Gelation Capability Research Articles

Gelation capability of cysteine-modified cyclo(L-Lys-L-Lys)s dominated by Fmoc and Trt protecting groups

A series of symmetrical peptidomimetics (3–8) based on cysteine-modified cyclo(L-Lys-L-Lys)s were synthesized, and their gelation capability in organic solvents was dominated by fluorenylmethyloxycarbonyl (Fmoc) and triphenylmethyl (Trt) protecting groups and the exchange of thiol-to-disulfide as well. The peptidomimetics holding Trt (3 and 4) showed no gel performance, while the Fmoc groups promoted 5 and 6 to give rise to thermo-reversible organogels in a number of organic solvents. The self-assembled fibrillar networks were distinctly evidenced in the organogels by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) observations. Fourier transform infrared spectroscopy (FT-IR) and fluorescence analyses revealed that the hydrogen bonding and π-π stacking play as major driving forces for the self-assembly of these organogelators. A β-turn secondary structure was deduced for the organogel of 6 by virtue of X-ray diffraction, FT-IR and circular dichroism (CD) measurements, and an interdigitated bilayer structure was also presented.

Hydrogels Triggered by Metal Ions as Precursors of Network CuS for DNA Detection.

The gelation behavior of lithocholate (LC(-) ) with different metal ions in water was investigated. The microstructures of hydrogels were determined to be three-dimensional (3D) networks of fibrous aggregates. The formation of fibrils was speculated to be mainly driven by the coordination between carboxylate of LC(-) and metal ions, accompanied by the assistance of noncovalent interactions such as electrostatic and hydrophobic interactions. The hydrogels, which can maintain the mechanical strength at higher temperature, exhibit thermal stability. Their gelation capability was enhanced with the increase in acidity. The hydrogels of LC(-) and Cu(2+) mixtures served as the precursors for producing network nanostructures of CuS nanoparticles. These new CuS networks exhibit high fluorescence quenching ability and can act as an effective fluorescent sensing platform for ssDNA detection.

A functionalized, injectable hydrogel for localized drug delivery with tunable thermosensitivity: Synthesis and characterization of physical and toxicological properties

Thermosensitive injectable hydrogels have been used for the delivery of pharmacological and cellular therapies in a variety of soft tissue applications. A promising class of synthetic, injectable hydrogels based upon oligo(ethylene glycol) methacrylate (OEGMA) monomers has been previously reported, but these polymers lack reactive groups for covalent attachment of therapeutic molecules. In this work, thermosensitive, amine-reactive and amine-functionalized polymers were developed by incorporation of methacrylic acid N-hydroxysuccinimide ester or 2-aminoethyl methacrylate into OEGMA-based polymers. A model therapeutic peptide, bivalirudin, was conjugated to the amine-reactive hydrogel to investigate effects on the polymer thermosensitivity and gelation properties. The ability to tune the thermosensitivity of the polymer in order to compensate for peptide hydrophilicity and maintain gelation capability below physiological temperature was demonstrated. Cell encapsulation studies using an H9 T-cell line (CD4+) were conducted to evaluate feasibility of the hydrogel as a carrier for cellular therapies. Although this class of polymers is generally considered to be non-toxic, it was found that concentrations required for gelation were incompatible with cell survival. Investigation into the cause of cytotoxicity revealed that a hydrolysis byproduct, diethylene glycol monomethyl ether, is likely a contributing factor. While modifications to structure or composition will be required to enable viable cell encapsulation, the functionalized injectable hydrogel has the potential for controlled delivery of a wide range of drugs.

Quality characteristics of restructured mutton slices developed by cold-set binding system

An investigation was carried out to evaluate the influence of various levels of carrageenan on cold-set gelation of restructured mutton slices (RMS). The addition of 1.5% carrageenan resulted in significantly (P<0.05) higher batter stability, water-holding capacity and cooking yield, than control, 0.5 and 1.0% carrageenan added RMS. Control sample had significantly (P<0.05) the highest diameter shrinkage than carrageenan added treatments. Addition of different levels of carrageenan did not significantly affect collagen content but collagen solubility of RMS was significantly (P<0.05) affected. The RMS processed with 1.5% carrageenan had significantly (P<0.05) highest moisture and lowest protein contents as compared to remaining treatments. Neither fat nor total ash content differed significantly by addition of various levels of carrageenan. Addition of carrageenan significantly (P<0.05) improved both moisture and fat retention values than the control. The RMS formulated with 1.5% carrageenan had significantly (P<0.05) recorded higher chewiness, gumminess, springiness and lowest hardness values than the control and remaining treatments. Addition of different levels of carrageenan significantly (P<0.05) influenced all sensory attributes (except flavour and mouth coating) and rated better for RMS with 1.5% level of carrageenan. It was concluded that, addition of 1.5% carrageenan level had recorded highest quality attributes of RMS due to its better gelation capabilities.

A Study on Synthesis and Gelation Capability of Fmoc and Boc Disubstituted Cyclo(L-Lys-L-Lys)s

A Study on Synthesis and Gelation Capability of Fmoc and Boc Disubstituted Cyclo(<i>L</i>-Lys-<i>L</i>-Lys)s

Monopyrrolotetrathiafulvalene-succinamide conjugates and their TCNQ charge transfer complex based supramolecular gels with multiple stimulus responsiveness.

A series of monopyrrolotetrathiafulvalene-succinamide conjugates and their 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) charge transfer (CT) complexes have been synthesized and investigated as new low-molecular mass organogelators. The gelation capability of these conjugates is highly dependent on the length of the alkyl chain of the terminal amide. Thus, only the short alkyl chain derivatives and could efficiently gelate cyclohexane and methylcyclohexane (MCH). Surprisingly, these gelators react with TCNQ to form stable CT complex gels in both cyclohexane and MCH. The FE-SEM images of the native gels reveal the characteristic gelation morphologies of microporous or fibrous structures, whereas the morphologies of CT complex gels show the fibrillar and globular aggregates in cyclohexane and MCH, respectively. SAXS study of the native gel and the CT complex gel of in cyclohexane suggests that the molecules maintain rectangular and hexagonal columnar molecular packing models in the gel phase, respectively. The native gels undergo a reversible gel-sol phase transition upon exposure to external stimuli, such as temperature and chemical oxidation/reduction. Alternatively, the corresponding CT complex gels exhibit a complicated response to external stimuli. Chemical oxidation by I2 results in the destruction of the gel state. However, neither Fe(3+) nor Cu(2+) can induce the collapse of the gel phase. Interestingly, all the gels show an irreversible gel-sol transition on successively triggering with trifluoroacetic acid and triethylamine. The reformation of the gel from the sol state is achieved just by the addition of water, showing the phase-selective gelation of the solvents from their mixtures with water.

A systematic study of peripherally multiple aromatic ester-functionalized poly(benzyl ether) dendrons for the fabrication of organogels: structure-property relationships and thixotropic property.

A new class of peripherally multiple aromatic ester-functionalized poly(benzyl ether) dendrons and/or dendrimers with different focal point substituents, surface groups, interior structures, as well as different generations have been synthesized and their structure-property relationships with respect to their gelation ability have been investigated systematically. Most of these dendrons are able to gel organic solvents over a wide polarity range. Evident dendritic effects were observed not only in gelation capability but also in thermotropic, morphological, and rheological characterizations. It was disclosed that subtle changes in peripheral ester functionalities and interior dendritic structures affected the gelation behavior of the dendrons significantly. Among all the dendrons studied, the second- and third-generation dendrons G0G2-Me and G0G3-Me with dimethyl isophthalates (DMIP) as peripheral groups exhibited the best capability in gelation, and stable gels were formed in more than 22 aromatic and polar organic solvents. The lowest critical gelation concentration (CGC) reached 2.0 mg mL(-1), indicating that approximately 1.35×10(4) solvent molecules could be entrapped by one dendritic molecule. Further study on driving forces in gel formation was carried out by using a combination of single-crystal/powder X-ray diffraction (XRD) analysis and concentration-dependent (CD)/temperature-dependent (TD) (1)H NMR spectroscopy. The results obtained from these experiments revealed that the multiple π-π stacking of extended π-systems due to the peripheral DMIP rings, cooperatively assisted by non-conventional hydrogen-bonding, is the key contributor in the formation of the highly ordered supramolecular and fibrillar network. In addition, these dendritic organogels exhibited unexpected thixotropic-responsive properties, which make them promising candidates with potential applications in the field of intelligent soft materials.

Multi-stimuli responsive metal-organic gel of benzimidazol-based ligands with lead nitrate and their use in removal of dyes from waste-water

A novel smart metal-organic gel (MOG) formed from biscarboxyl-functionalized benzimidazole derivative (D11) in the presence of lead nitrate has been investigated. The critical gel concentration for the formation of MOG was just 0.36 wt%, which exhibits a super gelation capability of D11. The coordination of the metal to the ligand D11 was found to play a vital role in the construction of the supramolecular MOG. Microstructures determined by SEM observation demonstrated that the MOG was formed by intertwined fibrils. Interestingly, the MOG exhibits pH-induced, thermo-induced, and chemical-induced reversible gel–sol transition. Meanwhile, this supramolecular MOG shows desirable absorption ability of methyl orange dye molecules in aqueous solution.

N‐Boc‐Protected 1,2‐Diphenylethylenediamine‐Based Dendritic Organogels with Multiple‐Stimulus‐Responsive Properties

A new class of poly(benzyl ether) dendrimers, decorated in their cores with N-Boc-protected 1,2-diphenylethylenediamine groups, were synthesized and fully characterized. It was found that the gelation capability of these dendrimers was highly dependent on dendrimer generation, and the second-generation dendrimer (R,R)-G(2)DPENBoc proved to be a highly efficient organogelator. A number of experiments (SEM, TEM, FTIR spectroscopy, (1)H NMR spectroscopy, rheological measurements, UV/Vis absorption spectroscopy, CD, and XRD) revealed that these dendritic molecules self-assembled into elastically interpenetrating one-dimensional nanostructures in organogels. The hydrogen bonding, π-π, and solvophobic interactions were found to be the main driving forces for formation of the gels. Most interestingly, these dendritic organogels exhibited smart multiple-stimulus-responsive behavior upon exposure to environmental stimuli such as temperature, anions, and mechanical stress.

Colour change and luminescence enhancement in a cholesterol-based terpyridyl platinum metallogel via sonication

Two organometallic terpyridyl platinum gelators containing hydrophobic cholesterol with or without large steric hindrance were synthesized and characterized. The complex with three bulky tert-butyl groups (1a) can form a stable gel in several kinds of solvent, such as alcohol, ethyl acetate and toluene with ultrasound irradiation. These sonicated gels display different colour and emission properties compared with their related solutions and precipitates. The intensity of the photoluminescence in gel or solid state of 1a is obviously enhanced by aggregation. The morphology, as well as the surface wettability of 1a can also be reversibly adjusted by sonication and heating. However, the complex without three bulky tert-butyl groups (1b) has poorer solubility and gelation capability, and lower luminescence quantum yield due to strong intermolecular π–π stacking and metal–metal interaction. The spectral and structural variation was characterized by UV-visible and fluorescence spectra, SEM and TEM images, and XRD analysis. The mechanism of the molecularly self-assembled pattern indicates that the large steric hindrance is the reason for the different gelation capabilities and emission properties of the two complexes. Sonication may change the molecular conformation of 1a and promote the ionic dipolar interaction and hydrophobic interactions for gelation, and thus switch the optical properties of the complex in the aggregated state.

Fluorescent hydrogels formed by CH–π and π–π interactions as the main driving forces: an approach toward understanding the relationship between fluorescence and structure

Amide-linked tripyridine derivatives 1, with a para-substituent, and 2, with a meta-substituent, were gelated in water or water-DMSO. The gelation capabilities of 1 and 2 were attributed to the cooperative effects of mainly CH-π and π-π stacking or strong intermolecular hydrogen bonding interactions between the amide groups. The fluorescence properties of gels 1 and 2 were dependent on the binding strength of the π-π stacking.

Temperature regulated supramolecular structures via modifying the balance of multiple non-covalent interactions

Gelation of lithocholic acid (LCA) mixed with zwitterionic alkyldimethylamine oxide, (CnDMAO, n = 10, 12, 14, 16, and 18), in water was detected. Hydrogels can only form at an appropriate hydrophilic–hydrophobic balance condition (n = 12, 14, and 16) with the highest gelation capability at n = 12. Microstructures of hydrogels were determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) observations, indicating that the hydrogels are formed by helically intertwined fibrils. The formation of the hydrogel fibrils was suspected to be driven by a delicate balance of multiple non-covalent interactions including hydrogen bonding, electrostatic interaction, hydrophobic interaction, and the steric effect of LCA molecules. It is very interesting that temperature changes alone can induce a reversible transition between the helical fibrils and vesicle bilayers. The breakage or reconstruction of the hydrogen bonds produced by the temperature change determined the phase structure transition, i.e., the temperature change could modify the balance of the weak interactions for the formation of hydrogels. The observation of modification of supramolecular structures via temperature change may provide an efficient strategy for the phase structure transition and also may find potential applications in biosensors, shape memory, templating of functional molecular materials, etc.

Polyvinylidene fluoride‐co‐chlorotrifluoroethylene and polyvinylidene fluoride‐co‐hexafluoropropylene nanofiber‐coated polypropylene microporous battery separator membranes

AbstractNanofiber‐coated polypropylene (PP) separator membranes were prepared by coating a Celgard® microporous PP membrane with electrospun polyvinylidene fluoride‐co‐chlorotrifluoroethylene (PVDF‐co‐CTFE) and PVDF‐co‐CTFE/polyvinylidene fluoride‐co‐hexafluoropropylene (PVDF‐co‐HFP) nanofibers. Three PVDF polymer solutions of varying compositions were used in the preparation of the nanofiber coatings. Two of the polymer solutions were PVDF‐co‐CTFE blends made using different types of PVDF‐co‐HFP copolymers. The PVDF‐co‐CTFE and PVDF‐co‐CTFE/PVDF‐co‐HFP blend nanofiber coatings have been found to have comparable adhesion to the PP microporous membrane substrate. The electrolyte uptakes and separator–electrode adhesion properties of nanofiber‐coated membranes were evaluated. Both the electrolyte uptake and the separator–electrode adhesion were improved by the nanofiber coatings. The improvement in electrolyte update capacity is not only related to the gelation capability of the PVDF copolymer nanofibers, but also attributed to the increased porosity and capillary effect on nanofibrous structure of the electrospun nanofiber coatings. Enhancement of the separator–electrode adhesion was owing to the adhesion properties of the copolymer nanofiber coatings. Compared with the PVDF‐co‐CTFE/PVDF‐co‐HFP blend nanofiber coatings studied, the PVDF‐co‐CTFE coating was more effective in improving the electrolyte uptake and separator–electrode adhesion. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

Room-Temperature Super Hydrogel as Dye Adsorption Agent

Supramolecular hydrogels were prepared in the mixtures of a chiral amphiphilic lithocholic acid (LCA) and a nonionic surfactant, dodecyldimethylamine oxide (C(12)DMAO), in water. With the addition of LCA to C(12)DMAO micellar solutions, a transition from micelles to gels occurs at room temperature. Hydrogels can form at very low concentrations (below 0.1 wt %), exhibiting a super gelation capability. The rheological measurements show a strong mechanical strength with an elastic modulus exceeding 5000 Pa and a yield stress exceeding 100 Pa. Microstructures determined by TEM, SEM, and AFM observations demonstrate that the gels are formed by intertwined helical fibrils. The formation of fibrils is induced by enormous cycles of units composed of two LCA molecules and four C(12)DMAO molecules driven by comprehensive noncovalent interaction, especially the hydrogen bonds produced in two reversed LCA molecules and the C(12)DMAOH(+)-C(12)DMAO pairs. The xerogels show excellent adsorption capability of the toxic dye with a maximum adsorption value of 202 mg·g(-1).

Poly(benzyl ether) dendrons without conventional gelation motifs as a new kind of effective organogelators

Two poly(benzyl ether) dendrons, decorated in their periphery with nitrile groups, were divergently synthesized and fully characterized. Their gelation properties were studied by using scanning electron microscopy (SEM), X-ray crystal structure analysis and concentration- and temperature-dependent 1H NMR spectroscopy. It was found that the gelation capability of these dendrons was highly dependent on dendron generation, and the second-generation dendron G2-CN proved to be highly efficient organogelator despite the lacking of any conventional gelation motifs, such as amides, long alkyl side chains and steroidal groups. The multiple strong π-π stacking interactions and hydrogen bonding interactions due to the peripheral isophthalonitrile motifs were proved to be the main driving forces to form the self-assembled gel.

Isomers of Metal–Organic Complex Arrays

Three metal-organic complex arrays (MOCAs) with a specific sequence of metal centers as well as that of amino acid units were synthesized. These MOCAs are also isomers exhibiting a gelation capability dependent on the location of the metal complexes in the arrays.

Revisiting differences in the thermoresponsive behavior of PNIPAAm and PMEO2MA aqueous solutions

In this work, we synthesized PNIPAAm and poly[2-(2-methoxyethoxy)ethyl methacrylate] (PEG analogue) with a similar degree of polymerization by ATRP. Their thermoresponsive behaviors in aqueous solution were inspected with phase diagrams, rheological properties and static/time resolved fluorescence analyses. We found that the gelation capability of the PNIPAAm solution was far superior to the PMEO2MA solution due to more pronounced physical interactions between PNIPAAm chains, whereas for PMEO2MA, weak intermolecular interactions fail to result in gelling in the selected concentration range during heating. This distinct property suggests that the PNIPAAm solution will be more suitable for use as an injectable embolic or drug loading material; while thermoresponsive PEG analogues can be a beneficial supplement or even alternative to PNIPAAm in non-thermogelling applications.

Determination of hydration stoichiometries and molar volumes of hydrated complexes in aqueous solutions of cellulosic ether polymers

Abstract Methods based on differential scanning calorimetry (DSC) and volumetric measurements were developed and used to determine the hydration stoichiometries and molar volumes of hydrated monomeric complexes of two polymers—methylcellulose (MC) and hydroxypropylmethyl cellulose (HPMC). When fully hydrated, the moles of bound water per mole of monomer were 5.9 and 10.7 for MC-A4M and HPMC-E4M, respectively. The molar volumes of the fully hydrated monomeric complexes were 486.9 and 580.0 mL/mole-monomer for MC-A4M and HPMC-E4M, respectively. The difference in bound water stoichiometries and molar volumes suggest a larger hydration layer consisting of bound water in HPMC than MC, which is consistent with its characteristic water affinity and gelation capabilities.

Colloidal gel from amphiphilic heteroarm polyelectrolyte stars in aqueous media

We report on the gelation capability of polystyrene/poly(2-vinyl pyridine) amphiphilic heteroarm polyelectrolyte stars in acidic salt-free aqueous media. The star polymers associate through hydrophobic interactions, by retraction of the stretched arms under no interdigitation conditions, in the dilute regime forming colloidal soft nanoparticles comprising about 6 stars, At concentrations significantly higher than the hydrodynamic overlap concentration (c>40c∗), the crowding of the colloidal nanoparticles drives a jamming transition, leading to a colloidal gel. The intermediate overlap regime (c∗<c<40c∗) is characterized by a significant compaction of the polyelectrolyte entities prior interdigitation and jamming.

Network chain density and relaxation of in situ synthesized polyacrylamide/hectorite clay nanocomposite hydrogels with ultrahigh tensibility

Nanocomposite hydrogels (NC gel) D-AM and S-AM were synthesized through in situ polymerization of acrylamide (AM) with hectorite clays of Laponite RD and RDS, respectively. The tensile performance of the NC gel was observed at different crosshead speeds and all of the NC gels exhibited an extremely high tensibility, e.g., the elongation at break even higher than 4000%, except for two samples with the lowest Laponite content of 1 w/v%. Strong tensile hysteresis was observed in the elongation–reversion curve, indicating a slow relaxation in the NC gels. Dynamic moduli G′ and G″ within linear viscoelasticity illustrated that the network structure was formed in these gels with the junction of Laponite platelets. The Laponite RD showed stronger gelation capability than the tetrasodium pyrophosphate modified Laponite RDS. The relaxation modulus G(t) for the NC gels was found to be similar to the slow rubber relaxation with the critical exponent n of about 0.16, much lower than 0.66–0.71 for the critical gel at the sol–gel transition. In comparison, the chemically cross-linked hydrogel showed almost no relaxation during the same time interval. The effective network chain density of the NC gel was determined from equilibrium shear modulus, which was evidently lower than that of the chemically cross-linked hydrogels. The present results reveal that the high deformability of these NC gels comes from their low effective network chain density with moderate relaxation.