PubMed · 6850732
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A Motycka. 1983-05-06. [The SQUID magnetometric technic].. https://pubmed.ncbi.nlm.nih.gov/6850732/
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The heteronuclear (15)N-{(1)H} NOE values are typically determined by taking the ratio of (15)N signal intensities recorded in the presence and absence of (1)H saturation prior to evolution of (15)N magnetization. Since the intensity ratio of two independent experiments is taken, complete recovery of (15)N magnetization during the scan repetition delay is critical to obtain reliable NOE values. Because it may not be practical to wait for the complete recovery of magnetization at high magnetic fields, Solomon equations may be used to correct measured NOE values. Here, based on experiments and simulations, we show that since the cross-correlation between (1)H-(15)N dipole and (15)N chemical shift anisotropy becomes significant at high fields for small or deuterated proteins, measured NOE values can not be accurately corrected based on the Solomon equations. We also discuss ranges of rotational correlation times and proton spin-flip rate, in which the NOE values can be corrected by the equations.
The mixed ligand complex [Ni(CMA)2(im)2(MeOH)2] (where CMA = 9,10-dihydro-9-oxo-10-acridineacetate ion, im = imidazole) was prepared, and its crystal and molecular structure were determined. The nickel ions are hexa-coordinated by four oxygen atoms of the carboxylate and hydroxyl groups and by two imidazole nitrogen atoms, to form a distorted octahedral arrangement. The structure consists of a one-dimensional network of the complex molecules connected by strong intermolecular hydrogen bonds. The weak intermolecular C-H...X hydrogen bonds and stacking interactions make up the 2-D structure. Very strong intramolecular hydrogen bonds significantly affect the geometry and vibrational characteristics of the carboxylate group. The UV-vis-NIR electronic spectrum was deconvoluted into Gaussian components. Electronic bands of the Ni(II) ion were assigned to suitable spin-allowed transitions in the D4h symmetry environment. The single ion zero-field splitting (ZFS) parameters for the S = 1 state of Ni(II), as well as the g components, have been determined by high-field and high-frequency EPR (HF-HFEPR) spectroscopy over the frequency range of 52-432 GHz and with the magnetic fields up to 14.5 T: D = 5.77(1) cm-1, E = 1.636(2) cm-1, gx = 2.29(1), gy = 2.18(1), and gz = 2.13(1). These values allowed us to simulate the powder magnetic susceptibility and field-dependent magnetization of the complex.
Proteins encapsulated within the aqueous core of reverse micelles are found to partially align in a magnetic field. The degree of alignment is sufficient to result in sizable residual 15N-1H dipolar couplings that can be easily measured. It is found that the magnetic susceptibility of the reverse micelle particle is not dominated by the encapsulated protein. The residual dipolar couplings are found to be structurally meaningful.