Evidence for intermediate S-states as initial phase in the process of oxygen-evolving complex oxidation

We have analyzed flash-induced period-four damped oscillation of oxygen evolution and chlorophyll fluorescence with the aid of a kinetic model of photosystem II. We have shown that, for simulation of the period-four oscillatory behavior of oxygen evolution, it is essential to consider the so-called intermediate S-state as an initial phase of each of the S_n-S_n+1, (n = 0, 1, 2, 3) transitions. The intermediate S-states are defined as []-states (n = 0, 1, 2, 3) and are formed with rate constant k_iSn ∼1.5 × 10⁶ s⁻¹, which was determined from comparison of theoretical predictions with experimental data. The assumed intermediate S-states shift the equilibrium in reaction more to the right and we suggest that kinetics of the intermediate S-states reflects a relaxation process associated with changes of the redox equilibrium in the above reaction. The oxygen oscillation is simulated without the miss and double-hit parameters, if the intermediate S-states, which are not the source of the misses or the double-hits, are included in the simulation. Furthermore, we have shown that the intermediate S-states, together with charge recombination, are prerequisites for the simulation of the period-four oscillatory behavior of the chlorophyll fluorescence.     

Trypanosoma cruzi: Biodistribution of technetium-99m pertechnetate in infected rats

With the aim of investigating the biodistribution of technetium-99 m pertechnetate () in rats infected with Y strain of Tripanosoma Cruzi, at the peak of parasitemia, (14th day of infection), we injected Wistar rats with 0.1 ml of (3.7 MBq). After 60 min, the percentage of radioactivity per gram was counted in several isolated organs and blood, using a gamma counter (1470 Wizard, PerkinElmer Finland). The uptake of increased significantly in blood and decreased in the colon of infected animals (p < 0.05). A significant reduction in serum iron and red blood cells and a significant increase in total proteins, leukocytes and lymphocytes in the infected rats were observed, compared with controls (p < 0.05). A reduction in muscle layer thickness of the colon and mononuclear inflammation were observed. These results conclusively demonstrate that T. cruzi infection would be associated with changes in the biodistribution of and in colon morphology, with potential clinical implications.     

A trade-off relationship between energetic cost and entropic cost for in vitro evolution

In this paper, we consider two complementary cost functions for the landscape exploring processes to obtain the global optimum sequence through in vitro evolution protocol: one is the entropic cost C_etp, which is based on the deviation from the uniformity of a mutant distribution in sequence space, and the other is the energetic cost C_eng, which is based on the total number of sequences to be generated and evaluated. Based on a prior knowledge about the structure of a given fitness landscapes, the conductor of the experiment can think up the efficient search algorithm (ESA), which requires the minimum number of points (=sequences) to be searched up to the global optimum. For five typical fitness landscapes, we considered their respective (putative) ESA, and based on the ESA. As a result, we found a trade-off relationship between and for every case, that is, is approximately equal to the logarithm of the volume of the sequence space. and are interpreted in terms of the information-theoretic concepts.     

Square-planar and trigonal prismatic silver(I) in bipyrimidine and oxalate bridged tetranuclear complexes and one-dimensional compounds: Synthesis and crystal structures

The reaction of [Ag₄(hfac)₄(THF)₂] (hfac⁻ = 1,1,1,5,5,5-hexafluoroacetylacetonate, THF = tetrahydrofurrane) with 2,2′-bipyrimidine (bpm) leads to single crystals. They crystallise in the triclinic system, space group . Their structure consists of [Ag₄(hfac)₄(μ₂-bpm)₃] tetranuclear complexes. In this complex, Ag(I) ions adopt distorted square planar and trigonal prismatic geometries. When [Ag₄(hfac)₄(THF)₂] is replaced by monohydrated silver(I) perchlorate, a one-dimensional (1D) compound with a formula of [[Ag(μ₂-bpm)]⁺]_n, is obtained as single crystals. They crystallise in the monoclinic system, space group P2₁/c. Their structure consists of [[Ag(μ₂-bpm)]⁺]_n chains separated by non-coordinated perchlorate ions. In the chains, the Ag(I) centres adopt a square planar geometry. Finally, starting from [[Ag(μ₂-bpm)]⁺]_n, and sodium oxalate , another 1D compound with a formula of [Ag(μ₂-bpm)(μ₂-ox)]_n, 4nH₂O is obtained as single crystals. They crystallise in the triclinic system, space group . In these chains, bipyrimidine and oxalate are alternate. They generate a square planar geometry around the Ag(I) cations.     

Crystal structures of [M(NTf2)3(H2O)n] (M = Eu and Yb) and a template effect of linear molecules on the 3D hydrogen bonding network structure of [Eu(NTf2)3(H2O)3]

Lewis acid catalysts [Eu(NTf₂)₃] and [Yb(NTf₂)₃] can be easily crystallized from a p-xylene solution in the presence of carboxylic acids and a small amount of water to give a trihydrate and a pentahydrate, respectively. In the crystallization of [Eu(NTf₂)₃(H₂O)₃], linear molecules such as n-alkanes and n-alkanoic acids act as templates to form crystals belonging to the trigonal space group with a hexagonal cylindrical structure, which is constructed by 3D hydrogen bonding network. On the other hand, [Eu(NTf₂)₃(H₂O)₃] crystallized in the cubic space group P2₁3 in the presence of a bulkier carboxylic acid, cyclohexanecarboxylic acid. In both [Eu(NTf₂)₃(H₂O)₃] crystals, ligands act as bidentate ligands coordinating to the Eu atom through two oxygen atoms. [Yb(NTf₂)₃] crystallized as a pentahydrate in the monoclinic space group P2₁/n, in which ligands coordinated to the Yb atom with only one oxygen atom.     

Dinuclear and polynuclear Cu(II) azido-bridged compounds with 7-azaindole as a ligand. Synthesis, characterization and 3D structures

In this study three new dinuclear Cu(II) compounds with the ligand 7-azaindole (abbreviated as Haza) and bridging end-on azide anions with the general formula [Cu₂(Haza)₄(N₃)₂(A)₂] (in which A =  (1), (2) and (3)) are reported, as well as a dinuclear-based polymeric compound with the overall formula [Cu₄(L)₆(N₃)₆(ClO₄)₂]_n·(CH₃OH)_2n (4). The latter compound contains both end-on and end-to-end azide anions. Full characterization of all four compounds has been performed by spectroscopic methods and by using 3D X-ray structure analysis.     

Trypanosoma cruzi: Immunological predictors of benznidazole efficacy during experimental infection

C3H/HeN male mice were infected with a lethal population of Trypanosoma cruzi and treated with benznidazole (Bz). Parasitemia, body weight and survival rate were registered during the therapy with significant improvement for T. cruzi-infected Bz-treated animals. Besides, flow cytometry resulted a useful method to discriminate between cured animals from those not cured by monitoring IgG₁ bound to live trypomastigotes levels. At the end of Bz therapy, the LT splenocyte compartment was studied for activation/memory cell surface markers ( and ). Cytofluorometric analysis showed that T. cruzi-infected untreated mice increased their activated LT numbers and this effect was completely abolished only in cured mice at the end of Bz administration. The same behavior was observed for the memory LT subpopulation correlating to an effector memory () displayed by T. cruzi infection. Bz treatment was able to modulate the immunological response by reducing the deleterious effect of the acute phase in all T. cruzi-infected mice.     

Binuclear diorganotin(IV) complexes with bis(O,O′-4-acyl-5-pyrazolonato) bis(bidentate) ligands

Syntheses, spectroscopic and thermal characterization are reported for the potentially tetradentate bis(O,O′-4-acyl-5-pyrazolone) pro-ligands HQ3QH and HQ4QH (in detail HQ3QH: 1,5-bis(5-hydroxy-1-phenyl-3-methyl-1H-pyrazol-4-yl)pentane-1,5-dione, HQ4QH: 1,6-bis(5-hydroxy-1-phenyl-3-methyl-1H-pyrazol-4-yl)hexane-1,6-dione) and their di-n-butyltin(IV) derivatives and . Single crystal X-ray structural characterizations of the proligand HQ4QH and of the binuclear tin(IV) complex are also reported; both the ligand and complex molecules are centrosymmetric, the latter having two independent molecules in the structure. Sn-C, O(acyl), O(pz) distances (〈 〉) are 2.121(3), 2.119(6) and 2.37(4) Å.     

Effect of magnesium chloride (2:1 electrolyte) on the aqueous solution behavior of some saccharides over the temperature range of 288.15-318.15 K: a volumetric approach

Infinite-dilution standard partial molar volumes, , for various mono-, di-, and trisaccharides, and their derivatives (methyl glycosides) at molalities ranging from 0.04 to 0.12 mol kg⁻¹ in aqueous solutions of magnesium chloride of 0.5, 1.0, 2.0, and 3.0 mol kg⁻¹, have been evaluated over a range of temperatures from 288.15 to 318.15 K by density measurements employing a vibrating-tube densimeter. These data have been utilized to determine the corresponding standard partial molar volumes of transfer, , of saccharides and methyl glycosides from water to aqueous magnesium chloride solutions. The values have been found to be positive, and their magnitudes increase with an increasing concentration of magnesium chloride in all cases. Partial molar expansion coefficients, and second derivatives thereof, have been estimated. The magnitude of values increases with an increase in temperature, indicating that hydration effects in solutions are strongly sensitive to temperature. Pair and higher order volumetric interaction coefficients (V_AB, V_ABB) have also been obtained from values by using the McMillan-Mayer theory. The various parameters have been discussed in terms of the solute (saccharide or methyl glycoside)-co-solute (magnesium chloride) interactions and are thus used to understand the mixing effects due to these interactions. These results have been compared with those earlier reported in the presence of electrolytes. An attempt is made to interpret the volumetric properties data in terms of the stereochemistry of the solutes.     

The R* rule and energy flux in a plant-nutrient ecosystem

The R* rule predicts that the species that can survive in steady state at the lowest level of limiting resource, R*, excludes all other species. Simple models indicate that this concept is not necessarily consistent with Lotka's conjecture that an ecological system should evolve towards a state of maximum power, Max(G), where G is the power, or rate of biomass production of the system. To explore the relationship in detail, we used a published model of a plant-nutrient system in which a plant can use various strategies, S, of allocation of energy between foliage, roots, and wood. We found that the allocation strategy, S_MinR*, that leads to , where is a limiting nutrient in soil pore water in our model (and equivalent to R* in Tilman's notation), is the same as the strategy, S_{MaxG_root}, for which energy flux to roots is maximized. However, that allocation strategy is different from the strategy, S_MaxG, that produces maximum power, or maximum photosynthetic rate, for the plant system, Max(G). Hence, we conclude that and Max(G) should not necessarily co-occur in an ecological system. We also examined which strategy, S_fit, was fittest; that is, eliminated any other strategies, when allowed to compete. The strategy S_fit differed from S_MinR*, S_MaxG, and S_{MaxG_root}, which we demonstrated mathematically. We also considered the feasible situation in which a plant is able to positively influence external nutrient input to the system. Under such conditions, the strategy, S_{MaxG_root}, that maximizes energy flux to roots was the same as the strategy, S_MaxR*, that leads to maximum concentration of available nutrient in soil pore water, , and not same as S_MinR*, for .     

Ruthenium(II) complexes possessing the η-p-cymene ligand

Complexes possessing a soft donor η⁶-arene and hard donor acetylacetonate ligand, [(η⁶-p-cymene)Ru(κ²-O,O-acac-μ-CH)]₂[OTf]₂ (1) (OTf = trifluoromethanesulfonate; acac = acetylacetonate) and {Ar′ = 3,5-(CF₃)-C₆H₃}, were prepared and fully characterized. The lability of the μ-CH linkage for complex 1 and the THF ligand of 2 allow access to the unsaturated cation [(η⁶-p-cymene)Ru(κ²-O,O-acac)]⁺. The reaction of with KTp {Tp = hydridotris(pyrazolyl)borate} produces . The azide complex forms upon reaction of with N₃Ar (Ar = p-tolyl), and reaction of with CHCl₃ at 100 °C yields the chloride-bridged binuclear complex . The details of solid-state structures of [(η⁶-p-cymene)Ru(κ²-O,O-acac-μ-CH)]₂[OTf]₂ (1), and are disclosed.     

Applicability of new spin trap agent, 2-diphenylphosphinoyl-2-methyl-3,4-dihydro-2H-pyrrole N-oxide, in biological system

Electron spin resonance using spin-trapping is a useful technique for detecting direct reactive oxygen species, such as superoxide (). However, the widely used spin trap 2,2-dimethyl-3,4-dihydro-2H-pyrrole N-oxide (DMPO) has several fundamental limitations in terms of half-life and stability. Recently, the new spin trap 2-diphenylphosphinoyl-2-methyl-3,4-dihydro-2H-pyrrole N-oxide (DPhPMPO) was developed by us. We evaluated the biological applicability of DPhPMPO to analyze in both cell-free and cellular systems. DPhPMPO had a larger rate constant for and formed more stable spin adducts for than DMPO in the xanthine/xanthine oxidase (X/XO) system. In the phorbol myristate acetate-activated neutrophil system, the detection potential of DPhPMPO for was significantly higher than that of DMPO (k_DMPO = 13.95 M⁻¹ s⁻¹, k_DPhPMPO = 42.4 M⁻¹ s⁻¹). These results indicated that DPhPMPO is a potentially good candidate for trapping in a biological system.     

Kinetics and mechanism of the oxidation of oxalic acid by tetrachloroaurate(III) ion

The oxidation of oxalic acid by tetrachloroaurate(III) ion in 0.005 ? [HClO₄] ? 0.5 mol dm⁻³ is first order in and a fractional order in [oxalic acid], the reactive entities being AuCl₃(OH)⁻ and ions. The pseudo first-order rate, k_obs, with respect to [Au(III)], is retarded by increasing [H⁺] and [Cl⁻]. The retardation by H⁺ ion is caused by the dissociation equilibrium . A mechanism in which a substitution complex, is formed from AuCl₃(OH)⁻ and ions prior to its rate limiting disproportionation into products is suggested. The rate limiting constant, k, has been evaluated and its activation parameters are reported. The equilibrium constant K₁ for the formation of the substitution complex and its thermodynamic parameters are also reported.     

3D coordination polymer of copper (II)-potassium (I): Crystal structure and thermal decomposition kinetics

A new heterometallacrown coordination polymer [K₂Cu(NPA)₂(H₂O)₄]_n (where H₂NPA = 3-nitro-phthalic acid) has been synthesized and it’s crystal structure has been elucidated. In the complex, the o-phthalate group coordinates to metal atoms behaving as both tetradentate and heptadentate coordination, the modes of which have been found for the first time. The thermal behaviors of this complex and the thermal decomposition kinetics have been studied. Kinetic analysis shows that the decomposition of title complex in the main range acts as two separate transitions with the first one being a double-step following reaction, , and the second being a three-step following reaction of t:f,f, . The kinetic parameters of these processes were also obtained.