Keijiro Ohshimo

Geometrical structures of iron oxide cluster cations have been analyzed by ion mobility mass spectrometry. The series of (FeO)n(+) and FenOn + 1(+) cluster cations were predominantly observed in a mass spectrum at high ion-injection energy into a drift cell. Arrival time distributions in the ion mobility spectrometry indicate that two structural isomers coexist for the (FeO)n(+) clusters at n ≥ 5. By comparison of experimental collision cross sections determined from the arrival times with theor

Structures and CO-adsorption reactivities of nickel oxide cluster cations were investigated by ion mobility mass spectrometry. The series of NinOn–2+, NinOn–1+ and NinOn+ cluster cations were predominantly observed in a mass spectrum at high ion-injection energy into an ion-drift cell. From the arrival time distributions of NinOn+ and NinOn–1+ in the ion mobility spectrometry, structural transition from two-dimensional (2D) ring to three-dimensional (3D) compact structures was found at n = 5. In

The conformation and electronic structure of dibenzo-24-crown-8 (DB24C8) complexes with K⁺ ion were examined by ion mobility-mass spectrometry (IM-MS), ultraviolet (UV) photodissociation (UVPD) spectroscopy in the gas phase, and fluorescence spectroscopy in solution. Three structural isomers of DB24C8 (SymDB24C8, Asym1DB24C8, and Asym2DB24C8) in which the relative positions of the two benzene rings were different from each other were investigated. The IM-MS results at 86 K revealed a

Size-dependent stabilities and intracluster reactions of potassium atom and acrylonitrile molecules (AN; CH2=CHCN) clusters were investigated. Previously reported magic numbers (intensity anomalies) of n=3k (k=1–4) using photoionization mass spectrum of K(AN)n, and size-specific elimination reactions (HCN elimination from clusters of n⩾3, and H2 elimination from n=3 and 6 clusters) were explained by a cyclohexane derivative formation in an intracluster trimeric cyclization (anionic oligomerizati

Long-distance proton transfer is a ubiquitous phenomenon in chemical and biological systems. Two mechanisms of proton transfer in solids are well established; the Grotthuss mechanism (proton-relay) and the vehicle mechanism. Previously, intramolecular proton transfer has been extensively studied in the gas phase to understand the proton transfer mechanism microscopically. However, only the Grotthuss mechanism was proposed so far for intramolecular proton transfer. Here we show the first evidence

Geometrical structures of titanium oxide cluster cations and anions have been investigated by ion mobility mass spectrometry and quantum chemical calculations based on density functional theory. Stable cluster compositions with respect to collision induced dissociation were also determined by changing ion injection energy to an ion drift cell for mobility measurements. The TinO2n-1 (+) cations and TinO2n (-) anions were predominantly observed at high injection energies, in addition to TinO2n (+)

We performed cryogenic ion mobility-mass spectrometry (IM-MS) to study conformations of dibenzo-crown-ether complexes with Na⁺ and K⁺ ions at 86 K in the gas phase. Four dibenzo-crown-ethers (dibenzo-18-crown-6, dibenzo-21-crown-7, dibenzo-24-crown-8, and dibenzo-30-crown-10) with different cavity ring sizes were investigated. For dibenzo-18-crown-6 complexes with Na⁺ and K⁺, only one type of conformer was assigned by comparing the experimental collisi

Structures of small sodium fluoride cluster cations, Na(n)F(n-1)(+), have been determined for n = 5-23 by ion mobility mass spectrometry. In the mass spectrum of Na(n)F(n-1)(+) cluster ions measured after collisions in the ion-drift cell, cuboid ions with near-regular hexahedron such as n = 14 (3 × 3 × 3), 23 (3 × 3 × 5), 38 (3 × 5 × 5), 63 (5 × 5 × 5), and 88 (5 × 5 × 7) were predominantly observed as magic numbers. By comparison of the collision cross sections obtained from the ion mobility me

The dynamic processes of conformational changes of supramolecules are important to understand the motion in synthetic supramolecules. Although a host-guest complex is the most basic supramolecule, a detailed mechanism of its conformational changes has rarely been studied. Here, we observed the large conformational change of a dibenzo-24-crown-8 complex with four guest ions (Ag⁺, Na⁺, K⁺, and NH₄⁺) at low temperature in the gas phase. The iso

Proton transfer is classified into two mechanisms: the Grotthuss (proton-relay) and vehicle mechanisms. It has been well studied on gas-phase proton transfer by a proton relay involving multiple molecules. However, a vehicle mechanism in which a single molecule transports a proton has rarely been reported. Here, we have obtained clear evidence that the proton transfers efficiently between the two protonation sites in protonated <i>p</i>-aminobenzoic acid (PABA·H⁺) by a single ammonia

We performed cryogenic ion mobility mass spectrometry and quantum chemical calculations of tetraalkylammonium (TAA) cations, (C_<i>n</i>H_2<i>n</i>+1)₄N⁺ (<i>n</i> = 4-8), to study geometrical structures of TAA cations. We measured collision cross sections (CCSs) of TAA cations with He buffer gas atoms at 86 K. In addition, CCSs were calculated for optimized structures of TAA ions to compare with experimental CCSs. For <i>n</i> = 4 and 5, calculated CCSs

Abstract Variable-temperature cryogenic ion mobility-mass spectrometry (VT-Cryo-IM-MS) was developed to examine the conformations of host-guest complexes. The VT-Cryo-IM-MS consists of an electrospray ionization source, a quadrupole ion trap, a cryogenic ion drift tube, and a time-of-flight mass spectrometer. The ion drift tube was cooled to 83 K with liquid nitrogen. Two sets of ion funnels are installed at the source and the drift tube to focus the ion beam. We used Li + -encapsulated fulleren

We investigated the photoionization mass spectrometry of clusters of alkali metal atoms (M = Li, Na and K) solvated with acrylonitrile (AN; CH2CHCN) molecules to obtain the information on size-dependent stability of the clusters. In the photoionization mass spectra of Mm(AN)n, strong ion signals were observed at M+(AN)3. The M+(AN)n (n = 6 and 9) ions were also clearly observed as magic numbers in the mass spectra of M = Na and K. By comparison with the mass spectrum of cluster ions formed by io