| 1. |
- Blondin, Geneviève, et al.
(författare)
-
Electron paramagnetic resonance study of the S=1/2 ground state of a radiolysis-generated manganese(III)-trimanganese(IV) form of [Mn-IV;O-4(6)(bipy)(6)](4+) (bipy=2,2'-bipyridine). Comparison with the photosynthetic Oxygen Evolving Complex
- 1997
-
Ingår i: Journal of the Chemical Society. Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1472-7773 .- 0300-9246 .- 1364-5447. ; 1997:21, s. 4069-4074
-
Tidskriftsartikel (refereegranskat)abstract
- gamma-Ray irradiation at liquid nitrogen temperature of a dimethylformamide solution of the tetranuclear complex [(Mn4O6)-O-IV(bipy)(6)](4+) (bipy = 2,2'-bipyridine) allowed the generation of the first mixed-valence tetranuclear system containing Mn-III and Mn-IV ions and exhibiting a S = 1/2 ground state. The X-band EPR spectrum of this tetranuclear system has been obtained. Simulations have been undertaken and the Mn hyperfine coupling tensors determined clearly show a (MnMn3IV)-Mn-III, composition for the EPR active species. A general approach for the analysis of the isotropic components of the Mn hyperfine tensors is presented in detail. This allowed the determination of the spin projection value for each Mn site. A three J coupling scheme assuming that the linear topology of the starting compound remains is able to reproduce these spin projection values if and only if the Mn-III ion is located at a terminal position in a N4O2 environment. The EPR signal of this [Mn4O6(bipy)(6)](3+) species is compared with the multiline signal observed in the S-2 state of the photosynthetic Oxygen Evolving Complex.
|
|
| 2. |
- Davydov, Roman, et al.
(författare)
-
The application of pesticides and mineral fertilizers in agriculture
- 2018
-
Ingår i: MATEC Web of Conferences. - : EDP Sciences.
-
Konferensbidrag (refereegranskat)abstract
- Regulation of using pesticides and agrochemicals application in agriculture is one of the important problem now, as also the problem of storage of mineral fertilizers and their improper using, which have negative influence on the chemical and the food security of the country. This paper discusses the features and benefits of monodisperse aerosols of pesticides in plant protection after a long-term research. A new line of development of science, engineering, industrial and innovative technologies-the author's project "Monodisperse Anthropogenic Aerosols" is proposed. The measures for its implementation are presented. © The Authors, published by EDP Sciences, 2018.
|
|
| 3. |
- Nivorozhkin, A L, et al.
(författare)
-
Structure and electrochemical studies of [(trispicMeen)ClFeIII OFeIII Cl(trispicMeen)](2+). Spectroscopic characterization of the mixed-valence Fe-III OFeII form. Relevance to the active site of dinuclear iron-oxo proteins
- 1997
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 36:5, s. 846-853
-
Tidskriftsartikel (refereegranskat)abstract
- The dinuclear species [(trispicMeen)(ClFeOFeCl)-O-III-Cl-III(trispicMeen)]Cl(OH)(H2O)(7) (1) (trispicMeen = N,N,N'-tris-(2-pyridylmethyl)-N'-methylethane- 1,2-diamine) was synthesized. It crystallizes in the monoclinic space group C2/c with a = 33.87(2) Angstrom, b = 17.42(2) Angstrom, c = 23.41(5) Angstrom, beta = 132.88(5)degrees, V = 10 121(25) Angstrom(3), and Z = 8. It contains an almost linear unit (Fe-O-Fe angle = 177.4(7)degrees). The potentially pentadentate Ligand is in fact only tetracoordinated with one pyridine not bound to the metal ion. The octahedral coordination of Fe(Ln) is completed by one chloride ion. The structure of [(bispicMeen)ClFeOFeCl(bispicMeen)]Cl-2 . CH3COCH3 . 2H(2)O (2) (bispicMeen = N,N'-bis(2-pyridylmethyl)-N'-methylethane-1,2-diamine) was also determined. It crystallizes in the monoclinic space group C2/c with a 11.124(4) Angstrom, b = 22.769(9) Angstrom, c = 15.874(6) Angstrom, beta = 97.79(4)degrees, V = 3984(3) Angstrom(3), and Z = 4. The main difference from 1 is that, in 2, the Fe-O-Fe unit is bent with an FeOFe angle 152.3(3)degrees. In cyclic voltammetry, 1 exhibits two reduction peaks at -0.230 and -0.960 V/SCE. They correspond respectively to the reduction to the (FeFeIII)-Fe-II and (FeFeIII)-Fe-II states. Cyclic voltammetry shows that the mixed-valent form [(trispicMeen)(ClFeOFeCl)-O-II-Cl-III(trispicMeen)](+) (E degrees = -0.175 V/SCE) is in equilibrium with another species (E degrees = +0.065 V/SCE) proposed to be [(trispicMeen)(FeOFeCl)-O-II-Cl-III(trispicMeen)](2+) in which a chloride ion has been displaced by the originally unbound pyridine. The equilibrium constant was estimated to be 90 M(-1), and the rate of the recombination of chloride to the [(trispicMeen)(FeOFeCl)-O-III-Cl-III(trispicMeen)](3+) complex was found equal to 3 x 10(5) M(-1) s(-1). Controlled potential electrolysis of an acetonitrile solution of 1 allowed the preparation of the mixed-valent Fe(II)-O-Fe(III) form which gives an almost isotropic EPR signal similar to that already observed with ore-bridged model compounds (Holt, et al. Inorg. Chem. 1993, 32, 5844. Hartman, et al. J. Am. Chem. Sec. 1987, 109, 7387) but different from the rhombic one observed in the mixed valent form of MMO. The mixed-valent forms slowly disproportionate to a mixture of (FeFeIII)-Fe-III and Fe(II) forms. The mixed-valent forms could be generated by radiolysis at 77 K, and an EPR study of the mixed-valent forms obtained by this procedure demonstrated that these species could not be protonated. Radiolysis of 1 at 77 K afforded the EPR spectrum of [(trispicMeen)(ClFeOFeCl)-O-II-Cl-III(trispicMeen)](+); upon annealing at 200 K, the solution gave an EPR spectrum very similar to that observed on the electrochemically reduced solution. This is in agreement with the observation of substitution of a chloride ligand. The mixed-valent form was not detected with the analogous complexes of the bispicen family: [(bispicMeen)ClFeOFeCl(bispicMeen)]Cl-2 . CH3COCH3 . 2H(2)O (2) and [(bispicMe(2)en)ClFeOFeCl(bispicMe(2)en)]Cl-2 (3). Upon reduction, these complexes quickly (at CV time scale) decompose to mononuclear species.
|
|
| 4. |
- Petrik, Igor D., et al.
(författare)
-
An Engineered Glutamate in Biosynthetic Models of Heme-Copper Oxidases Drives Complete Product Selectivity by Tuning the Hydrogen-Bonding Network
- 2021
-
Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 60:4, s. 346-355
-
Tidskriftsartikel (refereegranskat)abstract
- Efficiently carrying out the oxygen reduction reaction (ORR) is critical for many applications in biology and chemistry, such as bioenergetics and fuel cells, respectively. In biology, this reaction is carried out by large, transmembrane oxidases such as heme-copper oxidases (HCOs) and cytochrome bd oxidases. Common to these oxidases is the presence of a glutamate residue next to the active site, but its precise role in regulating the oxidase activity remains unclear. To gain insight into its role, we herein report that incorporation of glutamate next to a designed heme-copper center in two biosynthetic models of HCOs improves O2 binding affinity, facilitates protonation of reaction intermediates, and eliminates release of reactive oxygen species. High-resolution crystal structures of the models revealed extended, water-mediated hydrogen-bonding networks involving the glutamate. Electron paramagnetic resonance of the cryoreduced oxy-ferrous centers at cryogenic temperature followed by thermal annealing allowed observation of the key hydroperoxo intermediate that can be attributed to the hydrogen-bonding network. By demonstrating these important roles of glutamate in oxygen reduction biochemistry, this work offers deeper insights into its role in native oxidases, which may guide the design of more efficient artificial ORR enzymes or catalysts for applications such as fuel cells.
|
|
| 5. |
- Stenis, Jan, et al.
(författare)
-
Economic management instrument for enhanced supply of utilities to megacities
- 2019
-
Ingår i: International Scientific Conference "Digital Transformation on Manufacturing, Infrastructure and Service". - Bristol : IOP Publishing.
-
Konferensbidrag (refereegranskat)abstract
- A cost structure is proposed to enhance the supply of utilities to megacities on a regional operating scale. The introduced methodology involves business administration theory and economics and employs the previously introduced equality principle and the EUROPE (Efficient Use of Resources for Optimal Production Economy) model to impose shadow costs on supply losses to induce economic incentives to improve the functionality of megacities. A case study presents the practical application in an Asian context. It is concluded that the introduced methodology makes the megacities more efficient and improve their functionality. Profitability increases, the technology is advanced, and the environment improves when the EUROPE model is applied on activities that involve supply flows at higher policy analysis levels. Application of an introduced key factor encapsulates megacity aspects. The equity of the regional access to facilities is improved. The developed methods support decision-making when managing megacity supply.
|
|
| 6. |
- Sun, L C, et al.
(författare)
-
Binuclear ruthenium-manganese complexes as simple artificial models for photosystem II in green plants
- 1997
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 119:30, s. 6996-7004
-
Tidskriftsartikel (refereegranskat)abstract
- As part of a project aimed at developing models for photosystem II (PSII) in green plants, we have prepared a series of model compounds (7, 8, and 13). In these compounds, a photosensitizer, ruthenium(II) tris(bipyridyl) complex (to mimic the function of P-680 in PSII), was covalently linked to a manganese(II) ion through different bridging ligands. The structures of the compounds were characterized by electron paramagnetic resonance measurements and electrospray ionization mass spectrometry. The interaction between the ruthenium and manganese moieties within the complex was probed by steady-state and time-resolved emission measurements. When the binuclear complexes are exposed to flash photolysis in the presence of an electron acceptor such as methylviologen (MV2+), it could be shown that after the initial electron transfer from the excited state of Ru(II) in compound 7, forming Ru(III) and MV+., an intramolecular electron transfer from coordinated Mn(II) to the photogenerated Ru(III) occurred with a first-order rate constant of 1.8 x 10(5) s(-1), regenerating Ru(II). This is believed to be the first supramolecular system where a manganese complex has been used as an electron donor to a photo-oxidized photosensitizer, Possible extensions to develop the manganese donor, and thus to approach the function of reaction center in PSII, are indicated.
|
|
