László Nagy

Organotin(IV)n+ complexes formed with biologically active ligands: equilibrium and structural studies, and some biological aspects

Abstract The organotin(IV) cations form complexes with ligands containing {O}, {N}, {S}, or {phosphorus(O)} donor atoms with various composition and stability. The emergence of new experimental techniques (EXAFS, multinuclear 1 H-, 13 C-, 119 Sn-NMR, 119 Sn Mossbauer, etc., spectroscopic techniques) provided useful information about the structure and stabilities of the complexes formed. We reviewed the literature on these type of complexes taking into account the biological aspects of the complexes discussed.

Recent Plant Diversity Changes on Europe’s Mountain Summits

Climb Every Mountain Mountaintop floras across Europe appear to be responding to climatic change in terms of upslope species range shifts. Pauli et al. (p. 353) systematically analyzed data gathered from standardized permanent plots on 66 high-mountain environments across Europe. On average, mountaintop species numbers have increased significantly during the last decade. However, this increase is a net effect of gains and losses, with losses particularly affecting mountains of Mediterranean regions and their endemic species. This turnover is largely consistent with model predictions and indicates that high-altitude species, and in particular the rich endemic alpine flora of many Mediterranean mountain ranges, will come under increasing pressure in the predicted warmer and drier climates in this region. European mountaintop flower species richness is increasing on northern summits but decreasing on southern summits. In mountainous regions, climate warming is expected to shift species’ ranges to higher altitudes. Evidence for such shifts is still mostly from revisitations of historical sites. We present recent (2001 to 2008) changes in vascular plant species richness observed in a standardized monitoring network across Europe’s major mountain ranges. Species have moved upslope on average. However, these shifts had opposite effects on the summit floras’ species richness in boreal-temperate mountain regions (+3.9 species on average) and Mediterranean mountain regions (–1.4 species), probably because recent climatic trends have decreased the availability of water in the European south. Because Mediterranean mountains are particularly rich in endemic species, a continuation of these trends might shrink the European mountain flora, despite an average increase in summit species richness across the region.

Carbohydrates as ligands: coordination equilibria and structure of the metal complexes

Abstract Simple sugars and their derivatives — with oxygen, nitrogen, sulphur or phosphorous anchoring donor groups — form metal ion complexes of various composition and stability. The emergence of new experimental methods allowed the assignment of the metal binding sites in the different isomeric complexes of these multidentate ligands, and also the determination of the most effective chelating isomers of the ligands — being present as a mixture of different conformational and/or configurational isomers in solution. We review the literature on the metal ion complexes of carbohydrate type ligands with the emphasis on the past 20 years, discussing the equilibria and structure in aqueous solution together with the structures determined for the solid state complexes. Stability and structural data are collected for comparison.

Unusual coordination behavior of D-fructose towards dimethyltin(IV): metal-promoted deprotonation of alcoholic OH groups in aqueous solutions of low pH

Abstract To study the effect of the conformation of sugar hydroxy groups on metal complexation processes, complex formation of eight saccharides (D-fructose, L-sorbose, L-arabinose, D-arabinose, D-glucose, D-sorbitol, 2-deoxy-D-glucose and D-saccharose) with dimethyltin(IV) cations was investigated in aqueous solution by potentiometric equilibrium measurements, 13 C NMR, polarimetric and Mossbauer spectroscopic methods. The experimental results proved that deprotonation of D-fructose and L-sorbose is caused by the coordination of dimethyltin(IV) in the unusual low pH interval 4–6 in contrast to the other saccharides deprotonated in analogous way at pH > 8. Increasing the pH of the solution resulted in the formation of further complexes. Stability and composition of the species was determined by potentiometric studies. 13 C NMR measurements led to the assignment of the sugar OH groups participating in the processes. Mossbauer investigations in the quick-frozen solutions permitted the determination of the stereochemistry of tin(IV) in the complexes.

The local structures of Cu(II) and Zn(II) complexes of hyaluronate

Abstract Cu(II) and Zn(II) complexes of hyaluronate (Hy) were prepared. The local structures and binding sites were determined by Cu and Zn K-EXAFS and XANES measurements in the solid state. Both metal ions were found to be coordinated to Hy via carboxylate and oxygen atoms and probably O-1. The NH group of the acetamido moiety does not take part in the complexation. Analysis of the EXAFS spectra revealed that the oxygen coordination geometry around the Cu(II) ion (distorted octahedron) and the Cu–O bond length ( r eq =200 pm) in the Cu(II)–Hy complex are not very different from those in the hexaaqua Cu(II) ion (195 pm). The Zn(II)–Hy complex is tetra coordinated in a tetrahedral structure, with an average Zn-O bond length of 202 pm. The non-bonding Cu...C and Zn...C distances were determined to be 315 and 299 pm, respectively. These values and the large Debye–Waller factors indicate the macrochelate coordination mode of the ligand.

Photoinhibition and law of reciprocity in photosynthetic reactions of Synechocystis sp. PCC 6803

Summary The effect of irradiance (neutron, alpha, X- and visible electromagnetic rays) on biological systems (survivals of organs, tissue cultures, breakage of DNA) has been widely studied in radiology. The biological effect of radiation depends on the dose (D = I · t; I and t are the intensity and time of irradiance, respectively). In photosynthesis light is a substrate for the photoelectronic conversion and can be toxic to photosystem II (PSII) as well. This toxicity is expressed by the degradation of the reaction centre D 1 protein and, as a consequence, the loss of PSII activity of wild type and mutant Synechocystis cells being subjected to high light. The aim of the present study was to examine whether the photoinhibition of PSII follows the reciprocity law characteristic of a dose response. We measured the change of steady state level of room temperature fluorescence at 685 nm (due to the antenna and reaction center chlorophylls), variable chlorophyll fluorescence and oxygen evolution of wild type Synechocystis 6803 cells after exposure to high light intensities (1200-8000 µmol · m -2 · s -1 ) for different durations (0-20 min). We observed that the log of degree of PSII inactivation as a function of light intensity gave a straight line, indicating the validity of the reciprocity law. Average cross-sectional areas for inactivation were found to be 0.066 m 2 /mol (steady state oxygen evolution), 0.12 m 2 /mol (steady state level of F 685nm ), and 0.25 m 2 /mol (induction of F v /F max ).

Photoinhibition of carotenoidless reaction centers from Rhodobacter sphaeroides by visible light. Effects on protein structure and electron transport

Inhibition of electron transport and damage to the protein subunits by visible light has been studied in isolated reaction centers of the non-sulfur purple bacterium Rhodobacter sphaeroides. Illumination by 1100 μEm−2 s−1 light induced only a slight effect in wild type, carotenoid containing 2.4.1. reaction centers. In contrast, illumination of reaction centers isolated from the carotenoidless R26 strain resulted in the inhibition of charge separation as detected by the loss of the initial amplitude of absorbance change at 430 nm arising from the P+QB− → PQB recombination. In addition to this effect, the L, M and H protein subunits of the R26 reaction center were damaged as shown by their loss on Coomassie stained gels, which was however not accompanied by specific degradation products. Both the loss of photochemical activity and of protein subunits were suppressed in the absence of oxygen. By applying EPR spin trapping with 2,2,6,6-tetramethylpiperidine we could detect light-induced generation of singlet oxygen in the R26, but not in the 2.4.1. reaction centers. Moreover, artificial generation of singlet oxygen, also led to the loss of the L, M and H subunits. Our results provide evidence for the common hypothesis that strong illumination by visible light damages the carotenoidless reaction center via formation of singlet oxygen. This mechanism most likely proceeds through the interaction of the triplet state of reaction center chlorophyll with the ground state triplet oxygen in a similar way as occurs in Photosystem II.

Molecular identification of Trichoderma species associated with Pleurotus ostreatus and natural substrates of the oyster mushroom

Green mold of Pleurotus ostreatus, caused by Trichoderma species, has recently resulted in crop losses worldwide. Therefore, there is an emerging need for rapid means of diagnosing the causal agents. A PCR assay was developed for rapid detection of Trichoderma pleurotum and Trichoderma pleuroticola, the two pathogens causing green mold of P. ostreatus. Three oligonucleotide primers were designed for identifying these species in a multiplex PCR assay based on DNA sequences within the fourth and fifth introns in the translation elongation factor 1alpha gene. The primers detected the presence of T. pleurotum and/or T. pleuroticola directly in the growing substrates of oyster mushrooms, without the need for isolating the pathogens. The assay was used to assess the presence of the two species in natural environments in which P. ostreatus can be found in Hungary, and demonstrated that T. pleuroticola was present in the growing substrates and on the surface of the basidiomes of wild oyster mushrooms. Other Trichoderma species detected in these substrates and habitats were Trichoderma harzianum, Trichoderma longibrachiatum and Trichoderma atroviride. Trichoderma pleurotum was not found in any of the samples from the forested areas tested in this study.

Photosynthetic Machineries in Nano-Systems

Photosynthetic reaction centres are membrane-spanning proteins, found in several classes of autotroph organisms, where a photoinduced charge separation and stabilization takes place with a quantum efficiency close to unity. The protein remains stable and fully functional also when extracted and purified in detergents thereby biotechnological applications are possible, for example, assembling it in nano-structures or in optoelectronic systems. Several types of bionanocomposite materials have been assembled by using reaction centres and different carrier matrices for different purposes in the field of light energy conversion (e.g., photovoltaics) or biosensing (e.g., for specific detection of pesticides). In this review we will summarize the current status of knowledge, the kinds of applications available and the difficulties to be overcome in the different applications. We will also show possible research directions for the close future in this specific field.

The IleL229 → Met mutation impairs the quinone binding to the QB-pocket in reaction centers of Rhodobacter sphaeroides

A spontaneous mutant (R/89) of photosynthetic purple bacterium Rhodobacter sphaeroides R-26 was selected for resistance to 200 μM atrazin. It showed increased resistance to interquinone electron transfer inhibitors of o-phenanthroline (resistance factor, RF=20) in UQo reconstituted isolated reaction centers and terbutryne in reaction centers (RF=55) and in chromatophores (RF=85). The amino acid sequence of the QB binding protein of the photosynthetic reaction center (the L subunit) was determined by sequencing the corresponding pufL gene and a single mutation was found (IleL229 → Met). The changed amino acid of the mutant strain is in van der Waals contact with the secondary quinone QB. The binding and redox properties of QB in the mutant were characterized by kinetic (charge recombination) and multiple turnover (cytochrome oxidation and semiquinone oscillation) assays of the reaction center. The free energy for stabilization of QAQB− with respect to QA−QB was ΔGAB=−60 meV and 0 meV in reaction centers and ΔGAB=−85 meV and −46 meV in chromatophores of R-26 and R/89 strains at pH 8, respectively. The dissociation constants of the quinone UQo and semiquinone UQo− in reaction centers from R-26 and R/89 showed significant and different pH dependence. The observed changes in binding and redox properties of quinones are interpreted in terms of differential effects (electrostatics and mesomerism) of mutation on the oxidized and reduced states of QB.