利用荧光非辐射能量转移观察磺酸基聚电解质分子链形态

2-丙烯酰胺基-2-甲基丙磺酸(AMPS)与N,N-二甲基丙烯酰胺(DMAA)共聚合成了一系列电荷密度为5%～99%的强聚电解质,并分别用萘和芘标记.随试样电荷密度升高,用分子间非辐射能量转移(NRET)测定的聚电解质接触质量浓度ρ^*从0.55减小到0.25g/L,比激基缔合物荧光测定的ρ^*约小一个数量级.在稀溶液范畴内,随试样电荷密度增加,分子链间的NRET先减弱,至AMPS质量分数达30%后又增强.该现象可用Manning的反离子凝聚与聚电解质聚集理论予以定性说明.     

芘标记磺酸基聚电解质在水与DMSO中的荧光光谱

合成了芘标记单体N-(芘基)甲基-2-甲基丙烯酰胺(PyMA),其与2-丙烯酰胺基-2-甲基丙磺酸(AMPS)、N,N-二甲基丙烯酰胺(DMAA)共聚,得到含PyMA摩尔分数为0.1%、AMPS摩尔分数F_AMPS分别为0.033～0.896的芘标记磺酸基聚电解质.在DMSO和水中,F_AMPS<0.449时芘标记聚电解质的荧光光谱与PyMA的荧光光谱基本相同;当F_AMPS≥0.449时,芘的[0,1]和[0,3]跃迁的发射强度大幅度增强.芘标记的I₁/I₃值随聚电解质电荷密度增加逐渐减小,且随聚电解质浓度增加也减小,表明聚电解质体系中通过电离基团间吸引形成了分子主链的聚集.     

几种聚合物分子间激基缔合作用的研究

作者合成并纯化了聚[对苯二甲酸(聚四亚甲基醚二醇)酯](PPTMGTP)、聚[2、6-萘二甲酸(聚四亚甲基醚二醇)酯](PPTMGNDC)和聚[2,6-萘二甲酸(环氧丙烷-四氢呋喃共聚醚二醇)酯](PCPEGNDC)等三个新聚合物,测定了它们的凝胶渗透色谱和数均分子量,对它们在良溶剂和不良溶剂溶液中的荧光进行了研究, 严格地用实验证明了PPTMGTP溶液中链内非相邻激基缔合作用的存在, 进一步以链内非相邻攀基缔合作用为探针研究了高分子在溶液中的形态随溶剂和浓度的变化, 用激基缔合物荧光相对强度的浓度依赖性测出高分子线团开始感觉到邻近有其它线团存在而收缩的浓度C_s(PPTMGNDC氯仿溶液的C_s = 2.61×10^-3g/ml, PPTMGNDC乙酸乙醋溶液的C_s =4.0×10^-2g/ml)。首次提出用C.划分高分子溶液稀浓区和亚浓区的界限的新欢点,以链内非相邻和链间激基缔合作用为探针确定了高分子溶液链段空间密度趋于均一的浓度C⁺(PPTMGNDC级仿溶液C⁺ = 7.02×10^-2g/ml),认为C⁺是高分子溶液由亚浓区到浓区的转变浓度。     

(2-甲基丙烯酰氧乙基)三甲基氯化铵-丙烯酰胺反相微乳液共聚合特性研究

选用SPAN80与OP10复合乳化剂、K₂S₂O₈-Na₂SO₃氧化还原引发剂,进行(2-甲基丙烯酰氧乙基)三甲基氯化铵-丙烯酰胺反相微乳液共聚合反应.研究了单体配比、电解质浓度和乳化体系的油水比对共聚物分子量及离子度的影响,考察了该共聚合体系的反应特性.     

无盐聚电解质溶液的分子热力学模型

聚电解质在水处理和胶体领域应用广泛 ,在生物系统中 ,蛋白质和 DNA等均是聚电解质 .文献中已发表了不少聚电解质溶液的理论和模型 ,如基于柱型胞腔模型的 Poison- Boltzmann( PB)方程理论[1]及其改进型 ( MPB) [2 ] 、Manning反离子凝聚理论 [3 ] 、积分方程理论 [4] 及适合于工程应用的半经验模型 [5 ]等 ,但离工程实际应用的要求还相差较远 .最近 ,姜建文等 [6]建立的分子热力学模型 ,其预测结果与 MD模拟数据非常吻合 .本文在此基础上进一步考虑聚离子与反离子间的缔合作用 ,可以在中高浓度范围内很好地关联实验数据 .1　模　　型…     

倍硫磷的甲基在分子内和分子间迁移的质谱研究

甲基迁移反应在合成化学和生命科学领域具有重要意义.迄今为止，所报道的甲基迁移反应大多数发生在不同种类分子之间.因此，寻找新型甲基迁移反应具有一定的研究价值.本研究以环境中常见的杀虫剂倍硫磷为研究对象，采用电喷雾质谱技术为分析工具对反应体系进行高灵敏分析，探究在CF₃COOH及纳米二氧化钛（TiO₂）条件下，倍硫磷分子中发生甲基迁移反应的可能性.结果表明，在CF₃COOH和TiO₂共同作用下，倍硫磷分子中的甲基可以从同一分子的氧原子上迁移到不饱和硫原子上，发生分子内1，3-甲基迁移反应，形成异构体硫甲基化产物；同时，异构体产物中的甲基还可以从硫原子上再继续迁移到另一分子倍硫磷的不饱和硫原子上，发生分子间甲基迁移反应.同时结合密度泛函理论计算对倍硫磷分子内和分子间甲基迁移反应的过程进行动态模拟，并对其迁移机理进行解释.本研究发现了倍硫磷能发生分子内和分子间甲基迁移反应，提供了一种研究甲基迁移反应的质谱方法，为倍硫磷的降解研究提供了新思路.     

PAMPSLi/P(MMA-VAc)为基体的聚合物电解质

将聚(2-丙烯酰胺-2-甲基丙磺酸锂)(PAMPSLi)和聚(甲基丙烯酸甲酯-醋酸乙烯酯)[P(MMA-VAc)]与LiClO₄共混, 制备了复合聚合物电解质膜. 用FTIR, TG, XRD, DMA, SEM及电化学交流阻抗和机械性能测试对聚合物及其电解质膜的结构和性能进行了表征. 结果表明, PAMPSLi与P(MMA-VAc)共混后结晶状态发生变化, 交联网络变得密实, 提高了热稳定性和拉伸强度, 聚合物电解质膜含有较多微孔结构, 孔径为5~10 μm; 在20 ℃时, 当n(MMA)∶n(VAc)=2∶8, m(PAMPSLi)∶m[P(MMA-VAc)]=5∶95, m(LiClO₄)∶m(copolymer)=15∶85时, 聚合物电解质膜电导率可达到1.68×10^-3 S/cm, 且电导率未出现随LiClO₄含量的进一步增加而下降的现象. 将此电解质用于全固态电致变色显示器件表现出了优良的性能. 对加入PAMPSLi后聚合物电解质膜电导率和热稳定性提高的原因进行了初步探讨.     

新型表面分子印迹法制备苦参碱印迹材料及其分子识别特性

通过γ-(甲基丙烯酰氧)丙基三甲氧基硅烷的媒介, 将功能大分子聚甲基丙烯酸(PMAA)偶合接枝到硅胶微粒表面, 形成了接枝微粒PMAA/SiO₂, 采用本课题组建立的新型分子表面印迹技术, 以生物碱苦参碱(来源于苦豆子)为模板分子, 乙二醇二缩水甘油醚(EGDE)为交联剂, 对接枝在硅胶表面的PMAA大分子链进行了分子印迹, 制备了苦参碱表面分子印迹材料MIP-PMAA/SiO₂. 以另一种生物碱金雀花碱(亦来源于苦豆子)为对比物, 采用静态与动态两种方法研究了MIP-PMAA/SiO₂对苦参碱的结合性能与分子识别特性. 实验结果表明, 印迹材料MIP-PMAA/SiO₂对苦参碱具有特异的识别选择性与优良的结合亲和性, 相对于金雀花碱(与苦参碱共存于苦豆子植物中, 且结构彼此相似), 识别选择性系数为8.14. 此外, 印迹材料MIP-PMAA/SiO₂也具有良好的解吸性能, 以含氯化钠的乙酸水溶液作为洗脱液, 17个床体积内解吸率达到99.77%.     

部分水解聚丙烯酰胺水溶液的零剪切黏度和临界浓度

通过蠕变和振荡实验分别测定了部分水解聚丙烯酰胺(PHPA)水溶液的零剪切黏度(η₀)和线性黏弹区储能模量(G'), 并依据其浓度依赖性得到叠加浓度(C^*)和交叠浓度(C^*), 考察了温度、pH值和电解质(NaCl和CaCl₂)浓度的影响. 结果表明, 随着温度的升高和电解质浓度的增大, PHPA水溶液的η₀及G'减小, C^*和C^*增大; 电解质阳离子价态越高, 溶液黏度和临界浓度的变化越显著; 而随着pH值的增大, η₀及G'先增大后减小, C^*和C^*先减小后增大.     

季铵盐三聚表面活性剂在空气-水界面上单分子膜的崩溃压和分子极限面积

利用Langmuir膜天平研究了季铵盐三聚表面活性剂12-2-12-2-12在空气-水界面单分子膜的表面压-分子面积(π-A)等温线, 得到它的崩溃压对应的表面张力g_collapse和分子极限面积A_limit. 与12-2-12-2-12溶液临界胶束浓度对应的表面张力g_cmc和由Gibbs吸附方程得到的分子平均面积A_cmc相比较, 发现A_limit＜A_cmc, 而且g_collapse＞g_cmc. 分析12-2-12-2-12单分子膜的表面压随时间的衰减, 表明这个现象是由于表面活性剂从铺展单分子膜向水中溶解造成的, 而且初始表面压越大, 表面压的衰减越快.     

Fluorescence study of chromophore labeled strong polyelectrolyte bound with oppositely charged surfactant

Four strong polyelectrolyte samples of 2-(acrylamido)-2-methylpropanesulfonic acid (AMPS) and N,N-dimethylacrylamide (DMAA) were radically copolymerized with a single label of naphthalene or pyrene, with both labels and without label, containing about 40 mol % AMPS. Fluorescence nonradiative energy transfer (NRET) I_Py/I_Np, anisotropy r, I₁/I₃ and excimer emission I_E/I_M of pyrene labels were observed in dilute aqueous solutions with and without cationic surfactant of cetyltrimethylammonium bromide (CTAB). The overlap concentration was determined as 3 g/L from the appearance of intermolecular excimer. The variation of intra- and intermolecular NRET with total polyelectrolyte concentration showed that the charged chains preferentially interpenetrated each other rather than reduce their coil volume as their concentration beyond the overlap threshold. By binding with CTAB, the polyelectrolyte chain became more coiled as known from the reduced viscosity. The intramolecular NRET was dominant when [CTAB]Д᎒^-5 M and then the intermolecular NRET occurred at higher CTAB concentrations with hydrophobic aggregation between CTAB tails bound on different polyelectrolyte chains. The CTAB concentration corresponding to the maxima of I_Py/I_Np just is equal to the AMPS monomer concentration, indicating the formation of 1:1 binding between surfactant and polyelectrolyte in very dilute solutions. Added salt of NaCl up to 0.1 M hardly affected the intramolecular NRET but affected the I_Py/I_Np value for the intermolecular NRET.     

Investigation of cationic organic dyes used as molecular probes by liquid secondary ion mass spectrometry

The positive-ion mass spectra of twelve organic dyes used as molecular probes were measured using liquid secondary ion mass spectrometry (LSIMS). Nine of the twelve dyes were singly charged cations and the other three were doubly charged cations. The mass spectra of each of the dyes in m-nitrobenzyl alcohol contain abundant signals for the intact cation, C⁺ (singly charged cation dyes), or for singly-charged forms of the doubly charged cation formed by proton loss, [C²⁺? H⁺]⁺, or halogen counter ion attachment, [C²⁺ + X^?]⁺. Fragmentation is usually minimal under the conditions used. However, the cations of five of the singly charged compounds appear to undergo charge-remote fragmentation. Collision-induced dissociation experiments on a hybrid mass spectrometer of EBqQ geometry at collision energies up to 300 eV failed to access this fragmentation pathway. In contrast to the LSIMS of many other doubly charged organic compounds, two of the dicationic dyes produced a doubly charged ion of reasonable abundance (2–20%) in the mass spectrum. When glycerol was used as a matrix solvent, the addition of the matrix modifier trifluoroacetic acid increased the abundance of C²⁺.     

Investigation of polymer miscibility by spectroscopic methods. III. Labeling of poly(vinyl chloride), poly(methyl methacrylate) and poly(styrene-co-acrylonitrile) with fluorescent chromophores for nonradiative energy transfer studies

Poly(vinyl chloride) (PVC) is generally recognized as miscible with s.poly(methyl methacrylate) (s.PMMA), poly(?-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) copolymer (SAN) containing 27 wt % AN. Nonradiative energy transfer (NRET) is a very sensitive technique in the investigation of the polymer miscibility. To compare by NRET the actual degree of miscibility of the PVC/s.PMMA, PVC/PCL, and PVC/SAN polymer pairs, each polymer is to be labeled with a fluorescent chromophore to an extent of 1 or 2 mol %. This paper reports efficient pathways to attach anthracene (acceptor) or naphthalene (donor) onto preformed PVC, s.PMMA, and SAN samples. All the attempts for grafting carbazole (donor) moieties have failed, as well as any labeling of PCL whatever the nature of the chromophore.     

Capillary electrophoresis-electrospray mass spectra of the herbicides paraquat and diquat

The positive ion electrospray mass spectra of the quaternary ammonium salt herbicides paraquat and diquat are examined by on-line separation with capillary electrophoresis (CE) and by direct infusion of the analytes. The analytes are separated by CE in 7–10 min at pH 3.9 in 50% methanol-water by using several different separation buffer electrolytes. The capillary electrophoresis-electrospray ionization (CE-ES) mass spectra of paraquat and diquat consist primarily of doubly charged molecular ions, singly charged molecular ions, and singly charged deprotonated ions. The direct infusion spectra consist primarily of doubly charged molecular ions and singly charged deprotonated ions. The relative abundances of the doubly charged and deprotonated ions depend strongly on the presence or absence of ammonium ion in the CE separation buffer or the direct infusion solution. A deprotonation mechanism is proposed in which the free base ammonia is the deprotonating agent in the desolvating charged droplets or in the gas phase. The analytical potential of the CE-ES electrospray approach for environmental analyses is evaluated in terms of the precision of replicate injections, linear concentration range, and estimated detection limit.     

Interfacial nonradiative energy transfer in responsive core-shell hydrogel nanoparticles

Fluorescently labeled core-shell latex particles composed mainly of the thermoresponsive polymer poly-N-isopropylacrylamide (p-NIPAm) have been synthesized such that an energy transfer donor (phenanthrene) and an energy transfer acceptor (anthracene) are covalently localized in the core and shell, respectively. When the thermally induced particle deswelling is interrogated by photon correlation spectroscopy (PCS), a continuous (non-first order) phase transition is observed. Conversely, when the nonradiative energy transfer (NRET) efficiency is used to probe the collapse of these same particles, the phase transition event is observed to occur over a much smaller temperature range and approaches first-order (discontinuous) behavior. Furthermore, core-shell particles with differing shell thicknesses display identical phase transition temperatures when PCS is used to monitor the transition, while NRET measurements show a clear increase in collapse temperature as the shell thickness is increased. These apparently contradictory results are discussed in terms of a radial phase coexistence that exists in the microgel particles, which arises from a similarly radial inhomogeneity in the cross-linker concentration. The prospects for the NRET technique as a molecular-scale probe of nanostructured microgels are also discussed.     

Halogeno-substituted 2-aminobenzoic acid derivatives for negative ion fragmentation studies of N-linked carbohydrates

Negative ion electrospray mass spectra of high-mannose N-linked glycans derivatised with 2-aminobenzoic acids and ionised from solutions containing ammonium hydroxide gave prominent [M-H](-) ions accompanied by weaker [M-2H](2-) ions. Fragmentation of both types of ions gave prominent singly charged glycosidic cleavage ions containing the derivatised reducing terminus and ions from the non-reducing terminus that appeared to be products of cross-ring cleavages. Differentiation of these two groups of ions was conveniently achieved in a single spectrum by use of chloro- or bromo-substituted benzoic acids in order to label ions containing the derivative with an atom with a distinctive isotope pattern. Fragmentation of the doubly charged ions gave more abundant fragments, both singly and doubly charged, than did fragmentation of the singly charged ions, but information of chain branching was masked by the appearance of prominent ions produced by internal cleavages.     

A study of polymer blends by nonradiative energy transfer fluorescence spectroscopy

The nonradiative energy transfer (NRET) method has been used to study the miscibility of polymer blends in the solid state. This can be done by labeling the polymers with fluorescence donor and acceptor chromophores. The efficiency of energy transfer, which reveals the interpenetration of the chains, is measured by following changes in the fluorescence intensity ratio of the donor and acceptor as a function of the concentration of the polymer mixture and by comparison with reference values corresponding to totally miscible and totally immiscible systems. It is shown that the reference ratio corresponding to the absence of energy transfer must be determined by using donor-labeled and acceptor-labeled polymer films, instead of making measurements in chromophore solutions in organic solvents, as has usually been done. It is also shown that fluorescence quenching is important in such studies, since it can lead to variations of the fluorescence intensity ratio by more than an order of magnitude; this factor varies with blend concentration and is particularly sensitive to the presence of halogen atoms. The NRET technique has been applied to several PVC/CPVC binary blends and to PCL/PVC/CPVC ternary blends in which PVC and CPVC were labeled by naphthalene and anthracene, respectively [PCL is poly(ε-caprolactone), PVC is poly(vinyl chloride), and CPVC is chlorinated PVC]. For binary blends, the measured intensity ratios indicate the immiscibility of PVC with CPVC, although there is nonnegligible energy transfer between the two phases. For ternary blends, the intensity ratios indicate that the addition of up to 40 wt % of PCL to the immiscible PVC/CPVC binary system leads to the formation of two coexisting PCL/PVC and PCL/CPVC phases.     

Conformational dynamics and stability of HP35 studied with 2D IR vibrational echoes

Two-dimensional infrared (2D IR) vibrational echo spectroscopy was used to measure the fast dynamics of two variants of chicken villin headpiece 35 (HP35). The CN of cyanophenylalanine residues inserted in the hydrophobic core were used as a vibrational probe. Experiments were performed on both singly (HP35-P) and doubly CN-labeled peptide (HP35-P(2)) within the wild-type sequence, as well as on HP-35 containing a singly labeled cyanophenylalanine and two norleucine mutations (HP35-P NleNle). There is a remarkable similarity between the dynamics measured in singly and doubly CN-labeled HP35, demonstrating that the presence of an additional CN vibrational probe does not significantly alter the dynamics of the small peptide. The substitution of two lysine residues by norleucines markedly improves the stability of HP35 by replacing charged with nonpolar residues, stabilizing the hydrophobic core. The results of the 2D IR experiments reveal that the dynamics of HP35-P are significantly faster than those of HP35-P NleNle. These observations suggest that the slower structural fluctuations in the hydrophobic core, indicating a more tightly structured core, may be an important contributing factor to HP35-P NleNle's increased stability.     

Determination of atropine (hyoscyamine) sulfate in commercial products by liquid chromatography with UV absorbance and fluorescence detection: multilaboratory study

A liquid chromatographic (LC) method with 2 detection systems for determining atropine (hyoscyamine) sulfate in commercial products was tested in a multilaboratory study. Depending on the type of product, sample solutions are prepared in methanol or methanol-water (1 + 1). The standard solution contains about 1.0 mg atropine sulfate/100 mL and is prepared in the same solvent used in sample preparation. LC separations are performed on a 7.5 cm Novapak silica column. The mobile phase is prepared by mixing 970 mL methanol with 30 mL of a 1% aqueous solution of 1-pentanesulfonic acid, sodium salt. Detection is by 2 systems, UV absorbance detection at 220 nm and fluorescence detection with excitation at 255 nm and emission at 285 nm. The injection volume is 100 or 200 microL. The following materials were used for the study: 2 separate samples of tablets labeled to contain 0.4 mg atropine sulfate, 2 separate samples of extended-release tablets labeled to contain 0.375 mg hyoscyamine sulfate, one sample of atropine sulfate injection labeled to contain 2 mg/mL, and one sample of 1% (v/v) atropine sulfate ophthalmic. Eight participants analyzed 2 separate portions of the 6 samples by both detection systems. A ninth participant analyzed the samples in duplicate but only by UV absorbance detection because of the unavailability of a fluorescence detector. The relative standard deviation (RSD) between laboratories ranged from 1.4 to 3.3% for samples of tablets and injections but higher for ophthalmic solutions (5.1-5.2%). A linearity study was conducted in the originating laboratory before the multilaboratory study with 5 solutions ranging in concentration from 0.80 to 1.20 mg atropine sulfate in 100 mL. Average recoveries were 100.0% by UV absorbance detection and 99.9% by fluorescence detection; the RSDs were 1.1 and 1.2%, respectively.