A few comments on the internal rotations in DNA

Comments are given on the internal rotation angles in DNA molecules, their variations, and their oscillatory motions.     

Reduction‐Induced Highly Selective Uptake of Cesium Ions by an Ionic Crystal Based on Silicododecamolybdate

Cation adsorption and exchange has been an important topic in both basic and applied chemistry relevant to materials synthesis and chemical conversion, as well as purification and separation. Selective Cs⁺ uptake from aqueous solutions is especially important because Cs⁺ is expensive and is contained in radioactive wastes. However, the reported adsorbents incorporate Rb⁺ as well as Cs⁺, and an adsorbent with high selectivity toward Cs⁺ has not yet been reported. Highly selective uptake of Cs⁺ by an ionic crystal (etpyH)₂[Cr₃O(OOCH)₆(etpy)₃]₂[α‐SiMo₁₂O₄₀]?3 H₂O (etpy =4‐ethylpyridine) is described. The compound incorporated up to 3.8 mol(Cs⁺) mol(s)^?1 (where s=solid) by cation‐exchange with etpyH⁺ and reduction of silicododecamolybdate with ascorbic acid. The amount of Cs⁺ uptake was comparable to that of Prussian blue, which is widely recognized as a good Cs⁺ adsorbent. Moreover, other alkali‐metal and alkaline‐earth‐metal cations were almost completely excluded (<0.2 mol mol(s)^?1).     

Glass-state amorphous salt solids formed by freeze-drying of amines and hydroxy carboxylic acids: effect of hydrogen-bonding and electrostatic interactions

We studied effect of molecular interactions on the physical properties of binary freeze-dried solids and frozen aqueous solutions using model chemicals containing various functional groups (amino, carboxyl, hydroxyl). Thermal analysis of frozen solutions containing alkyl diamines and hydroxy di- or tricarboxylic acids showed thermal transitions (T(g)': glass transition of maximally freeze-concentrated phase) at temperatures higher than those of the individual solutes. A binary frozen solution containing 80 mM 1,3-diamino-2-hydroxypropane (single-solute T(g)'<-60 degrees C) and 120 mM citric acid (single-solute T(g)': -55.0 degrees C) made the transition at -30.8 degrees C. The molecular weight of the solutes had smaller effects on the transition temperatures of the frozen mixture component solutions. Lyophilization of some high T(g)' mixture frozen solutions (e.g., 1,3-diamino-2-hydroxypropane and citric acid) resulted in cake-structure amorphous solids with glass transition temperatures (T(g)) higher than those of the individual components. Networking of intense hydrogen-bondings and electrostatic interactions between the heterogeneous molecules through the multiple functional groups was suggested to reduce the component mobility in the amorphous freeze-concentrated phase and the freeze-dried solids. Controlling the interactions should be a key to optimizing the physical properties of multi-component amorphous freeze-dried pharmaceutical formulations.     

3-(Dimethylboryl)pyridine: synthesis, structure, and remarkable steric effects in scrambling reactions

A facile method for the synthesis of 3-(dimethylboryl)pyridine (1a) is described. Compound 1a assembles into a rigid cyclic tetramer stabilized via intermolecular boron-nitrogen coordination bonds both in the crystalline state and in solution. The outstanding structural feature of 1a, as compared with previously reported 3-(diethylboryl)pyridine (2a) (which adopts a cone conformation), is that the tetramer of 1a adopts a 1,2-alternate conformation. To investigate the effect of substituents at the boron atom on the stabilities of the oligomers, scrambling experiments of the component molecules using 1, 2, and 3-(di-n-butylboryl)pyridines 3 were carried out. Although heating at 80-90 degrees C for 20 h was required to attain the equilibrium of the scrambling reactions when the component molecules of the tetramers were 2 or 3, the scrambling in 1 proceeded under relatively mild conditions (60 degrees C, 3 h). This difference in reaction conditions required for 1, as compared to conditions required for 2 or 3, could not be explained solely by the stabilities based on bond lengths or THC. It appears that whereas only an S(N)1-type pathway may be involved in the scrambling of 2 or 3, both S(N)1- and S(N)2-type mechanisms operate simultaneously during scrambling reactions of 1 or an intermediate mechanism between S(N)1 and S(N)2 operates, which was supported by kinetic studies and calculations using model compounds.     

Methylenecyclopropanes in [4+1] cycloaddition with enones

A nickel-catalyzed [4+1] cycloaddition of enones with methylenecyclopropanes leading to dihydrofurans was developed. The reaction outcome is attributed to the transformation of methlenecyclopropane, which is incorporated into a five-membered ring as a one-carbon fragment.     

In vivo participation of artificial porphyrins in electron-transport chains: electrochemical and spectroscopic analyses of microbial metabolism

The effects of artificial porphyrins on the electron-transport chains of living microbes were investigated. The participation of porphyrins in the microbial electron-transport chains was demonstrated by spectroscopic and current-generation measurements. Large enhancement of the microbial current generation was accomplished by adding a cationic water-soluble manganese porphyrin as an electron mediator.     

Control of singlet oxygen generation photosensitized by meso-anthrylporphyrin through interaction with DNA

To control the activity of photosensitized singlet oxygen ((1)O(2)) generation, the electron donor-connecting porphyrin, 5-(9'-anthryl)-10,15,20-tris(p-pyridyl)porphyrin (AnTPyP), was designed and synthesized. AnTPyP became water-soluble by the protonation of the pyridyl moieties in the presence of 5 mM trifluoroacetic acid (pH 2.3). The photoexcited state of the porphyrin ring in an AnTPyP molecule was effectively deactivated by intramolecular electron transfer from the anthracene moiety within 0.04 ns in an aqueous solution. The deactivation was suppressed by the interaction with a DNA strand, resulting in the elongation of the lifetime of the porphyrin excited state and the enhancement of the fluorescence intensity. Furthermore, it was confirmed that the interaction enabled the photoexcited AnTPyP to generate (1)O(2). Selective (1)O(2) generation by forming a complex with DNA should be the initial step to realize the target selective photodynamic therapy.     

Dissociative Excitation of C2H2 in the Electron Cyclotron Resonance Plasma of Ar: Production of CH(A2Δ) Radicals and Formation of Hydrogenated Amorphous Carbon Films

The dissociative excitation reaction of C₂H₂ with the electron-cyclotron resonance plasma of Ar was investigated based on the electrostatic-probe measurements and on the optical emission spectroscopy of the CH(A²Δ–X²Π) transition. The density, n _e, and the temperature, T _e, of free electrons were controlled by adding H₂O molecules externally into the reaction region, and the dependence of the CH(A²Δ–X²Π) emission intensity on the addition of H₂O was observed to compare with the evaluated dependencies based on n _e and T _e. The mechanism of production of CH(A²Δ) was found, predominantly, to be the electron impact with the contribution of 10–20% of the electron-impact dissociation of C₂H radicals; the contribution of the ion–electron recombination was negligible. Hydrogenated amorphous carbon films were fabricated using the same reaction system. The atomic compositions, Raman spectra, and the hardness of films were discussed in terms of the variations of n _e and T _e upon the addition of H₂O molecules.     

Magnetic and transport properties of single-crystal Yb3Cu4Ge4

The magnetic and transport properties of single-crystal Yb₃Cu₄Ge₄ with the Gd₃Cu₄Ge₄-type orthorhombic structure are presented. Magnetization along the b-axis at 2 K saturates to 2.8_μB/Yb$2.8{\mu }_{\mathrm{B}}/\mathrm{Yb}$ at 3 kOe, while that along the a- and c-axes at 2 K are gradually increasing to the value of 1.5_μB/Yb$1.5{\mu }_{\mathrm{B}}/\mathrm{Yb}$ and 0.39_μB/Yb$0.39{\mu }_{\mathrm{B}}/\mathrm{Yb}$ at 50 kOe, respectively. The electrical resistivity within the ab-plane shows a metallic behavior in contrast to a broad maximum at around 30 K for that along the c-axis. Each resistivity for the principal axis suddenly decreases below 8 K. The specific heat shows a λ-type$\lambda \mathrm{-}\mathrm{type}$ sharp peak at 7.8 K. The electronic specific heat coefficient is estimated to be 29.4 mJ/mol Yb K² by fitting the magnetic part of the specific heat below 3 K. The magnetic entropy released up to T_C is 68% of that of R ln 2, expected for the doublet ground state. It is revealed that Yb₃Cu₄Ge₄ is categorized to a weak heavy-fermion system showing a ferromagnetic transition at 7.8 K with uniaxial anisotropy along the b-axis.