Synthesis and biological activity of novel mitomycin C analogs derived from mitomycin A

A variety of mitomycin C analogs were synthesized from mitomycin A and their biological activities were studied. Mitomycin A ( 1 ) underwent nucleophilic displacement reactions involving intramolecular hydrogen migrations upon treatment with nitrogen nucleophiles bearing mobile hydrogens, but the mode of hydrogen migration depended on the nature of the nucleophiles. The reaction with alkoxyamines gave compounds 6 and 7 which have the 5H-6-alkoxyimino-4,7-dione structure in ring A of 1 . However, the reaction with hydroxylamine and benzoylhydrazine afforded compounds 11 and 13 which have the 4-hydroxy-6-hydroxyimino-7-one structure and the 4-hydroxy-6-hydrazono-7-one structure, respectively, in ring A of 1 . These products were converted into various types of mitomycin C derivatives by methylation with methyl iodide or dimethyl sulfate. The mechanistic features of these reactions are discussed. The in vitro and in vivo biological activities were tested by using P388 leukemia and Sarcoma 180 tumor cells. Several of the synthesized compounds exhibited better activity than that of mitomycin C.     

Reconstruction of the signal produced by a directional sound source from remote multi-microphone recordings

A mathematical method for reconstructing the signal produced by a directional sound source from knowledge of the same signal in the far field, i.e., microphone recordings, is developed. The key idea is to compute inverse filters that compensate for the directional filtering of the signal by the sound source directivity, using a least-square error optimization strategy. Previous work pointed out how the method strongly depends on arrival times of signal in the microphone recordings. Two strategies are used in this paper for calculating the time shifts that are afterward taken as inputs, together with source directivity, for the reconstruction. The method has been tested in a laboratory environment, where ground truth was available, with a Polaroid transducer as source. The reconstructions are similar with both strategies. The performance of the method also depends on source orientation.     

Molecular Shape Selectivity for Polycyclic Aromatic Compounds on a Core–Shell Octadecylsilica Stationary Phase at Subambient Column Temperatures

Molecular shape selectivity for polycyclic aromatic compounds on a core–shell-type octadecylsilica (ODS) phase at subambient column temperatures was studied in reversed-phase liquid chromatography. The plate height on the core–shell ODS column was relatively stable at subambient column temperatures when compared with that of a conventional ODS column. In order to compare the sample diffusivities in the conventional and core–shell ODS columns, van Deemter plots were prepared. The plate height of the core–shell column was significantly lower than that of conventional column, suggesting an advantageous feature of the core–shell-type stationary phase especially at a high flowrate of the mobile phase. An enhanced molecular shape recognition capability of the core–shell ODS phase was also confirmed at subambient column temperature. The result could be consistent with an improved shape selectivity as normally observed on conventional ODS phases at low temperatures, however, the enhanced molecular shape recognition capability of the core–shell phase enables a good separation between benz[a]anthracene and chrysene at subambient column temperatures. Similar improved shape selectivities for terphenyl isomers were also confirmed on the core–shell phase.     

Crazing and shear deformation of polymer alloys

Crazing and/or shear yielding mechanisms in multiphase polymer alloys play a critical role in toughening. The present paper describes the use of finite element models (FEM) to simulate the crazing and shear deformation behaviour around the particles embedded in brittle or ductile matrices. The FEM simulation results on the stress distribution reveal that the dilatational stress within the rubber particles is high enough to cavitate. The stability of craze growth can be reached when the compliant particle is incorporated in a brittle matrix. On the other hand, shear yielding around the particle occurs in the equator of the particle/matrix interface when the stress locally exceeds the yield stress of the matrix. This yield-initiation stress increases with the increase in the elastic modulus and Poisson's ratio of the particles. The toughening mechanism, that cavitation occurs first followed by shear yielding to form a neck between the particles, is discussed based on the simulation results for the two-particle model.     

Synthesis of a soluble conjugated cumulene polymer: poly(biphenyl‐4,4′‐diyl‐1,4‐bis(4‐dodecyloxyphenyl)‐buta‐1,2,3‐triene‐1,4‐diyl)

A conjugated polymer with a butatriene segment in the main chain, poly(biphenyl‐4,4′‐diyl‐1,4‐bis(4‐dodecyloxyphenyl)buta‐1,2,3‐triene‐1,4‐diyl), was synthesized from 1,4‐bis(4‐bromophenyl)‐1,4‐bis(4‐dodecyloxyphenyl)buta‐1,2,3‐triene by dehalogenative polycondensation using Ni(cod)₂. The polymer was well soluble in usual organic solvents such as CHCl₃ and THF. Structural analyses and characterizations were carried out by IR, NMR, UV‐Vis, PL, and Raman spectroscopy, as well as electrical conductivity. It is suggested that π‐conjugation is extended to some degree through biphenylylene and butatrienylene linkages.     

Design and control of morphology for high performance polymer alloys

Ductile polymers are significantly toughened by the addition of an elastomeric phase. The rubber phase acts as a stress concentrator, cavitates during the loading process and initiates localized plastic deformation in matrix. This paper deals with the simulation of the deformation behavior of rubber toughened polycarbonate and the fracture process of the embedded rubber particle. A two-dimensional one particle- and two-particle model with varying surface-to-surface interparticle distances are established. The calculation showed that the polymer matrix has plastically deformed before cavitation for the one-particle model whereas cavitation occurs in the elastic state of the matrix for the two-particle model. Cavitation itself is proved to be a change from the particle-system towards a void-system for both cases. The toughness of the post-cavitated void-system is shown to be dependent on the surface-to-surface interparticle distance and the strain-hardening characteristic of the matrix polymer.