We report the generation of gas-phase riboguanosine radicals that were tagged at ribose with a fixed-charge 6-(trimethylammonium)­hexane-1-aminocarbonyl group. The radical generation relied on electron transfer from fluoranthene anion to noncovalent dibenzocrown-ether dication complexes which formed nucleoside cation radicals upon one-electron reduction and crown-ether ligand loss. The cation radicals were characterized by collision-induced dissociation (CID), photodissociation (UVPD), and UV–vis action spectroscopy. Identification of charge-tagged guanosine radicals was challenging because of spontaneous dissociations by loss of a hydrogen atom and guanine that occurred upon storing the ions in the ion trap without further excitation. The loss of H proceeded from an exchangeable position on N-7 in guanine that was established by deuterium labeling and was the lowest energy dissociation of the guanosine radicals according to transition-state energy calculations. Rate constant measurements revealed an inverse isotope effect on the loss of either hydrogen or deuterium with rate constants k H = 0.25–0.26 s–1 and k D = 0.39–0.54 s–1. We used time-dependent density functional theory calculations, including thermal vibronic effects, to predict the absorption spectra of several protomeric radical isomers. The calculated spectra of low-energy N-7-H guanine-radical tautomers closely matched the action spectra. Transition-state-theory calculations of the rate constants for the loss of H-7 and guanine agreed with the experimental rate constants for a narrow range of ion effective temperatures. Our calculations suggest that the observed inverse isotope effect does not arise from the isotope-dependent differences in the transition-state energies. Instead, it may be caused by the dynamics of post-transition-state complexes preceding the product separation.

Noncanonical nucleobases and nucleosides represent newly discovered species of relevance for DNA ionization. We report a targeted synthesis of gas-phase 9-methylene(1H)adenine cation radical (2 +• ) as a low-energy isomer of ionized 9methyladenine. Ion 2 +• showed unique collision-induced dissociation and UV−vis photodissociation action spectra that distinguished it from other cation radical isomers. Ab initio energy calculations with coupled cluster theory extrapolated to the complete basis set limit, CCSD(T)/CBS, identified cation radical 2 +• as the global energy minimum of the adenine-related C 6 H 7 N 5 +• isomers. The action spectrum of 2 +• was assigned on the basis of vibronic absorption spectra that were calculated with timedependent density functional theory for multiple vibrational configurations of thermal ions. The major dissociation of 2 +• proceeded by hydrogen loss that was elucidated by deuterium labeling at the exchangeable N-1 and NH 2 positions and C-8 position and by kinetic analysis. The dissociation involved a reversible rearrangement to intermediate dihydropteridine structures, yielding a protonated aminopteridine as the product, which was identified by multistep UV−vis action spectroscopy. We also report a computational study of related noncanonical isomers of 2′-deoxyadenosine cation radical having the radical defect at C-1′ that were found to be thermodynamically more stable than the canonical isomer in both the gas phase and aqueous solution. The noncanonical isomers were calculated to have extremely low ion−electron recombination energies of 4.42−5.10 eV that would make them dead-end hole traps if produced by DNA ionization.

This paper describes the preparation of enantioselective catalysts based on derivatives of imidazolidine-4-thione and theirs ubsequent anchoring by means of as ulfur atom on apolymeric carrier. First, we verified the catalytic activity and enantioselectivity in the Henry reactiono ft he homogeneous variants of the catalysts,i .e., the copper(II) complexeso f2 -(pyridine-2-yl)imidazolidine-4-thiones and 4-benzylsufanyl-2-(pyridine-2-yl)imidazolines themselves.I tw as found that these catalysts exhibit high enantioselectivity (up to 98% ee). Subsequently, the imidazolidine-4-thione catalysts were immobilized by anchoring to polymeric carriers based on ac opolymero fs tyrene and 4-vinylbenzylc hloride.These heterogeneous catalysts were analogously tested with regard to their catalytic activity and enantioselectivity in the Henry reaction, and more-over, the possibility of theirs eparation andr euse was studied.I tw as found that all the prepared immobilized catalysts are highly enantioselective (up to 97% ee). Their recycling ability wast ested in Henry reactiono f2 -methoxybenzaldehyde with nitromethane.I tw as found that they can be recycled more than ten times without anyd ecrease of their enantioselectivity.T herefore,t hey present ab etter means of catalysis than the original copper(II) complexes of imidazolidine-4-ones from both economic as wella s ecological points of view.T hus,s uch immobilized catalysts exhibit high applicationp otential for the asymmetric Henry reaction.Thes uspension of polymer 4-6 (300 mg) in as olution of copper(II) acetate (91 mg, 0.5 mmol) in methanol (12 mL) was stirred for 24 ha tr oom temperature.A fter filtration and washing with methanol (5 2 0mL), the catalyst was extracted in aS oxhlet extractor with methanol for 24 ha nd then dried under vacuum.

Cytidine ribonucleosides were furnished at O5′ with fixed-charge 6-trimethylammoniumhexan-1-aminecarbonyl tags and studied by UV−vis photodissociation action spectroscopy in the gas phase to probe isolated nucleobase chromophores in their neutral, protonated, and hydrogen-adduct radical forms. The action spectrum of the doubly charged cytidine conjugate showed bands at 310 and 270 nm that were assigned to the N3-and O2protonated cytosine tautomers formed by electrospray, respectively. In contrast, cytidine conjugates coordinated to dibenzo-18crown-6-ether (DBCE) in a noncovalent complex were found to strongly favor protonation at N3, forming a single-ion tautomer. This allowed us to form cytidine N3−H radicals by electron transfer dissociation of the complex and study their action spectra. Cytidine radicals showed only very weak absorption in the visible region of the spectrum for dipole-disallowed transitions to the low (A and B) excited states. The main bands were observed at 360, 300, and 250 nm that were assigned with the help of theoretical vibronic spectra obtained by time-dependent density functional theory calculations of multiple (>300) radical vibrational configurations. Collision-induced dissociations of cytidine radicals proceeded by major cleavage of the N1−C1′ glycosidic bond leading to loss of cytosine and competitive loss of N3-hydrogen atom. These dissociations were characterized by calculations of transition-state structures and energies using combined Born− Oppenheimer molecular dynamics and DFT calculations. Overall, cytidine radicals were found to be kinetically and thermodynamically more stable than previously reported analogous adenosine and guanosine radicals.

Four bacterial isolates, which produced polyunsaturated fatty acids (PUFA), were isolated from water samples of radioactive springs collected from Jáchymov spa. Jáchymov (Sankt Joachimsthal) is a city in northwestern Bohemia, where Marie and Pierre Curie isolated radium in 1898 from the mineral uraninite. To date, four springs (Agricola, Behounek, C1, and Curie) have been used for spa purposes, that is for the treatment of nervous and rheumatic disorders by constantly produced radioactive gas radon (222Rn) dissolved in the water. The radioactivity reaches 24 kBq/L. Using 16S rRNA gene sequence analysis, all four isolates were identified as members of the genus Kocuria, with two isolates designated 208 and 401 affiliated with Kocuria kristinae, while isolates 101 and 301 most likely with K. rhizophila. The content of fatty acids in polar lipids was determined by gas chromatography–mass spectrometry (GC–MS) and two PUFA, that is arachidonic and eicosapentaenoic, were identified. The position of double bonds was confirmed by GC–MS of 3‐pyridylcarbinol (formerly picolinyl) esters. We assume that all four isolates of Kocuria produce PUFA to increase the stability of cell membranes, which may be impaired by the reaction of the reactive oxygen species. These can arise, for example, because of α radiation during 222Rn decay.