Acceleration waves and stability

A method to examine the stability in case of weak discontinuity waves (acceleration waves) propagating in isotropic media in which mechanical relaxation phenomena occur is used in the case of non linearity. An upper bound for the initial distribution density is obtained.     

Diastereomeric half-sandwich Ru(II) cationic complexes containing amino amide ligands. Synthesis, solution properties, crystal structure and catalytic activity in transfer hydrogenation of acetophenone

The cationic complexes [(η⁶-arene)Ru(N,O-amino amide)X]Y (arene = p-cymene or indane; N,O-amino amide = (l)-proline amide or (l)-phenylalanine amide; X = Cl or I; Y = Cl, I or PF₆) have been synthesised and fully characterized by spectroscopic and analytical methods. In several cases (1a, 3a, 4a, 4b, 5) the metal configuration has been definitively established by X-ray analysis on single crystal. The lability of the metal center in solution has been studied by ¹H NMR and CD techniques. The highest configurational stability has been found in the complexes of the type [(η⁶-indane)Ru(N,O-proline amide)Cl]Y (4a,b). The complexes 1b, 2a-b, 3b, 4b and 5 are good precatalysts for the transfer hydrogenation of acetophenone in basic i-PrOH, with ee up to 76% at 30 °C. An ESI(+)-MS study of pre-catalytic solutions has provided useful information on the catalytic mechanism.     

Surface Adsorption and Photo-Reactivity of Sulfonylurea Herbicides

Photodegradation of two sulfonylurea herbicides, triasulfuron and thifensulfuron-methyl adsorbed on Preveza or Nea Malgara soils (Greece) was studied in outdoor and laboratory experiments. Herbicides on adsorbed phase and kept in the dark were characterised by a high reactivity, giving depletion curves that can be all described by a first order equation. In the irradiation experiments the kinetic behaviour of photodegradation was complex and characterised by a double step photoreaction. After a first period varying from 8 to 24 h the rate of reaction was reduced to 7-31% of the initial rate. The kinetic constant related to the degradation of triasulfuron practically showed the same values of those obtained for thifensulfuron-methyl. The half-lives obtained on Nea Malgara soil were generally higher than those obtained using Preveza soil. The observed behaviour is explained considering the photochemical properties of the herbicides, and the organic matter content of the soils.     

Measuring surface topography with scanning electron microscopy. I. EZEImage: a program to obtain 3D surface data.

Scanning electron microscopy (SEM) is widely used in the science of materials and different parameters were developed to characterize the surface roughness. In a previous work, we studied the surface topography with fractal dimension at low scale and two parameters at high scale by using the variogram, that is, variance vs. step log-log graph, of a SEM image. Those studies were carried out with the FERImage program, previously developed by us. To verify the previously accepted hypothesis by working with only an image, it is indispensable to have reliable three-dimensional (3D) surface data. In this work, a new program (EZEImage) to characterize 3D surface topography in SEM has been developed. It uses fast cross correlation and dynamic programming to obtain reliable dense height maps in a few seconds which can be displayed as an image where each gray level represents a height value. This image can be used for the FERImage program or any other software to obtain surface topography characteristics. EZEImage also generates anaglyph images as well as characterizes 3D surface topography by means of a parameter set to describe amplitude properties and three functional indices for characterizing bearing and fluid properties.     

Generalized heat-transport equations: parabolic and hyperbolic models

We derive two different generalized heat-transport equations: the most general one, of the first order in time and second order in space, encompasses some well-known heat equations and describes the hyperbolic regime in the absence of nonlocal effects. Another, less general, of the second order in time and fourth order in space, is able to describe hyperbolic heat conduction also in the presence of nonlocal effects. We investigate the thermodynamic compatibility of both models by applying some generalizations of the classical Liu and Coleman–Noll procedures. In both cases, constitutive equations for the entropy and for the entropy flux are obtained. For the second model, we consider a heat-transport equation which includes nonlocal terms and study the resulting set of balance laws, proving that the corresponding thermal perturbations propagate with finite speed.     

Measuring surface topography by scanning electron microscopy. II. Analysis of three estimators of surface roughness in second dimension and third dimension.

Scanning electron microscopy (SEM) is widely used in surface studies and continuous efforts are carried out in the search of estimators of different surface characteristics. By using the variogram, we developed two of these estimators that were used to characterize the surface roughness from the SEM image texture. One of the estimators is related to the crossover between fractal region at low scale and the periodic region at high scale, whereas the other estimator characterizes the periodic region. In this work, a full study of these estimators and the fractal dimension in two dimensions (2D) and three dimensions (3D) was carried out for emery papers. We show that the obtained fractal dimension with only one image is good enough to characterize the roughness surface because its behavior is similar to those obtained with 3D height data. We show also that the estimator that indicates the crossover is related to the minimum cell size in 2D and to the average particle size in 3D. The other estimator has different values for the three studied emery papers in 2D but it does not have a clear meaning, and these values are similar for those studied samples in 3D. Nevertheless, it indicates the formation tendency of compound cells. The fractal dimension values from the variogram and from an area versus step log-log graph were studied with 3D data. Both methods yield different values corresponding to different information from the samples.     

Synthesis and spectroscopic and structural characterization of two novel photoactivatable Ca2+ compounds

Two novel photoactivatable Ca(2+) compounds were synthesized to achieve a fast concentration jump of calcium ions in solution; this is of paramount importance for investigating the physiological cellular response. The light-sensitive ligands 4-(2-nitrophenyl)-3,6-dioxaoctane dioic acid (H2L1) and 4-(4,5-dimethoxy-2-nitrophenyl)-3,6-dioxaoctane dioic acid (H2L2) were generated by multistep syntheses, and the corresponding calcium complexes, Ca1 and Ca2, were isolated and characterized. The solution equilibria of H2L1 and H2L2 with Ca2+ were investigated; for both ligands, the formation of a 1:2 Ca2+/ligand species is detected and the complete characterization is presented. The crystal structures of Ca1 and Ca2 were determined. In Ca1 the solid state assembly is attained by a polymeric association of [(CaL1(H2O))2(mu-OH2)] dimeric units. Each calcium ion coordinates four oxygen atoms of one ligand (two ethereal, one carboxylic, and one bridging carboxylic oxygen atom), one water molecule, one bridging water molecule, and a carboxylate group of the other ligand within the dimer. The octacoordination of the metal is completed by an interaction with the adjacent dimeric unit. The crystal structure of the complex Ca2 does not show a polymeric nature, but it is a centrosymmetric dimer. The coordination number of the metal ion is still 8:4 oxygen atoms of the ligand; 3 water molecules; 1 bridging carboxylate group. A preliminary study of the photochemical features of the complexes Ca1 and Ca2 is reported: photoexcitation by a nanosecond pulsed UV laser induces the cleavage of the ligand. This drastically reduces the affinity of the ligand toward Ca2+, which is then released in solution.     

Dimerization and enzymatic activity of fungal 17β-hydroxysteroid dehydrogenase from the short-chain dehydrogenase/reductase superfamily

Background  

17β-hydroxysteroid dehydrogenase from the fungus Cochliobolus lunatus (17β-HSDcl) is a member of the short-chain dehydrogenase/reductase (SDR) superfamily. SDR proteins usually function as dimers or tetramers and 17β-HSDcl is also a homodimer under native conditions.     

"Venetian blinds" mechanism of solvation/desolvation in palladium(II) wheel-and-axle organic-inorganic diols

A family of organic-inorganic wheel-and-axle diols (Pd(LOH)(2)Cl(2), Pd(LOH)(2)(CH(3))Cl, Pd(LOH)(2)(CH(3)COO)(2), LOH = alpha-(4-pyridyl)benzhydrol) and several corresponding solvates are synthesized and characterized by single-crystal X-ray diffraction analysis. Their structures are compared to investigate the factors governing the modes of solid state association, the propensity to clathration, and the structural basis of guest inclusion. In all the complexes, the palladium coordination is a slightly distorted square. The LOH ligands coordinate Pd(2+) by means of the 4-pyridyl ring. In the chloride complexes solvation occurs with a 1:2 host/guest ratio by hydrogen bonding between the terminal -OH groups of the complex diol and one acceptor atom on the guest, and it is further assisted by guest stacking between host aryl rings. All solvates are organized in layers with practically invariant metrics, while the layers may be assembled in different arrangements. The structures of the nonsolvate compounds are related to the metrics of the solvate forms by rotation of the complex molecules within the layer plane. In all cases the nonsolvates are completely converted into the corresponding crystalline solvate forms by exposure to the vapor of the guest, and conversely they are quantitatively recovered from the solvate upon removal of the guest by mild conditions. On the basis of the structural data, it is proposed that the solvation/desolvation process proceeds by a concerted rotation of the complex molecules in the layer plane. The structural analysis of Pd(LOH)(2)(CH(3)COO)(2) and of its tetrahydrofuran monosolvate form suggests that the first step of the solid/gas solvation process may imply the clathration of 1 mol of guest between the aryl rings, which successively triggers the collective reorientation of the host molecules.