Reactivity of AlMe3 with titanium(IV) Schiff base complexes: X-ray structure of [Ti{(μ-Br)(AlMe2)}{(μ-Br)(AlMe2X)}(salen)] · C7H8 (X=Me or Br) and reactivity studies of mono-alkylated [Ti(Me)X(L)] complexes

[TiCl₂(salen)] (1) reacts with AlMe₃ (1:2) to give the heterometallic Ti(III) and Ti(IV) complexes [Ti{(μ-Cl)(AlMe₂)}{(μ-Cl)(AlMe₂X)}(salen)] (X=Me or Cl) (2) and [TiMe{(μ-Cl)(AlCl₂Me)}(salen)] (3). Addition of diethyl ether to 3 affords [Ti(Me)Cl(salen)] (4). The analogous reaction of [TiBr₂(salen)] (5) gives the crystallographically characterised [Ti{(μ-Br)(AlMe₂)}{(μ-Br)(AlMe₂X)}(salen)] (X=Me or Br) (6) and [Ti(Me)Br(salen)] (7) in a single step, whilst the comparable reaction of [TiCl₂{(3-MeO)₂salen}] (8) with AlMe₃ yields [Ti(Me)Cl{(3-MeO)₂salen}] (9) with no evidence of titanium(III) species. Reactivity of both halide and methyl groups of 4 has been probed using magnesium reduction, SbCl₅ and AgBF₄ halide abstraction and SO₂ insertion reactions. Hydrolysis of [Ti(Me)X(L)] complexes affords μ-oxo species [TiX(L)]₂(μ-O) [X=Cl, L=salen (13); X=Br, L=salen (14); X=Cl, L=(3-MeO)₂salen (15)].     

An investigation of enhanced secondary ion emission under Au n + (n=1–7) bombardment

We investigate the mechanism of the nonlinear secondary ion yield enhancement using Au(n)+ (n = 1, 2, 3, 5, 7) primary ions bombarding thin films of Irganox 1010, DL-phenylalanine and polystyrene on Si, Al, and Ag substrates. The largest differences in secondary ion yields are found using Au+, Au2+, and Au3+ primary ion beams. A smaller increase in secondary ion yield is observed using Au5+ and Au7+ primary ions. The yield enhancement is found to be larger on Si than on Al, while the ion yield is smaller using an Au+ beam on Si than on Al. Using Au(n)+ ion structures obtained from Density Functional Theory, we demonstrate that the secondary yield enhancement is not simply due to an increase in energy per area deposited into the surface (energy deposition density). Instead, based on simple mechanical arguments and molecular dynamics results from Medvedeva et al, we suggest a mechanism for nonlinear secondary ion yield enhancement wherein the action of multiple concerted Au impacts leads to efficient energy transfer to substrate atoms in the near surface region and an increase in the number of secondary ions ejected from the surface. Such concerted impacts involve one, two, or three Au atoms, which explains well the large nonlinear yield enhancements observed going from Au+ to Au2+ to Au3+ primary ions. This model is also able to explain the observed substrate effect. For an Au+ ion passing through the more open Si surface, it contacts fewer substrate atoms than in the more dense Al surface. Less energy is deposited in the Si surface region by the Au+ primary ion and the secondary ion yield will be lower for adsorbates on Si than on Al. In the case of Au(n)+ the greater density of Al leads to earlier break-up of the primary ion and a consequent reduction in energy transfer to the near-surface region when compared with Si. This results in higher secondary ion yields and yield enhancements on silicon than aluminum substrates.     

The chemistry of 2'' ,3''-seconucleosides II. Reactions and biological properties of 2'',3''-secopyrimidine ribonucleosides

Reaction of 2',3'-secouridine with acetone gave the 3',5'-$\text{O}$-isopropylidene derivative (1) which upon treatment with mesylchloride gave the 2'-$\text{O}$-mesyl compound (2). Replacement of the mesyl group of 2 with halide could be effected by reaction with a metal halide in DMF. The 3',5'-$\text{O}$-isopropylidene group was removed simultaneously to give a 2'-halogeno-2'-deoxy-2',3'-secouridine. 2',3'-Dichloro-2',3'-dideoxy-2',3'-secouridine upon treatment with base gave 6($\text{R}$)-chloromethyl-2($\text{R}$)-(uracil-1-yl)-1,4-dioxane in addition to O²,2'-anhydro-3'-chloro-3'-deoxy-2',3'-secouridine, as previously reported. 2',3'-Dichloro-2',3'-dideoxy-5'-0-trityl-2',3'-secouridine was converted to 2',3'-dichloro-2',3'-dideoxy-2',3'-secocytidine (16) $\text{via}$ a triazole derivative. Compound 16 was unstable and appeared to form O²,2'-anhydro-3'-chloro-3'-deoxy-2,3'-secocytidine upon standing at room temperature. 5-Vinyl- and 5-($\text{E}$) (2-bromovinyl) uridine dialdehydes have been made, as well as a number of other 5-substituted 2',3'-secouridine derivatives. None of the compounds obtained showed significant activity against a number of virus strains or tumor cell lines, except for 5-($\text{E}$)(2-bromovinyl) uridine dialdehyde, which was inhibitory to the growth of human lymphoblast (Raji, Namalva) cells at a concentration of 28 μ/ml.     

Humic substances of surface waters : Litter and soil throughflow relationships in two forested ecosystems

Humic substances were isolated from the vegetation throughfall, soil drainage waters and adjacent stream waters at two forested sites in the Central Region of Scotland. Fractionation on XAD-8 hydrophobic resin gave three humic substance components and one hydrophilic acid fraction. Norway spruce generally gave 2–3 times more dissolved organic carbon in the litter drainage compared with Sitka spruce, although there was little qualitative difference in organic acidity between the two litterflows. The humic substances in the drainage at ca. 1 m depth (BC horizon) showed considerable differences between sites, reflecting the types of soils and sources of soil water. Phenolic acids released on hydrolysis confirm the differences between sites and may indicate the sources of subsoil water and their relationships with the stream outputs.     

Solution NMR studies of iron(II) spin-crossover complexes

The 1H NMR spectra of a series of mono- and dinuclear pyridine complexes [FeL1(R1/R2)(py)2] and [Fe2L2(R1/R2)(py)4] have been investigated in a mixed toluene-d8/pyridine-d5 solution. The equatorial tetradentade Schiff base like ligands L1(R1/R2) and L2(R1/R2) with a N2O22- coordination sphere for each metal center have been obtained by condensation of a substituted malonodialdehyde (R1/R2 are Me/COOEt, Me/COMe, or OEt/COOEt) with o-phenylenediamine (L1(R1/R2)) or 1,2,4,5-tetraaminobenzene (L2(R1/R2)). The 1H NMR resonances were assigned by comparison of differently substituted complexes in combination with a line-width comparison. The 1H NMR shifts from 188 to 358 K show a strong influence of the spin state of the iron center. The behavior of the pure high-spin iron(II) complexes is close to ideal Curie behavior. Analysis of the resonance shifts of the spin-transition complexes can be used for determining the high-spin mole fraction of the complex in solution at different temperatures. Magnetic susceptibility measurements in solution using the Evans method were made for all six complexes. Significant differences between the spin-transition behavior of the complexes in solution of those in the solid state were found. However, the plots of microeff as a function of temperature obtained using the Evans method and those obtained by interpretation of the NMR shifts were virtually identical. The isotropic shifts of protons in the complexes proved to be suitable tools for following a spin transition in solution. Comparison of the microeff plots of the mono- and dinuclear complexes in solution reveals slight differences between the steepness of the curves that may be attributable to cooperative interactions between the metal centers in the case of the dinuclear complexes.     

Influence of the colloidal environment on the magnetic behavior of cobalt nanoparticles

The magnetic properties of 10 nm diameter surfactant-coated cobalt (Co) nanoparticles in 1,2-dichlorobenzene (DCB) are investigated by a series of sequential magnetic moment (m) vs temperature (T) measurements. A rapid rise in magnetic moment around 250 K during warming and an abrupt drop at 234 K during cooling are observed when a nonsaturating external magnetic field is applied. Differential scanning calorimetry (DSC) measurements demonstrate that the rapid rise and abrupt drop in magnetization are associated with the melting and freezing of the solvent. Magnetic measurements of these Co nanoparticles in DCB are also used to probe their aging over a period of 70 days. The saturation magnetic moment of Co nanoparticles in DCB stored in air at room temperature decreases by nearly 40% over 70 days. Transmission electron microscopy (TEM) characterizations are reported to show the time evolution in the size, shape, and crystalline structures of DCB-immersed nanoparticles.     

Benchmark studies of the BCRLM reactive scattering code: Implications for accurate quantum calculations

Summary The Bending Corrected Rotating Linear Model (BCRLM), developed by Hayes and Walker, is a simple approximation to the true multidimensional scattering problem for reactions of the type: A + BC AB + C. While the BCRLM method is simpler than methods designed to obtain accurate three-dimensional quantum scattering results, this turns out to be a major advantage in terms of our benchmarking studies. The computer code used to obtain BCRLM scattering results is written for the most part in standard FORTRAN and has been ported to several scalar, vector, and parallel architecture computers including the IBM 3090-600J, the Cray XMP and YMP, the Ardent Titan, IBM RISC System/6000, Convex C-1 and the MIPS 2000. Benchmark results will be reported for each of these machines with an emphasis on comparing the scalar, vector, and parallel performance for the standard code with minimum modifications. Detailed analysis of the mapping of the BCRLM approach onto both shared and distributed memory parallel architecture machines indicates the importance of introducing several key changes in the basic strategy and algorithms used to calculate scattering results. This analysis of the BCRLM approach provides some insights into optimal strategies for mapping three-dimensional quantum scattering methods, such as the Parker-Pack method, onto shared or distributed memory parallel computers.     

Expert systems for method development and validation in HPLC

ESCA, Expert Systems Applied to Chemical Analysis, started its research in March 1987, with the aim of building prototype expert systems for HPLC method development. Results of this research have been published as the work has progressed. The project is now completed and this paper summarises some of the overall project conclusions. Seven different expert systems have been built which tackle problems throughout the process of method development, four stand-alone systems and three integrated systems. The object of ESCA was to evaluate the applicability of expert system technology to analytical chemistry and not all the systems were built for commercial uses. Many of the systems tackle problems specific to one or more of the partners and thus may not be useful outside this environment. However, the results of the work are still pertinent to analysts wishing to build their own systems. These results are described, however, the emphasis of the paper is on those systems developed for method validation.Method validation for HPLC is a complex task which requires many characteristics of the method to be tested, e.g. accuracy, precision, etc. The expert systems built within ESCA concern the validation of precision. Two systems were developed for repeatability testing and ruggedness testing. The method validation process can be divided into several discrete stages, these include: (1) The selection of the method feature to test, for instance which factors can influence the ruggedness of a method. (2) The definition of a test procedure, for instance an efficient statistical design. (3) The execution of experiments and the interpretation of results. (4) A diagnosis of any observed problem. This paper describes these two systems in some detail and summarises some of the results obtained from their evaluation. It concludes that expert systems can be useful in solving analytical problems and the integration of several expert systems can provide extremely powerful tools for the analyst.     

Comparison of RAFT‐derived poly(vinylpyrrolidone) verses poly(oligoethyleneglycol methacrylate) for the stabilization of glycosylated gold nanoparticles

Carbohydrates dictate many biological processes including infection by pathogens. Glycosylated polymers and nanomaterials which have increased affinity due to the cluster glycoside effect, are therefore useful tools to probe function, but also as prophylactic therapies or diagnostic tools. Here, the effect of polymer structure on the coating of gold nanoparticles is studied in the context of grafting density, buffer stability, and in a lectin binding assay. RAFT polymerization is used to generate poly(oligoethyleneglycol methacrylates) and poly(N‐vinylpyrrolidones) with a thiol end‐group for subsequent immobilization onto the gold. It is observed that poly(oligoethylene glycol methacrylates), despite being widely used particle coatings, lead to low grafting densities which in turn resulted in lower stability in biological buffers. A depression of the cloud point upon nanoparticle immobilization is also seen, which might compromise performance. In comparison poly(vinylpyrrolidones) resulted in stable particles with higher grafting densities due to the compact size of each monomer unit. The higher grafting density also enabled an increase in the number of carbohydrates which can be installed per nanoparticle at the chain ends, and gave increased binding in a lectin recognition assay. These results will guide the development of new nanoparticle biosensors with enhanced specificity, affinity, and stability. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55, 1200–1208