Post-transition metal packing structure. Tin forms Zintl phases such as NaSn, BaSn, KSn and CaSn. It has good corrosion resistance in air on account of forming a thin protective oxide layer. Pure tin has no structural uses. It is used in lead-free solders, and as a hardening agent in alloys of other metals, such as copper, lead, titanium and zinc. Lead is a soft metal (MH 1.5, but hardens close to melting) which, in many cases, is unable to support its own weight. It has a close-packed structure (BCN 12) but an abnormally large inter-atomic distance that has been attributed to partial
C-rich stability element been mapped to a pyrimidine-rich segment of its 3' UTR. This region confers stability by directing the assembly of a specific alpha ribonucleoprotein complex at this site. Subsequently Holcik and Liebhaber identified three other highly stable eukaryotic mRNAs that assemble the alpha globin protein complex at homologous pyrimidine-rich regions within their 3'UTRs (rabbit lipoxygenase, rat tyrosine hydroxylase, and human alpha(I)-collagen). There is some debate as to the number and identity of trans-acting factors recruited to the C-rich element. However the alpha globin poly(C)-binding protein (alphaCP) is agreed to be the core constituent of what is known as the alpha complex.