Oxygen Bonding to Haemoglobin. 17O NMR Spectrum A Second Look

It was found that the upper concentration limit in detecting the oxygen-17 NMR signal from ordinary solvent water in solutions of oxyhaemoglobin is about 12 · 10-3 M (in haem). From samples of oxyhaemoglobin prepared with oxygen gas enriched to 62° /o in 170 a signal could be detected within a few days in spite of higher protein concentrations. Such signals increased in couple of weeks up to three times. However, within this period of time the sealed, dissolved oxyhaemoglobin became deoxygenated showing the characteristic colour change, while the NMR 170 signal persisted. The pressure above such sealed solutions diminished and the mass-spectroscopic analyses showed two- to threefold enrichment in 170 of solvent water after the deoxy-conversion, while in the gas phase oxygen ¥,Tas replaced by carbon dioxide. There is no deoxy-conversion in samples prepared under sterile conditions or in presence of sodium azide (equimolar with haem). It is concluded that owing to bacterial contamination in haemoglobin solutions prepared under ordinary conditions oxygen from the gas-phase is being reduced into water through bacterial metabolism. Thus, the observed 170 NMR signals were due to the solvent water enriched in 170. A former paper* claiming detection of 170 NMR signal from oxygen bound to haemoglobin is thus invalidated

Oxygen Bonding to Haemoglobin. 17O NMR Spectrum A Second Look

It was found that the upper concentration limit in detecting the oxygen-17 NMR signal from ordinary solvent water in solutions of oxyhaemoglobin is about 12 · 10-3 M (in haem). From samples of oxyhaemoglobin prepared with oxygen gas enriched to 62° /o in 170 a signal could be detected within a few days in spite of higher protein concentrations. Such signals increased in couple of weeks up to three times. However, within this period of time the sealed, dissolved oxyhaemoglobin became deoxygenated showing the characteristic colour change, while the NMR 170 signal persisted. The pressure above such sealed solutions diminished and the mass-spectroscopic analyses showed two- to threefold enrichment in 170 of solvent water after the deoxy-conversion, while in the gas phase oxygen ¥,Tas replaced by carbon dioxide. There is no deoxy-conversion in samples prepared under sterile conditions or in presence of sodium azide (equimolar with haem). It is concluded that owing to bacterial contamination in haemoglobin solutions prepared under ordinary conditions oxygen from the gas-phase is being reduced into water through bacterial metabolism. Thus, the observed 170 NMR signals were due to the solvent water enriched in 170. A former paper* claiming detection of 170 NMR signal from oxygen bound to haemoglobin is thus invalidated

Emergence of scale-free leadership structure in social recommender systems

The study of the organization of social networks is important for understanding of opinion formation, rumor spreading, and the emergence of trends and fashion. This paper reports empirical analysis of networks extracted from four leading sites with social functionality (Delicious, Flickr, Twitter and YouTube) and shows that they all display a scale-free leadership structure. To reproduce this feature, we propose an adaptive network model driven by social recommending. Artificial agent-based simulations of this model highlight a "good get richer" mechanism where users with broad interests and good judgments are likely to become popular leaders for the others. Simulations also indicate that the studied social recommendation mechanism can gradually improve the user experience by adapting to tastes of its users. Finally we outline implications for real online resource-sharing systems