Thermodynamic studies experiments

Unsually short NMR T, relaxation values were observed for the metal-bonded H-ligands in HCo(dppe)2, [Co(H2)(dppe)]+ (dppe = l,2-bis(diphenylphosphino)ethane), and CoH(CO) (PPh3)3.176 A theoretical analysis incorporating proton-meta) dipole-dipole interactions was able to reproduce these 7) values if an rCo H distance of 1.5 A was present, a value consistent with X-ray crystallographic experiments. A detailed structural and thermodynamic study of the complexes [H2Co(dppe)2]+, HCo(dppe)2, [HCo(dppe)2(MeCN)]+, and [Co(dppe)2(MeCN)]2+ has been reported.177 Equilibrium and electrochemical measurements enabled a thorough thermodynamic description of the system. Disproportionation of divalent [HCo(dppe)2]+ to [Co(dppe)2]+ and [H2Co(dppe)2]+ was examined as well as the reaction of [Co(dppe)2]+ with H2. 

The second reaction studied using lipase as catalyst was the reversible re-gioselective esterification of propionic acid and 2-ethyl- 1,3-hexanediol [180]. While the previously described reaction was almost irreversible, this reaction is equilibrium limited with an apparent equilibrium constant of 0.6 0.1. In addition, the accumulated water inhibits the enzyme. Therefore, only the removal of the water from the reaction zone assures high enzymatic activity as well as drives the reaction beyond thermodynamic equilibrium. Experiments with two... 

These sort of problems make it difficult to obtain reliable high temperature data on the aqueous chemistry of transition metal ions. Unfortunately the necessary timescales for even the simpler experimental studies are frequently too long for a Ph.D. student to make reasonable progress in 3 years from scratch or for industrial researchers to make much reportable progress before the patience of those supporting the work is exhausted. Results can be reported far more rapidly from, for example, corrosion experiments and since corrosion theories are in general of so little predictive value, each relevant alloy/electrolyte combination needs its own study. In such circumstances it is hardly surprising that thermodynamic studies have been (with a few notable exceptions) relatively poorly supported, while corrosion data continue to be amassed without any reliable thermodynamic framework within which to understand them. 

A number of ex situ spectroscopic techniques, multinuclear NMR, IR, EXAFS, UV-vis, have contributed to rationalise the overall mechanism of the copolymerisation as well as specific aspects related to the nature of the unsaturated monomer (ethene, 1-alkenes, vinyl aromatics, cyclic alkenes, allenes). Valuable information on the initiation, propagation and termination steps has been provided by end-group analysis of the polyketone products, by labelling experiments of the catalyst precursors and solvents either with deuterated compounds or with easily identifiable functional groups, by X-ray diffraction analysis of precursors, model compounds and products, and by kinetic and thermodynamic studies of model reactions. The structure of some catalysis resting states and several catalyst deactivation paths have been traced. There is little doubt, however, that the most spectacular mechanistic breakthroughs have been obtained from in situ spectroscopic studies. 

A strong argument in favor of the involvement of Strecker synthesis is that aldehydes and HCN are among the initial species formed in electric discharge experiments leading to a-amino acid formation. Mechanistic and thermodynamic studies (20) of systems derived from aqueous mixtures containing... 

Indeed, the experiements appear to be precise and carefully executed. The same may be said of the careful thermodynamic study of Picard and Gerdanian on slightly reduced rutile, where the results obtained are also treated in terms of point defects. Interpretation in terms of CS planes would seem to be at least as realistic an alternative as point defects, and it is a pity that the authors have not attempted such an analysis. Other recent papers on the physical and chemical properties of reduced rutile, such as that of Baumard on the chemical diffusivity of oxygen in oxygen-deficient rutile, or that of Izumi on dielectric properties, are also analysed in terms of point defects only. Similar criticisms therefore apply to these articles. In contrast, studies of oxygen-tracer diffusion in rutile and the Ti 02 -i phases by Bagshaw and Hyde are presented clearly, with no extrapolations made about the defect structure of the materials used. 

Solid Calcium Sulfite. Recent thermodynamic studies of calcium sulfite by mass spectroscopy indicated that calcium sulfite dissociates into calcium oxide and sulfur dioxide (12). Under atmospheric pressure, this dissociation reaction is slow in the range below 250°C. We find under these conditions substantial decomposition of sulfite, yielding sulfate, elemental sulfur as well as thiosulfate. These observations are consistent with experiments by Brewer (13), and confirm old observatons made by wet-analysis of these complex solids (14). Our work confirms seventy year old literature reports which suggested evidence for thiosulfate, trithionate and dithionate in old pulping sulfite liquor which yellows when kept in air-free, sealed ampules (15-18). 

For a binary solution the function f(P) reduces to a single parameter P, the relative chain length of the polymer, so that or x depends on T, , and P. The basic task in the thermodynamic study of binary solutions is to find this dependence by appropriate experiments. 

Imino IH NMR. Imino NMR spectroscopy is a powerful direct probe for the presence and nature of the base pairing in nucleic acids. As shown in Figure 6, the imino spectra for the control and the four stable a-containing duplexes exhibit resonances for the five chemically distinct imino protons in each self-complementary decamer, indicative of stable base pair formation. In addition, temperature dependent experiments showed no evidence for pre-melting of the base pairs comprising the a-nucleotides. Virtually identical NMR spectra have been obtained for the a-duplexes at optical concentrations (3 to 6 pM duplex), demonstrating that the duplex form exists under the conditions used in the thermodynamic studies. 

AP for Al. To select a consistent operating electron energy, it is essential to measure IE curves as part of each experiment in a thermodynamic study and to set the electron energy relative to the measured APs. 

Methods to determine co-crystal solubility are based on thermodynamic and kinetic approaches. Thermodynamic equilibrium experiments provide a measure of co-crystal solubilization processes, while kinetic studies provide insight about the time scales of dynamic processes and concentration fluctuations during co-crystal dissolution. From equilibrium measurements, we can extract information about the origin of co-crystal solution phase behavior and fine tune solution processes by controlling thermodynamic solubility. We can use the knowledge gained from equilibrium studies to design kinetic studies and separate the thermodynamic and kinetic contributions to the co-crystal dissolution and transformation behavior. 

The oxidative liquidAiquid extraction was selected, from a bibliographic survey, for investigations into actinide back-extraction from A1 matrices. A thermodynamic study aimed to determine the optimal conditions to perform the experimental study of the actinide back-extraction in chloride media. The thermodynamic predictions could be confirmed by the first experiments. These experiments lead to a better optimisation of the experimental procedure and device. 

In 1973, Mikheev et al. reported that a stable, monovalent Md ion could be produced in ethanol solutions and that it co-crystallized with CsQ [45]. However, Samhoun and co-workers studied the overall reduction of Md to the amalgam using controlled potential electrolysis they concluded that Md could not be considered a cesium-like element and no evidence was obtained consistent with a monovalent state [46,47]. Hulet et al. have recently repeated some of the co-crystallization experiments of Mikheev and performed a series of new experiments in an attempt to prepare Md by reduction with Sm in ethanol solutions and also in fused KQ media [37]. In these experiments, the behavior of Md was compared to tracer amounts of 3-i-, 2-i-, and 1-i-ions and Md consistently followed the 2 -i- ions. They concluded that Md cannot be reduced to a monovalent state with Sm as daimed by Mikheev. However, on the basis of the results of thermodynamic studies of the co-crystallization process of mendelevium with chlorides of alkali metals, the Russian investigators maintain that Md can be reduced to the monovalent state in water-ethanol solutions and that the co-crystallization of Md with salts of divalent ions can be explained as being due to the formation of mixed crystals [102,103]. An ionic radius of 1.17 A was calculated for Md from the results of the co-crystallization studies [104]. 

One of the primary aims of the thermodynamic study thus will be to determine the variance by means of experiments from which we will deduct the number of solid phases, an important information to model systems. The practice shows that this step, when it is possible, is much easier than the one that consists of determining the number of solid phases from direct experiments and then deducing the variance. 

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