Oxidative addition to dimethylplatinum (II) compounds containing bulky nitrogen ligands: crystal structures of compounds [PtMe3I{(Me2NCH2CH2NCH)Ar}] (Ar = phenanthryl or anthryl)

Oxidative addition of methyl iodide to platinum (II) compounds [PtMe₂{(Me₂NCH₂CH₂NCH)Ar}] (Ar = phenanthryl or anthryl) produced the corresponding platinum (IV) compounds. Processes aimed at reducing the steric crowding at the coordination sphere of the platinum (IV) centre such as C-C restricted rotation of the pendant part of the ligand leading to rotamers and isomerisation of the CN moiety have been detected in solution. The obtained platinum (IV) compounds were characterised by elemental analyses, mass spectrometry and NMR spectroscopy. According to the crystallographic characterisation, the anthracene derivative gave an E conformer while a Z conformation was obtained for the phenanthrene derivative. In order to rationalize the experimental results, DFT calculations have been performed.     

NMR-based methods and strategies for drug discovery

Nuclear Magnetic Resonance (NMR) spectroscopy has long been a favourite tool of chemists interested in host-guest systems because it permits access to a wealth of information about the molecular recognition reaction. NMR has evolved dramatically in the last 15 years and, in parallel with the development of NMR methods for the determination of protein structure, a variety of tools aimed at detecting protein ligand interactions have been proposed and are being now used both in industrial and academic laboratories as valuable tools for structure-based drug discovery. Very recent developments have considerably increased the fraction of therapeutic targets that can be tackled by NMR and significantly reduced the amount of sample required for analysis; in this tutorial review we outline the essential NMR-based techniques and describe some examples of their implementation as part of drug discovery programmes.     

PuPHOS: a synthetically useful chiral bidentate ligand for the intermolecular Pauson-Khand reaction

Here we describe the synthesis and use of the Pulegone-derived bidentate P,S ligands PuPHOS and CyPuPHOS in the intermolecular Pauson-Khand reaction. Ligand exchange reaction of hexacarbonyldicobalt-alkyne complexes with PuPHOS provides a diasteromeric mixture of complexes (up to 4.5:1) from which the major isomers can be conveniently separated by simple crystallization. An isomerization-crystallization sequence of the original mixture results in a dynamic resolution that allows the preparation of the pure major Co(2)(mu-TMSC(2)H)(CO)(4)-PuPHOS (15a) in a multigram scale. Pauson-Khand reaction of 15a with norbornadiene provided, for the first time, the corresponding enone 18 with up to 93% yield and 97% ee. The use of (+)-18 as a surrogate of chiral cyclopentadienone is also demonstrated. Copper-catalyzed Michael addition of a Grignard reagent followed by removal of the TMS group with TBAF were the most reliable methods to transform (+)-18 into valuable starting materials 20a-e for the enantioselective synthesis of cyclopentenoid systems.     

Analytic calculation of phase diagrams for solutions containing colloids or globular proteins

Second-order Barker–Henderson perturbation theory gives phase diagrams for colloid and protein solutions that include stable and metastable fluid–fluid, solid–fluid, and solid–solid phases. The potential of mean force is described by a hard-sphere interacting with a Yukawa potential. Calculations for different ranges of attraction show that, as expected, fluid–fluid coexistence becomes metastable when the potential becomes short-ranged. For a very short-ranged Yukawa potential, the phase diagram shows isostructural solid–solid equilibria with a critical point. To test more simplified models, phase diagrams from second-order Barker–Henderson perturbation theory are compared with those from the random-phase approximation for the fluid phase and the van der Waals theory for the solid phase; this comparison shows significantly different phase diagrams. Moreover, with a potential of mean force with primary and secondary minima, calculations using second-order perturbation theory identify conditions where colloidal and protein solutions can present two fluid–fluid regions, each with a critical point; however, the higher-density fluid–fluid region is likely to be metastable. The analytic calculations described here may be useful for interpretation of experimental phase diagrams and for guiding design of separation processes.     

A straightforward synthesis of (-)-phaseolinic acid

A concise approach to (-)-phaseolinic acid starting from commercially available (S)-oct-1-yn-3-ol is disclosed. The key steps are a ring-closing metathesis reaction to prepare a C(2)-symmetrical allylic diol and its desymmetrization to a gamma-butyrolactone by using an Ireland-Claisen rearrangement. The 2S,3S,4S configuration of the levogyre natural product has been confirmed.     

Constrained systems: A unified geometric approach

A general geometric framework is devised in order to contain the presymplectic and Lagrangian formalisms as particular cases. We call these objectsconstrained dynamical systems, since their dynamics usually lead toconstraints. Their most elementary properties are studied, and several related structures, especially morphisms, are defined. In particular, a stabilization algorithm is performed. As a byproduct, the dynamics and constraints of the Lagrangian formalism (with the second-order condition) are intrinsically obtained.     

Surface enhanced Raman spectroscopy study of the potential dependence of thymine on silver electrodes

The potential-induced changes in thymine coordination on polycrystalline silver electrodes are studied by surface enhanced Raman spectroscopy (SERS) for potentials positive to the potential of zero charge up to the end of the double layer range. Two distinct sets of spectra could be obtained in the range of potentials studied. Both states correspond to chemisorbed phases of thymine on silver, where a distinct heteroatom is deemed responsible for the bond with the surface. At less positive potentials, one of the ring oxygen atoms is responsible for the chemical bond and the molecule assumes a tilted position. At more positive potentials, one of the ring nitrogen atoms, possibly deprotonated, establishes a new bond with the surface, aligning the molecule's axis closer to the surface normal.This paper is dedicated to Prof. Wolf Vielstich on the occasion of his 80th birthday for his outstanding contributions to electrochemistry     

La transformation d'indolines en indoles et d'autres reactions apparentees

Phenylseleninic anhydride reacts rapidly with indolines at 0° to give, when the β-position is substituted, the corresponding indoles. When the β-position is unsubstituted β-phenylseleno- indoles are formed. These are readily reduced by nickel boride to the parent indole. Tetrahyrdroisoquinoline is dehydrogenated with comparable ease. Phenylseleninic acid is also an efficient agent for these dehydrogenations.     

Fabrication of colloidal crystals with tubular-like packings

Methods are reported for the fabrication of colloidal crystal wires with tubular packings. Both free and silica-encased wires have been prepared. Porous silicon membranes are infiltrated with silica spheres, treated with silane, and annealed. After removal of the silicon template, short annealing times were found to result in colloidal crystal wires with varied packing geometries, while repeated annealing cycles produced a thin translucent silica sheath around the wires. Packing in the wires varies with the channel diameter of the Si membrane. The channels used in this study typically produce colloidal crystal wires with six strands, though wires with four to seven strands have been observed. Both chiral and achiral packings are also possible.