Bericht über das „Symposium on Coagulation and Coagulant Aids“ vom 1. bis 3. April 1963 in Los Angeles,Cal. (USA)

Ohne Zusammenfassung     

Difference equations in statistical mechanics. II. Solid-on-solid models in two dimensions

A review and some new results are presented for the solid-on-solid models of wetting in two dimensions (i.e., line interfaces) with an emphasis on the difference equations arising in the transfer matrix calculations for these models. Methods for solving the appropriate difference equations exactly or approximately are surveyed, including specific results for short-range, long-range power-law, and applied field-like (binding) external potentials.     

Quantum critical behaviour of a disordered granular superconductor with charging effects

The effect of quantum fluctuations of the phase on the low-temperature critical behaviour of a three-dimensional disordered (site-diluted) granular superconductor with Coulomb interactions is studied using the renormalization group method. In the one-loop approximation the system exhibits a focus-type stable fixed point which gives rise to unusual critical behaviour with oscillating corrections to the scaling.     

Molecular-weight scaling of coexistence curves for monodisperse polymer solutions

The available data for the polymer volume fraction along the coexistence curves for monodisperse solutions of polystyrene in methylcyclohexane are used to derive the exponent z ≈ 0.61 such that the “correct” order parameter is only a function of ?M^Z (M is the polymer's molecular weight while ? is the reduced temperature). It is shown that a knowledge of the “correct” order parameter is unnecessary for a determination of z which is expected to be universal, i.e. independent of the polymer-solvent system.     

How far, how long: on the temporal scope of prosodic boundary effects

Acoustic lengthening at prosodic boundaries is well explored, and the articulatory bases for this lengthening are becoming better understood. However, the temporal scope of prosodic boundary effects has not been examined in the articulatory domain. The few acoustic studies examining the distribution of lengthening indicate that boundary effects extend from one to three syllables before the boundary, and that effects diminish as distance from the boundary increases. This diminishment is consistent with the pi-gesture model of prosodic influence [Byrd and Saltzman, J. Phonetics 31, 149-180 (2003)]. The present experiment tests the preboundary and postboundary scope of articulatory lengthening at an intonational phrase boundary. Movement-tracking data are used to evaluate durations of consonant closing and opening movements, acceleration durations, and consonant spatial magnitude. Results indicate that prosodic boundary effects exist locally near the phrase boundary in both directions, diminishing in magnitude more remotely for those subjects who exhibit extended effects. Small postboundary effects that are compensatory in direction are also observed.     

Kinetics and mechanism of the reactions of Pd(II) complexes with azoles and diazines. Crystal structure of [Pd(bpma)(H2O)](ClO4)2.2H2O

Substitution reactions of the complexes [Pd(bpma)(H2O)]2+, [Pd(bpma)Cl]+, [Pd(dien)(H2O)]2+ and [Pd(dien)Cl]+, where bpma = bis(2-pyridylmethyl)amine and dien = diethylentriamine or 1,5-diamino-3-azapentane, with some nitrogen-donor ligands such as triazole, pyrazole, pyrimidine, pyrazine and pyridazine, were studied in an aqueous 0.10 M NaClO4 at pH 2.8 using variable-temperature and -pressure stopped-flow spectrophotometry. The second-order rate constants indicate that the Pd(II) complexes of bpma, viz. [Pd(bpma)(H2O)]2+ and [Pd(bpma)Cl]+, are more reactive than the complexes of dien, viz. [Pd(dien)(H2O)]2+ and [Pd(dien)Cl]+. Also, the aqua complexes, [Pd(bpma)(H2O)]2+ and [Pd(dien)(H2O)]2+, are much more reactive than the corresponding chloro complexes. The most reactive nucleophile of the five-membered rings is triazole and for the six-membered rings the most reactive one is pyridazine. Activation parameters were determined for all reactions and the negative entropies and volumes of activation (Delta S++, Delta V++) support an associative ligand substitution mechanism. The crystal structure of [Pd(bpma)(H2O)](ClO4)2.2H2O was determined by X-ray diffraction. Crystals are monoclinic with the space group P2(1)/c. The coordination geometry of [Pd(bpma)(H2O)]2+ is distorted square-planar. The Pd-N (central) bond distance, 1.958(5) A, is shorter than the other two Pd-N distances, 2.007(5) and 2.009(5) A. The Pd-O distance is 2.043(5) A.     

Molecular fluorescent pH-probes based on 8-hydroxyquinoline

Three 5,7-pi-extended 8-benzyloxyquinolines, namely 5,7-diphenyl-, 5,7-bis(biphenyl-4-yl)- and 5,7-bis(4-dibenzothiophenyl)-8-benzyloxyquinoline were prepared and investigated as fluorescent pH-probes in nonaqueous solution. Absorption and photoluminescence spectra of the introduced compounds also including the starting material 8-benzyloxy-5,7-dibromoquinoline as well as their N-protonated counterparts were recorded and the results were rationalized by quantum-chemical calculations. A pronounced red shift of the emission occurred upon protonation of the non halogenated derivatives, while the dibromo-derivative is hardly emissive and is virtually not protonated under the conditions used. The diphenyl- and the bis(biphenyl)-derivative especially show promising photoluminescence quantum yields both in the parent and the protonated state making them candidates for the active component in pH sensing applications.     

Kinetic and mechanistic study on the reactions of [Pt(bpma)(H2O)]2+ and [Pd(bpma)(H2O)]2+ with some nucleophiles. Crystal structure of [Pd(bpma)(py)](ClO4)2

Substitution reactions of the complexes [Pd(bpma)(H2O)]2+ and [Pt(bpma)(H2O)]2+, where bpma = bis(2-pyridylmethyl)amine, with TU, DMTU and TMTU for both complexes and Cl-, Br-, I- and SCN- for the platinum complex, were studied in aqueous 0.10 M NaClO4 at pH 2.5 using a variable-temperature stopped-flow spectrophotometer. The pKa value for the coordinated water molecule in [Pd(bpma)(H2O)]2+ (6.67) is a unit higher than that of [Pt(bpma)(H2O)]2+. The observed pseudo-first-order rate constants k(obs) (s(-1)) obeyed the equation k(obs) = k2[Nu] (Nu = nucleophile). The second-order rate constants indicate that the Pd(II) complex is a factor of 10(3) more reactive than Pt(II) complex. The nucleophile reactivity attributed to the steric hindrance in case of TMTU and the inductive effect for DMTU was found to be DMTU > TU > TMTU for [Pt(bpma)(H2O)]2+ and DMTU approximately TU > TMTU for [Pd(bpma)(H2O)]2+. The trend for ionic nucleophile was I- > SCN- > Br- > Cl-, an order linked to their polarizability and the softness or hardness of the metal. Activation parameters were determined for all reactions and the negative entropies of activation (Delta S++) support an associative ligand substitution mechanism. The X-ray crystal structure of [Pd(bpma)(py)](ClO4)2 was determined; it belongs to the triclinic space group P1 and has one formula unit in the unit cell. The unit cell dimensions are a = 8.522(2), b = 8.627(2), c = 16.730(4) A; alpha = 89.20(2), beta = 81.03(2), gamma = 60.61(2) degrees ; V = 1055.7(5) A3. The structure was solved using direct methods in WinGX's implementation of SHELXS-97 and refined to R = 0.054. The coordination geometry of [Pd(bpma)(py)]2+ is distorted square-planar. The Pd-N(central) bond distance, 1.996(3) A, is shorter than the other two Pd-N distances, 2.017(3) and 2.019(3) A. The Pd-N(pyridine) distance is 2.037(3) A.     

Depth and angular profiles of inelastic low-energy electron scattering in condensed molecular samples

Angular distributions of electrons scattered elastically and inelastically from cold solid molecular films of ethylene and nitrogen in various proportions, grown from the gas phase at different temperatures, have been studied by high-resolution electron energy loss spectroscopy. The probing depth of dipole and impact scattering has been investigated by covering the sample by overlayers of argon of increasing thickness. The angular distribution measured for elastically and inelastically dipole-scattered electrons was found to be peaked about the specular direction for all surface conditions studied, while a diffuse angular distribution was possible for electrons that underwent dipole-forbidden scattering. These results allow us to identify favorable conditions for monitoring the composition of a solid sample during the course of reactions occurring under exposure to low-energy electrons.     

DNA localization and stretching on periodically microstructured lipid membranes

We study the conformational behavior of DNA molecules adsorbed on cationic-lipid membranes that are supported on grooved, one-dimensionally periodic microstructured surfaces. We reveal a striking ability of these periodically structured membranes to stretch DNA coils. We elucidate this DNA stretching phenomenon in terms of surface curvature dependent potential energy attained by the adsorbed DNA molecules. Because of it, DNA molecules undergo a localization transition causing them to stretch by binding to highly curved sections of the supported membranes.