Cavitation, shock waves and the invasive nature of sonoelectrochemistry

The invasive nature of electrodes placed into sound fields is examined. In particular, perturbations of the sound field due to the presence of the electrode support are explored. The effect of an electrode on the drive sound field (at approximately 23 kHz) is shown to be negligible under the conditions investigated in this paper. However, scattering of shock waves produced by cavity collapse is shown to exhibit a significant effect. To demonstrate this, multibubble sonoluminescence (MBSL) and electrochemical erosion measurements are employed. These measurements show an enhancement, due to the reflection by the solid/liquid boundary at the electrode support, of pressure pulses emitted when cavitation bubbles collapse. To first order, this effect can be accounted for by a correction factor. However, this factor requires accurate knowledge of the acoustic impedance of the interface and the electrolyte media. These are measured for two commonly employed substrates (soda glass and epoxy resin, specifically Epofix). A scattering model is developed which is able to predict the acoustic pressure as a function of position over a disk-like electrode substrate. The effects of shock wave reflection and materials employed in the electrode construction are used to clarify the interpretation of the results obtained from different sonoelectrochemical experiments. Given the widespread experimentation involving the insertion of electrodes (or other sensors) into ultrasonic fields, this work represents a significant development to aid the interpretation of the results obtained.     

Rotational spectra, structures, hyperfine constants, and the nature of the bonding of KrCuF and KrCuCl

Rotational spectra of KrCuF and KrCuCl have been measured in the frequency range 8-18 GHz, using a pulsed jet cavity Fourier transform microwave spectrometer. The molecules were prepared by ablating Cu metal with a pulsed Nd:YAG laser (1064 nm) and allowing the plasma to react with appropriate precursors (Kr plus SF(6) or Cl(2)) contained in the backing gas of the jet (Ar or Kr). Rotational constants, internuclear distances, vibration frequencies, and (83)Kr, Cu, and Cl nuclear quadrupole coupling constants have all been evaluated. The Kr-Cu bonds are short and the complexes are rigid. The (83)Kr coupling constant of KrCuF is large (128.8 MHz). The Cu nuclear quadrupole coupling constants differ radically from those of uncomplexed CuF and CuCl molecules. The results are supported by those of ab initio calculations, which have also yielded Mulliken populations, MOLDEN plots of valence molecular orbitals and Laplace concentrations, and electron localization functions. The results are consistent with those reported earlier for other noble gas-noble metal halide complexes. The results have been used to assess the nature of the bonding in the complexes and have produced good evidence for weak noble gas-noble metal chemical bonding.     

Chromatography in the nature

Summary A short review is given on the chromatographic processes occurring in the nature. Such processes are represented by the alteration of the composition of petroleum during its migration through earth rocks, the halochromatographic distribution of gases near oil and gas deposits as well as by other geological and biological phenomena.Editor's CommentsIn 1978, we are celebrating the seventy-fifth anniversary ofTswett's first paper on his investigations leading to the development of chromatography. On March 21, 1903,M. S. Tswett presented at the meeting of the Biological Section of the Warsaw Society of Natural Sciences a preliminary communication On a New Category of Adsorption Phenomena and their Application to Biochemical Analysis [1]. In this lecture, he reported on the first part of his experiments aimed to separate plant pigments.Tswett systematically tested a very large number of solids to check the possibility of using them as adsorbents; he definitely understood the nature of adsorption and already took an important step forward by being able to have spatial separation of several zones on the adsorbent.AlthoughTswett did not describe in 1903 his method (which was not yet finalized) as chromatography — this name was first used in 1906, in his two well-known papers [2, 3] — his investigations were already in a well advanced stage. Thus, we can safely characterize his 1903 communication as his first paper on chromatography.On the occasion of this anniversary, we hope to be able to publish a number of articles on the development of chromatography and its place in science, and our readers are urged to consider such contributions. The present article of Dr.Vigdergauz is the first in this series.L. S. Ettre     

Effects of chemical, physical, and technological processes on the nature of food allergens

A review is presented of studies of different processing techniques and their effect on the allergenicity and antigenicity of certain allergenic foods. An overview of investigated technologies is given with regard to their impact on the protein structure and their potential application in the production of hypoallergenic foods. The use of physical processes (such as heating, high pressure, microparticulation, ultrafiltration, and irradiation), chemical processes (such as proteolysis, fermentation, and refining by extraction), and biotechnological approaches, as well as the effects of these processes on individual allergenic foods, are included. Additionally, the implications of food processing for food allergen analysis with respect to food safety assessment and industrial quality control are briefly discussed.     

Variational nature, integration, and properties of Newton reaction path

The distinguished coordinate path and the reduced gradient following path or its equivalent formulation, the Newton trajectory, are analyzed and unified using the theory of calculus of variations. It is shown that their minimum character is related to the fact that the curve is located in a valley region. In this case, we say that the Newton trajectory is a reaction path with the category of minimum energy path. In addition to these findings a Runge-Kutta-Fehlberg algorithm to integrate these curves is also proposed.     

Chemical-garden formation, morphology, and composition. I. Effect of the nature of the cations

We have grown chemical gardens in different sodium silicate solutions from several metal-ion salts--calcium chloride, manganese chloride, cobalt chloride, and nickel sulfate--with cations from period 4 of the periodic table. We have studied their formation process using photography, examined the morphologies produced using scanning electron microscopy (SEM), and analyzed chemical compositions using X-ray powder diffraction (XRD) and energy dispersive X-ray analysis (EDX) to understand better the physical and chemical processes involved in the chemical-garden reaction. We have identified different growth regimes in these salts that are dependent on the concentration of silicate solution and the nature of the cations involved.     

On the complementary nature of CGC-MS,CGC-FTIR,and CGC-AED for water pollution control

Unequivocal identification of unknown pollutants is very difficult if only one dimension of information is used. Combining different hyphenated techniques can, on the other hand, lead to more reliable identification. Combination of the data provided by the different techniques is more important than on-line combination of the techniques themselves.     

Intramolecular interactions,orbital nature of electronic states,and lulinescence-spectroscopic properties of the phenoxasiline molecule

The electronic structure of the phenoxasiline (POS) molecule in the ground and electronically excited states has been calculated in the framework of the CNDO/S-CI method in sp and spd basis sets. The orbital nature of the S₁ and T₁ states and some luminescence-spectroscopic properties of POS have been determined theoretically and experimentally, and the influence of the l electrons of the oxygen atom and the d AO's of the silicon atom, as well as the geometry of the molecule, on them has been analyzed.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 22, No. 5, pp. 626–632, September–October, 1986.     

Covalent nature of the hydrogen bond

Conclusions The main conclusion derived from this work is that the H bond in all three FHF^–, FHFH, and HFHFH⁺ systems is a three-centered, two-electron, covalent chemical bond formed at the expense of 2a _1g (2a ₁) MO bonding. The 1a _1g MO bonding has little effect on H-bond stabilization. Thus the H bond is a one-orbital chemical bond with its formation corresponding, to that of a three-centered MO, as distinguished from molecules bonded by a two-centered MO (e.g., F₂ or HOOH [41]; hence the H bond is much weaker. The uniqueness of the H bond lies in its being the weakest covalent bond. It is precisely the covalent nature of the H bond that gives it its characteristic properties, i.e., saturability and strict compliance to structural requirements. In addition, the low dissociation barrier makes it easy to control the H bond under mild conditions, which is very important in biological systems.Translated from Zhurnal Strukturnoi Khimii, Vol. 26, No. 2, pp. 13–21, March–April, 1985.     

The nature of the indenyl effect

The eta(5)-to-eta(3) coordination shift of cyclopentadienyl (Cp=C(5)H(5)(-)) and indenyl (Ind=C(9)H(7)(-)) ligands in molybdenocene complexes, [(eta(5)-Cp')(eta(5)-Cp)Mo(CO)(2)](2+) (Cp'=Cp or Ind), driven by a two-electron reduction of those species, was studied and compared by means of molecular orbital calculations (B3LYP HF/DFT hybrid functional, DZP basis sets). The results obtained, in terms of optimized geometries, relative energies, and bond analysis parameters, compare well with the experimental data, and verify the well-known indenyl effect, that is, a significantly more facile eta(5)-to-eta(3) rearrangement for the indenyl ligand when compared to cyclopentadienyl. However, the study of the folding of free Cp and Ind, combined with the (eta(5/3)-Cp')-M bond analysis, shows that the observed difference is not the result of an intrinsic characteristic of the indenyl ligand, such as the traditionally accepted aromaticity gain in the benzene ring formed in eta(3)-Ind complexes. Instead, it is directly related to the Cp'-M bond strength. While the difference in the energy required to fold the two free ligands is negligible (< or =1 kcal mol(-1) for folding angles up to 20 degrees), the (eta(5)-Cp)-M bond is stronger than that of (eta(5)-Ind)-M; however, the opposite situation is found for the eta(3) coordination mode. The net result, for Cp'=Ind, is a destabilization of the eta(5) complexes and a stabilization of the eta(3) intermediates or transition states yielding smaller activation energies and faster reaction rates for processes in which that is the rate-determining step.     

Nonlinearity as the dominant of the nature

This issue of this journal is devoted to discussion of problems which are united by the term “nonlinear chemistry.” This term is spread on trivially wider spectrum of problems and approaches than the subject of chemistry itself; it includes spheres of conjugated sciences and even methodology of the whole natural science. Authors of all articles of current issue of the journal managed in a remarkable manner to find a way to present the consideration of definite systems and mechanisms of their transformations in harmony using the general approach to the discussed problem.     

On the nature of the phenylazo group

Three Hammett substituent constants for the p-phenylazo group were determined. The ionization of p-phenylazobenzoic acid in 50% ethanol gives a σ_p value of 0·26. The NBS bromination of p-phenylazotoluene vs toluene in benzene at 80° gives a σ⁺ value of ?0·15. The NBS bromination of 4-phenylazo-3-cyanotoluene vs m-tolunitrile in benzene at 80° give a σ^. value of 0·28. It is concluded that the phenylazo group is a ?I substituent and either a +M or ?M substituent depending on the reaction being studied. This makes the phenylazo group an activator in nucleophilic, electrophilic and free radical reactions.     

On the nature of DNA-duplex stability

The unwinding free energy of 128 DNA octamers was correlated with the sum of interaction energies among DNA bases and their solvation energies. The former energies were determined by using the recently developed density functional theory procedure augmented by London dispersion energy (RI-DFT-D) that provides accurate hydrogen-bonding and stacking energies highly comparable with CCSD(T)/complete basis set limit benchmark data. Efficient tight-binding DFT covering dispersion energy was also used and yielded satisfactory results. The latter method can be used for extended systems. The solvation energy was determined by using a C-PCM continuum solvent at HF level calculations. Various models were adopted to correlate theoretical energies with experimental unwinding free energies. Unless all energy components (hydrogen-bonding, intra- and interstrand-stacking, and solvation energies) were included and weighted individually, no satisfactory correlation resulted. The most advanced model yielded very close correlation (RMSE=0.32 kcal mol(-1)) fully comparable with the entirely empirical correlation introduced in the original paper. Analysis of the theoretical results shows the importance of inter- and intramolecular stacking energies, and especially the latter term plays a key role in determining DNA-duplex stabilization.     

Physical nature of the chemical bond

The effect of such variables as size of basis set, number of S and P type functions in the basis set, size of initial exponent in the basis set, size of multiplicative factor in the geometrical progression of exponents, and interatomic distance has been examined by a self-consistent-field calculation with Gaussian orbitals on HeH⁺. A quasi-optimized wave function has been obtained by allowing only the initial exponent and multiplicative factor to vary in the optimization process.     

On the nature of the anomeric effect

Calculations of the interaction energies of heteroatoms X and Y unshared electron pairs in structures (I) and (II) have been performed for molecules of 2-methoxytetrahydropyran and fluoromethanol, by semi-empirical EHMO and CNDO/2 methods, as well as by classical dipole-dipole approximation. This type of interaction was shown not to be a factor responsible for the stability of the gauche structure (II). The current interpretation that the anomeric effect is an electrostatic interaction of heteroatom unshared electron pairs (the “rabbit ears” effect) is, therefore, groundless.     

The nature of chromaticity of triphenylmethane,xanthene, phthalocyanine,and thiazine dyes

Works concerned with the origin of coloration of organic compounds are reviewed. Proofs are given that individual triphenylmethane, xanthene, phthalocyanine, and thiazine dye molecules do not absorb light in the visible range and are not chromogens, that is, do not determine compound chromaticity. Individual molecules of these dyes should be considered chromophoric particles, necessary but insufficient for coloration generation. Elementary chromogens of the dyes under consideration are dimers (supramolecular particles). The blue coloration of aromatic compound azulene has a similar origin.     

Prigogine and the many voices of nature

Ilya Prigogine was not a systematic author: his ideas, covering a wide arch of areas, are dispersed in his many writings. In particular, his philosophical thought has to be reconstructed mainly on the basis of his works in collaboration with Isabelle Stengers: La Nouvelle Alliance (1979), Order out of Chaos (1984), and Entre le Temps et l’éternité (1988). In this paper I undertake that reconstruction in order to argue that Prigogine’s position, when read in the light of Putnam’s internalist realism, can be characterized as an ontological pluralism. The main aim of this work is to show the striking parallelism between the philosophical views of Prigogine and Stengers and those of Hilary Putnam in Reason, Truth and History (1981). This task will lead me to critically review Prigogine’s general scientific program: the attempt to establish the foundations of objective irreversibility.