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Along with temperature, pressure is the most important physical parameter determining the thermodynamic properties and reactivity of chemical systems. In this work, we discuss the effects of high pressure on conformational properties of organic molecules and propose an approach toward calculation of conformational volume changes based on molecular dynamics simulations. The results agree well with the experimental data. Furthermore, we demonstrate that pressure can be used as an instrument for fine-tuning of molecular conformations and to propel a properly constructed molecular rotor possessing a suitable combination of energy and volume profiles. Key words: activation volume, reaction volume, volume profile, pressure-controlled molecular systems, molecular rotors. Comme la temperature, la pression est un parametre physique des plus importants qui determine les proprietes thermodynamiques et la reactivite des systemes chimiques. Dans le cadre des presents travaux, nous abordons les effets de pressions elevees sur les proprietes conformationnelles des molecules organiques et nous utilisons des simulations de dynamique moleculaire pour proposer une approche de calcul en vue de determiner les variations de volume conformationnel. Les resultats concordent bien avec les donnees experimentales. En outre, nous demontrons que la pression peut etre employee comme instrument de reglage de precision des conformations moleculaires et pour propulser un rotor moleculaire adequatement construit possedant une combinaison appropriee de profils energetique et volumique. [Traduit par la Redaction] Mots-cles : volume d'activation, volume de reaction, profil volumique, systemes moleculaires a pression controlee, rotors moleculaires., 1. Introduction The importance of pressure in chemistry can hardly be overstated. Along with temperature, pressure is the most important physical parameter determining the thermodynamic properties and reactivity of chemical [...]

Abstract: General properties of the empirical analytical functions used to describe the effect of pressure on rate and equilibrium constants in solution are reviewed, and the effects of experimental errors [...]

The present work continues the previous studies concerning the synthesis and characterization of molecularly imprinted polymers (MIPs) with sclareol as template and three poly(acrylonitrile-co-acrylic acid) (AN:AA) copolymers with different ratios between monomers as matrices. The previous studies of rheology, elemental analysis, infrared spectroscopy, size exclusion chromatography, thermogravimetry, differential scanning calorimetry, batch rebinding tests, and Scatchard analysis, which confirmed the molecular imprinting, are being completed with the current equilibrium and kinetic adsorption studies. For this purpose, eight adsorption isotherms and three kinetic adsorption models were applied to six sets of experimental data obtained after three sclareol-imprinted adsorbents (MIPs) and three nonimprinted adsorbents (NIPs) were submitted to batch adsorption experiments. After ordering the adsorption models according to the 'minimum sum of normalized errors (SNE)' criteria, it was concluded that the adsorption in sclareol imprinted AN:AA copolymers is characterized by low surface coverage, takes place on heterogeneous binding sites and is reversible, while for NIPs the results suggest a difficult adsorption and/or easiness of template extraction, and that NIPs have homogeneous, but nonimprinted micropores. For the kinetic experiments, the minimum SNE for MIPs points to the first order kinetic model, fact that suggests a physical adsorption of template molecules on the imprinted sites., INTRODUCTION The explosion of the molecularly imprinted polymers (MIPs) field had repercussions in all chemistry areas: synthesis, analytical chemistry, chemical engineering, and practical applications [1-6]. And all this due to [...]

By using a simplified model of small open liquid-like clusters with surface effects, in the gas phase, it is shown how the statistical thermodynamics of small systems can be extended to include metastable supersaturated gaseous states not too far from the gas-liquid equilibrium transition point. To accomplish this, one has to distinguish between mathematical divergence and physical convergence of the open-system partition function.

A study was conducted to apply the hybrid Hartree-Fock ab initio/density functional theory method to investigate the possibility of directly calculating the chemical equilibria for a given organic reaction with a particular focus on the industrial synthesis of amine systems. The main goal of the study was to develop a practical scheme to quantitatively or semi-quantitatively evaluate thermochemical properties for molecules of industrial interest using moderately high level, quantum mechanic techniques. Results are discussed.

In electrospray ionization (ESI), droplets with a surface excess charge are created. The rate of production of surface excess charge is a constant and is equal to the rate of ion production. The ions appearing in the mass spectrum are postulated to be those that formed the surface excess charge at the time of droplet formation (or their collision products). An equilibrium model based on competition among the ions in the solution for the limited number of excess charge sites has been developed. This model accurately predicts the response curves of singly-charged ionic analytes as a function of the concentration of electrolyte and other analytes and provides an explanation for the selective effectiveness of ESI. At low concentrations of total analyte (micromolar and less), the response curves are linear, indifferent to the presence of other low concentration analytes, and suppressed by electrolyte concentrations in excess of the minimum required. At higher analyte concentrations, the response becomes independent of analyte concentration but highly affected by the presence of other analytes.

An equilibrium model for simultaneous biodegradation and adsorption was developed and verified with existing data. For simplicity the model was restricted to only two components: one biodegradable and one not. The results from modeling over 300 hypothetical situations identified conditions where biodegradation significantly extends the service life of granular activated carbon (GAC) columns. When the nonbiodegradable chemical controls the service life, the only significant gains in service life occurred when the biodegradable and nonbiodegradable chemical had similar adsorbabilities. When the biodegradable chemical controls the service life, the service life was 1.2-7 times that with adsorption alone, depending on the relative adsorbability of the two chemicals. The increase in service life can be maximized by ensuring that biodegradation begins as soon as possible after start-up. The model provides a good screening tool for initial assessments of process feasibility, preliminary economic analyses, and planning of detailed experimental and computer modeling studies.

A comparison of two indefinite self-association models, equal equilibrium constant (EK) and attenuated equilibrium constant (AK) models, reveals a good agreement among the stacking equilibrium constants. The AK models show variation in the stack with entropy loss. The EK model assumes the stack length to be independent of the entropy change. The EK model is appropriate for studying cases that have weaker interactions and a low population of trimers and higher polymeric species.

A simple one-dimensional radiative-convective equilibrium model is used to investigate the relationship between the surface temperature and the outgoing infrared radiation at the top of the atmosphere. The model atmosphere has a gray infrared absorption coefficient and is composed of a radiative equilibrium stratosphere and a moist adiabat troposphere. An upper limit of the outgoing infrared radiation is found to exist. The existence of the upper limit is characterized by the radiation limits that appear when the optical depth of the entire atmosphere becomes sufficiently deep and the temperature structure around the levels where the optical depth is about unity approaches a fixed profile. This appearance of an upper limit differs from that found by Komabayashi and Ingersoll, which is obtained from the constraint of the stratospheric radiation balance. As one of those radiation limits, the outgoing infrared radiation has an asymptotic limit as the surface temperature increases. This is caused by the tropospheric structure approaching the water vapor saturation curve. It is considered that the asymptotic limits appearing in the radiatively and thermodynamically more complicated models utilized by Abe and Matsui and Kasting are corresponding to this asymptotic limit indicated in our model.

An educational approach in which students perform experiments that demonstrate explicitly the reversibility of chemical reactions and the possibility that chemical reactions do not go to completion has been developed. Little attention has been given to changing students conceptions of chemical reactions as a result of the introduction of the chemical equilibrium concept. There is evidence that students do not understand the dynamic nature of chemical equilibria.

The potentiometric ion sensors or ion-selective electrodes (ISEs) are characterized by small size, portability, low-energy consumption and low-cost. Miniaturized versions of both conventional and solid-contact ISEs are used for various applications like nonequilibrium regions.