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Sunflower seedlings subjected to increasing stress by water deficit: Changes in superoxide production related to the composition of thylakoid membranes
No full textFree radicals, such as the superoxide anion, can damage the photosynthetic apparatus. At the same time they are increasingly formed as by-products of electron transport during stress conditions. For this reason, we studied the kinetics of formation and decay of superoxide anions in relation to changes, induced by increasing water deficit, in the composition of thylakoids. Seedlings of sunflower (Helianthus annuus L. cv. Licia Stella) were subjected to either a mild, a moderate, or a severe water deficit. Upon illumination of thylakoid membranes containing Tiron, we found first order kinetics of formation and decay of the Tiron semiquinone radical. At each stress intensity a higher rate of superoxide formation than in the control was observed. The different decay rates suggested a changed chemical environment around the radical. In comparison with the control, the levels of carotenoids and hydrophobic proteins in the thylakoids decreased, and the lipid/protein ratio increased after a mild water deficit. After moderate drought, the increased levels of hydrophilic proteins and carotenoids seem unsufficient to limit the improved capacity to leak electrons from the thylakoids. After a severe water stress, a decrease in unsaturation and in linolenic acid as well as a loss of lipolytic antioxidants took place, which may have rendered the thylakoids more sensiive to attack by activated forms of oxygen. The results suggest that during water deficit, the interactions among membrane components change in relation to a changed chemical composition. Such changes are probably among the causes for changes in the conformation of proteins and in the position of various molecular species in he lipid bilayer, so that they become more exposed to molecular oxygen
The Reactivity of Halides of High-Valent Group 5 and 6 Elements with Organic Compounds: from Coordination Chemistry to Activation Reactions
No full textNiobium and tantalum pentahalides, molybdenum pentachloride and tungsten hexachloride are easily-available solid compounds, whose coordination chemistry was scarcely elucidated in the past. We have been involved in a systematic exploration of the reactivity of such halides with stoichiometric amounts of oxygen- and/or nitrogen-containing organic species. This approach provides the way to a variety of inorganic structural motifs [1]. Furthermore, the coordination to the metal centre may represent the preliminary step of transformation of the organic substrate, which usually takes place selectively and under mild conditions [2]. In a number of cases, the process results in the formation of stable metal-anion salts containing otherwise reactive organic cations [3]. The metal-halide bond energy value and the availability to the metal centre of a one-electron reduced oxidation state are the two key factors which drive the activation reactions, and provide uniqueness with respect to the parallel chemistry exhibited by high-valent main group element halides. Examples will be given with reference to arenes, natural α-aminoacids, alkyl-ureas, amines, etc
Proprietà antiossidanti di estratti acquosi di basilico
No full textLe più importanti malattie croniche e degenerative sono generate dai radicali liberi e le piante, ricche in antiossidanti, possono essere di ausilio per contrastare nell’uomo i danni dello stress ossidativo indotti dai radicali liberi. A seconda del tipo di solvente usato, gli estratti vegetali possono essere distinti in acquosi o lipidici. I primi contengono antiossidanti idrofilici tra cui possiamo annoverare la Vitamina C (acido ascorbico) e gli acidi fenolici che contribuiscono a determinare il potere antiradicalico totale di un estratto vegetale acquoso.
L’uso della coltivazione idroponica per le colture orticole presenta numerosi vantaggi tra i quali un miglior controllo delle condizioni di coltivazione e dell’uso di fitofarmaci, il che permette incrementi di resa. In Toscana esistono già aziende che applicano la coltura idroponica per la coltivazione del basilico e, dato il grande mercato esistente per la produzione del “pesto alla genovese”, si rende necessario conoscere eventuali variazioni delle proprietà nutraceutiche del prodotto ottenuto in idroponica rispetto a quello cresciuto a terra.
Il potere antiossidante di un estratto vegetale può essere valutato sia con tecniche spettrofotometriche sia utilizzando la tecnica di “Electron Spin Resonance” (ESR), che recentemente si è dimostrata più affidabile e sensibile di quella spettrofotometrica. Scopo del presente lavoro è stato quello di determinare, in foglie di basilico cresciute in idroponica, le variazioni del potere antiossidante mettendo a confronto la tecnica ESR con quella spettrofotometrica. L’analisi della composizione in vitamina C ed in acidi fenolici ha permesso di stabilire il contributo dei vari componenti alle variazioni del potere antiossidante degli estratti da foglie di piante di basilico cresciute in idroponica e a terra
Proprietà nutraceutiche del basilico coltivato in idroponica
No full textL’uso della coltivazione idroponica per le colture orticole presenta numerosi vantaggi tra i quali un miglior controllo delle condizioni di coltivazione e dell’uso di pesticidi, il che permette incrementi di resa. In Toscana esistono già aziende che applicano la coltura idroponica per la coltivazione del basilico e, dato il grande mercato esistente per la produzione del “pesto alla genovese”, si rende necessario conoscere eventuali variazioni delle proprietà nutraceutiche del prodotto ottenuto in idroponica rispetto a quello cresciuto a terra. Si fa sempre più strada l’ipotesi che le maggiori malattie croniche e degenerative siano generate dai radicali liberi e che le piante, ricche in antiossidanti, possano rappresentare un aiuto per contrastare nell’uomo i danni dello stress ossidativo indotti dai radicali liberi. Si possono distinguere due tipi principali di antiossidanti: quelli idrofilici tra cui la Vitamina C (acido ascorbico) e quelli idrofobici tra cui la Vitamina E (tocoferolo). Di conseguenza in un estratto vegetale è possibile distinguere un’attività antiossidante idrofilica ed una idrofobica che contribuiscono entrambe a determinare il potere antiradicalico totale di un estratto vegetale.
Scopo del presente lavoro è stato quello di determinare in foglie di basilico cresciute in idroponica le variazioni di composizione in vitamina C ed E, nonché le variazioni del potere antiossidante rispetto a foglie di piante cresciute a terra. In particolare, il potere antiossidante degli estratti idrofili e lipofili viene valutato sia con tecniche spettrofotometriche che utilizzando la tecnica di “Electron Spin Resonance” (ESR), che recentemente si è dimostrata più affidabile e sensibile di quella spettrofotometrica
Chemical changes and superoxide production in thylakoid membranes under water stress
No full textSunflower seedlings (Helianthus annuus cv. Isabel) subjected to a moderate level of water stress showed a reduced growth and a 0.1 MPa osmotic adjustment came into play. Thylakoid membranes isolated from stressed leaves showed decreased chlorophyll (Chl) and protein contents but the Chl a/Chl b and protein/Chl ratios were unchanged. Water stress caused a preferential hydrolysis in thylakoid proteins: the hydrophilic to hydrophobic protein ratio increased from 0.8 in the control to 4.5 in the stressed plants. However, the degree of unsaturation was unchanged and the electron spin resonance (ESR) measurements did not show an increased level of superoxide radical production by photosynthetic membranes
Impact of Leaf Removal on Phenolics and Antioxidant Activity of Trebbiano Berries (Vitis vinifera L.)
No full textLeaf removal is a canopy management practice widely applied in viticulture to enhance the phenol composition and concentration of grapes, which then results in improved wine quality. Many studies were carried out on red berried varieties, but information on white ones is scanty. The aim of the study was to assess the effect of basal leaf defoliation in post fruit set on the phenol composition, ascorbate level and antioxidant activity of Trebbiano grapes. Electron paramagnetic resonance was also employed to monitor the decay kinetics of 1,1-diphenyl-2-picrylhydrazyl which allowed the identification of antioxidants with different action rates. The results show that defoliation caused an increase in the phenolic acid (hydroxycinnamic and hydroxybenzoic acids) and flavonol concentrations of berries without changes in the composition. Both ascorbate and antioxidant activity were also enhanced in the berries from defoliated vines. Besides increasing the number of fast-rate antioxidants, leaf removal resulted in the formation of intermediate-rate ones. In the Trebbiano variety, leaf removal in the post fruit set may represent an effective strategy to enhance the phenolic composition and the antioxidant defense system of berries
Levels of antioxidants and nutraceuticals in basil grown in hydroponics and soil
No full textMediterranean diet, this research aimed to study the nutraceutical properties of basil (Ocimum basilicum cv. Genova) grown in hydroponics in comparison with that grown in soil. The antioxidant activities of aqueous and lipid extracts of basil leaves were evaluated both by spectrophotometric detection with the 2,20-azinobis(3-ethylbenzothiazoline-6-sulphonic acid) radical cation (ABTS+) and by electron paramagnetic resonance (EPR) detection with the stable radicals peroxylamine disulphonate (Fremy’s salt, hydrophilic) and 1,1-diphenyl-2-picrylhydrazyl (DPPH, lipophilic). From EPR decay kinetics analysis, it was possible to distinguish (in the lipid extract) a fast rate constant and a slow rate constant, likely attributable to two different kinds of lipophilic antioxidants. Hydroponic cultivation improved antioxidant
activity of both aqueous and lipid extracts, increasing the contents of vitamin C, vitamin E, lipoic acid, total phenols and rosmarinic acid
Copper(II) complexes with peptides based on the second cell binding site of fibronectin: Metal coordination and ligand exchange kinetics
No full textCopper(II) complexes with short peptides based on the second cell binding site of fibronectin, PHSFN and PHSEN, have been characterized by potentiometric, UV-vis, CD, EPR and NMR spectroscopic methods. The histidine imidazole nitrogen is the anchoring site for the metal ion binding. Thermodynamic and spectroscopic evidence is given that the side chain oxygen donor atom of glutamyl residue in Ac-PHSEN-NH2 is also involved in the binding up to physiological pH. To determine ligand exchange kinetic parameters after the imidazole nitrogen anchoring, proton relaxation enhancement NMR data have been collected for the two hydrogen atoms of the imidazole ring in the temperature range 293-315 K at pH 5.2 and globally treated within different kinetic models for ligand exchange. The best fitting model involves two steps. In the first one, which is slow, a water molecule disengages a carbonyl or a carboxylate group coordinated to the metal ion in the complex formed by PHSFN or PHSEN, respectively. This stage is one order of magnitude slower for PHSEN, due to entropic effects. In the second step, which is fast, the complex just formed exchanges with the ligand. In this step, no appreciable differences are found for the two cases examined
Studio della Fluidità di membrane tilacoidali sottoposte a stress ossidativo
No full textElectron paramagnetic resonance (EPR) spectroscopy was applied to the study of fluidity in thylakoids of
durum wheat (Triticum durum Desf. cv. Creso) treated with oxygen free radicals. The radicals were generated
by using Fe2+-EDTA and ascorbic acid and let to act either on thylakoid membranes isolated from leaves
or on leaves themselves, from which thylakoids were subsequently extracted. The oxidative treatment was
prolonged for periods ranging from 15 min to 3 h. Line shape analysis of EPR spectra recorded as a function
of temperature on concentrated suspensions of thylakoids labeled with 5-doxylstearic acid (5-DSA) allowed
to get information about the fluidity of differently treated membranes. An axially symmetric rotational diffusion
model, defined by the components of the rotational tensor Dpar and Dperp and by the diffusion tilt angle õ, was
assumed for the dynamics of the spin probes. Good agreement with experimental spectra was obtained with
a diffusion tilt angle continuously increasing with temperature and a high anisotropy ratio N ) Dpar/Dperp of
the spin probe rotational diffusion. High N values have been considered as an indication for the immobilization
of the spin probes in the hydrophobic part of the membranes. The changes of õ with temperature have been
interpreted in terms of chain isomerization within the probes. The differences found between the probe dynamics
in the differently treated thylakoids have been discussed on the basis of the time and type (on the leaves or
on the membranes) of oxidative treatment
Stable [M2F11]– (M = Nb, Ta) Salts of Protonated 1,3-Dimethoxybenzene
No full textThe 3:1 molar reactions of MF5 (M = Nb, 1a; M = Ta, 1b) with 1,3-dimethoxybenzene in CHCl3 led to the synthesis of the arenium salts [2,4-(OMe)2C6H5][M2F11] (M = Nb, 3a; M = Ta, 3b) in good yields. The reactions took place with the intermediate formation of (MF5)2[2-1,3-(OMe)2C6H4] (M = Nb, 2a; M = Ta, 2b), followed by monoelectron oxidation of the arene and production of MF4 (identified via EPR as the acetonitrile adduct). Compounds 3a,b were fully characterized both in solution (NMR) and in the solid state (X-ray and elemental analysis), while 2a,b were recognized by NMR in CD2Cl2 solution. The reactions of 1,3-dimethoxybenzene with Ag[NbF6] or Ag[Sb2F11] in CD2Cl2/CHCl3 afforded [2,4-(OMe)2C6H5]+. 1,3-dimethoxybenzene was inert toward the addition of H[SbF6](aq) under comparable experimental conditions
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