Hydrogen selenide (H 2 Se) is a central metabolite in the biological processing of selenium for incorporation into selenoproteins, which play crucial antioxidant roles in biological systems. Despite being integral to proper physiological function, this reactive selenium species (RSeS) has received limited attention. We recently reported an early example of a H 2 Se donor (TDN1042) that exhibited slow, sustained release through hydrolysis. Here we expand that technology based on the PSe motif to develop cyclic-PSe compounds with increased rates of hydrolysis and function through well-defined mechanisms as monitored by 31 P and 77 Se NMR spectroscopy. In addition, we report a colorimetric method based on the reaction of H 2 Se with NBD-Cl to generate NBD-SeH (λ max = 551 nm), which can be used to detect free H 2 Se. Furthermore, we use TOF-SIMS (time of flight secondary ion mass spectroscopy) to demonstrate that these H 2 Se donors are cell permeable and use this technique for spatial mapping of the intracellular Se content after H 2 Se delivery. Moreover, these H 2 Se donors reduce endogenous intracellular reactive oxygen species (ROS) levels. Taken together, this work expands the toolbox of H 2 Se donor technology and sets the stage for future work focused on the biological activity and beneficial applications of H 2 Se and related bioinorganic RSeS.

Reactive sulfur species (RSS) play critical roles in diverse chemical environments. Molecules containing sulfane sulfur (S0) have emerged as key species involved in cellular redox buffering as well as RSS generation, translocation, and action. Using cucurbit[7]­uril (CB[7]) as a model hydrophobic host, we demonstrate here that S8 can be encapsulated to form a 1:1 host guest complex, which was confirmed by solution state experiments, mass spectrometry, and X-ray crystallography. The solid state structure of CB[7]/S8 shows that the encapsulated S8 is available to nucleophiles through the carbonyl portals of the host. Treatment of CB[7]/S8 with thiols results in efficient reduction of S8 to H2S in water at physiological pH. We establish that encapsulated S8 is attacked by a thiol within the CB[7] host and that the resultant soluble hydropolysulfide is ejected into solution, where it reacts further with thiols to generate soluble sulfane sulfur carriers and ultimately H2S. The formation of these intermediate is supported by observed kinetic saturation behavior, competitive inhibition experiments, and alkylative trapping experiments. We also demonstrate that CB[7]/S8 can be used to increase sulfane sulfur levels in live cells using fluorescence microscopy. More broadly, this work suggests a general activation mechanism of S8 by hydrophobic motifs, which may be applicable to proteins, membranes, or other bimolecular compartments that could transiently bind and solubilize S8 to promote reaction with thiols to solubilize and shuttle S8 back into the redox labile sulfane sulfur pool. Such a mechanism would provide an attractive manifold in which to understand the RSS translocation and trafficking.

We investigated the chemistry of singlet oxygen with a cadmium–sulfur cluster, (Me4N)2[Cd4(SPh)10]. This cluster was used as a model for cadmium–sulfur nanoparticles. Such nanoparticles are often used in conjunction with photosensitizers (for singlet oxygen generation or dye-sensitized solar cells), and hence, it is important to determine if cadmium–sulfur moieties physically quench and/or chemically react with singlet oxygen. We found that (Me4N)2[Cd4(SPh)10] is indeed a very strong quencher of singlet oxygen with total rate constants for 1O2 removal of (5.8 ± 1.3) × 108 M–1 s–1 in acetonitrile and (1.2 ± 0.5) × 108 M–1 s–1 in CD3OD. Physical quenching predominates, but chemical reaction leading to decomposition of the cluster and formation of sulfinate is also significant, with a rate constant of (4.1 ± 0.6) × 106 M–1 s–1 in methanol. Commercially available cadmium–sulfur quantum dots (“lumidots”) show similar singlet oxygen quenching rate constants, based on the molar concentration of the quantum dots.

Reactive sulfur species (RSS) play critical roles in diverse chemical environments. Molecules containing sulfane sulfur (S0) have emerged as key species involved in cellular redox buffering as well as RSS generation, translocation, and action. Using cucurbit[7]uril (CB[7]) as a model hydrophobic host, we demonstrate here that S8 can be encapsulated to form a 1:1 host guest complex, which was confirmed by solution state experiments, mass spectrometry, and X-ray crystallography. The solid state structure of CB[7]/S¬8 shows that the encapsulated S¬8 is available to nucleophiles through the carbonyl portals of the host. Treatment of CB[7]/S8 with thiols results in efficient reduction of S8 to H2S in water at physiological pH. We establish that encapsulated S8 is attacked by a thiol within the CB[7] host and that the resultant soluble hydropolysulfide is ejected into solution, where it reacts further with thiols to generate soluble sulfane sulfur carriers and ultimately H2S. The formation of these intermediate is supported by observed kinetic saturation behavior, competitive inhibition experiments, and alkylative trapping experiments. We also demonstrate that CB[7]/S8 can be used to increase sulfane sulfur levels in live cells using fluorescence microscopy. More broadly, this work suggests a general activation mechanism of S8 by hydrophobic motifs, which may be applicable to proteins, membranes, or other bimolecular compartments that could transiently bind and solubilize S8 to promote reaction with thiols to solubilize and shuttle S8 back into the redox labile sulfane sulfur pool. Such a mechanism would provide an attractive manifold in which to understand the RSS translocation and trafficking.

We investigated the effect of the cation‐π interaction on the susceptibility of a tryptophan model system toward interaction with singlet oxygen, that is, type II photooxidation. The model system consists of two indole units linked to a lariat crown ether to measure the total rate of removal of singlet oxygen by the indole units in the presence of sodium cations (i.e. indole units subject to a cation‐π interaction) and in the absence of this interaction. We found that the cation‐π interaction significantly decreases the total rate of removal of singlet oxygen (kT) for the model system, that is, (kT = 2.4 ± 0.2) × 108 m−1 s−1 without sodium cation vs (kT = 6.9 ± 0.9) × 107 m−1 s−1 upon complexation of sodium cation to the crown ether. Furthermore, we found that the indole moieties undergo type I photooxidation processes with triplet excited methylene blue; this effect is also inhibited by the cation‐π interaction. The chemical rate of reaction of the indole groups with singlet oxygen is also slower upon complexation of sodium cation in our model system, although we were unable to obtain an exact ratio due to differences of the chemical reaction rates of the two indole moieties.