Helical Ribbon Aggregate Composed of a Crown-Appended Cholesterol Derivative Which Acts as an Amphiphilic Gelator of Organic Solvents and as a Template for Chiral Silica Transcription

Abstract

New crown-appended cholesterol-based organogelator 1, which has two cholesterol skeletons as a chiral aggregate-forming site, two amino groups as an acidic proton-binding site, and one crown moiety as a cation-binding site, was synthesized, and the gelation ability was evaluated in organic solvents. It can gelate acetic acid, acetonitrile, acetone, ethanol, 1-butanol, 1-hexanol, DMSO, and DMF under 1.0 wt %, indicating that 1 acts as a versatile gelator of various organic solvents. To characterize the aggregation mode in the organogel system, we observed a CD spectrum of the acetic acid gel 1. In the CD spectrum, the lambda(theta)=0 value appears at 353 nm, which is the same as the absorption maximum lambda(max) = 353 nm. The positive sign for the first Cotton effect indicates that the dipole moments of azobenzene chromophores tend to orient in a clockwise direction. Very surprisingly, the TEM images of the 1 + acetic acid gel resulted in the helical ribbon and the tubular structures. Sol-gel polymerization of tetraethoxysilane was carried out using 1 in the gel phase. The silica obtained from the 1 + acetic acid gel showed the helical ribbon with 1700-1800-nm pitches and the tubular structure of the silica with approximately 560-nm outer diameter. As far as can be recognized, all the helicity possesses a right-handed helical motif. Since the exciton-coupling band of the organogel also shows R (right-handed) helicity, we consider that a microscopic helicity is reflected by a macroscopic helicity.

Structural Transcription of Organogels to Mesoporous Silicas: A Chain-length Dependent Morphology and Pore Texture

“…In the present work, we demonstrate a chain-length dependent morphology and pore structure of mesoporous silicas, using organogels pre-formed by primary alkylamines (R-NH 2 , R=12, 14,16,18) in ethylene glycol as templates. As the chain length of alkylamines varies from 12 to 18, morphologies of resulted silica can change from layers to spheres and platelets, just as the cases observed in the parent organogels.…”

Formation and regulation of supramolecular chirality in organogel via addition of tartaric acid

“…The molecular packing of 1 in the xerogel state before and after addition of tartaric acid was further investigated by powder X-ray diffraction in Figure 5 [22][23][24], which strongly suggested a lamellar structure. After addition of 0.5 eq D-TA or L-TA, the series of peaks disappeared and a new peak at 2 = 2.59° with the corresponding d spacing value of 34.6 Å was emerged, which indicated the lamellar structure was changed.…”

Molecular Interactions in Natural and Synthetic Self-Assembly Systems

“…From the first reports of Shinkai group (Van Bommel et al, 2003a;Jung & Shinkai, 2004b;Jung et al, 2001c;Jung et al, 2000d;Tamaru et al, 2002e) the strategy was successfully employed and the reported experimental data are summarized and discussed in excellent reviews Yang et al, 2011;Llusar & Sanchez, 2008).…”