Synthesis and Conformations of Dendronized Poly(L-lysine)

Dendronized polymers based on a poly(L-lysine) backbone have been synthesized up to the fourth generation. The hydroxyl-terminated polymers are completely water-soluble, which makes them good candidates for drug delivery applications. The dendronized polypeptide backbones are helical at lower generations, but undergo a dramatic conformational change from alpha-helical to disordered upon increasing the dendron size to the third generation. This conformational change, attributed to steric repulsions between dendrons, is supported by spectroscopic measurements while chain extension upon dendronization is confirmed by scanning force microscopy.     

Crystallographic report: [1,3‐Di(mestityl)imidazol‐2‐ylidene]gallium iodide dihydride

The structure of the N‐heterocyclic gallium hydride complex, [GaH₂I{CN(Mes)C₂H₂N(Mes)}], Mes = mesityl, shows both hydride ligands to be bonded to the distorted tetrahedral gallium centre. Copyright © 2003 John Wiley & Sons, Ltd.     

Improved (1s)<Superscript>2</Superscript> variational model for helium

The ground-state energy of neutral helium is estimated variationally with a trial wavefunction of the form ϕ≈e ^−γ(rA/a _o)ⁿe^−γ(rB/a _o)ⁿ. This model represents a modification of traditional textbook examinations of this problem via inclusion of the power “n” as a second nonlinear variational parameter in addition to the usual effective nuclear charge γ and leads to an upper-limit on the ground state energy of −2.86107 E _h (E _h =1 hartree) in comparison with the traditional (n=1) result of −2.84766 E _h . This result represents a reduction of the percentage overestimate from the true ground-state energy (−2.90373 E _h ) of from 1.93 to 1.47. In comparison with the maximum accuracy obtainable from an uncorrelated trial wavefunction, −2.86168 E _h , the present trial wavefunction reduces the percentage overestimate from 0.49 (n=1) to 0.021. The optimum values of (n, γ) are determined to be ≈(0.897, 1.825).     

Mass spectrometric investigation of polyfluorinated C60. Evidence for the existence of C60F2n (n = 0–30)

Electron-capture negative ion chemical ionization (EC-NICI) and field desorption (FD) mass spectrometric techniques were utilized to examine polyfluorinated C₆₀. Two different samples from the same preparation, one prior to sublimation and the other sublimed material, were investigated. From the raw non-sublimed product in EC-NCI six series of ions corresponding to different numbers of attached oxygen atoms were obtained, which are represented by the formula [C₆₀F_2nO_m]^?, where n ranged from 0 to 30 and m from 0 to 5. The sublimed material in EC-NICI produced the same six series of ions with up to 48 fluorine atoms attached to C₆₀. The field desorption of the same sample produced similar results, but the signal-to-noise ratios of the spectra were low. Both samples, in the two different techniques examined, yielded C₆₀F₆₀ ions with only an even number of fluorine atoms attached. The present investigation, for the first time, provides direct experimental evidence for the existence of higher fluorinated C₆₀ up to C₆₀F₆₀ and multiple oxides of polyfluoro-C₆₀ with up to five oxygen atoms attached.     

Extending symmetric designs

If a symmetric 2-design with parameters (v, k, λ) is extendable, then one of the following holds: v = 4λ + 3, k = 2λ + 1; or v = (λ + 2)(λ² + 4λ + 2), k = λ² + 3λ + 1; or v = 111, k = 11, λ = 1; or v = 495, k = 39, λ = 3. In particular, there are at most three sets of extendable symmetric design parameters with any given value of λ. As a consequence, the only twice-extendable symmetric design is the 21-point projective plane.     

On the partial geometry pg(6, 6, 2)

We give some new representations of the partial geometry pg(6, 6, 2), which was constructed by van Lint and Schrijver, show a connection with a strongly regular graph based on the ternary Golay code, and determine the automorphism group of the geometry.     

Regiochemistry of nucleophilic displacements in chloroquinones

Nucleophilic displacement of halide from 2-halo 1,4-quinones occurs at the $\text{ipso}$ carbon or at the carbon vicinal to it depending on the nature of the nucleophile and the solvent.     

Product integration methods for second-kind Abel integral equations

The construction and convergence of high-order product integration methods for the second-kind Abel equation are discussed and the results of De Hoog and Weiss are generalised. Backward difference methods are introduced, and numerical results are presented which verify the theoretical rates of convergence.