The magnetic circular dichroism of five-membered ring heterocycles

The MCD spectra of pyrrole, furan, thiophene, selenophene and teburophene and some of their derivatives are reported and the corresponding energies, oscillator strengths, transition moment directions, and MCD terms are calculated from semi-empirical quantum mechanical calculations hi the π-electron approximation. The MCD spectrum of thiophene is only slightly perturbed by substituents, and this is also expected to be true of the quite similar MCD spectra of selenophene and tellurophene. These molecules can then be classified as “hard” chromophores. On the other hand, pyrrole and furan have different and much weaker MCD spectra which change shape considerably when substituents are introduced. The implications of these observations are further discussed.     

Confined plasmons in nanofabricated single silver particle pairs: experimental observations of strong interparticle interactions

We report on the optical properties of single isolated silver nanodisks and pairs of disks fabricated by electron beam lithography. By systematically varying the disk size and surface separation and recording elastic scattering spectra in different polarization configurations, we found evidence for extremely strong interparticle interactions. The dipolar surface plasmon resonance for polarization parallel to the dimer axis exhibited a red shift as the interdimer separation was decreased; as expected from previous work, an extremely strong shift was observed. The scattering spectra of single particles and pairs separated by more than one particle radius can be well described by the coupled dipole approximation (CDA), where the particles are approximated as point dipoles using a modified dipole polarizability for oblate spheroids. For smaller particle separations (d < 20 nm), the simple dipole model severely underestimates the particle interaction, indicating the importance of multipolar fields and finite-size effects. The discrete dipole approximation (DDA), which is a finite-element method, describes the experimental results well even at d < 20 nm, including particles that have metallic bridges.     

Synthesis of 11C-labelled N,N'-diphenylurea and ethyl phenylcarbamate by a rhodium-promoted carbonylation via [11C]isocyanatobenzene using phenyl azide and [11C]carbon monoxide

The reaction with phenyl azide and [11C]carbon monoxide to give N,N'-diphenyl[11C]urea and ethyl phenyl[11C]carbamate has been studied with the aim of development of a new methodology for carbonylation using [11C]carbon monoxide with high specific radioactivity. The synthesis of 11C-labelled N,N'-diphenylurea from phenyl azide and [11C]carbon monoxide, with 1,2-bis(diphenylphosphino)ethane-bound Rh(I) complex at 120 degrees C at a pressure of 35 MPa in the presence of aniline was accomplished in 82% trapping efficiency and 82% conversion yield. This approach was also useful for the synthesis of ethyl phenyl[11C]carbamate with lithium ethoxide as a nucleophilic reagent giving 90% trapping efficiency and 76% conversion yield. These reactions can be considered to proceed via a [11C]isocyanate or a [11C]isocyanate-coordinated Rh complex to give the corresponding 11C-products. This protocol provides the chemical basis for the synthesis of [11C]urea and [11C]carbamate derived from [11C]isocyanates.     

On the macro- and microphase separation of compatibilizers in immiscible polymer blends

Macro- and microphase separation of compatibilizing graft copolymers in melt-mixed polystyrene/polyamide-6 blends was studied by transmission electron microscopy and thermal analysis. Three different graft copolymers with main chains of polystyrene and side chains of poly(ethylene oxide) were used as additives at various concentrations. The polyamide-6 domain sizes decreased with increasing amounts of compatibilizing graft copolymers in the blends up to a saturation concentration, after which no further reduction was noted. Macrophase separation of the graft copolymers into discrete macrodomains 20–200 nm in size occurred at concentrations equal to or slightly lower than the saturation concentration. The macrodomains of the graft copolymers were microphase separated, and the sizes and shapes of the microdomains were found to largely depend on the graft copolymer structure and composition. As a consequence of microphase separation, poly(ethylene oxide) crystallinity was noted in blends with sufficiently high macrophase contents. Observations of a graft copolymer interphase between the polystyrene matrix and the polyamide-6 domains confirmed that the graft copolymer was present at the blend interfaces in some of the compatibilized blends. © 1996 John Wiley & Sons, Inc.     

The electrostatic interaction between a charged sphere and an oppositely charged planar surface and its application to protein adsorption

To calculate the electrostatic interaction between a charged sphere and a charged surface under the condition of constant charge density on the two surfaces is difficult. The theory presented in this paper provides an approximate solution to this problem when the charge of the two bodies is of opposite sign. The proposed calculation model is based on a solution of the Poisson–Boltzmann (P–B) equation for two oppositely charged planar surfaces to which the approximate integration procedure developed by Deryaguin is applied. The obtained expression is rather simple and is in good agreement with retention data for a protein in ion exchange chromatography. The developed model is physically more sound than the previously developed ‘slab’ model for protein retention. Under the experimental conditions of ion exchange chromatography of proteins, the two models give comparable numerical values for the ionic strength dependence of retention.     

Finding minimum height elimination trees for interval graphs in polynomial time

The elimination tree plays an important role in many aspects of sparse matrix factorization. The height of the elimination tree presents a rough, but usually effective, measure of the time needed to perform parallel elimination. Finding orderings that produce low elimination is therefore important. As the problem of finding minimum height elimination tree orderings is NP-hard, it is interesting to concentrate on limited classes of graphs and find minimum height elimination trees for these efficiently. In this paper, we use clique trees to find an efficient algorithm for interval graphs which make an important subclass of chordal graphs. We first illustrate this method through an algorithm that finds minimum height elimination for chordal graphs. This algorithm, although of exponential time complexity, is conceptionally simple and leads to a polynomial-time algorithm for finding minimum height elimination trees for interval graphs.This work was supported by grants from the Norwegian Research Council.     

The determination of nitrate and chloride in sodium hydroxide solutions by means of cation exchangers,in the manufacturing control of alkaline batteries

The most important types of alkaline batteries are described. A method for the determination of chloride and nitrate ions in sodium hydroxide solutions has been developed The analysis is performed in the following manner: the solution is passed through a layer of a cation exchanger in the hydrogenform,wherebythe sodium hydroxide is neutralized. The liberated hydrochloric and nitric acids respectively are determined through titration. This method has been used for the manufacturing control of nickel-cadmium batteries.     

Monitoring the DNA binding kinetics of a binuclear ruthenium complex by energy transfer: evidence for slow shuffling

The semirigid binuclear ruthenium complex Delta,Delta-[mu-(11,11'-bidppz)(phen)(4)Ru(2)](4+) has been shown to rearrange slowly from an initial groove-bound nonluminescent state to a final intercalated emissive state by threading one of its bulky Ru(phen)(2) moieties through the DNA base stack. When this complex binds to poly[d(A-T)(2)], a further increase in emission from the complex is observed after completion of the intercalation, assigned to reorganization of the intercalated complex. We here report a study of the threading process in poly[d(A-T)(2)], in which the minor groove binding dye DAPI is used as an energy transfer probe molecule to assess the distribution of ruthenium complex during and also after the actual threading phase. The emission from DAPI is found to change with the same rate as the emission from the ruthenium complex, and furthermore, DAPI does not disturb the binding kinetics of the latter, justifying it as a good probe of both the threading and the reorganization processes. We conclude from the change in the emission from both DAPI and the ruthenium complex with time that DAPI-ruthenium interactions are most pronounced during the process of threading of the complex, suggesting that the complexes are initially threaded slightly anticooperatively and thereafter redistribute along the DNA to reach their thermodynamically most favorable distribution. The final distribution is characterized by a small but significant binding cooperativity, probably as a result of hydrophobic interactions between the complex ions despite their tetravalent positive charges. The mechanism of "shuffling" the complex along the DNA chain is discussed, i.e., whether the ruthenium complex remains threaded (requiring sequential base-pair openings) or if unthreading followed by lateral diffusion within the ionic atmosphere of the DNA and rethreading occurs.