Hydrocarbon microtremors interpreted as nonlinear oscillations driven by oceanic background waves

Characteristic low frequency seismic signals have been observed in areas where hydrocarbon reservoirs are present. A possible interpretation is the excitation of hydrocarbon related resonances. Basic models of an oscillating liquid filled porous medium are investigated. Synthetic spectra of the ab initio Navier–Stokes equations and of basic linear and nonlinear one-dimensional oscillators show characteristic features of measured spectra when oceanic background waves around 0.1–0.2 Hz are assumed to be the external driving force.     

Optically active 4- and 5-coordinate transition metal complexes of bifurcated dipeptide Schiff bases

Symmetrical and unsymmetrical benzophenone Schiff bases of bifurcated dipeptides [e.g., Ar2C=N-CHR1- CONH-HNCO-CHR2-N=CAr2] have been synthesized using Boc methodology. These ligands may be regarded as chiral porphyrin mimics because of the alpha-carbons of the amino acids. The Schiff bases function as effective ligands for transition metals, particularly the late transition metals Ni(II), Cu(II), and Zn. Upon metal insertion, there is loss of the amide protons, resulting in N4 chelating ligands that retain the amino acid based chirality as well as newly generated metal-centered chirality, which for the Ni(II) complexes have been shown by X-ray analysis to be lambda (left-handed helix) if the amino acids are S. For Ni(II) and Cu(II), metal insertion results in highly colored complexes and is easily followed by UV-vis spectrophotometry. Several Ni(II) complexes were also characterized by 1H NMR. Co(II) and Mn(II) complexes were characterized by CW EPR. Two Cu(II) complexes, 7f.CuII and 7k.CuII, were characterized by EPR (ENDOR and ESEEM), which clearly showed the pentacoordinate nature of 7k.CuII.     

C-C bond formation via C-H bond activation: synthesis of the core of teleocidin B4

The core of teleocidin B4, a complex fragment of a natural product containing two quaternary stereocenters and a penta-substituted benzene ring, was synthesized in four C-C bond-forming steps starting from tert-butyl derivative 1. The first step involved alkenylation of the tert-butyl group with a vinyl boronic acid, followed by the successful annulation of the cyclohexane ring to the benzene nucleus via an intramolecular Friedel-Crafts reaction. The third step required a diastereoselective oxidative carbonylation of the geminal dimethyl group, followed at last by indole assembly via the alkenylation of the phenol nucleus, to afford the teleocidin B4 core. Noteworthy is the fact that steps 1 and 3 critically depended on the directing role of the aniline nitrogen (directed C-H bond functionalization).     

Crystallization kinetics for semicrystalline random copolymers of vinylidene chloride (VDC) with methyl acrylate (MA), and the effects on the internal morphology of the resin particles formed during synthesis

Isothermal crystallization kinetics for random copolymers of vinylidene chloride (VDC) with methyl acrylate (MA) is reported. Syntheses of many semicrystalline polymers follow heterogeneous reaction paths in which the macromolecule chains phase separate from the reaction mixtures. The internal particle morphology (the internal structure of the resin bead) from this type of reaction is granular and porous, as a result of the demixing processes accompanying polymer formation. Demixing in these polymers involves either liquid-liquid (L-L) phase separation followed by liquid-solid (L-S) transformation (crystallization) or L-S transformation alone. Crystallization (L-S transformation) must be an indispensable part of the process if a porous granular structure is to be expected. This is because L-S transformation is the most probable means by which the demixed structure can be stabilized against complete coalescence or agglomeration, which would lead to totally fused bead internal structure. This is particularly true if the glass transition temperature (T_g) is lower than the polymerization temperatures, as is the case with the VDC-MA copolymers. Copolymers that crystallize the fastest will have the finest (most porous) resin bead morphology. The result of this work is consistent with expectation. The homopolymer (PVDC) that crystallizes the fastest has the finest resin bead internal morphology. The copolymers show slower crystallization rates with increasing noncrystallizable MA content. Correspondingly, resin morphology measured by specific surface area decreased with increasing amounts of the noncrystallizable (MA) comonomer unit in the copolymer. This is clearly seen in SEM photographs of the internal bead structures of these copolymers. ©1995 John Wiley & Sons, Inc.     

Catalysis by amino acid-derived tetracoordinate complexes: enantioselective addition of dialkylzincs to aliphatic and aromatic aldehydes

Me(2)Zn and Et(2)Zn added to aromatic and aliphatic aldehydes in the presence of 3 mol % of 2. (S)-1-Phenylethanol (91% ee) and (S)-1-phenylpropanol (86% ee) were synthesized from benzaldehyde and (S)-1-furan-2-yl-1-propanol (86% ee) from 2-furaldehyde. Nonanal and 3-phenylpropanal provided (S)-3-undecanol (96% ee) and (S)-1-phenyl-3-pentanol (94% ee). A solid-phase variant was effective with reduced ee's (e.g., 86% ee --> 79% ee) for (S)-1-phenylpropanol.