Bioenergetics of iron snow fueling life on Europa.

The main sources of redox gradients supporting high-productivity life in the Europan and other icy ocean world oceans were proposed to be photolytically derived oxidants, such as reactive oxygen species (ROS) from the icy shell, and reductants (Fe(II), S(-II), CH4, H2) from bottom waters reacting with a (ultra)mafic seafloor. Important roadblocks to maintaining life, however, are that the degree of ocean mixing to combine redox species is unknown, and ROS damage biomolecules. Here, we envisage a unique solution using an acid mine drainage (AMD)-filled pit lakes analog system for the Europan ocean, which previous models predicted to be acidic. We hypothesize that surface-generated ROS oxidize dissolved Fe(II) resulting in Fe(III) (hydr)oxide precipitates, that settle to the seafloor as "iron snow." The iron snow provides a respiratory substrate for anaerobic microorganisms ("breathing iron"), and limits harmful ROS exposure since they are now neutralized at the ice-water interface. Based on this scenario, we calculated Gibbs energies and maximal biomass productivities of various anaerobic metabolisms for a range of pH, temperatures, and H2 fluxes. Productivity by iron reducers was greater for most environmental conditions considered, whereas sulfate reducers and methanogens were more favored at high pH. Participation of Fe in the metabolic redox processes is largely neglected in most models of Europan biogeochemistry. Our model overcomes important conceptual roadblocks to life in icy ocean worlds and broadens the potential metabolic diversity, thus increasing total primary productivity, the diversity and volume of habitable environmental niches and, ultimately, the probability of biosignature detection.

Novel Chimeric Amino Acid-Fatty Alcohol Ester Amphiphiles Self-Assemble into Stable Primitive Membranes in Diverse Geological Settings.

Primitive cells are believed to have been self-assembled vesicular structures with minimal metabolic components, that were capable of self-maintenance and self-propagation in early Earth geological settings. The coevolution and self-assembly of biomolecules, such as amphiphiles, peptides, and nucleic acids, or their precursors, were essential for protocell emergence. Here, we present a novel class of amphiphiles-amino acid-fatty alcohol esters-that self-assemble into stable primitive membrane compartments under a wide range of geochemical conditions. Glycine n-octyl ester (GOE) and isoleucine n-octyl ester (IOE), the condensation ester products of glycine or isoleucine with octanol (OcOH), are expected to form at a mild temperature by wet-dry cycles. The GOE forms micelles in acidic aqueous solutions (pH 2-7) and vesicles at intermediate pH (pH 7.3-8.2). When mixed with cosurfactants (octanoic acid [OcA]; OcOH, or decanol) in different mole fractions [XCosurfactant = 0.1-0.5], the vesicle stability range expands significantly to span the extremely acidic to mildly alkaline (pH 2-8) and extremely alkaline (pH 10-11) regions. Only a small mole fraction of cosurfactant [XCosurfactant = 0.1] is needed to make stable vesicular structures. Notably, these GOE-based vesicles are also stable in the presence of high concentrations of divalent cations, even at low pHs and in simulated Hadean seawater composition (without sulfate). To better understand the self-assembly behavior of GOE-based systems, we devised complementary molecular dynamics computer simulations for a series of mixed GOE/OcA systems under simulated acidic pHs. The resulting calculated critical packing parameter values and self-assembly behavior were consistent with our experimental findings. The IOE is expected to show similar self-assembly behavior. Thus, amino acid-fatty alcohol esters, a novel chimeric amphiphile class composed of an amino acid head group and a fatty alcohol tail, may have aided in building protocell membranes, which were stable in a wide variety of geochemical circumstances and were conducive to supporting replication and self-maintenance. The present work contributes to our body of work supporting our hypothesis for synergism and coevolution of (proto)biomolecules on early Earth.

Side Group of Hydrophobic Amino Acids Controls Chiral Discrimination among Chiral Counterions and Metal-Organic Cages.

The self-assembly of chiral Pd12L24 metal-organic cages (MOCs) based on hydrophobic amino acids, including alanine (Ala), valine (Val), and leucine (Leu), into single-layered hollow spherical blackberry-type structures is triggered by nitrates through counterion-mediated attraction. In addition to nitrates, anionic N-(tert-butoxycarbonyl) (Boc)-protected Ala, Val, and Leu were used as chiral counterions during the self-assembly of d-MOCs. Previously, we showed that l-Ala suppresses the self-assembly process of d-Pd12Ala24 but has no effect on l-Pd12Ala24, i.e., chiral discrimination. Here, we indicate when the amino acid used as the chiral counterion has a bulkier side group than the amino acid in the MOC structure, no chiral discrimination exists; otherwise, chiral discrimination exists. For example, Ala can induce chiral discrimination in all chiral MOCs, whereas Leu can induce chiral discrimination only in Pd12Leu24. Moreover, chiral anionic d- and l-alanine-based surfactants have no chiral discrimination, indicating that bulkier chiral counterions with more hydropohobic side groups can erase chiral discrimination.

Freshwater and Evaporite Brine Compositions on Hadean Earth: Priming the Origins of Life.

The chemical composition of aqueous solutions during the Hadean era determined the availability of essential elements for prebiotic synthesis of the molecular building blocks of life. Here we conducted quantitative reaction path modeling of atmosphere-water-rock interactions over a range of environmental conditions to estimate freshwater and evaporite brine compositions. We then evaluated the solution chemistries for their potential to influence ribonucleotide synthesis and polymerization as well as protocell membrane stability. Specifically, solutions formed by komatiite and tonalite (primitive crustal rocks) weathering and evaporation-rehydration (drying-wetting) cycles were studied assuming neutral atmospheric composition over a wide range of values of atmospheric partial pressure of CO2 (PCO2) and temperatures (T). Solution pH decreased and total dissolved concentrations of inorganic P, Mg, Ca, Fe, and C (PT, MgT, CaT, FeT, and CT) increased with increasing PCO2. The PCO2 and T dictated how the solution evolved with regard to minerals precipitated and ions left in solution. At T = 75°C and PCO2 < 0.05 atm, the concentration ratio of magnesium to calcium ion concentrations (Mg2+/Ca2+) was < 1 and predominantly metal aluminosilicates (including clays), dolomite, gibbsite, and pyrite (FeS2) precipitated, whereas at PCO2 > 0.05 atm, Mg2+/Ca2+ was > 1 and mainly magnesite, dolomite, pyrite, chalcedony (SiO2), and kaolinite (Al2Si2O5) precipitated. At T = 75°C and PCO2 > 0.05 atm, hydroxyapatite (HAP) precipitated during weathering but not during evaporation, and so, PT increased with each evaporation-rehydration cycle, while MgT, CaT, and FeT decreased as other minerals precipitated. At T = 75°C and PCO2 ∼5 atm, reactions with komatiite provided end-of-weathering solutions with high enough Mg2+ concentrations to promote RNA-template directed and montmorillonite-promoted nonenzymatic RNA polymerization, but incompatible with protocell membranes; however, montmorillonite-promoted RNA polymerization could proceed with little or no Mg2+ present. Cyclically evaporating/rehydrating brines from komatiite weathering at T = 75°C and PCO2 ∼5 atm yielded the following: (1) high PT values that could promote ribonucleotide synthesis, and (2) low divalent cation concentrations compatible with amino acid-promoted, montmorillonite-catalyzed RNA polymerization and with protocell membranes, but too low for template-directed nonenzymatic RNA polymerization. For all PCO2 values, Mg2+ and PT concentrations decreased, whereas the HCO3- concentration increased within increasing temperature, due to the retrograde solubility of the minerals controlling these ions' concentrations; Fe2+ concentration increased because of prograde pyrite solubility. Tonalite weathering and cyclical wetting-drying reactions did not produce solution compositions favorable for promoting prebiotic RNA formation. Conversely, the ion concentrations compatible with protocell emergence, placed constraints on PCO2 of early Earth's atmosphere. In summary: (1) prebiotic RNA synthesis and membrane self-assembly could have been achieved even under neutral atmosphere conditions by atmosphere-water-komatiite rock interactions; and (2) constraints on element availability for the origins of life and early PCO2 were addressed by a single, globally operating mechanism of atmosphere-water-rock interactions without invoking special microenvironments. The present results support a facile origins-of-life hypothesis even under a neutral atmosphere as long as other favorable geophysical and planetary conditions are also met.

Spatial survey of non-collagenous proteins in mineralizing and non-mineralizing vertebrate tissues ex vivo.

Bone biomineralization is a complex process in which type I collagen and associated non-collagenous proteins (NCPs), including glycoproteins and proteoglycans, interact closely with inorganic calcium and phosphate ions to control the precipitation of nanosized, non-stoichiometric hydroxyapatite (HAP, idealized stoichiometry Ca10(PO4)6(OH)2) within the organic matrix of a tissue. The ability of certain vertebrate tissues to mineralize is critically related to several aspects of their function. The goal of this study was to identify specific NCPs in mineralizing and non-mineralizing tissues of two animal models, rat and turkey, and to determine whether some NCPs are unique to each type of tissue. The tissues investigated were rat femur (mineralizing) and tail tendon (non-mineralizing) and turkey leg tendon (having both mineralizing and non-mineralizing regions in the same individual specimen). An experimental approach ex vivo was designed for this investigation by combining sequential protein extraction with comprehensive protein mapping using proteomics and Western blotting. The extraction method enabled separation of various NCPs based on their association with either the extracellular organic collagenous matrix phases or the inorganic mineral phases of the tissues. The proteomics work generated a complete picture of NCPs in different tissues and animal species. Subsequently, Western blotting provided validation for some of the proteomics findings. The survey then yielded generalized results relevant to various protein families, rather than only individual NCPs. This study focused primarily on the NCPs belonging to the small leucine-rich proteoglycan (SLRP) family and the small integrin-binding ligand N-linked glycoproteins (SIBLINGs). SLRPs were found to be associated only with the collagenous matrix, a result suggesting that they are mainly involved in structural matrix organization and not in mineralization. SIBLINGs as well as matrix Gla (γ-carboxyglutamate) protein were strictly localized within the inorganic mineral phase of mineralizing tissues, a finding suggesting that their roles are limited to mineralization. The results from this study indicated that osteocalcin was closely involved in mineralization but did not preclude possible additional roles as a hormone. This report provides for the first time a spatial survey and comparison of NCPs from mineralizing and non-mineralizing tissues ex vivo and defines the proteome of turkey leg tendons as a model for vertebrate mineralization.

Strong Enantiomeric Preference on the Macroion-Counterion Interaction Induced by Weakly Associated Chiral Counterions.

The role of chiral counterions on the attraction and self-assembly of chiral Pd12L24 metal organic cages (MOCs) with NO3- being the original counterion is studied by laser light scattering and isothermal titration calorimetry. Nitrates can trigger the self-assembly of macrocationic Pd12L24 into hollow spherical blackberry-type supramolecular structures via counterion-mediated attraction. Although chiral counteranions, such as N-(tert-butoxycarbonyl)-alanine (Boc-Ala), have weaker interaction with the MOCs compared to NO3-, they can induce different assembly behaviors between two enantiomeric MOCs by inhibiting the MOC-nitrate binding and weakening the interaction between them. The d-counterions are capable of selectively suppressing and slowing down the assembly of l-MOCs and also considerably decreasing their assembly size due to the much weaker MOC-nitrate interaction. The same scenario is observed for l-counterions when interacting with the d-MOCs. This study unveils the role of weakly associated chiral counterions on the central chiral macroions, especially their supramolecular structure formation, and provides additional evidence on the mechanism of the homochirality phenomenon.

Oligo(l-glutamic acids) in Calcium Phosphate Precipitation: Chain Length Effect.

The understanding of calcium phosphate precipitation is of major interest in different fields of science, including medicine, biomaterials, and physical chemistry. The presence of additive biomacromolecules has been known to influence various stages of the precipitation process from nucleation to crystal growth. In the current work, well-defined sequences of short, negatively charged peptides, oligo(l-glutamic acids), were utilized as a model, inspired by contiguous sequences of acidic amino acids in natural biomineralization proteins. The precipitate morphology and phases, the element time profile in solution and in the precipitates, as well as the kinetics during the precipitation process were analyzed to explain the effect of these short peptides on calcium phosphate precipitation. The results show that peptides can delay the phase transformation of an amorphous precursor phase to hydroxyapatite and that there is an optimal chain length for this effect at a given concentration of peptide. This study is the first part of a two-part series and is followed by a subsequent work to reveal the mechanism by which these short peptides influence the calcium phosphate precipitation.

Oligo(l-glutamic acids) in Calcium Phosphate Precipitation: Mechanism of Delayed Phase Transformation.

Proteins and their mimics that contain negatively charged sequences are important in natural and biomimetic mineralization. The mechanism by which these sequences affect calcium phosphate mineralization is not well understood. Here, peptides containing different numbers of repeat units of contiguous glutamic acid residues, oligo(l-glutamic acid)n (n = 3, 7, 8, 10), were investigated with regards to the mechanism in delaying the crystallization of amorphous calcium phosphate (ACP) while holding the amount of carboxylic acid groups in solution constant. Increasing peptide chain length increases the stability of ACP at a certain total amount of carboxylic acid groups in solution. This effect is shown to be due to stronger binding as well as binding to more calcium ions per peptide by the longer oligopeptides compared to the shorter ones. It is proposed that these associations delay the structural rearrangement of calcium ions and the dehydration of ACP, which are required for the crystallization of hydroxyapatite. The initial nucleation and the local structure of ACP, however, do not vary with chain length. This second part of a two-part series provides an improved mechanistic understanding of how organic additives, especially those with contiguous acidic amino acid sequences, modulate the kinetics of calcium phosphate precipitation and phase transformation.

Unraveling Chiral Selection in the Self-assembly of Chiral Fullerene Macroions: Effects of Small Chiral Components Including Counterions, Co-ions, or Neutral Molecules.

Lactic acid-functionalized chiral fullerene (C60) molecules are used as models to understand chiral selection in macroionic solutions involving chiral macroions, chiral counterions, and/or chiral co-ions. With the addition of Zn2+ cations, the C60 macroions exhibit slow self-assembly behavior into hollow, spherical, blackberry-type structures, as confirmed by laser light scattering (LLS), transmission electron microscopy (TEM), and atomic force microscopy (AFM) techniques. Chiral counterions with high charge density show no selection to the chirality of AC60 macroions (LAC60 and DAC60) during their self-assembly process, while obvious chiral discrimination between the assemblies of LAC60 and DAC60 is observed when chiral counterions with low charge density are present. Compared with chiral counterions, chiral co-ions show weaker effects on chiral selection with larger amounts needed to trigger the chiral discrimination between LAC60 and DAC60. However, they can induce a higher degree of discrimination when abundant chiral co-ions are present in solution. Furthermore, the self-assembly of chiral AC60 macroions is fully suppressed by adding significant amounts of neutral molecules with opposite chirality. Thermodynamic parameters from isothermal titration calorimetry (ITC) reveal that chiral selection is controlled by the ion pairing and the destruction of solvent shells between ions, and meanwhile originates from the delicate balance between electrostatic interaction and molecular chirality.

Semipermeable Mixed Phospholipid-Fatty Acid Membranes Exhibit K+/Na+ Selectivity in the Absence of Proteins.

Two important ions, K+ and Na+, are unequally distributed across the contemporary phospholipid-based cell membrane because modern cells evolved a series of sophisticated protein channels and pumps to maintain ion gradients. The earliest life-like entities or protocells did not possess either ion-tight membranes or ion pumps, which would result in the equilibration of the intra-protocellular K+/Na+ ratio with that in the external environment. Here, we show that the most primitive protocell membranes composed of fatty acids, that were initially leaky, would eventually become less ion permeable as their membranes evolved towards having increasing phospholipid contents. Furthermore, these mixed fatty acid-phospholipid membranes selectively retain K+ but allow the passage of Na+ out of the cell. The K+/Na+ selectivity of these mixed fatty acid-phospholipid semipermeable membranes suggests that protocells at intermediate stages of evolution could have acquired electrochemical K+/Na+ ion gradients in the absence of any macromolecular transport machinery or pumps, thus potentially facilitating rudimentary protometabolism.

Structure-Activity Relationships of Hydroxyapatite-Binding Peptides.

Elucidating the structure-activity relationships between biomolecules and hydroxyapatite (HAP) is essential to understand bone mineralization mechanisms, develop HAP-based implants, and design drug delivery vectors. Here, four peptides identified by phage display were selected as model HAP-binding peptides (HBPs) to examine the effects of primary amino acid sequence, phosphorylation of serine, presence of charged amino acid residues, and net charge of the peptide on (1) HAP-binding affinity, (2) secondary conformation, and (3) HAP nucleation and crystal growth. Binding affinities were determined by obtaining adsorption isotherms by mass depletion, and the conformations of the peptides in solution and bound states were observed by circular dichroism. Results showed that the magnitude of the net charge primarily controlled binding affinity, with little dependence on the other HBP features. The binding affinity and conformation results were in good agreement with our previous molecular dynamics simulation results, thus providing an excellent benchmark for the simulations. Transmission electron microscopy was used to explore the effect of these HBPs on calcium phosphate (Ca-PO4) nucleation and growth. Results indicated that HBPs may inhibit nucleation of Ca-PO4 nanoparticles and their phase transition to crystalline HAP, as well as control crystal growth rates in specific crystallographic directions, thus changing the classical needle-like morphology of inorganically grown HAP crystals to a biomimetic plate-like morphology.

Toward the Understanding of Small Protein-Mediated Collagen Intrafibrillar Mineralization.

The design of improved materials for orthopedic implants and bone tissue engineering scaffolds relies on materials mimicking the properties of bone. Calcium phosphate (Ca-PO4)-mineralized collagen fibrils arranged in a characteristic hierarchical structure constitute the building blocks of mineralized vertebrate tissues and control their biomechanical and biochemical properties. Large, flexible, acidic noncollagenous proteins (ANCPs) have been shown to influence collagen mineralization but little is known about mineralization mechanisms with the aid of small proteins. Osteocalcin (OCN) is a small, highly structured biomolecule known as a multifunctional hormone in its undercarboxylated form. Here, we examined the potential mechanism of collagen intrafibrillar mineralization in vitro mediated by OCN as a model protein. Rapid and random extrafibrillar mineralization of flakey Ca-PO4 particles was observed by transmission electron microscopy mainly on the outer surfaces of collagen fibrils of a preformed collagen scaffold in the absence of the protein. In contrast, the protein stabilized hydrated, spherical nanoclusters of Ca-PO4 on the outer surface of the fibrils, thereby retarding extrafibrillar mineralization. The nanoclusters then infiltrated the fibrils resulting in intrafibrillar mineralization with HAP crystals aligned with the fibrils. This mechanism is similar to that observed for unstructured ANCPs. Results of fibrillogenesis and immunogold labeling studies showed that OCN was associated primarily with the fibrils, consistent with ex vivo studies on mineralizing turkey tendon. The present findings contribute to expanding our understanding of collagen intrafibrillar mineralization and provide insight into design synthetic macromolecular matrices for orthopedic implants and bone regeneration.

Accuracy of Thermodynamic Databases for Hydroxyapatite Dissolution Constant.

Discrepancies have been noted in the solubility constant values of calcium phosphate minerals between various databases employed in widely used aqueous speciation calculation software programs. This can cause serious errors in the calculated speciation of waters when using these software programs. The aim of this communication was to bring to light these discrepancies. Experimental determinations of the hydroxyapatite (HAP) solubility product vary by as much as 10 orders of magnitude as a result of experimental challenges related to the presence of impurities in the HAP used, incongruent dissolution, and the contamination of solutions with dissolved carbon dioxide. It is suggested that the value used in the database Thermo.dat is consistent with experimental data devoid of common experimental problems, whereas other common databases use values that lead to a vastly overestimated solubility of HAP.

Bacterial Membrane Selective Antimicrobial Peptide-Mimetic Polyurethanes: Structure-Property Correlations and Mechanisms of Action.

The rise in prevalence of antibiotic resistant strains of bacteria is a very significant challenge for treating life-threatening infections worldwide. A source of novel therapeutics that has shown great promise is a class of biomolecules known as antimicrobial peptides. Previously, within our laboratories, we developed a new family of water-soluble antimicrobial polyurethanes that mimic antimicrobial peptides. Within this current investigation, studies were carried out to gain a greater understanding of the structure/property relationships of the polyurethanes. This was achieved by synthesizing a variety of pendant group functionalized polyurethanes and testing their effectiveness as an antimicrobial by carrying out minimum inhibitory concentration testing and determining their compatibility with blood cells. Additionally, insight into the mode of action of the polyurethanes was obtained through experiments using dye encapsulated phospholipids and assays of bacterial cells that indicated the ability of the polyurethanes to penetrate and disrupt membranes. Collectively, the results indicate that the addition of hydrophobic, uncharged polar, and anionic moieties do not have a strong influence on the antimicrobial activity; yet, the addition of hydrophobic groups enhances cytoplasmic membrane disruption, a larger proportion of cationic pendant groups promotes greater outer membrane disruption of Gram negative bacteria, and uncharged polar groups and anionic groups improve compatibility of the polyurethanes with mammalian cells.

Natural, incidental, and engineered nanomaterials and their impacts on the Earth system.

Nanomaterials are critical components in the Earth system's past, present, and future characteristics and behavior. They have been present since Earth's origin in great abundance. Life, from the earliest cells to modern humans, has evolved in intimate association with naturally occurring nanomaterials. This synergy began to shift considerably with human industrialization. Particularly since the Industrial Revolution some two-and-a-half centuries ago, incidental nanomaterials (produced unintentionally by human activity) have been continuously produced and distributed worldwide. In some areas, they now rival the amount of naturally occurring nanomaterials. In the past half-century, engineered nanomaterials have been produced in very small amounts relative to the other two types of nanomaterials, but still in large enough quantities to make them a consequential component of the planet. All nanomaterials, regardless of their origin, have distinct chemical and physical properties throughout their size range, clearly setting them apart from their macroscopic equivalents and necessitating careful study. Following major advances in experimental, computational, analytical, and field approaches, it is becoming possible to better assess and understand all types and origins of nanomaterials in the Earth system. It is also now possible to frame their immediate and long-term impact on environmental and human health at local, regional, and global scales.

Biological Response of and Blood Plasma Protein Adsorption on Silver-Doped Hydroxyapatite.

Hydroxyapatite (HAP) is an extensively used orthopedic biomaterial because of its high biocompatibility and osteoconductivity. Implant-related infection is a major cause of orthopedic device failure. Previous research showed that silver-doped hydroxyapatite nanoparticles (Ag-HAP NPs) have prominent antimicrobial activity, but their biocompatibility and plasma protein response remained unexplored. Here we investigated the effects of synthesis conditions on Ag-HAP NP antimicrobial (E. coli and S. epidermidis) activity, biocompatibility, and the adsorption of two blood plasma proteins, human serum albumin (HSA) and fibrinogen (Fib). It was found that synthesis pH affected the Ag content of Ag-HAP NPs and subsequent Ag+ release from the NPs in solution. This, in turn, affected antimicrobial efficiency and cytotoxicity to murine preosteoblast cells (MC3T3-E1). More HSA than Fib was adsorbed on a molar basis. The conformation of HSA changed drastically from predominantly α-helix and minor ß-sheet content in solution to greater ß-sheet than α-helix content when adsorbed. Correspondingly, the melting temperature Tm of HSA changed significantly from 76 °C in solution to ∼65-66 °C when adsorbed. Fib exhibited a modest decrease in α-helix content while the ß-sheet content increased modestly upon adsorption and its Tm remained unchanged at ∼60 °C. These differences in behavior of HSA and Fib are ascribed to the much smaller size of HSA, which allows a greater molecular packing density on the surface, which induces greater conformational changes. The protein adsorption behavior on Ag-HAP was similar to that on pure HAP. Thus, we show that Ag-HAP NPs have antimicrobial activity without deleterious effects on biocompatibility and blood plasma protein adsorption.

Effects of laser shock peening on the corrosion behavior and biocompatibility of a nickel-titanium alloy.

Nickel-titanium (NiTi) alloy is an attractive material for biomedical implant applications. In this study, the effects of laser shock peening (LSP) on the biocompatibility, corrosion resistance, ion release rate and hardness of NiTi were characterized. The cell culture study indicated that the LSP-treated NiTi samples had lower cytotoxicity and higher cell survival rate than the untreated samples. Specifically, the cell survival rate increased from 88 ± 1.3% to 93 ± 1.1% due to LSP treatment. LSP treatment was shown to significantly decrease the initial Ni ion release rate compared with that of the untreated samples. Electrochemical tests indicated that LSP improved the corrosion resistance of the NiTi alloy in simulated body fluid, with a decrease in the corrosion current density from 1.41 ± 0.20 µA/cm2 to 0.67 ± 0.24 µA/cm2 . Immersion tests showed that calcium deposition was significantly enhanced by LSP. In addition, the hardness of NiTi alloy increased from 226 ± 3 HV before LSP to 261 ± 3 HV after LSP. These results demonstrated that LSP is a promising surface modification method that can be used to improve the mechanical properties, corrosion resistance and biocompatibility of NiTi alloy for biomedical applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1854-1863, 2019.

Mineral-Lipid Interactions in the Origins of Life.

Protocells, the first life-like entities, likely contained three molecular components: a membrane, an information-carrying molecule, and catalytic molecules. Minerals have a wide range of properties that might have contributed to the synthesis and self-assembly of these molecular components. Minerals could have mediated the formation and concentration of prebiotic organic monomers, catalyzed their polymerization into biomolecules, and catalyzed protometabolic pathways, leading to protocell self-assembly. This review considers the following major aspects of protocell membrane-mineral interactions: (i) the effect of dissolved cations on the stability of mixed fatty acid and phospholipid vesicles; (ii) the rate of lipid self-assembly to vesicles; and (iii) the role of photocatalytic minerals in harvesting light energy to drive electron transfer reactions across membranes in the development of protometabolism.