Facile synthesis of 6-iodo-2,2′-dipivaloyloxy-1,1′-binaphthyl, a key intermediate of high reactivity for selective palladium-catalyzed monofunctionalization of the 1,1′-binaphthalene core

A high-yielding procedure for selective monoiodination of 2,2′-dihydroxy-1,1′-binaphthyl (BINOL) is reported. 6-Iodo-2,2′-dipivaloyloxy-1,1′-binaphthyl, obtained in three steps starting from BINOL in 88% overall yield, proved to be a highly efficient substrate in various palladium-catalyzed coupling (Stille, Heck, Sonogashira, and Suzuki coupling) and carbonylation reactions compared to the analogous 6-bromo derivative.     

LC Enantioseparation of β-Lactam Stereoisomers through the Use of β-Cyclodextrin-Based Chiral Stationary Phases

Direct liquid chromatographic methods were developed to investigate the enantioseparation of 19 β-lactams on three cyclodextrin-bonded chiral stationary phases: permethyl-β-cyclodextrin, β-cyclodextrin and R,S-hydroxypropyl-β-cyclodextrin, prepared by a novel synthetic route. 17 of the 19 β-lactam stereoisomers were partially or baseline-separated on at least one of the tested chiral stationary phases. The influence of the structures of the β-lactams (the positions and types of the substituents, the size of the attached rings) on the enantiomer separation is discussed. The permethylated β-cyclodextrin selector proved to be the most effective one for the tested analytes.     

Real-time nonlinear global state observer design for solar heating systems

Nowadays it is important to investigate and develop solar water heating systems as an environmentally friendly technology. For this reason we introduce a physically-based nonlinear mathematical model that applies to a wide range of solar heating systems. In commercial solar heating systems not all state variables are monitored by direct measurements, since some of them may be technically difficult or expensive to measure. For a better monitoring and more efficient control of the system it may be useful to estimate the unmeasured state variables.As a novelty, we apply a global nonlinear state observer to a solar domestic water heating system. The state observer has been established relatively recently in the field of control theory. The state observer we worked out enables us to estimate the unmeasured state variables in real-time. This observer is global in the sense that it works starting from any initial state. A further contribution of this work is a rather general algorithm for the practical application of the real-time estimation process, and we also give bounds of the estimation error and a practical method to decrease this error.Comparing calculated and measured values for a real particular solar heating system, we justify the usability of the state observer and the estimation process.On the basis of measured data, we show that the nonlinear mathematical model corresponding to the applied nonlinear observer is more accurate than the linear model corresponding to the classical linear Luenberger-type observer, so it is reasonable to apply the nonlinear observer.     

The interaction of heteroaryl-acrylates and alanines with phenylalanine ammonia-lyase from parsley

Acrylic acids and alanines substituted with heteroaryl groups at the beta-position were synthesized and spectroscopically characterized (UV, HRMS, (1)H NMR, and (13)C NMR spectroscopy). The heteroaryl groups were furanyl, thiophenyl, benzofuranyl, and benzothiophenyl and contained the alanyl side chains either at the 2- or 3-positions. While the former are good substrates for phenylalanine ammonia-lyase (PAL), the latter compounds are inhibitors. Exceptions are thiophen-3-yl-alanine, a moderate substrate and furan-3-yl-alanine, which is inert. Possible reasons for these exceptions are discussed. Starting from racemic heteroaryl-2-alanines their D-enantiomers were prepared by using a stereodestructive procedure. From the heteroaryl-2-acrylates, the L-enantiomers of the heteroaryl-2-alanines were prepared at high ammonia concentration. These results can be best explained by a Friedel-Crafts-type electrophilic attack at the aromatic part of the substrates as the initial step of the PAL reaction.     

Quasilinear molecule par excellence, SrCl2: structure from high-temperature gas-phase electron diffraction and quantum-chemical calculations--computed structures of SrCl2.argon complexes

The molecular geometry of strontium dichloride has been determined by high-temperature electron diffraction (ED) and computational techniques. The computation at the MP2 level of theory yields a shallow bending potential with a barrier of about 0.1 kcal mol(-1) at the linear configuration. The experimentally determined thermal average Sr--Cl bond length, r(g), is 2.625+/-0.010 A and the bond angle, angle-spherical(a), is 142.4+/-4.0 degrees . There is excellent agreement between the equilibrium bond lengths estimated from the experimental data, 2.607+/-0.013 A, and computed at different levels of theory and basis sets, 2.605+/-0.006 A. Based on anharmonic analyses of the symmetric and asymmetric stretching as well as the bending motions of the molecule, we estimated the thermal average structure from the computation for the temperature of the ED experiment. In order to emulate the effect of the matrix environment on the measured vibrational frequencies, a series of complexes with argon atoms, SrCl(2)Ar(n) (n=1-7), with different geometrical arrangements were calculated. The complexes with six or seven argon atoms approximate the interaction best and the computed frequencies of these molecules are closer to the experimental ones than those computed for the free SrCl(2) molecule.     

Structure of Ag(111)-p(4 x 4)-O: no silver oxide

The structure of the oxygen-induced p(4 x 4) reconstruction of Ag(111) is determined by a combination of scanning tunneling microscopy, surface x-ray diffraction, core level spectroscopy, and density functional theory. We demonstrate that all previous models of this surface structure are incorrect and propose a new model which is able to explain all our experimental findings but has no resemblance to bulk silver oxide. We also shed some light on the limitations of current density functional theories and the potential role of van der Waals interactions in the stabilization of oxygen-induced surface reconstructions of noble metals.     

Infrared emission and theoretical study of carbon monoxide adsorbed on alumina-supported Rh, Ir, and Pt catalysts

The infrared emission spectra of CO adsorbed on alumina-supported 1, 3, and 5 wt % Rh, Ir, and Pt metal-containing catalysts were studied at 423 and 473 K. While CO is adsorbed in dicarbonyl (dimer), linearly (on-top) bonded and bridged carbonyl forms on rhodium and platinum, the dimer form is dominant on iridium. The relative intensity of Rh-CO and Ir-CO linear bands decrease with increasing temperature compared to the intensity of the dicarbonyl bands; the corresponding bands on Pt behave the opposite way. Two dicarbonyl and two linear Pt-CO bands were identified in the infrared spectra of Pt/Al(2)O(3) catalysts. The surface structure (kinked or planar Pt atoms), the dispersity of the metal, the temperature, and the quantity of adsorbed CO on the surfaces all have an effect on the fine structure of the Pt-CO stretching bands. The metal-carbon and CO stretching force constants were calculated for surface dicarbonyl, linearly bonded CO, and bridged carbonyl species. The metal-carbon stretching wavenumbers and force constants were predicted and compared between surface species and metal carbonyl complexes. The iridium-carbon bonds were found always stronger than the Rh-C and Pt-C ones in all surface species. The observed stretching wavenumbers and force constants seem to support the idea that CO and metal-carbon bonds are always stronger in metal carbonyl complexes than in adsorbed surface species. The distribution and mode of CO adsorption on surface metal sites can be effectively studied by means of infrared emission spectroscopy.     

Adsorption of poly(ethylene oxide) at the air/water interface: a dynamic and static surface tension study

The adsorption of polyethylene oxide (PEO) homologues in a wide range of molecular weight (from M(PEO)=200 to 10(6)) at the air/aqueous solution interface was investigated by dynamic and static surface tension measurements. An approximate estimate for the lower limit of PEO concentration was given at which reliable equilibrium surface tension can be determined from static surface tension measurements. It was shown that the observed jump in the earlier published sigma-lg(c(PEO)) curves is attributable to the nonequilibrium surface tension values at low PEO concentrations. The adsorption behavior of short chain PEO molecules (M(PEO)1000) is similar to that of the ordinary surfactants. The estimated standard free energy of PEO adsorption, DeltaG(0), increases linearly with the PEO molecular weight until M(PEO)=1000. In this molecular weight range, DeltaG(0) was found to be approximately the fifth of the hydrophobic driving force related to the adsorption of a surfactant with the same number of methylene groups. In the case of the longer chain PEOs the driving force of adsorption is so high that the adsorption isotherm is near saturation in the experimentally available polymer concentration range. Above a critical molecular weight the PEO adsorption reveals universal features, e.g., the surface tension and the surface density of segments do not depend on the polymer molecular weight.     

Ordering transition and demixing of a binary mixture of thick and thin rodlike molecules in the presence of an external field

The effect of an external field (electric/magnetic) on the phase behavior of the binary mixture of very long thick and thin rodlike particles is studied. Both the thick and thin particles possess positive but different susceptibility anisotropics (Delta alpha). The difference in the extent of interaction between the external field and the two species is varied by means of a coupling parameter (l = Delta alpha(thick)/Delta alpha(thin)). Isotropic-nematic phase transition and demixing phase transitions taking place both in the isotropic and nematic phases are examined as a function of field strength on the level of the second virial theory of Onsager in the range of 0 < l <1. The approximate sixth order Legendre polynomial expansion method is used to represent the excluded volume interaction between the rodlike particles. It is found that the isotropic phase becomes weakly nematic (paranematic) in the presence of external field and the field orients both components in the direction of the field even if the field does not have direct interaction with the thick component (l = 0). Analytical expressions are derived for the external field induced order parameters and birefringence. The increasing field destabilizes both types of demixing transitions (isotropic-isotropic and nematic-nematic) and the paranematic-nematic phase transition. Moreover it induces closed loop immiscibility, and upper and lower critical points terminating the paranematic-nematic phase coexistence may occur for low values of the coupling parameter. It is interesting that while the phase boundaries of the paranematic-paranematic demixing and the paranematic-nematic transitions are very sensitive to the value of the coupling parameter at low pressures, the paranematic-nematic and nematic-nematic phase boundaries are practically independent of the coupling parameter at high pressures.