Path-dependency of the interaction between coaggregating and between non-coaggregating oral bacterial pairs--a thermodynamic approach

Coaggregation, i.e. specific recognition between bacteria from different species, is a well-described phenomenon in the human oral cavity but remains physically poorly understood. With our study we aimed at elucidating some aspects of the mechanism of the coaggregation between the oral bacteria Streptococcus oralis J22 and Actinomyces naeslundii 147, in particular with respect to the driving force for coaggregation and its pathway-dependency. To that end, the macroscopic turbidity of the bacterial suspension, the morphology of the coaggregates, binding isotherms and heats of interaction were compared between the above-mentioned coaggregating bacterial pair and a non-coaggregating pair, Streptococcus sanguis PK1889 and A. naeslundii 147. The coaggregating pair forms large aggregates, which rapidly sediment from the suspension while the non-coaggregating pair forms only very small coaggregates that remain homogeneously suspended. Coaggregation is further characterized by a high affinity between the partner cells that bind to each other in a strong cooperative mode. The interactions between both pairs occur under the release of heat and are thus enthalpically favorable. More heat is released for the coaggregating than for the non-coaggregating pair. Adding the coaggregating bacteria in steps to each other leads to saturation of enthalpically favorable binding sites. This is observed when the streptococcus is added to the actinomyces as well as when the addition is done the other way around. It is concluded that the cooperativity of the coaggregation process is based on an increase of entropy. It is furthermore shown that the density of the coaggregates as well as the heat effect of formation of these coaggregates depend on the number of steps in which the partner cells are added to each other. Adding S. oralis J22 in three steps to A. naeslundii 147 results in the formation of denser coaggregates under the release of less heat, as compared to that of addition in one step. These differences point to a larger entropy increase when in a step-wise mixing the coaggregating bacteria are allowed to form more densely-packed coaggregates.     

Experimentelle Untersuchungen über die Abhängigkeit der Reaktionsgeschwindigkeit bei der photolytischen Zersetzung von aromatischen Diazoverbindungen von deren Struktur

Zusammenfassung Berichtet wird über die Photolyse verschiedener Diazoverbindungen unter reproduzierbaren Bedingungen. Die Meßergebnisse werden in einer Tabelle zusammengestellt. In 5 Abbildungen wird die Abhängigkeit der Zersetzungsdauer von Variationen im Molekül graphisch dargestellt. In einer kurzen Übersicht werden die aus den experimentellen Befunden ableitbaren Zusammenhänge zwischen Struktur und Zersetzungsgeschwindigkeit dem experimentellen Teil vorangestellt.Mit 7 AbbildungenHerrn Prof. Dr.F. Asinger zum 60. Geburtstag gewidmet.     

Cyclic Iminoboranes: Analogues of Cycloalkynes

1‐Azido‐ and 1‐[trimethylsilyl(trimethylsilyloxy)]boracycloalkanes, (‐Y‐BX‐) [X = N₃ ( 2 ), N(OSiMe₃)SiMe₃ ( 3 ), Y = alkanediyl], were synthesized from the corresponding chloroboranes [X = Cl ( 1 )]. The following alkanediyl ring fragments were considered: Y = ‐CH₂‐CHMe‐CH₂‐CH₂‐ ( a ), 1, 5‐cyclooctanediyl ( b ), ‐(CH₂)₆‐ ( c ), ‐(CH₂)₇‐ ( d ), ‐CMe₂‐(CH₂)₆‐ ( e ), ‐C(‐CMe₂‐CH₂‐)‐(CH₂)₆‐ ( f ). The thermal elimination of N₂ (from 2 ) or (SiMe₃)₂O (from 3 ) is accompanied by the migration of one of the two alkanediyl ends from boron to nitrogen under ring expansion to give the cyclic iminoboranes 4 . Formed in solution, the iminoboranes react immediately with undecomposed starting material 2 or 3 under formation of the products 5 or 6 by azidoboration or aminoboration, respectively, of the BN multiple bond. The temperature for the decomposition of 2 depends on the ring size: the five‐membered ring compound 2a and the bicyclic six‐membered ring compound 2b decompose beneath 0 °C, the seven‐ and eight‐membered ring compounds 2c and 2d in boiling hexane and toluene, respectively, whereas the eight‐membered ring compounds 2e and 2f are decomposed in solution above 100 °C so slowly that only unidentified polymers are found. The boranes 3a and 3b , stable at room temperature, afford a temperature of 80 °C for decomposition in solution. The azidoboranes 2c ‐ f can be transported into the gas‐phase without decomposition and can be thermolyzed there at 270‐285 °C. The cyclic iminoboranes 4c ‐ e , formed in the hot tube, were condensed at ‐196 °C, but thereafter not characterized, because they either cyclotrimerized ( 4c , d ) or cyclodimerized ( 4e , e′ ; two isomers depending on which end of the 1, 1‐dimethylheptamethylene unit migrates) beneath ‐60 °C under formation of the corresponding borazines 10c , d or of the diazadiboretidine isomer mixture 9e , e′ , respectively; the spirocyclic borane 2f gives a mixture of unidentified products on gas‐phase thermolysis. The iminoboranes 4e , e′ can be trapped by ethyloboration with BEt₃ giving the products 8e , e′ . The acyclic azidoborane R(Me)BN₃ ( 2g ; R = 1‐methylcycloheptyl), formed after the ring‐contracting rearrangement of a boracyclooctane derivative, gives the isolated and characterized mixture of the acyclic iminoboranes MeB≡NR ( 4g ) and RB≡NMe ( 4g′ ) upon gas‐phase thermolysis; the stabilization of 4g , g′ gives the Dewar borazines 11g and 11g′ .     

A new method to analyze matrix-assisted laser desorption/ionization time-of-flight peptide profiling mass spectra

In protein and peptide mass spectrometry in which profiling of peaks is involved, their masses and intensities are important characteristics. Because of the relative low reproducibility of peak intensities associated with complex samples in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS), it is difficult to accurately assess the number of peaks and their intensities. In this study we evaluate these two characteristics for tryptic digests of cerebro-spinal fluid. We observed that the reproducibility of peak intensities was relatively poor (CV = 42%) and that additional normalization or spiking did not lead to a large improvement (CV = 30%). Moreover, at least seven mass spectra per sample were required to obtain a reliable peak list. An improvement of the sensitivity (i.e., eventually more peaks are detected) is observed if more replicates per sample are measured. We conclude that the reproducibility and sensitivity of peptide profiling can be significantly improved by a combination of measuring at least seven spectra per sample with a dichotomous scoring of the intensities. This approach will aid the analysis of large numbers of mass spectra of patient samples in a reproducible way for the detection and validation of candidate biomarkers.     

Results from interlaboratory comparisons of aldehyde-2,4 dinitrophenylhydrazone analysis

Within the framework of the SMT "Aldehydes" project (SMT4-CT97-2910) three laboratory comparisons have been organized in which artificial aldehyde hydrazone samples have been distributed among participating laboratories. To these samples potentially interfering compounds have been added to simulate as closely as possible real air or air emission samples.In addition to the "Aldehydes" project partners external EU laboratories have participated. It may, therefore, be assumed that the results of these comparisons reflect the state-of-the-art in the analytical determination of aldehydes in air samples using the 2,4-dinitrophenylhydrazine (DNPH)-method. In this paper several aspects of the organization of these comparisons and the overall results obtained are presented. These demonstrate that results obtained using liquid chromatographic techniques are usually comparable between laboratories within +/-2 times the coefficient of variation (approximately 6-15%), indicating the robustness of the methodology. In addition, laboratory (liquid chromatography) mean results can be made to agree with preparation concentrations at the 95% confidence levels after optimization of separation and integration conditions; these are mainly related to the measurement of formaldehyde in the presence of interferents and the measurement of low concentrations of acrolein and acetone. Some problem areas still remain, however--namely the measurement of glutaraldehyde and the measurement of low levels of acetone.     

Computational study of the adsorption energetics and vibrational wavenumbers of NH3 Adsorbed on the Ni(111) Surface

The structure and stabilities of NH(3) adsorbed on different sites of a Ni(111) surface are compared based on density functional, plane-waves calculations within a periodic framework. The surface has been modeled by 4- and 5-layer slabs with 2 x 2 and 3 x 3 unit cells. Calculated results are in good agreement with available experimental data, confirming the atop adsorption site to be the most favorable, with no preferred azimuthal orientation for the H atoms. For NH(3) adsorbed at the atop site, the one-dimensional potential energy profiles along the N-H and N-Ni bonds and the coupling between adjacent N-H bond oscillators have been calculated and fitted to an analytical expression using an accurate anharmonic potential model. Variational calculations have been performed to obtain frequencies for the N-H and N-Ni stretching vibrations and N-H stretching line widths. The model for calculating line widths has also been tested with CO adsorbed at the hcp hollow of the Ni(111) surface.     

Untersuchungen an Polyhalogeniden. XXVII. Über Tetra(n-propyl)ammoniumpolyiodide (n-Pr4N)In mit n = 3, 5, 7: Darstellung und strukturelle Charakterisierung eines Triiodids (n-Pr4N)I3, eines Pentaiodids (n-Pr4N)I5 und eines Heptaiodids (n-Pr4N)I7

Studies of Polyhalides. 27. On Tetra(n-propyl)ammonium Polyiodides (n-Pr₄N)I_n with n = 3, 5, 7: Preparation and Crystal Structures of a Triiodide (n-Pr₄N)I₃, a Pentaiodide (n-Pr₄N)I₅, and a Heptaiodide (n-Pr₄N)I₇ [(n-C₃H₇)₄N]I₃, [(n-C₃H₇)₄N]I₅ and [(n-C₃H₇)₄N]I₇ have been prepared by the reaction of tetra(n-propyl)ammoniumiodide [(n-C₃H₇)₄N]I with iodine I₂ in ethanol. Their crystal structures have been determined by single crystal X-ray diffraction methods. The triiodide is built up from layers of the quarternary ammonium ions n-Pr₄N⁺ and from two independent differently packed centrosymmetric triiodide ions I₃^? which alternate with each other along [100]. The pentaiodide ion forms slightly puckered almost squared nets perpendicular [001] of iodide ions which are connected with four iodine molecules by secondary bonds. The meshes from twelve iodine atoms include the cations. The centrosymmetric Z-shaped heptaiodide ion is built up from a linear symmetric triiodide ion and two iodine molecules forming twisted rope ladders along [001] which are separated by stacks of cations.     

Loading and release mechanisms of a biocide in polystyrene-block-poly(acrylic acid) block copolymer micelles

The kinetics of loading of polystyrene197-block-poly(acrylic acid)47 (PS197-b-PAA47) micelles, suspended in water, with thiocyanomethylthiobenzothiazole biocide and its subsequent release were investigated. Loading of the micelles was found to be a two-step process. First, the surface of the PS core of the micelles is saturated with biocide, with a rate determined by the transfer of solid biocide to micelles during transient micelle-biocide contacts. Next, the biocide penetrates as a front into the micelles, lowering the Tg in the process (non-Fickian case II diffusion). The slow rate of release is governed by the height of the energy barrier that a biocide molecule must overcome to pass from PS into water, resulting in a uniform biocide concentration within the micelle, until Tg is increased to the point that diffusion inside the micelles becomes very slow. Maximum loading of biocide into micelles is approximately 30% (w/w) and is achieved in 1 h. From partition experiments, it can be concluded that the biocide has a similar preference for polystyrene as for ethylbenzene over water, implying that the maximum loading is governed by thermodynamics.     

One-pot eco-friendly oxidative synthesis of imine carboxymethyl dialdehyde cellulosic fibers

Cellulose - The quest to efficiently produce renewable and sustainable functional cellulosic products has prompted the development of an environmentally sensitive and cost-effective method to...     

Photogeneration of two metastable NO linkage isomers with high populations of up to 76% in trans-[RuCl(py)4(NO)][PF6]2.1/2H2O

Two light-induced metastable NO linkage isomers with oxygen-bound (SI) and side-on configuration (SII) of NO are generated in trans-[RuCl(py)(4)(NO)][PF(6)](2).(1/2)H(2)O. Irradiation by light in the blue-green spectral range (450-530 nm) leads to the population of SI. A further irradiation by near infrared light (920-1100 nm) transfers SI into SII at temperatures below 150 K. The heat release during the thermal decay of the linkage isomers shows that SI and SII are separated from the ground state (GS) by potential barriers of E(A)(SI) = 0.70(3) eV and E(A)(SII) = 0.38(3) eV, and are energetically situated at 1.42(6) eV and 1.07(7) eV above the ground state, respectively. Maximum populations of 76% for SI and of 56% for SII can be generated, as determined by the decrease of the nu(NO) stretching absorption band of the ground state. The nu(NO) stretching vibration shifts to lower energies by 143 cm(-1) in SI and by 300 cm(-1) in SII, indicating that the linkage isomers are of the same type as found in other octahedrally coordinated transition-metal nitrosyl complexes. The experimental observations are in agreement with results from calculations by the density functional theory, which predict that the metastable states correspond to a side-on bonded (SII) and an isonitrosyl (SI) configuration of the NO ligand. The calculations provide the energy minima of the ground state and the metastable states SI and SII as well as the saddle points along the reaction coordinate Q. This reaction coordinate corresponds to a rotation of the NO ligand by about 90 degrees (SII) and 180 degrees (SI), and therefore allows the comparison between observed and calculated activation energies.