Selective transport of Pb2+ and Cd2+ across a phospholipid bilayer by a cyclohexanemonocarboxylic acid-capped 15-crown-5 ether.
A cyclohexanemonocarboxylic acid-capped 15-crown-5 ether was synthesized and found to be effective as an ionophore for Pb2+ and Cd2+, transporting them across a phospholipid bilayer membrane. Transport studies were carried out using 1-palmitoyl-2-oleoyl-sn-glycerophosphatidylcholine (POPC) vesicles containing the chelating indicator 2-([2-bis(carboxymethyl)amino-5-methylphenoxy]methyl)-6-methoxy-8-bis(carboxymethyl)aminoquinoline (Quin-2). Data obtained at pH 7.0 using this system, show that the synthetic ionophore transports divalent cations with the selectivity sequence Pb2+ > Cd2+ >> Zn2+ > Mn2+ > Co2+ > Ni2+ > Ca2+ > Sr2+. Selectivity factors, based on the ratio of individual initial cation transport rates, are 280 (Pb2+/Ca2+), 62 (Pb2+/Zn2+), 68 (Cd2+/Ca2+), and 16 (Cd2+/Zn2+). Plots of log initial rate versus logM(n+) or log ionophore concentration suggest that Pb2+ and Cd2+ are transported primarily as a 1:1 cation-ionophore complex, but that complexes with other stoichiometries may also be present. The ionophore transports Pb2+ and Cd2+ by a predominantly electrogenic mechanism, based upon an enhanced rate of transport that is produced by agents which dissipate transmembrane potentials. The rate of Pb2+ transport shows a biphasic pH dependence with the maximum occurring at pH approximately 6.5. The high selectivity for Pb2+ and Cd2+ displayed by the cyclohexanecarboxylic acid-capped 15-crown-5 ether suggests potential applications of this ionophore for the treatment of Pb and Cd intoxication, and removal of these heavy metals from wastewater.
Department of Molecular and Cellular Biochemistry, The Ohio State University, Columbus, OH 43210, United States.
Shawn A
SA
Hamidinia
Gregory E
GE
Steinbaugh
Warren L
WL
Erdahl
Richard W
RW
Taylor
Douglas R
DR
Pfeiffer
D002104:Cadmium / Q000737:chemistry* / Q000378:metabolism; D002413:Cations, Divalent / Q000737:chemistry; D043844:Crown Ethers / Q000737:chemistry*; D003509:Cyclohexanecarboxylic Acids / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D015759:Ionomycin / Q000737:chemistry; D007476:Ionophores / Q000737:chemistry; D007700:Kinetics; D007854:Lead / Q000737:chemistry* / Q000378:metabolism; D008564:Membrane Potentials; D008567:Membranes, Artificial; D015394:Molecular Structure; D008985:Monensin / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry
D002413:Cations, Divalent; D043844:Crown Ethers; D003509:Cyclohexanecarboxylic Acids; D007476:Ionophores; D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D002104:Cadmium; D007854:Lead; D015759:Ionomycin; D008985:Monensin; C028694:1-palmitoyl-2-oleoylphosphatidylcholine