The oligomerization of amino acids is an essential process in the chemical evolution of proteins, which are precursors to life on Earth. Although some researchers have observed peptide formation on clay mineral surfaces, the mechanism of peptide bond formation on the clay mineral surface has not been clarified. In this study, the thermal behavior of glycine (Gly) adsorbed on montmorillonite was observed during heating experiments conducted at 150 °C for 336 h under dry, wet, and dry-wet conditions to clarify the mechanism. Approximately 13.9 % of the Gly monomers became peptides on montmorillonite under dry conditions, with diketopiperazine (cyclic dimer) being the main product. On the other hand, peptides were not synthesized in the absence of montmorillonite. Results of IR analysis showed that the Gly monomer was mainly adsorbed via hydrogen bonding between the positively charged amino groups and negatively charged surface sites (i.e., Lewis base sites) on the montmorillonite surface, indicating that the Lewis base site acts as a catalyst for peptide formation. In contrast, peptides were not detected on montmorillonite heated under wet conditions, since excess water shifted the equilibrium towards hydrolysis of the peptides. The presence of water is likely to control thermodynamic peptide production, and clay minerals, especially those with electrophilic defect sites, seem to act as a kinetic catalyst for the peptide formation reaction.
The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) is a multidisciplinary investigation of fault mechanics and seismogenesis along subduction megathrusts and includes reflection and refraction seismic imaging, direct sampling by drilling, in situ measurements, and long-term monitoring in conjunction with laboratory and numerical modeling studies. The fundamental objectives of NanTroSEIZE are to characterize the nature of fault slip and strain accumulation, fault and wall rock composition, fault architecture, and state variables throughout an active plate boundary system. As part of the NanTroSEIZE program, operations during Integrated Ocean Drilling Program (IODP) Expedition 348 were planned to extend and case riser Hole C0002F, begun during IODP Expedition 326 in 2010 and continued during Expedition 338 in 2012, from 860 to 3600 meters below the seafloor (mbsf).Riser operations during Expedition 348 were carried out and deepened the hole to 3058 mbsf, a new maximum depth record in scientific ocean drilling. Operations included installation and cementing of 13 3 ⁄8 inch casing to 2008.9 mbsf and an 11¾ inch liner to 2922.5 mbsf, stabilizing the borehole for future deepening. Reaching this depth required two sidetracking operations from the original Hole C0002F, resulting in the designation of Holes C0002N and C0002P for the successively deeper sidetracks. During drilling, a suite of logging-while-drilling (LWD) and measurement-while-drilling (MWD), mud-gas, and cuttings data were collected over the interval from 2162.5 to 3058.5 mbsf in Hole C0002P, and a partial suite was collected in Hole C0002N. The interval from 2163 to 2218 mbsf was cored with the rotary core barrel (RCB). Planned future riser drilling operations will deepen the hole to penetrate the plate boundary fault at ~4600-5200 mbsf.Additionally, a test hole for a prototype slimhole small-diameter RCB (SD-RCB) coring system, Hole C0002M, was drilled in riserless mode near Hole C0002F. The hole was advanced to 475 mbsf, where four cores were collected to 512.5 mbsf.Overall, Expedition 348 sampled and logged a deep interval in Holes C0002N and C0002P within the inner accretionary wedge, from 856 to 3058.5 mbsf, including a never-before sampled zone in the lowermost ~1 km of drilling. Cores were collected over a 55.5 m interval from 2163 to 2218.5 mbsf. The sampled sedimentary rocks are composed of hemipelagic sediment and fine turbi-
Seafloor massive sulfide deposits have attracted much interest as mineral resources. Therefore, the potential environmental impacts of full-scale mining should be considered. In this study, we focused on metal and metalloid contamination that could be triggered by accidental leakage and dispersion of hydrothermal ore particulates from mining vessels into surface seawater. We determined the leaching potential of metals and metalloids from four hydrothermal ores collected from the Okinawa Trough into aerobic seawater and then evaluated the toxic effects of ore leachates on a phytoplankton species, Skeletonema marinoi–dohrnii complex, which is present ubiquitously in the ocean. Large amounts of metals and metalloids were released from the ground hydrothermal ores into seawater within 5 min under aerobic conditions. The main components of leachates were Zn + Pb, As + Sb, and Zn + Cu, which were obtained from the Fe–Zn–Pb-rich and Zn–Pb-rich zero-age, Ba-rich, and Fe-rich ores, respectively. The leachates had different chemical compositions from those of the ore. The rapid release and difference in chemical compositions between the leachates and the ores indicated that substances were not directly dissolved from the sulfide-binding mineral phase but from labile phases mainly on the adsorption–desorption interface of the ores under these conditions. All ore leachates inhibited the growth of S. marinoi–dohrnii complex but with different magnitudes of toxic effects. These results indicate that the fine particulate matter of hydrothermal ores is a potential source of toxic contamination that may damage primary production in the ocean. Therefore, we insist on the necessity for the prior evaluation of toxic element leachability from mineral ores into seawater to minimize mining impacts on the surface environment.
We observed the initial release rate of metals from four fresh (i.e., without long time exposure to the atmosphere) hydrothermal sulfide cores into artificial seawater. The sulfide samples were collected by seafloor drilling from the Okinawa Trough by D/V Chikyu, powdered under inert gas, and immediately subjected to onboard metal-leaching experiments at different temperatures (5 °C and 20 °C), and under different redox conditions (oxic and anoxic), for 1–30 h. Zinc and Pb were preferentially released from sulfide samples containing various metals (i.e., Mn, Fe, Cu, Zn, Cd, and Pb) into seawater. Under oxic experimental conditions, Zn and Pb dissolution rates from two sulfide samples composed mainly of iron disulfide minerals (pyrite and marcasite) were higher than those from two other sulfide samples with abundant sphalerite, galena, and/or silicate minerals. Scanning electron microscopy confirmed that the high metal-releasing sample contained several galvanic couples of iron disulfide with other sulfide minerals, whereas the low metal-releasing sample contained fewer galvanic couples or were coated by a silicate mineral. The experiments overall confirmed that the galvanic effects with iron disulfide minerals greatly induce the initial release of Zn and Pb from hydrothermal sulfides into seawater, especially under warm oxic conditions.Electronic supplementary materialThe online version of this article (10.1186/s12932-018-0060-9) contains supplementary material, which is available to authorized users.
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