Current Understanding of the Mechanism of Water Oxidation in Photosystem II and Its Relation to XFEL Data

2020 ◽  
Vol 89 (1) ◽  
pp. 795-820 ◽  
Author(s):  
Nicholas Cox ◽  
Dimitrios A. Pantazis ◽  
Wolfgang Lubitz

The investigation of water oxidation in photosynthesis has remained a central topic in biochemical research for the last few decades due to the importance of this catalytic process for technological applications. Significant progress has been made following the 2011 report of a high-resolution X-ray crystallographic structure resolving the site of catalysis, a protein-bound Mn4CaOx complex, which passes through ≥5 intermediate states in the water-splitting cycle. Spectroscopic techniques complemented by quantum chemical calculations aided in understanding the electronic structure of the cofactor in all (detectable) states of the enzymatic process. Together with isotope labeling, these techniques also revealed the binding of the two substrate water molecules to the cluster. These results are described in the context of recent progress using X-ray crystallography with free-electron lasers on these intermediates. The data are instrumental for developing a model for the biological water oxidation cycle.

1997 ◽  
Vol 38 (5) ◽  
pp. 780-789 ◽  
Author(s):  
B. Tirkkonen ◽  
A. Aukrust ◽  
E. Couture ◽  
D. Grace ◽  
Y. Haile ◽  
...  

Purpose: To determine the structure and various physicochemical properties of man-gafodipir (MnDPDP) trisodium, the active ingredient of Teslascan, a new organ-specific contrast medium for MR imaging. Material and Methods: The structure of MnDPDP trisodium crystals was determined by X-ray crystallography. The possible existence of polymorphism in MnDPDP trisodium was evaluated by powder X-ray diffraction, optical microscopy, thermal analysis and IR spectroscopy. In addition, various spectroscopic techniques and physicochemical measurements were used for characterisation of MnDPDP trisodium. Results: The crystallographic data obtained for MnDPDP trisodium show that the general core structure of the MnDPDP anion is similar to that seen in related substances. The metal coordination geometry is a distorted octahedron defined by 2 phenolate oxygens, 2 carboxylate oxygens and 2 amine nitrogens. The unit cell contains 2 MnDPDP anions, 6 sodium ions and 50 water molecules. The various spectroscopic data are consistent with the structure determined by X-ray crystallography. The product (Teslascan) has low viscosity, is isotonic with blood and has a physiological pH. Conclusion: MnDPDP trisodium is a crystalline, hygroscopic solid which is readily soluble in water. No evidence of polymorphism was seen in the samples studied.


2021 ◽  
pp. 174751982198965
Author(s):  
Guoqi Zhang

( E)-4-[2-(Pyridin-4-yl)vinyl]benzaldehyde, containing both a 4-vinylpyridine and an aldehyde functionality, is utilized to develop new, highly conjugated chalcone compounds and a bis-Schiff base azine compound. The chalcone-containing compounds are further explored for their protonation, methylation and silver(I) coordination chemistry using the pyridine moiety. In parallel, a cyano-containing analogue, ( E)-4-[2-(pyridin-4-yl)vinyl]benzonitrile is also synthesized and studied for its silver(I) coordination chemistry. These new compounds are fully characterized by mass spectrometry, elemental analysis and spectroscopic techniques. The methylated product of ( E)-1-(9-anthryl)-3-{4-[2-(pyridin-4-yl)vinyl]phenyl}prop-2-en-1-one and a silver complex of ( E)-4-[2-(pyridin-4-yl)vinyl]benzonitrile are structurally determined by X-ray crystallography.


2015 ◽  
Vol 112 (16) ◽  
pp. 4935-4940 ◽  
Author(s):  
Na Song ◽  
Javier J. Concepcion ◽  
Robert A. Binstead ◽  
Jennifer A. Rudd ◽  
Aaron K. Vannucci ◽  
...  

In aqueous solution above pH 2.4 with 4% (vol/vol) CH3CN, the complex [RuII(bda)(isoq)2] (bda is 2,2′-bipyridine-6,6′-dicarboxylate; isoq is isoquinoline) exists as the open-arm chelate, [RuII(CO2-bpy-CO2−)(isoq)2(NCCH3)], as shown by 1H and 13C-NMR, X-ray crystallography, and pH titrations. Rates of water oxidation with the open-arm chelate are remarkably enhanced by added proton acceptor bases, as measured by cyclic voltammetry (CV). In 1.0 M PO43–, the calculated half-time for water oxidation is ∼7 μs. The key to the rate accelerations with added bases is direct involvement of the buffer base in either atom–proton transfer (APT) or concerted electron–proton transfer (EPT) pathways.


Chemistry ◽  
2020 ◽  
Vol 2 (4) ◽  
pp. 796-804
Author(s):  
David John Watkin ◽  
Richard Ian Cooper

The Flack Parameter is now almost universally reported for all chiral materials characterized by X-ray crystallography. Its elegant simplicity was an inspired development by Howard Flack, and although the original algorithm for its computation has been strengthened by other workers, it remains an essential outcome for any crystallographic structure determination. As with any one-parameter metric, it needs to be interpreted in the context of its standard uncertainty.


2006 ◽  
Vol 59 (5) ◽  
pp. 320 ◽  
Author(s):  
Graham Smith ◽  
Urs D. Wermuth ◽  
Peter C. Healy ◽  
Jonathan M. White

The 1:1 proton-transfer brucinium compounds from the reaction of the alkaloid brucine with 5-nitrosalicylic acid, 3,5-dinitrosalicylic acid, and 5-sulfosalicylic acid, namely anhydrous brucinium 5-nitrosalicylate (1), brucinium 3,5-dinitrosalicylate monohydrate (2), and brucinium 5-sulfosalicylate trihydrate (3) have been prepared and their crystal structures determined by X-ray crystallography. All structures further demonstrate the selectivity of brucine for meta-substituted benzoic acids and comprise three-dimensional hydrogen-bonded framework polymers. Two of the compounds (1 and 3) have the previously described undulating brucine sheet host-substructures which incorporate interstitially hydrogen-bonded salicylate anion guest species and additionally in 3 the water molecules of solvation. The structure of 2 differs in having a three-centre brucinium–salicylate anion bidentate N+–H···O(carboxyl) hydrogen-bonding association linking the species through interstitial associations involving also the water molecules of solvation. A review of the crystallographic structural literature on strychnine and brucine is also given.


2020 ◽  
Author(s):  
Daniela Medas ◽  
Carlo Meneghini ◽  
Ilaria Carlomagno ◽  
Giovanni De Giudici

<p>Mining activities generate a large amount of waste materials that are often very unstable and represent a source of pollution. Phytomanagement, in terms of phytostabilization, is considered a suitable method to decrease environmental risks of metal-enriched mine wastes (Parraga-Aguado et al. 2013). This technique employs plants to achieve the surface stabilization of the wastes by acting as a barrier which decreases wind borne dust and water erosion, reduces metal-enriched leaching through metal accumulation in plant roots and provides metal immobilization in the rhizosphere (Robinson et al. 2009; Sun et al. 2016).</p><p>Most of the research has focused on the selection of the best spontaneously adapted plant species (endemic pioneer plants) for each specific mining site (Parraga-Aguado et al. 2013), because they may respond better and can survive easily compared to introduced alien species (Bradshaw 1997; Pandey 2015). Pioneer vegetation may improve edaphic conditions by increasing soil nutrient content (Rodríguez et al. 2007) or ameliorating soil acidity (Rufo and de la Fuente 2010), and thus may favor further establishment of other plant species.</p><p>The investigation of metal transfer from the geosphere to the vegetal tissues helps to understand the adaptive strategies of plant species and may be useful for soil remediation actions. Synchrotron radiation-based techniques represent the state of the art tools to investigate the microscopic processes occurring in plant-soil systems (Kopittke et al. 2017). X-ray diffraction, X-ray fluorescence and X-ray absorption spectroscopy (XAS), are particularly suited to determine the finest complementary details about the atomic and crystallographic structure, distribution of elements, their chemical speciation and their valence state. Here, we report a review of selected researches performed on different plant species (<em>Pistacia</em> <em>lentiscus</em> L., <em>Euphorbia pithyusa</em> subsp. <em>cupanii</em>, <em>Phragmites australis</em>, and <em>Helichrysum microphyllum</em> Cambess. subsp. <em>tyrrhenicum</em>), growing on metal contaminated substrates in abandoned mining areas in Sardinia (Italy).</p><p>Our results demonstrate that these plant species have developed their own adaptation strategy to grow and to survive in polluted environments, making them potential candidates to develop low-cost and self-sustainable vegetative covers aimed at reducing the dispersion of metals in soils and waters around these mine polluted sites.</p><p><strong>Acknowledgments</strong></p><p>The authors acknowledge CESA (E58C16000080003) from RAS and RAS/FBS (F72F16003080002) grants, FP7 ERANETMED2 72094 SUPREME, the POR FESR Sardegna 2014-2020 (project cluster Top-Down: TESTARE), the Grant of Excellence Departments, MIUR (ARTICOLO 1, COMMI 314 – 337 LEGGE 232/2016), and the CeSAR (Centro Servizi d'Ateneo per la Ricerca) of the University of Cagliari, Italy, for SEM analysis.</p><p><strong>References</strong></p><p>A. Bradshaw, Ecol. Eng. 8, 255 (1997).</p><p>P.M. Kopittke et al., J. Environ. Qual. 46, 1175 (2017).</p><p>V.C. Pandey, Ecol. Eng. 82, 1 (2015).</p><p>I. Parraga-Aguado et al., Environ. Pollut. 176, 134 (2013).</p><p>B.H. Robinson et al., CRC. Crit. Rev. Plant Sci. 28, 240 (2009).</p><p>N. Rodríguez et al., Arid L. Res. Manag. 21, 51 (2007).</p><p>L. Rufo and V. de la Fuente, Arid L. Res. Manag. 24, 301 (2010).</p><p>Z. Sun et al., Ecol. Eng. 86, 60 (2016).</p>


2007 ◽  
Vol 60 (5) ◽  
pp. 354 ◽  
Author(s):  
Paul V. Bernhardt ◽  
Raymond M. Carman ◽  
Tri T. Le

X-Ray crystallography affords the stereochemistry of three iodo compounds derived from mycophenolic acid. These included the crystallographic structure of a tertiary iodide.


Author(s):  
Sayuri Chong-Canto ◽  
Efrén V. García-Báez ◽  
Francisco J. Martínez-Martínez ◽  
Ángel Ramos-Organillo ◽  
Itzia I. Padilla-Martínez

A new cocrystal salt of metformin, an antidiabetic drug, and N,N’-(1,4-phenylene)dioxalamic acid, was synthesized by mechanochemical synthesis, purified by crystallization from solution and characterized by single X-ray crystallography. The structure revealed a salt-type cocrystal composed of one dicationic metformin unit, two monoanionic units of the acid and four water molecules namely H2Mf(HpOXA)2∙4H2O. X-ray powder, IR, 13C-CPMAS, thermal and BET adsorption-desorption analyses were performed to elucidate the structure of the molecular and supramolecurar structure of the anhydrous microcrystalline mesoporous solid H2Mf(HpOXA)2. The results suggest that their structures, conformation and hydrogen bonding schemes are very similar between them. To the best of our knowledge, the selective formation of the monoanion HpOXA⁻, as well as its structure in the solid, is herein reported for the first time. Regular O(-)∙∙∙C(), O(-)∙∙∙N+ and bifacial O(-)∙∙∙C()∙∙∙O(-) of n→* charge-assisted interactions are herein described in H2MfA cocrystal salts which could be responsible of the interactions of metformin in biologic systems. The results, support the participation of n→* charge-assisted interactions independently, and not just as a short contact imposed by the geometric constraint due to the hydrogen bonding patterns.


Sign in / Sign up

Export Citation Format

Share Document