Suppression of capillary wave broadening of interfaces in binary alloys due to elastic interactions

By Monte Carlo simulations in the constant-temperature--constant-pressure ensemble a planar interface between unmixed A-rich and B-rich phases of a binary (A, B) alloy on a compressible diamond lattice is studied. No significant capillary wave broadening of the concentration profile across the interface is observed, unlike lattice models of incompressible mixtures and fluids. The distortion of the lattice structure across the interface is studied.     

Analysis of the phase transitions in alkyl-mica by density and pressure profiles

In a previous work [Heinz, Castelijns, and Suter, J. Am. Chem. Soc. 115, 9500 (2003)], we developed an accurate force field and simulated the phase transitions in C18-mica (octadecyltrimethylammonium-mica) as well as the absence of such transitions in 2C18-mica (dioctadecyldimethylammonium-mica) between room temperature and 100 degrees C. Here we analyze (i) average z coordinates of the carbon atoms and interdigitation of the hydrocarbon bilayers, (ii) density profiles, and (iii) pressure profiles of the structures along all Cartesian axes. In C18-mica, the standard deviation in the z coordinate for the chain atoms is high and more than doubles in the disordered phase. The order-disorder transition is accompanied by a change in the orientation of the ammonium head group, as well as decreasing tensile and shear stress in the disordered phase. In 2C18-mica, the standard deviation in the z coordinate for the chain atoms is low and does not increase remarkably on heating. The backbones display a highly regular structure, which is slightly obscured by rotations in the C18 backbones and minor head group displacements at 100 degrees C. Close contacts between the bulky head groups with sidearms cause significant local pressure which is in part not relieved at 100 degrees C. An increase of the basal-plane spacing at higher temperature is found in both systems due to larger separation between the two hydrocarbon layers and an increased z spacing between adjacent chain atoms (=decreased tilt of the chains relative to the surface normal), and, in C18-mica only, a stronger upward orientation of the C18 chain at the ammonium head group. The likelihood for chain interdigitation between the two hydrocarbon layers is 24%-30% for C18-mica, and 65%-26% for 2C18-mica (for 20-100 degrees C).     

Elastic constants from microscopic strain fluctuations

Fluctuations of the instantaneous local Lagrangian strain epsilon(ij)(r,t), measured with respect to a static "reference" lattice, are used to obtain accurate estimates of the elastic constants of model solids from atomistic computer simulations. The measured strains are systematically coarse-grained by averaging them within subsystems (of size L(b)) of a system (of total size L) in the canonical ensemble. Using a simple finite size scaling theory we predict the behavior of the fluctuations as a function of L(b)/L and extract elastic constants of the system in the thermodynamic limit at nonzero temperature. Our method is simple to implement, efficient, and general enough to be able to handle a wide class of model systems, including those with singular potentials without any essential modification. We illustrate the technique by computing isothermal elastic constants of "hard" and "soft" disk triangular solids in two dimensions from Monte Carlo and molecular dynamics simulations. We compare our results with those from earlier simulations and theory.     

Desoxaphomin,das erste [13]Cytochalasan,ein möglicher biogenetischer Vorläufer der 24-Oxa-[14]cytochalasane

From cultures of a Phoma species (strain S 298) the hitherto unknown metabolite deoxaphomine has been isolated. On the basis of the spectral data, structure 1 of the (7S, 16R, 20R)-7,20-dihydroxy-16-methyl-10-phenyl-[13]cytochalasa-6(12),13^t,21^t-triene-1,23-dione is assigned to deoxaphomine. This structure is confirmed by the chemical degradation of 1 , yielding the products 4 and 6 which are identical with derivatives of phomine ( 2 )((7S,16R,20R)-7,20-dihydroxy-16-methyl-10-phenyl-24-oxa-[14]cytochalasa-6(12), 13^t,21^t-triene-1,23-dione) and cytohalasin D ( 8 ) ((7S,16S,18R,21R)-21-acetoxy-7,18-dihydroxy-16,18-dimethyl-10-phenyl-[11]sytochalasa-6(12),13^t,19^t-triene-1,17-dione). Deoxaphomine ( 1 ) is a potential biogenetic precursor of the 24-oxa-[14]cytochalasans. Preliminary results of the biological activity of deoxaphomine are reported.     

Über die Synthese von 4-Phenyl-[1,4]-diazepino[6,7,1-kl]phenthiazin-1(2H)-on

The preparation of 4-phenyl-[1.4]-diazepino[6.7.1-kl]phenothiazin-1(2H)-one (5) is described and some of its properties are compared with those of 1.4-benzodiazepines.     

Über die Synthese von 7-Methoxycarbonyl-5-phenyl-1H-thieno[2,3-e]1,4-diazepin-2(3H)-on

The preparation of 7-methoxycarbonyl-5-phenyl-1H-thieno[2,3-e]1,4-diazepin-2(3H)-one (8) and its 1-methyl-derivative (10) is described. Hydrolysation of these two products yielded neither of the two possible acids3 respectively13.     

Polymer-brush lubricated surfaces with colloidal inclusions under shear inversion

We characterize the response of compressed, sheared polymer-brush bilayers with colloidal inclusions to highly nonstationary inversion processes by means of molecular dynamics simulations and scaling theory. Bilayers with a simple (dimeric) solvent reveal an overshoot for the shear stress, while simulations of dry brushes without explicit solvent molecules fail to display this effect. We demonstrate that mechanical instabilities can be controlled by the inclusion of macromolecular structures, such as colloids of varying softness. Based on a recently developed theory, we suggest a scaling approach to determine a characteristic time for conformational and collective responses.     

Synthesis,characterization and properties of methylaminocellulose

Homogeneously prepared tosylcelluloses (TC) with degrees of substitution (DS) of DS_Tos 0.1–1.8 were used as intermediates for the synthesis of methylaminocelluloses (MAC) by nucleophilic substitution with methylamine. TC with DS_Tos up to 1.1 were shown to be valuable intermediates for selective synthesis of MAC with DS_MA varying from 0.1 to approximately 1. No nucleophilic substitution was observed at higher DS_Tos. At the chosen reaction conditions (60 °C, 48 h) residual tosyl moieties remained unchanged and little hydrolysis took place. The samples obtained were characterized by means of elemental analysis, FTIR and ¹³C CP/MAS NMR spectroscopy. ¹³C CP/MAS NMR spectroscopy was found to be an efficient tool for quantification of DS_MA. Furthermore, the swelling behaviour in water was investigated and preliminary tests concerning the bilirubin adsorption capacity of MAC were carried out.