Swelling and deswelling kinetics of poly(N-isopropylacrylamide) gels

Swelling and deswelling kinetics was investigated for three types of cylindrical poly(N-isopropylacrylamide) (PNIPA) gels differing in crosslink density. The temperature dependence curves of the volume of the gel specimens were different from one another. One of the gel specimens was considered as a critical gel showing the continuous volume phase transition. The volume change process of the specimens after a temperature jump was examined. In the deswelling processes with temperature jumps to temperatures higher than 35 degrees C, a phase separation was observed in the gel specimens and the volume change slowed down due to the homogenization after the phase separation. The value of the diffusion constant obtained without the phase separation decreased rapidly as temperature approaches the transition temperature. The rapid decrease for the critical gel indicates the emergence of the critical slowing-down. The value of the critical exponent for the correlation length suggests that the universality class for the volume phase transition of the critical PNIPA gel belongs to the class for the classical theory.     

Furopyridines. XXI. Synthesis of cyano derivatives of furo-[2,3-b]-, -[2,3-c]- and -[3,2-c]pyridine and their conversion to derivatives having another carbon-substituent

Cyanation of furo[2,3-b]-, -[2,3-c]- and -[3,2-c]pyridine N-oxides 1a, 1b and 1c by the Reissert-Henze method, reaction with benzoyl chloride and trimethylsilyl cyanide in dichloromethane and the reaction with trimethylsilyl cyanide and triethylamine in acetonitrile afforded 6-cyanofuro[2,3-b]- 2a , 7-cyanofuro[2,3-c]- 2b and 4-cyanofuro[3,2-c]pyridine 2c in moderate to excellent yield. The cyano group in 2a, 2b and 2c was converted to carboxamides 3a, 3b and 3c , ethyl imidates 5a, 5b and 5c and ethyl carboxylates 6a, 6b and 6c . Reaction of the N-oxides with trimethylsily bromide in acetonitrile gave the deoxygenated furopyridine 7a and 7d , bifuropyridyl 8b and 8c , and the N-oxide 9 of 8c .     

Preparation of polyimides from pyromellitic dithioanhydride and aromatic diamines

The reaction of phthalic thioanhydride and aniline yielded N-phenylphthalimide quite readily. The reaction was strongly dependent on solvent and temperature. Various additives tried as a reaction promoter were almost ineffective. By the extension of the model reaction, polyimides were prepared in a simple one-step synthesis from pyromellitic dithioanhydride and aromatic diamines in dimethylacetamide or other solvents. Polymers with inherent viscosity up to 0.3 in concentrated sulfuric acid were obtained in approximately quantitative yield.     

Spintronic Transport through Polyphenoxyl Radical Molecules

The coherent quantum transport properties through the spin-polarized polyphenoxyl radical molecule have been investigated, using the density-functional-derived tight-binding model and the Green's functions method. The majority and minority spin components exhibit considerably different transmission spectra in the vicinity of the Fermi level. Namely, each spin component carries a different amount of current when the bias voltage is applied between the two electrodes that sandwich the polyradical molecule. Therefore, if the magnetization axis of the polyradical is fixed by the external magnetic field, and if the spin flip does not occur during the transmission, the assumed molecular bridge is expected to work as a spin filter or a spin valve. Furthermore, as long as the bias voltage is weak, the total spin current is observed to be larger than the current through its reduced molecular form. It indicates that the adsorption of some chemical species on the radical sites can be sensed by the change in conductance of the molecular bridge.     

Practical and Efficient Method for α-Sialylation with an Azide Sialyl Donor Using a Microreactor

Efficient α-sialylation with a C5 azide sialyl donor was investigated under microfluidic conditions using a microreactor composed of a Comet X-01 micromixer and a tube reactor. Precise temperature control realized excellent α-selectivity, and Siaα(2,6)Gal, Siaα(2,3)Gal, and Siaα(2,9)Sia disaccharides were obtained in moderate to good yields.     

Electron transmission and quantum current distribution of C<Subscript>70</Subscript> molecule

The characteristics of electron transmission through C₇₀ molecule bridge in which two atomic chain leads are connected to long-axis carbon atoms are investigated theoretically by using tight-binding approach based on the Green’s function with only one π orbital electron per carbon atom. Electron transmission through C₇₀ molecule from the input to the output terminal is obtained. From the spectrum, the switching feature of the electron transmission through C₇₀ is found, and the oscillation property based on the quantized level is explained. The quantum current distributions inside C₇₀ molecule bridge are calculated and simulated by the quantum current density theory based on Fisher-Lee formula at the energy point E = −0.2 eV, where the transmission spectrum shows a peak. The maximum and the minimum bond quantum currents are presented, and the reason why the currents are distributed nonuniformly is explained by the phase difference of the atomic orbits. The result shows that the currents at each atomic site agree with Kirchhoff quantum current conservation law. Supported by the National Key Basic Research Development Project (Grant No. 2003CB716204), the International Corporation Project of the Education Department of China (Grant No. 20050360563), the Key Laboratory of Advanced Photonic and Electronic Materials of Jiangsu (Grant No. BM2003202) and the State Key Laboratory of Solid State Microstructures of Nanjing University     

One‐Pot Evolution of Ageladine A through a Bio‐Inspired Cascade towards Selective Modulators of Neuronal Differentiation

A bio‐inspired cascade reaction has been developed for the construction of the marine natural product ageladine A and a de novo array of its N1‐substituted derivatives. This cascade features a 2‐aminoimidazole formation that is modeled after an arginine post‐translational modification and an aza‐electrocyclization. It can be effectively carried out in a one‐pot procedure from simple anilines or guanidines, leading to structural analogues of ageladine A that had been otherwise synthetically inaccessible. We found that some compounds out of this structurally novel library show a significant activity in modulating the neural differentiation. Namely, these compounds selectively activate or inhibit the differentiation of neural stem cells to neurons, while being negligible in the differentiation to astrocytes. This study represents a successful case in which the native biofunction of a natural product could be altered by structural modifications.     

Chiral Iodotriptycenes: Synthesis and Catalytic Applications

New iodotriptycenes, including some chiral derivatives, have been synthesised, and their catalytic potential towards oxidative transformations has been investigated. The enantioselectivities observed in the products using chiral iodotriptycene catalysts are low, probably owing to the large distances between the coordinating groups and the iodine moieties in these compounds.     

Novel sequential sigmatropic rearrangements of allylic diols: application to the total synthesis of (-)-kainic acid

Sequential sigmatropic rearrangements (Claisen/Claisen and Claisen/Overman) of enantiopure allylic diols are described. The reactions proceeded in complete diastereoselectivity without protecting group manipulations. The sequential Claisen/Overman rearrangement was successfully applied to the total synthesis of (-)-kainic acid.