Molecular storage solutions for incorporating small molecules in crystalline matrices are of interest in the context of structure elucidation, decontamination, and slow release of active ingredients. Here we report the syntheses of 1,3,5,7-tetrakis(2,4-dimethoxyphenyl)adamantane, 1,3,5,7-tetrakis(4-methoxyphenyl)adamantane, 1,3,5,7-tetrakis(4-methoxy-2-methylphenyl)adamantane, and 1,3,5,7-tetrakis(4-methoxy-2-ethylphenyl)adamantane, together with their X-ray crystal structures. All four compounds crystallize readily. Only the octaether shows an unusual level of (pseudo)polymorphism in its crystalline state, combined with the ability to include a number of different small molecules in its crystal lattices. A total of 20 different inclusion complexes with guest molecules as different as ethanol or trifluorobenzene were found. For nitromethane and benzene, schemes for uptake and release are presented.
Tetrakis(dimethoxyphenyl)adamantane (TDA) readily forms crystalline inclusion complexes with reactive, toxic, or malodorous reagents, such as benzoyl chloride, acetyl chloride, cyclohexyl isocyanide, phosphorus trichloride, and trimethylsilyl chloride. The crystals are stable and largely free of the problematic properties of the free reagents. When exposed to solvents such as DMSO or MeOH, the reagents react, and a large portion of the TDA precipitates. The TDA-coated reagents may lead to a safer way of storing, handling, and delivering reagents, and ultimately to synthetic protocols that do not require fume hoods.
Recently, a tetraphenyladamantane octamethylether was shown to encapsulate a wide range of small molecules in its crystals. Uptake and release from the liquid phase were demonstrated, and crystalline inclusion complexes were prepared that act as formulation for obnoxious reagents. However, fewer than two equivalents of guest molecules were found within the crystal structures. Here we report the synthesis of 1,3,5,7-tetrakis(2,4-diethoxyphenyl)adamantane (TEO) and twelve X-ray crystal structures that contain up to 3.5 equivalents of guest molecules. After crystallization and drying, TEO gives a material that absorbs 30 wt % of p-xylene reversibly through the gas phase, and releases it again at 55 °C, suggesting that it may be used for the capture and release of aromatic hydrocarbons.
Oligonucleotide hybrids with organic cores as rigid branching elements and four or six CG dimer strands have been shown to form porous materials from dilute aqueous solution. In order to explore the limits of this form of DNA-driven assembly, we prepared hybrids with three or eight DNA arms via solution-phase syntheses, using H-phosphonates of protected dinucleoside phosphates. This included the synthesis of (CG)8TREA, where TREA stands for the tetrakis[4-(resorcin-5-ylethynyl)phenyl]adamantane core. The ability of the new compounds to assemble in a DNA-driven fashion was studied by UV-melting analysis and NMR, using hybrids with self-complementary CG zipper arms or non-self-complementary TC dimer arms. The three-arm hybrid failed to form a material under conditions where four-arm hybrids did so. Further, the assembly of TREA hybrids appears to be dominated by hydrophobic interactions, not base pairing of the DNA arms. These results help in the design of materials forming by multivalent DNA-DNA interactions.
A linear solution‐phase synthesis of branched oligonucleotides with adamantane as core has been developed. The method uses conventional phosphoramidites only, achieves chain assembly without chromatography of intermediates, and overcomes the low reactivity of adamantane‐1,3,5,7‐tetraol as core. The assembly of four‐arm hybrids with up to 32 nucleotides total was performed, with monodisperse products of up to 10 kDa in size. Overall yields of 20 % over 19 steps (hexamer arms) and 11 % over 25 steps (octamer arms) of HPLC‐purified compounds were obtained. The adamantane‐based hybrids show more DNA‐dominated assembly properties than their analogues with larger lipophilic cores. Reversible formation of macroscopic amounts of materials through hybridization was achieved, both for self‐complementary systems and two‐hybrid systems with two non‐self‐complementary DNA sequences.
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