Reactions of 2-pyridylphenylacetonitrile and 1,2-dicyano-1,2-diphenyl-1,2-di(2-pyridyl)ethane with cobalt(II), nickel(II), copper(II) and zinc(II) chlorides and copper(II) bromide

Summary 2-Pyridylphenylacetonitrile (ppa) is oxidized by copper(II) halides in 1,2-dichloroethane to 1,2-dicyano-1,2-diphenyl-1,2-di(2-pyridyl)ethane (dcppe), yielding 41 complexes of dcppe with copper(II) dihalide, [CuX₂(dcppe)₄] (green). Nickel(II) and zinc(II) chlorides react with ppa giving complexes of a general formula [MCl₂(ppa)₂].Dcppe reacts with copper(II), zinc(II) chlorides and copper(II) bromide yielding complexes of formulae [CuCl₂(dcppe)₄] (yellow), [ZnCl₂(dcppe)₂] and [CuBr₂(dcppe)]. No reaction is observed with cobalt(II) and nickel(II) chlorides.     

Diffuse-reflectance Fourier transform-infrared spectroscopic microanalysis of the flavonolignans

Diffuse-reflectance Fourier transform-infrared spectroscopic (DRIFT) microanalysis (10 g samples) of a selected series of flavonoids was studied, comparing to transmission FT-IR spectroscopic analysis of the same samples at the mg level. DRIFT was shown to be a useful, sample-saving and reliable IR technique for the structural analysis and compound identification of the mainSilybum genus 3-OH-flavonolignans (silybin, isosilybin, silydianin, silychristin and isosilychristin) and the dihydroflavonol taxifolin.     

Solar energy conversion from water photolysis by biological and chemical systems

The production of chemicals and fuels, or energy-rich compounds, from water by sunlight is described as a particularly attractive means for the conversion of solar energy to a valuable renewable resource. The redox properties of photoexcited molecules and the operating mechanism of light-driven systems are first considered. The mechanism of water oxidation carried out by higher plants and green algae-which is actually one of the most important biochemical reactions—as well as that of artificial photosystems, up-to-now designed trying to simulate the natural process with higher efficiency and simplicity, are likewise discussed. A number of biological and chemical light-driven systems are presented as practical ways to solar energy conversion.     

A proposal for the molecular basis of μ and δ opiate receptor differentiation based on modeling of two types of cyclic enkephalins and a narcotic alkaloid

Summary The molecular basis underlying the divergent receptor selectivity of two cyclic opioid peptides Tyr-c[N -d-Orn²-Gly-Phe-Leu-] (c-ORN) and [d-Pen², l-Cys⁵]-enkephalinamide (c-PEN) was investigated using a molecular modeling approach. Ring closure and conformational searching procedures were used to determine low-energy cyclic backbone conformers. Following reinsertion of amino acid side chains, the narcotic alkaloid 7-[(1R)-1-methyl-1-hydroxy-3-phenylpropyl]-6,14-endoethenotetrahydro oripavine (PEO) was used as a flexible template for bimolecular superpositions with each of the determined peptide ring conformers using the coplanarity and cocentricity of the phenolic rings as the minimum constraint. A vector space of PEO, accounting for all possible orientations for the C₂₁-aromatic ring of PEO served as a geometrical locus for the aromatic ring of the Phe⁴ residue in the opioid peptides. Although a vast number of polypeptide conformations satisfied the criteria of the opiate pharmacophore, they could be grouped into three classes differing in magnitude and sign of the torsional angle values of the tyrosyl side chain. Only class III conformers for both c-ORN and c-PEN, having tyramine dihedral angles ₁ =–150° ± 30° and ₂=–155° ± 20°, had significant structural and conformational properties that were mutually compatible while respecting the PEO vector space. Comparison of these properties in the context of the divergent receptor selectivity of the studied opioid peptides suggests that the increased distortion of the peptide backbone in the closure region of c-PEN together with the pendant ,-dimethyl group, combine to generate a steric volume which is absent in c-ORN and that may be incompatible with a restrictive topography of the receptor. The nature and stereo-chemistry of substituents adjacent to the closure region of the peptides could also modulate receptor selection by interacting with a charged () or neutral () subsite.     

Geometrization of the physics with teleparallelism. I. The classical interactions

A connection viewed from the perspective of integration has the Bianchi identities as constraints. It is shown that the removal of these constraints admits a natural solution on manifolds endowed with a metric and teleparallelism. In the process, the equations of structure and the Bianchi identities take standard forms of field equations and conservation laws.The Levi-Civita (part of the) connection ends up as the potential for the gravity sector, where the source is geometric and tensorial and contains an explicit gravitational contribution.Nonlinear field equations for the torsion result. In a low-energy approximation (linearity andlow energy-momentumtransfer), the postulate that only charge and velocities contribute to the source transforms these equations into the Maxwell system. Moreover, the affine geodesics become the equations of motion of special relativity with Lorentz force in the same approximation [J. G. Vargas,Found. Phys. 21, 379 (1991)]. The field equations for the torsion must then be viewed as applying to an electromagnetic/strong interaction.A classical unified theory thus arises where the underlying geometry confers their contrasting characters to Maxwell-Lorentz electrodynamics and to an Einstein's-like theory of gravity. The highly compact field equations must, however, be developed in phase-spacetime, since the connection is velocity-dependent, i.e., Finsler-like.Further opportunities for similarities with present-day physics are discussed: (a) teleparallelism allows for the formulation of the torsion sector of the theory as a flat space theory with concomitant point-dependent transformations; (b) spinors should replace Lorentz frames in their role as the subjects to which the connection refers; (c) the Dirac equation consistent with the frame bundle for a velocity-dependent metric with Lorentz signature generates a weak-like interaction in the torsion sector.Work done at the Department of Mathematics and Physics of the Interamerican University of Puerto Rico, San German, Puerto Rico 00683.