Josef Dadok

27Al and29Si magic angle spinning nuclear magnetic resonance spectroscopy of Al-substituted tobermorites

Solid-state27Al and29Si NMR spectroscopy with magic angle spinning (MAS) of samples was used to study several 1.13 nm tobermorites, most of which were deliberately substituted with aluminium.27Al MASNMR clearly showed that aluminium is tetrahedrally co-ordinated in tobermorite structures. In addition two different aluminium environments resonating at ∼ 57 and 64 ppm from [Al(H2O)6]3+ were detected.29Si MASNMR of pure, anomalous tobermorites showed resonances at −85.7 and −95.7 ppm from tetramethylsilane representing chain middle groups (Q2) and branching sites (Q3), respectively. Anomalous Al-substituted tobermorites, on the other hand, showed two to four resonances representing different silicon environments. One Al-substituted tobermorite showed two resonances at −84.6 and −91.5 ppm which were assigned to Q2(0 Al) and Q3 (1 Al), respectively. In the above tobermorite aluminium appeared to have substituted into branching sites only. Two other Al-substituted tobermorites, however, showed four distinct resonances at ∼ −82.0, −85.2, −92.0 and −96.0 and these were assigned to Q2 (1 Al), Q2 (0 Al), Q3 (1 Al) and Q3 (0 Al), respectively. Thus these two tobermorites showed substitution of aluminium in the chain middle groups as well as branching sites. Another Al-substituted tobermorite which showed a normal thermal behaviour exhibited, as expected, only Q2(0 Al) and Q2 (1 Al) sites resonating at −84.7 and ∼ −80.2 ppm, respectively. No Q3 sites were detected because few or no branching sites are present in this normal tobermorite. The results reported here clearly demonstrate the usefulness of solid-state27Al and29Si MASNMR spectroscopy for the investigation of short-range order in alumino-silicate materials.

Synthetic approaches to regioisomerically pure porphyrins bearing four different meso-substituents

Abstract Regioisomerically pure porphyrins bearing four different meso -substituents have been synthesized via a 9-step route starting from pyrrole and carbonyl-containing compounds. This synthesis builds on a one-flask synthesis of 1,9-unsubstituted dipyrromethanes. An acyl group is introduced selectively in the 1-position of the dipyrromethane by use of an acid chloride and the dipyrromethane Grignard reagent, which resembles the pyrrole Grignard reagent. In contrast to the 2- and 5-positions of a monomeric pyrrole, the 1- and 9-positions of a dipyrromethane are relatively non-interacting and can be functionalized independently. A 2-aryl-1,3-benzoxathiolium tetrafluoroborate, available from carbonyl containing compounds, serves as a latent acyl equivalent and alkylates regiospecifically the 9-position of a 1-acyldipyrromethane. Alternatively the 1- and 9-positions of a dipyrromethane can be functionalized independently by successive alkylations with two different 2-aryl-1,3-benzoxathiolium tetrafluoroborates. Hydrolysis of the mono or di(benzoxathiolyl)dipyrromethane followed by reduction of the 1,9-diacyl-dipyrromethane affords the corresponding dipyrromethane-diol. An acid-catalyzed MacDonald-type 2 + 2 condensation of the dipyrromethane-diol and a 1,9-unsubstituted dipyrromethane at room temperature followed by oxidation with DDQ gives the porphyrin bearing four different meso -substituents. The reaction sequence resulted in a single porphyrin isomer without acidolytic scrambling of the four meso -substituents. The porphyrin structures were confirmed by laser desorption mass spectrometry and by high field high resolution proton NMR spectroscopy. An entire synthesis can be performed in about two weeks. The controlled stepwise synthesis of porphyrins bearing four different meso -substituents should enable preparation of multi-functionalized porphyrin building blocks for application in the synthesis of bioorganic model systems.

Chemical characterization of a prominent phosphomonoester resonance from mammalian brain. 31P and 1H NMR analysis at 4.7 and 14.1 tesla

A prominent 31P NMR resonance at 3.84 ppm in mammalian brain has been identified as ethanolamine phosphate. The identification was based on 1H and 31P NMR findings (including pH titrations) at 4.7 and 14.1 T, as well as thin-layer chromatography studies. We previously incorrectly assigned the 3.84 ppm resonance to ribose-5-phosphate. The incorrect assignment occurred because the two compounds have very similar 31P chemical shifts, and because we did not carefully consider the effects of counter ions and ionic strengths when interpreting the 31P chemical shifts. In separate preliminary studies we have demonstrated ethanolamine phosphate to be high in immature developing brain and in the degenerating brain of Alzheimers and Huntingtons disease patients. Ethanolamine phosphate may therefore serve as a sensitive marker of membrane phospholipid turnover for both in vitro and in vivo 31P NMR studies.