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DOI: 10.1039/A804482A (Paper) Reference Section for: Chem. Commun., 1998, 1893-1894

The structure of the ionophoric antibiotic Na-tetronasin (M139603) in solution

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Tamas Martinek, Tamas Martinek, Frank G. Riddell, Trevor J. Rutherford, Sina Sareth and Charles T. Weller

Abstract

The structure of the ionophoric antibiotic sodium tetronasin (M139603) in chloroform solution has been determined using NMR spectroscopic methods and is shown to contain a water molecule bound to the sodium which is hydrogen bonded to oxygens in the molecule.

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  15. All spectra were obtained at 300 K on a Varian Unity-plus 500 spectrometer operating at 500.3 MHz for 1H, using standard pulse sequences unless otherwise stated.
  16. All molecular mechanics simulations were carried out on Silicon Graphics O2, Origin 200 and INDY computers using MSI/Biosym's CDiscover (Discover 95) software package in an Insight II environment. For the energy calculation the extensible Systematic Force Field (ESFF) was used with a 9.5 Å cut off for van der Waals and Coulomb interactions. The effect of solvent was taken into account by application of a distance dependent dielectric constant varying from 1 to an upper limit of 4.5. During the molecular dynamics calculations the velocity Verlet integrator and 1 fs timesteps were used. The temperature was controlled by direct velocity scaling with a 10 K temperature window. Minimisation was applied after every simulated annealing in cascade manner; steepest-descent, conjugate gradient (Fletcher algorithm), Newton method (BFGS algorithm). The iteration limit was 1500 steps, and the final convergence criterion was 0.0001 as maximum derivative.
  17. No allowance was made in this unweighted calculation for the relatively larger errors that occur with the smaller NOE observations.
  18. The root mean square deviation (rmsd) is here defined as:
     
    $${\rm msd}\equals \sqrt {{{\sum _n \left[ {{{J_{\lpar obs\rpar } \minus J_{\lpar calc\rpar } } \over {J_{\lpar obs\rpar } }}} \right]^2 } \over n}} $$ (1)
    .
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