Concentration dependence of the structure of aqueous solutions of lutetium nitrate according to X-ray diffraction

Aqueous solutions of lutetium nitrate over a wide range of concentrations are studied by X-ray diffraction under standard temperature and pressure. The low-angle peaks in experimental scattering intensity curves are interpreted. It is shown that the structure of these solutions can be of two types. It is found that a saturated solution and solutions concentrated to a molar ratio of 1: 20 have a quasi-crystalline structure resulting from interionic interactions. It is determined that dilute solutions form a water-like structure characterized by a tetrahedral network of hydrogen bonds between the water molecules. It is found that low-angle peaks also appear in the intensity curves of dilute solutions; this proves that the so-called “long-range” order is preserved in these solutions. It is revealed that in all the studied systems, the contributions to the total scattering pattern that are responsible for the occurrence of pre-peaks are intercationic interactions.     

Peculiarities of structure formation of epoxy-amine polymers upon curing of diglycidyl ester of diphenylolpropane with adamantane diamines

The peculiarities of structure formation of epoxy-amine polymers upon curing of diglycidyl ester of diphenylolpropane with adamantane diamines are discussed. It is shown that, at the initial stage of polycondensation, deceleration of the curing process takes place that is caused by glass transition of the polycondensation products. It is found that complete consumption of all functional groups is impossible without additional postcuring.     

Enthalpy of swelling of crosslinked copolymers of acrylic acid β-vinyloxyethylamide in water and ethanol

The thermodynamics of swelling of copolymers of acrylic acid β-vinyloxyethylamide with acrylamide and N-vinylpyrrolidone of various compositions in water and ethanol is investigated. It is established that the swelling of the copolymers in water is characterized by high negative enthalpy values and that the swelling in ethanol is an endothermic process. It is found experimentally that the hydrogels obtained experience contraction at elevated temperatures.     

Effect of isomerization of amino acid residues on the structure of aquaporin

The effect of isomerization of amino acid residues on the structure and water permeability of aquaporin has been investigated. It was established that the equilibrium configuration of the model D isomer is energetically less favorable than that of its natural L isomer. It is shown that the model D isomer of aquaporin is waterproof.     

Stability of two-dimensional growth of a packed body of proteins on a solid surface

Adsorption of proteins from the bulk is at times accompanied by a rearrangement which leads to the formation of closed packed bodies, that may or may not be crystalline. Mass transfer of protein molecules on a surface is modeled. Forced diffusion by van der Waals and electrostatic forces leads to segregation, which is eventually a different phase that is assumed to be thermodynamically favored. The net effective force in two-dimensions has been modeled approximately and shown to be much stronger and more long ranged than in the bulk: that is, under the same conditions, the protein molecules may not aggregate in the bulk they may aggregate on a surface. These forces have been used only indirectly but equivalently as an adsorption-desorption step at the interline. Eventually, a linear stability analysis of the growing body shows it to be unstable and would give rise to whiskers that are one molecule thick. This is what is observed experimentally. The conditions that give rise to the instability have been determined. The reverse case of rinsing of the protein molecules has also been studied experimentally and has been analyzed using the same mechanisms. Here it is seen that thicker inroads into the packed body cause the interline to take on a spongy appearance. It is conjectured that eventually islands will appear as seen in the experiments.     

Simple presentation of network theory of rubber,with a discussion of other theories

The approximations implicit in the use of the Gaussian network model for soft rubber are discussed. It is shown that the form of the stress–strain curve can be derived for this model simply, and without special assumptions about the form or behavior of the network. The common assumption that the network junctions are fixed, or can be treated as fixed, is discussed. It is shown that this picture of the situation is unrealistic: the junctions have a Brownian motion comparable to that of any portion of the intervening molecular segments. The introduction of this assumption is not generally admissible, but it will not affect the outcome of certain types of calculation; in particular, one can foresee that it need not affect the calculated form of the stress-strain curve. A particularly simple and straightforward calculation of the network entropy on this basis is given. Wall's theory of rubber is analysed. It is shown that Wall's postulates are not consistent with the network structure of rubber, and in general lead to different results.     

Effect of netropsin on one-electron oxidation of duplex DNA

The effect of netropsin on the oxidative reactions of duplex DNA was examined. One-electron oxidation of DNA creates a radical cation that migrates through duplex DNA and reacts primarily at GG steps. Netropsin is a dication that specifically binds primarily by hydrogen bonding in the minor groove at sites that have four or more contiguous A.T base pairs. We showed that the oxidation potential of netropsin is less than that of any of the four nucleobases. We find that netropsin quenches the oxidative reactions of DNA independent of whether it is specifically bound. Within the Perrin model of static quenching, a netropsin within a rather large fixed volume around the DNA is an effective quencher.     

NMR investigation of the segmental mobility of the soft phase of impact modified PVC

The segmental mobility of the elastomeric phase of impact modified PVC containing EVA (ethylene-vinyl acetate acetate co-polymer) has been studied with wide-line NMR. It is shown that the segmental mobility of the polymer of the soft phase is increased considerably by addition of didecylphenylphosphite to the system. It can therefore be concluded that this product is largely dissolved in the soft phase. For samples containing solid stabilizers which do not interfere with the soft phase, it is shown that the segmental mobility of the polymer of the EVA-phase is not greatly influenced by the lubricating effects of the stabilizers. The segmental mobility of the polymer of the soft phase is decreased by a grafting joint between the two polymer components. A decrease of the segmental mobility is also observed for the polymer of the soft phase upon milling of the powdered polymer compound. We consider that this effect can be explained only by the assumption that the PVC dissolves to some extent in the soft phase during the milling.     

Consistency of a set of chemical reactions

It is a useful feature of many general chemical kinetics programs that the user's reaction scheme is tested as far as possible before a calculation is started. Attempts are made to answer the question: How far can a reaction scheme be tested for consistency, with respect to mass conservation, without knowing the molecular weights of the species involved? It is found that this problem can be transformed so that it is solvable by the standard methods used in linear programming.     

Simulation of differential pulse polarography of irreversible EC mechanism

A reversible electrode reaction that is followed by totally irreversible chemical reaction is investigated theoretically. The influence of chemical reaction on two components of the net response of differential pulse polarogram is analyzed. It is demonstrated that this EC mechanism depends on two kinetic parameters and that their critical values can be used for the measurement of the rate constant of chemical reaction.     

Hydrodynamics of thin liquid films effect of the surfactant on the rate of thinning

Summary A theory of the effect of the surfactant on the rate of thinning of foam films is presented. The formulae obtained for the separately treated cases of low and high concentrations cover the whole concentration range. The effect of both bulk and surface diffusion is taken into consideration and it is demonstrated that the relative importance of the latter increases with the decrease of the film thickness. The role of the surface diffusion for the stability of foam films is discussed. It is shown that films stabilized with soluble surfactants never strictly obey Reynolds'eq. [19] so that the actual velocity of thinning can be substantially higher than that calculated by the quoted equation.     

Influence of dipalmitoylphosphatidylcholine on the dissolution of Brazilian chrysotile

It is known that Brazilian chrysotile is rapidly removed from the lungs, but quantitative studies about the influence of lung surfactants on chrysotile dissolution have not been investigated. In this work, the chemical behavior of chrysotile and its dissolution in the presence of dipalmitoylphosphatidylcholine (DPPC) were investigated in physiological conditions. The dissolution was investigated through quantification of magnesium and silicon released by chrysotile. At 37 degrees C, the magnesium concentration is similar to control (without DPPC), which is about 2.0x10(-4)molL(-1), meaning that the dissolution process is not affected by the presence of this surfactant. The same was observed for silicon. The silicon concentration released by chrysotile is similar in all media tested. It is known that the dissolution mechanisms of brucite and tridymite layers are different. From our results, we propose that under physiological conditions, the mechanism of brucite dissolution is based on its interaction with hydrogen ions and that the mechanism of tridymite dissolution is based on a hydrolysis process.     

Concentration dependence of the structure of aqueous solutions of samarium trichloride according to X-ray diffraction

Aqueous solutions of samarium chloride in a wide range of concentration under ambient conditions are studied by X-ray diffraction analysis. The small-angle peaks in experimental scattering intensity curves are interpreted. It is shown that highly concentrated solutions are characterized by a unique structure that differs heavily from the structure of dilute systems. It is found that small-angle peaks also appear in the intensity curves of dilute solutions, indicating that the so-called long-range order is preserved in these solutions. It is revealed that the contributions to the total scattering pattern that govern the appearance of prepeaks are interionic interactions of different types (e.g., cation-cation, anion-cation, and anion-anion interactions) in concentrated systems and the distances between the cations in dilute solutions.     

Dependence of the Rate of Electrodeposition of Metals at Mono- and Multielectrodes on Voltage in the Case of an Exaltation Mechanism of Mass Transport

Dependences of the rate of copper deposition on mono- and multielectrodes out of dilute solutions of acetic acid at voltages of 20–250 V are compared. It is established that the same rate of deposition in the case of a multielectrode (25 electrodes with a diameter of 0.1 mm) takes place at a voltage that is lower by 2.7 times than that in the case of a monoelectrode with a diameter of 0.5 mm and the same area. The same results are obtained during electrodeposition of cadmium and thallium. In order to explain this effect, a two-layered model of potential distribution is suggested. In accordance with this model, the resistance of electrolyte in the vicinity of a multielectrode is equal to the sum of the resistance of the layer nearest to the electrode (where it is determined by the sum of conductances to each microelectrode) and the external layer, where the potential distribution is close to hemispherical. It is shown that calculations in accordance with this model allow one to give an estimate of the effect's scale that agrees with experiment and to predict its possible limits following an increase in the number of electrodes that make up a multielectrode.     

Mechanistic implications of the equality of compensation temperatures in chromatography

A common interpretation of the observation that two processes exhibit similar compensation temperatures in an enthalpy-entropy plot is that the two processes occur via the same "mechanism". We show that this interpretation is not rigorously allowed. In fact, the only thing that can be concluded from the observation of identical compensation temperatures is that the relative contributions of enthalpy and entropy to the overall free energy are the same in the two processes. Since it is possible that two processes occur via different mechanisms that, by chance, result in the same relative blends of enthalpy and entropy, the observation of identical compensation temperatures cannot be used as evidence for mechanistic identity. If two processes exhibit different compensation temperatures, however, it can logically be concluded that the two processes are mechanistically distinct.     

Physical principles of catalysis of the curing of epoxy polymers in the presence of carbon nanotubes

A structural interpretation of the catalytic action of carbon nanotubes on the curing of epoxy polymers is proposed. It is based on the fractal analysis ideas. It is shown that essentially the only factor determining the kinetics of the curing process is the microgel structure characterized by its fractal dimension. The most important conclusion from the obtained results is the fact that the reaction rate dependences on the structural parameters are described by the same correlation for the epoxy polymer curing reaction both in the presence and absence of carbon nanotubes. This means that the catalytic effect of carbon nanotubes consists in a change in the structure of microgels.     

Thermodynamic parameters of solvation of nonelectrolytes in aqueous solutions of amides of carboxylic acids

Interaction and reorganization contributions to solvation enthalpies of nonelectrolytes in aqueous solutions of amides of carboxylic acids with different degree of N-substitution and N-methylpyrrolidone are calculated. The data are discussed using structurally thermodynamic characteristics of water-amide systems obtained by us previously. It is found that the type of concentration dependence of the solvation enthalpy of nonelectrolytes in all solutions investigated is determined by the type of reorganization component. It is shown that the highest solvation exothermicity of nonelectrolytes in water is due to the lowest value of the reorganization contribution in spite of that nonelectrolytes interact weaker with water than with non aqueous components.     

On the existence of primary methods of measurement

 There is much discussion in chemical metrology about the definition of primary methods of measurement, just as a couple of years ago there was debate about its predecessors, absolute methods and definitive methods. It is argued in this paper that the designation of certain methods as being primary only makes sense if there is an outstanding property identified that is common to all primary methods, and not present for all non-primary methods. The aim to identify primary methods should not blur our notion that it is the good practice of analytical chemistry that produces good results, not a particular method of analysis.     

Features of polytherms of the viscosity of Fe–B melts

It is established that the formation of a viscous film on the surface of a melt is possible during the viscosimetry of Fe–B melts under normal conditions. It is noted that the film has a considerable effect on the results from measurements and can lead to the appearance of additional features on polyterms. Thermodynamic analysis of the composition of surface layers shows that a viscous film contains mainly boron oxide B₂O₃. It is concluded that the evaporation of B₂O₃ from the surface of the alloy produces additional anomalies on the polytherm of viscosity.     

Mechanisms of antioxidant action: Sulphur compounds as inhibitors of mechanochemical degradation of rubber

It is shown that the stability of sulphur vulcanised natural rubber to mechanodegradation (fatigue) is associated with the formation of labile oxidation products. The addition of sulphides and their oxidation products to a non-sulphur vulcanisate has a similar effect. Stress relaxation shows that the initial rate of chain scission under stress is directly related to the fatigue resistance of the vulcanisate. However, the oxidation process also produces peroxidolytic antioxidants (PD-C). It is concluded that the fatigue resistance of sulphur vulcanisates is due to a combination of facile restructurisation and an oxidation chain-breaking mechanism.