A system of one dimensional balls with gravity

We introduce a Hamiltonian system with many degrees of freedom for which the nonvanishing of (some) Lyapunov exponents almost everywhere can be established analytically.Supported in part by the Sloan Foundation and the NSF Grant DMS-8807077     

Study of some interfering processes in the arsenic, antimony and selenium determination by hydride generation atomic absorption spectrometry

Summary A detailed study of interfering processes in the determination of As, Sb and Se using a twin-channel hydride generation flow-system is presented. The influence of As, Sb, Se and Sn on all three studied elements has a similar character and occurs in the gas phase only. In the presence of bismuth and tellurium interferences occur also in the liquid phase. It was found that arsenic and antimony may influence the analytical signals of elements with analytical lines in the range from 190 to 235 nm by non-specific absorption due to molecular band spectra.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Atom transfer radical polymerization of ionic liquid 2‐(1‐butylimidazolium‐3‐yl)ethyl methacrylate tetrafluoroborate

Polymeric forms of ionic liquids may have many potential applications because of their high thermal stability and ionic nature. They are generally synthesized by conventional free‐radical polymerization. Here we report a living/controlled free‐radical polymerization of an ionic liquid monomer, 2‐(1‐butylimidazolium‐3‐yl)ethyl methacrylate tetrafluoroborate (BIMT), via atom transfer radical polymerization. Copper bromide/bromide based initiator systems polymerized BIMT very quickly with little control because of fast activation but slow deactivation. With copper chloride as the catalyst and trichloroacetate, CCl₄, or ethyl α‐chlorophenylacetate as the initiator, BIMT was polymerized at 60 °C in acetonitrile with first‐order kinetics with respect to the monomer concentration. The molecular weight was linearly dependent on the conversion. The monomer concentration strongly affected the polymerization: a low monomer concentration caused the polymerization to be incomplete, probably because of catalyst disproportionation in polar solvents. The addition of a small amount of pyridine suppressed such disproportionation, but a further increase in the amount of pyridine greatly slowed the polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5794–5801, 2004     

R-matrix approach to multi-Hamiltonian Lax dynamics

Multi-Hamiltonian Lax dynamics for infinite systems is presented. The R-matrix formalism for 1 + 1 and (2 + 1)-dimensional field systems and (1 + 1)-dimensional lattice systems is revieved.     

Non-Hamiltonian systems separable by Hamilton–Jacobi method

We show that with every separable classical Stäckel system of Benenti type on a Riemannian space one can associate, by a proper deformation of the metric tensor, a multi-parameter family of non-Hamiltonian systems on the same space, sharing the same trajectories and related to the seed system by appropriate reciprocal transformations. These systems are known as bi-cofactor systems and are integrable in quadratures as the seed Hamiltonian system is. We show that with each class of bi-cofactor systems a pair of separation curves can be related. We also investigate the conditions under which a given flat bi-cofactor system can be deformed to a family of geodesically equivalent flat bi-cofactor systems.     

Spectrophotometric study of the formation of ternary complexes of iron(III) with some triphenylmethane dyes and cationic surfactants

The optimum conditions have been found for the formation of the ternary complexes of iron(III) with Chrome Azurol S (CAS), Eriochrome Cyanine R, and Pyrocatechol Violet in the presence of cetyltrimethylammonium (CTA), cetylpyridinium, or tetradecyldimethyl-benzylammonium ions. The pH range of the complex formation is limited mainly by the pertinent hydrolysis constants of the metal ions. The maximum absorbances were obtained for excess R and cationic surfactants, ensuring the formation of complexes with the highest R:Fe molar ratio. The method based on the Fe-CAS-CTA system (ε = 1.32 × 10⁵ liter mol⁻¹ cm⁻¹ at 628 nm) is most sensitive and is recommended for the spectrophotometric determination of iron.     

A stereoselective synthesis of 1,2-diols from α-hydroxyaldehydes

The addition of lithium acetylides to (20R)-20-hydroxypregnane-22-carboxaldehydes in the absence and in the presence of BF₃ afforded predominantly 20R,22R- or 20R,22s-diols, respectively, characteristic of ecdysones.     

Optoelectronic switches based on wide band gap semiconductors

Switching of photocurrent direction in semiconducting systems upon changes of the electrode potential or incident light wavelength was realized by a series of photoelectrodes covered with titania modified with pentacyanoferrate complexes, [Fe(CN)(5)L](n)(-) (L = NH(3), thiodiethanol, thiodipropanol). These materials were characterized by optical spectroscopy and electrochemistry. The structure of the surface complexes was modeled using simple quantum-chemical models. The electrodes described in this paper enable control of the photocurrent direction by two stimuli: Changing the wavelength or the photoelectrode potential easily switches the direction of photocurrent. The materials are different from those of similar characteristics studied by other authors: They are not composites comprising of two types of semiconductors but rather engineered uniform materials. The photocurrent switching phenomenon is an intrinsic feature resulting from a specific electronic structure of the surface-modified semiconductor.     

Gaseous arginine conformers and their unique intramolecular interactions

Extensive ab initio calculations were employed to characterize stable conformers of gaseous arginine, both the canonical and zwitterionic tautomers. Step-by-step geometry optimizations of possible single-bond rotamers at the B3LYP/6-31G(d), B3LYP/6-31++G(d,p), and MP2/6-31++G(d,p) levels yield numerous structures that are more stable than any known ones. The final electronic energies of the conformers were determined at the CCSD/6-31++G(d,p) level. The lowest energies of the canonical and zwitterionic structures are lower than the existing values by 2.0 and 2.3 kcal/mol, respectively. The relative energies, rotational constants, dipole moments, and harmonic frequencies of the stable conformers remain for future experimental verification. The conformational distributions at various temperatures, estimated according to thermodynamic principles, consist almost exclusively of the newly found structures. One striking feature is the occurrence of blue-shifting hydrogen bonds in all six of the most stable conformers. A unique feature of important conformations is the coexistence of dihydrogen and blue- and red-shifting hydrogen bonds. In addition to the hydrogen bonds, the stereoelectronic effects were also found to be important stabilization factors. The calculated and measured proton affinities agree within the theoretical and experimental uncertainties, affirming the high quality of our conformational search. The theoretical gas-phase basicity of 245.9 kcal/mol is also in good agreement with the experimental value of 240.6 kcal/mol. The extensive searches establish firmly that gaseous arginine exists primarily in the canonical and not the zwitterionic form.