Theoretical Treatment of Interaction Parameters in Multicomponent Metallic Solutions

A new theoretical equation for interaction parameter in multicomponent metallic solutions is developed using the pseudopotential formalism coupled with the free energy of the hard sphere system. The approximate expression for the pseudopotential term is given in terms of the heat of solution at infinite dilution, to allow easy evaluation of the interaction parameter in various multicomponent systems. This theory has been applied to 23 non-ferrous alloys based on Pb, Sn, Bi and indium. Comparison with the results of previous theoretical calculations using only the hard sphere model suggests that the inclusion of the pseudopotential term yields a quantitatively more correct prediction of interaction parameters in multicomponent metallic solutions. Numerical calculations were also made for 320 Fe-base solutions relevant to steelmaking and the agreement between calculation and experimental data appears reasonable, with 90% reliability in predicting the correct sign.

Thermodynamic consistency of the interaction parameter formalism

The apparent contradiction between the exact nature of the interaction parameter formalism as presented by Lupis and Elliott and the inconsistencies discussed recently by Pelton and Bale arise from the truncation of the Maclaurin series in the latter treatment. The truncation removes the exactness of the expression for the logarithm of the activity coefficient of a solute in a multi-component system. The integrals are therefore path dependent. Formulae for integration along paths of constant Xi,or X i/Xj are presented. The expression for In γsolvent given by Pelton and Bale is valid only in the limit that the mole fraction of solvent tends to one. The truncation also destroys the general relations between interaction parameters derived by Lupis and Elliott. For each specific choice of parameters special relationships are obtained between interaction parameters.

Mechanism of interaction of O-amino-D-serine with sheep liver serine hydroxymethyltransferase

The mechanism of interaction of 0-amino-D-serine (OADS) with sheep liver serine hydroxymethyltransferase (EC 2.1.2.1) (SHMT) was established by measuring changes in the enzyme activity,absorption spectra, circular dichroism (CD) spectra, and stopped-flow spectrophotometry. OADS was a reversible noncompetitive inhibitor (Ki = 1.8 pM) when serine was the varied substrate. The first step in the interaction of OADS with the enzyme was the disruption of enzyme-Schiff base, characterized by the rapid disappearance of absorbance at 425 nm (6.5 X lo3 M-' s-') and CD intensity at 430 nm. Concomitantly,there was a rapid increase in absorbance and CD intensity at 390 nm. The spectral properties of this intermediate enabled its identification as pyridoxal 5'-phosphate (PLP). These changes were followed by a slow unimolecular step (2 X s-') leading to the formation of PLP-OADS oxime, which was confirmed by its absorbance and fluorescence spectra and retention time on high-performance liquid chromatography. The PLP-OADS oxime was displaced from the enzyme by the addition of PLP as evidenced by the restoration of complete enzyme activity as well as by the spectral properties. The unique feature of the mechanism proposed for the interaction of OADS with sheep liver SHMT was the formation of PLP as an intermediate.

Mechanism of interaction of the antileukemic drug cytosine arabinoside with aromatic peptides : role of sugar conformation and peptide backbone

Interaction of the antileukemic drugs, cytosine-arabinoside (Ara-C) and adenosine-arabinoside (Ara-A) and a structural analogue, cytidine, with aromatic dipeptides has been studied by fluorescence and NMR spectroscopy. Ara-C and cytidine bind tryptophanyl and histidyl dipeptides but not tyrosyl dipeptides, while Ara-A does not bind to any of them. Both studies indicate association involving stacking of aromatic moieties. NMR spectra also indicate a protonation of the histidine moiety by Ara-C. In case of cytidine, the chemical shifts observed on binding to His-Phe imply that the backbone protons of the dipeptide participate in the binding. The conformation of the sugar and the base seem to play a very important role in the binding phenomenon as three similar molecules, Ara-C, Ara-A and cytidine bind in totally different ways.

Interaction of metal ions with nucleic acids and related compounds. II. Studies on Au(III)-nucleic acid system

The nature of interaction of Au(III) with nucleic acids was studied by using methods such as uv and ir spectrophotometry, viscometry, pH titrations, and melting-temperature measurements. Au(III) is found to interact slowly with nucleic acids over a period of several hours. The uv spectra of native calf-thymus DNA 9pH 5.6 acetate buffer containing (0.01M NaCIO4) showed a shift in λ max to high wavelengths and an increase in optical density at 260 nm. There was a fourfold decrease in viscosity (expressed as ηsp/c). The reaction was faster at pH 4.0 and also with denatured DNA (pH 5.6) and whole yeast RNA (pH 5.6). The order of preference of Au(III) (as deduced from the time of completion of reaction) for the nucleic acids in RNA > denatured DNA > DNA. The reaction was found to be completely reversible with respect KCN. Infrared spectra of DNA-Au(III) complexes showed binding to both the phosphate and bases of DNA. The same conclusions were also arrived at by melting-temperature studies of Au(III)-DNA system. pH titrations showed liberation of two hydroxylions at r = 0.12 [r = moles of HAuCl4 added per mole of DNA-(P)] and one hydrogen ion at r = 0.5. The probable binding sites could be N(1)/N(7) of adenine, N(7) and/or C(6)O of guanine, N(3) of cytosine and N(3) of thymine. DNAs differing in their (G = C)-contents [Clostridium perfingens DNA(G = C, 29%), salmon sperm DNA (G + C, 42%) and Micrococcus lysodeikticus DNA(G + C, 29%), salmon sperm DNA (G = C, 72%)] behaved differently toward Au(III). The hyperchromicity observed for DNAs differing in (G + C)-content and cyanide reversal titrations indicate selectivity toward ( A + T)-rich DNA at lw values of r. Chemical analysis and job's continuous variation studies indicated the existence of possible complexes above and below r = 1. The results indicate that Au(III) ions probably bind to hte phosphate group in the initial stages of the reaction, particularly at low values of r, and participation of the base interaction also increases. Cross-linking of the two strands by Au(III) may take place, but a complete collapse of the doulbe helix is not envisaged. It is probable that tilting of the bases or rotaiton of the bases around the glucosidic bond, resulting in a significant distrotion of the double helix, might take place due to binding of Au(III) to DNA.

Effect of soil preparation of boreal spruce forest on air and soil temperature conditions in forest regeneration areas.

The effect of scarification, ploughing and cross-directional plouhing on temperature conditions in the soil and adjacent air layer have been studied during 11 consecutive growth periods by using an unprepared clear-cut area as a control site. The maximum and minimum temperatures were measured daily in the summer months, and other temperature observations were made at four-hour intervals by means of a Grant measuring instrument. The development of the seedling stand was also followed in order to determine its shading effect on the soil surface. Soil preparation decreased the daily temperature amplitude of the air at the height of 10 cm. The maximum temperatures on sunny days were lower in the tilts of the ploughed and in the humps of the cross-directional ploughed sites compared with the unprepared area. Correspondingly, the night temperatures were higher and so the soil preparation considerably reduced the risk of night frost. In the soil at the depth of 5 cm, soil preparation increased daytime temperatures and reduced night temperatures compared with unprepared area. The maximum increase in monthly mean temperatures was almost 5 °C, and the daily variation in the surface parts of the tilts and humps increased so that excessively high temperatures for the optimal growth of the root system were measured from time to time. The temperature also rose at the depths of 50 and 100 cm. Soil preparation also increased the cumulative temperature sum. The highest sums accumulated during the summer months were recorded at the depth of 5 cm in the humps of cross-directional ploughed area (1127 dd.) and in the tilts of the ploughed area (1106 dd.), while the corresponding figure in the unprepared soil was 718 dd. At the height of 10 cm the highest temperature sum was 1020 dd. in the hump, the corresponding figure in the unprepared area being 925 dd. The incidence of high temperature amplitudes and percentage of high temperatures at the depth of 5 cm decreased most rapidly in the humps of cross-directional ploughed area and in the ploughing tilts towards the end of the measurement period. The decrease was attributed principally to the compressing of tilts, the ground vegetation succession and the growth of seedlings. The mean summer temperature in the unprepared area was lower than in the prepared area and the difference did not diminish during the period studied. The increase in temperature brought about by soil preparation thus lasts at least more than 10 years.

Productive coexistence and gain in agroforestry systems.

Productive coexistence and coexistence gain of populations were studied using nine years' data from field experiments of Taxodium ascendens-intercrop systems in Lixiahe, Jiangsu Province, China. A theoretical framework for productive coexistence in agroforestry was developed. Interaction patterns between trees and intercrops were presented within this framework. A model framework was developed to describe the coexistence gain and interaction of populations in T. ascendens-intercrop systems. Facilitation and resource sharing were identified as main contribution to the advantage of species combination in agroforestry. The model of population interaction developed in the present study was accepted for describing the interaction of populations in T. ascendens-intercrop systems, because it explained a high proportion of the variance of experimental data and fitted well the observations in most intercropping types. The model developed in the present study provides flexibility for describing different patterns of intra- and inter-specific interactions. Model coefficients were applied to the determination of the ecological compatibility of species. Managed T. ascendens-intercrop systems were advantageous as compared to a monoculture of trees or arable crops. In T. ascendens stands up to the age of three, arable crops contributed about 50-80 % of the total biomass yield of agroforestry. The diameter or height growth of T. ascendens was not significantly influenced by intercrops, indicating that intercropping under trees produced extra yields but did not depress the tree growth. When the trees were young (during the first three years), T. ascendens did not depress the crop yields, and a land equivalent ratio greater than unity was obtained together with a high yield of both components. The diameter and height of the trees were similar in four spacing configurations with an equal number of trees per hectare up to the age of eight, but wider between-rows open range were beneficial for the intercrops. The relationship between open-ranges and species coexistence was also analysed and the distribution of soil nutrients studied.

Analysis of forest soil chemistry and hydrology with a dynamic model ACIDIC.

In this study we analyze how the ion concentrations in forest soil solution are determined by hydrological and biogeochemical processes. A dynamic model ACIDIC was developed, including processes common to dynamic soil acidification models. The model treats up to eight interacting layers and simulates soil hydrology, transpiration, root water and nutrient uptake, cation exchange, dissolution and reactions of Al hydroxides in solution, and the formation of carbonic acid and its dissociation products. It includes also a possibility to a simultaneous use of preferential and matrix flow paths, enabling the throughfall water to enter the deeper soil layers in macropores without first reacting with the upper layers. Three different combinations of routing the throughfall water via macro- and micropores through the soil profile is presented. The large vertical gradient in the observed total charge was simulated succesfully. According to the simulations, gradient is mostly caused by differences in the intensity of water uptake, sulfate adsorption and organic anion retention at the various depths. The temporal variations in Ca and Mg concentrations were simulated fairly well in all soil layers. For H+, Al and K there were much more variation in the observed than in the simulated concentrations. Flow in macropores is a possible explanation for the apparent disequilibrium of the cation exchange for H+ and K, as the solution H+ and K concentrations have great vertical gradients in soil. The amount of exchangeable H+ increased in the O and E horizons and decreased in the Bs1 and Bs2 horizons, the net change in whole soil profile being a decrease. A large part of the decrease of the exchangeable H+ in the illuvial B horizon was caused by sulfate adsorption. The model produces soil water amounts and solution ion concentrations which are comparable to the measured values, and it can be used in both hydrological and chemical studies of soils.

Interaction of melittin with endotoxic lipid

Several amphipathic and cationic substances are known to bind lipid A, the toxic component of bacterial lipopolysaccharides. In this report, we have characterized, by fluorescence methods, the interaction of melittin, an amphipathic and basic 26-residue polypeptide isolated from bee venom, with lipid A. The stoichiometry of the complex appears to be two molecules of melittin to one of lipid A with a dissociation constant of 2.5 × 10 −6 M. The binding of melittin not only modifies the endotoxic properties of lipid A in a number of biological assays, but also results in abrogation of the hemolytic activity of melittin. A model of the complex is proposed based on the known structures of lipid A and melittin, and the observed stoichiometry of binding.

Anatase-rutile transformation in Fe/TiO2, Th/TiO2 and Cu/TiO2 catalysts and its possible role in metal-support interaction

Based on in-situ Mossbauer and X-ray diffraction studies, it is shown that in the Fe/TiO2 catalyst, the anatase-rutile transformation of the TiO2 support is facilitated by the Fe2+ ions formed during the reduction. The transformation occurs at lower temperatures in Th/TiO2 and Cu/TiO2 compared to pure TiO2. In general, the transformation of anatase to rutile seems to occur at or below the temperature (approximately 770 K) at which strong-metal-support-interaction manifests itself.

Therapeutic change in interaction

A process of change within a single case of cognitive-constructivist therapy is analyzed by means of conversation analysis (CA). The focus is on a process of change in the sequences of interaction, which consist of the therapist’s conclusion and the patient’s response to it. In the conclusions, the therapist investigates and challenges the patient’s tendency to transform her feelings of disappointment and anger into self-blame. Over the course of the therapy, the patient’s responses to these conclusions are recast: from the patient first rejecting the conclusion, to then being ambivalent, and finally to agreeing with the therapist. On the basis of this case study, we suggest that an analysis that focuses on sequences of talk that are interactionally similar offers a sensitive method to investigate the manifestation of therapeutic change. It is suggested that this line of research can complement assimilation analysis and other methods of analyzing changes in a client’s talk.