萃淋树脂分离-全差示光度法测定环境水样中铬(Ⅲ)和铬(Ⅵ)

用CL-TBP萃淋树脂分离富集Cr(Ⅲ)和C(Ⅵ)、对氨基二甲基苯胺做显色剂,采用全差示光度法测定环境水样中的Cr(Ⅲ)和Cr(Ⅵ).方法的表观摩尔吸收系数为3.42× 105L·md-1·cm-1,线性范围为0～0.16 mg/L,线性方程为A=6.7C+0.001,(C:mg/L),r=0.9996,Cr(Ⅲ)和Cr(Ⅵ)的检测限分别为8和6 μg/L.测定Cr(Ⅲ)和Cr(Ⅵ)分别为18.7和31.6μg/L,其相对标准偏差分别为3.1%(n=6)和2.4%(n=6).Cr(Ⅲ)和Cr(Ⅵ)的标准加入回收率为93.3%～102.3%.用本法测定环境水样中Cr(Ⅲ)和C(Ⅵ),结果满意.     

共振散射法测定中草药中的微量铬

研究了在H2SO4介质中,Cr(Ⅵ)与碘化物和淀粉形成离子缔合物的共振光散射增强现象,拟定了一种新的测定Cr(Ⅵ)的共振光散射方法,通过实验确定了溶液中Cr(Ⅵ)浓度与散射光强度之间的关系,在λex＝λem＝290 nm处,共振光散射最强,且共振光散射强度与Cr(Ⅵ)浓度呈线性关系,该方法简便快速,线性范围为34～400 μg/L,检出限为6.7 μg/L,可用于中草药样品中铬的测定.     

浊点萃取-石英双缝管捕集火焰原子吸收光谱法分析铬价态

在不同pH值的缓冲溶液中,亚硝基苯胲铵盐(铜铁试剂)可与Cr(Ⅵ)及Cr(Ⅲ)络合生成中性疏水络合物,以Triton X-114为萃取剂,浊点萃取分离富集Cr(Ⅵ)及总铬,石英双缝管原子捕集-火焰原子吸收光谱法(STAT-FAAS)测定铬价态.实验对浊点萃取时溶液的pH值、铜铁试剂和Triton X-114的用量、离心分离时间、平衡温度和时间等影响因素进行了研究.结果表明,分别在pH=3.0和6.0的溶液中,40 ℃恒温加热15 min后,离心5 min,Triton X-114浊点萃取Cr(Ⅵ)及总铬的富集倍数达到50倍(100 mL起初样品溶液/2 mL最终测定液).和普通火焰原子吸收光谱法(FAAS)相比,利用石英双缝管原子捕集技术,STAT-FAAS法测定铬的灵敏度提高了近5倍.本方法测定Cr(Ⅵ)及总铬的线性范围分别为0.005～0.5 mg/L和0.01～1.2 mg/L;检出限分别为0.66 μg/L和0.81μg/L.     

流动注射分光光度法快速测定水样中的铬

建立了用流动注射分光光度法快速检测水样中铬含量的方法.测定耗时140 s,测定频率25样/h.本法利用Cr(Ⅵ)和二苯碳酰二肼显色反应,Cr(Ⅵ)标准溶液的质量浓度在0.05～0.8 mm/L之间与吸光度呈线性.该法的检出限是4.0 μg/L,低于国家对Ⅰ类水的相关标准.应用此法分别测定了北京城区一些地表水中铬的含量,加标回收率在90.1%～113%之间.     

浊点萃取–火焰原子吸收光谱法分析水样中铬的存在形态

将浊点萃取与火焰原子吸收光谱法联用对水样中铬的形态进行检测,在pH 7.7条件下,络合剂1-(2-吡啶偶氮)-2-萘酚(PAN)只与Cr(Ⅲ)络合而不与Cr(Ⅵ)反应,实现了环境水样品中Cr(Ⅲ)与Cr(Ⅵ)的分别测定。对影响浊点萃取效率的主要因素如酸度、试剂量、反应温度、时间等进行了研究,在最佳条件下,铬富集倍数为20倍。Cr(Ⅲ)的质量浓度在0.005~1.0 mg/L内与吸光度线性良好,线性相关系数r=0.999 8。用该方法对0.30 mg/L的Cr(Ⅲ)标准溶液平行测定11次,测定结果的相对标准偏差为2.9%,检出限为5.74μg/L。将该法用于自来水、河水、三亚温泉水、工厂污水水中铬的形态分析并进行加标回收试验,回收率为90.0%~106.5%。该法富集倍数高、重现性好,测定结果准确可靠。     

浊点萃取-高效液相色谱法测定巢湖表层沉积物中铬的形态

以1-(2-噻唑偶氮)-2-萘酚(TAN)为络合试剂,非离子表面活性剂Triton X-114为萃取剂,浊点萃取同时富集Cr(Ⅲ)和Cr(Ⅵ),并于RP-C18柱上,用含4.5 mmol/L十六烷基三甲基溴化铵(CTMAB)和0.03mol/L HAc-NaAc缓冲溶液(pH5.5)的甲醇-水(体积比69∶31)溶液为流动相,对富集的Cr(Ⅲ)和Cr(Ⅵ)进行高效液相色谱快速分离、测定。对浊点萃取时溶液的pH值、TAN和Triton X-114的用量等影响因素进行了考察。在优化实验条件下,对100μg/L的Cr(Ⅲ)和Cr(Ⅵ)进行7次平行测定,保留时间的相对标准偏差分别为1.2%和0.9%,峰面积的相对标准偏差分别为4.7%和2.7%。Cr(Ⅲ)和Cr(Ⅵ)的线性范围均为50~5 000μg/L,检出限分别为7.5、3.5μg/L。大部分离子不干扰测定,该方法具有较高的灵敏度,可用于湖泊表层沉积物中铬形态的分析。     

交联羧甲基淀粉预富集-悬浮体进样-石墨炉原子吸收法测定水样中铬(Ⅲ)和铬(Ⅵ)

以交联羧甲基淀粉(CCMS)为吸附剂,悬浮体进样-石墨炉原子吸收法(GFAAS)测定环境水样中Cr(Ⅲ)和Cr(Ⅵ)形态。研究了溶液pH值、吸附时间、溶液体积、共存离子等对CCMS吸附Cr(Ⅲ)和Cr(Ⅵ)的影响。结果表明:在pH=6.0时,吸附15 min,CCMS可以选择性地吸附Cr(Ⅲ),对Cr(Ⅵ)不吸附,从而实现Cr(Ⅲ)和Cr(Ⅵ)的分离。将吸附Cr?的CCMS加0.1%的琼脂制成悬浮体直接进石墨炉检测,用1 mL 1%盐酸羟胺将Cr(Ⅲ)还原成Cr(Ⅵ),测总铬。方法对Cr(Ⅲ)的检出限为0.044μg/L,相对标准偏差(RSD)为10.4%(初始浓度CCr(Ⅲ)=1.0μg/L,n=11),富集倍数为50倍。将本方法应用于环境标准样品的测定,测得结果与标准值相符。     

嵌段分子筛聚合材料P123-SH萃取分离-石墨炉原子吸收光谱法分析痕量铬的形态

研究了嵌段分子筛聚合材料P123-SH萃取分离-石墨炉原子吸收光谱法对尿中痕量铬的形态分析方法,探讨了嵌段分子筛聚合材料P123-SH吸附铬的原理和最佳条件。在pH 7.0、常温下,Cr3+和Cr(Ⅵ)被很好的分离,且Cr3+可被该材料定量吸附,其吸附容量为6.15 mg/g。吸附的Cr3+可用2 mol/L的HCl洗脱,用石墨炉原子吸收法测定洗脱下来的Cr3+,往溶液中加入0.1%抗坏血酸将Cr(Ⅵ)还原为Cr3+测总铬,Cr(Ⅵ)含量为总铬减去Cr3+,方法测定Cr3+的检出限为0.011μg/L(3σ,n=11),线性范围为0.1～10μg/L,加标回收率在94%～106%之间,对0.50μg/L的Cr3+溶液平行测定7次,RSD为3.6%。方法可应用于生物样品和环境样品中痕量铬的形态分析。     

微乳相萃取分离富集-原子吸收光谱法分析铬形态

建立了一种微乳相萃取分离-石英双缝管原子捕集火焰原子吸收光谱法(STAT-FAAS)分析环境水样中铬形态的新方法。该方法中,Cr(Ⅲ)与8-羟基喹啉反应形成的疏水性配合物,经萃取进入微乳相,Cr(Ⅵ)留在水溶液中,从而实现Cr(Ⅲ)与Cr(Ⅵ)的相互分离。Cr(Ⅵ)含量的测定通过过氧化氢溶液将Cr(Ⅵ)还原为Cr(Ⅲ),按同样方法分析。实验对微乳相萃取的主要影响因素进行了优化。结果表明,经优化后实验条件为:平衡温度80℃,平衡时间10min,溶液酸度pH=9.0,NH3-NH4Cl缓冲溶液用量2.0mL,8-HQ用量0.05mmol;TritonX-100微乳液组成:m(TritonX-100):m(正戊醇):m(正己烷):m(水)=3.0:15:1.5:4.0。在此条件下,萃取的富集倍数达到25倍(50mL起初样品溶液/2mL最终测定液),线性范围为2.5～500μg/L,检出限为0.62μg/L,相对标准偏差(RSD)为3.8%(n=10,c=10μg/L)。本方法已成功地应用于电镀废水中铬形态分析。     

反相离子对色谱-电感耦合等离子体质谱联用技术测定水中痕量Cr(Ⅲ)与Cr(Ⅵ)

建立了反相离子对色谱(RPIPC)与电感耦合等离子体质谱(ICP-MS)联用技术快速分离测定水中痕量Cr(Ⅲ)和Cr(Ⅵ)的方法.通过考察流动相的pH值、离子对试剂及甲醇的浓度和EDTA的添加等对不同形态铬的保留时间及分离度的影响,确定当流动相组成为2.0 mmol/L TBA,5%(V/V)甲醇,pH=5.5时,Cr(Ⅲ)与Cr(Ⅵ)可达最佳分离.ICP-MS测定时选用碰撞池技术以消除40Ar12C+与35Cl16OH+对52Cr+的谱学干扰;进样100 μL时,Cr(Ⅲ)与Cr(Ⅵ)的检出限分别为0.15 μg/L和0.16 μg/L.加标回收率在93.6%～106.2%之间; RSD<4%(n=3).以本方法分析了某市自来水、雨水及某品牌纯净水中Cr(Ⅲ)与Cr(Ⅵ)的含量,结果令人满意.     

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.