Synthesis and characterization of immobilized PAMAM dendrons

This communication describes the synthesis and characterization of immobilized PAMAM dendrons onto a surface modified silicon wafer substrate (functionalized using plasma polymerized PAA) using a "growing from" strategy.     

Photophysical and computational investigations of bis(phosphine) organoplatinum(II) metallacycles

A series of endohedral and exohedral amine-functionalized ligands were synthesized and used in the construction of supramolecular D(2h) rhomboids and a D(6h) hexagon. These supramolecular polygons were obtained via self-assembly of 120° dipyridyl donors with 180° or 120° diplatinum precursors when combined in 1:1 ratios. Steady-state absorption and emission spectra were collected for each ligand and metallacycle. Density functional theory (DFT) and time-dependent DFT calculations were employed to probe the nature of the observed optical transitions for the rhomboids. The emissive properties of these bis(phosphine) organoplatinum metallacycles arise from ligand-centered transitions involving π-type molecular orbitals with modest contributions from metal-based atomic orbitals. The D(2h) rhomboid self-assembled from 2,6-bis(4-pyridylethynyl)aniline and a 60° organoplatinum(II) acceptor has a low-energy excited state in the visible region and emits above 500 nm, properties which greatly differ from those of the parent 2,6-bis(4-pyridylethynyl)aniline ligand.     

Assigning resources and targets to an organization’s activities

Each of an organization’s many activities transforms inputs into outputs. Managing these activities involves allocating input resources for some activities and assigning output targets for others. Making these decisions is especially difficult in the presence of uncertainty. In practice, many organizations address these problems by using a fairly simple “proportional allocation” heuristic (e.g., “allocate to each activity the same percentage increase (or decrease) in its resources or targets”). But proportional allocation does not consider the uncertainty inherent in the ability of each activity to make use of its resources (or meet its targets).     

Localised Evolved Gas Analysis by Micro-thermal Analysis

Micro-thermal analysis employs a scanning probe microscope fitted with a miniature resistive heater/thermometer to obtain images of the surface of materials and then perform localised thermo analytical measurements. We have demonstrated that it is possible to use the same configuration to pyrolyse selected areas of the specimen by rapidly heating the probe to 600–800°C. This generates a plume of evolved gases which can be trapped using a sampling tube containing a suitable sorbent placed close to the heated tip. Thermal desorption-gas chromatogaphy/mass spectrometry can then be used to separate and identify the evolved gases. This capability extends the normal visualisation and characterisation by micro-thermal analysis to include the possibility of localised chemical analysis of the sample (or a domain, feature or contaminant). The isolation and identification of natural products from a plant leaf are given as an example to illustrate this approach. Preliminary results from direct sampling of pyrolysis products by mass spectrometry are also presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tensor products and matrix differential calculus

This paper sets forth some of the principal results of the algebra of Kronecker products in a way which relates them directly to the abstract algebra of tensor products. The concepts and the results that are developed in this way are used to analyse three alternative definitions that have been proposed for the derivative of a matrix function Y=Y(X) with respect to its matrix argument X. It is argued that only one of these definitions is viable. The other definitions, which are widely used in econometrics, are not consistent with the classical representation of linear algebra via matrix theory; and they lead to serious practical difficulties that do not arise when the appropriate definition is adopted.     

Absolute frequency measurements of the 0002-0000, 2001-0000, and 1201-0000 bands of N2O by heterodyne spectroscopy

The absolute frequencies of 39 lines in the 00⁰2-00⁰0, 20⁰1-00⁰0, and 12⁰1-00⁰0 bands of N₂O in the range 4300–4800 cm^?1 have been measured by heterodyne frequency techniques. The lines were each measured in Doppler-limited absorption, with a color-center laser as a tunable probe of the N₂O and two stabilized CO₂ lasers as reference frequencies. New rovibrational constants have been fitted to these measurements. Tables of calculated transition frequencies are given, with estimated absolute uncertainties as small as 10^?4 cm^?1. The pressure shifts of four lines have been measured, and the values fall within the range of 0 to ?2 MHz/kPa (0 to ?0.2 MHz/Torr).     

Relative dioxygenation rates of some trans-Ir(CO)X(PR3)2 complexes: The effect of phosphine and halogen changes

Relative rates of dioxygen uptake by the complexes trans-Ir(CO)X(PPh₂R)₂ (R = Ph, Me, Et; X = F, Cl, Br, I) have been measured in dichloromethane and found to follow the order R = Ph<Et<Me and X = F <Cl<Br<I. The basicity of these trans-Ir(CO)X(L)₂ complexes, as measured by their affinity for dioxygen, is not reflected in the energy of the ν(CO) absorption in the parent compounds; a previous report that complex basicity ∝1/ν(CO) does not hold for the complexes reported here.