Modulation of Viscoelastic Properties of Physical Gels by Nanoparticle Doping: Influence of the Nanoparticle Capping Agent

Stereoselective Plasmonic Interaction in Peptide-tethered Photopolymerizable Diacetylenes Doped with Chiral Gold Nanoparticles

Designing polymeric systems with ultra-high optical activity is instrumental in the pursuit of smart artificial chiroptical materials, including the fundamental understanding of structure/property relations. Herein, we report a diacetylene (DA) moiety flanked by chiral D- and L-FF dipeptide methyl esters that exhibits efficient topochemical photopolymerization in the solid phase to furnish polydiacetylene (PDA) with desired control over the chiroptical properties. The doping of the achiral gold nanoparticles provides plasmonic interaction with the PDAs to render asymmetric shape to the circular dichroism bands. With the judicious design of the chiral amino acid ligand appended to the AuNPs, we demonstrate the first example of selective chiral amplification mediated by stereo-structural matching of the polymer-plasmonic AuNP hybrid pairs. Such ordered self-assembly aided by topochemical polymerization in peptide-tethered PDA provides a smart strategy to produce soft responsive materials for applications in chiral photonics.

The fabrication of bifunctional supramolecular glycolipid-based nanocomposite gel: insights into electrocatalytic performance with effective selectivity towards gold

Recovery, recycling, and reuse of metal waste have been re-intensified in the current era to build a sustainable future. In this context, gel nanocomposites were formulated by in situ reduction of gold within the low molecular weight gel matrix of synthetic glycolipid amphiphiles without using any external reducing/stabilizing agents. This strategy aroused the interest in formulating gel nanocomposites with preferential uptake of gold. The exclusive advantages owned by gold nanoparticle (GNP) embedded hydrogel offer an alternative to decorate the electrode surface without physical deposition/plating of the catalyst. Formation of GNP within the gel matrix was confirmed by the SPR peak in the UV-Visible spectrum. The particle size of 5-7 nm with zeta potential value in the range of -30.5 to -41.4 mV displayed good stability of nanoparticles in the gel matrix. Due to the encapsulation of nanoparticles within supramolecular assemblies of gel, a noteworthy increase in viscoelastic strength was observed, whereas the gelation behavior, melting temperature, and original fibrillar morphology of hydrogel remained intact. This hybrid gel exhibited good ionic conductivity (2.36 × 10-5 S cm-1) with appreciable ionic transport, remarkable oxygen reduction reaction (ORR) augmentation in reduction potential from 0 V to -0.12 V vs. Ag/AgCl as reference electrode, and excellent thermal stability in a wide temperature range. This green and efficient approach can pave the way for creating GNP-embedded hierarchical architecture that can act as bifunctional electrolyte/electrocatalyst material.

In-situ synthesis of metal nanoparticle embedded soft hybrid materials via eco-benign approach

The unique optical and electronic properties of metal nanoparticles and tunable properties of the organic templates encourage the scientific community to generate metal nanoparticle embedded soft hybrid materials for various novel utilities. Here, we discuss the in-situ synthesis of metal nanoparticle embedded soft hybrid materials via eco-benign approach which exclude the use of toxic reducing/capping agents or toxic reaction media. In this protocol, the gel matrix composed of benign organic templates act as reducing as well as stabilizing agent for the in-situ generation and stabilization of metal nanoparticles. As the incorporation of metal salts (as nanoparticle precursor) in the gel medium is required in this process, in most of the cases aqueous media were used for the generation of metal nanoparticle embedded soft hybrid materials. This discussion includes interesting findings from our laboratory where hybrid gel matrix composed of renewable chemicals was utilized for the in-situ synthesis of palladium nanoparticle embedded soft trihybrid material. The hybrid gel matrix rich in polyphenols/flavonoids was exploited to generate palladium nanoparticle embedded trihybrid gel through in-situ reduction of doped Pd (II) salts to stable PdNPs. The xerogel of this trihybrid material was utilized as recyclable heterogeneous catalyst for C-C coupling reaction in air under phosphene free condition and reduction reaction.

Cyclohexamer [-(d-Phe-azaPhe-Ala)2-]: good candidate to formulate supramolecular organogels

Molecular self-assembly is a fascinating process which has become an area of great interest in supramolecular chemistry, as it leads in certain cases to molecular gels. Organogels formulated from low molecular weight compounds (LMWOGs) have attracted much interest in the past decades due to their applications as new soft materials. Herein, we report on the ability of the cyclic pseudopeptide cyclo-[-(d-Phe-azaPhe-Ala)2-] (2) to self-assemble in some aromatic solvents and to form organogels driven by non-covalent forces, mainly hydrogen bonding and π-stacking interactions. Comprehensive FTIR and NMR studies emphasized that this cyclic aza-peptide adopts a β-turn conformation at low concentration in toluene, while an equilibrium between the monomeric states (intramolecular forces) and the supramolecular structures (intra- and intermolecular forces) is established at high concentration (gel state). Rheological investigations of the organogels highlight the dependence of their stiffness (up to ∼4 kPa) and sol/gel transition temperatures (up to 100 °C) as a function of the solvent and concentration of gelator used. The formulation of fibrous structures confirmed the phenomenon of self-assembly. Finally, we found that cyclo-[-(d-Phe-azaPhe-Ala)2-] is an effective organogelator for application in phase selective gelation (PSG) of organic solvents from aqueous/organic mixtures with recovery percents up to 96%.

Amphiphilic phenylalanine derivatives that temporally generate reactive oxygen species from water in the presence of Au(iii) ions

Amphiphilic derivatives of phenylalanine (ADFs) have strong self-assembling propensities and yield low molecular weight hydrogels on multiple occassions. The interaction of ADFs with metal ions can result in the morphological changes in the self-assemblies. Herein, we report the interesting consequences of the interaction between four N-protected ADFs with Au(iii) ions. In the case of ADF 1, the original nanofibrillar morphology of the self-assemblies spontaneously transformed into uniform nanoglobules of ∼80 nm in diameter upon addition of Au(iii) ions. A subsequent reduction of the Au(iii) ions to Au(0) nanoparticles (AuNPs) and the surface decoration of the nanoglobules with AuNPs were observed in the course of the next six to eight hours. Simultaneously, multiple reactive oxygen species (ROS) such as hydrogen peroxide (H₂O₂), hydroxyl radicals (˙OH), singlet oxygen and superoxide ions were also found to be present in the reaction medium. These ROS originate from water used as the reaction medium. The ROS production and the reduction of Au(iii) were inhibited upon deaeration of the reaction medium and the use of heavy water (D₂O) or organic solvents as the reaction medium, while an increase in the pH of the aqueous medium intensified both these processes. We exploited the temporal ROS generation using the mixture of 1 and Au(iii) ions towards anticancer therapy by enhancing the intracellular ROS levels. It is expected that this effort can be expanded into a viable anticancer therapy in the near future by modulating the amount and the rate of ROS-generation through judicious choice of the peptidic ligands and metal ions.

A Reductive Supramolecular Hydrogel: A Platform for Facile Fabrication of Diverse Metal-Nanoparticle-Decorated Conductive Networks with Spatiotemporal Control

Nanoparticle-hydrogel hybrid composites have a great potential for a broad range of applications, such as antibacterial materials, stimuli-responsive materials and catalysis. A novel supramolecular hydrogel system was developed using an amino acid based amphiphile containing a terminal pyrrole moiety as a gelator. The pyrrole moiety could serve as both reducing agent and monomer, and a variety of metal precursors penetrating into the hydrogel could be reduced in situ into metal nanoparticles while the pyrrole moieties preorganized in hydrogel were oxidized into polyprroles, affording metal-nanoparticle-decorated covalent conductive networks. This strategy allows the facile fabrication of diverse mono- or multimetallic nanoparticle-polymer networks from one hydrogel by a simple reaction-diffusion approach. More importantly, besides homogeneous composites, unique multisegment heterogeneous systems with spatiotemporal control were also easily accessible. Furthermore, based on the same multifunctional molecule, the fabrication of hierarchically pore-structured metal-nanoparticles-polymers as well as metal-nanoparticles-carbon structures was also realized.

An Li+-enriched Co2+-induced metallogel: a study on thixotropic rheological behaviour and conductance

An alkali base and counterion-selective red metallogel (1% w/v) has been synthesized by mixing the adipic acid-derived ligand H₂AL with LiOH, followed by the addition of 1 equivalent of Co(OAc)₂ in DMF. The addition of Co(OAc)₂ not only resulted in the formation of a 2 : 2 (M : L) complex, but also led to the consecutive steps of aggregation, fiber creation, entrapment of the solvent and eventually gelation. The metallogel formation and the mechanism behind gelation have been well characterized and established using various instrumental techniques such as FTIR spectroscopy, UV-vis spectroscopy, FE-SEM, TEM, PXRD, ESI-mass spectrometry, Job's plot and rheology analysis. Nyquist plots suggested a large decrease in the resistance value from 11.3 kΩ to 4.2 kΩ for the solution obtained from the ligand deprotonated by LiOH (AL^2-) and Co(OAc)₂ containing the metallogel. The Nyquist plot and resistance of the metallogel have also been studied under the influence of temperature and ultrasound stimuli. The extensive rheological measurements provide information about the strength of the gel network and the highly reversible nature and thixotropic behaviour of the metallogel.

Fabrication of soft-nanocomposites from functional molecules with diversified applications

With the increasing demand for new soft materials having excellent physical and biological characteristics and functionality, the design of hybrid materials offers a simple, yet versatile platform for the development of materials with specific and tunable properties. By definition a "soft-nanocomposite" is the combination of supramolecular self-assemblies with nanomaterials of different origins (inorganic/metallic nanoparticles and carbonaceous allotropes like carbon nanotubes and graphene) through covalent/non-covalent interactions. Dynamic supramolecular self-assemblies can serve as excellent hosts for the incorporation of these dimensionally different nanomaterials. Nanomaterials within the matrix of supramolecular self-assemblies can give rise to new characteristics due to the synergistic contribution of both materials. Although the very initial work intended to use molecular gels as media for the preparation and stabilization of nanoparticles, recent reports have suggested that amalgamation of different supramolecular self-assemblies with nanoparticles is advantageous for both constituents. These newly developed soft-nanocomposites have interesting properties including electrical conductivity, viscoelasticity, thermal robustness, magnetic, phase-selective, redox and near-infrared radiation sensitive properties and so on. This review will focus on some of the most recent advancements in the development of novel soft-nanocomposites. In particular, we intend to correlate various design strategies for synthesis as well as composite preparation from functional molecules with interesting applications in the area of supercapacitors, nanoelectronics, photovoltaic devices, chemical and biosensors, biomedicine and so on. We expect that this article will be a general and conceptual demonstration of various approaches to develop different soft-nanocomposites and will highlight their applications across disciplines.

Controlled mechanical properties and supramolecular chirality of hydrogels via pH change

In order to widen the use of soft materials in tissue engineering and life sciences, hydrogels with improved mechanical properties and controlled chirality are critical to achieve. A methodology is presented to enhance the mechanical properties and gain the control of chirality of two component hydrogels by merely varying the solution pH. pH change has been used as a way to ionize the specific functionalities into positive and negative charges. These positive and negative charges are crucial to provide a surge of electrostatic interactions to the components, imparting the improvement in stability and regulating their optical activity. Our goal is to throw light on the significance of opposite charges in the hydrogels for achievement of desired properties. •Role of ionisable groups is crucial to control viscoelastic and optical properties of supramolecular hydrogels.•Increasing the pH of the solution increases the number of negative ions by affecting the ionisable moieties, which interact with the positive charges in the solution.•Zeta potential of both materials has been analysed to ensure the presence of charged species.

Engineering hydrogel viscoelasticity

The aim of this study was to identify a method for modifying the time-dependent viscoelastic properties of gels without altering the elastic component. To this end, two hydrogels commonly used in biomedical applications, agarose and acrylamide, were prepared in aqueous solutions of dextran with increasing concentrations (0%, 2% and 5% w/v) and hence increasing viscosities. Commercial polyurethane sponges soaked in the same solutions were used as controls, since, unlike in hydrogels, the liquid in these sponge systems is poorly bound to the polymer network. Sample viscoelastic properties were characterised using the epsilon-dot method, based on compression tests at different constant strain-rates. Experimental data were fitted to a standard linear solid model. While increasing the liquid viscosity in the controls resulted in a significant increase of the characteristic relaxation time (τ), both the instantaneous (E_inst) and the equilibrium (E_eq) elastic moduli remained almost constant. However, in the hydrogels a significant reduction of both E_inst and τ was observed. On the other hand, as expected, E_eq - an indicator of the equilibrium elastic behaviour after the occurrence of viscoelastic relaxation dynamics - was found to be independent of the liquid phase viscosity. Therefore, although the elastic and viscous components of hydrogels cannot be completely decoupled due to the interaction of the liquid and solid phases, we show that their viscoelastic behaviour can be modulated by varying the viscosity of the aqueous phase. This simple-yet-effective strategy could be useful in the field of mechanobiology, particularly for studying cell response to substrate viscoelasticity while keeping the elastic cue (i.e. equilibrium modulus, or quasi-static stiffness) constant.

Li+-Induced fluorescent metallogel: a case of ESIPT-CHEF and ICT phenomenon

A fluorescent metallogel has been synthesized from non-fluorescent ingredients viz. the smallest possible LMW aromatic symmetrical gelator 1 and LiOH, whereas KOH produces a non-fluorescent solution, and regioisomer 2 with LiOH shows an ICT assisted fluorescent precipitate rather than a metallogel.

Fine-Tuning of Saponification-Triggered Gelation by Strategic Modification of Peripheral Substituents: Gelation Regulators

A pioneering approach towards controlling the efficiency of saponification assisted gelation in ethyl ester based Zn^II -complexes have been described. Using four new ester containing bis-salen Zn^II complexes (C1-C4) involving different para-azo phenyl substituted ligands it has been clearly shown that gelation efficiency is greatly influenced by the electronic effects of the substituents (-H (C1), -CH₃ (C2), -NO₂ (C3), and -OCH₃ (C4)). Morphological, photophysical, and rheological investigations corroborated the experimental observations well and established that gelation efficiency was enhanced with electron-withdrawing characteristics of substituents (C4<C2<C1<C3). This conclusion was also supported by DFT studies.

Alkali base triggered intramolecular charge transfer metallogels based on symmetrical A-π-D-chiral-D-π-A type ligands

Three l-tartaric acid based symmetrical A-π-D-chiral-D-π-A type structural isomeric nitrobenzylidenes (1-3) have been synthesized with intent to achieve isomer specific metallogels with intramolecular charge transfer properties. Alkali metal ions in these systems not only trigger charge transfer but also play a vital role in gelation. The presence of intramolecular rather than intermolecular charge transfer as well as aggregation has been well established by various kinds of experiments using UV-vis, CD, (1)H NMR, DFT and crystallography techniques. The role of alkali metal ions in triggering ICT was proved by titration with their respective crown ethers. Notably, Na(+) afforded twisted fiber morphology whilst Li(+) gave merely long range fibers. The true gel phase material was proved by detailed rheological studies.

Carbon-Nanotube-Mediated Electrochemical Transition in a Redox-Active Supramolecular Hydrogel Derived from Viologen and an l-Alanine-Based Amphiphile

A two-component hydrogelator (16-A)2 -V(2+) , comprising an l-alanine-based amphiphile (16-A) and a redox-active viologen based partner (V(2+) ), is reported. The formation the hydrogel depended, not only on the acid-to-amine stoichiometric ratio, but on the choice of the l-amino acid group and also on the hydrocarbon chain length of the amphiphilic component. The redox responsive property and the electrochemical behavior of this two-component system were further examined by step-wise chemical and electrochemical reduction of the viologen nucleus (V(2+) /V(+) and V(+) /V(0) ). The half-wave reduction potentials (E1/2 ) associated with the viologen ring shifted to more negative values with increasing amine component. This indicates that higher extent of salt formation hinders reduction of the viologen moiety. Interestingly, the incorporation of single-walled carbon nanotubes in the electrochemically irreversible hydrogel (16-A)2 -V(2+) transformed it into a quasi-reversible electrochemical system.

Anion triggered metallogels: demetalation and crystal growth inside the gel matrix and improvement in viscoelastic properties using Au-NPs

Progelator complex Zn-TRPA-2 undergoes Cl(-) triggered gelation to afford ZTP2G, while Zn-TRPA-2 capped Au-NPs under similar conditions gave another gel GNZTP2G which also represents a rare nano-composite metallogel. When Zn-TRPA-2 was triggered by Cl(-) and NO3(-) simultaneously, crystals of demetalated species NA-TRPA-2 grew inside the ZTP2G matrix. Interestingly, GNZTP2G exhibits superior viscoelastic properties over ZTP2G.

Strong and fast-recovery organic/inorganic hybrid AuNPs-supramolecular gels based on loofah-like 3D networks

Super strong and fast-recovery organic/inorganic hybrid gold nanoparticle (AuNPs)-supramolecular gels based on a three-dimensional loofah-like nanoscale network self-assembled by polyhedral oligomeric silsesquioxane (POSS) core supramolecular gelators are reported for the first time. Two series of POSS core organic/inorganic hybrid gelators, POSS-BOC-l-Homophenylalanine (POSS-Hpy) and POSS-Boc-Cys(Bzl)-OH (POSS-Cys), with two types of peripherals having different abilities for driving the self-assembly of AuNPs in gels were designed and synthesized, both of which self-assembled into three-dimensional loofah-like nanoscale gel networks producing hybrid physical gels with fast-recovery behaviors. The mechanical properties of the resultant hybrid gels were dramatically increased by as much as 100 times in the system of sulfur containing POSS-Cys gelators without destroying the fast-recovery behaviors, with the addition of AuNPs, which had direct interaction with AuNPs to give S-Au non-covalent driving force to lead AuNPs self-assemble onto the 3D loofah-like network nanofibres in the supramolecular hybrid gel system. However, in the POSS-Hpy gelator system without sulfur, no strong interaction with AuNPs existed and the POSS-Hpy nanocomposites showed no clear changes in morphology, thermal stability or rheological properties, confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), tube-inversion and rotational rheometer measurements. This indicated that the organic/inorganic hybrid gelator POSS-Cys could be applied to the formation of soft materials in which AuNPs were self-assembled and closely arranged into three-dimensional nanoscale networks. This hybrid material has great potential for applications in self-recovery, nano- and micron-scale electronic devices, because it has both a large mechanical strength and a fast-recovery capability.

Low molecular weight gels: potential in remediation of crude oil spillage and recovery

A molecular gelator which has strong gelation ability for different crude oils (light to heavy crudes), and a wide range of refinery products is reported for the first time for its potential application in oil spillage/recovery.

Selective aliphatic/aromatic organogelation controlled by the side chain of serine amphiphiles

Structural modifications in the side chain of N-Fmoc-l-serine amphiphiles induce the selective gelation of either aliphatic or aromatic hydrocarbon solvents.

Selective Extraction and In Situ Reduction of Precious Metal Salts from Model Waste To Generate Hybrid Gels with Embedded Electrocatalytic Nanoparticles

A hydrogel based on 1,3:2,4-dibenzylidenesorbitol (DBS), modified with acyl hydrazides which extracts gold/silver salts from model waste is reported, with preferential uptake of precious heavy metals over other common metals. Reduction of gold/silver salts occurs spontaneously in the gel to yield metal nanoparticles located on the gel nanofibers. High nanoparticle loadings can be achieved, endowing the gel with electrochemical activity. These hybrid gels exhibit higher conductances than gels doped with carbon nanotubes, and can be used to modify electrode surfaces, enhancing electrocatalysis. We reason this simple, industrially and environmentally relevant approach to conducting materials is of considerable significance.

Multifarious facets of sugar-derived molecular gels: molecular features, mechanisms of self-assembly and emerging applications

The remarkable capability of nature to design and create excellent self-assembled nano-structures, especially in the biological world, has motivated chemists to mimic such systems with synthetic molecular and supramolecular systems. The hierarchically organized self-assembly of low molecular weight gelators (LMWGs) based on non-covalent interactions has been proven to be a useful tool in the development of well-defined nanostructures. Among these, the self-assembly of sugar-derived LMWGs has received immense attention because of their propensity to furnish biocompatible, hierarchical, supramolecular architectures that are macroscopically expressed in gel formation. This review sheds light on various aspects of sugar-derived LMWGs, uncovering their mechanisms of gelation, structural analysis, and tailorable properties, and their diverse applications such as stimuli-responsiveness, sensing, self-healing, environmental problems, and nano and biomaterials synthesis.

Differential response of cholesterol based pyrimidine systems with oxyethylene type spacers to gelation and mesogen formation in the presence of alkali metal ions

A new series of lipophilic cholesteryl derivatives of 2,4,6-trichloro-pyrimidine-5-carbaldehyde has been synthesized. Oxyethylene spacers of variable lengths were inserted between the hydrogen bonding promoting pyrimidine core and the cholesteryl tail in order to understand their effect on the self-assembly of these compounds. Only compound 1a with the shortest spacer formed a gel in organic solvents such as n-butanol and n-dodecane. While other members (1b and c) having longer spacers led to sol formation and precipitation in n-butanol and n-dodecane respectively. The self-assembly phenomena associated with the gelation process were investigated using temperature-dependent UV-Vis and CD-spectroscopy. The morphological features of the freeze-dried gels obtained from different organic solvents were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The solid phase behaviours of these molecules and their associated alkali metal ion complexes were explored using polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The molecular arrangements in the xerogel and in the solid state were further probed using a wide-angle X-ray diffraction (WAXD) technique. Analysis of the wide-angle X-ray diffraction data reveals that this class of molecules adopts a hexagonal columnar organization in the gel and in the solid state. Each slice of these hexagonal columnar structures is composed of a dimeric molecular-assembly as a building block. Significant changes in the conformation of the oxyethylene chains could be triggered via the coordination of selected alkali metal ions. This led to the production of interesting metal ion promoted mesogenic behaviour.

Ag+-induced reverse vesicle to helical fiber transformation in a self-assembly by adjusting the keto–enol equilibrium of a chiral salicylideneaniline

A chiral salicylideneaniline shows Ag⁺-induced reverse vesicle-to-helical nanofiber transformation accompanied by sol-to-gel transition at room temperature.

Odd–even effect in a thiazole based organogelator: understanding the interplay of non-covalent interactions on property and applications

The effects of systematic change in the alkyl chain appended to the thiazole moiety on supramolecular gelation and nanoparticle synthesis were investigated.

Redox-switchable copper(I) metallogel: a metal-organic material for selective and naked-eye sensing of picric acid

Thiourea (TU), a commercially available laboratory chemical, has been discovered to introduce metallogelation when reacted with copper(II) chloride in aqueous medium. The chemistry involves the reduction of Cu(II) to Cu(I) with concomitant oxidation of thiourea to dithiobisformamidinium dichloride. The gel formation is triggered through metal-ligand complexation, i.e., Cu(I)-TU coordination and extensive hydrogen bonding interactions involving thiourea, the disulfide product, water, and chloride ions. Entangled network morphology of the gel selectively develops in water, maybe for its superior hydrogen-bonding ability, as accounted from Kamlet-Taft solvent parameters. Complete and systematic chemical analyses demonstrate the importance of both Cu(I) and chloride ions as the key ingredients in the metal-organic coordination gel framework. The gel is highly fluorescent. Again, exclusive presence of Cu(I) metal centers in the gel structure makes the gel redox-responsive and therefore it shows reversible gel-sol phase transition. However, the reversibility does not cause any morphological change in the gel phase. The gel practically exhibits its multiresponsive nature and therefore the influences of different probable interfering parameters (pH, selective metal ions and anions, selective complexing agents, etc.) have been studied mechanistically and the results might be promising for different applications. Finally, the gel material shows a highly selective visual response to a commonly used nitroexplosive, picric acid among a set of 19 congeners and the preferred selectivity has been mechanistically interpreted with density functional theory-based calculations.

Role of pH controlled DNA secondary structures in the reversible dispersion/precipitation and separation of metallic and semiconducting single-walled carbon nanotubes

Single-stranded DNA (ss-DNA) oligomers (dA20, d[(C3TA2)3C3] or dT20) are able to disperse single-walled carbon nanotubes (SWNTs) in water at pH 7 through non-covalent wrapping on the nanotube surface. At lower pH, an alteration of the DNA secondary structure leads to precipitation of the SWNTs from the dispersion. The structural change of dA20 takes place from the single-stranded to the A-motif form at pH 3.5 while in case of d[(C3TA2)3C3] the change occurs from the single-stranded to the i-motif form at pH 5. Due to this structural change, the DNA is no longer able to bind the nanotube and hence the SWNT precipitates from its well-dispersed state. However, this could be reversed on restoring the pH to 7, where the DNA again relaxes in the single-stranded form. In this way the dispersion and precipitation process could be repeated over and over again. Variable temperature UV-Vis-NIR and CD spectroscopy studies showed that the DNA-SWNT complexes were thermally stable even at ∼90 °C at pH 7. Broadband NIR laser (1064 nm) irradiation also demonstrated the stability of the DNA-SWNT complex against local heating introduced through excitation of the carbon nanotubes. Electrophoretic mobility shift assay confirmed the formation of a stable DNA-SWNT complex at pH 7 and also the generation of DNA secondary structures (A/i-motif) upon acidification. The interactions of ss-DNA with SWNTs cause debundling of the nanotubes from its assembly. Selective affinity of the semiconducting SWNTs towards DNA than the metallic ones enables separation of the two as evident from spectroscopic as well as electrical conductivity studies.

Peptide-Nanofiber-Supported Palladium Nanoparticles as an Efficient Catalyst for the Removal of N-Terminus Protecting Groups

Sonication-induced tryptophan- and tyrosine-based peptide bolaamphiphile nanofibers have been used to synthesize and stabilize Pd nanoparticles under physiological conditions. The peptide bolaamphiphile self-assembly process has been thoroughly studied by using several spectroscopic and microscopic techniques. The stiffness of the soft hydrogel matrix was measured by an oscillatory rheological experiment. FTIR and circular dichroism (CD) experiments revealed a hydrogen-bonded β-sheet conformation of peptide bolaamphiphile molecules in a gel-phase medium. The π-π stacking interactions also played a crucial role in the self-assembly process, which was confirmed by fluorescence spectroscopy. Electron (SEM and TEM) and atomic force microscopy (AFM) studies showed that the peptide bolaamphiphile molecules self-assemble into nanofibrillar structures. Pd nanoparticles were synthesized in the hydrogel matrix in which redox-active tryptophan and tyrosine residues reduce the metal ions to metal nanoparticles. The size of the Pd nanoparticles are in the range of 3-9 nm, and are stabilized by peptide nanofibers. The peptide-nanofiber-supported Pd nanoparticles have shown effective catalytic activity for the removal of N-terminus protecting groups of amino acids and peptides.

New frontiers in hybrid materials: noble metal nanoparticles – supramolecular gel systems

Recent developments in hybrid materials composed of noble metal nanoparticles and supramolecular gels are reviewed, with particular emphasis on synthetic procedures, characterization and potential applications.

Reinforcement of phenylalanine-based supramolecular hydrogels by hybridizing poly(N-isopropylacrylamide) nanogels

TEAB self-assembled into a 3D network structure and nanogels were hybridized within the system, resulting in reinforced hybridized hydrogels.

Synthesis of gold nanoparticles and nanoclusters in a supramolecular gel and their applications in catalytic reduction of p-nitrophenol to p-aminophenol and Hg(ii) sensing

Seven gelator molecules giving supramolecular gels produced Au-nanoparticles and fluorescent, small Au-nanoclusters. Such Au-nanoparticle containing gels catalyzed the reduction of p-nitrophenol to p-aminophenol without NaBH₄. The fluorescent Au-nanoclusters acted as a Hg(ii) sensor.