染料激光器混合染料体系的研究

分子间的能量转移是当今光化学、光生物学和光物理学中的一个重要课题，长期以来一直受到人们的广泛关注。六十年代染料激光器出现以后，人们很快就将这一原理应用研究染料激光器的工作物质。选择适当的混合染料溶液作为染料激光器的工作物质，可以提高某些染料的激光输出能量或扩展激光波长覆盖范围，这已成为分子间能量转移的一个新的应用领域。本文首先阐述分子间能量转移的基本理论并对混合染料体系的选择及其研究进行了文献综述。另外，对研究过程中，他人工作改采用的实验手段也进行了概述，特别对荧光寿命的测量讨论得较为仔细。实验中我们着重研究了R6G/Red B、R6G/NB两个二元体系和C440/C540/Saf.~(-1)、C440/Fl.Na/Saf.~(-1)以及R6G/Red B/Ox725三个三元混合染料体系。实验方法主要通过测量混合染料溶液的荧光光谱、荧光寿命和激光输出性能。激发源波长始终固定在337.1nm。荧光光谱和荧光寿命多是在英国Applied Photophysics公司生产的SP-70型纳秒荧光分光光度计上测量的。这套仪器的设置从激发、探测以至最后的数据处理（微机处理）都达到较高的灵敏度和精确度。更为主要的是采用了时间相关单光子计数技术这一新的测量方法，真有较高的时间分辨本领，为染料分子的短寿命测量提供了重复性极好的可靠数据。并且由于这套仪器的信噪比大，能够测出高浓度溶液情况下的荧光光谱，而一般地荧光光谱仪却很难探测。激光调谐范围的测量是在QJD-9型染料激光器上进行的，光路结构安排合理，各项技术指标都达到了较高水平。激光强度的测量是采用了通用的光路结构测量混合染料溶液的超辐射模式的激光输出。下面是我们的实验结果。1.R6G/Red B、R6G/NB二元混合染料体系。通过测量R6G/Red B混合染料溶液的荧光光谱，了解到给体R6G有较强的能量转移给受体Red B。又通过荧光寿命的测量，表明溶液浓度达到～10~(-3) mol.L~(-1)时，分子间的能量转移主要是共振转移，且符合Stern-Volmer关系。由此我们进行了一定量讨论，计算了不同浓度溶液中给体与受体分子间的平均距离R。激光性能的测量表明这一体系具有较大的激光强度输出，且通过改变给体、受体浓度可扩展调谐范围。对于R6G/NB，我们做了类似的研究。但与R6G/Red B不同的是，R6G/NB始终是双峰。激光性能测量表明此体系可以扩展调谐范围，且可改善NB的激光输出，降低泵浦阈值。2.C440/C540/Saf.-T、C440/Fl.Na/Saf.-T及R6G/Red B/Ox725三元体系。C440/C540/Saf.-T混合染料溶液的荧光光谱研究表明，三种染料分子之间有较强的能量转移发生，且与溶液浓度配比适当时，可以同时获得三个不同波段处的荧光发射，从而可望扩展波长调谐范围。见图1。对于C440/Fl.Na/Saf.-T混合溶液，我们主要是采用光谱手段，对能量转移过程做了研究。结果表明C440/Fl.Na之间以辐射转移为主要机制，Fl.Na/Saf.-T之间在波度稍大时，发生共振转移的可能性较强。另外对能量转移过程进行了一些定量的讨论。计算求得C440/Fl.Na的临距离R_o = 47.5A，小于Fl.Na/Saf.-T的临界距离R_o = 59.0A，因而后者发生共振转移的可能性较大。R6G/Red B/Ox725体系与前两体系相比是向长波长方向扩展了。激光性能的测量表明，此体系可以作为染料激光器的工作物质。实验结果还表明三种染料混合以后的激光性能比Red B/Ox725二组份混合的效果好得多。R6G/Red B/Ox725的超辐射是图2所示。

In vitro study on the binding of neutral red to bovine serum albumin by molecular spectroscopy

In this paper, the binding of neutral red (NR) to bovine serum albumin (BSA) under physiological conditions has been studied by spectroscopy method including fluorescence, circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy. The Stern-Volmer fluorescence quenching constant (K-SV), binding constant (K-b) and the number of binding sites (It) were measured by fluorescence quenching method. Fluorescence experiments were also performed at different ionic strengths. It was found K-SV was ionic strength dependent, which indicated the electrostatic interactions were part of the binding forces. The distance r between donor (BSA) and acceptor (NR) was obtained according to Foster's non-radiative energy transfer theory. CD spectroscopy and FT-IR spectroscopy were used to investigate the structural information of BSA molecules on the binding of NR, and the results showed no change of BSA conformation in our experimental conditions.

溶液pH对硫堇与DNA相互作用方式的影响

用电化学和光谱方法研究了溶液pH对硫堇(TH)与小牛胸腺脱氧核糖核酸(CT-DNA)相互作用方式的影响。电化学测量结果表明,在pH 7.2的磷酸盐缓冲溶液中,TH与CT-DNA之间的作用方式以嵌入结合为主,在pH6.5的磷酸盐缓冲溶液中,TH与CT-DNA之间的作用方式既存在嵌入结合也存在静电作用。荧光光谱测量结果表明,TH与DNA结合后其荧光发生猝灭,通过Stern-Volmer方程计算得到pH 6.5时TH-DNA体系的猝灭常数高于pH 7.2时的值,表明在pH 6.5的溶液中两者相互作用更强。圆二色谱(CD)实验结果也证实了这一结论。

长白山白眉蝮蛇蛇毒精氨酸酯酶的荧光淬灭研究

交替使用DEAE Sephadex A-50离子交换和Sephadex G-75 凝胶过滤层析技术，从长白山白眉蝮蛇蛇毒(A gkistrodon blom hoffii Ussurensis)中纯化得到了一种分子量为29458±15Da的精氨酸酯酶活性组分．本文研究了碘离子(I-)和丙烯酰胺(Acr)对这种精氨酸酯酶的荧光光谱的淬灭作用，I-和Acr对精氨酸酯酶荧光的淬灭符合Stern-Volmer公式．I-仅能淬灭精氨酸酯酶约54%的荧光，Acr可以将精氨酸酯酶荧光淬灭殆尽．I-和Acr对长白山白眉蝮蛇蛇毒精氨酸酯酶荧光淬灭作用的结果表明： 在精氨酸酯酶中含有两种类型的色氨酸残基， 而且处于不同的微环境当中.

红枫湖溶解有机质的分离富集、地球化学特征和环境效应

作为全球碳循环的主要组成部分，溶解有机质在水生生态系统的各种物理、化学和生物过程中起着十分重要的作用：它是湖泊异养型生物所需能量的主要提供者；是湖泊水体pH的调节剂和控制因素；能够与金属离子或有机污染物相互作用，从而影响它们的迁移转化、毒性和生物可利用性；溶解有机质也是饮用水氯化工艺中生成具有致癌作用消毒副产品的主要前驱物质。溶解有机质组成和结构十分复杂，一般由腐殖质和非腐殖质物质组成，相应的环境地球化学特征和行为也各不相同。因此，研究溶解有机质各分离组分的结构特征和环境效应，将有助于我们对溶解有机质复杂化学结构、循环特征及行为特征的深入理解；有助于揭示溶解有机质对环境中微量污染物的迁移、转化、毒性和生物有效性的影响机理和贡献因素；为水环境评价、预测、控制和管理提供科学依据。 本论文选择云贵高原山区湖泊—红枫湖为研究对象，利用XAD树脂分离技术，把湖泊水体中溶解有机质按极性的不同分成了疏水性酸、碱、中性物质和亲水性酸、碱、中性物质等六种有机组分。主要运用元素分析、有机碳分析仪、傅立叶变换红外光谱、紫外－可见分光光度，高效液相体积排阻色谱、三维荧光光谱和稳定同位素质谱仪等现代分析方法和手段，对各有机组分的地球化学特征及来源的进行了表征和探讨。同时利用荧光猝灭滴定技术研究了溶解有机质分离组分与铜的相互作用，利用顶空气相色谱法测定了各分离组分与氯气反应活性的大小，并确立了生成消毒副产物的主要前驱物质。本论文的研究成果主要有以下几点： 1.改进了分离流程：在XAD－8树脂分离溶解有机质流程的基础上，引入XAD－4树脂，对贵州红枫湖水体中溶解有机质进行了富集分离，得腐殖酸、富里酸、疏水性中性物质、亲水性酸、亲水性碱、亲水性中性物质等六种有机组分，回收率为82%。各分离组分的组成与其它天然水体的组成接近，其中以富里酸为主，占分离组分的51%。 2.溶解有机质分离组分化学结构特征的研究：元素分析表明疏水性组分具有较高的碳和硫含量，而亲水性组分O/C比较高，含有较多的含氧官能团；傅立叶变换红外光谱表明各分离组分在3424－3434 cm-1具有O-H和N-H的吸收峰，腐殖酸组分主要为含氮和聚糖物质，富里酸和亲水性酸表现强的羧基吸收峰。高效体积排阻色谱表明各六种有机组分的分子量较小，重均(Mw)和数均(Mn)分子量分别集中在1688-2355Da和1338-1928Da之间，其中Mw和紫外吸收比值(E2/E3)之间呈负相关关系；三维荧光光谱显示六种有机组分表现了4种不同类型的荧光峰，紫外区类富里酸荧光峰peakA和可见区类富里酸荧光峰peakC；疏水性中性物质还表现了两种类蛋白荧光峰peakB和peakD。荧光强度与紫外吸光系数SUVA254之间呈显著正相关关系，说明了产生荧光和紫外的物质具有某些相似的官能团，其中芳香官能团和共轭双键在这两类光谱的产生中具有重要作用。本研究进一步揭示了溶解有机质不同有机组分的分子量分布、荧光光谱特征和紫外吸收特征之间的一致性，反映了各有机组分之间的亲水、疏水与分子量、光谱特征之间的内在联系，本研究有助于加我们深对溶解有机质复杂性和相似性及化学结构与行为的进一步认识。 3.溶解有机质分离组分来源问题的探讨：我们利用δ13C及C/N比值并结合荧光光谱特征来指示溶解有机质的来源。各分离组分的δ13C及C/N比值表明富里酸主要来自陆源C3植被形成的土壤有机质，而腐殖酸、疏水性中性物质、亲水性酸、亲水性碱、亲水性中性物质属于陆源和内源的混合来源，其中腐殖酸、亲水性酸、亲水性碱接近红枫湖藻类一端，而疏水性中性物质和亲水性中性物质接近陆源一端。荧光光谱表明疏水性中性物质中含有类蛋白荧光峰，可能暗示了该组分还与人类活动有关。该研究加深了对溶解有机质来源的多样性和影响因素复杂性的认识。 4.溶解有机质分离组分与铜离子的相互作用，利用荧光猝灭滴定技术研究了分离组分与铜离子的相互作用，结果表明溶解有机质滴加铜离子后荧光强调显著降低，同时发射波长Em发生蓝移，而激发波长Ex基本不变，说明了分离有机组分在与铜离子相互作用后，π电子减少，共轭性和芳香型降低，直线型分子向非直线型分子转变；溶解有机质分离组分与铜相互作用的滴定曲线与修正的Stern-Volmer模型十分吻合；分离组分的稳定常数logK介于4.73-5.16之间（C峰）和4.64-5.24之间（A峰），logKA与logKC与总酸度以及与酚羟基之间存在显著相关性, 与羧基含量之间也有弱相关关系，说明铜离子优先与配体中强配位点（酚羟基）络合，其次为弱配位基（羧基）。该研究揭示了云贵高原山区湖泊溶解有机质分离组分与金属离子相互作用的差异性和影响因素，为水环境中金属离子迁移转化和毒性的评价提供理论依据。 5.溶解有机质分离组分卤代活性的比较：我们运用顶空气相色谱法测定了红枫湖分离组分与消毒剂反应生成有机卤代物的情况。结果表明红枫湖分离组分氯化消毒副产物主要以三氯甲烷(CHCl3)和二溴一氯甲烷(CHBr2Cl)为主，富里酸是生成三卤甲烷的主要前驱物质，同时富里酸的卤代反应活性也最强。该研究揭示了云贵高原山区湖泊中富里酸是生成消毒副产物的主要前驱物质，该组分以陆源有机质输入为主。因此，该研究对饮用水消毒具有一定的现实意义。

天然有机质与多环芳烃相互作用的荧光光谱学研究—以苝、菲和蒽为例

自然界水体（如地下水、湖泊、河流及海洋）中的天然有机质（NOM）因具有显著的生态及环境功能而受到人们的广泛关注。NOM作为全球碳循环的主要组成部分，是水体中异养型微生物生长所需碳及能量的重要来源。此外，NOM对湖泊生态系统中的多种物理、化学过程具有不同程度的影响：NOM中的有机酸对淡水体系的酸度具有控制作用而且对酸沉降有一定的缓冲作用；NOM通过减弱可见光及紫外线照射从而影响淡水系统的光化学环境，这一方面降低了水体中自养生物的繁衍速度，同时保护水生生物免受有害的紫外线辐射。更为重要的是，NOM能够影响环境中污染物的命运，比如重金属离子和疏水性有机污染物与天然有机质结合后，其迁移途径、溶解度、生物可利用性及毒性受到明显的控制，这样其对环境中生物的危害性减弱。多环芳烃（PAHs）是一类对环境危害极大的疏水性有机污染物，多数PAHs对有机体具有毒性和致癌性而被美国环保署（EPA）列为优先处理的污染物。因此，确定NOM-PAHs反应的强弱，即PAHs在NOM中的分配系数（Kdoc）以及NOM的物化特性对Kdoc的影响对于预测PAHs毒性和生物可利用性大小、了解NOM-PAHs相互作用的机理及确立污染预测模型具有十分重大的意义。前人的研究结果表明，多环芳烃与天然有机质相互作用的分配系数Kdoc的与PAHs的疏水度（即Kow大小）、NOM的物化特性（如芳香度、脂肪碳含量、分子量及极性等）和水化学参数（pH、离子强度等）有很大的相关性。然而，许多学者在NOM的物化特性对分配系数的影响方面存有较大分歧。前人在研究天然有机质与多环芳烃之间的相互作用时所用的NOM多为腐殖质，即水体NOM中的疏水性组分，而其中的亲水性组分与PAHs的结合作用文献中却鲜见提及，因此人们对其结合作用的特性如反应机理和结合作用强弱等的了解十分有限。 本论文利用XAD树脂分离技术把红枫湖水体中天然有机质分成了疏水性酸、碱、中性物质和亲水性酸、碱、中性物质等六种有机组分。同时运用元素分析、有机碳分析仪、紫外－可见分光光度，高效液相体积排阻色谱、三维荧光光谱和荧光偏振技术等现代分析方法，对各有机组分的物理、化学特性进行了表征。荧光光谱技术被用于研究水化学参数对腐殖质荧光特性和分子构型的影响以及测定Amherst腐殖酸（Amherst HA）、垃圾渗滤液富里酸（LF FA）和红枫湖NOM有机组分与多环芳烃苝、菲和蒽的结合系数（分配系数、条件稳定常数）并探讨了影响分配系数的各种因素和NOM与多环芳烃相互作用的机理。本论文的获得的主要结果如下： 1. 在水化学参数对腐殖质荧光特性及分子构型的影响方面： 在NOM与PAHs相互作用过程中，腐殖质的分子构型起着关键性的作用，而其分子构型又受到其本身的浓度、溶液的pH和离子强度等水化学参数的影响。本论文运用三维荧光光谱和荧光偏振技术研究了水化学参数对腐殖质荧光特性的影响，并由此推断其分子构型变化情况。实验结果表明随着腐殖质浓度、溶液的pH和离子强度的改变，腐殖质荧光特性（如荧光强度、荧光峰位和荧光偏振值等）出现不同程度的变化，揭示了腐殖质分子构型的改变。因此，本实验结果有利于深入了解腐殖质的分子构型及其对吸附PAHs的重要影响，对理解NOM的环境行为具有一定的理论价值。 2. 运用荧光猝灭滴定法研究Amherst HA和红枫湖NOM有机组分对多环芳烃苝、菲和蒽的吸附作用，结果表明NOM对多环芳烃的吸附能力与其中芳香结构单元有很强的相关性，logKdoc值与NOM在280 nm处的摩尔吸收（ε280）和分子量有线性度较高的正比关系，而C/H原子比值对不饱和碳含量（芳香度）并没有很好的指示作用。同时，脂肪碳（0－50 ppm）中的聚亚甲基碳对吸附PAHs也有很大的贡献，而有机组分的极性与分配系数有明显的负相关性。不同种类的多环芳烃与NOM有机组分的结合能力有很大的差异，这取决于不同PAHs的疏水度大小。本研究结果有利于弥合前人在NOM物化特性对PAHs吸附能力的影响方面的分歧，揭示了NOM的组成和结构在与PAHs等疏水性有机污染物相互作用方面的重要影响。 3. 在结合机理方面，苝与NOM有机组分结合的Stern－Volmer图具有较高的线性度，这表明其结合机理以疏水反应（或分配）为主，而菲和蒽与有机组分相互作用的吸附等温线显示较多的非线性特征表明极性反应为主要反应机理，结合过程以吸附为主。在红枫湖NOM有机组分中，疏水性组分显示对PAHs较高的结合能力，同时疏水性组分与PAHs相互作用的吸附等温线具有较高的线性度。这一结果揭示了不同种类的PAHs和各NOM有机组分之间结合机理的差异，加深了人们对NOM与PAHs相互作用机理的认识。 4. 前人在研究pH、离子强度等水化学参数对分配系数的影响方面得到的结果多有矛盾之处，同时，对实验结果的解释也不尽相同。本实验结果表明分配系数随pH增加而下降；离子强度对分配系数的影响比较复杂，就总体趋势而言，增加离子强度有利于对PAHs吸附能力的提高，这一结果初步揭示了水化学参数对PAHs分配系数的影响，丰富了人们对其影响机理的认识。 5. 运用荧光偏振技术测定了蒽与Amherst HA、LF FA和红枫湖NOM有机组分的条件稳定常数，结果如下：随着NOM浓度增加，蒽的荧光偏振值不断下降，这表明蒽的分子构型由平面线性向圆柱状转变。在所有NOM样品中，土壤源的Amherst HA与蒽结合的条件稳定常数最大（pH 4时logK=5.6，pH 6时 logK=5.4）；就NOM有机组分而言，疏水性组分的logK变化范围在pH 6时为（4.4－5.2），而亲水性组分为（4.3－4.8），这表明疏水性组分具有相对较高的蒽吸附能力。实验结果有利于了解PAHs与NOM相互作用前后的分子构型变化情况，揭示了不同的NOM有机组分在吸附PAHs过程中的差异。

Thin-film oxygen sensors using a luminescent polynuclear gold(I) complex

Robust thin-film oxygen sensors were fabricated by encapsulating a lipophilic, polynuclear gold(I) complex, bis{m-(bis(diphenylphosphino)octadecylamine-P,P')}dichlorodigold(I), in oxygen permeable polystyrene and ormosil matrices. Strong phosphorescence, which was quenched by gaseous and dissolved oxygen, was observed from both matrices. The polystyrene encapsulated dye exhibited downward-turning Stern-Volmer plots which were well fitted by a two-site model. The ormosil trapped complex showed linear Stern-Volmer plots for dissolved oxygen quenching but was downward turning for gaseous oxygen. No leaching was observed when the ormosil based sensors were immersed in flowing water over an 8 h period. Both films exhibited fully reversible response and recovery to changing oxygen concentration with rapid response times. (C) 2011 Elsevier B.V. All rights reserved.

Response characteristics of optical sensors for oxygen: models based on a distribution in tau(o) or kappa(q)

The features of two popular models used to describe the observed response characteristics of typical oxygen optical sensors based on luminescence quenching are examined critically. The models are the 'two-site' and 'Gaussian distribution in natural lifetime, tau(o),' models. These models are used to characterise the response features of typical optical oxygen sensors; features which include: downward curving Stern-Volmer plots and increasingly non-first order luminescence decay kinetics with increasing partial pressures of oxygen, pO(2). Neither model appears able to unite these latter features, let alone the observed disparate array of response features exhibited by the myriad optical oxygen sensors reported in the literature, and still maintain any level of physical plausibility. A model based on a Gaussian distribution in quenching rate constant, k(q), is developed and, although flawed by a limited breadth in distribution, rho, does produce Stern-Volmer plots which would cover the range in curvature seen with real optical oxygen sensors. A new 'log-Gaussian distribution in tau(o) or k(q)' model is introduced which has the advantage over a Gaussian distribution model of placing no limitation on the value of rho. Work on a 'log-Gaussian distribution in tau(o)' model reveals that the Stern-Volmer quenching plots would show little degree in curvature, even at large rho values and the luminescence decays would become increasingly first order with increasing pO(2). In fact, with real optical oxygen sensors, the opposite is observed and thus the model appears of little value. In contrast, a 'log-Gaussian distribution in k(o)' model does produce the trends observed with real optical oxygen sensors; although it is technically restricted in use to those in which the kinetics of luminescence decay are good first order in the absence of oxygen. The latter model gives a good fit to the major response features of sensors which show the latter feature, most notably the [Ru(dpp)(3)(2+)(Ph4B-)(2)] in cellulose optical oxygen sensors. The scope of a log-Gaussian model for further expansion and, therefore, application to optical oxygen sensors, by combining both a log-Gaussian distribution in k(o) with one in tau(o) is briefly discussed.

Effect of plasticizer viscosity on the sensitivity of an [RU(bpy)(3)(2+)(Ph4B-)(2)]-based optical oxygen sensor

The quenching of the electronically-excited, lumophoric state of [Ru(bpy)(3)(2+)(Ph4B-)(2)] by oxygen is studied in a wide variety of neat plasticizers. The Stern-Volmer constant, K-SV, is found to be inversely dependent upon the viscosity of the quenching medium, although the natural lifetime of the electronically excited state of [RU(bPY)(3)(2+)(Ph4B-)(2)] is largely independent of medium. The least viscous of the plasticizers tested, triethyl phosphate, did not, however, produce highly sensitive optical oxygen sensors when used to plasticize [RU(bPY)(3)(2+)(Ph4B-)(2)]-containing cellulose acetate butyrate (CAB) and poly(methyl methacrylate) (PMMA) films, Instead, the compatibility of the polymer-plasticizer combination, as measured by the difference in the values of the solubility parameter of the two, appears to be a major factor in determining the overall oxygen sensitivity of the thin plastic films. For highly compatible polymer-plasticizer combinations, the plasticizer with the lowest viscosity produces films of the highest oxygen sensitivity. This situation arises because in the film the quenching process is partly diffusion-controlled and, as a result, the quenching rate constant is inversely proportional to the effective viscosity of the reaction medium.

Use of luminescent gold compounds in the design of thin-film oxygen sensors

The use of two gold compounds incorporated into thin plastic films as luminescence quenching oxygen sensors is described. The films are sensitive both to gaseous oxygen and to oxygen dissolved in nonaqueous media such as ethanol. The luminescence quenching of these sensors by oxygen obeys the Stern-Volmer equation and Stern-Volmer constants of 5.35 x 10(-3) and 0.9 x 10(-3) Torr(-1) are found, respectively, for the two dyes in a polystyrene polymer matrix. The sensitivity of the films is strongly influenced by the nature of the polymer matrix, and greatest sensitivity was found in systems based an the polymers polystyrene or cellulose acetate butyrate. Sensitivity was not found to be temperature dependent though raising the temperature hom 15 to 50 degrees C did result in a slight decrease in emission intensity and a hypsochromic shift in the emission wavelength. The rate of response and recovery of the sensors can be increased either by decreasing film thickness or by increasing the operating temperature. The operational and storage stability of these films is generally good though exposure to light should be avoided as one of the dyes tends to undergo photobleaching probably due to a photoinduced ligand substitution reaction.

Photophysical Investigations of Thiophene Azomethine Derivatives

Une série de dimères composés de thiophène-aniline encombrée stériquement a été synthétisée. Les différents processus de désactivation de l’état singulet excité ont été étudiés par UV-visible, fluorescence, phosphorescence, photolyse par impulsion laser et calculs théoriques. Les graphiques de Stern-Volmer obtenus à partir des expériences de désactivation des états singulet et triplet ont démontré l’efficacité de l’azométhine à désactiver les fluorophores. Les calculs semi-empiriques AM1 examinant l’effet des substituants encombrés ont démontrés que les groupements tert-butyls sur l’aniline ont moins d’influence sur la barrière de rotation N-aryl que les substitutions alkyles en ont sur la rotation de thiophène-C. Les calculs Rehm-Weller basés sur les potentiels d’oxydation et de réduction ont montré que l’autodésactivation de l’état excité des azométhines se fait par transfert d’électron photoinduit menant à une éradication complète de la fluorescence. Des complexes métalliques contenant des ligands azométhines ont aussi été préparés. Le ligand est composé d’une unité hydroxyquinoline lié à un cycle thiophène. Les données photophysiques de ces complexes indiquent un déplacement bathochromique aussi bien en absorbance qu’en fluorescence. Des dispositifs de détection d’ion métallique ont été préparés et un exemple à partir d’une solution de cuivre a montré un déplacement bathochromique.

Interaction of flavonoids with bovine serum albumin: a fluorescence quenching study

The interaction between four flavonoids (catechin, epicatechin, rutin and quercetin) and bovine serum albumin (BSA) was investigated using tryptophan fluorescence quenching. Quenching constants were determined using the Stern-Volmer equation to provide a measure of the binding affinity between the flavonoids and BSA. The binding affinity was found to be strongest for quercetin, and ranked in the order quercetin>rutin>epicatechin=catechin. The pH in the range of 5 to 7.4 does not affect significantly (p<0.05) the association of rutin, epicatechin and catechin with BSA, but quercetin exhibited a stronger affinity at pH 7.4 than at lower pH (p<0.05). Quercetin has a total quenching effect on BSA tryptophan fluorescence at a molar ratio of 10:1 and rutin at approximately 25:1. However, epicatechin and catechin did not fully quench tryptophan fluorescence over the concentration range studied. Furthermore, the data suggested that the association between flavonoids and BSA did not change molecular conformation of BSA and that hydrogen bonding, ionic and hydrophobic interaction are equally important driving forces for protein-flavonoid association.

Synthesis, characterization, crystal structure, and DNA-binding of ruthenium(II) complexes of heterocyclic nitrogen ligands resulting from a benzimidazole-based quinazoline derivative

The reaction of cis-[RuCl2(dmso)(4)] with [6-(2-pyridinyl)-5,6-dihydrobenzimidazo[1,2-c] quinazoline] (L) afforded in pure form a blue ruthenium(II) complex, [Ru(L-1)(2)] (1), where the original L changed to [2-(1H-benzoimidazol-2-yl)-phenyl]-pyridin-2-ylmethylene-amine (HL1). Treatment of RuCl3 center dot 3H(2)O with L in dry tetrahydrofuran in inert atmosphere led to a green ruthenium(II) complex, trans-[RuCl2(L-2)(2)] (2), where L was oxidized in situ to the neutral species 6-pyridin-yl-benzo[4,5]imidazo[1,2-c] quinazoline (L-2). Complex 2 was also obtained from the reaction of RuCl3 center dot 3H(2)O with L-2 in dry ethanol. Complexes 1 and 2 have been characterized by physico-chemical and spectroscopic tools, and 1 has been structurally characterized by single-crystal X-ray crystallography. The electrochemical behavior of the complexes shows the Ru(III)/Ru(II) couple at different potentials with quasi-reversible voltammograms. The interaction of these complexes with calf thymus DNA by using absorption and emission spectral studies allowed determination of the binding constant K-b and the linear Stern-Volmer quenching constant K-SV

On the localization of water-soluble porphyrins in micellar systems evaluated by static and time-resolved frequency-domain fluorescence techniques

Fluorescence quenching of meso-tetrakis-4-sulfonatophenyl (TPPS4) and meso-tetrakis-4-N-methylpyridil (TMPyP) porphyrins is studied in aqueous solution and upon addition of micelles of sodium dodecylsulfate (SDS), cetyltrimethylammonium chloride (CTAC), N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) and t-octylphenoxypolyethoxyethanol (Triton X-100). Potassium iodide (KI) was used as quencher. Steady-state Stern-Volmer plots were best fitted by a quadratic equation, including dynamic (K-D) and static (K-s) quenching. Ks was significantly smaller than K-D. Frequency-domain fluorescence lifetimes allowed estimating bimolecular quenching constants, k(q). At 25 degrees C, in aqueous solution, TMPyP shows k(q), values a factor of 2-3 higher than the diffusional limit. TPPS4 shows collisional quenching with pH dependent k(q) values. For TMPyP quenching results are consistent with reported binding constants: a significant reduction of quenching takes place for SDS, a moderate reduction is observed for H PS and almost no change is seen for Triton X-100. Similar data were obtained at 50 C. For CTAC-TPPS4 system an enhancement of quenching was observed as compared to pure buffer. This is probably associated to accumulation of iodide at the cationic micellar interface. The attraction between CTAC headgroups and 1(-), and repulsion between SDS and 1(-), enhances and reduces the fluorescence quenching, respectively, of porphyrins located at the micellar interface. The small quenching of TPPS4 in Triton X-100 is consistent with strong binding as reported in the literature. (C) 2008 Elsevier B.V. All rights reserved.

Influence of the Bilayer Composition on the Binding and Membrane Disrupting Effect of Polybia-MP1, an Antimicrobial Mastoparan Peptide with Leukemic T-Lymphocyte Cell Selectivity

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)