Bio-inspired crystal growth induced by novel organic compounds

The growth of biogenic inorganic crystals demands much attention given the exceptional control of nucleation and growth that is evidenced in biological systems. In many cases the biological mineralization products are crystals engineered to express unique forms and habits; this being linked to the bio-function of minerals. It is acknowledged that the formation of these biogenic minerals is controlled by a complex directory of organic macromolecules which are chemically tailored to mediate the crystallization sequelae. In this study, an homologous series of sulphonated calix[4]arenes (further modified by the addition of an alkyl substituent (R = (CH₂)_nCH₃; n = 0-7)) were selected as chemical and structural mimics for some of the active components in the acidic macromolecules known to be associated with many biogenic mineral phases. Here, these calix[4]arenes were assayed for their ability to control the growth of barium sulphate. Their presence in the crystallization liquor induced the twinning of the barium sulphate crystals; two forms of twinning were observed. Interpenetrant (2-31) twins were noted for substituted calix[4]arenes when R = (CH₂)₂CH₃; and interpenetrant {610} twins when R = (CH₂)_nCH₃; n = 0-7. When R = (CH₂)_nCH₃; n = 0 or 1, the crystals also evidenced a novel acicular growth form. These effects were linked to the chemical properties of the calixarenes and structural recognition motifs created at the calix[4]arene/barium sulphate interface following the adsorption of these sulphonated moieties onto the nascent crystals. The results offer an insight into the mechanisms which may mediate such effects in vivo.