Synthesis and radical crosslinking reaction of poly (vinylcyclopropanone acetal)s

Synthesis and radical crosslinking reaction of poly (vinylcyclopropanone acetal)s ( 4 ), volume change on the crosslinking, and thermal analysis of 4 and the crosslinked polymers were carried out. 4 was prepared by the reaction of 1,1-dichloro-2-vinylcyclopropane with sodium dialkoxides. Radical crosslinking of 4a was carried out in the presence of AIBN, BPO, or DTBP at 60, 80, or 120°C, respectively. 4a afforded no dichloromethane-insoluble part in the crosslinking in chlorobenzene but afforded in 37% yield in bulk at 120°C. On the other hand, 4b afforded dichloromethane-insoluble part in 33% yield in the crosslinking in chlorobenzene at 120°C. Volume shrinkage of 4a and 4b on crosslinking at 120°C was 4.11 and 3.55%, respectively. Glass transition temperatures of the crosslinked polymers obtained from 4a and 4b were 28 and 163°C, respectively, which were 32 ～ 49°C higher than those before crosslinking. © 1994 John Wiley & Sons, Inc.     

Reaction of diazonium salts with transition metals : X. Formylation of arenediazonium salts with carbon monoxide and silyl hydrides under palladium catalysis

Arenediazonium tetrafluoroborates (ArN₂BF₄ where Ar = X-C₆H₄; X = H, 2-Me, 3-Me, 4-Me, 4-MeO, 4-MeCO, 4-EtOCO, 2-Ph, 2-Cl, 3-Cl, 4-Cl, 4-Br, 4-I, 3-NO₂ and 4-NO₂) were easily converted to aromatic aldehydes (ArCHO) in good yields through the palladium-catalyzed reaction with CO and Et₃SiH or polymethylhydrosiloxane (PMHS) at room temperature.     

Variation of reaction channel in a flavoenzyme model with a modified pyrimidine ring

A chiral 5-deazaflavin derivative with 2-hydroxymethylphenyl group at N(3) position of the pyrimidine ring has been synthesized. Oxidized form of the 5-deazaflavin derivative is reduced stereo-specifically: the hydroxymethyl group exerts steric inhibition in the absence of Mg²⁺, whereas it facilitates the approach of a reducing agent in the presence of Mg²⁺.     

The specific heat of linear polyethylene after annealing at low temperatures

After annealing at low temperature, linear polyethylene displays an unusual feature in its specific heat curve. On heating, a maximum is observed just above the annealing temperature. The magnitude of this excess specific heat is dependent on the initial level of crystallinity and the temperature and time of annealing. The maximum does not reappear on subsequent cooling followed by rapid heating and represents the formation and disappearance of an unstable structure. These results can be interpreted as a crystallization-melting phenomenon and are consistent with the wide-angle x-ray diffraction patterns. The optimum effects are observed in the β-region (?50°C to 0°C) and could possibly lead to complications in interpreting other phenomena in this temperature range.     

Stereo structures and absolute configurations of reaction products of dl-1,3-dimethylthymine epoxide with l-amino acid ethyl esters

Each reaction of dl-1,3-dimethylthymine epoxide ( 1 ) with L-amino acid ethyl esters (Pro-OEt, Met-OEt, Phe-OEt, and Trp-OEt) afforded the respective four optically active diastereomers 4–7 , stereo structures of which were definitely elucidated as shown in Chart 1 by an X-ray analysis of 4A and chemical means.     

Measurement of the branching ratio and asymmetry of the decay Xi degrees -->Sigma degrees gamma

We have studied the rare weak radiative hyperon decay Xi degrees -->Sigma degrees gamma in the KTeV experiment at Fermilab. We have identified 4045 signal events over a background of 804 events. The dominant Xi degrees -->Lambdapi degrees decay, which was used for normalization, is the only important background source. An analysis of the acceptance of both modes yields a branching ratio of B(Xi degrees -->Sigma degrees gamma)/B(Xi degrees -->Lambdapi degrees ) = (3.34+/-0.05+/-0.09)x10(-3). By analyzing the final state decay distributions, we have also determined that the Sigma degrees emission asymmetry parameter for this decay is alpha(XiSigma) = -0.63+/-0.09.     

Dehydration process in NaCl solutions under various external electric fields

Ionic motions at solid-liquid interface in supersaturated NaCl solutions have been investigated by molecular dynamics (MD) simulation for understanding crystal growth processes. The density profile in the vicinity of the interfaces between NaCl(100) and the supersaturated NaCl solution was calculated. Diffusion coefficients of water molecules in the solution were estimated as a function of distance from the crystal interface. It turned out that the structure and dynamics of the solution in the interfaces was different from those of bulk solution owing to electric fields depending on the surface charge. Therefore, the electric field was applied to the supersaturated solutions and dehydration phenomenon occurring in the process of the crystal growth was discussed. As the electric field increased, it was observed that the Na⁺ keeping strongly hydration structure broke out by the electric force. In supersaturated concentration, the solution structure is significantly different from that of dilution and has a complicated structure with hydration ions and clusters of NaCl. If the electric fields were applied to the solutions, the breakout of hydration structure was not affected with increasing the supersaturated ratio. This reason is that the cluster structures are destroyed by the electric force. The situation depends on the electric field or crystal surface structure.