A Dendron Based on Natural Amino Acids: Synthesis and Behavior as an Organogelator and Lyotropic Liquid Crystal

Self-Assembling Anti-Freezing Lamellar Nanostructures in Subzero Temperatures

The requirement for cryogenic supramolecular self-assembly of amphiphiles in subzero environments is a challenging topic. Here, the self-assembly of lamellar lyotropic liquid crystals (LLCs) are presented to a subzero temperature of -70 °C. These lamellar nanostructures are assembled from specifically tailored ultra-long-chain surfactant stearyl diethanolamine (SDA) in water/glycerol binary solvent. As the temperature falls below zero, LLCs with a liquid-crystalline Lα phase, a tilted Lβ phase, and a new folded configuration are obtained consecutively. A comprehensive experimental and computational study is performed to uncover the precise microstructure and formation mechanism. Both the ultra-long alkyl chain and head group of SDA play a crucial role in the formation of lamellar nanostructures. SDA head group is prone to forming hydrogen bonds with water, rather than glycerol. Glycerol cannot penetrate the lipid layer, which mixes with water arranging outside of the lipid bilayer, providing an ideal anti-freezing environment for SDA self-assembly. Based on these nanostructures and the ultra-low freezing point of the system, a series of novel cryogenic materials are created with potential applications in extremely cold environments. These findings would contribute to enriching the theory and research methodology of supramolecular self-assembly in extreme conditions and to developing novel anti-freezing materials.

Quinoline-cored Poly(Aryl Ether) Dendritic Organogels with Multiple Stimuli-Responsive and Adsorptive Properties

Functional supramolecular gel materials have potential applications in sensors, optical switches, artificial antennae, drug delivery and so on. In this paper, quinoline-cored poly(aryl ether) dendritic organogelators were designed, synthesized and fully characterized. The gelation behaviour of the dendritic organogelator was tested in organic solvents, mixed solvents and ionic liquids. The dendron Q-G1 was found to be an efficient and versatile organogelator toward various apolar and polar organic solvents with the critical gelation concentrations (CGCs) approaching 1.2×10^-2  mol/L, indicating one dendritic organogelator could immobilize 1.2×10³ solvent molecules in the organogel network. Interestingly, these dendrons exhibited excellent gel formation in ionic liquids. Notably, these dendritic organogels were found to display multiple stimuli-responsive properties toward external stimuli including heat, ultrasound and shear stress, with a reversible sol-gel phase transition. In addition, the dendritic organogel could effectively adsorb heavy metals and organic dyes. The removal rate of Pb²⁺ was up to 20% and the adsorption rate for Rhodamine B was as high as 89%.

Liquid Crystalline Hydrogel with Thermally Induced Reversible Shape Change and Water-Triggered Shape Memory

Liquid crystalline hydrogel (LCH) is synthesized through simultaneous polymerization of hydrophobic and hydrophilic monomers in an oil-in-water emulsion, resulting in phase-separated liquid crystalline network (LCN) embedded in a hydrogel matrix. This material features some properties and functions of both LCN and hydrogel, displaying stable LC phase over repeated hydration and dehydration cycles of the hydrogel matrix. Using mechanically stretched and photocrosslinked LCH, the thermally induced LC-isotropic phase transition in LCN domains can be translated into reversible macroscopic deformation of the LCH. Moreover, the LCH exhibits water absorption-controlled shape memory effect.

Designer Peptide and Protein Dendrimers: A Cross-Sectional Analysis

Dendrimers have attracted immense interest in science and technology due to their unique chemical structure that offers a myriad of opportunities for researchers. Dendritic design allows us to present peptides in a branched three-dimensional fashion that eventually leads to a globular shape, thus mimicking globular proteins. Peptide dendrimers, unlike other classes of dendrimers, have immense applications in biomedical research due to their biological origin. The diversity of potential building blocks and innumerable possibilities for design, along with the fact that the area is relatively underexplored, make peptide dendrimers sought-after candidates for various applications. This review summarizes the stepwise evolution of peptidic dendrimers along with their multifaceted applications in various fields. Further, the introduction of biomacromolecules such as proteins to a dendritic scaffold, resulting in complex macromolecules with discrete molecular weights, is an altogether new addition to the area of organic chemistry. The synthesis of highly complex and fully folded biomacromolecules on a dendritic scaffold requires expertise in synthetic organic chemistry and biology. Presently, there are only a handful of examples of protein dendrimers; we believe that these limited examples will fuel further research in this area.

Stearoyl-appended pendant amino acid-based hyperbranched polymers for selective gelation of oil from oil/water mixtures

Stearic acid-appended pendant amino acid-based poly(methacrylate) hyperbranched polymers were developed for the phase-selective organogelation of crude oil from a binary mixture of oil/water.

A Mechanochromic and Photochromic Dual-Responsive Co-assembly with Multicolored Switch: A Peptide-Based Dendron Strategy

In this contribution, we report a unique co-assembly composed of pyrene and spiropyran that were linked separately at the focal point of the same peptide-based dendron (Phe-Glu), in which the dendrons offer driving forces for the coaggregation. A series of co-assemblies with different weight ratios (Py-Phe-Glu/SP-Phe-Glu) were prepared and the morphology could be tuned. It is found that the resulting stable co-assembled organogel is double switchable triggered by light and heat. TEM revealed that, in the xerogel, Py-Phe-Glu formed rigid rod nanofibers with large diameters and acted as a rigid sketelon where the gracile interwoven fibrous structure of SP-Phe-Glu grew. More interestingly, the original powder of the co-assembled xerogel (1.0 mg/0.1 mg) not only displayed a sequential high-contrast tricolored switch from dark blue to bright cyan and to red under external force but also presented multistate accessible photochromic properties. Such mechanochromic and photochromic behaviors of the xerogel are mainly due to the transition of different excimers of pyrene and the force/photoinduced ring-opening reaction of spiropyran. It is rarely reported that self-assembled soft materials achieve mechanochromic and photochromic dual-responsive behaviors with a high-contrast multicolored switch. We believe the co-assembly strategy based on polypeptide dendrons can be extended to other systems for establishing novel intelligent fluorescent materials.

Glutamic acid derivatives as gelators for electrolyte of lithium ion batteries

Organic gelators were synthesized to prepare gel electrolyte with wider electrochemical stable window.

Metal induced gelation from pyridine cored poly(aryl ether) dendrons with in situ synthesis and stabilization of hybrid hydrogel composites

Metal induced gel formation from pyridine cored poly(aryl ether) dendrons has been achieved. In addition, the gel is successfully utilized for in situ synthesis and stabilization of silver nanoparticles (AgNPs), which form an unprecedented, well-organized arrangement on the nanofibers.

Tunable morphology and mesophase formation by naphthalene-containing poly(aryl ether) dendron-based low-molecular-weight fluorescent gels

Novel poly(aryl ether) dendron-based low-molecular-weight organogelaters (LMWG) containing naphthalene units at the core have been synthesized, and the self-assembly of the system has been examined in a variety of solvents and solvent mixtures. The compounds readily form gels with attractive critical gel concentration values associated with gelation-induced enhanced emission (GIEE). In addition to the remarkable properties of the previously reported anthracene and pyrene analogues (Rajamalli, P.; Prasad, E. Org. Lett.2011, 13, 3714 and Rajamalli, P.; Prasad, E. Soft Matter2012, 8, 8896), the self-assembled systems exhibit distinctly different structure-property relationships. Unlike the reported ones, the present system forms sheetlike morphology in nonpolar solvent mixtures, giant vesicles in polar solvent mixtures, and lamellar or hexagonal columnar phases in single solvents. The unique properties of the self-assembled systems, which were analyzed through electron microscopic (SEM, TEM, AFM) and spectroscopic techniques (POM, fluorescence), are attributed to the replacement of anthracene/pyrene units by naphthalene units. The present work unravels the subtle role of minute structural change in altering the properties of LMWGs based on poly(aryl ether) dendrons.

Reversible tuning luminescent color and emission intensity: a dipeptide-based light-emitting material

A smart luminescent material whose emission color and emission intensity can be separately modulated by external force is demonstrated. The rational manipulation of rich noncovalent interactions and fluorophore packing style promotes an in-depth understanding between supramolecular structure and photophysical property and offers an effective strategy to modulate the light-emitting property in a predicative way.

Click-dendronized poly(amide-triazole)s--effect of dendron size and polymer backbone symmetry on self-assembling and gelation properties

Nine dendronized poly(amide-triazole)s 2-Gm Gn (m=1-3, n=1-3), were prepared by the 1:1 copolymerization between AA-type dendritic diazides 4-Gm (m=1-3) and BB-type dendritic diacetylenes 5-Gn (n=1-3) under the copper(I)-mediated click coupling conditions. The degree of polymerization value of the polymers was found to range from 15-50, and decreased with increasing size of the dendron, suggesting steric hindrance had a retardation role on the copolymerization efficiency. Based on FT-IR and (1)H NMR studies, it was found that significantly strong, interchain hydrogen bonding between the amide units was present in the solution state after copolymerization, whereas the monomers 4-Gm and 5-Gn were devoid of any intermolecular hydrogen-bonding interaction. Hence a positive allosteric hydrogen-bonding effect was observed after polymerization, and could be rationalized by the zip effect. The strength of the interchain association in polymers 2-Gm Gn was found to decrease with increasing size of the dendron (i.e., 2-G1 G1>2-G1 G2>2-G2 G1≈2-G2 G2>2-G1 G3≈2-G3 G1>2-G2 G3≈2-G3 G2>2-G3 G3). Among the nine polymers, only 2-G1 G2 and 2-G2 G1 were good organogelators for aromatic solvents, while the 2-G2 G2 polymer, bearing the closest structural resemblance to the previously reported organogelator 1-G2 prepared from the polymerization of AB-type monomers, was devoid of gelating power. Careful analysis of structures of the present polymer series 2-Gm Gn and the previously reported series 1-Gn suggested that the polymer backbone symmetry played a subtle role in controlling their self-assembling and gelating properties.

Design and self-assembly of L-glutamate-based aromatic dendrons as ambidextrous gelators of water and organic solvents

A series of L-glutamate-based dendrons containing aromatic cores ranging from phenyl to naphthyl to anthryl were synthesized, and their self-assembly in organic solvents as well as in water was investigated. It was found that all of these dendrons formed organogels with hexane and simultaneously formed the hydrogels with water, thus exhibiting ambidextrous properties. Nanofiber structures are essentially formed in organogels and hydrogels, and some nanostrips are formed in some of the hydrogels. During gel formation, both hydrogen bonds between the amide groups and the pi-pi stacking between the aromatic rings played a predominant role in forming the ID nanostructures. Both the hydrogels and the organogels containing naphthyl and anthryl groups showed fluorescence emission. In comparison with the corresponding compounds in solution, the naphthyl-containing dendrons showed a strong enhancement of fluorescence in the gel. In the case of anthryl-containing dendrons, fluorescence enhancement was observed for the derivative with anthryl substituted at the 9 position, whereas a decrease was observed for the gels of the 2-substituted derivative. Although the chirality of L-glutamate could not be transferred to the aromatic chromophores in solution, it was transferred to the chromophores in gels as a result of the self-assembly and strong pi-pi interaction of the gelators. On the basis of the properties of the organogels and hydrogels, a thermally driven chiroptical switch was proposed. That is, the chirality disappeared when the gel was heated to solution, whereas it returned when cooled to a gel. The process can be repeated many times.