Tadatoshi Ota

Self-excitation in a porous membrane doped with sorbitan monooleate (Span-80) induced by an Na+ /K+ concentration gradient

The electrical potential across a fine-pore membrane doped with sorbitan monooleate (Span-80) imposed between aqueous solutions of NaCl and KCl was studied. It was found that this system showed rhythmic and sustained oscillations of electrical potential between the two aqueous solutions. These oscillations were attributed to the change of permeability of Na+ and K+ across the membrane, which originated from the phase transition of Span-80 molecules within the fine pores. Impedance measurement across the membrane also suggested a change in permeability. It was found that this membrane exhibited the property of differential negative resistance. In relation to this, it was shown that Na+ and K+ have different effects on the aggregation of Span-80 molecules. The mechanism of oscillation is discussed in relation to the ability of Span-80 molecules to behave as a dynamic channel through the membrane. This oscillatory phenomenon is interesting because in biological nervous membranes a difference between the concentrations of Na+ and K+ across the membranes is essential for excitability.

Oscillation of electrical potential in a porous membrane doped with glycerol α-monooleate induced by an Na+/K+ concentration gradient

The electrical potential across a fine-pore membrane doped with glycerol alpha-monooleate and separating aqueous solutions of 0.5 M NaCl and 0.5 M KCl was studied. It was found that this system showed rhythmic and sustained oscillations of electrical potential. These oscillations may be due to the phase transition of glycerol alpha-monooleate molecules within the fine pores. In relation to this, it is shown here that Na+ and K+ have different effects on the aggregation of glycerol alpha-monooleate. This oscillatory phenomenon is very interesting because in biological nervous membrane an Na+/K+ concentration difference across the membrane is essential for excitability.

Preparation and thermal behavior of spin polymers and their precursors based on azomethine mesogens

Abstract Chiral liquid crystalline spin molecules and their precursors have been prepared. Condensation of 4-substituted anilines and chiral 2-hydroxybenzaldehyde gave mesogenic vinyl monomers showing chiral smectic phases slightly above ambient temperature. Radical polymerization of them gave polymers with molecular weight of several tens of thousands in high yield. Treatment of the polymers with oxidizing reagents gave two types of polymers with unpaired electrons, i.e. phenoxy and amino spin polymers. In addition, stable nitroxy radicals with azomethine moiety were also prepared and their properties were examined.

Radical polymerization of ethyl α-benzoyloxymethylacrylate in benzene

Abstract The polymerization of ethyl α-benzoyloxymethylacrylate (EBMA), an α-disubstituted monomer, initiated with azobisisobutyronitrile (AIBN) was studied kinetically in benzene. The polymerization rate (Rp) at 60° was expressed by Rp = k[AIBN]0.5 [EBMA]1.6. The overall activation energy was calculated to be 53 kJ/mol. Rate constants of propagation (kp) and termination (kt) of EBMA were estimated as 990 and 2.9 × 106 l/mol · sec respectively at 60°, using the ESR-determined concentration of the propagating polymer radical. The large kp and rather low kt led to formation of poly(EBMA) with high molecular weight ( M n = 1−5 × 10 5 ). Thermogravimetry revealed that thermal degradation of poly(EBMA) began near 300° and the residue at 500° was only 2% of the initial polymer. Copolymerization of EBMA (M1) with St (M2) was also examined at 60° in benzene. The following copolymerization parameters were obtained according to the Kelen-Tudos method; r1 = 0.27 ± 0.01, r2 = 0.30 ± 0.02 giving Q1 = 0.93 and e1 = + 0.78.

Interaction between Drugs and Water-soluble Polymers. Part IV. Binding Position of Azathioprine with Bovine Serum Albumin Determined by Measuring Nuclear Magnetic Resonance Relaxation Time.

The interaction between azathioprine (AZ) and bovine serum albumin (BSA) is mainly due to hydrophobic binding according to the dependence of the binding constant on the ionic strength obtained by equilibrium dialysis. The binding constant and partition coefficient of AZ were smaller than those of warfarin, phenylbutazone and ibuprofen. Little variation in the proton chemical shift of AZ was observed whether there was an absence or presence of BSA (7.25 x 10(-5) M). The spin-lattice relaxation time (T1) of AZ decreased in the presence of BSA to 6-22%. The spin-spin relaxation rate (1/T2) of AZ increased 16-24 times for the methyl group and the imidazole ring and 8-13 times for the purine ring in the presence of BSA. The ratio of the spin-spin relaxation rate of the free AZ to the bound AZ ((1/T2)b/(1/T2)f) of the methyl group and the imidazole ring was 2-3 times larger than that of the purine ring. The binding of AZ to BSA was concluded to be mainly at the methyl group on the imidazole ring of AZ.

Radical polymerization of N-phenylitaconimide

Abstract N -Phenylitaconmide ( N PII), a cyclic analogue of N , N -disubstituted methacrylamide, is easily polymerized using radical initiators, the number-average molecular weights of the resulting polymers are in the range of 6000-18,000. The polymerization of N PII with dimethyl 2,2′-azobisisobutyrate (MAIB) was studied kinetically in THF at 50°. The polymerization rate ( R p ) was given by the equation; R r = k [MAIB] 0.52 [NPH] 2.5 . The polymerization had a low overall activation energy of 51 kJ/mol. Thermogravimetry revealed that thermal degradation of poly( N PII) occurred at 320° and the residue at 500° was 40% of the initial polymer. Copolymerization of N PII(M 1 ) and styrene (M 2 ) in THF at 50° gave monomer reactivity ratios of r 1 = 0.88 and r 2 = 0.06, leading to Q and c values of N PII of 4.0 and +0.90 respectively, indicating that N PII is a conjugative electron-accepting monomer.

An ESR Study of the Curing Reaction of Unsaturated Polyester with Vinyl Monomers and the Thermal Behavior of the Cured Polymers

Abstract The curing reaction of an unsaturated polyester (BAPM), prepared by polycondensation of Bisphenol A-di-(2-hydroxypropyl)ether and maleic anhydride, with vinyl monomers was investigated by IR and ESR. Thermal properties of the resulting polymer were studied by DSC and TMA. For the curing reaction of BAPM with styrene initiated with the cobalt naphthalate/1-hydroxycyclohexyl hydroperoxide system, the copolymerization process could be satisfactorily analyzed by the Mayo-Lewis integral equation for the usual homogeneous copolymerization. The reaction mixtures contained long-lived polymer radicals, the ESR spectra of which gave important information on the curing reaction. The DSC and TMA results showed that a microphase separation occurred in the cured polymer from BAPM and styrene. The phase separation was accelerated by treatment at -3°C. However, heat treatment above 150°C eliminated the phase separation. These phenomena were also confirmed by TEM examination.

Radical Polymerizations of Vinyl Monomers in the Presence of α-Ethylsulfenyl Acrylonitrile

Abstract Radical polymerizations of styrene, methyl methacrylate, and acrylonitrile were carried out at 60°C in the presence of α-ethylsulfenyl acrylonitrile (α-ESAN). The rate of polymerization was found to be reduced by the addition of α-ESAN, and induction periods were observed when a large amount of α-ESAN was added to the systems. The chain transfer constant of α-ESAN was determined to be 2.0 and 17 for the polymerizations of styrene and methyl methacrylate, respectively. The Q, and e, values of α-ESAN were evaluated as 4.9 and -1.9, respectively. The presence of chromium(II) acetate and a-ESAN results in enhancement of α-ESAN activity as a retarder. From these results and ESR measurements, a mechanism of chain transfer is discussed.

Polymerizable tautomers: 5. Solvent effects on radical polymerization and copolymerization of 5-hexene-2,4-dione

Abstract 5-Hexene-2,4-dione (AA) has been polymerized and copolymerized at 60°C in different solvents. An initiator order of 0.5 and monomer order above unity were obtained for the polymerization of AA in benzene and acetonitrile. A strong influence of the solvents on monomer reactivity ratios for the AA-styrene copolymerization system was observed. The contribution of electrostatic field effect and solute-solvent hydrogen bonding interactions was estimated separately and critically discussed using multiparametric regression analysis and empirical polarity parameters, according to the linear solvation energy relationship developed by Taft et al .

Long-lived polymer radicals in the polymerization of n-methylmethacrylamide in cyclohexane

Abstract The polymerization of N-methylmethacrylamide (NMMAm) with azo-bis-isobutyronitrile (AIBN) was kinetically investigated in cyclohexane which has a small affinity for NMMAm monomer. The polymerization proceeded heterogeneously. The polymerization rate (Rp) was expressed by the following equation: R p =k[ AIBN ] 0.72 [ NMMAm ] 0.82 The overall activation energy of the polymerization was calculated to be 104 kJ/mol. The initiator efficiency of AIBN was determined to be 0.47 and 0.51 at 45° and 50°C, respectively. The polymerization system was found to contain long-lived poly(NMMAm) radicals. The formation rate of the living polymer radicals was determined by ESR and then the efficiency of living polymer radical formation was estimated to be 0.28 and 0.29 at 45° and 50°C. Comparison of the efficiency of the initiator with that of living polymer radical formation reveals that about 60% of cyanopropyl radicals escaping from the solvent cage were converted into living poly(NMMAm) radicals. From an electron microscopic examination, the resulting poly(NMMAm) was found to form coral-like conglomerates.