Quantitative immunocytochemical assay for infectious avian retroviruses.

A simple and accurate immunocytochemical focus assay is described, whereby both transforming and non-transforming avian retroviruses can be enumerated. After virus infection of chick embryo fibroblasts, an agar overlay is applied; foci of infected cells (expression foci) are detected immunocytochemically after 5 to 7 days. The primary antibodies are monoclonal sera directed against either viral p19gag or pp60v-src. Detection of expression foci after transfection of cells with cloned viral DNA is also demonstrated

Ir(III)-PC(sp³)P Bifunctional Catalysts for Production of H₂ by Dehydrogenation of Formic Acid: Experimental and Theoretical Study

Reversible storage of hydrogen in the form of stable and relatively harmless chemical substances such as formic acid (FA) is one of the cornerstones of a fossil-fuel-free economy. Recently, Ru­(III)-PC­(sp³)P (where PC­(sp³)P = modular dibenzobarrelene-based pincer ligand possessing a pendant functional group) complex <b>1</b> has been reported as a mild and <i>E</i>-selective catalyst in semihydrogenation of alkynes with stoichiometric neat formic acid. Discovery of the additive-free protocol for dehydrogenation of FA launched further studies aiming at the rational design of highly efficient catalysts for this reaction operating under neutral conditions. We now report the results of our investigation on a series of bifunctionl PC­(sp³)P complexes equipped with different outer-sphere auxiliaries, that allowed us to identify an amine-functionalized Ir­(III)-PC­(sp³)P complex <b>3</b>, as a clean and efficient catalyst for the FA dehydrogenation. The catalyst is suitable for fuel-cell applications demonstrating a TON up to 5 × 10⁵ and TOF up to 2 × 10⁴ h^–1 (3.8 × 10⁵ and 1.2 × 10⁴ h^–1 with no additives). In addition to the practical value of the catalyst, experimental and computational mechanistic studies provide rationale for the design of improved next-generation catalysts

Conformational Flexibility of Dibenzobarrelene-Based PC(sp³)P Pincer Iridium Hydride Complexes: The Role of Hemilabile Functional Groups and External Coordinating Solvents

Bifunctional dibenzobarrelene-based PC­(sp³)P pincer iridium complex <b>1</b> is known as an efficient catalyst in acceptorless dehydrogenation of alcohols and hydrogenation/hydroformylation of alkenes. In order to shed light on the mechanism of the hydrogen formation/activation, we performed variable-temperature IR and NMR (¹H, ³¹P) analysis of intra- and intermolecular interactions involving a hydride ligand and hydroxymethyl cooperating group in <b>1</b> and its analogues. The results of the spectroscopic measurements in different media (dichloromethane, toluene, DMSO, and mixed solvents) were compared with the quantum chemical (DFT/M06 and B3PW91) calculations. The obtained data imply flexibility of the dibenzobarrelene-based scaffold, unprecedented for conventional pincer ligands. Both the CH₂OH-substituted complex <b>1</b> and its COOEt analogue <b>3</b> prefer facial configuration of the PCP ligand with a P–Ir–P angle of ca. 100°. Such geometries are stabilized by Ir···O interaction with the dangling functional group and differ by the mutual arrangement of the H and Cl ligands. The complexes show dynamic equilibrium between the two most stable <i>fac</i>-isomers, which can be transformed into the meridional ones in the presence of coordinating additives (CH₃CN, DMSO, or CO, but not Et₃N). The process is reversible for CH₃CN but irreversible for DMSO and CO, in agreement with the Lewis basicity of these molecules