In vitro and in vivo stability of polymerized mixed liposomes composed of 2,4‐octadecadienoyl groups of phospholipids

The in vitro stability, under freeze–thawing procedures, and in vivo degradation, in rat spleen, of two types of polymerized liposomes were examined: 1,2‐bis‐[2E, ­4E) ‐ octadecadienoyl] ‐ sn ‐ glycero ‐ 3 ‐ phosphocholine (DODPC) and 1‐acyl‐2‐[(2E, 4E)‐octadecadienoyl]‐sn‐glycero‐3‐phosphocholine (AODPC) were used as polymerizable phospholipids. The lipid composition of the liposomes was prepared as DODPC/Chol/SA (Chol = cholesterol, SA = stearicacid), AODPC/Chol/SA (7/7/2 by molar ratio), AODPC/DPPC/Chol/SA (3.5/3.5/7/2 by molar ratio). The liposomes were extruded through a 0.2 µm polycarbonate‐ filter to obtain the approximate particle size of 0.2 µm, and then irradiated with γ‐rays. Hemoglobin‐encapsulated liposomes were also prepared in the same manner with concentrated hemoglobin (Hb) solution. The DODPC/Chol/SA liposome exhibited no trace of particle size change nor Hb leakage. Although not as excellent as the former, the AODPC‐base liposome showed slightly diameter change (below 7.5%) with a substantial abatement of Hb leakage (<3.5%). Transmission electron microscopy observation of spleens also revealed more efficient degradability with AODPC/DPPC/Chol/SA liposome than with DODPC/Chol/SA liposome. Hb‐encapsulated AODPC/DPPC/Chol/SA liposome, after five freeze–thawing cycles, attained an Hb leakage below 3.5% with a particle size change of 0.7–7.5%, and reduced the spleen retention compared with the DODPC‐base liposome. These results suggest that AODPC/DPPC/Chol/SA liposome can be used as a long‐term preservable blood substitute. Copyright © 2000 John Wiley & Sons, Ltd.     

High capacity technology of nickel‐metal hydride batteries

The nickel‐metal hydride battery has been recognized as an important power source for various cordless appliances since its commercialization in 1990. Therefore, demands for capabilities of the batteries have been increasing. A key technology to meet these demands is improvement of the electrode materials. This work is focused on improving composition and microstructure of the bulk and surface states of hydrogen‐absorbing alloys used as the negative electrode material and the composition of the nickel hydroxide and additives used for the positive electrode.     

Polysilane spherulites and their high photoluminescence quantum yields

Large polysilane spherulites have been observed. The spherulites were prepared by controlling the removal rate of solvents from poly(n-butyl-n-pentylsilane) under a xylene atmosphere. The diameter of the spherulites was greater than 0.1 mm. The structure of the spherulites was compared with that of the polysilane powder by polarized microscopy, SEM, DSC, and x-ray diffractometry. A high photoluminescence quantum yield of 0.3 was obtained for the spherulites. © 1997 John Wiley & Sons, Inc.     

Thermally stable organic electroluminescent device using novel amorphous molecular charge-transport materials, 4,4′,4“-tris[bis(4′-tert-butyl-biphenyl-4-yl)amino]triphenylamine and 4,4,4“-tri(n-carbazolyl)triphenylamine

For the purpose of developing an amorphous molecular material with a high glass-transition temperature (Tg) and a low ionization potential for use as a charge-transport layer in organic electroluminescent (EL) devices, a novel starburst molecule, 4,4′,4“-tris[bis(4′-tert-butylbiphenyl-4-yl)amino]triphenylamine (t-Bu-TBATA), was designed and synthesized. t-Bu-TBATA was found to form readily a stable glass with a Tg of 203 °C. A multilayer EL device consisting of double hole-transport layers of t-Bu-TBATA and 4,4′,4“-tri(N-carbazolyl)triphenylamine and an emitting layer of tris(8-quinolinolato)aluminum was fabricated and its performances were examined. The device was found to exhibit good performances and to be thermally stable, operating even at 170 °C.     

Preparation of rapidly curable hydrogels from gelatin and poly (carboxylic acid) and their adhesion to skin

Papidly curable hydrogels were prepared through chemical crosslinking of gelatin with poly(carboxylic acid)s including poly (L-glutamic acid) (PLGA), hyaluronic acid (HA), and poly (acrylic acid) (PAA) by use of water-soluble carbodiimide (WSC). The effects of the nature of added poly (carboxylic acid)s on gelation of mixed gelatinpoly (carboxylic acid) aqueous solutions and adhesion of the resulting hydrogels to the mouse skin were evaluated. The addition of poly (carboxylic acid) s reduced the gelation time of gelatin aqueous solutions except for HA. Mixed gelatin-PLGA solutions were cured more rapidly than other mixed solutions and the gelation time was shortened with the increasing PLGA molecular weight. The resulting gelatin-PLGA hydrogels exhibited stronger adhesion to the mouse skin than gelatin-HA and gelatin-PAA hydrogels. The bonding strength increased with the increase in PLGA molecular weight up to 83,000 and thereafter decreased. The longer gelation time and lower adhesion of the gelatin-PAA hydrogels than the gelatin-PLGA hydrogels seem to be due to poorer compatibility of gelatin with PAA than with PLGA. The mixed gelatin-PLGA solution underwent phase separation when the concentration and molecular weight of PLGA became higher than a threshold. The insignificant or suppressive effect of HA addition might be ascribed to the HA-WSC reaction which was the least effective in hydrogel formation.     

Synthesis of [2-C]-oleanolic acid and [2-C]-myricerone

Synthetic way for ¹³C-labeled oleanolic acid 1 and myricerone 2 has been developed, starting from the parent 1 and 2. The procedure involves ring opening and closure of the A rings of these oleanane triterpenes. ¹³C was introduced into the 2-position by ¹³C-MeLi as an isotope source. Chelation controlled addition of methyllithium to -hydoxypentanone 11 is a common crucial step for labeling of 1 and 2, and judicious choice of protecting groups is essential for 2.     

Windmill-Like Porphyrin Arrays as Potent Light-Harvesting Antenna Complexes

Up to 14 porphyrin rings are present in the title compounds 1 , which are readily available with high regioselectivity from linear nickel–zinc porphyrins. Upon irradiation with light a rapid energy transfer from the peripheral porphyrin rings to the diporphyrin core takes place.     

Theoretical study of the π→π* excited states of linear polyenes: The energy gap between 11Bu+ and 21Ag− states and their character

Multireference perturbation theory with complete active space self-consistent field (CASSCF) reference functions is applied to the study of the valence π→π* excited states of 1,3-butadiene, 1,3,5-hexatriene, 1,3,5,7-octatetraene, and 1,3,5,7,9-decapentaene. Our focus was put on determining the nature of the two lowest-lying singlet excited states, 1¹B_u⁺ and 2¹A_g⁻, and their ordering. The 1¹B_u⁺ state is a singly excited state with an ionic nature originating from the HOMO→LUMO one-electron transition while the covalent 2¹A_g⁻ state is the doubly excited state which comes mainly from the (HOMO)²→(LUMO)² transition. The active-space and basis-set effects are taken into account to estimate the excitation energies of larger polyenes. For butadiene, the 1¹B_u⁺ state is calculated to be slightly lower by 0.1 eV than the doubly excited 2¹A_g⁻ state at the ground-state equilibrium geometry. For hexatriene, our calculations predict the two states to be virtually degenerate. Octatetraene is the first polyene for which we predict that the 2¹A_g⁻ state is the lowest excited singlet state at the ground-state geometry. The present theory also indicates that the 2¹A_g⁻ state lies clearly below the 1¹B_u⁺ state in decapentaene with the energy gap of 0.4 eV. The 0–0 transition and the emission energies are also calculated using the planar C_2h relaxed excited-state geometries. The covalent 2¹A_g⁻ state is much more sensitive to the geometry variation than is the ionic 1¹B_u⁺ state, which places the 2¹A_g⁻ state significantly below the 1¹B_u⁺ state at the relaxed geometry. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66 : 157–175, 1998     

Asymmetric anionic polymerization of (2-fluorophenyl)(4-fluorophenyl)(2-pyridyl)methyl methacrylate leading to a helical polymer

A novel racemic methacrylate, (2-fluorophenyl)(4-fluorophenyl)(2-pyridyl)-methyl methacrylate¹ (2F4F2PyMA), was synthesized and polymerized with chiral complexes of N,N′-diphenylethylenediamine monolithium amide (DPEDA-Li) with (−)-sparteine (Sp), (2S, 3S)-(+)-2,3-dimethoxy-1,4-bis(dimethylamino)butane (DDB), and (S)-(+)-1-(2-pyrrolidinylmethyl)pyrrolidine (PMP) in toluene at −78°C. The monomer showed higher resistance against methanolysis compared with triphenylmethyl methacrylate (TrMA) and several other analogues. In the asymmetric anionic polymerization of 2F4F2PyMA, PMP was found to be a more effective chiral ligand than DDB and Sp and gave quantitatively an optically active polymer with nearly perfect isotacticity. Enantiomer selection was observed in the polymerization of racemic 2F4F2PyMA with the chiral lithium complexes. Chiral recognition ability of the optically active poly(2F4F2PyMA) was examined by an enantioselective adsorption experiment. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2013–2019, 1998     

Synthesis of carbosilane block copolymers by means of a living anionic polymerization of 1,1-diethylsilacyclobutane

Block polymerization of 1,1-diethylsilacyclobutane with styrene derivatives and methacrylate derivatives was investigated. Sequential addition of styrene to a living poly(1,1-diethylsilabutane), which was prepared from phenyllithium and 1,1-diethylsilacyclobutane in THF–hexane at −48°C, gave poly(1,1-diethylsilabutane)-b-polystyrene. Similarly, addition of 4-(tert-butyldimethylsiloxy)styrene to the living poly(1,1-diethylsilabutane) provided poly(1,1-diethylsilabutane)-b-poly(4-(tert-butyldimethylsiloxy)styrene). Poly(1,1-diethylsilabutane)-b-poly(methyl methacrylate) was obtained by treatment of living poly(1,1-diethylsilabutane) with 1,1-diphenylethylene followed by an addition of methyl methacrylate. Poly(1,1-diethylsilabutane)-b-poly(2-(tert-butyldimethylsiloxy)ethyl methacrylate) was also synthesized by adding 2-(tert-butyldimethylsiloxy)ethyl methacrylate to the living poly(1,1-diethylsilabutane) which was end-capped with 1,1-diphenylethylene in the presence of lithium chloride. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2699–2706, 1998