Probing Hydrogen Bonding to Bound Dioxygen in Synthetic Models for Heme Proteins: The Importance of Precise Geometry

Laboratorium für Organische Chemie, ETH Zurich, Hönggerberg, HCI, 8093 Zurich, Switzerland.
Chemistry - A European Journal (Impact Factor: 5.73). 01/2009; 15(1):125-35. DOI: 10.1002/chem.200802077
Source: PubMed


Distal hydrogen bonding in natural dioxygen binding proteins is crucial for the discrimination between different potential ligands such as O(2) or CO. In the present study, we probe the chemical requirements for proper distal hydrogen bonding in a series of synthetic model compounds for dioxygen-binding heme proteins. The model compounds 1-Co to 7-Co bear different distal residues. The hydrogen bonding in their corresponding dioxygen adducts is directly measured by pulse EPR spectroscopy. The geometrical requirements for this interaction to take place were found to be narrow and very specific. Only two model complexes, 1-Co and 7-Co, form a hydrogen bond to bound dioxygen, which was characterized in terms of geometry and nature of the bond. The geometry and dipolar nature of this interaction in 1-Co-O(2) is more similar to the one in natural cobalt myoglobin (Co-Mb), making 1-Co the best model compound in the entire series.

4 Reads
  • [Show abstract] [Hide abstract]
    ABSTRACT: The construction and performance of a cryogenic 35GHz pulse electron nuclear double resonance (ENDOR) probehead for large samples is presented. The resonator is based on a rectangular TE(102) cavity in which the radio frequency (rf) B(2)-field is generated by a two turn saddle ENDOR coil crossing the resonator along the sample axis with minimal distance to the sample tube. An rf power efficiency factor is used to define the B(2)-field strength per square-root of the transmitted rf power over the frequency range 2-180MHz. The distributions of the microwave B(1)- and E(1)-field, and the rf B(2)-field are investigated by electromagnetic field calculations. All dielectrics, the sample tube, and coupling elements are included in the calculations. The application range of the probehead and the advantages of using large sample sizes are demonstrated and discussed on a number of paramagnetic samples containing transition metal ions.
    Journal of Magnetic Resonance 07/2009; 200(1):81-7. DOI:10.1016/j.jmr.2009.06.007 · 2.51 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This Microreview presents a concise overview of the different synthetic approaches that have been applied to porphyrin dendrimers over the years, with the porphyrin macrocycle(s) being embedded variously as the dendritic cores, at the peripheries, within the branching units, or spread throughout entire dendritic architectures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
    European Journal of Organic Chemistry 10/2009; 2009(28):4719 - 4752. DOI:10.1002/ejoc.200900512 · 3.07 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Two-pulse electron spin echo envelope modulation (ESEEM) line widths are influenced by transverse electron spin relaxation, which is in turn induced by local field fluctuations. Simultaneous analysis of the decays of the unmodulated and modulated parts of the ESEEM signal provides deeper insight into the relaxation of a spin system consisting of an electron spin 1/2 coupled to N(I) nuclei with spin 1/2. Standard two-pulse ESEEM formulas either do not account for relaxation or assume uniform relaxation for all lines. In general, the relaxation rates on allowed and forbidden transitions may not be the same. Experimental results obtained on a single crystal of Cu(II)-doped l-histidine suggest that such a difference exists. Theoretical considerations show that in such a case the product rule for two-pulse ESEEM does not extend to expressions including relaxation. Product rules in general do not properly account for relaxation in three-pulse ESEEM and HYSCORE experiments. Decay of the apparently non-oscillatory part of the two-pulse echo may be strongly affected by modulation interference. Such interference of difference frequencies of matrix nuclei may cause a rather flat initial feature, which was previously attributed solely to non-exponential phase relaxation of electron spin transitions due to spin diffusion of the matrix nuclei. In addition, the sometimes observed drastic initial decay of the time domain signal is related to modulation interference of multiple-quantum coherences that arise from a strong cross-suppression effect.
    Journal of Magnetic Resonance 08/2012; 223:187-97. DOI:10.1016/j.jmr.2012.08.005 · 2.51 Impact Factor
Show more

Carlos Calle