Reactivity of a Carbon-Supported Single-Site Molybdenum Dioxo Catalyst for Biodiesel Synthesis

A single-site molybdenum dioxo catalyst, <b>(O</b>_<b>c</b><b>)</b>_<b>2</b><b>Mo­(</b><b>O)</b>_<b>2</b><b>@C</b>, was prepared via direct grafting of MoO₂Cl₂(dme) (dme = 1,2-dimethoxyethane) on high-surface-area activated carbon. The physicochemical and chemical properties of this catalyst were fully characterized by N₂ physisorption, ICP-AES/OES, PXRD, STEM, XPS, XAS, temperature-programmed reduction with H₂ (TPR-H₂), and temperature-programmed NH₃ desorption (TPD-NH₃). The single-site nature of the Mo species is corroborated by XPS and TPR-H₂ data, and it exhibits the lowest reported MoO_<i>x</i> <i>T</i>_max of reduction reported to date, suggesting a highly reactive Mo^VI center. <b>(O</b>_<b>c</b><b>)</b>_<b>2</b><b>Mo­(</b><b>O)</b>_<b>2</b><b>@C</b> catalyzes the transesterification of a variety of esters and triglycerides with ethanol, exhibiting high activity at moderate temperatures (60–90 °C) and with negligible deactivation. <b>(O</b>_<b>c</b><b>)</b>_<b>2</b><b>Mo­(</b><b>O)</b>_<b>2</b><b>@C</b> is resistant to water and can be recycled at least three times with no loss of activity. The transesterification reaction is determined experimentally to be first order in [ethanol] and first order in [Mo] with Δ<i>H</i>^⧧ = 10.5(8) kcal mol^–1 and Δ<i>S</i>^⧧ = −32(2) eu. The low energy of activation is consistent with the moderate conditions needed to achieve rapid turnover. This highly active carbon-supported single-site molybdenum dioxo species is thus an efficient, robust, and low-cost catalyst with significant potential for transesterification processes

Chemobiosis reveals tardigrade tun formation is dependent on reversible cysteine oxidation.

Tardigrades, commonly known as 'waterbears', are eight-legged microscopic invertebrates renowned for their ability to withstand extreme stressors, including high osmotic pressure, freezing temperatures, and complete desiccation. Limb retraction and substantial decreases to their internal water stores results in the tun state, greatly increasing their ability to survive. Emergence from the tun state and/or activity regain follows stress removal, where resumption of life cycle occurs as if stasis never occurred. However, the mechanism(s) through which tardigrades initiate tun formation is yet to be uncovered. Herein, we use chemobiosis to demonstrate that tardigrade tun formation is mediated by reactive oxygen species (ROS). We further reveal that tuns are dependent on reversible cysteine oxidation, and that this reversible cysteine oxidation is facilitated by the release of intracellular reactive oxygen species (ROS). We provide the first empirical evidence of chemobiosis and map the initiation and survival of tardigrades via osmobiosis, chemobiosis, and cryobiosis. In vivo electron paramagnetic spectrometry suggests an intracellular release of reactive oxygen species following stress induction; when this release is quenched through the application of exogenous antioxidants, the tardigrades can no longer survive osmotic stress. Together, this work suggests a conserved dependence of reversible cysteine oxidation across distinct tardigrade cryptobioses