Coordination of pyridinethiols in gold(I) complexes

High-yield synthesis of gold(I) thionato complexes, bis(pyridine-2-thionato)gold(I) chloride (1) and bis(pyridine-4-thionato)gold(I) chloride (2), are described. According to their solid-state structures, a linear coordination of Au(I), equiplanar coordination of the ligands and two weak gamma-agostic interactions are found in both of these complexes despite of different relative positions of N and S atoms in the pyridinethionato ligands. Density functional theory calculations on 1 and 2 reproduce the observed X-ray structures. Even though the C-H...Au interactions of Au(I) and two pyridine moieties (2.83 and 2.88 A in 1 and 2.86 A in 2) are relatively weak, according to calculations they seem to provide further stabilization for the coordination and orientation of the ligands. In 1 the shortest Au...Au distances of 3.50 A indicate that aurophilic interactions, even though weak, are present in the solid state, whereas in 2 these interactions are absent.     

Sizes of pentagonal clusters in fullerenes

Stability and chemistry, both exohedral and endohedral, of fullerenes are critically dependent on the distribution of their obligatory 12 pentagonal faces. It is well known that there are infinitely many IPR-fullerenes and that the pentagons in these fullerenes can be at an arbitrarily large distance from each other. IPR-fullerenes can be described as fullerenes in which each connected cluster of pentagons has size 1. In this paper we study the combinations of cluster sizes that can occur in fullerenes and whether the clusters can be at an arbitrarily large distance from each other. For each possible partition of the number 12, we are able to decide whether the partition describes the sizes of pentagon clusters in a possible fullerene, and state whether the different clusters can be at an arbitrarily large distance from each other. We will prove that all partitions with largest cluster of size 5 or less can occur in an infinite number of fullerenes with the clusters at an arbitrarily large distance of each other, that 9 partitions occur in only a finite number of fullerene isomers and that 15 partitions do not occur at all in fullerenes.     

Synchrotron and neutron powder diffraction study of phase transition in weberite-type Nd3NbO7 and La3NbO7

La₃NbO₇ and Nd₃NbO₇ are insulating compounds that have an orthorhombic weberite-type crystal structure and undergo a phase transition at about 360 and 450 K, respectively. The nature of the phase transitions was investigated via heat capacity measurements, synchrotron X-ray and neutron diffraction experiments. It is here shown that above the phase transition temperature, the compounds possess a weberite-type structure described by space group Cmcm (No. 63). Below the phase transition, the high temperature phase transforms into a weberite-type structure with space group Pmcn (No. 62). The phase transformation primarily involves the off-center shifting of Nb⁵⁺ ions inside the NbO₆ octahedra, combined with shifts of one third of the Ln³⁺ (Ln³⁺=La³⁺ and Nd³⁺) ions at the center of the LnO₈ polyhedra towards off-center positions. The phase transition was also proven to have great impacts on the dielectric properties.     

Urinary peptides as a diagnostic tool for renal failure detected by matrix-assisted laser desorption/ionisation mass spectrometry: an evaluation of their clinical significance

The development of new analytical methodologies related to the proteome for the evaluation of renal physiology and pathology is surely of wide interest for physicians, giving them new tools for monitoring complications associated with diabetes, such as end-stage renal disease. In the present study, the clinical significance of the urinary abundance of two peptides, SGSVIDQSRVLNLGPITR (the uromodulin precursor, m/z 1912) and IGPHypGPHypGLMGPP [present in the collagen-α-5(IV) chain precursor, m/z 1219], detected by matrix- assisted laser desorption/ionisation mass spectrometry (MALDI/MS) in microalbuminuric or nephropathic diabetic patients and in non-diabetic nephropathic patients was evaluated. A progressive increase in the abundance of the ion at m/z 1219 and a decrease in the abundance of the ion at m/z 1912 have been found in diabetic microalbuminuric, diabetic-nephropathic and nephropathic patients. Linear correlations are present between serum creatinine values and the abundances of the ions at m/z 1219 (positive correlation, r=0.3645, P<0.0001) and at m/z 1912 (negative correlation, r=-0.3053, P<0.0005). Correlations between the MALDI data and the estimated glomerular filtration rate were also found, while relationships with urinary albumin excretion were found only in sub-sets of patients. Analysis of receiver operating characteristic curves showed a sensitivity up to 96% and a specificity of up to 84% for the two ionic species, or their ratio, for distinguishing diabetic patients with different degrees of nephropathy from healthy subjects, proving that the urinary abundance of the two peptides at m/z 1219 and m/z 1912, determined with MALDI/MS, may be considered as a possible diagnostic tool for the determination of progression toward renal failure, also with the aim of monitoring kidney function, in diabetic patients.     

Do Rhodium Bis(σ‐amine‐borane) Complexes Play a Role as Intermediates in Dehydrocoupling Reactions of Amine‐boranes?

The recently synthesized rhodium complex [Rh{P(C₅H₉)₂(η²‐C₅H₇)}(Me₂HNBH₃)₂]BAr^F₄ ( 2 ), which incorporates two amine‐boranes coordinated to the rhodium center with two different binding modes, namely η¹ and η², has been used to probe whether bis(σ‐amine‐borane) motifs are important in determining the general course of amine‐boranes dehydrocoupling reactions. DFT calculations have been carried out to explore mechanistic alternatives that ultimately lead to the formation of the amine‐borane cyclic dimer [BH₂NMe₂]₂ ( A ) by hydrogen elimination. Sequential concerted, on‐ or off‐metal, intramolecular dehydrogenations provide two coordinated amine‐borane molecules. Subsequent dimerization is likely to occur off the metal in solution. In spite of the computationally confirmed presence of a BH???NH hydrogen bond between amine‐borane ligands, neither a simple intermolecular route for dehydrocoupling of complex 2 is operating, nor seems [Rh{P(C₅H₉)₂(η²‐C₅H₇)} B ]⁺ to be important for the whole dehydrocoupling process.     

Electron ionization mass spectra of alkylated sulfabenzamides

Mono‐, di‐ and trialkyl derivatives of 'sulfabenzamide' (N‐4‐aminophenylsulfonylbenzamide) have been prepared and their electron ionization (EI) mass spectra examined. It is found that the fragmentation of N‐alkylsulfabenzamides (alkyl = CH₃ to n‐C₅H₁₁) proceeds via a very specific rearrangement process. The proposed mechanism involves an intermediate formation of distonic molecular ions, and the driving force for this process is the formation of stable N‐alkylphenylcyanide cations [R‐N⁺ ? CC₆H₅]. The findings are confirmed by exact mass measurements, tandem mass spectrometry (MS/MS) experiments and deuterium labeling. Published in 2011 by John Wiley & Sons, Ltd.     

The nature of the C–As bonds in arsaalkynes: an atoms in molecules and electron localization function study

The nature of the C–As bonds present in a series of six neutral and anionic arsaalkynes was investigated. The optimized geometries, vibrational frequencies, and wavefunctions of all the studied species were computed using density functional theory (B3LYP/6-311++G(2d,2p)). To understand the bonding characteristics, Atoms in Molecules theory and topological analysis of the electron localization function were used. For comparison, natural bond orbital analysis was also performed. The results suggest that in five of the six studied compounds, the C–As bonds are essentially triple bonds, with similar characteristics to the C–P analogues in phosphaalkynes.     

Charge transport in poly-imidazole membranes: a fresh appraisal of the Grotthuss mechanism

A detailed theoretical investigation of the charge transport mechanism in poly(4-vinyl-imidazole) (P4VI), the parent polymer of a series of N-heterocyclic-based membranes used as an electrolyte in proton exchange membrane fuel cells, is presented. In particular, Density Functional Theory (DFT) results obtained for small model systems (protonated imidazole dimers and trimers) suggest that the commonly accepted conduction mechanism, based on a sequential proton transfer between imidazole moieties, could be impeded by the geometrical constraints imposed by the polymeric backbone. Indeed only one kind of proton transfer reaction is energetically allowed between adjacent imidazoles, so that a rotation of the protonated imidazole is required for a second proton transfer. Molecular dynamics simulations on a larger model (15 oligomers with an excess proton) show that the rotation of the imidazole carrying the excess proton is a soft large amplitude motion. These results allow us to propose a new proton conduction mechanism in P4VI, where a frustrated rotation of the protonated imidazole before each proton transfer reaction represents the rate-limiting step. Furthermore, in contrast with the Grotthuss proton transport mechanism in water, our results indicate that here it is the same proton which could be successively transferred. From a chemical point of view, these new insights into the mechanism are relevant for a rational design of modified azole-based systems for Proton Exchange Membrane Fuel Cells.     

Structuring of photosensitive material below diffraction limit using far field irradiation

In this paper, we report on in-situ atomic force microscopy (AFM) studies of topographical changes in azobenzene-containing photosensitive polymer films that are irradiated with light interference patterns. We have developed an experimental setup consisting of an AFM combined with two-beam interferometry that permits us to switch between different polarization states of the two interfering beams while scanning the illuminated area of the polymer film, acquiring corresponding changes in topography in-situ. This way, we are able to analyze how the change in topography is related to the variation of the electrical field vector within the interference pattern. It is for the first time that with a rather simple experimental approach a rigorous assignment can be achieved. By performing in-situ measurements we found that for a certain polarization combination of two interfering beams [namely for the SP (?, ?) polarization pattern] the topography forms surface relief grating with only half the period of the interference patterns. Exploiting this phenomenon we are able to fabricate surface relief structures with characteristic features measuring only 140 nm, by using far field optics with a wavelength of 491 nm. We believe that this relatively simple method could be extremely valuable to, for instance, produce structural features below the diffraction limit at high-throughput, and this could significantly contribute to the search of new fabrication strategies in electronics and photonics industry.