Asymmetric Organocatalytic Stepwise [2+2] Entry to Tetra‐Substituted Heterodimeric and Homochiral Cyclobutanes

An asymmetric synthesis of tetra‐substituted cyclobutanes involving an organocatalytic, stepwise [2+2]‐cycloaddition is described. The secondary‐amine‐catalyzed method allows for the hetero‐dimerization of two different cinnamic‐acid‐derived sub‐units, opening a novel one‐step assembly to densely functionalized, head‐to‐tail coupled dimeric cyclobutanes in high enantiomeric excess. A series of selective synthetic interconversions in these sensitive cycloadducts is also described.     

Thermal Decomposition of Fullerene Derivatives A Synthesis Method of New Fullerene Based Molecules

The thermal decomposition of methano-fullerene derivatives such as ethoxycarbonyl methano[60] fullerene and various isomers of bis-(ethoxycarbonyl methano)[60] fullerene leads to new fullerene derivatives, which have been preliminary characterized. The analysis of separated species was performed by UV-VIS, IR, H- and C-NMR, STM, FAB, LDI and MALDI-TOF MS spectroscopy. One of the isolated phases is a C₁₂₂ molecule with a dumbbell-like structure. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular and electronic structure of several heterofullerene BNC58 and B2N2C56 oligomers and [B2N2C56] n macromolecule

Molecular and electronic structure of heterofullerene BNC₅₈ (C _s) and B₂N₂C₅₆ (C _2h) monomers, B₂N₂C₁₁₆ and B₄N₄C₁₁₂ dimers, and B₆N₆C₁₆₈ trimer (the last three molecules withC _2h symmetry) was simulated by the MNDO method. Clusters BNC₅₈ and B₂N₂C₅₆ are formed by replacement of carbon atoms participating in one or two of the most distant oppositely lying (6,6)-type C−C bonds in fullerene C₆₀ by B and N atoms. In one of the two studied isomers of the B₂N₂C₁₁₆ dimer, the monomers are linked by the four-membered carbon cycle, while the heteroatoms form the most distant oppositely lying bonds of the dimer. In the other isomer of the B₂N₂C₁₁₆ dimer, as well as in the B₄N₄C₁₁₂ dimer and B₆N₆C₁₆₈ trimer, the monomers are linked by four-membered B₂N₂ cycles with alternation of the atoms. For all the systems studied, the optimum geometric parameters, heats of formation, ionization potentials, and atomic charges were calculated. Dimerization energies of heterofullerenes BNC₅₈ and B₂N₂C₅₆ lie in the range from 33 to 49 kcal mol⁻¹. It was found that the B₂N₂C₁₁₆ dimer, in which the monomers are linked by the four-mernbered carbon cycle, is the most stable system. In the case of B₂N₂C₅₆ trimerization, the energy gain (compared to the triple monomer energy) is about twice as large as the dimerization energy. Molecular structure of the quasi-linear [B₂N₂C₅₆) _n macromolecule was simulated, and extended Hückel calculations of its energy band structure by the crystal orbital method were performed. It was found that the electron energy spectrum is of semiconducting type (the band gap is equal to 1.27 eV. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 431–435, March, 1999.     

Double gyroid structures made of asymmetric dimers

Gyroid cubic phases are interesting for both scientists and engineers due to possible applications in electronic devices. New series of dimeric molecules, despite their flexible molecular structure, can display double gyroid cubic phase with Ia3d symmetry and lattice parameter corresponding to double molecular length. The cubic phase is structurally related to columnar phase and both phases often coexist in the same temperature window. Apparently, for studied compounds stronger molecular asymmetry promotes cubic structure. Interestingly, for the examined compounds the transition between two isotropic liquids was observed.     

High-Temperature Gas-Phase Electron Diffraction: Unexpected Dimer Structures Among Metal Halides

Gas-phase electron diffraction (GED) studies at high temperatures have several special common features that justify their separate discussion. Due to the difficulties connected with the experiment this technique has developed only in a few laboratories. Most often inorganic systems are studied; lower-valence metal halides and metal oxides. Their low volatility requires high-temperature experimental conditions. Due to the complex vapor composition, other techniques, such as quadrupole mass spectrometry and, to an increasing degree, quantum chemical calculations accompany these GED studies. The analyses often reveal unanticipated structures. In this paper some unexpected and interesting structures of metal halide dimers will be shown, some from GED, others from computations carried out in connection with the high-temperature GED studies of metal halide systems of low volatility.Dedicated to the memory of Professor Victor P. Spiridonov.     

Oxadiazole-based unsymmetrical chiral liquid crystal dimers: synthesis and mesomorphic properties

The synthesis and liquid crystalline properties of novel chiral Schiff's base dimers containing the 1,3,4-oxadiazole ring are reported. The length of the terminal S-alkyl chain has been varied. All the compounds synthesised were thermally stable and exhibited enantiotropic mesomorphism, showing either SmC*–SmA–TGB–N*–BP or SmC*–SmA phase sequence.     

Taxol Inclusion Complexes with a Cyclodextrin Dimer: Possibilities to Detoxify Chemotherapeutics and to Target Drugs Specifically to Tumors?

The natural drug, paclitaxel (taxol), is highly effectiveas a tumor chemotherapeuticwith a low probability of inducing chemoresistance,but shows severe toxic side effectsat the therapeutic dose. How can this toxicitybe overcome? Here we report the synthesisof cyclodextrin dimers connected at thesecondary face by amide-bonded aliphatic spacers. The spacer length of one of the dimers referred to asdiβCD(2N-A4C5A4) or dimer 7cmatches the distance between the twobenzoic acid residues of paclitaxel. We investigated the physical inclusion of taxol into this dimer using the TNS-label competition method. Affinity constants with the dimer in comparison to free β-cyclodextrin are found to be of the order of 10⁷ l/mole.When included into the cyclodextrin dimer, the drug shows a considerable time delay of incorporation into human tumor cell cultures (OAT SCLC cells) or a total exclusion from the cells. This is the prerequisite to avoid intoxication of other organs of a patient. Possibilities are discussed to detoxify chemotherapeutics and to target their inclusioncomplexes specifically to tumors using specific biological signals.     

Preparation,spectral and thermal properties of new Isoflavone derivatives: mesomorphic properties and DFT studies

The four new homologous series of symmetric Isoflavon dimers were synthesised using varied alkyl/aryl diamines in linear sense. The chemical structures of the molecules were characterised by IR, NMR and CHNS analysis. Further, Liquid crystalline properties were verified using the combination of differential scanning calorimetry (DSC) and polarised optical microscope (POM). The molecular systems studied here reveal that LC property depends on the length of the middle connecting diamine spacer along with terminal alkyl spacer. The lower members favour to exhibit smectic A phase, whereas higher members exhibit nematic mesophase. The nature of LC property behaviours is supported by molecular geometries studied by DFT calculations.