Scaling factors for the prediction of vibrational spectra. II. The aniline molecule and several derivatives

The structure of aniline was studied by semiempirical, ab initio, and density functional methods. Complete geometry optimization of the minimum energy structure and of the transition states for internal rotation and inversion of the amino group was carried out using several levels. The performance of the different methods in calculating and describing the vibrational frequencies of aniline was determined. The normal modes were characterized by the magnitudes and direction of the displacement vectors. Three procedures were used to obtain the scaled frequencies, two of them new, using specific scale factors and scaling equations from the benzene molecule. The errors obtained were compared with those calculated through other standard procedures. A reassignment of several bands was made. A comparison of the cost‐effective method and procedure of scaling was carried out. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

On the Motion of Shells in General Relativity

We use Lanczos equations to analyze the motionof shells in the gravitational field of a sphericallysymmetric central body. A first integral of Israel'smatching conditions is used to show that the motion of the shell depends on the equation of stateof the shell matter. In particular, the case of abarotropic equation of state is analyzed. The questionof how the type of motion determines the equation of state for the matter of the shell is alsoinvestigated.     

Experimental adiabatic vortex ratchet effect in Nb films with asymmetric pinning trap

Nb films grown on top of an array of asymmetric pinning centers show a vortex ratchet effect. A net flow of vortices is induced when the vortex lattice is driven by fluctuating forces on an array of pinning centers without reflection symmetry. This effect occurs in the adiabatic regime and it could be mimiced only by reversible DC driven forces.     

On the beam propagation through active media

An analytical iterative procedure has been established to determine the amplitude of a laser beam propagating through an active medium. The treatment is valid for both homogeneous and inhomogeneous broadening, and for arbitrary inhomogeneities of the parameters characterizing the active medium, namely, the refractive index, the small-signal gain and the saturation intensity. After a supplementary approximation, a thin-sheet gain approach is derived from the first iteration. The formalism enables us to provide analytical criteria for evaluating both the accuracy of each iteration and the propagation distances for which the thin-sheet solution can be used. This revised version was published online in November 2006 with corrections to the Cover Date.     

A rare head-head binding pattern in bisbenzylisoquinoline alkaloids

Bioassay-guided fractionation of Berberis tabiensis against Culex quinquefasciatus third instar larvae afforded a new bisbenzyltetrahydroisoquinoline alkaloid having an unusual head-head binding pattern. This new alkaloid (tabienine B) is the first member of this family found to possess a diphenyl ether bridge in C-6 and C-7'.     

Rhodium-Catalyzed C,C-Double Bond Cleavage by Molecular Oxygen

Acetylacetonatorhodiumolefin systems, allylrhodium complexes, or (Ph₃P)₃RhCl catalyzed the conversion of alkenes and molecular oxygen to carbonyl compounds via C?C-bond cleavage. For example, 2,3-dimethyl-2-butene was transformed into acetone. Butadiene and isoprene also undergo oxidative C?C-bond cleavage to form acrylaldehyde and related compounds.     

Changing exchange bias in spin valves with an electric current

We show that a high-density electric current, injected from a point contact into an exchange-biased spin valve, systematically changes the exchange bias. The bias can either increase or decrease depending upon the current direction. This observation is not readily explained by the well-known spin-transfer torque effect in ferromagnetic metal circuits, but could be evidence for the recently predicted current-induced torques in antiferromagnetic metals.     

Mechanical properties of blends of PAMAM dendrimers with poly(vinyl chloride) and poly(vinyl acetate)

Hybrid blends of poly(amidoamine) PAMAM dendrimers with two linear high polymers, poly(vinyl chloride), PVC, and poly(vinyl acetate), PVAc, are reported. The interaction between the blend components was studied using dynamic mechanical analysis, xenon nuclear magnetic resonance (NMR) spectroscopy, and tensile property measurements. The data suggest a much higher degree of interaction between components of PVAc-containing blends compared to those containing PVC. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2111–2117, 1998     

A facile preparation of some novel class II mesoionic xanthine acyclonucleosides

The synthesis of the first examples of Class II mesoionic xanthine acyclonucleosides is described. A series of mesoionic anhydro-(8-methoxyalkyl-5-hydroxy-7-oxothiazolo[3,2-a]pyrimidinium hydroxides), Class II mesoionic analogs isoconjugate with xanthine, were prepared by the thermal condensation of methoxyalkyl-2-aminothiazoles with substituted bis(2,4,6-trichlorophenyl)malonic esters. The memoxyalkyl-2-aminothiazoles were prepared via an aromatic nucleophilic substitution reaction between 2-bromothiazole and the appropriate methoxyalkylamine in excess. The resulting 8-methoxyalkyl-substituted mesoionic xanthines were demethylated using iodotrimethylsilane in acetonitrile at room temperature to afford the corresponding mesoionic anhydro-(8-hydroxyalkyl-5-hydroxy-7-oxothiazolo[3,2-a]pyrimidinium hydroxides) as the Class II mesoionic xanthine acyclonucleosides.