Stacey N. Barnaby

Ellagic acid promoted biomimetic synthesis of shape-controlled silver nanochains

In this work, ellagic acid (EA), a naturally occurring plant polyphenol, was utilized for the biomimetic synthesis of silver (Ag) nanoparticles, which over a period of time formed extended branched nanochains of hexagonal-shaped silver nanoparticles. It was found that EA not only has the capability of reducing silver ions, resulting in the formation of Ag nanoparticles, due to its extended polyphenolic system, but also appears to recognize and affect the Ag nanocrystal growth on the (111) face, leading to the formation of hexagon-shaped Ag nanocrystals. Initially, various Ag nanocrystal shapes were observed; however, over a longer period of time, a majority of hexagonal-shaped nanocrystals were formed. Although the exact mechanism of formation of the nanocrystals is not known, it appears that EA attaches to the silver nuclei, leading to lower surface energy of the (111) face. Further, the nanocrystals fuse together, forming interfaces among the aggregates, and, with time, those interfaces become lesser, and the nanoparticles merge together and share the same single crystallographic orientation, which leads to the formation of long elongated chains of hexagonal nanoparticles. This biomimetic approach may be developed as a green synthetic method to prepare building blocks with tunable properties for the development of nanodevices. Further, we explored the antibacterial properties and found that the tandem of EA-Ag nanochains substantially enhanced the antibacterial properties of both gram-positive and gram-negative bacteria compared to silver nanoparticles or EA alone. Additionally, the materials were also utilized for imaging of mammalian NRK (normal rat kidney) cells.

Fabrication of ellagic acid incorporated self-assembled peptide microtubes and their applications

Ellagic acid (EA), a plant polyphenol known for its wide-range of health benefits was encapsulated within self-assembled threonine based peptide microtubes. The microtubes were assembled using the synthesized precursor bolaamphiphile bis(N-α-amido threonine)-1,5-pentane dicarboxylate. The self-assembly of the microstructures was probed at varying pH. In general, tubular formations were observed at a pH range of 4-6. The formed microtubes were then utilized for fabrication with EA. We probed the ability of the microtubes as drug release vehicles for EA as well as for antibacterial applications. It was found that the release of EA was both pH and concentration dependent. The biocompatibility as well as cytotoxicity of the EA-fabricated microtubes was examined in the presence of mammalian normal rat kidney (NRK) cells. Finally the antibacterial effects of the EA incorporated peptide microtubes was examined against Escherichia coli and Staphylococcus aureus.

Growth of Se Nanoparticles on Kinetin Assemblies and their Biocompatibility Studies

In this work we examined the growth and self-assembly of kinetin nano and microstructures under varying conditions followed by the utilization of the formed structures as templates for the growth of selenium nanoparticles. It was found that the self-assembly of kinetin nanostructures is pH and concentration dependant. The optimal pH for self-assembly was found to be between pH 5–7. The self-assembly of the nanostructures was aided by aromatic π–π stacking, solvophobic interactions, as well as hydrogen bonding interactions. The sizes of the nanostructures ranged from 200 nm–500 nm in diameter, which grew into microstructures over a longer period of time. The assemblies were then used as templates for the growth of selenium nanoparticles. The formation of the nanoconjugates was confirmed by spectroscopic and electron microscopic analysis. The utility of the nanoconjugates as anti-oxidants was examined by conducting the 2,2-diphenyl-1-picrylhydrazyl (DPPH·) assay, where in selenium nanoparticles bound kinetin nanofibers showed the ability to scavenge free radicals. Further, the biocompatibility of the materials was examined in the presence of normal rat kidney cells (NRK). Thus, such nanomaterials may potentially be useful as a new family of antioxidants for biological applications and for nanodevice fabrications.

Self-assembling peptide assemblies bound to ZnS nanoparticles and their interactions with mammalian cells.

Self-assembling peptide sequences (both synthetic and natural) have emerged as a new group of building blocks for diverse applications. In this work we investigated the formation of assemblies of three diverse peptide sequences derived from the crustacean cardioactive peptide CCAP (1-9), a cardioaccelerator and neuropeptide transmitter in crustaceans, atrial natriuretic hormone ANP (1-28), a powerful vasodilator secreted by heart muscle cells of mammals, as well as adamstsostatin peptide ADS (1-17), which functions as an inhibitor of angiogenesis. The formation of assemblies was found to be dependent upon the sequences as well as the pH in which the assemblies were grown. The secondary structural transformation of the peptides was studied by circular dichroism as well as FTIR spectroscopy. In order to render the sequences luminescent, we conjugated the assemblies with ZnS nanoparticles. Finally the interactions of the peptide bound ZnS nanoparticles with mammalian normal rat kidney cells were explored. In some cases the nanoconjugates were found to adhere not only to the cellular membranes but also extend into the cytoplasm. Thus, such nanocomposites may be utilized for cell penetration and have the potential to serve as coercive multifunctional vectors for bioimaging and cellular delivery.

Biomimetic Formation of Pd and Au-Pd Nanocomposites and their Catalytic Applications

In this work, we probed the formation of gallic acid (GA) assemblies. It was observed that nanoassemblies of varying morphologies were formed depending upon the growth conditions. We then utilized the assemblies as templates for the growth of palladium (Pd) nanoparticles for developing catalytic systems biomimetically. Further, amide conjugates of GA were synthesized and self-assembled for the formation of uniformly coated assemblies of Pd nanoparticles and Au-Pd nanocomposites. Their catalytic abilities were explored by examining the degradation of para-nitrophenol. Thus, we have developed a new class of nanocomposites that were found to be effective catalytic nanomaterials via green synthesis.

Fabrication of Collagen–Elastin-Bound Peptide Microtubes for Mammalian Cell Attachment

Abstract In this work we have designed self-assembled peptide-based microconstructs and examined their interactions with elastin and collagen for potential application as scaffolds for chondrocyte cell attachment. Being biological in nature, peptide-based nano- and microstructures have intrinsic molecular recognition properties which allow extensive chemical, conformational and functional diversity. We have synthesized a new peptide bolaamphiphile, bis(N-α-amido-val)-1,5-pentane dicarboxylate, and examined its self-assembly at varying pH values. The formation of high-density networks of nano- and microtubular structures was found to be in the range of pH 4–6. The formed microtubes were then covalently bound to varying concentrations of the extracellular matrix protein elastin, a versatile protein that allows for an extensive array of physical and chemical modifications to attune properties towards diverse necessities of biomedical applications. We found that binding to microtubes was concentration dependent. The morphological and chemical changes complementing the processes of self-assembly and binding to elastin were examined by electron microscopic and spectroscopic methods. Furthermore, we also incorporated the extracellular matrix protein type-I collagen, a critical constituent for designing biocompatible scaffolds, into the elastin functionalized micro-tubes. Since the main goal is to develop highly biocompatible protein functionalized microstructures that support cellular interactions, we examined the interactions of the microcomposites with chondrocyte cell line, in order to assess the biocompatibility and interaction between the microconstructs and the cells. The designed elastin and collagen-bound peptide microtubes may potentially serve as a new class of biomaterials by promoting cell growth and proliferation.

Biomimetic growth of gallic acid–ZnO hybrid assemblies and their applications

In this study, we probed the biomimetic formation of gallic acid (GA)–ZnO nanoparticle hybrids. It was found that the morphologies formed were dependent upon pH values, resulting in GA–ZnO hybrids of varying shapes such as micro or nanoplates or fibers. The formed supramolecular GA–ZnO hybrids were found to be luminescent as indicated by confocal microscopy and were utilized for the photocatalytic degradation of the organic dye methylene blue. We also explored the bactericidal effects of the hybrids on Staphylococcus aureus (S. aureus) as well as Escherichia Coli (E. Coli). Thus, we have developed a new class of shape-controlled nanohybrid assemblies via mild, green synthetic methods that may be utilized for photocatalytic degradation for environmental remediation as well as for antibacterial applications.

ELLAGIC ACID DIRECTED GROWTH OF Au–Pt BIMETALLIC NANOPARTICLES AND THEIR CATALYTIC APPLICATIONS

In this work, we report the facile formation of bimetallic nanoparticles of Au–Pt in the presence of the plant polyphenol ellagic acid (EA). It was found that EA formed micro-fibrillar assemblies, which aggregated into micro-bundles under aqueous conditions. Those micro-bundles acted as templates for the growth of Au nanoparticles, as well as bimetallic Au–Pt nanoparticles biomimetically. At higher concentrations of EA, it was observed that in addition to forming fibrous micro-bundles, columnar assemblies of EA were formed in the presence of the metal nanoparticles. The formation of the assemblies was found to be concentration dependent. It appears that upon binding to metal ions and subsequent formation of the nanoparticles, morphological changes occur in the case of EA assemblies. The morphological changes observed were probed by electron microscopy. Further, the ability of the materials to degrade the toxic aromatic nitro compound 2-methoxy-4-nitroaniline was explored, where 50% degradation was observed within 15 min, indicating that such hybrid materials may have potential applications in environmental remediation.

pH tunable self-assembly of chicoric acid and their biocompatibility studies

We report for the first time, the pH tunable self-assembly of chicoric acid, an HIV-I integrase inhibitor, which displayed a remarkable tendency to self-assemble at room temperature into varying nano- and microstructures. Furthermore, those assemblies were then functionalised with gold (Au) nanoparticles. We then investigated the biocompatibility of the materials by conducting in vitro cell attachment and cytotoxicity studies using normal rat kidney cells. The studies revealed that the biomaterials were non-toxic and biocompatible, and showed considerable adhesion to the cells. These results suggest that the assemblies could potentially be used for a variety of applications, such as carriers for targeted drug delivery as well as optoelectronics and sensors. Furthermore, the formation of highly organised nano- and microstructures of medicinally significant phytohormones such as chicoric acid is of particular interest as it might help in further understanding the supramolecular assembly mechanism of higher organised biological structures for the development of building blocks for various device fabrications.

Ellagic Acid Nanotubular and Poly-Cationic Conjugates as Nano-Carriers for Delivery into Mammalian Cells

Ellagic acid (EA) is a naturally occurring plant polyphenol formed by the hydrolysis of ellagitannins, which are primarily found in grapes, nuts and fruits. EA has been known to have potent anticarcinogenic activities, however, its insolubility under physiological conditions limits its potential applications. In this work, we have prepared complexes of ellagic acid with peptide nanotubes and polycations such as low molecular weight polyethylenimine (PEI), polyarginine and polylysine to enhance its properties for drug delivery. In particular, polycations such as PEI are well known non-viral vectors. Briefly, EA nanofibers were grown by self-assembly and were complexed with peptide nanotubes or poly cations at varying temperature and pH. The formation of the nanocomplexes was confirmed by zeta-potential analysis. The morphologies of the complexes were examined by electron microscopy. Because of the rigid core of EA that offers shape consistence, and the poly-cation shells that passivate the surfaces, core−shell nanoconjugates whose average diameters were dependent upon the concentrations and pH were formed. In the formed complexes, the charged amine groups of the polycations most likely interact with the partially deprotonated carboxylate and hydroxyl groups of EA. In some cases, the EA was coupled with rhodamine to examine the effect of bound versus unbound nanocomplexes formed using confocal microscopy. The interactions of the complexes with mammalian cells were examined by live-cell imaging in the presence of normal rat kidney cells. The anticarcinogenic effects of the nanoprobes was explored using HeLa cells. Finally, the ability of the nanocomplexes for drug release was examined at varying pH and concentrations. Such nanocomplexes may have potential applications not only for anticarcinogenic activities but may also help probe mechanisms involved with EA based biodegradable polycationic-based delivery and cellular attachment towards use in varying therapeutic applications.