument adapted to in situ Raman analysis of objects of art

The analysis of precious artefacts and antiquities demands care in order to minimise the risk of accidental damage during measurement. Mobile fibre-optic-based Raman instruments offer a means to avoid destructive sampling and eliminate the need to transport artefacts for spectrochemical analysis. In this work we present a new mobile instrument developed and optimised for the in situ Raman investigation of objects of art and antiquities. The instrument is controlled by a portable computer. Selected mounts cover many types of artefacts. Newly written software routines organise spectra together with measurement parameters and facilitate calibration of the instrument. The present paper describes this new Raman instrument and discusses some challenges in the transition from a laboratory environment to in situ investigations in museums.     

A density functional derived vibrational force field for β-ionone Use of the ultraviolet resonance Raman intensities to check the vibrational analysis accuracy

In the present article we aim to determine an accurate and transferable molecular force field for β-ionone in order to perform molecular dynamics calculations on the retinal isomers. For β-ionone, a force field is derived from calculations using the Density Functional Theory (DFT). The force constants expressed in the internal coordinate space were scaled fitting theoretical to experimental vibrational wavenumbers. The validity of the force field was checked using a comparison between calculated and observed resonance Raman intensities obtained from the A-term part (Franck–Condon) of the scattering tensor.     

To the Knowledge of Interpseudohalogens: A Contribution to Cyanogen Isocyanate (NC–NCO)

Cyanogen isocyanate (NC–NCO) has been prepared and studied using a combined experimental and theoretical approach. A crystalline film of the interpseudohalogen species was stabilized by vapor deposition on a cold substrate (T = –100 °C). From IR spectroscopy on the “free” molecule, trapped in a matrix of solid argon, the connectivity and geometry of this unstable interpseudohalogen was deduced and substantiated by theoretical calculations. With this information, the crystal structure of NCNCO in the solid state could be analysed using powder X‐ray diffraction [Pbca (No. 61), a = 7.63(1) Å, b = 6.50(2) Å, c = 6.03(6) Å; V = 299.5(1) ų]. The compound transforms into amorphous polymeric C₂N₂O at T > –68 °C. The results obtained were compared with recent findings and further discussed in the general context of C–N–(O) chemistry.     

Carbon nanotubes as solid-phase extraction sorbents prior to atomic spectrometric determination of metal species: A review

New materials have significant impact on the development of new methods and instrumentation for chemical analysis. From the discovery of carbon nanotubes in 1991, single and multi-walled carbon nanotubes – due to their high adsorption and desorption capacities – have been employed as sorption substrates in solid-phase extraction for the preconcentration of metal species from diverse matrices. Looking for successive improvements in sensitivity and selectivity, in the past few years, carbon nanotubes have been utilized as sorbents for solid phase extraction in three different ways: like as-grown, oxidized and functionalized nanotubes. In the present paper, an overview of the recent trends in the use of carbon nanotubes for solid phase extraction of metal species in environmental, biological and food samples is presented. The determination procedures involved the adsorption of metals on the nanotube surface, their quantitative desorption and subsequent measurement by means of atomic spectrometric techniques such as flame atomic absorption spectrometry, electrothermal atomic absorption spectrometry or inductively coupled plasma atomic emission spectrometry/mass spectrometry, among others. Synthesis, purification and types of carbon nanotubes, as well as the diverse chemical and physical strategies for their functionalization are described. Based on 140 references, the performance and general properties of the applications of solid phase extraction based on carbon nanotubes for metal species atomic spectrometric determination are discussed.