The complex [Ph4P]2[Cu(bdt)2] (1(red)) was synthesized by the reaction of [Ph4P]2[S2MoS2CuCl] with H2bdt (bdt = benzene-1,2-dithiolate) in basic medium. 1(red) is highly susceptible toward dioxygen, affording the one electron oxidized diamagnetic compound [Ph4P][Cu(bdt)2] (1(ox)). The interconversion between these two oxidation states can be switched by addition of O2 or base (Et4NOH = tetraethylammonium hydroxide), as demonstrated by cyclic voltammetry and UV-visible and EPR spectroscopies. Thiomolybdates, in free or complex forms with copper ions, play an important role in the stability of 1(red) during its synthesis, since in its absence, 1(ox) is isolated. Both 1(red) and 1(ox) were structurally characterized by X-ray crystallography. EPR experiments showed that 1(red) is a Cu(II)-sulfur complex and revealed strong covalency on the copper-sulfur bonds. DFT calculations confirmed the spin density delocalization over the four sulfur atoms (76%) and copper (24%) atom, suggesting that 1(red) has a "thiyl radical character". Time dependent DFT calculations identified such ligand to ligand charge transfer transitions. Accordingly, 1(red) is better described by the two isoelectronic structures [Cu(I)(bdt2, 4S(3-,)*)](2-) ↔ [Cu(II)(bdt2, 4S(4-))](2-). On thermodynamic grounds, oxidation of 1(red) (doublet state) leads to 1(ox) singlet state, [Cu(III)(bdt2, 4S(4-))](1-).
Summary
The designed “ATCUN” motif (amino-terminal copper and nickel binding site) is a replica of naturally occurring ATCUN site found in many proteins/peptides, and an attractive platform for multiple applications, which include nucleases, proteases, spectroscopic probes, imaging, and small molecule activation. ATCUN motifs are engineered at periphery by conjugation to recombinant proteins, peptides, fluorophores, or recognition domains through chemically or genetically, fulfilling the needs of various biological relevance and a wide range of practical usages. This chemistry has witnessed significant growth over the last few decades and several interesting ATCUN derivatives have been described. The redox role of the ATCUN moieties is also an important aspect to be considered. The redox potential of designed M-ATCUN derivatives is modulated by judicious choice of amino acid (including stereochemistry, charge, and position) that ultimately leads to the catalytic efficiency. In this context, a wide range of M-ATCUN derivatives have been designed purposefully for various redox- and non-redox-based applications, including spectroscopic probes, target-based catalytic metallodrugs, inhibition of amyloid-β toxicity, and telomere shortening, enzyme inactivation, biomolecules stitching or modification, next-generation antibiotic, and small molecule activation.
SARS-CoV-2 encoded papain-like protease (PLpro) harbors a labile Zn
site
(Cys
189
–X–X–Cys
192
–X
n
–Cys
224
–X–Cys
226
)
and a classic catalytic site
(Cys
111
–His
272
–Asp
286
),
which play key roles for viral replication and hence represent
promising drug targets. In this Viewpoint, both sulfur-based
drugs and peptides-based inhibitors may block Cys residues in
the catalytic and/or Zn site of CoV-2-PLpro, leading to
dysfunction of CoV-2-PLpro and thereby halting viral
replication.
Because of the uninterrupted spread
of novel severe acute respiratory
syndrome coronavirus 2 (SARS-CoV-2) infectious disease (COVID-19)
with substantial illness and mortality rates, there is an urgent requirement
of suitable antiviral agent/therapy to control this pandemic, but
not yet established. The primary cause of SARS-CoV-2 infection is
the crosstalk between the SARS-CoV-2 and host surface receptor protein,
human angiotensin-converting enzyme 2 (hACE2), prior to cellular entry.
Hence, blocking at the initial stage of virus entry could be a promising
strategy/therapy to combat the SARS-CoV-2 infection. Many drugs as
SARS-CoV-2 blocker have been proposed. Among them, peptide-based antivirals
are one. This Viewpoint discusses the potential antiviral role and
feasibility of two classes of peptides for prevention of SARS-CoV-2
infection, where (1) a designed peptide (replication of virus binding
domain of hACE2), and (2) antimicrobial peptides (AMPs; natural and
first line host defense peptide), both may reduce virus load into
the host cell by blocking cellular surface receptors and/or disruption
of virus cell membrane at the stage of virus entry. These finding
may provide a novel antiviral therapy against COVID-19, which might
control the current global health crisis.
Simple Cu-thiolate chemistry was developed to demonstrate the presence of copper clusters with {Cu 4 S 6 }, {Cu 5 S 7 } and {Cu 6 S 4 } cores in relevance to copper-containing metallothioneins.
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