Analysis of the interfacial properties of fibrillated and nonfibrillated oral streptococcal strains from electrophoretic mobility and titration measurements: evidence for the shortcomings of the 'classical soft-particle approach'

Chemical and structural intricacies of bacterial cells complicate the quantitative evaluation of the physicochemical properties pertaining to the cell surface. The presence of various types of cell surface appendages has a large impact on those properties and therefore on various interfacial phenomena, such as aggregation and adhesion. In this paper, an advanced analysis of the electrophoretic mobilities of fibrillated and nonfibrillated strains (Streptococcus salivarius HB and Streptococcus salivarius HB-C12, respectively) is performed over a wide range of pH and ionic strength conditions on the basis of a recent electrokinetic theory for soft particles. The latter extends the approximate formalism originally developed by Ohshima by solving rigorously the fundamental electrokinetic equations without restrictions on the bacterial size, charge, and double layer thickness. It further allows (i) a straightforward implementation of the dissociation characteristics, as evaluated from titration experiments, of the ionogenic charged groups distributed throughout the bacterial cell wall and/or the surrounding exopolymer layer and (ii) the inclusion of possible specific interactions between the charged groups and ions from the background electrolyte other than charge-determining ions. The theory also enables an estimation of possible swelling/shrinking processes operating on the outer polymeric layer of the bacterium. Application of the electrokinetic model to HB and HB-C12 clearly shows a significant discrepancy between the amount of surface charges probed by electrophoresis and by protolytic titration. This is ascribed to the specific adsorption of cations onto pristine charged sites in the cell wall. Physicochemical parameters pertaining to the hydrodynamics (softness degree) and electrostatics of the bacterial cell wall (HB-C12) and soft polymeric layer (HB) are quantitatively derived.     

Spectroscopy and photophysics of self-organized zinc porphyrin nanolayers. 2. Transport properties of singlet excitation

Exciton diffusion has been studied in 5-25-nm-thick films of zinc tetra-(p-octylphenyl)-porphyrin (ZnTOPP) spin-coated onto quartz slides by intentional doping with quenchers using steady-state as well as time-resolved fluorescence spectroscopy. The fluorescence spectra of the films are very similar to those of solutions, indicating emission from localized exciton states. From the dependence of the fluorescence quenching on the quencher concentration and fluorescence lifetime measurements, the exciton diffusion can be concluded to be quasi-one-dimensional with an exciton diffusion length of 9 +/- 3 nm and an intrastack energy-transfer rate constant of 10(11)-10(12) s(-1). From fluorescence anisotropy decay measurements, we conclude that neighboring stacks aggregate in a herringbone structure, forming ordered domains that are randomly oriented in the substrate plane. These measurements indicate an interstack energy-transfer rate constant of (7 +/- 2) x 10(10) s(-1).     

Rational Unfoldings of ± X k and their relation with geometric equilibrium theory

In this paper, two theorems determine the locus B (buoyancy locus) of the centre of gravity of the displaced water of a ship with any number of 2n sides, as a function of the arbitrary continuous curves that make up those sides, and that generalize the classical wall-sided case (n=1). Although the theorems may have interest from the pure geometrical point of view, they have been obtained with a view to simulate processes in biology that, in analogy to the self-righting of ships, are self-regulating, such as the neural control of body heat and the servo-control of the heart rate.     

Analysis of deuterium effects on the rate of multiphonon relaxation in hydrated cesium chloromanganate crystals (CsMnCl3-2H2O, -2D2O)

The assumption that OH (OD) stretch vibrations in CsMnCl₃-2H₂O and -2D₂O govern the rate of the ⁴T₁ → ⁶A₁ multiphonon transitions in Mn²⁺ is shown to account quantitatively for the observed 16-fold increase in the ⁴T₁ lifetime upon replacing H₂O by D₂O. The argument is generalized to include other coordination compounds.     

ALTERED SPECTRAL PROPERTIES OF THE B875 LIGHT-HARVESTING PIGMENT-PROTEIN COMPLEX IN A Rhodobacter sphaeroides MUTANT LACKING pufX

Abstract— Mutants of Rhodobacler sphac, roicies lacking the pufX gene are unable to grow photosynthetically and have been reported to show impaired cyclic electron flow and elevated B875 levels when grown at low oxygen tension. An examination of the low-temperature optical properties of chromatophores from a pufx- strain, obtained by complementation of a pufLMX mutant in trans with pufQBALM , encoding polypeptides of the B875 antenna and reaction center complexes, revealed that the absorption and fluorescence emission maxima and the fluorescence polarization rise over the B875-Qy band were shifted to lower energies. These results suggest that the pufX gene product may limit the aggregation state of the B875 complex, assuring the proper functional arrangement of antenna and reaction ccntcr components within the cores of the photosynthetic units.     

The electrocapillary effect at an electrode modified with an insoluble redox-active self-assembled monolayer

The interface between an electrolyte solution and a metal electrode coated with an oxidatively adsorbed, redox-active monolayer of long-chain thiols has been examined from a thermodynamic point of view. The electrode potential is assumed to vary within the region where no reductive desorption of the thiol occurs, so that the interface may formally be regarded as ideally polarizable. The analysis leads to an expression describing the potential dependence of interfacial tension in terms of the charge density on the metal, salt concentration, dielectric properties of the organic film, and the redox properties of the active terminal groups, which vary with the (average) distance from the electrode surface. This result generalizes the classical Lippmann equation to modified electrodes of the type considered.     

Preventing nitrite contamination in tetramethylammonium peroxynitrite solutions

Peroxynitrite prepared from superoxide and nitric oxide in liquid ammonia does not contain detectable levels of nitrite. However, the dissolution of nitrite salts can lead to variable levels of peroxynitrite depending on the conditions used to disolve the salt. Low levels of nitrite result when frozen peroxynitrite solutions are first brought to +1 degrees C and then to room temperature. These undergo only 2-3% decomposition after 1 h, in contrast with the findings of a recent report (Lymar, S. V.; Khairutdinov, R. F.; Hurst, J. K. Inorg. Chem. 2003, 42, 5259-5266), where high levels of nitrite ( approximately 20%) result from rapid thawing of these solutions to room temperature. Warming the frozen peroxynitrite solution directly to room temperature in 30 min leads to a nitrite level of 28%.     

LIGHT DOSIMETRY FOR PHOTODYNAMIC THERAPY BY WHOLE BLADDER WALL IRRADIATION

Abstract In Photodynamic Therapy (PDT) there is a need for accurate quantitative light dosimetry. This has become particularly apparent in the treatment of superficial bladder cancer, either by focal or by whole bladder wall irradiation. We have studied this problem using a spherical model of the bladder, consisting of two concentric thin-walled plastic spheres, 8 and 10 cm in diameter. The inner sphere was filled with water or with a light-scattering medium. The space between the spheres was filled with an optically tissue equivalent liquid. An isotropic light source was placed at the center of the spheres. Light energy fluence rates (light "dose rates") during PDT of the bladder simulated in this manner, were measured using a specially developed miniature light detector and were also calculated using a mathematical model. These data were confirmed by measurements in vivo (dog bladder). In the case of focal irradiation at a wavelength of 630 nm, the ratio (R) between the true light fluence rate at the bladder surface and the fluence rate due to the primary light beam is somewhat larger than 1, depending on the diameter of the primary beam. The maximum ratio is 2, for a beam diameter of several centimeters. In the case of whole bladder wall PDT, R is larger than 5. This is due to the strong scattering of (red) light by tissue and indicates that the intensity of the primary beam, which is usually reported, is not a good measure of the true fluence rate for whole bladder wall PDT. When the light source is moved away from the center of the spheres, the rate of change of the fluence rate at the bladder wall is more than a factor of 2 larger when the bladder cavity is filled with a light-scattering suspension, as compared with water. The use of a light-scattering medium may therefore not be advantageous to achieve a uniform light distribution across the bladder wall.