Spectroscopic parameters of nucleophilic and electrophilic reactivity

Reactions of a distinct charge transfer nature (exampled by those between N,N-dimethylaniline and N-methyl cations) are associated with charge transfer bands, in the visible, of energy hν = I ? E + C where I is the ionisation energy of the nucleophile, E is the electron affinity of the electrophile and C is a correction term. As an example, the reaction between N,N-dimethylaniline and N-methylacridinium chloride is examined in detail. Tables of I are given for anions in adiponitrile solution and of hν for cations in dimethylaniline/alcohol solution; low values of I correspond with greater nucleophilic activity and low values of hν with greater electrophilic activity.     

The surface potential barrier in secondary emission from semiconductors

A model for the calculation of secondary electron energy distributions due to bombardment of an amorphous surface by electrons is presented. It takes into account the possibilities of reflexion and tunneling at the surface potential barrier. The general shape of the energy distributions obtained are compared with some typical experimental data. The advantages of the expression obtained for the secondary electron energy distribution are its simplicity and the fact that it can fit the experimental data of a great number of different materials, thus rendering it useful in calculations relating to electron multipliers or other secondary emission devices.     

Reflection asymmetry of the fission transition nucleus 235U

An analysis of the energy variation of the fission cross section and fragment angular distributions for the ²³⁴U (n,f) reaction reveals that the nuclear is reflection assymetric at the inner barrier.     

Ag6(PMo10V2O40](CH3COO).8H2O: A 3D macrocationic polyoxometallic Keggin complex

Silver atoms and strongly interlinking Keggin units ensure the tridimensionnal macrocationic structure of [Ag(6)(PMo(10)V(2)O(40))](CH(3)COO).8H(2)O, which catalyzes O(2)-based oxidation of p-methoxytoluene in acetic acid by air.     

A general solution-phase approach to oriented nanostructured films of metal chalcogenides on metal foils: the case of nickel sulfide

Oriented films of nickel sulfide nanostructures, ranging from hierarchical dendrites to nanobelts and nanorods, were hydrothermally grown on Ni foils. This approach has proven to be a general method for preparing nanostructured metal chalcogenides films on corresponding metal foils.     

Nanostructure of Solid Precipitates Obtained by Expansion of Polystyrene-block-Polybutadiene Solutions in Near Critical Propane: Block Ratio and Micellar Solution Effects

In contrast to incompressible liquid solutions, compressible near-critical solutions of block copolymers allow for controlling rapid structure transformations with pressure alone. For example, when dissolved in near-critical propane, polystyrene-block-polybutadiene can form a random molecular solution at high pressures, a micellar solution at moderate pressures, and a solvent-free precipitate at low pressures. In contrast to the unstructured virgin copolymer, such a propane-treated precipitate rapidly self assembles toward structures characteristic of equilibrated block copolymers, such as lamellae, spheres or cylinders, which depend on the block ratio rather than on the decompression rate or temperature, at least within the rate and temperature ranges investigated in this work. At lower temperatures, however, say below 40 °C, glass transition of the styrene-butadiene diblocks can inhibit independent structure formation while crystallization of their hydrogenated-butadiene analogs can preserve the micellar-solution structure.     

A Molecular Imaging Approach to Mercury Sensing Based on Hyperpolarized 129Xe Molecular Clamp Probe

Mercury pollution, in the form of mercury ions (Hg²⁺), is a major health and environmental hazard. Commonly used sensors are invasive and limited to point measurements. Fluorescence‐based sensors do not provide depth resolution needed to image spatial distributions. Herein we report a novel sensor capable of yielding spatial distributions by MRI using hyperpolarized ¹²⁹Xe. A molecular clamp probe was developed consisting of dipyrrolylquinoxaline (DPQ) derivatives and twocryptophane‐A cages. The DPQ derivatives act as cation receptors whereas cryptophane‐A acts as a suitable host molecule for xenon. When the DPQ moiety interacts with mercury ions, the molecular clamp closes on the ion. Due to overlap of the electron clouds of the two cryptophane‐A cages, the shielding effect on the encapsulated Xe becomes important. This leads to an upfield change of the chemical shift of the encapsulated Xe. This sensor exhibits good selectivity and sensitivity toward the mercury ion. This mercury‐activated hyperpolarized ¹²⁹Xe‐based chemosensor is a new concept method for monitoring Hg²⁺ ion distributions by MRI.