Band 225, Heft 1 -

Quantum thermodynamics describes dynamic processes by means of the operators of entropy production P and time t . P and t do not commute. It exists the non-vanishing t – P commutator [ t , P ]= ik . Here the Boltzmann constant k has the physical meaning of a quantum of entropy. The t – P commutator immediately leads us to the t – P uncertainty relation Δ t Δ P ≥ k /2. Hence the observables t and P are not sharply defined simultaneously. Similar uncertainty relations can also be expected for other pairs of conjugate variables with products of the physical meaning of an entropy. The free energy F and the reciprocal temperature (1/ T ) are the respective conjugate variables of an isolated system of many particles, which leads us to the F –(1/ T ) uncertainty relation ǀΔ F ǁΔ(1/ T )ǀ≥ k /2. It can be traced back to the t – P uncertainty relation mentioned above. In this way the Helmholtz free energy F and the temperatur T are introduced into quantum thermodynamics. The uncertainties ǀΔ F ǀ→0 and ǀΔ T ǀ→0 are negligible at low temperatures T →0, and quantum thermodynamics turns into the time-independent classical thermodynamics. Against this the uncertainties ǀΔ F ǀ→∞ and ǀΔ T ǀ→∞ grow unlimited at high temperatures T →∞, and classical thermodynamics loses its sense. In the limit of one particle the uncertainties cannot be neglected even at low temperatures. However a detailed discussion shows that the free energy f of a single particle vanishes within the whole range of temperatures T . This defines the particle entropy σ =ε/ T = ak . The dimensionless entropy number a connects the particle energy ε= akT with the temperature T . The entropy number a of a single (s) independent particle can be calculated with the extended, temperature-dependent Schrödinger equation A s φ=aφ . Here A s =−( Λ 2 /4 π )∇ 2 means the dimensionless entropy operator describing the entropy number a and thus the particle entropy σ = ak . Λ is the thermal de Broglie wave length. Finally we calculate by means of quantized particle entropies σ the internal energy E , the Helmholtz free energy F , the entropy S , the chemical potential μ , and the equation of state of an ideal gas of N monatomic free particles in full agreement with classical thermodynamics. We also calculate the partition function q = V / Λ 3 of a single free particle within the volume V . Here Λ 3 is a small volume element taking into account the wave–particle dualism of a single free particle of mass m at temperature T . Extension to a system of N free particles leads us to a simple geometrical model and to the conclusion that an ideal gas of independent particles becomes instable below a critical temperature T C . T C corresponds to the critical temperature T BE of Bose–Einstein condensation.

By using quantum mechanical DFT calculations, the most probable structures of free benzo-18-crown-6 ligand (abbrev. L) and the cationic complex species CsL + and CsL 2 + were derived. In the CsL + and CsL 2 + complexes, the “central” cation Cs + is bound by strong bond interactions to the corresponding ethereal oxygen atoms of the parent crown ligand L. The interaction energies of the CsL + and CsL 2 + complex species were found to be -272.5 and -385.0kJ/mol, respectively, confirming the formations of the considered complexes.

The effect of the alloying elements and some inorganic inhibitors (WO 4 2- , MoO 4 2- , SiO 3 2- and CrO 4 2- anions) on the uniform and pitting corrosion characteristics of Al-6061, Al-4.5% Cu, Al-7.5% Cu, Al-6% Zn and Al-12% Zn alloys were studied in 0.04M KSCN solution. Susceptibility of the tested alloys towards pitting corrosion was investigated using transient (potentiostatic and galvanostatic) measurements. An independent method of chemical analysis, namely ICP-AES (inductively coupled plasma atomic emission spectroscopy) was also used to study the effect of the alloying elements and the tested inorganic anions on the uniform corrosion of these materials. Results obtained were compared with pure Al. ICP measurements revealed that the alloyed Cu and alloyed Zn enhance uniform corrosion of the Al samples, while WO 4 2- , MoO 4 2- , SiO 3 2- and CrO 4 2- anions suppressed it. Transient measurements showed that nucleation of pit takes place after an incubation time ( t i ) . The rate of pit initiation and growth ( t i -1 ) increased with increase in SCN - concentration, applied anodic current, applied anodic potential and solution temperature. This rate of pit initiation and growth decreased in presence of inorganic inhibitors to an extent depending on the concentration and type of the introduced inhibitor. Alloyed Zn was found to accelerate pitting attack, while alloyed Cu suppressed it. Among the tested Al alloys, Al-6061 presented the highest resistance towards uniform and pitting corrosion processes. SiO 3 2- and CrO 4 2- were the most efficient anions in inhibiting uniform and pitting corrosion processes of Al in these solutions.

Zinc oxide nanostructures were synthesized via sol–gel methods in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) amide and in isopropanol, respectively, using zinc acetate dihydrate as a precursor. The synthesized ZnO powders were characterized by means of XRD, SEM-EDX, TGA-DTA and UV-Vis diffuse reflectance spectroscopy. The XRD results of the ZnO powders obtained in either the ionic liquid or in isopropanol exhibit a wurtzite structure with a high degree of crystallinity. The sol–gel growth of ZnO particles in [BMP]TFSA produces a significantly different crystal structure compared with ZnO particles obtained using isopropanol. Hexagonal ZnO nanorods were obtained using isopropanol. However, spherical ZnO nanoparticles were obtained using the ionic liquid. The UV-Vis diffuse reflectance spectra show a slight increase in the band gap of the ZnO powder synthesized using the ionic liquid compared with that of the ZnO prepared using isopropanol. Furthermore, the specific surface area of ZnO prepared using [BMP]TFSA (14.5m 2 g -1 ) is higher than that of ZnO prepared using isopropanol (6.5m 2 g -1 ).

CO oxidation over polycrystalline ruthenium dioxide was monitored in an in-situ XRD setup. The evolution of the bulk state of the catalyst was followed by in-situ XRD during reaction, while the surface morphology and chemical state before and after reaction were investigated by HRSEM and EDX. The commercial RuO 2 powder was calcined prior reaction to ensure the formation of completely oxidized RuO 2 . This pre-calcined RuO 2 is initially inactive in CO oxidation regardless of the CO/O 2 feed ratio and requires an induction period, the length of which strongly depends whether the catalyst is diluted with boron nitride or not. After this induction period oscillations in the CO 2 yield occur under O 2 -rich conditions only. These oscillations exhibit two time constants for the diluted catalyst, while the low frequency oscillations were not observed in the case of undiluted RuO 2 . Furthermore, the state of the catalyst after activation in O 2 -rich feed conditions differs dramatically from the state after activation in CO-rich feed conditions. Firstly, the catalyst activated in an O 2 -rich atmosphere remains inactive under CO-rich conditions in contrast to the catalyst activated in CO-rich conditions which is afterwards active under all feed ratios examined. Secondly, the surface morphology of the catalyst is quite different. While the apical surfaces of the RuO 2 crystals become roughened upon activation in the CO-rich feed, they become facetted under O 2 rich activation conditions. Therefore, we conclude that at least two different active surface states on the bulk RuO 2 catalyst exist.

Solvation behaviour of some copper(I) perchlorate complexes has been investigated in binary mixtures of acetonitrile (AN) and dimethylsulphoxide (DMSO) containing 1.0, 0.8, 0.6, 0.4, 0.2 and 0 mol fraction of AN at 298 K by molar conductances and viscosity measurements. The conductance data have been analyzed by using the Shedlovsky method to calculate limiting molar conductance ( Λ o ) and the viscosity data by the Jones–Dole equation to evaluate viscosity B-coefficients of various salts. Limiting ion conductances ( λ i o ), solvated radii ( r i ) and ionic viscosity B ± coefficients in all solvent systems have been evaluated using Gill´s modification based on Bu 4 NBPh 4 as a reference electrolyte. The studies show that all copper(I) complexes are solvated and the extent of solvation is stronger in AN and AN rich regions than in DMSO and DMSO rich regions. The ClO 4 - ion is poorly solvated in AN+DMSO mixtures. The viscosity results are in good agreement with the results obtained from the conductance studies.

The kinetics of oxidation of chloramphenicol (CHP) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.10 mol dm -3 was studied spectrophotometrically. The reaction between DPC and CHP in alkaline medium exhibits 1:2 stoichiometry (CHP: DPC). The main oxidation products were identified by spot test, IR, NMR and GCMS spectral studies. The reaction is of first order in DPC and CHP concentrations. As the alkali concentration increases the rate of reaction increases with fractional order dependence on alkali concentration. Increase in periodate concentration decreases the rate. A suitable mechanism is proposed. The reaction constants involved in the different steps of the mechanism were calculated. The activation parameters with respect to slow step of the mechanism are computed and discussed. Thermodynamic quantities are also determined.

The kinetics of oxidation of gabapentin (Neurontin) (GP) by diperiodatonickelate(IV) (DPN) in aqueous alkaline medium was studied spectrophotometrically. The reaction is first order with respect to [DPN] and is an apparent less than unit order, each in [GP] and [alkali] under the experimental conditions. Reaction rate increases with increase in ionic strength and in solvent polarity of the medium. Addition of reaction products has no effect on the reaction rate. A mechanism involving the formation of a complex between the oxidant and substrate has been proposed. The products are identified by spot test, IR and NMR studies. The reaction constants involved in the mechanism were evaluated. There is a good agreement between the observed and calculated rate constants under varying experimental conditions. The activation parameters with respect to the slow step of scheme were evaluated and discussed.

The effect of cationic surfactant cetyltrimethylammonium bromide (CTAB) on the oxidation of L-leucine by N-bromophthalimide (NBP) has been studied at 308 K. The reaction exhibits first order dependence on NBP and L-leucine and negative and fractional order dependence on HClO 4 . The effects of KCl, KBr, phthalimide and mercuric acetate have also been studied and summarized. The rate of reaction increased with an increase in dielectric constant of the medium. CTAB strongly catalyzes the reaction and typical k obs and CTAB profile was observed, i.e. , with a progressive increase in CTAB, the reaction rate increased and after achieving a peak k obs decreased at higher concentrations of CTAB. The results are treated quantitatively in terms of “Piszkiewicz” and “Raghvan and Srinivasan's” models. The various activation parameters in presence and absence of CTAB have been also evaluated. A suitable mechanism consistent with the experimental findings has been proposed. The rate constant in micellar phase k M , cooperativity index ( n ), binding constant ( K 1 and K 2 ) have been computed.

This paper describes the application of LFER in the form of Taft correlation to understand the mechanism of the esterification of propanoic acid with different alcohols over heterogeneous catalyst, Dowex 50Wx4. The rate constant (k 1 ) in the rate equation decreases with change of alcohols in the order methanol, ethanol, n-propyl, n-butyl, n-pentyl, iso-butyl, iso-propyl and sec-butyl (2-buthanol). The reaction of propanoic acid with alcohols fits the Taft equation, log k 1 /k CH 3 = 1.0061 E s - 0.0012, which implies that the steric effect of the substituent governs that reaction and the mechanism is similar between the different alcohols. The experimental results were modelled according to a simple second-order model. It was found that the equilibrium constant of this reaction does not depend on the structure of the organic alcohols, and has for 333 K the value 4.04.