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An ion mobility mass spectrometry (IM‐MS) investigation using a Synapt G2 mass spectrometer was conducted to separate anions generated from the three regioisomers of sulfobenzoic acid. The results revealed that the differences in arrival time distributions (ATDs) were inadequate to differentiate the isomers unambiguously. However, the ATD profiles of the product ions, generated by fragmenting the respective mass‐selected m/z 201 precursor ions in the Trap region of the three‐compartment traveling‐wave ion guide of the Synapt G2 mass spectrometer, were distinctly different, enabling definitive differentiation of the isomers. An arrival‐time peak for an ion of m/z 157 resulting from the loss of CO2 from the respective precursors was common to all three mobilograms. However, only the profile recorded from the para‐isomer exhibited a unique arrival‐time peak for an ion of m/z 137, originating from an SO2 loss. Such a peak corresponding to an SO2 loss was absent in the ATD profiles of the ortho‐ and meta‐isomers. Additionally, the mobilogram of the meta‐isomer displayed a unique peak at 3.42 ms. Based on its product ion spectrum, this peak was attributed to the bisulfite anion (m/z 81; HSO3ˉ). Previously, this meta‐isomer specific m/z 81 ion had been proposed to originate from a two‐step process involving the intermediacy of an m/z 157 ion formed by CO2 loss. However, our detailed tandem mass spectrometric experiments suggest that the m/z 81 is not a secondary product but rather an ion that originated from a direct elimination of a benzyne derivative from the m/z 201 precursor ion. [ABSTRACT FROM AUTHOR]

Michler's ketone (MK) is a dimethylamino ketone that undergoes facile protonation under electrospray-ionization conditions to produce an ion of m/z 269. Initial LC-MS results showed that the collision-induced dissociation (CID) spectra of the m/z 269 ion depend heavily on the composition of the chromatographic mobile phase. Subsequent ion-mobility separation of the mass-selected m/z 269 ion revealed that protonated MK exists as two tautomeric forms. Moreover, the relative population of the two protomeric forms in the ion ensemble depends on the nature of the ambient molecules present in the atmospheric pressure ion source. For example, the ion-mobility arrival-time profile acquired from the mass-selected m/z 269 ion generated from an acetonitrile solution showed two peaks of near equal intensity. The peak with the shorter arrival time represented the O-protomer and that with the longer arrival time represented the N-protomer. However, when methanol or ammonia vapors were introduced to the ambient-pressure ion source, the intensity of the N-protomer peak decreased rapidly and that of the O-protomer signal soared until it became the dominant peak. When the introduction of methanol (or ammonia) vapors was stopped, the mobilogram signals gradually reverted back to their initial intensities. To rationalize this observation, we propose that the N-protomer of MK in the presence of methanol vapor undergoes transformation to the O-protomer by a Grotthuss-type mechanism via a methanol-based solvent bridge. [ABSTRACT FROM AUTHOR]

Catalytic efficacy of the nickel(II)-diphosphine systems in the dehydrogenation of 1-phenylethanol to acetophenone under acceptorless conditions was investigated. Steric and electronic factors of the phosphine ligands were found to play an important role in the catalysis, while the nature of the base used and the reaction conditions, viz. time, temperature, and stoichiometry, have also shown major influence. Based on the preliminary analysis, a homogeneous pathway, perhaps involving nickel hydride species, was proposed. Due to the gradual disintegration of the catalytic species, deterioration of catalytic activity was observed resulting into low to moderate conversions. Among the series of catalysts examined, the highest conversion of 52% was exhibited by the catalyst C4, dichloro(1,2-bis(diphenylphosphino)ethane) nickel(II) (5 mol%), when loaded with 50 mol% of sodium ethoxide in toluene at 120 °C. [ABSTRACT FROM AUTHOR]

Dental fluorosis discoloration and maxillary anterior tooth spacing are problems that require aesthetic management. Various factors will influence the selection of restorative techniques and materials used for the treatment. The digital smile designing (DSD) is a tool that helps in diagnostic vision, improve communication, and enhance predictability throughout the treatment in esthetic dentistry. In this case report, a simplified version of DSD using Microsoft PowerPoint was described. Here, we also discuss the management of dental fluorosis and a maxillary anterior tooth spacing of a young female by microabrasion, frenectomy, and direct composite restoration. [ABSTRACT FROM AUTHOR]