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yxfandrew

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小弟因实验紧张，无法完成老师布置的翻译文献的任务。特此悬赏100金币，求一篇文献的中文翻译。

Environ. Sci. Technol. 2003, 37, 2929-2935

Solid-State and Multidimensional Solution-State NMR of Solid Phase
Extracted and Ultrafiltered Riverine Dissolved Organic Matter

要求：1.周4中午之前给我翻译稿
2.翻译要准确通顺（准确度95％以上）

[ Last edited by yxfandrew on 2007-6-13 at 10:03 ]

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yxfandrew

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Chemical Extraction versus Physical Fractionation: A
Comparison. In general, C18 solid phase extraction separates
molecules according to hydrophobicity, and ultrafiltration
separates by size and shape. Solid-state 13C NMR analysis of
DOM samples prepared by solid phase extraction show
elevated aliphatic:aromatic ratios compared to ultrafiltered
samples (Table 1).Whencomparing solid-stateNMRspectra
of seasonally collected DOM by both techniques, we can
resolve large differences in broad resonances and, thus, in
the chemical composition of these two types ofDOMisolates
(Figure 1).
As shown in Figure 1, the coarse resolution of solid-state
NMR allows us to discriminate only to a certain extent the
different chemical structure of isolated DOM fractions.
Solution-state NMR better resolves molecular patterns in
DOMstructure. Solid phase extractedDOMmainly contains
aliphatic esters, ethers, hydroxyl groups, and smaller quantities
of sugars. Ultrafiltered DOM is partially composed of
peptides and proteins, with further evidence for aliphatic/
fatty acid materialandsugars.Thesolid-state 13CNMRspectra
indicate a higher content of aromatic material in this fraction,
as compared with the solid phase extracted DOM fraction.
It appears as if C18 solid phase extraction preferentially
selects for aliphatic compounds and loses important structures
such as proteins, aromatics, and some sugars. Ultrafiltration
recovers amuchwider range of biomacromolecules,
dominated by proteins, sugars, and fatty acids.
Environmental Significance. Resolving the molecular
traits of freshwater DOM components is key for understanding
the sources and processing of organic compounds in
riverine systems and their role in the global carbon cycle.
Rivers not only transport but also transform organic compounds
and therefore link the carbon cycle of the continents
to that of the oceans (24, 25).
NMR analysis of solid phase extracted DOM from the
River Tagliamento hasshowna dominance of aliphatic esters.
As bacteria and microalgae constitute an important pool of
living biomass in aquatic systems and are major sources for
DOM (26, 27), we suggest that this lipophilic DOM isolate
comprises important microbialmembranecomponents such
as those found in prokaryotes and algae. Similar sources
were identified for hydrophobic-type DOM extracted from
soils (28, 29). The ether and hydroxyl groups identified in the
solid phase extracted DOM are associated with aliphatic
chains and hence are probably derived from either transformed
plant inputs into the river, such as plant cuticles, or
from hydroxy fatty acids, generally indicative of cellular
material.Wealso identified some signals attributed to sugars,
which are derived from multiple sources such as cellulose
and hemicellulose from vascular plants, algal biomass, and
microorganisms (1, 6, 30).Wesuggest a predominant vascular
plant origin for these sugars because these materials constitute
substantial components of riparian vegetation (26,
31), and there is tight coupling between terrestrial and aquatic
areas along the River Tagliamento. The presence of sugars
indicates that these compounds are either diagenetically
reworked or persist protected and therefore escape degradation
processes. A recent study by Kaiser et al. (in preparation)
showed that the utilization of this solid phase extractedDOM
by natural bacterioplankton was very low and reflected its
nonreactive nature.
The analysis of ultrafiltered DOM from the River Tagliamento
shows the presence of peptide/protein-type compounds.
Their occurrence is of special interest because
proteins/peptides are usually viewed as labile DOM components
with relatively short biological turnover times,
ranging on the order of minutes to hours (32). However,
Kaiser et al. (in preparation) found that this ultrafilteredDOM
was not readily consumed by natural bacterioplankton. The
protein/peptide structures identified from the ultrafiltered
DOM may indicate the presence of degradation-resistant
protein structures, possibly bacterial-derived membrane
components or carbohydrate cross-linked amides (33, 34).
The formation of microbially resistant ligno-protein complexes
in humus has been documented (35). Several recent
studies proposed the encapsulation of protein in humic acids
(16, 36). If proteins contained in the ultrafiltered DOM from
the River Tagliamento, originated from surrounding soils,
theymayhave undergone similar diagenetic transformations,
making them less susceptible to microbial utilization. For
future studies, we suggest to investigate the structure and
bioavailability of this protein/peptide-rich material to better
understand its origin, transformation, and fate in natural
freshwater and marine systems. Furthermore, we emphasize
the potential of 2-DNMRstudies added to the list of methods
that can be utilized in such ventures.
Acknowledgments
The authors are grateful to the Tagliamento Research Group
for their enormous assistance with water sampling and other
field work. We specially thank Yu-Ping Chin for all his
enthusiasm, consistent support, and advice tomakethis work
possible. Many critical comments by Laura Sigg, Andreas
Kappler, Christopher Robinson, and Jim Burdon helped to
considerably improve the manuscript. This work was supported
by EAWAG and the National Science Foundation
(OCE-9711596), (CHE-0089147) and (CHE-0089173). The
NMRspectra were recorded in the Department of Chemistry,
The Ohio State University, Columbus, OH.