Laser photolysis of 2-phenylheptamethyltrisilane

Two transient absorptions have been detected in the 266 nm laser photolysis of 2-phenylheptamethyltrisilane in cyclohexane solution at room temperature, and their time evolution was recorded in the presence and absence of air and added trapping agents. The shorter-lived 440 nm transient (t1/2 < 20μs) is tentatively assigned to the silylene :SiMePh and the more persistent 380 nm transient to the disilene MePhSiSiMePh. The reactivity of this silylene is much lower than had been expected.     

Hg diffusion in books of XVIII and XIX centuries by synchrotron microprobe

The pigment vermilion (HgS) was used to color the fore edge, tail and head of books. Dissemination and quantification of Hg present in the ink used to color books from XVIII and XIX centuries are reported. Mercury is a very toxic element for the human body, therefore it is extremely important to know whether Hg tends to disseminate throughout the paper or stays confined to the borders of the books with less danger for readers. Synchrotron X-ray microprobe was used to evaluate Hg dissemination from the border to the centre of the paper sheet. The diffusion pattern of Hg was compared with the results obtained by a portable X-ray fluorescence spectrometer and mean quantitative calculations were obtained by a stationary X-ray fluorescence system with triaxial geometry. The results showed high concentrations of Hg in the external regions, but no diffusion was observed for the inner parts of the paper.     

Characterisation of foxing stains in eighteenth to nineteenth century drawings using non-destructive techniques

The reddish-brown, brown or yellowish stains of circular or irregular shape known as foxing spots have been fully described in conservation literature but still, this phenomenon does not find any scientific agreement since many hypotheses have been raised concerning their origin. In this work a contribution to foxing definition not only focussed on its appearance but also reported on its chemical information. For this purpose foxing stains present in drawings from two Portuguese artists dated from the eighteenth to nineteenth centuries were observed under ultra-violet light and optical microscope and analysed by three non-invasive spectroscopy techniques. The observations carried out on the stains provided information on their surface morphology. The use of energy-dispersive X-ray fluorescence revealed a variation on the elemental content between foxing and paper region. Although the results from X-ray diffraction analysis showed no signs of cellulose degradation in foxing stains, Fourier-transformed infrared analysis revealed the presence of oxide groups. Both the information on the chemical nature and surface morphology of the stains achieved in this study will contribute to increase foxing formation information and develop future protocols for conservation purposes.     

High pressure studies on the misfolding and aggregation of p53 in cancer and of α-synuclein in Parkinson’s disease

ABSTRACT

High pressure research can be used to aid in answering why some polypeptide chains reversibly unfold and others adopt a misfolding conformation culminating in aggregation. This topic is one of the fundamental questions in biology that we seek to understand, and for that, we have been experimentally applying pressure to proteins for the last 20 years. Here, we exemplify how pressure research should be used to identify preamyloidogenic protein intermediates as well as to dissociate supramolecular complexes. We believe that the applications of high pressure to understand the behavior of proteins are diverse and can help biologists answer fundamental questions of biomedical relevance.     

The phenylcarbene rearrangement revisited

The evolution of mechanistic ideas about the phenylcarbene rearrangement has been reviewed, and three closely linked problems have been identified toward whose solution this research has been aimed: 1. Why do the ratios of the stable end products from the rearrangements of o-, m- and p-tolylmethylene differ when all three reactions have been throught to pass through a common intermediate? 2. Why does the rearrangement of 2-methylcycloheptatrienylidene lead to exclusive formation of styrene? 3. What is the mechanism of styrene formation from o-tolylmethylene? New mechanisms have been proposed in which m- and p-tolylmethylene can rearrange to styrene without necessarily being converted to o-tolylmethylene. The formation of a small amount of 2,6-dimethylstyrene from the rearrangement of 3,4,5-trimethylphenylmethylene is viewed as evidence for such a mechanism, and a set of interconverting norcaradienylidenes are believed to be the crucial intermediates. Other alternatives are considered and rejected on the basis of the rearrangement products of 3,5-dimethyl- and 3,4,5-trimethylphenylmethylene.     

Intermediate range order in concentrated aqueous solutions of copper nitrate. X-ray diffraction and Raman investigations

Concentrated aqueous solutions of copper nitrate of different concentrations (0.66 mol dm⁻³ up to 4.84 mol dm⁻³) have been investigated by X-ray diffraction at room temperature. In these solutions a maximum of intensity (prepeak) is observed at low values of Q (approx. 0.6 to 1 Å⁻¹) suggesting the existence of an intermediate range order in their structure, in agreement with previous investigations on different electrolytes. In order to get information on the solvation shell of the copper cation, Raman spectroscopy experiments have been performed for the more concentrated solution. Polarization observations, isotopic substitution of the solvent and the comparison with a Raman spectrum of a concentrated aqueous solution of aluminum nitrate were performed in order to improve the interpretation of the obtained results with these convergent observations.     

X-Ray diffraction investigations of concentrated aqueous solutions of calcium halides

Concentrated aqueous solutions of calcium chloride and calcium bromide have been investigated by X-ray diffraction. In the diffraction patterns of aqueous chloride solutions of different concentrations, a maximum of intensity is observed in the region 0.6–1.1 Å⁻¹, while in the investigated aqueous bromide solution no maximum is observed in that region. This pre-peak suggests the existence of positional correlations in solution beyond direct contact. The interpretation is similar to the one proposed by the authors in previous investigations, and is supported by the calculations based on ad hoc molecular models. The influence of the anion is discussed.     

Pelseneeriol-1 and -2: new furanosesquiterpene alcohols from porostome nudibranch Doriopsilla pelseneeri

The paper reports the first chemical study of the porostome nudibranch Doriopsilla pelseneeri collected off the Portuguese coast (Atlantic Ocean). Two new furanosesquiterpene alcohols, pelseneeriol-1 (1) and pelseneeriol-2 (2), have been isolated together with known compounds, 15-acetoxy-ent-pallescensin-A (5), and dendocarbin-A (6), from the mantle of the nudibranch, whereas euryfuran (3) and drimane ester mixture 4 were identified in the extract of the internal glands. The structures of 1 and 2 have been determined by extensive spectroscopic studies as well as by comparison with literature model compounds. In order to assess the relative stereochemistry of 1 and 2, full NMR assignment of related sponge metabolite microcionin-2 (8) and of co-occurring sesquiterpenes 9-11, that have been re-isolated from the Mediterranean sponge Fasciospongia cavernosa, has been also conducted. In particular, the relative stereochemistry of tricyclic sesquiterpene microcionin-1 (9) has now been rigorously assigned by detailed analysis of NOE difference experiments.     

Thermal-, pressure-, and light-induced spin transition in novel cyanide-bridged FeII-AgI bimetallic compounds with three-dimensional interpenetrating double structures (FeIILx[Ag(CN)2]2).G

Low-spin, high-spin and spin-transition behaviours have been observed for the doubly interpenetrating three-dimensional bimetallic compounds (FeII(pz)[Ag(CN)2]2).pz (pz = pyrazine), (FeII(4,4'-bipy)2[Ag(CN)2]2) (4,4'-bipy = 4,4'-bipyridine), and (FeII(bpe)2[Ag(CN)2]2) (bpe = bispyridylethylene), respectively. The single crystals of the bpe derivative undergo a spin transition with a large hysteresis loop at about 95 K. After several warming and cooling cycles, the single crystals become a microcrystalline powder with 50% spin transition. Influence of pressure--as well as light-induced excited spin-state trapping (LIESST) on the thermal 50% spin transition of the microcrystalline sample has also been investigated. Thermal spin-transition behaviour has also been induced at pressures higher than 1 bar for the 4,4'-bipy derivative. Both the 4,4'-bipy and bpe derivatives show strong pressure dependence of the spin state at 300 K.