Isoperibol Solution Calorimetry Research Articles

Thermodynamics of glyme-sodium dodecyl sulfate (SDS) mixed micelle formation via isoperibol solution calorimetry: Temperature, and concentration effects

The enthalpies of mixed micelle formation (ΔmicH) for a number of sodium dodecyl sulfate (SDS)/glycol ether (glyme) systems were determined as a function of the concentration of the glycol ether in the mixed solvent systems and temperature via isoperibol solution calorimetry. The glycol ethers investigated in the present work were diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TEGDME), tetraethylene glycol dimethyl ether (TetraEGDME), and diethylene glycol diethyl ether (DEGDEE). The data from the isoperibol solution calorimeter was also used to directly determine the CMC values of the SDS/glyme mixed micelles. The entropies and Gibbs energies of mixed micellization (ΔmicSandΔmicG) were calculated by the application of the charged pseudo-phase separation model to the calorimetric enthalpies and CMC values. In general, CMC values and mixed micelle formation enthalpies depended strongly on the glyme structure and its concentration in the mixed solvents. The relative contributions to micelle thermodynamics by the ethylene oxide groups and the alkyloxy chain endcaps, and how the locus of solubilization influences the intramicellar surfactant/cosurfactant interactions, are interpreted in terms of alkyl chain interactions, hydrophobic effects, and electrostatic contributions.

Calorimetric determination of the thermodynamics of alcohol-surfactant mixed micelle formation: Temperature and concentration effects

The thermodynamic parameters of surfactant/alcohol mixed micelles were determined in mixtures of sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) in a series of solvents composed of varying concentrations of n-propanol (C3OH), n-butanol (C4OH), and n-pentanol (C5OH). Conductivity studies were used to determine CMC values and the degrees of counterion binding. Isoperibol solution calorimetry was used to directly determine CMC values and enthalpy of micellization (ΔmicH). From these experimentally determined values, the Gibbs energy and entropy of micellization were calculated as a function of temperature and alcohol concentration. In general, CMC values decreased with increasing alcohol carbon chain length and concentration but increased with temperature. The effects of temperature, alcohol carbon chain length, and alcohol concentration on the energetics of these mixed micellar systems are explained in terms of the relative contributions to ΔmicH by alkyl chain interactions, hydrophobic effects, and electrostatic contributions.

Thermodynamics of Mixed Micellization of Isomeric Hexanediols in Sodium Dodecyl Sulfate

The thermodynamic parameters of mixed micelle formation (Δ mic G°, Δ mic H°, Δ mic S°) have been determined for a series of mixed micelles consisting of two isomeric hexanediols (1,2-hexanediol and 1,6-hexanediol) in sodium dodecylsulfate micellar solutions. The enthalpies of micellization were determined directly from isoperibol solution calorimetry. Gibbs energies and entropies of micelle formation were obtained from the application of the charged pseudo-phase model of micelle formation to the calorimetric critical micelle concentration values. The location of the alcohols in the micellar palisade layer has been determined from two-dimensional nuclear Overhauser enhancement spectroscopy (NOESY) experiments. The calorimetric titration data indicates that the placement of the hydroxyl groups on the six carbon backbone greatly affects the energetics of the micelle formation process. From the NMR data, the location of the cosurfactant in the micelle has been determined. These results indicate that the locus of solubilization affects the subtle balance of forces responsible for the formation of the mixed aggregates.

Stability of lyophilized human growth hormone

To evaluate relationships between the extent of protein–excipient interactions, structural relaxation of an amorphous matrix, and the physico-chemical stability of a protein, human growth hormone (hGH) was lyophilized with sucrose and trehalose in a 1:2 weight ratio. The protein–excipient interactions were analyzed immediately after lyophilization with isoperibol solution calorimetry (ISC), water sorption analysis (WSA), differential scanning calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR). The physical and chemical stability of hGH during storage at 50 °C was monitored by reverse phase (RP)–HPLC, SEC–HPLC and UV absorption spectroscopy. The hGH formulation containing sucrose demonstrated greater protein–excipient interactions and faster initial relaxation times compared to the trehalose formulation. Although both formulations had similar chemical stability (rate of deamidation), physical stabilities (e.g. degree of aggregation) were different. The hGH/sucrose formulation manifested a higher rate and lower extent of insoluble aggregate formation. The decreased amount of aggregation in the sucrose formulation could be correlated with a greater extent of protein–excipient interactions and the presence of a more homogeneous mixture. In contrast, the higher rate of aggregation in the sucrose formulation could be directly correlated with the higher molecular mobility of the matrix.

B(C6F5)3- vs Al(C6F5)3-Derived Metallocenium Ion Pairs. Structural, Thermochemical, and Structural Dynamic Divergences

The thermodynamic and structural characteristics of Al(C6F(5)3-derived vs B(C6F5)3-derived group 4 metallocenium ion pairs are quantified. Reaction of 1.0 equiv of B(C6F5)3 or 1.0 or 2.0 equiv of Al(C6F5)3 with rac-C2H4(eta5-Ind)2Zr(CH3)2 (rac-(EBI)Zr(CH3)2) yields rac-(EBI)Zr(CH3)(+)H3CB(C6)F5)(3)(-) (1a), rac-(EBI)Zr(CH3)+H3CAl(C6F5)(3)(-) (1b), and rac-(EBI)Zr2+[H3CAl(C6F5)3](-)(2) (1c), respectively. X-ray crystallographic analysis of 1b indicates the H3CAl(C6F5)(3)(-) anion coordinates to the metal center via a bridging methyl in a manner similar to B(C6F5)3-derived metallocenium ion pairs. However, the Zr-(CH3)(bridging) and Al-(CH3)(bridging) bond lengths of 1b (2.505(4) A and 2.026(4) A, respectively) indicate the methyl group is less completely abstracted in 1b than in typical B(C6F5)3-derived ion pairs. Ion pair formation enthalpies (DeltaH(ipf)) determined by isoperibol solution calorimetry in toluene from the neutral precursors are -21.9(6) kcal mol(-1) (1a), -14.0(15) kcal mol(-1) (1b), and -2.1(1) kcal mol(-1) (1b-->1c), indicating Al(C6F5)3 to have significantly less methide affinity than B(C6F5)3. Analogous experiments with Me2Si(eta5-Me4C5)(t-BuN)Ti(CH3)2 indicate a similar trend. Furthermore, kinetic parameters for ion pair epimerization by cocatalyst exchange (ce) and anion exchange (ae), determined by line-broadening in VT NMR spectra over the range 25-75 degrees C, are DeltaH++(ce) = 22(1) kcal mol(-1), DeltaS++(ce) = 8.2(4) eu, DeltaH++(ae) = 14(2) kcal mol(-1), and DeltaS++(ae) = -15(2) eu for 1a. Line broadening for 1b is not detectable until just below the temperature where decomposition becomes significant ( approximately 75-80 degrees C), but estimation of the activation parameters at 72 degrees C gives DeltaH++(ce) approximately 22 kcal mol(-1)and DeltaH++(ae) approximately 16 kcal mol(-1), consistent with the bridging methide being more strongly bound to the zirconocenium center than in 1a.

The use of isoperibol calorimetry for the study of age-related changes in glucose uptake by erythrocytes

Isoperibol solution calorimetry was used to determine in vitro erythrocyte glucose uptake changes as a function of erythrocyte age. Glucose concentrations were determined by phosphorylation with Mg 2+ /ATP 2- in the presence of hexokinase. The differential heat of the standard reaction was found to be -70.3 kJ mol -1 (-16.8 kcal mol -1 ). Lower amounts of glucose were taken up by 'expired,' older than 90 days, cells (0.37 mmol/5 mL packed cells) than by 'fresh,' immediately after blood collection, cells (0.87 mmol/5 mL packed cells). Statistical analyses of the data revealed significant differences in extent of glucose uptake between fresh cells and expired cells (p<0.05).

Effect of Solid State Transition on the Physical Stability of Suspensions Containing Bupivacaine Lipid Microparticles

Bupivacaine lipid microparticles were prepared and evaluated as a parenteral sustained-release dosage form for postoperative pain management. Bupivacaine free base was incorporated into a molten tristearin matrix and lipid microparticles were subsequently formed from this molten mixture by a spray-congealing process. A 3% injectable bupivacaine lipid microparticle suspension was prepared by dispersing 30% bupivacaine lipid microparticles in an aqueous medium containing carboxymethylcellulose (CMC), mannitol, and Tween 80. Upon room temperature storage, the fluid suspension gradually changed into a nonflowing semisolid (gelation) as a result of crystal growth of bupivacaine. However, suspensions prepared with bupivacaine lipid microparticles that were previously annealed at an elevated temperature remained fluid upon long-term storage. Differential scanning calorimetry (DSC), x-ray powder diffraction (XRPD), and isoperibol solution calorimetry were used to investigate the changes in the solid-state properties of tristearin and bupivacaine in the lipid microparticles before and after the heat treatment. The DSC and XRPD results indicate that after 24 hours of heating at 40°C, tristearin was completely converted from the unstable α form to the stable β form. Using the isoperibol solution calorimetric method, bupivacaine was found to transform into a more stable form after the lipid microparticles were heated at 60°C for 24 hours. The generation of the unstable solid forms of tristearin and bupivacaine was attributed to the resolidification of both components from the molten mixture during the spray-congealing process.

Preparation and physicochemical properties of niclosamide anhydrate and two monohydrates

The intent of the study was to prepare and characterize three crystal forms of niclosamide namely the anhydrate and the two monohydrates and to investigate the moisture adsorption and desorption behavior of these crystal forms. The crystal forms were prepared by recrystallization and were characterized by differential scanning calorimetry, thermogravimetric analysis, isoperibol solution calorimetry, Karl Fischer titration, and X-ray powder diffractometry. Moisture adsorption by the anhydrate at increased relative humidities and two temperatures, 30 and 40 °C, was measured while the desorption from the monohydrates was determined at 45, 55, and 65 °C for monohydrate H A and 75, 90, and 100 °C for monohydrate H B. Thermal analysis and solution calorimetry showed that monohydrate H B is more stable than monohydrate H A and solubility measurements showed the solubility of the crystal forms decreased in the order: anhydrate⪢monohydrate H A>monohydrate H B. With an increase in temperature and relative humidity niclosamide anhydrate adsorbed moisture to form monohydrate H A by a random nucleation process. Dehydration of monohydrate H A at increased temperatures followed zero order kinetics and resulted in a change to the anhydrate. Monohydrate H B was transformed to the anhydrate at higher temperatures by a three-dimensional diffusion mechanism.

Enthalpies of formation of SrPbO 3 and Sr 2PbO 4

Alkaline–earth plumbates are important accessory phases in {(bismuth, lead) + strontium + calcium + copper + oxygen} (“BSCCO”) high-temperature superconductor materials. Reliable values for standard molar enthalpies of formation (Δ f H 0 m) of the plumbates are therefore an essential part of the BSCCO high-temperature superconductor thermodynamic data base. To obtain Δ f H 0 m of SrPbO 3 and Sr 2PbO 4, we measured the enthalpies of solution of SrO,PbO 2,SrPbO 3, and Sr 2PbO 4 in 6 mol· dm −3 HCl by isoperibol solution calorimetry and derived the values of Δ f H 0 m for the strontium plumbates from Hess cycles. The values obtained were Δ f H 0 m ( SrPbO 3,298.15 K)=−(949.3±3.5) kJ· mol −1 and Δ f H 0 m ( Sr 2 PbO 4,298.15 K)=−(1565.1±6.9) kJ· mol −1 . In previous experiments, we measured the total vapor pressures over SrPbO 3 by Knudsen effusion vacuum thermogravimetry. In the present paper, these data were used for an independent derivation of Δ f H 0 m ( SrPbO 3,298.15 K) via a van’t Hoff extrapolation, which yielded −(945.8±7.5) kJ· mol −1 , in good agreement with the value obtained calorimetrically. Our determination of Δ f H 0 m ( Sr 2 PbO 4,298.15 K) agrees well with a recently published value obtained from electrochemical measurements.

Thermodynamics of micellization of ionic surfactant/alkoxyethanol mixed micelles as a function of temperature

Estimates of the thermodynamic parameters of micellization (ΔmicG°, ΔmicH°, and ΔmicS°) have been determined for a series of mixed micelles consisting of ionic surfactants (sodium dodecylsulfate and dodecyltrimethylamonium bromide) and medium chain length alkoxyethanols as the co surfactant. The enthalpies of micellization have been measured directly for the above systems using isoperibol solution calorimetry; the Gibbs energies and entropies of micellization are obtained by application of the mass-action model to the critical micelle concentration values from the calorimetric titration experiments. The thermodynamic properties of mixed micelle formation with alcohol concentration and temperature are in excellent agreement with our previous results. However, there does appear to be some dependence of the thermodynamic properties of mixed micelle formation on the charge of the ionic surfactant. These dependencies are discussed in terms of the manner in which the ethylene oxide group of the alcohol interacts with the ionic head groups and the location of the solubilizates in the micellar interior.

The thermodynamic properties of Ce2O3(s) fromT → 0 K to 1500 K

The thermodynamic properties of cerium sesquioxide, Ce 2O 3(s), have been measured. From the low-temperature adiabatic heat capacity measurements in the temperature range 3 K to 420 K, the values forCop , m and Smo, (115.0 ± 0.3)J · K−1 · mol−1 and (148.8 ± 0.4)J · K−1 · mol−1, respectively, have been obtained. The high-temperature enthalpy increment has been measured in the temperature range 470 K to 883 K. The enthalpy of solution has been measured by using isoperibol solution calorimetry at T= 298.15 K in 0.250 mol · dm−3HCl(aq). Using all available literature values, the standard molar enthalpy of formation has been derived: ΔfHom {Ce 2O 3(s) , 298.15 K} =−(1812.4 ± 1.3)kJ · mol−1. The thermodynamic properties have been calculated to T= 1500 K.

Calorimetric and NMR Investigations of the Micellar Properties of Sodium Dodecyl Sulfate in Aqueous Mixtures of Isomeric Butanediols

The enthalpies (ΔmicH°), entropies (ΔmicS°), and Gibbs energies (ΔmicG°) of micelle formation have been determined for a series of sodium dodecyl sulfate (SDS)/butanediol isomer micelles using isoperibol solution calorimetry. Nuclear magnetic resonance (NMR) paramagnetic relaxation enhancement experiments were used to determine the degree of solubilization of the isomeric butanediols (BTDs) in a 0.100 M solution of SDS micelles. In addition, the manner in which the butanediol cosolvents interact with SDS micelles, as a function of the position of substitution of the hydroxyl groups on the four-carbon backbone, has been examined closely via 13C NMR spectroscopy. All of these results are interpreted in terms of the differences in the interaction of the isomeric butanediols with SDS micelles because of the addition of the second hydroxyl headgroup on the four-carbon backbone of the alcohol, when compared to the well-studied SDS/1-butanol (C4OH) mixed micellar system.

Thermodynamics in Surfactant Solutions: Determination of the Micellization Enthalpy and Entropy of Alcohol/Surfactant Mixed Micelles. A Comparison of Calorimetric Methods with Temperature Differentiation of the ln Xcmc Values

The variation of the critical micelle concentration (cmc) has been determined for sodium dodecyl sulfate (SDS) in water and in increasing concentrations of 1-butanol (C 4 OH) at temperatures ranging from 25 to 55 °C. Estimates of the thermodynamic parameters of micellization (Δ mic G o , Δ mic H o , and Δ mic S o ) are obtained from the variation of the ln X cmc with the absolute temperature (method 1). In addition, the enthalpies of micellization have been measured directly for the above systems and SDS/1-pentanol (C 5 OH) mixed micelles, by use of isoperibol solution calorimetry (method 2) over the same temperature range. The results from both methods, as a function of increasing temperature, indicate a shift in the driving force for the formation of micelles in the direction of decreasing enthalpy, in agreement with the literature. However, as a function of increasing alcohol concentration, the enthalpies from methods 1 and 2 are not comparable. Some possible reasons for the discrepancy will be discussed. Finally, we have examined the influence of the cosurfactant (alcohol) chain length on the thermodynamics of mixed micellization.

Cobalt-carbon bond disruption enthalpies: the first reliable measurement of a Co-methyl BDE via solution thermochemical methods

The determination of the strength of the metal-carbon /sigma/ bonds has become very important because such bonds have been implicated as or demonstrated to be integral components of many homogeneous catalytic cycles. The use of iodinolytic isoperibol solution calorimetry for the measurement of the absolute value of the bond disruption energies, D(Co-R), for pyCo(CH)/sub 2/R where py=pyridine, DH = the monoanion of dimethylglyoxime, and R = I, CH/sub 3/, CH/sub 2/C/sub 6/H/sub 5/, or CH(CH/sub 3/)/sub 2/ is reported herein. The assumption is made that the pyCo(DH)/sub 2/ moiety remains basically unchanged so that the enthalpy of iodinolysis for the reaction can be expressed as the difference in bond disruption enthalpies for bonds being made or broken in the iodinolysis reaction. It is felt that values of D(Co-R) determined in nonpolar solvents should be a tolerably good approximation for gas-phase data.

Die Bildungsenthalpie von Zinndijodid, SnJ2 (c)

The heat of reaction for SnJ2 (c)+J2 (c)+4045 CS2 (l)=[SnJ4; 4045 CS2] (sol) has been determined to be (−41.12±0.55) kJ mol−1, [(−9.83±0.13) kcal mol−1] by isoperibol solution calorimetry. Combining this result with the heat of formation of SnJ4 in CS2 determined in a previous investigation11 the value (−153.9±1.40) kJ mol−1, [(−36.9±0.33) kcal mol−1] has been derived for the heat of formation, ΔHfι (SnJ2;c; 298.15 K), of tin diiodide.