A5010961896- Photosynthetic Processes and Mechanisms
- Spectroscopy and Quantum Chemical Studies
- Crystallization and Solubility Studies
- X-ray Diffraction in Crystallography
- Electron Spin Resonance Studies
- Photoreceptor and optogenetics research
- Metal complexes synthesis and properties
- Metal-Catalyzed Oxygenation Mechanisms
- Magnetism in coordination complexes
- Lanthanide and Transition Metal Complexes
- Free Radicals and Antioxidants
- Mitochondrial Function and Pathology
- Inorganic and Organometallic Chemistry
- Porphyrin and Phthalocyanine Chemistry
- Metalloenzymes and iron-sulfur proteins
- Curcumin's Biomedical Applications
- Analytical Chemistry and Chromatography
- Synthesis and biological activity
- Fungal Plant Pathogen Control
- Advanced NMR Techniques and Applications
- Metal-Organic Frameworks: Synthesis and Applications
- Plant nutrient uptake and metabolism
- Enzyme Structure and Function
- Analytical Methods in Pharmaceuticals
National Centre of Scientific Research "Demokritos"
2008-2024
University of Padua
2011-2017
National and Kapodistrian University of Athens
2002
The tetramanganese-calcium cluster of the oxygen-evolving complex photosystem II adopts electronically and magnetically distinct but interconvertible valence isomeric forms in its first light-driven oxidized catalytic state, S2 . This bistability is implicated gating final states preceding O-O bond formation, it unknown how biological system enables emergence controls effect. Here we show that Mn4 CaO5 resting (dark-stable) S1 state orientational Jahn-Teller arising from a directional change...
Among the intermediate catalytic steps of water-oxidizing Mn
Over the last decade importance of nitric oxide (NO) in plant signaling has emerged. Despite its recognized biological role, sensitivity and effectiveness methods used for measuring NO concentration plants are still under discussion. Among these, electron paramagnetic resonance (EPR) is a well-accepted technique to detect NO. In present work we report constraints using 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) samples as spin trap quantitative measurement EPR...
Photosystem II preparations poised in the S2···QA state produce no detectable intermediate during straightforward illumination at liquid helium temperatures. However, upon flash range of 77−190 K, they a transient which −10 °C advances to S3 or after rapid cooling 10 K gives rise 116 G wide metalloradical EPR signal. The latter decays with half-times on order few minutes, presumably by charge recombination, and can be regenerated repeatedly K. constraints for Tyr Z oxidation are attributed...
In biological water oxidation, a redox-active tyrosine residue (D1-Tyr161 or YZ) mediates electron transfer between the Mn4CaO5 cluster of oxygen-evolving complex and charge-separation site photosystem II (PSII), driving through progressively higher oxidation states Si (i = 0–4). contrast to lower S-states (S0, S1), in (S2, S3) cluster, YZ cannot be oxidized at cryogenic temperatures due accumulation positive charge S1 → S2 transition. However, by illumination 77–190 K followed rapid...
IspG is a [4Fe-4S] cluster-containing protein, and the [4Fe-4S](+) species proposed to be catalytically relevant species. However, attempts reported in literature failed detect In this study, using potent reduction system, we have successfully detected with X-band EPR spectroscopy. addition, improved Escherichia coli activity 550 nmol min(-1) mg(-1), which approximately 20-fold greater than that of NADPH-Fpr-FldA system literature.
The O2-evolving complex of photosystem II, Mn4Ca, cycles through five oxidation states, S0,..., S4, during its catalytic function, which involves the gradual abstraction four electrons and protons from two bound water molecules. direct oxidant is tyrosine neutral radical, YZ•, transiently produced by highly oxidizing power photoexcited chlorophyll species P680. EPR characterization YZ• has been limited, until recently, to inhibited (non-oxygen-evolving) preparations. A number relatively...
Tyr Z of photosystem II mediates electron transfer from the water splitting site, a Mn4Ca cluster, to specialized chlorophyll assembly P680. Due its proton-limited redox properties and proximity Mn it is thought play critical role in proton-coupled reactions that constitute four-step oxidation mechanism (so-called S-state transitions) molecular oxygen. Spectroscopic evidence for radical has been scarce intact preparations (it difficult probe optically, too short-lived EPR characterization)...
We report the trapping of two metalloradical intermediates corresponding to transitions S 2 3 and 0 oxygen evolving complex (OEC) Photosystem II (PSII), in preparations containing methanol, at temperatures near that half inhibition respective S‐state transitions. The first intermediate, with an EPR width 160 G, is assigned , based on its similarity one previously characterized after 10 K. second a splitting ∼80 G tentatively . signal weaker than one, both are stable cryogenic temperatures.
Abstract Among the intermediate catalytic steps of water‐oxidizing Mn 4 CaO 5 cluster photosystem II (PSII), final metastable S 3 state is critically important because it binds one substrate and precedes O 2 evolution. Herein, we combine X‐ Q‐band EPR experiments on native methanol‐treated PSII Spinacia oleracea show that preparations correspond to a previously uncharacterized high‐spin ( S= 6) species. This confirmed as major component also in intact photosynthetic membranes, coexisting...
An artificial oxygen-evolving complex (OEC) contains a tetranuclear CoIII4O4 cubic cluster ligated with acetate and pyridine molecules, light-activated Ru(bpy)32+ moiety (bpy = 2,2'-bipyridine), the sacrificial electron acceptor S2O82- side. A recent EPR investigation of this system showed formation high-spin Co(II) ion under visible-illumination conditions. It has been supported that center originates from is involved in process. The present report focused on further characterization d7...
Tetronic acids, 4-hydroxy-5H-furan-2-ones, constitute a class of heterocyclic compounds with potent biological and pharmacological activity. The beta, beta'-tricarbonyl moiety plays an integral role in systems forms variety metal complexes. In this report, we present the complexation reactions 3-ethoxycarbonyl tetronic acids acetates chlorides Cu(II) Co(II). These complexes have been studied by means EPR spectroscopy magnetic susceptibility measurements. From obtained results, preliminary...
The thermally assisted reaction of Cr(NO
Abstract The tetramanganese–calcium cluster of the oxygen‐evolving complex photosystem II adopts electronically and magnetically distinct but interconvertible valence isomeric forms in its first light‐driven oxidized catalytic state, S 2 . This bistability is implicated gating final states preceding O−O bond formation, it unknown how biological system enables emergence controls effect. Here we show that Mn 4 CaO 5 resting (dark‐stable) 1 state orientational Jahn–Teller arising from a...
The 3-acyl tetramic acids constitute a growing class of natural products displaying range biological activities. g , ' tricarbonyl moiety present in the acid provides suitable site for bidentate complexation to metal, which increases activity. For dielectric study N-acetyl-3-butanoyl and series its complexes with Cu(II) Co(II) symmetric asymmetric forms, we used Thermally Stimulated Depolarization Currents (TSDC) technique. drastic decrease intensity TSDC peaks complexes, compared above...