Benzomorphan related compounds. XIV. Synthesis of 2-(2-pyrrolylmethyl)- and 2-(2-indolylmethyl)tetrahydropyridines and cyclization to pyrrolo[3,2-f]morphans

The synthesis of 2-{2-pyrrolylmethyl)- and 2-(2-indolylmethyl)tetrahydropyridines by condensation of 2-cyanopyridines with appropriate pyrrole or indole derivatives followed by ketone reduction, quaternization and sodium borohydride reduction are described. The acid-induced cyclization of 2-(2-pyrrolylmethyl)tetrahydropyridines affords 4,5,6,7,8,9-hexahydro-4,8-methanopyrrolo[2,3-d]azocine systems (pyrrolo[3,2-f]-morphans), although the method fails with N-benzyl substituted pyrroles. The acid treatment of 2-(2-indolylmethyl)tetrahydropyridines and of 2-indolyl tetrahydro-2-pyridyl ketones is not a suitable procedure for the preparation of indolo[3,2-f]morphans, because of the protonation of indole nucleus or carbonyl group, respectively.     

Encapsulation of the ferritin protein in sol-gel derived silica glasses

A significant recent development in sol-gel science has been the encapsulation of biomolecules such as proteins and enzymes in optically transparent silica glasses. This paper reports on the encapsulation of an iron (Fe) storage protein, ferritin, to develop a magnetic silica glass. Native ferritin, which has a nanometer-sized microcrystalline Fe oxide core, was encapsulated in optically transparent silica glasses using the sol-gel process. Fe could be released from ferritin but could not be reconstituted into apoferritin when the protein was trapped in the pores of the glass. Transmission electron microscopy of ferritin-doped aged silica gels indicated that crystallinity of the Fe oxide core was retained upon sol-gel encapsulation. Magnetic measurements on ferritin-doped silica gels indicated the material to be paramagnetic, but not superparamagnetic.     

Synthesis and comprehensive characterizations of new cis-RuL(2)X(2) (X = Cl, CN, and NCS) sensitizers for nanocrystalline TiO(2) solar cell using Bis-phosphonated bipyridine ligands (L)

The preparation and the properties of several ruthenium complexes of the general formula cis-RuL(2)X(2) with L = 2,2'-bipyridine-4,4'-bisphosphonic acid, L' = 2,2'-bipyridine-5,5'-bisphosphonic acid, and X = Cl, CN, or NCS are reported. The synthesis of these complexes relies on the preparation of the key intermediates cis-Ru(bipyridinebis(diethyl ester phosphonate))Cl(2). The ground-state second pK(a) values of the thiocyanato complexes were determined and are 6.0 and 6.1 for cis-RuL(2)(NCS)(2) and for cis-RuL'(2)(NCS)(2), respectively. For these species, (13)C NMR and IR demonstrate that the thiocyanato ligands are bound to Ru via the N atom. The new complexes exhibit a blue-shifted electronic absorption spectrum with respect to the analogous complexes containing carboxylic acid groups. Density functional theory molecular orbital calculations show that the LUMO of the bipyridine phosphonated ligands is at higher energy than the corresponding dicarboxylate complexes and that the thiocyanato ligands are not simple spectator ligands, whose role is to enrich electron density on the ruthenium, but are also involved in transitions from PiRu-NCS to Pibpy that extend the absorbance of the dye in the low energy part of the absorption spectrum. The photoaction spectra recorded in a sandwich regenerative photovoltaic cell indicate that the cyano and thiocyanato complexes containing the bipyridine substituted in 4,4' positions exhibit a 90-95% photoconversion efficiency on the MLCT band, whereas those containing the bipyridine substituted in 5,5' positions display lower efficiency (60-65%). The most efficient complex in the series is cis-RuL(2)(NCS)(2); however, its overall efficiency is about 30% lower than the analogue cis-Ru(H(2)dcb)(2)(NCS)(2) (H(2)dcb = 2,2'-bipyridine-4,4'-dicarboxylic acid) due to a lower absorbance in the red part of the visible spectrum.     

Enantioselective formal synthesis of uleine alkaloids from phenylglycinol-derived bicyclic lactams

A two-step route for the enantioselective construction of the tetracyclic ring system of uleine alkaloids, involving the stereoselective conjugate addition of an appropriate indole-containing nucleophile to a chiral bicyclic delta-lactam and the subsequent cyclization on the indole 3-position of the resulting 4,5-disubstituted 2-piperidone, has culminated in the formal total synthesis of several alkaloids of this group.     

Enantioselective synthesis of cis- and trans-3,5-disubstituted piperidines. Synthesis of 20S- and 20R-dihydrocleavamine

[reaction: see text] Diastereoselective alkylation at the carbonyl alpha-position of chiral nonracemic lactams 2 and 3, the former prepared by cyclocondensation of (R)-phenylglycinol with a racemic gamma-substituted delta-oxoester in a process that involves a dynamic kinetic resolution and the latter by a subsequent equilibration, provides access to enantiopure cis- and trans-3,5-disubstituted piperidines. The usefulness of the approach is illustrated with the synthesis of the alkaloids 20S- and 20R-15,20-dihydrocleavamine.     

Nitrogen Sorption Studies of Silica Particles Obtained in Emulsion and Microemulsion Media

The internal surface structures of silica aerogel particles synthesized using different catalysts in emulsion and microemulsion media have been investigated by means of N(2) adsorption and desorption isotherms. Surface fractal dimensions have been computed using different methods: Frankel-Halsey-Hill plots of the adsorption isotherms, the thermodynamic fractal isotherm equation, and a modification of the thermodynamic fractal isotherm equation. Silica aerogels synthesized in emulsion media with an acidic catalyst have a high specific surface area without micropores and show two separate ranges of scales where the surface fractal dimensions are different and constant. Silica aerogels synthesized in emulsion media with a basic catalyst have a moderate specific surface area with a high percentage of micropores and show constant surface fractal dimensions over a larger range. Silica aerogels synthesized in microemulsion media with a basic catalyst have a low specific surface area with a moderate percentage of micropores and show a moderate range of scales over which the surface fractal dimension is constant. Analyses by both the thermodynamic and modified thermodynamic methods give similar ranges of the surface fractal dimensions of the silica particles. Copyright 2000 Academic Press.     

About the calculation of exchange coupling constants using density-functional theory: the role of the self-interaction error

The effect of the correction of the self-interaction error on the calculation of exchange coupling constants with methods based on density-functional theory has been tested in simple model systems. The inclusion of the self-interaction correction cancels the nondynamical correlation energy contributions simulated by the commonly used functionals. Hence, such correction should be important in the accurate determination of exchange coupling constants. We have also tested several recent functionals to calculate exchange coupling constants in transition-metal complexes, such as meta-GGA functionals or new formulations of hybrid functionals. The influence of the basis set and of the use of pseudopotentials on the calculated J values has also been evaluated for a Fe(III) dinuclear complex in which the paramagnetic centers bear several unpaired electrons.     

Kinetic investigation of the sorption of water by barium chloride monohydrate

Using thermogravimetry under controlled water vapour pressure, the kinetics for the rehydration reaction BaCl₂·H₂O(s) + H₂O(g) → BaCl₂ · 2 H₂O(s) was investigated as a function of various parameters of relevance in chemical heat pumps, i.e. the number of cycles, storage time, extent of dehydration, and particle size. The effect of cycling is interpreted in terms of a fragmentation process, as confirmed by scanning electron microscopy studies. Reaction rate isotherms were determined at four different temperatures (34.5, 40.3, 44.5 and 50.5°C), in the pressure range 18–66 torr. An inhibition pressure domain is observed. This effect is assumed to result from the formation of capillary condensed water. The presence of adsorbed water is clearly evidenced by wide-line NMR measurements.     

Preparation of acentric porous coordination frameworks from an interpenetrated diamondoid array through anion-exchange procedures: crystal structures and properties

The formation, crystal structures, and properties of a series of three-dimensional (3-D) Cu(II) coordination polymers, [[Cu(L)2(H2O)2](PF6)2(H2O)(1.25)]n (1), [[CuL(N3)2](H2O)(1.5)]n (2), and [[CuL(H2O)(SO4)](H2O)2]n (3), with an angular bridging ligand 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (L) are reported. Complex 1 crystallizes in the tetragonal I4(1)/a space group (a = b = 13.462(2) A, c = 46.47(1) A, Z = 8), complex 2 in the orthorhombic Pna2(1) space group (a = 6.379(2) A, b = 10.060(3) A, c = 27.232(9) A, Z = 4), and complex 3 in the orthorhombic P2(1)2(1)2(1) space group (a = 5.510(2) A, b = 10.576(4) A, c = 28.34(1) A, Z = 4). Different polymeric frameworks are obtained by only varying the counterions. These include the 2-fold interpenetrated diamondoid structure of 1, the acentric alpha-Po network of 2, and the chiral open framework of 3 with (6(3)).(6(9).8) topology. The interesting anion-exchange, porous, and magnetic properties of these coordination supramolecules have been investigated in detail.