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Karstic sinkholes are peculiar structures hosting specific biological communities. Birds are still little studied in this regard. This note reports, for the first time, original data relating to the density of breeding species occurring within a sinkhole in central Italy obtained with a fine-grained and time-expensive sampling technique (mapping method). The results were compared with data sampled with the point counts method carried out in the same phenological period. We recorded 22 breeding species, all typical of meso-thermophilous forests and ecotonal habitats of hilly central Italy. Among them, two species (Turdus merula and Troglodytes troglodytes), typical of shady, undergrowth habitats, were recorded in the deepest part of the sinkhole (−70 m from the top). No significant differences emerged between the relative frequencies of the species obtained with the two methods, except for Luscinia megarhynchos (overestimated with the mapping method) and Aegithalos caudatus (underestimated). At the community level, the comparison of the two methods revealed similar values in univariate diversity metrics, Whittaker plots did not show a significant difference (ANCOVA test), and ordinary least squares regression between the frequencies showed a highly significant correlation. Therefore, in these peculiar habitats, data obtained from the two methods are comparable: since the point counts method needs lower sampling effort, it appeared to be more effective when compared to the mapping method to study these peculiar habitats. [ABSTRACT FROM AUTHOR]

Two selanyl compounds, 5-(phenylselanyl)pentanoic acid (1) and 5-(benzylselanyl)pentanoic acid (2), were investigated for their reactivity towards one-electron oxidants, particularly the radiolytically generated hydroxyl radical (˙OH). The reactions of compounds 1 and 2 with ˙OH led to the formation of transient absorptions, characterized by peak wavelengths (λmax) at 630 nm and 560 nm, respectively. Concentration-dependent absorption studies revealed that the transient from 1 with λmax of 630 nm corresponds to a dimer species featuring a two-centre–three-electron (2c–3e) bond. Conversely, the species exhibiting λmax of 560 nm for 2 was identified as a monomer radical cation. To validate the identities of these transients, compounds 1 and 2 underwent reactions with specific one-electron oxidants, namely the dibromide radical (Br2˙−) and carbonate radical anion (CO3˙−). The differences in the reactivities of the transients derived from compounds 1 and 2 were distinguished by measuring their ability to oxidize glutathione, a biologically important thiol. Interestingly, the transient from compound 2 exhibited a relatively lower oxidizing ability than the transient from compound 1. Compound 2 also demonstrated higher scavenging rate constants in reactions with Br2˙−, CO3˙−, and peroxyl radicals (derived from thermal degradation of 2,2′-azobis(2-amidinopropane) hydrochloride, AAPH). Computational calculations were carried out employing the M05-2X/6-311+G(d,p)/SMD method to offer additional proof in favor of dimer radical species during the interactions of compound 1 with ˙OH. The calculations revealed a competitive formation of both σ- and π-type dimer radicals from compound 1. However, the experimental spectrum primarily corresponded to the σ-type dimer, as indicated by the predicted λmax (630 nm) using the TDDFT method. This study shows that the benzyl-containing selanyl system is a better free radical scavenger than the phenyl-containing selanyl system, highlighting its potential as a potent free radical scavenger. [ABSTRACT FROM AUTHOR]