Teresa Roncal-Herrero

Protein sequences bound to mineral surfaces persist into deep time

Proteins persist longer in the fossil record than DNA, but the longevity, survival mechanisms and substrates remain contested. Here, we demonstrate the role of mineral binding in preserving the protein sequence in ostrich (Struthionidae) eggshell, including from the palaeontological sites of Laetoli (3.8 Ma) and Olduvai Gorge (1.3 Ma) in Tanzania. By tracking protein diagenesis back in time we find consistent patterns of preservation, demonstrating authenticity of the surviving sequences. Molecular dynamics simulations of struthiocalcin-1 and -2, the dominant proteins within the eggshell, reveal that distinct domains bind to the mineral surface. It is the domain with the strongest calculated binding energy to the calcite surface that is selectively preserved. Thermal age calculations demonstrate that the Laetoli and Olduvai peptides are 50 times older than any previously authenticated sequence (equivalent to ~16 Ma at a constant 10°C). DOI: http://dx.doi.org/10.7554/eLife.17092.001

Phosphate mineral reactivity: from global cycles to sustainable development

Abstract A survey of the surface-area-normalized dissolution rates of major phosphate bearing minerals shows these rates to vary by >8 orders of magnitude with a general dissolution-rate trend sturvite > britholite ∼ fluoroapatite > variscite > monazite ∼ rhabdophane. This trend reflects the relative strength of the metal-oxygen bonds holding together the phosphate tetrahedra in the mineral structure. Due to the high surface-area-normalized reactivity of fluoroapatite, and the high surface area of natural variscite and rhabdophane, it seems likely that these minerals buffer the concentration of P and the rare-earth elements in many natural waters. As such, the solubility of these minerals plays a significant role in the global phosphorus cycle, and may potentially provide clues for future sustainable phosphorus use.

Crystallization of citrate-stabilized amorphous calcium phosphate to nanocrystalline apatite: a surface-mediated transformation

This work explores the mechanisms underlying the crystallization of citrate-functionalized amorphous calcium phosphate (cit-ACP) in two relevant media, combining in situ and ex situ characterization techniques. Results demonstrate that citrate desorption from cit-ACP triggers the surface-mediated transformation to nanocrystalline apatite (Ap). Our findings shed light on the key role of citrate, an important component of bone organic matrix, and the medium composition in controlling the rate of transformation and the morphology of the resulting Ap phase.

Synergistic Biomineralization Phenomena Created by a Combinatorial Nacre Protein Model System

In the nacre or aragonite layer of the mollusk shell, proteomes that regulate both the early stages of nucleation and nano-to-mesoscale assembly of nacre tablets from mineral nanoparticle precursors exist. Several approaches have been developed to understand protein-associated mechanisms of nacre formation, yet we still lack insight into how protein ensembles or proteomes manage nucleation and crystal growth. To provide additional insights, we have created a proportionally defined combinatorial model consisting of two nacre-associated proteins, C-RING AP7 (shell nacre, Haliotis rufescens) and pseudo-EF hand PFMG1 (oyster pearl nacre, Pinctada fucata), whose individual in vitro mineralization functionalities are well-documented and distinct from one another. Using scanning electron microscopy, flow cell scanning transmission electron microscopy, atomic force microscopy, Ca(II) potentiometric titrations, and quartz crystal microbalance with dissipation monitoring quantitative analyses, we find that both nacre proteins are functionally active within the same mineralization environments and, at 1:1 molar ratios, synergistically create calcium carbonate mesoscale structures with ordered intracrystalline nanoporosities, extensively prolong nucleation times, and introduce an additional nucleation event. Further, these two proteins jointly create nanoscale protein aggregates or phases that under mineralization conditions further assemble into protein-mineral polymer-induced liquid precursor-like phases with enhanced ACC stabilization capabilities, and there is evidence of intermolecular interactions between AP7 and PFMG1 under these conditions. Thus, a combinatorial model system consisting of more than one defined biomineralization protein dramatically changes the outcome of the in vitro biomineralization process.

Variscite dissolution rates in aqueous solution: does variscite control the availability of phosphate in acidic natural waters?

Abstract The dissolution rates of natural well-crystallized variscite (AlPO4.2H2O) were measured from the evolution of aqueous Al and P concentrations in closed and mixed-flow through reactors at 25°C and from 1.5 to 9 pH. Measured dissolution rates decrease with increasing pH from 5.05 × 10−16 mol/cm2/s at pH = 1.51 to 4.92 × 10−17 mol/cm2/s at pH = 5.89 and then increase with increasing pH to 1.64 × 10−17 mol/cm2/s at pH = 8.99. Estimates of the time required to equilibrate a mildly acidic, initially Al- and P-free solution with variscite based on measured dissolution rates and solubility products suggests it takes no more than several weeks to equilibrate this mineral with soil pore fluids. This result suggests that variscite can buffer aqueous phosphate concentrations in a significant number of near surface environments.

Semiconductor–Metal Nanofloret Hybrid Structures by Self-Processing Synthesis

We present a synthetic strategy that takes advantage of the inherent asymmetry exhibited by semiconductor nanowires prepared by Au-catalyzed chemical vapor deposition (CVD). The metal-semiconductor junction is used for activating etch, deposition, and modification steps localized to the tip area using a wet-chemistry approach. The hybrid nanostructures obtained for the coinage metals Cu, Ag, and Au resemble the morphology of grass flowers, termed here Nanofloret hybrid nanostructures consisting of a high aspect ratio SiGe nanowire (NW) with a metallic nanoshell cap. The synthetic method is used to prepare hybrid nanostructures in one step by triggering a programmable cascade of events that is autonomously executed, termed self-processing synthesis. The synthesis progression was monitored by ex situ transmission electron microscopy (TEM), in situ scanning transmission electron microscopy (STEM) and inductively coupled plasma mass spectrometry (ICP-MS) analyses to study the mechanistic reaction details of the various processes taking place during the synthesis. Our results indicate that the synthesis involves distinct processing steps including localized oxide etch, metal deposition, and process termination. Control over the deposition and etching processes is demonstrated by several parameters: (i) etchant concentration (water), (ii) SiGe alloy composition, (iii) reducing agent, (iv) metal redox potential, and (v) addition of surfactants for controlling the deposited metal grain size. The NF structures exhibit broad plasmonic absorption that is utilized for demonstrating surface-enhanced Raman scattering (SERS) of thiophenol monolayer. The new type of nanostructures feature a metallic nanoshell directly coupled to the crystalline semiconductor NW showing broad plasmonic absorption.

Reaction pathways and textural aspects of the replacement of anhydrite by calcite at 25 °C

Abstract The replacement of sulfate minerals by calcium carbonate polymorphs (carbonation) has important implications in various geological processes occurring in Earth surface environments. In this paper we report the results of an experimental study of the interaction between anhydrite (100), (010), and (001) surfaces and Na2CO3 aqueous solutions under ambient conditions. Carbonation progress was monitored by glancing incidence X-ray diffraction (GIXRD) and scanning electron microscopy (SEM). We show that the reaction progresses through the dissolution of anhydrite and the simultaneous growth of calcite. The growth of calcite occurs oriented on the three anhydrite cleavage surfaces and its formation is accompanied by minor vaterite. The progress of the carbonation always occurs from the outer-ward to the inner-ward surfaces and its rate depends on the anhydrite surface considered, with the (001) surface being much more reactive than the (010) and (100) surfaces. The thickness of the formed carbonate layer grows linearly with time. The original external shape of the anhydrite crystals and their surface details (e.g., cleavage steps) are preserved during the carbonation reaction. Textural characteristics of the transformed regions, such as the gradation in the size of calcite crystals, from ∼2 µm in the outer region to ∼17 µm at the calcite-anhydrite interface, the local preservation of calcite crystalographic orientation with respect to anhydrite and the distribution of the microporosity mainly within the carbonate layer without development of any significant gap at the calcite-anhydrite interface. Finally, we compare these results on anhydrite carbonation with those on gypsum carbonation and can explain the differences on the basis of four parameters: (1) the molar volume change involved in the replacement process in each case, (2) the lack/existence of epitactic growth between parent and product phases, (3) the kinetics of dissolution of the different surfaces, and (4) the chemical composition (amount of structural water) of the parent phases.