Jeffery L. Yarger

C36, a new carbon solid

Under appropriate non-equilibrium growth conditions, carbon atoms form relatively stable hollow clusters of well-defined mass number, collectively known as fullerenes. The mass production, purification and condensation of such clusters into a molecular solid is generally essential to full experimental characterization: the initial discovery of C60, for example, had to await a bulk synthesis method six years later before detailed characterization of the molecule was possible. Gas-phase experiments,, have indicated the existence of a wide range of fullerene clusters, but beyond C60 only a few pure fullerene solids have been obtained, most notably C70. Low-mass fullerenes are of particular interest because their high curvature and increased strain energy owing to adjacent pentagonal rings could lead to solids with unusual intermolecular bonding and electronic properties. Here we report the synthesis of the solid form of C36 by the arc-discharge method. We have developed purification methods that separate C36 from amorphous carbon and other fullerenes, to yield saturated solutions, thin films and polycrystalline powders of the pure solid form. Solid-state NMR measurements suggest that the molecule has D6h symmetry, and electron-diffraction patterns are consistent with a tightly bound molecular solid with an intermolecular spacing of 6.68 Å. We observe large increases in the electrical conductivity of the solid on doping with alkali metals.

Vitrification of a monatomic metallic liquid

Although the majority of glasses in use in technology are complex mixtures of oxides or chalcogenides, there are numerous examples of pure substances—‘glassformers’—that also fail to crystallize during cooling. Most glassformers are organic molecular systems, but there are important inorganic examples too, such as silicon dioxide and elemental selenium (the latter being polymeric). Bulk metallic glasses can now be made; but, with the exception of Zr50Cu50 (ref. 4), they require multiple components to avoid crystallization during normal liquid cooling. Two-component ‘metglasses’ can often be achieved by hyperquenching, but this has not hitherto been achieved with a single-component system. Glasses form when crystal nucleation rates are slow, although the factors that create the slow nucleation conditions are not well understood. Here we apply the insights gained in a recent molecular dynamics simulation study to create conditions for successful vitrification of metallic liquid germanium. Our results also provide micrographic evidence for a rare polyamorphic transition preceding crystallization of the diamond cubic phase.

Determining Secondary Structure in Spider Dragline Silk by Carbon−Carbon Correlation Solid-State NMR Spectroscopy

Two-dimensional (2D) (13)C-(13)C NMR correlation spectra were collected on (13)C-enriched dragline silk fibers produced from Nephila clavipes spiders. The 2D NMR spectra were acquired under fast magic-angle spinning (MAS) and dipolar-assisted rotational resonance (DARR) recoupling to enhance magnetization transfer between (13)C spins. Spectra obtained with short (150 ms) recoupling periods were utilized to extract distinct chemical shifts for all carbon resonances of each labeled amino acid in the silk spectra, resulting in a complete resonance assignment. The NMR results presented here permit extraction of the precise chemical shift of the carbonyl environment for each (13)C-labeled amino acid in spider silk for the first time. Spectra collected with longer recoupling periods (1 s) were implemented to detect intermolecular magnetization exchange between neighboring amino acids. This information is used to ascribe NMR resonances to the specific repetitive amino acid motifs prevalent in spider silk proteins. These results indicate that glycine and alanine are both present in two distinct structural environments: a disordered 3(1)-helical conformation and an ordered beta-sheet structure. The former can be ascribed to the Gly-Gly-Ala motif while the latter is assigned to the poly(Ala) and poly(Gly-Ala) domains.

Quantitative Correlation between the protein primary sequences and secondary structures in spider dragline silks.

Synthetic spider silk holds great potential for use in various applications spanning medical uses to ultra lightweight armor; however, producing synthetic fibers with mechanical properties comparable to natural spider silk has eluded the scientific community. Natural dragline spider silks are commonly made from proteins that contain highly repetitive amino acid motifs, adopting an array of secondary structures. Before further advances can be made in the production of synthetic fibers based on spider silk proteins, it is imperative to know the percentage of each amino acid in the protein that forms a specific secondary structure. Linking these percentages to the primary amino acid sequence of the protein will establish a structural foundation for synthetic silk. In this study, nuclear magnetic resonance (NMR) techniques are used to quantify the percentage of Ala, Gly, and Ser that form both beta-sheet and helical secondary structures. The fraction of these three amino acids and their secondary structure are quantitatively correlated to the primary amino acid sequence for the proteins that comprise major and minor ampullate silk from the Nephila clavipes spider providing a blueprint for synthetic spider silks.

Non-invasive determination of the complete elastic moduli of spider silks

Spider silks possess natures most exceptional mechanical properties, with unrivalled extensibility and high tensile strength. Unfortunately, our understanding of silks is limited because the complete elastic response has never been measured-leaving a stark lack of essential fundamental information. Using non-invasive, non-destructive Brillouin light scattering, we obtain the entire stiffness tensors (revealing negative Poissons ratios), refractive indices, and longitudinal and transverse sound velocities for major and minor ampullate spider silks: Argiope aurantia, Latrodectus hesperus, Nephila clavipes, Peucetia viridans. These results completely quantify the linear elastic response for all possible deformation modes, information unobtainable with traditional stress-strain tests. For completeness, we apply the principles of Brillouin imaging to spatially map the elastic stiffnesses on a spider web without deforming or disrupting the web in a non-invasive, non-contact measurement, finding variation among discrete fibres, junctions and glue spots. Finally, we provide the stiffness changes that occur with supercontraction.

Frontiers of high pressure research II: application of high pressure to low-dimensional novel electronic materials

Contributors. Preface. Acknowledgements. Evangelos Anastassakis (1938-2000). Material Synthesis at High Pressures. Stabilization of Unusual Oxidation States of Transition Metals in Oxygen Lattices: Correlations with the Induced Electronic Phenomena G. Demazeau. Synthesis and Properties of Low dimensional F-Element Chalocogenide Compounds P.K. Dorhout, C.R. Evenson, IV. Synthesis and High-Pressure Behavior of C6N9H3*HCl: A graphitic material with a two-dimensional C-N network G.H. Wolf, et al. Plasma Polymerization of Thin Films Using Aniline and p-Xylene Precursors A. Dumitru, et al. Pressure-Induced Phase Transitions. Compressibility, Pressure-Induced Amorphisation and Thermal Collapse of Zeolites G.N. Greaves. Pressure-induced H-transfers in the networks of hydrogen bonds A. Katrusiak. The Light Elements at High Pressure, in Layered Form, and in Combination N.W. Ashcroft. Pressure-induced Phase Transitions in GaSe-, TlGaSe2- and CdGa2S4-type Crystals K.R. Allakhverdiev. Influence of Pressure on the Physical Properties of Chain TlSe-type Crystals K.R. Allakhverdiev, S.S. Ellialtiogammalu. Impendance Spectroscopy at Super High Pressures A.N. Babushkin, et al. Optical Properties of A2CuCl4 Layer Perovskites under Pressure: Structural Correlations F. Rodriguez, et al. The Effect of Pressure-Induced Collapse of Correlation and Hunds Rules on Structure and Electronic Properties of Transition-Metal Compounds M. Paz-Pasternak, et al. Pressure Tuning of Condensation and Ordering of Charge-Transfer Strings H. Cailleau, et al. From Ferroelectric to Quantum Paraelectric: Ktal-xNbxO3(KTN), a Model System G.A.Samara. Molecular Solids Under High Pressures. Quartz like phases in CO2 at very high pressure from ab initio simulations R. Ahuja, et al. Progress in Experimental Studies of Insulator-Metal Transitions at Multimegabar Pressures R.J. Hemley, et al. Solid Oxygen as Low dimensional System by Spectroscopic Studies A. Brodyanski, et al. Evolution of Rotational Spectrum in Solid Hydrogen with Pressure: Implications for Conversion and other Properties M.A. Strzhemechny. An Influence of the Pressure on Metastability of the HCP Phase of Solid Nitrogen B. Kuchta, et al. Semiconductors, 2-D Impurity States, Quantum Dots. X-ray Study of Strain Relaxation in Heteroepitaxial Layers of Semiconductors Annealed under High Hydrostatic Pressure J. Bak-Misiuk. Application of High Temperature-Pressure Treatment for Investigation of Defect Creation in Basic Materials of Modern Micro-electronics: Czochralski Silicon and Solicon Containing Films A. Misiuk. Pressure-induced Phase Transformations in Semiconductors under Contact Loading V. Domnich, Y. Gogotsi. Far-Infrared Spectroscopy of Quasi-2D Impurity States in Semiconductor Nanostructures under High Hydrostatic Pressure B.A. Weinstein, et al. Probing the Effects of Three-Dimensional Confinement on the Electronic Structure of InP under Hydrostatic Pressure C.S. Menoni, et al. Pressure Studies in InGaN/GaN Quantum Wells D. Patel, et al. Superconductivity. What High Pressure Studies Have Taught Us about High-Temperature Superconductivity J.S. Schilling. Anisotropic Low-Dimensional Superconductors Close to an Electronic Topological Transition G.G.N. Angilella, et al. Pressure-Induced Superconducting Phase Separation in Oxygen-Doped La2-xSrxCuO4+&dg

Solid-state NMR evidence for elastin-like β-turn structure in spider dragline silk

Two-dimensional homo- and heteronuclear solid-state MAS NMR experiments on (13)C/(15)N-proline labeled Argiope aurantia dragline silk provide evidence for an elastin-like beta-turn structure for the repetitive Gly-Pro-Gly-X-X motif prevalent in major ampullate spidroin 2 (MaSp2).

Solid-state NMR investigation of major and minor ampullate spider silk in the native and hydrated states.

Silks spun from the major (Ma) and minor (Mi) ampullate glands by the spider Nephila clavipes respond to water differently. Specifically, Ma silk supercontracts (shrinks 40-50% in length) while Mi silk does not contract at all when hydrated with water. In the present study, 1H --> 13C cross polarization magic angle spinning (CP-MAS), 13C MAS NMR collected with dipolar decoupling, and two-dimensional wide-line separation spectra are presented on Mi silk in its native and hydrated state and comparisons are made to Ma silk. This combination of NMR data demonstrates that water plasticizes Mi and Ma silk similarly, with an increase in chain dynamics observed in regions containing Gly, Glu, Ser, Tyr, Leu, and a fraction of Ala when the Mi silk is hydrated. Resonances that correspond to the poly(Ala) and poly(Gly Ala) motifs of Ma and Mi silk are predominately rigid indicating that water does not penetrate these beta-sheet domains.

Quantifying the fraction of glycine and alanine in β-sheet and helical conformations in spider dragline silk using solid-state NMR

Solid-state two-dimensional refocused INADEQUATE MAS NMR experiments resolve distinct helical and beta-sheet conformational environments for both alanine and glycine in Nephila clavipes dragline silk fibers; the fraction of alanine and glycine in beta-sheet structures is determined to be 82% +/- 4% and 28% +/- 5%, respectively.

Solid-State NMR Comparison of Various Spiders’ Dragline Silk Fiber

Major ampullate (dragline) spider silk is a coveted biopolymer due to its combination of strength and extensibility. The dragline silk of different spiders have distinct mechanical properties that can be qualitatively correlated to the protein sequence. This study uses amino acid analysis and carbon-13 solid-state NMR to compare the molecular composition, structure, and dynamics of major ampullate dragline silk of four orb-web spider species ( Nephila clavipes , Araneus gemmoides , Argiope aurantia , and Argiope argentata ) and one cobweb species ( Latrodectus hesperus ). The mobility of the protein backbone and amino acid side chains in water exposed silk fibers is shown to correlate to the proline content. This implies that regions of major ampullate spidroin 2 protein, which is the only dragline silk protein with any significant proline content, become significantly hydrated in dragline spider silk.