Sarvesh K. Soni

Self-Assembled Enzyme Capsules in Ionic Liquid [BMIM][BF4] as Templating Nanoreactors for Hollow Silica Nanocontainers

Most of the self-assembly studies have hitherto explored the aqueous media as fluid phase for self-assembly of amphiphilic biomacromolecules, wherein architectural modification of biomolecules is generally a prerequisite for self-assembly of modified biomolecules. We demonstrate for the first time that ionic liquids can act as nonaqueous designer solvents to self-assemble amphiphilic biomacromolecules without requiring their prior modification. To this end, we show that enzyme (phytase) molecules self-assembled in the presence of an appropriate ionic liquid, resulting in the formation of enzyme capsules. Phytase capsules synthesized using this approach were further used as templating nanoreactors for the synthesis of enzyme-containing hollow silica nanocontainers. In situ immobilized phytase enzyme in the silica nanocontainers, when subjected to enzyme-reusability application, establishes them as excellent reusable biocatalysts.

Structural evaluation and catalytic performance of nano-Au supported on nanocrystalline Ce0.9Fe0.1O2−δ solid solution for oxidation of carbon monoxide and benzylamine

In this work, we systematically investigated the structure–activity performance of nanosized Au/CeO2 and Au/Ce0.9Fe0.1O2−δ catalysts, along with nanocrystalline CeO2 and Ce0.9Fe0.1O2−δ supports, for the oxidation of carbon monoxide and benzylamine. An extensive physicochemical characterization was undertaken using XRD, BET surface area, BJH analysis, TG-DTA, XPS, TEM, Raman, AAS and CHN analyses. XRD studies confirmed the formation of smaller sized Ce0.9Fe0.1O2−δ nanocrystallites due to the incorporation of Fe3+ ions into the CeO2 lattice. Interestingly, Raman analysis revealed that the addition of Au remarkably improves the structural properties of the supports, evidenced by F2g peak shift and peak broadening, a significant observation in the present work. TEM images revealed the formation of smaller Au particles for Au/Ce0.9Fe0.1O2−δ (∼3.6 nm) compared with Au/CeO2 (∼5.3 nm), attributed to ample oxygen vacancies present on the Ce0.9Fe0.1O2−δ surface. XPS studies indicated that Au and Fe are present in metallic and +3 oxidation states, respectively, whereas Ce is present in both +4 and +3 oxidation states (confirming its redox nature). Activity results showed that the incorporation of Fe outstandingly enhances the efficacy of the Au/CeO2 catalyst for both CO oxidation and benzylamine oxidation. A 50% CO conversion was achieved at ∼349 and 330 K for Au/CeO2 and Au/Ce0.9Fe0.1O2−δ catalysts, respectively. As well, the Au/Ce0.9Fe0.1O2−δ catalyst showed ∼99% benzylamine conversion with ∼100% dibenzylimine selectivity for 7 h reaction time and 403 K temperature, whereas only 81% benzylamine conversion was achieved for the Au/CeO2 sample under similar conditions. The excellent performance of the Au/Ce0.9Fe0.1O2−δ catalyst is mainly due to the existence of smaller Au particles and an improved synergetic effect between the Au and the Ce0.9Fe0.1O2−δ support. It is confirmed that the oxidation efficiency of the Au catalysts is highly dependent on the preparation method.

Cationic Amino Acids Specific Biomimetic Silicification in Ionic Liquid: A Quest to Understand the Formation of 3-D Structures in Diatoms

The intricate, hierarchical, highly reproducible, and exquisite biosilica structures formed by diatoms have generated great interest to understand biosilicification processes in nature. This curiosity is driven by the quest of researchers to understand natures complexity, which might enable reproducing these elegant natural diatomaceous structures in our laboratories via biomimetics, which is currently beyond the capabilities of material scientists. To this end, significant understanding of the biomolecules involved in biosilicification has been gained, wherein cationic peptides and proteins are found to play a key role in the formation of these exquisite structures. Although biochemical factors responsible for silica formation in diatoms have been studied for decades, the challenge to mimic biosilica structures similar to those synthesized by diatoms in their natural habitats has not hitherto been successful. This has led to an increasingly interesting debate that physico-chemical environment surrounding diatoms might play an additional critical role towards the control of diatom morphologies. The current study demonstrates this proof of concept by using cationic amino acids as catalyst/template/scaffold towards attaining diatom-like silica morphologies under biomimetic conditions in ionic liquids.

Self-Assembled Histidine Acid Phosphatase Nanocapsules in Ionic Liquid [BMIM][BF4] as Functional Templates for Hollow Metal Nanoparticles

We report the biomacromolecular self-assembly of histidine acid phosphatase (HAP), an enzyme of significant biomedical and industrial importance, in the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF(4)]). The spontaneous self-assembly of HAP enzyme in [BMIM][BF(4)] results in the formation of HAP nanocapsules. The HAP enzyme molecules were found to retain their enzymatic activity after the self-assembly process, which enabled us to utilize self-assembled HAP capsules as self-catalyzing templates for the synthesis of a range of hollow metal nanoparticles (Au, Ag, Pd, and Ni) without employing any additional reducing agent. The hollow metal nanospheres with HAP encapsulated within their cavity were found to retain enzymatic activity for at least up to four cycles, as demonstrated in the case of Au-coated HAP capsules as the model system.

Microfluidic Synthesis of Nanoparticles and their Biosensing Applications

ABSTRACT We present an extensive overview of the evolution and progress made in the field of microstructures and nanostructures preparation using microfluidic techniques in recent times. A microfluidic system creates particles that are within a narrow range of shape and size distribution. It enables controlling the shape, size and composition of nanomaterials (NMs) for various applications. A brief evaluation of the advantages of both droplet-based and continuous flow synthesis of nanoparticles (NPs) is discussed in detail and compared with the traditional wet chemical batch synthesis approach. Due to increasing applications of biosensing, nanobiotechnology, nanomedicine and diagnostics devices, special attention should be paid to metal NPs developed through microfluidic routes.

Self-Assembled Functional Nanostructure of Plasmid DNA with Ionic Liquid [Bmim][PF6]: Enhanced Efficiency in Bacterial Gene Transformation

The electrostatic interaction between the negatively charged phosphate groups of plasmid DNA and the cationic part of hydrophobic ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6]), initiates spontaneous self-assembly to form the functional nanostructures made up of DNA and ionic liquid (IL). These functional nanostructures were demonstrated as promising synthetic nonviral vectors for the efficient bacterial pGFP gene transformation in cells. In particular, the functional nanostructures that were made up of 1 μL of IL ([Bmim][PF6]) and 1 μg of plasmid DNA can increase the transformation efficiency by 300-400% in microbial systems, without showing any toxicity for E. coli DH5α cells. (31)P nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron (XPS) spectroscopic analysis revealed that the electrostatic interaction between negatively charged phosphate oxygen and cationic Bmim(+) tends to initiate the self-assembly process. Thermogravimetric analysis of the DNA-IL functional nanostructures showed that these nanostructures consist of ∼16 wt % ionic liquid, which is considered to provide the stability to the plasmid DNA that eventually enhanced the transformation efficiency.

Intrinsic therapeutic and biocatalytic roles of ionic liquid mediated self-assembled platinum–phytase nanospheres

We herein report the inherent antitumor efficiency of self-assembled phytase enzyme nanospheres and enhance their efficiency by decorating with platinum nanoparticles and with the anticancer drug curcumin. Firstly, controlled self-assembly of phytase enzyme in an Ionic Liquid 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF4], led to the formation of therapeutically active phytase nanospheres. These nanospheres were further decorated with platinum nanoparticles by adding the platinum ions to these spheres and the nanoparticles formation was mediated by the specific interaction between the histidine residue (in active site of phytase enzymes) and the platinum ions and subsequent reduction of the ions into nanoparticles. The enzyme spheres act as a functional soft template for the as-formed platinum nanoparticles. These Platinum decorated hybrid biomacromolecular phytase nanospheres were loaded with the anticancer drug curcumin and all the different kinds of nanospheres were subjected to in vitro cytotoxicity for their anticancer effect on three different kinds of cancer cell lines i.e. MCF-7, Hep-G2 and THP-1 derived human macrophages. We observed a gradual increase in the anticancer effect caused by only phytase nanospheres (25%), platinum–phytase nanospheres (37%), phytase–curcumin (78%) and platinum–phytase–curcumin nanospheres (90%) that establishes this protein based system as a robust combinatorial drug delivery vehicle. The platinum–phytase spheres also proved their usability as a highly efficient green and reusable biocatalytic system for phytate degradation. The present work facilitates our understanding of ionic liquid based synthesis for multifunctional protein based drug delivery vehicles incorporating combinatorial chemotherapy for potential application as biopharmaceutical agents for tumor treatment and bio-catalysis.

Self-assembled lipase nanosphere templated one-pot biogenic synthesis of silica hollow spheres in ionic liquid [Bmim][PF6]

The spontaneous self-assembly of hydrophobic enzymatic protein triacylglycerol acylhydrolase (commonly known as lipase and a member of the serine hydrolase family) in hydrophobic 1-butyl-3-methylimidazolium hexafluorophosphate [Bmim][PF6] and in hydrophilic 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF4] ionic liquids resulted in the formation of lipase enzyme nanocapsules of different morphology. The lipase enzyme capsules were found to retain varying enzyme activity in both cases with both kinds of lipase capsules acting as self-catalyzing functional templates for the hydrolysis of silica precursors into silica. The presence of silica and its interaction with biomolecules was proved by X-ray Photoemission Spectroscopy (XPS). Interestingly, hollow silica spheres were obtained in the case of [Bmim][PF6] ionic liquid, while solid silica spheres were obtained in the case of [Bmim][BF4] ionic liquid for the same enzyme. The structural orientation of the enzyme within the capsules, their functional templating to obtain silica particles of varying morphology and finally their combined catalytic activity depend on the initial lipase-ionic liquid interaction. The enzyme activity of all these materials was evaluated against the esterification reaction between oleic acid (fatty acid) and butanol, i.e. biodiesel production. The relative enzyme activity was found to be 93.30% higher in the case of lipase nanocapsules synthesized in [Bmim][PF6] and its in situ templating action to make hollow silica spheres further enhanced the residual activity. Furthermore time dependent kinetics of esterification by hollow silica spheres has also been shown here. Hollow silica spheres can also be used as a reusable catalyst for up to 6 cycles. This work demonstrates that the choice of ionic liquid is critical in controlling the self-assembly of enzymes as the ionic liquid–enzyme interaction plays a major role in retaining capsule activity and enzyme function.

A QCM-based ‘on–off’ mechanistic study of gas adsorption by plasmid DNA and DNA–[Bmim][PF6] construct

The study of the adsorption behavior of disease markers such as ammonia (NH3) and acetaldehyde (CH3CHO) with biomaterials is important, as it will improve our understanding of their interaction behavior and enable the development of self-diagnosis technologies, among others. In this study, three types of DNA-based biomaterials were synthesized (pGFP plasmid DNA isolated from E. coli DH5α, a DNA–ionic liquid construct (DNA–IL) and DNA–ionic liquid–gold chloride (DNA–IL–Au)) and their adsorption capacities for NH3 and CH3CHO were tested by utilizing a gravimetric transducer, namely, a quartz crystal microbalance (QCM). Pristine DNA itself displayed high sensitivity towards both gases, with a pristine DNA-based QCM displaying magnitudes of response of ∼3.74 and 2.62 ng cm−2 μg−1 following 10 minutes of exposure to 600 ppm NH3 and CH3CHO, respectively. Interestingly, no response was observed when these gases were exposed to the DNA–IL complex, which comprised DNA modified with the hydrophobic IL [Bmim][PF6]. However, when the DNA–IL complex was further treated with HAuCl4, the biomaterial (DNA–IL–Au) regained its adsorption capacity, exhibiting magnitudes of adsorption/response up to 140% and 36% higher than its DNA counterpart toward NH3 and CH3CHO, respectively. It was also observed that the utilization of DNA–IL–Au significantly reduced the sensitivity of the QCM device to humidity content, which indicates that the developed biomaterial can be readily employed to detect NH3 and CH3CHO in humid environments. Further study showed that the magnitudes of the QCM response of the DNA and DNA–IL–Au materials toward the different concentrations of NH3 and CH3CHO that were tested follow the loading ratio correlation (LRC), which thus indicates that the developed materials can potentially be utilized as sensitive layers for the detection of biomarker gases that are produced in the body as a result of biomedical disorders. In addition, a plausible sorption mechanism has also been proposed on the basis of the interaction of DNA with the ionic liquid and HAuCl4 (experimentally proved by XPS and FTIR), which strongly indicates the role of the phosphates and nucleobases of DNA for the electrostatic binding of NH3 and CH3CHO, respectively.

Fluoride adsorption on a cubical ceria nanoadsorbent: function of surface properties

Fluoride adsorption onto a cubical ceria nanoadsorbent has been explored using batch as well as column studies, under various experimental conditions such as ionic strength, pH, surface loading, and the influence of major co-existing anions. High adsorption (Langmuir adsorption capacity; 80.64 mg g−1) was attained at pH 7.0 within 2 h at an adsorbent dose of 1 g L−1. Involvement of an inner-sphere complexation mechanism (ligand exchange mechanism) of fluoride adsorption has been confirmed by Fourier transform infrared spectroscopy (FTIR), O 1s X-ray photoelectron spectroscopy (XPS) and zeta potential (ζ) studies where, ligand exchange between the metal–hydroxyl (M–OH) groups and fluoride ions took place. X-ray powder diffraction (XRD) showed the amorphous nature of the developed nanoadsorbent, responsible for the high removal efficiency. The point of zero charge of the developed nanoadsorbent shifted from pH 6 to 5 after fluoride adsorption indicating the specific adsorption of fluoride. Real water analysis using fixed column adsorption indicated that the effectively treatable volume of water was ∼130-bed volume (BV) when the breakthrough point was set at 1.5 mg L−1. The cost benefit analysis demonstrated the better economic viability of the developed cubical ceria nanoadsorbent for fluoride removal compared to other traditional adsorbents.