The reactive chemisorption of alkyl iodides at Cu(110) and Ag(111) surfaces: a combined STM and XPS study

The chemisorption of methyl and phenyl iodide has been studied at Cu(110) and Ag(111) surfaces at 290 K with STM and XPS. At both surfaces dissociative adsorption of both molecules leads to chemisorbed iodine, with the STM showing c(2 x 2) and (square root 3 x square root 3)R30 structures at the Cu(110) and Ag(111) surfaces, respectively. At the Cu(110) surface a comparison of coexisting c(2 x 2) I(a) and p(2 x 1) O(a) domains shows the iodine adatoms to be chemisorbed in hollow sites with evidence at low coverage for diffusion in the (110) direction. In the case of methyl iodide no carbon adsorption is observed at either the silver or the copper surfaces, but chemisorbed phenyl groups are imaged at the Cu(110) surface after exposure to phenyl iodide. The STM images show the phenyl groups as bright features approximately 0.7 nm in diameter and 0.11 nm above the iodine adlayer, reaching a maximum surface concentration after approximately 6 Langmuir exposure. However, the phenyl coverage decreases with subsequent exposures to PhI and is negligible by approximately 1000 L exposure, consistent with the formation and desorption of biphenyl. The adsorbed phenyls are located above hollow sites in the substrate, they are stabilized at the top and bottom of step edges and in paired chains (1.1 nm apart) on the terraces with a regular interphenyl spacing within the chains of 1.0 nm in the (110) direction. The interphenyl ring spacing and diffusion of individual phenyls from within the chains shows that the chains do not consist of biphenyl species but may be a precursor to their formation. Although the XPS data shows carbon present at the Ag(111) surface after exposure to PhI, no features attributable to phenyl groups were observed by STM.     

The use of capillary electrophoresis with entangled polymer matrix to analyse plasmid DNA and a cationic lipid/cholesterol liposome: DNA complex

Summary A liposome based gene therapeutic product is being developed for the treatment of cystic fibrosis. The product comprises a complex of plasmid DNA and a cationic lipid/cholesterol liposome. Using CE with an entangled polymer matrix, routine separations of linear, supercoiled and open-circle conformers of DNA in plasmid DNA and the liposome complex have been performed. The CE method has been used to support novel quality control and process validation for the manufacture of plasmid DNA and to monitor the degradation of DNA in the liposome complex. Significant features of the method are simple sample preparation and the use of direct UV detection, avoiding the use of potentially mutagenic reagents.     

A survey of low velocity and coaxial jet noise with application to prediction

A review of recent published data on low velocity jet noise is given together with previously unpublished results taken from the Rolls-Royce Noise Research Programme on model rigs and full-scale engines. Noise correlations are given which show that at low jet velocities, the low frequency exhaust noise which is commonly referred to as jet noise, emitted from the fan stream of a turbofan engine is considerably lower in level than that from the (hot) centre stream. From this result, a new prediction procedure for coaxial jet noise of turbofan engines is then developed. Comparisons are given which show that this method gives good correlation with measured results from a number of full-scale turbofan engines. The importance of accurate estimation of the “ground reflection effect” is clearly demonstrated. A critical review of published jet noise data from model coaxial jets is given and the need for further extensive testing emphasized.     

Effect of terminal amino acids on the stability and specificity of PNA-DNA hybridisation

The effect of various charged or hydrophobic amino acids on the hybridisation of fully complementary and mismatch PNA-DNA duplexes was investigated via UV melting curve analysis. The results described here show that the thermal stability and binding specificity of PNA probes can be modified by conjugation to amino acids and these effects should be considered in experimental design when conjugating PNA sequences to solubility enhancing groups or cell transport peptides. Where stabilisation of a duplex is important, without there being a corresponding need for specific binding to fully complementary targets, the conjugation of multiple lysine residues to the C-terminus of PNA may be the best probe design. If, however, the key is to obtain maximum discrimination between fully complementary and mismatch targets, a replacement of glutamic acid for lysine as the routine solubility enhancing group is recommended.     

Total synthesis of nigellicine and nigeglanine hydrobromide

[reaction: see text] The first syntheses of the pyridazinoindazolium alkaloids nigellicine and nigeglanine hydrobromide via a common intermediate are described. Ortho-lithiation/acylation and the direct amination of an isatin ring system are the key steps in the synthesis.     

The Effect of Polydispersity in Primary Particle Size on Measurement of the Fractal Dimension of Aggregates

The use of the mass fractal dimension has become a popular method of characterising the structure of aggregates of fine particles. This parameter is often inferred from scattering experiments that exhibit a power law correlation between scattered intensity and the scattering vector. In this paper we demonstrate deviations from this behaviour that occur when the particles making up the aggregate are not monodisperse, even though the aggregate maintains the same fractal structure as observed in the monodisperse case. We have performed light scattering experiments with aggregating colloidal haematite and performed DLCA computer simulations to explain the observed behaviour. The behaviour can influence the determination of the mass fractal dimension, as can other factors such as scattering effects from primary particles.     

Progress toward a rationally designed, chemically powered rotary molecular motor

Building on prototype 1, which achieves 120 degrees of phosgene-powered unidirectional rotation to rotamer 6 (see Figure 5 in the full article), 7 was designed to accomplish repeated unidirectional rotation (see Scheme 7). Compound 7 contains an amino group on each blade of the triptycene and a 4-(dimethylamino)pyridine (DMAP) unit to selectively deliver phosgene (or its equivalent) to the amine in the "firing position". The synthesis of 7 is described: the key constructive steps are a benzyne addition to an anthracene to generate the triptycene, a stilbene photocyclization to construct the helicene, and a Stille coupling to incorporate the DMAP unit. The DMAP unit was shown to regioselectively relay 1,1'-carbonyldiimidazole (but not phosgene) to the proximal amino group, as designed, but rotation of the triptycene does not occur. Extensive attempts to troubleshoot the problem led to the conclusion that the requisite intramolecular urethane formation, as demonstrated in the prototype (1 --> 4), does not occur with 7 (to give 85) or 97 (to give 100). We speculate that either (i) hydrogen bonding between the hydroxypropyl group and functionality present in 7 but absent from 1 or (ii) a Bürgi-Dunitz (or similar) interaction involving the DMAP (see 106) prevents achievement of a conformation conducive to intramolecular urethane formation.     

Relationship between Floc Short Range Structure and Sediment Compaction

This paper studies the short and long‐range structure of silica aggregates using the small angle light scattering technique. Silica particles were made to aggregate by the addition of MgCl₂, with and without continuous shear. Two different short‐range structures were observed for different aggregation conditions. The small angle light scattering reveals two different floc structures at different length scales, a very compact floc at short length scale and a loose floc at large length scale. The sediments of these flocs were studied by allowing them to settle under gravity and consolidate at different centrifugal forces. The results show that the floc short‐range structure is important in governing the compaction behaviour of sediment.     

N-halamines from rice straw

The cellulosic part of rice straw was modified to develop N-halamine derivatives for disinfection. The process involved cross-linking of the cellulosic material with amino/amide/imide containing compounds; cyclic and acyclic. The structures of the prepared materials were identified using FTIR and solid state ¹³CNMR. The modified materials were halogenated to form N-halamines and the antimicrobial activity of each evaluated against examples of Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli) using a variety of methods; agar plate, blended agar, stirred flask and in columns. One of the N-halamines achieved a 9 log reduction against both E. coli and S. aureus in 4 h. In addition, no S. aureus growth was recorded on agar plates blended with 0.5 g of this same material.