Reactivity of a phosphinito-bridged PtI-PtI complex with nucleophiles: substitution versus addition

As a result of the strong electrophilic character of the Pt bound to O, the phosphinito-bridged PtI complex [(PHCy2)Pt(micro-PCy2){kappa2P,O-micro-P(O)Cy2}Pt(PHCy2)](Pt-Pt) (1) undergoes attack at the O-bound Pt atom by molecules such as di- and tricyclohexylphosphane, dicyclohexylphosphane oxide, and dicyclohexylphosphane sulfide. Thus, reaction of 1 with PHCy2 gives the symmetric PtI dimer [(PHCy2)Pt(micro-PCy2)]2(Pt-Pt) (2), while the hydrido-bridged complex syn-[(PHCy2){kappaP-P(O)Cy2}Pt(micro-PCy2)(micro-H)Pt(PHCy2){kappaP-P(O)Cy2}](Pt-Pt) (4) is obtained from reaction of 1 with P(O)HCy2; the thiophosphinito complex [(PHCy2)Pt(micro-PCy2){kappa2P,S-micro-P(S)Cy2}Pt(PHCy2)](Pt-Pt) (8) forms selectively in reaction of 1 with P(S)HCy2. For comparison, the reaction with PCy3 results only in ligand substitution, affording [(PCy3)Pt(micro-PCy2){kappa2P,O-micro-P(O)Cy2}Pt(PHCy2)](Pt-Pt) (5). DFT studies confirmed the remarkable electrophilicity of the oxygen-bound Pt and shed light on the nature of the metal-metal bond in Pt dimers.     

Portable X-ray fluorescence device reveals the artistic palette of Carlo Bononi,Baroque artist from Ferrara

The principal aim of the in situ X-ray fluorescence (XRF) analysis on the canvas “The Coronation of the Virgin” was to characterise the colour palette of Carlo Bononi (Ferrara, 1580–1632), a lesser-known artist of the early Baroque period in Ferrara. More than 100 points were collected by means of an XRF spectrometer, but the presence of many overlapping painted layers left some doubts about the preparation and the background layers. The scanning electron microscopy with energy dispersive spectrometer analysis on two samples resolved some of these doubts. The results obtained indicate the use of typical 17th century pigments, such as lead white, vermilion, azurite and a copper-based green. For yellow pigments, the artist used the yellow ochre in some cases, while in others he used lead-tin yellow. We also individuated at least three different shades of umber. Almost all the pigments have been identified and they are the first step in establishing the technical apparatus necessary to understand the modus operandi of the Ferrarese artist.     

Carboxylation and decarboxylation of active site Lys 84 controls the activity of OXA-24 β-lactamase of Acinetobacter baumannii: Raman crystallographic and solution evidence

The class D β-lactamases are characterized by the presence of a carboxylated lysine in the active site that participates in catalysis. Found in Acinetobacter baumannii, OXA-24 is a class D carbapenem hydrolyzing enzyme that exhibits resistance to most available β-lactamase inhibitors. In this study, the reaction between a 6-alkylidiene penam sulfone inhibitor, SA-1-204, in single crystals of OXA-24 is followed by Raman microscopy. Details of its reaction with SA-1-204 provide insight into the enzyme's mode of action and help define the mechanism of inhibition. When the crystal is maintained in HEPES buffer, the reaction is fast, shorter than the time scale of the Raman experiment. However, when the crystal holding solution contains 28% PEG 2000, the reaction is slower and can be recorded by Raman microscopy in real time; the inhibitor's Raman bands quickly disappear, transient features are seen due to an early intermediate, and, at approximately 2-11 min, new bands appear that are assigned to the late intermediate species. At about 50 min, bands due to all intermediates are replaced by Raman signals of the unreacted inhibitor. The new population remains unchanged indicating (i) that the OXA-24 is no longer active and (ii) that the decarboxylation of Lys84 occurred during the first reaction cycle. Using absorbance spectroscopy, a one-cycle reaction could be carried out in aqueous solution producing inactive OXA-24 as assayed by the chromogenic substrate nitrocefin. However, activity could be restored by reacting aqueous OXA-24 with a large excess of NaHCO(3), which recarboxylates Lys84. In contrast, the addition of NaHCO(3) was not successful in reactivating OXA-24 in the crystalline state; this is ascribed to the inability to create a concentration of NaHCO(3) in large excess over the OXA-24 that is present in the crystal. The finding that inhibitor compounds can inactivate a class D enzyme by promoting decarboxylation of an active site lysine suggests a novel function that could be exploited in inhibitor design.     

De Novo Design,Synthesis and Characterisation of MP3, A New Catalytic Four‐Helix Bundle Hemeprotein

A new artificial metalloenzyme, MP3 (MiniPeroxidase 3), designed by combining the excellent structural properties of four‐helix bundle protein scaffolds with the activity of natural peroxidases, was synthesised and characterised. This new hemeprotein model was developed by covalently linking the deuteroporphyrin to two peptide chains of different compositions to obtain an asymmetric helix–loop–helix/heme/helix–loop–helix sandwich arrangement, characterised by 1) a His residue on one chain that acts as an axial ligand to the iron ion; 2) a vacant distal site that is able to accommodate exogenous ligands or substrates; and 3) an Arg residue in the distal site that should assist in hydrogen peroxide activation to give an HRP‐like catalytic process. MP3 was synthesised and characterised as its iron complex. CD measurements revealed the high helix‐forming propensity of the peptide, confirming the appropriateness of the model procedure; UV/Vis, MCD and EPR experiments gave insights into the coordination geometry and the spin state of the metal. Kinetic experiments showed that Fe^III–MP3 possesses peroxidase‐like activity comparable to R38A–hHRP, highlighting the possibility of mimicking the functional features of natural enzymes. The synergistic application of de novo design methods, synthetic procedures, and spectroscopic characterisation, described herein, demonstrates a method by which to implement and optimise catalytic activity for an enzyme mimetic.     

Charge-sensitive vibrational modes in the (EDT-TTF-OX)2AsF6 chiral molecular conductors

Infrared and Raman spectra of three chiral molecular conductors (EDT-TTF-OX)₂AsF₆, comprising of two salts based on enantiopure EDT-TTF-OX donor molecules and one based on their racemic mixture, have been measured as a function of temperature. In the frequency range of the C=C stretching vibrations of EDT-TTF-OX, charge-sensitive modes are identified based on theoretical calculations for neutral and oxidized EDT-TTF-OX using density functional theory (DFT) methods. The positions of C=C stretching modes in both Raman and infrared spectra of the (EDT-TTF-OX)₂AsF₆ materials are analyzed assuming a linear relationship between the frequency and charge of the molecule. The charge density on the EDTTTF-OX donor molecule is estimated to be +0.5 in all investigated materials and does not change with temperature. Therefore we suggest, that M-I transition observed in (EDT-TTF-OX)₂AsF₆ chiral molecular conductors at low temperature is not related to the charge ordering mechanism.     

Multiplication Operators Between the Lipschitz Space and the Space of Bounded Functions on a Tree

In this paper, we characterize the bounded and the compact multiplication operators between the space of bounded functions on the set of vertices of a rooted infinite tree T and the Banach space of complex-valued Lipschitz functions on T. We also determine the operator norm and the essential norm for the bounded multiplication operators between these spaces and show that there are no isometries among such operators.     

Twists and turns in the hierarchical self-assembly pathways of a non-amphiphilic chiral supramolecular material

The formation of helical self-assembled fibres by a C(3) symmetric molecule incorporating three tetrathiafulvalene units is shown to be influenced dramatically by the processing conditions, leading to a variety of different chiral forms, including unprecedented croissants.     

Analysis of breath by proton transfer reaction time of flight mass spectrometry in rats with steatohepatitis induced by high-fat diet

Breath testing has been largely used as a diagnostic tool, but the difficulties in data interpretation and sample collection have limited its application. We developed a fast (< 20?s), on-line, non-invasive method for the collection and analysis of exhaled breath in awake rats based on proton transfer reaction time of flight mass spectrometry (PTR-ToF-MS) and applied it to investigate possible relationships between pathologies induced by dietary regime and breath composition. As a case study, we investigated rats with dietary induced non-alcoholic steatohepatitis (NASH) and modifications induced by coffee addition to the diet. We considered two different diets (standard and high fat) complemented with two different drinking possibilities (water or decaffeinated coffee) for a total of four groups with four rats each. Several spectrometric peaks were reliable markers for both dietary fat content and coffee supplementation. The high resolution and accuracy of PTR-ToF-MS allowed the identification of related compounds such as methanol, dimethyl sulphide, dimethyl sulphone and ammonia. In conclusion, the rapid and minimally invasive breath analysis of awake rats permitted the identification of markers related to diet and specific pathologic conditions and provided a useful tool for broader metabolic investigations. Copyright ? 2012 John Wiley & Sons, Ltd.