George John

Silver-nanoparticle-embedded antimicrobial paints based on vegetable oil

Developing bactericidal coatings using simple green chemical methods could be a promising route to potential environmentally friendly applications. Here, we describe an environmentally friendly chemistry approach to synthesize metal-nanoparticle (MNP)-embedded paint, in a single step, from common household paint. The naturally occurring oxidative drying process in oils, involving free-radical exchange, was used as the fundamental mechanism for reducing metal salts and dispersing MNPs in the oil media, without the use of any external reducing or stabilizing agents. These well-dispersed MNP-in-oil dispersions can be used directly, akin to commercially available paints, on nearly all kinds of surface such as wood, glass, steel and different polymers. The surfaces coated with silver-nanoparticle paint showed excellent antimicrobial properties by killing both Gram-positive human pathogens (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli). The process we have developed here is quite general and can be applied in the synthesis of a variety of MNP-in-oil systems.

Self-assembled prodrugs: an enzymatically triggered drug-delivery platform.

Enzyme catalysis as a tool to disassemble supramolecular hydrogels to control the release of encapsulated drugs provides an opportunity to design a wide range of enzyme-specific low-molecular-weight hydrogelators. In this proof-of-concept work, we report the synthesis of low-molecular-weight amphiphilic prodrugs as hydrogelators from a well-known drug acetaminophen (which belongs to a class of drugs called analgesics (pain relievers) and antipyretics (fever reducers)). We have shown the ability of prodrugs to self-assemble to form hydrogels that could subsequently encapsulate a second drug such as curcumin, which is a known chemopreventive and anti-inflammatory hydrophobic drug. Upon enzyme-triggered degradation, the hydrogel released single or multiple drugs at physiologically simulated conditions in vitro. Given that the degradation products consist of the drug and a fatty acid, this approach has an advantage over polymer-based prodrugs that generate polymer fragments with heterogeneous chain lengths upon degradation that may present complex toxicity profiles. Additionally, drug-release occurred without burst release. Spectrophotometric experiments supported the drug-release, and the rate was controlled by modulation of temperature and enzyme concentration. Mesenchymal stem cells treated with prodrugs retained their stem cell properties including the capacity of multi-lineage differentiation, and maintained their adhesive and proliferation capacities with high viability. The present biomaterials could have broad applications as drug-delivery vehicles and cell invasive matrices.

In situ Synthesis of Metal Nanoparticle Embedded Free Standing Multifunctional PDMS Films

We demonstrate a simple one-step method for synthesizing noble metal nanoparticle embedded free standing polydimethylsiloxane (PDMS) composite films. The process involves preparing a homogenous mixture of metal salt (silver, gold and platinum), silicone elastomer and the curing agent (hardener) followed by curing. During the curing process, the hardener crosslinks the elastomer and simultaneously reduces the metal salt to form nanoparticles. This in situ method avoids the use of any external reducing agent/stabilizing agent and leads to a uniform distribution of nanoparticles in the PDMS matrix. The films were characterized using UV-Vis spectroscopy, transmission electron microscopy and X-ray photoemission spectroscopy. The nanoparticle-PDMS films have a higher Youngs modulus than pure PDMS films and also show enhanced antibacterial properties. The metal nanoparticle-PDMS films could be used for a number of applications such as for catalysis, optical and biomedical devices and gas separation membranes.

Biorefinery: A Design Tool for Molecular Gelators

Molecular gels, the macroscopic products of a nanoscale bottom-up strategy, have emerged as a promising functional soft material. The prospects of tailoring the architecture of gelator molecules have led to the formation of unique, highly tunable gels for a wide spectrum of applications from medicine to electronics. Biorefinery is a concept that integrates the processes of converting biomass/renewable feedstock and the associated infrastructure used to produce chemicals and materials, which is analogous to petroleum-based refinery. The current review assimilates the successful efforts to demonstrate the prospects of the biorefinery concept for developing new amphiphiles as molecular gelators. Amphiphiles based on naturally available raw materials such as amygdalin, vitamin C, cardanol, arjunolic acid, and trehalose that possess specific functionality were synthesized using biocatalysis and/or chemical synthesis. The hydrogels and organogels obtained from such amphiphiles were conceptually demonstrated for diverse applications including drug-delivery systems and the templated synthesis of hybrid materials.

Morphological control of helical solid bilayers in high-axial-ratio nanostructures through binary self-assembly

Mixed molecular species of cardanyl glucoside derived from renewable resources provide nanotubes upon self-assembly in water, while the saturated homologue generated a twisted fibrous morphology. The cardanyl glucoside mixture was fractionated into four individual components in order to study their contribution to the nanotube formation. The rational control of self-assembled helical morphologies was achieved by binary self-assembling of the saturated and monoene derivatives. This method can generate a diversity of self-assembled high-axial-ratio nanostructures (HARNs), ranging from twisted ribbons and helical ribbons to nanotubes.

Lithium storage mechanisms in purpurin based organic lithium ion battery electrodes

Current lithium batteries operate on inorganic insertion compounds to power a diverse range of applications, but recently there is a surging demand to develop environmentally friendly green electrode materials. To develop sustainable and eco-friendly lithium ion batteries, we report reversible lithium ion storage properties of a naturally occurring and abundant organic compound purpurin, which is non-toxic and derived from the plant madder. The carbonyl/hydroxyl groups present in purpurin molecules act as redox centers and reacts electrochemically with Li-ions during the charge/discharge process. The mechanism of lithiation of purpurin is fully elucidated using NMR, UV and FTIR spectral studies. The formation of the most favored six membered binding core of lithium ion with carbonyl groups of purpurin and hydroxyl groups at C-1 and C-4 positions respectively facilitated lithiation process, whereas hydroxyl group at C-2 position remains unaltered.

Design and development of soft nanomaterials from biobased amphiphiles

Design and development of different forms of soft matter from renewable (biomass) feedstocks is gaining attention in current research. This highlight summarizes our continuing efforts towards the effective utilization of renewable resources for new chemicals, fuels and soft materials, and selected successful stories in that direction. Cashew nut shell liquid, an industrial by-product, was used as a raw material to synthesize aryl glycolipids which upon self-assembly generated an array of soft materials such as lipid nanotubes, twisted/helical nanofibers, low-molecular-weight hydro/organogels and liquid crystals. These soft architectures were fully characterized by using different techniques. In another example, amygdalin, a by-product of the apricot industry, was used to develop novel amphiphiles, which showed unprecedented gelation properties in a wide range of solvents. To take these soft nanomaterials to a second level, we successfully demonstrated the utility of these hydrogels as drug delivery vehicles. Intriguingly, enzyme catalysis was used as a tool to make and break the hydrogels, which apparently triggered controlled drug delivery. We believe these results and this highlight will motivate us and others in the field of biobased materials research, green chemistry and soft material development through self-assembly processes, to design and develop new functional materials from plant/crop-based renewable resources, otherwise underutilized.

Power from nature: designing green battery materials from electroactive quinone derivatives and organic polymers

Current lithium ion battery technologies suffer from challenges derived from the eco-toxicity, costliness, and energetic inefficiency of contemporary inorganic materials used in these devices. Small organic molecules containing polycyclic aromatic moieties and polar functional groups have recently been presented as attractive electron donors that bind lithium and other small metal ions. This has endowed them with the potential to replace traditional inorganic electrodes consisting of metal composites. A family of naturally occurring carbonyl compounds, or quinones, have been of particular interest to the scientific community. However, they themselves have been plagued by issues of low voltages, poor conductivity, and capacity fading due to solubility in common polar electrolytes. Herein, we review a number of theoretical and experimental solutions to this problem, which include the use of heterocyclic derivatives, polymers, and conductive supramolecular carbon frameworks as electrochemical property enhancers, or stabilizers, of potential organic electrodes. This review focuses on the benign synthesis, current status, and future direction of organic battery materials with the aim of developing sustainable energy storage systems to meet the demands of a greener future.

Prodrugs as self-assembled hydrogels: a new paradigm for biomaterials.

Prodrug-based self-assembled hydrogels represent a new class of active biomaterials that can be harnessed for medical applications, in particular the design of stimuli responsive drug delivery devices. In this approach, a promoiety is chemically conjugated to a known-drug to generate an amphiphilic prodrug that is capable of forming self-assembled hydrogels. Prodrug-based self-assembled hydrogels are advantageous as they alter the solubility of the drug, enhance drug loading, and eliminate the use of harmful excipients. In addition, self-assembled prodrug hydrogels can be designed to undergo controlled drug release or tailored degradation in response to biological cues. Herein we review the development of prodrug-based self-assembled hydrogels as an emerging class of biomaterials that overcome several common limitations encountered in conventional drug delivery.

Smart amphiphiles: hydro/organogelators for in situ reduction of gold.

New urea containing gels have been used to prepare and stabilise gold nanoparticles by in situ reduction.