Carotenoids and Related Compounds. Part 36.. Further syntheses of zeaxanthin and rhodoxanthin

A modification of a previously reported synthesis of zeaxanthin ( 1 ), and routes to both zeaxanthin and rhodoxanthin ( 2 ) from α-ionone, are described.     

Calculation of the static and dynamic triaxial shapes of 24Mg

The Skyrme interaction is used in a Hartree-Fock calculation of ²⁴Mg with triaxial symmetry. A transition between axial and triaxial shapes is studied as a function of the spin-orbit strength. The effect of the other components of the interaction on the shape of ²⁴Mg is examined. Constrained Hartree-Fock calculations of the energy surface and the cranking mass parameter are used for the calculation of the intrinsic γ-vibration. The main result of the dynamical calculation is that despite the different equilibrium shapes obtained with the two forces SIII and SV, the triaxiality obtained by considering the zero-point γ-oscillation is essentially the same for both forces.     

Energy surfaces,collective potentials and collective inertia parameters

The Hill-Wheeler equation is used to derive a collective Hamiltonian from an energy surface. Two simple ansatz are proposed for the collective Hamiltonian, which is then calculated explicitly in a hierarchy of approximations. The consistency of the method is verified in an illustrative example.     

The quantitation of butyltin and cyclohexyltin compounds in the marine environment of British Columbia

A HPLC/GF AA procedure based on the use of C-18 columns is described for the quantitation of butyltin species in marine samples. When a mass spectrometer was used as detector (HPLC MS), evidence was obtained for the presence of other tin compounds in the samples. Extracts of samples were treated with CH₃MgBr and examined by using GC MS; the presence of Bu_nSnMe_4?n (n = 3–1, Bu = butyl) and Cy_nSnMe_4?n (n = 3,2, Cy = cyclohexyl) was confirmed in the derivatized seawater, bivalve flesh, and bivalve shell samples. Quantitative data are given for butyl- and cyclohexyl-tin species in seawater and the surface microlayer, and oyster flesh.     

Polyhalogenoaromatic compounds : XXXV. Metal-halogen exchange between n-butyllithium and polyhalogenobipyridines

Metal—halogen exchange between n-butyllithium and 2,2'-dibromohexachloro-4,4,bipyridine takes place at the 2- and 2'-positions; no rearrangement leading to 3-(5-)lithiobipyridines is observed. In the transition state for the metal—halogen exchange reaction the substrate probably has partial carbanionic character.     

On the interpretation of negative collective masses

The occurrence of a negative mass in the effective Hamiltonian governing a collective degree of freedom can be understood as indicating the presence of a nonlocal effective Hamiltonian. The practical consequences of such a situation are analyzed.     

Structural study by NMR of an oxorhenium-RGD decapeptide complex for application in radiotherapy

The decapeptide Arg-Gly-Asp-Ser-Cys-Arg-Gly-Asp-Ser-Tyr, which contains two Arg-Gly-Asp (RGD) moieties in its sequence, has been successfully labeled with radioactive rhenium (Re-188) yielding a single, stable oxorhenium complex. This complex is being evaluated for possible application in oncology as a target-specific radiotherapeutic agent, because its radioactive technetium-99m analogue has already been applied for the scintigraphic detection of malignant melanoma in humans. For structural characterization purposes, the complex of the decapeptide was synthesized at the macroscopic level using nonradioactive rhenium (Re-185/Re-187). NMR and mass spectral analysis of the nonradioactive oxorhenium complex revealed that the decapeptide coordinates to the oxorhenium core through the N(amide) of Asp3, the N(amide) of Ser4, and the N(amide) and S(thiolate) atoms of Cys5 to form a complex of the ReO[N(3)S] type.     

On Discrete Painlevé Equations Associated with the Lattice KdV Systems and the Painlevé VI Equation

A new integrable nonautonomous nonlinear ordinary difference equation is presented that can be considered to be a discrete analogue of the Painlevé V equation. Its derivation is based on the similarity reduction on the two-dimensional lattice of integrable partial differential equations of Korteweg–de Vries (KdV) type. The new equation, which is referred to as generalized discrete Painlevé equation (GDP), contains various "discrete Painlevé equations" as subcases for special values/limits of the parameters, some of which have already been given in the literature. The general solution of the GDP can be expressed in terms of Painlevé VI (PVI) transcendents. In fact, continuous PVI emerges as the equation obeyed by the solutions of the discrete equation in terms of the lattice parameters rather than the lattice variables that label the lattice sites. We show that the bilinear form of PVI is embedded naturally in the lattice systems leading to the GDP. Further results include the establishment of Bäcklund and Schlesinger transformations for the GDP, the corresponding isomonodromic deformation problem, and the self-duality of its bilinear scheme.