Fe 3 O 4 as a magnetically reusable Fenton nanocatalyst for the oxidation of thiols to sulfonic acid and sulfides to sulfoxides and sulfones

Synthesis and conformational preferences of peptides and proteins with cysteine sulfonic acid

Cysteine sulfonic acid (Cys-SO₃H; cysteic acid) is an oxidative post-translational modification of cysteine, resulting from further oxidation from cysteine sulfinic acid (Cys-SO₂H). Cysteine sulfonic acid is considered an irreversible post-translational modification, which serves as a biomarker of oxidative stress that has resulted in oxidative damage to proteins. Cysteine sulfonic acid is anionic, as a sulfonate (Cys-SO₃^-; cysteate), in the ionization state that is almost exclusively present at physiological pH (pK_a ∼ -2). In order to understand protein structural changes that can occur upon oxidation to cysteine sulfonic acid, we analyzed its conformational preferences, using experimental methods, bioinformatics, and DFT-based computational analysis. Cysteine sulfonic acid was incorporated into model peptides for α-helix and polyproline II helix (PPII). Within peptides, oxidation of cysteine to the sulfonic acid proceeds rapidly and efficiently at room temperature in solution with methyltrioxorhenium (MeReO₃) and H₂O₂. Peptides containing cysteine sulfonic acid were also generated on solid phase using trityl-protected cysteine and oxidation with MeReO₃ and H₂O₂. Using methoxybenzyl (Mob)-protected cysteine, solid-phase oxidation with MeReO₃ and H₂O₂ generated the Mob sulfone precursor to Cys-SO₂^- within fully synthesized peptides. These two solid-phase methods allow the synthesis of peptides containing either Cys-SO₃^- or Cys-SO₂^- in a practical manner, with no solution-phase synthesis required. Cys-SO₃^- had low PPII propensity for PPII propagation, despite promoting a relatively compact conformation in ϕ. In contrast, in a PPII initiation model system, Cys-SO₃^- promoted PPII relative to neutral Cys, with PPII initiation similar to Cys thiolate but less than Cys-SO₂^- or Ala. In an α-helix model system, Cys-SO₃^- promoted α-helix near the N-terminus, due to favorable helix dipole interactions and favorable α-helix capping via a sulfonate-amide side chain-main chain hydrogen bond. Across all peptides, the sulfonate side chain was significantly less ordered than that of the sulfinate. Analysis of Cys-SO₃^- in the PDB revealed a very strong propensity for local (i/i or i/i + 1) side chain-main chain sulfonate-amide hydrogen bonds for Cys-SO₃^-, with >80% of Cys-SO₃^- residues exhibiting these interactions. DFT calculations conducted to explore these conformational preferences indicated that side chain-main chain hydrogen bonds of the sulfonate with the intraresidue amide and/or with the i + 1 amide were favorable. However, hydrogen bonds to water or to amides, as well as interactions with oxophilic metals, were weaker for the sulfonate than the sulfinate, due to lower charge density on the oxygens in the sulfonate.

Hybrid Materials Based on Imidazo[4,5-b]porphyrins for Catalytic Oxidation of Sulfides

Heterogenized metalloporphyrin catalysts for oxidation reactions are extensively explored to improve chemical production. In this work, manganese meso-tetraarylporphyrins were immobilized on hydrated mesoporous titanium dioxide (SBET = 705 m2 g−1) through carboxylate or phosphonate anchoring groups separated from the macrocycle by the 2-arylimidazole linker fused across one of the pyrrolic rings of the macrocycle. The element composition of two mesoporous hybrid materials thus obtained were investigated and the integrity of the immobilized complexes was shown by different physicochemical methods. Finally, the catalytic efficiency of the more stable material Mn(TMPIP)/TiO2 with the phosphonate anchor was evaluated in the selective oxidation of sulfides to sulfoxides by molecular oxygen in the presence of isobutyraldehyde (IBA). The heterogenized complex has shown excellent catalytic activity exhibiting a turnover (TON) of ~1100 in a single catalytic run of the sulfoxidation of thioanisole. The catalyst was successfully reused in seven consecutive catalytic cycles.

Heparin-like anticoagulant polypeptides with tunable activity: Synthesis, characterization, anticoagulative properties and clot solubilities in vitro

Due to the uncontrollable anticoagulant activity and limited source, Heparin, which is commonly used in clinical anticoagulation therapies, faces the risk of spontaneous bleeding and thrombocytopenia. Herein, a series of anionic poly(amino acid) s poly (l-Serine-ran-L-Glutamic acid-ran-L-Cysteine-SO₃) (PSEC-SO₃) were prepared by the controlled Ring Opening Polymerization (ROP) of N-Carboxyanhydrides (NCAs). The anticoagulant activities of PSEC-SO₃ can be regulated by simply adjusting the feeding ratio of monomers. In vitro tests show that these polypeptides can effectively prolong the Activated Partical Thromboplastin Time (APTT) and inhibit Factor IIa and Factor Xa, but has no significant effect on Prothrombin Time (PT) and Thrombin Time (TT), which indicates that PSEC-SO₃ mainly act on the intrinsic pathway. In summary, the activity-tunable heparin-like polypeptides are expected to have good application prospects in the anticoagulant field.