The Physical Aspects of the Primary Interaction of Therapeutic Ultrasound with Biological Tissue

Biophysics - The biophysical aspects of the effects of ultrasound on biological tissues are considered. A mathematical model that describes the effects of the primary interaction of mechanical...     

Hydration of nucleic acid bases studied using novel atom-atom potential functions

New simple atom-atom potential functions for simulating behavior of nucleic acids and their fragments in aqueous solutions are suggested. These functions contains terms which are inversely proportional to the first (electrostatics), sixth (or tenth for the atoms, forming hydrogen bonds) and twelfth (repulsion of all the atoms) powers of interatomic distance. For the refinement of the potential function parameters calculations of ice lattice energy, potential energy and configuration of small clusters consisting of water and nucleic acid base molecules as well as Monte Carlo simulation of liquid water were performed. Calculations using new potential functions give rise to more linear hydrogen bonds between water and base molecules than using other potentials. Sites of preferential hydration of five nucleic bases - uracil, thymine, cytosine, guanine and adenine as well as of 6,6,9-trimethyladenine were found. In the most energetically favourable sites water molecular interacts with two adjacent hydrophilic centres of the base. Studies of interaction of the bases with several water molecules showed that water-water interactions play an important role in the arrangement of the nearest to the base water molecules. Hydrophilic centres are connected by "bridges" formed by hydrogen bonded water molecules. The results obtained are consistent with crystallographic and mass-spectrometric data.     

Transformation of ferromagnetic suspensions in the animal body

Ferromagnetic suspension (FS) was introduced into rat and mouse organisms by different ways. Transformation of FS into some organs was estimated by ESR-method within the temperature region 80-250 K. It was shown that FS introduced in the animal organism was utilized in it very quickly.     

Modeling DNA Hydration: Comparison of Calculated and Experimental Hydration Properties of Nuclic Acid Bases

Abstract

Hydration properties of individual nucleic acid bases were calculated and compared with the available experimental data. Three sets of classical potential functions (PF) used in simulations of nucleic acid hydration were juxtaposed: (i) the PF developed by Poltev and Malenkov (PM), (ii) the PF of Weiner and Kollman (WK), which together with Jorgensen's TIP3P water model are widely used in the AMBER program, and (HI) OPLS (optimized potentials for liquid simulations) developed by Jorgensen (J). The global minima of interaction energy of single water molecules with all the natural nucleic acid bases correspond to the formation of two water-base hydrogen bonds (water bridging of two hydrophilic atoms of the base). The energy values of these minima calculated via PM potentials are in somewhat better conformity with mass-spectrometric data than the values calculated via WK PF. OPLS gave much weaker water-base interactions for all compounds considered, thus these PF were not used in further computations. Monte Carlo simulations of the hydration of 9- methyladenine, 1-methyluracil and 1-methylthymine were performed in systems with 400 water molecules and periodic boundary conditions. Results of simulations with PM potentials give better agreement with experimental data on hydration energies than WK PF. Computations with PM PF of the hydration energy of keto and enol tautomers of 9-methyl- guanine can account for the shift in the tautomeric equilibrium of guanine in aqueous media to a dominance of the keto form in spite of nearly equal intrinsic stability of keto and enol tautomers. The results of guanine hydration computations are discussed in relation to mechanisms of base mispairing errors in nucleic acid biosynthesis. The data presented in this paper along with previous results on simulation of hydration shell structures in DNA duplex grooves provide ample evidence for the advantages of PM PF in studies of nucleic-acid hydration.     

Survival of the mutant clone. III. Catastrophic selection. The inadequacy of the selection coefficient for assessing clone fate]

Majorant estimations of the probabilities pr for the surviving of the clone of the dividing cells have been obtained in the catastrophic situation (monotonous diminishing of the clone almost to zero during the period of time from t=0 to t=T, T approximately 100 generation). At t=0 the clone consisted of 10(6) individuals. Average selection coefficient (s) was found to determine pr only roughly, that is the clone with s greater than --0.09 survives almost in all cases, whereas the clone with s greater than --0.13 becomes extinct practically always. Within this interval ps-inversion can be observed, i.e. preferential surviving of the clone with a worse s value. Results of three communications lead to the conclusion that the mutants with small selective advantage practically cannot be selected.     

Effect of hepatic adhesion factor, contactin, on the mechanical properties of ultrastructural elements of hepatocyte contact

Injection of isotonic fluid under heightened pressure 20--30 mm of Hg into the bed of the liver reveals inhomogeneity of the mechanical properties of the simple junction of heptacytes: the zone where the divergence of the contact surfaces is observed is interrupted by highly adhesive regions (HAR) where the normal distance between the membranes is preserved. The adhesive factor acts as an organizer of the inhomogeneity of the simple junction: when it is introduced in vivo, new HAR appear in the simple junction. On account of contact-tropic activity of adhesive factor we termed it--contactin.