Matching Items (5)

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Nuclear magnetic resonance (NMR) spectroscopic characterization of nanomaterials and biopolymers

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Nanomaterials have attracted considerable attention in recent research due to their wide applications in various fields such as material science, physical science, electrical engineering, and biomedical engineering. Researchers have developed

Nanomaterials have attracted considerable attention in recent research due to their wide applications in various fields such as material science, physical science, electrical engineering, and biomedical engineering. Researchers have developed many methods for synthesizing different types of nanostructures and have further applied them in various applications. However, in many cases, a molecular level understanding of nanoparticles and their associated surface chemistry is lacking investigation. Understanding the surface chemistry of nanomaterials is of great significance for obtaining a better understanding of the properties and functions of the nanomaterials. Nuclear magnetic resonance (NMR) spectroscopy can provide a familiar means of looking at the molecular structure of molecules bound to surfaces of nanomaterials as well as a method to determine the size of nanoparticles in solution. Here, a combination of NMR spectroscopic techniques including one- and two-dimensional NMR spectroscopies was used to investigate the surface chemistry and physical properties of some common nanomaterials, including for example, thiol-protected gold nanostructures and biomolecule-capped silica nanoparticles.

Silk is a natural protein fiber that features unique properties such as excellent mechanical properties, biocompatibility, and non-linear optical properties. These appealing physical properties originate from the silk structure, and therefore, the structural analysis of silk is of great importance for revealing the mystery of these impressive properties and developing novel silk-based biomaterials as well. Here, solid-state NMR spectroscopy was used to elucidate the secondary structure of silk proteins in N. clavipes spider dragline silk and B. mori silkworm silk. It is found that the Gly-Gly-X (X=Leu, Tyr, Gln) motif in spider dragline silk is not in a β-sheet or α-helix structure and is very likely to be present in a disordered structure with evidence for 31-helix confirmation. In addition, the conformations of the Ala, Ser, and Tyr residues in silk fibroin of B. mori were investigated and it indicates that the Ala, Ser, and Tyr residues are all present in disordered structures in silk I (before spinning), while show different conformations in silk II (after spinning). Specifically, in silk II, the Ala and Tyr residues are present in both disordered structures and β-sheet structures, and the Ser residues are present primarily in β-sheet structures.

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Date Created
  • 2017

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Characterizing nanomaterials and protic ionic liquids utilizing nuclear magnetic resonance spectroscopy

Description

Structural details of phosphonic acid functionalized nanomaterials and protic ionic liquids (PILs) were characterized using nuclear magnetic resonance (NMR) spectroscopy. It is well known that ligands play a critical

Structural details of phosphonic acid functionalized nanomaterials and protic ionic liquids (PILs) were characterized using nuclear magnetic resonance (NMR) spectroscopy. It is well known that ligands play a critical role in the synthesis and properties of nanomaterials. Therefore, elucidating the details of ligand-surface and ligand-ligand interactions is crucial to understanding nanomaterial systems more completely.

In an effort to further the understanding of ligand-surface interactions, a combination of multi-nuclear (1H, 29Si, 31P) and multi-dimensional solid-state NMR techniques were utilized to characterize the phosphonic acid functionalization of fumed silica nanoparticles using methyl phosphonic acid (MPA) and phenyl phosphonic acid (PPA). Quantitative 31P MAS solid-state NMR measurements indicate that ligands favor a monodentate binding mode. Furthermore, 1H-1H single quantum-double quantum (SQ-DQ) back-to-back (BABA) 2D NMR spectra of silica functionalized with MPA and PPA indicate that the MPA and PPA are within 4.2±0.2 Å on the surface of the nanomaterial.

The ligand capping of phosphonic acid (PA) functionalized CdSe/ZnS core-shell quantum dots (QDs) was investigated with a combination of ligand exchange, solution and solid-state 31P NMR spectroscopy. In order to quantify the ligand populations on the surface of the QDs, ligand exchange facilitated by PPA resulted in the displacement of the PAs, and allowed for quantification of the free ligands using 31P liquid state NMR.

In addition to characterizing nanomaterials, the ionicity and transport properties of a series of diethylmethylamine (DEMA) based protic ionic liquids (PILs) were characterized, principally utilizing NMR. Gas phase proton affinity was shown to be a better predictor for the extent of proton transfer, and in turn the ionicity of the PIL, than using ∆pKa. Furthermore, pulsed field gradient (PFG) NMR was used to determine that the exchangeable proton diffuses with the cation or the anion based on the strength of the acid used to generate the PILs.

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Date Created
  • 2015

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Determining the molecular structure of animal silks and related peptide mimics

Description

An animal's ability to produce protein-based silk materials has evolved independently in many different arthropod lineages, satisfying various ecological necessities. However, regardless of their wide range of uses and their

An animal's ability to produce protein-based silk materials has evolved independently in many different arthropod lineages, satisfying various ecological necessities. However, regardless of their wide range of uses and their potential industrial and biomedical applications, advanced knowledge on the molecular structure of silk biopolymers is largely limited to those produced by spiders (order Araneae) and silkworms (order Lepidoptera). This thesis provides an in-depth molecular-level characterization of silk fibers produced by two vastly different insects: the caddisfly larvae (order Trichoptera) and the webspinner (order Embioptera).

The molecular structure of caddisfly larval silk from the species Hesperophylax consimilis was characterized using solid-state nuclear magnetic resonance (ss-NMR) and Wide Angle X-ray Diffraction (WAXD) techniques. This insect, which typically dwells in freshwater riverbeds and streams, uses silk fibers as a strong and sticky nanoadhesive material to construct cocoons and cases out available debris. Conformation-sensitive 13C chemical shifts and 31P chemical shift anisotropy (CSA) information strongly support a unique protein motif in which phosphorylated serine- rich repeats (pSX)4 complex with di- and trivalent cations to form rigid nanocrystalline β-sheets. Additionally, it is illustrated through 31P NMR and WAXD data that these nanocrystalline structures can be reversibly formed, and depend entirely on the presence of the stabilizing cations.

Nanofiber silks produced by webspinners (order Embioptera) were also studied herein. This work addresses discrepancies in the literature regarding fiber diameters and tensile properties, revealing that the nanofibers are about 100 nm in diameter, and are stronger (around 500 MPa mean ultimate stress) than previous works suggested. Fourier-transform Infrared Spectroscopy (FT-IR), NMR and WAXD results find that approximately 70% of the highly repetitive glycine- and serine-rich protein core is composed of β-sheet nanocrystalline structures. In addition, FT-IR and Gas-chromatography mass spectroscopy (GC-MS) data revealed a hydrophobic surface coating rich in long-chain lipids. The effect of this surface coating was studied with contact angle techniques; it is shown that the silk sheets are extremely hydrophobic, yet due to the microstructural and nanostructural details of the silk surface, are surprisingly adhesive to water.

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Date Created
  • 2014

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Elucidating the molecular dynamics, structure and assembly of spider dragline silk proteins by Nuclear Magnetic Resonance (NMR) spectroscopy

Description

Spider dragline silk is an outstanding biopolymer with a strength that exceeds steel by weight and a toughness greater than high-performance fibers like Kevlar. For this reason, structural and dynamic

Spider dragline silk is an outstanding biopolymer with a strength that exceeds steel by weight and a toughness greater than high-performance fibers like Kevlar. For this reason, structural and dynamic studies on the spider silk are of great importance for developing future biomaterials. The spider dragline silk comprises two silk proteins, Major ampullate Spidroin 1 and 2 (MaSp1 and 2), which are synthesized and stored in the major ampullate (MA) gland of spiders. The initial state of the silk proteins within Black Widow MA glands was probed with solution-state NMR spectroscopy. The conformation dependent chemical shifts information indicates that the silk proteins are unstructured and in random coil conformation. 15N relaxation parameters, T1, T2 and 15N-{1H} steady-state NOE were measured to probe the backbone dynamics for MA silk proteins. These measurements indicate fast sub-nanosecond timescale backbone dynamics for the repetitive core of spider MA proteins indicating that the silk proteins are unfolded, highly flexible random coils in the MA gland. The translational diffusion coefficients of the spider silk proteins within the MA gland were measured using 1H diffusion NMR at 1H sites from different amino acids. A phenomenon was observed where the measured diffusion coefficients decrease with an increase in the diffusion delay used. The mean displacement along the external magnetic field was found to be 0.35 μm and independent of the diffusion delay. The results indicate that the diffusion of silk protein was restricted due to intermolecular cross-linking with only segmental diffusion observable.

To understand how a spider converts the unfolded protein spinning dope into a highly structured and oriented in the super fiber,the effect of acidification on spider silk assembly was investigated on native spidroins from the major ampullate (MA) gland fluid excised from Latrodectus hesperus (Black Widow) spiders. The in vitro spider silk assembly kinetics were monitored as a function of pH with a 13C solid-state Magic Angle Spinning (MAS) NMR approach. The results confirm the importance of acidic pH in the spider silk self-assembly process with observation of a sigmoidal nucleation-elongation kinetic profile. The rates of nucleation and elongation and the percentage of β-sheet structure in the grown fibers depend on pH.

The secondary structure of the major ampullate silk from Peucetia viridians (Green Lynx) spiders was characterized by X-ray diffraction (XRD) and solid-state NMR spectroscopy. From XRD measurement, β-sheet nano-crystallites were observed that are highly oriented along the fiber axis with an orientational order of 0.980. Compare to the crystalline region, the amorphous region was found to be partially oriented with an orientational order of 0.887. Further, two dimensional 13C-13C through-space and through-bond solid-state NMR experiments provide structural analysis for the repetitive amino acid motifs in the silk proteins. The nano-crystallites are mainly alanine-rich β-sheet structures. The total percentage of crystalline region is determined to be 40.0±1.2 %. 18±1 % of alanine, 60±2 % glycine and 54±2 % serine are determined to be incorporated into helical conformations while 82±1 % of alanine, 40±3 % glycine and 46±2 % serine are in the β-sheet conformation.

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Date Created
  • 2015

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Molecular structure and dynamics of spider silk and venom proteins investigated by nuclear magnetic resonance

Description

Spider dragline silk is well known for its outstanding mechanical properties - a combination of strength and extensibility that makes it one of the toughest materials known. Two proteins, major

Spider dragline silk is well known for its outstanding mechanical properties - a combination of strength and extensibility that makes it one of the toughest materials known. Two proteins, major ampullate spidroin 1 (MaSp1) and 2 (MaSp2), comprise dragline silk fibers. There has been considerable focus placed on understanding the source of spider silk's unique mechanical properties by investigating the protein composition, molecular structure and dynamics. Chemical compositional heterogeneity of spider silk fiber is critical to understand as it provides important information for the interactions between MaSp1 and MaSp2. Here, the amino acid composition of dragline silk protein was precisely determined using a solution-state nuclear magnetic resonance (NMR) approach on hydrolyzed silk fibers. In a similar fashion, solution-state NMR was applied to probe the "13"C/"15"N incorporation in silk, which is essential to understand for designing particular solid-state NMR methods for silk structural characterization. Solid-state NMR was used to elucidate silk protein molecular dynamics and the supercontraction mechanism. A "2"H-"13"C heteronuclear correlation (HETCOR) solid-state NMR technique was developed to extract site-specific "2"H quadrupole patterns and spin-lattice relaxation rates for understanding backbone and side-chain dynamics. Using this technique, molecular dynamics were determined for a number of repetitive motifs in silk proteins - Ala residing nanocrystalline &beta-sheet; domains, 3"1"-helical regions, and, Gly-Pro-Gly-XX &beta-turn; motifs. The protein backbone and side-chain dynamics of silk fibers in both dry and wet states reveal the impact of water on motifs with different secondary structures. Spider venom is comprised of a diverse range of molecules including salts, small organics, acylpolyamines, peptides and proteins. Neurotoxins are an important family of peptides in spider venom and have been shown to target and modulate various ion channels. The neurotoxins are Cys-rich and share an inhibitor Cys knot (ICK) fold. Here, the molecular structure of one G. rosea tarantula neurotoxin, GsAF2, was determined by solution-state NMR. In addition, the interaction between neurotoxins and model lipid bilayers was probed with solid-state NMR and negative-staining (NS) transmission electron microscopy (TEM). It is shown that the neurotoxins influence lipid bilayer assembly and morphology with the formation of nanodiscs, worm-like micelles and small vesicles.

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Date Created
  • 2014