Anion complexation via C-H...X interactions using a palladacyclic receptor

A novel organometallic receptor binds anions in solution and in the solid state, with complexes stabilised through a series of C-HX interactions, as evidenced by 1H NMR spectroscopy, X-ray crystallography and computational models.     

Preparation of a mercaptopropyl bonded silica intermediate in supercritical carbon dioxide: synthesis, characterisation and chromatography of a quinine based chiral stationary phase

This research examines the preparation of a mercaptopropyl bonded silica intermediate in supercritical carbon dioxide (sc-CO(2)) and the subsequent conversion in sc-CO(2) to a quinine derived chiral stationary phase (CSP). The effects of reaction temperature, pressure and time on the surface coverage of the silica intermediate were investigated when porous silica particles (Exsil-Avanti, 3microm) were reacted with 3-trimethoxymercaptopropylsilane in sc-CO(2). We present results which demonstrate that a stable mercaptopropyl bonded silica intermediate can be successfully prepared under supercritical conditions of 40 degrees C, 483bar, in a substantially reduced reaction time of 1h with superior surface coverages compared to organic solvent based methods. The further utility of this supercritical fluid technology was demonstrated by the free radical addition of a quinine derived chiral selector onto a mercaptopropyl bonded silica intermediate in sc-CO(2). This supercritical fluid generated chiral stationary phase (CSP) was utilised for the direct LC enantioseparation of a series of 3,5-dinitrobenzoyl (DNB) amino acids. Bonded silica samples were characterised using elemental analysis, diffuse reflectance infrared fourier transform (DRIFT) spectroscopy, solid state (13)C and (29)Si CP-MAS NMR spectroscopy, and thermogravimetric analysis (TGA). This supercritical fluid functionalisation approach offers an efficient and cleaner alternative to existing organic solvent based approaches for the preparation of bonded silica phases.     

Five-coordinate Pd(II) orthometallated triarylphosphite complexes

The reaction of the orthopalladated triarylphosphite complexes [{Pd(mu-Cl){kappa(2)-P,C-P(OC(6)H(2)-2,4-R(2))(OC(6)H(3)-2,4-R(2))}(2)] (R = H, (t)Bu) with bis(2-diphenylphosphinoethyl)phenylphosphine leads to a five-coordinate palladium(II) (R = H) and a mixture containing four-and five-coordinate species (R = (t)Bu). The crystal structure of the five-coordinate species [Pd{kappa(2)-P,C-(P(OC(6)H(4))(OC(6)H(5))(2)}{bis(2-diphenylphosphinoethyl)phenylphosphine}][SbF(6)] is presented. This complex reacts with hydrogen peroxide or [AuCl(tht)] to give four-coordinate complexes in which the displaced phosphine residue is either oxidised or coordinated to gold chloride; this demonstrates that the five-coordinate complexes are labile in solution. By contrast, the reactions of the dimeric precursors with 1,1,1-tris(diphenylphosphinomethyl)ethane give four-coordinate complexes in the solid state, although evidence is presented that the smaller phosphite-containing system is five-coordinate at room temperature or higher in solution.     

Diastereoselective spiroannulation of phenolic substrates: advances towards the asymmetric formation of the manumycin m-C7N core skeleton

The asymmetric syntheses of two new spirolactones prepared in optically pure form from L-3-nitrotyrosine are described. The key step, an oxidative spiroannulation, was carried out on the optically active phenols 11a and 11b and afforded the new spirolactones 5a and 5b in 85% and 83% yields, respectively, as mixtures (3:1 dr) of diastereomers. The major diastereomers from these mixtures could be isolated in optically pure form by trituration using acetone-hexanes as the solvent. Thus, the optically active spirolactones (+)-5a (+ 92.8 degrees, c=0.125 acetone) and (+)-5b (+112.0 degrees, c= 0.125 acetone) were obtained after four synthetic steps from L-3-nitrotyrosine in 41% and 43% yield, respectively.     

Phase-matching condition between acoustic and optical waves in doped fibers

A new technique, recently proposed [1] for achieving phase-matching in Brillouin scattering in a dielectric fiber doped by three-level Λ-type ions, can lead to a dramatic increase of efficiency of ponderomotive nonlinear interaction between electromagnetic waves and holds promise for applications in quantum optics. In this paper, we investigate possibilities to establish phase-matching condition for acoustic modes in confined geometries that exhibit nonzero cutoff frequencies.     

Generation of sub-Poissonian light by a four-level microlaser with a high-Q cavity

We develop a kinetic theory that describes the behavior of a monatomic four-level laser when the atom is fixed inside a high-Q optical cavity. Such a statement of the problem is similar to that used in the experiment of G. M. Meyer, H.-J. Briegel, and H. Walther [Europhys. Lett. 37, 317 (1997)]. The condition that the number of photons is large and the photon fluctuations are small is employed. We show that by selecting the parameters of the periodic electromagnetic pulses exciting the atom one can achieve regular pumping of the upper laser level and generate sub-Poissonian laser light. We also discuss the reasons why the statistical pattern of the radiation differs from the micromaser pattern with regular injection of atoms. Zh. éksp. Teor. Fiz. 116, 485–502 (August 1999)     

Revisiting the Electrochemical Impedance Spectroscopy of Magnesium with Online Inductively Coupled Plasma Atomic Emission Spectroscopy

The electrochemical impedance of reactive metals such as magnesium is often complicated by an obvious inductive loop with decreasing frequency of the AC polarising signal. The characterisation and ensuing explanation of this phenomenon has been lacking in the literature to date, being either ignored or speculated. Herein, we couple electrochemical impedance spectroscopy (EIS) with online atomic emission spectroelectrochemistry (AESEC) to simultaneously measure Mg‐ion concentration and electrochemical impedance spectra during Mg corrosion, in real time. It is revealed that Mg dissolution occurs via Mg²⁺, and that corrosion is activated, as measured by AC frequencies less than approximately 1 Hz approaching DC conditions. The result of this is a higher rate of Mg²⁺ dissolution, as the voltage excitation becomes slow enough to enable all Mg²⁺‐enabling processes to adjust in real time. The manifestation of this in EIS data is an inductive loop. The rationalisation of such EIS behaviour, as it relates to Mg, is revealed for the first time by using concurrent AESEC.     

Solid‐Phase Parallel Synthesis of Functionalised Medium‐to‐Large Cyclic Peptidomimetics through Three‐Component Coupling Driven by Aziridine Aldehyde Dimers

The first solid‐phase parallel synthesis of macrocyclic peptides using three‐component coupling driven by aziridine aldehyde dimers is described. The method supports the synthesis of 9‐ to 18‐membered aziridine‐containing macrocycles, which are then functionalized by nucleophilic opening of the aziridine ring. This constitutes a robust approach for the rapid parallel synthesis of macrocyclic peptides.     

Theoretical basis for a new subnatural spectroscopy via correlation interferometry

A new line-narrowing effect in coincidence interferometry yielding subnatural resolution of atomic transition frequencies is proposed and analyzed. The approach utilizes second-order photon correlation properties of the radiation field. This is in contrast to the first-order measurements associated with time delay spectroscopy, which is known to yield subnatural resolution. Connections between the two techniques are investigated.Dedicated to the memory of Professor Julian Schwinger, a role model for us all