Complex formation of large-ring cyclodextrins with iodine in aqueous solution as revealed by isothermal titration calorimetry

Complex formation of large cyclodextrins(CDs) having DP 21–32 with iodine in aqueous KI solution was studied by isothermal titration calorimetry. The curves obtained for the titration of the CDs with iodine cannot be analyzed by a model based on a single set of identical sites, but, rather, by a model assuming 1 : 2 complex formation with identical interacting sites. For the two identical interacting sites, the binding constants K₁ and K₂ (K₁ < K₂), defined relative to the progress of saturation, lie in the range 0.7 to 7.3×10³ M^–1 and 3.0 to 62.6×10³ M^–1, respectively. The values of ΔH₂ and T ΔS₂ lie in the range –34.9 to –136.4 kJ·mol^–1 and –15.5 to –112.8 kJ·mol^–1, respectively. The largest values of –T ΔS₂ obtained for a CD of DP 26 can, in part, be attributed to a large decrease in conformational flexibility of the CD which occurs during complex formation.     

Template directed reversible photochemical ligation of oligodeoxynucleotides

We demonstrated that 5-vinyldeoxyuridine ((V)U) and 5-carboxyvinyldeoxyuridine ((CV)U) can be used to photoligate a longer oligonucleotide (ODN) from smaller ODNs on a template. By performing irradiation at 366 nm, these artificial nucleotides make photoligated ODNs with high efficiency without any side reactions. Moreover, by performing irradiation at 312 nm, these photoligated ODNs were reversed to the original ODN. (V)U needs to be irradiated 366 nm for 6 h, but (CV)U needs to be irradiated at 366 nm for 15 min. Finally, we made a self-assembled structure with an ODN containing (CV)U and observed the photoligated ODN by photoirradiation.     

Autonomic healing of a pinhole in polyethylene and photografted polyethylene‐g‐poly(hexyl methacrylate) films

The structural changes of polyethylene (PE) and photografted polyethylene‐g‐poly(hexyl methacrylate) (PE‐g‐PHMA) with the mechanical formation of pinholes were evaluated with differential scanning calorimetry, wide‐angle X‐ray scanning, and small‐angle X‐ray scanning. The crystallinity and the long period of the lamella increased with pricking under extremely high compression stress. The partial transformation of an orthorhombic crystal into a monoclinic one was also detected. The autonomic healing of pinholes in PE and PE‐g‐PHMA was studied in detail. The degree of healing increased with an increase in the grafting ratio of poly(hexyl methacrylate) (PHMA). Three mechanisms for the healing were investigated and related to the molecular motions of PE and PHMA grafted chains, which were evaluated with dynamic mechanical analyses. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1705–1714, 2004     

One-Pot Reduction of Sulfoxides with NaBH4, CoCl2 · 6H2O Catalyst,and Moist Alumina

Sulfoxides are reduced by a combination of sodium borohydride, a catalytic amount of cobalt(II) chloride hexahydrate, and chromatographic neutral alumina preloaded with a small amount of water (moist alumina) in hexane to produce the corresponding sulfides in good to excellent yields under mild conditions. An interesting structural influence of sulfoxides on their reactivity is observed.

One-Pot System for Reduction of Epoxides Using NaBH4, PdCl2 Catalyst,and Moist Alumina

Reduction of epoxides with sodium borohydride, a catalytic amount of palladium(II) chloride, and chromatographic neutral alumina preloaded with a small amount of water (moist alumina) in hexane gave alcohols in good to excellent yields and good selectivity of the desired products under mild conditions. The reaction system was operationally simple and environmentally friendly. The alumina can be recovered simply and reused a number of times without any treatment and with good activity.     

Lignified materials as a potential medicinal resource. IV. Dehydrogenation polymers of some phenylpropenoids and their capacity to stimulate polymorphonuclear cell iodination.

Based on our recent finding regarding diverse biological activities of natural lignified materials, synthetic dehydrogenation homo- and copolymers were prepared using 3 p-hydroxylated cinnamic acids and coniferyl alcohol in order to explore the role of lignin skeleton in the activities displayed by natural lignins. The synthetic polymers stimulated polymorphonuclear cell iodination as potently as the natural lignified materials.     

A Convenient Biphasic System (Alumina-Dichloromethane) for the Efficient Aromatic Monochlorination of Alkyl Phenyl Ethers with Sodium Chlorite in the Catalytic Presence of Manganese(III) Salt

A combination of sodium chlorite, (salen)manganese(III) catalyst, and chromatographic neutral alumina in dichloromethane can be successfully utilized for the aromatic monochlorination of a variety of alkyl phenyl ethers in excellent to quantitative yields under mild and anhydrous conditions.     

Formation of O6,7-dimethylguanine residues in calf thymus deoxyribonucleic acid treated with carcinogenic N-methyl-N-nitrosourea in vitro

Treatment of calf thymus deoxyribonucleic acid (DNA) in vitro with a methylating carcinogen, N-methyl-N-nitrosourea (MNU), in phosphate buffer (pH 7.2) resulted in formation of O6,7-dimethylguanine residues in DNA besides the well-known methylated DNA adducts, 7-methylguanine, O6-methylguanine and 3-methyladenine. The product ratio (%) of O6,7-dimethylguanine versus 7-methylguanine was 0.32 after one MNU treatment. The significance of formation of O6,7-dimethylguanine residues in DNA is discussed briefly in relation to the carcinogenicity of MNU.     

Studies on chemical carcinogens and mutagens. XXVII alkylating property of mutagenic N-trimethylsilylmethyl-N-nitrosourea,a silicon-analogue of N-neopentyl-N-nitrosourea,in aqueous media

The kinetics for hydrolysis and the chemoselectivity toward nucleophiles of mutagenic N-trimethylsilylmethyl-N-nitrosourea, a silicon analogue of N-neopentyl-N-nitrosourea, were studied.