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Inorganic pyrophosphatase (PPase) is an enzyme that catalyzes the hydrolysis of the phosphoanhydride bond in pyrophosphate (PPi) to release inorganic phosphate (Pi) and simultaneously exchange oxygen isotopes between Pi and water. Here, we quantified the exchange kinetics of oxygen isotopes between five Pi isotopologues (P18O4, P18O316O, P18O216O2, P18O16O3, and P16O4) and water using Raman spectroscopy and 31P nuclear magnetic resonance (NMR) during the PPase-catalyzed 18O–16O isotope exchange reaction in Pi-water and PPi-water systems. At a high PPi concentration (300 mM), hydrolysis of PPi by PPase was predominant, and only a small fraction of PPi (≪1%) took part in the reversible hydrolysis–condensation reaction (PPi ↔ Pi), leading to the oxygen isotope exchange between Pi and water. We demonstrated that Raman and NMR methods can be equally applied for monitoring the kinetics of the oxygen exchange between the Pi isotopologue and water. It was found that the isotope exchange determined by the spectroscopic methods was detectable as low as 0.2% 18O abundance, but the reliability below 1% was much lower. Given that high P concentrations (≥1 mM) are required in these methods, environmental application of these methods is limited to rare high P conditions in engineered and agricultural environments.
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Monitoring Silane Sol-Gel Kinetics with In-Situ Optical Turbidity Scanning and Dynamic Light Scattering
Organosilanes (e.g., R’-SiOR3) provide hydrophobic functionality in thin-film coatings, porous gels, and particles. Compared with tetraalkoxysilanes (SiOR4), organosilanes exhibit distinct reaction kinetics and assembly mechanisms arising from steric and electronic properties of the R’ group on the silicon atom. Here, the hydrolysis and condensation pathways of n-propyltrimethoxy silane (nPM) and a tri-fluorinated analog of nPM, 3,3,3-trifluoropropyl trimethoxy silane (3F), were investigated under aqueous conditions at pH 1.7, 2.0, 3.0, and 4.0. Prior to hydrolysis, 3F and nPM are insoluble in water and form a lens at the bottom (3F) or top (nPM) of the solutions. This phase separation was employed to follow reaction kinetics using a Turbiscan instrument to monitor hydrolysis through solubilization of the neat silane lens while simultaneously tracking condensation-induced turbidity throughout the bulk solution. Dynamic light scattering confirmed the silane condensation and particle aggregation processes reported by the turbidity scanning. Employing macroscopic phase separation of the starting reactants from the solvent further allows for control over the reaction kinetics, as the interfacial area can be readily controlled by reaction vessel geometry, namely by controlling the surface area to volume. In-situ turbidity scanning and dynamic light scattering revealed distinct reaction kinetics for nPM and 3F, attributable to the electron withdrawing and donating nature of the fluoro- and organo-side chains of 3F and nPM, respectively.
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- Award ID(s):
- 1705874
- PAR ID:
- 10191442
- Date Published:
- Journal Name:
- Molecules
- Volume:
- 24
- Issue:
- 16
- ISSN:
- 1420-3049
- Page Range / eLocation ID:
- 2931
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/molecules24162931
