Period 6 element heavy metal, lead is a neurotoxin that accumulates both in soft tissues and the bones. Lead poisoning has been documented from ancient Rome, ancient Greece, and ancient China. Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent other metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead. It is a brittle metal with a silvery white color when newly made, but often seen in air with a pink tinge owing to the surface
Chemical ligation with an N-terminal Ser or Thr residue. The chemoselective reaction between the peptide SAL ester and 1,2-hydroxylamine group of Ser or Thr leads to the formation of an N,O-benzylidene acetal linked intermediate, which undergoes acidolysis to afford a natural peptidic Xaa-Ser/Thr linkage. This method does not involve the use of unnatural amino acids, and it is simple to operate. Ser/Thr ligation provides a complementary method for protein chemical synthesis and semisynthesis. Schnölzer M, Kent SB. 1992, "Constructing proteins by dovetailing unprotected synthetic peptides: backbone-engineered HIV protease." "Science". 256:221-5 Dawson PE, Muir TW, Clark-Lewis I, Kent SB. 1994, "Synthesis of proteins