A SOLID NMR STUDY OF POLYETHERESTER-UREAS

The morphology of some polyetherester-ureas were studied by ^(13)C CP/MAS and ~1H wide-line NMR spectroscopy. It was found that the HDI and MDI based polymers have well crystallized hard segments, whereas the TDI and HMDI based ones have not. For HDI/MDI based polymers, the presented results suggest that the distribution of two kinds of hard segment units is mainly in a block form. The influences of the different hard segment and chain length on the mobility of the soft segment were also studied.

Characterization of humic acids extracted from the sediments of the various rivers and lakes in China

The humic acids (HAs) isolated from the sediments of the various rivers,lakes,and reservoirs in China were studied using elemental analyzer,fourier transform infrared (FT-IR),and CP/MAS 13C nuclear magnetic resonance (NMR) spectroscopy.The results showed that the HAs were characterized by some common chemical and physicochemical properties,but they also pose some differences in the C-containing functional groups.The C/N,C/H,O/C,and O/H ratios differ widely for the various HAs,showing that the elemental comp...

Changes in organic C stability within soil aggregates under different fertilization patterns in a greenhouse vegetable field

Knowledge of the stability of soil organic C(SOC)is vital for assessing SOC dynamics and cycling in agroecosystems.Studies have documented the regulatory effect of fertilization on SOC stability in bulk soils.However,how fertilization alters organic C stability at the aggregate scale in agroecosystems remains largely unclear.This study aimed to appraise the changes of organic C stability within soil aggregates after eight years of fertilization(chemical vs.organic fertilization)in a greenhouse vegetable field in Tianjin,China.Changes in the stability of organic C in soil aggregates were evaluated by four methods,i.e.,the modified Walkley-Black method(chemical method),13C NMR spectroscopy(spectroscopic method),extracellular enzyme assay(biological method),and thermogravimetric analysis(thermogravimetric method).The aggregates were isolated and separated by a wet-sieving method into four fractions:large macroaggregates(>2 mm),small macroaggregates(0.25–2 mm),microaggregates(0.053–0.25 mm),and silt/clay fractions(<0.053 mm).The results showed that organic amendments increased the organic C content and reduced the chemical,spectroscopic,thermogravimetric,and biological stability of organic C within soil aggregates relative to chemical fertilization alone.Within soil aggregates,the content of organic C was the highest in microaggregates and decreased in the order microaggregates>macroaggregates>silt/clay fractions.Meanwhile,organic C spectroscopic,thermogravimetric,and biological stability were the highest in silt/clay fractions,followed by macroaggregates and microaggregates.Moreover,the modified Walkley-Black method was not suitable for interpreting organic C stability at the aggregate scale due to the weak correlation between organic C chemical properties and other stability characteristics within the soil aggregates.These findings provide scientific insights at the aggregate scale into the changes of organic C properties under fertilization in greenhouse vegetable fields in China.

Study of native oil-bearing rocks of the Cuban basin by high resolution NMR spectroscopy

Application of high resolution^(13)C nuclear magnetic resonance(NMR)spectroscopy to characterize Cuba oil and oil-containing rock samples from Cuban basin was demonstrated.The chemical shifts of^(13)C NMR functional groups for later determination the composition of the oil and rock samples were determined.The different contribution of the studied samples in the aliphatic and aromatic areas was determined.Molar fractions of primary,secondary,quaternary,tertiary,aromatic groups,aromaticity factor and the mean length of hydrocarbon chain length of aliphatic hydrocarbons were estimated.Comparative analysis on the quantitative level for all major hydrocarbon components,the aromaticity factor and the mean length of the hydrocarbon chain were carried out.

NMR chemical shifts of carbon atoms and characteristic shift ranges in the oil sample

Application of high resolution^(13)C nuclear magnetic resonance(NMR)spectroscopy to characterize crude oil was demonstrated.The chemical shifts of^(13)C NMR functional groups that determine the composition of the oil sample were determined.Molar fractions of primary,secondary,quaternary,tertiary,aromatic groups,aromatic factor and average hydrocarbon chain length of aliphatic hydrocarbons of the oil sample according to^(13)C NMR spectra were determined.Detailed description of the^(13)C NMR spectra of the oil sample using a single consideration of three NMR spectra:^(13)C,^(13)C Attached Proton Test(APT),^(13)C with Gated Decoupling(GD)was performed.The different contribution of the studied oil sample in the aliphatic(10e75 ppm)and aromatic(115e165 ppm)areas of the^(13)C NMR spectra was determined.The presence of all major hydrocarbon components in the studied oil sample was established on the quantitative level,the aromaticity factor and the mean length of the hydrocarbon chain were evaluated.Quantitative fractions of aromatic molecules and functional groups constituting oil hydrocarbons were determined.In this work we demonstrate that the attached proton test and gated decoupling^(13)C NMR spectroscopy can afford all information to complete the chemical shift assignment of an oil sample,especially for determination of long range 1He^(13)C coupling constants and^(13)C multiplicity.