A versatile synthesis of new pyrimidinyl nitronyl nitroxides.

Pyrimidinyl nitronyl nitroxides where the bis-N-oxy fragment is included in a six-membered ring were prepared from diacetonamine by a sequence of reactions including a Grignard reaction, a Ritter reaction and oxidation of the intermediate pyrimidine; the properties of the 2-phenyl-substituted representative are fully described.

Cahn-Ingold-Prelog descriptors of absolute configuration for carbon cages.

A simplified procedure is described for assigning Cahn-Ingold-Prelog descriptors to stereocentres in spheroalkanes (the CnHn molecules, with n even, based on trivalent, polyhedral carbon frameworks, a class which subsumes the fulleranes). By extension, similar descriptors can be found for the atoms of fullerenes and related carbon-only molecules. Assignment maps are given for chiral fullerenes C28 C76, C78, C84 and C140, and for a number of spheroalkanes. Cases of breakdown of the simple procedure for triangle-rich spheroalkane molecular graphs are discussed.

Chirality and symmetry aspects of spheroarenes, including fullerenes.

The design of the smallest spheroarenes (C(N) molecules based on trivalent polyhedral framework, a class which subsumes fullerenes) of any point-group symmetry is presented. The role of Curie's principle is discussed. Some molecules whose carbon backbone is a nonplanar graph are described.

Fullerenes as tilings of surfaces

If a fullerene is defined as a finite trivalent graph made up solely of pentagons and hexagons, embedding in only four surfaces is possible: the sphere, torus, Klein bottle, and projective (elliptic) plane. The usual spherical fullerenes have 12 pentagons; elliptic fullerenes, 6; and toroidal and Klein-bottle fullerenes, none. Klein-bottle and elliptic fullerenes are the antipodal quotients of centrosymmetric toroidal and spherical fullerenes, respectively. Extensions to infinite systems (plane fullerenes, cylindrical fullerenes, and space fullerenes) are indicated. Eigenvalue spectra of all four classes of finite fullerenes, are reviewed. Leapfrog fullerenes have equal numbers of positive and negative eigenvalues, with 0, 0, 2, or 4 eigenvalues zero for spherical, elliptic, Klein-bottle, and toroidal cases, respectively.

A stereospecific synthesis of (+/-)-5,8-disubstituted indolizidines and (+/-)-1,4-disubstituted quinolizidines found in poison frog skins.

An efficient, high-yield stereospecific route to three (+/-)-5, 8-disubstituted indolizidines, (209B (I), 209I (II), 223J (III)) and two (+/-)-1,4-disubstituted quinolizidines (207I (IV), 233A (V)), racemates of alkaloids found in the skins of neotropical and Madagascan poison frogs is reported. The structures of the natural alkaloids were thereby established by chiral GC comparison with the exception of indolizidine 209B (I) for which a natural 209B could no longer be detected.

Quantitative analysis of C60 fullerene in blood and tissues by high-performance liquid chromatography with photodiode-array and mass spectrometric detection.

A high-performance liquid chromatographic (HPLC) assay method for C60 fullerene, in blood, liver and spleen using photodiode-array detection or mass spectrometric detection (LC-MS) and C70 fullerene, as the internal standard, is described. The recovery from mouse blood and tissues spiked with micronized C60 exceeds 90%. The method is linear from 0.05 to 200 mg of C60 per liter of blood and from 0.05 to 5.00% of C60 per tissue weight. The limit of detection of the method is 0.1 ng of C60 per injection. This method was applied to mouse blood and tissue samples after intraperitoneal administration of a micronized C60 suspension.

Dynamic nuclear polarization with nitroxides dissolved in biological fluids.

The most widely used free radicals for dynamic nuclear polarization (DNP) experiments or related Overhauser imaging are nitroxides. The DNP parameters in biological fluids were measured in order to provide guidelines for the design of new nitroxides, adapted to the biological applications of DNP. Eighteen nitroxides were studied at a concentration of 1 mM. Extrapolation at complete electron paramagnetic resonance saturation and proton longitudinal-relaxation-time measurements enable calculation of the coupling factor between nitroxide free electrons and water protons. In deoxygenated phosphate-buffered solutions, the NMR signal enhancement by DNP ranged from -36.3 to -6.7, and the coupling factor ranged from 0.31 to 0.03. Nitroxides with a long side chain yield poor enhancement, although their relaxivity is far greater than that of nitroxides with small chains. In a 1 mM albumin solution, the loss in enhancement factor is mainly caused by the fact that proton relaxation occurs via interactions, not only with the dissolved free radicals but also with the albumin macromolecules. In serum, the enhancement factor is lower than that in an albumin solution, because of the higher protein concentration in serum. In red-blood-cell suspensions, the enhancement factor was further decreased. Two effects contribute to this decrease: first, the increased viscosity due to the presence of red blood cells, and second, the susceptibility effects of the paramagnetism of deoxyhemoglobin. The high sensitivity to oxygen of DNP in phosphate-buffered solution is also greatly reduced when nitroxides are dissolved in blood.(ABSTRACT TRUNCATED AT 250 WORDS)