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悬赏100金币代翻译文献一篇（周4交货） 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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9楼2007-06-13 14:22:18
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In this study we used multidimensional solution-state NMRto elucidate the differences in the chemical composition of solid phase extracted and ultrafiltered DOM isolates. DOM was isolated from water sampled from an oligotrophic river, the River Tagliamento (Italy). The recovery of total DOMwas up to 42% with both isolation techniques. In addition to 1- and 2-D solution-state NMR, we also applied 1-D solidstate 13C NMR spectroscopy for DOM characterization. 13C NMR spectroscopy only produced broad overlapping resonances, thus allowing a bulk characterization of DOM composition. However, it demonstrated that the bulk chemical composition of the two DOM fractions exhibited minor spatial-temporal changes. The 2-D experiments (TOCSY, HMQC) showed that the solid phase extracted hydrophobic DOM contained predominantly aliphatic esters, ethers, and hydroxyl groups, whereas the ultrafiltered DOM was comprised partially of peptides/protein, with further evidence for a small amount of aliphatic/fatty acid material. Sugars were present in both DOM fractions. The results show the two isolation techniques selected for different suites of compounds within the bulk DOM pool. Introduction Multiple analysis techniques, ranging from NMR spectroscopy to GC-MS, have been applied to examine the specific chemical features of DOM (1-4). Most of these techniques require that DOM, present in low concentrations in natural water samples, be concentrated using isolation methods such as XAD or C18 solid phase extraction and ultrafiltration (5). These methods also allow recoveringDOMas a solid powder that can be analyzed by solid-state NMR (6, 7). Hitherto, mostly one-dimensional (1-D)NMRspectroscopy, solid-state 13C NMR in particular, was applied to elucidate the DOM chemical composition. However,manypublished solid-state 13C NMR spectra exhibit only broad resonance peaks and often suffer from poor spectral quality due to sample complexity, and some even contain “spinning sidebands”. Advances in solid-state NMR have drastically reduced the effect of spinning sidebands and allow the analysis of smaller sample quantities with increased sensitivity (8). Nevertheless, theseNMRspectra still often exhibit broad overlapping peaks, due to the presence of paramagnetic materials and the dipolar interactions present in solid materials. In contrast, multidimensional solution-state NMR can give highly resolved information, even for complex mixtures (9). Multidimensional experiments (10) can be used to correlate the chemical shifts of different carbon and proton atoms and identify shortand long-range connectivities. In using isolation techniques to concentrate DOM, one must be aware that different isolation methods, e.g., C18 solid phase extraction and ultrafiltration, select for chemically different compounds. This is the first study in which homoand multinuclear solution-stateNMRmethods were used to compare the chemical composition of DOM isolated by C18 solid phase extraction and ultrafiltration. The goals of our study were (i) to use state-of-the-art NMR methods to elucidate the differences in the chemical composition ofDOM isolates derived by chemical and physical fractionation techniques and (ii) to demonstrate that solution-state NMR spectroscopy is a tool of high potential for investigating the molecular nature of heterogeneousDOMmixtures.Weshow that NMR methods improve functional group assignments and aid in the understanding of DOM chemical structure. Materials and Methods Study Area and Sample Collection. C18 solid phase extracted hydrophobicandultrafilteredDOMsamplescomefrom water of the Tagliamento River, northeastern Italy. The river is the last unregulated river in Europe, flowing unrestrained from the alpine headwaters to its mouth in the northern Adriatic Sea (11). Water samples for C18 solid phase extraction and ultrafiltration were collected seasonally from the main channel in the headwater, major, and transition flood plains from spring 1999 to 2000. The samples are part of a larger study in which material was collected seasonally from three longitudinally aligned stations (Kaiser et al., in preparation). Water was collected during low-, medium-, and high-flow conditions (Table 1). Throughout the year, the main channel river water displayed temperatures of 10.9(2.5 °C,pHvalues of 8.13(0.14, and alkalinities of 2.8(0.5mM.Water samples for DOM fractionation were collected with clean 50 L highdensity polyethylene (HDPE) carboys and transported back to the field station. Immediately following collection, water samples were filtered through muffled glass fiber filters (GF/F) and prerinsed 0.2 ím Durapore filters (142 mm diameter, Millipore) and stored in clean 50 L carboys. DOM Fractionation and Isolation. For chemically fractionating DOM into hydrophobic and hydrophilic compounds, a Mega Bond Elute C18 column (C18 loaded silica, 60CC, Varian) was used after acidification with 32% hydrochloric acid (Suprapur) topH2.8. Flow rates ranged between 3 and 5 L h-1. Of the total dissolved organic carbon (DOC <0.2 ím), 29-42% was recovered as a sorbed hydrophobic fraction (Table 1), being comparable to other literature values (7, 12). A Filtron tangential flow ultrafiltration system with a polyethersulfone membrane (1 kDa nominal weight cutoff) was used for fractionating bulk DOM into pseudo high- and low-molecular weightDOMportions, following the protocol of Benner et al. (13). Filtration rates ranged between 6 and 8Lh-1 using one 0.46m2 cassette filter (Centrasette, Filtron). The water temperature ranged from 20 to 22 °C during ultrafiltration. Recovery of isolated DOC was 12-22% of the total DOC (Table 1). The total organic carbon (TOC) concentrations of the unfiltered water and the DOC concentrations of all different DOM fractions were measured to determine a carbon mass balance (Table 1). Samples were stored at 4 °C in the dark and immediately transported to the laboratory (EAWAG, Switzerland). DOM adsorbed on the C18-phase was eluted by gentle vacuum-filtration using HPLC-grade methanol (Merck). The methanol was removed from the DOM by rotoevaporation and freeze-drying. Next, the extract was redissolved in MQ-UV water (Millipore). The aqueous solid phase extracted or ultrafiltered DOM samples were cationexchanged (Bio-Rad,AG50WandAGMP-50) to remove trace metals (14) andthen concentrated by freeze-drying for further elemental and spectroscopic characterization. Tar-like ultrafilteredDOM(except the spring 2000 sample) was redissolved in methanol and freeze-dried. However, we could not reach solid phase or completely remove all the methanol from the ultrafiltrate, as shown by the intense resonance at 55 ppm in the solid-state NMR spectra (Figure 1E-G). Redissolution in MQ-UV water, neutralization to pH 8.1, and subsequent freeze-drying finally resulted in reaching a solid phase. The dried material was scraped from the Teflonbeaker and stored sealed in muffled glass tubes (Supelco) at 4 °C in the dark. Solution-state NMR experiments were performed only on solid phase extracted DOM from early summer 1999 and ultrafiltered DOM from spring 2000, due to sufficient time and sample availability. TOC and DOC Measurements. Water samples were collected directly after fractionation for ultrafiltered samples and after freeze-drying and redissolution in MQ-UV water for solid phase extracted DOM. The samples were collected in acid-rinsed, muffled 40 mL EPA glass vials, sealed with Teflon-lined caps, and stored frozen until analysis. TOC and DOC concentrations were determined by high-temperature catalytic oxidation with a Shimadzu 5050A analyzer (15). Solid-State 13C Ramp NMR Spectroscopy. NMR spectra were obtained as described by Zang et al. (16) and Dria et al. (8) using the ramp cross polarization magic angle spinning (ramp CPMAS) pulse program and two pulse phase modulated (TPPM) decoupling on a Bruker DSX 300 NMR spectrometer, operating at a frequency of 300 MHz for 1Hor 75.48 MHz for 13C. Approximately 20-30 mg of sample was placed in a 4 mm (outside diameter) NMR rotor between Teflon spacers and sealed with a Kel-F cap. Samples were spun at a frequency of 13 kHz using a contact time of 2 ms anda1srecycle delay time. For the samples, 80 000-100 000 acquisitions (scans) were collected. For each sample’s free induction decay, 1024 complex data points were collected and zero-filled to a total of 4096 data points. The samples were Fourier transformed, and 100 Hz line-broadening was applied and phased appropriately. The carboxyl carbon of glycine (176.03 ppm) provided a secondary reference for all solid-state spectra. Solution-State NMR Spectroscopy. Before analysis by NMR spectroscopy, samples were resuspended in MQ-UV water, and, to ensure solubility, thepHwas raised to 10 using a 0.1 M NaOH solution. To remove excess metal ions, the DOMsolution was passed in series over two IR-1200H cationexchange resins. The eluent was freeze-dried and further dried over P2O5 at 35 °C for 24 h to reduce the water signal in the proton NMR spectra. Finally, the DOM (20 mg) was dissolved in DMSO-d6 (0.75 mL). Solution-state NMR data were acquired using a Bruker Avance 400 MHz NMR spectrometer fitted with a QNP 1H, 13C, 15N, and 31P probe. 1-D protonNMR(1024 scans) analyses were carried out with a 2 s recycle delay time and processed with 1 Hz linebroadening. Total Correlation Spectroscopy (TOCSY) spectra (256 scans, TD (F1) 1024, TD (F2) 512) were acquired using a 60 ms mixing time, with Time-Proportional Phase Incrementation (TPPI). The data processing used a sine-squared function with a phase shift of 90° in both dimensions. Heteronuclear Multiple Quantum Coherence (HMQC) spectra (512 scans, TD (F1) 1024, TD (F2) 512, J1 (1H-13C) 145 Hz) were acquired using a BIlinear Rotation Decoupling (BIRD) pulse train and TPPI. F1 was obtained with a sine-squared function with phase shift of 90°, while F2 was processed with a Gaussian-broadening of 0.001 and line-broadening of -1. |
10楼2007-06-15 00:08:47