Christine Cordier

XPS, NMR and FTIR structural characterization of polysiloxane-immobilized amine ligand systems

Abstract The polysiloxane-immobilized monoamine ligand systems were made by hydrolytic polycondensation of Si(OEt) 4 and (EtO) 3 Si(CH 2 ) 3 NH 2 . These materials were examined by XPS, FTIR and NMR techniques. The analysis indicates that the amine ligand groups almost exist in the free form in the alkaline media and in the cation form in the acid media. 13 C NMR and FTIR spectra combined with the XPS results shows that there is some leaching of small oligomeric ligand containing groups from the siloxane network.

Hydrogen bonding and solvent effects in heteroaryldi(1-adamantyl)methanols: an NMR and IR spectroscopic study

Reaction of the organolithium derivatives of certain heteroaromatics [2-furanyl, 2-thienyl, 2-thiazolyl, 2-pyridyl and 2-(3-methylpyridyl)] with di(1-adamantyl) ketone gives potentially rotameric tertiary alcohols. With 2-pyridyl- and 2-(3-methylpyridyl)lithium only the syn isomer is obtained. The syn isomer makes up 85–100% of (2-furanyl)diadamantylmethanol and 80–90% of the 2-thienyl derivative, depending on the NMR solvent. In chloroform or benzene the 2-thiazolyl derivative is a 2∶1 mixture, the isomer with the sulfur atom syn to the OH group predominating; in DMSO or in the solid state this is the sole species. The IR absorption frequency for OH stretching correlates with the corresponding proton NMR shift in chloroform and with its temperature dependence, Δδ/ΔT. In pyridine Δδ/ΔT is either large (–20 ppb/°C) or small (–1 to –2 ppb/°C) for intermolecular and intramolecular hydrogen-bonded species, respectively. Semi-empirical calculations (AM1 and PM3) suggest that the anti alcohols should be the more stable in the gas phase, but solvent effects and hydrogen bonding, in the case of the pyridyl derivatives, appear to reverse this situation, making the isomer with OH syn to the heteroatom the principal, and sometimes the only, species observed in solution.

Covalent binding of a bridged pyridinium aldehyde with the self-complementary decamer [d(ATGACGTCAT)]2. Gel analysis, MALDI mass spectrometry and NMR studies

Gel analysis, MALDI-TOF mass spectrometry and NMR spectroscopy show that a tethered pyridinium aldehyde, from a new class of DNA-interacting agents, binds to the self-complementary [d(ATGACGTCAT)]2 decamer. The reaction proceeds via a two-step pathway: fast non-covalent outside association (complex formation) is followed by slow covalent addition (adduct formation) upon temperature increase. Both interactions occur mainly at the central CpG in the oligonucleotide, the latter leading finally to the reversible formation of an aminal through nucleophilic attack of the exocyclic guanine amino group in the minor groove of the helix.

Thermal fragmentation of 1-substituted spiro[adamantane-2,2′-adamantane] derivatives

Thermolysis of 1-hydroxy- or 1-acetoxy[1]diadamantane gives mixtures of 3-(adamantylidene)-bicyclo[3.3.1]non-6-ene,3, 3-(2-adamantyl)bicyclo[3.3.1]nova-2,6- and -2,7-dienes, 4, and 2-(3-noradamantyl)-2,4-dehydroadamantane, 7. At low conversion 3 and 7 are the major products, while one isomer of 4, the 2,6-diene, predominates in the equilibrium mixture. Pd/C-catalysed hydrogenation of the dienes in ethanol gives first 3-(2-adamantyl)bicyclo[3.3.1]non-2-ene, 5, and then endo-3-(2-adamantyl)bicyclo[3.3.1]nonane, 6. Hydrocarbon 7 is not hydrogenated under these conditions; it is converted into a mixture of 3 and 4(2,6) upon heating. Mechanisms for the fragmentation of the 1-[1]diadamantyl carbocation are discussed. While a 1,4-hydride shift may contribute to the reactions of the [1]diadamantane system, molecular mechanics calculations suggest that the ready formation of an olefin from 1-hydroxyspiro [adamantane-2,9′-bicyclo[3.3.1]nonane] is best interpreted in terms of a 1,5-hydride shift involving the chair-boat conformation of the bicyclononane system.

Thermal rearrangement of 1-substituted spiro[adamantane-2,2′-adamantane] derivatives

Tertiary 1-halospiro[adamantane-2,2′-adamantane] derivatives (1-halo[1]diadamantanes) have been synthesised by reaction of the 1-[1] diadamantyl cation with appropriate nucleophiles. Thermolysis of 1-chloro- or 1-bromo-[1]diadamantane, but not the 1-fluoro derivative, gives the corresponding secondary 4-halo derivative in good yield. By 1H and 13C NMR spectroscopy and by X-ray crystallography it has been established that the 4-bromo [1]diadamantane isolated is the anti isomer, with the Br–C–C–Cspiro torsion angle close to 170°, this being the less strained of the two possible 4-substituted isomers, according to molecular mechanics calculations. Possible mechanisms for the rearrangement are discussed.