Hiroshi Sakai

Influence of cationic molecules on the hairpin to duplex equilibria of self-complementary DNA and RNA oligonucleotides

A self-complementary nucleotide sequence can form both a unimolecular hairpin and a bimolecular duplex. In this study, the secondary structures of the self-complementary DNA and RNA oligonucleotides with different sequences and lengths were investigated under various solution conditions by gel electrophoresis, circular dichroism (CD) and electron paramagnetic resonance (EPR) spectroscopy and a ultraviolet (UV) melting analysis. The DNA sequences tended to adopt a hairpin conformation at low cation concentrations, but a bimolecular duplex was preferentially formed at an elevated cationic strength. On the other hand, fully matched RNA sequences adopted a bimolecular duplex regardless of the cation concentration. The thermal melting experiments indicated a greater change in the melting temperature of the bimolecular duplexes (by ∼20°C) than that of the hairpin (by ∼10°C) by increasing the NaCl concentration from 10 mM to 1 M. Hairpin formations were also observed for the palindrome DNA sequences derived from Escherichia coli, but association of the complementary palindrome sequences was observed when spermine, one of the major cationic molecules in a cell, existed at the physiological concentration. The results indicate the role of cations for shifting the structural equilibrium toward a nucleotide assembly and implicate nucleotide structures in cells.

Amino acid ester salt recognition by ferrocene-based ditopic receptor bearing oligoethylene glycol with pendant bipy subunits: CV, UV-vis and ESR studies

The novel ferrocene-based ditopic receptor 1 was synthesized. This receptor bears two oligoethylene glycol arms with pendant 2,2-bipyridine unit at the identical cyclopentadienyl rings, Cu(I) cation binds to 1 to form the 1 : 1 complex (1.Cu(I)) with the cavity consisting of polyether, and the resulting complex acts as a receptor for amino acid ester salts to give the ditopic complex (1.Cu(I).AAOMe-HCl). The 1H NMR spectrum of 1.Cu(I).LeuOMe-HCl exhibits strong broadening at the bipyridine region, and the ESR spectrum of the same sample gives the signals assigned as Cu(II) species. With these data, the binding of 1.Cu(I) towards AAOMe.HCl leads to the conformational change, and the Cu(I) complex is simultaneously oxidized to the Cu(II) complex.

57Fe Mössbauer spectra and X-ray structural analyses of iodide salts for 1′,1‴-bis(α- and β-naphthylmethyl)-1,1″-biferrocenes

Abstract The relation between the mixed-valence state and crystal structure of iodide salts for 1′,1‴-bis(α- and β-naphthylmethyl)-1,1″-biferrocenes has been studied by means of 57Fe Mossbauer spectroscopy and X-ray structural analysis. Time change of 57Fe Mossbauer spectroscopy was first observed for only the α-naphthylmethyl derivative; the trapped-valence state (metastable phase) of the Fe atom in the salt gradually changes into the detrapped-valence state (stable phase) on standing at room temperature for one month. There are two independent monocations in the β-naphthylmethyl derivative. Both salts (α-naphthylmethyl derivative in stable phase and β-naphthylmethyl derivative) gave the detrapped-valence state of 57Fe Mossbauer spectra, implying the equivalence of the oxidation state of the two Fe atoms. X-ray diffraction studies of both salts support the above results, i.e. both monocations sit on the center of symmetry and the Feue5f8C(Cp) distances (2.064(2) A for the α-naphthylmethyl derivative and 2.061(9) and 2.056(7) A for the β-naphthylmethyl derivative) are close to the mean values of ferrocene and ferrocenium ion.

Mechano chemical synthesis of a silver ion conductor in the system AgI-Ag3PO4

A high-energy ball-milling process was applied to the preparation of silver ion conductors from the compositions 80AgI 20Ag 3 PO 4 and 60AgI 40Ag 3 PO 4 (mol%); the composition 80AgI 20Ag 3 PO 4 corresponds to that of the crystalline Ag 7 I 4 PO 4 superionic phase, and the composition 60AgI 40Ag 3 PO 4 is reported as a typical composition of the superionic conducting glasses in this system. For the composition 80AgI 20Ag 3 PO 4 , ball milling for longer than 190 h led to the formation of an unknown new crystalline phase, and the new phase showed a high ion conductivity of 6 X 10 -2 S cm -1 at room temperature. The conductivity is higher than that of the crystalline Ag 7 I 4 PO 4 phase. The ball-milling process for the composition 60AgI - 40Ag 3 PO 4 made it amorphous, and the ball-milled sample showed a high ion conductivity very similar to that of melt quenched glass with the same chemical composition.

Iron-57 Mössbauer spectroscopic and X-ray diffraction studies on the mixed-valence state of binuclear ferrocene derivatives with long alkyl substituents

The mixed-valence states of biferrocene derivatives with long alkyl substituents, which have a layered structure, have been investigated by means of 57Fe Mossbauer spectroscopy and X-ray powder diffraction. An interesting even–odd character in the number of carbon atoms of the alkyl chain is found in the relationship between the crystal structure and the mixed-valence state. The mixed-valence states of 1′,1‴-bis(dodecyl)-1,1″-biferrocenium triiodide change in accordance with a transformation of the crystal structure in the solid state. An X-ray diffraction analysis for this salt obtained from dichloromethane at 0 °C showed that both the cation and the anion are situated at a centre of symmetry and the dodecyl substituent has the all-trans conformation. The layers are located in the ab plane.

Effect of calcining temperature on the tetragonal-to-monoclinic phase transition characteristics in 2 mol% yittria-doped zirconia ceramics

Two types of tetragonal-to-monoclinic (t-m) phase transitioncharacteristics were observed in the 2Y-TZP powder samples. In thesample calcined below 1200°C, the t-m phase transitionoccurred below 200°C, and the fraction of the monoclinic phaseincreased sigmoidally. At the beginning of the transition, thefraction of the monoclinic phase increased gradually, and the latticestrain remained unchanged. The abrupt increase in the monoclinicphase accompanying the increase in the lattice strain of thetetragonal phase followed this. Finally, the fraction of themonoclinic phase was saturated, and the lattice strain dropped to0%. The reaction between the adsorbed water and 2Y-TZP was essentialfor the t-m phase transition of 2Y-TZP to occur in air at around roomtemperature. The lattice strain stored in the tetragonal latticeassisted the phase transition. On the other hand, the fraction of themonoclinic phase increased, accompanied by a decrease in the latticestrain in the 1400°C calcined powder. After the fraction ofthe monoclinic phase was almost saturated, the lattice strain droppedto 0%. A gas-solid reaction between the water vapor in air and2Y-TZP and the diffusion of OH− ion into the 2Y-TZP lattice wereessential for this type of t-m phase transition.

Application of the Mössbauer spectroscopy to the study of the oxidation state of azaferrocene derivatives

Azaferrocene has two active sites of iron and nitrogen atoms. Drastic change of the oxidation state in iodine oxidation of azaferrocene is observed by introducing the methyl substituents into the pyrrole ring, while all the N-methylates show a similar electronic state. It was revealed that an introduction of methyl substituent to the pyrrole ring promotes the oxidation of nitrogen atom in pyrrole ring more than the central iron atom.

Mössbauer spectra of (Fe0.5Zn0.5)PS3 and its pyridine intercalate

Mössbauer spectra of (Fe0.5Zn0.5)PS3, which is isomorphous with FePS3, were measured at 300 and 80 K, and were compared with those of FePS3. We succeeded in preparing (Fe0.5Zn0.5)PS3 intercalated with pyridine. In the XRD pattern of the intercalate the diffraction peaks corresponding to (Fe0.5Zn0.5)PS3 were completely missing, suggesting that the intercalation was completely performed with pyridine. The Mössbauer spectra were changed significantly by the intercalation suggesting the charge transfer from guest molecules to the host matrix. The replacement of iron by zinc has no influence on the electronic state of the iron atom, except for the magnetic interaction.

Mössbauer Spectra of FePS3-Cobaltocene Intercalation Compound

Abstract Mössbauer spectra of the FePS3-cobaltocene intercalation compound were measured in the temperature range of 300K to 10K. The spectra, distinct from those of pure FePS3, suggest the charge transfer from cobaltocene to Fe-S antibonding orbitals of the FePS3 host lattice.

Phase Transition in 1′, 1′″-Dihexylbiferrocenium Triiodide Accompanied by a Change In Mixed-Valence State

Abstract Two different crystals of 1′, 1′″-dihexylbiferrocenium triiodide were obtained from the different solution (hexane or dichloromethane). The salt prepared from hexane has a longer interlayer distance and gives trapped-valence state of Fe atoms, while the salt recrystallized from dichloromethane has a shorter interlayer distance and gives typical fusion-type valence detrapping of the mixed- valence state on the 57Fe Mossbauer spectroscopy. By annealed at 323 K the latter changes into the former salt. The X-ray diffraction study of the latter supports the results of the 57Fe Mossbauer spectroscopy.