Free differential algebras: Their use in field theory and dual formulation

The gauging of free differential algebras (FDA's) produces gauge field theories containing antisymmetric tensors. The FDA's extend the Cartan-Maurer equations of ordinary Lie algebras by incorporating p-form potentials (p>1). We study here the algebra of FDA transformations. To every p-form in the FDA, we associate an extended Lie derivative l generating a corresponding gauge transformation. The field theory based on the FDA is invariant under these new transformations. This gives geometrical meaning to the antisymmetric tensors. The algebra of Lie derivatives is shown to close and provides the dual formulation of FDA's.     

Diffusion in a one-dimensional gas of hard point particles

We simulate the classical diffusion of a particle of massM in an infinite one-dimensional system of hard point particles of massm in equilibrium. Each computer run corresponds to about 10⁸ collisions of the diffusive particle. We find that (t) 1/t fort large enough, and a crossover from an M m regime where=2 to=3 forM=m. The diffusion constant has a sharp maximum atM=m. We study moments x(t)² and x(t)⁴, and examine the behavior ofq ² (t)=x(t)⁴/3x(t)²². We find thatq(t)1 (consistent with a normal distribution) in theM limit (for all timest) and in the t limit for allM. On sabbatical leave from IVIC-Instituto Venezolano de Investigaciones Cientificas.     

Anodic behaviour of mono- and bisdithiafulvenyl-9,9′-spirobifluorene: insertion of vinylogous TTF into the spirobifluorenyle framework

New three-dimensional copolymers containing 9,9′-spirobifluorenyl-ethylene units were prepared by anodic oxidation of 9,9′-spirobifluorenes 2-mono- or 2,7′-disubstituted by a dithiafulvenyl unit. The synthesis, physicochemical properties and electrochemistry of both monomers and derived oligomers and polymers are reported.     

Synthesis and acid-base properties of (1H-benzimidazol-2-yl-methyl)phosphonate (Bimp2-). Evidence for intramolecular hydrogen-bond formation in aqueous solution between (N-1)H and the phosphonate group

The synthesis of (1H-benzimidazol-2-yl-methyl)phosphonic acid, H2(Bimp)+/-, is described: 2-chloromethylbenzimidazole was reacted with ethylchloroformate to give 1-carboethoxy-2-chloromethylbenzimidazole which was treated with trimethyl phosphite and after hydrolysis with aqueous HBr H2(Bimp)+/- was obtained. In H2(Bimp)+/- one proton is at the N-3 site and the other at the phosphonate group; both acidity constants were determined in aqueous solution by potentiometric pH titrations (25 degrees C; I = 0.1 M, NaNO3) and this furnished the pKa values of 5.37 +/- 0.02 and 7.41 +/- 0.02, respectively. The acidity constant for the release of the primary proton from the P(O)(OH)2 group of H3(Bimp)+ was estimated: pKa = 1.5 +/- 0.2. Moreover, Bimp2- can be further deprotonated at its neutral (N-1/N-3)H site to give the benzimidazolate residue, but this reaction occurs only in strongly alkaline solution (KOH); application of the H_ scale developed by G. Yagil (J. Phys. Chem., 1967, 71, 1034) together with UV spectrophotometric measurements gave pKa = 14.65 +/- 0.12. Comparisons with acidity constants taken from the literature show that this latter pKa value is far too large and this allows the conclusion that an intramolecular hydrogen bond is formed between the (N-1/N-3)H site and the phosphonate group of Bimp2-; the formation degree of this hydrogen-bonded isomer is estimated to be 98 +/- 2%. The general relevance of this and the other results are shortly discussed and the species distribution for the Bimp system in dependence on pH is provided.     

Crystal structures and voltammetric behavior of three copper(II) complexes derived from bulky Schiff bases

Three Schiff base copper(II) complexes have been prepared and characterized by elemental analysis, mass spectra, i.r., electronic spectra, _eff and X-ray crystal structures. Cyclic voltammetry studies on the complexes indicate a dependence of the cathodic potentials upon electronic effects, but independence on the solid state structure.     

SPECA: a program for the calculation of thermodynamic equilibrium constants from spectrophotometric data

A computer program called SPECA and written in compiled BASIC (Microsoft QuickBasic Ver. 4.5) has been written for the calculation of thermodynamic constants in solution equilibria studies from spectrophotometric measurements. In order to calculate the thermodynamic constants it is necessary to introduce different theories to estimate the activity coefficients of the system involved under investigation. In this version of the program the equations proposed in the models of Debye-Hückel. Specific Interaction Theory (SIT) or the Modified's Bromley Theory can be chosen. To achieve its purpose, the program uses absorbance and activity or free concentration data of one of the components, normally H(+), and it is not limited with respect to the number of components that can be studied. Minimization of the error square sum in the absorbance, which can be absolute or relative, is carried out using the Levenberg-Marquardt-Nash algorithm at three different levels: equilibrium constants in the first level, molar absorptivities in the second and interaction coefficients in the third for those systems using the SIT or the Modified Bromley's Theories.     

Use of a continuous flow solid-phase spectroscopic sensor using two sensing zones: determination of thiamine and ascorbic acid

A simple, rapid, inexpensive, and automated flow-through solid-phase spectroscopic sensing device is proposed for the sequential determination of 2 vitamins: thiamine and ascorbic acid. The vitamins are concentrated on ion-exchange gels, thiamine on Sephadex SP C-25, and ascorbic acid on Sephadex QAE A-25; both solid supports are packed in 2 different flow cells. The absorbance is monitored directly on the solid phase with a double-beam spectrophotometer at 250 nm, without derivatization or additional elution. With the use of 2 carrier/self-eluting solutions (0.1 5M sodium acetate/acetic acid and 0.18M citric acid/K2HPO4) and a sample volume of 1000 microL, the sensor responds linearly in the range of 0.5-15 and 3-50 microg/mL with detection limits of 0.14 and 0.36 microg/mL for thiamine and ascorbic acid, respectively. When the method was applied to synthetic samples and pharmaceutical preparations, precise and accurate values were obtained.     

Study of the ESI-mass spectrometry ionization mechanism of Fischer carbene complexes

By means of deuterium-labeling experiments, we have carried out a systematic ESI-MS study to determine the mechanism of ESI ionization of alkenyl and alkynyl group 6 Fischer carbene complexes. These compounds can be ionized under ESI conditions only in the presence of additives such as hydroquinone (HQ) or tetrathiafulvalene (TTF). Our results demonstrate that in the ESI source an anion-radical is formed after the initial HQ- or TTF-mediated electron transfer to the metallic carbene complex. For alkenyl carbene complexes, this species evolves by extrusion of a hydrogen radical to form an allenylchromium anion that is detected as the [M - H](-) ion in the mass spectrum. The preference for this mechanistic pathway could be rationalized by DFT calculations. In the case of alkynyl carbene complexes, experiments combining deuterated substrate, additive, and solvent demonstrate that the previously proposed allene-anion carbene complex is not formed. Instead, the H transfer from the ethoxy group in the anion radical, followed by extrusion of a hydrogen radical, leads to an allenyl anion that is detected in the ESI-MS as [M - H - CO](-).