Disentangling Driving Force Effects, Polar Effects, /H Imbalance, and Other Influences on H-Atom Transfer Reactions.

Hydrogen atom transfer (HAT) reactions and their kinetic barriers Δ are important in organic and inorganic chemistry. This study examines factors that influence Δ, reporting the kinetics and thermodynamics of HAT from various ruthenium bis(acetylacetonate) pyridine-imidazole complexes to nitroxyl radicals. Across these 36 reactions, the Δ and Δ can be independently varied, with different sets of Ru complexes primarily tuning either their ps or their °s.

Polar Effects in Hydrogen Atom Transfer Reactions from a Proton-Coupled Electron Transfer (PCET) Perspective: Abstractions from Toluenes.

Rate constants for hydrogen atom transfer (HAT) reactions of substituted toluenes with -butyl, -butoxy, and -butylperoxyl radicals are reanalyzed here using the free energies of related proton transfer (PT) and electron transfer (ET) reactions, calculated from an extensive set of compiled or estimated p and ° values. The Eyring activation energies Δ do not correlate with the relatively constant Δ, but do correlate close-to-linearly with Δ and Δ. The slopes of correlations are similar for the three radicals except that the Bu barriers shift in the opposite direction from the oxyl radical barriers─a clear example of the qualitative "polar effect" in HAT reactions.

Independent Tuning of the p or the in a Family of Ruthenium Pyridine-Imidazole Complexes.

Two series of Ru(acac)(py-imH) complexes have been prepared, one with changes to the acac ligands and the other with substitutions to the imidazole. The proton-coupled electron transfer (PCET) thermochemistry of the complexes has been studied in acetonitrile, revealing that the acac substitutions almost exclusively affect the redox potentials of the complex (|Δ| ≫ |Δp|·0.059 V) while the changes to the imidazole primarily affect its acidity (|Δp|·0.

Free Energies of Proton-Coupled Electron Transfer Reagents and Their Applications.

We present an update and revision to our 2010 review on the topic of proton-coupled electron transfer (PCET) reagent thermochemistry. Over the past decade, the data and thermochemical formalisms presented in that review have been of value to multiple fields. Concurrently, there have been advances in the thermochemical cycles and experimental methods used to measure these values.

Bimodal Evans-Polanyi Relationships in Hydrogen Atom Transfer from C(sp)-H Bonds to the Cumyloxyl Radical. A Combined Time-Resolved Kinetic and Computational Study.

The applicability of the Evans-Polanyi (EP) relationship to HAT reactions from C(sp)-H bonds to the cumyloxyl radical (CumO) has been investigated. A consistent set of rate constants, , for HAT from the C-H bonds of 56 substrates to CumO, spanning a range of more than 4 orders of magnitude, has been measured under identical experimental conditions. A corresponding set of consistent gas-phase C-H bond dissociation enthalpies (BDEs) spanning 27 kcal mol has been calculated using the (RO)CBS-QB3 method.

Acute Lymph Node Slices Are a Functional Model System to Study Immunity Ex Vivo.

The lymph node is a highly organized and dynamic structure that is critical for facilitating the intercellular interactions that constitute adaptive immunity. Most ex vivo studies of the lymph node begin by reducing it to a cell suspension, thus losing the spatial organization, or fixing it, thus losing the ability to make repeated measurements. Live murine lymph node tissue slices offer the potential to retain spatial complexity and dynamic accessibility, but their viability, level of immune activation, and retention of antigen-specific functions have not been validated.

Immunofluorescence staining of live lymph node tissue slices.

Explants of lymphoid tissue provide a rare opportunity to assess the organization of the immune system in a living, dynamic environment. Traditionally, ex vivo immunostaining is conducted in fixed tissue sections, while live tissues are analyzed using genetically engineered fluorescent reporters or adoptively transferred, pre-labelled cell populations. Here, we validated a protocol for immunostaining and imaging in live, thick slices of lymph node tissue, thus providing a spatial "map" of the lymph node while maintaining the viability and functionality of the slices.