Characterization of two distinctly different mineral-related proteins from the teeth of the Camarodont sea urchin Lytechinus variegatus: Specificity of function with relation to mineralization

The majority of the mineral phase of the Lytechinus variegatus tooth is comprised of magnesium containing calcite crystal elements, collectively arranged so that they appear as a single crystal under polarized light, as well as under X-ray or electron irradiation. However, the crystal elements are small, and in spite of the common alignment of their crystal axes, are not the same size or shape in different parts of the tooth. The toughness of the tooth structure arises from the fact that it is a composite in which the crystals are coated with surface layers of organic matter that probably act to inhibit crack formation and elongation. In the growth region the organic components represent a greater part of the tooth structure. In the most heavily mineralized adoral region the primary plates fuse with inter-plate pillars. Using Scanning Electron Microscopy; TOF-SIMS mapping of the characteristic amino acids of the mineral related proteins; and isolation and characterization of the mineral-protected protein we report that the late-forming inter-plate pillars had more than a three-fold greater Mg content than the primary plates. Furthermore, the aspartic acid content of the mineralrelated protein was highest in the high Mg pillars whereas the mineral-protected protein of the primary plates was richer in glutamic acid content.These results suggest that the Asp-rich protein(s) is important for formation of the late developing inter-plate pillars that fuse the primary plates and increase the stiffness of the most mature tooth segment. Supported by NIDCR Grant DE R01-01374 to AV.     

Electrochemical potentials of layered oxide and olivine phosphate with aluminum substitution: A first principles study

First-principles prediction of enhancement in the electrochemical potential of LiCoO₂ with aluminum substitution has been realized through earlier experiments. For safer and less expensive Li-ion batteries, it is desirable to have a similar enhancement for alternative cathode materials, LiFePO₄ and LiCoPO₄. Here, we present first-principles density functional theory based analysis of the effects of aluminum substitution on electrochemical potential of LiCoO₂, LiFePO₄ and LiCoPO₄. While Al substitution for transition metal results in increase in electrochemical potential of LiCoO₂, it leads to reduction in LiFePO₄ and LiCoPO₄. Through comparative topological analysis of charge density of these materials, we identify a ratio of Bader charges that correlates with electrochemical potential and determine the chemical origin of these contrasting effects: while electronic charge from lithium is transferred largely to oxygen in LiCoO₂, it gets shared by the oxygen and Co/Fe in olivine phosphates due to strong covalency between O and Co/Fe. Our work shows that covalency of transition metal–oxygen bond plays a key role in determining battery potential.     

ENHANCED TUNABILITY AND RELAXOR CHARACTERISTICS IN CALCIUM SUBSTITUTED BARIUM ZIRCONIUM TITANATE THIN FILMS

ABSTRACT

Thin films of BaZr_0.25Ti_0.75O₃ in which Ba^{2 +} is partially substituted by Ca^{2 +} are prepared by a sol-gel method. Phases and dielectric properties of the films are studied.The crystal structure of BaZr_0.25Ti_0.75O₃ is cubic and does not change with Ca substitution upto x = 0.25 in Ba_1-xCa_xZr_0.25Ti_0.75O₃. A change from a normal to relaxor behavior is observed for x = 0.20 as indicated by a change in the frequency of dielectric maxima with temperature and other parameters.The dielectric constant and transition temperatures are found to increase with increasing Ca substitution. A tunabilty of 71%, much higher than reported in literature for this material, is observed for x = 0.1 i.e for Ba_0.9Ca_0.1Zr_0.25Ti_0.75O₃.     

Dual gas sensing properties of graphene-Pd/SnO2 composites for H2 and ethanol: Role of nanoparticles-graphene interface

In the present work, role of palladium (Pd) and tin oxide (SnO₂) nanoparticles (NPs) deposited on graphene has been investigated in terms of dual gas sensing characteristics of ethanol and H₂ between two temperatures. The incorporation of nanoparticles into graphene has been observed which results a large change in the sensing response towards these gases. It is investigated that, incorporation of isolated Pd NPs on the graphene facilitates the room temperature sensing of H₂ gas with fast response and recovery time whereas, isolated SnO₂ NPs on graphene enables the detection of ethanol at 200 °C. However, combination of isolated Pd and SnO₂ NPs on graphene shows improved sensitivity and good selectivity towards H₂ and ethanol, usually not observed in chemiresistive gas sensors. Catalytic PdH interaction and corresponding change in work function of nanoparticles on hydrogenation resulting in modifications in electronic exchange between Pd, SnO₂ and graphene are responsible for the observed behavior. These results are important for developing a new class of chemiresistive type gas sensor based on change in the electronic properties of the graphene and NPs interfaces.     

Stability field diagrams for <Emphasis Type="Italic">Ln</Emphasis>–O–Cl systems

Isothermal stability field diagrams for Ln?O?Cl systems (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) are developed by taking partial pressures of volatile components oxygen and chlorine as variables. Thermodynamic properties of all the oxides and trichlorides (LnCl₃) are available in the literature. However, data for oxychlorides (LnOCl) and dichlorides (LnCl₂) are limited. Based on systematic trends in stability of these compounds across the lanthanide series, missing data are estimated to construct the diagrams for 13 Ln?O?Cl systems at 1000 K. All the lanthanide elements form stable LnCl₃ and LnOCl. Dichlorides of Nd, Sm, Eu, Dy, Tm and Yb are stable. For systems in which dichlorides are unstable (Ln = La, Ce, Pr, Gd, Tb, Ho, Er), the LnOCl is in equilibrium with the metal (Ln) and the stability field of LnOCl is sandwiched between those of oxides and trichlorides. Stability field diagrams of lanthanide systems forming stable LnCl₂ are of two kinds: in the first kind (Ln = Nd, Dy) the stability fields of Ln and LnOCl are in contact and the stability field of LnOCl separates the fields of chlorides and oxides. In diagrams of the second kind (Ln = Sm, Eu, Tm, Yb) there is a direct equilibrium between the oxides and dichlorides at low partial pressures of oxygen and chlorine. There is no contact between the stability fields of Ln and LnOCl; the stability field of LnOCl intervenes between the oxide and chloride phases only at higher partial pressures.     

Mechanical and thermal characterization of <Emphasis Type="Italic">cis</Emphasis>-polyisoprene and <Emphasis Type="Italic">trans</Emphasis>-polyisoprene blends

Measurements of mechanical and thermal transport properties have been made on the blends of cis-polyisoprene (CPI) and trans-polyisoprene (TPI) prepared by a solution casting method. Characterization of these blends has been done using wide angle X-ray scattering. Thermo-mechanical, mechanical, and thermal transport properties have been determined employing dynamic mechanical analyzer (DMA) and transient plane source. Storage modulus and tan δ as determined from DMA have been found to increase and decrease with the increase in TPI content, respectively. Mechanical properties such as Young’s modulus and tensile strength, as determined from strain–stress behavior of CPI/TPI blends, have been found to increase with increasing TPI content. This increase in properties has been explained on the basis of the crosslink density, calculated using theory of rubber elasticity. Thermal transport properties such as thermal conductivity, thermal diffusivity, and volumetric heat capacity are higher for all the three blends as compared to their pure components.     

Morphological and mechanical characterization of a PMMA/CdS nanocomposite

Thick film of poly(methyl methacrylate) (PMMA)/CdS nanocomposite have been synthesized by the solution casting process. The nanostructure of the CdS particles has been ascertained through the small angle X-ray scattering (SAXS) technique. The surface morphological characterization of the PMMA/CdS nanocomposite has been done through scanning electron microscopy (SEM) analysis. The variation of mechanical loss factor (Tanδ) with temperature and tensile properties of prepared samples have been studied using Dynamic Mechanical Analyzer (DMA). This study reveals that the glass transition temperature (T_g), Young’s modulus, and fracture energy of the PMMA/CdS nanocomposite are greatly influenced by the existence of interfacial energetic interaction between dispersed CdS nanoparticles and the matrix of PMMA.     

Thickness-Dependent Mechanical Behaviour of Aluminium-Coated Polyethylene Terephthalate (PET) Films

Mechanical behaviour of aluminium-coated PET films has been investigated through Dynamic Mechanical Analyser. Aluminium is coated on PET substrate by vacuum thermal evaporation method. As thickness of aluminium coating increases from 150 nm to 350 nm, tensile strength decreases from 108.88 MPa to 99.25 MPa. This mechanical behaviour is correlated with microstructure and its evolution with the thickness of aluminium coating. Al-PET film consists of fine globular grains and average grain size increases monotonically with the film thickness. The relative contribution of the grain size to the strength of aluminium thin films is in good agreement with Hall-Patch equation.     

Characterization of two distinctly different mineral-related proteins from the teeth of the Camarodont sea urchin Lytechinus variegatus: Specificity of function with relation to mineralization

The majority of the mineral phase of the Lytechinus variegatus tooth is comprised of magnesium containing calcite crystal elements, collectively arranged so that they appear as a single crystal under polarized light, as well as under X-ray or electron irradiation. However, the crystal elements are small, and in spite of the common alignment of their crystal axes, are not the same size or shape in different parts of the tooth. The toughness of the tooth structure arises from the fact that it is a composite in which the crystals are coated with surface layers of organic matter that probably act to inhibit crack formation and elongation. In the growth region the organic components represent a greater part of the tooth structure. In the most heavily mineralized adoral region the primary plates fuse with inter-plate pillars. Using Scanning Electron Microscopy; TOF-SIMS mapping of the characteristic amino acids of the mineral related proteins; and isolation and characterization of the mineral-protected protein we report that the late-forming inter-plate pillars had more than a three-fold greater Mg content than the primary plates. Furthermore, the aspartic acid content of the mineral-related protein was highest in the high Mg pillars whereas the mineral-protected protein of the primary plates was richer in glutamic acid content.These results suggest that the Asp-rich protein(s) is important for formation of the late developing inter-plate pillars that fuse the primary plates and increase the stiffness of the most mature tooth segment. Supported by NIDCR Grant DE R01-01374 to AV.