Solvent/Gelator Interactions and Supramolecular Structure of Gel Fibers in Cyclic Bis-Urea/Primary Alcohol Organogels

Abstract

An organogel system consisting of trans-(1S,2S)-bis(ureidododecyl)cyclohexane (SS-BUC) and a series of primary alcohols was explored with optical polarizing microscopy (OPM), electron microscopy, circular dichroism (CD), wide-angle X-ray scattering (WAXS), and synchrotron small-angle X-ray scattering (SAXS). OPM, SAXS, and especially WAXS showed that the gel fiber of SS-BUC/methanol gels essentially consists of SS-BUC crystal itself. SAXS showed that the SS-BUC crystal in the gel takes a lamella with a domain spacing of 5.2 nm. When we left the gel at room temperature, the spacing decreased to 3.1 nm after several months. This distance change may correspond to the structural transition from a double-layer structure to an intercalated-layer structure, which was proposed by Feringa et al. (Chem.-Eur. J. 1999, 5, 937-950) as a possible arrangement of the molecular packing. When the gels in ethanol, propanol, butanol, or octanol were examined, they never showed crystalline peaks in WAXS and SAXS, indicating the amorphous nature of the gels. With increasing the alkyl chain length from ethanol to octanol, dramatic changes were observed in the CD spectrum in the 200-500-nm range. Because these CD changes are correlated to the absorbance of urea, those can be considered as the evidence that the solvents strongly relate to the spatial arrangement between the adjacent urea groups. For the amorphous gels, the cross-sectional correlation function [gammaCu] was directly obtained by the inverse Hankel transform of the SAXS data. The value of gammaCu for the gels is decreased with increasing u (distance between the two scattering bodies, see eq 5). Furthermore, it more rapidly decreases than that of the rigid cylinder model. This feature can be explained by the speculation that many solvent molecules permeate into the SS-BUC fiber. There was a clear difference between ethanol and the other gels, indicating that the solvents with a longer alkyl chain give the more permeated and diffused fiber. This permeated fiber (i.e., wet fiber) can rationalize the dramatic CD change, by presuming that the permeated solvent molecules alter the molecular stacking form.

TiO2 Sphere‐Tube‐Fiber Transition Induced by Oligovaline Concentration Variation

“…Simple peptide gelators that are easily manufactured in large amounts are thus of great interest to the (bio)materials community and are currently intensely researched. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Peptide-controlled mineralization has been used for the fabrication of various well-defined inorganic materials like calcium phosphate, [21] calcium carbonate, [22,23] and silica. [14,[24][25][26][27][28][29][30] These approaches have led to several interesting and useful geometries and topologies of the inorganics.…”

Synthesis and characterization of nanoarchitectures from fatty acid derivatives of 2,6-diaminopyridine and 2-aminopyridine

“…Scheme 1 Synthetic route to 3a-c, Reaction of 1 (2.5 mm) with 2a-c (5 mm) and Et 3 N (5 mm) in THF (50 mL) at RT forces that put the building blocks (self-assemblies) into a well-defined nanoarchitecture can be understood and elaborated by many workers [40][41][42][43][44][45][46][47][48][49][50]. The organization of building blocks into ordered structures is facilitated by a combination of many different non-covalent interactions such as H-bonding, Pi-Pi stacking and hydrophobic interactions.…”

Challenges and breakthroughs in recent research on self-assembly

“…Hanabusa and coworkers have worked extensively on low molecularweight gelators based on molecular structures of ureylene [196], diaminocyclohexane [197], and cyclohexanetricarboxamide [198]. Sakurai and coworkers reported gel fibers from cyclic bisurea derivatives [199]. Shinkai and coworkers developed organogels with cholesterol-based [200] and sugar-based [201] molecular designs.…”