The optimal packing of circles on a sphere

The closest packing ofx circles on the surface of a sphere is calculated in the same way that the stereochemical arrangement of atoms around a central atom is determined. A number of improved packings have been discovered for x = 19 to 80. A notable feature is that the structures are generally of low symmetry. The packing densityp, defined as the fraction of the spherical surface that is enclosed by the circles, increases only very slowly as the number of circles increases and the values remain substantially below that for a close packed plane, or for an octahedron or icosahedron.     

A study of the analytical behaviour of selected synthetic and naturally occurring coumarins using liquid chromatography, ion trap mass spectrometry, gas chromatography and polarography and the construction of an appropriate database for coumarin characterisation

The aim of this paper is to provide analytical chemical information on a range of naturally occurring and synthetic coumarins. This analytical chemical information on liquid chromatography-electrospray ionisation-mass spectrometry (HPLC-ESI-MS), ion trap mass spectrometry (ESI-MSⁿ), gas chromatography-flame ionisation detection (GLC-FID) and polarographic behaviour is then incorporated into a database which is of use in identifying unknown coumarins isolated from natural sources. This paper is also concerned with understanding the effect of functional groups in coumarins on their analytical chemical behaviour using the above techniques.     

Synthetic,Sodium-Ion-Conducting Tris(Macrocycle) Channels that Function in a Phospholipid Bilayer Membrane: An Overview

Abstract

A family of tris(macrocyclic) compounds of the form sidearm<N18N>C_n<N18N>C_n<N18N>sidearm, has been prepared, characterized chemically, and assayed by dynamic ²³Na-NMR for the ability to transport sodium cations in a mixed phosphatidylglycerol/phosphatidylcholine vesicle system. A number of control experiments have been conducted that reinforce the hypothesis that cation transport occurs by a channel mechanism. The tris(macrocycle) channels proved to be functional at a level of 25–50% of that found for the natural pentadecapeptide channel gramicidin. Fluorescence data confirm the expected position of the channel within the bilayer.     

Novel Sulfonamide Derivatives as Inhibitors of Histone Deacetylase

Inhibition of the enzyme histone deacetylase (HDAC) is emerging as a novel approach to the treatment of cancer. A series of novel sulfonamide derivatives were synthesized and evaluated for their ability to inhibit human HDAC. Compounds were identified which are potent enzyme inhibitors, with IC₅₀ values in the low nanomolar range against enzyme obtained from HeLa cell extracts, and with antiproliferative effects in cell culture. Extensive characterization of the structure–activity relationships of this series identified key requirements for activity. These include the direction of the sulfonamide bond and substitution patterns on the central phenyl ring. The alkyl spacer between the aromatic head group and the sulfonamide functionality also influenced the HDAC inhibitory activity. One of these compounds, m 11.1 , also designated PXD101, has entered clinical trials for solid tumors and haematological malignancies.     

Equation of state and liquid-vapor equilibria of one- and two-Yukawa hard-sphere chain fluids: theory and simulation

The accuracy of several theories for the thermodynamic properties of the Yukawa hard-sphere chain fluid are studied. In particular, we consider the polymer mean spherical approximation (PMSA), the dimer version of thermodynamic perturbation theory (TPTD), and the statistical associating fluid theory for potentials of variable attractive range (SAFT-VR). Since the original version of SAFT-VR for Yukawa fluids is restricted to the case of one-Yukawa tail, we have extended SAFT-VR to treat chain fluids with two-Yukawa tails. The predictions of these theories are compared with Monte Carlo (MC) simulation data for the pressure and phase behavior of the chain fluid of different length with one- and two-Yukawa tails. We find that overall the PMSA and TPTD give more accurate predictions than SAFT-VR, and that the PMSA is slightly more accurate than TPTD.     

Perturbing the Hofmeister series: a steroid-based anion receptor with preorganised quaternary ammonium and H-bond donor groups

Preorganised urea groups moderate the anion-exchange properties of cationic receptor 2, favouring halide extraction and promoting anion transport through a bulk liquid membrane.     

Studies toward an ideal fluorescence method to measure palladium in functionalized organic molecules: effects of sodium borohydride, temperature, phosphine ligand, and phosphate ions on kinetics

Residual metals in fine chemicals are currently detected by using inductively coupled plasma mass spectrometry, which requires expensive instrumentation and does not have high-throughput capabilities. Although fluorescent probes can be amenable to high-throughput analyses of metals, the utility of such analyses is limited due to the lack of generality. Herein, we report a significant improvement (≈19-fold) to our previously reported catalysis-based fluorescent probe for palladium. Specifically, we found that slightly elevated temperature dramatically improved the generality of the method and that the deallylation reaction of the nonfluorescent compound 1 was accelerated by phosphate ions in aqueous media. This method was capable of detecting 0.2 ppb palladium. We demonstrated reasonably accurate palladium detection in various active pharmaceutical ingredients and highly functionalized organic compounds.     

High rate performance of lithium manganese nitride and oxynitride as negative electrodes in lithium batteries

The performance of Li_7.9MnN_3.2O_1.6 and Li₇MnN₄ as electrode materials in lithium batteries was analyzed. At 1C rate, capacities of 180 and 230 mAh/g, respectively, were obtained after 50 cycles. If the first charge is done at 0.1C, outstanding capacities of 120–135 mAh/g are observed after 100 cycles at 5C. More lithium can be removed during the charge at 0.1C, leading to a large amount of lithium vacancies that enhance mobility and rate capability. It is proposed that incomplete filling of the vacancies occurs upon cycling, so that the mobility remains high. This performance compares well to that of Li₄Ti₅O₁₂.