Types Of Interaction Forces Research Articles

The effect of pressure on the specific surface area and density of nanocrystalline ceramic powders

Nanocrystalline LaFeO 3, LaCoO 3, La 1 -xSr xFeO 3 and La 1 -xSr xFe 1 -yCo yO 3 powders were compacted at room temperature, under pressures of 0.0, 0.5, 1.0 and 1.5 GPa, respectively. The specimens were examined by rotating anode X-ray diffractometry and their specific surface areas and densities measured. Results show that deformation, fracture and phase transition can occur to different extents in the nanocrystalline materials subjected to different compaction pressures. The characteristics of the interfaces, which are changed under the contact stresses between adjacent crystalline grains, are related to the compaction pressure and the types of interaction forces between interfacial atoms, which may be between those of van der Waal's bonds and covalent bonds. The specific surface area and the density of the nanocrystalline materials change with increasing compaction pressure.

Structure of acid casein gels 2. Dynamic measurements and type of interaction forces

The time dependence of the mechanical behaviour and the type of interaction forces in acid casein gels were studied by dynamic rheological and permeability measurements. Gels were formed by quiescent heating of casein dispersions acidified in the cold to pH 4.6; they were investigated after an ageing time of 16 h or more. The dynamic moduli increased with frequency ω over an ω range of 10 −3 to 10 rad s −1 indicating that a considerable proportion of the bonds in an acid casein gel have a relaxation time between 0.1 and 10 3 s. The ratio of the loss to storage modulus was independent of ω at 30°C but increased with decreasing ω at lower temperatures and decreased at higher ones. This indicates that acid casein gels become relatively more viscous over longer time scales at lower temperatures. The dynamic moduli strongly decreased with increasing measuring temperature. Since most types of interaction forces, except hydrophobic interactions which increase in strength with temperature in the range considered, are not strongly temperature dependent this points to an indirect effect, involving reconformation of the protein molecules and particles. The dynamic moduli as a function of the pH showed a small but significant maximum near the isoelectric pH. For the formation of a casein gel the ionic strength had to be at least about 0.1 M. Further raising of the ionic strength by addition of NaCl resulted for acid skim milk gels at first in a small increase of the storage modulus and upon further addition in a decrease. These results point to (mainly attractive) electrostatic interactions being important in acid casein gels, besides hydrophobic interactions and, probably, the ever present Van der Waals attraction, as well as steric and entropic effects related to protein conformation. Experiments with sodium caseinate gels in which part of the NaCl was replaced by CaCl 2 point to a specific effect of Ca on gel formation and properties.

Immobilization of immunoglobulins on silica surfaces. Kinetics of immobilization and influence of ionic strength.

The kinetics of, and the influence of ionic strength on, the immobilization of rabbit immunoglobulin G (IgG) on different types of well-characterized silica surfaces were investigated. Adsorptive immobilization was compared with covalent attachment via thiol-disulphide exchange reactions. The amount of immobilized IgG on five different types of silica surfaces as a function of IgG concentration, at two different ionic strengths, was determined. The IgG-solid-surface interaction involved different types of interaction forces, depending on the surface chemistry of the solid surface. The solid-surface chemistry is an important parameter determining the immobilized amount of IgG. When conditions for covalent attachment of IgG to the surfaces were fulfilled, the IgG showed high affinity and the immobilized amount of IgG showed a fast saturation. Changes in ionic strength showed no significant influence on the kinetics of immobilization on these surfaces. The amount of covalently attached IgG was partially ionic-strength-dependent, indicating that adsorptive interactions were involved. The results are of fundamental interest for the development of new immunosensors based on surface-concentration-measuring devices.

Transport Coefficients of Expanded Fluid Metals

The viscosities and the self-diffusion coefficients of expanded fluid mercury and caesium have been calculated as a function of pressure and temperature up to their critical points with the aid of a modified Enskog theory. The results are compared with the transport coefficients of other liquid metals and of non-polar and polar fluids applying the principle of corresponding states. The thermal conductivities of fluid metals along the full coexistence line are also discussed. A classification of the transport phenomena in fluids with various types of interaction forces - including expanded fluid metals - is given

Interactions of Xanthine Derivatives with Bovine Serum Albumin II: Spectrophotometric Studies

The spectral characteristics in aqueous solution of a number of xanthine derivatives were found to be influenced by the presence of bovine and human serum albumin. The observed effects were assumed to be due to the binding of the xanthines by the protein. Changes in spectra were thus used as the basis for an experimental method for determining the extent and nature of the small molecule-protein interaction. The effects of temperature, pH, and protein modification on binding behavior were studied. Comparative studies on a number of structurally different xanthines were conducted. The results indicate that a rather specific orientation of the protein molecule was required for optimal interaction. Expansion or other configurational changes induced by pH or temperature effects resulted in decreased binding. The binding site appears to contain a grouping which can hydrogen-bond with the xanthine. The participation of other types of interaction forces are suggested also. The spectral characteristics in aqueous solution of a number of xanthine derivatives were found to be influenced by the presence of bovine and human serum albumin. The observed effects were assumed to be due to the binding of the xanthines by the protein. Changes in spectra were thus used as the basis for an experimental method for determining the extent and nature of the small molecule-protein interaction. The effects of temperature, pH, and protein modification on binding behavior were studied. Comparative studies on a number of structurally different xanthines were conducted. The results indicate that a rather specific orientation of the protein molecule was required for optimal interaction. Expansion or other configurational changes induced by pH or temperature effects resulted in decreased binding. The binding site appears to contain a grouping which can hydrogen-bond with the xanthine. The participation of other types of interaction forces are suggested also.