Redox kinetics as a probe of the supramolecular interaction of alpha- and beta-cyclodextrins with amphiphilic nickel(II) complexes of pentaazamacrocycles bearing aliphatic tails

Host-guest interactions between alpha- and beta-cyclodextrins and nickel(II) polyazamacrocycles bearing aliphatic pendant arms (n-butyl, n-octyl and n-dodecyl) have been investigated, using redox kinetics as a probe, to estimate binding constants. Electrospray mass spectrometry shows the formation of inclusion complexes in aqueous solution. Cyclic voltammetric measurements show the cyclodextrins to have no effect on the redox potentials for the nickel( II/III) couples. Kinetics of oxidation of the nickel( II) complexes to the tervalent state exhibits rate retardation in the presence of the cyclodextrins. The outer-sphere oxidation of the nickel( II) macrocycles by aqua( 5, 5, 7, 12, 12, 14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1-acetato) nickel(III), [Ni(hmca)(OH2)](2+) obeys the rate law: Rate = k(obs)[Ni-III(hmca)(OH2)] = [k(2) + k(3)K(CD)][(NiL)-L-II][Ni-III(hmca)(OH2)]/(1 + K-CD[CD]) where k(2) is the rate constant for oxidation of the nickel(II) macrocycle in the absence of cyclodextrins, and k(3) is that for oxidation of the {NiL.CD} inclusion complex.PT: J; CR: BAR R, 1988, TRENDS BIOTECHNOL, V6, P1 BENDER ML, 1978, CYCLODEXTRIN CHEM BRESLOW R, 1998, CHEM REV, V98, P1997 BRODOVITCH JC, 1981, INORG CHEM, V20, P1667 CONNORS KA, 1987, BINDING CONSTANTS ME CONNORS KA, 1997, CHEM REV, V97, P1325 HAINES RI, 2003, CAN J CHEM, V81, P186 HAINES RI, 2003, J INCL PHENOM MACRO, V47, P25 HOLBREY JD, 1995, J CHEM SOC DA, P1769 LEHN JM, 1985, J CHEM SOC CHEM COMM, P1794 LEHN JM, 1992, J CHEM SOC CHEM COMM, P1434 LIANG XY, 2004, CHEM SOC REV, V33, P246 LINDOY LF, 1989, CHEM MACROCYCLIC LIG MIRZOIAN A, 1997, CHEM-EUR J, V3, P1052 MOROI Y, 1992, MICELLES THEORETICAL NEWKOME GR, 1998, CHEM COMMUN 0907, P1821 OGURA K, 1984, J CHEM SOC FARAD T 1, V80, P2243 SAENGER W, 1980, ANGEW CHEM INT EDIT, V19, P344 SAJI T, 1985, J CHEM SOC CHEM COMM, P865 SZEJTLI J, 1982, CYCLODEXTRINS THEIR SZEJTLI J, 1996, COMPREHENSIVE SUPRAM, V3 UMEZAWA Y, 1988, ANAL CHEM, V60, P2392 WANG Y, 1998, CHEM-EUR J, V4, P864 XU JD, 1986, INORG CHIM ACTA, V111, P61; NR: 24; TC: 0; J9: J INCL PHENOM MACROCYCL CHEM; PG: 6; GA: 158YTSource type: Electronic(1