ESR, electrochemical and reactivity studies of antitrypanosomal palladium thiosemicarbazone complexes

Cyclic voltammetry (CV) and electron spin resonance (ESR) techniques were used in the investigation of novel palladium complexes with bioactive thiosemicarbazones derived from 5-nitrofurane or 5-nitrofurylacroleine. Sixteen palladium complexes grouped in two series of the formula [PdCl(2)HL] or [PdL(2)] were studied. ESR spectra of the free radicals obtained by electrolytic reduction were characterized and analyzed. The ESR spectra showed two different hyperfine patterns. The stoichiometry of the complexes does not seem to affect significantly the hyperfine constants however we observed great differences between 5-nitrofurane and 5-nitrofurylacroleine derivatives. The scavenger properties of this family of compounds were lower than Trolox.     

The donor ability of the chelated carbonate ligand: protonation and metallation of [(L)Co(O2CO)]+ complexes in aqueous solution

The syntheses and X-ray structures of [Co(Me-tpa)O(2)COZnCl(3)], [Co(pmea)O(2)COZnCl(3)].H(2)O [Co(trpyn)O(2)COZn(OH(2))(4)OCO(2)Co(trpyn)](ZnCl(4))(2).H(2)O, [Co(trpyn)(O(2)COH)]ZnCl(4).3H(2)O and [Co(trpyn)(O(2)CO)]ClO(4) are reported (Me-tpa = [(6-methyl-2-pyridyl)methyl]bis(2-pyridylmethyl)amine, pmea = bis(2-pyridylmethyl)-2-(2-pyridylethyl)amine, trpyn = tris(2-(1-pyrazolyl)ethyl)amine). The chelated bicarbonate complex [Co(trpyn)(O(2)COH)]ZnCl(4).3H(2)O is isolated as a crystalline solid from an acidic solution of the parent carbonate [Co(trpyn)(O(2)CO)]ClO(4), and X-ray structural analysis shows that lengthening of the C[double bond, length as m-dash]O(exo) bond and shortening of the C-O(endo) bond accompanies protonation. The bimetallic complex [Co(Me-tpa)O(2)COZnCl(3)] results from the unexpected coordination of ZnCl(3)(-) to the exo O atom of a chelated carbonate ligand. This complex is obtained from both acidic and neutral solutions in which [Zn(2+)] = 1.0 M, while the structurally similar complex [Co(pmea)O(2)COZnCl(3)].H(2)O is isolated from an analogous neutral solution. The trimetallic complex [Co(trpyn)O(2)COZn(OH(2))(4)OCO(2)Co(trpyn)](ZnCl(4))(2).H(2)O crystallises on prolonged standing of [Co(trpyn)(O(2)CO)]ClO(4) in a neutral solution having [Zn(2+)] = 1.0 M. The Zn-O bond lengths in all three complexes are indicative of bonds of significant strength. DFT calculations show that the nature of the bonding interaction between the Co(iii) ion and the endo O atoms of the carbonate ligand remain essentially unaffected by coordination of Zn(2+) to the exo O atom. They also show that such coordination of Zn(2+) decreases the C-O(exo) bond order.     

High fluidity and soft elasticity of the inner membrane of Escherichia coli revealed by the surface rheology of model Langmuir monolayers

We have studied the equilibrium and linear mechanical properties of model membranes of Escherichia coli built up as Langmuir monolayers of a native lipid extract using surface thermodynamics, fluorescence microscopy, and surface rheology measurements. The experimental study has been carried out at different temperatures across the physiological operative range 15-37 degrees C. Lipid phase coexistence has been revealed over a broad pressure range by fluorescence microscopy. The presence of ordered domains has been invoked to explain the emergence of shear elasticity accompanying the hydrostatic compression elasticity typical of fluid monolayers. The surface rheology measurements point out the soft character of E. coli membranes; i.e., upon deformation they react as a near-ideal compliant body with minimal energy dissipation, thus optimizing the effectiveness of external stresses in producing membrane deformations. These mechanical features appear to be independent of temperature, suggesting the existence of a passive thermoregulation mechanism.     

Immuno-column for on-line quantification of human serum IgG antibodies to Helicobacter pylori in human serum samples

This study report an human serum IgG antibodies to Helicobacter pylori quantitation procedure based on the multiple use of an immobilized H. pylori antigen on an immuno-column incorporated into an a flow-injection (FI) analytical system. The immuno-adsorbent column was prepared by packing 3-aminopropyl-modified controlled-pore glass (APCPG) covalently linking H. pylori antigens in a 3-cm of Teflon tubing (0.5 i.d.). Antibodies in the serum sample are allowed to react immunologically with the immobilized H. pylori antigen, and the bound antibodies are quantified by alkaline phosphatase (AP) enzyme-labeled second antibodies specific to human IgG. p-Aminophenyl phosphate (pAPP) was converted to p-aminophenol (pAP) by AP and an electroactive product was quantified on glassy carbon electrode (GCE) modified with multiwall carbon nanotubes (MWCNT) (GCE-CNTs) at 0.30 V. The total assay time was 25 min. The calculated detection limits for amperometric detection and the ELISA procedure are 0.62 and 1.8 UmL(-1), respectively. Reproducibility assays were made using repetitive standards of H. pylori-specific antibody and the intra- and inter-assay coefficients of variation were below 5%. The immuno-affinity method showed higher sensitivity and lower time-consumed, demonstrate its potential usefulness for early assessment of human serum immunoglobulin G (IgG) antibodies to H. pylori.     

Synthesis and crystal structure of thorium bis(hydrogenphosphate) monohydrate

Microcrystals of Th(HPO 4) 2.H 2O were hydrothermally obtained from a Th(NO 3) 4-CO(NH 2) 2-H 3PO 3-H 2O system ( T = 180 masculineC). The structure [orthorhombic, Pbca, a = 9.1968(2) A, b = 18.6382(2) A, c = 8.7871(2) A], unlike alpha-Zr(HPO 4) 2.H 2O-type layered compounds, consists of a three-dimensional framework with PO 4 tetrahedra coordinated to Th atoms. The water molecule is also coordinated to the Th atom and projected toward small channels running along the directions of the a and c axes. The ThO 6O(w) environment could be described as a highly distorted pentagonal bipyramid.     

Synthesis of 10-membered and larger rings via free radical methods

The purpose of this review is to discuss 1) how free radical chemistry has contributed to development of new methodologies for the construction of 10-membered and larger macrocycles over the past 32 years; 2) the most well-developed free radical methods for constructing 10-membered and larger rings; and 3) how these methodologies have contributed to solving certain key steps in the synthesis of natural products.     

Rocking bidirectional lasers

We study the emission properties of a class A bidirectional laser under the action of an amplitude modulated injected signal, i.e. a rocked bidirectional laser. We derive two coupled autonomous amplitude equations valid close to the emission threshold and study their solutions. The most relevant result is that while in the absence of rocking the laser can only emit in either of the two unidirectional solutions, under suitable rocking conditions cw bidirectional emission appears and, moreover, it coexist bistably with unidirectional emission.     

Spectroscopic and catalytic characterization of a functional Fe(III)Fe(II) biomimetic for the active site of uteroferrin and protein cleavage

A mixed-valence complex, [Fe(III)Fe(II)L1(μ-OAc)(2)]BF(4)·H(2)O, where the ligand H(2)L1 = 2-{[[3-[((bis(pyridin-2-ylmethyl)amino)methyl)-2-hydroxy-5-methylbenzyl](pyridin-2-ylmethyl)amino]methyl]phenol}, has been studied with a range of techniques, and, where possible, its properties have been compared to those of the corresponding enzyme system purple acid phosphatase. The Fe(III)Fe(II) and Fe(III)(2) oxidized species were studied spectroelectrochemically. The temperature-dependent population of the S = 3/2 spin states of the heterovalent system, observed using magnetic circular dichroism, confirmed that the dinuclear center is weakly antiferromagnetically coupled (H = -2JS(1)·S(2), where J = -5.6 cm(-1)) in a frozen solution. The ligand-to-metal charge-transfer transitions are correlated with density functional theory calculations. The Fe(III)Fe(II) complex is electron paramagnetic resonance (EPR)-silent, except at very low temperatures (<2 K), because of the broadening caused by the exchange coupling and zero-field-splitting parameters being of comparable magnitude and rapid spin-lattice relaxation. However, a phosphate-bound Fe(III)(2) complex showed an EPR spectrum due to population of the S(tot) = 3 state (J= -3.5 cm(-1)). The phosphatase activity of the Fe(III)Fe(II) complex in hydrolysis of bis(2,4-dinitrophenyl)phosphate (k(cat.) = 1.88 × 10(-3) s(-1); K(m) = 4.63 × 10(-3) mol L(-1)) is similar to that of other bimetallic heterovalent complexes with the same ligand. Analysis of the kinetic data supports a mechanism where the initiating nucleophile in the phosphatase reaction is a hydroxide, terminally bound to Fe(III). It is interesting to note that aqueous solutions of [Fe(III)Fe(II)L1(μ-OAc)(2)](+) are also capable of protein cleavage, at mild temperature and pH conditions, thus further expanding the scope of this complex's catalytic promiscuity.     

The role of UV-B radiation in aquatic and terrestrial ecosystems--an experimental and functional analysis of the evolution of UV-absorbing compounds

We analysed and compared the functioning of UV-B screening pigments in plants from marine, fresh water and terrestrial ecosystems, along the evolutionary line of cyanobacteria, unicellular algae, primitive multicellular algae, charophycean algae, lichens, mosses and higher plants, including amphibious macrophytes. Lichens were also included in the study. We were interested in the following key aspects: (a) does the water column function effectively as an 'external UV-B filter'?; (b) do aquatic plants need less 'internal UV-B screening' than terrestrial plants?; (c) what role does UV screening play in protecting the various plant groups from UV-B damage, such as the formation of thymine dimers?; and (d) since early land 'plants' (such as the predecessors of present-day cyanobacteria, lichens and mosses) experienced higher UV-B fluxes than higher plants, which evolved later, are primitive aquatic and land organisms (cyanobacteria, algae, lichens, mosses) better adapted to present-day levels of UV-B than higher plants? Furthermore, polychromatic action spectra for the induction of UV screening pigments of aquatic organisms have been determined. This is relevant for translating 'physical' radiation measurements of solar UV-B into 'biological' and 'ecological' effects. From the action spectra, radiation amplification factors (RAFs) have been calculated. These action spectra allow us to determine any mitigating or antagonistic effects in the ecosystems and therefore qualify the damage prediction for the ecosystems under study. We summarize and discuss the main results based on three years of research of four European research groups. The central theme of the work was the investigation of the effectiveness of the various screening compounds from the different species studied in order to gain some perspective of the evolutionary adaptations from lower to higher plant forms. The induction of mycosporine-like amino acids (MAAs) was studied in the marine dinoflagellate Gyrodinium dorsum, the green algal species Prasiola stipitata and in the cyanobacterium Anabaena sp. While visible (400-700 nm) and long wavelength UV-A (315-400 nm) showed only a slight effect, MAAs were effectively induced by UV-B (280-315 nm). The growth of the lower land organisms studied, i.e. the lichens Cladina portentosa, Cladina foliacaea and Cladonia arbuscula, and the club moss Lycopodiumannotinum, was not significantly reduced when grown under elevated UV-B radiation (simulating 15% ozone depletion). The growth in length of the moss Tortula ruralis was reduced under elevated UV-B. Of the aquatic plants investigated the charophytes Chara aspera showed decreased longitudinal growth under elevated UV-B. In the 'aquatic higher plants' studied, Ceratophyllum demersum, Batrachium trichophyllum and Potamogeton alpinus, there was no such depressed growth with enhanced UV-B. In Chara aspera, neither MAAs nor flavonoids could be detected. Of the terrestrial higher plants studied, Fagopyrum esculentum, Deschampsia antarctica, Vicia faba, Calamagrostis epigejos and Carex arenaria, the growth of the first species was depressed with enhanced UV-B, in the second species length growth was decreased, but the shoot number was increased, and in the latter two species of a dune grassland there was no reduced growth with enhanced UV-B. In the dune grassland species studied outdoors, at least five different flavonoids appeared in shoot tissue. Some of the flavonoids in the monocot species, which were identified and quantified with HPLC, included orientin, luteolin, tricin and apigenin. A greenhouse study with Vicia faba showed that two flavonoids (aglycones) respond particularly to enhanced UV-B. Of these, quercetin is UV-B inducible and mainly located in epidermal cells, while kaempferol occurs constitutively. In addition to its UV-screening function, quercetin may also act as an antioxidant. Polychromatic action spectra were determined for induction of the UV-absorbing pigments in three photosynthetic organisms, representing very different taxonomic groups and different habitats. In ultraviolet photobiology, action spectra mainly serve two purposes: (1) identification of the molecular species involved in light absorption; and (2) calculation of radiation amplification factors for assessing the effect of ozone depletion. Radiation amplification factors (RAFs) were calculated from the action spectra. In a somewhat simplified way, RAF can be defined as the percent increase of radiation damage for a 1% depletion of the ozone layer. Central European summer conditions were used in the calculations, but it has been shown that RAF values are not critically dependent on latitude or season. If only the ultraviolet spectral region is considered, the RAF values obtained are 0.7 for the green alga Prasiola stipitata, 0.4 for the dinoflagellate Gyrodinium dorsum, and 1.0 for the cyanobacterium Anabaena sp. In the case of P. stipitata, however, the effect of visible light (PAR, photosynthetically active radiation, 400-700 nm) is sufficient to lower the RAF to about 0.4, while the PAR effect for G. dorsum is negligible. RAFs for some damage processes, such as for DNA damage (RAF=2.1 if protective effects or photorepair are not considered [1]), are higher than those above. Our interpretation of this is that if the ozone layer is depleted, increased damaging radiation could overrule increased synthesis of protective pigments. In addition to investigating the functional effectiveness of the different screening compounds, direct UV effects on a number of key processes were also studied in order to gain further insight into the ability of the organisms to withstand enhanced UV-B radiation. To this end, the temperature-dependent repair of cyclobutane dimers (CPD) and (6-4) photoproducts induced by enhanced UV-B was studied in Nicotiana tabacum, and the UV-B induction of CPD was studied in the lichen Cladonia arbuscula. Also, photosynthesis and motility were monitored and the response related to the potential function of the screening compounds of the specific organism.     

Stability of Gold and Platinum Nanowires on Graphite Edges

The stability of coinage and noble metal nanowires supported on graphite steps is examined by density functional theory. In particular, we study the stability of supported gold and platinum wires and compare their chemical properties with those of surfaces and bare wires. A substantially stronger bond with graphite was found for platinum wires due to unfilled antibonding states, which are occupied in the case of gold. This difference has direct consequences for the adsorption of hydrogen. This reaction can occur either on the wire or directly on graphite steps. In the case of gold, the reaction is favoured on steps, while on platinum wires, it has no thermodynamical preferences. Our results suggest that, in early stages of wire formation, hydrogen could desorb gold from graphite, but not platinum.