Nuclear Magnetic Resonance Characterization of a Paramagnetic DNA-drug Complex with High Spin Cobalt; Assignment of the 1H and 31P NMR Spectra, and Determination of Electronic, Spectroscopic and Molec

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• 作者：Gochin ; Miriam
• 关键词：DNA ; chromomycin ; cobalt ; paramagnetic ; hyperfine shift ; paramagnetic relaxation ; susceptibility
• 刊名：Journal of Biomolecular NMR
• 出版年：1998
• 出版时间：1998
• 年：1998
• 卷：12
• 期：2
• 页码：243-257
• 全文大小：711 KB

文摘

The proton NMR spectrum of the ternary complex between the octamerduplex d(TTGGCCAA)2, two molecules of the drugchromomycin-A3, and a divalent cobalt ion has been assigned.Assignment procedures used standard two-dimensional techniques and reliedupon the expected NOE contacts observed in the equivalent diamagneticcomplex containing zinc. The magnetic susceptibility tensor for the cobaltwas determined and used to calculate shifts for all nuclei, aiding in theassignment process and verification. Relaxation, susceptibility, temperatureand field dependence studies of the paramagnetic spectrum enableddetermination of electronic properties of the octahedral cobalt complex. Theelectronic relaxation rate τs was determined to be 2.5± 1.5 ps; the effective isotropic g value was found to be2.6 ± 0.2, indicating strong spin-orbit coupling. The magneticsusceptibility 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 timeof 8 ns was obtained for the complex. Both macroscopic and microscopicsusceptibility measurements revealed deviations from Curie behavior over thetemperature range accessible in the study. Non-selective relaxation rateswere found to be inaccurate for defining distances from the metal center.However, pseudocontact shifts could be calculated with high accuracy usingthe dipolar shift equation. Isotropic hyperfine shifts were factored intocontact and dipolar terms, revealing that the dipolar shift predominates andthat contact shifts are relatively small.