Die Bestimmung der Bildungsenthalpien von in thermischen Zersetzungsreaktionen auftretenden Verbindungen durch Einwurfkalorimetrie — Bildungsenthalpie AlCl3 · 6 H2O,amorph-Al2O3, γ-Al2O3, Al2O3 · 2 H2O · 2 HCl

Zusammenfassung Die Bestimmung der Bildungsenthalpien von Verbindungen, die als stabile Produkte an thermischen Zersetzungsreaktionen beteiligt sind, erfolgte durch Messung der Reaktionsenthalpien. Die kalorimetrischen Experimente wurden in einem Einwurfkalorimeter ausgeführt, welches auf der Grundlage des WÄrmeflu\prinzips arbeitet. An Hand der Bestimmung der Standardbildungsenthalpie des Calciumcarbonates wurde die Me\methodik überprüft. Die Reproduzierbarkeit der kalorimetrischen Messungen betrÄgt im untersuchten Temperaturbereich von 298 K bis 1600 K gleich ±2%. Die Bildungsenthalpien unter Standardbedingungen _BH ₂₉₈ in kJ/mol für AlCl₃ · 6H₂O, amorph-Al₂O₃, –Al₂O₃,Al₂O₃ · 2 H₂O · · 2 HCl betragen –2667 ± 8, –1625 ± 39, –1654 ± 39, –2626 ± 4.

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The heats of formation of stable compounds produced during thermal decomposition reactions were determined by measurements of enthalpies of reactions. The investigations were performed by using a heat-flow dropping calorimeter. The validity of the method was confirmed by measurement of the heat of formation of calcium carbonate. All calorimetric results had an accuracy of ± 2 %. The heats of formation under standard conditions, _bH ₂₉₈ kJ mol^–1, for AlCl₃ · 6 H₂O, amorphous Al₂O₃, -Al₂O₃ and Al₂O₃ · 2 H₂O · 2 Hcl are –2667±8, –1625±39, –1654±39, and –2626 ± 4, respectively.

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Résumé On a déterminé à partir des mesures des enthalpies de réaction la chaleur de formation des composés stables qui participent aux processus de dégradation thermique. Les expériences calorimétriques ont été effectuées dans un calorimètre à chute à flux de chaleur. On a vérifié la méthode de mesure en déterminant l'enthalpie de formation standard du carbonate de calcium. La reproductibilité des mesures calorimétriques est de 2% entre 298 K et 1600 K. Les enthalpies de formation _BH ₂₉₈ ^– en kJ/mole, dans les conditions standards de AlCl₃ · · 6 H₂O, Al₂O₃ amorphe, -Al₂O₃, Al₂O₃ · 2 H₂O · 2 HCl s'élèvent respectivement à –2667 ± 8, –1625± 39, –1654±39, –2626±4.

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, . . . ±2%. _B H ₂₉₈ (.^–1) AlCl₃ 6H₂O, ,-Al₂O₃ Al₂O₃. 2H₂O. 2HCl , , –2667 ± 8, –1625 ± 39, –1654 ± 39 –2626 ± 4.

     

Photoacoustic soot sensor for in-situ black carbon monitoring

The PhotoAcoustic Soot Sensor (PASS) for in situ black carbon mass monitoring is presented. The sensor combines a high-power laser diode ( = 802 nm;P = 450 mW) and a novel spectrophone setup to achieve a portable sensor system for black carbon measurements. The acoustic resonator with aQ-factor of 300 is operated in its 2nd azimuthal mode at 6670 Hz. To estimate the effects of the window position, laser beam collimation, and different loss mechanisms on spectrophone sensitivity a model treating these effects with respect to the signal strength of the azimuthal modes is described. It gives a cell constant of 5.8 V/(W m^–1) in good agreement with 5.9 V/(W m^–1) obtained from measurements with particulate carbon. Additionally, this model permits a method for an absolute calibration of the spectrophone. To improve the signal-to-noise ratio, the photoacoustic signal is estimated by a weighted least-squares fit to an averaged line profile of the excited normal mode instead of a direct measurement of peak height. Finally, the application of this data processing algorithm yields a detection limit of 1.5 × 10^–6 m^–1 or 0.5 g black carbon per m³     

Nanoparticles based on polyelectrolyte complexes: effect of structure and net charge on the sorption capability for solved organic molecules

 The sorption of solved organic molecules such as p-nitrophenol or dyes on previously formed nanoparticles based on polyelectrolyte/micelle complexes or polycation/polyanion complexes was studied. It could be shown that the sorption capability strongly depends on the structure and properties of the complex particles. Investigations have been made with complex particles that differ in their hydrophobic/hydrophilic structure, size and net charge. Such complex aggregates could be prepared by mixing the cationic surfactant dodecylamido-ethyldimethylbenzylammonium chloride, the polycations poly(diallyldimethylammonium chloride) or poly(methacryloyloxyethyldimethylbenzylammonium chloride) and the copolymers of maleic acid with propene or methylstyrene as anionic components. It is found that the sorption capability increases with increasing molar mass and hydrophobic properties of the components used. In addition, the concentration ratio c _polym/c _org.poll that was required to reach optimal sorption conditions could be decreased by the use of macromolecules with high molar masses. The best results were obtained by using cationic stabilized complex particles formed with high-molar-mass polycations as sorbents for anionic dye molecules. Received: 10 November 1999 Accepted: 24 February 2000     

On a Sharp Interface Model for Phase Transitions in Steel

Steel is one of the most widely used materials in the world with a broad spectrum of properties. The microstructure and the distribution of the different phases are of great importance, since they each possess different properties. A sharp interface model for the austenite-ferrite phase transition is presented. Mechanical effects due to eigenstrains resulting from the different densities of the phases are taken into account. The governing PDEs in each phase are a diffusion equation for the carbon concentration and the balance of momentum. Across the free interface, separating the two phases, the physical quantities may have discontinuities, which are controlled by jump conditions. Consistency of the model with the 2nd law of thermodynamics is shown. Numerical simulations for these types of free boundary problems are quite complex and involve appropriate methods to determine the interface position. One possibility to circumvent the explicit determination of the free boundary is the use of regularization techniques in form of phase field methods, where the interface is tracked implicitly. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Laser desorption in transmission geometry inside a Fourier-transform ion cyclotron resonance mass spectrometer

We report here the first application of laser desorption (LD) in transmission geometry (backside irradiation of the sample through a transparent support) inside a Fourier-transform ion cyclotron resonance mass spectrometer (FT-ICR). A probe-mounted fiber optic assembly was used to simplify the implementation of this LD technique. This setup requires little or no instrument modifications, has minimum maintenance requirements, and is relatively inexpensive to build. The performance of the probe was tested by determining the molecular weight of a commercial polystyrene standard from its matrix-assisted laser desorption/ionization (MALDI) spectrum. The measured average molecular weight is comparable to that obtained for the same sample by MALDI in the conventional top-illumination arrangement (reflection geometry) and by the manufacturer of the sample by gel permeation chromatography. The average velocities measured for ions evaporated by transmission mode LD of several neat samples are about half the velocity of those obtained by using the reflection geometry. Therefore, transmission mode irradiation of the sample holds promise to desorb ions that are easier to trap in an ICR cell. An oscillating capillary nebulizer was adapted for the deposition of analytes to improve sampling reproducibility.     

Prognostic Value of Immunohistochemical Markers for Locally Advanced Rectal Cancer

The aim of this study is to reveal the potential roles of apoptosis markers (Bcl2 and p53), proliferation markers (Ki-67 and CyclD1), and the neuroendocrine marker Chromogranin A as markers for the radioresistance of rectal cancer. Statistically significant differences were found in the expression of p53, Ki-67, and Chromogranin A in groups of patients with and without a favorable prognosis after radiotherapy. The survival analysis revealed that the marker of neuroendocrine differentiation, Chromogranin A, also demonstrated a high prognostic significance, indicating a poor prognosis. Markers of proliferation and apoptosis had no prognostic value for patients who received preoperative radiotherapy. Higher Chromogranin A values were predictors of poor prognosis. The results obtained from studying the Chromogranin A expression suggest that the secretion of biologically active substances by neuroendocrine cells causes an increase in tumor aggressiveness.     

Visible-Light-Mediated Liberation and In Situ Conversion of Fluorophosgene

The first example for the photocatalytic generation of a highly electrophilic intermediate that is not based on radical reactivity is reported. The single-electron reduction of bench-stable and commercially available 4-(trifluoromethoxy)benzonitrile by an organic photosensitizer leads to its fragmentation into fluorophosgene and benzonitrile. The in situ generated fluorophosgene was used for the preparation of carbonates, carbamates, and urea derivatives in moderate to excellent yields via an intramolecular cyclization reaction. Transient spectroscopic investigations suggest the formation of a catalyst charge-transfer complex-dimer as the catalytic active species. Fluorophosgene as a highly reactive intermediate, was indirectly detected via its next downstream carbonyl fluoride intermediate by NMR. Furthermore, detailed NMR analyses provided a comprehensive reaction mechanism including a water dependent off-cycle equilibrium.     

Phosphite copper(I) trifluoroacetates [((RO)3P)mCuO2CCF3] (m = 1, 2, 3): synthesis, solid state structures and their potential use as CVD precursors

Metal-organics [((RO)(3)P)(m)CuO(2)CCF(3)] (R = CH(3): 11a, m = 1; 11b, m = 2; 11c, m = 3. R = CH(2)CH(3): 12a, m = 1; 12b, m = 2; 12c, m = 3. R = CH(2)CF(3): 13a, m = 1; 13b, m = 2; 13c, m = 3) are either accessible by the reaction of [((RO)(3)P)(m)CuCl] (R = CH(3): 5a, m = 1; 5b, m = 2; 5c, m = 3. R = CH(2)CH(3): 6a, m = 1; 6b, m = 2; 6c, m = 3) with [KO(2)CCF(3)] (7), or treatment of [Cu(2)O] (8) with HO(2)CCF(3) (9) and P(OR)(3) (2, R = CH(3); 3, R = CH(2)CH(3); 4, R = CH(2)CF(3)). (31)P{(1)H} NMR spectra [((CH(3)O)(3)P)(m)CuO(2)CCF(3)] (m = 1, 1.5, 2, 2.5, 3, 3.5, and 4) have been studied at 25 and -80 °C showing phosphite ligand exchange in solution. The molecular structures of 11a and 13a-13c in the solid state are reported. Complexes 11a and 13a are tetramers featuring μ-η(2)(1κO:2κO')- and μ(3)-η(2)(1κO:2κO':3κO')-(11a) or μ(3)-η(2)(1κO:2κO':3κO')-bonded O(2)CCF(3) ligands (13a) with the Cu(I) ions being part of CuPO(2) and CuPO(3) units (11a), while in 13a solely a CuPO(3) moiety is present. Skeletal isomerism of 11a vs. 13a is discussed. Compound 13b is dimeric ({CuP(2)O(2)}(2)) with pseudo-tetrahedral Cu environments and μ-η(2)(1κO:2κO')O(2)CCF(3) functionalities. In monomeric 13c the O(2)CCF(3) ligand is η(1)(κO)-bonded to a tetra-coordinated Cu(i) ion. The thermal solid state properties of 11, 12 and 13 were studied by Thermo Gravimetry (TG). These complexes decompose by phosphite elimination, decarboxylation and dealkylation. Hot-wall Chemical Vapour Deposition (CVD) experiments were carried out at 380 °C using 11c as precursor for the deposition of copper onto pieces of TiN-coated oxidized silicon substrates. Copper layers of high purity were obtained with grain sizes between 200-1200 nm.     

Effect of excluded volume on 2D discrete stochastic chemical kinetics

The stochastic simulation algorithm (SSA) is widely used in the discrete stochastic simulation of chemical kinetics. The propensity functions which play a central role in this algorithm have been derived under the point-molecule assumption, i.e., that the total volume of the molecules is negligible compared to the volume of the container. It has been shown analytically that for a one-dimensional system and the A + A reaction, when the point-molecule assumption is relaxed, the propensity function need only be adjusted by replacing the total volume of the system with the free volume of the system. In this paper we investigate via numerical simulations the impact of relaxing the point-molecule assumption in two dimensions. We find that the distribution of times to the first collision is close to exponential in most cases, so that the formalism of the propensity function is still applicable. In addition, we find that the area excluded by the molecules in two dimensions is usually higher than their close-packed area, requiring a larger correction to the propensity function than just the replacement of the total volume by the free volume.     

Divergent Mechanistic Routes for the Formation of gem‐Dimethyl Groups in the Biosynthesis of Complex Polyketides

The gem‐dimethyl groups in polyketide‐derived natural products add steric bulk and, accordingly, lend increased stability to medicinal compounds, however, our ability to rationally incorporate this functional group in modified natural products is limited. In order to characterize the mechanism of gem‐dimethyl group formation, with a goal toward engineering of novel compounds containing this moiety, the gem‐dimethyl group producing polyketide synthase (PKS) modules of yersiniabactin and epothilone were characterized using mass spectrometry. The work demonstrated, contrary to the canonical understanding of reaction order in PKSs, that methylation can precede condensation in gem‐dimethyl group producing PKS modules. Experiments showed that both PKSs are able to use dimethylmalonyl acyl carrier protein (ACP) as an extender unit. Interestingly, for epothilone module 8, use of dimethylmalonyl‐ACP appeared to be the sole route to form a gem‐dimethylated product, while the yersiniabactin PKS could methylate before or after ketosynthase condensation.