Ligand field-tuned single-molecule magnet behaviour of 2p-4f complexes

Three new 2p-4f complexes of [Ln(acac)(3)(NIT-2Py)]·0.5NIT-2Py [Ln(III) = Gd(1), Dy(2)] and [Dy(tfa)(3)(NIT-2Py)]·0.5C(7)H(16) (3) (NIT-2Py = 2-(2'-pyridyl)- 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; acac = acetylacetonate and tfa = trifluoroacetylacetonate) have been synthesized, and structurally and magnetically characterized. The X-ray structural analysis exhibits that the three complexes show similar mononuclear structures, in which NIT-2Py radical chelates the Ln(III) ion through the oxygen atom of the NO group and the nitrogen atom from the pyridine ring. The static magnetic measurements on the three complexes exhibit ferromagnetic coupling between the lanthanide ion and the radical. Compared to the silence of the out-of-phase ac susceptibility of complex 3, the magnetic relaxation behavior of complex 2 is observed, suggesting single-molecule magnet behavior. The different magnetic relaxation behaviours of 2 and 3 are due to their slightly different crystal structure around the Dy(III) ions. It was demonstrated that the spin dynamic can be modified by the careful adjustment of the ligand field around the metal center.     

Modulating spin dynamics of cyclic LnIII-radical complexes (LnIII = Tb, Dy) by using phenyltrifluoroacetylacetonate coligand

Three novel ring-like compounds formulated as [Ln(Phtfac)(3)(NITpPy)](2) (Ln(III) = Gd 1, Tb 2, Dy 3; HPhtfac = 4,4,4-trifluoro-1-phenylbutane-1,3-dione; NITpPy = 2-(4-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl-3-oxide) were synthesized and structurally and magnetically characterized. Three compounds possess cyclic dimer structure in which each pyridine substituted radical links two different metal ions through the oxygen of nitroxide group and the pyridine nitrogen. DC magnetic studies show the Ln(III) ion interacts ferromagnetically with the directly bonding nitronyl nitroxide. Both Tb(III) and Dy(III) clusters show frequency-dependent ac magnetic susceptibilities, indicating single-molecule magnet behavior. It is demonstrated that the β-diketonate coligand may play an important role in determining the magnetic relaxation for the lanthanide-radical system.     

A fluorescence enhancement-based sensor for hydrogen sulfate ion

Sugar-aza-crown ether-based cavitand 1 can act as a selective turn-on fluorescence sensor for hydrogen sulfate ion in methanol among a series of tested anions. Spectroscopic studies, particularly NMR spectroscopy, revealed that the C-H hydrogen bonding between 1,2,3-triazole ring of cavitand 1 and hydrogen sulfate ion is crucial for the high selectivity of the receptor for hydrogen sulfate.     

KF polymerase-based fluorescence aptasensor for the label-free adenosine detection

We have developed a simple, inexpensive, and label-free method for the selective detection of adenosine. Klenow fragment polymerase (KF polymerase) is a commonly-used 5' to 3' DNA polymerase, it also has 3' to 5' exonuclease activity that can digest single-stranded DNA. An adenosine binding DNA aptamer was employed, the aptamer was split into two pieces of single-stranded DNA (aptamer-A1 + aptamer-A2). Without the addition of adenosine, aptamer-A1 and aptamer-A2 existed as single-stranded DNA which could be efficiently degraded by the exonuclease activity of KF polymerase. Much reduced background fluorescence was obtained when SYBR Green dye was added. However, in the presence of adenosine, aptamer-A1 and aptamer-A2 bound to adenosine, and hybridization of the complementary sequences resulted in the formation of a duplex DNA structure, which could initiate DNA polymerization. The addition of SYBR Green dye resulted in a very high fluorescence enhancement, which could be used for the quantification of adenosine.     

新型三嗪桥连的双1,8-萘酰亚胺衍生物的合成及其光物理行为

以1,8-萘酰亚胺和三聚氯氰为主要原料, 合成了两种由三嗪环桥连的双1,8-萘酰亚胺化合物3 和5. 采用紫外-可见光谱和荧光光谱等手段考察了两种化合物在不同溶剂中的光物理行为. 与参比化合物N-丁基-1,8-萘酰亚胺相比, 在二氯甲烷、三氯甲烷和甲醇等极性溶剂中, 化合物3和5除了在短波区(λ<400 nm)存在1,8-萘酰亚胺的特征荧光发射峰外, 在长波区(>450 nm)均产生一个较强的新荧光发射峰, 表现出分子内激基缔合物的光物理行为. 与化合物5相比, 由于化合物3特殊的构象异构, 其荧光强度发生严重的猝灭. 在非极性溶剂甲基环己烷中, 化合物5 由于存在较强的分子间氢键作用而聚集, 受激后形成了较稳定的分子间激基缔合物, 但未观察到明显的分子内激基缔合物的形成. 在甲苯溶剂中, 化合物3和5与甲苯分子形成了激基复合物, 并未形成分子内激基缔合物. 进一步研究3和5的固态激发态性质, 发现化合物3和5的固体薄膜受激后分别在465和469 nm处出现激基缔合物的特征荧光发射峰.     

Quantum-correlated photon pair generation in tellurite microstructured optical fibers

We theoretically investigated the generation of quantum-correlated photon pair through spontaneous four-wave mixing in tellurite microstructured optical fiber (MOF). We evaluated the performance of photon pair generation in tellurite fibers based on Raman gain coefficient spectra. It was shown that the TBSN16P6W tellurite fiber provided a low Raman noise on correlation photon generation over a wide pump-idler detuning range. We can choose proper tellurite composition to obtain a low Raman gain window over wide range for correlated photon pair generation. We also designed the tellurite MOF structure to obtain a small dispersion value with high nonlinear coefficient at telecommunication wavelengths, thus realize efficient quantum-correlated photon pair generation.     

Charge rate influence on the electrochemical performance of LiFePO<Subscript>4</Subscript> electrode with redox shuttle additive in electrolyte

Overcharge performance of LiFePO₄ cells is investigated through adding 2, 5-ditertbutyl 1, 4-dimethoxybenzene (DDB) as redox shuttle into electrolyte (RS electrolyte) at different charge rate. RS electrolytes with DDB works well as overcharge protection at low charge rate of less than 0.1 C. Novel charge/discharge characteristics are observed when charge rate increases in the cell with RS electrolyte. Especially, larger discharge capacities are obtained at the same discharge rate after charge rate gets higher than 0.1 C rate. Discharge capacity is larger in the cell with RS electrolyte than that in the cell without RS electrolyte at the same charge and discharge rate. At the same charge rate, cells with RS electrolyte have better cycling performances and larger discharge capacity than that with conventional electrolyte. These indicate that DDB accumulates in cathode with cycling and influences electrode–electrolyte interface reactions.     

平行因子分析法在太湖水体三维荧光峰比值分析中的应用

以太湖水样三维荧光光谱数据为例,提出在采用平行因子分析法(PARAFAC)处理后的荧光数据中提取荧光峰强度计算荧光峰比值进行水环境分析评价的方法,较直接在水样原始荧光谱图中获取的荧光峰强度更加准确客观。天然水体中各水样间由于受荧光团复杂多样性等因素的影响,某类荧光物质荧光峰的激发发射波长位置并不是固定不变的,就同一水样而言各类荧光峰之间的相互重叠干扰也将影响到荧光峰强度和位置的准确判断。而在PARAFAC模型各因子中提取相应荧光峰值可以保证各水样间同类荧光物质荧光峰在同一位置又有效减弱同一水样中各类荧光物质荧光峰之间的相互干扰,更加高效准确的利用荧光峰比值进行水环境分析。区域差异性分析时水样因子得分比值的区域变化与原始荧光峰比值变化趋势是一致的。     

An alternating variable method for the maximal correlation problem

The maximal correlation problem (MCP) aiming at optimizing correlations between sets of variables plays an important role in many areas of statistical applications. Up to date, algorithms for the general MCP stop at solutions of the multivariate eigenvalue problem (MEP), which serves only as a necessary condition for the global maxima of the MCP. For statistical applications, the global maximizer is quite desirable. In searching the global solution of the MCP, in this paper, we propose an alternating variable method (AVM), which contains a core engine in seeking a global maximizer. We prove that (i) the algorithm converges globally and monotonically to a solution of the MEP, (ii) any convergent point satisfies a global optimal condition of the MCP, and (iii) whenever the involved matrix A is nonnegative irreducible, it converges globally to the global maximizer. These properties imply that the AVM is an effective approach to obtain a global maximizer of the MCP. Numerical testings are carried out and suggest a superior performance to the others, especially in finding a global solution of the MCP.     

Molecularly imprinted aptamers of gold nanoparticles for the enzymatic inhibition and detection of thrombin

We prepared thrombin-binding aptamer-conjugated gold nanoparticles (TBA-Au NPs) through a molecularly imprinted (MP) approach, which provide highly efficient inhibition activity toward the polymerization of fibrinogen. Au NPs (diameter, 13 nm), 15-mer thrombin-binding aptamer (TBA(15)) with different thymidine linkers, and 29-mer thrombin-binding aptamer (TBA(29)) with different thymidine linkers (Tn) in the presence of thrombin (Thr) as a template were used to prepare MP-Thr-TBA(15)/TBA(29)-Tn-Au NPs. Thrombin molecules were then removed from Au NPs surfaces by treating with 100 mM Tris-NaOH (pH ca. 13.0) to form MP-TBA(15)/TBA(29)-Tn-Au NPs. The length of the thymidine linkers and TBA density on Au NPs surfaces have strong impact on the orientation, flexibility, and stability of MP-TBA(15)/TBA(29)-Tn-Au NPs, leading to their stronger binding strength with thrombin. MP-TBA(15)/TBA(29)-T(15)-Au NPs (ca. 42 TBA(15) and 42 TBA(29) molecules per Au NP; 15-mer thymidine on aptamer terminal) provided the highest binding affinity toward thrombin with a dissociation constant of 5.2 × 10(-11) M. As a result, they had 8 times higher anticoagulant (inhibitory) potency relative to TBA(15)/TBA(29)-T(15)-Au NPs (prepared in the absence of thrombin). We further conducted thrombin clotting time (TCT) measurements in plasma samples and found that MP-TBA(15)/TBA(29)-T(15)-Au NPs had greater anticoagulation activity relative to four commercial drugs (heparin, argatroban, hirudin, and warfarin). In addition, we demonstrated that thrombin induced the formation of aggregates from MP-TBA(15)-T(15)-Au NPs and MP-TBA(29)-T(15)-Au NPs, thereby allowing the colorimetric detection of thrombin at the nanomolar level in serum samples. Our result demonstrates that our simple molecularly imprinted approach can be applied for preparing various functional nanomaterials to control enzyme activity and targeting important proteins.