Miniatyrisering av elektronikkomponenter

The paper describes the main features of the miniaturization technique used for production of circuit elements. Integrated circuits (microblocks) are believed to dominate in the near future, while micro-circuits produced by thin-film-technique, and discrete active and passive components should be much less frequent. The influence of the miniaturization on the size and the speed of computers is particularly stressed.     

Nucleic acid-metal interactions. III. Complexes of Ag(I) with adenine and 1-methyladenine from studies of UV and IR dichroic spectra

Attempts to characterize nucleic acid-silver interactions raise questions about how the free nucleic acid bases interact with silver ions in dilute aqueous solution. Studies of ultraviolet and infrared dichroism lead to the conclusion that with silver(I) ions in dilute solution adenine forms linear polymers, whereas 1-methyladenine forms dimers. The composition and structure of the complexes are further discussed against the background of the spectroscopic results.     

Numerical solutions to 2D Maxwell–Bloch equations

Rare-earth-doped crystals contain inhomogeneously broadened two-level atoms. Optical propagation and nonlinear interaction in the crystals can be described by the Maxwell–Bloch equations. We show a consistent numerical approach that solves Maxwell’s equations by using the FFT-finite difference beam propagation method and the Bloch equations by using the finite difference method. Numerical simulation results are given for an off-axis 3-pulse photon echo.     

Effect of various surfactants on stability and thermophysical properties of nanofluids

Journal of Thermal Analysis and Calorimetry - The effect of Fe3O4 nanoparticles and carbon nanotubes (CNTs) on the viscosity of a nanofluid is experimentally investigated from 278 to 313 K...     

Influence of nanotopography on phospholipid bilayer formation on silicon dioxide

We have investigated the effect of well-defined nanoscale topography on the 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid vesicle adsorption and supported phospholipid bilayer (SPB) formation on SiO2 surfaces using a quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). Unilamellar lipid vesicles with two different sizes, 30 and 100 nm, were adsorbed on pitted surfaces with two different pit diameters, 110 and 190 nm, as produced by colloidal lithography, and the behavior was compared to results obtained on flat surfaces. In all cases, complete bilayer formation was observed after a critical coverage of adsorbed vesicles had been reached. However, the kinetics of the vesicle-to-bilayer transformation, including the critical coverage, was significantly altered by surface topography for both vesicle sizes. Surface topography hampered the overall bilayer formation kinetics for the smaller vesicles, but promoted SPB formation for the larger vesicles. Depending on vesicle size, we propose two modifications of the precursor-mediated vesicle-to-bilayer transformation mechanism used to describe supported lipid bilayer formation on the corresponding flat surface. Our results may have important implications for various lipid-membrane-based applications using rough or topographically structured surfaces.     

Glutathione transferase: new model for glutathione activation

Glutathione transferases are enzymes of the cellular detoxification system that metabolize a vast spectrum of xenobiotic and endobiotic toxic compounds. They are homodimers or heterodimers and each monomer has an active center composed of a G-site in which glutathione (GSH) binds and an H-site for the electrophilic substrate. When GSH binds to the G-site, the pKa value of its thiol group drops by 2.5 units; this promotes its deprotonation and, therefore, produces a strong nucleophilic thiolate that is able to react with the electrophilic substrate. The mechanism behind the deprotonation of the thiol group is still unknown. Some studies point to the fact that the GSH glutamyl alpha-carboxylate group is essential for GSH activation, whereas others indicate the importance of the active-center water molecules. On the basis of QM/MM calculations, we propose a mechanism of GSH activation in which a water molecule, acting as a bridge, is able to assist in the transfer of the proton from the GSH thiol group to the GSH glutamyl alpha-carboxylate group, after an initial GSH conformational rearrangement. We calculated the potential of mean force of this GSH structural rearrangement that would be necessary for the approach of both groups and we then performed a QM/MM ONIOM scan of water-assisted proton transfer. The overall free-energy barrier for the process is consistent with experimental studies of the enzyme kinetics.     

Kinetic characterization of an extremely slow DNA binding equilibrium

We here exploit the recently reported thermodynamic preference for poly(dAdT)(2) over mixed-sequence calf thymus (ct) DNA of two binuclear ruthenium complexes, DeltaDelta-[mu-bidppz(bipy)4Ru2](4+) (B) and DeltaDelta-[mu-bidppz(phen)(4)Ru(2)](4+) (P), that bind to DNA by threading intercalation, to determine their intrinsic dissociation rates. After adding poly(dAdT)(2) as a sequestering agent to B or P bound to ct-DNA, the observed rate of change in luminescence upon binding to the polynucleotide reflects the rate of dissociation from the mixed sequence. The activation parameters for the threading and dissociation rate constants allow us for the first time to characterize the thermodynamics of the exceedingly slow threading intercalation equilibrium of B and P with ct-DNA. The equilibrium is found to be endothermic by 33 and 76 kJ/mol, respectively, and the largest part of the enthalpy difference between the complexes originates from the forward threading step. At physiological temperature (37 degrees C) B and P have dissociation half-lives of 18 and 38 h, respectively. This is to our knowledge the slowest dissociating noncovalently bound DNA-drug reported. SDS sequestration is the traditional method for determination of rate constants for cationic drugs dissociating from DNA. However, the rates may be severely overestimated for slowly dissociating molecules due to unwanted catalysis by the SDS monomers and micelles. Having determined the intrinsic dissociation rates with poly(dAdT)(2) as sequestering agent, we find that the catalytic effect of SDS on the dissociation rate may be up to a factor of 60, and that the catalysis is entropy driven. A simple kinetic model for the SDS concentration dependence of the apparent dissociation rate suggests an intermediate that involves both micelles and DNA-threaded complex.