连续流动条件下含氮Beta分子筛催化甲缩醛-异丁烯Prins反应

采用高温氨气氮化法,制备了一系列含氮Beta分子筛样品,并在连续流动条件下,考察了其催化甲缩醛与异丁烯经Prins缩合制异戊二烯的反应性能.利用XRD、 N₂吸附/脱附、元素分析、 ²⁹SiMAS NMR、 NH₃-TPD、 CO₂-TPD和TG等方法对氮化分子筛的结构、酸碱性和反应后积碳进行了表征,研究了反应条件及样品的酸碱性对反应性能的影响.结果表明,以35%甲缩醛水溶液为反应物,在320℃、 2 MPa、异丁烯与甲缩醛摩尔比为7的适宜条件下,铵型Beta为前驱体制备的催化剂对甲缩醛的转化率达99%,异戊二烯的产率达85%.氮化后少量的酸性位和较多的碱性位有利于维持甲缩醛较高的转化率、较高的异戊二烯产率及较低的反应积碳量.催化剂再生6次后仍保持75%异戊二烯产率,样品中Si―N键削弱导致酸碱性变化是再生后反应性能下降的主要原因.     

Gas-phase thermochemical properties of some tri-substituted phenols: A density functional theory study

The study of the energetics of phenolic compounds has a considerable practical interest since this family of compounds includes numerous synthetic and naturally occurring antioxidants. In this work, density functional theory (DFT) has been used to investigate gas-phase thermochemical properties of the following tri-substituted phenols: 2,4,6-trimethylphenol, 2,6-dimethyl-4-tert-butylphenol, 2,6-dimethyl-4-methoxyphenol, 2,4,6-tri-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-methoxyphenol, 2,4,6-trimethoxyphenol, 2,6-dimethoxy-4-methylphenol and 2,6-dimethoxy-4-tert-butylphenol. Molecular structures were computed with the B3LYP and the ωB97X-D functionals and the 6-31G(d) basis set. More accurate energies were obtained from single-point energy calculations with both functionals and the 6-311++G(2df,2pd) basis set. Standard enthalpies of formation of the phenolic molecules and phenoxyl radicals were derived using an appropriate homodesmotic reaction. The OH homolytic bond dissociation enthalpies, gas-phase acidities and adiabatic ionization enthalpies were also calculated. The general good agreement found between the calculated and the few existent experimental gas-phase thermochemical parameters gives confidence to the estimates concerning the phenolic compounds which were not yet experimentally studied.     

全氟磺酸功能化碳纳米管的制备及其催化性能

采用全氟磺酸-全氟乙烯共聚物的液相沉积方法制备了全氟磺酸功能化碳纳米管催化剂,利用N2吸附、扫描电子显微镜、透射电子显微镜、傅里叶变换红外光谱以及酸碱滴定等方法对材料的结构和酸性进行了表征,考察了温度和溶剂对催化剂稳定性的影响.结果表明,催化剂在极性和非极性溶液中均十分稳定,并且具有良好的热稳定性,使用温度可达300°C.该催化剂在对苯二酚与叔丁醇的烷基化反应中表现出优异的催化性能,其催化活性与稳定性均高于聚苯乙烯磺酸功能化的碳纳米管催化剂.     

Acid-Catalysed Hydrolysis of Some Aromatic Cyclic Sulfamates

The acid catalysed hydrolysis of some cyclic sulfamates, X-3-(p-tolylsulfonyl)-1,2,3-benzoxathiazole 2,2-dioxides ( 1a , X = Me; 1b , X = H; 1c , X = Cl; 1d , X = NO 2 ) have been studied in concentrated aqueous sulfuric and perchloric acid solutions. Analysis of the data by the Excess Acidity Method, activation parameters, substituent, solvent deuterium isotope effect and order of the catalytic effects of the acids are all in agreement with an A-1 mechanism in the studied range.     

Gradient reversed-phase high-performance chromatography of ionogenic analytes

This review highlights the basis of gradient reversed-phase high-performance liquid chromatography (RP-HPLC) of ionogenic analytes.We describe pH-gradient RP-HPLC in strict theoretical terms, with examples of experiments to provide improvements in analyte separations and peak shapes, and an original method of pK_a determination.Finally, we present the concept of the combined pH/organic-modifier gradient mode of RP-HPLC and illustrate it with applications. It allows optimization of separation of ionogenic analytes, along with a method for determining their biorelevant physico-chemical parameters [e.g., hydrophobicity (log k_w) and acidity (pK_a)]. The method is applicable to drugs and other xenobiotic mixtures, including individual analytes of interest assayed in biological fluids.     

光谱法研究酸度对一种白杨素衍生物与牛血清白蛋白相互作用的影响

在3种酸度条件下,采用多种光谱技术对一种白杨素衍生物和牛血清白蛋白的相互作用进行了研究.结果表明该衍生物和牛血清白蛋白可形成基态复合物,静态、动态猝灭方式同时存在,以静态猝灭为主.通过计算获得了在不同温度及酸度条件下的结合常数及结合位点数.该衍生物在碱性条件下和牛血清白蛋白的结合能力较强.在pH 7.40的生理条件下,...     

Buffer Standards for pH Measurement of N-(2-Hydroxyethyl)piperazine-N′-2-ethanesulfonic Acid (HEPES) for I=0.16 mol⋅kg−1 from 5 to 55 °C

The values of the second dissociation constant, pK ₂, of N-(2-hydroxyethyl) piperazine-N′-2-ethanesulfonic acid (HEPES) have been reported at twelve temperatures over the temperature range 5 to 55 °C, including 37 °C. This paper reports the results for the pa _H of eight isotonic saline buffer solutions with an I=0.16 mol⋅kg⁻¹ including compositions: (a) HEPES (0.01 mol⋅kg⁻¹) + NaHEPES (0.01 mol⋅kg⁻¹) + NaCl (0.15 mol⋅kg⁻¹); (b) HEPES (0.02 mol⋅kg⁻¹) + NaHEPES (0.02 mol⋅kg⁻¹) + NaCl (0.14 mol⋅kg⁻¹); (c) HEPES (0.03 mol⋅kg⁻¹) + NaHEPES (0.03 mol⋅kg⁻¹) + NaCl (0.13 mol⋅kg⁻¹); (d) HEPES (0.04 mol⋅kg⁻¹) + NaHEPES (0.04 mol⋅kg⁻¹) + NaCl (0.12 mol⋅kg⁻¹); (e) HEPES (0.05 mol⋅kg⁻¹) + NaHEPES (0.05 mol⋅kg⁻¹) + NaCl (0.11 mol⋅kg⁻¹); (f) HEPES (0.06 mol⋅kg⁻¹) + NaHEPES (0.06 mol⋅kg⁻¹) + NaCl (0.10 mol⋅kg⁻¹); (g) HEPES (0.07 mol⋅kg⁻¹) + NaHEPES (0.07 mol⋅kg⁻¹) + NaCl (0.09 mol⋅kg⁻¹); and (h) HEPES (0.08 mol⋅kg⁻¹) + NaHEPES (0.08 mol⋅kg⁻¹) + NaCl (0.08 mol⋅kg⁻¹). Conventional pa _H values, for all eight buffer solutions from 5 to 55 °C, have been calculated. The operational pH values with liquid junction corrections, at 25 and 37 °C have been determined based on the NBS/NIST standard between the physiological phosphate standard and four buffer solutions. These are recommended as pH standards for physiological fluids in the range of pH = 7.3 to 7.5 at I=0.16 mol⋅kg⁻¹.     

偶氮基杯芳烃化合物的合成及其偶氮-醌腙互变异构性质

通过芳胺的重氮化-偶合反应合成了8个偶氮基杯芳烃化合物, 其结构经IR, 1H NMR, ESI-MS和元素分析表征. 通过UV-Vis, 1H NMR和IR考察了溶液pH值对所合成化合物5,11,17,23-四[(2-苯并噻唑基)偶氮基]-25,26,27,28-四羟基杯芳烃(3)和5,17-二[(1-萘基)偶氮基]-25,26,27,28-四羟基杯芳烃(4)的偶氮-醌腙互变异构的影响. 结果表明, 随着溶液pH值增加, 醌腙体在偶氮-醌腙互变异构平衡中的比例增加, 当pH≥10时, 几乎全部转变为醌腙体. 特别当溶液pH=-1时, 化合物4可以形成一种大的共轭体系, 使其λmax由477 nm红移至545 nm.     

Cu-[M’]MOR和Ag-[M’]MOR (M’=B,Al, Ga,Fe)的酸性

采用Dmol3程序中基于密度泛函理论(DFT)的广义梯度方法(GGA)和BLYP方法以及DND基组, 研究了丝光沸石H-[M']MOR、Cu-[M']MOR和Ag-[M']MOR(M'=B, Al, Ga, Fe)结构及其对NH3分子的吸附, 获得了吸附平衡构型和吸附能. NH3分子在H-[M']MOR中的吸附主要是通过NH3分子中氮原子上的孤对电子与质子酸位作用, NH3分子在H-[Al]MOR、H-[Ga]MOR和H-[Fe]MOR上发生化学吸附, 而在H-[B]MOR上发生物理吸附, 这与文献结果相符. NH3分子与Cu-[M']MOR 和Ag-[M']MOR分子筛之间主要通过氮上的孤对电子和平衡离子(Cu+和Ag+)的s空轨道间配位作用而发生化学吸附. 吸附能数据表明, 在H-[M']MOR、Cu-[M']MOR 和Ag-[M']MOR中, A1原子进入骨架导致H-[A1]MOR、Cu-[A1]MOR和Ag-[A1]MOR的酸强度最强; 对于同一种原子取代的丝光沸石, 其酸强度次序为: Cu-[M']MOR > Ag-[M']MOR > H-[M']MOR. 此外, 还对吸附前后的沸石中平衡离子(H+、Cu+和Ag+)及NH3分子的Mulliken电荷集居数作了研究和分析.     

Sn-Al-β分子筛酸性在葡萄糖转化反应中作用的固体NMR研究

制备了一系列具有不同酸性质的β分子筛催化剂, 通过固体核磁共振(NMR)探针分子技术对其酸性质进行了表征, 并考察了其催化葡萄糖转化为乙酰丙酸甲酯的性能. 吸附三甲基磷的³¹P NMR实验结果表明, 含有骨架Sn以及Al原子的Sn-Al-β催化剂同时具有Br?nsted与Lewis酸性. 通过2-¹³C-丙酮探针分子区分出 3种酸强度的Br?nsted酸位, 其中一种酸强度接近“超强酸”, 可能是由于空间邻近的Br?nsted酸位和Lewis酸位发生协同作用产生的. 葡萄糖转化为乙酰丙酸甲酯的催化反应结果表明, 相比于分别只含有Lewis酸位和Br?nsted酸位的Sn-β和Al-β样品以及两者的物理混合样品, Sn-Al-β分子筛催化剂具有高催化活性与产物选择性, 这主要是由于Br?nsted酸位和Lewis酸位的协同作用产生了强Br?nsted酸位, 这种强Br?nsted酸位进一步导致了更高的催化活性.