Magnetic effects in hydroperoxide decomposition in mixed micelles with cationic surfactants

The retardation effect of oxygen and external magnetic field on the yield of radicals in hydroperoxide decomposition in catalytic nanoreactors was discovered. Mixed reverse micelles formed by the cationic surfactants (Surf) and hydroperoxide {mLOOH...nSurf} play the role of nanoreactors. Similar effects of oxygen and external magnetic field (60–150 mT) on the yield of radicals are observed in the catalytic decomposition of hydroperoxide in the presence of acetylcholine. It is noteworthy that the retardation effect of the magnetic field decreases in the presence of paramagnetic particles such as oxygen and relatively stable radicals.     

Magnetic field effect on electrochemical oscillations during iron dissolution

A fairly low magnetic field of ca. 30 mT was found to affect the period and the amplitude of the self-sustained current oscillation of an iron electrode. This was observed much distinctively when the direction of the applied field was normal to the electrode surface, i.e., non-magnetohydrodynamic (MHD) configuration. The Flade potential of the iron electrode was not affected by the magnetic field intensity of up to 4 T. The observed magnetic field effect was attributed to the depression of the natural convection in the vicinity of the electrode surface which was caused by the two local paramagnetic body forces, the magnetic field gradient force and/or the concentration gradient force.     

Magnetic susceptibility-induced alignment of proteins in reverse micelles

Proteins encapsulated within the aqueous core of reverse micelles are found to partially align in a magnetic field. The degree of alignment is sufficient to result in sizable residual 15N-1H dipolar couplings that can be easily measured. It is found that the magnetic susceptibility of the reverse micelle particle is not dominated by the encapsulated protein. The residual dipolar couplings are found to be structurally meaningful.     

Synthesis of nanosize metallic and alloyed particles in ordered phases

Functionalized reverse micelles have been used to synthesize Copper and Cobalt nanoparticles differing by their size and shape. They can be also used to synthesize Fe–Cu alloy (at 30% Fe) and composite (at 70% Fe) particles. In the case of Fe–Cu system, the magnetic properties are presented.     

Electrostimulation of proliferation of the denitrifying bacterium Pseudomonas stutzeri

The electrostimulation of proliferation of the denitrification strain Pseudomonas stutzeri occurs in an anaerobic culture by a magnetic flux around 1 mT inducing a low current in the electric field fermenter wrapped by Helmholtz coils. After 10 h of treatment the biomass was higher than in the control fermenter by 10–30% depending on magnetic flux intensity.     

Engineering Iron–Nickel Nanoparticles for Magnetically Induced CO2 Methanation in Continuous Flow

Induction heating of magnetic nanoparticles (NPs) is a method to activate heterogeneous catalytic reactions. It requires nano-objects displaying high heating power and excellent catalytic activity. Here, using a surface engineering approach, bimetallic NPs are used for magnetically induced CO₂ methanation, acting both as heating agent and catalyst. The organometallic synthesis of Fe₃₀Ni₇₀ NPs displaying high heating powers at low magnetic field amplitudes is described. The NPs are active but only slightly selective for CH₄ after deposition on SiRAlOx owing to an iron-rich shell (25 mL min⁻¹, 25 mT, 300 kHz, conversion 71 %, methane selectivity 65 %). Proper surface engineering consisting of depositing a thin Ni layer leads to Fe₃₀Ni₇₀@Ni NPs displaying a very high activity for CO₂ hydrogenation and a full selectivity. A quantitative yield in methane is obtained at low magnetic field and mild conditions (25 mL min⁻¹, 19 mT, 300 kHz, conversion 100 %, methane selectivity 100 %).     

Engineering Iron–Nickel Nanoparticles for Magnetically Induced CO2 Methanation in Continuous Flow

Induction heating of magnetic nanoparticles (NPs) is a method to activate heterogeneous catalytic reactions. It requires nano‐objects displaying high heating power and excellent catalytic activity. Here, using a surface engineering approach, bimetallic NPs are used for magnetically induced CO₂ methanation, acting both as heating agent and catalyst. The organometallic synthesis of Fe₃₀Ni₇₀ NPs displaying high heating powers at low magnetic field amplitudes is described. The NPs are active but only slightly selective for CH₄ after deposition on SiRAlOx owing to an iron‐rich shell (25 mL min^?1, 25 mT, 300 kHz, conversion 71 %, methane selectivity 65 %). Proper surface engineering consisting of depositing a thin Ni layer leads to Fe₃₀Ni₇₀@Ni NPs displaying a very high activity for CO₂ hydrogenation and a full selectivity. A quantitative yield in methane is obtained at low magnetic field and mild conditions (25 mL min^?1, 19 mT, 300 kHz, conversion 100 %, methane selectivity 100 %).     

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.     

Compressive properties of magnetorheological elastomer with different magnetic fields and types of filler

Magnetorheological elastomer (MRE) specimens were prepared to find the optimum compressive characteristics using different types and amounts of iron powder. A magnetic field of up to 2 T was applied during vulcanization. Among the four types of iron powders, the specimen with round‐shaped carbonyl iron powder and small grain size shows higher magnetic effects than that with bigger and irregularly shaped electrolyte iron powder. However, the compressive modulus of the rubber with electrolyte iron powder is higher without magnetic treatment at a given amount. In general, the bigger and irregularly shaped iron particles tend to move slowly and produce nonuniform distribution when a magnetic field is applied. The experimental results show that the mechanical properties are better when applying a magnetic field of 1.5 T compared with 2.0 T during the specimen vulcanization. Applying a magnetic field of 300 mT during the compression test enhanced the compressive modulus by 12% to 15%. The rate of increase of the modulus decreased exponentially with prestrain.     

Dynamics of magnetic-field-induced clustering in ionic ferrofluids from Raman scattering

Using Raman spectroscopy, the authors have investigated the aggregation/disgregation of magnetic nanoparticles in dense ionic ferrofluids (IFF) into clusters due to the action of an inhomogeneous external magnetic field. Evidence for changes in particle density and/or effective cluster size were obtained from the variation of the Raman intensity in a time window from 10 s to 10 min for magnetic fields up to 350 mT and at a temperature of 28 degrees C. Clustering sets in already at very low fields (>15 mT) and the IFF samples exhibit a clear hysteresis in the Raman spectra after releasing the magnetic field, which lasts for many hours at room temperature. The authors determined the characteristic times of the two competing processes, that of field-induced cluster formation and, at room temperature, that of thermal-activated dissociation, to range from 100 to 150 s.     

Exploring the extent of magnetic field effect on intermolecular photoinduced electron transfer in different organized assemblies

Magnetic field effect (MFE) on the photoinduced electron transfer (PET) between phenazine (PZ) and the amines, N,N-dimethylaniline , N,N-diethylaniline, 4,4'-bis(dimethylamino)diphenylmethane (DMDPM), and triethylamine, has been studied in micelles, reverse micelles, and small unilamellar vesicles (SUVs) with a view to understand the effect of spatial location of the donor and acceptor moieties on the magnetic field behavior. The structure of the assembly is found to influence greatly the PET dynamics and hence the MFE of all the systems studied. The magnetic field behavior in micelles is consistent with the hyperfine mechanism, but high B(1/2) values have been obtained which have been ascribed to hopping and lifetime broadening. The variation of MFE with W(0), in reverse micelles, proves yet again that the MFE maximizes at an optimum separation distance between the acceptor and donor. This is the first example of such behavior for intermolecular PET in heterogeneous medium. We have also reported for the first time MFE on intermolecular PET in SUVs. In this case, the PZ-DMDPM system responds most appreciably to an external field compared to the other acceptor-donor systems because it is appropriately positioned in the bilayer. The differential behavior of the amines has been discussed in terms of their confinement in different zones of the organized assemblies depending on their bulk, hydrophobic, and electrostatic effects.     

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.     

Magnetic field effect on photoinduced electron transfer between [Cu(phen)2]2+ and DNA

The magnetic field effect (MFE) on the photoinduced electron transfer (PET) reaction between the [Cu(phen)2]2+ complex and DNA has been studied in homogeneous buffer medium and in reverse micelles. The copper complex on photoexcitation can oxidize DNA in a deoxygenated environment. A prominent MFE is found even in a homogeneous aqueous medium for the triplet born radicals. The process of partial intercalation of [Cu(phen)2]2+ complex within DNA is responsible for such a rare observation. In reverse micelles, the MFE is not very much prominent because of the large separation distance between the component radicals of the geminate radical ion pairs generated through PET.     

Large-strain behaviour of Magneto-Rheological Elastomers tested under uniaxial compression and tension,and pure shear deformations

The large-strain behaviour of Magneto-Rheological Elastomers (MREs) is characterised experimentally under uniaxial compression, uniaxial tension and pure shear deformation, in the absence and in the presence of magnetic fields. MREs are ‘smart’ materials that can alter their properties instantaneously by the application of external stimuli. They hold great potential for use in adaptive stiffness devices. So far, the large-strain behaviour of MREs has not been well explored, and their behaviour under pure shear deformation has not been characterised. Tests on silicone rubber based isotropic and anisotropic MREs, with and without the application of an external magnetic field have been performed in this investigation. The MR effect, defined as the increase in tangent moduli, is studied versus large engineering strain. Strains were measured optically using a Digital Image Correlation (DIC) system. Relative MR effects up to 284% were found under uniaxial tension, when a magnetic field strength of 290 mT was applied with the loading direction parallel to the direction of particle alignment.     

The influence of cholesterol on the generation of radicals in mixed reverse micelles of cationic surfactants with hydroperoxides

Cationic surfactants (S+) and acetylcholine (ACh), the most important neurotransmitter playing an essential role in the neuromuscular and cognitive activity of living beings, form mixed reverse micelles with hydroperoxides (ROOH) in organic media, where ROOH decay into free radicals is catalytically accelerated. Adding cholesterol (Chol, 30 mol.%) to pyridinium (СРВ) and cetyltimethylammonioum (СТАВ) bromides, reduces the radical generation rate in ROOH catalytic decay several times. However, a higher radical initiation rate is observed in the case of less ordered and larger ACh–ROOH reverse micelles. A Chol additive does not essentially affect the size of СТАВ and СРВ micelles with hydroperoxides but results in their decrease in the case of ACh–ROOH.

     

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.     

The Effect of Sample Age and Neutron Radiation to Dynamic Nuclear Polarization Parameters in Some Asphaltene Suspensions

Nuclear magnetic resonance and the Overhauser effect type dynamic nuclear polarization experiments were performed to study suspensions of asphaltene in the xylene isomers at a low magnetic field of 1.44 mT at room temperature. Intermolecular spin-spin interactions occur between nuclear spins of hydrogen in the solvent medium and the free electron spins in the asphaltene micelles. The samples were prepared in three different asphaltene concentrations at vacuum. The samples were waited for four years and dynamic nuclear polarization parameters were found via dynamic nuclear polarization experiments performed again. Thus, it was investigated the effect of sample age to dynamic nuclear polarization parameters. In addition, the medium concentrations of each sample were exposed to radiation for 48 hours and neutron radiation effects to the dynamic nuclear polarization parameters were investigated. The results are discussed.     

Effect of electromagnetic fields on the denitrification activity of Paracoccus denitrificans

Enzymatic activity (denitrification) of Paracoccus denitrificans was estimated electrochemically by reduction of duroquinone (DQ). Graphite electrodes covered with whole bacterial cells behind a dialysis membrane were used for measurement. P. denitrificans reduce nitrate and/or nitrite under anaerobic conditions to nitrogen gas. DQ acts as an electron mediator. After donation of the electrons to the respiratory system of the bacteria, produced DQ is reduced to durohydroquinone on the electrode surface electrocatalytically. P. denitrificans were exposed to low-frequency magnetic field (10 mT, 50 Hz) for 24 min. In comparison with the control samples, the reduction peak of I-E curves that represent denitrification activity of the cells decreased significantly after magnetic field exposure. The decrease of the peak current was about 20%. The CFU-colony forming units-method was used to estimate the number of surviving bacteria. After 24 min exposure of 10 mT magnetic field P. denitrificans culture on electrode indicates 21% bacterial death.     

Nonionic surfactants: a key to enhance the enzyme activity at cationic reverse micellar interface

The primary objective of the present study is to understand how the different nonionic surfactants modify the anisotropic interface of cationic water-in-oil (W/O) microemulsions and thus influences the catalytic efficiency of surface-active enzymes. Activity of Chromobacterium viscosum lipase (CV-lipase) was estimated in several mixed reverse micelles prepared from CTAB and four different nonionic surfactants, Brij-30, Brij-92, Tween-20, and Tween-80/water/isooctane/n-hexanol at different z ([cosurfactant]/[surfactants]) values, pH 6 (20 mM phosphate), 25 degrees C across a varying range of W0 ([water]/[surfactants]) using p-nitrophenyl-n-octanoate as the substrate. Lipase activity in mixed reverse micelles improved maximum up to approximately 200% with increasing content of non-ionic surfactants compared to that in CTAB probably due to the reduced positive charge density as well as plummeted n-hexanol (competitive inhibitor of lipase) content at the interfacial region of cationic W/O microemulsions. The highest activity of lipase was observed in CTAB (10 mM) + Brij-30 (40 mM)/isooctane/n-hexanol)/water system, k2 = 913 +/- 5 cm3 g-1 s-1. Interestingly, this observed activity is even higher than that obtained in sodium bis (2-ethyl-1-hexyl) sulfosuccinate (AOT)/n-heptane reverse micelles, the most popular W/O microemulsion in micellar enzymology. To ascertain the influence of non-ionic surfactants in improving the activity of surface-active enzymes is not limited to lipase only, we have also investigated the catalytic activity of Horseradish peroxidase (HRP) in different mixed W/O microemulsions. Here also following the similar trend as observed for lipase, HRP activity enhanced up to 2.5 fold with increasing concentration of nonionic surfactants. Finally, the enzyme activity was correlated with the change in the microenvironment of mixed reverse micelles by steady-state fluorescence study using 8-anilino-1-napthalenesulphonic acid (ANS) as probe.     

Effect of a weak magnetic field on the reaction between neutral free radicals in isotropic solution

Radical recombination following the photodissociation of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone in isotropic solution was monitored using time-resolved infrared spectroscopy. The rate of radical recombination was determined to decrease in the presence of a magnetic field of greater than 5 mT and to increase in the presence of a magnetic field smaller than 5 mT.