Antal Rockenbauer

Magnetic Fullerenes inside Single-Wall Carbon Nanotubes

C(59)N magnetic fullerenes were formed inside single-wall carbon nanotubes by vacuum annealing functionalized C(59)N molecules encapsulated inside the tubes. A hindered, anisotropic rotation of C(59)N was deduced from the temperature dependence of the electron spin resonance spectra near room temperature. Shortening of the spin-lattice relaxation time T(1) of C(59)N indicates a reversible charge transfer toward the host nanotubes above approximately 350 K. Bound C(59)N-C(60) heterodimers are formed at lower temperatures when C(60) is coencapsulated with the functionalized C(59)N. In the 10-300 K range, T(1) of the heterodimer shows a relaxation dominated by the conduction electrons on the nanotubes.

EPR Studies of the Binding Properties, Guest Dynamics, and Inner-Space Dimensions of a Water-Soluble Resorcinarene Capsule

Nitroxide free radicals have been used to study the inner space of one of Rebeks water-soluble capsules. EPR and (1) H NMR spectroscopy, ESI-MS, and DFT calculations showed a preference for the formation of 1:2 complexes. EPR titrations allowed us to determine binding constants (Ka ) in the order of 10(7)  M(-2) . EPR spectral-shape analysis provided information on the guest rotational dynamics within the capsule. The interplay between optimum hydrogen bonding upon capsule formation and steric strain for guest accommodation highlights some degree of flexibility for guest inclusion, particularly at the center of the capsule where the hydrogen bond seam can be barely distorted or slightly disturbed.

New Amino-Acid-Based β-Phosphorylated Nitroxides for Probing Acidic pH in Biological Systems by EPR Spectroscopy.

There is increasing interest in measuring pH in biological samples by using nitroxides with pH‐dependent electron paramagnetic resonance (EPR) spectra. Aiming to improve the spectral sensitivity (ΔaX) of these probes (i.e., the difference between the EPR hyperfine splitting (hfs) in their protonated and unprotonated forms), we characterized a series of novel linear α‐carboxy, α′‐diethoxyphosphoryl nitroxides constructed on an amino acid core and featuring an (α or α′)‐C−H bond. In buffer, the three main hfs (aN, aH, and aP) of their EPR spectra vary reversibly with pH and, from aP or aH titration curves, a two‐ to fourfold increase in sensitivity was achieved compared to reference imidazoline or imidazolidine nitroxides. The crystallized carboxylate 10 b (pKa ≈3.6), which demonstrated low cytotoxicity and good resistance to bioreduction, was applied to probe stomach acidity in rats. The results pave the way to a novel generation of highly sensitive EPR pH markers.

Synthesis and Characterization of the Perthiatriarylmethyl Radical and Its Dendritic Derivatives with High Sensitivity and Selectivity to Superoxide Radical

EPR spectroscopy, coupled with the use of tetrathiatriarylmethyl (TAM) radicals, has been a reliable method to detect the superoxide radical (O2.- ). However, the specificity and biocompatibility of TAM radicals need to be further improved. Although derivatization may overcome the drawbacks of current TAM radicals, esterification or amidation through the carboxylic groups greatly changes their redox properties and makes them inert to O2.- . Herein, the synthesis of a perthiatriarylmethyl (PST) radical and its dendritic derivatives, PST-TA and PST-NA, in which PST is covalently linked with dendrons containing three (TA) and nine (NA) carboxylic acids, respectively. The results show that PST rapidly reacts with O2.- to yield a unique quinone methide product. Dendritic modification of PST slightly decreases the reactivities of PST-TA and PST-NA, but notably increases their biostability toward various oxidoreductants. The detection limit of PST-NA to O2.- was estimated to be 2.1 nm min-1 over 60 min of detection. Importantly, PST-NA shows threefold higher sensitivity to O2.- in the presence and absence of ascorbic acid than that of the classic spin-trapping technique. In addition, the application of PST-NA to detect extracellular O2.- generation in stimulated RAW 264.7 macrophages was also explored. This study demonstrates that PST-NA has great potential for specific detection and quantitation of O2.- in extracellular sites.

The reaction of 2-(tetrazol-5-yl)alkyl ketones and of 2-(tetrazol-5-yl)alkanoic acid derivatives with lead tetraacetate. A novel method of preparation of alk-2-ynyl ketones and alk-2-ynoic acid derivatives

The majority of tetrazolylacetyl derivatives 2 and 7, when treated with lead tetraacetate in dry 1,4-dioxane at room or lower temperature, are oxidized with elimination of molecular nitrogen mainly to the corresponding alkynoyl derivatives 4 and 8, respectively. Vinylidenes (25) have been shown to be the intermediates of the reaction. The reaction does not take place when either the tetrazolyl group is N-substituted or the carbon atom separating the tetrazolyl and the carbonyl groups is disubstituted or these two groups are separated by two carbon atoms as in compound 17. The reaction offers a convenient method for the conversion of 2-cyanoacetyl derivatives into alk-2-ynoyl derivatives via intermediate tetrazolylacetyl derivatives. The 4-methoxyanilide 7o reacts differently, affording the fused heterocyclic compounds 19o and 20o.