Two-component Gel Research Articles

Chiral Assembly Preferences and Directing Effects in Supramolecular Two-Component Organogels.

The impact of chirality on the self-assembly of supramolecular gels is of considerable importance, as molecular-scale programming can be translated into nanostructuring and ultimately affect macroscopic performance. This paper explores the effect of chirality on the assembly of two-component gels comprised of a second-generation dendritic lysine peptide acid, containing three chiral centres, and an amine. This combination forms an acid–amine complex that assembles into nanofibres through peptide-peptide hydrogen bonds, leading to organogels. With achiral amines, a racemic mixture of l,l,l and d,d,d dendritic peptide acids surprisingly forms the best gels—more commonly, mixing enantiomers suppresses gelation. Thermodynamic studies demonstrate that depending on the amine, the greater stability of heterochiral gels can either be entropically or enthalpically driven. With amines possessing “R” chirality, the l,l,l peptide acid consistently forms more effective gels than its d,d,d analogue. Furthermore, in mixed gels, l,l,l sometimes imposes its assembly preference onto d,d,d. In summary, this paper demonstrates a rare example in which heterochiral gels are preferred, and also explores directing effects when each component in a two-component gel is chiral.

Molecular Design Strategy for a Two-Component Gel Based on a Thermally Activated Delayed Fluorescence Emitter

Luminescent materials that can spontaneously assemble into highly ordered networks are essential to improve the quality of thin films in stacked device architectures and enhance the performances of solution-processed organic light emitting devices (OLEDs). Herein, we report two pyridine-decorated thermally activated delayed fluorescence (TADF) emitters, 3PyCzBP and 4PyCzBP. 4PyCzBP shows robust two-component gel formation in the presence of either tartaric acid or succinic acid along with significant emission enhancement. Morphology studies reveal that these gels consist of homogeneous nanofibers assembled in hierarchical supramolecular networks. Transient photoluminescence spectra confirm that the gels emit via a TADF mechanism, making them the first examples of TADF gels. These nanofibers are promising candidates as self-assembled emitting nanofibers in thin films in solution-processed OLEDs.

Diffusion across a gel-gel interface - molecular-scale mobility of self-assembled 'solid-like' gel nanofibres in multi-component supramolecular organogels.

This paper explores macroscopic-scale diffusion of the molecular-scale building blocks of two-component self-assembled organogel nanofibres using a diffusion cell in which two different gels are in contact with one another. Both components of the 'solid-like' nanofibres (lysine peptide dendron acids and amines) can diffuse through these gels and across a gel-gel interface, although diffusion is significantly slower than that of a non-interactive additive in the 'liquid-like' phase of the gel. Amine diffusion was probed by bringing similar gels with different amines into contact. Dendron acid diffusion was tested by bringing similar gels with enantiomeric dendrons into contact. Surprisingly, dendron and amine diffusion rates were similar, even though the peptide dendron is more intimately hydrogen bonded in the self-assembled nanofibres. It is proposed that thermal disassembly of the acid-amine complex delivers both components into the liquid-like phase, allowing them to diffuse via a decomplexation/recomplexation mechanism. This is a rare observation in which molecules assembled into solid-like gel nanofibres are mobile - in dynamic equilibrium with the liquid-like phase. Gel nanofibre diffusion and reorganisation are vital in understanding dynamic materials processes such as metastability, self-healing and adaptability.

Novel two-component gels with multi-stimuli response: the gel–sol phase transition and color changes

A smart two-component gelator system was prepared by a combination of d-gluconic acetal derivatives and terpyridyl moieties.

Stereochemical effects on dynamics in two-component systems of gelators with perfluoroalkyl and alkyl chains as revealed by vibrational circular dichroism.

A mixture of chiral low-molecular weight gelators, (1R,2R)- or (1S,2S)-N,N'-diperfluoroheptanoyl-1,2-diaminocyclohexane (denoted as RR- or SS-CF7, respectively) and (1R,2R)- or (1S,2S)-N,N'-diheptanoyl-1,2-diaminocyclohexane (denoted as RR- or SS-CH7, respectively), was used as a two-component gelator in acetonitrile solvent. The process of gelation was investigated by time-step vibrational circular dichroism (VCD) spectroscopy. The method enabled us to study the dynamical behavior of CF7 and CH7 molecules independent of their characteristic vibrational bands. We focused on the effects of the chirality relation between the two gelators. In the case of the enantiomeric mixtures (RR-CF7/RR-CH7 or SS-CF7/SS-CH7), the two components exhibited different time-courses in their VCD spectra. As for CF7, the couplet peak intensities assigned to C[double bond, length as m-dash]O stretching increased with time, while those for CH7 remained low. In the case of the racemic mixture (RR-CF7/SS-CH7 or SS-CF7/RR-CH7), the intensities of the peaks assigned to the C[double bond, length as m-dash]O stretching vibration for both CF7 and CH7 molecules maintained a constant level with time. The VCD results were compared with the SEM images of the freeze-dried gel samples taken at various time intervals. Furthermore, the mechanisms for the gelation of two-component systems are discussed.

Novel supramolecular organogel based on β-cyclodextrin as a green drug carrier for enhancing anticancer effects

Two-component gel of β-cyclodextrin as gelator and glycerol as solvent is investigated. This novel gel loading with 5-fluorouracil or methotrexate can enhance anticancer abilities effectively. So, the blank β-cyclodextrin gel can be a candidate for versatile drug delivery. The morphology of the gel is characterized by OM and SEM. The rheology and DSC are also applied to study the properties of the obtained gel. The mechanism of gel formation is analyzed by FT-IR and XRD, indicating the main driving forces for gel formation are self-aggregation of β-cyclodextrins and H-bondings between glycerol molecules. Amazingly, an in vitro cytotoxicity assay on human hepatocellular carcinoma cells lines shows that the drug-loaded gels with 5-fluorouracil or methotrexate exhibit better anti-cancer effects than that of those two drugs. Hence, the present work developed a new and low-cost drug carrier, which has potential application in drug delivery.

Preparation and Absorption Capacities of Two-Component Supramolecular Gels

Background: Two-component gels are a class of gel system which have different functionalized chemical groups and nanoparticles. The aim of this paper is to introduce readers to the new two-component gels system composed of N-(4-aminobenzoyl)-L-glutamic acid diethyl ester with polyacrylic acid by the self-assembly in different solvents. The obtained morphological and spectral data demonstrate that the single or mixed solvents make a great difference on the gelation abilities of these studied supramolecular gels. Keywords: Two-component gels, nanostructure, self-assembly, adsorption capacity, xerogels, Supramolecular gels.

Preparation and self-assembly of two-component organogels via hexafluoropropane amino derivative and different acids

ABSTRACTIn this paper, new two-component organogels via hexafluoropropane amino derivative and acids with different molecular skeletons were designed and prepared. Their gelation behaviors in some solvents were tested and investigated as new two-component organic gelators. The obtained experimental data demonstrated that the solvents and molecular skeletons played a crucial role in regulating the gelation behaviors and fabrication of nanostructures. Suitable solvents seemed favorable for the formation of supramolecular gels due to cooperation of multi-intermolecular weak forces. Rational self-assembly modes in organogels were proposed and discussed. The present research work may demonstrate new insight to design new two-component soft materials with special nanostructures.

Two-component organogels of phosphorous-based organic acids and diamine

ABSTRACTPhosphorous-based organic acids (P) and diamine (M) were used to produce a supramolecular PM complex at a 2:1 molar ratio, which then formed a stable gel in dimethyl sulfoxide (DMSO) and N, N-dimethylformamide (DMF). According to SEM, the morphologies of the aggregates depended on the steric substitute of phosphorous-based organic acids and the structure of the complementary diamine. 31P NMR and FTIR spectroscopies revealed that hydrogen bonding within the PM complex was the main driving force for the self-aggregation. XRD studies revealed that the two-component gelators mainly assemble into a stricter lamellar structure when increasing the rigidity of the complementary component. In contrast, the gelators with the aliphatic unit mainly assembled into a random lamellar structure and showed more possibility of deforming. As such, the results in this paper demonstrate how structure effects in two-component gel system of phosphorous-based organic acids and diamine can control self-assembly process.

Redox-responsive molecular gels based on camptothecin prodrug with disulfide linkage for controlled and sustained drug release

A novel camptothecin (CPT) prodrug was successfully synthesized by conjugating CPT to adamantanecarboxylic acid (AD) via a cleavable disulfide linkage. The resulting CPT-ss-AD prodrug could act as a low molecular weight gelator to form molecular gels in water/water-miscible organic solvent mixture. Meanwhile, biodegradable amphiphilic block copolymer mPEG-b-P (MAC-co-DTC) (PPMD) was also employed as an organic framework together with CPT-ss-AD to form gel structure. CPT-ss-AD/PPMD gel exhibited less compact molecular arrangement but much more stability than CPT-ss-AD gel. The two kinds of gels could effectively release the original CPT under reductive condition at a near-constant rate without any initial burst. As compared to CPT-ss-AD single-component gel, the two-component gel, CPT-ss-AD/PPMD, had a significantly higher release rate of CPT, while 3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide (MTT) assays also indicated highly potent cytotoxic activity against HeLa cells.

A supramolecular gel electrolyte formed from amide based co-gelator for quasi-solid-state dye-sensitized solar cell with boosted electron kinetic processes

Abstract A supramolecular gel electrolyte ( T gel > 100 °C) is formed from N,N ′-1,8-octanediylbis-dodecanamide and iodoacetamide as two-component co-gelator, and introduced into the quasi-solid-state dye-sensitized solar cells (QS-DSSCs). The different morphologies of microscopic network between two-component and single-component gel electrolytes have influence on the diffusion of redox couple in gel electrolytes and further affect the electron kinetic processes in QS-DSSCs. Compared with the single-component gel electrolyte, the two-component gel electrolyte has less compact gel network and weaker steric hindrance effect, which provides more effective charge transport channel for the diffusion of I 3 /I − redox couple. Meanwhile, the NH 2 groups of iodoacetamide molecules interact with Li + and I 3 − , which also accelerate the transport of I 3 − /I − and decrease in the I 3 − concentration in the TiO 2 /electrolyte interface. As a result, nearly a 12% improvement in short-circuit photocurrent density ( J sc ) and much higher open circuit potential ( V oc ) are found in the two-component gel electrolyte based QS-DSSC. Consequently, the QS-DSSC based on the supramolecular gel electrolyte obtains a 17% enhancement in the photoelectric conversion efficiency (7.32%) in comparison with the QS-DSSC based on the single-component gel electrolyte (6.24%). Furthermore, the degradations of these QS-DSSCs are negligible after one sun light soaking with UV cutoff filter at 50 °C for 1000 h.

Cyclodextrin-Assisted Two-Component Sonogel for Visual Humidity Sensing.

In this work, two naphthalimide-based compounds, 1a and 1b, have been designed and synthesized. Both compounds can form stable two-component gels in n-propanol or n-butanol upon addition of α-cyclodextrin (α-CD) followed by sonication at room temperature. Interestingly, the 1a/α-CD gel is thixotropic and very sensitive to water. Addition of a small amount of water induces rapid gel collapse, allowing further development of the gel as a visual relative humidity sensor. Specificity of the sensor has been confirmed using several approaches, such as scanning electron microscopy and fluorescence, Fourier transform infrared, and 1H NMR spectroscopy experiments. The results show that α-CD acts as a junction for the assembly of 1a or 1b through hydrogen bonding between hydroxyl and amide groups. Upon addition of water, α-CD interacts with the adamantane group of 1a via an incomplete host-guest encapsulation, resulting in the dissociation of the hydrogen-bonding-assisted two-component assembly, accompanied by gel collapse.

PB20 液晶性を示す2成分系ゲル化剤の開発(液晶化学材料,ポスター発表,2015年日本液晶学会討論会)

PB20 液晶性を示す2成分系ゲル化剤の開発(液晶化学材料,ポスター発表,2015年日本液晶学会討論会)

Scaleable two-component gelator from phthalic acid derivatives and primary alkyl amines: acid-base interaction in the cooperative assembly.

A series of phthalic acid derivatives (P) with a carbon-chain tail was designed and synthesized as single-component gelators. A combination of the single-component gelator P and a non-gelling additive n-alkylamine A through acid-base interaction brought about a series of novel phase-selective two-component gelators PA. The gelation capabilities of P and PA, and the structural, morphological, thermo-dynamic and rheological properties of the corresponding gels were investigated. A molecular dynamics simulation showed that the H-bonding network in PA formed between the NH of A and the carbonyl oxygen of P altered the assembly process of gelator P. Crude PA could be synthesized through a one-step process without any purification and could selectively gel the oil phase without a typical heating-cooling process. Moreover, such a crude PA and its gelation process could be amplified to the kilogram scale with high efficiency, which offers a practical economically viable solution to marine oil-spill recovery.

Two-Component Fluorescent-Semiconducting Hydrogel from Naphthalene Diimide-Appended Peptide with Long-Chain Amines: Variation in Thermal and Mechanical Strengths of Gels.

Two-component fluorescent hydrogels have been discovered, containing the mixtures of naphthalene diimide (NDI)-conjugated peptide-functionalized bola-amphiphile and primary amines with long alkyl chains at physiological pH 7.46. The aggregation-induced enhanced emission associated with an NDI-appended peptide in aqueous medium is rare, as water is known to be a good quencher of fluorescence. In this study, an NDI-containing gelator peptide forms a highly fluorescent aggregate in aqueous medium. Absorption and emission spectroscopic techniques reveal the formation of J-aggregates among the chromophoric moieties in their aggregated state in aqueous medium. However, this NDI-containing peptide does not form any gel in aqueous medium. In the presence of the primary amines with long alkyl chains in the buffer solution, it forms two-component fluorescent hydrogels exhibiting bright yellow fluorescence under a UV lamp (365 nm). Probably, the acid-amine interaction between the amines and the bola-amphiphile triggers the gel formation, as evident from Fourier transform infrared data, indicating the presence of a carboxylate group (-COO-) and an ammonium species (NH3+) in the coassembled two-component gel system. Low- and wide-angle powder X-ray diffraction and small-angle X-ray scattering further support the fact that the coassembled state in the gel form is produced by the supramolecular interaction between the NDI-based bola-amphiphile and the long-chain amines. Field-emission scanning electron microscopy and high-resolution transmission electron microscopy images reveal that the π-conjugated coassembled hydrogels exhibit nanofibrillar network morphologies. Interestingly, the coassembled hydrogels exhibit an enhanced fluorescence emission, excited-state lifetime, and quantum yield when compared with those of the NDI-containing amphiphile alone in its self-assembled state in aqueous medium. Moreover, the thermal stability and mechanical strength of these gels have been successfully tuned by varying the alkyl chain length of the corresponding amine. Moreover, these NDI-peptide-conjugated soft materials exhibit semiconducting behavior in their respective coassembled states. This holds future promise to use these peptide-appended NDI-based coassembled soft materials for applications in optoelectronic and other devices.

Two-component dendritic gel: Influence of the aromatic chain length on the organogel stability and supramolecular architecture

Abstract we report the influence of the aromatic chain length on the organogel stability and supramolecular structure. First, we designed and readily prepared a two-component dendritic gelator based on a combination of a third-generation poly(urethane amide) dendron and a rigid aromatic spacer chain ( e.g. , 1,4-diazine, 4,4′-dipyridy, 1,4-bis(pyrid-4-yl)benzene, 4,4-di(4-pyridyl)biphenyl) in 2:1 molar ratio. All two-component gelators were easy to gelate aromatic solvents, especially toluene and p -xylene. When the length of aromatic spacer chain was increased, the gel-to-solution transition temperature first increased, and then decreased. The supramolecular structures and morphologies in xerogel samples of gelators have been carefully studied using the transmission electron microscopy and the atomic force microscopy characterizations. We demonstrated that the stability and supramolecular structures of organogels could be well controlled and regulated by simple length regulation of the aromatic spacer chain in two-component gelator, and thus we believe that applying this kind of method will provide significant new insights for the fabrication of soft materials for various applications.

Tunable self-assembly of two-component gels from novel sorbitol-appended compounds

A smart two-component gelator system was prepared by a combination of two good gelators based on sorbitol-appended compounds.

Fabrication of palladium nanoparticles as effective catalysts by using supramolecular gels

Abstract Two-component supramolecular gels were made through self-assembly of tetrazolyl derivatives and Pd(OAc)2. The robust gels indicated high storage modulus (>10,000 Pa) and loss modulus, which were studied by rheological measurements. The formed Pd nanoparticles (∼9 nm) obtained during the formation of the gel showed effective catalytic hydrogenation of nitrobenzene and could be recovered and reused without loss of activity.

Multicomponent gels: Remote control for self-assembly.

A patterned, spatially resolved gel has now been devised. The two-component gel is formed by sequential assembly of two independent networks of fibres, and the subsequent selective removal of one network by irradiation.

Photoisomerization-induced morphology and transparency transition in an azobenzene based two-component organogel system

A two-component gel containing long chain alkylated gallic acid (GA) and photochromic phenazopyridine (PAP) was prepared. The gel was thoroughly characterized by UV–visible and IR spectra, SEM and POM images, XRD diffraction and dynamic oscillatory measurements. The structure and transparency of the two-component gel can be reversibly changed by alternative UV light irradiation and warming in the palm of the hand. This kind of soft material has potential application in upscale surface functional materials.