Bibliography - S.C.B. Myneni

1. Reina, R., A. C. Leri, and S.C.B. Myneni, 2004: Cl K-edge X-ray Spectroscopic Investigation of Enzymatic Formation of Organochlorines in Weathering Plant Material. Environmental Science and Technology, 38(3), doi:10.1021/es0347336 783-789
   [ Abstract ]

   The contribution of halocarbons from plant weathering to the total organohalogen budget of terrestrial systems is gaining recognition. To evaluate the formation of such halocarbons, speciation of chlorine in Sequoia sempervirens (redwood) needles was examined in the presence of an external chloroperoxidase (CPO) enzyme using Cl K-edge X-ray absorption spectroscopy. The Cl forms in fresh and naturally weathered needles and in model laboratory reactions were compared. To provide a straightforward analogue to the enzymatic chlorination in plants, chlorination reactions were conducted for phenol, a common moiety of plant macromolecules. Plant material chlorination was also examined in the presence of hypochlorite in an ancillary mechanistic investigation. The dominant form of Cl in fresh, unreacted plant material was found to be inorganic Cl-, which was partially converted to organochlorine in the presence of CPO. Chlorination is affected by the nature of reactant (CPO, H₂O₂) addition, reaction time, and temperature. The organochlorines produced in these laboratory investigations closely resemble those produced during the natural weathering of redwood needles. A striking consistency in chlorine speciation observed among the various sample types suggests that (i) CPO produced by terrestrial organisms could play a vital role in the generation of organochlorines associated with the degradation of plant material and (ii) initial targets of enzymatic chlorination might include lignin-like macromolecules rich in aromatic character and hydroxyl groups. These findings lend further credibility to a significant biogenic contribution to the global organohalogen burden by elucidating a probable route of enzymatic chlorination of natural organic matter in terrestrial systems.

2. Bruant, R., D. E. Giammar, S.C.B. Myneni, and Catherine A. Peters, October 2002: Effect of pressure, temperature, and aqueous carbon dioxide concentration on mineral weathering as applied to geologic storage of carbon dioxide. Proceedings of the 6th International Conference on Greenhouse Gas Control Technologies (GHGT-6), http://www.princeton.edu/~cmi/research/kyoto02/bruant%20et%20al.kyoto%2002.pdf,
   [ Abstract ]

   CO₂ mediated dissolution of silicate minerals and subsequent precipitation of carbonates in deep saline aquifers may allow permanent trapping of carbon dioxide. However, the time-scales and extents of the reactions are poorly understood for CO₂ receptor formation conditions. To address these shortcomings, experiments were conducted to investigate the effects of pressure, temperature, and aqueous solution composition on rates and mechanisms of silicate mineral dissolution and carbonate precipitation. A high pressure/high temperature flow-through reactor system was used to derive steady-state dissolution rates of crushed forsteritic olivine. The system allowed continuous monitoring of temperature, pressure, and pH, and periodic sampling of effluent fluids for dissolved ion concentration analysis. Preliminary measurements of dissolution rates indicate good agreement with previously published measurements at ambient conditions. Increasing the pressure from 1 to 100 bar under constant CO₂ conditions increased the dissolution rate by ~80%. The same reactions were studied in batch systems using an array of analytical techniques to investigate dissolution mechanisms and secondary precipitate formation. The extent of olivine dissolution in the batch reactors increased with temperature, PCO₂, and surface area. Precipitation of magnesium-rich carbonates on reacted olivine was observed at initial magnesite saturation indices greater than 1.6.

3. Myneni, S.C.B., 2002: Formation of stable chlorinated hydrocarbons in weathering plant material. Science, 295, doi:10.1126/science.1067153 1039-1041
   [ Abstract ]

   Though several chlorinated organic compounds produced by humans are carcinogenic and toxic, some are also produced by the biotic and abiotic processes in the environment. In situ x-ray spectroscopy data indicate that natural organic matter in soils, sediments, and natural waters contain stable, less volatile organic compounds with chlorinated phenolic and aliphatic groups as the principal Cl forms. These compounds are formed at rapid rates from the transformation of inorganic Cl during humification of plant material and, thus, play a critical role in the cycling of Cl and of several major and trace elements in the environment and may infuence human health.

4. Myneni, S.C.B., 2002: Soft X-ray spectroscopy and spectromicroscopy studies of organic molecules in the environment. Rev. Mineral. Geochem. Appl of Synchrotron Radiation in Low-Temp Geochemistry and Env Science, 49, doi:10.2138/gsrmg.49.1.485 485-579
   [ Abstract ]

   Organic molecules are found everywhere and play an important role in almost all biogeochemical processes occurring on the surface of the Earth (Aiken et al. 1985; Thurman 1985; Schwartzenbach et al. 1993; Senesi and Miano 1994). They are found in soluble and insoluble phases, coatings on mineral and colloidal particles, and in gas phase molecules in soils, sediments and aquatic systems. The activities of macro- and micro- fauna and flora release organic molecules of various sizes and composition. Photochemical reactions in the atmosphere also add certain small chain molecules to the organic carbon content in the environment. Significant compositional variations occur in natural organic molecules, which include small chain carboxylic acids, alcohols and amino acids; and polymeric, polyfunctional and polydisperse macromolecules such as humic and fulvic acids. The behavior of small chain molecules and their influence on different geochemical reactions is well understood. However, understanding of the chemistry of biopolymers and their role in different biogeochemical processes in the environment is poor, which may be attributed to the unavailability of instrumentation to examine the chemistry of natural organic molecules in their pristine state.

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