13 research outputs found
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