Szabad gyökök termodinamikai paramétereinek meghatározása ESR-spektroszkópiával biológiai és modell rendszerekben = Determination of thermodynamic parameters for free radicals by ESR-spectroscopy in biologic and model systems

A projekt tárgya új ESR szimulációs eljárás kidolgozása és alkalmazása szabad gyökök termodinamikai tulajdonságainak meghatározása céljából. Kifejlesztettünk egy felület szimulációs eljárást, melyben a felületet az ESR spektrumsorozat alkotja a hőmérséklet, mint második dimenzió függvényében. A spektroszkópiai és a termodinamikai paraméterek egyidejű optimalizálása az információ integrálása révén lehetővé teszi összetett spektrumrendszerek egyértelmű felbontását. A módszert alkalmaztuk reaktív oxigén speciesek dinamikai tulajdonságainak vizsgálatára biológiai közegben. Szabad gyökös reakciókat generáló fém-komplexek termodinamikai tulajdonságait is vizsgáltuk az új technika segítségével. A módszert 13 hazai és külföldi kutatócsoport is felhasználta, és az eredményekből 27 tudományos publikáció készült. | The project aimed to develop and apply new computer simulation method for the evaluation of ESR spectra in order to investigate the thermodynamic properties of free radicals. We developed a new surface simulation technique, where the surface was constructed from a series of ESR spectra recorded as a function of temperature, which is considered as a second dimension. The simultaneous optimization of spectroscopic and thermodynamic parameters allows obtaining a unique decomposition of highly complex spectra by integrating the available information. The method was applied to study the dynamic properties of reactive oxygen species in biologic media. Transition metal complexes initiating free radical processes were also studied by the new technique. 13 Hungarian and foreign research groups were involved in the utilization of method, which resulted in 27 communications

The role of onium salts in the oxidation of hydrocarbons by O2 catalysed by cationic phase-transfer reagents

Experimental and theoretical evidence is presented that cationic phase-transfer catalysts promote the homolytic decomposition of hydroperoxide initiators into radicals, this being a fundamental step in the catalysis of the oxidation of hydrocarbons by O-2. Such decomposition of the model substance tert-butyl hydroperoxide (t-BHP) results in O-2, tert-butanol (90-95%) di-tert-butyl peroxide (5-10%) and traces of CO2. The stoichiometric ratio Delta[t-BHP]/Delta O-2 was found to have a value of 2, independently of the nature of the counteranion present. It is assumed that the interaction between hydroperoxide and onium cation is mainly electrostatic in nature and that its effectivity depends on the positive charge density on the onium cation, which is controlled by the nature and dimensions of the counteranion. The role of water in the decomposition of t-BHP is also elucidated

Multifrekvenciás elektron spin rezonancia erősen korrelált fémekben és szupravezetőkben = Multifrequency electron spin resonance in strongly correlated metals and superconductors

A projekt célja olyan szilárd testek elektron spin rezonancia vizsgálata, amelyekben az elektron-elektron korrelációk alapvetően fontosak. A vizsgált kuprát, szerves és fullerén vegyületek fémek, szupravezetők vagy a szupravezetéshez közel álló mágnesesen rendezett anyagok, amelyekben az elektron korrelációnak lényeges szerepe van. Megmértük és egy elméletet dolgoztunk ki a MgB2 szervetlen szupravezető vezetési elektron spin élettartamára, ami alapvető fizikai mennyiség. Befejeztük egy, a magas hőmérsékletű szupravezetéshez közel álló kuprát rendszer mágneses fázis diagramjának meghatározását. Az ET2Cu[N(CN)2]Cl réteges szerves gyenge ferromágnes rezonancia módusainak feltérképezésével egy régóta megfejthetetlen problémát oldottunk meg egy, a szupravezetés és mágnesség határán lévő anyagra. A Parmai Egyetem (Olaszország) és a Cambridge-i Egyetem (Nagy Britannia) kutatóival együttműködve megmutattuk, hogy a Li4C60 fullerén vegyület egy ionos vezető, amely alkalmazható lehet elektromos telepekben. Az eredményeket magas impaktú tudományos folyóiratokban közöltük. A munka két PhD tézis alapjául szolgált. Az ESR spektrumok fejlődése megújította az érdeklődést a módszer iránt. A nagy frekvenciás ESR spektrométert felújítottuk, új kvázi-optikai hidat, nagyteljesítméníű mm-hullámú forrást, mérőfejeket és egy rezgésmentes tartószerkezetet helyeztünk üzembe. Az érzékenységet egy nagyságrenddel megnöveltük. | The aim of the project was an electron spin resonance investigation of solids in which electron-electron correlations are of fundamental importance. The cuprate, organic and fullerene compounds investigated are metals, superconductors or magnetically ordered systems related to superconductivity in which electron correlations play an essential role. We measured and proposed a theory of the conduction electron spin life time in an inorganic superconductor, MgB2. We completed work on the magnetic phase diagram of a cuprate system close to high temperature superconductivity. The mapping of the magnetic resonance modes of a layered organic weak ferromagnet, ET2Cu(N(CN)2)Cl, solved a long standing problem of a material at the borderline of magnetic order and superconductivity. We showed, in collaboration with researchers at the University of Parma (Italy) and University of Cambridge (UK) that the fullerene compound, Li4C60 is a crystalline superionic conductor with possible applications in electrical batteries. Results were published in high impact scientific journals. The work served the basis for the completion of two PhD thesis. The recent progress of high frequencies ESR spectrometers has renewed interest in the method. The high frequency ESR spectrometer has been reconstructed, a new quasi optical bridge, a powerful mm-wave source, probe heads and a vibration free supporting structure were installed. As a result the sensitivity was increased by an order of magnitude

Comprehensive Synthesis of Monohydroxy-Cucurbit[n]urils (n=5, 6, 7, 8): High Purity and High Conversions

We describe a photochemical method to introduce a single alcohol function directly on cucurbit[n]urils (n = 5, 6, 7, 8) with conversions of the order 95-100% using hydrogen peroxide and UV light. The reaction was easily scaled up to 1 g for CB[6] and CB[7]. Spin trapping of cucurbituril radicals combined with MS experiments allowed us to get insights about the reaction mechanism and characterize CB [5], CB[6], CB[7], and C13[8] monofunctional compounds. Experiments involving O-18 isotopically labeled water indicated that the mechanism was complex and showed signs of both radical and ionic intermediates. DFT calculations allowed estimating the Bond Dissociation Energies (BDEs) of each hydrogen atom type in the CB series, providing an explanation of the higher reactivity of the "equatorial" C-H position of CB[n] compounds. These results also showed that, for CB [8], direct functionalization on the cucurbituril skeleton is more difficult because one of the methylene hydrogen atoms (H-b) has its BDE lowering within the series and coming close to that of H-c, thus opening the way to other types of free radicals generated on the CB[8] skeleton leading to several side products. Yet CB[5]-(OH)(1) and CB[8]-(OH)(1), the first CB[8] derivative, were obtained in excellent yields thanks to the soft method presented here

Intercalation and coordination of copper(II)-2,2′-bipyridine complexes into graphite oxide

Copper-intercalated graphite oxides (GO) were prepared by adding complex solutions of cupric ions and 2,2′-bipyridine (L) ligands to exfoliated GO dispersion at pH = 7. High adsorption capacity (>140 mg Cu/g GO) was found for adsorption from equimolar solution of Cu2+ and L, while the excess of ligand results in progressively decreasing adsorbed amounts. Electron paramagnetic resonance spectra revealed two principal adsorption mechanisms: the CuL3 2 + complex undergoes ion exchange adsorption, while CuL2+ and CuL2 2 + bind to graphene oxide layers by coordination. © 2014 Elsevier Ltd. All rights reserved

Metabolic stability of superoxide adducts derived from newly developed cyclic nitrone spin traps

Reactive oxygen species are by-products of aerobic metabolism involved in the onset and evolution of various pathological conditions. Among them, the superoxide radical is of special interest as the origin of several damaging species such as H2O2, hydroxyl radical, or peroxynitrite (ONOO-). Spin trapping coupled with ESR is a method of choice to characterize these species in chemical and biological systems and the metabolic stability of the spin adducts derived from reaction of superoxide and hydroxyl radicals with nitrones is the main limit to the in vivo application of the method. Recently, new cyclic nitrones bearing a triphenylphosphonium or permethylated β-cyclodextrin moiety have been synthesized and their spin adducts demonstrated increased stability in buffer. In this article, we studied the stability of the superoxide adducts of four new cyclic nitrones in the presence of liver subcellular fractions and biologically relevant reductants using an original setup combining a stopped-flow device and an ESR spectrometer. The kinetics of disappearance of the spin adducts were analyzed using an appropriate simulation program. Our results highlight the interest of the new spin trapping agents CD-DEPMPO and CD-DIPPMPO for specific detection of superoxide with high stability of the superoxide adducts in the presence of liver microsomes. © 2013 Elsevier Inc. All rights reserved

ESR study of the spin adducts of three analogues of DEPMPO substituted at C-4 or C-3

In the research program of some new derivatives of spin-trap DEPMPO (5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide) leading to various radical adducts with photogenic ESR signals, three phosphorylated pyrroline-N-oxides were studied in spin trapping. These nitrones were proved to trap a variety of free radicals to afford adducts presenting characteristic ESR signals enabling unambiguous identification of the radical species trapped. From the general patterns of the signals, the adduct geometries were determined. Two of the nitrones bore a hydroxylmethyl substituent (HM) on the pyrroline ring, either at C-3 or at C-4. The two diastereoisomers of nitrone 4-HMDEPMPO, whose synthesis has been already described, were separately studied. The isomer (4R*,5R*) of 4-HMDEPMPO afforded stereoselectively, with superoxide or peroxyl radicals, trans adducts versus the phosphoryl group, however, they formed two rotamer sets in chemical exchange. In comparison with DEPMPO adducts, the exchanges rates of the conformer sets of 4-HMcisDEPMPO-OOH and 4-HMcisDEPMPO-(OOBu)-Bu-t were 9-fold or 2-fold smaller respectively. The eight-line signals of theses adducts were easily recognisable. The trapping of the same radicals with the other diastereoisomer (4S*,5R*)-4-HMDEPMPO or with (3S*,5R*)-3-HMDEPMPO, obtained via oxidation of a phosphorylated pyrroline, led to more complicated spectra owing to the formation of diastereoisomer adducts. The signal of each diastereoisomer adduct was simulated with two species in conformational exchange. In comparison with DEPMPO, the cis-C-4-substitution was proved to slow by 26-fold the exchange rate between the two rotamer sets of the trans superoxide adduct versus the phosphoryl group. The trans-C-3-substitution was proved to slow by 18-fold, at 223 K, the exchange rate between the two rotamer sets of the trans terbutylperoxyl adduct. The last nitrone, a bicyclic one, named MEOOPPO (6a-methyl-(6-ethoxy-5-oxa-6-oxaphospholan-6-yl)-1-pyrroline-N-oxide) was obtained directly from (4R*,5R*)-4-HMDEPMPO in basic conditions. Superoxide with the rigid MEOOPPO reacts exclusively in trans addition versus the phosphoryl group, however, the adduct obtained in aqueous buffer was not very persistent and the nitrone was partially degraded during 30 min storage. For every nitrone, the hydroxyl radical was not added stereoselectively on one ring face and some diasteroisomer adducts were obtained