Effect of bicarbonate ions on the crystallization of calcite on self-assembled monolayers

We use molecular dynamics simulations to investigate the nucleation of calcite crystals on self-assembled monolayers. We show how the presence of bicarbonate ions adsorbed on the monolayer surface can both aid nucleation and control the orientation of the growth of the crystal. Using a simple model of the nucleation process and calculated interfacial energies, we calculate the enhancement (with respect to the homogeneous nucleation rate) of the nucleation of calcite on the (012) and (0001) faces. The calculations show clearly that the (012) face is favored over the (0001) face and that the nucleation rate is enhanced for self-assembled monolayers made from molecules containing an even number of carbon atoms in the alkyl chain over those containing an odd number.     

Determination of total and speciated sulfur content in petrochemical samples using a pulsed flame photometric detector

The pulsed flame photometric detector (PFPD) has the advantage of being able to measure the concentration of individual sulfur compounds and total sulfur content in a petrochemical sample in a single gas chromatography run. Because it is an equimolar response detector, the PFPD's sulfur response is independent of a compound's molecular structure, and this feature allows quantitation of the total or speciated sulfur content in complex samples using a single calibrant. This paper is a survey describing a variety of applications using the PFPD for sulfur quantitation in petrochemical matrices. Several different approaches to quantitation are described, and simple techniques for circumventing the quenching of the sulfur signal by coeluting hydrocarbon peaks are discussed. Examples from a range of real-world samples are presented.     

Adsorption and desorption of binary mixtures in confined geometry: A pilot positron annihilation study

In confined (nanometer-scale) geometry, the effects of substrate forces and finite size produce a shift of the gas liquid phase boundary from that found in corresponding bulk. The pore transitions also show marked hysteresis. The phase behaviour of a binary gas mixture in confined geometry is likely to depend on the miscibility of the system and the interaction between the substrate and the individual fluid molecules/atoms. Here, we present the results of a pilot positronium annihilation study of the condensation and evaporation of argon-nitrogen mixtures confined in 4 nm diameter cylindrical pores in VYCOR glass.     

Characterization of AMA1-RON2L complex with native gel electrophoresis and capillary isoelectric focusing

Rhoptry neck protein 2 (RON2) binds to the hydrophobic groove of apical membrane antigen 1 (AMA1), an interaction essential for invasion of red blood cells (RBCs) by Plasmodium falciparum (Pf) parasites. Vaccination with AMA1 alone has been shown to be immunogenic, but unprotective even against homologous challenge in human trials. However, the AMA1-RON2L (L is referred to as the loop region of RON2 peptide) complex is a promising candidate, as preclinical studies with Freund's adjuvant have indicated complete protection against lethal challenge in mice and superior protection against virulent infection in Aotus monkeys. To prepare for clinical trials of the AMA1-RON2L complex, identity and integrity of the candidate vaccine must be assessed, and characterization methods must be carefully designed to not dissociate the delicate complex during evaluation. In this study, we developed a native Tris-glycine gel method to separate and identify the AMA1-RON2L complex, which was further identified and confirmed by Western blotting using anti-AMA1 monoclonal antibodies (mAbs 4G2 and 2C2) and anti-RON2L polyclonal Ab coupled with mass spectrometry. The formation of complex was also confirmed by Capillary Isoelectric Focusing (cIEF). A short-term (48 h and 72 h at 4°C) stability study of AMA1-RON2L complex was also performed. The results indicate that the complex was stable for 72 h at 4°C. Our research demonstrates that the native Tris-glycine gel separation/Western blotting coupled with mass spectrometry and cIEF can fully characterize the identity and integrity of the AMA1–RON2L complex and provide useful quality control data for the subsequent clinical trials.     

Valence orbital response to pseudorotation of tetrahydrofuran: a snapshot using dual space analysis

The pseudorotation of tetrahydrofuran (THF) (C(4)H(8)O) has been studied using density functional theory, with respect to the valence orbital responses to the ionization potentials and to orbital electron and momentum distributions. Three conformations of THF, the global minimum structure C(s), local minimum structure C(2), and a transition state structure C(1), which are characteristic configurations on the potential energy surface, are examined using the SAOP/et-pVQZ//B3LYP/6-311++G** models with the aforementioned dual space analysis. It is noted in the ionization energy spectra that the minimum structures C(s) and C(2) are not directly connected by pseudorotation, but through the transition state structure C(1). As a result, some orbitals of the C(s) conformer are able to "correlate" to orbitals of the C(2) conformer without a strict symmetry constraint, i.e., orbital 7a' of the C(s) conformer is correlated to orbital 5b of the C(2) conformer. It is also noted that although the valence orbital ionization potentials are not significantly altered by the pseudorotation of THF, their spectra (mainly due to excitation) are quite different indeed. Detailed orbital analysis based on dual space analysis is given. The valence orbital behavior of the conformations is orbital dependent. It can be approximately divided into three groups: the "signature group" is associated with orbitals experiencing significant changes. The frontier orbitals are in this group. The "nearly identical group" includes orbitals without apparent changes across the conformations. Most of the orbitals showing a certain degree of distortion during the pseudorotation process belong to the third group. The present study demonstrates that a comprehensive understanding of the pseudorotation of THF and its dynamics requires multidimensional information and that the information gained from momentum space is complementary to that from the more familiar coordinate space.     

The unexpected chemistry of a bis(phospholyl)acetylene

The reaction of lithium 3,4‐dimethyl‐phospholide with tetrachloroethylene gives the corresponding 1,2‐bis(phospholyl)acetylene that has been characterized by X‐ray crystal structure analysis of its bis(pentacarbonylmolybdenum) complex. The reaction with sulfur leads to the corresponding disulfide that spontaneously undergoes a self‐condensation via a Diels‐‐Alder cycloaddition between the CC triple bond and the phosphole dienic system giving, after aromatization by loss of the phosphorus bridge, the corresponding 1,2‐bis(phospholyl)benzene. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:537–541, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20457     

Melting curve of silicon to 15 GPa determined by two-dimensional angle-dispersive diffraction using a Kawai-type apparatus with X-ray transparent sintered diamond anvils

The melting curve of silicon has been determined up to 15 GPa using a miniaturized Kawai-type apparatus with second-stage cubic anvils made of X-ray transparent sintered diamond. Our results are in good agreement with the melting curve determined by electrical resistivity measurements [V.V. Brazhkin, A.G. Lyapin, S.V. Popova, R.N. Voloshin, Nonequilibrium phase transitions and amorphization in Si, Si/GaAs, Ge, and Ge/GaSb at the decompression of high-pressure phases, Phys. Rev. B 51 (1995) 7549] up to the phase I (diamond structure)—phase II (β-tin structure)—liquid triple point. The triple point of phase XI (orthorhombic, Imma)—phase V (simple hexagonal)—liquid has been constrained to be at 14.4(4) GPa and 1010(5) K. These results demonstrate that the combination of X-ray transparent anvils and monochromatic diffraction with area detectors offers a reliable technique to detect melting at high pressures in the multianvil press.     

Low Noise mm-Wave Amplifier Design Methodology

A design methodology for mm-wave LNAs is presented. The optimum bias point selection is outlined. The stabilisation strategy is described, and the impact of packaging requirements on the amplifier design is discussed. A bond wire compensation technique is detailed. The tradeoff between input match and noise figure is presented, and a design with a suitable tradeoff is¹ developed. A very simple inter-stage match requirement is a novel outcome of this design approach. An effective means of achieving a broadband response is also outlined. A four stage 30 – 50 GHz LNA design was fabricated and characterised in a customised package. A maximum MMIC gain of 28 dB at 32 GHz was achieved, and the gain exceeded 20 dB over the frequency range 26 – 44 GHz. A noise figure of 4.5 dB and a P1dB of +11 dBm were also obtained. It is the authors' opinion that the methodology presented in this paper will be of significant interest to other mm-wave LNA designers.     

Aplidiopsamine A, an antiplasmodial alkaloid from the temperate Australian ascidian, Aplidiopsis confluata

A polyaromatic alkaloid, aplidiopsamine A was isolated from the temperate Australian ascidian, Aplidiopsis confluata, and its structure was determined from interpretation of mass, 1D and 2D NMR spectra. Aplidiopsamine A is the first alkaloid to possess the tricyclic aromatic substructure 3H-pyrrolo[2,3-c]quinoline conjugated to an adenine. Aplidiopsamine A exhibited significant inhibition of growth of chloroquine resistant and sensitive strains of the malaria parasite, Plasmodium falciparum, and minimal toxicity toward human cells.