Magnetic properties of nickel-zinc ferrites synthesized from liquid solutions produced in chemical and electrochemical processing of metals

Nickel-zinc ferrite was prepared by coprecipitation from liquid waste formed in chemical and electrochemical processing of metals.     

A theoretical study of the structure and bonding of UOX4 (X = F, Cl, Br, I) molecules: the importance of inverse trans influence.

During nitroxide-mediated polymerization (NMP) in the presence of a nitroxide R2(R1)NO*, the reversible formation of N-alkoxyamines [P-ON(R1)R2] reduces significantly the concentration of polymer radicals (P*) and their involvement in termination reactions. The control of the livingness and polydispersity of the resulting polymer depends strongly on the magnitude of the bond dissociation energy (BDE) of the C-ON(R1)R2 bond. In this study, theoretical BDEs of a large series of model N-alkoxyamines are calculated with the PM3 method. In order to provide a predictive tool, correlations between the calculated BDEs and the cleavage temperature (T(c)), and the dissociation rate constant (k(d)), of the N-alkoxyamines are established. The homolytic cleavage of the N-OC bond is also investigated at the B3P86/6-311++G(d,p)//B3LYP/6-31G(d), level. Furthermore, a natural bond orbital analysis is carried out for some N-alkoxyamines with a O-C-ON(R1)R2 fragment, and the strengthening of their C-ON(R1)R2 bond is interpreted in terms of stabilizing anomeric interactions.     

Extensions of Szegö's theory of orthogonal polynomials,III

Let {ø _n (dμ)} be a system of orthonormal polynomials on the unit circle with respect to a measuredμ. Szegö's theory is concerned with the asymptotic behavior ofø _n (dμ) when logμ′∈L ¹. In what follows we will discuss the asymptotic behavior of the ratioø _n (dμ ₂)/ø _n (dμ ₁) on the unit circle whendμ ₁ anddμ ₂ are close in a sense (e.g.,dμ ₂=gdμ ₁, where g≥0 is such thatQ(e ^it )g(t) andQ(e ^it )/g(t) are bounded for a suitable polynomialQ) and μ ₁ ^′ >0 almost everywhere or (a somewhat weaker requirement) lim _n→∞Φ _n (dμ ₁,0)=0 for the monic polynomial Φ _n . The asymptotic behavior of the same fraction outside the unit circle was discussed in an earlier paper.     

Fluorescence of crystalline 4-(dimethylamino)benzonitrile. Absence of dual fluorescence and observation of single-exponential fluorescence decays

The fluorescence spectrum of crystals grown from newly synthesized 4-(dimethylamino)benzonitrile (DMABN), measured from 25 down to −112 °C, consists of a single emission band originating from a locally excited (LE) state. The fluorescence decay of the DMABN crystals is single exponential at all temperatures investigated. These results show that intramolecular charge transfer (ICT) does not occur in crystalline DMABN. The additional red-shifted emission bands and multiexponential fluorescence decays previously reported for DMABN crystals are attributed to a minor amount of the impurity 4-(dimethylamino)benzaldehyde, the synthetic precursor of commercial DMABN.     

Density functional study of the conformational space of 4C1 D-glucuronic acid

The conformational space of (4)C(1) alpha- and beta-d-glucuronic acid was scanned by HF/3-21G(p) calculations followed by optimization of the 15 most stable structures for each, using the B3LYP density functional theory method in conjunction with a diffuse polarized valence triple-zeta basis set. We found a general preference of the alpha anomers in the isolated molecules in agreement with the large endo-anomeric hyperconjugation effects in these structures. From the other intramolecular interactions (exo-anomeric hyperconjugation, hydrogen-bonding, dipole-dipole, and steric interactions), the effect of the hydrogen bonding is the most pronounced and plays a major role in determining the stability order within the alpha and beta series. The most stable conformer of both alpha and beta (4)C(1) d-glucuronic acid is the structure with the maximum number (5) of intramolecular hydrogen bonds. Introduction of solvent (water) effects by the SCI-PCM model resulted in two characteristic changes of the energetic properties: the gas-phase stability order changed considerably, and the energy range of the 15 most stable conformers decreased from 30 to 15 kJ/mol. The geometrical parameters reflect well the superimposed effects of hyperconjugation and hydrogen-bonding interactions. Most characteristics are the variations of the C-O bond distances (within a range of 0.04 A) upon the combined intramolecular effects.     

Behavior of Humic Acid as a Micellar Phase in Micellar Electrokinetic Chromatography (MEKC)

The possibility of humic acids acting as micellar phase in micellar electrokinetic chromatography was evaluated. We investigated the separation of naphthalene in capillary electrophoresis using various samples of humic acids as micellar phase under different pH conditions, concentrations of humic acid, and temperature. The humic acid samples studied were from different origins including peat, vermicompost and a commercial sample acquired from Aldrich. Methanol was used as a marker for the electroosmotic flow. The results indicate that the formation of micelle depends on the number and nature of the hydrophobic association sites in an aqueous humic acid solution and on the origin and concentration of the humic acid at a defined pH. At lower pH values, the possibility of the humic acid molecule forming pseudomicelles increases due to a combination of neutralized and dissociated charged sites.     

Hard-soft acid-base interactions of silylenes and germylenes

A detailed investigation of the electrophilic and nucleophilic character of singlet silylenes and germylenes, divalent compounds of silicon and germanium, respectively, substituted by first- and second-row elements is presented. In a first part, the Lewis acid properties of these compounds were studied through their complexation reaction with the Lewis bases NH3, PH3, and AsH3. The results indicate that this complexation is most favorable with the hardest base NH3, classifying these compounds as hard Lewis acids. This is confirmed by the linear correlation between the interaction energies and the value of the electrostatic potential, used as an approximation to the local hardness, near the empty p orbital of these compounds, indicating a charge-controlled interaction in the complex. Also the electrophilicity index, proposed by Parr et al., computed both at the global and the local level, correlates linearly with the complexation energies of the compounds with NH3. The Lewis base character of these silylenes has been investigated, through their interaction with the acids BH3 and AlH3. Also in this case, the electrostatic potential can be used to probe the reactivity of the compounds. It will finally be demonstrated that an increasing stability of the silylenes and germylenes is accompanied by an increase in their nucleophilicity and a decrease of the electrophilicity.     

Stochastic theory of size exclusion chromatography by the characteristic function approach

A general stochastic theory of size exclusion chromatography (SEC) able to account for size dependence on both pore ingress and egress processes, moving zone dispersion and pore size distribution, was developed. The relationship between stochastic-chromatographic and batch equilibrium conditions are discussed and the fundamental role of the 'ergodic' hypothesis in establishing a link between them is emphasized. SEC models are solved by means of the characteristic function method and chromatographic parameters like plate height, peak skewness and excess are derived. The peak shapes are obtained by numerical inversion of the characteristic function under the most general conditions of the exploited models. Separate size effects on pore ingress and pore egress processes are investigated and their effects on both retention selectivity and efficiency are clearly shown. The peak splitting phenomenon and peak tailing due to incomplete sample sorption near to the exclusion limit is discussed. An SEC model for columns with two types of pores is discussed and several effects on retention selectivity and efficiency coming from pore size differences and their relative abundance are singled out. The relevance of moving zone dispersion on separation is investigated. The present approach proves to be general and able to account for more complex SEC conditions such as continuous pore size distributions and mixed retention mechanism.     

New materials for sorption of hydrogen

The influence of temperature, duration of thermal treatment, and oxidation modes of the aluminum base on processes in which intermetallic compounds LiLaAl are formed by the method of electrochemical cathodic intercalation was studied. The optimal modes of formation of LiLaAl_ox compounds exhibiting high sorption capacity for hydrogen were determined.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 9, 2004, pp. 1516–1519.Original Russian Text Copyright © 2004 by Olshanskaya, Sobgaida, Popova.