Characteristics of Gelation by Amides Based on trans-1,2-Diaminocyclohexane: The Importance of Different Substituents

Six diamides were prepared from trans-(1R,2R)-1,2-diaminocyclohexane and the corresponding racemate and were subsequently used as gelators. Three chiral compounds and their racemates were prepared. One of the chiral compounds and its racemate contained two n-dodecanoylamino groups as the same substituents. The other two chiral compounds and their racemates contained different substituents: 10-undecenoylamino and 2-heptyl-undecanoylamino groups, and 5-hydroxypentanoylamino and 2-heptylundecanoylamino groups. Their gelation abilities were evaluated on the basis of the minimum gel concentration using eight solvents. The thermal stability and transparency of the gels were investigated by UV-vis spectroscopy using three-component mixed solvents of hexadecyl 2-ethylhexanoate, liquid paraffin, and decamethyl cyclopentasiloxane (66 combinations). The gel-to-sol phase-transition temperatures were also studied. The viscoelastic behavior of the gels was studied by rheology measurements in the strain sweep mode. Aggregates constructing three-dimensional networks were studied by transmission electron microscopy and circular dichroism spectroscopy. The molecular packing of the gels was evaluated by small angle X-ray scattering (SAXS).ArticleBULLETIN OF THE CHEMICAL SOCIETY OF JAPAN.90(3):312-321(2017)journal articl

‘Crystal lattice engineering,’ an approach to engineer protein crystal contacts by creating intermolecular symmetry: Crystallization and structure determination of a mutant human RNase 1 with a hydrophobic interface of leucines

A protein crystal lattice consists of surface contact regions, where the interactions of specific groups play a key role in stabilizing the regular arrangement of the protein molecules. In an attempt to control protein incorporation in a crystal lattice, a leucine zipper-like hydrophobic interface (comprising four leucine residues) was introduced into a helical region (helix 2) of the human pancreatic ribonuclease 1 (RNase 1) that was predicted to form a suitable crystallization interface. Although crystallization of wild-type RNase 1 has not yet been reported, the RNase 1 mutant having four leucines (4L-RNase 1) was successfully crystallized under several different conditions. The crystal structures were subsequently determined by X-ray crystallography by molecular replacement using the structure of bovine RNase A. The overall structure of 4L-RNase 1 is quite similar to that of the bovine RNase A, and the introduced leucine residues formed the designed crystal interface. To characterize the role of the introduced leucine residues in crystallization of RNase 1 further, the number of leucines was reduced to three or two (3L- and 2L-RNase 1, respectively). Both mutants crystallized and a similar hydrophobic interface as in 4L-RNase 1 was observed. A related approach to engineer crystal contacts at helix 3 of RNase 1 (N4L-RNase 1) was also evaluated. N4L-RNase 1 also successfully crystallized and formed the expected hydrophobic packing interface. These results suggest that appropriate introduction of a leucine zipper-like hydrophobic interface can promote intermolecular symmetry for more efficient protein crystallization in crystal lattice engineering efforts