Self-Assembled Vesicle-Carbon Nanotube Conjugate Formation through a Boronate-Diol Covalent Linkage.

A vesicle-single walled carbon nanotube (CNT) conjugate was developed by a boronic acid-diol covalent linkage between a self-assembled vesicle and dispersed CNT. Trimesic acid based phenylboronic acid appended triple-tailed amphiphiles (T1 and T1S) were synthesized that formed monolayered vesicles through H-aggregation in DMSO-water (2:1 v/v) and pure water, respectively. Aqueous CNT dispersion was prepared with cholesterol-based glucose-functionalized amphiphile (D1). These two supramolecular self-assemblies were covalently linked by using a boronic acid-diol interaction between a phenylboronic acid based T1S vesicle and 1,2-diol moieties of glucose tethered dispersing agent (D1) to develop a vesicle-CNT conjugate. Lewis acid-base chemistry was exploited to form this boronate-diol adduct between two supramolecular self-assemblies. The formation of vesicles, CNT dispersion, and the vesicle-CNT conjugate was characterized by microscopic and spectroscopic techniques. Anticancer drug doxorubicin was encapsulated within this T1S-vesicle-D1-CNT conjugate with a higher loading capacity compared to the individual cargo carrier (vesicle or CNT). This cytocompatible T1S-vesicle-D1-CNT conjugate successfully delivered loaded doxorubicin within a B16F10 melanoma cell and also exhibited better cellular transportation ability compared to the drug-loaded vesicle or CNT. This was further reflected in an enhanced killing efficiency of the cancer cells by the vesicle-CNT conjugate compared to the drug-loaded vesicle or CNT.

Hydrophobic End-Modulated Amino-Acid-Based Neutral Hydrogelators: Structure-Specific Inclusion of Carbon Nanomaterials.

Hydrophobic end-modulated l-phenylalanine-containing triethylene glycol monomethyl ether tagged neutral hydrogelators (1-4) are developed. Investigations determine the gelators' structure-dependent inclusion of carbon nanomaterials (CNMs) in the self-assembled fibrillar network (SAFIN). The gelators (1, 3, and 4) can immobilize water and aqueous buffer (pH 3-7) with a minimum gelator concentration of 10-15 mg mL(-1). The hydrophobic parts of the gelators are varied from a long chain (C-16) to an extended aromatic pyrenyl moiety, and their abilities to integrate 1 D and 2 D allotropes of carbon (i.e., single-walled carbon nanotubes (SWNTs) and graphene oxide (GO), respectively) within the gel are investigated. Gelator 1, containing a long alkyl chain (C-16), can include SWNTs, whereas the pyrene-containing 4 can include both SWNTs and GO. Gelator 3 fails to incorporate SWNTs or GO owing to its slow rate of gelation and possibly a mismatch between the aggregated structure and CNMs. The involvement of various forces in self-aggregated gelation and physicochemical changes occurring through CNM inclusion are examined by spectroscopic and microscopic techniques. The distinctive pattern of self-assembly of gelators 1 and 4 through J- and H-type aggregation might facilitate the structure-specific CNM inclusion. Inclusion of SWNTs/GO within the hydrogel matrix results in a reinforcement in mechanical stiffness of the composites compared with that of the native hydrogels.

Solvent Induced Morphological Evolution of Cholesterol Based Glucose Tailored Amphiphiles: Transformation from Vesicles to Nanoribbons.

Supramolecular self-assembly of low molecular mass amphiphiles is of topical interest with the urge to achieve precise control over the formation of various self-aggregated structures. Particularly, fabrication of multifarious nanostructures from single molecular backbone would be highly advantageous for task specific applications of the self-aggregates. To this end, the present study reports the solvent triggered evolution of hierarchical self-assembled structures of cholesterol based glucose appended amphiphiles and the pathway of structural transition. The amphiphiles formed bilayered vesicles in water and gels in different organic solvents. In DMSO-water solvent mixture, it showed gradual transition in the morphology of self-aggregates from vesicle-to-fiber and intermediate morphologies depending on the solvent compositions. Microscopic and spectroscopic investigations showed that morphological transformation took place through fusion, elongation and twisting of self-aggregates owing to the reorganization of the amphiphiles (H-type to J-type) in varied solvent polarity. Moreover, sheetlike molecular organization originating from hydrogen bonding and solvophobic interaction played a vital role in the formation of nanoribbons that led to the formation of gel fibril network. This study endows a new strategy to develop solvent induced multistructured self-aggregates from a single molecular scaffold, unraveling the route of forming hierarchical self-assembly.

Phenylboronic Acid Appended Pyrene-Based Low-Molecular-Weight Injectable Hydrogel: Glucose-Stimulated Insulin Release.

A pyrene-containing phenylboronic acid (PBA) functionalized low-molecular-weight hydrogelator was synthesized with the aim to develop glucose-sensitive insulin release. The gelator showed the solvent imbibing ability in aqueous buffer solutions of pH values, ranging from 8-12, whereas the sodium salt of the gelator formed a hydrogel at physiological pH 7.4 with a minimum gelation concentration (MGC) of 5 mg mL(-1) . The aggregation behavior of this thermoreversible hydrogel was studied by using microscopic and spectroscopic techniques, including transmission electron microscopy, FTIR, UV/Vis, luminescence, and CD spectroscopy. These investigations revealed that hydrogen bonding, π-π stacking, and van der Waals interactions are the key factors for the self-assembled gelation. The diol-sensitive PBA part and the pyrene unit in the gelator were judiciously used in fluorimetric sensing of minute amounts of glucose at physiological pH. The morphological change of the gel due to addition of glucose was investigated by scanning electron microscopy, which denoted the glucose-responsive swelling of the hydrogel. A rheological study indicated the loss of the rigidity of the native gel in the presence of glucose. Hence, the glucose-induced swelling of the hydrogel was exploited in the controlled release of insulin from the hydrogel. The insulin-loaded hydrogel showed thixotropic self-recovery property, which hoisted it as an injectable soft composite. Encouragingly, the gelator was found to be compatible with HeLa cells.

Pyrene-based fluorescent ambidextrous gelators: scaffolds for mechanically robust SWNT-gel nanocomposites.

With the rapid progress in the development of supramolecular soft materials, examples of low-molecular-weight gelators (LMWGs) with the ability to immobilise both water and organic solvents by the same structural scaffold are very limited. In this paper, we report the development of pyrene-containing peptide-based ambidextrous gelators (AGs) with the ability to efficiently gelate both organic and aqueous solvents. The organo- and hydrogelation efficiencies of these gelators are in the range 0.7-1.1% w/v in various organic solvents and 0.5-5% w/v in water at certain acidic pH values (pH 2.0-4.0). Moreover, for the first time, AGs have been utilised to prepare single-walled carbon-nanotube (SWNT)-included soft nanocomposites in both hydro- and organogel matrices. The influence of different non-covalent interactions such as hydrogen bonding, hydrophobic, π-π and van der Waals interactions in self-assembled gelation has been studied in detail by circular dichroism, FTIR, variable-temperature NMR, 2D NOESY and luminescence spectroscopy. Interestingly, the presence of the pyrene moiety in the structure rendered these AGs intrinsically fluorescent, which was quenched upon successful integration of the SWNTs within the gel. The prepared hydro- and organogels along with their SWNT-integrated nanocomposites are thermoreversible in nature. The supramolecular morphologies of the dried gels and SWNT-gel nanocomposites have been studied by transmission electron microscopy, fluorescence microscopy and polarising optical microscopy, which confirmed the presence of three-dimensional self-assembled fibrillar networks (SAFINs) as well as the integrated SWNTs. Importantly, rheological studies revealed that the inclusion of SWNTs within the ambidextrous gels improved the mechanical rigidity of the resulting soft nanocomposites up to 3.8-fold relative to the native gels.

Structure and properties of cholesterol-based hydrogelators with varying hydrophilic terminals: biocompatibility and development of antibacterial soft nanocomposites.

The present work demonstrates a rational designing and synthesis of cholesterol-based amino acid containing hydrogelators with the aim to improve the biocompatibility of these amphiphilic molecules. A thorough structure-property correlation of these hydrogelators was carried out by varying the hydrophilic terminal from a neutral amine to a quaternized ammonium chloride. The amphiphiles having a cationic polar head as the hydrophilic domain and cholesterol as the hydrophobic unit showed better water gelation efficiency (minimum gelation concentration (MGC) ∼0.9-3.1%, w/v) than the analogous free amines. Presumably, the additional ionic interactions for the quaternized amphiphiles might have played the crucial role in gelation as counterions also got involved in hydrogen bonding with solvent molecules. Hence, the attainment of desired hydrophilic-lipophilic balance (HLB) of hydrophobic cholesterol in combination with the appropriate hydrophilic terminal led to the development of efficient hydrogels. Microscopic investigations revealed the formation of various supramolecular morphologies of hydrogels due to the variation in the molecular structure of the amphiphile. Spectroscopic investigations showed the involvement of hydrogen-bonding, hydrophobic, and π-π interactions in the self-assembled gelation. Importantly, biocompatibility of all the cholesterol-based hydrogelators tested against human hepatic cancer derived HepG2 cells showed increased cell viability than the previously reported alkyl-chain-based amphiphilic hydrogelators. In order to incorporate broad spectrum antibacterial properties, silver nanoparticles (AgNPs) were synthesized in situ within the hydrogels using sunlight. The amphiphile-AgNP soft nanocomposite exhibited notable bactericidal property against both gram-positive and gram-negative bacteria.

Dissipation of self-assemblies by fusion of complementary gels: an elegant strategy for programmed enzymatic reactions.

Cholesterol based phenylboronic acid and glucose tailored complementary gels were developed which underwent mutual self-destruction upon mixing due to the formation of a boronate-diol adduct. This dissipation of the complementary gels was employed in a programmed enzymatic reaction and in pro-drug activation.

Synthesis of a Low-Molecular-Weight Fluorescent Ambidextrous Gelator: Development of Graphene- and Graphene-Oxide-Included Gel Nanocomposites.

Low-molecular-weight fluorescent supramolecular ambidextrous gelators have drawn enormous attention owing to their ever-increasing number of potential applications. In this study, we synthesized a low-molecular-weight fluorescent ambidextrous gelator consisting of hydrophobic pyrenebutyric acid moieties at the N termini of a central l-lysine, and an ethyleneoxy unit coupled with 1-(3-aminopropyl)imidazole via a succinic acid linker as a hydrophilic moiety at the C terminus. This compound showed efficient hydrogelation and organogelation, having minimum gelation concentrations of 0.5 % (w/v) in a DMSO/water mixture (1:4 v/v) and 0.2 % (w/v) in nitrobenzene. The presence of the pyrene moieties in the structure rendered the ambidextrous gelator fluorescent. Significant amounts of both graphene oxide and reduced graphene oxide were included within these gels to form a stable soft nanohybrid. Hydrogen bonding, π-π stacking and van der Waals interactions are the key factors for self-assembly leading to gelation. The complementary interactions between the π-electronic surface of 2D graphene sheet and the aromatic pyrene moieties of the gelator play key roles in the inclusion of the nanomaterials into the gels. The inclusion of carbon nanomaterials within the gels resulted in a notable improvement in the stiffness of the soft nanocomposites compared to native gels. The native gels and soft nanocomposites have shear thinning properties and are thixotropic in nature.

Water-in-oil microemulsion doped with gold nanoparticle decorated single walled carbon nanotube: scaffold for enhancing lipase activity.

The present work reports the development of water-in-oil (w/o) microemulsion doped with newly designed nanocomposite comprising of gold nanoparticle (GNP) decorated single walled carbon nanotube (SWNT). This nanocomposite included cationic reverse micelle was used to boost the catalytic activity of a surface-active enzyme, Chromobacterium viscosum lipase (CV lipase). SWNT was non-covalently dispersed using cetyltrimethylammonium bromide (CTAB), cetylalaninetrimethylammonium chloride (CATAC) while GNP was synthesized by reduction of HAuCl4 with reducing/stabilizing agent trisodium citrate. Counterion exchange between cationic SWNT dispersing agent and anionic capping agent of GNP led to the formation of GNP decorated SWNT (SWNT-GNP) nanocomposite. This newly developed SWNT-GNP included CTAB reverse micelle was characterized by several microscopic and spectroscopic techniques. Interfacially located SWNT-GNP included w/o microemulsion (confirmed from biphasic and fluorescence experiment) was used as a proficient host for enhancing the catalytic activity of lipase. Lipase activity within this self-assembled soft nanocomposite improved up to 3.9-fold (second order rate constant, k2=1694±16 cm(3) g(-1) s(-1)) compared to standard CTAB reverse micelle (k2=433±7 cm(3) g(-1) s(-1)). In case of cetyltripropyl ammonium bromide (CTPAB) based reverse micelle, the observed lipase activity improved to k2=2036±11 cm(3) g(-1) s(-1) in the presence of SWNT-GNP composite. Notably, this catalytic activity of lipase within SWNT-GNP included reverse micelle was till date the highest activity found in any w/o microemulsion. The attainment of flexibility in enzyme conformation at the augmented interface was verified using circular dichroism (CD) spectroscopy.

Graphene oxide in cetyltrimethylammonium bromide (CTAB) reverse micelle: a befitting soft nanocomposite for improving efficiency of surface-active enzymes.

Herein, we report the successful inclusion of 2D allotrope of carbon, graphene oxide (GO) in cetyltrimethylammonium bromide (CTAB)/isooctane/n-hexanol/water reverse micelle without compromising the stability of water-in-oil (w/o) microemulsion. This newly developed self-assembled nanocomposites act as proficient host for surface-active enzymes, lipase, horseradish peroxidase (HRP), and soybean peroxidase (SBP). Lipase activity within GO-doped CTAB reverse micelles remarkably improved by 3.8-fold compared to that was observed in only CTAB reverse micelle (second-order rate constant, k2=433±7 cm3 g(-1) s(-1)). In case of GO-doped CTAB reverse micelle, the observed enzyme activity (k2=1653±11 cm3 g(-1) s(-1)) is till date the highest ever activity of lipase in CTAB w/o microemulsions. In case of HRP and SBP, the catalytic efficiency maximally increased up to 2.6-fold and 2.3-fold, respectively. Electrostatic attraction between cationic head group of CTAB and anionic surface of GO as well as intrinsic amphiphilic character of GO possibly resulted in the confinement of this 2D nanosheet at the interface of reverse micelles. Integration of GO at the interface augmented the interfacial space in vicinity of surface-active enzyme. This enlarged interface might have accommodated higher amount of substrate and lipase with flexibility in its conformation resulting in marked improvement in the enzyme activity. Interfacial localization of GO was established by fluorescence spectroscopy. In addition, change in secondary structure of lipase in presence of 2D carbon allotrope was substantiated by circular dichroism spectroscopy.