Contributions to the theory of first‐exit times of some compound processes in queueing theory

We consider compound processes that are linear with constant slope between i.i.d. jumps at time points forming a renewal process. These processes are basic in queueing, dam and risk theory. For positive and for negative slope we derive the distribution of the first crossing time of a prespecified level. The related problem of busy periods of single‐server queueing systems is also studied. This revised version was published online in June 2006 with corrections to the Cover Date.     

Bis-(8-oxo quinoline)diorgano tellurium(IV) compounds; structural and spectroscopic studies

Three new compounds of the type R₂Te(OR′)₂ are reported in which R′ bears a potentially co-ordinating group: bis-(8-hydroxo quinoline)dimethyltellurium (I) bis-(8-oxo-2-methyl quinoline)dimethyltellurium (II), and bis-(8-oxo-quinoline) di-(p-tolyl)tellurium (III). The crystal structures of II and III have been determined. The primary geometry around tellurium in both cases can be described as ψ-trigonal bipyramidal but long Te N contacts in the range 2.840(6)–2.899(4) Å which lie well within the van der Waals distance imply extension of the co-ordination sphere. Variable temperature multi-nuclear (¹ H, ¹³C, ¹²⁵Te) studies of the compounds I, II, and III in solution indicate the presence of a single species over the range 216–343 K. The data do not distinguish between the presence of a single 14-Te-6 pertellurane seen in the crystallographic studies, or that of such a species in equilibrium, rapid on the ¹H and ¹²⁵Te timescales, with the 10-Te-4 tellurane.     

Interactions of bovine serum albumin with aluminum polyoxocations and aluminum hydroxide

Interactions of aqueous solutions of aluminum polyoxocations (Al13-mers and Al30-mers) and aluminum hydroxide suspensions of varying particle sizes (26, 55, and 82 nm) with a model protein, bovine serum albumin (BSA), have been investigated using potentiometry, conductometry, viscometry, 27Al solution NMR, UV-vis spectroscopy, dynamic light scattering, zeta-potential measurements, thermogravimetry, X-ray diffraction, and scanning electron microscopy. Increasing amounts of BSA partially convert Al13-mers and, to a larger extent, Al30-mers into amorphous Al hydroxide without gel formation. At the same time, BSA molecules can form unstable aggregates in the Al polyoxocation solutions which redisperse easily upon standing. In the case of Al hydroxide sols, BSA addition causes substantial gelation, the extent of which is proportional to the amount of BSA added and inversely related to the Al hydroxide particle size. Upon freeze-drying or centrifugation of Al species-BSA solutions, an interesting sheetlike morphology with 150-200 nm wide nanoribbons is observed for pure Al hydroxide nanoparticles and for solutions of Al polyoxocations with the highest amount of BSA studied. On the basis of the combined solution, colloidal and solid-state characterization of model Al species-BSA systems, a qualitative model of possible interactions in the Al polyoxocation-BSA and Al hydroxide-BSA systems is proposed wherein core-shell hybrid nanoparticles are formed from protein "core" and Al polyoxocation "shell" or Al hydroxide "core" and protein "shell".     

Identification of localised and delocalised adsorbate orbitals on W(100) by photoelectron spectroscopy

The comparison of the photoelectron spectra of chemisorbed layers taken with glancing photon incidence and those with normal photon incidence permits a qualitative determination of the degree of delocalisation of the various orbitals at the surface. For glancing photon incidence, both localised and delocalised orbitals can be photoionised. However, for normally incident photons, those orbitals localised around particular atomic sites have a much higher photoionisation cross section than those orbitals extensively delocalised in the plane of the surface. Examples of this behaviour in the spectra of hydrogen and carbon monoxide on W(100) are presented.     

Rate Enhancement Effects in the Dabco Catalysed Synthesis of Hydroxyalkenoate Esters

Marked acceleration of the catalytic coupling of aldehydes with methyl acrylate is achieved by varying either the aldehyde or the catalytic system. Rapid and efficient formation of heterocyclic derivatives with significant synthetic potential is described.     

A Robust Metal–Organic Framework for Dynamic Light‐Induced Swing Adsorption of Carbon Dioxide

Adsorbents for CO₂ capture need to demonstrate efficient release. Light‐induced swing adsorption (LISA) is an attractive new method to release captured CO₂ that utilizes solar energy rather than electricity. MOFs, which can be tailored for use in LISA owing to their chemical functionality, are often unstable in moist atmospheres, precluding their use. A MOF is used that can release large quantities of CO₂ via LISA and is resistant to moisture across a large pH range. PCN‐250 undergoes LISA, with UV flux regulating the CO₂ desorption capacity. Furthermore, under UV light, the azo residues within PCN‐250 have constrained, local, structural flexibility. This is dynamic, rapidly switching back to the native state. Reusability tests demonstrate a 7.3 % and 4.9 % loss in both adsorption and LISA capacity after exposure to water for five cycles. These minimal changes confirm the structural robustness of PCN‐250 and its great potential for triggered release applications.     

Reversible Switching between Highly Porous and Nonporous Phases of an Interpenetrated Diamondoid Coordination Network That Exhibits Gate‐Opening at Methane Storage Pressures

Herein, we report that a new flexible coordination network, NiL₂ (L=4‐(4‐pyridyl)‐biphenyl‐4‐carboxylic acid), with diamondoid topology switches between non‐porous (closed) and several porous (open) phases at specific CO₂ and CH₄ pressures. These phases are manifested by multi‐step low‐pressure isotherms for CO₂ or a single‐step high‐pressure isotherm for CH₄. The potential methane working capacity of NiL₂ approaches that of compressed natural gas but at much lower pressures. The guest‐induced phase transitions of NiL₂ were studied by single‐crystal XRD, in situ variable pressure powder XRD, synchrotron powder XRD, pressure‐gradient differential scanning calorimetry (P‐DSC), and molecular modeling. The detailed structural information provides insight into the extreme flexibility of NiL₂ . Specifically, the extended linker ligand, L , undergoes ligand contortion and interactions between interpenetrated networks or sorbate–sorbent interactions enable the observed switching.