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 chicoric-acid-directed luminescent silver nanodendrites.

In this work, we report the formation of well-defined silver nanodendrites via biomineralization under mild conditions in a single step, in the presence of the plant phytohormone chicoric acid (CA), a well-known HIV-I integrase inhibitor. CA played a dual role as reductant as well as directed the growth of the nanodendrites, which were found to grow primarily in the [111] and [200] directions. In addition to the formation of highly ordered hierarchical structures, the formed Ag nanodendrites were found to exhibit luminescence, as observed by confocal microscopy. This study not only demonstrates a new method for the preparation of luminescent silver nanodendrites using a simple, environmentally friendly biological method, but also indicates the ability of CA, a potent HIV-integrase inhibitor, to interact with silver ions which may shed light on its potential for additional biomedical and biosensor applications.

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.

pH dependent spontaneous growth of ellagic acid assemblies for targeting HeLa cells.

Herein, we have studied the self-assembly and the spontaneous growth of microassemblies of the plant polyphenol ellagic acid for HeLa cancer cell imaging and therapy. The growth of the assemblies was studied at varying pH over time. It was found that initially microspheres were formed which gradually transformed into microfibers via nucleation and polymerization process. The optimum growth of microfibers was found to be in the pH range of 6-8. We have shown that the microfibers successfully adhered to the HeLa cell membranes and inhibited their proliferation. This biological approach, using assemblies derived from plant polyphenols, may be used for direct cellular drug delivery and may potentially help develop a simple and economical method to create building blocks with desired properties for a new generation of sensors, bioimaging and drug delivery systems.

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.

Quantitative morphologic classification of layer 5 neurons from mouse primary visual cortex.

The understanding of any neural circuit requires the identification and characterization of all its components. Morphologic classifications of neurons are, therefore, of central importance to neuroscience. We use a quantitative method to classify neurons from layer 5 of mouse primary visual cortex, based on multidimensional clustering. To reconstruct neurons, we used Golgi impregnations and biocytin injections, as well as DiOlistics, a novel technique of labeling neurons with lipophilic dyes. We performed computerized 3-D reconstructions of 158 layer 5 cells to measure a series of morphologic variables. Principal component analysis and cluster analysis were used for the classification of cell types. Five major classes of cells were found: group 1 includes large pyramidal neurons with apical dendrites that reach layer 1 with an apical tuft; group 2 consists of short pyramidal neurons and large multipolar cells with "polarized" dendritic trees; group 3 is composed of less extensive pyramidal neurons; group 4 includes small cells; and group 5 includes another set of short pyramidal neurons in addition to "atypically oriented" cells. Our sample included a relatively homogeneous group of 27 neurons that project to the superior colliculus, which clustered mainly in group 1, thus supporting the validity of the classification. Cluster analysis of neuronal morphologies provides an objective method to quantitatively define different neuronal phenotypes and may serve as a basis for describing neocortical circuits.