Two Completely Different Mechanisms for Highly Specific Na+ Recognition by DNAzymes

Our view of the interaction between Na⁺ and nucleic acids was changed by a few recently discovered Na⁺‐specific RNA‐cleaving DNAzymes. In addition to nonspecific electrostatic interactions, highly specific recognition is also possible. Herein, two such DNAzymes, named EtNa and Ce13d, are compared to elucidate their mechanisms of Na⁺ binding. Mutation studies indicate that they have different sequence requirements. Phosphorothioate (PS) substitution at the scissile phosphate drops the activity of EtNa 140‐fold, and it cannot be rescued by thiophilic Cd²⁺ or Mn²⁺, whereas the activity of PS‐modified Ce13d can be rescued. Na⁺‐dependent activity assays indicate that two Na⁺ ions bind cooperatively in EtNa, and each Na⁺ likely interacts with a nonbridging oxygen atom in the scissile phosphate, whereas Ce13d binds only one Na⁺ ion in a well‐defined Na⁺ aptamer, and this Na⁺ ion does not directly interact with the scissile phosphate. Both DNAzymes display a normal pH–rate profile, with a single deprotonation reaction required for catalysis. For EtNa, Na⁺ fails to protect the conserved nucleotides from dimethyl sulfate attack, and no specific Na⁺ binding is detected by 2‐aminopurine fluorescence, both of which are different from those observed for Ce13d. This work suggests that EtNa binds Na⁺ mainly through its scissile phosphate without significant involvement of the nucleotides in the enzyme strand, whereas Ce13d has a well‐defined aptamer for Na⁺ binding. Therefore, DNA has at least two distinct ways to achieve highly selective Na⁺ binding.     

Global Folding of a Na+-Specific DNAzyme Studied by FRET

Recently, a few RNA-cleaving DNAzymes have been isolated with excellent specificity for Na⁺, and some of them contain a Na⁺-binding aptamer. This metal recognition mechanism is different from that of most previously reported DNAzymes. When using 2-aminopurine (2AP) as a probe, interesting local folding induced by Na⁺ was recently observed. In this work, FRET was used to probe the global folding of the Ce13d DNAzyme; one of the Na⁺-specific DNAzymes. FRET pairs were at different locations, which yielded a total of five constructs to probe the three-way junction structure with a large loop. With endlabeled DNAzymes, the global structure appears to be quite rigid with little folding upon adding up to 200 mm monovalent metal ions, although some minor differences were observed between Li⁺, Na⁺, and K⁺. This lack of significant conformational change is also consistent with circular dichroism spectroscopy data. The loop was then labeled with an internal tetramethylrhodamine fluorophore at the G14 position, and its cleavage activity was partially retained. A clear Na⁺-dependent folding was observed with spectral crossover. From a biosensing standpoint, global folding based sensors are unlikely to work due to the overall rigid structure of the DNAzyme. Therefore, the best way to use this DNAzyme to discriminate Na⁺ from K⁺ is based on cleavage activity, followed by probing local folding, whereas global folding is the least effective for metal discrimination.     

Tb3+激活硅酸盐玻璃的发光性能及其X射线转换屏应用研究

通过成分设计、试样制备得到了荧光性能良好的Tb^3 激活硅酸盐发光玻璃,利用荧光光度计测试了玻璃的激发光谱和发射光谱,在能量为9MeV的X射线电荷耦合器件(charge-coupled device,CCD)摄像系统中,比较了Tb^3 激活硅酸盐玻璃转换屏与Gd2O2s：Tb多晶转换屏的发光性能。结果表明：在Tb^3 激活硅酸盐发光玻璃的发射波长中,543nm处的绿光发射最强,并且在X射线和紫外线的激发下,发射峰有不同程度的分裂。当Tb^3 浓度增加时,由于能量在Tb^3 离子间发生了无辐射共振转移,发光玻璃的蓝色荧光减弱,绿色荧光增强。发光玻璃在X射线CCD摄像系统中的使用效果良好,成像质量较高,可望作为X射线转换屏在CCD摄像系统中获得应用。     

Enhanced up-conversion luminescence of Tb3+-Yb3+ doped glass ceramics by doping Li+

Tb³⁺-Yb³⁺ co-doped transparent glass ceramics (GCs) containing Y₂Ti₂O₇ crystal phases were synthesized by the melt crystallization. The light transmittance of GCs in the visible region reached 78%, and the average grain size was 278 nm under the optimal heat treatment conditions (720 °C/2 h). The GCs exhibited greater up-conversion luminescence intensity than precursor glass, and the reason for this result was explained in accordance with the Judd-Ofelt theory. Moreover, the introduction of Li⁺ did not change the crystalline phase of GCs. The emission intensity of the green light of the 8% Li ⁺ doped GCs was significantly enhanced by nearly 4.48 times under 980 nm excitation. The XRD refinement results suggest that the enhanced luminescence intensity is correlated with the change of the Y₂Ti₂O₇ crystal lattice caused by Li⁺ doping. The relevant luminescence mechanism was elucidated. The results suggest that Li⁺ doped transparent GCs open novel avenues for green UC applications.     

Luminescence characteristics of SrZnSO:M (M = Bi3+, Mn2+ and Tb3+) phosphors

Bi³⁺/Tb³⁺/Mn²⁺-activated SrZnSO phosphors were prepared to investigate their luminescence characteristics. The SrZnSO:Bi³⁺, SrZnSO:Mn²⁺ and SrZnSO:Tb³⁺ phosphors, excited by the NUV/blue light, show blue, orange and green emissions, respectively. The Bi³⁺ → Tb³⁺, Tb³⁺ → Mn²⁺ and Bi³⁺ → Mn²⁺ energy transfer processes take place in Bi³⁺/Tb³⁺-, Tb³⁺/Mn²⁺-, Bi³⁺/Mn²⁺- and Bi³⁺/Tb³⁺/Mn²⁺-activated SrZnSO phosphors, which result in tunable luminescence of these phosphors. The CIE coordinates were calculated on the basis of the emission spectra, and they reflect the emission color changes of phosphors. For the Bi³⁺/Tb³⁺-, Tb³⁺/Mn²⁺- and Bi³⁺/Mn²⁺- activated SrZnSO phosphors, the emission points are located in the cyan, yellow and white light regions, respectively. For the Bi³⁺/Tb³⁺/Mn²⁺-activated SrZnSO phosphors, the light is in warm white light region.     

Tb3+掺杂钼酸盐玻璃陶瓷的制备及发光性能表征

采用熔融-晶化法制备了Tb3+掺杂的CaMoO4为主晶相的透明钼酸盐玻璃陶瓷。利用DSC、XRD、SEM确定了该体系玻璃样品的最佳热处理制度：715℃保温2.5 h;随着热处理时间的增加,玻璃陶瓷中的晶粒尺寸逐渐变大;利用UV-Vis-NIR得到样品玻璃陶瓷在可见光区的透过率可达80%;并利用荧光光谱讨论了在相同热处理条件下,不同Tb3+掺杂浓度对玻璃陶瓷样品发光性能的影响,研究表明Tb3+掺杂浓度为7.0mol%时样品的荧光强度最大。     

铽离子荧光探针对钙调素的研究与进展

Tb3 离子能够取代钙调素中的钙离子而影响其生物功能,因此可作为荧光探针对钙调素进行研究.概述了Tb3 离子荧光探针对钙调素的研究进展情况.     

Probing Local Folding Allows Robust Metal Sensing Based on a Na+-Specific DNAzyme

Fluorescent metal sensors based on DNA often rely on changes in end-to-end distance or local environmental near fluorophore labels. Because metal ions can also nonspecifically interact with DNA through various mechanisms, such as charge screening, base binding, and increase or decrease in duplex stability, robust and specific sensing of metal ions has been quite challenging. In this work, a side-by-side comparison of two signaling strategies on a Na⁺-specific DNAzyme that contained a Na⁺-binding aptamer was performed. The duplex regions of the DNAzyme was systematically shortened and its effect was studied by using a 2-aminopurine (2AP)-labeled substrate strand. Na⁺ binding affected the local environmental of the 2AP label and increased its fluorescence. A synergistic process of Na⁺ binding and forming the duplex on the 5′-end of the enzyme strand was observed, and this end was close to the aptamer loop. Effective Na⁺ binding was achieved with a five base-pair stem. The effect on the 3′-end is more continuous, and the stem needs to form first before Na⁺ can bind. With an optimized substrate binding arm, a FRET-based sensor has been designed by labeling the two ends of a cis form of the DNAzyme with two fluorophores. In this case, Na⁺ failed to show a distinct difference from that of Li⁺ or K⁺; thus indicating that probing changes to the local environment allows more robust sensing of metal ions.     

Luminescence and electrical properties of Eu-modified Bi0.5Na0.5TiO3 multifunctional ceramics

The Eu³⁺-modified Bi_0.5Na_0.5TiO₃ (BNT) ceramics have been fabricated by the solid-state reaction method. The impact of Eu³⁺ doping on the structure, photoluminescence, and electrical properties has been studied by XRD, SEM, PL spectra, and LCR meter. X-ray diffraction analysis reveals that the crystal structure of the samples is well matched with the trigonal perovskite, and the optimal temperature of presintering is 880°C. The Eu³⁺-doped BNT ceramics show excellent red fluorescence at 614 nm corresponding to the ⁵D₀→⁷F₂ transition of Eu³⁺ under 466 nm excitation and relatively long fluorescence lifetime. The BNT-0.02Eu ceramic density is up to 5.68 g/cm³ and the relative density is up to 94.6% with sintering temperature 1075°C. The piezoelectric constant (d₃₃) of samples has been significantly improved up to 110 pC/N by Eu³⁺ doping. The BNT-0.03Eu ceramic presintered at 880°C and sintered at 1050°C has good dielectric properties and excellent luminescence properties. Eu³⁺-doped BNT ceramics make it potential applications for novel integrated electro-optical and multifunctional devices.     

掺铽的铝酸锶铕镝磷光体的发光特性及晶相分析

采用高温固相法在弱还原气氛下制备了掺入Tb3 的SrAl2O4:Eu2 ,Dy3 磷光体.研究了Tb3 对SrAl2O4:Eu2 ,Dy3 磷光体的发光性能的影响.结果发现,引入Tb3 以后,对基质SrAl2O4的晶体结构基本上没有影响,也未改变磷光体的发光光谱,却使磷光体的初始亮度显著提高,并使余辉时间延长.其余辉强度随时间的变化由最初的快衰减过程和随后的慢衰减过程组成,符合t-1.1的双曲线规律.并初步探讨了Tb3 的作用机制.     

GdF3∶Eu3+和NaGdF4∶Eu3+发光粉的可控合成与发光性质

采用聚乙烯吡咯烷酮(PVP)辅助水热法合成了GdF3∶Eu3+和NaGdF4∶Eu3+发光粉。利用X射线衍射(XRD)、扫描电子显微镜和荧光光谱对样品的结构、形貌和发光性能进行了研究。XRD分析表明:GdF3晶相到NaGdF4晶相的转换可以通过改变初始溶液pH值、PVP加入量和NaF与稀土离子(Gd3+和Eu3+)摩尔配比等合成条件实现。NaGdF4∶Eu3+发光粉的形貌受合成条件的影响。荧光光谱研究表明:GdF3∶Eu3+发光粉主发射峰位于593nm处,来自于Eu3+的5 D0→7 F1磁偶极跃迁;NaGdF4∶Eu3+发光粉主发射峰位于616nm,来自于Eu3+的5 D0→7 F2电偶极跃迁。2个样品中Gd3+与Eu3+离子之间存在较好的能量传递,而NaGdF4晶格更有利于2种离子的能量传递。     

掺Tb3+钛酸铅粉末的制备和结晶行为

采用溶胶喂胶法制备了Tb^3 掺杂钛酸铅(PbTiO3，PT)超细粉末，分别用差热分析、透射电子显微镜、X射线衍射仪对其相结构、形貌特性以及晶粒粒径等进行了分析测试。结果表明：这种粉末在约600℃热处理温度下，由非晶基体转变形成钙钛矿相的过程已逐步完成，其晶粒平均尺寸约为18nm，比未掺Tb抖的PT粉末中的钙钛矿晶粒尺寸略小。形成的钙钛矿结构中，Tb^3 取代Pb^2 进入晶格位置，产生阳离子空位，诱发晶格畸变，使钙钛矿相的析晶能力比相同热处理条件下未掺杂Tb^3 的PT低。另外，掺Tb^2 的PT中钙钛矿相的晶轴比c／a比未掺Tb^3 的PT中的低，这类似于产生了赝立方结构，降低了从立方相向这种四方相转化的势垒，有效地抑制了较高温下焦绿石相的产生，使掺Tb^3 的PT中焦绿石相稳定存在的温度比未掺Tb^3 的PT中低约100℃。     

Tb3＋自敏化效应与Gd3＋-Tb3＋能量转移对硅酸盐玻璃发光性能的影响

研究了Tb3+自敏化效应与Gd3+-Tb3+能量转移对硅酸盐玻璃发光性能的影响.结果表明,随着Tb3+掺杂量的增加,Tb3+的400～450 nm蓝色荧光发射减弱,而485 nm和545 nm绿光发射增强.Tb3+掺杂硅酸盐玻璃中,Tb3+之间存在能量转移,产生自敏化效应,这种转移是由Tb3+之间电偶极-电四极的相互作用引起的共振能量转移.Gd3+通过Gd3+-Tb3+间的能量转移对Tb3+的发光起敏化作用,这种能量转移主要是偶极与偶极相互作用引起的共振转移.     

Superdense Tb3+-activated borogermanate-tellurite scintillating glasses

Novel Tb³⁺-activated borogermanate-tellurite scintillating glasses with a maximum density of 7.15 g/cm³ aimed at detection of high-energy rays were prepared by a melt-quenching method for the first time. The concentration-dependent optical properties including transmittance, photoluminescence, luminescence dynamic behaviors, and X-ray excited luminescence in the as-prepared Tb³⁺-activated borogermanate-tellurite glasses were studied. The optimal content of Tb₂O₃ in the superdense borogermanate-tellurite glasses is revealed to be 7 mol% under both 275 nm ultraviolet light and X-ray excitation. The integral scintillation efficiency of Tb³⁺-activated borogermanate-tellurite scintillating glass is about 33.71% of the standard Bi₄Ge₃O₁₂ (BGO) scintillating crystal.     

Tb3+掺杂Faraday磁光玻璃的研究进展

Tb^3 掺杂Faraday磁光玻璃是一种新型的功能材料，在光纤通信和传感领域有广阔的应用前景。综合介绍了磁光玻璃Faraday效应的基本原理。Tb^3 掺杂Faraday磁光玻璃的Verdet常数是电子有效跃迁波长λt，有效跃迁几率Ct，单位体积内的顺磁离子数N和绝对温度T等参数的函数，同时还受到基质玻璃的影响。虽然Verdet常数越大、磁光效应的灵敏度越高，但是应该在保证磁光玻璃综合特性和改进热稳定性和化学稳定性的基础上提高Verdet常数。     

Tb3+、Eu3+,N-苯基邻氨基苯甲酸-1,10-邻菲咯啉配合物的发光性能研究

合成了一种新型的稀土Eu3+、Tb3+的N-苯基邻氦基苯甲酸-1,10-邻菲咯啉异多核配合物,通过红外光谱对其配位情况进行了表征,并用荧光光谱详细研究了其发光性能,讨论了配合物的分子内能量传递过程和电子转移之间的竞争.     

Thermoluminescence features of alumina-mixed borophosphate glasses with Tb3+ ions for dosimetric applications

Amorphous barium borophosphate materials doped with small quantity of terbium ions and with the addition of some amounts of alumina were prepared. Thermoluminescence (TL) characteristics of these glasses were investigated after irradiating them with different doses of γ-rays (in the range 0.5-8.0 kGy). The TL emission exhibited a dosimetric peak at about 210°C. The TL output under this glow peak is observed to increase with the γ-ray dose. For any fixed γ-ray dose, the TL output is increased with increase in Al₂O₃ content up to 3.0 mol%, and beyond this concentration, quenching of TL is visualized. The dose response of TL output of these glasses exhibited linear behavior in the dose range 0.5-4.0 kGy. The mechanisms responsible for TL emission and the variation of TL output with the concentration of Al₂O₃ are quantitatively discussed in terms of structural defects induced during γ-ray irradiation. Finally, it is concluded that these glasses are potential materials for dosimetry applications in the dose range 0.5-4.0 kGy.     

Tb3+激活硅酸盐发光玻璃的研究进展

简要介绍了研究发光玻璃的必要性,发光玻璃的要求及分类,综合评述了Tb3+激活硅酸盐发光玻璃的研究现状,并对研究中存在的问题和研究方向做了进一步探讨.     

Er3+和Yb3+共掺锗硅酸盐玻璃的上转换发光性能

采用熔融-淬火法制备了基体为30SiO2-20GeO2-15Al2O3-5B2O3-30CaF2的Er3+和Yb3+共掺锗硅酸盐玻璃.采用X射线衍射仪、荧光光谱仪和热分析仪对样品进行了表征.结果表明:Er2O3含量从0.5％(摩尔分数,下同)增加到2.0％时,玻璃转变温度Tg和Tx-Tg(Tx为第一析晶温度)数值均有明显下降.Yb2O3含量从1.5％增加到4.5％时,玻璃上转换红光发光强度数量级由103提高到105,对其中1个样品在740℃热处理12h后发现,微晶化处理并未对Er的上转换发光产生有益影响.     

Tb~(3+)在Lu_3Ga_5O_(12)中的光致发光性质及浓度猝灭机制

采用高温固相合成法在还原气氛中制备了(Lu1–xTbx)3Ga5O12荧光粉,研究了其晶体结构、光致发光性能以及Tb3+掺杂浓度对荧光粉性能的影响规律与机制。研究表明:荧光粉具有石榴石型晶体结构,当x增加时,晶格膨胀。荧光粉的激发光谱由归属于Tb3+的4f 8→4f 7 5d1跃迁的A、B两个宽激发带以及归属于4f 8→4f 8跃迁的一些窄谱峰构成;随x的增加,A、B带发生红移,带间距缩小。在紫外光激发下,荧光粉发射绿光;发射光谱对应于Tb3+的5D4→7FJ和5D3→7FJ跃迁,其中5D4→7F5跃迁发射最强。5D4→7FJ各跃迁发射的浓度猝灭以交互作用为主,猝灭浓度xm=0.08。与5D4→7FJ跃迁相比,5D3→7FJ猝灭浓度低,猝灭机制以电偶极–电偶极相互作用下交叉弛豫为主。