Aku Suhonen

Cation binding resorcinarene bis-crowns: the effect of lower rim alkyl chain length on crystal packing and solid lipid nanoparticles

A group of seven resorcinarene bis-crown ethers (CNBC5) with two polyether bridges at the upper rim and either propyl, butyl, pentyl, heptyl, nonyl, decyl or undecyl groups at the lower rim were synthesized and their binding properties with Cs+ were investigated by NMR titration. The bis-crowns form 1 : 2 complexes with Cs+ with binding constants of log K 4–5. Crystal structures of bis-crowns and their Cs+ and K+ complexes were studied and different packing motifs were found depending on the alkyl chain length. Short ethyl, propyl and butyl alkyl chains gave a layer or pillar packing where the polar and non-polar regions cannot be distinguished, whereas longer pentyl and decyl chains formed bilayers. Amphiphilic properties and self-assembly in water were studied by preparing solid lipid nanoparticles (SLNs) from the bis-crowns. All investigated compounds formed stable SLNs showing amphiphilic character, which in the case of the short chain bis-crowns probably arises from their locked boat conformation separating the polar face of the molecule from the non-polar face.

Folding Patterns in a Family of Oligoamide Foldamers

A series of small, unsymmetrical pyridine-2,6-dicarboxylamide oligoamide foldamers with varying lengths and substituents at the end groups were synthetized to study their conformational properties and folding patterns. The @-type folding pattern resembled the oxyanion-hole motifs of enzymes, but several alternative folding patterns could also be characterized. Computational studies revealed several alternative conformers of nearly equal stability. These folding patterns differed from each other in their intramolecular hydrogen-bonding patterns and aryl-aryl interactions. In the solid state, the foldamers adopted either the globular @-type fold or the more extended S-type conformers, which were very similar to those foldamers obtained computationally. In some cases, the same foldamer molecule could even crystallize into two different folding patterns, thus confirming that the different folding patterns are very close in energy in spite of their completely different shapes. Finally, the best match for the observed NOE interactions in the liquid state was a conformation that matched the computationally characterized helix-type fold.

Structural analysis of two foldamer-type oligoamides – the effect of hydrogen bonding on solvate formation, crystal structures and molecular conformation

The crystal structures and molecular conformations of two foldamer-type oligoamides were analyzed. One polymorphic form and seven solvates were found for N1,N3-bis(2-benzamidophenyl)benzene-1,3-dicarboxamide (the benzene variant), and two polymorphic forms and six solvates for N2,N6-bis(2-benzamidophenyl)pyridine-2,6-dicarboxamide (the pyridine variant). Three crystal structures of the benzene variant and seven structures of the pyridine variant were solved using single crystal X-ray diffraction. The crystal structures showed that the different modes of intramolecular hydrogen bonding strongly affect the conformation and folding of the molecules, which is most evidently seen with the strongly folded helical structure of the pyridine variant. NOESY experiments suggest that the intramolecular hydrogen bonding is stable enough to retain a folded or partially folded conformation even in solution.

The missing member of the partially O-alkylated resorcinarene family: synthesis and conformation of methyl tetramethoxy resorcinarene.

An improved Lewis acid catalyzed synthesis method for methyl tetramethoxy resorcinarene is described, which produced the missing lower rim methyl derivative of this partially O-alkylated resorcinarene family. Structural characterization by means of variable temperature NMR experiments and single crystal X-ray diffraction studies furthermore revealed that the resorcinarene core adopts different conformations in the solid state and in solution.

Conformational properties and folding analysis of a series of seven oligoamide foldamers

33 crystal structures (11 unsolvated and 22 solvates) of a series of seven oligoamide foldamers were analysed. The crystal structures revealed that despite the structural and environmental differences the series of foldamers prefer only two general conformations, a protohelical @-conformation and a sigmoidal S-conformation. Both conformations also have preferred crystal packing motifs and solvate forming tendencies. Hydrogen bonding was found to be the most decisive factor in conformational preference, but steric properties, the type of the peripheral substituents, as well as solvent and aromatic interactions were also found to have an effect on the conformational details and crystal form.

Supramolecular chirality and symmetry breaking of fluoride complexes of achiral foldamers

Aromatic oligoamide foldamers containing a central pyridine-2,6-dicarbonyl motif are partially preorganized to favor the binding of fluoride anions. In the solid state, the foldamer-fluoride complexes form achiral, polar and chiral crystal structures depending on the chemical structure of the foldamer. One of the six foldamers studied here, a C2v symmetrical foldamer (1), formed repeatedly chiral crystal structures when crystallized with tetra-butylammonium fluoride, showing supramolecular bulk chirality and symmetry breaking in crystallization.

CCDC 1555255: Experimental Crystal Structure Determination

Related Article: Riia Annala, Aku Suhonen, Heikki Laakkonen, Perttu Permi, Maija Nissinen||Chem.-Eur.J.|||doi:10.1002/chem.201703985

CCDC 1555258: Experimental Crystal Structure Determination

Related Article: Riia Annala, Aku Suhonen, Heikki Laakkonen, Perttu Permi, Maija Nissinen||Chem.-Eur.J.|||doi:10.1002/chem.201703985

CCDC 1555254: Experimental Crystal Structure Determination

Related Article: Riia Annala, Aku Suhonen, Heikki Laakkonen, Perttu Permi, Maija Nissinen||Chem.-Eur.J.|||doi:10.1002/chem.201703985

CCDC 1555260: Experimental Crystal Structure Determination

Related Article: Riia Annala, Aku Suhonen, Heikki Laakkonen, Perttu Permi, Maija Nissinen|2017|Chem.-Eur.J.|23|16671|doi:10.1002/chem.201703985