Megalo-Cavitands: Synthesis of Acridane[4]arenes and Formation of Large, Deep Cavitands for Selective C70 Uptake.

Deep cavitands, concave molecular containers, represent an important supramolecular host class that has been explored for a variety of applications ranging from sensing, switching, purification and adsorption to catalysis. A major limitation in the field has been the cavitand volume that is restricted by the size of the structural platform utilized (diameter approx. 7 Å). We here report the synthesis of a novel, unprecedentedly large structural platform, named acridane[4]arene (diameter approx. 14 Å), suitable for the construction of cavitands with volumes of up to 814 Å3 . These megalo-cavitands serve as size-selective hosts for fullerenes with mM to sub-µM binding affinity for C60 and C70 . Furthermore, the selective binding of fullerene C70 in the presence of C60 was demonstrated.

Xanthene[n]arenes: Exceptionally Large, Bowl-Shaped Macrocyclic Building Blocks Suitable for Self-Assembly.

A new class of macrocycles denoted as "xanthene[n]arenes" was synthesized. In contrast to most other macrocycles, they feature a conformationally restricted bowl shape due to the attached alkyl groups at the linking methylene units. This facilitates the synthesis of cavitands and the self-assembly to molecular capsules via noncovalent interactions. The derivatization potential of the novel macrocycles was demonstrated on the xanthene[3]arene scaffold. Besides a deep cavitand and an oxygen-embedded zigzag hydrocarbon belt[12]arene, a modified macrocycle was synthesized that self-assembles into a hydrogen-bonded tetrameric capsule, demonstrating the potential of xanthene[n]arenes as a new set of macrocyclic building blocks.

Interaction of Cm(III) with human serum albumin studied by time-resolved laser fluorescence spectroscopy and NMR.

The complexation of Cm(III) with human serum albumin (HSA) was investigated using time-resolved laser fluorescence spectroscopy (TRLFS). The Cm(III) HSA species is dominating the speciation between pH 7.0 and 9.3. The first coordination sphere is composed by three to four H2O molecules and five to six coordinating ligands from the protein. For the complex formation at pH 8.0 a conditional stability constant of logK = 6.16 ±â€¯0.50 was determined. Furthermore, information on the Cm(III) HSA binding site were obtained. With increasing Cu(II) concentration the Cm(III) HSA complexation is suppressed whereas the addition of Zn(II) has no effect. This points to the complexation of Cm(III) at the N-terminal binding site (NTS) which is the primary Cu(II) binding site. NMR experiments with Cu(II), Eu(III) and Am(III) HSA show a decrease of the peak assigned to the His C2 proton of His 3, which is part of the NTS, with increasing metal ion concentration. This confirms the complexation of Eu(III) and Am(III) at the Cu(II) binding site NTS. The results presented in this study contribute to a better understanding of relevant biochemical reactions of incorporated actinides.