Observations on quasi-uniform products

We prove that any product of quotient maps in the category of quasi-uniform spaces and quasi-uniformly continuous maps is a quotient map. We also show that a quasi-uniformly continuous map from a product of quasi-uniform spaces into a quasi-pseudometric T₀-space depends on countably many coordinates.Furthermore we characterize those quasi-uniformities that are unique in their quasi-proximity class and prove that this property is preserved under arbitrary products in the category of quasi-uniform spaces.     

Nanoscopic phase-analysis of SiC containing BaTiO3-ceramic

The formation of fresnoite (Ba₂TiSi₂O₈) from BaTi_1.01O_3.02 by addition of SiC was investigated in the temperature range from 700 to 1350?°C. Solid state reactions at the interface of grains indicate a formation of fresnoite below the temperature of liquid-phase-formation at about 1250?°C.     

Synthesis and NMD A Antagonistic Properties of the Enantiomers of 4-(3-phosphonopropyl)piperazine-2-carboxylic acid (CPP) and of the unsaturated analogue (E)-4-(3-phosphonoprop-2-enyl)piperazine-2-carboxylic acid (CPP-ene)

The (R)- and (s)-enantiomers of 4-(3-phosphonopropyl)piperazine-2-carboxylic acid (D - and L -CPP, resp.; 15 and 16 , resp.), and of its unsaturated analogue (E)-4-(3-phosphonoprop-2-enyl)piperazine-2-carboxylic acid (D - and L -CPP-ene, resp.; 13 and 14 , resp.) were prepared. The absolute configuration of the enantiomers was determined by a chemical correlation of the menthyl ester 7 with D -asparagine. The affinity of these derivatives for the NMDA receptor was determined by displacement of [³H]CPP in rat cerebral cortical membranes. In two functional tests (the frog hemisected spinal cord preparation and the sodium efflux test from rat brain slices), D -CPP-ene appears to be the most potent, enantiomerically pure, competitive NMDA antagonist known to date.     

Conformational and NBO analysis on cis and trans isomers of methyl-1-(4-hydroxy-3-methoxyphenyl)-1,2,3,4-tetrahydro-9H-β-carboline-3-carboxylate

The cis and trans-methyl-1-(4-hydroxy-3-methoxyphenyl)-1,2,3,4-tetrahydro-9H-β-carboline-3-carboxylates were prepared and ¹H and ¹³C NMR spectra were recorded for both isomers. Conformational and NBO analysis were carried out for the cis and trans isomers. Conformer structures were pre-optimized using the hybrid method B3LYP along with the 6-311+G(d) basis set. Frequency calculations were employed to confirm the structures as minimum points. Potential energy surfaces (PES) were built at the same level of theory. Geometries obtained from DFT calculations were used to perform NBO analysis by the NBO 3.1 module in GAUSSIAN 03. The results obtained through theoretical calculations revealed that the shielding observed at C1 for the trans isomer can be attributed to carbomethoxy γ-effect, together with the hyperconjugative effect, while only hyperconjugative effects were found to explain the shielding of C3. The higher chemical shift value of C3 of the cis isomer was attributed to the carbonyl substituent, which plays an important role by capturing part of the electronic density in C3.     

Synthesis and nucleophilic substitution of stable 6-halo-pentafulvenes

The reaction of 2,4-di-t-butyl-cyclopentadiene-1-carbaldehyde with oxalyl chloride or oxalyl bromide provides stable 6-chloro- and 6-bromo-pentafulvenes, respectively. Several nucleophilic displacement reactions of the new compounds are described.     

A new approach towards redispersable polyelectrolyte–surfactant complex nanoparticles

Redispersable and weakly cross-linked block copolymer particles with a core-shell structure were prepared by the use of a macroinitiator. Subsequent sulfonation of the polystyrene core and complex formation with a variety of cationic surfactants led to sterically stabilized, redispersable polyelectrolyte-surfactant complex particles with spherical shape and diameters of about 400 nm. Spontaneous microphase separation of the hydrophobic surfactant tails and the hydrophilic entities of the polyelectrolyte and the surfactant headgroups induces mesostructure formation within the particle cores. The characteristic lengths of the mesostructures formed depend mainly on the chain lengths of the surfactants and vary between 2 and 4 nm. For the first time, preformed nanoparticles were used as constrained nanogeometries for polyelectrolyte-surfactant complex formation.     

Two-photon state selection and angular momentum polarization probed by velocity map imaging: application to H atom photofragment angular distributions from the photodissociation of two-photon state selected HCl and HBr

A formalism for calculating the angular momentum polarization of an atom or a molecule following two-photon excitation of a J-selected state is presented. This formalism is used to interpret the H atom photofragment angular distributions from single-photon dissociation of two-photon rovibronically state selected HCl and HBr prepared via a Q-branch transition. By comparison of the angular distributions measured using the velocity map imaging technique with the theoretical model it is shown that single-photon dissociation of two-photon prepared states can be used for pathway identification, allowing for the identification of the virtual state symmetry in the two-photon absorption and/or the symmetry of the dissociative state. It is also shown that under conditions of excitation with circularly polarized light, or for excitation via non-Q-branch transitions with linearly polarized light the angular momentum polarization is independent of the dynamics of the two-photon transition and analytically computable.