阳离子Gemini表面活性剂12-3-12与DNA在模拟体液中的相互作用研究

采用紫外透射光谱、透射电镜、原子力显微镜、圆二色谱(CD)等方法探讨了阳离子Gemini表面活性剂C12H25N+(CH3)2-(CH2)3-(CH3)2N+C12H25·2Br-(12-3-12)与DNA在模拟体液(SBF)中的相互作用。结果表明,SBF中较高反离子浓度不但屏蔽了DNA和12-3-12之间的静电吸引作用,而且促进了12-3-12聚集体的产生和生长,导致低盐条件下体系中出现的沉淀溶解现象的消失。SBF中DNA与12-3-12之间存在强烈的相互作用;随着12-3-12的加入,表面活性剂分子在DNA链周围聚集,类网络结构的DNA逐渐变为类似于串珠的复合物,随后出现尺寸较大的类球形复合物以及较大复合物与较小表面活性剂聚集体共存的现象。CD谱结果显示,SBF中12-3-12可以诱导DNA的构象发生改变,由自然的B构型变成高度致密的ψ相。分子动力学模拟的离子液体中表面活性剂与带相反电荷聚电解质的相互作用过程及模式与实验结果吻合良好。模拟结果也表明,SBF中较高的反离子浓度提高了聚电解质的可压缩程度,导致相同条件下SBF中聚电解质的均方回旋半径远小于稀盐水溶液(10mmol/L Na Br)体系中的聚电解质均方回旋半径。较强的离子强度不但导致体系中聚电解质和带相反电荷表面活性剂之间的相互作用存在"假饱和"现象,而且也造成体系中表面活性剂在聚电解质周围聚集数显著提高。     

C12EO4与氨丙基三乙氧基硅烷水溶液自组装和流变性研究

研究了3-氨丙基三乙氧基硅烷(APTES)和非离子表面活性剂十二烷基聚氧乙烯(C₁₂EO₄)水溶液的相行为、溶液自聚集作用和流变性, 小角度X-射线散射(SAXS)、低温透射电子显微镜(cryo-TEM)和氘谱核磁共振(²H NMR)测定确定了溶液中聚集体结构, 测定了聚集体混合物溶液的流变性质. 结果表明: 随着溶液混合物组分的变化, 溶液聚集体结构发生了改变, 在L_α相区内, 恒定C₁₂EO₄浓度, 随着APTES浓度增加聚集体结构由高曲率聚集体转变为低曲率的层状结构; 而在恒定APTES浓度时, 随着C₁₂EO₄增加, L_α相由低粘弹性的囊泡溶液转变为粘弹性极高的密堆积囊泡和平面层状结构共存的类凝胶相, 溶液聚集体结构和结构转变是由于APTES水解产物插入至C₁₂EO₄胶束引起的. 非离子表面活性剂和氨基硅烷混合物溶液相结构及结构转变的新结果对于完全理解该类混合物的实际应用, 特别是作为模板合成硅材料的应用具有重要理论意义.     

氢氧化镁共沉淀法测定海水中纳摩尔级活性磷酸盐

利用海水中Mg(2+)与OH-生成沉淀时会共沉淀PO(3-4)的特性,富集海水中PO(3-4),富集后的Mg(OH)2沉淀用酸溶解,应用磷钼蓝-分光光度法测定.对试剂用量、离心速度及时间、Mg(OH)2,溶解用酸种类、H/Mo等实验参数和条件进行了优化.并采用与常规磷钼蓝法介质一致的H2SO4作为Mg(OH)2沉淀溶解...     

在吐温-80存在下硫氰酸盐-邻菲绕啉分光光度法测定矿石中铁

吐温-80-硫氰酸盐-邻菲绕啉显色体系测定矿石中铁,在3×10~(-1)—1×10~(-3)mol/L硝酸酸度下,形成稳定的三元胶束增溶络合物,最大吸收波长λ=520nm,ε=1.96×10~4,标准偏差为0.0026%,变异系数为0.88%,络合物能稳定1.5小时,在0—40微克/50毫升内服从比尔定律。分析步骤称取0.1000—0.5000克试样于银坩埚中,加入4—6克氢氧化钠,置高温炉中于400℃保温15分钟,再升温到700℃保持3分钟,取出冷却。用热水浸取,洗入300毫升烧杯中。用浓硝酸中和至沉淀溶解,再过量1毫升,煮沸使溶液清亮,取下冷却,移     

高效液相色谱法测定大鼠组织中双酚A和4-壬基酚浓度

建立了大鼠组织中双酚A和4-壬基酚的提取和含量测定方法。大鼠组织样品经甲醇-乙酸铵缓冲液匀浆、 正己烷-乙醚混合溶剂提取、氮气吹干后用流动相溶解,以乙腈-0.01 mol/L乙酸铵缓冲液(pH 4.5)(体积比为75∶25)为流动相,经C18色谱柱分离,在激发波长227 nm、发射波长313 nm下进行荧光检测。大鼠心、脑、肝和肾脏组织样品中,双酚A的检出限为3.2~4.6 ng/g,4-壬基酚的检出限为11.8~15.6 ng/g;日内检测精密度为0.89%~4.50%,日间检测精密度为3.10%~12     

高效液相色谱-质谱法测定压敏胶及其制品中9种邻苯二甲酸酯

采用高效液相色谱-质谱( HPLC - MS)法,对压敏胶及其制品中的9种邻苯二甲酸酯进行同时测定.以乙酸乙酯为溶剂溶解压敏胶,甲醇沉淀高聚物,以3 000 r/min离心5min,清液定容后,用HPLC -MS分析检测.采用Xterra-Phenyl色谱柱,流动相为乙腈-水,流速为1 mL/min,选择离子监测.在优...     

液相色谱-三级质谱法分析尿液中β2-受体激动剂及β-受体阻断剂多组分残留

建立了SPE柱净化结合液相色谱-三级质谱测定尿液中12种β-受体激动剂和4种β-受体阻断剂的方法.尿液样品经冷冻离心,加人β-葡萄糖苷酸酶酶解后,以高氯酸沉淀蛋白,经HLB和MCX固相萃取柱净化.在Waters Atlantis(R)T3色谱柱上以甲醇和含0.1%甲酸流动相进行梯度洗脱分离,采用ESI源正离子模式进行三...     

12-冠-4对非质子Li-O2电池氧电极的影响

Li-O₂电池放电产物Li₂O₂由于在有机溶剂中溶解度较差,会堵塞气体通道,这是Li-O₂电池面临的一个主要挑战。在本工作中,我们选择12-冠-4做为添加剂捕获Li⁺,来研究其对氧电极放电产物溶解性的影响,并采用了多种电化学表征方法,包括循环伏安法和旋转圆盘电极等。结果显示,仅仅添加5%的12-冠-4就能明显提高氧还原产物$\text{O}_{2}^{-}$的稳定性,并减少固体Li₂O₂的生成。结合软硬酸碱和第一性原理计算对上述实验结果进行了解释。     

明胶溶液中沉淀法制备纯相β-磷酸三钙

本文以明胶、硝酸钙Ca(NO₃)₂和磷酸氢二铵(NH₄)₂HPO₄为前驱体,初始Ca/P为1.5,制备了纯相的β-磷酸三钙.红外谱图和X射线晶体衍射结果表明,溶液中直接沉淀得到的产物为缺钙磷灰石,该产物在明胶浓度≥0.22 %(质量分数)时热转化为纯相的β-磷酸三钙.通过晶体尺寸计算和比表面积测定,缺钙磷灰石的晶体大小随着明胶用量的增加而变小.透射电镜结果显示溶液中直接沉淀的缺钙磷灰石呈针状形貌,经过高温煅烧后,针状的缺钙磷灰石将相互融合形成葡萄状的β-磷酸三钙.差热/热重结果表明,明胶与生成的缺钙磷灰石形成了化学键合,这将有助于吸附较多的水分子,随后水分子与缺钙磷灰石发生化学反应生成羟基磷灰石,羟基磷灰石继续与沉淀中的偏磷酸钙反应生成β-磷酸三钙.本文还研究了明胶对纯相β-磷酸三钙的生成机理.     

钼及钨之测定——Ⅺ.以4-氨基-4’-氯联苯作沉淀剂

4-氨基-4′-氯联苯可以用作钨(Ⅵ)的沉淀剂。适宜於沉淀的溶液酸度为pH 1.5—3.1。应在室温沉淀,继在近沸温度静置。沉淀剂用量应为理论值1.25倍。测定过4—75毫克三氧化钨均能得满意的结果。根据热解曲线沉淀只能灼烧为三氧化钨而称重。灼炼温度为625--850°。文中尚报告数称碱金属盐的影响。 4-氨基-4′-氯联苯之钼酸盐在pH1.8--2.8时亦能定量沉淀,其溶解度较相应的钨酸盐为高。但有希望用作钼(Ⅵ)之沉淀剂。     

Ethanol or/and captopril-induced precipitation and secondary conformational changes of human serum albumin

We determined the secondary structure of solid-state native human serum albumin (HSA) and its precipitates induced by ethanol, captopril, or a captopril/ethanol mixture. A transmission Fourier transform infrared (FT-IR) microspectroscopy equipped with a thermal analyzer was used. The secondary structural composition of solid-state native HSA was 54% alpha-helices (1655 cm(-1)), 22% beta-turns (1679 cm(-1)), and 23% beta-sheets (1633 cm(-1)). After ethanol treatment, a new peak was observed at 1690 cm(-1), and the peak at 1633 cm(-1) was more apparent in the HSA precipitates. The corresponding compositions consisted of 59% alpha-helices, 17% beta-turns, and 24% beta-sheets. After treatment with captopril with or without ethanol, the percentage of alpha-helices and beta-turns decreased in both HSA precipitates, but the percentage of beta-sheets increased. The temperature-dependent structural transformation from alpha-helices/random coils to beta-sheets for the solid-state HSA samples occurred at markedly different onset temperatures. The onset temperature for native HSA was 85 degrees C, and that for HSA precipitates obtained from ethanol, captopril, or captopril/ethanol was 100, 48 or 57 degrees C, respectively. The thermal-induced structural transformation from alpha-helices/random coils to beta-sheets implies a partial unfolding structure in these HSA samples.     

液相一步合成金红石型超细TiO2

二氧化钛在自然界中存在三种结晶形态:金红石型、锐钛矿型和板钛矿型.金红石型TiO₂因其折射率高,性能优越,因而得到广泛的应用^[1～3].传统金红石型TiO₂的制备需经高温固相反应,经历由无定形→锐钛矿→金红石的转化过程.     

Search for lowest-energy structure of Zintl dianion Si(12)(2-), Ge(12)(2-), and Sn(12)(2-)

We perform an unbiased search for the lowest-energy structures of Zintl dianions (Si(12)(2-), Ge(12)(2-), and Sn(12)(2-)), by using the basin-hopping (BH) global optimization method combined with density functional theory geometric optimization. High-level ab initio calculation at the coupled-cluster level is used to determine relative stabilities and energy ranking among competitive low-lying isomers of the dianions obtained from the BH search. For Si(12)(2-), all BH searches (based on independent initial structures) lead to the same lowest-energy structure Si(12a)(2-), a tricapped trigonal prism (TTP) with C(s) group symmetry. Coupled-cluster calculation, however, suggests that another TTP isomer of Si(12c)(2-) is nearly isoenergetic with Si(12a)(2-). For Sn(12)(2-), all BH searches lead to the icosahedral structure I(h)-Sn(12a)(2-), i.e., the stannaspherene. For Ge(12)(2-), however, most BH searches lead to the TTP-containing Ge(12b)(2-), while a few BH searches lead to the empty-cage icosahedral structure I(h)-Ge(12a)(2-) (named as germaniaspherene). High-level ab initio calculation indicates that I(h)-Ge(12a)(2-) and TTP-containing Ge(12b)(2-) are almost isoenergetic and, thus, both may be considered as candidates for the lowest-energy structure at 0 K. Ge(12a)(2-) has a much larger energy gap (2.04 eV) between highest occupied molecular orbital and lowest unoccupied molecular orbital than Ge(12b)(2-) (1.29 eV), while Ge(12b)(2-) has a lower free energy than I(h)-Ge(12a)(2-) at elevated temperature (>980 K). The TTP-containing Si(12a)(2-) and Ge(12b)(2-) exhibit large negative nuclear independent chemical shift (NICS) value (approximately -44) at the center of TTP, indicating aromatic character. In contrast, germaniaspherene I(h)-Ge(12a)(2-) and stannaspherene I(h)-Sn(12a)(2-) exhibit modest positive NICS values, approximately 12 and 3, respectively, at the center of the empty cage, indicating weakly antiaromatic character.     

Crown compounds for anions: sandwich and half-sandwich complexes of cyclic trimetric perfluoro-o-phenylenemercury with polyhedral closo-[B10H10]2- and closo-[B12H12]2- anions

It has been shown by IR and NMR spectroscopy that cyclic trimeric perfluoro-o-phenylenemercury (o-C6F4-Hg)3 (1) is capable of binding closo-[B10H10]2- and closo-[B12H12]2- anions to form complexes [[(o-C6F4Hg)3](B10-H10)]2- (2), [[(o-C6F4Hg)3]2(B10H10)]2-(3), [[(o-C6F4Hg)3](B12H12)]2- (4), and [[(o-C6F4Hg)3]2(B12H12)]2- (5). According to IR data, the bonding of the [B10H10]2- and [B12H12]2- ions to the macrocycle in these complexes is accomplished through the formation of B-H-Hg bridges. Complexes 2, 3, and 5 have been isolated in analytically pure form and have been characterized by spectroscopic means. X-ray diffraction studies of 3 and 5 have revealed that these compounds have unusual sandwich structures, in which the polyhedral di-anion is located between the planes of two molecules of 1 and is bonded to each of them through two types of B-H-Hg bridges. One type is the simultaneous coordination of a B-H group to all three Hg atoms of the macrocycle. The other type is the coordination of a B-H group to a single Hg atom of the cycle. According to X-ray diffraction data, complex 2 has an analogous but half-sandwich structure. The obtained complexes 2-5 are quite stable; their stability constants in THF/acetone (1:1) at 20 degrees C have been determined as 1.0 x 10(2)Lmol(-1), 2.6 x 10(3)L(2)mol(2), 0.7 x 10(2)Lmol(-1), and 0.98 x 10(3)L(2)mol(-2), respectively.     

Formation of p-phenylenediamine-crown ether-[PMo12O40]4- salts

Electron transfer from the electron donor of p-phenylenediamine (PPD) to the electron acceptor of (H+)3[PMo12O40]3- forms a one-electron-reduced Keggin cluster of [PMo12O40]4-, bearing a S = 1/2 spin, while proton transfer from the proton donor of (H+)3[PMo12O40]3- to the proton acceptor of PPD yielded mono- and diprotonated cations of 4-aminoanilinium (HPPD+) and p-phenylenediammonium (H2PPD2+). By introduction of crown ether receptors during the crystallization process, supramolecular cations of (HPPD+)(crown ethers) and/or (H2PPD2+)(crown ethers) were successfully introduced into three new alpha-[PMo12O40]4- salts of (H2PPD2+)2([12]crown-4)4[PMo12O40]4- (1), (HPPD+)4([15]crown-5)4[PMo12O40]4- (2), and (HPPD+)2(H2PPD2+)([18]crown-6)4[PMo12O40]4- (3) as the countercation. The protonated states of PPD and molecular-assembly structures of the supramolecular cations depended on the size of the crown ethers. In salt 3, a novel mixed-protonated state of HPPD+ and H2PPD2+ was confirmed to be complexed in the cation structure. According to the changes in the cation structures, the anion arrangements were modulated from those of the two-dimensional layer for salt 1 to the isolated cluster for salts 2 and 3. The temperature-dependent magnetic susceptibilities of salts 1-3 were consistent with the isolated spin arrangements of [PMo12O40]4-. The electronic spectra of salts 1-3 indicated the intervalence optical transition from pentavalent Mo(V) to hexavalent Mo(VI) ions within the [PMo12O40]4- cluster. Temperature-dependent electron spin resonance spectra of salt 2 revealed the delocalization-localization transition of the S = 1/2 spin at 60 K. The spin on the [PMo12O40]4- cluster was localized on a specific Mo(V) site below 60 K, which was thermally activated with an activation energy of 0.015 eV.     

Gemini表面活性剂(12-6-12)和DNA的相互作用

应用紫外光谱、荧光探针、zeta 电位、动态光散射和凝胶电泳等方法探讨了阳离子gemini 表面活性剂C₁₂H₂₅N⁺(CH₃)₂―(CH₂)₆―(CH₃)₂N⁺C₁₂H₂₅·2Br^-(12-6-12)与DNA之间的相互作用. 研究结果表明, 与传统表面活性剂相比, 偶联表面活性剂特殊的分子结构使其与DNA的作用更强烈. DNA引导表面活性剂在其链周围形成类胶束结构, 开始形成类胶束时对应的表面活性剂临界聚集浓度(CAC)比纯表面活性剂临界胶束浓度(CMC)低两个数量级. CAC与DNA的浓度无关, 而与表面活性剂之间的疏水作用以及表面活性剂与DNA之间的静电吸引作用密切相关. Zeta 电位和凝胶电泳结果显示了DNA链所带负电荷逐渐被阳离子表面活性剂中和的过程. 借助原子力显微镜(AFM)成功观察到了松散的线团状DNA, 球状体随机地分散在DNA链上形成类似于串珠的结构、尺寸较大的球形复合物以及其由于吸附多余的表面活性剂重新带正电而被溶解得到的较小DNA/12-6-12聚集体. 圆二色(CD)光谱结果显示, 12-6-12可以诱导DNA的构象发生改变.     

High-precision isotopic ratio measurement system for methane (12CH3D/12CH4,13CH4/12CH4) by using near-infrared diode laser absorption spectroscopy

We demonstrate that the absorption spectroscopic method can be applied to a precise deltaD (an index of 12CH3D/12CH4) and delta13C (an index of 13CH4/12CH4) analysis for methane samples of natural isotopic abundance. We chose an appropriate absorption line pair whose absorption coefficients have nearly the same temperature dependences so as to minimize the temperature effect in absorbance ratio measurements. We measured 12CH3D/12CH4 ratio by using near-infrared external cavity diode lasers and a new type multi-pass cell. The deltaD value can be determined from the 12CH3D/12CH4 signal-intensity ratio with a fine correction by taking account of the interference of 13CH4 lines. Similarly, the delta13C value is determined from the 13CH4/12CH4 signal-intensity ratio, which is measured by using distributed-feedback laser and a modified Herriot-type cell and corrected for the abundance of 12CH3D. The precision was +/-0.7 and +/-0.027/1000 for deltaD and delta13C, respectively.     

Oxidation pattern of small silicon oxide clusters: structures and stability of Si6On (n = 1-12)

We have performed systematic ab initio calculations to study the structures and stability of Si(6)O(n)() clusters (n = 1-12) in order to understand the oxidation process in silicon systems. Our calculation results show that oxidation pattern of the small silicon cluster, with continuous addition of O atoms, extends from one side to the entire Si cluster. Si atoms are found to be separated from the pure Si cluster one-by-one by insertion of oxygen into the Si-O bonds. From fragmentation energy analyses, it is found that the Si-rich clusters usually dissociate into a smaller pure Si clusters (Si(5), Si(4), Si(3), or Si(2)), plus oxide fragments such as SiO, Si(2)O(2), Si(3)O(3), Si(3)O(4), and Si(4)O(5). We have also studied the structures of the ionic Si(6)O(n)(+/-) (n = 1-12) clusters and found that most of ionic clusters have different lowest-energy structures in comparison with the neutral clusters. Our calculation results suggest that transformation Si(6)O(n)+(a) + O --> Si(6)O(n+1)+(a) should be easier.     

12]Annulene radical anions revisited: evaluation of structure assignments based on computed energetic and electron spin resonance data

We report density functional and coupled cluster calculations on numerous monocyclic and bicyclic (CH)12(*-) isomers. At the RCCSD(T)/cc-pVDZ//UB3LYP/6-31+G* level, a nearly planar, bond-equalized radical anion of 1,7-di-trans-[12]annulene (4a(*-)) is lowest in energy; several other isomers and conformations lie within 3 kcal/mol of 4a(*-). RCCSD(T)/AUG-cc-pVDZ//UB3LYP/6-31+G* results place the all-cis isomer 3(*-) slightly below 4a(*-) in energy. Validation studies on the heptalene radical anion, [16]annulene radical anion, and tri-trans-[12]annulene radical anion indicate that electron spin resonance (ESR) hyperfine coupling constants (aH values) computed at the BLYP/EPR-III level on DFT geometries give much better agreement with experimental values than those computed using B3LYP/6-31G*. We were unable to locate any C12H12(*-) isomer that could account for the ESR spectrum previously attributed to a highly twisted structure for the 1,7-di-trans-[12]annulene radical anion. Our computed energetic and ESR data for [12]annulene radical anions and their valence isomers suggest that 4a(*-) may have been made, yet its ESR spectrum was incorrectly assigned to the bicyclic isomer 6b(*-). Finally, the computed (1)H NMR shift values of the dianion of 4 reveal a distinct diatropic ring current that should aid in its characterization.     

Synthesis of molecular sieve AlPO4-12

A member of the novel family of crystalline microporous aluminophosphates, AlPO₄-12, was synthesized by hydrothermal crystallization using different aluminum-containing compounds. Three new crystalline phases were obtained by varying the composition of the reaction mixture. The effect of the synthesis conditions on the hudrothermal process and the kinetics of crystallization are discussed. The apparent activation energies obtained for AlPO₄-12 are 20.9 and 14.6 kcal/mol for nucleation and crystallization, respectively. The adsorption isotherms of one AlPO₄-12 product were measured.