Formation Of Supramolecular Gels Research Articles

Morphological Evaluation of Supramolecular Soft Materials Obtained through Co-Assembly Processes.

Low-molecular-weight gelators (LMWGs) are compounds with an intrinsic tendency to self-assemble forming various supramolecular architectures via non-covalent interactions. Considering that the development of supramolecular assemblies through the synergy of molecules is not entirely understood at the molecular level, this study introduced a Fmoc-short peptide and four Fmoc-amino acids as building blocks for the self-assembly/co-assembly process. Hence, we investigated the formation of supramolecular gels starting from the molecular aggregation following two triggering approaches: solvent/co-solvent method and pH switch. The complex morphological analysis (POM, AFM, and STEM) offered an insight into the spontaneous formation of well-ordered nanoaggregates. Briefly, POM and AFM images demonstrated that self-assembled gels present various morphologies like dendrimer, spherulite, and vesicle, whereas all co-assembled supramolecular systems exhibit fibrillar morphologies as a result of the interaction between co-partners of each system. STEM study has confirmed that the molecules interact and join together, finally forming a fibrous network, an aspect seen in both self-assembled and co-assembled gels. XRD allowed the determination of the molecular arrangement. The study emphasized that the Fmoc motif protected the amino groups and facilitated gelation through additional π-π interactions.

Formation of Supramolecular Gels from Host–Guest Interactions between PEGylated Chitosan andα‐Cyclodextrin

AbstractChitosan‐based hydrogels are prepared via the formation of polypseudorotaxanes (PPR), by selectively threadingα‐cyclodextrin (α‐CD) macrocycles onto polymeric chains, which, through the formation of microcrystalline domains, act as junction points for the network. Specifically, host–guest inclusion complexes are formed betweenα‐CD and PEGylated chitosan (PEG‐Ch), resulting in the formation of supramolecular gels. PEG‐grafted chitosan is obtained with a reaction yield of 79.8%, a high degree of grafting (50.9% GW) and water solubility (≈16 mg mL−1), as assessed by turbidimetry. A range of compositions for mixtures of PEG‐Ch solutions (0.2–0.8% w/w) andα‐CD solutions (2−12% w/w, or 0.04–0.2% mol) are studied. Regardless of PEG content, gels are not formed at lowα‐CD concentrations (<4%). Dynamic rheology measurements reveal stiff gels (G’ above 15k) and a narrow linear viscoelastic region, reflecting their brittleness. The highest elastic modulus is obtained for a hydrogel composition of 0.4% PEG‐Ch and 6%α‐CD. Steady‐state measurements, cycling between low and high shear rates, confirm the thixotropic nature of the gels, demonstrating their capacity to fully recover their mechanical properties after being exposed to high stress, making them good candidates to use as in‐situ gel‐forming materials for drug delivery to topical or parenteral sites.

In Situ Supramolecular Gel Formed by Cyclohexane Diamine with Aldehyde Derivative.

Low-molecular-weight gels have great potential for use in a variety of fields, including petrochemicals, healthcare, and tissue engineering. These supramolecular gels are frequently metastable, implying that their properties are kinetically controlled to some extent. Here, we report on the in situ supramolecular gel formation by mixing 1,3-cyclohexane diamine (1) and isocyanate derivative (2) without any catalysis at room temperature in various organic solvents. A mixture of building blocks 1 and 2 in various organic solvents, dichloromethane, tetrahydrofuran, chloroform, toluene, and 1,4-dioxane, resulted in the stable formation of supramolecular gel at room temperature within 60–100 s. This gel formation was caused by the generation of urea moieties, which allows for the formation of intermolecular hydrogen-bonding interactions via reactions 1 and 2. In situ supramolecular gels demonstrated a typical entangled fiber structure with a width of 600 nm and a length of several hundred μm. In addition, the supramolecular gels were thermally reversible by heating and cooling. The viscoelastic properties of supramolecular gels in strain and frequency sweets were enhanced by increasing the concentration of a mixed 1 and 2. Furthermore, the supramolecular gels displayed a thixotropic effect, indicating a thermally reversible gel.

Stereocomplex formation and hierarchical structural changes during heating of supramolecular gels obtained by polylactide racemic blends

Solvents that are capable of forming crystalline complexes with poly(ʟ-lactide) (PLLA) have been known to form thermoreversible gels. However, the gelation behavior of linear PLLA/poly(ᴅ-lactide) (PDLA) blends has not been studied. Herein, the formation of supramolecular gels using PLLA/PDLA blends in N,N-dimethylformamide (DMF) is reported. The structural changes of these gels were investigated in multiple length scales during heating. In blend gels, both homopolymers crystallize into the ε form. On heating, DMF molecules that are present in the crystal lattice of the ε form are expelled out by keeping the lamellar structure intact and the structure transformed to the α form. At 45 °C, stereocomplex (SC) crystals are also formed due to the activated thermal motion of enantiomeric chains in the presence of solvent. The α form became unstable at ∼75 °C and the enantiomeric polymer chains reorganized into the SC. In the case of low molecular weight blend gels, high chain mobility and chain diffusion ability resulted in the more stable SC. A structural model is proposed to explain the phase transition behavior of blend gels. This study not only enhances the fundamental understanding of SC formation but also provides opportunities to exploit the molecular recognition in helical polymers.

Reaction induced supramolecular gelation with the evolution of circularly polarized luminescence

Chemically reaction triggered formation of supramolecular gels and enhancement of emission.

Triterpenoid-PEG Ribbons Targeting Selectivity in Pharmacological Effects.

(1) Background: To compare the effect of selected triterpenoids with their structurally resembling derivatives, designing of the molecular ribbons was targeted to develop compounds with selectivity in their pharmacological effects. (2) Methods: In the synthetic procedures, Huisgen 1,3-dipolar cycloaddition was applied as a key synthetic step for introducing a 1,2,3-triazole ring as a part of a junction unit in the molecular ribbons. (3) Results: The antimicrobial activity, antiviral activity, and cytotoxicity of the prepared compounds were studied. Most of the molecular ribbons showed antimicrobial activity, especially on Staphylococcus aureus, Pseudomonas aeruginosa, and Enterococcus faecalis, with a 50–90% inhibition effect (c = 25 µg·mL−1). No target compound was effective against HSV-1, but 8a displayed activity against HIV-1 (EC50 = 50.6 ± 7.8 µM). Cytotoxicity was tested on several cancer cell lines, and 6d showed cytotoxicity in the malignant melanoma cancer cell line (G-361; IC50 = 20.0 ± 0.6 µM). Physicochemical characteristics of the prepared compounds were investigated, namely a formation of supramolecular gels and a self-assembly potential in general, with positive results achieved with several target compounds. (4) Conclusions: Several compounds of a series of triterpenoid molecular ribbons showed better pharmacological profiles than the parent compounds and displayed certain selectivity in their effects.

Supramolecular hydrogelation via host-guest anion recognition: Lamellar hydrogel materials for the release of cationic cargo

Supramolecular hydrogelation via host-guest anion recognition: Lamellar hydrogel materials for the release of cationic cargo

Supramolecular gel formation regulated by water content in organic solvents: self-assembly mechanism and biomedical applications.

As one of the most important and fruitful methods, supramolecular self-assembly has a significant advantage in designing and fabricating functional soft materials with various nanostructures. In this research, a low-molecular-weight gelator, N,N′-di(pyridin-4-yl)-pyridine-3,5-dicarboxamide (PDA-N4), was synthesized and used to construct self-assembled gels via a solvent-mediated strategy. It was found that PDA-N4 could form supramolecular gels in mixed solvents of water and DMSO (or DMF) at high water fraction (greater than or equal to 50%). By decreasing the water fraction from 50% to 30%, the gel, suspension and solution phases appeared successively, indicating that self-assembled aggregates could be efficiently modulated via water content in organic solvents. Moreover, the as-prepared PDA-N4 supramolecular gels not only displayed solid-like behavior, and pH- and thermo-reversible characteristics, but also showed a solution–gel–crystal transition with the extension of aging time. Further analyses suggested that both the crystal and gel had similar assembled structures. The intermolecular hydrogen bonding between amide groups and the π–π stacking interactions between pyridine groups played key roles in gel formation. Additionally, the release behavior of vitamin B12 (VB12) from PDA-N4 gel (H2O/DMSO, v/v = 90/10) was evaluated, and the drug controlled release process was consistent with a first-order release mechanism. The human umbilical venous endothelial cell culture results showed that the PDA-N4 xerogel has good cytocompatibility, which implied that the gels have potential biological application in tissue engineering and controlled drug release.

Enhanced Circularly Polarized Luminescence in Emissive Charge-Transfer Complexes.

Achieving a large dissymmetry factor (glum ) is a challenge in the field of circularly polarized luminescence (CPL). A chiral charge-transfer (CT) system consisting of chiral electron donor and achiral electron acceptor shows bright circularly polarized emission with large glum value. The chiral emissive CT complexes could be fabricated through various approaches, such as grinding, crystallization, spin coating, and gelatinization, by simply blending chiral donor and achiral acceptor. The structural synergy originating from π-π stacking and strong CT interactions resulted in the long-range ordered self-assembly, enabling the formation of supramolecular gels. Benefiting from the large magnetic dipole transition moment in the CT state, the CPL activity of CT complexes exhibited large circular polarization. Our design strategy of the chiral emissive CT complexes is expected to help the development of new molecular engineering strategies for designing highly efficient CPL-active materials.

Enhanced Circularly Polarized Luminescence in Emissive Charge‐Transfer Complexes

AbstractAchieving a large dissymmetry factor (glum) is a challenge in the field of circularly polarized luminescence (CPL). A chiral charge‐transfer (CT) system consisting of chiral electron donor and achiral electron acceptor shows bright circularly polarized emission with large glum value. The chiral emissive CT complexes could be fabricated through various approaches, such as grinding, crystallization, spin coating, and gelatinization, by simply blending chiral donor and achiral acceptor. The structural synergy originating from π–π stacking and strong CT interactions resulted in the long‐range ordered self‐assembly, enabling the formation of supramolecular gels. Benefiting from the large magnetic dipole transition moment in the CT state, the CPL activity of CT complexes exhibited large circular polarization. Our design strategy of the chiral emissive CT complexes is expected to help the development of new molecular engineering strategies for designing highly efficient CPL‐active materials.

Carbohydrate-supramolecular gels: Adsorbents for chromium(VI) removal from wastewater

HypothesisTo overcome the contamination of water by heavy metals the adsorption of the pollutant on gel phases is an attractive solution since gels are inexpensive, potentially highly efficient and form a distinct phase while allowing diffusion of the contaminated water throughout the material. This work tests the chromium(VI) adsorbent capacity of new supramolecular gels for Chromium(VI) removal from wastewater. ExperimentsFirst hydrophobic imidazolium salts of carbohydrate anions were synthesised as new gelators. Subsequently, they were dissolved in a solvent by heating and, after cooling overnight, to give the formation of supramolecular gels. The properties of the resulting gels, such as thermal stability, mechanical strength, morphology, rheology, and kinetics of gel formation, were studied as a function of gelator structure, gelation solvent and pollutant removal efficiency. FindingsCarbohydrate-derived gels showed the best removal capacity, i.e. 97% in 24 h. Interestingly, in one case, the reduction of chromium(VI) to chromium(III) also occurred after the adsorption process, and this phenomenon has been analysed using 1H NMR spectroscopy, IR spectroscopy, and SEM. The most efficient gel can reach an adsorption capacity of 598 mg/g in contrast to a value of 153 mg/g for the most effectively best hydrogels reported to date. The new gel can be also recycled up to 4 times. These findings suggest that these new, supramolecular hydrogels have potential applications in environmental remediation.

Supramolecular Organogels Based on N-Benzyl, N'-Acylbispidinols.

The acylation of unsymmetrical N-benzylbispidinols in aromatic solvents without an external base led to the formation of supramolecular gels, which possess different thicknesses and degrees of stability depending on the substituents in para-positions of the benzylic group as well as on the nature of the acylating agent and of the solvent used. Structural features of the native gels as well as of their dried forms were studied by complementary techniques including Fourier-transform infrared (FTIR) and attenuated total reflection (ATR) spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and small-angle X-ray scattering and diffraction (SAXS). Structures of the key crystalline compounds were established by X-ray diffraction. An analysis of the obtained data allowed speculation on the crucial structural and condition factors that governed the gel formation. The most important factors were as follows: (i) absence of base, either external or internal; (ii) presence of HCl; (iii) presence of carbonyl and hydroxyl groups to allow hydrogen bonding; and (iv) presence of two (hetero)aromatic rings at both sides of the molecule. The hydrogen bonding involving amide carbonyl, hydroxyl at position 9, and, very probably, ammonium N-H+ and Cl− anion appears to be responsible for the formation of infinite molecular chains required for the first step of gel formation. Subsequent lateral cooperation of molecular chains into fibers occurred, presumably, due to the aromatic π−π-stacking interactions. Supercritical carbon dioxide drying of the organogels gave rise to aerogels with morphologies different from that of air-dried samples.

Atmospheric water triggers supramolecular gel formation of novel low molecular weight maslinic and oleanolic triterpenic derivatives

Novel maslinic and oleanolic triterpenic derivatives behave as supramolecular gelators. These compounds have the capacity to gelify DMSO and DMF by slowly capturing atmospheric water.

Applications of Pillar[n]arene-Based Supramolecular Assemblies.

Macrocycles are an important player in supramolecular chemistry. In 2008, a new class of macrocycles, "pillar[n]arenes", were first discovered. Research efforts in the area of pillar[n]arenes have elucidated key properties, such as their shape, reaction mechanism, host-guest properties, and their versatile functionality, which has contributed to the development of pillar[n]arene chemistry and their applications to various fields. This Minireview describes how pillar[n]arene-based supramolecular assemblies can be applied to supramolecular gel formation, reactions, light-harvesting systems, drug-delivery systems, biochemical applications, separation and storage materials, and surface chemistry.

Cover Feature: Solvent Control over Supramolecular Gel Formation and Fluorescence for a Highly Crystalline π-Conjugated Polymer (Chem. Asian J. 16/2018)

Cover Feature: Solvent Control over Supramolecular Gel Formation and Fluorescence for a Highly Crystalline π-Conjugated Polymer (Chem. Asian J. 16/2018)

Solvent Control over Supramolecular Gel Formation and Fluorescence for a Highly Crystalline π-Conjugated Polymer.

In π-conjugated polymers (πCPs), crystallinity and fluorescence typically exhibit a trade-off relationship. Here, we have synthesized a highly crystalline and fluorescent π-conjugated polymer with a simple alternating structure of 1,2,4,5-tetrafluorophenylene and 3,3'-dihexyl-2,2'-bithiophene units. In film, the polymer exhibited efficient red-colored fluorescence, an improved quantum yield (Φsol =13 %→Φfilm =23 %) and a crystalline structure. Interestingly, supramolecular gel formation occurred in appropriate solvents, and the macrostructure and fluorescence properties of the gel could be directly controlled by the choice of the solvent. The polymer self-assembled into a spherical form that exhibited red fluorescence in non-aromatic solvent (1,2-dichloroethane) and into a fibrous form that exhibited yellow fluorescence in aromatic solvent (mesitylene).

Solvent‐Controlled Assembly of Aromatic Glutamic Dendrimers for Efficient Luminescent Color Conversion

AbstractA binary supramolecular system where self‐sorting and coassembly behavior can be switched by changing the solvent polarity is hereby reported. Glutamic dendron is separately conjugated with pyrene and naphthalimide luminophores through an alkyl spacer. The resulting structurally similar building units can self‐assemble into one‐dimensional micro/nanostructures with hexagonal and lamellar packing, respectively. Varying solvents from polar aqueous solution to nonpolar decane is evidenced to profoundly inverse the superchirality and switch self‐sorted assembly to coassembly of the two building blocks. The moisture sensitivity of the naphthalimide moiety is considered the primary driving force for the self‐sorting phenomenon in aqueous solution, resulting in inevitable hydration to repel its stacking with hydrophobic pyrene moiety. On the other hand, the naphthalimide unit can integrate segmentally with the pyrene unit in decane, greatly facilitating the nanofiber growth and supramolecular gel formation along with improved energy transfer efficiency between luminophores. As a result, the coassembly‐based thin films show efficient luminescent color conversion upon the UV light irradiation. This research presents a useful route for the fabrication of controllable solution‐processed light emitting devices from self‐assembled multicomponent systems.

Preparation and adsorption capacities evaluation of supramolecular two-component gels nanostructures via fluorine-containing diacid and glutamic acid amino derivative

ABSTRACTIn this paper, new two-component supramolecular gels via 2,2-bis(4-carboxyphenyl)hexafluoropropane and N-(4-Aminobenzoyl)-L-glutamic acid diethyl ester have been prepared and tested in ethanol/water mixed solvents. Scanning electron microscope (SEM), Transmission electron microscope (TEM), powder X-ray diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FT-IR) were measured to characterize the morphology and nanostructure of the prepared supramolecular gels. The obtained experimental data reveal that different mixed solvents ratios play an important role in regulating formation of nanostructures and the gelation behaviors. Favorable volume ratios in ethanol/water mixed solvents seemed suitable for the formation of supramolecular gels due to cooperation of multi-intermolecular weak forces. SEM and TEM observations indicate that the gelator molecules self-assemble into different aggregate nanostructures including sheets, rods, bar shape, and belt in different solvents ratios. The adsorption capacities of the as-obtained supramolecular gels on model dyes demonstrate good removal rates with the adsorption process according to rather pseudo-first-order model than pseudo-second-order model. The present research work show it potential to prepare new gel soft materials and promising candidates for wastewater treatment.

Supramolecular Gel Formation Based on Glycolipids Derived from Renewable Resources.

The potential applications of self-assembled supramolecular gels based on natural molecules encouraged the researchers to develop a versatile synthetic method for their structural analogues. Herein, we report a facile synthesis of glycolipid from renewable resources, cashew nut shell liquid,d and d-glucose in good yield. Gelation behavior of these glycolipids were studied in a wide range of solvents and oils. To our delight, compound 5b formed a hydrogel with Critical gelator concentration (CGC) of 0.29% w/v. Morphological analysis of the hydrogel depicts the formation of twisted fibers with an entangled network. Formation of a twisted fibrous structure was further identified by CD spectral studies with respect to temperature. The molecular self-assembly assisted by hydrogen bonding, hydrophobic, and π–π stacking interactions were identified by X-ray diffraction (XRD) and FTIR studies. Rheological analysis depicted the mechanical strength and stability of the hydrogel, which is crucial in predicting the practical applications of supramolecular soft materials.

A Low-Molecular-Weight Gelator Composed of Pyrene and Fluorene Moieties for Effective Charge Transfer in Supramolecular Ambidextrous Gel.

Charge-transfer (CT) gel materials obtained from low-molecular-weight (LMW) compounds through a supramolecular self-assembly approach have received fascinating attention by many researchers because of their interesting material property and potential applications. However, most of the CT gel materials constructed were of organogels while the construction of CT gels in the form of a hydrogel is a challenge because of the solubility issue in water, which considerably limits the use of CT hydrogels. Herein, for the first time, we report a new LMW gelator [Nα-(fluorenylmethoxycarbonyl)-Nε-(δ-butyric-1-pyrenyl)-l-lysine, (FmKPy)], composed of two functional moieties such as fluorenylmethoxycarbonyl and pyrene, which not only parade both hydro and organo (ambidextrous) supramolecular gel formation but also exhibit CT ambidextrous gels when mixed with an electron acceptor such as 2,4,7-trinitro-9-fluorenone (TNF). This finding is significant as the established CT organogelator in the literature did not form an organogel in the absence of an electron acceptor or lose their gelation property upon the addition of the acceptor. CT between pyrene and TNF was confirmed by the color change as well as the appearance of the CT band in the visible region of the absorption spectrum. CT between FmKPy and TNF was supported by the solvent dilution method using tetrahydrofuran as the gel breaker and pyrene fluorescence quenching in the case compound containing pyrene and TNF. The morphology of FmKPy ambidextrous gels indicates the fibrous nature while the self-assembled structure is primarily stabilized by π-π stacking among fluorenyl and pyrenyl moieties and hydrogen bonding between amide groups. The FmKPy-TNF CT ambidextrous gel retains the fibrous nature; however, the size of the fibers changed. In FmKPy-TNF CT gels, TNF is intercalated between pyrene moieties in the self-assembled structure as confirmed by fluorescence quenching and powder X-ray diffraction. The FmKPy ambidextrous gel exhibits significant properties such as low minimum gelation concentration (MGC), thixotropic nature, pH stimuli response, and high thermal stability. Upon the addition of TNF, the FmKPy-TNF CT ambidextrous gel maintains all these properties except MGC which increased for FmKPy-TNF. Because pyrene-based LMW organogels have been developed widely for many applications while their hydrogels were limited, the current finding of the pyrene-based ambidextrous fluorescent gel with the CT property provides a wide opportunity to use FmKPy as a soft material maker and also for potential applications in fields like surface coating, three-dimensional printing, and so forth.