Synthesis and Detection of Oxygen-18 Labeled Phosphate

Phosphorus (P) has only one stable isotope and therefore tracking P dynamics in ecosystems and inferring sources of P loading to water bodies have been difficult. Researchers have recently employed the natural abundance of the ratio of 18O/16O of phosphate to elucidate P dynamics. In addition, phosphate highly enriched in oxygen-18 also has potential to be an effective tool for tracking specific sources of P in the environment, but has so far been used sparingly, possibly due to unavailability of oxygen-18 labeled phosphate (OLP) and uncertainty in synthesis and detection. One objective of this research was to develop a simple procedure to synthesize highly enriched OLP. Synthesized OLP is made up of a collection of species that contain between zero and four oxygen-18 atoms and, as a result, the second objective of this research was to develop a method to detect and quantify each OLP species. OLP was synthesized by reacting either PCl5 or POCl3 with water enriched with 97 atom % oxygen-18 in ambient atmosphere under a fume hood. Unlike previous reports, we observed no loss of oxygen-18 enrichment during synthesis. Electrospray ionization mass spectrometertry (ESI-MS) was used to detect and quantify each species present in OLP. OLP synthesized from POCl3 contained 1.2% P18O16O3, 18.2% P18O216O2, 67.7% P18O316O, and 12.9% P18O4, and OLP synthesized from PCl5 contained 0.7% P16O4, 9.3% P18O316O, and 90.0% P18O4. We found that OLP can be synthesized using a simple procedure in ambient atmosphere without the loss of oxygen-18 enrichment and ESI-MS is an effective tool to detect and quantify OLP that sheds light on the dynamics of synthesis in ways that standard detection methods cannot

Calculation of the expected amount of each oxygen labeled phosphate (OLP) species formed with completely random assortment of the oxygen atoms and comparison to the actual results from OLP synthesized with fresh POCl₃ in December 2008.

<p>†Number of different ways this combination of oxygen-16 and oxygen-18 atoms can be arranged around the phosphorus atom.</p><p>‡Probability was calculated by taking the amount of each oxygen atom (62.2 and 37.8% for oxygen-18 and oxygen-16, respectively) to the power of the number of that atom contained in the OLP species (e.g., the probability for <i>m/z</i> 99 is 0.378³ * 0.622¹ = 0.033594).</p><p>§Calculated by multiplying the number of combinations by the probability.</p

Electrospray ionization spectra of labeled and unlabeled phosphate species.

<p>Relative abundance of (a) unlabeled phosphate (<i>m/</i>z = 97) and (b) ¹⁸O-labeled phosphate species (<i>m/z</i> = 99, 101, 103, and 105) as determined by ESI-MS.</p

Alteration of Membrane Compositional Asymmetry by LiCoO₂ Nanosheets

Given the projected massive presence of redox-active nanomaterials in the next generation of consumer electronics and electric vehicle batteries, they are likely to eventually come in contact with cell membranes, with biological consequences that are currently not known. Here, we present nonlinear optical studies showing that lithium nickel manganese cobalt oxide nanosheets carrying a negative ζ-potential have no discernible consequences for lipid alignment and interleaflet composition in supported lipid bilayers formed from zwitterionic and negatively charged lipids. In contrast, lithiated and delithiated LiCoO₂ nanosheets having positive and neutral ζ-potentials, respectively, alter the compositional asymmetry of the two membrane leaflets, and bilayer asymmetry remains disturbed even after rinsing. The insight that some cobalt oxide nanoformulations induce alterations to the compositional asymmetry in idealized model membranes may represent an important step toward assessing the biological consequences of their predicted widespread use

Malic Acid Carbon Dots: From Super-resolution Live-Cell Imaging to Highly Efficient Separation

As-synthesized malic acid carbon dots are found to possess photoblinking properties that are outstanding and superior compared to those of conventional dyes. Considering their excellent biocompatibility, malic acid carbon dots are suitable for super-resolution fluorescence localization microscopy under a variety of conditions, as we demonstrate in fixed and live trout gill epithelial cells. In addition, during imaging experiments, the so-called “excitation wavelength-dependent” emission was not observed for individual as-made malic acid carbon dots, which motivated us to develop a time-saving and high-throughput separation technique to isolate malic acid carbon dots into fractions of different particle size distributions using C₁₈ reversed-phase silica gel column chromatography. This post-treatment allowed us to determine how particle size distribution influences the optical properties of malic acid carbon dot fractions, that is, optical band gap energies and photoluminescence behaviors

Malic Acid Carbon Dots: From Super-resolution Live-Cell Imaging to Highly Efficient Separation

As-synthesized malic acid carbon dots are found to possess photoblinking properties that are outstanding and superior compared to those of conventional dyes. Considering their excellent biocompatibility, malic acid carbon dots are suitable for super-resolution fluorescence localization microscopy under a variety of conditions, as we demonstrate in fixed and live trout gill epithelial cells. In addition, during imaging experiments, the so-called “excitation wavelength-dependent” emission was not observed for individual as-made malic acid carbon dots, which motivated us to develop a time-saving and high-throughput separation technique to isolate malic acid carbon dots into fractions of different particle size distributions using C₁₈ reversed-phase silica gel column chromatography. This post-treatment allowed us to determine how particle size distribution influences the optical properties of malic acid carbon dot fractions, that is, optical band gap energies and photoluminescence behaviors