ISSN:
1573-5001
Keywords:
DNA
;
chromomycin
;
cobalt
;
paramagnetic
;
hyperfine shift
;
paramagnetic relaxation
;
susceptibility
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract The proton NMR spectrum of the ternary complex between the octamer duplex d(TTGGCCAA)2, two molecules of the drug chromomycin-A3, and a divalent cobalt ion has been assigned. Assignment procedures used standard two-dimensional techniques and relied upon the expected NOE contacts observed in the equivalent diamagnetic complex containing zinc. The magnetic susceptibility tensor for the cobalt was determined and used to calculate shifts for all nuclei, aiding in the assignment process and verification. Relaxation, susceptibility, temperature and field dependence studies of the paramagnetic spectrum enabled determination of electronic properties of the octahedral cobalt complex. The electronic relaxation rate τs was determined to be 2.5 ± 1.5 ps; the effective isotropic g value was found to be 2.6 ± 0.2, indicating strong spin-orbit coupling. The magnetic susceptibility tensor was determined to be χxx = 8.9 * 10-3 cm3/mol, χyy = 9.5 * 10-3 cm3/mol, χzz = 12.8 * 10-3 cm3/mol. A tentative rotational correlation time of 8 ns was obtained for the complex. Both macroscopic and microscopic susceptibility measurements revealed deviations from Curie behavior over the temperature range accessible in the study. Non-selective relaxation rates were found to be inaccurate for defining distances from the metal center. However, pseudocontact shifts could be calculated with high accuracy using the dipolar shift equation. Isotropic hyperfine shifts were factored into contact and dipolar terms, revealing that the dipolar shift predominates and that contact shifts are relatively small.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1008289724077
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