The influence of temperature on the elastic behaviour of structured dispersions

The modulus of fast elastic deformation (G ₀) for a dispersion of silica in decane varies with temperature (at constant concentration by weight). It is shown that

1. with an increase in temperature the volume fraction of the solid decreases, due to the relative high thermal expansion of the liquid medium.
2. if one tries to correct for this decrease ofΦ, the dependence ofG ₀ with temperature is linear with a positive slope of 228 N m^?2 K^?1. This value is much greater than the expected one for the entropic part (0.92 N m^?2 K^?1).

We take this as a proof for the existence of an important temperature dependence of the energetic part of the free energy of deformation, which is due to the different change of the dielectric permittivities of the particles and the solvent. The possibility of a layer of structured solvent, which is destructed by increasing temperature, is also discussed.     

Hippurathydrolase,ein neues Enzym aus Mikroorganismen, 2. Mitt.: Enzymeigenschaften

Characteristic properties of the new enzymehippurate hydrolase are reported:

1. The Michaelis constant for hippurate hydrolysis is 5.5·10^?4 mole/l at 5° and pH 7.5. The specific activity of the purified enzyme preparation is 7.5 μmole/minute · mg enzyme protein at 37° and pH 7.5. The pH optimum is 7.5.
2. The effects of temperature on the reaction rate and on the stability of the enzyme were determined.
3. The effects of various inhibitors (HgCl₂, pCMB, EDTA, 8-hydroxyquinoline) and cations were studied. Participation of metal ions in the catalytic function ofhippurate hydrolase was not detectable.

     

Thermisches Phasenverhalten homologer α- und β-methylverzweigtkettiger Lecithine im wassergesättigten Zweiphasengebiet

1. By means of differential scanning calorimetry the phase transition temperatures (T _u) and phase transition enthalpies (ΔH _u) ofα- andβ-branched lecithins were determined. The lecithin samples contained 50% water per weight.
2. The occurrence of the pre-transition was dependent on the position of the methyl group in the acid residue as well as on the length of the carbon chains. TheΔH _u values of the pre-transition were about 2.5 kJ·mol^?1.
3. The hydration number (HZ) (number of water molecules per lecithin headgroup) was independent on the position of the methyl group and the length of the acyl group. The average HZ-values for all the lecithins studied is about HZ=14+-1.
4. The influence of the chain length of theα- andβ- branched acyl groups affects the thermodynamical parameters of the main transitions (gel→L _α). TheΔH _m andT _m-values increased as the chain length increases.

     

Einfluß der thermischen Vorgeschichte auf die Phasenumwandlungen von Dipalmitoyllecithin/Wasser-Mischungen

1. The influence of the thermal pretreatment (first and second heating run, annealing process) on the phase transition temperaturesT _m, enthalpiesΔ¯H _m and the specific heatc _sp of 1,2-dipalmitoyllecithin-water-mixtures was studied by differential scanning calonmetry.
2. The differences in theT _m- andΔ¯H _m-data of the main transition of the first and second heating run were found in the concentration rangex ^w<0,75. In the concentration rangex _W>0.75 these differences disappear.
3. The annealing process of a 1,2-dipalmitoyllecithin-water-mixturex _W=0,89 leads to a splitting of the main transition peak in two separate peaks with a different shape. This behaviour may imply that 1,2-dipalmitoyllecithin coexists in two different hydration states.

     

Charakterisierung der Mischbarkeitseigenschaften binärer Monoschichten durch Messung der Gleichgewichtsspreitungsdrucke

1. The equilibrium spreading pressures were studied as a function of composition of the following binary systems by use of the Wilhelmy-method atT=295 K on aqueous substrate:

octadecyldiethylphosphine oxide/1-hexadecanol (I)

octadecyldiethylphosphine oxide/1-eicosanol (II)

octadecyldiethylphosphine oxide/stearic acid (III)

1. The equilibrium spreading pressures of the pure components of the systems I und II, respectively, decrease due to addition of the corresponding components of mixture. A minimum occurs at the mole fractionx=0,50. The equilibrium spreading pressures of mixtures of system III rise with increasing mole fraction of octadecyldiethylphosphine oxide.
2. The three spreading diagrams are based on one general type. The phase rule is applied and shows that the components of the 3 systems must be immiscible in the monolayer but miscible in the bulk phase.

     

Kinetic parameters of the thermal decomposition of Cu(II) and Zn(II) salts of carboxylic acids

The kinetic parameters of thermal decomposition of Cu(II) and Zn(II) salts of carboxylic acids were investigated on the basis of the respective thermal curves. The values of the activation energy (E _a) of thermal decomposition, reaction order (n), frequency factor (A) and velocity constant (k) (in the Arrhenius kinetic equation), established from thermal data, were compared. Based on the initial decomposition temperature, the following sequences of stabilities of the studied compounds have been proposed:

1. Cu(CH₃COO)₂ (235°)>Cu(C₆H₅O₇)₂ (220°)>Cu(HCOO)₂ (150°)>>Cu(OH)₂·Cu(CO₃) (50°)
2. Zn(C₁₈H₃₅O₂)₂ (305°)>ZnCO₃ (210°)>Zn(CH₃COO)₂ (170°)

     

Einsatz der echten Integration in der Atomabsorptions-Spektroskopie

An improvement of the signal-to-noise ratio in atomic absorption spectroscopy may be obtained by each of the following three methods of signal averaging:

increase of the time constant

digital signal averaging

true integration of the signal

The most adequate of these methods appears to be true integration. Two examples are presented to demonstrate the improved signal-to-noise ratio due to the application of this method:

trace analysis of mercury in water by means of flameless AAS. The detection limit appears to be 0.2 ng which corresponds to a concentration of 2 · 10^?13 g/ml.

trace analysis of copper in human urine by means of flame AAS: 1,3 · 10^?8 g/ml copper could be detected without any solvent extraction process.

     

Le systeme Z α, β-dinitrostilbene — E α, β-dinitrostilbene

Z-α,β-dinitrostilbène (Z-DNS) is employed as amine reagent. The absence of isomerization into E-DNS by heating was verified using DTA. The Z-DNS-E-DNS phase diagram was established, and the following data obtained:

for E-DNS,T _f =459 K, ΔH _f =15 kJ·mpl^?1, and solid-solid phase transition atT=439 K.

for Z-DNS,T _f =380 K, ΔH _f =20 kJ·mol^?1.

The binary phase diagram exhibits a eutectic equilibrium at 368 K with the liquid composition 89相似文献   

Kompressionsverhalten und Gleichgewichtsspreitungsdrucke binärer monomolekularer Dipalmitoylkephalin/Dimyristoylkephalin-Mischungen

1. The concentration dependence of theF/A-isotherms (premixed spreading, separate spreading) and the equilibrium spreading pressuresF ^e of the system dipalmitoylcephaline/dimyristoyl-cephaline were studied atT=298 K. The results were analysed and compared by means of thermodynamics with respect to miscibility of the components.
2. The spreading technique (pre-mixed spreading, separate spreading (with and without barrier), does not essentially influence the run of theF/A-isotherm. Alone, the collaps pressuresF _K differ.
3. The concentration dependence of theF/A-isotherms of premixed spread monolayers is analysed in terms of theA-x ^σ-diagram. The additivity of molecular areas at all surface pressures are assumed to indicate complete miscibility of the cephalins.
4. The phase rule according to Crisp was applied to analyse the spreading diagram in connection with the phase diagram of the mixtures in bulk. The results show that the cephalins are completely miscible in the monolayer.
5. The experimental collaps pressuresF _K of pre-mixed spread monolayers are very much larger than the equilibrium collapse presuresF _K calculated according to Garrett. The difference indicate the strong supercompression of mixed film during the compression.

     

Theoretical study of the visible photodissociation spectrum of Ar 3 +

The photodissociation of Ar ₃ ⁺ is studied following a consistent theoretical approach from the Potential Energy Surfaces to the dynamics. Six P.E.S. are computed according to a D.I.M.-like model Hamiltonian. Transition dipole moments are determined using a similar method. The 4-D dynamics of this system is obtained with the H.W.D. method (Hemiquantal dynamic with the Whole DIM basis). All the 4 nuclear degrees of freedom and all the 6 electronic states are involved in the dynamical calculations, allowing for very general investigations. The main theoretical results are:

1. the spectrum essentially results from a Σ → Σg transition to the second excited electronic state along with a symmetric stretching motion
2. excited Ar ₃ ⁺ molecules almost all dissociate in Ar⁺ + 2 Ar
3. dissociation in Ar ₂ ⁺ + Ar requires special conditions such as low laser excitation and is predicted to increase with a specific excitation of the bending mode
4. the dominant symmetric stretching motion induces a bimodal kinetic energy distribution of the fragments.

All these points are in close agreement with experimental results.     

Die Bildungsenthalpie von SnJ4

The changes of enthalpy for the reactions

1. Sn(c)+2I₂(c)+4165 CS₂(l)=[SnI₄; 4165 CS₂] (sol.),
2. SnI₄(c)+4223 CS₂(l)=[SnI₄; 4223 CS₂] (sol.)

At 298,15 K have been found by solution calorimetry to be ΔH ₁=(?46.7±0.3) and ΔH ₂=(+3.2±0.1) kcal Mol^?1, resp. Neglecting the heat of dilution which is approximately zero these values give ΔH _f ^o (SnI₄; c; 298 K)=9?49.9±0.4) kcal Mol^?1 for the enthalpy of formation of SnI₄. From existing literature data the standard entropy is calculated to beS ^o(SnI₄; c; 298 K)=69,7 cal Mol^?1 K^?1 giving ΔG _f ^o (SnI₄; c; 298 K)=?50,5 kcal Mol^?1 for the corresponding change in theGibbs free energy.     

Kompressionsverhalten und Gleichgewichtsspreitungsdrücke binÄrer monomolekularer Dimyristoylkephalin/Dilauroylkephalin-Mischungen

1. The concentration dependence of theF/A-isotherms (premixed spreading, separate spreading) and the equilibrium spreading pressuresF ^e of the system dimyristoyl-cephaline/dilauroyl-cephaline were studied atT=295 K. The results were analysed and compared with respect to the miscibility using thermodynamical criteria.
2. It was shown that various spreading techniques lead to different experimental results. In the case of the premixed spreading it is formed initially an equilibrium monolayer. The analysis of the concentration dependence of the phase transition point (liquid expanded → condensed) shows that the components are completely miscible.
3. From theF/A-isotherms of premixed spreading the A(area)-x ^τ (surface concentrations-diagrams were calculated. The deviation from the ideal behaviour of the A-x ^τ-curves is caused by a phase separation.
4. From the concentration dependence of the equilibrium spreading pressures by means of the surface phase rule follows that the components are approximately ideally miscible.
5. By the analysis of the collapse and equilibrium spreading pressures follows that the mixed films during the compression are in a metastabile state.

     

TG and DSC kinetics of thermal decomposition and crystallization processes

The simplen ^th order model equation combined with the Arrhenius approach of the temperature dependency of the reaction rate constant is widely used in thermal analysis. The new Mettler software package for thermal analysis, GraphWare TA72 allows to access a full model comprising the power law and the crystallization kinetics (AvramiErofe'ev). The kinetics of the following reactions are studied to illustrate some applications:

thermal decomposition of dissolved dibenzoylperoxide, (dynamic and isothermal DSC measurement)

crystallization of polyethylene terephthalate (PET) (isothermal DSC measurements).

The kinetic model applied and the accuracy of the kinetic data obtained are discussed by means of a comparison of a predicted behaviour with the kinetic data measured isothermally.     

Direct determination of pair natural orbitals

A method is proposed to solve the two-electron Schrödinger equation by a rapidly converging iterative procedure. The wavefunction is obtained in terms of its NO's. The special features of the present method are:

1. Each iteration requires only the computational equivalent of a conventional Hartree-Fock iteration.
2. Within each iteration we improve simultaneously the NO's, the CI expansion coefficients and the total energy.
3. The construction of a CI matrix is never required.

We further propose simplified NO-equations the solution of which requires a small fraction of computertime only. As examples of the efficiency of these methods we report applications to the 1¹ Sstate of He, the 1¹∑ _g ⁺ , 1³∑ _u ⁺ states of H₂, and IEPA,PNO-CI, and CEPA type computations on CH₄.     

Synthesis,structures and properties of three copper complexes created via in situ ligand cross-coupling reactions

Three copper complexes {[Cu₂(L¹)₂]·I₃} _n (1), [Cu(L²)₂] (2), and [Cu₂I₂(L³)₂(MBI)₂] (3) (MBI = 2-mercaptobenzimidazole, L¹ = N-(benzothiazol-2-yl)acetamidine anion, L² = N-(thiazol-2-yl) acetamidine anion, L³ = 3-methyl-[1,2,4]thiadiazolo[4,5-a]benzimidazole) have been synthesized solvothermally by the reactions of CuI with 2-benzothiazolamine, 2-aminothiazole and 2-mercaptobenzimidazole (MBI), respectively, in acetonitrile. In situ C–N (or C–S) cross-coupling ligand reactions were observed in all three complexes, and hypothetical reaction mechanisms are proposed for the formation of the ligands and their complexes. The single-crystal X-ray structural analysis reveals that both the Cu(II) and Cu(I) atoms are located in pseudo-tetrahedral environments in complex 1, and L¹ acts as a double bidentate ligand which coordinates with the Cu(I) and Cu(II) atoms to form a 1D coordination polymer. Unlike complex 1, the Cu(II) atom in complex 2 is in a square planar geometry, coordinated by two L² ligands with relatively small steric hindrance. In complex 3, the Cu(I) atoms have a distorted tetrahedral geometry, being coordinated by one nitrogen atom from L³, two sulfur atoms of MBI ligands, and one iodide. The sulfur atoms from MBI ligands bridge two Cu(I) atoms to form a binuclear complex. All three complexes exhibit relatively high thermal stabilities. Complex 1 displays intense fluorescence emission at 382 nm and complex 3 displays two intense fluorescence emissions at 401 and 555 nm.     

The effect of potential aqueous pollutants on the solubility of Pb+2 in cerussite—Calcite phase

The results of this work show:

1. Pb⁺² is rapidly immobilized from aqueous solutions using calcite or aragonite, CaCO₃, and the Pb⁺² is precipitated as PbCO₃ (cerussite) on the surface of the CaCO₃ (the Pb⁺²-CaCO₃ phases),
2. using CaCO₃, the concentration of Pb⁺² in certain solutions can be reduced below environmentally tolerated concentrations, and
3. organics present in solutions and natural waters can mobilize Pb⁺² from Pb⁺²-calcite phases; with effluent waters from a paper factory, and 1:1 Ca⁺²-EDTA being more effective than lignin sulfonates, 1:1 Ca⁺²-tartrate, soap, detergent, water from a sewage treatment plant, and ordinary river water.

     

3-(diallylamino)propanenitrile ((C3H5)2NC2H4CN, L) π-complexes with copper(I) ionic salts. Syntheses and crystal structures of compounds [Cu(H+L)ClO4]ClO4 · H2O, [Cu(H+L)BF4]BF4 · H2O, and [Cu(H+L)(H2O)]SiF6 · H2O

Qualitative single crystals of ??-complexes Cu(H⁺L)(ClO₄)]ClO₄ · H₂O (I), Cu(H⁺L)(BF₄)]BF₄ · H₂O (II), and [Cu(H⁺L)(H₂O)]SiF₆ · H₂O (III) are synthesized from solutions of 3-(diallylamino)propanenitrile (L) in propanol, ethanol, and methanol-water acidified with the corresponding acid to pH 3.5?C5 and from the copper(II) salts (Cu(ClO₄)₂ · 6H₂O, Cu(BF₄)₂ · 6H₂O, and CuSiF₆ · 4H₂O) using the alternating-current electrochemical method on copper wire electrodes. The crystal structures of the complexes are determined. All compounds crystallize in the monoclinic crystal system: complexes I and II are isostructural, space group P2₁/n, Z = 4. For compound III, space group P2₁/c, Z = 8. Unit cell parameters: for I a =7.8153(3), b = 16.7824(7), c = 12.4426(5) ?, ?? = 93.410(2)°, V = 1629.1(1) ?³; for II, a = 7.6755(4), b = 16.7119(7), c = 12.3784(6) ?, ?? = 94.354(2)°, V = 1583.2(1); and for III a = 9.826(2), b = 24.009(3), c = 12.061(2) ?, ?? = 91.820(6)°, V = 2843.9(7) ?³. The trigonal pyramidal coordination of the copper atom in complexes I-III is formed by two C=C bonds of the allyl groups of H⁺L, the nitrile N atom of the adjacent cation of the ligand, and the O or F atom of the ClO ₄ ^? or BF ₄ ^? anions. In structure III, the apical position of the pyramid is occupied by the O atom of the water molecule, since the SiF ₆ ^2? anion is considerably remote from the copper(I) atom. However, this anion is bound to the organic cation by hydrogen bonds F??H (2.05?C2.51 ?).     

Copper complexes of two isomeric NS2-macrocycles

Two isomeric NS₂-macrocycles incorporating a xylyl group at ortho (o -L) and meta (m -L) positions were employed and their copper complexes (1?C5) were prepared and structurally characterized. The copper(II) nitrate complexes [Cu(L)(NO₃)₂] (1: L = o -L, 2: L = m -L) for both ligands were isolated. In each case, the copper center is five-coordinated with a distorted square pyramidal geometry. Despite the overall geometrical similarity, 1 and 2 show the different ligand conformation due to the discriminated packing pattern. Reaction of o -L with copper(II) perchlorate afforded complex 3 containing two independent complex cations [Cu(o -L)(H₂O)(DMF)(ClO₄)]⁺ and [Cu(o -L)(H₂O)(DMF)]²⁺; the coordination geometry of the former is a distorted octahedron while the latter shows a distorted square pyramidal arrangement. In the reactions of copper(I) halides (I or Br), o -L gave a mononuclear complex [Cu(o-L)I] (4) with a distorted tetrahedral geometry, while m -L afforded a unique exodentate 2:1 (ligand-to-metal) complex [trans-Br₂Cu(m-L)₂] (5) adopting a trans-type square-planar arrangement.     

Generalized quantum mechanical two-centre problems

If χ _i (χ _k ) is an exact generalized diatomic orbital (solution of Eq. (1) of text), a sequence of functions χ _i ^(N) converging to χ _i may be constructed so that matrix elements of frequently occurring operators between χ _i ^(N) and χ _k ^(N) may be computed without any numerical integration. Exact expectation values are given for kinetic and potential energy, dipole moment, θ ²=x ²+y ², and quadrupole moment 3z ²?r ², for various ratios of nuclear charges Z ₁,Z ₂ and for several distances R. Special subjects discussed in terms of computed expectation values are:

1. R-dependence of the contributions to total energy of HeH²⁺ in state 2pσ and of LiH³⁺ in state 3dσ
2. RZ-and λ-dependence of dipole and quadrupole moment functions in state 1sσ
3. Some properties of those generalized diatomic orbitals which approach, for R going to 0, Slater-type atomic functions.