Induction of a Four‐Way Junction Structure in the DNA Palindromic Hexanucleotide 5′‐d(CGTACG)‐3′ by a Mononuclear Platinum Complex

Four‐way junctions (4WJs) are supramolecular DNA assemblies comprising four interacting DNA strands that in biology are involved in DNA‐damage repair. In this study, a new mononuclear platinum(II) complex 1 was prepared that is capable of driving the crystallization of the DNA oligomer 5′‐d(CGTACG)‐3′ specifically into a 4WJ‐like motif. In the crystal structure of the 1 –CGTACG adduct, the distorted‐square‐planar platinum complex binds to the core of the 4WJ‐like motif through π–π stacking and hydrogen bonding, without forming any platinum–nitrogen coordination bonds. Our observations suggest that the specific molecular properties of the metal complex are crucially responsible for triggering the selective assembly of this peculiar DNA superstructure.     

Simplicity of lie module triple systems

We analyze how certain constructions of Lie module triple systems affect the structure theory, particularly simplicity. We are thus able to show that there is no upper bound on the number of summands in a direct sum decomposition of a simple Lie module triple system as a module for its inner derivation algebra.     

Laboratory,Field and Modeling Studies of Radon‐222 as a Natural Tracer for Monitoring NAPL Contamination

The recently developed natural radon tracer method has potential as a rapid, lowcost, nondestructive, and noninvasive method for quantifying NAPL contamination. In the subsurface, radon222 (radon) is produced by the decay of naturally occurring radium226 contained in the mineral fraction of aquifer solids. In groundwater radon occurs as a dissolved gas, with a halflife of 3.83 days. In the absence of NAPL, the radon concentration in groundwater quickly reaches a maximum value that is determined by the mineral composition of the aquifer solids, which controls the rate of radon emanation. In the presence of NAPL, however, the radon concentration in the groundwater is substantially reduced due to the preferential partitioning of radon into the organic NAPL phase. A simple equilibrium model and supporting laboratory studies show the reduction in radon concentration can be quantitatively correlated with residual NAPL saturation. Thus, by measuring the spatial distribution in radon it may be possible to identify locations where residual NAPL is present and to quantify the NAPL saturation. When the basic processes of partitioning, radon emanation from the aquifer solids, and firstorder decay are incorporated into an advective/dispersive transport model, good agreement is obtained with the results of laboratory and field experiments. Model sensitivity analyses shows many factors can contribute to the radon concentration response, including the length of the NAPL zone, NAPL saturation, groundwater velocity, porosity, and radon emanation. Thus, care must be taken when applying the radon method to locate and quantify NAPL contamination in the subsurface.     

The reactivity of the clean and contaminated (0001̄) polar and the (101̄0) prism ZnO surfaces to chlorine

The reactivities of the (0001̄) and (101̄O) surfaces of zinc oxide to chlorine gas have been studied by a range of techniques. In the case of the (0001̄) oxygen polar surface investigations were made with the surface both atomically clean and with a known level of carbon and calcium contamination. Comparison is made with our earlier results on the (0001) surface which showed a high level of reactivity due to the increased electrostatic stability on adsorption of the electronegative gas. Both the oxygen polar and the prism surface showed a much lower reactivity to chlorine than the zinc face: contamination by carbon and calcium on the former surface reduced the reactivities still further. This result conflicts with comparable data for oxygen adsorption where previous work has shown a greater take-up of oxygen on the oxygen face than the zinc face. Unlike the zinc face, no LEED superstructures were observed on any of, the three surfaces, but in common with the (0001) there were significant electron beam desorption effects. Two states could be identified: one was rapidly removed in ~10 μA min exposure to the beam, the other in much longer periods. Work function and ELS data were consistent with atomic adsorption of chlorine on all surfaces. An exception was the (101̄O) at high exposures where a work function decrease took place following the initial increase: this may indicate a second molecular state.     

Extension of the asymptotically-correct approximation to Fowler-Guggenheim adsorption

The epitaxial growth of antimony on to atomically clean tungsten has been studied by reflection high energy electron diffraction, and an attempt made to evaluate the influence of the substrate symmetry by using the three crystal planes, (100), (110) and (112). The growth was found to be dependent on the deposition conditions. Evaporation in high background pressures (P > 1 × 10^?8 Torr) and using high evaporation rates $\text{(10}\text{monolayers}\text{min}\text{)}$ led initially to an amorphous layer on all three surfaces. This crystallised partially at thicknesses of about 150 Å leaving the close packed pseudocubic (111) plane parallel to the surface. Using ultra-high vacuum conditions (P < 5 × 10^?9 Torr during evaporation) and low evaporation rates (3 monolayers per minute) a series of submonolayer structures formed, different for each surface and depending strongly on the surface symmetry and lattice parameters. Continued evaporation led to the formation of three dimensional islands of antimony. For all three surfaces, the majority of these islands consisted of normal bulk antimony with its pseudocubic (100) plane parallel to the surface. However, a smaller amount of a hitherto unreported face centred cubic phase of antimony was also found on each surface. A comparison of the results obtained on the three surfaces in terms of the relative influence of the substrate and absorbate atomic interactions has been made.     

Structural investigation of polyaniline/Nylon 6 blends by small-angle neutron scattering and small- and wide-angle X-ray scattering

The structure of blends of Nylon 6 with deuterated polyaniline emeraldine base (D-PANI-EB) and fully doped D-PANI salts (D-PANI-ES) formed from camphorsulfonic acid (CSA), methanesulfonic acid (MSA), or dodecyl benzenesulfonic acid (DBSA) were investigated by small-angle neutron (SANS) and X-ray scattering. The blends were formed from hexafluoro-2-propanol solutions and had volume fractions of 0.038, 0.20, and 0.40 for D-PANI/CSA, 0.20 and 0.40 for D-PANI/MSA, 0.24 and 0.44 for D-PANI/DBSA, and 0.07, 0.14, and 0.31 for D-PANI-EB. The SANS results are compared with a number of standard models for two-phase systems. No evidence was found for significant molecular mixing. In some cases the inverse power law model is in reasonable agreement with observations, and in the case of the lowest concentration of D-PANI/CSA there is an indication of mass fractal structure. This was not found at the higher concentrations. The results establish that the blends with the smaller more polar dopants CSA and MSA behave similarly and are unlike either the D-PANI/DBSA blends or those with D-PANI-EB. There is evidence that the simple picture of two pure phases is inadequate for these materials. With the exception of the D-PANI/DBSA blend which has a relatively low scattering contrast, the results indicate that the lower limit of volume fraction for application of SANS is a few percent D-PANI-ES in Nylon 6. X-ray scattering was used to demonstrate the presence of Nylon 6 lamellae and residual peaks attributable to the pure components. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2765–2774, 1997     

Influence of column design on process-scale ion-exchange chromatography

The performance of two new designs of pump-packed axial flow process chromatography columns have been evaluated for the preparative anion-exchange chromatography of hen egg-white proteins using Whatman Express-Ion Exchanger Q. A 16 1 Side-Pack column and a 24 1 IsoPak column containing Express-Ion Q were used in this study. In each case ca. 20 1 feedstock containing 5-7 g protein/l, was applied per litre packed bed at flow-rates of ca. 150 and 300 cm/h. In each case the ovalbumin binding capacity was ca. 70 g/l packed bed with ca. 100% (w/w) recovery of applied protein. A clean-in-place procedure involving storage in 0.5 M NaOH was effective in maintaining chromatographic performance in all cases. These data were consistent with our previous work using the more traditionally configured slurry-packed axial flow columns. Each of these column designs were easy to use facilitating rapid packing with this adsorbent and in the case of IsoPak rapid pump unpacking. The introduction of these column designs significantly improves the task of column packing, hitherto a labour intensive, physically demanding and potentially unreproducible process.     

A multicentered approach to integrated QM/QM calculations. Applications to multiply hydrogen bonded systems

A multicentered integrated QM/QM technique has been developed. By separating high-level calculations in distinct regions of molecules, the multicentered approach supplants a single large high-level calculation with several smaller calculations. Due to the steep polynomial scaling of traditional ab initio quantum chemical methods, this separation significantly enhances the computational efficiency of QM/QM methods. The straightforward implementation of this multicentered approach is illustrated with several large poly-alcohols that form hydrogen bonds with water. The largest alcohol-water complex contains 81 atoms. For properly selected model systems, this multicentered approach introduces essentially no error in the dissociation energies of these complexes relative to conventional QM/QM schemes. This multicentered technique should be easily extended to other, more general integrated methods (QM/MM, ONIOM, etc).