Showing papers by "Tokyo University of Science published in 1995"

Formation of Polyion Complex Micelles in an Aqueous Milieu from a Pair of Oppositely-Charged Block Copolymers with Poly(ethylene glycol) Segments

Abstract: Stable and monodispersive polyion complex micelles were prepared in an aqueous milieu through electrostatic interaction between a pair of oppositely-charged block copolymers with poly(ethylene glycol) segments : poly(ethylene glycol)-poly(L-lysine) block copolymer (PEG-P(Lys)) and poly(ethylene glycol)-poly(α,β-aspartic acid) block copolymer (PEG-P(Asp)). It was confirmed from photon correlation spectroscopy (dynamic light scattering) that the scaled average characteristic line width (Γ/K 2 ) was independent of the magnitude of the scattering vector (K 2 ), and the diffusion coefficient (D T ) kept constant regardless of the concentration, indicating that the polyion complex micelles were spherical particles without any secondary aggregates. Further, polydispersity indexes (μ2/Γ 2 ) were always less than 0.1 in the range of the measured concentration (1-10 mg/mL). The hydrodynamic radius at infinite dilution of polyion complex micelles was then determined to be 15.2 nm by using the Stokes-Einstein equation. The unimodal size distribution with d w /d n of 1.07 was confirmed from the correlation function profile by the histogram analysis. The size of polyion complex micelles was unchanged even after a 1-month storing, suggesting that the polyion complex micelles are in thermodynamic equilibrium. Viscosity measurement as well as laser-Doppler electrophoresis provided evidence of the stoichiometry of the polyion complex micelles formation. These polyion complex micelles have potential utility as vehicles for charged compounds, i.e., proteins and nucleic acids, in the field of drug delivery.

Spontaneous Vesicle Formation from Aqueous Solutions of Didodecyldimethylammonium Bromide and Sodium Dodecyl sulfate Mixtures

Abstract: Spontaneous vesicle formation in the aqueous mixture of didodecyldimethylammonium bromide (DDAB) and sodium dodecyl sulfate (SDS) has been investigated with differential interference microscopy, transmission electron microscopy, glucose trapping experiments, ζ potential measurements, and surface tension measurements. The micrographs of the DDAB-SDS mixtures confirm the spontaneous formation of polydispersed vesicles including giant vesicle with a diameter less 40 μm. The captured volume of the DDAB -SDS mixtures is 2.2 L/mol at the SDS mole fraction (X SDS ) of 0.64 and decreases with increasing X SDS . Vesicle formation in DDAB-SDS mixtures will occur in the X SDS range of 0.64-0.75, below the total surfactant concentration of 2.2 wt %. Surface tension measurements for the mixtures exhibit very low values, 23 mN/m, indicating the ion-pairing of DDAB and SDS, a pseudo-zwitterionic surfactant. This surfactant favors the morphology of a vesicle. The mechanism of vesicle self-formation is the penetration of SDS into the DDAB molecules. In addition, spontaneous vesicles are also formed in the mixture of DDAB and sodium decyl sulfate.

A Novel Reactive Polymeric Micelle with Aldehyde Groups on Its Surface

Abstract: It is reported that amphiphilic AB block copolymers form in selective solvents micellar structures.' These nanospheric particles combine the advantages given by the hydrophobic core, which can act as a vehicle for medical drugs, and the unique properties of a hydrophilic ~ h e 1 1 . ~ ~ PEO chains attached to a surface or forming the corona of a nanospheric particle in an aqueous medium exhibit rapid chain motions and have a large excluded volume. The steric repulsion resulting from a loss of configurational entropy of the bound PEO upon the approach of a foreign particle and the low interfacial free energy contribute to the extraordinary properties of PEO-covered surface^.^-'^ The small size, apparent thermodynamic stability, and exceptional biological features of polymeric micelles favor their application in the biomedical field.11-14 Recently, a facile and quantitative synthetic method for the formation of heterobifunctional poly(ethy1ene oxide) was reported.15J6 If one of the functional end groups in the heterobifunctional PEO can selectively initiate the polymerization of a hydrophobic monomer, a new heterobifunctional AB block copolymer can be created, retaining the other functional group (acetal group) a t the PEO chain end. As a core-forming segment, polylactide (PLA) was chosen for the following reasons: (1) The ring-opening reaction of a lactide can be initiated by the living chain end of potassium ethylene oxide without any side reaction. (ii) PLAS are biodegradable and nontoxic polymers, which are widely utilized as implant materials. This is an important prerequisite considering a future application of this system in the biomedical field. (iii) Nanoparticles, consisting of block copolymers of a-methoxypoly(ethy1ene oxide) and PLA are suited for drug de1i~ery.l~ Furthermore, the micelle formation and transformation of acetal into aldehyde groups on the micelle surface were discussed. An aldehyde group reacts rapidly with primary amino groups, forming a Schiff base, a chemical path which could be employed in the hture for conjugations with proteins. Experimental Section. Materials and Methods. Commercial tetrahydrofuran (THF), 3,3-diethoxypropanol, ethylene oxide (EO), and lactide were purified conventionally.l8 Potassium naphthalene was used as a THF solution.1g GPC measurements were carried out using a Shimadzu 6A liquid chromatograph equipped with a PEO-calibrated TSK gel column (G4000HXL, G3000HXL, G2500HXL) and an internal RI detector (RID-6A). THF containing 2% of triethylamine was used as eluent a t a flow rate of 1 mumin. 'H-NMR

Solubilization of Some Synthetic Perfumes by Anionic-Nonionic Mixed Surfactant Systems. 1

Abstract: The solubilization of synthetic perfumes (eugenol, linalool, benzyl acetate, α-ionone, α-hexylcinnamaldehyde, and d-limonene) by sodium dodecyl sulfate (SDS)/hexadecyl poly(oxyethylene) ethers (C 16 POE 20 ) mixed surfactants has been studied by measurement of the maximum additive concentration (MAC) and the distribution coefficient between the micellar and bulk phase (K). The MAC of the perfume at any mole fraction of C 16 POE 20 increases with the hydrophilicity of the perfume. The MAC of the more hydrophilic perfume in the mixed systems is smaller than the calculated MAC (assuming additivity) because of hydrophilic-hydrophilic interactions between the head groups of anionic and nonionic surfactants in the mixed micelle. On the other hand, the radius of the mixed micelle in these systems is large compared to the radii of pure component micelles, causing the MAC values of the less hydrophilic perfumes in the mixed systems to be larger than the calculated MAC. Moreover, the values ofKfor each perfume in the mixture ofthe surfactants are smaller than the ideal K values ; this effect increases with a decrease in the hydrophilicity of the perfume, except in the case of d-limonene. The magnitude of these changes in K values in the surfactant mixtures depends on the relative importance of surfactant-surfactant and surfactant-perfume interactions.

Langmuir-Blodgett film of amphiphilic C60 carboxylic acid

Abstract: An amphiphilic C 60 molecule with a substituent having a hydrophilic carboxylic group at the end was found to form a monolayer at the air-water interface and the structure of the Langmuir-Blodgett (LB) film (Z-type) was elucidated. The shortest distance between the C 60 was estimated to be 0.95 nm using a limiting area per molecule of 0.78 nm 2 at the air-water interface, assuming the close packing of the C 60 moiety in two dimensions. Adjacent C 60 moieties have an electronic interaction which was shown in the red-shift of the characteristic bands in the UV/vis absorption spectrum of the LB film compared with that of a solution spectrum. Several lines of evidence suggested that the molecule has an oblique orientation in the LB film and exists in a pairwise manner due to the dimer formation of the carboxylic groups within a monolayer, not between the adjacent monolayers. The AFM observations revealed that the surface of a single-layer LB film, which consists of domains of ca. 0.1 μm in diameter, is rather smooth and that the undulation is ±1 nm for most of the surface except for defects such as vacancy and bilayer regions. The area fractions of the monolayer, the vacancy, and the bilayer regions were estimated to be 88 ± 7, 7 ± 5, 5 ± 3%, respectively. The layer structure was also confirmed using X-ray diffraction analyses which indicate the repeat distance of ca. 2.6 nm along the surface normal of the multilayer LB film.

Preparation of Ferroelectric Bi4Ti3O12 Thin Films with c-Axis Orientation by Atmospheric-Pressure Metal-Organic Chemical Vapor Deposition

Abstract: Ferroelectric Bi4Ti3O12 thin films were prepared by the metal-organic chemical vapor deposition (MOCVD) method at atmospheric pressure using Bi( o-C7H7)3 and Ti( i-OC3H7)2(DPM)2 as metalorganic sources Assist Ar gas flow rate effects on the growth of the thin films were also examined Thin films obtained were characterized by XRD analysis, SEM, AFM and D-E hysteresis loop observations Most of the single-phase Bi4Ti3O12 thin films with c-axis orientation were deposited on Pt/Ti/SiO2/Si and Pt substrates above 500° C Completely c-axis-oriented Bi4Ti3O12 thin films were prepared on Pt plates at 600° C, which showed good ferroelectric properties: remanent polarization of 10 µ C/cm2, coercive field of 18 kV/cm and leakage current on the order of 10-9 A/cm2

Excitonic emissions from CuInSe2 on GaAs(001) grown by molecular beam epitaxy

Abstract: CuInSe2 epitaxial films grown on (001)‐oriented GaAs substrates by molecular beam epitaxy have been characterized by means of low temperature photoluminescence spectroscopy at T=2–102 K. Distinct emission lines were observed near the band gap, and have been investigated further with varying sample temperature. An emission at 1.0386 eV (EX1) became broader with increasing sample temperature, and still remained up to T=102 K. A distinct, sharp emission at 1.0311 eV (IX1) which disappeared at a significantly lower temperature than the other peaks was observed only in films with weak donor‐related emissions. We attribute such emissions to the ground‐state free exciton [FEn=1] and exciton bound to neutral acceptor [A0,X], respectively. The band gap of CuInSe2 epitaxial films was also determined to be Eg=1.046 eV at 2 K using the reported exciton binding energy of Eex=7 meV.

Global existence of small solutions to the Davey-Stewartson and the Ishimori systems

Abstract: We study the initial-value problems for the Davey-Stewartson systems and the Ishimori equations. Elliptic-hyperbolic and hyperbolic-elliptic cases were treated by the inverse scattering techniques ([2--4, 10, 13--15, 32] for the Davey-Stewartson systems and [28, 29, 33] for the Ishimori equations). Elliptic-elliptic and hyperbolic-elliptic cases were studied (in [16, 17] for the Davey-Stewartson systems and [31] for the Ishimori equations) without the use of the inverse scattering techniques. Existence of a weak solution to the Davey-Stewartson systems for the elliptic-hyperbolic case is also obtained in [16] with a smallness condition on the data in $L^2$ and a blow-up result was also obtained for the elliptic-elliptic case. By using the sharp smoothing property of solutions to the linear Schrodinger equations the local existence of a unique solution to the Davey-Stewartson systems for the elliptic-hyperbolic and hyperbolic-hyperbolic cases was established in [30] in the usual Sobolev spaces with a smallness condition on the data. We prove the local existence of a unique solution to the Davey-Stewartson systems for the elliptic-hyperbolic and hyperbolic-hyperbolic cases in some analytic function spaces without a smallness condition on the data. Furthermore we prove existence of global small solutions of these equations for the elliptic-hyperbolic and hyperbolic-hyperbolic cases in some analytic function spaces.

Novel pH-sensitive hydrogels of segmented poly(amine ureas) having a repetitive array of polar and apolar units in the main chain

Abstract: The pH-responsive swelling/deswelling of novel segmented poly(amine ureas) (SPAU) with a repetitive array of polar (N,N'-diethylethylenediamine) and apolar (diethylenephenylene) units in the main chain was examined as a function of ionic strength and temperature. An end-isocyanated polyamine was prepared by the 2:1 addition reaction of 4,4'-methylenediphenyldiisocyanate (MDI) to telechelic polyamine having secondary amino groups at both ends. The isocyanated polyamine was extended by the reaction with equimolar ethylenediamine to form a segmented poly(amine urea) (SPAU). The SPAU exhibited reproducible swelling/deswelling in response to pH changes. A discontinuous 270-fold change in the swelling degree was observed at a critical pH, indicating a phase transition. The shift of ethylenediamine units to the trans conformation on double protonation may play a role in the swelling transition through a stiffening of the polymer strands. The hysteresis observed in the swelling/deswelling cycle in water at 30 o C disappeared upon addition of 0.05 M NaCl or upon lowering of the temperature to 4 o C. The regulation of solute transport across the SPAU matrix responding to a change in external pH was demonstrated using vitamin B 12 as a model solute, suggesting the formation of a barrier layer at the surface of the film that stopped solute diffusion at high pH. SPAUs can be cast on substrates of any shape, providing mechanically strong pH-responsive surface coatings

Photoluminescence studies in CuAlSe2 epilayers grown by low‐pressure metalorganic chemical‐vapor deposition

Abstract: Low‐temperature photoluminescence (PL) spectra were investigated for CuAlSe2 epilayers grown on GaAs(001) substrates by means of low‐pressure metalorganic chemical‐vapor deposition. PL properties were studied with relation to metalorganic precursors used for the growth. High‐quality undoped epilayers exhibited PL peaks related to a free exciton (2.739 eV) and a bound exciton (2.677 eV). The other undoped epilayers exhibited PL bands at 2.3, 2.4, and 2.5 eV originating from donor‐acceptor (D‐A) pair recombinations. Some of them were found to have a common activation energy for the thermal quenching of 50±10 meV. The PL spectrum changed drastically by impurity doping. Intense green emissions at 2.51 and 2.43 eV were observed in Zn and Mg‐doped epilayers, respectively, which were interpreted as D‐A pair recombinations based on the dependencies of the PL spectra on excitation intensity, decay time, and temperature. The donor and the acceptor activation energies (ED and EA) were estimated to be 110 and 230 meV...

Solving combinatorial optimization problems by nonlinear neural dynamics

Abstract: The new approach for combinatorial optimization problems using chaotic dynamics is discussed. We show effectiveness of chaotic neuro dynamics for solving combinatorial optimization problems by applying the chaotic neural network to traveling salesman problems. In this paper, we adopt the chaotic neural network model with two internal states, corresponding to mutual interactions which minimize an energy function and refractoriness which induce chaotic dynamics. We investigate relationships between solving abilities and different model parameters such as decay parameters of two internal states, Lyapunov exponents and first order statistics of firing patterns.

Heteroepitaxial Growth of CuGaS 2 Layers by Low-Pressure Metalorganic Chemical Vapor Deposition

Abstract: Heteroepitaxial growth of CuGaS2 was studied by low-pressure metalorganic chemical vapor deposition using normal-tripropylgallium as a new Ga precursor, combined with cyclopentadienylcoppertriethylphosphine and ditertiarybutylsulfide. Structural and optical properties were characterized in detail. The epilayer showed the c[001]-oriented growth on both GaAs(001) and GaP(001) substrates. The lattice parameter c of the epilayers was smaller than that of the bulk single crystal. Magnitude of the residual lattice strain for CuGaS2/GaP(001) was found to be larger than that for CuGaS2/GaAs(001), even though the lattice mismatch for the former was smaller than that for the latter. The strain is considered to be introduced during cooling after the growth. A photoluminescence peak at 2.493 eV (8 K) was assigned to a free exciton emission, because the peak energy agreed with A-exciton energy obtained from photoreflectance spectra.

Nuclease activity of a hydroxamic acid derivative in the presence of various metal ions

Abstract: Phenanthridine-linked hydroxamic acid 1 effectively cleaves ColE1 DNA in the presence of transition (ferrous, ferric and vanadyl) or lanthanide(III)(lutetium, thulium and europium) metal ions; in the presence of the former, the cleavage is inhibited by free radical scavengers, but in the latter case it is not.

Changes in Genetic and Enzymatic Inhibiting Effects of Organophosphorus Pesticides during Aqueous Chlorination

Abstract: Chlorine is widely used as a disinfectant in water treatment and in the food industry. Five organophosphorus pesticides (EPN, diazinon, fenitrothion, malathion and parathion) were, therefore, subjected to aqueous chlorination with hypochlorite to evaluate inhibitory effect on cholinesterase (ChE) activity and mutagenic effect of these reaction products. Treatment with hypochlorite of thiophosphorus (P=S) pesticide solutions was shown to produce compounds with a great inhibiting effect on ChE activity, but, further reactions resulted in decrease in the ChE inhibiting activity. Aqueous chlorination with hypochlorite of these P=S compound solutions was also shown to produce compounds with mutagencity onS. typhimuriumTA98 without S9 mix. The production of mutagens is dependent on the parent pesticides, the solution pH values, and the reaction time.

Raman spectra of CuAlSe2 heteroepitaxial layers

Abstract: Room‐temperature Raman spectra were measured for CuAlSe2 heteroepitaxial layers grown on GaAs (001) and GaP (001) substrates. A remarkable difference in the polarized Raman spectra was noted, and the results were attributed to be due to the lattice orientation of the epilayers on the basis of the polarization selection rules of Raman active modes. Two vibrational modes were assigned, namely the A1 mode at 189 cm−1 and longitudinal‐optical B2 mode at 89 cm−1.

Binding Constants of Symmetric or Antisymmetric Electrolytes and Aggregation Numbers of Oil-in-Water Type Microemulsions with a Nonionic Surfactant

Abstract: The effects of electrolytes (symmetric and antisymmetric) on the phase behavior, the apparent cloud point, the ζ-potential, the particle size, and the surface charge density of an oil-in-water type (O/W type) microemulsion forming in solutions of a nonionic surfactant (tetraethylene glycol monodecyl ether, C 10 -POE 4 )/n-decane/brine have been examined. Additions of NaSCN and/or Ca(SCN) 2 result in increasing the temperature where the O/W-type microemulsions formed, while additions of NaCl, NaNO 3 , CaCl 2 , and/or NH 2 CONH 2 decrease the temperature. When the concentrations of NaSCN and/or Ca(SCN) 2 increase, the apparent cloud points of the O/W-type microemulsion increase, while there is a decrease in the particle sizes of the microemulsion droplets. On the other hand, as the concentrations of NaCl, NaNO 3 , CaCl 2 , or NH 2 CONH 2 increase, the apparent cloud point of the microemulsion decreases slightly, but their particle sizes increase. The electrophoretic mobilities of the microemulsion droplets can be measured only in the systems containing NaSCN or Ca(SCN) 2 . Moreover, the ζ-potential and the surface charge density show negative values at a given salinity, though C 10 POE 4 does not possess a charged component in a molecule. Applying formulas described in this article, the adsorption of anion (SCN-) to the hydrophilic moieties of C 10 POE 4 microemulsions is shown to be greater than those of cations (Na + or Ca 2+ ). The binding constants (K) of anion and cation to the hydrophilic groups of C 10 POE 4 microemulsions are found to be K Na = 0 M -1 , K Ca = 0.2 M -1 , 10.0 M -1 < K SCN < 12.0 M -1 and the adsorption density of C 10 POE 4 molecules on the oil/water interface (N) is found to be N = 0.3 nm -2 ; the surfactant (C 10 POE 4 ) numbers per O/W-type microemulsion droplet decrease (a few thousands to a few hundreds) with the increasing concentration of NaSCN and/or Ca(SCN) 2 .

Unusual conformational stability of a sterically crowded atropisomer of methyl[α4-5,10,15,20-tetrakis(2′-phenylphenyl)porphyrinato]aluminium: a possibility of CH–π bonding interactions in organometallic porphyrin systems

Abstract: Through conformational studies on the topologically well-defined atropisomeric systems of organo-aluminium and -cobalt porphyrins, e.g. methyl[α4-5,10,15,20-tetrakis(2′-phenylphenyl)porphyrinato]aluminium (α4-1a), the presence of intramolecular CH–π bonding interactions are indicated between alkyl groups bonded to the central metal atoms and aromatic rings located at the ortho position of the meso phenyl substituents upon proximal orientation.

Novel DNA binding protiens highly specific to UV-damaged DNA sequences from embryos of Drosophila melanogaster

Abstract: Three new proteins which selectively bind to UV-damaged DNA were identified and purified to near homogeneity from UV-irradiated Drosophila melanogaster embryos through several column chromatographies. These proteins, tentatively designated as D-DDB P1, P2 and P3, can be identified as different complex bands in a gel shift assay by using UV-irradiated TC-31 probe DNA. Analysis of the purified D-DDB P1 fraction by native or SDS-polyacrylamide gel electrophoresis and FPLC-Superose 6 gel filtration demonstrated that it is a monomer protein which is a 30 kDa polypeptide. The D-DDB P2 protein is a monopolypeptide with a molecular mass of 14 kDa. Both D-DDB P1 and P2 highly prefer binding to UV-irradiated DNA, and have almost no affinity for non-irradiated DNA. Gel shift assays with either UV-irradiated DNA probes demonstrated that D-DDB P1 may show a preference for binding to (6-4) photoproducts, while D-DDB P2 may prefer binding to pyrimidine dimers. Both these proteins require magnesium ions for binding. D-DDB P1 is an ATP-preferent protein. These findings are discussed in relation to two recently described [Todo and Ryo (1991) Mutat. Res., 273, 85-93; Todo et al. (1993) Nature, 361, 371-374] DNA-binding factors from Drosophila cell extracts. A possible role for these DNA-binding proteins in lesion recognition and DNA-binding proteins in lesion recognition and DNA repair of UV-induced photo-products is discussed.

Direct-detection optical synchronous CDMA systems with double optical hard-limiters using modified prime sequence codes

Abstract: An optical code-division multiple-access (CDMA) system with double optical hard-limiters is proposed where the optical hard-limiters are placed before and after an optical correlator. Moreover, the effect of the optical hard-limiter on the performance of the optical synchronous CDMA systems using modified prime sequence codes is analyzed under the assumption of Poisson shot noise model for the receiver photodetector where noise due to the detector dark currents exists. We evaluate the performance under average power and bit rate constraints. Our results show that using the single optical hard-limiter slightly degrades the performance of the optical CDMA systems. Moreover, we show that the optical CDMA systems with double optical hard-limiters have better performance than other conventional CDMA systems without and with the optical hard-limiter when the number of simultaneous users is not so large.