Microporous poly(vinyl methyl ether) hydrogels prepared by γ-ray irradiation at different heating rates

We prepared thermoresponsive and microporous polymer hydrogels by γ-ray irradiation of aqueous solutions poly(vinyl methyl ether) (PVME) at different heating rates. Under all temperature programs, opaque and heterogeneous PVME gels formed, which swelled at temperatures below the lower critical solution temperature and shrank at temperatures above it. All of the samples contained porous and phase-separated structures. The shape and size of the gel pores varied depending on the temperature programs. Gels having a sponge-like continuous porous structure formed only when the radiation-induced crosslinking was carried out at an optimum heating rate, which we found to be 0.11–0.13°C min⁻¹. For temperature changes between 10°C and 40°C, gels with this structure showed rapid volume transitions on a time scale of about a minute.     

Structural observation of heterogeneous poly(N-isopropyl acrylamide-co-acrylic acid) hydrogels in highly hydrated states

Heterogeneous hydrogels were prepared by -ray irradiation of aqueous solutions of N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc) having various compositions above the lower critical solution temperature. The structures of the poly(N-isopropylacrylamide) (PNIPAAm) gel and poly(NIPAAm-co-AAc) gels in both their highly hydrated and their natural states were observed by environmental scanning electron microscopy. The heterogeneous structures of the homopolymer gel and the copolymer gels whose AAc contents were between 10–50% consisted of interconnected microspheres. In the copolymer gel with a high AAc content, the structure became a largely interconnected one which lacked micro-droplets. The hydrophobic interaction caused by hydrogen bonding between the unionized carboxylic acid groups of AAc and the amide groups of NIPAAm, the rates of polymerization, and the aggregation rates play important roles in the formation of interconnected microsphere gel structures.     

Total synthesis of epoxyquinols A, B, and C and epoxytwinol A and the reactivity of a 2H-pyran derivative as the diene component in the Diels-Alder reaction

Full details of two versions of the total synthesis of epoxyquinols A, B, and C and epoxytwinol A (RKB-3564D) are described. In the first-generation synthesis, the HfCl(4)-mediated diastereoselective Diels-Alder reaction of furan with Corey's chiral auxiliary has been developed. In the second-generation synthesis, a chromatography-free preparation of an iodolactone, by using acryloyl chloride as the dienophile in the Diels-Alder reaction of furan, and the lipase-mediated kinetic resolution of a cyclohexenol derivative have been developed. This second-generation synthesis is suitable for large-scale preparation. A biomimetic cascade reaction involving oxidation, 6pi-electrocyclization, and then Diels-Alder dimerization is the key reaction in the formation of the complex heptacyclic structure of epoxyquinols A, B, and C. Epoxytwinol A is synthesized by the cascade reaction composed of oxidation, 6pi-electrocyclization, and formal [4 + 4] cycloaddition reactions. A 2H-pyran, generated by oxidation/6pi-electrocyclization, acts as a good diene, reacting with several dienophiles to afford polycyclic compounds in one step. An azapentacyclic compound is synthesized by a similar cascade reaction composed of the four successive steps: oxidation, imine formation, 6pi-azaelectrocyclization, and Diels-Alder dimerization.     

Simultaneous determination of iron(II), iron(III), and titanium(IV) by flow injection analysis using kinetic spectrophotometry with Tiron

Summary Two flow injection analysis systems have been worked out for the simultaneous determination of Fe(III), Fe(II), and Ti(IV) based on the kinetic spectrophotometry with Tiron. The first system uses a silver reductor column and a single detector with two flow cells aligned in the same optical path to yield two peaks corresponding to (a) Ti(IV)-Tiron and (b) Ti(IV) plus total iron(III)-Tiron complexes. An another sample injection without the silver column yields a single peak which corresponds to Ti(IV) plus Fe(III)-Tiron complexes. With the two sample aliquot injections the system permits simultaneous determinations with throughput of 30 samples/h in the g to several tens g range of each species. The second system is a multidetection system with or without the silver reductor column using the same spectrophotometry with Tiron, in which the entrapment of the sample plug into a closed system allows its repetitive passage through a single detector. With the advantage of much simpler instrumentation, the system permits 6 samples/h to be analyzed for the three metal species with somewhat lower precisions than the first system.     

The use of 2-O-propagyloxycarbonyl protecting group in the selective formation of 1,2-trans-glycosidic linkage

The effect of N-phenylcarbamoyl (Car) and propagyloxycarbonyl (Poc) protecting groups at the O-2 position of donors was examined. The usefulness of Poc group in the selective formation of 1,2-trans-glycosidic linkage is shown by comparing the reactivity of donors having Car or acyl (Bz) groups.     

Constituents of Panacis Japonici Rhizoma. VI The Structure of Chikusetsu-Saponin II,IVC

Chikusetsusaponin II and IVc, the minorsaponins of Panacis japonici rhizoma (rhizome of Panax japonicum C.A. MEYER) have been isolated. The structure of these saponins were established as being oleanolic acid-(3)-[β-D-glucopyranosyl (1→6)]-β-D-glucuronopyranoside and 20S-protopanaxatriol-6-(O-α-L-rhamnopyranosyl (1→2)-β-D-glucopyranoside]-20-O-β-D-glucopyranoside. Chikusetsusaponin II is a new structure, while chikusetsusaponin IVc is identical with ginsenoside-Re, isolated from P. ginseng C. A. MEYER.     

XPS Analysis of Lead Zirconate Titanate Thin Films Prepared Via a Sol-Gel Process

The crystalline phase and composition of sol-gel-derived lead zirconate titanate (PbZr _x Ti_{1 – x} O₃, PZT) thin films were determined by an X-ray photoelectron spectroscopic (XPS) data processing technique. As a result, it was proved that existence of the surface layer with several tens nm in thickness, of which the crystalline phase and composition were different from those of the inside of the thin films, was found. The newly developed XPS analytical technique is much applicable for the characterization of PZT thin film surface.     

Humidity controlled thermal analysis

The low temperature formation of crystalline zinc oxide via thermal decomposition of zinc acetylacetonate monohydrate C₁₀H₁₄O₄Zn·H₂O was studied by humidity controlled thermal analysis. The thermal decomposition was investigated by sample-controlled thermogravimetry (SCTG), thermogravimety combined with evolved gas analysis by mass spectrometry (TG-MS) and simultaneous differential scanning calorimetry and X-ray diffractometry (XRD-DSC). Decomposition of C₁₀H₁₄O₄Zn·H₂O in dry gas by linear heating began with dehydration around 60°C, followed by sublimation and decomposition above 100°C. SCTG was useful because the high-temperature parallel decompositions were inhibited. The decomposition changed with water vapor in the atmosphere. Formation of ZnO was promoted by increasing water vapor and could be synthesized at temperatures below 100°C. XRD-DSC equipped with a humidity generator revealed that C₁₀H₁₄O₄Zn·H₂O decomposed directly to the crystalline ZnO by reacting with water vapor.     

A one-step preparation of pyrido[3,4-d]pyrimidine ring system by reaction of 5-formyl-1,3,6-trimethyl-pyrimidine-2,4(1H,3H)-dione with primary amines

6,7-Dihydropyrido[3,4-d]pyrimidine-2,4(1H,3H)-diones were obtained in high yields from the reaction of 5-formyl-1,3,6-trimethylpyrimidine-2,4(1H,3H)-dione ( 1 ) and primary amines. For this pyridopyrimidine synthesis the following reaction pathway is proposed; the [1,5]-hydrogen shift of 1 gives a 5,6-dihydro-5,6-dimethylenepyrimidine-2,4(1H,3H)-dione intermediate. The cycloaddition reaction of the intermediate with aldimines from 1 and the primary amines affords 5,6,7,8-tetrahydropyrido[3,4-d]pyrimidine-2,4(1H,3H)-diones, which are dehydrated to the final products.     

Electron spin resonance study on homogeneous catalysts derived from n-butyl titanate and triethylaluminum

ESR spectra of homogeneous catalyst systems derived from n-butyl titanate and triethylaluminum at Al/Ti molar ratios of 1.0–10 were observed in toluene solution at several temperatures from ?78°C to +25°C. In the whole range of Al/Ti molar ratios, a single signal with a g value of 1.951 was observed at ?78°C and was associated with the first reaction intermediate. With increasing temperature, the intensity of the signal decreased gradually, while two series of signals appeared, depending on the Al/Ti molar ratio. At an Al/Ti molar ratio of 1.7, seven kinds of signals with g values of 1.960, 1.946, 1.950, 1.959, 1.980, 1.977, and 1.978, respectively, were observed. On the other hand, four kinds of signals with g values of 1.934, 1.966, 1.952, and 1.979, respectively, were found at Al/Ti molar ratios larger than 3. The structures of the species corresponding to the signals were discussed on the basis of the ESR spectra, the order of their growth and their hyperfine structures being considered. Two series of ESR signal were correlated to two kinds of active species for polymerization of styrene and butadiene, respectively.