619 research outputs found
Insights into finding a mismatch through the structure of a mispaired DNA bound by a rhodium intercalator
We report the 1.1-Å resolution crystal structure of a bulky rhodium complex bound to two different DNA sites, mismatched and matched in the oligonucleotide 5'-(dCGGAAATTCCCG)2-3'. At the AC mismatch site, the structure reveals ligand insertion from the minor groove with ejection of both mismatched bases and elucidates how destabilized mispairs in DNA may be recognized. This unique binding mode contrasts with major groove intercalation, observed at a matched site, where doubling of the base pair rise accommodates stacking of the intercalator. Mass spectral analysis reveals different photocleavage products associated with the two binding modes in the crystal, with only products characteristic of mismatch binding in solution. This structure, illustrating two clearly distinct binding modes for a molecule with DNA, provides a rationale for the interrogation and detection of mismatches
The Emerging Role of E-Agribusiness - State of the Art and Perspectives in Germany
The aim of this paper is to describe and analyse the emerging role of electronic agribusiness and the corresponding consequences in Germany. The study was carried out as a consecutive step by step procedure, including empirical surveys in farm and agribusiness small and medium size enterprises, accompanied by case studies in agribusiness firms, and a technology assessment expert survey. The results indicate that internet penetration on farm and agribusiness enterprise levels is rather high, but currently information and communication activities clearly dominate over commercial business activities. The case studies show that the internal communication changed significantly due to the implementation of internet applications like emailing, newsgroups, periodic information sheets and video-conferencing. Additionally, external communication changes according to the availability of internet features, e.g. suppliers of parts established internet networks for co-ordinated sales activities. The technology assessment expert survey indicates a gain in importance for pre- and after-sales services and communication activities by using internet technologies. Conclusions are - among others - an increasing importance of e-agribusiness and correspondingly an acceleration of structural change, but low or no expected effects on ecological parameters and on the labour market.E-Business, E-Agribusiness, Technology assessment, Survey, Germany, Agribusiness,
The mechanism of oxygen isotope fractionation during N2O production by denitrification
The isotopic composition of soil-derived N2O can help differentiate between N2O production pathways and estimate the fraction of N2O reduced to N2. Until now, δ18O of N2O has been rarely used in the interpretation of N2O isotopic signatures because of the rather complex oxygen isotope fractionations during N2O production by denitrification. The latter process involves nitrate reduction mediated through the following three enzymes: nitrate reductase (NAR), nitrite reductase (NIR) and nitric oxide reductase (NOR). Each step removes one oxygen atom as water (H2O), which gives rise to a branching isotope effect. Moreover, denitrification intermediates may partially or fully exchange oxygen isotopes with ambient water, which is associated with an exchange isotope effect. The main objective of this study was to decipher the mechanism of oxygen isotope fractionation during N2O production by denitrification and, in particular, to investigate the relationship between the extent of oxygen isotope exchange with soil water and the δ18O values of the produced N2O. We performed several soil incubation experiments. For the first time, ∆17 O isotope tracing was applied to simultaneously determine the extent of oxygen isotope exchange and any associated oxygen isotope effect. We found bacterial denitrification to be typically associated with almost complete oxygen isotope exchange and a stable difference in δ18O between soil water and the produced N2O of δ18O(N2O / H2O) = (17.5±1.2) ‰. However, some experimental setups yielded oxygen isotope exchange as low as 56 % and a higher δ18O(N2O / H2O) of up to 37‰. The extent of isotope exchange and δ18O(N2O / H2O) showed a very significant correlation (R2 = 0.70, p < 0.00001). We hypothesise that this observation was due to the contribution of N2O from another production process, most probably fungal denitrification. An oxygen isotope fractionation model was used to test various scenarios with different magnitudes of branching isotope effects at different steps in the reduction process. The results suggest that during denitrification the isotope exchange occurs prior to the isotope branching and that the mechanism of this exchange is mostly associated with the enzymatic nitrite reduction mediated by NIR. For bacterial denitrification, the branching isotope effect can be surprisingly low, about (0.0±0.9) ‰; in contrast to fungal denitrification where higher values of up to 30‰ have been reported previously. This suggests that δ18O might be used as a tracer for differentiation between bacte- 5 rial and fungal denitrification, due to their different magnitudes of branching isotope effect
Oxygen isotope fractionation during N2O production by soil denitrification
The isotopic composition of soil-derived N<sub>2</sub>O can help differentiate
between N<sub>2</sub>O production pathways and estimate the fraction of N<sub>2</sub>O
reduced to N<sub>2</sub>. Until now, <i>δ</i><sup>18</sup>O of N<sub>2</sub>O has been rarely
used in the interpretation of N<sub>2</sub>O isotopic signatures because of the
rather complex oxygen isotope fractionations during N<sub>2</sub>O production by
denitrification. The latter process involves nitrate reduction mediated
through the following three enzymes: nitrate reductase (NAR), nitrite
reductase (NIR) and nitric oxide reductase (NOR). Each step removes one
oxygen atom as water (H<sub>2</sub>O), which gives rise to a branching isotope
effect. Moreover, denitrification intermediates may partially or fully
exchange oxygen isotopes with ambient water, which is associated with an
exchange isotope effect. The main objective of this study was to decipher
the mechanism of oxygen isotope fractionation during N<sub>2</sub>O production by
soil denitrification and, in particular, to investigate the relationship
between the extent of oxygen isotope exchange with soil water and the
<i>δ</i><sup>18</sup>O values of the produced N<sub>2</sub>O.
<br><br>
In our soil incubation experiments Δ<sup>17</sup>O isotope tracing was applied
for the first time to simultaneously determine the extent of oxygen isotope
exchange and any associated oxygen isotope effect. We found that N<sub>2</sub>O
formation in static anoxic incubation experiments was typically associated
with oxygen isotope exchange close to 100 % and a stable difference
between the <sup>18</sup>O ∕ <sup>16</sup>O ratio of soil water and the N<sub>2</sub>O
product of
<i>δ</i><sup>18</sup>O(N<sub>2</sub>O ∕ H<sub>2</sub>O) = (17.5 ± 1.2) ‰.
However, flow-through experiments gave lower oxygen isotope exchange down to
56 % and a higher <i>δ</i><sup>18</sup>O(N<sub>2</sub>O ∕ H<sub>2</sub>O) of up to
37 ‰. The extent of isotope exchange and
<i>δ</i><sup>18</sup>O(N<sub>2</sub>O ∕ H<sub>2</sub>O) showed a significant correlation
(<i>R</i><sup>2</sup> = 0.70, <i>p</i> < 0.00001). We hypothesize that this
observation was due to the contribution of N<sub>2</sub>O from another production
process, most probably fungal denitrification.
<br><br>
An oxygen isotope fractionation model was used to test various scenarios with
different magnitudes of branching isotope effects at different steps in the
reduction process. The results suggest that during denitrification, isotope
exchange occurs prior to isotope branching and that this exchange is mostly
associated with the enzymatic nitrite reduction mediated by NIR. For
bacterial denitrification, the branching isotope effect can be surprisingly
low, about (0.0 ± 0.9) ‰, in contrast to fungal
denitrification where higher values of up to 30 ‰ have been reported
previously. This suggests that <i>δ</i><sup>18</sup>O might be used as a tracer for
differentiation between bacterial and fungal denitrification, due to their
different magnitudes of branching isotope effects
Remote Ligand Modifications Tune Electronic Distribution and Reactivity in Site-Differentiated, High-Spin Iron Clusters: Flipping Scaling Relationships
We report the synthesis, characterization, and reactivity of [LFe₃O(^RArIm)₃Fe][OTf]₂, the first Hammett series of a site-differentiated cluster. The cluster reduction potentials and CO stretching frequencies shift as expected on the basis of the electronic properties of the ligand: electron-donating substituents result in more reducing clusters and weaker C–O bonds. However, unusual trends in the energetics of their two sequential CO binding events with the substituent σ_p parameters are observed. Specifically, introduction of electron-donating substituents suppresses the first CO binding event (ΔΔH by as much as 7.9 kcal mol⁻¹) but enhances the second (ΔΔH by as much as 1.9 kcal mol⁻¹). X-ray crystallography, including multiple-wavelength anomalous diffraction, Mössbauer spectroscopy, and SQUID magnetometry, reveal that these substituent effects result from changes in the energetic penalty associated with electronic redistribution within the cluster, which occurs during the CO binding event
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