Effect of molar ratio and concentration on the rheological properties of two-component supramolecular hydrogels: tuning of the morphological and drug releasing behaviour.

Self-assembled supramolecular hydrogels offer great potential as biomaterials and drug delivery systems. Specifically, peptide-based multicomponent hydrogels are promising materials due to their advantage that their mechanical and physical properties can be tuned to enhance their functionalities and broaden their applications. Herein, we report two-component assembly and formation of hydrogels containing inexpensive complementary anionic, BUVV-OH (A), and cationic, KFFC12 (B), peptide amphiphiles. Individually, neither of these components formed a hydrogel, while mixtures with compositions 1 : 1, 1 : 2, and 2 : 1 (molar ratio) as A : B show hydrogel formation (Milli-Q water, at pH = 6.79). These hydrogels displayed a good shear-thinning behaviour with different mechanical stabilities and nano-fibrous network structures. The 1 : 1 hydrogel shows good cell viability for human embryonic kidney (HEK-293) cells and CHO cells indicating its non-cytotoxicity. The biocompatible, thixotropic 1 : 1 hydrogel with a nanofiber network structure shows the highest mechanical strength with a storage modulus of 3.4 × 103 Pa. The hydrogel is able to encapsulate drugs including antibiotics amoxicillin and rifampicin, and anticancer drug doxorubicin, and it exhibits sustainable release of 76%, 70%, and 81% respectively in vitro after 3 days. The other two mixtures (composition 1 : 2 and 2 : 1) are unable to form a hydrogel when they are loaded with these drugs. Interestingly, it is noticed that with an increase in concentration, the mechanical strength of a 1 : 1 hydrogel is significantly enhanced, showing potential that may act as a scaffold for tissue engineering. The two-component gel offers tunable mechanical properties, thixotropy, injectability, and biocompatibility and has great potential as a scaffold for sustained drug release and tissue engineering.

A Silver-Based Integrated System Showing Mutually Inclusive Super Protonic Conductivity and Photoswitching Behavior.

Photoinduced electricity and proton conductivity led fuel cells have emerged, inter alia, as highly promising systems for unconventional energy harvesting. Notwithstanding their individual presence with widely acclaimed results, an integrating system with mutually inclusive manifestation of both features has hitherto not been reported in the literature. To achieve this objective, our approach was to design a ligand system incorporating prerequisite features of both systems, like extended conjugation instigating photophysical activity and functional groups facilitating ionic conduction. As such, we report herein the design, synthesis, and characterization of a pyridyl-pyrazole-based silver compound that exhibits an excellent photocurrent generation and very high proton conductivity. The X-ray single-crystal structure of the Ag complex fully supports our notion, showing extensive π-π conjugated aromatic rings with a protruding free sulfonic group, facing toward solvent-filled channels with numerous supramolecular interactions. The nanoscopic silver metallogel induces semiconductive features in the system which ultimately result in photoresponse behavior in terms of photocurrent generation with an whopping photocurrent gain (Ion/Ioff) of 21.2. To complete the idea of an integrated system, the proton conductivity values were also measured for both gel and crystalline states, while the former state yields a better result. The maximum proton conductivity value turns out to be 1.03 × 10-2 S cm-1 at 70 °C, which is higher than or comparable to those of well-known systems in the literature for proton conductivity.

Adipic acid directed self-healable supramolecular metallogels of Co(II) and Ni(II): intriguing scaffolds for comparative optical-phenomenon in terms of third-order optical non-linearity.

Two brilliant outcomes of supramolecular self-assembly directed, low molecular weight organic gelator based self-healable Co(II) and Ni(II) metallogels were achieved. Adipic acid as the low molecular weight organic gelator and dimethylformamide (DMF) solvent are employed for the metallogelation process. Rheological analyses of both gel-scaffolds reveal mechanical toughness as well as visco-elasticity. Thixotropic behaviours of both the gels were scrutinized. Morphological variations due to the presence of two different metal ions with diverse metal-ligand coordinating interactions were established. The mechanistic pathways for forming stable metallogels of Co(II)-adipic acid (Co-AA) and Ni(II)-adipic acid (Ni-AA) were judiciously developed through infrared absorption spectral analysis. The nonlinear optical properties, such as the third-order process, of these synthesized metallogels were scrutinized by means of the Z-scan method at a beam excitation wavelength of 750 nm by a femtosecond laser with different excitation intensities ranging from 64 to 140 GW cm-2. The third-order nonlinear optical susceptibility (χ(3)) of the order of 10-14 esu was obtained from the measured Z-scan data. Both the metallogels exhibit positive nonlinear refraction and reverse saturable (RSA) absorption at high-intensity excitation. Co(II) and Ni(II) metallogels show nonlinear refractive indices (n2I) of (3.619 ± 0.146) × 10-6 cm2 GW-1 and (3.472 ± 0.102) × 10-6 cm2 GW-1, respectively, and two photon absorption coefficients (ß) of (1.503 ± 0.045) × 10-1 cm GW-1 and (1.381 ± 0.029) × 10-1 cm GW-1 at an excitation intensity of 140 GW cm-2. We also studied the optical limiting properties with a limiting threshold of 9.57 mJ cm-2. Therefore, both metallogels can be considered promising materials for photonic devices: for instance, for optical switching and optical limiting.

A croconate-directed supramolecular self-healable Cd(II)-metallogel with dispersed 2D-nanosheets of hexagonal boron nitride: a comparative outcome of the charge-transport phenomena and non-linear rectifying behaviour of semiconducting diodes.

The use of croconic acid disodium salt (CADS) as an organic gelator with Cd(II) salt to obtain an efficient soft-scaffold supramolecular self-healable metallogel (Cd-CADS) in N,N-dimethyl formamide (DMF) media was investigated following an ultrasonication technique. The experimentally scrutinized rheological values of the fabricated metallogel not only revealed the visco-elastic property and mechanical stiffness, but also exposed the self-healable behaviour of the gel material. Two-dimensional (2D) nanosheets of hexagonal boron nitride (h-BN) were incorporated within the gel network to obtain a 2D nanosheet dispersed metallogel of Cd(II) croconate (h-BN@Cd-CADS). The microstructural investigations of the original gel network and hexagonal boron nitride (h-BN) 2D nanosheet dispersed gel-network were performed through field emission scanning electron microscopy (FESEM) and established the interconnecting rod-like fibrous type morphological patterns and inter-connected hexagonal type rod-shaped architecture pattern, respectively. High resolution transmission electron microscopy (HRTEM) was used to visualize the morphological distinction of the Cd-CADS metallogel with the h-BN 2D nanosheets. The infrared spectral (FT-IR) outputs helped to identify the formation pathway to construct the semi-solid self-healing flexible metallogel and h-BN 2D nanosheet dispersed metallogel nanocomposite, respectively. Fascinating electronic-charge transportation was revealed in the as-fabricated Cd-CADS and h-BN@Cd-CADS metallogel-based devices. Furthermore, h-BN 2D-nanosheet-directed modulation of the non-linear rectifying feature of the supramolecular Cd-CADS-metallogel was observed, with the h-BN@Cd-CADS metallogel showing a greater rectifying property, implying that it has a higher conductivity compared to the Cd-CADS metallogel.

Synergistic Experimental and Theoretical Studies of Luminescent-Magnetic Ln2Zn6 Clusters.

The present work is part of our ongoing quest for developing functional inorganic complexes using unorthodox pyridyl-pyrazolyl-based ligands. Accordingly, we report herein the synthesis, characterization, and luminescence and magnetic properties of four 3d-4f mixed-metal complexes with a general core of Ln2Zn6 (Ln = Dy, Gd, Tb, and Eu). In stark contrast to the popular wisdom of using a compartmental ligand with separate islands of hard and soft coordinating sites for selective coordination, we have vindicated our approach of using a ligand with overcrowded N-coordinating sites that show equal efficiency with both 4f and 3d metals toward multinuclear cage-cluster formation. The encouraging red and green photolumiscent features of noncytotoxic Eu2Zn6 and Tb2Zn6 complexes along with their existence in nanoscale dimension have been exploited with live-cell confocal microscopy imaging of human breast adenocarcinoma (MCF7) cells. The magnetic features of the Dy2Zn6 complex confirm the single-molecule-magnet behavior with befitting frequency- and temperature-dependent out-of-phase signals along with an Ueff value of ∼5 K and a relaxation time of 8.52 × 10-6 s. The Gd2Zn6 complex, on the other hand, shows cryogenic magnetic refrigeration with an entropy change of 11.25 J kg-1 K-1 at a magnetic field of 7 T and at 2 K. Another important aspect of this work reflects the excellent agreement between the experimental results and theoretical calculations. The theoretical studies carried out using the broken-symmetry density functional theory, ORCA suite of programs, and MOLCAS calculations using the complete-active-space self-consistent-field method show an excellent synergism with the experimentally measured magnetic and spectroscopic data.

A Nd6 molecular butterfly: a unique all-in-one material for SMM, MCE and maiden photosensitized opto-electronic device fabrication.

Besides iron, ironically neodymium (Nd) is the most ubiquitously used metal for magnetic purposes, even among the lanthanides, when it comes to the field of molecular magnetism, yet it ranks among the least studied metals. However, strong apathy towards this magnetic lanthanide means that vital information will be missed, which is required for the advancement of the subject. Herein, we have successfully demonstrated the usefulness of a hexanuclear neodymium complex as a magnetic material, and also in electronic device fabrication. A {NdIII6} cage with an aesthetically pleasing butterfly topology was synthesized using a rather non-conventional N-rich pyridyl-pyrazolyl based ligand. The cage shows single molecule magnet (SMM) properties, with an effective energy barrier, Ueff, value of 3.4 K and relaxation time, τ0, of 3.1 × 10-4 s, originating from an unusual occurrence of metal centres with different coordination environments. Furthermore, magnetic studies reveal significant cyrogenic magnetic cooling, with a magnetic entropy change of 8.28 J kg-1 K-1 at 5 T and 3 K. To the best of our knowledge, the titular compound is the only example of a Nd-complex that exhibits concomitant magnetocaloric effect (MCE) and SMM properties. Complete active space self-consistent field (CASSCF) calculations were carried out to shed light on the origin of the magnetic anisotropy and magnetic relaxation of the compound. The same uniqueness is also true for the first electronic investigation carried out on the Nd complex. The maiden electronic device fabricated using the Nd complex shows an interesting intertwining of electronic and optical features, which contribute towards its improved photosensitized optoelectronic data.

Fascinating interlocked triacontanuclear giant nanocages.

We report herein three air, thermal and solvent stable interlocked triacontanuclear giant nanocages, generated using a node and spacer concept. Interestingly, the crystal structures of the cages are not only nano-dimensional but also exist in the nano-dimension range, which was corroborated with microscopic images. The combination of microscopic and crystallographic data, in effect, led us to a unique advantageous situation of generating nanomaterials with hard-to-come-by structural information at the molecular level.

Lanthanide clusters of phenanthroline containing a pyridine-pyrazole based ligand: magnetism and cell imaging.

In this contribution, we report the synthesis, characterization and luminescence-magnetic properties of Ln-clusters (Ln = Gd3+, Eu3+ and Tb3+) using a new pyridine-pyrazole functionalized ligand fitted with a chromophoric phenanthroline backbone. The unorthodox N-rich ligand forms isostructural trinuclear lanthanide complexes with a topology that closely resembles two interdigitating hairpins. The clusters crystallize in chiral space groups and also exhibit chirality for bulk samples, which were further confirmed using solid state CD spectra. Magnetic studies on the complexes reveal their interesting features while the Gd cluster shows a significant cryogenic magnetic cooling behaviour with a moderately high magnetic entropy change of -23.42 J kg-1 K-1 at 7 T and 2 K. On the other hand, Eu and Tb complexes exhibit interesting fluorescence properties. The compounds were subsequently used as fluorescent probes for the imaging of human breast adenocarcinoma (MCF7) cells. Live cell confocal microscopy images show that the complexes penetrate beyond the usual cytoplasm region and can be useful in imaging the nucleus region of MCF7 cells.

Pyridine-pyrazole based Al(iii) 'turn on' sensor for MCF7 cancer cell imaging and detection of picric acid.

We report herein the development of a new pyridine-pyrazole based bis-bidentate asymmetric chemosensor that shows excellent turn-on chelation-enhanced Al3+-responsive fluorescence. The presence of two 'hard' phenolic hydroxyl groups plays a pivotal role in switching-on the sensing through coordination to the 'hard' Al3+ ion, while the mechanism can be interpreted by the chelation-enhanced fluorescence (CHEF) process. The X-ray single structure show a planar conjugated structure of the ligand, which was further stabilized by extensive H-bonding and π-π stacking. The photophysical studies related to the sensing behavior of the titular ligand toward aluminum was investigated in detail using various spectroscopic techniques like UV-Vis, photoluminescence, fluorescence and time-correlated single-photon count (TCSPC) and time-resolved NMR. The spectroscopic methods also confirm the selective detection of Al3+ ion in the presence of other metal ions. The theoretical calculations using Density Functional Theory (DFT) and the Time Dependent Density Functional Theory (TD-DFT) provide further insight on the mechanistic aspects of the turn-on sensing behavior including the electronic spectra of both the ligand and the complex. Interestingly, the as-synthesized H2DPC-Al complex can also be utilized as a fluorescence-based sensor for various nitroaromatics including picric acid, for which an INHIBIT logic gate can also be constructed. The as synthesized complex was subsequently used as a fluorescent probe for imaging of human breast adenocarcinoma (MCF7) cells using live cell confocal microscopic techniques.

Utilization of counter anions for charge transportation in the electrical device fabrication of Zn(II) metal-organic frameworks.

The present work reports the fabrication of anion-induced electrical devices with Zn(ii) metal-organic frameworks. The essence of our electronic device fabrication is to utilize the anionic species entrapped inside of the three-dimensional network of the MOFs for charge transportation. The idea is to generate MOFs as a host-guest system with encapsulated anions or anion-solvent clusters as guests and a cationic yet insulating three-dimensional framework as the host. Accordingly, we have synthesized two Zn(ii) MOFs using a neutral bispyrazole-based ligand, which results in a cationic chassis with substantial void space and porous channels inside the network. For both MOFs, the porous channels are occupied by infinitely hydrogen bonded networks of anions and anion-solvent clusters. This provides an excellent platform for anionic species-induced charge transportation and improved electrical conductivity. Indeed, the impedance spectroscopy data and current density-voltage (J-V) characteristics of the fabricated electrical devices further vindicate our idea. The current-voltage measurements clearly indicate the usefulness of modified host-guest-type MOFs for electronic device fabrication with corroborating conductivity values of 8.71 × 10-5 S m-1 and 5.79 × 10-4 S m-1 for compound 1 and compound 2, respectively.

Peptide-Based Gel in Environmental Remediation: Removal of Toxic Organic Dyes and Hazardous Pb2+ and Cd2+ Ions from Wastewater and Oil Spill Recovery.

A dipeptide-based synthetic amphiphile bearing a myristyl chain has been found to form hydrogels in the pH range 6.9-8.5 and organogels in various organic solvents including petroleum ether, diesel, kerosene, and petrol. These organogels and hydrogels have been thoroughly studied and characterized by different techniques including high-resolution transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and rheology. It has been found that the xerogel obtained from the peptide gelator can trap various toxic organic dyes from wastewater efficiently. Moreover, the hydrogel has been used to remove toxic heavy metal ions Pb2+ and Cd2+ from wastewater. Dye adsorption kinetics has been studied, and it has been fitted by using the Freundlich isotherm equation. Interestingly, the gelator amphiphilic peptide gels fuel oil, kerosene, diesel, and petrol in a biphasic mixture of salt water and oil within a few seconds. This indicates that these gels not only may find application in oil spill recovery but also can be used to remove toxic organic dyes and hazardous toxic metal ions from wastewater. Moreover, the gelator can be recycled several times without significant loss of activity, suggesting the sustainability of this new gelator. This holds future promise for environmental remediation by using peptide-based gelators.

A free-standing, self-healing multi-stimuli responsive gel showing cryogenic magnetic cooling.

A novel Fe(iii)-based gel was synthesized via the self-assembly of Fe(iii) and pyridine 2,6 dicarboxylic acid. The synthesized gel has remarkable mechanical strength as well as self-sustainability. The metallogel also has thixotropic as well as self-healing properties. The metallogel shows amazing colourimetric NH3 sensing with unique gel-to-gel transformation. Magnetic studies on the as-synthesized gel reveal significant cryogenic magnetic cooling behavior. Last but not least, to the best of our knowledge, this would be the first case where MCE is investigated for any reported metallogel.

The aging effect on the enhancement of thermal stability, mechanical stiffness and fluorescence properties of histidine-appended naphthalenediimide based two-component hydrogels.

A histidine attached naphthalenediimide (NDI)-containing amphiphilic molecule (NDIP) self-assembles into nanotubes in aqueous solution at pH 6.6 as revealed by high-resolution transmission electron microscopy studies. This histidine-appended NDI forms a two-component hydrogel in the presence of tartaric acid at a molar ratio of 1 : 2. A morphological transformation was observed from a nanotube structure in the non-gel aggregated state of histidine appended NDI to interconnected cross-linked nanofibers of the two-component hydrogel in the presence of tartaric acid. Interestingly, the gel exhibits an unusual behavior upon aging compared to the fresh gel. It is found that the thermal stability and gel stiffness increase very significantly upon aging. Another important feature noted is that the very weak fluorescence of the fresh gel is transformed into bright greenish fluorescence upon aging. These results suggest that intermolecular interactions among the gelator molecules and tartaric acid in the gel phase slowly increase with time to form a mechanically very stiff and thermally robust gel.

Cytidine-Derived Hydrogels with Tunable Antibacterial Activities.

We herein report the preparation of hydrogels by the Ag+ ion induced assembly of cytidine and boronic acids. These hydrogels, presumably formed by an i-motif like arrangement of cytidine and its boronate ester analogues, possess excellent thixotropic and self-healing properties. The hydrogels exhibit potent antimicrobial activity that can be tuned by varying the functional groups in their boronic acid component. These hydrogels could find potential use as antimicrobial agents and stimuli-responsive drug delivery systems.