Norio Morishita

Structural changes of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) fractionated with acetone-water solution

Biosynthesized poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)) copolymers with 3HV mole fraction of 36 and 61% were fractionated by fractional precipitation methods using a solution of acetone-water. Both samples were mixtures of random copolymers having a wide variety of 3HV composition. The melting points of the fractionated samples showed pseudoeutectic changes with minimum breaking point at ca. 40 mol% 3HV. The fractionated samples whose 3HV composition range was from 36 to 56 mol% showed a single melting peak and the coexistence of both P(3HB) and P(3HV) crystal phases. The crystal lattice of the copolymer was of either P(3HB) or P(3HV) type depending on whether the 3HV composition was lower or higher than this range, respectively. The crystal phase transition of isodimorphism for P(3HB-co-3HV), therefore, occurred in a broad composition range from 36 to 56 mol% 3HV, which corresponded to the pseudoeutectic composition range. The amorphous density estimated by density measurement decreased linearly as the 3HV composition increased, showing a breaking point at ca. 30 mol% 3HV. The crystalline density estimated by the X-ray method was obtained over the whole range of 3HV composition. Crystallinity estimated by the density method was almost parallel to that evaluated by the X-ray method.

Study of the dissociation of neutral intermediates using charge inversion mass spectrometry

In charge inversion experiments using a tandem mass spectrometer, mass-selected positive ions are made to collide with an alkali metal target, and the resulting negative ions formed upon two-electron transfer are mass-analyzed. The internal energy depositions are measured for the so-called thermometer molecule W(CO)6. The difference between the centered value of the internal energy of W(CO)6 and the energy level of the precursor ion is in good agreement with the ionization energy of the Cs target. This correlation indicates that dissociation occurs from energy-selected neutrals formed via near-resonant neutralization.

Discrimination of C3H4+ isomeric ions by charge inversion mass spectrometry using an alkali metal target

Abstract Charge inversion mass spectrometry was performed using an MS/MS instrument in which mass-selected positive ions were made to collide with alkali metal targets, and the resulting negative ions formed upon two-electron transfer were mass analyzed. Charge inversion spectra using Cs targets were measured for C3H4+ ions produced from allene (CH2ue5fbCue5fbCH2) and propyne (CH3Cue5fbCH) by electron impact. The peak associated with C3H4- in the charge inversion spectra is twice as intense for propyne as for allene, whereas the profile of the peaks associated with C3Hn− (n = 0–2) is similar for both isomeric precursors. The kinetic energy release values at FWHM of the peak associated with C3H3− formed from allene ions and propyne ions are 0.28 ± 0.04 eV and 0.64 ± 0.06 eV, respectively. A clear differentiation between the isomeric precursors can be made on the basis of these differences in the charge inversion spectra. The differences observed are attributed to the formation of excited C3H4 states by near-resonant neutralizations of allene and propyne ions. Collisionally activated dissociation (CAD) spectra using He targets were measured for the same C3H4+ isomeric precursor ions. The CAD spectra are similar for both isomeric precursor ions, although slight differences were detected in the weak peaks associated with the species formed upon Cue5f8C bond cleavage. Charge inversion mass spectrometry using alkali metal targets was found to provide a much clearer differentiation between the isomeric ions of unsaturated hydrocarbons than CAD.

Definitive evidence for the existence of a long-lived vinylidene radical cation, H2C=C+.

Charge inversion mass spectra of C2H2+ ions produced by electron impact from HC≡CH and CH2=CCl2 were measured using K and Cs targets. Clear differences in the charge inversion spectra between HC≡CH and CH2=CCl2 indicate that the C2H2+ ion formed from CH2CCl2 is H2C=C+⋅. The lifetime of H2C=C+⋅ is found to be longer than 8.5 μs, and the state is proposed to be the 2B1 ground-state rather than the 4A2 state.

A new technique to study the dissociation of energy-selected neutral intermediates

Abstract The dissociation of excited species is one of the most important types of chemical reactions, and it has been investigated by using either molecular collision or photon excitation. Mass spectrometry is suited to generate and probe unstable intermediates in the gas phase and has enabled the investigation of the dissociation of various stable and unstable ions. However, investigation of neutral species using this technique has been difficult because of their lack of electronic charge. In this work we have used mass spectrometry to measure collision-induced dissociation (CID) spectra and charge-inversion spectra of CD 3 OH + and CH 3 OD + . The major dissociation process in CID was found to involve elimination of a hydrogen atom from the methyl group, whereas dissociation in the charge-inversion mass spectrometer was found to be via elimination of a hydrogen atom from the hydroxyl group. Hydrogen atom elimination from the hydroxyl group has also been reported as the major process in the photo-induced dissociation of neutral methanol. This demonstrates the usefulness of charge-inversion mass spectrometry as a technique for the investigation of the dissociation of neutral intermediates.

Dissociation mechanism of electronically excited C3H4 isomers by charge inversion mass spectrometry

Abstract The mechanism for dissociation of C3H4 isomers to form neutral radicals was investigated by charge inversion mass spectrometry using alkali metal targets. Electronically excited allene and propyne were formed from the corresponding positive ions by neutralization with alkali metal, and the neutral fragments resulting from dissociation of the excited molecules were converted into negative ions which were mass-analyzed and detected. From the comparison of peak intensities and peak widths among allene, propyne and 3,3,3-trideutero-propyne (CD3CCH), the dissociation mechanism of electronically excited C3H4 was elucidated. The principal feature of the dissociation process involves the loss of two H atoms from the electronically excited hydrocarbons, which is attributed not to two independent Cue5f8H bond cleavages, but rather to loss of a H2 molecule. The loss of a H2 molecule has a higher activation energy than loss of a H atom, despite the final state of the former having a lower heat of formation than that of the latter. In a Cue5f8H bond cleavage, the weaker the bond, the more easily it is cleaved. Cleavage of a Cue5f8C bond is substantially less favorable than the loss of hydrogen atoms, even though the former has a lower energy than the later. This may be attributed to the lower frequency of the Cue5f8C bond vibration compared with that of the Cue5f8H bond.

Evidence for a difference in the dissociation mechanisms of acetylene (HCCH) and vinylidene (H2CC:) from charge inversion mass spectrometry

Vinylidene and acetylene are the simplest hydrocarbon isomers, and vinylidene is the simplest unsaturated carbene. The charge inversion mass spectra of C2H2+ cations derived from acetylene using Na, K, Rb and Cs targets were found to be clearly different from those derived from vinylidenechloride (1,1-dichloroethylene). The process of formation of the negative ions in charge inversion mass spectrometry is via near-resonant neutralization followed by spontaneous dissociation, and then endothermic negative ion formation. The intensity of the C2− peak relative to the C2H− peak in these spectra increased with decreasing ionization potential of the targets for both of the isomeric C2H2+ cations. The formation of the C2− anion is proposed to result from the dissociation of excited C2H2 neutrals into C2 and H2. The dependence on target species of the intensities of the C2− peak relative to the C2H− peak for HCCH and H2CC: cannot be rationalized by the internal energy of the excited C2H2 neutrals. The differences indicate that the isomeric C2H2 neutrals dissociate into C2H and H prior to 1,2-hydrogen atom migration.

13C n.m.r. and g.p.c.—low-angle laser light scattering measurements on polyacrylonitrile prepared by urea clathrate polymerization in the solid state for the optimization of tacticity

The molecular weight and molecular weight distribution of isotactic polyacrylonitrile (PAN) prepared by urea clathrate polymerization in the solid state were studied by the g.p.c.—low-angle laser light scattering (l.a.l.l.s.) method. The experimental details of this method for PAN are described. Measurements were carried out on three different kinds of urea clathrate PAN, and the results were compared with those of free-radical PAN (i.e. prepared using the aqueous redox slurry system). The characteristics of the urea clathrate PAN were (1) an asymmetrical shape in the g.p.c.—L.a.l.l.s. curve and (2) a remarkable contribution of the lower-molecular-weight component to the high stereoregularity (>80%) of the sample. An experimental prediction for the solid-state synthesis of a perfectly stereoregular PAN sample (isotacticity of 100%) has been derived from a combination of the g.p.c.—l.a.l.l.s, and 13 C n.m.r. results.

Effects of Electron Irradiation on CuInS2 Crystals

The effect of electron irradiation on CuInS2 single-crystals grown using traveling heater method has been examined using photoluminescence (PL). It has been found that the emission intensities for exciton and donor-acceptor pair transitions decrease, and that the appearance of the structures in deep PL band increases. The peaks which appeared after the electron irradiation appear to be due to the recombination emission, involving deep donors and deep acceptors.