Synthesis and Application of Aurophilic Poly(Cysteine) and Poly(Cysteine)-Containing Copolymers

Abstract

Abstract:The redox capacity, as well as the aurophilicity of the terminal thiol side groups, in poly(Cysteine) lend a unique characteristic to this poly(amino acid) or polypeptide. There are two major application fields for this polymer: (i) biomedical applications in drug delivery and surface modification of biomedical devices and (ii) as coating for electrodes to enhance their electrochemical sensitivity. The intended application determines the synthetic route for p(Cysteine). Polymers to be used in biomedical applications are typically polymerized from the cysteine N-carboxyanhydride by a ring-opening polymerization, where the thiol group needs to be protected during the polymerization. Advances in this methodology have led to conditions under which the polymerization progresses as living polymerization, which allows for a strict control of the molecular architecture, molecular weight and polydispersity and the formation of block copolymers, which eventually could display polyphilic properties. Poly(Cysteine) used as electrode coating is typically polymerized onto the electrode by cyclic voltammetry, which actually produces a continuous, pinhole-free film on the electrode via the formation of covalent bonds between the amino group of Cysteine and the carbon of the electrode. This resulting coating is chemically very different from the well-defined poly(Cysteine) obtained by ring-opening polymerizations. Based on the structure of cysteine a significant degree of cross-linking within the coating deposited by cyclic voltammetry can be assumed. This manuscript provides a detailed discussion of the ring-opening polymerization of cysteine, a brief consideration of the role of glutathione, a key cysteine-containing tripeptide, and examples for the utilization of poly(Cysteine) and poly(Cysteine)-containing copolymers, in both, the biomedical as well as electrochemical realm.

Polyphilicity—An Extension of the Concept of Amphiphilicity in Polymers

“…Thiophilic polymers are known and have been used since 1985 for the purification of immunoglobulins [202,203,204,205,206,207]. Also, polymers having cysteine repeat units can be considered as aurophilic, because of the strong affinity of SH-groups to gold [208]. It should be noted that the term aurophilicity has a different meaning in organic chemistry [209].…”

Secondary Structure-Driven Self-Assembly of Thiol-Reactive Polypept(o)ides

“… 54 Of note, in our case, the addition of chaotropic thiourea, freshly purified by vacuum sublimation, did not help to overcome this limitation but solely resulted in homopolymer formation ( Figure S1 ). 55 Nevertheless, as summarized in Table 1 , three sets containing four reactive amphiphilic polypept(o)ides have been prepared successfully. These polymers are characterized by comparable chain lengths of 170 and 200 for hydrophilic pSar and 10 to 44 for the hydrophobic reactive S -ethylsulfonyl-protected blocks.…”

A novel avian isolate of hepatitis E virus from Pakistan

“…The conserved serine residue in the PSAP motif found among Orthohepevirus isolates is also found in the Pak aHEV sequences, which may be a potential phosphorylation site for MAP kinase [32]. The N-terminal half of Pak aHEV ORF3 is hydrophobic, with a high proportion of cysteine residues (27.5%), which may reinforce ORF3 protein folding in the extracellular environment through disulfide bond formation when HEV virions egress the host cell, and act as metal binding motifs inside the host cell [22, 32, 33]. Pak aHEV ORF3 sequences contain unique amino acid changes S15 T, A31T, Q35H and G46D compared to other aHEV genotypes.…”