Ag(I) ion mediated formation of a C-A mispair by DNA polymerases

Silver turns up the A-C: In the presence of Ag(I) ions, a DNA polymerase incorporated deoxyadenosine (from dATP) at the site opposite cytosine in the template strand to afford the full-length product (see scheme), meaning that DNA polymerases prefer a C-Ag(I)-A base pair to the more thermodynamically stable C-Ag(I)-C base pair.     

Barrier height imaging of magnetic films: Use for studying the initial growth of Co films and the surface structure of FePt films

Barrier-height (BH) imaging using scanning tunneling microscopy (STM) was used to study the growth of Co films on Au(001) surfaces. We have observed BH of metastable bcc Co film (> 1 ML) for the first time, and that showed a large BH value (~ 6 eV), whereas the observed BH of the Au(001) surface (~ 3.5 eV) was consistent with the previous results. The origin of the large BH was qualitatively understood by considering that 3d electrons for tunneling are dominant for the Co(001) surface. We have observed numerous islands with different sizes and heights after 0.15 ML Co coverage and successfully obtained, from the BH imaging, an element-specific contrast, i.e. recognizing aggregated Au islands and Co islands, and information about inhomogenities of BH with proper consideration of the artifacts near the step edges. The height modification by the large BH difference is discussed.STM/BH studies of FePt films revealed two kinds of monolayer heights, the sum which was equal to the c axis lattice constant of L1₀ FePt. Two different dI/dz signal levels were observed on atomically flat terraces.     

Nucleation and Growth Behavior of Twin Region Around Yield Point of Polycrystalline Pure Ti

The aim of the present study is to investigate the nucleation and growth behavior of twin region around yield point of polycrystalline pure Ti under deformation. Firstly, we prepare commercial polycrystalline pure Ti plate, and investigate the microstructure and pole figures using an Electron Backscatter Diffraction Patterns device. Secondly, tensile specimens are cut out from 0°, 30°, 45° and 90° relative to plate rolling direction. Then, we measure the macroscopic stress–strain curve, local strain distribution and nucleation and growth of twin region arising in specimens under uniaxial tensile loading. Results show the anisotropic characteristics in those behaviors. Those could be related to c axis in hcp lattice. However, detailed anisotropic mechanism may have something to do with several interactions between slips and twins arising in its body. It is also understood that the avalanche behavior of twin region nucleation occurs as a result of larger twin region formation, with inhomogeneous small twin region nucleation in transient process. Finally, we could suppose the bridge mechanism of deformation behaviors from macroscale to microscale for polycrystalline pure Ti under deformation.     

STATIC QUENCHING OF EXCITED STATE OF TRIS(BIPYRIDINE)RUTHENIUM(II) COMPLEX-CONTAINING POLYMER BY SODIUM ANTHRAQUINONE-2-SULFONATE

Abstract— Quenching of excited state of Ru(bpy)₂(poly-4-methyl-4'-vinyl-2,2'-bipyridine)Cl₂ by sodium anthraquinone-2-sulfonate was found to be a static process. The quenching was interpreted by application of a modified Perrin model. Radius of the quenching sphere was estimated to correspond to 6.65 monomer units and was unchanged on varying the Ru²+ content of the polymer. Energy migration along the polymer chain was denied.     

SYNTHESES AND PHOTOREDOX PROPERTIES OF POLYELECTROLYTES FUNCTIONALIZED WITH 5-DEAZAFLAVIN

Abstract— Anionic polyelectrolytes functionalized with the 5-deazaflavin group (dFl) were synthesized. The lifetime of the triplet excited dFl in the polyelectrolytes with a 2-mol% dFl content (AdFl-2) was about 10 times longer than that of a low molecular weight analog (AdFl-M). 2-Mercaptoethanol (RSH) reduced the triplet dFl with the rate constant of k _red= 2.01 × 10⁸ M ⁻¹ s⁻¹ for AdFl-M and k _red= 4.4 × 10⁷ M ⁻¹ s⁻¹ for AdFl-2. A zwitterionic viologen (SPV) oxidized the triplet dFl with the rate constant of k _red= 3.69 × 10⁹ M ⁻¹ s⁻¹ for AdFl-M and k _ox= 7.4 × 10⁸ M⁻¹ s⁻¹ for AdFl-2. The smaller rate constants for the polymer system were discussed in terms of the hindering effect of the macromolecular microenvironment. The back electron transfer was shown to be drastically slowed in the AdFl-2-SPV system as a result of the intensive electrostatic effect of the polyelectrolytes. The buildup of the viologen radicals was studied under the steady-state illumination of the three component systems including viologen and RSH. The dFl group was demonstrated to serve as a very efficient photosensitizer in the oxidative cycle in case back electron transfer was retarded. This is the case of the AdFl-2-SPV system which gave the quantum yield of about 0.4 for the SPV⁻ buildup. By comparison, the AdFl-2-MV²+ system resulted in a much slower buildup of MV +radicals.     

Photochemistry of 4(3H)-pyrimidin-4-ones. Formation of medium-ring lactams

Upon irradiation, 4(3H)-pyrimidin-4-one(1) afforded a di-imine derivative(2) which, when hydrolyzed in an acidic methanol solution, gave N-methyl acetoacetamide(3). On the other hand, the fused 4(3H)-pyrimidin-4-ones, (4) and (5), gave medium-ring lactams(6) and (7), which were hydrolyzed in an acidic methanol solution to give (8) and (9), respectively.     

AMPHIPHILIC COPOLYMERS AS MEDIA FOR LIGHT-INDUCED ELECTRON TRANSFER–I. ELECTROSTATIC EFFECT ON THE FORWARD REACTION AS STUDIED BY FLUORESCENCE QUENCHING

Abstract— Fluorescence quenching of amphiphilic copolymers, poly(9-vinylphenanthrene-co-sodium 2-acrylamido-2-methylpropanesulfonate) (APh) and poly(9-vinylphenanthrene-co-3-methacrylamidopropyltrimethylammonium methyl sulfate) (QPh), in aqueous solution, was studied using methyl viologen (MV²⁺) or 4,4'-bipyridinium-1, 1'-bis(trimethylenesulfonate) (SPV) as oxidative quenchers. The fluorescence of the excited phenanthrene groups in APh was found to be efficiently quenched by MV²⁺. The apparent second-order rate constant for the quenching, k_q, ranged in the magnitude of 10¹¹ -10¹²M^-1 s^-1, which are well beyond the diffusion-controlled limit. This is presumably due to an increase of the effective concentration of MV²⁺ around the fluorophore in the copolymer resulting from electrostatic attraction between MV²⁺ and anionic segments of APh. This strong electrostatic interaction also favors the formation of ground-state EDA (electron donor acceptor) complex between the phenanthrene residue and MV²⁺. Such striking behaviors were not observed with the related model compound. Unexpectedly, the quenching with SPV, a zwitterionic quencher, was also enhanced in the polymer system (k_q= 2–6 × 10¹⁰M^-1 s^-1), suggesting the presence of some attractive interaction between APh and SPV. Contrary to the APh system, the fluorescence quenching of the corresponding cationic polymer (QPh) with MV²⁺ was strongly diminished (k_q= 5 × 10⁸M^-1 s^-1). This indicates that the polycation of QPh effectively prevents the access of MV²⁺ to the polymer.     

Competitive formation of 10- and 7-membered hydrogen-bonded rings of proline-containing model peptides

Intramolecularly hydrogen-bonded structures of proline-containing model peptides with a sequence of N-tert-butoxycarbonyl-prolyl-Xaa-NHCH3 [Xaa = Gly (glycyl), Ala (alanyl), Phe (phenylalanyl), Leu (leucyl), Ile (isoleucyl), and Val (valyl)] were studied by proton nuclear magnetic resonance and infrared spectroscopy. Variation of chemical shifts of amide protons with composition change of DMSO-d6/CDCl3 mixed solvents were found to be a good measure of intramolecular hydrogen bonding of peptides in CDCl3 solution. It has been shown that 10- and 7-membered hydrogen-bonded rings, which should have the beta- and gamma-turn like structures in proteins, respectively, form competitively with each other. It is suggested that the equilibrium between the two hydrogen-bonded rings is determined by steric hindrance due to a side chain of the Xaa residue. Free energies for formation of the 10- and 7-membered hydrogen-bonded rings, deltaG10 and deltaG7, were estimated from the solvent composition-dependent change of the chemical shifts. A good correlation between deltaG10 and the occurrence frequencies of residues Xaa at the (i + 2)th position for the beta-turns in proteins has been found.     

Control of photobleaching in photodynamic therapy using the photodecarbonylation reaction of ruthenium phthalocyanine complexes via stepwise two-photon excitation

In this study, we have investigated the photochemical properties and photodynamic effects of ruthenium phthalocyanine (RuPc(CO)(Py)) and naphthalocyanine (RuNc(CO)(Py)) complexes. When a nanosecond-pulsed laser is used, the photodecarbonylation of our Ru complexes efficiently proceeds via stepwise two-photon excitation, while the reaction yields are negligibly small when a continuous-wave (CW) laser is employed. The pulsed laser selective photodecarbonylation decreases the Q-band absorbance, which satisfies what the photodynamic therapy (PDT) requires of the photobleaching. For RuPc(CO)(Py), the photochemical reactions including both the photodecarbonylation and just photobleaching occur in HeLa cells in vitro. Toxicity and phototoxicity tests indicate that our RuPc(CO)(Py) and RuNc(CO)(Py) complexes in concentrations of 0.3-1 microM and 1-2 microM, respectively, are applicable as PDT agents. The phototoxicity is consistent with the photochemical properties of these complexes, namely, excited triplet lifetimes (10 and 4.8 micros for the Pc and Nc complexes, respectively) and singlet oxygen yields (0.48 and 0.35 for the Pc and Nc complexes, respectively). On the basis of these results, we propose a novel concept for achieving a greater depth of necrosis in PDT as follows: (1) PDT of upper cellular layers using CW-laser irradiation; (2) efficient photobleaching in upper cellular layers using pulsed dye-laser irradiation, which results in an increase in the therapeutic depth of red light; (3) PDT directed toward deeper tumor tissues using CW laser irradiation. In addition, these Ru complexes are promising as CO release agents for investigative biochemistry.