Novel ring transformation reactions of xanthine derivatives

The novel ring transformation reactions were found in the reactions of 1,3,7,9-tetra-alkyl-8,9-dihydroxanthines and acetylenic compounds. The reaction of the dihydroxanthine with DMAD gave a propellane type compound and with methyl propiolate afforded the similar type compound and a pyrimido[4,5-b]diazepine derivative. The mechanism of these reactions was also discussed.     

Regioselective 1,4-addition of nucleophiles to 1,3-diene monoepoxides catalyzed by palladium complex

1,3-Diene monoepoxides react with nucleophiles in the presence of palladium complex as a catalyst under neutral conditions to give 1,4-adducts selectively. The 1,4-adducts are allylic alcohols and there is a possibility of another nucleophilic attack. Ester of Monarch butterfly pheromone was prepared.     

Femtosecond laser-induced stimulation of a single neuron in a neuronal network

We demonstrated the stimulation of neurons at a single-cell level in cultured neuronal network by a focused femtosecond laser. When the femtosecond laser was focused on a neuron loaded with a fluorescent calcium indicator, the fluorescence intensity immediately increased at the laser spot, suggesting that intracellular Ca²⁺ increases in the neuronal cell due to the femtosecond laser irradiation. The probability of Ca²⁺ elevation at the laser spot depended on the average laser power, irradiation time, and position of the focal point along the optical axis, indicating that the femtosecond laser activates neurons because of multiphoton absorption. Moreover, after laser irradiation of a single neuron cultured on multielectrode arrays, the evoked electrical activity of the neurons was demonstrated by electrophysiological systems, which concluded that the focused femtosecond laser could achieve stimulating a single neuron in a neuronal network with high spatial and temporal resolution.     

A hydrogel with rubber elasticity transition

Reaction between dimethyldivinylsilane and 3,6-diazaoctane in the presence of 3-lithio-3,6-diazaoctane yields a new telechelic oligomer, poly(silamine), which consists of alternating 3,3-dimethyl-3-silapentane and N,N′-diethylethylenediamine units in the main chain. Poly(silamine) shows unique phase transition properties in response to the degree of protonation of amino groups in the polymer. Poly(silamine) also shows a strong interaction with several anions. Due to the interaction between poly(silamine) and anions along with the protonation of amino groups in the poly(silamine), the rubber elasticity of poly(silamine) is drastically changed. A discrete volume change can be observed when the environmental pH of the poly(silamine) gels is varied. This can be explained not only by a change in ionic osmotic pressure but also by a change in the rubber elasticity of the networks in the gel.     

Synthesis of (S)-γ-Lactones with a Combination of Lipase-Catalyzed Resolution and Mitsunobu Reaction

Six kinds of (S)-γ-lactones [e.g., (S)-γ-decalactone, (S)-γ-undecalactone, and (S)-γ-jasmolactone] were synthesized with 71–88% yields and >97% optical purities by combining lipase-catalyzed resolution with the Mitsunobu reaction.     

Formation of Stable and Monodispersive Polyion Complex Micelles in Aqueous Medium from Poly(L-lysine) And Poly(Ethylene Glycol)-Poly(Aspartic Acid) Block Copolymer

Abstract

In this study, the formation of polyion complex micelles from a pair of poly(L-lysine) homopolymers (P(Lys)) and poly(ethylene glycol)-poly(aspartic acid) block copolymers (PEG-P(Asp)) with varying chain length was demonstrated in aqueous medium. There exists the lower critical chain length in the charged segments of both P(Lys) and PEG-P(Asp) to form stable polyion complex micelles in nanometric scale. The scaled average characteristic line width (ΓTK²) was independent on the detection angles for all combinations, suggesting that the formed polyion complex micelles may have a spherical shape. Furthermore, the transitional diffusion coefficient (D_T) had no concentration dependence, indicating the micelle system was free from secondary aggregates (the cluster of micelles). It is of interest that the micellar size was almost constant (ca. 50 nm) regardless of the change in the chain length of the charged segments. Size distribution was extremely narrow, and the values of variance μ₂/Γ ²) were always less than 0.1. Laser-Doppler electrophoresis measurements revealed that the polyion complex micelles were electrically neutral, suggesting that the PEG corona surrounding the polyion complex core may contribute to their stable dispersion in an aqueous medium through steric repulsion of the tethered hydrophilic chain, in this case, PEG. This system was considerably stable against the change in ionic strength, and it maintained a constant diameter in the region below 0.4 M NaCl. However, they dissociated under high ionic strength condition as 0.6 M NaCl. The system may have potential utility to include charged peptides and nucleotides in the core, delivering these biologically useful substances into a target site in the body.     

Unique inclusion properties of crystalline powder p-tert-butylthiacalix[4]arene toward alcohols and carboxylic acids

Powdery crystals of p-tert-butylthiacalix[4]arene (2) selectively include EtOH from 1:1 mixtures of MeOH-EtOH and EtOH-PrOH, and EtCO(2)H from HCO(2)H-EtCO(2)H. On the other hand, no acid is included from HCO(2)H-MeCO(2)H, even though MeCO(2)H is included from the neat acid. The origins of these phenomena are discussed based on X-ray analysis of inclusion crystals prepared separately by crystallization.     

Automated sample preparation using in-tube solid-phase microextraction and its application -- a review

Sample preparation, such as extraction, concentration, and isolation of analytes, greatly influences their reliable and accurate analysis. In-tube solid-phase microextraction (SPME) is a new effective sample preparation technique using an open tubular fused-silica capillary column as an extraction device. Organic compounds in aqueous samples are directly extracted and concentrated into the stationary phase of capillary columns by repeated draw/eject cycles of sample solution, and they can be directly transferred to the liquid chromatographic column. In-tube SPME is an ideal sample preparation technique because it is fast to operate, easy to automate, solvent-free, and inexpensive. On-line in-tube SPME-performed continuous extraction, concentration, desorption, and injection using an autosampler, is usually used in combination with high performance liquid chromatography and liquid chromatography-mass spectrometry. This technique has successfully been applied to the determination of various compounds such as pesticides, drugs, environmental pollutants, and food contaminants. In this review, an overview of the development of in-tube SPME technique and its applications to environmental, clinical, forensic, and food analyses are described.