Synthesis of Helical Phenolic Resin Bundles through a Sol-Gel Transcription Method

Chiral and helical polymers possess special helical structures and optical property, and may find applications in chiral catalysis and optical devices. This work presents the preparation and formation process of helical phenolic resins through a sol-gel transcription method. A pair of bola-type chiral low-molecular-weight gelators (LMWGs) derived from valine are used as templates, while 2,4-dihydroxybenzoic acid and formaldehyde are used as precursors. The electron microscopy images show that the phenolic resins are single-handed helical bundles comprised of helical ultrafine nanofibers. The diffused reflection circular dichroism spectra indicate that the helical phenolic resins exhibit optical activity. A possible formation mechanism is proposed, which shows the co-assembly of the LMWGs and the precursors

Control the Morphologies and the Pore Architectures of Mesoporous Silicas through a Dual-Templating Approach

Mesoporous silica nanospheres were prepared using a chiral cationic low-molecular-weight amphiphile and organic solvents such as toluene, cyclohexane, and tetrachlorocarbon through a dual-templating approach. X-ray diffraction, nitrogen sorption, field emission scanning electron microscopy, and transmission electron microscopy techniques have been used to characterize the mesoporous silicas. The volume ratio of toluene to water plays an important role in controlling the morphologies and the pore architectures of the mesoporous silicas. It was also found that mesoporous silica nanoflakes can be prepared by adding tetrahydrofuran to the reaction mixtures

Chirality-Driven Parallel and Antiparallel β‑Sheet Secondary Structures of Phe–Ala Lipodipeptides

Four Phe–Ala lipodipeptides with different stereochemical structures are observed to self-assemble into twisted nanoribbons in water. The handedness of the twisted nanoribbons is controlled by the chirality of the phenylalanine near the alkyl chain, while the stacking handedness of the phenyl and carbonyl groups is determined by the alanine at the C-terminal. The homochiral and heterochiral lipodipeptides self-assemble into parallel and antiparallel β-sheet structures, respectively. The ¹H NMR, FTIR, X-ray diffraction, and circular dichroism characterizations indicate that these phenomena are mainly driven by the interaction between neighboring phenyl groups and H-bonding among the amide groups

Terminal Is Important for the Helicity of the Self-Assemblies of Dipeptides Derived from Alanine

The organization of peptides and proteins attracts much attention, due to the biofunctionalities of the self-assemblies. Herein, four dipeptides derived from alanine were synthesized. It was found that the handedness of their self-assemblies was controlled by the chirality of the alanines at the terminals. The organic self-assemblies were studied using circular dichroism, ¹H NMR, Fourier transform infrared, field-emission electron microscopy, transmission electron microscopy, and X-ray diffraction. The results indicated that the electrostatic interactions among the carboxylate groups and H-bondings among the amide groups at the terminals play important roles in the formation of the organic self-assemblies

Solvent-Induced Handedness Inversion of Dipeptide Sodium Salts Derived from Alanine

The relationship between amino acid sequences and their resulting nanostructure has been well studied, but that between amino acid chirality and nanostructure handedness has not. Four dipeptide sodium salts with long alkyl chains derived from l- and d-alanines were synthesized. The behavior of their self-assembly into physical gels in water and THF was studied using field-emission scanning electron microscopy, circular dichroism (CD), FT-IR spectroscopy, ¹H NMR spectroscopy, and X-ray diffraction. The dipeptide salts organized into twisted nanoribbons, whose handedness was controlled by the terminal alanine chirality. The handedness of nanoribbons formed in water was opposite to that of those formed in THF. The dipeptide salts self-assembled into similar interdigitated bilayer structures in water and THF, but CD spectra of the gels indicated that the stacking of carbonyl groups was opposite. The formation of this handedness inversion is proposed to arise from the difference in interlayer distance and chiral stacking of carbonyl groups near the C-terminals