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.
Hamidinia
Shawn A
SA
Department of Molecular and Cellular Biochemistry, The Ohio State University, Columbus, OH 43210, United States.
Steinbaugh
Gregory E
GE
Erdahl
Warren L
WL
Taylor
Richard W
RW
Pfeiffer
Douglas R
DR
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