Five humic fractions were obtained from a uniformly 15N-labelled soil by extraction with 0.1 mol L-1 Na4P207, 0.1 mol L-1 NaOH, and HF/HCI-0.1 mol L-1 NaOH, consecutively, and analyzed by 13C and 15N CPMAS NMR (cross ...Five humic fractions were obtained from a uniformly 15N-labelled soil by extraction with 0.1 mol L-1 Na4P207, 0.1 mol L-1 NaOH, and HF/HCI-0.1 mol L-1 NaOH, consecutively, and analyzed by 13C and 15N CPMAS NMR (cross polarization and magic angle spinning nuclear magnetic resonance). Compared with those of native soils humic fractions studied as a whole contained more alkyls, methoxyls and O-alkyls, being 27%-36%, 17%-21% and 36%-40%, respectively, but fewer aromatics and carboxyls (being 14%-20% and 13%-90%, respectively). Among those humic fractions, the humic acid (HA) and fulvic acid (FA) extracted by 0.1 mol L-1 Na4P207 contained slightly more carboxyls than corresponding humic fractions extracted by 0.1 mol L-1 NaOH, and the HA extracted by 0.1 mol L-1 NaOH after treatment with HF/HCI contained the least aromatics and carboxyls. The distribution of nitrogen functional groups of soil humic fractions studied was quite similar to each other and also quite similar to that of humic fraction from native soils. More than 75% of total N in each fraction was in amide form, with 9%-13% present as aromatic and/or aliphatic amines and the remainder as hoterocyclic N.展开更多
Nitrogen forms of humic substances from a subalpine meadow soil, a latentic red soil and a weathered coal and the effect of acid hydrolysis on N structures of soil humic substances were studied by using 15N cross-pola...Nitrogen forms of humic substances from a subalpine meadow soil, a latentic red soil and a weathered coal and the effect of acid hydrolysis on N structures of soil humic substances were studied by using 15N cross-polarization magic angle spinning nuclear magnetic resonance (CPMAS NMR) spectroscopy. Of the detectable 15N-signal intensity in the spectra of soil humic substances 71%-79% may be attributed to amide groups, 10%-18% to aromatic/aliphatic amines and 6%~11% to indole- and pyrrole-like N. Whereas in the spectrum of the fulvic acid from weathered coal 46%, at least, of the total 15N-signal intensity might be assigned to pyrrole-like N, 14% to aromatic/aliphatic ammes, and the remaining intensities could not be assigned with certainty. Data on nonhydrolyzable residue of protein-sugar mixture and a 15N-labelled soil fulvic acid confirm the formation of nonhydrolyzable heterocyclic N during acid hydrolysis. Project (No. 39790100) supported by the National Natural Science Foundation of China.展开更多
X-ray photoelectron spectroscopy (XPS) was applied to examine the N structures of soil humic substances and some of their analogues. It was found that for soil humic substances XPS method gave similar results as those...X-ray photoelectron spectroscopy (XPS) was applied to examine the N structures of soil humic substances and some of their analogues. It was found that for soil humic substances XPS method gave similar results as those obtained by 15N CPMAS NMR (cross-polarization magic-angle spinning nuclear magnetic resonance) method. 70%～86% of total N in soil humic substances was in the form of amide, and 6%～13% was presented as amines, with the remaining part as heterocyclic N. There was no difference in the distribution of the forms of N between the humic substances from soils formed over hundreds or thousands of years and the newly formed ones. For fulvic acid from weathered coal and benzoqu inone- (N H-4 )-2 S O-4 polymer the XPS results deviated significantly from the 15N CPMAS NMR data.展开更多
^15N-labelled phenolic polymers were synthesized by reactions of p-benzoquinone and 1,4-diphenol with ^15N-labelled glycine and were studied by using ^15N CP-MAS NMR technique in combination with chemical approaches.R...^15N-labelled phenolic polymers were synthesized by reactions of p-benzoquinone and 1,4-diphenol with ^15N-labelled glycine and were studied by using ^15N CP-MAS NMR technique in combination with chemical approaches.Results showed that the proportion of polymer nitrogen as N-phenyl amino acid N was not as great as expected,only accounting for 5%-15%;and most of N in polymers occurred in the forms of amide,pyrrole-and indole-like nitrogen,aliphatic amines and isonitrile.It seems that great differences existed between synthetic humic acids and soil humic acids in the type and distribution of nitrogen forms.展开更多
In this paper,the nitrogen forms in newly-formed humic substances,including humic acid (HA),fulvic acid (FA) and humic acid in humin (HAI),were studied by using the ^15N CP-MAS NMR technique in combination with chemic...In this paper,the nitrogen forms in newly-formed humic substances,including humic acid (HA),fulvic acid (FA) and humic acid in humin (HAI),were studied by using the ^15N CP-MAS NMR technique in combination with chemical approaches.Results show that the majority of nitrogen in HA,FA and HAI was in the amide form with some presented as aliphatic and/ or aromatic amines and some as pyrrole type nitrogen,although the contents of nonhydrolyzable nitrogen in them differed greatly from each other (15-55%).展开更多
THE ~15N NMR study is of general interest in the analysis of the protein conformations in solu-tions. When NMR is applied to the conformation study of macrobiomolecules, a heteronuclearmultiple quantum coherence (HMQC...THE ~15N NMR study is of general interest in the analysis of the protein conformations in solu-tions. When NMR is applied to the conformation study of macrobiomolecules, a heteronuclearmultiple quantum coherence (HMQC) spectrum of ~15N is usually measured first, so that theamide protons are assigned before other experiments, such as the total correlation展开更多
The normally underused ^1H-^15N HMBC spectra of thirteen C18-diterpenoid alkaloids have been determined for the first time. As a result, the significant effects of the substituents of nitrogen atoms, the conformations...The normally underused ^1H-^15N HMBC spectra of thirteen C18-diterpenoid alkaloids have been determined for the first time. As a result, the significant effects of the substituents of nitrogen atoms, the conformations of A ring, and protonation, on the nitrogen-15 chemical shifts are demonstrated.展开更多
Apramycin is unique in the aminoglycoside family due to its octodiose moiety. However, either the biosynthesis process or the precursors involved are largely unknown. Addition of glycine, as well as serine or threonin...Apramycin is unique in the aminoglycoside family due to its octodiose moiety. However, either the biosynthesis process or the precursors involved are largely unknown. Addition of glycine, as well as serine or threonine, to the Streptomyces tenebrabrius UD2 fermentation medium substantially increases the production of apramycin with little effect on the growth of mycelia, indicating that glycine and/or serine might be involved in the biosynthesis of apramycin. The 13C-NMR analysis of [2-13C] glycine-fed (25% enrichment) apramycin showed that glycine specifically and efficiently incorporated into the only N-CH3 substituent of apramycin on the C7′ of the octodiose moiety. We noticed that the in vivo concentration of S-adenosyl methionine increased in parallel with the addition of glycine, while the addition of methione in the fermentation medium significantly decreased the productivity of apra-mycin. Therefore, the methyl donor function of glycine is proposed to be involved in the methionine cycle but methionine itself was proposed to inhibit the methylation and methyl transfer processes as previously reported for the case of rapamycin. The 15N NMR spectra of [2-13C,15N]serine labeled apramycin indicated that serine may also act as a limiting precursor contributing to the ―NH2 substituents of apramycin.展开更多
基金Project (No. 39790100) supported by the National Natural Science Foundation of China.
文摘Five humic fractions were obtained from a uniformly 15N-labelled soil by extraction with 0.1 mol L-1 Na4P207, 0.1 mol L-1 NaOH, and HF/HCI-0.1 mol L-1 NaOH, consecutively, and analyzed by 13C and 15N CPMAS NMR (cross polarization and magic angle spinning nuclear magnetic resonance). Compared with those of native soils humic fractions studied as a whole contained more alkyls, methoxyls and O-alkyls, being 27%-36%, 17%-21% and 36%-40%, respectively, but fewer aromatics and carboxyls (being 14%-20% and 13%-90%, respectively). Among those humic fractions, the humic acid (HA) and fulvic acid (FA) extracted by 0.1 mol L-1 Na4P207 contained slightly more carboxyls than corresponding humic fractions extracted by 0.1 mol L-1 NaOH, and the HA extracted by 0.1 mol L-1 NaOH after treatment with HF/HCI contained the least aromatics and carboxyls. The distribution of nitrogen functional groups of soil humic fractions studied was quite similar to each other and also quite similar to that of humic fraction from native soils. More than 75% of total N in each fraction was in amide form, with 9%-13% present as aromatic and/or aliphatic amines and the remainder as hoterocyclic N.
基金supported by the National Natural science Foundation of China.(No.39790100)
文摘Nitrogen forms of humic substances from a subalpine meadow soil, a latentic red soil and a weathered coal and the effect of acid hydrolysis on N structures of soil humic substances were studied by using 15N cross-polarization magic angle spinning nuclear magnetic resonance (CPMAS NMR) spectroscopy. Of the detectable 15N-signal intensity in the spectra of soil humic substances 71%-79% may be attributed to amide groups, 10%-18% to aromatic/aliphatic amines and 6%~11% to indole- and pyrrole-like N. Whereas in the spectrum of the fulvic acid from weathered coal 46%, at least, of the total 15N-signal intensity might be assigned to pyrrole-like N, 14% to aromatic/aliphatic ammes, and the remaining intensities could not be assigned with certainty. Data on nonhydrolyzable residue of protein-sugar mixture and a 15N-labelled soil fulvic acid confirm the formation of nonhydrolyzable heterocyclic N during acid hydrolysis. Project (No. 39790100) supported by the National Natural Science Foundation of China.
基金Project (No. 39790100) supported by the National Natural Science Foundation of China.
文摘X-ray photoelectron spectroscopy (XPS) was applied to examine the N structures of soil humic substances and some of their analogues. It was found that for soil humic substances XPS method gave similar results as those obtained by 15N CPMAS NMR (cross-polarization magic-angle spinning nuclear magnetic resonance) method. 70%～86% of total N in soil humic substances was in the form of amide, and 6%～13% was presented as amines, with the remaining part as heterocyclic N. There was no difference in the distribution of the forms of N between the humic substances from soils formed over hundreds or thousands of years and the newly formed ones. For fulvic acid from weathered coal and benzoqu inone- (N H-4 )-2 S O-4 polymer the XPS results deviated significantly from the 15N CPMAS NMR data.
基金Project supported by the National Natural Science Foundation of China.
文摘^15N-labelled phenolic polymers were synthesized by reactions of p-benzoquinone and 1,4-diphenol with ^15N-labelled glycine and were studied by using ^15N CP-MAS NMR technique in combination with chemical approaches.Results showed that the proportion of polymer nitrogen as N-phenyl amino acid N was not as great as expected,only accounting for 5%-15%;and most of N in polymers occurred in the forms of amide,pyrrole-and indole-like nitrogen,aliphatic amines and isonitrile.It seems that great differences existed between synthetic humic acids and soil humic acids in the type and distribution of nitrogen forms.
基金Project supported by the National Natural Science Foundation of China
文摘In this paper,the nitrogen forms in newly-formed humic substances,including humic acid (HA),fulvic acid (FA) and humic acid in humin (HAI),were studied by using the ^15N CP-MAS NMR technique in combination with chemical approaches.Results show that the majority of nitrogen in HA,FA and HAI was in the amide form with some presented as aliphatic and/ or aromatic amines and some as pyrrole type nitrogen,although the contents of nonhydrolyzable nitrogen in them differed greatly from each other (15-55%).
文摘THE ~15N NMR study is of general interest in the analysis of the protein conformations in solu-tions. When NMR is applied to the conformation study of macrobiomolecules, a heteronuclearmultiple quantum coherence (HMQC) spectrum of ~15N is usually measured first, so that theamide protons are assigned before other experiments, such as the total correlation
基金the National Natural Science Foundation of China (No.81273387) for the financial support of this research
文摘The normally underused ^1H-^15N HMBC spectra of thirteen C18-diterpenoid alkaloids have been determined for the first time. As a result, the significant effects of the substituents of nitrogen atoms, the conformations of A ring, and protonation, on the nitrogen-15 chemical shifts are demonstrated.
文摘Apramycin is unique in the aminoglycoside family due to its octodiose moiety. However, either the biosynthesis process or the precursors involved are largely unknown. Addition of glycine, as well as serine or threonine, to the Streptomyces tenebrabrius UD2 fermentation medium substantially increases the production of apramycin with little effect on the growth of mycelia, indicating that glycine and/or serine might be involved in the biosynthesis of apramycin. The 13C-NMR analysis of [2-13C] glycine-fed (25% enrichment) apramycin showed that glycine specifically and efficiently incorporated into the only N-CH3 substituent of apramycin on the C7′ of the octodiose moiety. We noticed that the in vivo concentration of S-adenosyl methionine increased in parallel with the addition of glycine, while the addition of methione in the fermentation medium significantly decreased the productivity of apra-mycin. Therefore, the methyl donor function of glycine is proposed to be involved in the methionine cycle but methionine itself was proposed to inhibit the methylation and methyl transfer processes as previously reported for the case of rapamycin. The 15N NMR spectra of [2-13C,15N]serine labeled apramycin indicated that serine may also act as a limiting precursor contributing to the ―NH2 substituents of apramycin.
