New organogels based on an anthracene derivative with one urea group and its photodimer: fluorescence enhancement after gelation

Evaluation of thermoresponsive properties and biocompatibility of polybenzofulvene aggregates for leuprolide delivery

In this study, a polybenzofulvene derivative named poly-6-MOEG-9-BF3k, was evaluated as polymeric material for the production of injectable thermoresponsive nano-aggregates able to load low molecular weight peptidic drug, like the anticancer leuprolide. Thermoresponsive behavior of poly-6-MOEG-9-BF3k was studied in aqueous media by evaluating scattering intensity variations by means of DLS in function of temperature. Zeta potential measurements and SEM observations were also carried out. Moreover, critical aggregation temperature of the poly-6-MOEG-9-BF3k polymer was evaluated by pyrene fluorescence analysis. Then, the ability of prepared thermoresponsive aggregates to protect this model oligopeptide drug and regulate its release rate in function of external temperature was evaluated in vitro. Finally, biocompatibility of poly-6-MOEG-9-BF3k aggregates was tested in vitro on a healthy cell line (human bronchial epithelial cell; 16-HBE) and in vivo on rat animal model upon subcutaneous administration.

Fluorescence-enhanced organogels and mesomorphic superstructure based on hydrazine derivatives

New low-molecular-mass organic gelators (LMOGs) bearing hydrazine linkage and end-capped by phenyl, namely 1,4-bis[(3,4-bisalkoxyphenyl)hydrozide]phenylene (BPH-n, n = 4, 6, 8, 10), were designed and synthesized. These organogelators have shown great ability to gel a variety of organic solvents to form stable organogels with the critical gelation concentration as low as 8.7 x 10(-4) mol L(-1) (0.06 wt %). The formed gel has a high gel-sol transition temperature (T(gel)) at low gelation concentration. Aggregation-induced emission (AIE) has been observed after gelation though conventional chromophore units not incorporated in BPH-n. The fluorescence quantum yields of xerogel are 2 orders higher than that of dilute solution. In addition, the BPH-n (n = 6, 8, 10) exhibited thermotropic hexagonal column (Col(h)) mesophase, which are stable at room temperature as revealed by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X-ray diffraction (XRD) studies.

Glucose-based fluorescent low-molecular mass compounds: creation of simple and versatile supramolecular gelators

Five novel glucose-based naphthalene derivatives with linkers containing hydrazine, ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, and 1,6-hexanediamine, respectively (1, 2, 3, 4, and 5) were designed and prepared. The gelation test revealed the following points: (1) within the 30 solvents tested, 1 gels water only; (2) in contrast, 2 gels not only water, but also 11 of the organic solvents tested, a typical "ambidextrous gelator"; (3) 3, 4, and 5, however, gel organic solvents only, and the numbers of solvents gelled are 11, 11 and 13, respectively. Clearly, these compounds are effective low-molecular mass gelators, and show transitions from a low-molecular mass hydrogelator to an ambidextrous gelator and then to low-molecular mass organogelators with a slight increase in the length of the spacers. Interestingly, 5 is a super gelator to acetonitrile, of which the minimum gelation concentration is only 0.07%, w/v. The morphology, microstructure and molecular aggregation of the system strongly depend on the transition, as revealed by SEM, contact angle, energy dispersive X-ray spectroscopy, and XRD measurements. More interestingly, an aggregation-induced enhanced emission was observed along with gelation. Furthermore, the system appeared as a supramolecular chiroptical switch in the sol-gel process that is the chirality disappeared when the gel was heated to solution, whereas it reappeared when cooled to a gel.

Organic-inorganic hybrid supramolecular gels of surfactant-encapsulated polyoxometalates

A new type of hybrid supramolecular gel derived from a synergetic self-assembling of organic and inorganic components has been prepared through encapsulating a series of polyoxometalate (POM) clusters with ammonium surfactants bearing two alkyl chains. Among the general organic solvents we employed, some of surfactant-encapsulated POM (SEP) complexes readily gel with nonpolar solvents. Proper alkyl chain density, alkyl chain length, and shape of POM are proven to be favorable for fabricating stable SEP gels based on the results of critical gelation concentration and transition temperature from gel to solution. In addition, the shape of POM influences the aggregation morphologies of SEPs, stripes and spheres in gel phases, as confirmed by polarizing optical microscopic and scanning electron microscopic images. X-ray diffractions reveal that all the SEPs in gel states possess similar lamellar aggregation structures with POM layer inside and alkyl chain bilayers shielding from the nonpolar solvent on both sides. The combination of solvent effect, electrostatic, and dipole interaction is thought to be responsible for the formation of SEP gels.

New cholesterol-based gelators with maleimide unit and the relevant Michael adducts: chemoresponsive organogels

Compound 1 containing cholesteryl and maleimide units can gel a few organic solvents such as cyclohexane. It is interesting to note that the gel-sol transition can be triggered by addition of trace amounts of thiol and triethylamine. In this regard, we successfully demonstrate the proof of principle for designing chemoresponsive gels by incorporating the reactive groups into the gelators. Additionally, the Michael adducts 2 and 3 were prepared. Compounds 2 and 3 can also gel several organic solvents. The results also show that slight molecular structural variation has a large effect on the gelation ability of the compound. These organogels were characterized with SEM, AFM, CD, and XRD. Interestingly, gelation-induced CD spectra were observed for gels of 1, 2, and 3.

Soft functional materials induced by fibrillar networks of small molecular photochromic gelators

Low-molecular-mass organogelators (LMOGs) based on photochromic molecules aggregate in selected solvents to form gels through various spatio-temporal interactions. The factors that control the mode of aggregation of the chromophoric core in the LMOGs during gelation, gelation-induced changes in fluorescence, the formation of stacked superstructures of extended pi-conjugated systems, and so forth are discussed with selected examples. Possible ways of generating various light-harvesting assemblies are proposed, and some unresolved questions, future challenges, and their possible solutions on this topic are presented.

Dendritic effect on supramolecular self-assembly: organogels with strong fluorescence emission induced by aggregation

A novel class of dumbbell-shaped dendritic molecules with a p-terphenylene core was synthesized, and their self-assembling properties were investigated. The incorporation of bulky dendritic wedges to the central stiff aromatic scaffolds could finely tune their solubility in many organic solvents. Unlike the self-assembly behavior of p-terphenylen-1,4"-ylenebis(dodecanamide), the p-terphenylene cored different generation dendritic molecules could form gels in several kinds of organic solvents through a cooperative effect of the pi-pi stacking, hydrogen-bonding, and van der Waals forces. Interestingly, significant fluorescence enhancement was observed after gelation. Extensive investigations with atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), theological measurements, UV-vis absorption spectroscopy, FT-IR spectroscopy, 1H NMR, and X-ray powder diffraction (XRD) revealed that these dendritic molecules self-assembled into elastically interpenetrating one-dimensional nanostructures in organogels.

Cholesterol-appended aromatic imine organogelators: a case study of gelation-driven component selection

This letter describes a novel approach for developing organogelators through the formation of reversible imine bonds from two molecular components and the enriching behavior of the gelating imines. Cholesterol-appended aniline 1 and 4-substituted benzaldehydes 2a-d did not gelate any solvents. Their condensation products, imines 3a-d, however, could gelate alcohols because of the enhanced stacking interaction of the imine unit. For a further component selectivity test, the reactions of the mixture of 1, 2b-d, and cholesterol-free aniline 7 (1:1:1) in different solvents were performed. The resulting imines were reduced to the corresponding amines and analyzed with 1H NMR. It was revealed that, for the reactions resulting in no formation of the gel phase, imines 8a-c formed from 2b-d and 7 were obtained as the major product (64-76%) and all of the reactions that led to the formation of the gel phase gave rise to 3b-d as the major product (55-61%).

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

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

Unusual luminescence enhancement of metallogels of alkynylplatinum(II) 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine complexes upon a gel-to-sol phase transition at elevated temperatures

A series of alkynylplatinum(II) complexes of 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine has been synthesized and characterized by (1)H NMR, IR, FAB mass spectrometry, and elemental analysis; the photophysical properties have also been investigated. All the complexes have been shown to exhibit interesting gelation properties. Scanning electron microscopy (SEM) of the xerogels showed a network of fibrous structures, typical of morphologies of organogels/metallogels. Interestingly, two of the complexes were found to show strong luminescence enhancement upon a gel-to-sol phase transition upon increasing the temperature. This unusual behavior is rarely encountered, as it represents a sharp contrast to that exhibited by other typical thermotropic organogels and metallogels reported so far. Variable-temperature UV-vis and luminescence spectroscopies were performed to probe the gel-to-sol phase transition. Concentration-dependent, variable-temperature, and time-resolved emission studies in dilute benzene solution have also been made to provide further insights into the spectroscopic origin in the sol forms. A quantitative treatment of the system based on the Birks scheme has been performed.