Serine/threonine protein phosphatase-5 (PP5; PPP5C) is a member of the phosphoprotein phosphatase (PPP) gene family. The PPP catalytic domains feature a bimetal system (M₁/M₂), an associated bridge hydroxide (W¹(OH⁻)), an M₁-bound water/hydroxide (W²), and a highly conserved core sequence. The PPPs are presumed to share a common mechanism: The seryl/threonyl phosphoryl group of the phosphoprotein coordinates the metal ions, W¹(OH⁻) attacks the central phosphorous atom, rupturing the antipodal phosphoester bond and releasing the phosphate-free protein. Also, a histidine/aspartate tandem is responsible for protonating the exiting seryl/threonyl alkoxide. Here, we employed quantum-based computations on a large section of the PP5 catalytic site. A 33-residue, ONIOM(UB3LYP/6-31G(d):UPM7) model was built to perform computations using methylphosphate dianion as a stand-in substrate for phosphoserine/phosphothreonine. We present a concerted transition state (TS) in which W¹(OH⁻) attacks the phosphate center at the same time that the exiting seryl/threonyl alkoxide is protonated directly by the His³⁰⁴/Asp²⁷⁴ tandem, with W² assigned as a water molecule: W²(H₂O). Arg²⁷⁵, proximal to M₁, stabilizes the substrate and TS by binding both the ester oxygen (O^γ) and a phosphoryl oxygen (O¹) in a bidentate fashion; in the product state, Tyr⁴⁵¹ aids in decoupling Arg²⁷⁵ from O¹ of the product phosphate ion. The reaction is exothermic (ΔH = −2.0 kcal/mol), occurs in a single step, and has a low activation barrier (ΔH^‡ = +10.0 kcal/mol). Our work is an improvement over an earlier computational study that also found bond rupture and alkoxide protonation to be concerted, but concluded that Arg²⁷⁵ is deprotonated during the reactant and TS stages of the pathway. In that earlier study, the critical electron-withdrawal role that Arg²⁷⁵ plays during the hydroxide attack was not correctly accounted for.

Boronium (+3) cations, L4B3+, are rare and scarcely studied. But, thanks to their rigid tetrahedral shape and high cationic charge they may be promising tectons for creating hybrid organic-inorganic solids, especially since a single cation can serve as a nucleating center around which three anions can be assembled. However, the few boronium (+3) cations which have been reported are generally water-sensitive, a factor which is a potential impediment to the former endeavor (as is the case with many perovskite photovoltaics). Herein we report the synthesis and characterization (X-ray, NMR, DSC, TGA, CV) of multiple boronium (+3) salts, all of which are highly water stable across the 1-14 pH range. And, as a preliminary investigation of the template-tecton hypothesis, the BETI- [bis(pentafluoroethanesulfonyl)imide] salt of a representative cation was prepared. Significantly, the crystals of the latter were determined by X-ray crystallography to feature continuous, fluorine-rich veins.