Absolute stereostructures of halenaquinol and halenaquinol sulfate,pentacyclic hydroquinones from the okinawan marine sponge xestospongia sapra, as determined by theoretical calculation of CD spectra

The absolute stereostructures of two pentacyclic hydroquinones, halenaguinol ($\text{1}$) and halenaquinol sulfate ($\text{2}$) from the Okinawan marine sponge Xestospongia sapra, have been determined by means of theoretical calculation of CD spectra.     

Photographic measurements of propagation speeds of the conducting zone in polyaniline films during electrochemical switching

In order to observe the propagation of a conducting zone of a polyaniline film in response to anodic switching, propagation perpendicular to the film surface was simulated by propagation along the film by mounting the film on an insulated plate. A polyaniline film electrochemically deposited on an indium tin oxide (ITO) electrode was reinforced by casting polymethylmethacrylate solution on the film. It was peeled off the ITO, chemically reduced and then potentiostatically oxidized at one end in 1 mol dm⁻³ H₂SO₄ solution. Dynamic growth of the conducting zone was observed through an optical microscope. A well-defined boundary between the conducting zone and the insulating zone was seen. The contrast of the boundary did not vary with the electrolysis time, the growth length or the applied potential. The growth rate decreased slightly with the electrolysis time as a result of IR drop across the film. A differential equation for growth rate involving the effect of the IR drop was presented and solved to give more accurate values of the rate. The logarithmic growth ratio exhibited a linear relation with the applied potential, indicating a charge-transfer rate of the Tafel type. The anodic transfer coefficient was 0.2 and the rate constant was 5 × 10⁻⁵ m s⁻¹. The propagation on a molecular scale was discussed on the basis of the experimental results.     

Purealin,a novel enzyme activator from the Okinawan marine sponge Psammaplysilla purea

Purealin , a novel secondary metabolite, which modurates enzymic reactions of ATPases, has been isolated from the okinawan marine sponge $\text{Psammaplysilla}$$\text{purea}$ and the structure has been determined by the ¹H-¹H homonuclear and ¹H-¹³C heteronuclear NMR chemical shift correlations and CD spectra.     

Configurational stabilization of mixed-valence states in the star-burst tetranuclear ruthenium complex bridged with acetylene links

A new tetranuclear ruthenium complex in which a metal was bridged radially to three identical metals with acetylene links showed a mixed-valence state in cyclic voltammograms. The peak potential difference for the mixed-valence state was twice the potential difference for a mixed-valence state of the corresponding binuclear complex. This fact suggests stabilization of the mixed-valence state twice by configurational modification of redox centers. However, this is inconsistent with the prediction from the additive pair model of the redox interaction. A quantum chemical model of the redox interaction was presented, in which the potential difference was expressed by the overlap integral S and the nearest neighbor interaction energy between the reduced center and the oxidized one. Application of the theory gave a negative value of S, which demonstrated reasonably the stabilization of the mixed-valence state from a quantum chemical viewpoint.     

Conformation of dithia[3.3]- and [2.2] azuleno(2,6)pyridinophanes

Four azuleno(2,6)pyridinophanes (1–4) were synthesized and their conformations were found by NMR spectroscopy to be very similar to those of the corresponding azulenometacyclophanes. A transverse conformational change was observed for [2.2](5,7)azuleno(2,6)pyridinophane.     

Inclusion of Bisphenols by Cyclodextrin Derivatives

Complexation of various kinds of bisphenols (BPs) with cycloheptaamylose(β-cyclodextrin, β-CD) derivatives (β-CD, hydroxyethyl-β-CD (HE-β-CD), 2,6-di-O-methyl-β-CD (DM-β-CD) and polymerised β-CD (L-Poly-β-CD)) was examined fluorimetrically using2-anilinonaphthalene-6-sulfonic acid (2,6-ANS) as a probe. From the inhibitory effectof BPs on the inclusion of 2,6-ANS by the β-CD derivatives, the associationconstants (K_ass) of BPs with the β-CD derivatives were determined.The K_ass values for bisphenol B (BPB) with β-cyclodextrin derivatives except for L-Poly-β-CD were always larger than those for other BPs including bisphenol A (BPA), due to the interaction between the non-polar cavity and hydrophobic BPB. Thermodynamic parameters indicated that the entropy change was always largely negative (-90～ -120 J/mol...K in the β-CD system, for example), and the inclusion of bisphenols into the CD cavity was completely enthalpy-driven. The very largely negative entropy change might be mainly due to the tight fixation of guest molecules in the CD cavity, resulting in the loss of freedom of both CD and guest molecules. The effect of the structure of guest and host molecules on the association was also examined.     

Absorption spectroscopic and ESR studies on one-electron reduction products of copper(II) and oxovanadium(IV) tetraphenylporphyrins produced by γ-radiolysis in 2-methyltetrahydrofuran solutions at 77 K

Optical absorption spectra of one-electron reduced species of copper(II) and oxovanadium(IV) tetraphenylporphyrins. Cu(II)TPP and V(IV)OTPP, in 2-methyltetrahydrofuran at 77 K reveal that not the central metal but the porphyrin ligand is reduced by an excess electron. The triplet ESR spectrum resulting from the spin-spin interaction between two odd electrons located on the porphyrin ligand and the central metal is observed for the one-electron reduced species of V(IV)OTPP while not for that of Cu(II)TPP.     

Optimization of Parameters for Cr(VI) Adsorption on Used Black Tea Leaves

Dynamic characteristics of Cr(VI) sorption on used black tea leaves (UBTLs) as a low-cost adsorbent are studied. Batch experiments were conducted to evaluate the effects of Cr(VI) concentration, solution pH and temperature on the removal process. Both of adsorption and reduction, involved in the process, are affected by the processing parameters. The adsorption kinetics is described successfully using pseudo-second order rate equation and the rate constant decreases with increasing the initial concentration of Cr(VI) up to 150 mg/L (for 0.1 g/L UBTLs) then becomes slow. Experimental and calculated kinetic data for equilibrium are well expressed by Langmuir isotherm. The solution pH has a profound effect on the adsorption rate. The rate constant increases linearly with an increase in temperature, and the low value of activation energy of adsorption, 16.3 kJ/mol, indicates that Cr(VI) is easily adsorbed on UBTLs. The maximum Cr(VI) adsorptive conditions, with a minimum reduction, were achieved from the dynamics of operational parameters: the initial Cr(VI) concentration < 150 mg/L (for 0.1 g/L UBTLs); the initial solution pH = 1.54–2.00 and the processing temperature < 50 ^∘C, for the possibility of its practical application.     

Synthesis, characterization, and detailed electrochemistry of binuclear ruthenium(III) complexes bridged by bisacetylacetonate. Crystal and molecular structures of [[Ru(acac)2]2(tae)] (acac = 2,4-pentanedionate ion, tae = 1,1,2,2-tetraacetylethanate dianion)

Binuclear beta-diketonatoruthenium(III) complexes [[Ru(acac)(2)](2)(tae)], [[Ru(phpa)(2)](2)(tae)], and [(acac)(2)Ru(tae)Ru(phpa)(2)] and binuclear and mononuclear bipyridine complexes [[Ru(bpy)(2)](2)(tae)](PF(6))(2) and [Ru(bpy)(2)(Htae)]PF(6) (acac = 2,4-pentanedionate ion, phpa = 2,2,6,6-tetramethyl-3,5-heptanedionate ion, tae = 1,1,2,2-tetraacetylethanate dianion, and bpy = 2,2'-bipyridine) were synthesized. The new complexes have been characterized by (1)H NMR, MS, and electronic spectral data. Crystal and molecular structures of [[Ru(acac)(2)](2)(tae)] have been solved by single-crystal X-ray diffraction studies. Crystal data for the meso isomer of [[Ru(acac)(2)](2)(tae)] have been confirmed by the dihedral angle result that two acetylacetone units of the bridging tae ligand are almost perpendicular to one another. A detailed investigation on the electrochemistry of the binuclear complexes has been carried out. The electrochemical behavior details of the binuclear complexes have been compared with those of the mononuclear complexes obtained from the half-structures of the corresponding binuclear complexes. Studies on the effects of solvents on the mixed-valence states of Ru(II)-Ru(III) and Ru(III)-Ru(IV) complexes have been carried out by various voltammetric and electrospectroscopic techniques. A correlation between the comproportionation constant (K(c)) and the donor number of the solvent has been obtained. The K(c) values for the binuclear complexes have been found to be low because of the fact that two acetylacetone units of the bridging tae ligand are not in the same plane, as revealed by the crystal structure of [[Ru(acac)(2)](2)(tae)].