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David W. Boykin - One of the best experts on this subject based on the ideXlab platform.

  • Applications of 17O NMR Spectroscopy to Natural Products Chemistry
    Structure and Chemistry (Part D), 1995
    Co-Authors: David W. Boykin
    Abstract:

    Publisher Summary 17O NMR Spectroscopy is emerging as a useful adjuvant to other spectroscopic methodologies for acquiring structural information. Oxygen, the most abundant element on earth, widely occurs in many types of natural products. Detection of oxygen by NMR Spectroscopy can be achieved for the l7O isotope. However, by use of modern instrumentation and wise choices of experimental conditions (pulse repetition time, solvent, temperature, and concentration), spectra with acceptable signal-to-noise ratio can be obtained generally in less than four hours (and often in less than one hour) for molecules with molecular weights of less than 300. Even though most of the relationships developed between structure and 170 NMR chemical shifts are empirical they are valuable predictive tools. Increasing interest in and the study of the origins of l7O NMR chemical shifts should place these relationships on a more solid theoretical foundation in the years ahead. The rapid growth in numbers of publications that apply 17O NMR Spectroscopy to natural product problems clearly indicates the growing importance of this methodology to the field.

  • 17O NMR Spectroscopy: intramolecular hydrogen bonding in 7-hydroxyindanones
    Journal of Molecular Structure, 1993
    Co-Authors: David W. Boykin, Arvind Kumar
    Abstract:

    Abstract Natural abundance 17O NMR chemical shift data for seven substituted indanones including four hydroxyindanones, three fluorenones including two hydroxyfluorenones, and seven 2-methyleneindanones including four hydroxymethyleneindanones, at 75°C in acetonitrile are reported. The hydroxyindanones, the one hydroxyfluorenone and the hydroxymethyleneindanones capable of intramolecular hydrogen bonding exhibit carbonyl 17O NMR signals which are shielded relative to those incapable of intramolecular hydrogen bonding. The intramolecular hydrogen bonding component (ΔδHB) of the carbonyl 17O NMR chemical shift was determined to be 9.8 ± 1.2 and 10.9 ± 1.4 ppm for the hydroxyindanones and the hydroxymethyleneindanones, respectively. The small ΔδHB values for these hydroxyindanones relative to other ketone systems (about 50 ppm) are discussed in terms of molecular mechanics calculated hydrogen bond geometry.

  • 17O NMR Spectroscopy: Study of intramolecular hydrogen bonding in phenols and salicylaldehydes
    Magnetic Resonance in Chemistry, 1993
    Co-Authors: David W. Boykin, S. Chandrasekaran, Alfons L. Baumstark
    Abstract:

    Natural abundance 17O NMR data for fifteen 2- and 4-substituted phenols, ten 3-and 5-substituted 2-hydroxybenzaldehydes and eight 3-substituted benzaldehydes, recorded at 75°C in acetonitrile are reported. The chemical shift change due to intramolecular hydrogen bonding for the phenolic oxygen was found to be 10–14 ppm shielding. In acetonitrile, the 17O NMR chemical shift for phenol signals was insensitive to added water up to water concentrations of 0.5 mole fraction. The 17O NMR chemical shifts of the 4-substituted phenols gave an excellent correlation (r = 0.990) with anisole 17O NMR data; the data also correlated moderately well with σ− (r = 0.974). The chemical shifts of the 3-substituted benzaldehydes were correlated with σ+ values (r = 0.991). A plot of the carbonyl chemical shift data for the substituted 2-hydroxybenzaldehydes versus the carbonyl data for 3-substituted benzaldehydes gave a slope of 0.87 and with r = 0.960. The plot of the 4-substituted phenol data with that for OH of the corresponding 2-hydroxybenzaldehydes gave a slope of 1.04 with r = 0.996. Proton to oxygen coupling for the phenolic group of several of the intramolecular hydrogen bonded systems was observed directly [J(OH) = 58–92 Hz]. MM2 and MOPAC calculations predict that the hydrogen bond distances and angles for the substituted 2-hydroxybenzaldehydes and the partial atomic charges for the carbonyl groups (AMI) were essentially constant. After corrections for electronic effects the chemical shift changes due to hydrogen bonding for the donor (ΔδHBD) and acceptor (ΔδHBA) of the carbonyl–phenol intramolecular bonding system were 5–12 and 30 ± 2 ppm, respectively. The ΔδHBA value was between those for keto and ester acceptors consistent with the relative basicity of the aldehyde group. The ΔδHBD value was substantially larger than those for phenolic donors to keto and ester groups.

  • 17O NMR Spectroscopy proton oxygen coupling in simple alcohols at natural abundance
    Heteroatom Chemistry, 1992
    Co-Authors: S. Chandrasekaran, David W. Boykin
    Abstract:

    17O NMR data are reported for 3-pentanol (1), cyclopentanol (2), cyclohexanol (3), and cycloheptanol (4). The 17O NMR signals for 1–4 appeared as doublets, shown to arise from proton–oxygen coupling (1JOH = 76 ± 3 Hz) by proton decoupling experiments. The effect of concentration, temperature, and solvent was examined in detail for 2. Proton—oxygen coupling was observed at low concentrations, decreased at lower temperatures, and was sensitive to solvent.

  • 17O NMR Spectroscopy: Intramolecular hydrogen bonding in hydroxypyridine carboxy esters
    Journal of Heterocyclic Chemistry, 1992
    Co-Authors: David W. Boykin, Arvind Kumar
    Abstract:

    Natural abundance 17O NMR chemical shift data for 8 aryl esters and 10 pyridine carboxy esters, including 6 ortho-hydroxy esters, recorded in acetomitrile at 75° are reported. The carbonyl group 17O NMR chemical shift data for methyl 2-, 3- and 4-pyridinecarboxylate are correlated with σ+ constants. The hydrogen bonding component (ΔδHB) to the ester carbonyl 17O NMR chemical shift for the intramolecular hydrogen bonded ortho-hydroxy systems are 9.8 ppm, 13.6 ppm and 4.3 ppm for benzoates, 2-pyridinecarboxylates and 4-pyridinecarboxylates, respectively. The relationships of the ester ΔδHB values to other hydrogen bond acceptor ΔδHB values are discussed.

Frederic W. Patureau - One of the best experts on this subject based on the ideXlab platform.

Jianfeng Zhu - One of the best experts on this subject based on the ideXlab platform.

  • Quadrupole Central Transition 17O NMR Spectroscopy of Biological Macromolecules in Aqueous Solution
    Journal of the American Chemical Society, 2010
    Co-Authors: Jianfeng Zhu
    Abstract:

    We demonstrate a general nuclear magnetic resonance (NMR) spectroscopic approach in obtaining high-resolution 17O (spin-5/2) NMR spectra for biological macromolecules in aqueous solution. This approach, termed quadrupole central transition (QCT) NMR, is based on the multiexponential relaxation properties of half-integer quadrupolar nuclei in molecules undergoing slow isotropic tumbling motion. Under such a circumstance, Redfield’s relaxation theory predicts that the central transition, mI = +1/2 ↔ −1/2, can exhibit relatively long transverse relaxation time constants, thus giving rise to relatively narrow spectral lines. Using three robust protein−ligand complexes of size ranging from 65 to 240 kDa, we have obtained 17O QCT NMR spectra with unprecedented resolution, allowing the chemical environment around the targeted oxygen atoms to be directly probed for the first time. The new QCT approach increases the size limit of molecular systems previously attainable by solution 17O NMR by nearly 3 orders of mag...

  • Solid‐State 17O NMR Spectroscopy of Large Protein–Ligand Complexes
    Angewandte Chemie (International ed. in English), 2010
    Co-Authors: Jianfeng Zhu, Victor V. Terskikh
    Abstract:

    Peer reviewed: YesNRC publication: Ye

  • Quadrupole-Central-Transition 17O NMR Spectroscopy of Protein-Ligand Complexes in Solution
    Journal of the American Chemical Society, 2009
    Co-Authors: Jianfeng Zhu, Irene C. M. Kwan
    Abstract:

    We report the first 17O quadrupole-central-transition (QCT) NMR spectroscopic study of protein−ligand complexes in solution. This work shows that it is possible to obtain high resolution 17O NMR spectra for 17O-labeled ligands bound to proteins. At high magnetic fields such as 21.14 T, this 17O QCT NMR approach should be applicable to studies of all oxygen-containing functional groups in large proteins (>30 kDa).

Ivan Hung - One of the best experts on this subject based on the ideXlab platform.

  • Functional stability of water wire-carbonyl interactions in an ion channel.
    Proceedings of the National Academy of Sciences of the United States of America, 2020
    Co-Authors: Joana Paulino, Ivan Hung, Xiaoling Wang, Zhehong Gan, Eduard Y. Chekmenev, Huan-xiang Zhou, Timothy A. Cross
    Abstract:

    Water wires are critical for the functioning of many membrane proteins, as in channels that conduct water, protons, and other ions. Here, in liquid crystalline lipid bilayers under symmetric environmental conditions, the selective hydrogen bonding interactions between eight waters comprising a water wire and a subset of 26 carbonyl oxygens lining the antiparallel dimeric gramicidin A channel are characterized by 17O NMR Spectroscopy at 35.2 T (or 1,500 MHz for 1H) and computational studies. While backbone 15N spectra clearly indicate structural symmetry between the two subunits, single site 17O labels of the pore-lining carbonyls report two resonances, implying a break in dimer symmetry caused by the selective interactions with the water wire. The 17O shifts document selective water hydrogen bonding with carbonyl oxygens that are stable on the millisecond timescale. Such interactions are supported by density functional theory calculations on snapshots taken from molecular dynamics simulations. Water hydrogen bonding in the pore is restricted to just three simultaneous interactions, unlike bulk water environs. The stability of the water wire orientation and its electric dipole leads to opposite charge-dipole interactions for K+ ions bound at the two ends of the pore, thereby providing a simple explanation for an ∼20-fold difference in K+ affinity between two binding sites that are ∼24 A apart. The 17O NMR Spectroscopy reported here represents a breakthrough in high field NMR technology that will have applications throughout molecular biophysics, because of the acute sensitivity of the 17O nucleus to its chemical environment.

  • High-Resolution 17O NMR Spectroscopy of Structural Water.
    The journal of physical chemistry. B, 2019
    Co-Authors: Eric G. Keeler, Vladimir K. Michaelis, Christopher B. Wilson, Ivan Hung, Xiaoling Wang, Zhehong Gan, Robert G. Griffin
    Abstract:

    The importance of studying site-specific interactions of structurally similar water molecules in complex systems is well known. We demonstrate the ability to resolve four distinct bound water environments within the crystal structure of lanthanum magnesium nitrate hydrate via 17O solid state nuclear magnetic resonance (NMR) Spectroscopy. Using high-resolution multidimensional experiments at high magnetic fields (18.8-35.2 T), each individual water environment was resolved. The quadrupole coupling constants and asymmetry parameters of the 17O of each water were determined to be between 6.6 and 7.1 MHz, 0.83 and 0.90, respectively. The resolution of the four unique, yet similar, structural waters within a hydrated crystal via 17O NMR Spectroscopy demonstrates the ability to decipher the unique electronic environment of structural water within a single hydrated crystal structure.

  • Solid‐State 17O NMR Reveals Hydrogen‐Bonding Energetics: Not All Low‐Barrier Hydrogen Bonds Are Strong
    Angewandte Chemie (International ed. in English), 2017
    Co-Authors: Ivan Hung, Zhehong Gan, Andreas Brinkmann, Xianqi Kong
    Abstract:

    While NMR and IR spectroscopic signatures and structural characteristics of low-barrier hydrogen bond (LBHB) formation are well documented in the literature, direct measurement of the LBHB energy is difficult. Here, we show that solid-state 17O NMR Spectroscopy can provide unique information about the energy required to break a LBHB. Our solid-state 17O NMR data show that the HB enthalpy of the O⋅⋅⋅H⋅⋅⋅N LBHB formed in crystalline nicotinic acid is only 7.7±0.5 kcal mol−1, suggesting that not all LBHBs are particularly strong.

Sharon E. Ashbrook - One of the best experts on this subject based on the ideXlab platform.