Synthesis and orientation study of a magnetically aligned liquid‐crystalline chitin/poly(acrylic acid) composite

A high magnetic field of 5 T was used to fabricate a magnetically aligned, optically anisotropic, liquid‐crystalline chitin/poly(acrylic acid) composite. The aligned mesophase was fixed by photoinitiated free‐radical polymerization. From an examination of polarized optical micrographs and an X‐ray diffraction study, a high degree of orientation of 0.70 was observed for the composite with a higher liquid‐crystalline chitin concentration (10.70 wt %); the orientation was reduced with a decreased chitin concentration at a given acrylic acid concentration. The X‐ray data for the developed composite showed a uniplanar orientation for the chitin crystallites, with its molecular long axes perpendicular to the direction of the magnetic field. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 711–714, 2003     

Some New Results on Key Distribution Patterns and Broadcast Encryption

This paper concerns methods by which a trusted authority can distribute keys and/or broadcast a message over a network, so that each member of a privileged subset of users can compute a specified key or decrypt the broadcast message. Moreover, this is done in such a way that no coalition is able to recover any information on a key or broadcast message they are not supposed to know. The problems are studied using the tools of information theory, so the security provided is unconditional (i.e., not based on any computational assumption).In a recent paper st95a, Stinson described a method of constructing key predistribution schemes by combining Mitchell-Piper key distribution patterns with resilient functions; and also presented a construction method for broadcast encryption schemes that combines Fiat-Naor key predistribution schemes with ideal secret sharing schemes. In this paper, we further pursue these two themes, providing several nice applications of these techniques by using combinatorial structures such as orthogonal arrays, perpendicular arrays, Steiner systems and universal hash families.     

Reactions de photoaddition de benzo[b]selenophenes avec l'acetylene dicarboxylate de methyle et avec le dichloro-1,2 ethylene

Photoirradiated in presence of acetophenone, benzo[b]selenophene and its 3-methyl derivative add to dimethyl acetylenedicarboxylate. In each ease, the primary reaction product is unstable and has not been isolated. Photoexeited in its triplet state (the energy of which is in the neighbourhood of 69 $\text{kcal}\text{mole}$) benzo[b]selenophene and its 2- and 3-methyl, 2,3 dimethyl, 3 acetoxy and 2-methyl-3-acetoxy derivatives add to 1,2 dichloroethylene leading to cyclobutanes. Neither cyclo-addition occurs in absence of photosensitiser. Single-crystal X-ray analysis gave the structures of the two adducts of 3-acetoxybenzo[b]selenophene with trans-1,2-dichloroethylene. In both compounds the chlorine atoms are trans.     

3-(Triethoxysilyl)propionitrile sol-gel coating

3-(Triethoxysilyl)propionitrile (TESPN) sol-gel has been prepared under different conditions. It was employed for coating the surfaces of quartz and aluminum. Infrared (IR) and Raman spectra of TESPN and TESPN sol-gels have been recorded in the study of the sol-gel process. Transmission and reflection absorption IR (RAIR) spectra of TESPN sol-gel coated quartz and aluminum have also been collected for better understanding the film formation on the substrate surfaces. Spectra collected at different temperatures indicated that the silane film on quartz decomposes at 700 degrees C. Results from thermal gravimetric analysis (TGA) supported this result. Based on the group frequencies and the spectral behavior in different states, some vibrational modes were assigned to the observed bands. The anticorrosion behavior of the sol-gel coated aluminum in comparison with the uncoated metal was evaluated by measuring the potentiodynamic polarization and electrochemical impedance spectra (EIS).     

A mild deprotection strategy for allyl-protecting groups and its implications in sequence specific dendrimer synthesis

A mild deprotection strategy for allyl ethers under basic conditions in the presence of a palladium catalyst is described. Under these conditions, aryl allyl ethers can be cleaved selectively in the presence of alkyl allyl ethers. These conditions are also effective in the deprotection of allyloxycarbonyl groups. The utility of the current methodology in sequence specific dendrimer synthesis is demonstrated.     

Reactivity of DNA guanyl radicals with phenolate anions

Guanine bases are the most easily oxidized sites in DNA. Electron-deficient guanine species are major intermediates produced in DNA by the direct effect of ionizing radiation (ionization of the DNA itself) because of preferential hole migration within DNA to guanine bases. By using thiocyanate ions to modify the indirect effect (ionization of the solvent), we are able to produce these single-electron-oxidized guanine radical species in dilute aqueous solutions of plasmid DNA where the direct effect is negligible. The guanyl radical species produce stable modified guanine products. They can be detected in the plasmid by converting them to strand breaks after incubation with a DNA repair enzyme. If a phenol is present during irradiation, the yield of modified guanines is decreased. The mechanism is reduction of the guanine radical species by the phenol. It is possible to derive a rate constant for the reaction of the phenol with the guanyl radical. The pH dependence shows that phenolate anions are more reactive than their conjugate acids, although the difference for guanyl radicals is smaller than with other single-electron-oxidizing agents. At physiological pH values, the reduction of a guanyl radical entails the transfer of a proton in addition to the electron. The relatively small dependence of the rate constant on the driving force implies that the electron cannot be transferred before the proton. These results emphasize the potential importance of acidic tyrosine residues and the intimate involvement of protons in DNA repair.     

Kinetics of the hydrogen abstraction *CH3 + alkane --> CH4 + alkyl reaction class: an application of the reaction class transition state theory

Kinetics of the hydrogen abstraction reaction (*)CH(3) + CH(4) --> CH(4) + (*)CH(3) is studied by a direct dynamics method. Thermal rate constants in the temperature range of 300-2500 K are evaluated by the canonical variational transition state theory (CVT) incorporating corrections from tunneling using the multidimensional semiclassical small-curvature tunneling (SCT) method and from the hindered rotations. These results are used in conjunction with the Reaction Class Transition State Theory/Linear Energy Relationship (RC-TST/LER) to predict thermal rate constants of any reaction in the hydrogen abstraction class of (*)CH(3) + alkanes. Our analyses indicate that less than 40% systematic errors on the average exist in the predicted rate constants using the RC-TST/LER method while comparing to explicit rate calculations the differences are less than 100% or a factor of 2 on the average.     

Domino "[3+3]-cyclization-homo-Michael" reactions of 1,3-bissilyl enol ethers with 1,1-diacylcyclopropanes

The Lewis acid mediated domino "[3+3]-cyclization-homo-Michael" reaction of 1,3-bissilyl enol ethers with 1,1-diacylcyclopropanes allows an efficient one-pot synthesis of functionalized salicylates containing a halogenated side chain. A great variety of substitution patterns could be realized by variation of the starting materials and of the Lewis acid. The mechanism of the domino process was studied.     

Accumulation and distribution of elements in rice /seed,brand layer,husk/ by neutron activation analysis

Various rice samples /seed, brand layer, husk/ from Vietnam were analyzed for Se, Hg, Cr, Ni, Sc, Rb, Fe, Zn and Co by neutron activation analysis. The concentration values found /seed/ were the following: Se 0.04–0.07 ppm, Hg 0.02–0.07 ppm, Cr 2.13–8.65 ppm, Ni 1.56–4.95 ppm, Sc 0.02–0.06 ppm, Rb 0.84–2.71 ppm, Fe 26.31–96.07 ppm, Zn 10.65–27.39 ppm and Co 0.02–0.15 ppm. The values were reported in ppm /dry weight/. Statistical analysis /t-test, t=0.05/ showed that the content of elements varies between sorts of rice; the content of Rb, Fe, Ni, Cr of rice husk was significantly higher than in rice seed and brand layer.