preparation-highly-porous-coordination-polymer-coatings-on

Preparation of Highly Porous Coordination Polymer Coatings on Macroporous Polymer Monoliths for Enhanced Enrichment of Phosphopeptides

We describe a protocol for the preparation of hybrid materials based on highly porous coordination polymer coatings on the internal surface of macroporous ...

E. O. Lawrence Berkeley National Laboratory

The parallel-mode electron paramagnetic resonance (EPR) spectrum of the S(1) state of the oxygen-evolving complex (OEC) shows a multiline signal centered around g=12, indicating an integer spin system. The series of [Mn(2)(2-OHsalpn)(2)] complexes were structurally characterized in four oxidation levels (Mn(II)(2), Mn(II)Mn(III), Mn(III)(2), and Mn(III)Mn(IV)). By using bulk electrolysis, the [Mn(III)Mn(IV)(2-OHsalpn)(2)(OH)] is oxidized to a species that contains Mn(IV) oxidation state as detected by X-ray absorption near edge spectroscopy (XANES) and that can be formulated as Mn(IV)(4) tetramer. The parallel-mode EPR spectrum of this multinuclear Mn(IV)(4) complex shows 18 well-resolved hyperfine lines center around g=11 with an average hyperfine splitting of 36 G. This EPR spectrum is very similar to that found in the S(1) state of the OEC. This is the first synthetic manganese model complex that shows an S(1)-like multiline spectrum in parallel-mode EPR.

The first spectroscopic model for the S1 state multiline signal of the OEC.

The pulsed EPR inversion recovery sequence has been utilized to monitor the temperature dependence of the electron spin-lattice relaxation rate of the Mn cluster of the Photosystem II oxygen evolving complex poised in a variety of S (2) state forms giving rise to g = 2 multiline EPR signals. A previous study (Lorigan and Britt (1994) Biochemistry 33: 12072-12076) showed that for PS II membranes treated with 5% ethanol, the S (2) state Mn cluster relaxes via the Orbach spin-lattice relaxation mechanism, where the relaxation is enhanced via phonon scattering off an excited state spin manifold, in this case at an energy of Delta = 36.5 cm(-1) above the S = 1/2 ground state giving rise to the multiline EPR signal. Parallel experiments are reported for PS II membranes with 5% methanol, treated with ammonia, and following short and long term dark adaptation. In each case, the temperature dependence of the electron spin-lattice relaxation rate is consistent with Orbach relaxation, and the range of excited state energies is relatively narrow (33.8 cm(-1) </= Delta </= 39.7 cm(-1)). In addition, short term dark adapted (6 min, 'active state') PS II membranes show biphasic recovery traces which indicate that a minority fraction of the oxygen evolving complexes are trapped in a form with greatly slowed spin-lattice relaxation.

Electron spin-lattice relaxation studies of different forms of the S(2) state multiline EPR signal of the Photosystem II oxygen-evolving complex.

Rieske and Rieske-type proteins are electron transport proteins involved in key biological processes such as respiration, photosynthesis, and detoxification. They have a [2Fe-2S] cluster ligated by two cysteines and two histidines. A series of mutations, L135E, L135R, L135A, and Y158F, of the Rieske protein from Thermus thermophilus has been produced which probe the effects of the neighboring residues, in the second sphere, on the dynamics of cluster reduction and the reactivity of the ligating histidines. These properties were probed using titrations and modifications with diethyl pyrocarbonate (DEPC) at various pH values monitored using UV-Visible and circular dichroism spectrophotometry. These results, along with results from EPR studies, provide information on ligating histidine modification and rate of reduction of each of the mutant proteins. L135R, L135A, and Y158F react with DEPC similarly to wild type, resulting in modified protein with a reduced [2Fe-2S] cluster in <90 min, whereas L135E requires >15 h under the same conditions. Thus, the negative charge slows down the rate of reduction and provides an explanation as to why negatively charged residues are rarely, if ever, found in the equivalent position of other Rieske and Rieske-type proteins.

Article	Year
The first spectroscopic model for the S1 state multiline signal of the OEC. Biochimica et biophysica acta\| PubMed ID: 15100027	2004
Electron spin-lattice relaxation studies of different forms of the S(2) state multiline EPR signal of the Photosystem II oxygen-evolving complex. Photosynthesis research\| PubMed ID: 16228419	2000
The reduction rates of DEPC-modified mutant Thermus thermophilus Rieske proteins differ when there is a negative charge proximal to the cluster. Journal of biological inorganic chemistry : JBIC : a publication of the Society of Biological Inorganic Chemistry\| PubMed ID: 24916128	2014

David Britt

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