Critical Gelation Concentration Research Articles

Solvent-Dependent Nanostructures Based on Active π-Aggregation Induced Emission Enhancement of New Carbazole Derivatives of Triphenylacrylonitrile.

In the present study, the carbazole and 2,3,3-triphenylacrylonitrile (TPAN) nanostructures (2-CTPAN and 2,2'-CTPAN) have been designed and synthesized by Pd-catalyzed Sonogashira cross-coupling reaction. CTPAN exhibit aggregation-induced emission enhancement (AIEE) behavior in water with high fluorescence quantum yield. Both the compounds show tunable self-assembly in water as well as in N,N-dimethylformamide (DMF) by extended π-π stacking interactions. CTPAN can be self-assembled into spherical particles in water and the structures of these self-assemblies have been investigated using X-ray diffraction. Interestingly, 2-CTPAN and 2,2'-CTPAN form organogels with a critical gelation concentration (CGC) of 11 and 15 mg mL-1 , respectively, in DMF and exhibit acicular and rod shaped morphology, respectively. The single-crystal structure of 2-CTPAN shows that the intermolecular C-H⋅⋅⋅π interactions lock the molecular conformation into a staircase-shaped supramolecular assembly. These AIEE active compounds reveal high water dispersibility, strong yellow fluorescence with high quantum yield, promising photostability and excellent biocompatibility, which make them potential bioimaging agents.

Insights into a novel class of azobenzenes incorporating 4,6-O-protected sugars as photo-responsive organogelators.

A novel class of 4,6-O-butylidene/ethylidene/benzylidene β-d-glucopyranose gelator functionalized with photo-responsive azobenzene moieties were designed and synthesized and also characterized using different spectral techniques. These azobenzene-based organogelators can gel even at lower concentrations (critical gelation concentration – 0.5% and 1%). A morphological study of the gels shows one-dimensional aggregated bundles and helical fibres. The main driving force for the self-assembly is through cooperative interactions exhibited by the different groups viz., sugar hydroxyl (hydrogen bonding interaction), azobenzene (aromatic π–π interaction) and alkyl chain of the protecting group (van der Waals interaction).

New C-terminal hydrazide L-Leucine derivatives as multi-solvent low molecular weight organogelators

Three new low-molecular-weight gelators (LMWGs) based on L-Leucine derivatives bearing different chain lengths (i.e. 9, 12 or 16) were designed and synthesized (designated as 1-3). The N-terminal is carrying the various alkyl chain lengths where the C-terminal is modified with hydrazide moiety. The prepared gelators 1-3 were fully characterized using 1H, 13C NMR, FTIR and mass spectroscopy. The gelation behavior has also been investigated using different organic solvents and oils with determination of critical gelation concentration (CGC). The self-assembly process was investigated by recording FTIR spectra gel states to investigate the driving forces for gelation process. The morphology of the prepared xerogels was studied using SEM.

Effect of cellulose nanocrystals on the performance of drug loaded in situ gelling thermo-responsive ophthalmic formulations

Triblock poloxamer copolymer (PM) has been extensively utilized to deliver various ophthalmic pharmaceutical compounds. The aim of efficient ophthalmic drug delivery strategy is to attain the longer precorneal resident time and good bioavailability of drugs. In this pursuit, the influence of cellulose nanocrystals (CNC) on the in situ gelation behavior of PM and in vitro release of pilocarpine hydrochloride from the nanocomposites formulations was studied. The critical concentration of gelation of PM being 18% (wt/v) was dropped to 16.6% (wt/v) by the addition of a very low percentage of CNC. The reinforcing nature of CNC via H-bonding in the in situ nanocomposite gel also led to an increase in gel strength along with the sustained release of loaded drugs when compared with the pure PM gel. All formulations revealed that the drug release mechanism is controlled by the Fickian diffusion. Thus, the CNC has a significant effect on the gelation behavior, gel strength, and drug release kinetics of PM-CNC formulations.

Chirality-Enabled Liquid Crystalline Physical Gels with High Modulus but Low Driving Voltage.

Self-supporting liquid crystalline physical gels with facile electro-optic response are highly desirable, but their development is challenging because both the storage modulus and driving voltage increase simultaneously with gelator loading. Herein, we report liquid crystalline physical gels with high modulus but low driving voltage. This behavior is enabled by chirality transfer from the molecular level to three-dimensional fibrous networks during the self-assembly of 1,4-benzenedicarboxamide phenylalanine derivatives. Interestingly, the critical gel concentration is as low as 0.1 wt %. Our findings open doors to understanding and exploiting the role of chirality in organic gels.

Self-Assembly and Hydrogelation of Coil–Sheet Poly(l-lysine)-block-poly(l-threonine) Block Copolypeptides

This study reports the self-assembly and hydrogelation of coil–sheet poly(l-lysine)-block-poly(l-threonine) (PLL-b-PLT) block copolypeptides. Our experiments showed that the PLL-b-PLT block copolypeptides with degrees of polymerization (DPs) between 30 and 60 can self-assemble to form fibrils due to the packing of sheetlike PLT at low polymer concentrations; moreover, further increasing the polymer concentration can result in the formation of transparent hydrogels due to fibril entanglements. The hydrogelation was determined by the orientation and packing of the fibril assemblies, which aremainly dictated by the balance between the intermolecular hydrogen bonding interactions and charge repulsion exerted respectively by sheetlike PLT and positively charged, coil PLL segments. The noncovalent interactions can be manipulated by varying the polypeptide chain length and composition, which would result in these block copolypeptides exhibiting different critical gelation concentrations (CGCs), gel molecular ass...

Synthesis and supramolecular self-assembly of glutamic acid-based squaramides.

We describe the preparation and characterization of two new unsymmetrical squaramide-based organogelators. The synthesis of the compounds was carried out by subsequent amine condensations starting from dimethyl squarate. The design of the gelators involved a squaramide core connected on one side to a long aliphatic chain and on the other side to a glutamic acid residue. The gelator bearing the free carboxylic groups showed a lower gelation capacity than its precursor diester derivative. Some selected gels were further studied by infrared spectroscopy, rheology and electron microscopy. Critical gelation concentrations and gel-to-sol transition temperatures were also determined for each case. In addition, the superior squaramide diester gelator was compared with an analogue triazole-based gelator in terms of critical gelation concentration, gelation kinetics and thermal phase transition.

Enzyme responsive supramolecular hydrogels assembled from nonionic peptide amphiphiles

Smart peptide hydrogels are of great interest for their great potential applications. Here, we report a facile approach to prepare a class of enzyme-responsive hydrogels in a scalable manner. These hydrogels self-assemble from a family of nonionic peptide amphiphiles (PAs) synthesized by sequential ring-opening polymerization (ROP) of γ-benzyl- L -glutamate N -carboxyanhydride (BLG-NCA) and L -tyrosine N -carboxyanhydride (Tyr-NCA), followed by subsequent aminolysis. These PA samples can readily form a clear hydrogel with a critical gelation concentration as low as 0.5 wt%. The incorporation of tyrosine residues offers hydrophobicity, hydrogen-bonding interaction and enzyme-responsive properties. The hydrogel-to-nanogel transition is observed under physiological conditions in the presence of horseradish peroxidase (HRP) and hydrogen peroxide (H2O2). The obtained PA hydrogels are ideal candidates for the new generation of smart scaffolds.

Физико-химическое и технологическое исследование интерполимерного комплекса полиметакриловой кислоты и полиэтиленгликоля как основы для создания матричных систем

Проведено изучение физико-химических и технологических свойств интерполимерного комплекса полиметакриловой кислоты и полиэтиленгликоля, известного под торговым названием «Композиционный полимерный носитель» (ФГУП НИИ Полимеров, Россия). Данный полимер является вспомогательным веществом, использующемся в технологии твердых лекарственных форм как матрицеобразователь и как пленкообразователь для достижения пролонгированного и замедленного высвобождения. С целью расширения возможностей применения композиционного полимерного носителя изучены растворимость полимера в водных растворах и органических растворителях, технологические и поверхностно-активные свойства полимера, определена критическая концентрация гелеобразования. Получены экспериментальные образцы таблеток и пероральных гелей модельных веществ, близких по физико-химическим свойствам, на основе композиционного полимерного носителя в различных концентрациях, для которых изучали технологические, реологические и биофармацевтические свойства. Показана перспективность использования полимера в составе как твердых, так и мягких лекарственных форм для обеспечения пролонгированного высвобождения лекарственных веществ.

Polymer Probe Diffusion in Globular Protein Gels and Aggregate Suspensions.

Transport properties of macromolecules in dense aggregate suspensions and gels of proteins are important for usage of these biomaterials in areas such as pharmaceutics, food, and cosmetics. The mobility of polymers in protein gels has received some attention in the past, but the mobility in dense aggregate suspensions has not yet been investigated. In this study, self-diffusion of probe dextran chains was studied in suspensions of aggregates with different size and morphology and in gels using fluorescence recovery after photobleaching over a wide range of concentrations. Brownian diffusion of the probes was observed in aggregate suspensions as well as in weak gels formed just beyond the critical gel concentration. Diffusion of polymers in dense suspensions of protein aggregates depends not only on the concentration but also on the size and morphology of the aggregates. It is not directly related to the viscosity or the dynamic correlation length. Diffusion of polymers in protein gels is anomalous and occurs on logarithmic time scales. The recovery of the fluorescence for densely cross-linked gels was logarithmic with time, suggesting an exponential distribution of diffusion coefficients.

Effect of Starch on the Equilibrium of Boric Acid

We have reported that behavior of starch depended on the existing of boric acid. Noteworthy, gelation behavior of soluble starch, one of the modified starch, was different from other native starches. Critical concentration of starch gelation (CCSG), in other words, the minimum concentration of starch to form gel, was increased as the amount of boric acid increased when soluble starch was employed. On the contrary, CCSG of native starches (corn, wheat, and potato) was decreased as the amount of boric acid increased. We have also tested drying process of gelatinized starches to evaluate the effect of boric acid on the water-holding ability of starch. When soluble starch was employed, no difference of the rate of water loss from gelatinized starch at 100 °C was observed, irrespective of the existing of boric acid. In contrast, the drying rate of native starches were strongly affected and suppressed in the presence of boric acid. Based on these fact, we assumed that the effect of boric acid changes depending on the type of starch. It is well known that boric acid B(OH)3 is shifted to B(OH)4 - above pH 9.24. Therefore, dry tolerance of gelatinized starch was expected to be shifted by pH value. To confirm the effect of pH on the dry tolerance of gelatinized starch in the presence of boric acid, we measured the rate of water loss from gelatinized starch at 100 °C. The rates of the water loss from all tested starches were shifted to be smaller by increasing pH value. The rate of water loss from native starches were gradually shifted to be smaller, while that from soluble starch dropped between pH 9 and 10. Kinetic analysis of water loss from gelatinized starch revealed that there were two phases in the process of water loss from gelatinized starch until complete water loss. Then, we analyzed the initial stage of the dry process by regarding this process as the first order reaction. Plots of the rate constant, k value versus pH value showed like titration curves in every dry process of starches. Interestingly, inflection point of the dry process using soluble starch differed from native starches. The inflection point was around pH 9, whereas those of native starches were around pH 8. This fact indicates the equilibrium of boric acid may vary by depending on the type of starch. To investigate that change of the equilibrium of boric acid in the presence of starch, gelatinized starch in the presence of boric acid were measured by Raman spectroscopy. Raman spectra of gelatinized starch in the presence of boric acid revealed much amount of starch inhibited change of three-coodinated boric acid to four-coodinated even in high basic aqueous solution. Detailed analysis is currently being investigated and will be presented at this meeting.

Ratiometric Indicator Based on Vibration-Induced Emission for in Situ and Real-Time Monitoring of Gelation Processes

Monitoring specific processes such as gelation in a ratiometric and visual manner is of scientific value and has practical implications but remains challenging. Herein, an innovative fluorescent low-molecular-weight gelator (DPAC-CHOL) capable of revealing and self-revealing the gelation processes in situ and in real time via the ratiometric fluorescence change from orange-red to blue has been developed. By virtue of its vibration-induced emission attribute, the gelation point, critical gelation concentration, and the internal stiffness of the gel networks of DPAC-CHOL and other gelation systems could be facilely evaluated in a ratiometric and naked-eye-observable fashion. Noteworthily, the DPAC-CHOL-doped gelation system Ph-CHOL can quantitatively identify the environmental temperature in a daily-concerned range (i.e., 20-55 °C). This work not only provides a versatile advanced material but also opens up a new avenue for the investigation of gelation systems.

Helical Structure of Nucleation in a Solution of a Chiral Trifluoroacetylated Amino Alcohol

The occurrence of a nanoscale disperse phase in the homochiral solutions of N-trifluoroacetylated α-amino alcohols (TFAAAs) was found experimentally by the observation of the Tyndall effect and dynamic light scattering (DLS) measurements. The nanoscale fraction was observed at concentrations lower than the critical concentration of gelation and string formation (c*). Direct optical microscopy showed that, as a rule, strings with a helical structure resulted from the homogeneous nucleations. Chirooptical measurements revealed some signs of helicity below the concentration threshold (c*). The molecular dynamics simulation of the condensation of a homochiral TFAAA in heptane showed that TFAAA molecular aggregates 2–3 nm in diameter were formed already after 100 ns. These aggregates have some signs of the homogeneous nucleations with a helical structure, and they can be considered as the nuclei of helical strings.

Synthesis, Characterization, and Self-Assembly of a Tetrathiafulvalene (TTF)–Triglycyl Derivative

In this work, we describe the synthesis, characterization, and self-assembly properties of a new tetrathiafulvalene (TTF)–triglycyl low-molecular-weight (LMW) gelator. Supramolecular organogels were obtained in various solvents via a heating–cooling cycle. Critical gelation concentrations (CGC) (range ≈ 5–50 g/L) and thermal gel-to-sol transition temperatures (Tgel) (range ≈ 36–51 °C) were determined for each gel. Fourier transform infrared (FT-IR) spectroscopy suggested that the gelator is also aggregated in its solid state via a similar hydrogen-bonding pattern. The fibrillar microstructure and viscoelastic properties of selected gels were demonstrated by means of field-emission electron microscopy (FE-SEM) and rheological measurements. As expected, exposure of a model xerogel to I2 vapor caused the oxidation of the TTF unit as confirmed by UV-vis-NIR analysis. However, FT-IR spectroscopy showed that the oxidation was accompanied with concurrent alteration of the hydrogen-bonded network.

Gelation properties of terpyridine gluconic acid derivatives and their reversible stimuli-responsive white light emitting solution

Two gluconic acid derivatives C3 and C6 bearing a terpyridyl moiety were designed and synthesized. Thanks to the hydrophilic interaction from glucosyl moiety, C3 and C6 can dissolve in polar solvents and gel aromatic solvents with a critical gel concentration of weight 1.5%. The solution consisting of organic ligand C3 as sensitizer and Ln(III) ions as emitters can realize white light emission with thermo- and chemical stimuli-response properties in luminescence spectra. Further, the self-assemblies of C3 and C6 were examined by the combination of the theoretical calculations via hybrid density functional theory (DFT) with 1H nuclear magnetic resonance (1HNMR) and powder X-ray diffraction (PXRD) analysis. The study actually provides a reliable method for the formation of potential functional smart materials.

Component effect of stem cell-loaded thermosensitive polypeptide hydrogels on cartilage repair

Biophysical properties of the desired biomimetic scaffolds, such as porosity and elasticity, have been proven associated with the efficacy of cartilage regeneration. In this work, the copolymers of poly(l-alanine)-block-poly(ethylene glycol)-block-poly(l-alanine) (PA-PEG-PA) and poly(l-alanine-co-l-phenylalanine)-block-poly(ethylene glycol)-block-poly(l-alanine-co-l-phenylalanine) (PAF-PEG-PAF) with different ratios of alanine to phenylalanine were synthesized. The introduction of a hydrophobic amino acid, i.e., phenylalanine, into polyalanine-based thermosensitive hydrogel led to the enhanced gelation behaviors and upregulated mechanical properties. Moreover, the increase of phenylalanine content resulted in the enlarged pore size and enhanced mechanical strength of PAF-PEG-PAF thermogel, followed by the regeneration of hyaline-like cartilage with reduced fibrous tissue formation in vivo. The findings indicated the great potential of thermosensitive polypeptide hydrogels in cartilage tissue engineering. Statement of SignificanceArticular cartilage defect has limited self-repair ability due to the lack of blood supply and innervation, which may lead to knee osteoarthritis afterwards. Injectable hydrogels are demonstrated possessing outstanding properties as biomimetic scaffolds in cartilage tissue engineering, while the effect of biophysical properties on the efficacy of cartilage regeneration has not been revealed. Herein, the poly(ethylene glycol)-polypeptide triblock copolymers with different ratios of alanine to phenylalanine were synthesized. The sol-to-gel transition temperature and the critical gelation concentration decreased as the increased amount of phenylalanine unit, resulting in the enlarged pore size and enhanced mechanical strength. These features lead to better regeneration of hyaline-like cartilage with reduced fibrous tissue formation, indicating great potential of thermosensitive polypeptide hydrogels for efficient cartilage repair.

Isosteric Substitution of 4 H-1,2,4-Triazole by 1 H-1,2,3-Triazole in Isophthalic Derivative Enabled Hydrogel Formation for Controlled Drug Delivery.

In this work, we demonstrated that the simple substitution of the 1,2,4-triazole moiety in 5-( 4H-1,2,4-triazol-4-yl)isophthalic acid (5-TIA) by the 1 H-1,2,3-triazol-5-yl unit enables the preparation of a hydrogelator (click-TIA). In sharp contrast to 5-TIA, its isostere click-TIA undergoes self-assembly in water upon sonication, leading to the formation of stable supramolecular viscoelastic hydrogels with a critical gelation concentration of 6 g/L. Hydrogels made of click-TIA as well as hybrid hydrogels made of the mixture click-TIA + 5-TIA (molar ratio 1:0.2) were used to compare different properties of the materials (i.e., rheological properties, thermal properties, mechanical stability, morphology). In terms of toxicity, neither click-TIA nor 5-TIA showed cytotoxic effects on cellular viability of HeLa cells up to 2.3 × 10-3 g/L when compared to untreated cells incubated with DMSO. Furthermore, the hydrogels were used for the encapsulation and in vitro controlled release of oxytetracycline that followed first-order kinetics. For the hydrogel made of click-TIA, a maximum drug release of ∼60% was reached after ∼8 h within a pH range between 6.5 and 10. However, the release rate was reduced to approximately half of its value at pH values between 1.2 and 5.0, whereas the use of hybrid hydrogels made of click-TIA + 5-TIA allowed to reduce the original rate at pH ≤ 6.5.

Poly(carbonate urethane)-Based Thermogels with Enhanced Drug Release Efficacy for Chemotherapeutic Applications.

In this study, we report the synthesis and characterisation of a thermogelling poly(carbonate urethane) system comprising poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG) and poly(polytetrahydrofuran carbonate) (PTHF carbonate). The incorporation of PTHF carbonate allowed for the control of the lower critical solution temperature (LCST) and decreased critical gelation concentration (CGC) of the thermogels significantly. In addition, the as-prepared thermogels displayed low toxicity against HepG2, L02 and HEK293T cells. Drug release studies were carried out using doxorubicin (Dox). Studies conducted using nude mice models with hepatocellular carcinoma revealed that the Dox-loaded poly(PEG/PPG/PTHF carbonate urethane) thermogels showed excellent in vivo anti-tumour performance and effectively inhibited tumour growth in the tested model.

デンプンのゲルに対するホウ砂の添加効果およびゲルの保水能評価

As result of evaluation of the effect of borax on starch gelation, the critical concentration of starch gelation decreased with increasing borax concentration when native starches were used, while the critical concentration of starch gelation increased when soluble starch was used. When soluble starch was employed, no significant difference was observed. In contrast, addition of borax reduced the rate of drying of native starch gels, suggesting that addition of borax is effective for increasing the water-retention of native starches. These results suggest that the possible site of attachment for borate ester is dependent on the local structure of the starch, such as helix or branching configuration.

The sol-gel transition of ultra-low solid content TEMPO-cellulose nanofibril/mixed-linkage β-glucan bionanocomposite gels.

We present the preparation, morphological analysis, and rheological characterization of ultra-low solid content gels prepared by physically cross-linking TEMPO-oxidized cellulose nanofibrils (TEMPO-CNF) with the soluble plant-cell-wall polysaccharide, mixed-linkage β-glucan (MLG). Of particular note, gel formation was rapidly induced by very small amounts of MLG (e.g. 0.125% w/v) at extremely low TEMPO-CNF concentration (0.05% w/v), which independently were otherwise fluid and thus easily handled. Rheology of these bionanocomposite gel systems as a function of MLG and TEMPO-CNF concentrations revealed that the critical gel concentration of MLG and TEMPO-CNF followed a power-law relation of the concentration of the other component. Surprisingly, these systems also exhibited an additional transition to thick gels at high TEMPO-CNF and MLG concentrations that was visible only at low frequencies. Cryogenic scanning electron microscopy (cryo-SEM) imaging of admixture solutions and gels revealed increased network crowding with increasing MLG amounts. The data are consistent with the hypothesis that non-covalent cellulose-MLG interactions, analogous to those occurring within plant cell walls, drive gel formation. The ability to tune gel physical properties simply by controlling CNF (a promising forest bioproduct) and MLG (a readily available agricultural polysaccharide) fractions at very low solid and polymer content opens new possibilities for material applications in diverse industries.