葡萄糖改性尿素的反应特征及其对尿素转化率的影响

张英强; 袁亮; 张水勤; 李燕婷; 王立艳; 赵秉强

doi:10.11674/zwyf.2021347

葡萄糖改性尿素的反应特征及其对尿素转化率的影响

Reaction characteristics of glucose-modified urea and its effects on the urea conversion rate

摘要

摘要:
目的利用葡萄糖对尿素改性可延缓尿素水解，提高尿素氮肥利用率。从葡萄糖与尿素的反应特征、产物结构方面，研究其作用机理及葡萄糖添加量对尿素分解的影响。
方法将葡萄糖按10%的比例加入到熔融尿素中获得葡萄糖改性尿素，利用傅里叶变换红外光谱(FTIR)、X射线光电子能谱(XPS)和液相色谱–质谱联用(LC-MS)分析葡萄糖改性尿素的化学结构、物质组成和相对分子质量。将葡萄糖按照0.2%、0.5%和1.0%的比例添加到熔融尿素中制备出3种比例的葡萄糖改性尿素，在3个样品分别加入脲酶溶液(1 U/mg)，于(25±2)℃恒温箱中培养30 min后，用比色法测定剩余尿素的含量，计算尿素的分解率。
结果 1)葡萄糖与尿素反应后，FTIR位于1599 cm⁻¹处伯酰胺NH₂变角振动消失，3441 cm⁻¹处伯胺NH₂反对称伸缩振动强度减弱，推测葡萄糖与尿素胺基发生反应，XPS C 1s和N 1s图谱分别出现未知形态的碳结构(―C_X)和氮结构(―N_X)，醛基碳(―CHO)消失，O 1s图谱发现醛基的C=O化学键发生断裂，证明葡萄糖的醛基与尿素的胺基反应生成了新的产物。依据LC-MS分析，葡萄糖中的醛基与尿素的胺基发生亲核加成反应，生成了含有C=N结构的物质。2)与普通尿素的分解率(20.16%)相比，添加0.2%、0.5%和1.0%比例的葡萄糖改性尿素的转化率分别为15.5%、3.3%、11.0%，其中葡萄糖添加比例为0.5%的改性尿素处理降幅高达16.9个百分点。
结论尿素熔融条件下加入葡萄糖，葡萄糖的C=O化学键断裂，碳原子与尿素中的氮原子结合形成C=N键。C=N键结构的存在延缓了尿素的水解，进而显著降低了脲酶对其分解率。葡萄糖添加量对葡萄糖改性尿素的分解率影响显著，以葡萄糖添加比例为0.5%的处理效果最佳。

Abstract:
Objectives Glucose-modified urea (GMurea) has high fertilizer use efficiency but low decomposition. We investigated the mechanism responsible for decreasing the conversion rate of glucose-modified urea from its structural perspective under various glucose addition rate.
Methods Glucose (10%) was added to molten urea to produce glucose-modified urea. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and liquid chromatography-mass spectrometry (LC-MS) were employed to characterize the chemical structure, material composition and relative molecular mass of the glucose-modified urea. Glucose-modified urea containing 0.2%, 0.5% and 1.0% of glucose were prepared, then urease solution (1 U/mg) was added and incubated at (25±2)℃ for 30 min. The remaining urea was tested using spectrophotometer.
Results 1) In the mixture of glucose and melted urea, the FTIR at 1599 cm^–1, the primary amide NH₂ variable angle vibration disappeared, and the primary amine NH₂ at 3441 cm^–1 weakened the asymmetric stretching vibration intensity. It was speculated that glucose reacted with the urea amine group. In addition, XPS C 1s and N 1s spectra showed unknown carbon structure (―C_X) and nitrogen structure (―N_X), and aldehyde-based carbon (―CHO) disappeared, and the O 1s spectrum showed that the C=O chemical bond of the aldehyde group was broken, indicating that the aldehyde group of glucose reacted with the amine group of urea to form a new product. The aldehyde group in glucose underwent a nucleophilic addition reaction with the amine group of urea to produce a substance containing a C=N structure through LC-MS analysis. 2) All the three ratios of glucose-modified urea reduced the decomposition rate of urea. The decomposition rate of urea and GMurea containing 0.2%, 0.5% and 1.0% glucose were significantly different vis – 20.16%, 15.5%, 3.3%, and 11.0%, respectively. Reduction in the rate of urea decomposition was markedly higher by 0.5% modification treatment, with 16.9 percentage points lower than that of ordinary urea.
Conclusions The formation of C=N bond between glucose and urea slowed down the decomposition of urea by urease. The glucose addition ratio has significant impact on the decomposition of glucose-modified urea, with an optimal glucose addition of 0.5%.

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