CO/CO2 potentiometric titrations of carbon monoxide dehydrogenase from Clostridium thermoaceticum and the effect of CO2

Acetogenic carbon monoxide dehydrogenases catalyze the reversible oxidation of CO to CO2 and the synthesis of acetyl-coenzyme A, utilizing two novel Ni-Fe-S active sites (the C- and A-clusters, respectively) and an [Fe4S4]2+/1+ cluster (the B-cluster) that serves to transfer electrons. Enzyme samples were titrated under equilibrium conditions using various partial pressures of CO in Ar and CO2 atmospheres. EPR signal intensities from each cluster were analyzed as a function of potential using the Nernst equation. The presence of CO2 raised the reduction potentials of the A-, B-, and C-clusters, and it appeared to increase the strength of CO (substrate for acetyl-CoA synthesis) binding to the reduced A-cluster. Carbon dioxide also appeared to stabilize an intermediate EPR-silent state of the C-cluster and alter the saturation/relaxation properties of the reduced B-cluster. Simulations assuming n values (number of e- involved in reduction) larger than appropriate for the individual reactions generally fit better to the titration data than those which assumed the appropriate n, indicating positive redox cooperativity. Carbon dioxide did not inhibit 1,10-phenanthroline from removing the labile Ni from the A-cluster, but it did inhibit the CO/acetyl-coenzyme A exchange activity, probably by causing CO to bind more tightly to the A-cluster. Taken together, these results indicate a significant CO2-dependent conformational change affecting the properties of all three clusters and both subunits. Since the enzyme operates in vivo in a CO2 environment, the CO2-induced conformation may be mechanistically important.     

Pathophysiological and clinical aspects of the CO2 pneumoperitoneum (CO2-PP)

Experimental studies demonstrated a severe cardiac load of the CO2 pneumoperitoneum caused by an accelerated after- and a decreased preload. Patients displaying cardiovascular risks are therefore often rejected from laparoscopic surgery. Hence, the pathophysiological changes and the intraoperative risk of the CO2 pneumoperitoneum in high-risk cardiopulmonary patients (NYHA II-III, n = 15) undergoing laparoscopic cholecystectomy are described. The changes in cardiac after- and preload seem to be due to the elevated intraabdominal pressure rather than transperitoneally resorbed CO2 and are reversible by desufflation. In one patient conversion to open operation had to be performed because of a severe drop in cardiac output and right ventricle ejection fraction. Mixed oxygen saturation was predicting intraoperative worsening in this case. The described pathophysiological changes may seem to be well tolerated even in high-risk cardiac patients. Monitoring of hemodynamics should include an arterial catheter line and blood gas analyses. Pharmacologic interventions or pressureless laparoscopic procedures might not be necessary as long as laparoscopic cholecystectomy is performed.     

Thermal and carbothermic decomposition of Na2CO3 and Li2CO3

In order to elucidate the decomposition mechanism of Na₂CO₃ and Li₂CO₃ in mold-powder systems employed in the continuous casting of steel, decompositions of Na₂CO₃ and Li₂CO₃ were investigated using thermogravimetric (TG) and differential scanning calorimetric (DSC) methods at temperatures up to 1200 °C, under a flow of argon gas. For the case of pure Na₂CO₃, the thermal decomposition started from its melting point and continued as the temperature was increased, but at a very slow rate. For Li₂CO₃, however, the decomposition occurred at much faster rates than that for Na₂CO₃. When carbon black was added to the carbonate particles, the decomposition rates of both Na₂CO₃ and Li₂CO₃ were significantly enhanced. From mass-balanced calulations and X-ray diffraction (XRD) analyses of the reaction products, it is concluded that decompositions of Na₂CO₃ and Li₂CO₃ with carbon black take place according to the respective reactions of Na₂CO₃ (1) + 2C (s) = 2Na (g) + 3CO (g) and Li₂CO₃ (l) + C (s) = Li₂O (s) + 2CO (g). It was found that liquid droplets of Na₂CO₃ were initially isolated due to carbon particles surrounding them, but, as the carbon particles were consumed, the liquid droplets were gradually agglomerated. This effected a reduction of the total surface area of the carbonate, resulting in a dependence of the decomposition rate on the amount of carbon black. For the case of Li₂CO₃, on the other hand, hardly any agglomeration occurred up to the completion of decomposition, and, hence, the rate was almost independent of the amount of carbon black mixed. The apparent activation energies for the decomposition of Na₂CO₃ and Li₂CO₃ with carbon black were found to be similar and were estimated to be 180 to 223 kJ mole⁻¹.     

CO/CO2气氛对Fe3C形成的影响规律

利用X-ray衍射和失重法研究了CO/CO2混合气体还原氧化铁过程中Fe3C的生成规律,得到3Fe 2CO=Fe3C CO2的反应标准自由能表达式为:△G°= -151 470 168.78T,绘制了碳化铁生成热力学平衡图,与实验结果基本吻合.     

CO2--emphysema in laparoscopic surgery. Changes in pulmonary CO2-elimination

We report on two patients with subcutaneous carbon dioxide (CO2) emphysema that developed during laparoscopic surgery with CO2 pneumoperitoneum (PP), in whom pulmonary elimination of CO2 (ECO2, Servo ventilator with integrated CO2 analyzer 930, Siemens) was continuously monitored. Patient 1 was a 61-year-old man with laparoscopic herniotomy. ECO2 immediately before PP was 120 ml/min x m2 and increased rapidly after 45 min PP to a maximum value of 340 ml/min x m2. At that time, minute ventilation had been increased from 7 to 11 l/min and PaCO2 had risen from 35 to 57 mm Hg. At the end of the procedure the patient showed excessive subcutaneous emphysema. Patient 2 was a 71-year-old woman in whom diagnostic laparoscopy was performed for staging of a pancreatic tumor. ECO2 immediately before PP was 140 ml/min x m2, increasing dramatically after 45 min PP to a maximum value of 529 ml/min x m2 (Fig. 1). At that time minute ventilation had been increased from 6.2 to 12.5 l/min and PaCO2 had risen from 40 to 77 mm Hg. PP was terminated and the patient was found to have extreme subcutaneous emphysema. She was mechanically ventilated for a further 40 min to normalize PaCO2 and ECO2. It seems reasonable to suppose that an increase in ECO2 by more than 100% of control during CO2-PP is an early sign of CO2 emphysema. In this situation hypercapnia is potentially life-threatening. Evidently, reabsorption of CO2 from loose connective tissue is far more rapid and effective than CO2 resorption from the peritoneal cavity.(ABSTRACT TRUNCATED AT 250 WORDS)     

CO2分压对油管钢CO2/H2S腐蚀的影响

采用高温高压釜、失重法和扫描电镜，对不同CO2分压(310．2642、930．7926、1551．3210、2171．8494kPa)条件下油管钢N80和P110的CO2／H2S腐蚀进行了研究。结果表明，随着CO2分压的升高，两种钢的CO2／H2S腐蚀速率均单调增加；除了CO2分压极低的情况以外，P110钢的腐蚀速率总是大于N80钢。     

Reduction of solid wustite in H2/H2O/CO/CO2 gas mixtures

The reduction of dense wustite in H₂/H₂O/CO/CO₂ gas mixtures has been carried out at temperatures between 1073 and 1373 K. The critical conditions for the formation of porous iron product morphologies have been identified and the results discussed in relation to the breakdown of dense iron layers on wustite surfaces. Formerly with the University of Queensland.     

Effect of Na2O on the Reduction of Fe2O3 Compacts with CO/CO2

Compacts of Fe₂O₃ and Fe₂O₃ doped with varying amounts of Na₂O were isothermally reduced at several temperatures, using CO/CO₂ mixed gas in a vertical resistance furnace. To determine the effect of Na₂O on the reduction of Fe₂O₃ compacts, the mass loss due to oxygen removal was continuously recorded, from which the reduction rate and rate constant were obtained. Na₂O was found to retard the reduction of Fe₂O₃ compacts. The apparent activation energy (E _a) of reaction and the mathematical relationship for pore gas diffusion suggested that the reduction behavior at the initial stages was controlled by a combination of pore gas diffusion and interfacial chemical reaction. At the intermediate and late stages of reduction, pore gas diffusion was the sole contributing factor. Morphological examination of the reduced compacts showed the formation of a liquid phase during the reduction process, which appeared to lower the rate of reaction.     

碳酸盐中二氧化碳的测定

本文叙述了碳酸盐中二氧化碳的测定方法,通过试验研究,提出了用酸分解试样,产生的二氧化碳用烧碱石棉吸收,根据重量差别,计算出二氧化碳含量检测方法。该方法简单、准确,用于生产分析,结果满意。     

转炉应用CO2技术

 通过对转炉顶吹CO2的热力学分析,结合实验室模拟转炉顶吹O2＋CO2混合气体试验结果,确立了CO2在转炉中应用的关键参数。得出在转炉中顶吹纯CO2虽可脱碳,但温降较大,顶吹CO2供气强度为3.0 m3/(t·min)时,钢液温降速率为15.1 ℃/min;通过喷吹O2＋CO2混合气体可实现温度平衡,但CO2配比的最大理论比例为79.1%;随着混合气体中CO2比例增大,吹炼终点钢液碳氧积降低,当[φ(CO2)∶][φ(O2)＝1][∶]1时可控碳氧积为(25～32)×10－8。     

The nu1 + 5nu3 Dyad of 12CO2 and 13CO2

It has been recently shown that intraventricular injections of nerve growth factor (NGF) prevent the effects of monocular deprivation in the rat. We have tested the localization and the molecular nature of the NGF receptor(s) responsible for this effect by activating cortical trkA receptors in monocularly deprived rats by cortical infusion of a specific agonist of NGF on trkA, the bivalent antirat trkA IgG (RTA-IgG). TrkA protein was detected by immunoblot in the rat visual cortex during the critical period. Rats were monocularly deprived for 1 week (P21-28) and RTA-IgG or control rabbit IgG were delivered by osmotic minipumps. The effects of monocular deprivation on the ocular dominance of visual cortical neurons were assessed by extracellular single cell recordings. We found that the shift towards the ipsilateral, non-deprived eye was largely prevented by RTA-IgG. Infusion of RTA-IgG combined with antibody that blocks p75NTR (REX), slightly reduced RTA-IgG effectiveness in preventing monocular deprivation effects. These results suggest that NGF action in visual cortical plasticity is mediated by cortical TrkA receptors with p75NTR exerting a facilitatory role.     

CO2 conversion and decarburization kinetics of CO2 gas and liquid Fe-C alloy at 1873 K

The reactions between CO2 gas and liquid Fe-C alloy with different initial carbon concentrations at 1873 K were investigated using experimental results,thermody...     

CO2 电弧焊接工艺实践

CO2电弧焊是一种高效率的焊接方法，是二十世纪50年代初期发展起来的一种新的焊接技术，现在已在国内外获得广泛应用。舞钢机加公司铆锻车间也已经普遍使用。现将其焊接工艺介绍如下，供大家参考。     

CO2 laser surgery in osteomyelitis

Spirituality is a critical component of the holistic mind-body-spirit model embraced by Hospice. Hospice chaplains, as part of the caregiving team, must understand their abilities and limitations in providing spiritual guidance to others who may differ in religious and spiritual beliefs.