The
bioavailable iron is essential for all living organisms, and
the dissolution of iron oxide contained in dust and soil is one of
the major sources of bioavailable iron in nature. Iodine in the polar
atmosphere is related to ozone depletion, mercury oxidation, and cloud
condensation nuclei formation. Here we show that the chemical reaction
between iron oxides and iodide (I–) is markedly
accelerated to produce bioavailable iron (Fe(II)aq) and
tri-iodide (I3
–: evaporable in the form
of I2) in frozen solution (both with and without light
irradiation), while it is negligible in aqueous phase. The freeze-enhanced
production of Fe(II)aq and tri-iodide is ascribed to the
freeze concentration of iron oxides, iodides, and protons in the ice
grain boundaries. The outdoor experiments carried out in midlatitude
during a winter day (Pohang, Korea: 36°0′ N, 129°19′
E) and in an Antarctic environment (King George Island: 62°13′
S 58°47′ W) also showed the enhanced generation of Fe(II)aq and tri-iodide in ice. This study proposes a previously
unknown abiotic mechanism and source of bioavailable iron and active
iodine species in the polar environment. The pulse input of bioavailable
iron and reactive iodine when ice melts may influence the oceanic
primary production and CCN formation.
This study reports an energy-resolved mass spectrometric (ERMS) strategy for the characterization of position isomers derived from the reaction of hydroxyl radicals ((●)OH) with diphenhydramine (DPH) that are usually hard to differentiate by other methods. The isomer analogues formed by (●)OH attack on the side chain of DPH are identified with the help of a specific fragment ion peak (m/z 88) in the collision-induced dissociation (CID) spectrum of the protonated molecule. In the negative ion mode, the breakdown curves of the deprotonated molecules show an order of stability (supported by density functional theory (DFT) calculations) ortho > meta > para of the positional isomers formed by the hydroxylation of the aromatic ring. The gas phase stability of the deprotonated molecules [M - H](-) towards the benzylic cleavage depends mainly on the formation of intramolecular hydrogen bonds and of the mesomeric effect of the phenol hydroxyl. The [M - H](-) molecules of ortho and meta isomers result a peak at m/z 183 with notably different intensities because of the presence/absence of an intramolecular hydrogen bonding between the OH group and C9 protons. The ERMS approach discussed in this report might be an effective replacement for the conventional methods that requires very costly and time-consuming separation/purification methods along with the use of multi-spectroscopic methods.
The freezing-enhanced dissolution
of iron oxides by various ligands
has been recently proposed as a new mechanism that may influence the
supply of bioavailable iron in frozen environments. The ligand-induced
dissolution of iron oxides is sensitively affected by the kind and
concentration of ligands, pH, and kind of iron oxides. While most
ligands are thought to be freeze-concentrated in the ice grain boundary
region along with iron oxides to enhance the iron dissolution, this
study found that some ligands, such as ascorbic acid, suppress the
iron dissolution in frozen solution relative to that in aqueous solution.
Such ligands are proposed to be preferentially incorporated in the
ice lattice bulk and not freeze-concentrated in the liquid-like grain
boundary. The experimental analysis estimated that the ionized forms
of ligands (e.g., iodide ions) are hardly present in the ice bulk
region (<3%) and enhance the iron dissolution in frozen solution
(relative to that in aqueous solution), whereas some neutral ligands
(e.g., undissociated ascorbic acid) are significantly trapped in the
ice bulk (>50%) and suppress the iron dissolution compared to the
aqueous counterpart. The present results reveal that the ligand-induced
dissolution of iron oxide in frozen solution is not always enhanced
relative to aqueous solution but depends upon the kind of ligand and
experimental conditions.
The (●)OH-induced reactions of both lawsone and juglone result in the mono and di-hydoxylated derivatives. The demonstration of the various isomeric products using mass spectrometry is a clear proof of the addition probability of (●)OH at different positions of lawsone and juglone, which is generally a difficult task using other analytical techniques.
Mechanistic aspects of diphenhydramine (DPH) oxidation induced by hydroxyl (•OH) and sulfate (SO4•−) radicals have been explored in detail by pulse radiolysis technique and high resolution mass spectrometry (HRMS). The transient absorption spectrum along with HRMS analysis undoubtedly established the non‐position selective hydroxylation of DPH by •OH (a; k2 = (1.08 ± 0.06) × 1010 dm3 mol−1 s−1; λmax: 335 nm) led to various transformation products (i ‐ vii) including isomeric mono (Ia‐d), di (IIa‐c) and tri (VIIa‐e) hydroxylated analogues. On the other hand, SO4•− (specific one electron oxidant) ultimately generates another hydroxylated adduct radical ‘c’ λmax: 330 nm, k2=(5.70 ± 0.03) × 109dm3 mol−1 s−1) which is formed as a result of preferential hydroxylation of initially formed radical cation ‘b’ at ipso position. The mechanism leading to the formation of various transformation products induced by •OH and SO4•− are thoroughly discussed. The mechanistic findings obtained from our studies (especially in the case of less investigated oxidant like SO4•−) are capable to enrich the fundamental understanding on environmentally relevant reactions initiated by •OH and SO4•−.
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