The synthesis of some bidentate ligands containing both phosphine and nitrile groups

Both (C₆H₅)₂P(CH₂)₃CN and (C₆H₅)₂P(CH₂)₄CN have been obtained from the reaction of Br(CH₂)_nCN (n = 3, 4) with (C₆H₅)₂POCH₃ followed by reduction with (C₆H₅)₂SiH₂. These phosphine-nitrile ligands form L₂PdCl₂ complexes which are shown by IR measurements to have trans geometries with the phosphine portions of the ligands coordinated. Reactions of o-BrC₆H₄CN with CH₃(CH₂)₃Li followed by R₂PCl (R = C₆H₅ or (CH₃)₂N) have been used to provide good yields of the corresponding R₂P-o-C₆H₄CN products.     

Density functional theory studies on the mechanisms of regioselective allylic and cis-vinylic deprotonation of allyl amides and allylamines

A density functional theory (B3LYP/6-31+G) study was undertaken in an effort to learn more about the mechanisms controlling the regioselective deprotonations of the synthetically versatile N-lithio-N-(tert-butyl)allylamide 1 and N-lithio-N-(trimethylsilyl)allylamine 2 compounds. The calculations suggest that deprotonation of 1 occurs exclusively at the allylic position. This agrees with experimental results. The calculations also suggest that deprotonation of allylamine 2 exclusively at the cis-vinylic position is due to kinetic control.     

Application of the Sol-Gel Method at the Fabrication of Microstructure Fibers

This paper presents results on using the sol-gel process for the preparation of microstructure fibers (MSFs). In this preparation the sol-gel method is used for the formation of bonds between silica tubes and silica rods in the input stacks for MSF drawing and for filling-in the interstices between these parts. Gels applied on the stacks were prepared from sols composed of tetraethoxysilane, phosphorous oxychloride, boron tribromide, ethanol, HCl and water. Pastes prepared from the sols and solid fabricated through heat treatment of the sols at 1000°C were also used. The sols were applied on the stacks by the dip-coating method and the pastes were applied manually. The formed xerogels were heat-treated at temperatures of up to 1000°C. The MSFs of the grapefruit type were drawn from the stacks at a temperature of about 1900°C. Waveguiding properties of the fibers were examined under their excitation by an inclined collimated beam. It has been found that the sol-gel method is suitable particularly for filling-in the interstices at the end of the stack, which enables pressure control inside holes of the stack during MSF drawing.     

The first synthesis and cytostatic activity of novel 6-(fluoromethyl)purine bases and nucleosides

Two alternative approaches to the synthesis of novel 6-(fluoromethyl)purine bases and nucleosides are described either by direct deoxyfluorination or by multistep functional group transformations starting from 6-(hydroxymethyl)purines. 6-(fluoromethyl)purine ribonucleoside displayed significant cytostatic effects.     

Graphs with maximum connectivity index

Let G be a graph and d_v the degree (=number of first neighbors) of its vertex v. The connectivity index of G is χ=∑ (d_ud_v)^−1/2, with the summation ranging over all pairs of adjacent vertices of G. In a previous paper (Comput. Chem. 23 (1999) 469), by applying a heuristic combinatorial optimization algorithm, the structure of chemical trees possessing extremal (maximum and minimum) values of χ was determined. It was demonstrated that the path P_n is the n-vertex tree with maximum χ-value. We now offer an alternative approach to finding (molecular) graphs with maximum χ, from which the extremality of P_n follows as a special case. By eliminating a flaw in the earlier proof, we demonstrate that there exist cases when χ does not provide a correct measure of branching: we find pairs of trees T, T′, such that T is more branched than T′, but χ(T)>χ(T′). The smallest such examples are trees with 36 vertices in which one vertex has degree 31.     

Thermo-oxidative degradation of some elastomers with a high content of 3,4 isoprene units

New elastomers with high content of 3,4 isoprene units have been developed during the last decades in an attempt to ensure superior performances of the final products and the present study is devoted to the investigation of some peculiarities of their ageing behaviour. On thermo-oxidative degradation, 3,4 isoprene units are less affected in comparison to cis-1, 4 and trans-1, 4 isoprene units. The degradation process consists mainly in splitting of the main chains at temperatures of 80–100 °C while at higher temperatures (120–130 °C) branching becomes a significant modification and this reaction is enhanced for the polymers containing preponderantly 3,4 units. Such behaviour leads to the fact that the processability of polymers containing high amounts of 1,2 and 1,3 isoprene units is less affected by thermo-oxidative degradation in comparison with cis-1, 4-polyisoprene, which could be explained by the fact that large amounts of double bonds are not present in the backbone of macromolecules but in the pendent groups.     

Solubility of Uric Acid in Lithium Chloride Solutions

Summary.  The solubility of anhydrous uric acid was measured in 0.30 mol dm⁻³ LiCl solutions as a function of hydrogen ion concentration at 25 and 37°C. No influence of the lithium ion on the solubility of uric acid was detected. The “litholytic” effect of lithium reported in literature can possibly be explained by the higher solubility of lithium hydrogenurate as compared to other alkali metal hydrogenurates. Corresponding author. E-mail: koenigsb@chem.murdoch.edu.au Received November 21, 2002; accepted December 10, 2002 Published online April 7, 2003 RID="a" ID="a" Dedicated to Professor Heinz Gamsj?ger on the occasion of his 70th birthday     

Permethylated 6I-alkenoylamino-6I-deoxy β-cyclodextrin derivatives as modifiers of photoluminescence sensor response of porous silicon

A set of permethylated 6^I-(ω-alkenoyl)-6^I-amino-6^I-deoxy-β-cyclodextrin derivatives with different chain length of the alkenoyl group (used as a spacer) was synthesized. These derivatives were attached by photochemically activated hydrosilylation reaction to the surface of porous silicon. Photoluminescence response of the modified PS to controlled concentrations of various molecules in gas phase revealed strong host-guest interactions between β-cyclodextrin and the detected molecules. The strongest interaction was observed for aromatic molecules, which have the optimal size to fit into the β-cyclodextrin molecular cavity.     

Dynamics of nanoscopic water: vibrational echo and infrared pump-probe studies of reverse micelles

The dynamics of water in nanoscopic pools 1.7-4.0 nm in diameter in AOT reverse micelles were studied with ultrafast infrared spectrally resolved stimulated vibrational echo and pump-probe spectroscopies. The experiments were conducted on the OD hydroxyl stretch of low-concentration HOD in the H2O, providing a direct examination of the hydrogen-bond network dynamics. Pump-probe experiments show that the vibrational lifetime of the OD stretch mode increases as the size of the reverse micelle decreases. These experiments are also sensitive to hydrogen-bond dissociation and reformation dynamics, which are observed to change with reverse micelle size. Spectrally resolved vibrational echo data were obtained at several frequencies. The vibrational echo data are compared to data taken on bulk water and on a 6 M NaCl solution, which is used to examine the role of ionic strength on the water dynamics in reverse micelles. Two types of vibrational echo measurements are presented: the vibrational echo decays and the vibrational echo peak shifts. As the water nanopool size decreases, the vibrational echo decays become slower. Even the largest nanopool (4 nm, approximately 1000 water molecules) has dynamics that are substantially slower than bulk water. It is demonstrated that the slow dynamics in the reverse micelle water nanopools are a result of confinement rather than ionic strength. The data are fit using time-dependent diagrammatic perturbation theory to obtain the frequency-frequency correlation function (FFCF) for each reverse micelle. The results are compared to the FFCF of water and show that the largest differences are in the slowest time scale dynamics. In bulk water, the slowest time scale dynamics are caused by hydrogen-bond network equilibration, i.e., the making and breaking of hydrogen bonds. For the smallest nanopools, the longest time scale component of the water dynamics is approximately 10 times longer than the dynamics in bulk water. The vibrational echo data for the smallest reverse micelle displays a dependence on the detection wavelength, which may indicate that multiple ensembles of water molecules are being observed.     

Applications of synchrotron radiation in forensic trace evidence analysis

Synchrotron radiation sources have proven to be highly beneficial in many fields of research for the characterization of materials. However, only a very limited proportion of studies have been conducted by the forensic science community. This is an area in which the analytical benefits provided by synchrotron sources could prove to be very important. This review summarises the applications found for synchrotron radiation in a forensic trace evidence context as well as other areas of research that strive for similar analytical scrutiny and/or are applied to similar sample materials. The benefits of synchrotron radiation are discussed in relation to common infrared, X-ray fluorescence, tomographic and briefly, X-ray diffraction and scattering techniques. In addition, X-ray absorption fine structure analysis (incorporating XANES and EXAFS) is highlighted as an area in which significant contributions into the characterization of materials can be obtained. The implications of increased spatial resolution on microheterogeneity are also considered and discussed.