Singlet Oxygen–mediated Hydroxyl Radical Production in the Presence of Phenols: Whether DMPO–·OH Formation Really Indicates Production of ·OH?¶

The reaction of singlet oxygen (1O2) generated by ultraviolet-A (UVA)-visible light (lambda > 330 nm) irradiation of air-saturated solutions of hematoporphyrin with phenolic compounds in the presence of a spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), gave an electron spin resonance (ESR) spectrum characteristic of the DMPO-hydroxyl radical spin adduct (DMPO-*OH). In contrast, the ESR signal of 5,5-dimethyl-2-pyrrolidone-N-oxyl, an oxidative product of DMPO, was observed in the absence of phenolic compounds. The ESR signal of DMPO-*OH decreased in the presence of either a *OH scavenger or a quencher of *O2 and under anaerobic conditions, whereas it increased depending on the concentration of DMPO. These results indicate both 1O2- and DMPO-mediated formation of free *OH during the reaction. When DMPO was replaced with 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide (DEPMPO), no DEPMPO adduct of oxygen radical species was obtained. This suggests that 1O2, as an oxidizing agent, reacts little with DEPMPO, in which a strong electron-withdrawing phosphoryl group increases the oxidation potential of DEPMPO compared with DMPO. A linear correlation between the amounts of DMPO-*OH generated and the oxidation potentials of phenolic compounds was observed, suggesting that the electron-donating properties of phenolic compounds contribute to the appearance of *OH. These observations indicate that 1O2 reacts first with DMPO, and the resulting DMPO-1O2 intermediate is immediately decomposed/reduced to give *OH. Phenolic compounds would participate in this reaction as electron donors but would not contribute to the direct conversion of 1O2 to *OH. Furthermore, DEPMPO did not cause the spin-trapping agent-mediated generation of *OH like DMPO did.     

Formation of Supramolecular Polymers Constructed by Cyclodextrins with Cinnamamide

-Cyclodextrin having cinnamamide at 6- or 3-positions (6-CiNH--CD, 3-CiNH--CD) and -cyclodextrin with cinnamamide on 6-position (6-CiNH--CD) have been prepared. Supramolecular structures were formed in the solid state or aqueous solutions and characterized by measurements of NMR and vapor pressure osmometry (VPO). The results indicate that 6-CiNH--CD formed insoluble supramolecular polymers in the solid state, while 6-CiNH--CD and 3-CiNH--CD formed supramolecular complexes in aqueous solutions. 6-CiNH--CD was found to form a dimer in an aqueous solution. 3-CiNH--CD formed intermolecular complexes to give supramolecular polymers. The differences of the position of guest part on cyclodextrins caused to give a variety of supramolecular structures in aqueous solutions.     

The influence of polytypic structures on the M011-->M101 solid-solid phase transition of n-C36H74: an application of the oblique infrared transmission method

The molecular displacements on the M011-->M101 phase transition of n-hexatriacontane (n-C36H74) have been investigated with an IR microscope designed for the oblique infrared transmission method. It has been clarified that two polytypic structures of the M011 modification, single-layered structure (Mon) and double-layered one (Orth II), both transform to the M101 modification of single-layered structure with their respective mechanisms. On the M011(Mon)-->M101 transition, the inclination direction of molecular axis is changed by 90 degrees through an intermediate state in which the molecular chain is set perpendicular to the basal plane of the single crystal. On the other hand, a polymorphic-polytypic composite structural change on the M011(Orth II)-->M101 transition is accomplished through two kinds of molecular displacements occurring alternately along the stacking direction of molecular layers.     

Study of thermodynamic stabilities of polytypes of n-C36H74 by solubility measurements and incoherent inelastic neutron scattering

The thermodynamic properties of the two polytypes of n-hexatriacontane (n-C36H74), single-layered structure Mon and double-layered structure Orth II have been investigated by means of solubility measurements and incoherent inelastic neutron scattering. The solubility measurements reveal that Orth II is more stable than Mon by 1.2 kJ/mol because of the advantage of larger entropy. The neutron scattering measurements show that the vibrational modes of Orth II shift to the lower frequencies compared with those of Mon in the frequency region below 120 cm(-1). The advantage of Orth II in vibrational entropy due to the low-frequency shifts is estimated to be 9.6 J K(-1)/mol at 288 K under the harmonic approximation, which nearly agrees with the entropy difference of 6.8 J K(-1)/mol between Mon and Orth II determined by solubility measurements. These results suggest that the difference in vibrational entropy due to low-frequency modes mainly contributes to the relative thermodynamic stabilities of polytypic structures of long-chain compounds. From the frequency of methyl torsional mode, it is suggested that the cohesive force at the lamellar interface is stronger in Mon than in Orth II.     

High resolution emission Fourier transform infrared spectra of the 4p-5s and 5p-6s bands of ArH

In the 2500-8500 cm(-1) region several strong emission bands of (40)ArH were observed by Fourier transform spectroscopy through a dc glow discharge in a mixture of argon and hydrogen. Rotational-electronic transitions of the two previously unstudied 4p-5s and 5p-6s,v = 0-0, bands of (40)ArH were measured and assigned in the 6060 and 3770 cm(-1) regions, respectively. A simultaneous fit of the emission transitions of the 4p-5s and 5p-6s bands and an extended set of transitions of the 6s-4p band observed by Dabrowski, Tokaryk, and Watson [J. Mol. Spectrosc. 189, 95 (1998)] and remeasured in the present work yielded consistent values of the spectroscopic parameters of the electronic states under investigation. In the branch of the 4p-5s band with transitions of type (Q)Q(f(3)e) we observed a narrowing in the linewidths with increasing rotational quantum number N. The rotational dependence of the linewidth is caused by predissociation of the 5s state by the repulsive ground 4s state through homogeneous coupling and changes in overlap integrals of the vibrational wave functions with the rotational level. Analysis was based on the Fermi's golden rule approximation model. In the 4p-5s band region a vibrational sequence ofv(')-v(")=1-1, 2-2, and 3-3 were recorded and a number of transitions belonging to the strongest (Q)Q(f(3)e) form branch of the 1-1 band were analyzed.     

Laser-ionization mass-spectrometric studies on laser ablation of a nitrogen-rich polymer at 532 nm and 1064 nm

Laser-ionization Time-Of-Flight (TOF) mass-spectrometric studies have been carried out on the 532 nm and 1064 nm laser ablation products from a nitrogen-rich polymer. The polymer used had an elemental composition of C_6.0N_8.9H_3.4 and consisted of C=N, C-N, and N-H chemical bonds. The TOF mass spectra observed were composed of various peaks (150 amu) depending on the ablation laser wavelength. The primary peaks were assigned to C⁺, CN⁺, CHnN⁺ ₂ (n=1–3) and C₂H₂N⁺ ₃ for 532 nm ablation, and C⁺, C⁺ ₃, HCN⁺, HCCN⁺, CH₂NH⁺, HNCN⁺, H₃NCN⁺, and C₄H₄N⁺ ₇ for 1064 nm ablation. The flight velocity distributions with peak velocities ranging from 8.6×10³ cm/s to 3.8×10⁴ cm/s were measured for these products. The distinct velocity distributions observed between small and large products indicate the presence of two origins in the fragment ejection process from the polymer for both 532 nm and 1064 nm ablation. Furthermore, we suggest an importance of the translational energy of the fragments for the product generation in the laser plume.     

Coprecipitation with metal hydroxides for the determination of beryllium in seawater by graphite furnace atomic absorption spectrometry

Coprecipitation first with magnesium hydroxide, next with tin(IV) hydroxide is developed for the determination of traces of beryllium in sea-water. To a 200-ml sample is added a sodium hydroxide solution to form magnesium hydroxide at pH 11.5, on which beryllium is quantitatively coprecipitated. The precipitate is separated by centrifugation and dissolved in 2 ml of 12 mol/l hydrochloric acid. The resulting solution (ca. 10 ml) is mixed with 2 mg of tin (IV) carrier and the pH is adjusted to 5.0 to collect the beryllium on tin (IV) hydroxide, leaving magnesium ions in the solution. The tin (IV) hydroxide is centrifuged, dissolved in 0.1 ml of 5 mol/l hydrobromic acid, and then diluted to 1 ml with water. Magnesium is so added as to be 500 g/ml for increasing the sensitivity about four times, and the beryllium in the solution is determined by graphite furnace atomic absorption spectrometry. The experiments with synthetic seawater samples showed that pg — g amounts of beryllium can be coprecipitated on the metal hydroxides and beryllium at the low ng/1 level can be determined with reasonable precision (RSD < 10%). The detection limit of the proposed method is 0.5 ng/l of beryllium in seawater.     

Mechanism of plasma-initiated polymerization: Concerning the nature of solvent effects on the lifelike polymerization of water-soluble vinyl monomers

To provide a satisfactory basic understanding of the solvent effect of plasma-initiated polymerization, we have carried out several kinds of polymerizations of various water-soluble vinyl monomers. It has been shown that aqueous solution of such vinyl monomers underwent the polymerizations induced by methyl isobutyrate (MIB) plasma-exposed glass surface. The invisible ultrathin polymer film trapping an active radical species deposited on the plasma-exposed glass surface apparently induced the polymerizations. The efficiency, however, was largely dependent on the solvent used: the solvent can be considered to act as “an initiation-activator” for the lifelike postpolymerization. The nature of the solvent effect was ascribed to the physicomechanical property such as swelling ability and/or solubility toward the ultrathin film formed on the glass surface. Thus it has been suggested that the choice of good-balanced combination between the structural feature of the plasma-induced ultrathin polymer film and the solvent as an initiation-activator is important to achieve activity of a desired solution polymerization.     

Selective formation of AAB- and ABC-type heterotrimeric alpha-helical coiled coils

The alpha-helical coiled coils have a representative amino acid sequence of (abcdefg)(n) heptad repeats. We previously reported that two peptides named IZ-2A and IZ-2W formed an (IZ-2A)(2)/IZ-2W heterotrimer with an Ala-Ala-Trp interaction in the hydrophobic core. In this paper, we describe the selective formation of AAB- and ABC-type heterotrimers. To increase the selectivity of the AAB-type heterotrimeric formation, Lys residues at the f position were mutated to either an Ala or a Gln residue to form IZ-2A(fA) or IZ-2W(fQ). Separately, both IZ-2A(fA) and IZ-2W(fQ) have a random structure at pH 7 and 20 degrees C. However, together IZ-2A(fA) and IZ-2W(fQ) form a 2:1 complex with a thermal transition midpoint (Tm) of 48 degrees C. This procedure was applied to prepare the ABC-type heterotrimer, in which two sets of Ala-Ala-Trp interactions were designed in the hydrophobic core. Interhelical interaction between the e and g positions and the alpha-helical propensity of the amino acid at the f position were also considered in the design. The resultant three peptides selectively formed the ABC-type heterotrimer with a Tm of 51 degrees C. Other peptide combinations had random coil properties.