Relationships between nonadiabatic bridged intramolecular, electrochemical, and electrical electron-transfer processes

Fermi's golden rule is used to develop relationships between rate constants for electron transfer in donor-bridge-acceptor and electrode-bridge-acceptor systems and resistances across metal-bridge-electrode and metal-bridge-tip junctions. Experimental data on electron-transfer rates through alkanethiolate, oligophenylene, and DNA bridges are used to calculate the electronic coupling matrix element per state through these moieties. The formulation is then used to predict the resistance of these bridges between two gold contacts. This approach provides a straightforward method for experimentalists to assess the self-consistency between intramolecular electron-transfer rate constants and low-bias resistances measured for molecularly bridged junctions between two metallic contacts. Reported resistances for alkanethiolate bridges vary by a factor of 20, with predicted resistances falling within this range. However, comparisons between carboxylato and directly linked alkanethiolate bridges suggest differences between the coupling at the interface to either the redox center or the gold electrode in such systems. Calculated resistances for oligophenylene bridges are close to those measured experimentally in a similar oligophenylene system.     

Electronic structures and conductivity in peptide nanotubes

Self-assembling cyclic D,L-peptide nanotubes are electronically insulating and possess wide band gaps (E(g) > 4 eV). Our ab initio electronic structure calculations indicate that the presence of aromatic rings in the side chain of peptide nanotubes significantly reduces the band gap. We investigate the conductivity of the modified peptide nanotubes through calculations of the electron tunneling probability. The electron tunneling probability through a molecule depends on the length of the molecule, L, as e-beta(E)L, where the tunneling beta(E)-factor is strongly energy-dependent. We have calculated beta(E) in three types of peptide nanotubes that have different sequences of amino acid residue, (L-Gln, D-Ala)(4), (L-Gln, D-Leu)(4) and (L-Gln, D-Phe)(4), using the complex band structure approach. We find large beta values near midgap, making these peptide nanotubes a poor tunneling conductor.     

Circular dichroism spectra of DNA hairpins studied by the green function method

The circular dichroism (CD) spectrum of a large biological molecule represented as an array of interacting chromophores is investigated. The configuration-averaged Green function formalism is developed to describe the CD and absorption spectra. The perturbation theory expansion is derived for absorption and CD spectra in the case of strong interaction of chromophores with their environment (solvent and/or internal dynamics) compared to their interaction with each other. We apply this formalism to study CD spectra of DNA hairpins.     

Accurate determination of an immunosuppressant in stented swine tissues with LC–MS/MS

During stent development, accurate monitoring of the drug concentration in animal tissues can provide critical information on how the drug is released into the circulation and the surrounding tissues. To establish the relationship between the drug concentration and the distance from the stent to the target tissue, a comprehensive strategy was developed for sample collection, sample homogenization and sample storage as well as sample analysis. This strategy was developed with the analytical chemists and animal surgical specialists working together as a team. The optimized sampling process was designed to yield a representative sample, appropriately located and of an appropriate size. The sampling process was also designed to eliminate the potential for carryover and cross-contamination. During sample processing, the analyte solution was spiked into blank tissues using a sharp needle and a gas-tight syringe to prepare tissue quality control samples. These tissue quality controls were then used to evaluate the stability of the drug in solid tissue and homogenate, the homogenization carryover, the cross-contamination and the recovery of the drug during method validation and to monitor the overall process of drug analysis of the swine tissues. This thorough strategy has been applied to the accurate determination of zotarolimus in swine tissues for regulated toxicology studies. The entire process was controlled, including precise tissue sampling, compound-based tissue homogenization, method validation, and the application of the method to regulated toxicokinetics studies. The results demonstrate that analytical chemistry concepts can be successfully integrated into toxicokinetics studies in order to collect precise samples and obtain meaningful results. The strategy can be applied to similar toxicokinetics studies of locally administrated drugs in tissues.     

The electrochemical reduction of an unsaturated mixed-metal cluster anion: Synthesis and x-ray crystal structure of [(Ph3P)2N][{Os3H(CO)10}2Ag]

The unsaturated mixed-metal cluster anion [{Os₃H(CO)₁₀}₂Ag]^? has been prepared by the reaction of [(Ph₃P)₂N][Os₃H(CO)₁₁] with Ag[PF₆], and the anion has been shown by an X-ray analysis to consist of an Ag^I atom linking together two “Os₃H(CO)₁₀” fragments. The electrochemistry of this complex has been investigated and it has been shown to undergo two one-electron reductions.     

Preparation of N-phenyl-substituted quinolinium derivatives labeled with tritium by chemonuclear synthesis

A chemonuclear method of synthesis is proposed for obtaining difficultly available phenyl-substituted derivatives of quinoline labeled with tritium. The ion-molecule reaction of free phenyl cations, generated on β-decay of tritium, with the nucleophilic centers of heterocyclic compounds is the basis of the synthesis. The onium derivatives synthesized possess significant inhibitory antimicrobial activity and are promising for a detailed study of the reaction mechanisms and metabolic processes using radioactive indicators.     

Pressure-induced structural transformations of the Zintl phase sodium silicide

The high-pressure behaviour of NaSi has been studied using Raman spectroscopy and angle-dispersive synchrotron X-ray diffraction to observe the onset of structural phase transformations and potential oligomerisation into anionic Si nanoclusters with extended dimensionality. Our studies reveal a first structural transformation occurring at 8–10 GPa, followed by irreversible amorphisation above 15 GPa, suggesting the formation of Si–Si bonds with oxidation of the Si⁻ species and reduction of Na⁺ to metallic sodium. We have combined our experimental studies with DFT calculations to assist in the analysis of the structural behaviour of NaSi at high pressure.     

An investigation into two bin packing problems with ordering and orientation implications

This paper considers variants of the one-dimensional bin packing (and stock cutting) problem in which both the ordering and orientation of items in a container influences the validity and quality of a solution. Two new real-world problems of this type are introduced, the first that involves the creation of wooden trapezoidal-shaped trusses for use in the roofing industry, the second that requires the cutting and scoring of rectangular pieces of cardboard in the construction of boxes. To tackle these problems, two variants of a local search-based approximation algorithm are proposed, the first that attempts to determine item ordering and orientation via simple heuristics, the second that employs more accurate but costly branch-and-bound procedures. We investigate the inevitable trade-off between speed and accuracy that occurs with these variants and highlight the circumstances under which each scheme is advantageous.     

High capacity gas storage by a 4,8-connected metal-organic polyhedral framework

The polyhedral complex [Cu(4)L(H(2)O)(4)]solv (NOTT-140) shows a 4,8-connected structure of rare scu topology comprising octahedral and cuboctahedral cages; desolvated NOTT-140a shows a total CO(2) uptake of 314.6 cm(3) (STP) cm(-3) at 20 bar, 293 K, and a total H(2) uptake of 6.0 wt% at 20 bar, 77 K.     

Designed synthesis of TS-1 crystals with controllable b-oriented length

TS-1 crystals with controllable b-oriented length (sheet-like morphology, TS-1-S; chain-like morphology, TS-1-C) have been rationally synthesized from addition of organic additives (urea and fluorinated surfactant of FC-4) in the starting titanosilicate gels, and catalytic and adsorptive measurements show that TS-1-S samples are very active in Beckmann rearrangement of cyclohexanone oxime, whereas TS-1-C samples are selective in adsorption for para-xylene.