Liquid-liquid extraction of copper(I) by cyclic tetrathio ethers

The liquid-liquid extraction of copper(I) with 12-, 13-, 15- and 16-membered cyclic tetrathio ethers ([n]aneS₄, where n represents the total number of carbon and sulphur atoms in the cyclic ligand ring) was examined stoichiometrically using picrate ion (Pic^?) for the formation of the ion pair. Copper(I) was extracted with four ligands (L) into 1,2-dichloroethane as the ion-pair compound, [Cu(I)L]⁺Pic^?. The extraction constant, K_ex, with each ligand was determined. As the ring size of cyclic tetrathio ethers increases, the log K_ex values, including that previously reported for [14]aneS₄, increase from 7.7 to 9.4. The value of Δ log K_ex, which represents the increase in log K_ex due to the addition of one carbon atom to the macrocyclic ring, was large between [13]aneS₄ and [14]aneS₄ (Δ log K_ex=1.0) and small between [14]aneS₄ and [15]aneS₄ (Δ log K_ex=0.1).     

Influence of amino acid side chain packing on Fe-methionine coordination in thermostable cytochrome C

Paramagnetic NMR and optical studies of the oxidized forms of mesophile Pseudomonas aeruginosa cytochrome c(551) and its quintuple mutant (F7A/V13M/F34Y/E43Y/V78I), and thermophile Hydrogenobacter thermophilus cytochrome c(552) demonstrated that the amino acid side chain packings in the protein interior influence the coordination bond between the heme iron and the axial methionine in the proteins. The strength of heme axial coordinations was found to correlate with the overall protein thermostability.     

Radiation-induced solid-state polymerization of trioxane under high pressure

The in-source polymerization of trioxane in the solid state was investigated over a wide range of temperature and pressure, i.e., from 30 to 140°C and up to 7000 kg/cm², respectively. In the polymerization that was carried out slightly below the melting point under pressure, the higher the pressure, the higher the rate of polymerization. It was confirmed that the maximum rate of solid-state polymerization of trioxane occurs near the melting points, even under elevated pressure. The rate of polymerization decreased with increasing pressure at constant temperature. The shape of the time–conversion curves may be classified into two types, i.e., one which is typical of high pressure and low temperature, and the other which is typical of low pressure and high temperature. Changes in the shape of the conversion—intrinsic viscosity curves occurred coincidentally. Thus, three regions for the different “polymerization characteristic” were determined as functions of polymerization temperature and pressure. Explanations are given for the above-mentioned polymerization characteristic.     

Aryl-aryl coupling reaction using a novel and highly active palladium reagent prepared from Pd(OAc)2, 1,3-bis[diphenylphosphino]propane (DPPP), and Bu3P

A palladium-assisted coupling reaction of aryl triflate with arene was investigated, and a novel Pd reagent prepared from equimolar Pd(OAc)2, 1,3-Bis[diphenylphosphino]propane (DPPP), and Bu3P was developed. This method is useful for intramolecular biaryl coupling reactions, not only between aryl triflate and arene (triflate-amide), but also between aryl halide and arene (halo-amide).     

Synthesis of stable and cell-type selective analogues of cyclic ADP-ribose, a Ca(2+)-mobilizing second messenger. Structure--activity relationship of the N1-ribose moiety

We previously developed cyclic ADP-carbocyclic ribose (cADPcR, 2) as a stable mimic of cyclic ADP-ribose (cADPR, 1), a Ca(2+)-mobilizing second messenger. A series of the N1-ribose modified cADPcR analogues, designed as novel stable mimics of cADPR, which were the 2"-deoxy analogue 3, the 3"-deoxy analogue 4, the 3"-deoxy-2"-O-(methoxymethyl) analogue 5, the 3"-O-methyl analogue 6, the 2",3"-dideoxy analogue 7, and the 2",3"-dideoxydidehydro analogue 8, were successfully synthesized using the key intramolecular condensation reaction with phenylthiophosphate-type substrates. We investigated the conformations of these analogues and of cADPR and found that steric repulsion between both the adenine and N9-ribose moieties and between the adenine and N1-ribose moieties was a determinant of the conformation. The Ca(2+)-mobilizing effects were evaluated systematically using three different biological systems, i.e., sea urchin eggs, NG108-15 neuronal cells, and Jurkat T-lymphocytes. The relative potency of Ca(2+)-mobilization by these cADPR analogues varies depending on the cell-type used: e.g., 3"-deoxy-cADPcR (4) > cADPcR (2) > cADPR (1) in sea urchin eggs; cADPR (1) > cADPcR (2) approximately 3"-deoxy-cADPcR (4) in T-cells; and cADPcR (2) > cADPR (1) > 3"-deoxy-cADPcR (4) in neuronal cells, respectively. These indicated that the target proteins and/or the mechanism of action of cADPR in sea urchin eggs, T-cells, and neuronal cells are different. Thus, this study represents an entry to cell-type selective cADPR analogues, which can be used as biological tools and/or novel drug leads.     

Kinetics of polymer translocation through a pore

We theoretically study kinetics of a polymer threading through a pore embedded in a flat membrane. We numerically solve three coupled kinetic equations for the number n(1) of polymer segments in one side of the membrane and expansion factors of the polymer chain in each side of the membrane. We find the time evolution n(1) proportional to t(1/(1+nu)) at late stages and the translocation time tau(t) is scaled as tau(t) proportional to 1+nu) for large number n of the polymer segments, where nu is the effective size exponent of the radius of gyration of the polymer. When the polymer is translocated into a region with a good solvent condition (nu=3/5), we obtain n(1) proportional to t(5/8) and tau(t) proportional to n(8/5).     

Preparation and photochromic properties of oligomeric poly(dimethylsiloxane) with the spiropyran or spirooxazine moiety in the side chain

Spirobenzopyran 1 , with the 3-(diethoxymethylsilyl)-propyl group at the N atom, was synthesized. The condensation reaction of the spiropyran 1 and diethoxydimethylsilane gave oligomeric poly(dimethylsiloxane) with the spiropyran moiety in the side chain. The oligomer was photochromic; its colour changed from colorless to purple-red on uv irradiation and the color faded on visible irradiation or on standing in the dark. The half-decay time of the thermal decoloration was about twice that of monomeric spiropyran dissolved in the dimethylsiloxane oligomer. Photochromic poly(dimethylsiloxane) with the spirooxazine moiety in the side chain was also prepared.     

Light-driven molecular hinge: a new molecular machine showing a light-intensity-dependent photoresponse that utilizes the trans-cis isomerization of azobenzene

[reaction: see text] A new class of molecular machine exhibits a hingelike motion upon photoirradiation. The motion (close and open) can be operated by alternate irradiation with UV and visible light. The trans/trans and cis/cis isomers are thermally stable at 40 degrees C, and the photochemical closure reaction (from trans/trans to cis/cis isomer) is dependent on the intensity of the light used because of the short-lived intermediate (trans/cis isomer).     

Trans-cis Photoisomerization of 1-Methyl-4-(4′-hydroxystyryl)pyridinium in inclusion complexes ofβ-cyclodextrin and its derivatives

The effects of -cyclodextrin (-CyD), heptakis(2,6-di-O-methyl)--cyclodextrin (DMCyD) and heptakis(2,3,6-tri-O-methyl)--cyclodextrin (TMCyD) ontrans-cis photoisomerization of 1-ethyl-4-(4-hydroxystyryl)pyridinium (POH) have been studied in aqueous solutions. The ratio of [cis]/[trans] for POH in the photostationary state at pH 8.54 was remarkably reduced by the presence of CyD or DMCyD. The reduction of the [cis]/[trans] ratio in the photostationary state was explained in terms of the shift of the equilibrium of POH ₊ ^trans PO _trans + H^– toward PO _trans formation. The binding constants of CyD and DMCyD for PO _trans were 2.00- and 1.36-fold larger than those for POH ₊ ^trans , respectively. The binding constants of TMCyD for both species are much smaller than those of CyD and DMCyD. This result indicates that PO _trans , which has a betain structure, forms stable complexes with CyD and DMCyD with its hydrophobic parts inside and the charged parts outside the CyD cavities.