靶向性磁共振成像造影剂的研究进展

综述了靶向性磁共振成像造影剂的研究进展,着重介绍了近年来在设计与合成具有靶向给药功能造影剂的研究概况,分别列出了亲脂性基团、VB6族化合物及其衍生物、糖类等功能基团作为靶向基团的水溶性顺磁性造影剂的配体结构。     

Hydrothermal synthesis of magnetite nanoparticles as MRI contrast agents

Magnetite (Fe₃O₄) nanoparticles prepared using hydrothermal approach were employed to study their potential application as magnetic resonance imaging (MRI) contrast agent. The hydrothermal process involves precursors FeCl₂·4H₂O and FeCl₃ with NaOH as reducing agent to initiate the precipitation of Fe₃O₄, followed by hydrothermal treatment to produce nano-sized Fe₃O₄. Chitosan (CTS) was coated onto the surface of the as-prepared Fe₃O₄ nanoparticles to enhance its stability and biocompatible properties. The size distribution of the obtained Fe₃O₄ nanoparticles was examined using transmission electron microscopy (TEM). The cubic inverse spinel structure of Fe₃O₄ nanoparticles was confirmed by X-ray diffraction technique (XRD). Fourier transform infrared (FTIR) spectrum indicated the presence of the chitosan on the surface of the Fe₃O₄ nanoparticles. The superparamagnetic behaviour of the produced Fe₃O₄ nanoparticles at room temperature was elucidated using a vibrating sample magnetometer (VSM). From the result of custom made phantom study of magnetic resonance (MR) imaging, coated Fe₃O₄ nanoparticles have been proved to be a promising contrast enhanced agent in MR imaging.     

Peptide derivatized lamellar aggregates as target-specific MRI contrast agents

The relaxivity behaviour and the structural characterization of new supramolecular aggregates (bilayer structures and micelles) obtained by combining two different amphiphilic monomers are reported. One monomer, (C18)(2)DTPAGlu-Gd, contains a very stable gadolinium complex, and the other, DSPE-PEG(2000)-CCK8, contains the bioactive CCK8 peptide. Samples that contained only DSPE-PEG(2000)-CCK8, or up to 50 % (C18)(2)DTPAGlu-Gd, aggregated as double-layer structures (lamellar aggregates) with a thickness of approximately 80-100 A, as evaluated by SANS measurement and Cryo-TEM imaging. A transition to micelle formation was observed when the amount of (C18)(2)DTPAGlu-Gd in the aggregate was increased. These were rod-like micelles approximately 40 A in radius and >200 A in length. The proton relaxivities for both lamellar aggregates and rod-like micelles were the same (17.2 mM(-1) s(-1)), although the values were the results of different combinations of local and global contributions. The in vitro target selectivity of aggregates that contained the CCK-8 peptide was demonstrated by using nuclear medicine techniques.     

Development of intravascular contrast agents for MRI using gadolinium chelates

Two MRI contrast agents (CAs) composed of Gd‐DO3A conjugated to amino acid building blocks derived from glutamic acid ( CA1 ) and lysine ( CA2 ) have been synthesized by using novel alkyne and propionate linkers, and subsequently characterized. In vitro cell viability assays showed insignificant cytotoxicity of both CAs at low concentrations up to 0.2 mM . The longitudinal relaxivities (r₁) of CA1 and CA2 measured at 9.4 T are 6.4 and 5.4 mM ^?1 s^?1 in H₂O at 25 °C, respectively. Both r₁ values are higher than those of CAs in clinical use: Gd‐DTPA (Magnevist, Bayer Schering, Germany) and Gd‐DOTA (Dotarem, Guerbet, France). In vivo imaging in Wistar rats demonstrated considerable signal enhancement (～50 %) in the brain artery by CA2 , but lower signal enhancement (～30 %) by CA1 . In contrast to Dotarem, which showed a similar signal enhancement as CA2 , the enhancement by CA2 remained high (～30 %), even at 52 min post‐injection. This demonstrates that CA2 has a much longer blood half‐life (68.1 min), which could be advantageous for angiography and tissue targeting.     

The challenge of T1 contrast agents for high-magnetic field MRI

Magnetic resonance imaging (MRI) is one of the most powerful diagnostic techniques used in clinics. The need for higher spatial resolution and better sensitivity led to the development of imagers working at high magnetic fields. The routine clinical use of 3 T MR systems raised the demand for MRI contrast agents working at this field or above. In the following we summarize the research in our research group on such high-field contrast agents.     

质子交换膜电解水制氢技术的发展现状及展望

氢能是支撑起智能电网和可再生能源发电规模化的最佳能源载体,而电解水制氢是实现制氢规模化的重要途径。在多种电解水制氢技术中,质子交换膜电解水技术由于具备电流密度大、产氢纯度高、响应速度快等优势,吸引了科学界和工业界的广泛重视。本文首先介绍了质子交换膜电解池的结构组成以及各组成的主要作用,对比分析了碱性电解池、固体氧化物电解池与质子交换膜电解池的技术差异,并结合电解水析氢反应以及析氧反应的机理阐释,分别介绍了两步半反应的常用催化剂;然后,从最初的实验室研究阶段到目前兆瓦级别的质子交换膜电解水系统,回顾了该技术的发展历程以及应用现状;其次,从制氢成本、电堆性能及电堆寿命等多角度分析目前该技术面临的瓶颈问题;最后,根据质子交换膜电解池的技术优势,并针对上游间歇性可再生能源的需求以及和下游产业的联合应用,对其未来前景进行了展望。     

Multiphysics modeling of proton exchange membrane water electrolysis: From steady to dynamic behavior

Proton exchange membrane water electrolysis (PEMWE) is currently developed for the design of mature industrial-scale manufactures with commercialization. It needs reducing hydrogen production cost by lowering material cost and increasing operating current density. In engineering perspectives, the study of electrolytic performance during dynamic operation is crucial for PEMWE system management and process control. However, there is few multiphysics models of PEMWE considering transient behavior. The one-dimensional (1D) comprehensive dynamic multiphysics model allows to explore temporal transport phenomena in the PEMWE, and predict electrolytic performance. The 1D model is endorsed by the spatially lumped model from the literature. Changing values of structural and physical properties of porous transport layers (PTLs) and catalyst layers (CLs) allows the observation of their effects on the electrolytic performance and transport phenomena in two-phase flow regime. It suggests that the appropriate PTL properties, and CL fabrication method can lower the cost and remain high electrolytic performance.     

质子交换膜燃料电池两相水管理研究进展

对质子交换膜燃料电池水管理、尤其是两相水管理建模研究的内容、发展阶段、面临挑战进行了全面综述.就膜、扩散层和流道中的两相水管理研究分别加以论述,并就水管理研究面临的挑战进行了分析.     

Synthesis and characterization of a new water-soluble endohedral metallofullerene for MRI contrast agents

Water-soluble amino acid derivatives of gadolinium (Gd) endohedral metallofullerenes (AAD-EMFs), Gd@C₈₂O_m(OH)_n(NHCH₂CH₂COOH)_l (m ≈ 6, n ≈ 16 and l ≈ 8) are synthesized by a direct reaction of the pure endohedral metallofullerene Gd@C₈₂ with an excess of alkaline solution of β-alanine. The structure of the AAD-EMFs is characterized by FTIR, XPS and laser-desorption time-of-flight (LD-TOF) mass spectrometries. Water proton relaxivity analysis indicates that the longitudinal relaxivity R₁ (the effect on 1/T₁, 9.1 mM⁻¹ s⁻¹) of AAD-EMFs is higher than that of the commercial MRI contrast agent, Magnevist (gadolinium-diethylenetriaminepentaacetic acid, Gd-DTPA, 5.6 mM⁻¹ s⁻¹). The MRI phantom studies are performed to confirm the high efficiency of this sample as MRI contrast agents.     

Improving the relaxivity by dimerizing Gd-AAZTA: Insights for enhancing the sensitivity of MRI contrast agents

The synthesis of a dimeric derivative of Gd-AAZTA is reported. It retains the basic properties of the parent complex (q = 2, high stability) and displays a relaxivity of 14.0 mM^?1 s^?1 at 20 MHz and 298 K. The outstanding relaxivity is the result of the increased molecular reorientational time and of the contribution arising from 4 to 5 water molecules in the second coordination sphere of the Gd(III) ions.     

Recombinantly expressed gas vesicles as nanoscale contrast agents for ultrasound and hyperpolarized MRI

Ultrasound and hyperpolarized magnetic resonance imaging enable the visualization of biological processes in deep tissues. However, few molecular contrast agents are available to connect these modalities to specific aspects of biological function. We recently discovered that a unique class of gas‐filled protein nanostructures known as gas vesicles could serve as nanoscale molecular reporters for these modalities. However, the need to produce these nanostructures via expression in specialized cultures of cyanobacteria or haloarchaea limits their broader adoption by other laboratories and hinders genetic engineering of their properties. Here, we describe recombinant expression and purification of Bacillus megaterium gas vesicles using a common laboratory strain of Escherichia coli, and characterize the physical, acoustic, and magnetic resonance properties of these nanostructures. Recombinantly expressed gas vesicles produce ultrasound and hyperpolarized ¹²⁹Xe MRI contrast at subnanomolar concentrations, thus validating a simple platform for their production and engineering. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2927–2933, 2018     

质子交换膜燃料电池膜中气态水管理模型

分析质子交换膜燃料电池的膜水含量与运行参数的关系,从工程方法的角度建立水传输模型.模型分析得到,要提高膜的水合程度,需要通过增湿反应气体.过高的增湿反应气体又会引起阴极扩散层水的泛滥,需通过调节反应气体流量来缓解水的泛滥.为保证膜的高水合程度和低的阴极扩散层水的泛滥,建立了膜水含量的神经网络控制模型,为电池水管理奠定了基础.     

Enhanced performance of CO poisoned proton exchange membrane fuel cells via triode operation

The effect of triode operation on the performance of CO poisoned PEM fuel cells was investigated. In this mode of operation a third, auxiliary, electrode is introduced in addition to the anode and the cathode. Application of electrolytic current in the auxiliary circuit, comprising the cathode and the auxiliary electrode was found to significantly enhance the time-averaged power output of a state-of-the-art PEMFC unit operating with a 70 ppm CO in H₂ atmospheric pressure mixture. Both normal and triode operation were found to lead to self-sustained current and potential oscillations in the fuel cell circuit over wide ranges of external resistive load. The time averaged increase in power output was found to be typically a factor of three higher than the power output in conventional fuel cell operation and up to a factor of 1.32 larger than the power sacrificed in the auxiliary circuit. The mechanism of the enhanced anodic electrocatalysis was investigated via the use of two reference electrodes and the results are discussed together with a possible design for application of the triode concept in stacks.     

Synthesis and evaluation of paramagnetic particulates as contrast agents for magnetic resonance imaging (MRI)

Formulations based on novel particulate ion-exchange resins, containing a wide range of paramagnetic transition and rare-earth metals bound to their surfaces, have been synthesised as potential contrast agents for the magnetic resonance imaging (MRI) of the gastro-intestinal (GI) tract of man. They have been evaluated in terms of their effects upon the spin-lattice (R₁) and spin-spin (R₂) relaxation rates of the protons of water. Careful selection of the polymer, spacer-arm, ligand and paramagnetic ion provides a means for subtle molecular tailoring. Further potential applications have been highlighted based on the observed properties of such formulations.     

质子交换膜水电解制氢膜电极研究进展

质子交换膜水电解（PEMWE）制氢具有可适用于风能太阳能等可再生能源的间歇性和波动性、能量转换效率高、启动快速、占地小等优点,成为目前绿氢制取重点关注的技术。膜电极作为水电解制氢关键核心部件,对于水电解制氢的性能、效率和寿命至关重要,并随着量产规模的扩大在系统成本中的占比越来越高。发展高性能、低成本和高耐久性的膜电极对于绿氢的低成本大规模制取具有重要意义。本文综述了近年来质子交换膜电解水制氢膜电极中质子交换膜、催化层、多孔传输层等关键材料部件以及膜电极制备技术的研究进展和成果,并进行了简要评述。从膜电极设计和开发的角度系统地梳理了如何提高电解制氢性能、降低水电解制氢膜电极成本等方面的进展。最后,就未来膜电极研发的方向提出了建议。     

Electric field effects on proton transfer between ionizable groups and water in ion exchange membranes

The water splitting effect observed during current flow through ion exchange membranes is studied by examining the effect of including different types of molecules, in the adjacent aqueous phase, on the flows of the hydrogen and hydroxyl ions. The result are consistent with what one would except if the ions were produced in protonation and deprotonation reactions, involving ionizable groups of the molecules and water in the membrane surface, for which the rate constants are at least 6–50 times the free solution values. The rate constants might be increased because of an effect due to the strong electric field ( > 10⁸ V m^?1) in the surface.     

Hydration behavior of perfluorinated and hydrocarbon-type proton exchange membranes: Relationship between morphology and proton conduction

The relationships between morphology and proton conduction for Nafion membranes and hydrocarbon-type proton exchange membranes, namely, sulfonated poly(arylene ether ether ketone) (S-PEEK) and sulfonated poly(arylene ether sulfone) (S-PES), were investigated by small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). The direct simultaneous observation of surface morphology and active regions of proton conduction on membranes by combined high-resolution AFM phase imaging and an electrochemical technique at controlled humidity provided significant morphological information, particularly for the hydrocarbon-type membranes that exhibit few or no features on SAXS profiles. For the Nafion membranes, the active proton paths became denser and congregated with each other at over 60% RH, resulting in the formation of well-connected networks. For the hydrocarbon-type membranes, however, only the relatively small and dispersed proton paths were observed, which showed no significant change even as water content increased. We have demonstrated that the differences in microscopic morphology between the Nafion and hydrocarbon-type membranes are associated with the differences between their macroscopic proton conductivities.     

Novel hydrophilic–hydrophobic multiblock copolyimides as proton exchange membranes: Enhancing the proton conductivity

A series of novel multiblock copolymers based on sulfonated copolyimides were developed and evaluated for use as proton exchange membranes (PEMs). In these multiblock copolyimides, the hydrophilic blocks were composed of the sulfonated dianhydride and the sulfonated diamine, with sulfonic acid groups on every aromatic ring (i.e., fully sulfonated). This molecular design was implemented to effectively enhance the proton conductivity. The properties of the multiblock copolyimides with varying IEC values or block lengths were investigated to obtain a better understanding of the relationship between molecular structure and properties of proton exchange membranes. The water uptake and proton conductivity were found to be highly dependent upon their structure. The block copolymers displayed significantly higher proton conductivities, especially at low relative humidity than the random copolymers with a similar IEC. The results indicated that the distribution of sulfonic acid and the length of the blocks play a key role on properties of proton exchange membranes.     

Patterned catalyst layer boosts the performance of proton exchange membrane fuel cells by optimizing water management

Mass transport is crucial to the performance of proton exchange membrane fuel cells, especially at high current densities. Generally, the oxygen and the generated water share same transmission medium but move towards opposite direction, which leads to serious mass transfer problems. Herein, a series of patterned catalyst layer were prepared with a simple one-step impressing method using nylon sieves as templates. With grooves 100 μm in width and 8 μm in depth on the surface of cathode catalyst layer,the maximum power density of fuel cell increases by 10% without any additional durability loss while maintaining a similar electrochemical surface area. The concentration contours calculated by finite element analysis reveal that the grooves built on the surface of catalyst layer serve to accumulate the water nearby while oxygen tends to transfer through relatively convex region, which results from capillary pressure difference caused by the pore structure difference between the two regions. The separation of oxidant gas and generated water avoids mass confliction thus boosts mass transport efficiency.     

Electrochemical performance of Ni/TiO2 hollow sphere in proton exchange membrane water electrolyzers system

This work presents the electrocatalytic evaluation of Ni/TiO₂ hollow sphere materials in PEM water electrolysis cell. All the electrocatalysts have shown remarkably enhanced electrocatalytic properties in comparison with their performance in aqueous electrolysis cell. According to cyclic voltammetric results, 0.36 A cm^?2 peak current density has been exhibited in hydrogen evolution reaction (HER) from 30 wt% Ni/TiO₂ electrocatalyst. 15 wt% Ni-doped titania sample has shown the best result in oxygen evolution reaction (OER) with the anodic peak current density of 0.3 A cm^?2. In the anodic polarization curves, the performance of 15 wt% Ni/TiO₂ hollow sphere electrocatalyst was evaluated up to 140 mA cm^?2 at comparatively lower over-potential value. 20 wt% Ni/TiO₂ hollow sphere electrocatalyst has also shown electrochemical stability in PEM water electrolyzer for 48 h long analysis. The comparative electrocatalytic behavior of hollow spherical materials with non-sphericals is also presented, which clearly shows the influence of hollow spherical structure in greater electrocatalytic activity of the materials. The physical characterization of all the hollow spherical materials is presented in this work, which has confirmed their better electrochemical behavior in PEM water electrolyzer.