Comparison of electric light scattering and birefringence for polydisperse suspensions

Summary A review is made of the existing theoretical expressions, describing the change of the scattered light intensity and the birefringence by application of an electrical field to a colloid solution.Furthermore, the geometrical functions for disc-shaped particles are calculated in this article for the case of electric light scattering and are. presented graphically. In addition, expressions are derived for the average value of the electrical polarizability () for the case of polydisperse solutions.

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Zusammenfassung Es wird ein überblick über die existierenden theoretischen Beziehungen gegeben, die die Änderung der Intensität des Streulichtes und der Doppelbrechung von Kolloidsuspensionen im elektrischen Feld beschreiben.Weiterhin sind die geometrischen Funktionen für scheibchenförmige Teilchen in dieser Arbeit für den Fall der elektrooptischen Lichtstreuung berechnet und grafisch dargestellt. Außerdem werden Beziehungen für den Mittelwert der elektrischen Polarisierbarkeit () für den Fall polydisperser Suspensionen abgeleitet.

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With 1 figure and 1 table     

Structure‐Based Design of Inhibitors of the Aspartic Protease Endothiapepsin by Exploiting Dynamic Combinatorial Chemistry

Structure‐based design (SBD) can be used for the design and/or optimization of new inhibitors for a biological target. Whereas de novo SBD is rarely used, most reports on SBD are dealing with the optimization of an initial hit. Dynamic combinatorial chemistry (DCC) has emerged as a powerful strategy to identify bioactive ligands given that it enables the target to direct the synthesis of its strongest binder. We have designed a library of potential inhibitors (acylhydrazones) generated from five aldehydes and five hydrazides and used DCC to identify the best binder(s). After addition of the aspartic protease endothiapepsin, we characterized the protein‐bound library member(s) by saturation‐transfer difference NMR spectroscopy. Cocrystallization experiments validated the predicted binding mode of the two most potent inhibitors, thus demonstrating that the combination of de novo SBD and DCC constitutes an efficient starting point for hit identification and optimization.     

On the low frequency dispersion of the electrooptic effects

Summary The paper studies the factors which could be responsible for the difference between the high and low frequency electrooptic effects, the neglect of which could lead to erroneous conclusions about the particle electric properties. The presented considerations are illustrated by experimental data for an aqueous palygorskite suspension. New possibilities are demonstrated for the obtaining of information from the low frequency dispersion of the electrooptic effects. On the basis of the experimental data concerning the dispersion behaviour of palygorskite, the hypothesis is suggested for the existence of a slow longitudinal electric polarizability acting at frequencies of the applied field below 60 Hz.

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Zusammenfassung In der Arbeit wurden die Faktoren diskutiert, welche für die Unterschiede der elektrooptischen Effekte bei hohen und niedrigen Frequenzen verantwortlich sind. Auf Grund experimenteller Daten mit wäßrigen Palygorskitsuspensionen wird eine langsam longitudinale elektrische Polarisierbarkeit postuliert, die bei den angewandten Feldstärken bei Frequenzen unter 60 cm^-1 wirksam wird.

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With 6 figures     

Polypeptide multilayer films on colloidal particles: an in situ electro-optical study

The buildup of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) multilayers on beta-FeOOH colloidal particles was investigated by means of electro-optics and electrophoresis. The films were built at different (acidic) pH in the absence of salt. We found that the thickness of the film grows linearly when the fully charged PLL (at pH 5.5) is combined with almost fully charged PGA (at pH 6.5), with a thickness of about 2 nm per single layer. When the fully charged PLL is combined with weakly charged PGA (at pH 4.5), the film thickness increases exponentially with the number of deposited layers. The thickness of the exponentially growing film increases to 300 nm after deposition of 16 layers. The exponential film growth is attributed to the ability of the PLL to diffuse "in" and "out" of the film bulk at each deposition step. The variation in the electrical polarizability of the film-coated particles was also monitored as a function of the number of adsorbed layers. The result reveals that the PLL chains, which can diffuse into the film bulk, have no measurable contribution to the electro-optical effect of the films terminated with PLL. It is only due to the polarization of counterions of the PLL adsorbed on the film surface.     

*-Identities of Minimal Degree in Matrix Algebras of Low Order

Let M6(K,*) be the 6 × 6 matrix algebra with symplectic involution over a field K of characteristic 0. We consider *-polynomial identities in symmetric to the involution matrices and prove that their minimal degree in M6(K,*) is 9. For special *-polynomials we make the conjecture that their minimal degree in M2n(K,*) for n 2 is 4n.     

Formation of polyelectrolyte multilayers from polysaccharides at low ionic strength

Layer-by-layer deposition of sodium carboxymethylcellulose (NaCMC) and chitosan (CHI) was used to create polyelectrolyte multilayers on ellipsoidal beta-FeOOH particles at low ionic strength. Using electro-optics, we investigated the formation of films in dependence on the polyelectrolyte charge density by controlling pH of the dipping solutions. We found out a linear growth of the CMC/CHI films when they are constructed from highly charged CHI (at pH 4.0) and weakly charged NaCMC (at pH 4.0 and 5.5). The hydrodynamic thickness of the film constructed at pH 4.0/4.0 is unusually large for a linearly growing film (ca. 220 nm after deposition of 8 bilayers), but it strongly decreases (ca. 4 times) with increasing ionization of NaCMC (at pH 5.5). In both cases, the multilayer buildup proceeded through a series of adsorption-desorption steps. This was explained by a partial loss of CHI from the film surface on exposure to the solution of longer NaCMC molecules. The irregular film growth correlated quite well with the variations in the electrical polarizability of the polymer-coated particles. This correlation enabled us to conclude that the adsorption of both polymers occurs only on the film surface, with no diffusion in and out of the film bulk during deposition of each CMC/CHI bilayer.     

Electrostatic complexation of a double hydrophilic block polyelectrolyte and proteins of different molecular shape

The electrostatic complexation between the polyelectrolyte block of the novel double hydrophilic copolymer quaternized poly(3,5‐bis(dimethylaminomethylene) hydroxystyrene)‐b‐poly(ethylene oxide) (QNPHOS‐PEO) and proteins of different molecular shape, that is globular bovine serum albumin (BSA) or rod‐like bovine fibrinogen (FBG), is investigated by means of dynamic, static, and electrophoretic light scattering, as well as analytical ultracentrifugation measurements. The solution behavior, structure, and properties of the formed complexes at pH 7 and 0.01 M ionic strength, as a function of the protein concentration in the solution (or equivalently the charge ratio of the two components), depend on the protein concentration and molecular characteristics. Moreover, the structure of the complexes is greatly influenced by the intrinsic structure of the block polyelectrolyte, which forms rather loose multichain aggregates, due to hydrophobic interactions. A direct correlation between the stability of the preformed complexes against the increase of the solution ionic strength and their structure is established. Finally, the spectroscopic structural investigation of both complexed proteins reveals no signs of protein denaturation upon complexation. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1515–1529