Search

A eletro-oxidação de ácido fórmico vem sendo discutida por muito tempo na literatura, em particular, a natureza do intermediário ativo no caminho direto tem sido debatida. Recentemente alguns grupos relataram novos aspectos deste processo por meio da análise da oxidação de ácido fórmico e sua dependência com o pH da solução. A maioria dos estudos, no entanto, foi realizado sob condições convencionais, ou seja, próximas ao estado de equilíbrio termodinâmico. Alternativamente, o sistema pode ser estudado longe do equilíbrio pelo controle da corrente, nessas condições a oxidação de moléculas orgânicas pequenas sobre platina pode apresentar a formação de padrões e mostrar comportamentos oscilatórios. Pelas condições drasticamente diferentes se poderia alcançar um melhor entendimento do rede complexo de reação, qual fica escondido em experimentos convencionais. Dessa maneira, a dependência do pH de oxidação de ácido fórmico foi revisitada em voltametria cíclica e estendida a uma ampla região de temperatura e condições oscilatórias. Algumas observações adicionais podem ser obtidas: a) a dependência do pH, como relatada anteriormente, pode ser reproduzida, reforçando a proposição do formiato mais provável como espécie ativa, em lugar do ácido fórmico; b) em meio ácido um terceiro caminho ao lado dos caminhos direito e indireto poderia ser ativo; c) padrões oscilatórios foram encontrados em meio alcalino e evidenciaram o carácter bloqueante de espécies oxigenadas como responsável pela formação de padrões; d) geralmente, todos os processos envolvidos diretamente ou indiretamente, podem ser muito propensos a variações pequenas no pH e temperatura da solução, que a atividade deles pode mudar significativamente e o sistema apresentar resultados diferentes sob condições similares. Adicionalmente, os estudos foram estendidos à oxidação de metanol, qual permitido um visto diferenciado na adsorção de espécies carbonáceas e oxigenadas, as quais principalmente poderiam ter caráter inibitório. Apesar disso, como os resultadas mostraram sob algumas condições, uma interação efetiva de ambas espécies via o mecanismo de Langmuir-Hinshelwood pode ocorrer, que o caminho direito da oxidação pode mostrar uma atividade mais alta e as padrões oscilatórios desaparecem. Observou-se ainda que o ácido fórmico produzido como subproduto parcialmente oxidado poderia ter um papel importante na reação da eletro-oxidação de metanol. Ao fim foi encontrado que não apenas ajustamentos como ligar platina com ouro pode melhorar o desempenho do catalisador pelos efeitos eletrônicos e ligantes, mas também modificações no conteúdo da solução, como a oxidação simultânea do ácido fórmico e metanol poderiam permitir um aumento no desempenho. Em ambos os casos a formação de CO pode ser oprimida, que o processo mais ativo, notadamente a oxidação direta do ácido fórmico é mais pronunciada. The electro-oxidation of formic acid remained under discussion for a long time in literature, where especially the active intermediate in the direct oxidation pathway was discussed controversially. Recently some groups reported new insight by the analysis of the formic acid oxidation in dependence on the bulk solution pH. Yet, the majority of the studies are carried out under conventional conditions, which are close to the thermodynamic equilibrium. On the other hand the system can be driven far from equilibrium by controlling the current, conditions where the oxidation of small organic molecules over platinum may undergo pattern formation and show oscillatory behaviour. Due to the drastically different conditions one may get a better understanding of the complex reaction network, which remains hidden in conventional experiments. Thus, the pH dependence of formic acid oxidation was revisited under steady state voltammetry and extended to a wide temperature range and oscillating conditions. Here insight could be given in various points: a) the pH dependence, as reported earlier, could be reproduced and strongly suggests formate rather than formic acid as most active species; b) in acidic media a third pathway beside direct and indirect ones may be active; c) newly found oscillation patterns in alkaline media revealed the site blocking character of adsorbed water species as possible origin for pattern formation; and d) generally, all surface processes, which are directly or indirectly involved, can be very susceptible to small variations in the bulk solution pH and temperature, that their activity can change significantly and the system emerge different results under similar conditions. Further effort was done to extend the study to methanol oxidation, which allowed a differentiated view on the adsorption of carbonaceous and oxygenated species, which may have mostly inhibiting character. Yet, as the results showed under some conditions, an effective interaction of both species via Langmuir-Hinshelwood mechansim can be realized, that the direct oxidation pathway can undergo higher activity and oscillation patterns may cease. It could also be found, that the produced formic acid as partially oxidized by-product may have a crucial role in the reaction network of the electro-oxidation of methanol. At last it could be found, that not just adjustments like alloying of platinum with gold can enhance the catalyst performance by electronic and ligand effects, but also modifications in the solution content, such as simultaneous oxidation of formic acid and methanol allow an increasing performance. In both ways the formation of CO can be suppressed, that the most active process, namely the direct oxidation of formic acid is more pronounced.

Cold atmospheric pressure plasma from a plasma jet was used to improve the adhesion properties of polypropylene (PP). Differences in adhesion were at first observed for either air or N2 as process gas, tested on a PP-acrylic pressure sensitive adhesive (PSA) model system. For a deeper understanding changes in the surface chemistry and topography on PP after plasma jet treatment, using several different O2/N2 mixtures, were investigated in a comprehensive surface analytical study. Independent of the gas composition a majority of plasma induced polar groups exist as water soluble low molecular weight oxidized material (LMWOM), located within the first few nanometers. Consequently, the observed changes in the surface chemistry for various process gas compositions are mainly attributed to differences in the formed LMWOM. However, these chemical changes indicated also differences in the interaction mechanism of plasma reactive species with the polymer surface and therefore, in the resulting plasma-polymer etching process. Hence, significant changes in the topography have been observed for different process gas compositions, which could be reliably correlated with the obtained adhesion results.

Allgemeine Prinzipien der perioperativen Kreislaufuberwachung Die Uberwachung der postoperativen Herz-Kreislauf-Funktion bzw. des Volumenhaushaltes stutzt sich im Wesentlichen auf eine nichtinvasive Funktionsdiagnostik, ferner auf die Bestimmung der Hamoglobinkonzentration im Plasma und auf die Inspektion von Wundgebiet und Drainageflussigkeit. Nach groseren Eingriffen bzw. schweren chirurgischen Traumata wird eine zunehmende Invasivitat der postoperativen Uberwachungsmasnahmen erforderlich, die mit dem zusatzlichen Einsatz eines zentralen Venenkatheters (ZVK) beginnt, in der nachsten Stufe die zusatzliche kontinuierliche Uberwachung der Urinausscheidung und zuletzt die kontinuierliche invasive Uberwachung des arteriellen Blutdrucks umfasst. Das Ausmas der Laboruberwachung bzw. der klinischen Kontrollen wird ganz wesentlich durch den intraoperativen Verlauf (Blutungskomplikationen, Gerinnungsversagen, diffuse Diathese) vorgegeben. ◘ Tab. 78.1 fasst die allgemeinen Zielwerte der postoperativen Uberwachung zusammen. Die Differenzialdiagnostik der postoperativen Kreislaufinsuffizienz orientiert sich an der Pathophysiologie, die im Wesentlichen Storungen des Volumenhaushaltes, des peripheren Widerstandes und der myokardialen Pumpfunktion beinhaltet.

In the present study, the erythropoietic activity of fetal serum was characterized. Using fetal bovine serum (FBS) as a source of the erythropoietic activity and serum-free cultures of fetal mouse livers (FMLC assay) as a detection system, we found that FBS stimulated colony formation from late erythroid progenitor cells (CFU-E) in a dose-dependent fashion. The slope of the dose-response curve, however, was significantly different from that for erythropoietin (Ep), the best-characterized erythropoietic activity so far. The erythropoietic activity of FBS was found in the 120-160- and 40-70-kD range at neutral pH. In the presence of 1 M acetic acid, however, the erythropoietic activity had an apparent molecular mass between 3 and 13 kD. From ion exchange experiments with DEAE-cellulose, the isoionic point of the activity was estimated to about pH 5. Furthermore, the erythropoietic activity of FBS was found to be co-eluted on Sephadex G-150 with the binding proteins of insulinlike growth factors (IGF). The IGF I concentration determined by radioimmunoassay was 70 ng IGF I/ml. The Ep activity of FBS was less than 5 mU/ml when determined with the posthypoxic polycythemic mouse assay for Ep. These results suggest that the erythropoietic activity of FBS is related to IGF and not to Ep. The erythropoietic activity of FBS was abolished by an antiserum against IGF I. Furthermore, IGF I was a factor of approximately 40 more potent than IGF II in stimulating erythroid colony formation. All of these findings suggest that the erythropoietic activity of FBS is IGF I.

We studied the hormonal millieu and possibility of altered thyroid function in 25 patients in a surgical intensive care unit (ICU) who had severe life-threatening illnesses. Sixteen patients had septic complications and nine patients had multiple-system injuries. On admission to the ICU, serial measurements were begun of thyroxine (T4), triiodothyronine (T3), T4-binding globulin, thyrotropin (thyroid-stimulating hormone [TSH]), corticotropin (adrenocorticotropic hormone [ACTH]), cortisol, prolactin, human growth hormone, catecholamine, insulin and glucose, lactate, retinol-binding protein, prealbumin, and transferrin levels. All patients initially had low normal levels of T4 (4.5 +/- 2 micrograms/dL) and T3 (55 +/- 26 ng/dL), with normal TSH levels (2.3 +/- 2.3 microU/mL) (the "low T3 syndrome"). The 11 surviving patients had their levels increase to normal before leaving the ICU (T4, 7.0 +/- 2.1 micrograms/dL; T3, 110 +/- 48 ng/dL; and TSH, no change). The 14 patients who died showed further decreases before death (T4, 2.6 +/- 2.1 micrograms/dL; T3, 30.6 +/- 23.5 ng/dL; and TSH, 0.9 +/- 0.7 microU/mL). The corticotropin, cortisol, prolactin, and growth hormone levels were normal throughout the study. Catecholamine levels were high initially and decreased in surviving patients. Epinephrine levels increased greatly in nonsurvivors before death, and the norepinephrine-epinephrine ratio decreased from 5.7:1 to 2:1. After protirelin (thyroid-releasing hormone [TRH]) stimulation, the TSH level increased either minimally or not at all in six patients who eventually died. This indicates hypothalamic-pituitary dysregulation or suppression, and altered release and/or peripheral metabolism of T4. Whether this represents a deficiency of thyroid hormone for cell and organ function remains to be established.