Alexander Schwenger

Synthesis of eight-arm, branched oligonucleotide hybrids and studies on the limits of DNA-driven assembly.

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.

Tetrakis(dimethoxyphenyl)adamantane (TDA) and its inclusion complexes in the crystalline state: a versatile carrier for small molecules.

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.

Reagents with a Crystalline Coat

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.

High-Loading Crystals of Tetraaryladamantanes and the Uptake and Release of Aromatic Hydrocarbons from the Gas Phase

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.

Encapsulating Active Pharmaceutical Ingredients in Self-Assembling Adamantanes with Short DNA Zippers

Formulating pharmaceutically active ingredients for drug delivery is a challenge. There is a need for new drug delivery systems that take up therapeutic molecules and release them into biological systems. We propose a novel mode of encapsulation that involves matrices formed through co‐assembly of drugs with adamantane hybrids that feature four CG dimers as sticky ends. Such adamantanes are accessible via inexpensive solution‐phase syntheses, and the resulting materials show attractive properties for controlled release. This is demonstrated for two different hybrids and a series of drugs, including anticancer drugs, antibiotics, and cyclosporin. Up to 20 molar equivalents of active pharmaceutical ingredients (APIs) are encapsulated in hybrid materials. Encapsulation is demonstrated for DNA‐binding and several non‐DNA binding compounds. Nanoparticles were detected that range in size from 114–835 nm average diameter, and ζ potentials were found to be between −29 and +28 mV. Release of doxorubicin into serum at near‐constant rates for 10 days was shown, demonstrating the potential for slow release. The encapsulation and release in self‐assembling matrices of dinucleotide‐bearing adamantanes appears to be broadly applicable and may thus lead to new drug delivery systems for APIs.

Capturing and Stabilizing Folded Proteins in Lattices Formed with Branched Oligonucleotide Hybrids

The encapsulation of folded proteins in stabilizing matrices is one of the challenges of soft‐matter materials science. Capturing such fragile bio‐macromolecules from aqueous solution, and embedding them in a lattice that stabilizes them against denaturation and decomposition is difficult. Here, we report that tetrahedral oligonucleotide hybrids as branching elements, and connecting DNA duplexes with sticky ends can assemble into materials. The material‐forming property was used to capture DNA‐binding proteins selectively from aqueous protein mixtures. The three‐dimensional networks also encapsulate guest molecules in a size‐selective manner, accommodating proteins up to a molecular weight of approximately 159 kDa for the connecting duplex lengths tested. Exploratory experiments with green fluorescent protein showed that, when embedded in the DNA‐based matrix, the protein is more stable toward denaturation than in the free form, and retains its luminescent properties for at least 90 days in dry form. The noncrystalline biohybrid matrices presented herein may be used for capturing other proteins or for producing functional materials.