•Coarse and fine NH4-illite clay fractions•Crystal size effect on B and Li isotopic composition•Boron and lithium isotopes of NH4, K-illite: magmatic fluid source•Lithium isotope of fine NH4-illite-smectite clay fraction: magmatic fluid source•Boron, lithium and nitrogen isotopes of NH4-illite-smectite: organic sedimentary sourceCoarse (2.0–0.2 μm) and fine (< 0.2 μm) clay fractions of NH4-illite-smectite (I-S) mixed-layered and K-illite/(NH4, K)-illite (I) mixed phases that vary in age and trace element composition were collected from the fossil hydrothermal system of Harghita Bãi, East Carpathians. Boron and Li isotope ratios were measured by secondary ion mass spectrometry (SIMS), and N by isotope ratio mass spectrometry (IRMS) with the aim to characterize the isotope geochemistry and source of light elements fixed in authigenic NH4-illitic clays.Boron in NH4-I-S clays ranges from 513 to 1457 ppm and reached ~ 1000 ppm in the K-I/(NH4, K)-I. The δ11B (‰) measured in NH4-I-S ranges from − 12.6 to − 22.4 (± 0.3‰) and in K-I/(NH4, K)-I is consistently − 5.5 to − 5.1 (± 0.3‰). Boron isotopes systematically become lighter in the NH4-I-S series as temperature increased from 90 to 270 °C. Low Li content (1 to 8 ppm) was found in illitic clay fractions. The δ7Li (‰) shows negative values ranging from − 8.6 to − 12.3 (± 0.8‰) for the coarser (2.0–0.2 μm) NH4-I-S clays and from + 4.3 to + 14.1 (± 1‰) for the finer (< 0.2 μm) fraction of NH4-I-S and K-I/(NH4, K)-I clays. The N (%) measured in the NH4-I-S clays ranges from 0.70 to 1.50 (± 0.2%), whereas in the K-I/(NH4, K)-I is about 0.70 (± 0.2%). The δ15N (‰) ranges from + 4.8 to + 7.4 (± 0.6) for most NH4-I-S and NH4, K-I clays, with one outlier for NH4-I-S of + 14.6 (± 0.6).The δ11B of K-I/(NH4, K)-I clays reflect a magmatic source, whereas the NH4-I-S series is consistent with the influx of isotopically light-B waters derived from hydrothermal leaching of continental evaporites and/or organic-rich sediments. The δ7Li signature measured on K-I/(NH4, K)-I clays also support a magmatic fluid, enriched in heavy Li, followed by precipitation of coarser NH4-I-S from more recent sedimentary contributions of isotopically light Li. This interpretation is also supported by the δ15N, which reflect an influx of waters from an organic sediment origin. The δ15N of + 14.6‰ (± 0.6) measured on NH4-I-S could be attributed to the presence of meteoric waters mixed with hydrothermal fluids. The isotopic data obtained trace the mobility of magmatic and organic – sedimentary components in the upper continental crust.

Hydrothermal organic transformations under geochemically relevant conditions can result in complex product mixtures that form via multiple reaction pathways. The hydrothermal decomposition reactions of the model ketone dibenzyl ketone form a mixture of reduction, dehydration, fragmentation, and coupling products that suggest simultaneous and competitive radical and ionic reaction pathways. Here we show how Norrish Type I photocleavage of dibenzyl ketone can be used to independently generate the benzyl radicals previously proposed as the primary intermediates for the pure hydrothermal reaction. Under hydrothermal conditions, the benzyl radicals undergo hydrogen atom abstraction from dibenzyl ketone and para-coupling reactions that are not observed under ambient conditions. The photochemical method allows the primary radical coupling products to be identified, and because these products are generated rapidly, the method also allows the kinetics of the subsequent dehydration and Paal–Knorr cyclization reactions to be measured. In this way, the radical and ionic thermal and hydrothermal reaction pathways can be studied separately.

Chemical analyses of E. coli killed by aqueous leachates of an antibacterial clay show that intracellular concentrations of Fe and P are elevated relative to controls. Phosphorus uptake by the cells supports a regulatory role of polyphosphate or phospholipids in controlling Fe2+. Fenton reaction products can degrade critical cell components, but we deduce that extracellular processes do not cause cell death. Rather, Fe2+ overwhelms outer membrane regulatory proteins and is oxidized when it enters the cell, precipitating Fe3+ and producing lethal hydroxyl radicals.