反相高效液相色谱法测定强化奶粉中β-胡萝卜素含量

采用碱皂化石油醚提取,Kromasil C18柱分离,以甲醇∶氯仿=75∶25等度淋洗,二极管阵列检测器检测,测定了强化奶粉中β-胡萝卜素含量.对最佳皂化用碱量、皂化时间、α、β-胡罗卜素及β-胡罗卜素异构体分离条件进行了探索.该方法回收率为91.6%~96.3%,其标准偏差、变异系数分别为1.64%及1.76%.方法简便、快速,精密度及准确度在允许范围内,适用于奶粉中β-胡罗卜素的测定.     

Molecular dynamics simulation of room-temperature ionic liquid mixture of [bmim][BF4] and acetonitrile by a refined force field

1-Butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) is one of the promising room-temperature ionic liquids. To test the refined force field for [bmim][BF4] proposed in our previously work (J. Phys. Chem. B, 2004, 108, 12978-12989), thermodynamic properties of mixtures of [bmim][BF4](1)+ acetonitrile (2) are presented by using molecular dynamics over the whole concentration range. The calculated densities are in good agreement with the experimental data with deviations less than 2%, indicating the force field is applicable to the mixtures. In addition, the diffusion constants, viscosities, heats of vaporization, cohesive energy densities and excess properties of the mixtures are reported. The microscopic structures are discussed in detail, corresponding to the thermodynamic properties.     

微波消解-氢化物发生原子荧光法测定塑料原料及其制品中的砷、汞

采用微波消解进行样品前处理，以硫脲为预还原剂，用氢化物发生原子荧光法测定塑料原料及其制品中的砷、汞。测定砷和汞的线性范围均为0～8μg／L，砷、汞的检出限分别为0．005、0．076μg／L，测定结果的相对标准偏差分别为4.96％～7．38％、2．94％～7．20％(n=6)，回收率分别为92．0％～103．2％、92．0％～98.0％。     

Controlled/“Living “Radical Polymerization of(-)-Menthyl Methacrylate

The atom transfer radical polymerization(ARP)of (-)-menthyl methacrylatc((-)-MnMA) mediated by CuCl/bipyridine and ethy1 2-bromopropionate or 1-phenylethyl bromide in THF system has been studied.The dependence of the specific rotation on molecular weight and the CD of Poly((-)-MnMA) thus obatined was investigated.     

钯（0）／离子交换树脂对有机锡试剂和有机卤化物偶联反应的催化性能和结构表征

制备了强碱性阴离子交换树脂（）负载钯（０）催化剂，发现它对有机锡试剂和有机卤化物的偶联反应有很高的催化活性，分离容易，可重复使用．起催化作用的是金属态把．ＸＰＳ等实验结果表明，在催化剂中钯作为桥将功能基－Ｎ（ＣＨ３）３与ＯＨ－联结起来．催化剂中的把可以看作是两配位的和配位不饱和的，经过氧化加成、金属交换、还原消除过程完成催化反应．     

SAPO-34分子筛骨架稳定性的研究

利用差热分析，原位ＸＲＤ技术，高温条件下的焙烧和水蒸气处理并关联其催化性能变化，研究了ＳＡＰＯ－３４分子筛的热及水热稳定性，差热分析结果表明，ＳＡＰＯ－３４的骨架破坏温度高于１３００Ｋ，原位ＸＲＤ跟踪研究证实，ＳＡＰＯ－３４分子筛原粉在高温焙烧以除掉有机胺及随后的降温过程中无明显的骨架破坏；而焙烧型ＳＡＰＯ－３４在空气中放置一定时间后，水分子吸附微孔中明业降低样品的ＸＲＤ峰强度，且降低幅度随放置时     

Syntheses and structures of structurally diverse potassium beta-diketiminates derived from the ligand [(N(SiMe3)C(Ph))2CH

The compounds [K((mu-N(SiMe3)C(Ph))2CH)(thf)2]infinity 1, [K(mu-N(SiMe3)C(Ph)C(H)C(Ph)NH)L]2 [L = (thf)2 2, tmen 3], [K(mu-NSi(Me)2C(Ph)C(H)C(Ph)N)(thf)3]2 4 and [K(N(H)C(Ph))2CH](thf)0.5 5 have been prepared from K[(N(SiMe3)C(Ph))2CH] and the X-ray structures of 1-4 are reported.     

SPECTROSCOPY AND FLUORESCENCE QUENCHING OF TYROSINE IN LIMA BEAN TRYPSIN/CHYMOTRYPSIN INHIBITOR AND MODEL PEPTIDES

The effects of citrate ion concentration and pH on the optical spectra and fluorescence decay have been measured for several tyrosine model compounds and lima bean trypsin/chymotrypsin inhibitor, a protein containing one tyrosine at position 69 and seven disulfides but no tryptophan, in order to determine the location and environment of Tyr 69. Tyrosine in the protein is protected from citrate collisional quenching, as indicated by the dynamic quenching constant 9 to 15 times smaller than those for the model peptides. Static quenching remains, with a Stern-Volmer constant of about 1.0 M-1, somewhat smaller than those of L-tyrosine, tyrosine-glutamate, and leucine-tyrosine-leucine. The elevated pKa of Tyr 69, greater than or equal to 11.6, also indicates protein protection from solvent ions. Though Coulomb repulsion of the Glu 70/citrate pair may play a role in the shielding of Tyr 69 from citrate, our measurements indicate that steric effects of the protein structure are more important. Tyrosinate emission in the protein at neutral pH is minimal.     

Fluorescence decay and quenching of pyrene labeled on sulfonate polyelectrolytes in salt-free aqueous solutions

Fluorescence decay and quenching of pyrene labels on copolymers of 2-acrylamido-2-methylpropanesulphonic acid (AMPS) and N,N-dimethylacrylamide were observed in dilute salt-free aqueous solutions as a function of the mole fraction F_AMPS of AMPS from 0 to 0.896. Monoexponential decay was found for the samples of F_AMPS<0.35 and biexponential decay for the samples of F_AMPS>0.35. The fast decay component is 80%, and the averaged lifetime 〈τ〉 and lifetime τ₁ of the fast decay is decreased with increasing F_AMPS. Quenching efficiency of Cu²⁺, I⁻, CH₃NO₂, and dinitrobenzene to the pyrene label was investigated in the framework of Stern-Volmer plot. With increasing F_AMPS the quenching efficiency of Cu²⁺ is increased while that of I⁻ decreased. For the neutral quenchers, the quenching rate constant k_q increases when F_AMPS<0.449 then decreases, showing a decline of accessibility to the pyrene label. These results were interpreted consistently with the counterion condensation concept, where condensed counterions caused the polyelectrolyte chains to aggregate. The existence of less-polar “temporal aggregated domain” in highly charged polyelectrolytes appears to lead to the slower decay and lower accessibility of the pyrene labels.