Sequoiamonascins a-d: novel anticancer metabolites isolated from a redwood endophyte

Aspergillus parasiticus, a fungal isolate from the bark of a redwood tree (Sequoia sempervirens), has been shown to produce the antitumor metabolites sequoiatones A and B and more recently the sequoiatones C-F. We have also isolated another series of compounds with a new carbon skeleton, the sequoiamonascins. The structures of sequoiamonascins A-D were deduced by interpretation of their spectral data and that of some reaction products. The sequoiamonascins were isolated by brine shrimp lethality-guided fractionation and were submitted to the NCI for anticancer evaluation.     

Synthetic magnetic opals

We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there exists no report in literature on any BiNi compound which is magnetic.     

Temperature hysteretic effect and its influence on colossal magnetoresistance of La0.33Nd0.33Ca0.33MnO3

Electrical resistance (R) measurements of a bulk La_0.33Nd_0.33Ca_0.33MnO₃ perovskite in magnetic fields up to 40 kOe have revealed anomalous temperature hysteretic effects both in 0 Oe and 20 kOe magnetic fields. The sharp peak observed in the R vs. T plot indicates the occurrence of metal-to-insulator (M-I) transition at a temperature of T _MI=110 K and 140 K, for cooling and warming paths, respectively. An applied magnetic field of 20 kOe reduces the resistance and shifts T _MI to 160 K and 185 K for cooling and warming, respectively. We have observed a much higher resistance in the cooling path than in the warming path leading to the hysteretic resistance ratio (R _cool/R _warm) of 200 at 110 K and 1.8 at 160 K for 0 Oe and 20 kOe, respectively. Record values of colossal magnetoresistance (CMR) have been achieved. The CMR value reaches nearly 99% in the temperature ranges of 90 K to 140 K and 90 K to 170 K for 20 kOe and 40 kOe magnetic fields in the cooling mode, respectively. The observed unusual behavior is attributed to the co-existence of La-rich and Nd-rich domains assumed to be distributed randomly in the compound.     

Marine natural products—XV : Polyhalogenated cyclic monoterpenes from the red alga plocamium cartilagineum of antarctica

Examination of the red alga Plocamium cartilagineum (L.) Dixon collected along the Antarctic Peninsula yielded several new cyclic halogenated monoterpenes. The structures of a 2,4-dichloro-trans-1-chloro-vinyl-1-methyl-5-methylene-cyclohexane, a 2-chloro-4-bromo-trans-1-chlorovinyl-1-methyl-5-methylene-cyclohexane, a 2-chloro-trans-1-chlorovinyl-1-methyl-5-chloromethyl-4-cyclohexene, and a 2,5-dichloro-4-bromo-trans-1-chlorovinyl-1-methyl-5-bromomethyl-cyclohexane are described. The structures were determined by spectroscopic methods and chemically related to the halogenated monoterpene violacene.     

Cyclobutadieneiron tricarbonyl carboxylic acids: Synthesis and acidity

Two carboxylic acid derivatives of the cyclobutadieneiron tricarbonyl (I) system have been synthesized and their pK_a values determined. It appears that I tends to be electron withdrawing by induction and electron releasing by resonance.     

Ultra-low-frequency dust-electromagnetic modes in self-gravitating magnetized dusty plasmas

Obliquely propagating altra-low-frequency dust-electromagnetic waves in a self-gravitating, warm, magnetized, two fluid dusty plasma system have been investigated. Two special cases, namely, dust-Alfvén mode propagating parallel to the external magnetic field and dustmagnetosonic mode propagating perpendicular to the external magnetic field have also been considered. It has been shown that effects of self-gravitational field, dust fluid temperature, and obliqueness significantly modify the dispersion properties of these ultra-low-frequency dust-electromagnetic modes. It is also found that in parallel propagating dust-Alfvén mode these effects play no role, but in obliquely propagating dust-Alfvén mode or perpendicular propagating dust-magnetosonic mode the effect of self-gravitational field plays destabilizing role whereas the effect of dust/ion fluid temperature plays stabilizing role.