Electrochemical Studies on the Thermodynamics of Electron Transfer and Ligand Binding of Several Metalloporphyrins in Aprotic Solvents
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The utility of electrochemistry as a tool for studying physical properties of metalloporphyrins has been recognized extensively during the last several years (1,2). It is now well known that the half wave potentials for metalloporphyrin electrooxidation-reduction are directly influenced by the number and type of complexed axial ligands and that these may, in some instances, be related to the dioxygen carrying ability of the M(II) metalloporphyrin where M is Co(3-6), Fe (7-9) or Mn (10). Enthalpy and entropy values for complexation of cobalt(II) (4,11,12) and iron(II) (13) porphyrins, by several Lewis bases have been reported, but similar data for Lewis base complexation is not available for the oxidized cobalt(III) and iron(III) species. This data is of some interest in that changes of solvation and/or ligand binding, concomitant with electron transfer, may produce large entropie effects which would significantly shift the half wave potentials as a function of temperature and couldWe present a hybrid solvation model with first solvation shell to calculate solvation free energies. This hybrid model combines the quantum mechanics and molecular mechanics methods with the analytical expression based on the Born solvation model to calculate solvation free energies. Based on calculated free energies of solvation and reaction profiles in gas phase, we set up a unified scheme to predict reaction profiles in solution. The predicted solvation free energies and reaction barriers are compared with experimental results for twenty bimolecular nucleophilic substitution reactions. These comparisons show that our hybrid solvation model can predict reliable solvation free energies and reaction barriers for chemical reactions of small molecules in aqueous solution.
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철결핍빈혈에서 cobalt 배설율검사의 진단적 가치를 검토할 목적으로 1974년 4월부터 1976년 4월까지 서울대학교 의과대학 부속병원 내과와 원자력병원에 입원하였던 철결핍성빈혈 22예, 재생불량성빈혈 3예, 용혈성빈혈 2예, 기타 각종질환 58예, 대조군 11예, 총계 96예를 대상으로 58CoCl2는 이용하여 cobalt 배설율검사를 시행하는 한편, 적혈구형태, 적혈구지수, 혈청철, 총철결합능, 골수철검사와 비교관찰하여 다음과 같은 결론을 얻었다. 1) 철대사와 혈액학적으로 정상이라고 생각되는 대조군의 6시간 cobalt 배설율은 평균 2.8±1.77%(1.0∼6.8%)이었으며, 24시간 cobalt 배설율은 평균 6.1±4.31%(1.9∼15.2%)였다. 2) 철결핍성빈혈의 경우에는 6시간 cobalt 배설율이 평균 18.3±5.88%(10.2∼25.0%)이었으며, 24시간 cobalt 배설율은 평균 41.8±6.83%(29.0∼54.5%)로서 대조군과 비교하여 6배이상 증가돼 있었다. 3) 골수철함량이 정상인 증례에서는 빈혈이 유무에 관계없이 6시간 및 24시간 cobalt 배설율은 모두 대조군과 유의한 차이가 없었다. 4) 6시간 cobalt 배설율과 24시간 cobalt 배설율간에는 밀접한 상관관계를 볼 수 있었으나, 실제적인 면에 있어서는 24시간 cobalt 배설율검사가 더 정확한 것으로 생각되었다. 5) 골수철함량이 정상인 증례의 24시간 cobalt 배설율은 1.2∼26.6%의 동요범위를 보인 반면, 철결핍성빈혈예의 24시간 cobalt 배설율은 29.0∼54.5%의 동요범위를 보였으며 양군간에 중복을 볼 수 없었다. 그러므로 빈혈환자에서 24시간 cobalt 배설율이 27%이상이면 철결핍성빈혈을 의심할 수 있는 것으로 생각되었다. 6) Cobalt 배설율은 골수철함량이 감소함에 따라 대체로 증가하는 경향을 보였으나 상당한 중복을 볼 수 있었고, 특히 골수철함량이 1+인 경우는 철결핍이나 골수철함량이 정상인 경우와 중복되어 통계학적으로 유의한 차이를 볼 수 없었다. 7) 골수철검사로 확인된 철결핍성빈혈의 경우, cobalt 배설율은 전예에서 증가된 반면, 적혈구형태는 40%에서, 적혈구지수는 30∼60%에서, transferrin 포화율은 70%에서 이상소견을 보였다. 이상의 성적을 종합하면 cobalt 배설율검사는 철결핍성빈혈을 진단하는데 간단하고 민감하며 정확한 검사법으로 골수철검사의 실제적인 대체검사로 이용될 수 있는 것으로 생각된다.
Cobalt extraction techniques
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Objective: The aim was to estimate the various physiochemical properties of a molecule and the de-solvation cost for its binding to macromolecular receptors, the solvation free energy is a fundamental thermodynamics that has to be used. Here, a new solvation free energy carried out through the improvement of the existing solute-solvent interaction model and test its applicability in estimating the solvation free energies of vascular endothelial growth factor receptor-2 (VEGFR-2) inhibitors are discussed. Methods: The molecular dynamics program GROMACS, which is designed for free energy calculations and bond simulations, has been used to understand the solvation free energies. Results: The estimates of the solvation free energies of VEGFR-2 inhibitor molecules showed a reasonable accuracy by combining the effects from the solvent exposed and self-solvation regions. This significant contribution of free energies is thus consistent with the stability of the inhibitors in the solvent. Conclusion: The estimated solvation free energies from the new model illustrated a good association with the solute-solvent interaction. The current solvation model is thus expected to be more useful in supporting the stability of the inhibitors within a solvent. Keywords: GROMACS, Solvation free energy, VEGFR-2.
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The free energy of transfer of a solute from one medium to another, which is the free energy of solvation if the first medium is the gas phase and the second is a liquid-phase solution, controls all solvation and partitioning phenomena. The SM5.4 quantum mechanical solvation model allows for the calculation of (i) partitioning free energies between the gas phase and a solvent (i.e., free energies of solvation) or (ii) partitioning free energies between two solvents. The model provides a framework for interpreting the factors responsible for differential solvation effects and can be used to predict solvation effects on chemical equilibria and kinetics—examples in this chapter include partitioning of the nucleic acid bases between water and chloroform, solvation effects on anomeric conformational equilibria, and solvation effects on the rate of the Claisen rearrangement.
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SUMMARY Cobalt, as cobalt sulphate and cobalt-EDTA, was applied to pastures at 15 sites in south-east Scotland. Herbage cobalt and extractable soil cobalt concentrations were monitored at these sites over the period 1978–81. Although the sites were located in a generally cobalt-deficient area, considerable variation between sites was observed both in the concentration of cobalt present in untreated pasture and in the response to cobalt additions. There was no significant correlation between herbage cobalt concentrations and soil cobalt status as determined by acetic acid extraction. Application of cobalt sulphate (6 kg/ha) increased herbage cobalt concentrations at all sites but at several sites the response was short-lived. In general, cobalt-EDTA was less effective than cobalt sulphate in increasing herbage cobalt concentrations. Extractable soil cobalt concentrations of the control areas showed some variability between samplings, but the variability was much greater for the cobalt-treated plots. Cobalt applied to pastures was found to accumulate in the top 0–4 cm layer of soil and penetrated deeper only in soils of low pH. Overall, only a third of the cobalt applied to pastures as cobalt sulphate was recovered by acetic acid extraction of the soil and less than 20% of the cobalt applied as cobalt-EDTA.
Cobalt extraction techniques
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Enthalpy of atomization
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