Selective recognition of Ca ions using novel polymeric phenols

In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: The research described here elucidates the fundamental interactions of various cations with phenolic moieties constituting the side chains of novel copolymers. The phenolic group was chosen because similar interactions of the tyrosine (Tyr) moiety in proteins with alkaline earth cations are of particular interest for some biochemical systems where both the alkaline earth cations and the aromatic compounds are abundant. The present study has revealed the preferred binding site for our polymeric systems. The interactions of metal ions with organic ligands are of special interest to understand various biochemical processes [1–6]. The research described here elucidates the fundamental interactions of various cations with phenolic moieties constituting the side chains of novel copolymers. The phenolic group was chosen because investigations of the interactions of the tyrosine (Tyr) moiety in proteins with alkaline earth cations have been well emphasized in recent years [7–8]. Another interesting feature of phenolic groups is the presence of multiple side-chain binding sites (the π-site along with the oxygen non-bonded electrons site) [9–11]. Thus it would be interesting to know what the preferred binding sites will be for the metal ions in our polymeric system. Herein we have studied the interactions of the phenolic moiety with alkali and alkaline earth metal ions using the co-polymers 1a–c constituted by the phenols and polyethylene glycol (PEG) (Scheme 1). The polymers 1a–c were synthesized by our recently developed biocatalytic approach [12–16]. The advantage of using the PEG unit is that it confers solubility to these aromatic polyester polymers in aqueous medium. 2. Materials and methods 2.1. Materials Novozyme-435 (Candida antarctica Lipase B), an immobilized enzyme, was a gift from Novozymes Inc., Denmark, and was dried over P 2 O 5 under vacuum prior to use. Poly(ethylene glycol) was dried under vacuum for 24 h before use, and acetone was dried by distillation over fused potassium carbonate. All other chemicals and solvents were of analytical grade and were used as received unless otherwise noted. Gel permeation chromatography (GPC) was used to determine the molecular weights and molecular weight distributions, M w /M n of