Excited-state intramolecular proton transfer molecules bearing o-hydroxy analogues of green fluorescent protein chromophore

o-Hydroxy analogues, 1a-g, of the green fluorescent protein chromophore have been synthesized. Their structures and electronic properties were investigated by X-ray single-crystal analyses, electrochemistry, and luminescence properties. In solid and nonpolar solvents 1a-g exist mainly as Z conformers that possess a seven-membered-ring hydrogen bond and undergo excited-state intramolecular proton transfer (ESIPT) reactions, resulting in a proton-transfer tautomer emission. Fluorescence upconversion dynamics have revealed a coherent type of ESIPT, followed by a fast vibrational/solvent relaxation (<1 ps) to a twisted (regarding exo-C(5)-C(4)-C(3) bonds) conformation, from which a fast population decay of a few to several tens of picoseconds was resolved in cyclohexane. Accordingly, the proton-transfer tautomer emission intensity is moderate (0.08 in 1e) to weak (～10(-4) in 1a) in cyclohexane. The stronger intramolecular hydrogen bonding in 1g suppresses the rotation of the aryl-alkene bond, resulting in a high yield of tautomer emission (Φ(f) ≈ 0.2). In the solid state, due to the inhibition of exo-C(5)-C(4)-C(3) rotation, intense tautomer emission with a quantum yield of 0.1-0.9 was obtained for 1a-g. Depending on the electronic donor or acceptor strength of the substituent in either the HOMO or LUMO site, a broad tuning range of the emission from 560 (1g) to 670 nm (1a) has been achieved.     

SrB_6的固相合成及其形成机理

稀土、碱土金属硼化物属难熔类金属无氧型化合物具有高熔点、高强度和化学稳定性高的特点其中许多还具有特殊的功能性如低的电子功函数、比电阻恒定、在一定温度范围内热膨胀值为零、不同类型的磁序以及高的中子吸收系数等１～４。这些优越性能决定其在现代技术各种器件组元中有广泛的应用前景。许多国家相继开展了该类材料的研究其中ＳｒＢ６及其复合材料用作高温绝缘体、核反应堆的控制棒等已引起多方重视此外文献５用扫描隧道电子显微镜分析了ＳｒＢ６的结构与性能在研究铝合金的变质过程中发现ＳｒＢ６能显著缩短有效变质时间６。但迄今…     

Comprehensive studies on an overall proton transfer cycle of the ortho-green fluorescent protein chromophore

Initiated by excited-state intramolecular proton transfer (ESIPT) reaction, an overall reaction cycle of 4-(2-hydroxybenzylidene)-1,2-dimethyl-1H-imidazol-5(4H)-one (o-HBDI), an analogue of the core chromophore of the green fluorescent protein (GFP), has been investigated. In contrast to the native GFP core, 4-(4-hydroxybenzylidene)-1,2-dimethyl-1H-imidazol-5(4H)-one (p-HBDI), which requires hydrogen-bonding relay to accomplish proton transfer in vivo, o-HBDI possesses a seven-membered-ring intramolecular hydrogen bond and thus provides an ideal system for mimicking an intrinsic proton-transfer reaction. Upon excitation, ESIPT takes place in o-HBDI, resulting in a ～600 nm proton-transfer tautomer emission. The o-HBDI tautomer emission, resolved by fluorescence upconversion, is comprised of an instantaneous rise to a few hundred femtosecond oscillation in the early relaxation stage. Frequency analysis derived from ultrashort pulse gives two low-frequency vibrations at 115 and 236 cm(-1), corresponding to skeletal deformation motions associated with the hydrogen bond. The results further conclude that ESIPT in o-HBDI is essentially triggered by low-frequency motions and may be barrierless along the reaction coordinate. Femtosecond UV/vis transient absorption spectra also provide supplementary evidence for the structural evolution during the reaction. In CH(3)CN, an instant rise of a 530 nm transient is resolved, which then undergoes 7.8 ps decay, accompanied by the growth of a rather long-lived 580 nm transient species. It is thus concluded that following ESIPT the cis-proton transfer isomer undergoes cis-trans-isomerization. The results of viscosity-dependent dynamics are in favor of the one-bond-flip mechanism, which is in contrast to the volume-conserving isomerization behavior for cis-stilbene and p-HBDI. Further confirmation is given by the picosecond-femtosecond transient IR absorption spectra, where several new and long-lived IR bands in the range of 1400-1500 cm(-1) are assigned to the phenyl in-plane breathing motions of the trans-proton transfer tautomer. Monitored by the nanosecond transient absorption, the 580 nm transient undergoes a ～7.7 μs decay constant, accompanied by the growth of a new ～500 nm band. The latter is assigned to a deprotonated tautomer species, which then undergoes the ground-state reverse proton recombination to the original o-HBDI in ～50 μs, achieving an overall, reversible proton transfer cycle. This assignment is unambiguously supported by pump-probe laser induced fluorescence studies. On these standpoints, a comparison of photophysical properties among o-HBDI, p-HBDI, and wild-type GFP is discussed in detail.     

SrB6的固相合成及其形成机理

稀土、碱土金属硼化物属难熔类金属无氧型化合物,具有高熔点、高强度和化学稳定性高的特点,其中许多还具有特殊的功能性,如低的电子功函数、比电阻恒定、在一定温度范围内热膨胀值为零、不同类型的磁序以及高的中子吸收系数等。这些优越性能决定其在现代技术各种器件组元中有广泛的应用前景。许多国家相继开展了该类材料的研究,其中SrB6及其复合材料用作高温绝缘体、核反应堆的控制棒等已引起多方重视,此外,文献用扫描隧道电子显微镜分析了SrB6的结构与性能,在研究铝合金的变质过程中,发现SrB6能显著缩短有效变质时间。但迄今为止,系统介绍SrB6粉末合成的文章未见报道,本文研究以SrCO3,B4C和活性C粉为原材料,固相合成SrB6粉的工艺,以及不同温度和保温时间对SrB6粉末合成的影响,探讨合成SrB6粉末的最佳工艺,并对其形成机理作了简要介绍。     

The complete replacement of antibodies by protein-imprinted poly(ethylene-co-vinyl alcohol) in sandwich fluoroimmunoassays

The replacement of antibodies by molecularly imprinted polymers (MIPs) has been investigated for many decades. However, indirect protocols (including natural primary and secondary antibodies) are still utilized to evaluate the ability of MIP thin films to recognize target molecules. MIPs can be prepared as either a thin film or as particles, and cavities that are complementary to the template can be generated on their surfaces. We have prepared thin film MIPs and particle MIPs prepared by solvent evaporation and phase inversion, respectively, from solutions of poly(ethylene-co-vinyl alcohol) (pEVAL) in the presence of the target analytes amylase, lysozyme, and lipase. These were first adsorbed on MIP thin films and by MIP particles that contain fluorescent quantum dots. Sandwich fluoroimmunoassays were then conducted to quantify them in MIP-coated 96-well microplates. The method was applied to determine amylase in saliva, and results were compared with a commercial analytical system.

     

The complete replacement of antibodies by protein-imprinted poly(ethylene-co-vinyl alcohol) in sandwich fluoroimmunoassays

The replacement of antibodies by molecularly imprinted polymers (MIPs) has been investigated for many decades. However, indirect protocols (including natural primary and secondary antibodies) are still utilized to evaluate the ability of MIP thin films to recognize target molecules. MIPs can be prepared as either a thin film or as particles, and cavities that are complementary to the template can be generated on their surfaces. We have prepared thin film MIPs and particle MIPs prepared by solvent evaporation and phase inversion, respectively, from solutions of poly(ethylene-co-vinyl alcohol) (pEVAL) in the presence of the target analytes amylase, lysozyme, and lipase. These were first adsorbed on MIP thin films and by MIP particles that contain fluorescent quantum dots. Sandwich fluoroimmunoassays were then conducted to quantify them in MIP-coated 96-well microplates. The method was applied to determine amylase in saliva, and results were compared with a commercial analytical system.