An application of EGA-MS with skimmer interface to pyrolysis behavior of DHTAM, an antibacterial and antifungal material with thermostability

An application of evolved gas analysis-mass spectrometry (EGA-MS) with skimmer interface was carried out to investigate the pyrolysis mechanism of an antibacterial and antifungal material that is expected with thermostability. The skimmer interface between a furnace and a vacuum chamber with a mass spectrometer transmitted the gaseous species, which were trapped by a general capillary interface. As a result, it became clear that the thermostability of antimicrobial activity was limited by the heat resistance of the coordinate bond between nitrogen and silver in the silver chelate.     

Temperature-driven oxygenation rate control by polymeric photosensitizer

A polymeric photosensitizer, poly(NIPAM-co-BP), consisting of N-isopropylacrylamide (NIPAM) and benzophenone (BP) units, demonstrates a temperature-controlled oxygenation activity in water. The system promotes a heat-induced oxygenation enhancement at <17 degrees C and suppression at >22 degrees C. This unprecedented photo-oxygenation activity is triggered by a heat-induced phase transition of the polymer from coil to micelle, and then to globule state, cleverly controlling the stability and diffusion of singlet oxygen and the location of substrate.     

Photodissociation of naphthalene dimer radical cation during the two-color two-laser flash photolysis and pulse radiolysis-laser flash photolysis

Photodissociation of naphthalene (Np) dimer radical cation (Np2*+) to give naphthalene radical cation (Np*+) and Np and the subsequent regeneration of Np2*+ by the dimerization of Np*+ and Np were directly observed during the two-color two-laser flash photolysis in solution at room temperature. When Np2*+ was excited at the charge-resonance (CR) band with the 1064-nm laser, the bleaching and recovery of the transient absorption at 570 and 1000 nm, assigned to the local excitation (LE) and CR bands of Np2*+, respectively, were observed together with the growth and decay of the transient absorption at 685 nm, assigned to Np*+. The dissociation of Np2*+ proceeds via a one-photon process within the 5-ns laser flash to give Np*+ and Np in the quantum yield of 3.2 x 10(-3) and in the chemical yield of 100%. The recovery time profiles of Np2*+ at 570 and 1000 nm were equivalent to the decay time profile of Np*+ at 685 nm, suggesting that the dimerization of Np*+ and Np occurs to regenerate Np2*+ in 100% yield. Similar experimental results of the photodissociation and regeneration of Np2*+ were observed during the pulse radiolysis-laser flash photolysis of Np in 1,2-dichloroethane. The photodissociation mechanism can be explained based on the crossing between two potential surfaces of the excited-state Np2*+ and ground-state Np*+.     

Formation of microstructured silicon surfaces by electrochemical etching using colloidal crystal as mask

Silicon disk arrays and silicon pillar arrays with a close-packed configuration having an ordered periodicity were fabricated by the electrochemical etching of a silicon substrate through colloidal crystals used as a mask. The colloidal crystals were directly prepared by the self-assembly of polystyrene particles on a silicon substrate. The transfer of a two-dimensional hexagonal array of colloidal crystals to the silicon substrate could be achieved by the selective electrochemical etching of the exposed silicon surfaces, which were located in interspaces among adjacent particles. The diameter of the tip of the silicon pillars could be controlled easily by changing the anodization conditions, such as current density and period of electrochemical etching.     

Theoretical study on the lowest-frequency mode of the flavin ring

The dynamic aspects along the normal vibrational motions of the lowest frequencies in the oxidized, radical, and reduced states of flavin (isoalloxazine) have been studied. In comparison with the twist motions in the oxidized state, the butterfly motions in the radical and reduced states turned out to bring more significant variations to the frontier molecular orbital energies and to the charge distributions on the atoms of the pyrazine ring in isoalloxazine. It can be considered that the electron transfers from and to the isoalloxazine ring can be adjusted or controlled by these variations. In the reduced states the electron release from the molecule, and in the radical states the electron release from or acceptance by the molecule, could be impelled by the butterfly motions, while in the oxidized state the electron acceptance by the molecule could be accelerated slightly by the twist motion. Received: 30 September 1998 / Accepted: 20 January 1999 / Published online: 7 June 1999     

Size‐Dependent Thermochromism through Enhanced Electron–Phonon Coupling in 1 nm Quantum Dots

1 nm CuO quantum dots (QDs) were produced in size‐controlled super‐micropores of a silica matrix. The reversible color change of the QDs from pale blue to deep green was clearly observed in a wide temperature range from 298 to 673 K. This particular thermochromism is ascribed to an enhanced bandgap shift depending on temperature with a strong electron–phonon coupling in the confined space of the 1 nm QDs.     

Delocalization of positive charge in π-stacked multi-benzene rings in multilayered cyclophanes

In the present study, delocalization of a positive charge in π-stacked multi-benzene rings in multilayered para- and meta-cyclophanes, in which benzene rings are connected by propyl chains to form a chromophore array with the face-to-face structure, was investigated by means of transient absorption spectroscopy during the pulse radiolysis using dichloroethane as a solvent. The local excitation and charge resonance (CR) bands were successfully observed. It was revealed that the CR band shifted to the longer wavelength side with the number of the benzene rings. The stabilization energy estimated from the peak position of the CR band showed the efficient charge delocalization over the cyclophanes. Furthermore, the CR bands showed the slight spectral change attributable to the change in distribution of the conformers. The substantially long lifetime of the CR band can be explained on the basis of the smaller charge distribution on the outer layers of the multilayered cyclophanes.     

Post-translational His-Cys cross-linkage formation in tyrosinase induced by copper(II)-peroxo species

Autocatalytic formation of His-Cys cross-linkage in the enzyme active site of tyrosinase from Aspergillus oryzae has been demonstrated to proceed by the treatment of apoenzyme with Cu(II) under aerobic conditions, where a (μ-η(2):η(2)-peroxo)dicopper(II) species has been suggested to be involved as a key reactive intermediate.     

Isolation of salsolinol, a tetrahydroisoquinoline alkaloid, from the marine sponge Xestospongia cf. vansoesti as a proteasome inhibitor

Salsolinol (1), a tetrahydroisoquinoline alkaloid, was isolated from the marine sponge Xestospongia cf. vansoesti collected in Indonesia as a proteasome inhibitor, along with three salsolinol derivatives, norsalsolinol (2), cis-4-hydroxysalsolinol (3), and trans-4-hydroxysalsolinol (4). Compounds 1 and 2 inhibited the chymotrypsin-like activity of the proteasome with IC(50) values of 50 and 32 μg/ml, respectively, but 3 and 4 showed no inhibitory effect even at 100 μg/ml.