Self-assembled peptide nanostructures for electrical, optical, and magnetic applications

Field of study: Physics.Dr. Suchismita Guha, Dissertation Supervisor.Includes vita."May 2018."Bio-nanotechnology has become a widespread exciting field of research as the basic biological structure of bio-inspired materials and nanotechnology share the common length scale. Bio-nanotechnology, which is mainly based on bio-inspired nanostructured materials, has potential applications in nanomedicine, drug delivery, bio-sensors, and bio-degradable electronic devices. The nanostructures obtained from biomolecules are attractive due to their biocompatibility for molecular recognition, ease of chemical modification, and the ability to scaffold other organic and inorganic materials. Peptide nanostructures formed through the self-assembly process of the basic building block of diphenylalanine show promising applications in biodegradable electronic devices, drug delivery, catalysis agent, waveguide, and frequency converter. This research focusses on the self-assembly process in a dipeptide, L, L diphenylalanine (FF) and exploring its electronic, optical, and magnetic properties. The role of solvents in the self-assembly process of FF is explored by combining density functional theory (DFT) along with experimental characterization techniques such as electron microscopy, Raman scattering, and x-ray diffraction (XRD). One of the objectives of this work was to explore the nonlinear optical (NLO) properties of FF nanostructures via second harmonic generation (SHG). The ratio of the nonlinear optical coefficients was obtained from individual FF nanotubes as a function of the tube diameter and thermal annealing conditions. The ratio of the shear to the longitudinal component (d15/d33) of the NLO coefficient increases with the diameter of the tubes. One of the transverse components, d31, of the NLO coefficient is found to be negative, and its magnitude with respect to the longitudinal component (d33) increases with the tube diameter. Thermal treatment of individual FF tubes has a similar effect as increasing the diameter of the tubes in SHG polarimetry. The functionalization of FF micro-nanostructures (FF-MNS) with nanomaterials was studied. FF-MNS with Ag or Au nanoparticles were explored in surface-enhanced Raman scattering (SERS). Such self-assembled nanostructures provide a natural template for tethering Au and Ag nanoparticles (Nps) due to its fractal surface. The FF-MNS undergo an irreversible phase transition from hexagonal packing (hex) to an orthorhombic (ort) structure at [about] 150 [degree]C. The metal Nps form chains on hex FF-MNS as inferred from transmission electron microscopy images and a uniform non-aggregated distribution in the ort phase. The SERS spectra obtained from R6G bound to FF-MNSs with AuNps show a higher enhancement for the ort phase compared with the hex phase. The experimental results agree well with our calculated Raman spectra of model systems using DFT. Our results indicate that FF-MNS both in the hex and ort phase can be used as substrates for SERS analysis with different metal Nps, opening up a novel class of optically active bio-based substrates. The use of magnetic nanoparticles with biomolecules offers a versatile path for tuning the functionality of the composite material for several applications. The functionalization of FF-MNS with cobalt ferrite (CFO) magnetic nanoparticles was achieved. The interaction between CFO nanoparticles and FF-MNS was investigated by optical spectroscopy, x-ray photoelectron spectroscopy (XPS), and magnetization measurements. The changes in the XPS data from pristine FF-MNS and CFO:FF-MNS are indicative of a charge transfer process from CFO to FF-MNS, changing the electronic states of the Fe2+ and Co2+ ions. A comparison of the magnetic characterization from CFO nanoparticles and CFO:FF-MNS shows a higher saturation magnetization from the nanocomposite sample, which is attributed to a change in the cationic distribution in CFO upon binding with the peptide. We were further successful in demonstrating the application of FF-MNS as a bio-degradable active layer in an organic light emitting diode (OLED). FF-MNS were functionalized with two blue-emitting conducting polymers: di-octyl-substituted polyfluorene (PF8) and ethyl-hexyl polyfluorene (PF2/6), and used as an active layer in an OLED architecture. A combination of molecular dynamics and experimental characterization techniques reveals a stronger binding mechanism for PF8 compared to PF2/6 with FF-MNS. Biodegradability tests from FF-MNS:PF8 nanocomposite films show more than 80% weight loss in 2 h by enzymatic action compared to PF8 pristine films, which do not degrade. Self-assembled FF-MNS with organic semiconductors open up a new generation of biocompatible and biodegradable materials in organic electronics.Includes bibliographical references (pages 131-139)

Evaluation of Antibacterial Activity and Cytotoxicity of Green Synthesized Silver Nanoparticles Using Hemidesmus Indicus R.Br.

In this work, Silver nanoparticle with potent antimicrobial activity was produced by plant mediated green synthesis of silver nitrate. Characterization of silver nanoparticle revealed that nanoparticles were crystalline in nature. TEM analysis confirmed the spherical shape of nanoparticle billow 20 nm of size. X-ray diffraction analysis reveals that the silver nanoparticles are crystals. Investigation of the antibacterial properties of silver nanoparticles against gram positive S. aureus and gram negative P. aeruginosa offered a minimum inhibition concentration of 12.5 µg/ml for both the cases. In addition, silver nanoparticles were able to decrease the viability of both PA-1 cell line (derived from human ovary Teratocarcinoma), and A549 (human non-small cell lung alveolar epithelial cell line) in a dose dependent manner

Effects of temperature and adsorbates on the composition profile of Pt-Rh nanocatalysts : A comparative study

Monte-Carlo simulation technique has been used to investigate the effect of temperature and adsorbed gases on the composition profile of unsupported Pt-Rh nanocatalysts. For a 2406 atom fcc cubo-octahedral Pt$_{\rm{}50}$Rh$_{\rm{}50}$ nanocatalyst the shell-wise composition for all the eight shells has been simulated. For the temperatures 700 K, 1000 K and 1300 K, the top shell of clean Pt-Rh nanocatalysts is found to be mildly Pt-enriched, while the second shell is Pt-depleted. The Pt concentration of the top shell shows a maximum at T = 1000 K. In presence of a quarter monolayer of adsorbed oxygen the top shell shows Rh enrichment, while all the other shells show Pt-enrichment. This is true for all the three temperatures for which the composition profiles have been studied.Comment: 9 pages (LATEX), 4 postscript figures ; Accepted for publication in Physica

Down Regulation of Phosphatidylinositol Glycan Class S (PIGS) by siRNA Sensitizes HeLa Cells to UV and H2O2

Our research group had recently found that an endoplasmic reticulum membrane protein, phosphatidylinositol glycan class S (PIGS), interacts with a protein involved in DNA repair, DNA polymerase beta (pol) (using yeast 2 hybrid system), suggesting a role of PIGS in base excision repair pathway. As an essential component of glycosylphosphatidylinositol (GPI) transamidase, PIGS helps many eukaryotic proteins to anchor on the cell surface. In the absence of PIGS, the carbonyl intermediate of GPI is not generated, and GPI biosynthesis remains incomplete. In order to further our understanding of the function of PIGS, we knocked down the gene by using siRNA technology in HeLa cells. The knocked down cell lines were tested for their sensitivity to ultraviolet (UV) radiation and hydrogen peroxide (H2O2) toxicity. The proliferation activity was compared by wound-healing assay. Apoptosis was studied by DNA fragmentation assay, colony forming assay, and caspase assay. Wound healing assay result indicates remarkably higher (1.5-2.7 times) proliferation rate of PIGS knocked down cells. The results from the sensitivity test to UV and H2O2, assessed using DNA fragmentation assay, show that PIGS siRNA cells are more sensitive than the control cells. Apoptosis of these sensitive cells is mediated by the release of cytochrome C in the cytosolic fraction followed by activation of caspase 9, 3 respectively. Therefore, in the future, RNAi technology may be used in the therapy of cervical cancer by depleting PIGS and then treating the patients with UV and H2O2

Advanced technologies in the modern era for augmented patient health care and drug delivery

The objective of the work is to recognize the recent advancements in the modern health care and drug delivery systems. The article describes few recent developments in technology like artificial intelligence, personalized medicines, customized medicines, 3D printing, bioelectronic devices and tele pharmacy, which have the potential to augment health care and drug delivery in coming times. Personalized medication ensures precise health care as per the individual genetic makeup of the patients. The 3D printing technology enables to deliver tailor made solutions to fulfil individual patient requirements. Bioelectronic medicines and devices are new technology where the patient wears a device and its electrical signal cures certain ailments. Tele pharmacy ensures that the technological advances of telecommunications are also passed on to the patient health care sector. Moreover, it can be said that all these modern developments ensure that the quality of life improves and there comes a better control on the health care costs. Keywords: artificial intelligence, personalized medicines, customized medicines, 3D printing, bioelectronic devices and tele pharmac

Spatial distribution of atoms in gas-covered Pd-X nanoparticles (X= Ag, Cu, Ni, Pt)

A Monte-carlo (MC) simulation procedure has been developed where the pair bond energies are allowed to take into account the various coordination numbers of surface atoms and the presence of adsorbates. The pair bond energies are calculated from partial bond energies of atoms which, in turn, are calculated from modified tight binding model in the second moment approximation. The model has been applied to study the role of adsorption of hydrogen, oxygen, carbon monoxide and nitric oxide on the surface composition and surface bond geometry of bimetallic Pd-X (X = Ag, Cu, Ni, Pt) nanoparticles having fcc cubo-octahedral geometry with 201, 586, 1289 and 2406 atoms. The results are compared with the known experimental results. Importance of the results in studying reactions on supported bimetallic catalysts has been highlighted.Comment: 15 pages (Latex) + 38 figures (eps