单分子磁体的研究进展

单分子磁体为纳米尺寸,磁特性源自单个分子的内部,可以独立地作为一个磁功能单元,是突破尺寸对传统磁体性能制约的一条连径。已知单分子磁体基本上是含Mn、Fe、V、Cr和一些其他金属元素的簇合物．有望用来制造分子器件、磁存储材料等。本文介绍了一些典型的单分子磁体的研究和发展趋势。     

单分子磁体的研究进展

单分子磁体为纳米尺寸,磁特性源自单个分子的内部,可以独立地作为一个磁功能单元,是突破尺寸对传统磁体性能制约的一条途径。已知单分子磁体基本上是含Mn、Fe、V、Cr和一些其他金属元素的簇合物,有望用来制造分子器件、磁存储材料等。本文介绍了一些典型的单分子磁体的研究和发展趋势。     

The use of polyoxometalates in charge transfer salts

Several Organo/mineral charge transfer salts based on the polyoxometalates anions with the Keggin and Lindquist structures have been prepared with organic radical cations derived from TTF (Tetrathiafulvaalene) by the electrocrystallization technique. Electron transfer from the organic units to the anionic part has been evidenced in the [(TTF)₆(HPM₁₂O₄₀)(Et₄N), M=Mo, W] salts leading to the first radical cation salt with delocalized paramagnetic centers on the polyoxmetalate. Additionally, a metallic state has been observed in (BEDT-TFF)₅VW₅O₁₉, 5H₂O (BEDT=Bisethyleneditithio) containing substituted Lindquist anion.TMTTF Tetramethyltetrathiafulvalene - TMTSF Tetramethyl-tetraselena Fulvalene - BEDT-TTF or ET Bis (Ethylenedithiotetrathiafulvalene) - TPTTF Tetraphenyltetrathiafulvalene - DMDPTTF Dimethyldiphenyl-TTF - Et⁴N=(C²H⁵)N Tetraethylammonium - MDT-TTF Methylenedithiotetrathiafulvalene - DMET-TTF Dimethyl Ethylene Dithio Tetrathiafulvalene - M(dmit)² Bis-[bis(dimercapto-dithiol-thione)metal(II)]     

Non-invasive histochemistry of plant materials by magnetic resonance microscopy

Summary We have combined nuclear magnetic resonance (NMR) imaging on the microscopic scale with chemical shift selection to demonstrate the application of magnetic resonance imaging (MRI) to plant histochemistry. As an example of the method we have obtained separate images of the distribution of reserve oil and anethole in dried fennel mericarps. The technique can be employed to separately image the distribution of aromatics, carbohydrates, oils, water and possibly fatty acids in suitable plant materials.Abbreviations NMR nuclear magnetic resonance - MRI magnetic resonance imaging - COSY correlation spectroscopy - TMS tetramethylsilane     

Mn(II)-monosubstituted polyoxometalates as candidates for contrast agents in magnetic resonance imaging

Two mono-substituted manganese polyoxometalates, K(6)MnSiW(11)O(39) (MnSiW(11)) and K(8)MnP(2)W(17)O(61) (MnP(2)W(17)), have been evaluated by in vivo and in vitro experiments as the candidates of potential tissue-specific contrast agents for magnetic resonance imaging (MRI). T1-relaxivities of 12.1mM(-1)s(-1) for MnSiW(11) and 4.7 mM(-1)s(-1) for MnP(2)W(17) (400 MHz, 25 degrees C) were higher than or similar to that of the commercial MRI contrast agent (GdDTPA). Their relaxivities in BSA and hTf solutions were also reported. After administration of MnSiW(11) and MnP(2)W(17) to Wistar rats, MR imaging showed longer and remarkable enhancement in rat liver and favorable renal excretion capability. The signal intensity increased by 74.0+/-4.9% for the liver during the whole imaging period (90 min) and by 67.2+/-5.3% for kidney within 20-70 min after injection at 40+/-3 micromol kg(-1) dose for MnSiW(11). MnP(2)W(17) induced 71.5+/-15.1% enhancement for the liver in 10-45 min range and 73.1+/-3.2% enhancement for kidney within 5-40 min after injection at 39+/-3 micromol kg(-1) dose. In vitro and in vivo study showed MnSiW(11) and MnP(2)W(17) being favorable candidates as the tissue-specific contrast agents for MRI.     

Carbon coated magnetic nanoparticles for local drug delivery using magnetic implants

Bioferrofluids obtained from carbon coated iron nanoparticles are promising candidates for magnetic drug delivery. The carbon cages render the particles biocompatible, and provide a good support for drug adsorption. We propose a method in which gold plated permanent magnets are implanted directly in the affected organ, close to the tumour, by endoscopic techniques. The bioferrofluid charged with the chemotherapeutic agent is injected and the particles attracted to the magnet, then desorption of the drug takes place at the tumoral region. This method seems to be more promising, costless and effective than that based on the application of external magnetic fields. Preliminary results of drug adsorption and a preclinical experimental animal model are described.     

多信道脑部磁刺激仪的磁场有限元仿真

利用外部的交变磁场,可以对大脑神经系统进行无创刺激.用有限元分析软件--ANSYS对多信道脑部磁刺激仪在不同工作模式下产生的磁场进行了模拟,并将其与实验测量值进行了比较.结果表明,两者之间的误差小于6%,ANSYS能有效模拟多信道磁刺激仪所产生的磁场.通过对仿真结果进行分析得出：改变多信道磁刺激仪工作线圈的位置,可以调整所产生磁场的位置及形状;增加刺激靶位置邻近的工作线圈个数,可以有效改善磁刺激的深度.     

褐飞虱成虫体内磁性物质检测

地磁定向是昆虫远距离迁飞定向的重要机制之一.本研究以褐飞虱Nilaparvata lugens长翅型和短翅型成虫为研究对象,利用MPMS-7型号超导量子干涉磁强计(磁场范围为±4.8 mA/m,温度范围为1.9 ～ 400 K)检测虫体内的磁性物质,明确其体内的分布状况.结果表明:褐飞虱长翅型雄成虫整个虫体的温度退磁曲...     

Progress in molecular modelling of DNA materials

The unique molecular recognition properties of DNA molecule, which store genetic information in cells, are responsible for the rise of DNA nanotechnology. In this article, we review the recent advances in atomistic and coarse-grained force fields along with simulations of DNA-based materials, as applied to DNA–nanoparticle assemblies for controlled material morphology, DNA–surface interactions for biosensor development and DNA origami. Evidently, currently available atomistic and coarse-grained representations of DNA are now at the stage of successfully reproducing and explaining experimentally observed phenomena. However, there is a clear need for the development of atomistic force fields which are robust at long timescales and in the improvement of the coarse-grained models.     

Reversible immobilization of glucoamylase onto magnetic polystyrene beads with multifunctional groups

A novel and simple process for the surface functionalization of micron-sized monodisperse magnetic polystyrene (PS) microbeads was reported. The polystyrene seed particles were prepared prior to the dispersion polymerization method. Afterwards, series of surface chemical modifications on polystyrene microspheres were conducted, and three end-functional microspheres with carboxyl, imidazolyl and sulphydryl groups were obtained. The functional magnetic polystyrene microspheres were prepared by impregnation and subsequent precipitation of ferric and ferrous ions into the polystyrene particles. Finally, the functional magnetic polystyrene was used for the reversible immobilization of glucoamylase via metal-affinity adsorption. The results indicated that the obtained immobilized glucoamylase presented excellent reusability, applicability, magnetic response and regeneration of supports. The magnetic PS microspheres retained >65% of its initial activity at 65 °C over 6 h; and the lowest residual activity of immobilized glucoamylase prepared by regenerated supports still remained about 50% of the initial activity after the 10th cycles.     

Protein separation and identification using magnetic beads encoded with surface-enhanced Raman spectroscopy

This article presents a prototype of a surface-enhanced Raman spectroscopy (SERS)-encoded magnetic bead of 8 μm diameter. The core part of the bead is composed of a magnetic nanoparticle (NP)-embedded sulfonated polystyrene bead. The outer part of the bead is embedded with Ag NPs on which labeling molecules generating specific SERS bands are adsorbed. A silica shell is fabricated for further bioconjugation and protection of SERS signaling. Benzenethiol, 4-mercaptotoluene, 2-naphthalenethiol, and 4-aminothiophenol are used as labeling molecules. The magnetic SERS beads are used as substrates for protein sensing and screening with easy handling. As a model application, streptavidin-bound magnetic SERS beads are used to illustrate selective separation in a flow cytometry system, and the screened beads are spectrally recognized by Raman spectroscopy. The proposed magnetic SERS beads are likely to be used as a versatile solid support for protein sensing and screening in multiple assay technology.     

A morphological classification of bacteria containing bullet-shaped magnetic particles

Abstract We have studied isolated magnetic bacteria using light and electron microscopy, and classified those which contain bullet-shaped magnetic particles into four distinct morphological types, designated BS-1 to BS-4. Two of the types, BS-1 and BS-2, are new, and have unusual arrangements of magnetic particles. The rod-shaped bacterium BS-1 has a dense network of several thousand magnetic particles, whereas BS-2, a coccus, contains magnetic particles arranged radially in bands.     

The use of trans-4-cotininecarboxylate to construct a polymeric copper(II) azido complex: Hydro(solvo)thermal synthesis, structure and magnetic properties

A new pyridyl-carboxylate ligand, the anion of trans-4-cotininecarboxylic acid, HL, 1, has been used to prepare a new polymeric copper(II) complex, [CuLN₃]_2n, 2, based on a [CuLN₃]₂ dimeric building block. The single crystal structures of both 1 and 2 have been determined and 1 has been found to be in its zwitterionic configuration. The structure of 2 is a one-dimensional tape-like polymeric structure based on an end-on azido-bridged binuclear [Cu₂N₃]₂ backbone moiety. Magnetic studies reveal that 2 is close to paramagnetic from 2 to 300 K with a Curie constant of 1.094 emu K/mol, a Weiss temperature of 0.73 K and a corresponding μ_eff of 2.09 μ_B. A fit of χ_MT for 2 with S₁ = S₂ = ½, yields g = 2.441(6), J = −0.49(3) cm⁻¹, zJ = −0.38(2) cm⁻¹ and N(α) = 0.00053(12) emu/mol, a fit that indicates the presence of both very weak intramolecular intrachain antiferromagnetic exchange coupling within the one-dimensional tape-like chains and very weak interchain antiferromagnetic exchange coupling between these chains.     

Molecular photoacoustic tomography of breast cancer using receptor targeted magnetic iron oxide nanoparticles as contrast agents

In this report, we present a breast imaging technique combining high‐resolution near‐infrared (NIR) light induced photoacoustic tomography (PAT) with NIR dye‐labeled amino‐terminal fragments of urokinase plasminogen activator receptor (uPAR) targeted magnetic iron oxide nanoparticles (NIR830‐ATF‐IONP) for breast cancer imaging using an orthotopic mouse mammary tumor model. We show that accumulation of the targeted nanoparticles in the tumor led to photoacoustic contrast enhancement due to the high absorption of iron oxide nanoparticles (IONP). NIR fluorescence images were used to validate specific delivery of NIR830‐ATF‐IONP to mouse mammary tumors. We found that systemic delivery of the targeted IONP produced 4‐ and 10‐fold enhancement in photoacoustic signals in the tumor, compared to the tumor of the mice that received non‐targeted IONP or control mice. The use of targeted nanoparticles allowed imaging of tumors located as deep as 3.1 cm beneath the normal tissues. Our study indicates the potential of the combination of photoacoustic tomography and receptor‐targeted NIR830‐ATF‐IONP as a clinical tool that can provide improved specificity and sensitivity for breast cancer detection. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal Structural Framework of Lithium Super‐Ionic Conductors

As technologically important materials for solid‐state batteries, Li super‐ionic conductors are a class of materials exhibiting exceptionally high ionic conductivity at room temperature. These materials have unique crystal structural frameworks hosting a highly conductive Li sublattice. However, it is not understood why certain crystal structures of the super‐ionic conductors lead to high conductivity in the Li sublattice. In this study, using topological analysis and ab initio molecular dynamics simulations, the crystal structures of all Li‐conducting oxides and sulfides are studied systematically and the key features pertaining to fast‐ion conduction are quantified. In particular, a unique feature of enlarged Li sites caused by large local spaces in the crystal structural framework is identified, promoting fast conduction in the Li‐ion sublattice. Based on these quantified features, the high‐throughput screening identifies many new structures as fast Li‐ion conductors, which are further confirmed by ab initio molecular dynamics simulations. This study provides new insights and a systematic quantitative understanding of the crystal structural frameworks of fast ion‐conductor materials and motivates future experimental and computational studies on new fast‐ion conductors.     

Analysis of the distribution of flowing erythrocytes in a model vessel under an inhomogeneous magnetic field

Changes in the distribution of flowing erythrocytes in a straight cylinder were studied under an inhomogeneous magnetic field. The magnetic field was applied perpendicular to a cylinder, which had a 90° side vessel at the end (oriented towards the magnetic field) to detect changes in the erythrocyte distribution within the cylinder. (1) The attraction of paramagnetic erythrocytes by the magnetic field was demonstrated by an increase in the concentration (or number) of erythrocytes drawn into the side vessel. The flow of diamagnetic, oxygenated erythrocytes was unaffected. (2) The degree of attraction of the paramagnetic erythrocytes was proportional to ``(magnetic susceptibility)' and to ``(magnetic flux density) × (magnetic field gradient)' up to 10 T²/m, but it saturated at high magnetic field. The onset of the saturation depended on the magnetic susceptibility of the erythrocytes. (3) The degree of attraction depended on the hematocrit of the flowing erythrocyte suspension, with a maximum value at a low hematocrit. These phenomena are explained on the basis of the balance between the paramagnetic attractive force of the magnetic field and the collision rate between erythrocytes. Received: 2 May 1996 / Accepted: 1 July 1996     

Crystal structure and magnetic behavior of decamethylferrocenium bis(2-thioxo-1,3-dithiole-4,5-diselenolato)nickelate(III)

The synthesis, crystal structure and magnetic properties of the charge transfer salt [Fe(Cp^∗)₂][Ni(dsit)₂], dsit = (2-thioxo-1,3-dithiole-4,5-diselenolato) are described. The crystal structure consists of layers composed by parallel chains, where side-by-side pairs of cations, alternate with face-to-face pairs of anions, ?D⁺D⁺A⁻A⁻D⁺D⁺A⁻A⁻?. The acceptors in the AA pairs are strongly dimerized through a Ni-Se bond. Short interdimer contacts (Se-Se and S-S) give rise to a porous 3D network, and the [Fe(Cp^∗)₂]⁺pairs are located in the cavities of the acceptors network. The [Fe(Cp^∗)₂]⁺ donors are relatively isolated leading to weak DA and DD interactions and the magnetic behavior of this compound can be basically described as the sum of two contributions: one from nearly independent donors, and the second from the acceptors network, with strong AA AFM coupling, both intradimer and between dimers in adjacent chains.     

Static magnetic field effects on human subjects related to magnetic resonance imaging systems

Goal: This paper reviews recent studies evaluating human subjects for physiologic or neuro-cognitive function adverse effects resulting from exposure to static magnetic fields of magnetic resonance imaging systems.

Materials and Methods: The results of three studies are summarized. Two studies evaluated exposure to a maximum of 8 Tesla (T). The first series studied 25 normal human subjects’ sequential vital signs (heart rate, blood pressure, blood oxygenation, core temperature, ECG, respiratory rate) measured at different magnetic field strengths to a maximum of 8 T. A second series of 25 subjects were studied at 0.05 and 8 T (out and in the bore of the magnet), performing 12 different standardized neuro-psychological tests and auditory–motor reaction times. The subjects’ comments were recorded immediately following the study and after a three-month interval. The third study contained 17 subjects, placed near the bore of a 1.5 T magnet, and it used six different cognitive, cognitive–motor, or sensory tests.

Results: There were no clinically significant changes in the subjects’ physiologic measurements at 8 T. There was a slight increase in the systolic blood pressure with increasing magnetic field strength. There did not appear to be any adverse effect on the cognitive performance of the subjects at 8 T. A few subjects commented at the time of initial exposure on dizziness, metallic taste in the mouth, or discomfort related to the measurement instruments or the head coil. There were no adverse comments at 3 months. The 1.5 T study had two of the four neuro-behavioral domains exhibiting adverse effects (sensory and cognitive–motor).

Conclusions: These studies did not demonstrate any clinically relevant adverse effects on neuro-cognitive testing or vital sign changes. One short-term memory, one sensory, and one cognitive–motor test demonstrated adverse effects, but the significance is not clear.     

Stimuli-Responsive magnetic nanoparticles for monoclonal antibody purification

Monoclonal antibodies (mAbs) are important therapeutic proteins. One of the challenges facing large-scale production of monoclonal antibodies is the capacity bottleneck in downstream processing, which can be circumvented by using magnetic stimuli-responsive polymer nanoparticles. In this work, stimuli-responsive magnetic particles composed of a magnetic poly(methyl methacrylate) core with a poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AA)) shell cross-linked with N, N'-methylenebisacrylamide were prepared by miniemulsion polymerization. The particles were shown to have an average hydrodynamic diameter of 317 nm at 18°C, which decreased to 277 nm at 41°C due to the collapse of the thermo-responsive shell. The particles were superparamagnetic in behavior and exhibited a saturation magnetization of 12.6 emu/g. Subsequently, we evaluated the potential of these negatively charged stimuli-responsive magnetic particles in the purification of a monoclonal antibody from a diafiltered CHO cell culture supernatant by cation exchange. The adsorption of antibodies onto P(NIPAM-co-AA)-coated nanoparticles was highly selective and allowed for the recovery of approximately 94% of the mAb. Different elution strategies were employed providing highly pure mAb fractions with host cell protein (HCP) removal greater than 98%. By exploring the stimuli-responsive properties of the particles, shorter magnetic separation times were possible without significant differences in product yield and purity.