高分辨NMR研究金属盐对水溶性铑膦配合物分子结构的影响

用高分辨NMR研究了NaCl、NiSO₄、CuSO₄、Fe₂(SO₄)₃和Cr₂(SO₄)₃对水溶性铑膦配合物HRh(CO)(TPPTS)₃[TPPTS;P(m-C₆H₄SO₃Na)₃]分子结构的影响.³¹P(¹H)和¹HNMR谱显示,于室温下在HRh(CO)(TPPTS)₃中加入的NaCl或NiSO₄对配合物的特征³¹P(¹H)和¹HNMR谱峰无明显影响;当加入CuSO₄后,配合物的Rh-H质子峰强度弱化明显,进而消失,且原配合物的特征磷谱峰强度减弱,新生成的磷物种谱峰逐渐成为磷谱的主要物种.当加入Fe₂(SO₄)₃或Cr₂(SO₄)₃后,三价金属离子的强顺磁性使NMR灵敏度下降,谱峰宽化,该2种盐均易与水溶性铑膦配合物产生强烈的相互作用,易使配合物特征谱峰消失.实验结果表明,上述金属盐对配合物结构破坏性大小的顺序为;Fe₂(SO₄)₃>Cr₂(SO₄)₃>CuSO₄》NiSO₄～NaCl.     

硫敏化卤化银感光乳剂灰雾属性的研究

用硫代硫酸钠对单分散八面体溴化银模型乳剂进行硫敏化,在不同成熟时间得到不同大小的灰雾值。将不同成熟时间的乳剂的单颗粒层在氧化还原缓冲溶液(由FeNH₄(SO₄)₂·12H₂O、FeSO₄(NH₄)₂SO₄·6H₂O和KBr组成)中处理,加入柠檬酸钠调节溶液的氧化还原电位,电位变化范围为50-630mV;乳剂的单颗粒层用余粒分析法求得。     

铜在玻璃碳电极上的阴极伏安特性及其在铜矿分析中的应用

本文研究了NH₃-NH₄Cl溶液中铜在稳定玻璃碳电极上的线性变势阴极伏安特性.确定铜氨络离子在玻璃碳电极上的还原分两步进行.在2.5MNH₃-0.75MNH₄Cl中,第一个波是Cu(NH₃)₄²⁺可逆地还原到Cu(NH₃)₂⁺,其峰电势为-0.28伏,与理论值一致.峰电流与电势变化速度及浓度的关系符合Randles-evcik方程.第二个波是Cu(NH₃)₂⁺不可逆地还原为铜,当电势变化速度改变时,其峰电势在-0.69～-0.84伏之间.第一个波峰电流的相对标准误差不大于±2.4%,温度系数约为+1.3%/度.本文在氨性底液中用铜在玻璃碳电极上还原的第一个波以测定铜矿中的铜.在极谱法中用的第二个波有[Co(NH₃)₆]³⁺前波及Tl⁺重波,它们在第一个波中均变为后波,从而克服了它们对铜测定的干扰.测定结果与标准样的数据吻合,与示波极谱的数据一致.测定矿样的相对标准误差在±0.37～3.2%之间,符合矿石分析的要求.     

FeOOH明胶复合纳米粒子的制备与表征

采用两步法制备具有弱磁性的FeOOH纳米粒子和FeOOH明胶复合纳米粒子. 透射电镜、扫描电镜、红外光谱、X射线衍射和磁滞回线等测量结果表明: 在一定FeCl₃/Fe₂(SO₄)₃/H₂O摩尔比条件下, 加入十二烷基苯磺酸钠(ABS)溶液, 可制备粒径为30～150 nm弱磁性FeOOH纳米粒子, 其磁性可达6.5×10^－6 emu/g. 弱磁性FeOOH纳米粒子可被明胶包裹. 随着FeCl₃/Fe₂(SO₄)₃摩尔比减小或明胶浓度增加, 纳米球粒径增大, 磁性降低. 随着固化时间增加, FeOOH明胶复合纳米粒子的粒径先增大后减小.     

菲罗啉大环双核Fe3+配合物的合成及其荧光性质

根据文献方法合成大环配体L,通过溶剂法与金属盐Fe(ClO₄)₂·6H₂O反应合成了两个新的菲罗琳大环双核Fe₃₊配合物[Fe₂(L)(μ-O)(DMF)₄]·4ClO₄(1, CCDC： 1834054）和[Fe₂(L)(μ-O)(SCN)₄]·4ClO₄(2, CCDC： 1834055）,其结构经IR和元素分析表征。晶体结构解析表明：1属三斜晶系,2属单斜晶系。配合物中两个铁原子通过一个氧桥进行连接,由于氧桥的连接使得配体发生折叠进而产生了π-π堆积。配体荧光滴定实验显示,配体L对过渡金属存在响应,随着过渡金属离子的加入,配体的荧光强度不断减弱。     

阴离子磺酸盐型Gemini表面活性剂与PEO-PPO-PEO嵌段共聚物相互作用的研究

用差示扫描微量热、等温滴定微量量热、动态光散射和核磁共振(NOESY,弛豫时间)技术,研究了在pH＝9时阴离子磺酸盐型Gemini表面活性剂12-3-12(SO₃)₂与PEO-PPO-PEO嵌段共聚物F127 (EO₉₇PO₆₉EO₉₇)和P123 (EO₂₀PO₇₀EO₂₀)之间的相互作用. 研究发现,随着12-3-12(SO₃)₂浓度的增大,聚合物的临界胶束温度(CMT)降低. 与传统的单链离子表面活性剂相比,12-3-12(SO₃)₂具有更强的降低共聚物CMT的能力. 此外,在低于聚合物的CMT时,12-3-12(SO₃)₂与聚合物单体可以形成聚合物/表面活性剂胶束聚集体;在高于聚合物的CMT时,12-3-12(SO₃)₂的加入首先与聚合物单体和胶束的混合物或聚合物胶束形成聚合物/12-3-12(SO₃)₂混合胶束,然后随着12-3-12(SO₃)₂浓度的增大,混合胶束逐步解离为小的聚集体,但是,即使在很高的12-3-12(SO₃)₂浓度时,混合胶束也未完全解离.     

SCR脱硝过程中SO2催化氧化的原位红外研究

采用工业用V₂O₅-WO₃/TiO₂催化剂,基于傅里叶原位红外光谱(FT-IR)技术考察SO₂的氧化过程及烟气组分对SO₂氧化行为的影响;结果表明,SO₂在催化剂表面氧化主要是首先吸附在催化剂表面V₂O₅活性位上,占据其O原子,以SO^2-₃形式存在,后与催化剂表面V⁵⁺-OH发生反应,生成金属硫酸盐(VOSO₄)中间产物,O₂重新氧化催化氧化过程中由于被SO₂夺取O原子而被还原的V₂O₅物种,使V⁴⁺转化为V⁵⁺,促进金属硫酸盐(VOSO₄)向SO₃转化;SO₂与NO、NH₃的竞争吸附阻碍SO₂在V₂O₅活性点位上的氧化;在SCR中,NO的脱除与SO₂的氧化是相互抑制的关系。     

簇合物[Fe2(CO)8]2-和[Fe3S(CO)9]2-成簇类型的光谱探讨及电子光谱和电子结构研究

在Fe(CO)₅+[Et₄N]₂MoS₄相同体系中,改变原料配比及碱度,可得到3种簇合物:(Ⅰ)[Et₄N]₂[Fe₂(CO)₈]、(Ⅱ)[Et₄N]₂[Fe₃S(CO)₉]、(Ⅲ)[Et₄N]₃[FeMo₂S₈O₂]。本文用电子光谱法考察了各簇合物的生成条件。根据X光结构分析,用群分解的EHMO程序,计算了(Ⅰ)、(Ⅱ)簇合物阴离子骨架能级,并研究了它们的电子光谱及电子结构。     

苯二甲酰基桥联铁硫配合物[(μ-RS)Fe2(CO)6]2(μ-OCC6H4CO-μ)的合成及表征

通过由Fe₃(CO)₁₂、RSH和Et₃N所形成的[(μ-CO)(μ-RS)Fe₂(CO)₆]Et₃NH于室温下分别与对或间苯二甲酰氯的原位反应,首次合成6个结构新颖的苯二甲酰基桥联铁硫配合物[(μ-RS)·Fe₂(CO)₆]₂(μ-p-OCC₆H₄CO-p-μ)(R=Et,n-Bu,t-Bu)以及[(μ-RS)Fe₂(CO)₆]₂(μ-m-OCC₆H₄CO-m-μ)(R=n-Pr,n-Bu,t-Bu).经元素分析、IR光谱及¹HNMR表征了它们的结构,并讨论了产物的生成过程.此外,还提出了合成对苯二甲酰氯的一种新方法.     

电活性铁氰化镍膜电极对稀土钇的电控离子分离

通过电沉积方法分别在镀铂石英晶片和铂基底上制备了电活性铁氰化镍膜,并考察了膜电极在含钇离子溶液中的电控离子交换性能. 在0.1 mol·L^-1的硝酸钇溶液中,使用循环伏安法及石英晶体微天平技术测试考察了铁氰化镍膜对钇离子的置入释放性能及对应的质量变化,同时比较了铁氰化镍膜电极在Y(NO₃)₃和Sr(NO₃)₂溶液中的电化学性能. 在0.1 mol·L^-1 [Y(NO₃)₃ + Sr(NO₃)₂]混合溶液中,通过循环伏安法分析了薄膜对Y³⁺/Sr²⁺离子的选择性. 用扫描电子显微镜观察了铁氰化镍膜的表面形貌,并通过X射线光电子能谱仪测定了膜在氧化和还原状态下的元素组成. 结果表明,铁氰化镍膜在含Y³⁺溶液中具有良好的离子交换行为,其中氧化过程薄膜质量减少,对应着钇离子的释放;还原过程薄膜质量增加,对应钇离子的置入;在0.0 V或0.9 V调控膜电极的氧化还原状态实现对钇离子的有效分离.     

Enantiomer separation by CEC——Enantiomer separation by packed-capillary electrochromatography

Three chiral compounds were successfully separated in a short time with two enantiomer separation models on packed-capillary electrochromatography (CEC). (i) 75 μm I.D. capillaries were packed with 5 μm β-cyclodextrin (β-CD) chiral stationary phase (CSP). Effects of voltage, pH and concentration of organic modifier on electroosmotic flow (EOF) and chiral separations were investigated systematically. Enantiomers of a neutral compound (benzoin) and a neutral drug (mephenytoin) were separated within a short time with high efficiency. Efficiency of 32 000 theoretical plates per meter and resolution (R_s) of 1.42 were achieved for enantiomers of benzoin using a βCD packed column with 6.2 cm packed length. Efficiency of 45 000 theoretical plates per meter and R_s of 3.40 were obtained for enantiomers of mephenytoin. Especially, the enantiomer separation of mephenytion was performed in just 3.4 min with R_s of 2.60. (ⅱ) 75 μm I.D. capillary was packed with octadecylsilica particles (ODS). Chiral separat     

Regioselectivity of olefin oxidation by iodosobenzene catalyzed by metalloporphyrins : control by the catalyst

The regioselectivity of the oxidation of three monosubstituted olefins, 6-phenoxyhex-1-ene, hex-1-ene and styrene, by iodosobenzene in the presence of various Fe-, Mn- or Cr-tetraaryl-porphyrins, was studied. It was found that, besides epoxides, known products from such systems, allylic alcohols and aldehydes were formed, the latter not being derived from the corresponding epoxides. The relative importance of these reactions greatly depends upon both the metal and porphyrin constituents of the catalyst. More particularly, the competition between epoxidation and allylic hydroxylation can be efficiently controlled by non-bonded interactions between the olefin and porphyrin substituents. No hydroxylation of the aromatic rings and no oxidative dealkylation of the ether function was detected.     

Glycosidase inhibition by macrolide antibiotics elucidated by STD-NMR spectroscopy

A glycosynthase approach was attempted to glycodiversify macrolide antibiotics, using DesR, a family-3 retaining beta-glucosidase involved in the self-resistance mechanism of methymycin production. STD-NMR was used to probe enzyme-substrate interactions. Analysis of competitive STD-NMR experiments between erythromycin A and a chromogenic substrate (pNP-beta-d-glucose) with the hydrolytically inactive nucleophile mutants led us to discover a family of unprecedented glycosidase inhibitors. Analysis of kinetic data with wild-type DesR determined that erythromycin is a competitive inhibitor of the glucosidase (IC50 = 2.8 +/- 0.3 microM and Ki = 2 +/- 0.2 microM) with respect to the hydrolysis of pNP-beta-d-glucose. Comparable inhibitory data was obtained for clarithromycin; however, the inhibitory effect of azithromycin was weak and no significant inhibition was observed with methymycin or d-desosamine. This report documents significant inhibition of glycosidases by macrolide antibiotics and provides insight into the design of novel glycosidase inhibitors based on the macrolactone ring of macrolide antibiotics.     

Membrane solubilization by detergent: resistance conferred by thickness

The commonly held model for membrane dissolution by detergents/surfactants requires lipid transport from the inner to the outer bilayer leaflet ('flip-flop'). Although applicable to many systems, it fails in cases where cross-bilayer transport of membrane components is suppressed. In this paper we investigate the mechanism for surfactant-induced solubilization of polymeric bilayers. To that end, we examine the dissolution of a series of increasingly thick, polymer-based vesicles (polymersomes) by a nonionic surfactant, Triton X-100, using dynamic light scattering. We find that increasing the bilayer thickness imparts better resistance to dissolution, so that the concentration required for solubilization, after a fixed amount of time, increases nearly linearly with membrane thickness. Combining our experimental data with a theoretical model, we show that the dominant mechanism for the surfactant-induced dissolution of polymeric vesicles, where polymer flip-flop across the membrane is suppressed, is the surfactant transport through the bilayer. This mechanism is different both qualitatively and quantitatively from the mechanisms by which surfactants dissolve pure lipid vesicles.     

Antibiotic recognition by binuclear metallo-beta-lactamases revealed by X-ray crystallography

Metallo-beta-lactamases are zinc-dependent enzymes responsible for resistance to beta-lactam antibiotics in a variety of host bacteria, usually Gram-negative species that act as opportunist pathogens. They hydrolyze all classes of beta-lactam antibiotics, including carbapenems, and escape the action of available beta-lactamase inhibitors. Efforts to develop effective inhibitors have been hampered by the lack of structural information regarding how these enzymes recognize and turn over beta-lactam substrates. We report here the crystal structure of the Stenotrophomonas maltophilia L1 enzyme in complex with the hydrolysis product of the 7alpha-methoxyoxacephem, moxalactam. The on-enzyme complex is a 3'-exo-methylene species generated by elimination of the 1-methyltetrazolyl-5-thiolate anion from the 3'-methyl group. Moxalactam binding to L1 involves direct interaction of the two active site zinc ions with the beta-lactam amide and C4 carboxylate, groups that are common to all beta-lactam substrates. The 7beta-[(4-hydroxyphenyl)malonyl]-amino substituent makes limited hydrophobic and hydrogen bonding contacts with the active site groove. The mode of binding provides strong evidence that a water molecule situated between the two metal ions is the most likely nucleophile in the hydrolytic reaction. These data suggest a reaction mechanism for metallo-beta-lactamases in which both metal ions contribute to catalysis by activating the bridging water/hydroxide nucleophile, polarizing the substrate amide bond for attack and stabilizing anionic nitrogen intermediates. The structure illustrates how a binuclear zinc site confers upon metallo-beta-lactamases the ability both to recognize and efficiently hydrolyze a wide variety of beta-lactam substrates.