大孔阳离子交换树脂分离纯化Zwittermicin A

以抑菌圈为指标,通过离子交换法对双效菌素Zwittermicin A进行了分离纯化,并研究其抑菌活性。首先通过静态法比较D151、D113、D001-cc 3种大孔阳离子交换树脂吸附效果,结果表明,D151对ZwittermicinA分离纯化效果最好。利用单因素轮换法,确定了ZwittermicinA的最佳纯化工艺为:上柱样品的最佳pH=7;第1次冲洗液NH4H2PO4的最适浓度为5mmol/L;第2次冲洗液CH3COONH4的最适浓度为30mmol/L;1mol/L氨水洗脱液的最少用量为12.7mL/cm3树脂;Zwittermicin A的总收率达90%以上。利用红外光谱仪对D151树脂的吸附前后进行了分析。     

无限长湍流相位屏产生方法

在考虑时间特性的激光大气湍流数值模拟中,构造满足要求的湍流相位屏对大气湍流的模拟尤为重要,为此提出基于多点预测的相位协方差插值方法产生湍流相位屏,由多个已知点的相位值对新插值点的相位值进行预测,推导出了插值点的预测矩阵及其残余方差的表达式,并对插值后生成的相位屏的空间统计特性进行了验证。数值模拟结果表明:该方法产生的湍流相位屏与大气湍流的统计特性符合得较好,随着用于预测的已知点数的增加,模拟生成的湍流相位屏的精度提高,并可以进行连续插值生成无限长的湍流相位屏。     

关于几类2阶ai-半环生成的簇的研究

借助半环的格林关系研究了由所有2阶ai-半环生成的半环簇S2的一些子簇．其次,定义了与S2中半环的元素相关的同余关系,并揭示了同余关系之间的联系．     

Efficient capillary electrophoresis separation and determination of free amino acids in beer samples

Simultaneous detection of various o‐phthalaldehyde (OPA)‐labeled amino acids (AAs) in food samples was reported based on CE separation. Ionic liquid was used for the first time for CE analysis of AAs with in‐capillary derivatization. Several other additives, including SDS, α/β‐CD, and ACN, as well as key parameters for CE separation (buffer pH value, separation voltage), were also investigated. Our results show that the multiple additive strategy exhibits good stable and repeatable character for CE analysis of OPA‐labeled AAs, for either in‐capillary derivatization or CE separation, and allows simultaneous quantification of different OPA‐labeled AAs in a large concentration range of 50 μM to 3.0 mM with LOD down to 10 μM. Seventeen OPA‐labeled AAs, except for two pairs of AAs (His/Gln and Phe/Leu), which were separated with resolutions of 1.1 and 1.2, respectively, were baseline separated and identified within 23 min using the present multiple additive strategy. The method was successfully applied for simultaneous analysis of AAs in seven beer samples and as many as eleven trace‐amount AAs were detected and quantified, indicating the valuable potential application of the present method for food analysis.     

One-pot synthesis of a new rhodamine-based dually-responsive pH sensor and its application to bioimaging

A new colorimetric and fluorescent sensor for the highly acidic pH was developed from rhodamine B, 1-(2-aminoethyl)piperazine, and 4-chloro-7-nitro-2,1,3-benzoxadiazole. The sensor could be synthesized in one pot with an 82.5% yield, and for the first time N,N-diisopropylethylamine was found to be crucial for the rhodamine spirolactam formation. The sensor responded to pH rapidly, visibly, reversibly, highly selectively, and sensitively. From pH 7.77 to 2.03, the absorption and fluorescence intensity of the sensor increased by 285 and 50.3 folds, respectively. The pK_a value based on the fluorescence titration was 2.87. Fluorescent imaging of living cells treated with the sensor in different pH media indicated that the sensor could provide intracellular pH information.     

The role of cold crystallization of homochiral crystallites in the superb heat resistant poly(lactic acid)

The superb heat resistance poly(lactic acid) (PLA) were prepared by blending PLA and poly(d ‐lactic acid) (PDLA) with various molecular weight (M_n). Formation of the stereocomplex in the blends was confirmed by differential scanning calorimetry and wide‐angle X‐ray diffraction. The results of the heat resistance implied it is possible that elevating the Vicat penetration temperature of PLA up to 150°C by blending with PDLA. The cold crystallization of homochiral crystallites is proven to be the critical factor affecting the heat resistance of PLA. While the PLA or PLA/PDLA blends were heated to cold crystallization temperature of samples, both the crystal content and the rigid amorphous region content are increased due to the cold crystallization and tethering effect, and the stiffness and heat resistance of the sample are improved. The cold crystallization homochiral crystallites kinetics of PLA and PLA/PDLA blends was also studied. The results showed the activation energy (?E) of cold crystallization increased from 120.30 kJ/mol to 144.66 kJ/mol with the increasing of PDLA content from 2% to 10%.     

Electrocatalytically Active Fe-(O-C2)4 Single-Atom Sites for Efficient Reduction of Nitrogen to Ammonia

Single-atom catalysts have demonstrated their superiority over other types of catalysts for various reactions. However, the reported nitrogen reduction reaction single-atom electrocatalysts for the nitrogen reduction reaction exclusively utilize metal–nitrogen or metal–carbon coordination configurations as catalytic active sites. Here, we report a Fe single-atom electrocatalyst supported on low-cost, nitrogen-free lignocellulose-derived carbon. The extended X-ray absorption fine structure spectra confirm that Fe atoms are anchored to the support via the Fe-(O-C₂)₄ coordination configuration. Density functional theory calculations identify Fe-(O-C₂)₄ as the active site for the nitrogen reduction reaction. An electrode consisting of the electrocatalyst loaded on carbon cloth can afford a NH₃ yield rate and faradaic efficiency of 32.1 μg h⁻¹ mg_cat.⁻¹ (5350 μg h⁻¹ mg_Fe⁻¹) and 29.3 %, respectively. An exceptional NH₃ yield rate of 307.7 μg h⁻¹ mg_cat.⁻¹ (51 283 μg h⁻¹ mg_Fe⁻¹) with a near record faradaic efficiency of 51.0 % can be achieved with the electrocatalyst immobilized on a glassy carbon electrode.