Dehydration‐fragmentation mechanism of cathinones and their metabolites in ESI‐CID

Various cathinone‐derived designer drugs (CATs) have recently appeared on the drug market. This study examined the mechanism for the generation of dehydrated ions for CATs during electrospray ionization collision‐induced dissociation (ESI‐CID). The generation mechanism of dehydrated ions is dependent on the amine classification in the cathinone skeleton, which is used in the identification of CATs. The two hydrogen atoms eliminated during the dehydration of cathinone (primary amine) and methcathinone (secondary amine) were determined, and the reaction mechanism was elucidated through the deuterium labeling experiments. The hydrogen atom bonded to the amine nitrogen was eliminated with the proton added during ESI, in both of the tested compounds. This provided evidence that CATs with tertiary amine structures (such as dimethylcathinone and α‐pyrrolidinophenones [α‐PPs]) do not undergo dehydration. However, it was shown that the two major tertiary amine metabolites (1‐OH and 2″‐oxo) of CATs generate dehydrated ions in ESI‐CID. The dehydration mechanisms of the metabolites of α‐pyrrolidinobutiophenone (α‐PBP) belongs to α‐PPs were also investigated. Stable‐isotope labeling showed the dehydration of the 1‐OH metabolite following a simple mechanism where the hydroxy group was eliminated together with the proton added during ESI. In contrast, the dehydration mechanism of the 2″‐oxo metabolite involved hydrogen atoms in three or more locations along with the carbonyl group oxygen, indicating that dehydration occurred via multiple mechanisms likely including the rearrangement reaction of hydrogen atoms. These findings presented herein indicate that the dehydrated ions in ESI‐CID can be used for the structural identification of CATs.     

Ionization and solvation of HCl adsorbed on the D2O-ice surface

The interaction of HCl with the D(2)O-ice surface has been investigated in the temperature range 15-200 K by utilizing time-of-flight secondary ion mass spectroscopy, temperature-programmed desorption, and x-ray photoelectron spectroscopy. The intensities of sputtered H(+)(D(2)O) and Cl(-) ions (the H(+) ions) are increased (decreased) markedly above 40 K due to the hydrogen bond formation between the HCl and D(2)O molecules. The HCl molecules which form ionic hydrates undergo H/D exchange at 110-140 K and a considerable fraction of them dissolves into the bulk above 140 K. The neutral hydrates of HCl should coexist as evidenced by the desorption of HCl above 170 K. They are incorporated completely in the D(2)O layer up to 140 K. The HCl molecules embedded in the thick D(2)O layer dissolve into the bulk, and the ionic hydrate tends to segregate to the surface above 150 K.     

Surface diffusion and entrapment of simple molecules on porous silica

Interactions of simple molecules with the surface of porous silica have been investigated using time-of-flight secondary ion mass spectrometry and temperature programmed desorption. A monolayer of water diffuses into pores at temperatures higher than 110 K. Multilayers of water are also incorporated in pores via sequential surface diffusion. In contrast, a methanol monolayer tends to stay on the surface up to 150 K, and carbon dioxide diffuses into pores rather gradually. Results can be explained as the contribution of hydrogen bonds between the adsorbate–substrate and adsorbate–adsorbate interactions. The predominance of the former (latter) might be responsible for single-molecule migration of methanol and carbon-dioxide (collective diffusion of water molecules) on the surface. These molecules are entrapped at higher coordination sites in pores, as revealed from thermal desorption peaks appearing at higher temperatures than those from non-porous silica. However, no significant difference is observed in desorption kinetics of CF₂Cl₂, Kr, CH₄, and N₂ molecules between the porous and non-porous silica substrates.     

Surface and interface effects on structural transformation of vapor-deposited ethylbenzene films

We have investigated how the structures of vapor-deposited glassy films change with increasing temperature by using time-of-flight secondary ion mass spectrometry and ion scattering spectroscopy. It is found that intermixing of the topmost layer of an ethylbenzene film occur at temperature (~ 80 K) considerably lower than the glass transition temperature (T_g = 118 K) when the film is deposited at 20 K. This phenomenon can be interpreted as the occurrence of a two-dimensional liquid that diffuses into pores of the film, which is evidenced from comparison with surface diffusivity measurements using a porous silicon layer. For nonporous films deposited at higher temperatures, the molecules intermix gradually prior to the abrupt film morphology change at T_g. This phenomenon can be interpreted as decoupling between translational diffusivity and viscosity in the bulk. The film thickness has no significant effects on the evolution of supercooled liquid at T_g except for the monolayer film, whereas crystallization is quenched for the films thinner than 8 monolayers. The roles of the 2D liquid on the surface and an immobilized layer formed at the interface are discussed in finite-size effects on the glass-liquid transition and crystallization.     

Wavelength dependence of polyyne preparation by liquid-phase laser ablation using pellet targets

The amount of polyynes produced by Nd:YAG laser (355, 532, and 1064 nm) ablation of fullerene and graphite pellet targets was the largest for 1064 nm ablation, contrary to the powder target in the previous report. This result is believed to come from the difference in the main polyyne-production area in liquids in the optical cell, depending on the pellet and powder targets.     

Studies on heat transfer and flow characteristics in subcooled flow boiling—Part 1. Boiling characteristics

Measurement of wall temperature profile and photographic observation are performed for R-113 subcooled boiling flow in a channel with heat fluxes up to the CHF. The incipient boiling superheats measured are little affected by mass velocity and liquid subcooling. Hysteresis in boiling observed by increasing and decreasing heat flux seems to be ascribed to variation in size of active nucleation cavities on the wall. Increasing heat flux up to the CHF, the bubble density on the heated surface increases and remarkably large coalescent bubbles appear periodically near the heating section outlet.     

Glass-liquid transition of carbon dioxide and its effect on water segregation

The interactions between CO(2) and D(2)O molecules have been investigated by using time-of-flight secondary ion mass spectrometry in the temperature rage 13-120 K. The monolayer of CO(2) tends to wet or intermix with the D(2)O film below 40 K and dewets the surface above 60 K. The water nanoclusters deposited on the CO(2) multilayers also start to segregate at 50-60 K and are finally incorporated in the bulk at 85-90 K, where the morphology of the film changes abruptly together with the desorption rate of the CO(2) molecules. The break at 85 K should be caused by the occurrence of the fluidized film whereas the glass-transition temperature of CO(2), as determined from the onset of translational molecular diffusion, is assigned to 50 K. This behavior may be related to the ultraviscous nature of the supercooled liquid, arising from the decoupling between the translational molecular diffusion and viscosity. The He(+) irradiation of the mixed CO(2)-D(2)O ice and the D(2)(+) irradiation of the CO(2) ice at 13 K do not yield any surface residues assignable to H(2)CO(3) and its precursors above 100 K. This result may be related to the segregation between the CO(2) and D(2)O molecules.     

Hydration of NaCl on glassy, supercooled-liquid, and crystalline water

Interactions of sodium chloride with amorphous and crystalline water films, leading to the possible formation of a dilute NaCl solution, were investigated using time-of-flight secondary ion mass spectrometry as a function of temperature. A monolayer of NaCl tends to remain on the surface or in subsurface sites of thick amorphous solid water films (200 monolayers); the Na+ ion is hydrated preferentially, whereas the Cl- ion is segregated at the surface. The hydration structure of NaCl is fundamentally unchanged for viscous liquid water that appears at temperatures higher than 136 K. The solubility of NaCl increases abruptly at 160 K because of the evolution of supercooled liquid water, which can hydrate the Cl- ion efficiently. However, the diffusion of the ions toward the bulk of supercooled liquid water is interrupted by crystallization; therefore, the dilute NaCl solution that is characterized by completely separated Na+-Cl- pairs may not be formed. When NaCl is deposited on the crystalline ice film, hydration of NaCl is enhanced above 160 K as well, indicating that a liquidlike phase coexists with crystals.     

Interaction of water with LiCl, LiBr, and LiI in the deeply supercooled region

The hydration mechanism of lithium halides was studied using time-of-flight secondary ion mass spectrometry as a function of temperature. The lithium halides embedded in thin films of amorphous solid water segregate to the surface at temperatures higher than 135-140 K, with efficiency increasing in the order of LiCl, LiBr, and LiI. A monolayer of LiCl and LiI adsorbed on the surface of amorphous solid water tends to diffuse into the bulk at 160 K. The infrared absorption band revealed that the aqueous lithium-halide solutions and crystals are formed simultaneously at 160 K; these phenomena are explicable as a consequence of the evolution of supercooled liquid water. The strong surfactant effect is inferred to arise from hydration of a contact ion pair having hydrophilic (lithium) and hydrophobic (halide) moieties. Furthermore, bulk diffusion of lithium halides might result from the formation of a solvent-separated ion pair in supercooled liquid water. The presence of two liquid phases of water with different local structures is probably responsible for the formation of these two hydrates, consistent with the calculated result reported by Jungwirth and Tobias[J. Phys. Chem. B 106, 6361 (2002)].     

Synthesis and characterization of titanium and zirconium complexes with silicone-bridged phenoxycyclopentadienyl ligands

Dimethylsilyl(2,3,4,5-tetramethylcyclopentadienyl)(3-tert-butyl-5-methyl-2-phenoxy)titanium dichloride (1a), a useful catalyst precursor for olefin copolymerization, was synthesized at high yield starting from allyl-protected phenolic ligand 3a,which was first treated with 2 equiv. of n-BuLi to selectively give the dilithium salt of 3a along with 1-heptene, a coupling product of a protected allyl ether moiety and butyl anion. Addition of TiCl₄ to the resulting dilithium salt of 3a in toluene afforded 1a in 50% isolated yield. This methodology could be applied to the preparation of related titanium and zirconoium complexes 1b-1d, 8 with silicone-bridged Cp-phenoxy ligands, whereas the reaction starting from methyl-protected precursor 2a did not produce the zirconium complex 8. Copolymerization of ethylene and 1-hexene with the newly prepared complexes was also investigated.