Electronic structure of single-wall carbon nanotubes studied by resonant inelastic X-ray scattering

F in the nanotubes, indicating that metallic nanotubes are present in the sample. Received: 2 April 1998     

Efficient Synthesis of N‐Cyano α and β‐Amino Esters

A versatile method for the synthesis of N‐cyano α and β‐amino esters is described. Reaction of different amino esters with cyanogen bromide in dry ether gave the corresponding N‐cyano α and β‐amino esters in excellent yields.     

Synthesis and characterisation of immunogens for the production of antibodies against small hydrophobic molecules with biosignature properties

In the present study, five different classes of small hydrophobic molecular targets, atypical for antibody generation, were structurally modified in order to introduce suitable reactive functionalities and/or spacers which allow covalent coupling to a carrier protein resulting in a stable carrier-hapten complex. These targets were chosen to serve as markers of extant and/or extinct life in the context of the development of the Life Marker Chip (LMC), an antibody-based instrument, which is being developed by a UK-led international consortium for flight to Mars on board the joint ESA/NASA Mars exploration ExoMars mission. The hapten-protein conjugates were designed to be used as immunogens for antibody generation and immunoassay reagents in subsequent stages of the LMC development. The extent of protein modification due to covalent attachment of hapten was determined by two independent methods, i.e. trinitrobenzenesulfonic acid (TNBSA) titrations of remaining protein reactive groups and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) of the resultant hapten-protein conjugates. In a further quality validation step, the conjugates were presented to an animal's immune system and polyclonal antibody titres with moderate specificity were obtained. These results suggest that conjugates synthesized as described herein can successfully be used in the generation of antibodies targeting small hydrophobic molecules.     

Correlation of structure and spin–phonon coupling in (La,Nd) doped BiFeO3 films

We studied the effect of structural change on the spin–phonon coupling in doped BiFeO₃ (BFO) films (Bi_0.8La_0.1Nd_0.1FeO₃) grown on SrTiO₃ (001) substrate. The temperature‐dependent Raman studies show phonon anomalies in the vicinity of magnetic ordering temperature T_N owing to the spin–phonon coupling. Doped films exhibit strong anomalies in the line widths of Raman bands around T_N revealing the presence of strong spin–lattice coupling. The modification in structure as a result of A‐site doping in BFO films plays an important role in controlling the nature of spin–phonon coupling. Copyright © 2014 John Wiley & Sons, Ltd.     

Raman spectroscopic investigations on transition‐metal dichalcogenides MX2 (M = Mo,W; X = S,Se) at high pressures and low temperature

Transition‐metal dichalcogenides have been investigated using Raman spectroscopy both being off‐resonance and in resonance. The first‐order Raman spectra of MoS₂, MoSe₂, WS₂ and WSe₂ single crystal synthesized by vapor transport technique have been studied as a function of hydrostatic pressure (0–20 GPa) and temperature (80–300 K). Isobaric and isothermal mode‐Grüneisen parameters have been determined from the temperature and pressure‐dependent Raman spectra. The pressure dependence of the chalcogen–chalcogen and metal–chalcogen force constant has been obtained using a central force model. Separation of the temperature dependence of Raman mode wavenumbers into quasi‐harmonic and purely anharmonic contributions using measured high‐pressure Raman data allows us to extract the changes in the phonon wavenumbers arising exclusively due to anharmonic interactions. Copyright © 2014 John Wiley & Sons, Ltd.     

Optical,thermal, and structural properties of Nb2O5–TeO2 and WO3–TeO2 glasses

Glass samples from two systems, Nb₂O₅–TeO₂ and WO₃–TeO₂, were prepared at two melt quenching rates and characterized by density, DSC, UV-visible, and Raman spectroscopy. Addition of Nb₂O₅ decreased the density while increase in the WO₃ concentration increased the density. Glasses prepared at higher quenching rates had smaller densities than glasses of the same composition prepared at lower quenching rate although the short-range structure of both glasses were identical, as revealed by Raman spectroscopy. Optical studies found an intense absorption band just below the absorption edge in both the glass series. This band was attributed to electronic transitions of Nb⁵⁺ and W⁶⁺ ions and a lone pair of electrons on Te atoms. Glass transition temperature increased with increase in Nb₂O₅ and WO₃ mol% due to the increase in average bond strength in the glass network. Raman spectroscopy showed that the concentration of TeO₄ units decreased with the increase in Nb₂O₅ and WO₃ concentrations.     

Tandem synthesis of aromatic amides from styrenes in water

An expedient one-pot synthesis of aromatic amides has been reported from styrenes in the presence of N-bromosuccinimide and iodine by using aqueous ammonia in water. The reaction proceeds through the formation of α-bromoketone as an intermediate in the presence of NBS and water. α-Bromoketone on reaction with iodine forms bromodiiodoketone which on nucleophilic substitution with aqueous ammonia gives aromatic amide. Substituted aromatic amides were obtained in good yields with wide functional group compatibility.     

Variable-temperature x-ray structural investigation of [Fe[HC(3,5-Me2pz)3]2](BF4)2 (pz= pyrazolyl ring): observation of a thermally induced spin state change from all high spin to an equal high spin-low spin mixture, concomitant with the onset of nonmerohedral twinning

The complex [Fe[HC(3,5-Me(2)pz)(3)](2)](BF(4))(2) (pz = pyrazolyl ring) undergoes a phase transition that occurs concomitantly with a thermally induced spin conversion between the high-spin (HS, S = 2) and low-spin (LS, S = 0) states. Above 204 K the compound is completely HS with the structure in the C2/c space group with Z = 4. A crystal structure determination of this phase was performed at 220 K yielding the cell constants a = 20.338(2) A, b = 10.332(1) A, c = 19.644(2) A, beta = 111.097(2) degrees, and V = 3851.5(6) A(3). There is one unique iron(II) site at this temperature. Below 206 K the compound converts to a 50:50 mixture of HS and LS. The radical change in the coordination sphere for half of the iron(II) sites, most notably a shortening of the Fe-N bond distances by ca. 0.2 A, that accompanies this magnetic transition causes a phase transition. The crystal system changes from C-centered monoclinic to primitive triclinic with Z = 2 with two half-molecules on independent inversion centers. A crystal structure determination was performed at 173 K in space group P1 with a = 10.287(2) A, b = 11.355(3) A, c = 18.949(4) A, alpha = 90.852(4) degrees, beta = 105.245(4) degrees, gamma = 116.304(4) degrees, and V = 1892.3(8) A(3). All specimens investigated below the phase transition temperature were determined to be nonmerohedral twins. Temperature cycling between these two forms does not appear to degrade crystal quality. Previous magnetic susceptibility measurements indicate a second, irreversible increase in the magnetic moment the first time the crystals are cooled below 85 K. A crystal structure determination at 220 K of a specimen precooled to 78 K was not significantly different from those not cooled below 220 K.