Comparison of microbial activity in some Brazilian soils by microcalorimetric and respirometric methods

The microbial activity in a Rhodic eutrudox (R), a Typic eutrudox (V) and a Quartzipsamment (Q) was monitored by respirometric and calorimetric methods. CO₂ evolution was monitored for 98 days by titrimetry and conductimetry for control amended samples (A) with 25% of cattle manure (E), municipal refuse compost (L), earthworm casts (H) or 1.25 kg ha⁻¹ of trifluralin (T). Average values of all treatments through respiration at the end of the incubation period were 5.24±0.34, 6.13±0.31 and 6.50±0.33, in mg CO₂ g⁻¹ soil, for R, V and Q, respectively, by titrimetry and 8.89±0.44, 10.41±0.54 and 10.41±0.52, in mg CO₂ g⁻¹ soil, for R, V and Q, respectively, for conductimetry. Excellent correlation (r=1.00) between titrimetry and conductimetry was observed. The decreasing order for respiration was E, H, L and T. After each incubation time, the conductimetric values were higher than those for titrimetry, for all treatments of these Brazilian soils. Average values of the exothermic thermal effect were: 0.58±0.02, 0.60±0.02 and 0.67±0.01 kJ g⁻¹ soil, for R, V and Q, respectively, for 103 days. A significant correlation coefficient of 0.91 and P<0.0001 between calorimetric and respirometric values over 98 days was observed. Based on the obtained calorimetric results, it can be proposed that this technique should be as a useful analytical method for determining the microbial activity in soils.     

Static electric field effects at the surface of a metallic cluster

A jellium/free-electron model is used to estimate the static electric field at the surface of a metal cluster. The electric field near a cluster with a radius of 10–50 au is found to deviate significantly from the field at the same distance from an infinite metallic plane. This will influence several adsorbate properties, including bonding. At a smooth planar surface the field is sufficiently strong to cause significant contributions to the dipole and transition moments of an admolecule. These contributions become even more important at the surface of a cluster. It is postulated that microscopic roughness may enhance the electron-transfer contribution to surface-enhanced Raman scattering, since the Fermi energy of electrons in a protuberance is increased relative to the bulk. Moreover, for the same reason, the molecule-metal interaction is increased when the molecule is adsorbed at a protuberance. Finally, by means of a WKB formula derived from the model, an accurate prediction can be made of the “magic numbers” which refer to the enhanced abundances of certain clusters when formed in an atomic beam. Therefore these numbers are likely to be determined by the symmetry of the problem and not by the detailed nature of the one-electron potential.     

Surface behaviour of some phenol para-derivatives adsorbed at the free surface of water

Comparison is made between two methods for the determination of the average orientation angle of molecules adsorbed at the free surface of water; one based on electric surface potential measurements, the other on second harmonic generation. Assuming that the model of energetics of adsorbed molecules is similar to that of a system of non-interacting permanent dipoles in an external homogeneous field, the parameters of the probability density function in the form exp[ —a cos(0-0_o)], a =w/kT, w, being the absolute orientational energy, have been calculated for phenol, p-methyl-, p-nitro-, and p-bromophenol.     

The osmotic and activity coefficients of some guanidinium salts at 298.15 K

Osmotic and activity coefficients are reported for aqueous solutions of six guanidinium salts at (298.15 ± 0.01) K, and these coefficients are compared with those of other uni-univalent electrolytes. The results are consistent with previously reported spectral results that indicated hydrogen bonding of guanidinium ion with chloride ion in aqueous solutions.     

Molecular properties of acetone and some of its chloroderivatives adsorbed at the surface of water

The relations between the electric surface potential (V) and the surface tension () of aqueous solutions of acetone, chloroacetone, 1,3-dichloroacetone, and their concentration were investigated. The vertical components of dipole moments of the above mentioned compounds were determined using the Helmholtz equation. The calculations were carried out on the basis of surface excess values, which were obtained from surface tension measurements and surface potential changes. Once the vertical component of dipole moments were found and the orientation of adsorbed molecules was assumed, the local dielectric permittivities of the surface monolayer were estimated.     

Empirical equation for predicting the surface tension of some liquid metals at their melting point

A new empirical equation is proposed for predicting the surface tension of some pure metals at their melting point. The investigation has been conducted adopting a statistical approach using some of the most accredited data available in literature. It is found that for Ag, Al, Au, Co, Cu, Fe, Ni, and Pb the surface tension can be conveniently expressed in function of the latent heat of fusion and of the geometrical parameters of an ideal liquid spherical drop. The equation proposed has been compared also with the model proposed by Lu and Jiang giving satisfactory agreement for the metals considered.     

Electrical properties and surface orientation of some salicylic acid derivatives at water/air interface

Surface activity, effective dipole moments and orientation of molecules at the interface were determined from surface tension () and surface potential (V), measured on aqueous solutions of salicylic acid, acetylsalicylic acid and salicylaldoxime.Applying the Demchak and Fort formula [1], the components of the effective dipole moments were calculated, which are connected to the reorientation of water molecules, hydrophilic and hydrophobic groups and local dielectric permittivities. From the effective dipole moments the orientation angles of the molecules at the water/air interface were estimated.     

The activity of calcium chloride in aqueous solutions of some amino acids at 25°C

The activity coefficients of calcium chloride in aqueous solutions of the amino acids glycine, β-alanine, γ-amino butyric acid, ε-aminocaproic acid, and glycylglycine have been determined with cells utilizing a calcium ion-exchange electrode. Application of the cross-differential relationship allows a measure of the variation of the salting-in parameter across the series of amino acids. The variation of this parameter is discussed using a semiempirical approach developed earlier.     

Role of electric field on surface wetting of polystyrene surface

The role of surface charge in fluid flow in micro/nanofluidics systems as well as the role of electric field to create switchable hydrophobic surfaces is of interest. In this work, the contact angle (CA) and contact angle hysteresis (CAH) of a droplet of deionized (DI) water were measured with applied direct current (DC) and alternating current (AC) electric fields. The droplet was deposited on a polystyrene (PS) surface, commonly used in various nanotechnology applications, coated on a doped silicon (Si) wafer. With the DC field, CA decreased with an increase in voltage. Because of the presence of a silicon oxide layer and a space charge layer, the change of the CA was found to be lower than with a metal substrate. The CAH had no obvious change with a DC field. An AC field with a positive value was applied to the droplet to study its effect on CA and CAH. At low frequency (lower than 10 Hz), the droplet was visibly oscillating. The CA was found to increase when the frequency of the applied AC field increased from 1 Hz to 10 kHz. On the other hand, the CA decreased with an increasing peak-peak voltage at or lower than 10 kHz. The CAH in the AC field was found to be lower than in the DC field and had a similar trend to static CA with increasing frequency. A model is presented to explain the data.     

A microenvironmental redox shift at a charged surface detected by papain activity

The relative activity of an SH-enzyme, papain, is decreased by increasing the mole ratio of oxidizing disulfide to reducing thiol in solution. The same inverse relationship applies to papain adsorbed on charged clay particles, but electrostatic interactions among the charged particles and charged disulfides and thiols significantly shift the dependence. Papain activity thus reflects the microenvironmental redox potential in the vicinity of the charged particles. The redox pairs cystine dimethylester-cysteine ethylester, dithiodiglycolic acidmercaptoacetic acid, and dithiodiglycol-mercaptoethanol were used in the assays. A special form of the Boltzmann distribution must be used to calculate mole ratios of ions of different charge near a charged interface.     

Ligand field effect at oxide-metal interface on the chemical reactivity of ultrathin oxide film surface

Ultrathin oxide film is currently one of the paramount candidates for a heterogeneous catalyst because it provides an additional dimension, i.e., film thickness, to control chemical reactivity. Here, we demonstrate that the chemical reactivity of ultrathin MgO film grown on Ag(100) substrate for the dissociation of individual water molecules can be systematically controlled by interface dopants over the film thickness. Density functional theory calculations revealed that adhesion at the oxide-metal interface can be addressed by the ligand field effect and is linearly correlated with the chemical reactivity of the oxide film. In addition, our results indicate that the concentration of dopant at the interface can be controlled by tuning the drawing effect of oxide film. Our study provides not only profound insight into chemical reactivity control of ultrathin oxide film supported by a metal substrate but also an impetus for investigating ultrathin oxide films for a wider range of applications.     

Adsorption of some mixtures of surface active substances at the mercury electrode: Kalousek commutator measurements

Adsorption behaviour at the mercury electrode of some mixtures of surface-active substances, relevant and important for natural and polluted seawater, has been studied on the basis of capacity current measurements using the polarographic method of discontinuously changing potential known as the Kalousek commutator technique.The total adsorption effects of different mixtures of selected surface-active substances (albumin, lecithin, oleic acid, Triton-X-100, sodium dodecyl sulphate) were determined in the seawater as a supporting electrolyte and compared with the values calculated from the individual isotherms.     

Thermal surface ionization of some complex salts

Thermal ionization on the surface of a heated wire is applied to the volatilization products of alkali salts of carboxylic and sulfonic acids, and to quaternary ammonium salts. The mass spectra of the alkali salts exhibit almost exclusively cationized molecules. They provide evidence for the evaporation of intact clustered molecules even under conditions of a slow rate of evaporation of the salts. The method appears to be of interest for selective detection of alkali salts from complex mixtures. With the ammonium salts [R₄N]⁺ ions are formed by thermal surface ionization of intact salt molecules. The evaporation of these molecules could be detected at rather low temperatures.     

Adsorption and surface characteristics of some pigments

The study of the heterogeneous nature of pigment surfaces was carried out by means of the adsorption of polar organic molecules from organic solvents onto the surface of a number of industrial pigments and extenders, including titanium dioxide, talc, barium sulphate, lead chromate, etc. An adsorption pattern was observed which suggested the existence of “Selective Polar Adsorption”, this being quite distinctive from purely physical (capillary condensation type) adsorption and chemisorption. Apparently the surfaces of pigments and extenders consist of a number of distinctive “active” areas, each particular area adsorbing selectively a specific type of polar group. Every pigment can be characterized by the size, number and type of these individual areas, which give a “fingerprint” of the pigment and which apparently depends more on the origin of the pigment than on its chemical structure.