The Application of REDOR NMR to Understand the Conformation of Epothilone B.

The structural information of small therapeutic compounds complexed in biological matrices is important for drug developments. However, structural studies on ligands bound to such a large and dynamic system as microtubules are still challenging. This article reports an application of the solid-state NMR technique to investigating the bioactive conformation of epothilone B, a microtubule stabilizing agent, whose analog ixabepilone was approved by the U.S. Food and Drug Administration (FDA) as an anticancer drug. First, an analog of epothilone B was designed and successfully synthesized with deuterium and fluorine labels while keeping the high potency of the drug; Second, a lyophilization protocol was developed to enhance the low sensitivity of solid-state NMR; Third, molecular dynamics information of microtubule-bound epothilone B was revealed by high-resolution NMR spectra in comparison to the non-bound epothilone B; Last, information for the macrolide conformation of microtubule-bound epothilone B was obtained from rotational-echo double-resonance (REDOR) NMR data, suggesting the X-ray crystal structure of the ligand in the P450epoK complex as a possible candidate for the conformation. Our results are important as the first demonstration of using REDOR for studying epothilones.

Solid-state 31P NMR investigation on the status of guanine nucleotides in paclitaxel-stabilized microtubules.

Microtubule dynamics is a target for many chemotherapeutic drugs. In order to understand the biochemical effects of paclitaxel on the GTPase activity of tubulin, the status of guanine nucleotides in microtubules was investigated by (31)P cross-polarization magic angle spinning (CPMAS) NMR. Microtubules were freshly prepared in vitro in the presence of paclitaxel and then lyophilized in sucrose buffer for solid-state NMR experiments. A (31)P CPMAS NMR spectrum with the SNR of 25 was successfully acquired from the lyophilized microtubule sample. The broadness of the (31)P spectral lines in the spectrum indicates that the molecular environments around the guanine nucleotides inside tubulin may not be as crystalline as reported by many diffraction studies. Deconvolution of the spectrum into four spectral components was carried out in comparison with the (31)P NMR spectra obtained from five control samples. The spectral analysis suggested that about 13% of the nucleotides were present as GTP and 37% as GDP in the ß-tubulin (E-site) of the microtubules. It was found that most of the GDPs were present as GDP-Pi complex in the microtubules, which seems to be one of the effects of paclitaxel binding.

Nuclear magnetic resonance study of superprotonic conductor Rb4LiH3(SO4)4 single crystals.

To investigate the molecular dynamics of a Rb4LiH3(SO4)4 crystal below superionic phase transitions, we examined the temperature dependences of the NMR spectra and the spin-lattice relaxation time, T1, of the (1)H, (7)Li, and (87)Rb nuclei. The symmetry of (1)H signals resembles the Pake doublet containing a pair of dipolar-coupled protons. From the temperature dependence of T1, the activation energy of proton at high temperature is twice of those of (7)Li and (87)Rb. A striking feature was the formation of the weak hydrogen bond creating a significant influence of proton at high temperatures due to the mobility of the hydrogen-bond protons. And, we compared these data with (1)H and (7)Li results for (NH4)4LiH3(SO4)4 and K4LiH3(SO4)4 crystals, which have similar structures.

The effects of Mo doping on 0.3Li[Li0.33Mn0.67]O2·0.7Li[Ni0.5Co0.2Mn0.3]O2 cathode material.

Mo doped Li excess transition metal oxides formulated as 0.3Li[Li(0.33)Mn(0.67)]O(2)·0.7Li[Ni(0.5-x)Co(0.2)Mn(0.3-x)Mo(2x)]O(2) were synthesized using the co-precipitation process. The effects of the substitution of Ni and Mn with Mo were investigated for the density of the states, the structure, cycling stability, rate performance and thermal stability by tools such as first principle calculations, synchrotron X-ray diffraction, field-emission SEM, solid state (7)Li MAS nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), elemental mapping by scanning TEM (STEM), inductively coupled plasma atomic emission spectrometry (ICP-AES) and a differential scanning calorimeter (DSC). It was confirmed that high valence Mo(6+) doping of the Li-excess manganese-nickel-cobalt layered oxide in the transition metal enhanced the structural stability and electrochemical performance. This increase was due to strong Mo-O hybridization inducing weak Ni-O hybridization, which may reduce O(2) evolution, and metallic behavior resulting in a diminishing cell resistance.

Rotational-echo double-resonance NMR distance measurements for the tubulin-bound Paclitaxel conformation.

The important anticancer drug Taxol (paclitaxel, PTX) owes its unique activity to its ability to bind to tubulin in a stoichiometric ratio and promote its assembly into microtubules. The conformation of the microtubule-bound drug has been the focus of numerous research efforts, since the inability of polymerized tubulin to form crystals precludes structure proof by X-ray crystallography. Likewise, although the alpha,beta-tubulin dimer structure has been solved by electron crystallography, the 3.7 A resolution is too low to permit direct determination of either ligand conformation or binding pose. In this article, we present experimental results from 2H{19F} REDOR NMR that provide direct confirmation that paclitaxel adopts a T-shaped conformation when it is bound to tubulin.

Investigating sorption on iron-oxyhydroxide soil minerals by solid-state NMR spectroscopy: a 6Li MAS NMR study of adsorption and absorption on goethite.

High-resolution 2H MAS NMR spectra can be obtained for nanocrystalline particles of goethite (alpha-FeOOH, particle size approximately 4-10 nm) at room temperature, facilitating NMR studies of sorption under environmentally relevant conditions. Li sorption was investigated as a function of pH, the system representing an ideal model system for NMR studies. 6Li resonances with large hyperfine shifts (approximately 145 ppm) were observed above the goethite point of zero charge, providing clear evidence for the presence of Li-O-Fe connectivities, and thus the formation of an inner sphere Li+ complex on the goethite surface. Even larger Li hyperfine shifts (289 ppm) were observed for Li+-exchanged goethite, which contains lithium ions in the tunnels of the goethite structure, confirming the Li assignment of the 145 ppm Li resonance to the surface sites.