Fast and pervasive diagenetic isotope exchange in foraminifera tests is species-dependent

Oxygen isotope compositions of fossil foraminifera tests are commonly used proxies for ocean paleotemperatures, with reconstructions spanning the last 112 million years. However, the isotopic composition of these calcitic tests can be substantially altered during diagenesis without discernible textural changes. Here, we investigate fluid-mediated isotopic exchange in pristine tests of three modern benthic foraminifera species (Ammonia sp., Haynesina germanica, and Amphistegina lessonii) following immersion into an 18O-enriched artificial seawater at 90 °C for hours to days. Reacted tests remain texturally pristine but their bulk oxygen isotope compositions reveal rapid and species-dependent isotopic exchange with the water. NanoSIMS imaging reveals the 3-dimensional intra-test distributions of 18O-enrichment that correlates with test ultra-structure and associated organic matter. Image analysis is used to quantify species level differences in test ultrastructure, which explains the observed species-dependent rates of isotopic exchange. Consequently, even tests considered texturally pristine for paleo-climatic reconstruction purposes may have experienced substantial isotopic exchange; critical paleo-temperature record re-examination is warranted.

The Kinetic Model of Diffusion and Reactions in Powder Catalysts during Temperature Programmed Oxygen Isotopic Exchange Process

The mathematical model of diffusion in powder oxide catalysts during the process of temperature programmed oxygen isotopic exchange is proposed. The diffusion is considered together with the homogeneous and heterogeneous oxygen isotopic exchange processes. The matrix forms of exchange rate equations of simple and complex heteroexchange, and homoexchange reactions which obtain symmetrical forms are analyzed. The quantitative values of model parameters are found from the fitting of experimental data taken from literature of temperature programmed oxygen isotopic exchange process in catalysts ZrO2 and CeO2. The fittings show a good matching of model results with experimental data. The shapes of kinetic curves registered during temperature programmed oxygen isotopic exchange process are analyzed and the influence of various process parameters such as activation energies of simple and complex heteroexchange, oxygen surface concentration of catalyst, ratio of catalysts surface and volume of reactor, diffusion activation energy is considered. The depth profiles of diffusing oxygen species in oxide catalysts powder are calculated.

Characterization of polystyrene and polyacrylic based polymeric materials exposed to oxidative degradation

The characterization of oxidative degraded polystyrene-based resin (R1) and polyacrylic based resin (R2) resins in H2O2 and HClO4 degradation medium were made based on the kinetics and thermodynamic data obtained for the ion-isotopic exchange reactions using such resins. For the reactions performed by using resins degraded in H2O2 medium, the reaction rate (k) values obtained for the fresh R1 (0.315 min–1) and R2 (0.187 min–1) resins decreases to 0.300 and 0.155 min–1 respectively for the resins degraded in 20% H2O2 medium, which further decreases to 0.289 and 0.142 min–1 respectively for the resins degraded in 30% H2O2 medium. A similar trend in the results were observed for the reactions performed by using the above resins degraded in HClO4 medium. The higher values of k (min–1) and low values of various thermodynamic parameters for the ion-isotopic exchange reactions performed by using fresh and degraded polystyrene-based resin R1 resins suggests superior degradation stability as compared to polyacrylic based R2 resin.

Recent Advances in the Clinical Translation of Silicon Fluoride Acceptor (SiFA) 18F-Radiopharmaceuticals

The incorporation of silicon fluoride acceptor (SiFA) moieties into a variety of molecules, such as peptides, proteins and biologically relevant small molecules, has improved the generation of 18F-radiopharmaceuticals for medical imaging. The efficient isotopic exchange radiofluorination process, in combination with the enhanced [18F]SiFA in vivo stability, make it a suitable strategy for fluorine-18 incorporation. This review will highlight the clinical applicability of [18F]SiFA-labeled compounds and discuss the significant radiotracers currently in clinical use.