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Class I glutaredoxins reversibly reduce glutathione- and nonglutathione disulfides with the help of reduced glutathione (GSH) using either a monothiol mechanism or a dithiol mechanism. The monothiol mechanism exclusively involves a single glutathionylated active-site cysteinyl residue, whereas the dithiol mechanism requires the additional formation of an intramolecular disulfide bond between the active-site cysteinyl residue and a resolving cysteinyl residue. While the oxidation of glutaredoxins by glutathione disulfide substrates has been extensively characterized, the enzyme-substrate interactions for the reduction of S-glutathionylated glutaredoxins or intramolecular glutaredoxin disulfides are still poorly characterized. Here we compared the thiol-specificity for the reduction of S-glutathionylated glutaredoxins and the intramolecular glutaredoxin disulfide. We show that S-glutathionylated glutaredoxins rapidly react with a plethora of thiols and that the 2nd glutathione-interaction site of class I glutaredoxins lacks specificity for GSH as a reducing agent. In contrast, the slower reduction of the partially strained intramolecular glutaredoxin disulfide involves specific interactions with both carboxylate groups of GSH at the 1st glutathione-interaction site. Thus, the dithiol mechanism of class I glutaredoxins promotes specificity for GSH as a reducing agent, which might explain the prevalence of dithiol glutaredoxins in pro- and eukaryotes.

Abstract With efficiency surpassing 25%, perovskite solar cells (PSCs) have received much attention because of their excellent potential in photovoltaic field. However, there are some challenging issues still exist which need to be addressed. One issue is that the surface/interface and grain boundaries related defects and traps could work as charge recombination centers during the device operation, compromising the charge transfer as well as the device performance. Another issue is the leakage of toxic Pb, which may cause undesired contamination to water or soil and make devices not appropriate to work outdoors. Herein, the dithiol molecule was introduced to passivate surface defects and traps as well as reduce the Pb leakage. The unsaturated Pb2+ usually acting as recombination centers could coordinate with thiol group to reduce the recombination. Meanwhile, the beneficial band bend was observed, which facilitates the interface charge transfer. Crucially, we confirmed dithiol molecule could help reduce the Pb leakage. Retarded dissolution of PbI2 into water was observed for perovskite films after dithiol treatment, which eventually contributed less Pb leakage. Overall, this study proposes a universal strategy for defects passivation and reduced lead leakage, which is promising for environmental stable optoelectronic applications.

Unreacted lead iodide is commonly believed playing an important role in the performance of perovskite solar cells (PSCs). However, the excess lead iodide acts like a double-edged blade, which hampers the long-term stability of devices. Here, we used the ethanedithiol (EDT) as the solvent to process Spiro-OMeTAD (Spiro) layer. Due to the strong coordination between EDT and Pb (II), the unreacted PbI2 at the perovskite films surface was effectively passivated, which suppressed the degradation of the perovskite layer without sacrificing the efficiency. Moreover, the hydrophobic EDT also enhanced the moisture stability of devices, thus prolonged the device lifetime. With EDT-Spiro layer, a stabilized power conversion efficiencies from 17.11% up to 19.23% was achieved in the corresponding device. More importantly, a significant enhancement of the long-term stability of PSCs was observed under the N2 atmosphere without sealing for 30 days.