Interplay between crystal and magnetic structure of the anion-radical salt (N-Me-2,6-di-Me–Py)(TCNQ)2 (Py is pyridine)

Genuine organic anion-radical salt (N-Me-2,6-di-Me–Py)(TCNQ)₂ with pyridine-based cation was synthesized and its crystal structure was resolved. The DC magnetic susceptibility was measured in temperature range from 2 K to 300 K in magnetic fields 10 mT, 100 mT and 1 T. Zero field cooling (ZFC) and field cooling (FC) modes were used. The results were studied in terms of one-dimensional magnetic models and we have found that the most suitable of them is an antiferromagnetic linear Heisenberg S = 1/2 system with small amount of free spins. An additional peak observed at low temperatures can be explained by an interchain coupling between free chain-end spins.     

Hyperfine coupling dependence of the effects of weak magnetic fields on the recombination reactions of radicals generated from polymerisation photoinitiators

The recombination reactions of free radicals formed from the photolysis of a series of polymerisation photoinitiators were studied using time-resolved infrared spectroscopy. All molecules showed Zeeman magnetic field effects (MFEs) in the field range 0-37 mT and those molecules that produced radical pairs with average hyperfine couplings greater than 5 mT showed substantial inverted field effects at fields of less than 10 mT (so-called low field effects, LFEs). Monte Carlo simulations with full treatment of all the isotropic hyperfine couplings in the spin Hamiltonian reproduced well the observed field effects. The use of the usual analysis based on the calculated B1/2 value for the radical pair was found to be inappropriate in systems with substantial LFEs, but simple correlations between this B1/2 value and the observed field features were established.     

Effects of low-frequency magnetic fields on the viability of yeast Saccharomyces cerevisiae

A 50 Hz magnetic field effect on the growth of yeasts Saccharomyces cerevisae was studied. The cylindrical coil induced magnetic fields with inductions up to 10 mT. Duration of exposure varied up to 24 min. Exposure took place at laboratory temperature (24-26 degrees C) and the air ventilator maintained the temperature at the place of the sample. We measured the growth curves of yeasts in broth and we calculated the number of CFU (colony forming units) on solid soil. We found that magnetic field decreases the number of yeasts, and slowed down their growth. The result is similar to the experiments with bacteria E. coli, S. aureus and L. adecarboxylata. It seems that the magnetic fields kill a part of yeasts and the bigger part of them survives and continues in their growth.     

Acute effects of whole-body exposure to static magnetic fields and 50-Hz electromagnetic fields on muscle microcirculation in anesthetized mice

Acute microhemodynamic effects of static and alternating magnetic fields at a threshold level were investigated on modulating the muscle capillary mirocirculation in pentobarbital-anesthetized mice. The skin in a tibialis anterior was circularly removed with 1.5 mm diameter for intravital-microscopic recording of the capillary blood velocity in the tibialis anterior muscle. Fluorescein isothiocyanate (FITC)-labeled dextran (MW 150 kDa) was used for an in vivo fluorescent plasma marker of the muscle capillaries. Following a bolus injection of FITC-dextran solution into the caudal vein, the peak blood velocity in the muscle capillaries was measured prior to, during, and following exposure to static magnetic fields (SMF) or 50-Hz electromagnetic fields (EMF) using a fluorescence epi-illumination system. The whole body of experimental animals, placed on the observing stage of a fluorescence microscope, was exposed to SMF (0.3, 1 and 10 mT) or 50-Hz EMF (0.3 and 1 mT) for 10 min using a specially devised electromagnet. For sham exposure, the electromagnet was not energized. During exposure and post-exposure to SMF of 10 mT, the peak blood velocity significantly increased as compared to sham exposure. After the withdrawal of SMF and 50-Hz EMF of 1 mT, significant similar effects on the blood velocity were present or enhanced. These findings suggest that field intensity of 1 mT might be considered as a threshold level for enhancing muscle microcirculation under pentobarbital-induced hypnosis.     

Photoassisted magnetization of fullerene C60 with magnetic-field trapped Raman scattering

We report a photoassisted method to magnetize microcrystal fullerene C(60) at room temperature by exciting it to triplet states via a proper laser radiation and then trapping the spin-polarized states under a strong magnetic field. Novel changes on Raman scattering of the C(60) microcrystals were observed in the presence and absence of the magnetic field. In particular, the Raman spectra were found to exhibit a "hysteresis" phenomenon when the external magnetic field was removed. In light of this, we propose magnetic-field-trapped Raman spectroscopy (MFTRS) and employ first-principle calculations to reproduce the Raman activities of C(60) at different states. Further, MFTRS of the fullerene is demonstrated to originate from its photoassisted magnetization (PAM). The PAM strategy enables the magnetization of materials which consist of only light elements; meanwhile, the MFTRS investigation may open a new research field in Raman spectroscopy.     

In Situ and Ex Situ Low‐Field NMR Spectroscopy and MRI Endowed by SABRE Hyperpolarization

By using 5.75 and 47.5 mT nuclear magnetic resonance (NMR) spectroscopy, up to 10⁵‐fold sensitivity enhancement through signal amplification by reversible exchange (SABRE) was enabled, and subsecond temporal resolution was used to monitor an exchange reaction that resulted in the buildup and decay of hyperpolarized species after parahydrogen bubbling. We demonstrated the high‐resolution low‐field proton magnetic resonance imaging (MRI) of pyridine in a 47.5 mT magnetic field endowed by SABRE. Molecular imaging (i.e. imaging of dilute hyperpolarized substances rather than the bulk medium) was conducted in two regimes: in situ real‐time MRI of the reaction mixture (in which pyridine was hyperpolarized), and ex situ MRI (in which hyperpolarization decays) of the liquid hyperpolarized product. Low‐field (milli‐Tesla range, e.g. 5.75 and 47.5 mT used in this study) parahydrogen‐enhanced NMR and MRI, which are free from the limitations of high‐field magnetic resonance (including susceptibility‐induced gradients of the static magnetic field at phase interfaces), potentially enables new imaging applications as well as differentiation of hyperpolarized chemical species on demand by exploiting spin manipulations with static and alternating magnetic fields.     

Effects of sinusoidal magnetic field on adherence inhibition of leucocytes: preliminary results.

The leucocyte surface properties manifest the cell-mediated immunity. The response of the cell-mediated immunity to external magnetic field was examined by observing leucocyte adherence to solid state surfaces. In the presence of antigen, leucocytes taken from cancer patients exhibit decreased adherence in contrast with adherence of leucocytes from healthy humans. After 1 h exposure to a sinusoidal magnetic field of 50 Hz and of 1 mT or 10 mT, adherence of leucocytes taken from cancer patients is strongly increased. The 1 mT magnetic field has stronger effect than the 10 mT field.     

Raman microprobe spectrometer installed in a super-conducting magnet.

A Raman microprobe spectrometer that could be installed in the bore of a cryogen free super-conducting magnet (10 T) was designed and constructed for the investigation of the external magnetic field effect on the Raman spectra of molecular aggregates in solutions and at interfaces. The performance of the present instrument was demonstrated by measuring the magnetic field effect (0 - 10 T) on the resonance Raman spectra of diprotonated meso-tetra-(sulfonatophenyl)porphine aggregates in an acidic solution. The Raman shifts of the aggregates were not significantly influenced even in 10 T. However, the relative intensity of 1123 cm(-1) peak (nu(C(a)-N)) was interestingly enhanced about 20% under the magnetic fields higher than 2.5 T.     

Effects of low-frequency magnetic fields on bacteria Escherichia coli.

The effects of low-frequency magnetic fields (Bm=2.7-10 mT, f=50 Hz, time of exposure t=0-12 min, laboratory temperature) on the viability and oxidoreductive activity of gram-negative bacteria Escherichia coli were investigated. The growth of these bacteria was negatively affected by such fields. We compared two experimental systems--solenoid [Sb. Lek. 99 (1998) 455] and a cylindrical spool--to find differences between nonhomogeneous and "more homogeneous" magnetic fields. We observed analogous effects in both experimental conditions. The growth curve of the exposed bacteria was lower than the control one. The ability of bacteria to form colonies decreased with increasing magnetic field intensity and with increasing time of exposure. The oxidoreductive activity was measured using reduction of a tetrazolium salt. The decrease in oxidoreductive activity with increasing time of exposure was observed, but the effect was due to a lower amount of bacteria surviving the exposure to the magnetic fields. The decrease in oxidoreductive activity and ability to form colonies were compared with the assumption that the effect of magnetic field is probably bactericidal.     

RESEARCH NOTE: TRIPLET RADICAL ION PAIR STATE OF THE Zn-PORPHYRIN-VIOLOGEN DYAD AS A MAGNETIC FIELD SENSITIVE PROBE OF PHASE TRANSITIONS IN SMALL UNILAMELLAR VESICLES

The magnetic field effect on the recombination kinetics of the triplet radical ion pair state (RIPS) of the Zn-porphyrin-viologen dyad (P-Ph-Vi2+) in the small unilamellar vesicles (SUV) of D,L-dipalmitoyl-alpha-phosphatidylcholine has been studied by the nanosecond laser flash photolysis technique at 5-60 degrees C. The increase in temperature from 25 to 40 degrees C enhances the rate constant (kr) of the RIPS recombination in zero magnetic field from 0.9 x 10(6) to 1.6 x 10(6) s-1, while kr is temperature insensitive at 5-25 and 40-60 degrees C. The typical break in the kr temperature dependence is observed in the temperature range of the phase transition of the SUV bilayers from the solid to the fluid state. The kr value in a strong magnetic field (B = 0.24 T) is equal to 2.7 x 10(5) s-1 and it is independent of temperature at 5-60 degrees C. The shape of the magnetic field dependence of kr is unaffected by the phase transition of the SUV bilayers and is characterized by the existence of an initial plateau of kr at B = 0 to 0.5 mT.     

Magnetic field affects enzymatic ATP synthesis

The rate of ATP synthesis by creatine kinase extracted from V. xanthia venom was shown to depend on the magnetic field. The yield of ATP produced by enzymes with 24Mg2+ and 26Mg2+ ions in catalytic sites increases by 7-8% at 55 mT and then decreases at 80 mT. For enzyme with 25Mg2+ ion in a catalytic site, the ATP yield increases by 50% and 70% in the fields 55 and 80 mT, respectively. In the Earth field the rate of ATP synthesis by enzyme, in which Mg2+ ion has magnetic nucleus 25Mg, is 2.5 times higher than that by enzymes, in which Mg2+ ion has nonmagnetic, spinless nuclei 24Mg or 26Mg. Both magnetic field effect and magnetic isotope effect demonstrate that the ATP synthesis is an ion-radical process, affected by Zeeman interaction and hyperfine coupling in the intermediate ion-radical pair.     

Perdeuterated Conjugated Polymers for Ultralow‐Frequency Magnetic Resonance of OLEDs

The formation of excitons in OLEDs is spin dependent and can be controlled by electron‐paramagnetic resonance, affecting device resistance and electroluminescence yield. We explore electrically detected magnetic resonance in the regime of very low magnetic fields (<1 mT). A pronounced feature emerges at zero field in addition to the conventional spin‐ Zeeman resonance for which the Larmor frequency matches that of the incident radiation. By comparing a conventional π‐conjugated polymer as the active material to a perdeuterated analogue, we demonstrate the interplay between the zero‐field feature and local hyperfine fields. The zero‐field peak results from a quasistatic magnetic‐field effect of the RF radiation for periods comparable to the carrier‐pair lifetime. Zeeman resonances are resolved down to 3.2 MHz, approximately twice the Larmor frequency of an electron in Earth's field. However, since reducing hyperfine fields sharpens the Zeeman peak at the cost of an increased zero‐field peak, we suggest that this result may constitute a fundamental low‐field limit of magnetic resonance in carrier‐pair‐based systems. OLEDs offer an alternative solid‐state platform to investigate the radical‐pair mechanism of magnetic‐field effects in photochemical reactions, allowing models of biological magnetoreception to be tested by measuring spin decoherence directly in the time domain by pulsed experiments.     

Para-hydrogen induced polarization of amino acids, peptides and deuterium-hydrogen gas

Signal Amplification by Reversible-Exchange (SABRE) is a method of hyperpolarizing substrates by polarization transfer from para-hydrogen without hydrogenation. Here, we demonstrate that this method can be applied to hyperpolarize small amounts of all proteinogenic amino acids and some chosen peptides down to the nanomole regime and can be detected in a single scan in low-magnetic fields down to 0.25 mT (10 kHz proton frequency). An outstanding feature is that depending on the chemical state of the used catalyst and the investigated amino acid or peptide, hyperpolarized hydrogen-deuterium gas is formed, which was detected with (1)H and (2)H NMR spectroscopy at low magnetic fields of B(0) = 3.9 mT (166 kHz proton frequency) and 3.2 mT (20 kHz deuterium frequency).     

Comparison of the low-frequency magnetic field effects on bacteria Escherichia coli, Leclercia adecarboxylata and Staphylococcus aureus

This work studies biological effects of low-frequency electromagnetic fields. We have exposed three different bacterial strains-Escherichia coli, Leclercia adecarboxylata and Staphylococcus aureus to the magnetic field (t<30 min, B(m)=10 mT, f=50 Hz) in order to compare their viability (number of colony-forming units (CFU)). We have measured the dependence of CFU on time of exposure and on the value of the magnetic field induction B(m). Viability decreases with longer exposure time and/or higher induction B(m) for all strains, but the quantity of the effect is strain-dependent. The highest decrease of the viability and the biggest magnetic field effect was observed with E. coli. The smallest magnetic field effect appears for S. aureus. From the measurement of the growth dynamics we have concluded that the decrease of the CFU starts immediately after the magnetic field was switched on.     

Effects of static magnetic field on electrolyte solutions under kinetic condition

Electrolyte solutions were exposed for different time to weak static magnetic field (MF) generated from a stack of magnets (B = 15 mT) at the flow rate of 1.4 mL/s. The conductivity was measured as a function of time following the application of MF. It was found that the changes in conductivity depend on the kind of electrolyte and the magnetic exposure time and are related to the thermodynamic function of hydration.     

铁酸钴纳米晶的低温合成、谱学表征及磁性

以十六烷基三甲基溴化铵（CTAB）为模板,Fe(NO3)3·9H2O和Co(NO3)2·6H2O为前躯体,NaOH为沉淀剂,低温回流合成了磁性铁酸钴纳米晶。利用X射线衍射、透射电子显微镜、红外光谱、拉曼光谱等测试技术对产品的结构进行了表征,借助振动样品磁强计测定了样品的室温磁性能。结果表明,铁酸钴纳米晶为单相立方尖晶石结构,纳米晶的平均粒径为15-20 nm。铁酸钴纳米晶在室温外加磁场下表现出明显的磁滞现象,饱和比磁化强度MS=36.5 A.m2/kg,矫顽力HC=5.89×104 A/m。     

Magnetic modulation of the luminescence of pyrene-N,N-dimethylaniline exciplexes in solutions of reverse micelles

An external magnetic field was found to enhance the luminescence of pyrene-N,N-dimethylaniline exciplexes in a solution of reverse micelles containing water, OT Aerosol, and pentanol (0.6%, B=30 mT). The field dependence of the relative change in the intensity of the exciplex fluorescence does not reach saturation for fields with magnetic induction up to 30 mT, which is not observed in polar homogeneous solutions. These results may be attributed to the circumstance that a significant fraction of pyrene (up to 30%) is localized in the interphase of the reverse micelles.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1918–1920, August, 1990.     

Primary root growth rate of Zea mays seedlings grown in an alternating magnetic field of different frequencies

We have studied the effect of an alternating magnetic field on the growth rate of primary roots in Zea mays. Corn seedlings were grown in the dark, under constant conditions of temperature (25°C) and humidity (100%). They were also subjected to a 5 mT magnetic field, alternating at frequencies of either 5, 10, 20 or 40 Hz. The rate of primary root growth, in plants grown at each frequency, was measured and compared to a control group. Control plants were grown under similar conditions, in the absence of the magnetic field. The growth rate of primary roots in seedlings grown at each of the magnetic field frequencies used, was increased compared to the control group. The highest growth rate was seen in seedlings exposed to a magnetic field alternating at 10 Hz.     

Water absorption in polyethylene under external electric fields

Monte Carlo simulations of the solubility and structure of water in polyethylene in thermodynamic equilibrium with liquid water were performed in external fields ranging from 2 x 10(5) to 4 x 10(9) V/m. For a given equilibrium temperature and pressure, the water solubility decreases at higher fields. This occurs since it is energetically favorable for water molecules to be in the pure water phase than in the polyethylene matrix at high field strengths, and results in an increased density in the water phase. However, fields relevant to high voltage conduction (in the absence of defects that can lead to large local field strengths) do not change the solubility. In addition, at large fields the number of water clusters decreases for all cluster sizes. The rate of decrease is highest for large clusters, and a larger fraction of water molecules exist as monomers in the polyethylene matrix at high fields. Large fields also cause alignment of the water molecules, which leads to more clusters with linear topologies and hence an increase in the cluster radius of gyration.     

A Paramagnetic Compass Based on Lanthanide Metal-Organic Framework

Macroscopic compass-like magnetic alignment at low magnetic fields is natural for ferromagnetic materials but is seldomly observed in paramagnetic materials. Herein, we report a “paramagnetic compass” that magnetically aligns under ∼mT fields based on the single-crystalline framework constructed by lanthanide ions and organic ligands (Ln-MOF). The magnetic alignment is attributed to the Ln-MOF's strong macroscopic anisotropy, where the highly-ordered structure allows the Ln-ions’ molecular anisotropy to be summed according to the crystal symmetry. In tetragonal Ln-MOFs, the alignment is either parallel or perpendicular to the field depending on the easiest axis of the molecular anisotropy. Reversible switching between the two alignments is realized upon the removal and re-adsorption of solvent molecules filled in the framework. When the crystal symmetry is lowered in monoclinic Ln-MOFs, the alignments become even inclined (47°-66°) to the field. These fascinating properties of Ln-MOFs would encourage further explorations of framework materials containing paramagnetic centers.