Abstract
Low frequency (S-band) EPR and electron nuclear double resonance (ENDOR) data have been used to provide a detailed description of the magnetic environment of the cupric complex of the antitumor antibiotic, bleomycin. S-band EPR spectra show well resolved nitrogen hyperfine structure in both gl and g regions. Computer simulation of these spectra are consistent with binding to four donor nitrogen atoms, three with AN = 10 gauss and one with AN = 15 G. ENDOR data confirm the presence of at least two inequivalent nitrogens with AN approximately 11 and 15 G. In addition, at least six proton couplings were evident in the ENDOR spectrum although these could not be unambiguously assigned. Diminution of the matrix ENDOR signal in D2O relative to that in H2O was found; this demonstrates the accessibility of H2O to the metal site.
Highlights
Double resonance (ENDOR) data have been used to spectra arepoorly resolved because of a multitude of nitrogen provide a detailed description.of the magneticenviron- and protoncouplings which result in broadEPR spectra
Nitrogen and proton couplings, as well as nitrogen quadrupole interactions have been measured for cupric complexes usingENDOR spectroscopy [17,18,19]
Recent S-band EPR studies havuetilized enhanced resolution of the m1 = -112 component in thegl region to determine nitrogen couplings for cupriccomplexes [20,21,22,23,24,25]. This increase in resolution canbe attributed toa narrowing of the linewidth for the ml = -1/2 component due to cancellation of a microwave frequency and a m1-dependent term in theexpression for the line width [20,25]. Using these techniqueswhich improve the resolution of EPR parameters, this study addresses the problem of whether three or four in-plane nitrogens from bleomycin are boundto cupric ion
Summary
S-band EPR spectra show well resolved nitrogen hyperfine structure in both gl and g, regions. Recent S-band EPR studies havuetilized enhanced resolution of the m1 = -112 component in thegl region to determine nitrogen couplings for cupriccomplexes [20,21,22,23,24,25]. Using these techniqueswhich improve the resolution of EPR parameters, this study addresses the problem of whether three or four in-plane nitrogens from bleomycin are boundto cupric ion.
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