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.     

Effect of charge distribution on the translocation of an inhomogeneously charged polymer through a nanopore

We investigate the voltage-driven translocation of an inhomogeneously charged polymer through a nanopore by utilizing discrete and continuous stochastic models. As a simplified illustration of the effect of charge distribution on translocation, we consider the translocation of a polymer with a single charged site in the presence and absence of interactions between the charge and the pore. We find that the position of the charge that minimizes the translocation time in the absence of pore-polymer interactions is determined by the entropic cost of translocation, with the optimum charge position being at the midpoint of the chain for a rodlike polymer and close to the leading chain end for an ideal chain. The presence of attractive and repulsive pore-charge interactions yields a shift in the optimum charge position toward the trailing end and the leading end of the chain, respectively. Moreover, our results show that strong attractive or repulsive interactions between the charge and the pore lengthen the translocation time relative to translocation through an inert pore. We generalize our results to accommodate the presence of multiple charged sites on the polymer. Our results provide insight into the effect of charge inhomogeneity on protein translocation through biological membranes.     

Effect of interactions on molecular fluxes and fluctuations in the transport across membrane channels

Transport of molecules across membrane channels is investigated theoretically using exactly solvable one-dimensional discrete-state stochastic models. An interaction between molecules and membrane pores is modeled via a set of binding sites with different energies. It is shown that the interaction potential strongly influences the particle currents as well as fluctuations in the number of translocated molecules. For small concentration gradients, the attractive sites lead to largest currents and fluctuations, while the repulsive interactions yield the largest fluxes and dispersions for large concentration gradients. Interaction energies that lead to maximal currents and maximal fluctuations are the same only for locally symmetric potentials, where transition states are equally distant from the neighboring binding sites, while they differ for the locally asymmetric potentials. The conditions for the most optimal translocation transport with maximal current and minimal dispersion are discussed. It is argued that, in this case, the interaction strength is independent of local symmetry of the potential of mean forces. In addition, the effect of the global asymmetry of the interaction potential is investigated, and it is shown that it also strongly affects the particle translocation dynamics. These phenomena can be explained by analyzing the details of the particle entering and leaving the binding sites in the channel.     

X‐Tream quality assurance in synchrotron X‐ray microbeam radiation therapy

Microbeam radiation therapy (MRT) is a novel irradiation technique for brain tumours treatment currently under development at the European Synchrotron Radiation Facility in Grenoble, France. The technique is based on the spatial fractionation of a highly brilliant synchrotron X‐ray beam into an array of microbeams using a multi‐slit collimator (MSC). After promising pre‐clinical results, veterinary trials have recently commenced requiring the need for dedicated quality assurance (QA) procedures. The quality of MRT treatment demands reproducible and precise spatial fractionation of the incoming synchrotron beam. The intensity profile of the microbeams must also be quickly and quantitatively characterized prior to each treatment for comparison with that used for input to the dose‐planning calculations. The Centre for Medical Radiation Physics (University of Wollongong, Australia) has developed an X‐ray treatment monitoring system (X‐Tream) which incorporates a high‐spatial‐resolution silicon strip detector (SSD) specifically designed for MRT. In‐air measurements of the horizontal profile of the intrinsic microbeam X‐ray field in order to determine the relative intensity of each microbeam are presented, and the alignment of the MSC is also assessed. The results show that the SSD is able to resolve individual microbeams which therefore provides invaluable QA of the horizontal field size and microbeam number and shape. They also demonstrate that the SSD used in the X‐Tream system is very sensitive to any small misalignment of the MSC. In order to allow as rapid QA as possible, a fast alignment procedure of the SSD based on X‐ray imaging with a low‐intensity low‐energy beam has been developed and is presented in this publication.     

Novel enhanced applications of QSPR models: Temperature dependence of aqueous solubility

A model developed to predict aqueous solubility at different temperatures has been proposed based on quantitative structure–property relationships (QSPR) methodology. The prediction consists of two steps. The first one predicts the value of k parameter in the linear equation , where S_w is the value of solubility and T is the value of temperature. The second step uses Random Forest technique to create high‐efficiency QSPR model. The performance of the model is assessed using cross‐validation and external test set prediction. Predictive capacity of developed model is compared with COSMO‐RS approximation, which has quantum chemical and thermodynamic foundations. The comparison shows slightly better prediction ability for the QSPR model presented in this publication. © 2016 Wiley Periodicals, Inc.     

Modelling counter-current and dual counter-current chromatography using longitudinal mixing cell and eluting counter-current distribution models

Two well known approaches are considered to analyze the processes of counter-current and dual counter-current chromatography: the longitudinal mixing cell model and the Craig's counter-current distribution model. The cell model represents perfectly mixed, equally sized cells in series. The number of cells characterizes the rates of longitudinal mixing in the stationary and mobile phases. In the eluting counter-current distribution (CCD) model, the CCC process is considered as a continuous form of Craig's counter-current distribution. For a cascade of equilibrium stages theoretical elution profiles of the CCC process by using the CCD and cell model approaches have been compared. It is shown that in general, distribution functions of the CCD and cell models differ. It is established that the distribution of a solute between two solvent phases in the dual CCC process is determined by the extraction factor c, the total number of equilibrium stages n and the position of the sample inlet m by the equation Q(x)=(1-c(m))/(1-c(n+1)) with c=F(2)K(D)/F(1) (K(D), F(1), F(2) and Q(x) are the distribution constant, the phase flow-rates and the portion of solute eluted by the first phase, respectively).     

Hardy spaces and partial derivatives of conjugate harmonic functions

In this paper we give necessary and sufficient conditions for a harmonic vector and all its partial derivatives to belong to for all .

     

Steady Nonsymmetrical Gravity Waves with Shear in Water

A new type of steady two-dimensional inviscid gravity wave with shear is computed numerically. These waves appear at relatively low amplitudes and lack symmetry with respect to any crest or trough. A boundary integral formulation is used to obtain a one-parameter family of nonsymmetrical solutions through a symmetry-breaking bifurcation.     

Antiferromagnetic spin glass in doped Ge near insulator-metal transition

A low-temperature (3–100 K) electron spin resonance (ESR) study of the spin system of neutral As donors in Ge showed that on the insulator side of the insulator-metal transition the single-spin density exponentially disappears as T → 0. Such spins are bound into pairs to give an antiferromagnetic (AF) phase. Upon increasing the temperature the AF phase is destroyed, the single-spin density and, as a result, the ESR absorption signal becomes stronger. The temperature dependences of the densities of the pairs and single spins are typical for a chaotic distribution of neutral donors. In this case, there is no Néel temperature. For a low degree of compensation, the crystal lattice of Ge with the AF phase is actually a nanostructured system characterized by anisotropic internal stresses that are the strongest along one of the [110] directions. These stresses give rise to the anisotropy of the g-factor which is responsible for experimentally observed splitting of the ESR line. The compensating impurities destroy the AF phase and reduce this splitting. Local stresses are present in this case, too, but now they appear because of the Coulomb interaction of oppositely charged impurities and have no preferred orientation.     

Synchronous ultrasonic Doppler imaging of magnetic microparticles in biological tissues

We considered applicability of acoustic imaging technology for the detection of magnetic microparticles and nanoparticles inside soft biological tissues. Such particles are widely used for magnetically targeted drug delivery and magnetic hyperthermia. We developed a new method of ultrasonic synchronous tissue Doppler imaging with magnetic modulation for in vitro and in vivo detection and visualization of magnetic ultradisperse objects in soft tissues. Prototype hardware with appropriate software was produced and the method was successfully tested on magnetic microparticles injected into an excised pig liver.