羧基化多壁碳纳米管固相萃取-液相色谱-串联质谱法测定环境水体中四溴双酚A和双酚A

建立了羧基化碳纳米管固相萃取-液相色谱-串联质谱联用检测环境水体中四溴双酚A和双酚A的方法。比较了多壁碳纳米管、C60和羧基化多壁碳纳米管作为固相吸附剂对水体中四溴双酚A和双酚A的吸附效率。固相萃取浓缩后的样品经Thermo Scientific Hypersil C18色谱柱（150 mm×4.6 mm,3 μm）分离,采用串联质谱负离子模式进行检测。结果表明,四溴双酚A和双酚A在0.02~1.0 mg/L范围内具有良好的线性关系（r²≥0.99）,空白样品中的检出限（S/N=3）分别为0.04 μg/L和0.2 μg/L。将所建立的方法应用于实际环境水体中四溴双酚A和双酚A的检测,添加回收率在82%~99%之间,精密度小于5.0%,该方法可用于复杂环境样品中痕量四溴双酚A和双酚A的检测。     

高效液相色谱荧光检测法对一次性纸杯中双酚A的迁移规律研究

建立了一次性纸杯中双酚A的高效液相色谱检测方法并根据国家标准和欧盟有关模拟物规定的指令,研究了一次性纸杯中双酚A在不同模拟物中的迁移规律。考察了纸杯中双酚A对内向食物迁移的规律及其对外向人体迁移的规律,并对浸泡时间、温度、不同模拟物条件下的双酚A的迁移进行了研究。使用高效液相色谱荧光检测双酚A,检出限为10μg/kg,双酚A的线性范围为0.05~50 mg/kg;加标回收率为88%~95%;相对标准偏差(RSD)为2.7%~3.8%。     

双酚A分子印迹材料的制备及其识别特性研究

以双酚A为模板分子,α-甲基丙烯酸为功能单体,乙二醇二甲基丙烯酸酯为交联剂,偶氮二异丁腈为引发剂制备了双酚A印迹聚合物。采用动态和静态两种方法研究了该印迹材料对双酚A的结合性能与分子识别特性。印迹材料对模板分子双酚A具有良好的特异性识别作用,经过Scatchard模型分析,双酚A印迹聚合物上有两类不同性质的结合位点,两种结合位点的解离常数分别为1.36和44.78 m L/g,对双酚A的最大表观吸附量分别为24.56μmol/g和312.6μmol/g。将该聚合物应用于固相萃取中,以食品包装材料为样品的加标回收实验表明,此印迹材料可以对痕量双酚A进行富集分离测定,且可重复使用。     

土壤悬浮液中双酚A的光降解研究

实验研究了双酚A在土壤表面的吸附特征及在土壤悬浮液中的光降解.研究结果表明,双酚A在土壤表面的吸附为单分子的化学吸附,用Langmuir模型或Freundlich模型拟合时相关性较好.在高压汞灯(λ=300nm)照射下,双酚A在土壤悬浮液中能快速降解,降解速度随酸度的增大而加快.在此体系中双酚A光降解动力学遵循Langmuir-Hinshelwood(H-L)方程,在土壤量不超过10g/L的条件下,降解率随土壤量增加而增加,加入腐殖酸可以促进双酚A的光解,同时增大光照强度有利于双酚A的降解.     

液相色谱-三重四极杆质谱同时测定食品接触材料中双酚A、双酚F与双酚S的迁移量

采用液相色谱-三重四极杆质谱(LC-MS/MS)建立了食品接触材料中双酚A、双酚F和双酚S化合物的同时测定方法。双酚A、双酚F和双酚S在样品中通过与食品模拟物在一定温度、时间接触的状态下迁移到食品模拟物中,以C18色谱柱进行分离,甲醇-氨水为流动相洗脱,采用电喷雾离子源(ESI),多反应监测(MRM)负离子模式进行扫描,同位素内标法定量。结果表明,双酚A、双酚F和双酚S的色谱分离良好,双酚A和双酚F在1~50μg/L质量浓度范围内与其峰面积均呈线性关系,BPS在0.1~50μg/L质量浓度范围内与其峰面积呈线性关系。BPA和BPF的最低检出限为0.3μg/L,BPS的最低检出限为0.05μg/L。加标回收率为83.6%~102.6%,相对标准偏差(RSD)为3.5%~8.9%。该方法快速可靠、准确简便,适用于食品接触材料中双酚A、双酚F和双酚S化合物的检测。     

氟烷基取代的双酚A类衍生物的合成

利用相转移催化剂十六烷基三甲基溴化铵(CTMAB)催化的连二亚硫酸钠引发的苯酚衍生物与含氟碘代烷的氟烷基化反应, 合成了含氟烷基取代的酚类化合物. 研究了双酚A与含氟碘代烷的氟烷基化反应, 得到了一类重要的含氟单体, 即含氟烷基取代的双酚A衍生物. 通过改变含氟碘代烷与双酚A的摩尔比, 可以得到单取代、二取代和四取代的含氟烷基双酚A衍生物.     

ABS塑料中双酚A和壬基酚标准样品的研制

正双酚A(BPA)和壬基酚(NP)作为良好的塑料添加剂,广泛用于塑料玩具、奶瓶、水瓶,以及其他数百种日用品的制造。双酚A和壬基酚都属于"环境激素",作为典型的环境内分泌干扰物已经引起人们的广泛关注。近年来,美国、加拿大、欧盟等发达国家和地区陆续认定双酚A为有毒化学物质,并对儿童用品、食品包装、饮料容器等纷纷制订了双酚A限量标准,甚至对某些儿童用品完全禁用双酚A。     

高效液相色谱法研究双酚A二烯丙基醚的转位反应

用工业原料双酚A和3-氯丙烯制备出纯度高于90%的双酚A二烯丙基醚,利用热重分析法确定了双酚A二烯丙基醚发生Claisen﹡转位反应的温度为200℃左右。利用高压液相色谱技术,在不同温度条件下,分别考查了二烯丙基双酚A的产品含量、外观与反应时间的关系。结果表明,在190℃、200℃、210℃条件下,二烯丙基双酚A的最高含量分别为56.2%、59.7%、57.5%,最佳反应时间分别为270 mins、130 mins、90 mins。200℃时产品色泽为琥珀色,其余产品颜色发黑。二烯丙基双酚A的形成不是一步完成的,经过了中间产物的形成及转化过程。     

食品包装材料中双酚A在食品模拟物中迁移规律的研究

食品塑料包装材料的安全是保障食品安全的重要一环,包装材料中的双酚A潜在迁移性对人体健康的危害已引起社会的关注. 分别选取蒸馏水、3%乙酸(体积分数)和10%乙醇(体积分数)3种食品模拟物,浸泡已知双酚A含量的食品包装材料,在一定的时间点测试浸泡液中双酚A含量,研究迁移量与模拟物之间的关系. 结果表明,在不同食品模拟物下包装材料中双酚A的迁移量不同,其特定迁移量顺序为10%乙醇溶液>3 %乙酸溶液>蒸馏水. 并研究了温度、时间及微波作用影响食品包装材料中双酚A向食品中的迁移量,结果表明,双酚A向食品中迁移量随接触时间的延长、温度的升高而增加,微波作用能显著提高包装材料中双酚A向食品中的迁移量.     

双酚A的流动注射化学发光法测定

基于双酚A对鲁米诺 铁氰化钾化学发光反应体系的化学发光的抑制作用,建立了一种测定环境雌激素双酚A的流动注射化学发光分析新方法。双酚A的浓度在8.0×10-7～1.0×10-5mol/L范围内与ΔI成良好的线性关系,检出限为3.05×10-7mol/L,已用于聚碳酸酯塑料水溶出液中双酚A的测定。     

Structure and ethanol complexation of cyclic tetrasaccharide in aqueous solution studied by NMR and molecular mechanics

The structure and ethanol complexation of a cyclic tetrasaccharide (CTS) in aqueous solution were investigated by proton NMR spectroscopy and molecular mechanics calculations. Two glucose units, A and B, of CTS are alternatively bonded by alpha-1,3 and alpha-1,6 linkages. The overlapped signals of protons A5, A6S, A6R, B3, B6S and B6R were resolved by spectral simulations to determine their chemical shifts and vicinal coupling constants. All vicinal coupling constants except for the A5-A6 spin system are consistent with the dihedral angles in the X-ray crystal structure. Each of protons A5, A6S, and A6R in the two units of A is equivalent with respect to the chemical shift. The vicinal coupling constants of (3)J(5-6S) and (3)J(5-6R) for unit A are close to the average of two rotamers that are present in crystals. The intensities of cross-peaks in the rotating frame nuclear Overhauser effect spectroscopy (ROESY) spectrum were rather well correlated with the effective distances calculated for the X-ray structure and molecular mechanics structures calculated in vacuo and water, although they are slightly better correlated with molecular mechanics structure in vacuo than with the other structures. From the changes of the chemical shifts of several CTS protons with increasing ethanol concentration, it was suggested that adsorption sites of ethanol on the plate structure of CTS are protons B2 and B4 (site B) in the concave face side and protons A1 and A2 (site A) in the convex back side. The binding constants for sites A and B are 0.0061 and 0.0176 M(-1), respectively. These binding constants are much smaller than a value of 4.1 M(-1) for the ethanol-alpha-cyclodextrin complex.     

Slow photoelectron velocity-map imaging spectroscopy of the n-methylvinoxide anion

High resolution photoelectron spectra of the n-methylvinoxide anion and its deuterated isotopologue are obtained by slow electron velocity-map imaging. Transitions between the X?(1)A' anion ground electronic state and the radical X?(2)A" and A?(2)A' states are observed. The major features in the spectra are attributed to transitions involving the lower energy cis conformers of the anion and neutral, while the higher energy trans conformers contribute only a single small peak. Franck-Condon simulations of the X?(2)A" ← X?(1)A' and A?(2)A' ← X?(1)A' transitions are performed to assign vibrational structure in the spectrum and to aid in identifying peaks in the cis-n-methylvinoxy X? (2)A" band that occur only through vibronic coupling. The experimental electron affinity and A? state term energy are found to be EA = 1.6106 ± 0.0008 eV and T(0) = 1.167 ± 0.002 eV for cis-n-methylvinoxy.     

PHASE STRUCTURE AND COMPATIBILITY OF LADDERLIKE POLYPHENYLSILSESQUIOXANE (PPSQ)/POLYCARBONATE (PC) BLENDS PREPARED BY SOLUTION CASTING*

Blends of PC and PPSQ (A) with high M_w and good ladderlike regularity or PPSQ(B) withlow M_w and more defective Si-atoms in its structure have been prepared by solution casting. Thedispersed spheres (PPSQ(A)-rich) are unevenly dispersed in the continuous PC-rich phase and there isno phase-inversion as PPSQ(A) content increases when the percentage of PPSQ(A) is not more than70%. PPSQ(B)-rich spheres are evenly dispersed in the continuous phase (PC-rich) and phase-inversion occurs when PPSQ(B) percentage is up to 70%. T_g of PPSQ(A)/PC or PPSQ(B)/PC at somecompositions are lower than that of pure PC due to the enlarged free-volume of PC-rich phase becausesome spheres of rigid PPSQ chains are included in the PC-rich phase. PC and PPSQ(A) or PPSQ(B)are partially compatible. The compatibility of PC and PPSQ(B) is better than that of PC and PPSQ(A)with high M_w and good ladderlike regularity. Heat history has some influence on the T_gs andcompatibility of PPSQ(A)/PC and PPSQ(B)/PC blends.     

Two-dimensional liquid chromatography of diblock copolymers: Simulation at various adsorption interaction conditions

Diblock copolymers, which are heterogeneous in both molar mass and composition, can be fully characterized by using two-dimensional chromatography. Since the size-exclusion, the adsorption, and the critical interaction based modes of chromatography are possible for each of the polymers A and B, this leads to a variety of options for 2D-chromatography of copolymers AB. Using the theory of chromatography of block copolymers, 2D-chromatograms are simulated that correspond to the most interesting of these options. Orthogonal 2D-chromatograms are expected, if in the 1st dimension the critical condition is created for A, while in the 2nd dimension – for B. The situations, where A and B are both adsorbable, as well as those where the conditions of adsorption for A and SEC for B are created, are also considered. In particular, it is shown that the 2nd dimension combination of the critical condition for A and SEC – for B is preferable than that with SEC condition for both A and B. The simulated 2D-chromatograms of low- and high molar mass diblock copolymers, as well as of copolymers with one short block are compared with the reported real ones; it is concluded that the corresponding virtual and real 2D-chromatograms are qualitatively very similar.     

Dynamics of water molecules in the active-site cavity of human cytochromes P450

We have studied the dynamics of water molecules in six crystal structures of four human cytochromes P450, 2A6, 2C8, 2C9, and 3A4, with molecular dynamics simulations. In the crystal structures, only a few water molecules are seen and the reported sizes of the active-site cavity vary a lot. In the simulations, the cavities are completely filled with water molecules, although with approximately 20% lower density than in bulk water. The 2A6 protein differs from the other three in that it has a very small cavity with only two water molecules and no exchange with the surroundings. The other three proteins have quite big cavities, with 41 water molecules on average in 2C8 and 54-58 in 2C9 and 3A4, giving a water volume of 1500-2100 A3. The two crystal structures of 2C9 differ quite appreciably, whereas those of 3A4 are quite similar. The active-site cavity is connected to the surroundings by three to six channels, through which there is a quite frequent exchange of water molecules (one molecule is exchanged every 30-200 ps), except in 2A6. Most of the channels are observed also in the crystal structures, but two to three channels in each protein open only during the simulations. There are no water molecules close to the heme iron ion in these simulations of the high-spin ferric state (the average distance to the closest water molecule is 3.3-5 A), and there are few ordered water molecules in the active sites, none of which is conserved in all proteins.     

Radiation-induced silver agglomeration in molecular sieves: A comparison between A and X zeolites

The stabilization conditions of silver atoms and clusters in hydrated and dehydrated AgNa-A and AgNa-X zeolites γ-irradiated at 77 K have been studied by ESR. It was found that silver agglomeration mechanisms in hydrated A and X zeolites are very similar and are controlled by the migration of silver atoms into the -cages. In dehydrated zeolites agglomeration leads to completely different silver clusters in A and X zeolites. Small cationic clusters are stabilized in A zeolites and metallic clusters in X zeolites. Various factors affecting the agglomeration process in A and X zeolites are discussed.     

Parametric effects of the potential energy function on the geometrical features of ternary lennard-jones clusters

The impact of parameters in potential function for describing atomic or molecular clusters is complex due to the complicated potential energy surface. Ternary Lennard-Jones (TLJ) A(l)B(m)C(n) clusters with two-body potential are investigated to study the effect of parameters. In the potential, the size parameter (σ(AA)) of A atoms is fixed, and corresponding parameters of B and C atoms (relative to A atoms), i.e., σ(BB)/σ(AA) and σ(CC)/σ(AA) > 1.00, are used to control the atomic interaction among A, B, and C atoms in TLJ clusters. The minimum energy configurations of A(l)B(m)C(n) clusters with different species are optimized by adaptive immune optimization algorithm. Ternary cluster structures, bonds, and energies of the putative minima are studied. The results show that two different structures based on double-icosahedra are found in 30-atom TLJ clusters. Furthermore, with increasing potential size parameters of B and C atoms, A atoms tend to be more compact for the increasing numbers of A-A bonds, but the short-range attractive part in TLJ clusters becomes weaker. To lower the potential energy, B and C atoms grow around the A atoms in pursuit of a compact configuration. The results are also approved in A(l)B(m)C(n) (l + m + n = 9-55) clusters and A(l)B(m)C(n) (l = 13, m + n = 42) clusters.     

Fast neutron activation analysis at Texas A&M University

Fast neutron generators are used at Texas A & M University to provide a supply of high energy neutrons for nuclear analytical measurements. A series of neutron activation analysis procedures have been developed for determining various major, minor and trace constituents in a variety of materials. These procedures are primarily developed to compliment our reactor based NAA program, thereby expanding the list of determinable elements to include those difficult or impossible to measure using thermal neutrons. A few typical methods are discussed. The unique implementation of the methodologies at Texas A & M are explained.     

The vibrational spectrum of the secondary electron acceptor, A1, in photosystem I

Photosystem I (PSI) is a multisubunit protein complex which carries out light-induced, transmembrane charge separation in oxygenic photosynthesis. In PSI, the electron-transfer pathway consists of chlorophyll and phylloquinone molecules, as well as iron-sulfur clusters. There are two phylloquinone molecules, which are located in structurally symmetric positions in the reaction center. It has been proposed that both phylloquinone molecules are active as the A1 secondary electron acceptor in bidirectional electron-transfer reactions. The PSI A1 acceptors are of interest because they have the lowest reduction potential of any quinone found in nature. In this work using light-induced FT-IR spectroscopy, isotope-edited spectra are presented, which attribute vibrational bands to the carbonyl stretching vibrations of A1 and A1- and the quinoid ring stretching vibration of A1. Bands are assigned by comparison with hybrid Hartee-Fock density functional calculations, which predict vibrational frequencies, amplitudes, and isotope shifts for the phylloquinone singlet and radical anion states. The results are consistent with an environmental interaction increasing the frequency of the singlet CO vibration and decreasing the frequency of the anion radical CO vibration, relative to model compounds. This environmental interaction may be the asymmetric hydrogen bond to A1/A1-, electrostatic interactions with charged amino acid side chains, or a pi-pi interaction with the indole ring of a nearby tryptophan. Such differential effects on the structure of A1 and A1- may be associated with a destabilization of the anion radical. These studies give novel information concerning the effect of the protein matrix on the PSI electron-transfer cofactor.