Rydberg spectra of bis(η-benzene)chromium derivatives: Gas-phase photoabsorption study of bis(η-1,2,4-trimethylbenzene)chromium and bis(η-1,2,4,5-tetramethylbenzene)chromium

The gas-phase electronic absorption spectra of (η⁶-1,2,4-C₆H₃Me₃)₂Cr (1) and (η⁶-1,2,4,5-C₆H₂Me₄)₂Cr (2) have been measured for the first time and compared with those recorded in n-pentane solution. The gas-phase spectra of both compounds show transitions from the non-bonding chromium 3d_z² orbital to molecular Rydberg s, p and d levels. The first ionisation potentials have been determined from the Rydberg frequencies as 4.994±0.009 and 4.862±0.009 eV for 1 and 2, respectively. Detailed assignments of Rydberg bands have been made on the basis of analysis of the quantum defects and term values. The Rydberg structures agree with the C₁, C_s or C₂ conformation for 1 and the D_2d geometry for 2 in the gas phase. In crystal, however, the molecule of 2 appears to adopt an eclipsed conformation close to D_2h as indicated by the X-ray diffraction. The influence of ring methylation on the Rydberg term values has been analysed for the first time.     

Prodrugs for amines

The purpose of this work is to review the published strategies for the production of prodrugs of amines. The review is divided in two main groups of approaches: those that rely on enzymatic activation and those that take advantage of physiological chemical conditions for release of the drugs. A compilation of the most important approaches is presented in the form of a table, where the main advantages and disadvantages of each strategy are also referred.     

Charge transport in self-organized pi-stacks of p-phenylene vinylene oligomers

We have studied the mobility of charge carriers along self-organizing pi-stacks of hydrogen-bonded phenylene vinylene oligomers in solution, by time-resolved microwave conductivity measurements. The value deduced for the mobility along the stacks is 3 x 10(-3) and 9 x 10(-3) cm2/(V s) for holes and electrons, respectively. Additionally, we have calculated the mobility along the pi-stacks using a hopping model based on parameters from density functional theory. The mobility values obtained from these calculations are in good agreement with the experimental values if it is assumed that there are relatively large twist angles between neighboring molecules in the stack. It is shown that a significantly higher mobility can be attained if the twist angle between neighboring oligomers is reduced.     

The Choquet integral representation in the affine vector-valued case

LetX be any compact convex subset of a locally convex Hausdorff space andE be a complex Banach space. We denote byA(X, E) the space of all continuous and affineE-valued functions defined onX. In this paper we prove thatX is a Choquet simplex if and only if the dual ofA(X, E) is isometrically isomorphic by a selection map toM _m (X, E*), the space ofE*-valued,w*-regular boundary measures onX. This extends and strengthens a result of G. M. Ustinov. To do this we show that for any compact convex setX, each element of the dual ofA(X, E) can be represented by a measure inM _m (X, E*) with the same norm, and this representation is unique if and only ifX is a Choquet simplex. We also prove that ifX is metrizable andE is separable then there exists a selection map from the unit ball of the dual ofA(X, E) into the unit ball ofM _m (X, E*) which is weak* to weak*-Borel measurable.This work will constitute a portion of the author's Ph.D. Thesis at the University of Illinois.     

Improved FIB milling process for TEM preparation of NiAlPt bulk alloy samples containing residual stress

NiAlPt alloys which undergo complex martensitic and twinning transformations during thermal cycling were prepared for Transmission Electron Microscopy (TEM) analysis using the Focused Ion Beam (FIB) milling process. Coupons of alloys that underwent cyclic heating, with no prior isothermal heat treatment contained a build-up of residual stress that caused sections of the foil to crack or buckle during the thinning process, rendering them useless. The solution was to mill strain isolation trenches perpendicular to the area of interest. These trenches acted as reservoirs for the released residual stress. This step was conducted in conjunction with reducing the beam current much earlier in the thinning process, thus ensuring minimum damage to the section being thinned. These two modifications of the standard FIB milling process, with emphasis on the strain isolation trenches, allowed for successful preparation of TEM samples from a bulk alloy containing residual stress.     

Bacillus anthracis: toxicology, epidemiology and current rapid-detection methods

B. anthracis, the causative agent for anthrax, has been well studied for over 150 years. Due to the genetic similarities among various Bacillus species, as well as its existence in both a spore form and a vegetative state, the detection and specific identification of B. anthracis have been proven to require complex techniques and/or laborious methods. With the heightened interest in the organism as a potential biological threat agent, a large number of interesting detection technologies have recently been developed, including methods involving immunological and nucleic acid-based assay formats. The technologies range from culture-based methods to portable Total Analysis Systems based on real-time PCR. This review with 170 references provides a brief background on the toxicology and epidemiology of B. anthracis, discusses challenges associated with its detection related to genetic similarities to other species, and reviews immunological and, with greater emphasis, nucleic acid-based detection systems. Harriet A. Clancy is currently on active duty with the U.S. Army’s 3rd COSCOM (Corps Support Command)     

Solvent‐driven symmetry of self‐assembled nanocrystal superlattices—A computational study

The preference of experimentally realistic sized 4‐nm facetted nanocrystals (NCs), emulating Pb chalcogenide quantum dots, to spontaneously choose a crystal habit for NC superlattices (Face Centered Cubic (FCC) vs. Body Centered Cubic (BCC)) is investigated using molecular simulation approaches. Molecular dynamics simulations, using united atom force fields, are conducted to simulate systems comprised of cube‐octahedral‐shaped NCs covered by alkyl ligands, in the absence and presence of experimentally used solvents, toluene and hexane. System sizes in the 400,000–500,000‐atom scale followed for nanoseconds are required for this computationally intensive study. The key questions addressed here concern the thermodynamic stability of the superlattice and its preference of symmetry, as we vary the ligand length of the chains, from 9 to 24 ? CH₂ groups, and the choice of solvent. We find that hexane and toluene are “good” solvents for the NCs, which penetrate the ligand corona all the way to the NC surfaces. We determine the free energy difference between FCC and BCC NC superlattice symmetries to determine the system's preference for either geometry, as the ratio of the length of the ligand to the diameter of the NC is varied. We explain these preferences in terms of different mechanisms in play, whose relative strength determines the overall choice of geometry. © 2012 Wiley Periodicals, Inc.