Spin labelling of human erythrocytes with nitroxide radicals

Summary Human erythrocytes were labelled with nitroxide, the spin label SYNVAR 101, under various experimental conditions. A study was made of the influence of antireductants on the labelling efficiency and the kinetics of the radical decay during the labelling process. The antireductant hydrogen peroxide was effective in suppressing the decay, whereas ferricyanide was not very effective in this role. The nitroxide radical concentration in a nondialyzed plasma suspension of spin-labelled erythrocytes continuously decayed exponentially with a time constant of 35 min. Nitroxide radicals in nondialyzed plasma exhibited a similar decay to a final residual value which was small relative to the initial concentration. Dialyzing the plasma raised the residual concentration to three quarters of the initial value without changing the decay time.

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Riassunto Eritrociti umani sono marcati con ossido di azoto, il marchio di spin SYNVAR 101, in varie condizioni sperimentali. Si è fatto uno studio dell’influenza degli agenti antiriducenti sulla capacità di marcare e sulla cinetica del decadimento dei radicali durante il processo di marcatura. Il perossido d’idrogeno antiriducente era efficacie nel sopprimere il decadimento, mentre il ferrocianuro non era molto efficacie in questo roulo. La concentrazione dei radicali dell’ossido di azoto in una sospensione di plasma non dializzato degli eritrociti marcati secondo lo spin decade continuamente in maniera esponenziale con una costante di tempo di 35 min. I radicali dell’ossido di azoto nel plasma non dializzato esibiscono un decadimento simile al valore residuo finale che era piccolo in relazione alla concentrazione iniziale. Dializzare il plasma aumenta la concentrazione residua a tre quarti del valore iniziale senza cambiare il tempo di decadimento.

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Резюме В различных эксрериментальных условиях метятся человеческие эритроциты с окисью азота. Исследуются влияния антивосстановителя на эффективность нанесения метки и кинетику распада радикалов в процессе нанесения метки, Перекись водорода, как антивосстановитель, является эффективной для подавления распада, тогда как феррицианид не очень эффективен в этой. Концетрация радикалов окиси азота в суспензии недиализированной плазмы эритроцитов со спиновой меткой уменьшается эксоненциально с временной постоянной, равной 35 мин. Радикалы окиси азота в недиализированной плазме обнаруживают аналогичный распад, причем конечная остаточная величина концентрации оказывается малой по сравнений с начальной концентрацией. Диализация рлазмы увеличивает остаточную концентрацию до трех четвертых начальной без изменения времени распада.

     

Analysis of fluorescence kinetics upon intense picosecond laser pumping: Excitation dynamics in photosynthesizing systems

A new method for the fluorescence kinetics analysis is presented in this work. It permits one to obtain new information, both quantitative and qualitative, about the processes in any condensed molecular system. As an example, this method was applied to the light-harvesting antenna of photosynthesizing organisms. The time dependence of the bimolecular quenching rate of excitons, γ, was found. The experimental value of γ is obtained without any preliminary theoretical considerations. The character of γ-time dependence permits one to find the values of the coefficient of the diffusion D = 4 × 10^-3cm²s^-1 and Förster annihilation radius $\text{R}{}_0\text{= 100}\text{A}\text{?}$, within the limits of the diffusive model.     

Quantum dynamics as a stochastic process in phase space

It is shown that quantum dynamics is equivalent to a stochastic process in phase space. The process is described by normalized but not necessarily positive probability distributions (“pseudoprobabilities”). Evolution of the simultaneous probability distribution of momentum and coordinate exactly conincides with the dynamics of the Wigner function of a quantum system. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 110, No. 3, pp. 454–458, March, 1997.     

INVESTIGATION OF MIGRATION PARAMETERS OF ELECTRON EXCITATION ENERGY IN PHOTOSYNTHETIC and ARTIFICIAL SYSTEMS

Abstract— The technique for the determination of diffusion parameters on the basis of nonlinear fluorescence quenching and excitation energy capturing by the traps is discussed. The nonstationary character of the processes of excitation capturing by traps and of singlet-singlet annihilation which occur upon the system excitation by a picosecond pulse is taken into account. The obtained values of the diffusion parameters in the artificial pigment-polymer antenna system (the diffusion coefficient ∼ 10^-2 cm² s^-1 and the diffusion length ∼ 500 Å) are close to those in the photosynthesizing systems. It is also shown that the method of the determination of diffusion parameters on the basis of excitation capturing by the reaction centres may be applied for the study of the native photosynthetic systems.     

Convergence properties of high-Reynolds-number separated flow calculations

The convergence properties of an iterative solution technique for the Reduced Navier–Stokes equations are examined for two-dimensional steady subsonic flow over bump and trough geometries. Techniques for decreasing the sensitivity to the initial pressure approximation, for fine meshes in particular, are investigated. They are shown to improve the robustness of the relaxation process and to decrease the computational work required to obtain a converged solution. A semi-coarsening multigrid technique that has previously been found to be particularly advantageous for high-Reynolds-number (Re) flows with flow separation and with highly stretched surface-normal grids is applied herein to further accelerate convergence. Solutions are obtained for the laminar flow over a trough that is more severe than has been considered to date. Sufficient axial grid refinement in this case leads to a shock-like reattachment and, for sufficiently large Re, to a local ‘divergence’ of the numerical computations. This ‘laminar flow breakdown’ appears to be related to an instability associated with high-frequency fine-grid modes that are not resolvable with the present modelling. This behaviour may be indicative of dynamic stall or of incipient transition. The breakdown or instability is shown to be controllable by suitable introduction of transition turbulence models or by laminar flow control, i.e. small amounts of wall suction. This lends further support to the hypothesis that the instability is of a physical rather than numerical character and suggests that full three-dimensional analysis is required to properly capture the flow behaviour. Another inference drawn from this investigation is that there is a need for careful grid refinement studies in high-Re flow computations, since coarser grids may yield oscillation-free solutions that cannot be obtained on finer grids.     

INVOLVEMENT OF NEAR-UV-INDUCED SYNTHESIS OF SEROTONIN IN PHOTOPROTECTION AND IN POTENTIATION OF FAR-UV LETHALITY IN THE YEAST CANDIDA GUILLIERMONDII

Abstract— This paper considers mechanisms of near-UV (334nm) induced photoprotection as well as potentiation of far-UV (254 nm) lethality in Candida guilliermondii. Using exogenous precursors of serotonin, it appears that the above two mechanisms involve photoactivated synthesis of serotonin. It has been postulated that the serotonin effect could take place by binding to DNA.     

Dynamics of a polymer attached to a surface: Bead and spring model

The Smoluchowski formalism is used to solve the problem of a bead of frictional resistance β attached to a surface with a spring of force constant _k over which a linear shear field of strenght α flows. The power dissipation is given by βα²kT/_k. k and T have their usual meanings. The result is generalized to an n-bead polymer. It is found that the power dissipation of a Rouse model polymer attached to a surface at one end is twice that of an identical polymer flowing freely in solution. If the force constant _k arises from an entropy force, then, because of the effect of the surface on the number of polymer configurations, there is an additional factor of two. The same relationship is expected to also hold for the frequency-dependent power dissipation. It is argued that a net circulation exists in the beads above the surface and that the magnitude of the circulation is roughly comparable to that which exists in a polymer freely rotating in solution under a shear field of the same magnitude.     

The TEM characterization of the lamellar structure of osteoporotic human trabecular bone

The lamellar structure of osteoporotic human trabecular bone was characterized experimentally by means of transmission electron microscopy (TEM). More specifically, the TEM was used to determine if trabecular bone exhibits similar lamellar structural motifs as cortical bone by analyzing unmineralized, mineralized and demineralized bone, and to study the influence of the osteocyte network on the lamellar structure of osteoporotic trabecular bone. Comparison with normal trabecular bone is included. This paper summarizes partial results of a larger study, which addressed the characterization of the hierarchical structure of normal versus osteoporotic human trabecular bone [Rubin, M.A., 2001. Multiscale characterization of the ultrastructure of trabecular bone in osteoporotic and normal humans and in two inbred strains of mice. MS Thesis, Georgia Institute of Technology.] at several structural scales.