Volume Change Of Reaction Research Articles

Structural Volume Changes in Photoinduced Electron Transfer Reactions. Laser-Induced Optoacoustic Studies of Speciation during the Quenching Reaction of Excited Ru(bpy)32+ by Fe(III) in Aqueous Solutions

Laser-induced optoacoustic spectroscopy has been applied to the photoinduced electron-transfer reaction between Ru(bpy)32+ and various salts of Fe(III) [Fe(ClO4)3, Fe2(SO4)3, and FeCl3]. The reaction volume changes associated with photoinduced ligand exchange derived from these measurements allowed the determination of partial molar volumes at high dilutions of several species such as FeSO4, FeSO4+, Fe(SO4)2-, Fe(OH)2+, FeCl+, FeCl2+, and FeCl2+, not attainable from other techniques. The volume change of oxidation of Ru(bpy)32+ to Ru(bpy)33+ at high dilution was also calculated.

Devolatilization‐generated fluid pressure and deformation‐propagated fluid flow during prograde regional metamorphism

The obstruction to fluid flow formed by the rocks overlying a metamorphic devolatilization front causes the fluid pressure gradient in the reacting rocks to diverge from lithostatic. This drives deformation in tandem with the fluid pressure anomaly generated by the volume change of the reaction. Numerical simulations show that once the vertical extent of the reacted rocks is comparable to the compaction length, compaction processes caused by the difference between confining and fluid pressure gradients generate a positive fluid pressure anomaly (effective pressure <0) above the reaction front, irrespective of the reaction volume change. Consequent dilational deformation propagates the anomaly upward, leading to underpressuring and densification at the reaction front and detachment of a wave of anomalous fluid pressure and porosity. Creep is a viable mechanism for such wave propagation for crustal viscosities <1015 MPa s. Continuous upward strengthening of the crust increases the wavelength and amplitude of the fluid pressure waves and thereby the likelihood of hydrofracture. Order of magnitude strength contrasts are adequate to arrest wave propagation, forming water sills that become increasingly stable in the absence of deviatoric stress. Although the fluid pressure gradient within a wave may be near hydrostatic, Rayleigh convection is unlikely. Thus, in the absence of lateral perturbations, fluid flow is upward and episodic, despite continuity of devolatilization. Porosity waves provide a mechanism for temporal focusing of metamorphic fluid fluxes with the potential to increase the efficacy of heat and mass transport.

Nature of the Water Structure inside the Pools of Reverse Micelles Sensed by Laser-Induced Optoacoustic Spectroscopy

Reaction volume changes, ΔVR, enthalpy content, ΔHMLCT, and decay lifetimes, τ2, of the metal-to-ligand charge transfer (MLCT) complex of (2,2‘-bipyridine)tetracyanoruthenate(II) complex, Ru(bpy)(CN)42-, inside the water pools of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles dispersed in n-alkanes, were determined using laser-induced optoacoustic spectroscopy (LIOAS). Emission quantum yields, Φem, of the complex were also determined by steady-state measurements. The enthalpy content of the MLCT state of Ru(bpy)(CN)42- was not dependent on the amount of water inside the reverse micelles (defined as the molar ratio R = [H2O]/[AOT]) and was, within experimental error, similar to that in water. However, the values of τ2 and Φem decrease while those of ΔVR increase as the values of R are incremented from 3 to 10. At the larger R values, τ2, Φem, and particularly ΔVR resemble the values in neat water. These results are interpreted to arise from the type of water involved in the hydrogen bond interactions between the cyanide ligands of the complex and the water molecules (second-sphere donor−acceptor interactions). In this framework, for reverse micelles solutions at R ≥ 10, the hydrogen bonds are made with the “free” water in the inner pool. For R < 10 the properties of Ru(bpy)(CN)42- are indicative of a more rigid microenvironment in the micellar core. Thus, the photophysical properties (and particularly ΔVR) of Ru(bpy)(CN)42- are very sensitive to its microenvironment and serve as a probe of the type of water involved in the hydrogen bonding. A combination of the LIOAS data from temperature-dependent measurements in neat water with those for the same complex in reverse micelles dispersed in various n-alkanes at high R values improved in 1 order of magnitude the accuracy of the ΔHMLCT and ΔVR values for the MLCT state.

Mobility of norbornane-type substrates and water accessibility in cytochrome P-450 cam

The behaviour of norbornane-type substrates bound to oxidised cytochrome P-450 cam (CYP 101) in 60% (w/w) glycerol-containing phosphate buffer was investigated using electronic absorption spectroscopy. The high-pressure dependence study revealed that the value of the spin-state reaction-volume change decreased from −70 to −22.8 cm 3/mol with decreasing high-spin state content from 99 to 63%. Simultaneously, the values for the enthalpy and entropy determined from the low-temperature dependence of the spin-state transition decreased from 73.7 to 24.3 kJ/mol and from 310.4 to 88.9 J/mol K, respectively. Under our experimental conditions the pH-value of the buffer remained at low temperatures and high pressures in the range of pH 7–8, in which no pH-value-induced spin-state conversion occurred. Therefore, the secondary effect of the temperature and pressure-induced pH change can be disregarded as being responsible for the observed spin-state transition effects. Substrate dissociation constants were determined. From the temperature-jump experiments (297 K to 180 K) we found a higher mobility in the active site for the substrates in the sequence (1 R)-camphor, (1 S)-camphor, camphane, (1 R)- and (1 S)-camphorquinone, norcamphor, and norbornane. Our findings can be explained by the incomplete fit of the methyl groups of the norbornane-type substrate to the protein, in particular to the I-helix, predominantly determining the substrate mobility and water accessibility to the protein.

New Application of the Transient Grating Method to a Photochemical Reaction: The Enthalpy, Reaction Volume Change, and Partial Molar Volume Measurements

A new application of the time-resolved transient grating method for measuring the enthalpy and reaction volume changes in a photochemical reaction is described in detail. From the temporal profile ...

Reaction volume and enthalpy changes in photochemical reaction detected by the transient grating method; photodissociation of diphenylcyclopropenone

A method for the measurement of reaction volume ( ΔV) and enthalpy ( ΔH) changes of a photochemical reaction is presented based on the transient grating technique. Since ΔV and ΔH contributions are detected separately by the time-resolved manner, this new method does not require changing the temperature or the solvent. If the diffusion constants of the species are very different, the partial molar volume of each chemical species can be determined. This method is applied to the photodissociation reaction of diphenylcyclopropenone. This method also provides a very accurate and convenient way to measure the diffusion constant of gaseous molecules in liquids.

Hydrolysis of β‐lactoglobulin by thermolysin and pepsin under high hydrostatic pressure

AbstractHydrolysis of β‐lactoglobulin with thermolysin and pepsin at pressures ranging between 0.1 and 350 MPa showed a significant increase of cleavage rates. Pressure‐induced changes of susceptibility to hydrolysis of β‐lactoglobulin proteolytic sites were also observed. The pressure, raised to 200 MPa, accelerates the hydrolysis of β‐lactoglobulin by thermolysin and changes obtained peptide profiles. Initially, higher pressure makes the N‐terminal, and to a smaller extent, C‐terminal peptide fragments of β‐lactoglobulin molecule, more susceptible to removal by thermolysin. This indicates combined influence of pressure‐induced thermolysin activation and partial unfolding of β‐lactoglobulin by compression at neutral pHs.The rates of hydrolysis of β‐lactoglobulin by pepsin (negligible at 0.1 MPa) are increased considerably with pressure up to 300 MPa. The Susceptibility of β‐lactoglobulin proteolytic sites to peptic cleavage remains constant over all the studied pressure range. The lack of significant qualitative changes in the peptic peptide profiles produced at different pressures and at clearly pressure‐dependent rates points to negative reaction volume changes as the major factor in peptic hydrolysis of β‐lactoglobulin under high pressure. Thus the β‐lactoglobulin molecule resists pressure‐induced unfolding in acid pHs and yields to it in neutral pHs. © 1995 John Wiley &amp; Sons, Inc.

A through solution model for volume changes of cement hydration

Changes of volume, temperature and bonding forces accompany every chemical reaction. Cement hydration leads to volume shrinkage during CSH formation and is influenced by a twofold phase transition. Dissociation of cement into pore solution leads to volume swelling while the followig crystallisation process produces volume shrinking. In the Through Solution (TS) — model presented here, the volume changes of cement reaction are described on the base of a consecutive reaction A - X- Z. The initial product A is considered as bulk volume of cement. X as a transition state product becomes the most important factor for the total reaction rate. The final product Z, as the volume of water bonded CS-phases, is regarded as the degree of hydration. The model has been shown to give adequate results for common cement reaction types.

Confidence intervals for thermodynamic constants

Phase equilibrium experiments using the same reactants and run at different temperatures and pressures give rise to linear constraints on thermodynamic variables, such as entropies, enthalpies, and volume changes of reaction. Linear programming has been applied to this problem to determine maxima and minima for these parameters separately.Since these temperatures and pressures are measured or set with uncertainty, their nominal values as reported by the experimenter need not define the same feasible region as that defined by their true values. Clearly, then, the ranges resulting from the linear programming procedure will not represent the reasonable ranges of parameter values. This paper explores the problem of inference on these parameters when a normal error distribution is postulated for temperature and pressure. Current methodologies and their relation to the field of statistical inference are discussed. Two algorithms for generating bounds on the entropies and enthalpies are presented. The first uses a normal approximation to the location of feasible region vertices and makes allowances for variations in the constraints contributing to this vertex to construct confidence intervals for the extrema in random linear programs in order to generate bounds holding for one parameter at a time. The second generates bounds holding simultaneously for all parameters. A comparison of these confidence intervals with those generated by conventional methods demonstrates that estimates of thermodynamic variables have far less variability than commonly believed.

Micellar effect on the kinetics of the base equilibrium of amino acids studied by the ultrasonic absorption method

Ultrasonic relaxation absorption has been measured in aqueous solutions of amino acids (tryptophan, leucine, glycine, phenylalanine, asparagine) in the absence and in the presence of micelles of sodium dodecylsulphate. The relaxation absorption was ascribed to the base equilibrium of amino acids, and the rate constants, the base dissociation constant, and the volume change of the reaction were obtained. The smaller micellar catalytic effect for the base equilibrium of amino acids, compared to those of amines and ammonia was ascribed to the electrostatic effect of the carboxylate group. The reaction mechanism, including the interactions of amino acid and the SDS micelles, were discussed.

Fluid controlled eclogitization of granulites in deep crustal shear zones, Bergen arcs, Western Norway

During the Caledonian orogeny large parts of the western margin of the Baltic shield were disrupted, sliced and stacked. Caledonian deformation resulted in a massif thickening of the continental crust. Mafic granulites and granulite facies meta-anorthosites build up a large portion of the Bergen Arcs terrane in southwestern Norway. The rocks represent typical Precambrian continental lower crust. These rocks experienced extensive eclogitization in response to stacking and crustal thickening during the Caledonian orogenic cycle. Eclogite formation resulted from shear deformation and associated infiltration of H2O-rich fluids (XH2O≥0.75). During an early stage, eclogite facies mineralogy formed in extension fractures (veins). The veins are probably related to hydraulic fracture systems which transported the inferred fluid phase. During the main stage, eclogitization occurred along shear zones ranging from centimeters to tens of meters in thickness. Eclogite forming reactions are shown to consume H2O, alkalies and to release SiO2. Much of the SiO2 released by the eclogitization process can be found in late quartz vein systems. The eclogitization took place at a temperature of about 700°C and a pressure between 18 and 21 kbar. Fluid infiltration was supported by a decrease in rock volume during reaction (ΔVsolids<0). The negative volume change of reaction occurs despite that the process of eclogitization involves hydration reactions. The formation of eclogite from granulite produces approximately 15 KJ heat per 100 cm3 original granulite. Numerical modeling of the regional temperature effects associated with partial hydration of the lower crust suggests that these processes may not cause large perturbations on the geotherm. Both, transport of heat and matter by advection of the fluid phase is negligible on a regional scale.

ChemInform Abstract: Determination of the Enthalpy and Reaction Volume Changes of Organic Photoreactions Using Photoacoustic Calorimetry.

AbstractTwo methods of photoacoustic calorimetry are used to measure volume changes following photoexcitation which are caused by both the thermal deposition of energy and the photoinitiated reaction volume change.

Determination of the enthalpy and reaction volume changes of organic photoreactions using photoacoustic calorimetry

Photoacoustic calorimetry (PAC) can be used to measure both the thermal and reaction volume changes for photoinitiated reactions. The photoreactions of 2,3-diazabicyclo(2.2.1)hept-2-ene (DBH), diphenylcyclopropenone (DPC), and trans-stilbene (TS) are investigated by PAC. The resolution of these experimental volume changes is accomplished by either a temperature dependence or a binary solvent mixture method. The thermal volume changes yield the enthalpies of reaction in solution, which can be compared to literature values. In two cases (DPH and DPC), the values are more endothermic than those predicted from gas-phase heats of formation. The differences can possibly be attributed to differential solvation of the reactants and products in the polar solvents employed. Absolute reaction volume changes for the photoreactions are also obtained for the photoreactions. PAC is a useful alternative technique to pressure-dependence studies to obtain this information. These volume changes can further be time-resolved to provide kinetic information about the photoprocesses.

Acoustic absorption in L-cysteine solutions at physiological pH and temperature measured using a novel technique

Absorption of ultrasound in L-cysteine has been measured at 37 °C for the pH range 6.8–8.0 for 0.2 and 0.5 mol dm–3 solutions. A new pulse-transmission technique has been used which produces continuous absorption spectra for the range 2–50 MHz, enabling accurate determination of relaxation frequency (f0) within this range. The variation of f0 with concentration and pH is explained in terms of a mechanism involving both intra- and inter-molecular proton transfer. For the first time, values have been determined for the volume change of the intramolecular proton-transfer reaction and for a number of the individual ionization rate constants for cysteine.

Tube‐wall reactor modelling for multiple reaction networks with non‐linear kinetics and volume change

AbstractTube‐wall reactors are gaining importance for highly exothermic and fast chemical reactions because of their simple construction and improved temperature control. A generalized mathematical model of the non‐isothermal annular tube‐wall reactors for simultaneous catalytic reactions with mixed type non‐linear reaction kinetics and volume change is developed. Numerical solutions of two‐dimensional component transfer equations, heat transfer equation and fluid flow equation may be obtained with appropriate boundary conditions using a recently developed orthogonal collocation method for annular geometries. The model has been successfully applied to the tube‐wall reactors for the Fischer‐Tropsch Synthesis. Comparison between model predictions and previous experimental results is good.

Sound wave propagation in fluids with coupled chemical reactions

A hydroacoustic theory is presented which accounts for sound absorption and dispersion in a multicomponent mixture of reacting fluids. A set of first-order acoustic equations without diffusion is assumed for the case where several coupled reactions can occur simultaneously. General results are obtained in the form of a biquadratic characteristic equation (called the Kirchhoff–Langevin equation) for the complex propagation variable χ=−(α+iω/c) in which α is the attenuation coefficient, c is the phase speed of the progressive wave, and ω is the angular frequency. Computer simulations of sound absorption spectra have been made for three different chemical systems, each comprised of two-step chemical reactions using physicochemical data available in the literature. The chemical systems studied include (1) water–dioxane, (2) aqueous solutions of glycine, and (3) cobalt polyphosphate mixtures. Explicit comparisons are made between the exact biquadratic characteristic solution and the approximate equation (sometimes referred to as a Debye equation), previously applied to interpret the experimental data for the chemical reaction contribution to the absorption versus frequency. The relative chemical reaction and classical viscothermal contributions to the sound absorption are also presented. Several discrepancies are discussed that can arise when estimating thermodynamic data (chemical reaction heats or volume changes) for multistep chemical reaction systems when making dilute solution or constant density assumptions.

Binding of N-dansylgalactosamine to the lectin from Erythrina cristagalli as followed by stopped-flow and pressure-jump relaxation kinetics.

The binding kinetics of N-dansylgalactosamine to the lectin from Erythrina cristagalli have been studied using stopped-flow and pressure-jump chemical relaxation by monitoring ligand fluorescence. Both methods gave results which are consistent with a simple bimolecular association reaction. The association rate constant, k + 1 = 4.8 X 10(4) M-1 s-1, is far too low to be controlled by diffusion; the dissociation rate is 0.4-0.66 s-1, depending upon the method of determination and the experimental conditions. Identical reaction-rate parameters were obtained at pH 7.3, where soluble aggregates can be present in the lectin solution and at pH 4.7 where such aggregates are absent. The slow rates of carbohydrate binding seem to be characteristic for most lectins and lend support to the idea that they are evolutionary related and have structurally similar binding sites. Analysis of the relaxation amplitudes of the pressure-jump experiments yielded a molar reaction volume change, delta V0, upon binding of +7 ml/mol. This volume change can be caused by desolvation of the ligand upon binding.

KINETIC STUDIES ON THE HIGH-PRESSURE DIELS–ALDER REACTION OF TROPONE WITH MALEIC ANHYDRIDE

Abstract The rates and activation parameters of the (4+2)π cycloaddition of tropone with maleic anhydride were measured in the range of 105–135 °C at pressures up to 2000 bar in cumene and in DMF. The values of activation volume and the volume change of reaction revealed a deviation to a great extent from those of (6+4)π process of tropone with cyclopentadiene, but to a small extent from the other (4+2)π process.

Hydroacoustic analysis of multiple relaxation kinetics

This investigation presents a hydroacoustic theory which accounts for sound absorption and dispersion in a multicomponent mixture of reacting fluids (assuming a set of first‐order acoustic equations without diffusion) such that several coupled reactions can occur simultaneously. General results are obtained in the form of a biquadratic characteristic equation (called the Kirchhoff‐ Langevin equation) for the complex propagation variable χ = (α + ωi/c) in which α is the attenuation coefficient, c is the phase speed of the progressive wave, and ω is the angular frequency. Computer simulations of sound absorption spectra have been made for three different chemical systems each comprised of two‐step chemical reactions using physico‐chemical parameter data available in the literature. The chemical systems studied include (1) water‐dioxane, (2) glycine‐water, and (3) cobalt polyphosphate water mixtures. Explicit comparisons are made between the biquadratic characteristic solution and the approximate equation (sometimes referred to as a Debye equation) previously applied to interpret the experimental data for the total chemical absorption versus frequency. The relative chemical reaction and classical viscothermal contributions to the sound absorption are also presented. Several discrepancies that can arise when estimating thermodynamic data (i.e., chemical reaction heats or volume changes) for multistep chemical reaction systems when making dilute solution or constant density assumptions are discussed.

Design of a non-isothermal tube wall reactor with a multicomponent reaction mixture and volume change

An analysis of a non-isothermal tube wall reactor with multicomponent reaction mixture and varying volume is considered under turbulent flow conditions