Light-harvesting heptadecameric porphyrin assemblies

New porphyrin assemblies containing 17 porphyrin molecules are constructed by using free base TPP-type porphyrins having eight pyrazine moieties 1. Spectroscopic titration of dimeric [meso-tetrakis(2-carboxy-4-nonylphenyl)porphyrinato]zinc(II) 2 with these porphyrins shows that the processes of the formation of the heptadecameric porphyrin assemblies may be analyzed as eight independent equilibrium processes with an identical binding constant. All binding constants are larger than 5 x 107 M-1 which is the determinable upper limit of the present titration method. In all cases, the fluorescence spectrum of the 1:8 mixture of 1 and 2 consists of the major fluorescence of 1 and the minor one of 2.pyrazine complex even in the presence of the large excess of the antenna pigments. The observed spectra are well reconstructed by the form of faF1 + fbF2, where F1 and F2 are the fluorescence of 1 and the 2.pyrazine complex measured separately at the corresponding concentrations. Interestingly, the general trend that values of fa are nearly equal to those of r564 x (1 - fb) in all cases is found, where r564 is the absorption ratios of the 2.pyrazine moiety and the central free base porphyrin in the assemblies at 564 nm. The observation indicates the excitation of the central porphyrin is directly enhanced by the absorption of the antenna pigments even in such large scale assemblies. Thus, the antenna effect for 1 having largest r564 results in 77 times fluorescence enhancement of the central free base porphyrin. The systems also show interesting dependency of energy-transfer efficiencies on the topological arrangement of the antenna elements.     

Strong two-photon absorption of self-assembled butadiyne-linked bisporphyrin

Two-photon absorption (2PA) properties of self-assembled porphyrins were investigated. The butadiyne-linked porphyrin array exhibited a 20 times larger 2PA cross section than the meso-meso-linked self-assembled array due to the expansion of pi-conjugation. Higher-order nonlinear absorption was also observed in the former porphyrin.     

Estimated ionicB-coefficients from NMR measurements in aqueous electrolyte solutions

¹⁷O-NMR spin-lattice relaxation timesT ₁ of D₂O molecules were measured at 5–85°C in D₂O solutions of alkali metal halides (LiClCsCl, KBr, and KI), DCl, KOD, Ph₄PCl, NaPh₄B, and tetraalkylammonium bromides (Me₄NBrAm₄NBr) in the concentration range 0.1–1.4 mol-kg^–1 TheB-coefficients of the electrolytes obtained from the concentration dependence of relaxation ratesR ₁=1/T₁ were divided into the ionicB-coefficients by three methods: (i) the assumption ofB (K⁺)=B(Cl^–), (ii) the assumption ofB(Ph₄P⁺)=B(Ph₄B^–), and (iii) the use ofB(Br^–) obtained from a series ofB(R₄NBr). It was found that Methods (ii) and (iii) resulted in an abnormal temperature dependence of theB-coefficients of alkali metal ions and a negative values of rotational correlation times _c at lower temperatures for hydroxide and halide ions. These results suggest that the methods based on the van der Waals volume are not adequate for the ionic separation of NMRB-coefficients. From the analysis using the assumption ofB(K⁺)=B(Cl^–), it was found that D₃O⁺, OD^–, and Me₄N⁺ ions are the intermediates between structure makers and breakers, and that the hydrophobicity of phenyl groups is weaker than that of alkyl groups due to the interactions between water molecules and -electrons in phenyl groups.     

Artificial membranes from multiblock copolymers. : I. Fabrication of a charge-mosaic membrane and preliminary tests of dialysis and piezodialysis

We succeeded in preparing a charge-mosaic membrane from pentablock copolymers of the BABCB type by selectively introducing anion- and cation-exchange groups into the separated microphases. The three-layer lamellar structure of the starting pentablock copolymer film was not disturbed by the modifications. The membrane obtained showed a piezodialytic effect for aqueous solutions of sodium chloride. It also showed a high permeability for sodium chloride only in aqueous solutions of sodium chloride mixed with non-electrolytes such as saccharose. Marked pH-dependent permeabilities were also observed for amino acids.     

The basic research on physiological property of functionalized hyaluronan—I. Effect of hyaluronan and sulfated hyaluronan on cell proliferation of human epidermal keratinocytes

Hyaluronan (HA) is one of the polysaccharides that is found widely in connective tissue of mammals, and it has no sulfate group and high molecular weight in comparison with other glycosaminoglycans. Glycosaminoglycans are deeply concerned with the manifestation of biofunctions not only by their physical properties but also by physiological ones. In this study, sulfated HA (S‐HA) with various degrees of sulfate substitution and high molecular weight will be synthesized in order to give HA new biological functions. Moreover, the effect of HA and S‐HA on cell proliferation of human epidermal keratinocytes in vitro will be discussed. HA did not affect lag phase, but growth rate (metabolic turnover) of the cell in a logarithmic growth phase which was controlled by the molecular weight of HA. S‐HA stimulated the cell proliferation in the low concentration region under 1 μg/ml. While it inhibited the cell proliferation in the high concentration region over 10 μg/ml. It strongly suppressed the cell proliferation in the logarithmic growth metaphase. These facts were considered to be caused by the change of the cell‐matrix and/or cell–cell interactions. Copyright © 2004 John Wiley & Sons, Ltd.     

Gallium-mediated allyl transfer from bulky homoallylic alcohol to aldehydes via retro-allylation: stereoselective synthesis of both erythro- and threo-homoallylic alcohols

Retro-allylation of bulky gallium homoallylic alkoxides occurs to generate (Z)- and (E)-crotylgallium reagents stereospecifically, starting from erythro- and threo-homoallylic alcohols, respectively. The (Z)- and (E)-crotylgallium reagents immediately reacted with aromatic aldehydes to afford the corresponding erythro- and threo-homoallylic alcohols, respectively. [reaction: see text]     

Chiral bis(amino alcohol)oxalamide gelators-gelation properties and supramolecular organization: racemate versus pure enantiomer gelation

Four new chiral bis(amino alcohol)oxalamides (1-4: amino alcohol=leucinol, valinol, phenylglycinol, and phenylalaninol, respectively) have been prepared as low-molecular-weight organic gelators. Their gelation properties towards various organic solvents and mixtures were determined and these were then compared to related bis(amino acid) oxalamide gelators. Spectroscopic (FTIR, (1)H NMR) and X-ray diffraction studies revealed that the primary organization motif of (S,S)-1 and racemate 1 (rac-1) in lipophilic solvents involved the formation of inverse bilayers. The X-ray crystal structure of (S,S)-1 also shows this type of bilayer organization. The crystal structure of rac-2 reveals meso bilayers of hydrogen-bonded aggregates. Within the bilayers formed, the gelator molecules are connected by cooperative hydrogen bonding between oxalamide units and OH groups, while the interbilayer interactions are realized through lipophilic interactions between the iBu groups of leucinol. Oxalamide meso-1 lacks any gelation ability and crystallizes in monolayers. In dichloromethane rac-1 forms an unstable gel; this is prone to crystallization as a result of the formation of symmetrical meso bilayers. In contrast, in aromatic solvents rac-1 forms stable gels; this indicates that enantiomeric bilayers are formed. Oxalamide rac-1 is capable of gelling a volume of toluene three times larger than (S,S)-1. A tranmission electron microscopy investigation of rac-1 and (S,S)-1 toluene gels reveals the presence of thinner fibers in the former gel, and, hence, a more compact network that is capable of immobilizing a larger volume of the solvent. The self-assembly of these types of gelator molecules into bilayers and subsequent formation of fibrous aggregates can be explained by considering the strength and direction of aggregate forces (supramolecular vectors) in three-dimensional space.     

Effect of growth substrates on production of new soluble glucose 3-dehydrogenase in Halomonas (Deleya) sp. α-15

Halomonas (Deleya) sp. α-15 produces new co-factor binding soluble glucose 3-dehydrogenase (G3DH), which oxidizes the third hydroxy group of pyranose. This study investigated the condition of efficient production of G3DH using Halomonas (Deleya) sp. α-15. This enzyme was inducible, and α-methyl-D-glucoside, isopropyl-thioga lactopyranoside (IPTG) and lactose were revealed to be suitable carbon sources for G3DH induction. Maximum G3DH production was achieved by using minimal medium containing 0,8% (w/v) lactose with a productivity of 470U/1.     

Macroporous ZrO2 ceramics prepared from colloidally stable nanoparticles building blocks and organic templates

ZrO2 macroporous materials with well-ordered structures were prepared using nano-ZrO2 particles as the building materials and polystyrene spheres as the organic templates. A well-dispersed nano-ZrO2 suspension with a narrow particle size distribution was prepared by deagglomeration of as-received nano-ZrO2 powders via ultrasonication, and then centrifugation was performed to remove agglomerated bigger particles. Negatively charged polystyrene spheres were uniformly coated with positively charged nano-ZrO2 particles by means of electrostatic attraction at pH 4. Green samples were prepared by slip casting from colloidally stable suspension of nano-ZrO2 coated polystyrene spheres. ZrO2 macroporous materials with well-ordered microstructure derived from the nano-ZrO2 coated polystyrene spheres.     

A new carotenoid,halocynthiaxanthin from the sea squirt, halocynthiaroretzi

A new carotenoid, halocynthiaxanthin (5,6-epoxy-3,3′-dihydroxy-7′,8′-didehydro-5,6,7,8-tetrahydro-β,β-caroten-8-one) has been isolated from the Japanese sea squirt, $\text{Halocynthia}$ roretzi.