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Many genetic and environmental factors lead to interindividual variations in the metabolism and transport of drugs, profoundly affecting efficacy and toxicity. Precision dosing, that is, targeting drug dose to a well characterized subpopulation, is dependent on quantitative models of the profiles of drug-metabolizing enzymes (DMEs) and transporters within that subpopulation, informed by quantitative proteomics. We report the first use of ion mobility–mass spectrometry for this purpose, allowing rapid, robust, label-free quantification of human liver microsomal (HLM) proteins from distinct individuals. Approximately 1000 proteins were identified and quantified in four samples, including an average of 70 DMEs. Technical and biological variabilities were distinguishable, with technical variability accounting for about 10% of total variability. The biological variation between patients was clearly identified, with samples showing a range of expression profiles for cytochrome P450 and uridine 5′-diphosphoglucuronosyltransferase enzymes. Our results showed excellent agreement with previous data from targeted methods. The label-free method, however, allowed a fuller characterization of the in vitro system, showing, for the first time, that HLMs are significantly heterogeneous. Further, the traditional units of measurement of DMEs (pmol mg−1HLM protein) are shown to introduce error arising from variability in unrelated, highly abundant proteins. Simulations of this variability suggest that up to 1.7-fold variation in apparent CYP3A4 abundance is artifactual, as are background positive correlations of up to 0.2 (Spearman correlation coefficient) between the abundances of DMEs. We suggest that protein concentrations used in pharmacokinetic predictions and scaling to in vivo clinical situations (physiologically based pharmacokinetics and in vitro-in vivo extrapolation) should be referenced instead to tissue mass.

The intrinsic reactivity of a manganese(V)‐oxo porphyrin complex, a typically fleeting intermediate in catalytic oxidation reactions in solution, has been elucidated in a study focused on its gas‐phase ion‐chemistry. The naked high‐valent MnV‐oxo porphyrin intermediate 1([(tpfpp)MnVO]+; tpfpp=meso‐tetrakis(pentafluorophenyl)porphinato dianion), has been obtained by controlled treatment of [(tpfpp)MnIII]Cl (2‐Cl) with iodosylbenzene in methanol, delivered in the gas phase by electrospray ionization and assayed by FT‐ICR mass spectrometry. A direct kinetic study of the reaction with selected substrates, each containing a heteroatom X (X=S, N, P) including amines, sulfides, and phosphites, was thus performed. Ionic products arising from electron transfer (ET), hydride transfer (HT), oxygen‐atom transfer (OAT), and formal addition (Add) may be observed, with a predominance of two‐electron processes, whereas the product of hydrogen‐atom transfer (HAT), [(tpfpp)MnIVOH]+, is never detected. A thermochemical threshold for the formation of the product radical cation allows an evaluation of the electron‐transfer ability of a MnV‐oxo complex, yielding a lower limit of 7.85 eV for the ionization energy of gaseous [(tpfpp)MnIVO]. Linear free‐energy analyses of the reactions of para‐substituted N,N‐dimethylanilines and thioanisoles indicate that a considerable amount of positive charge is developed on the heteroatom in the oxidation transition state. Substrates endowed with different heteroatoms, but similar ionization energy display a comparable reaction efficiency, consistent with a mechanism initiated by ET. For the first time, the kinetic acidity of putative hydroxo intermediates playing a role in catalytic oxidations, [(tpfpp)FeIVOH]+and [(tpfpp)MnIVOH]+, has been investigated with selected reference bases, revealing a comparatively higher basicity for the ferryl, [(tpfpp)FeIVO], with respect to the manganyl, [(tpfpp)MnIVO], unit. Finally, the neat association reaction of 2has been studied with various ligands showing that harder ligands are more strongly bound.

Functional models of the Compound I intermediate of mono-oxygenase heme enzymes, namely [(TPFPP)•+FeIV=O]+and [(TPFPP)MnV=O]+(TPFPP = meso-tetrakis (pentafluorophenyl)porphyrinato dianion), are obtained as bare species by electrospray ionization from solutions of appropriate precursors and their reactivity is investigated in the gas-phase. By an alternative approach involving the reaction of a gaseous oxidant, the naked core of Compound I, [(PP–IX)•+FeIV=O]+(PP–IX = protoporphyrin IX dianion) has been produced as well. This achievement, unprecedented in studies run in solution, is now made possible working in the gas-phase. The long lifetime ensured by the dilute gas-phase allows both structural details and elementary steps of the catalytic activity of these high-valent oxo–metal intermediates to be revealed. Depending on the features of the oxo–metal complex, ionic products are formed with neutral substrates involving: (i) addition, (ii) oxygen atom transfer and (iii) formal hydride transfer. In contrast, ionic products indicative of a net initial hydrogen atom transfer event are never observed. The reaction pathways of these ultimate catalytic intermediates, void of any trans axial ligand, counterion, solvent or protein environment, are thus elucidated.

Anion–π interactions between a π‐acidic aromatic system and an anion are gaining increasing recognition in chemistry and biology. Herein, the binding features of an electron‐deficient aromatic system (1,3,5‐trinitrobenzene (TNB)) and selected anions (OH−, Br−, and I−) are examined in the gas phase by using the combined information derived from collision‐induced dissociation experiments at variable energy, infrared multiple‐photon dissociation spectroscopy, and quantum chemical calculations. We provide spectroscopic evidence for two different structural motifs of anion–arene complexes depending on the nature of the anion. The TNB–OR−complexes (R=H, or alkyl groups which were studied earlier) adopt an anionic σ‐complex structure whereby RO−attacks the aromatic ring with covalent bond formation, and develops a tetrahedral ring carbon bound to H and OR. The halide complexes rather conform to a structure in which the TNB moiety is hardly altered, and the halogen is placed on an unsubstituted carbon atom over the periphery of the ring at a C–X distance that is appreciably longer than a typical covalent bond length. The ensuing structural motif, previously characterized in the solid state and named weak σ interaction, is now confirmed by an IR spectroscopic assay in the gas phase, in which the sampled species are unperturbed by crystal packing or solvation effects.

The reactivity of naked oxygenating intermediates is proven!The ultimate high‐valent manganese(V)–porphyrin complex, devoid of any additional transligand, is produced as a naked, gaseous species. An insight into its inherent reactivity is obtained providing definitive evidence of pronounced epoxidation activity. In contrast, the trans‐dioxo–MnV–porphyrin is remarkably inert.

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