Use of direct and indirect methods in diaphragm cell method for estimation of liquid diffusivities of biosolutes

Summary Use of direct method (DM) and indirect method (IM) with a diaphragm cell for estimation of liquid diffusivities of biosolutes were compared. Aqueous diffusivities of seven biosolutes covering a wide molecular weight range were estimated for the comparison. Diffiisivities estimated through IM deviated from literature values more than DM especially in the case of macromolecules. The possible reasons for this were discussed.     

Trehalose matrix effects on electron transfer in Mn-depleted protein-pigment complexes of Photosystem II

The kinetics of flash-induced re-reduction of the Photosystem II (PS II) primary electron donor P₆₈₀ was studied in solution and in trehalose glassy matrices at different relative humidity. In solution, and in the re-dissolved glass, kinetics were dominated by two fast components with lifetimes in the range of 2–7 μs, which accounted for >85% of the decay. These components were ascribed to the direct electron transfer from the redox-active tyrosine Y_Z to P₆₈₀⁺. The minor slower components were due to charge recombination between the primary plastoquinone acceptor Q_A^? and P₆₈₀⁺. Incorporation of the PS II complex into the trehalose glassy matrix and its successive dehydration caused a progressive increase in the lifetime of all kinetic phases, accompanied by an increase of the amplitudes of the slower phases at the expense of the faster phases. At 63% relative humidity the fast components contribution dropped to ~50%. A further dehydration of the trehalose glass did not change the lifetimes and contribution of the kinetic components. This effect was ascribed to the decrease of conformational mobility of the protein domain between Y_Z and P₆₈₀, which resulted in the inhibition of Y_Z → P₆₈₀⁺ electron transfer in about half of the PS II population, wherein the recombination between Q_A^? and P₆₈₀⁺ occurred. The data indicate that PS II binds a larger number of water molecules as compared to PS I complexes. We conclude that our data disprove the “water replacement” hypothesis of trehalose matrix biopreservation.     

Teaching Density with a Little Drama

This article provides an example of an innovative science activity applied in a science methods course for future elementary teachers at a small university in northeastern Turkey. The aim of the activity is to help prospective elementary teachers understand the density concept in a simple way and see an innovative teaching example.