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A Heterobimetallic FeIIIMnII Complex of an Unsymmetrical Dinucleating Ligand: A Structural and Functional Model Complex for the Active Site of Purple Acid Phosphatase of Sweet Potato
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
Vise andre og tillknytning
Rekke forfattare: 112014 (engelsk)Inngår i: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, Vol. 2014, nr 13, s. 2204-2212Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The heterodinuclear mixed-valence complex [FeMn(ICIMP)(OAc)(2)Cl] (1) {H2ICIMP = 2-(N-carboxylmethyl)-[N-(N-methylimidazolyl-2-methyl)aminomethyl]-[6-(N-isopropylmethyl)-[N-(N-methylimidazolyl-2-methyl)]aminomethyl-4-methylphenol], an unsymmetrical N4O2 donor ligand} has been synthesized and fully characterized by several spectroscopic techniques as well as by X-ray crystallography. The crystal structure of the complex reveals that both metal centers in 1 are six-coordinate with the chloride ion occupying the sixth coordination site of the Mn-II ion. The phenoxide moiety of the ICIMP ligand and both acetate ligands bridge the two metal ions of the complex. Mossbauer spectroscopy shows that the iron ion in 1 is high-spin Fe-III. Two quasi-reversible redox reactions for the complex, attributed to the (FeMnII)-Mn-III/(FeMnII)-Mn-II (at -0.67 V versus Fc/Fc(+)) and (FeMnII)-Mn-III/(FeMnIII)-Mn-III (at 0.84 V), were observed by means of cyclic voltammetry. Complex 1, with an Fe-III-Mn-II distance of 3.58 angstrom, may serve as a model for the mixed-valence oxidation state of purple acid phosphatase from sweet potato. The capability of the complex to effect organophosphate hydrolysis (phosphatase activity) has been investigated at different pH levels (5.5-11) by using bis(2,4-dinitrophenyl)phosphate (BDNPP) as the substrate. Density functional theory calculations indicate that the substrate coordinates to the Mn-II ion. In the transition state, a hydroxide ion that bridges the two metal ions becomes terminally coordinated to the Fe-III ion and acts as a nucleophile, attacking the phosphorus center of BDNPP with the concomitant dissociation of the leaving group.

sted, utgiver, år, opplag, sider
2014. Vol. 2014, nr 13, s. 2204-2212
Emneord [en]
Metalloenzymes, Mixed-valent compounds, Moessbauer spectroscopy, Density functional calculations, Transition states, Hydrolysis
HSV kategori
Forskningsprogram
organisk kemi
Identifikatorer
URN: urn:nbn:se:su:diva-105221DOI: 10.1002/ejic.201301375ISI: 000335197600004OAI: oai:DiVA.org:su-105221DiVA, id: diva2:732135
Forskningsfinansiär
Knut and Alice Wallenberg FoundationSwedish Research Council
Merknad

AuthorCount:11;

Tilgjengelig fra: 2014-07-03 Laget: 2014-06-24 Sist oppdatert: 2017-10-19bibliografisk kontrollert
Inngår i avhandling
1. Quantum Chemical Modeling of Phosphoesterase Mimics and Chemistry in Confined Spaces
Åpne denne publikasjonen i ny fane eller vindu >>Quantum Chemical Modeling of Phosphoesterase Mimics and Chemistry in Confined Spaces
2017 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

In this thesis, density functional theory is employed in the study of two kinds of systems that can be considered to be biomimetic in their own ways. First, three binuclear metal complexes, synthesized by the group of Prof. Ebbe Nordlander, have been investigated. The complexes are designed to resemble the active sites of phosphatase enzymes and have been examined in complexes where either two Zn(II) ions or one Fe(III) and one Mn(II) ion are bound. These dinuclear compounds were studied as catalysts for the hydrolysis of bis(2,4-dinitrophenyl) phosphate and the transesterification of 2-hydroxypropyl p-nitrophenyl phosphate, which are model systems for the same reactions occurring in DNA or RNA. It was found that the two reactions take place in similar ways: a hydroxide ion that is terminally bound to one of the metal centers acts either as a nucleophile in the hydrolysis reaction or as a base in the transesterification. The leaving groups depart in an effectively concerted manner, and the formed catalyst-product complexes are predicted to be the resting states of the catalytic cycles. The rate-determining free energy barriers are identified from the catalyst-product complex in one catalytic cycle to the transition state of nucleophilic attack in the next.

Another type of biomimetic modeling is made with an aim of imitating the conceptual features of selective binding of guests and screening them from solute-solvent interactions. Such features are found in so-called nanocontainers, and this thesis is concerned with studies of two capsules synthesized by the group of Prof. Julius Rebek, Jr. First, the cycloaddition of phenyl acetylene and phenyl azide has experimentally been observed to be accelerated in the presence of a capsule. Computational studies were herein performed on this system, and a previously unrecognized structure of the capsule is discovered. Two main factors are then identified as sources of the rate acceleration compared to the uncatalyzed reaction, namely the reduction of the entropic component and the selective destabilization of the reactant supercomplex over the transition state.

In the second capsule study, the alkane binding trends of a water-soluble cavitand was studied. It is found that implicit solvation models fail severely in reproducing the experimental equilibrium observed between binding of n-decane by the cavitand monomer and encapsulation in the capsule dimer. A mixed explicit/implicit solvation protocol is developed to better quantify the effect of hydrating the cavitand, and a simple correction to the hydration free energy of a single water molecule is proposed to remedy this. The resulting scheme is used to predict new hydration free energies of the cavitand complexes, resulting in significant improvement vis-à-vis experiments.

The computational results presented in this thesis show the usefulness of the quantum chemical calculations to develop understanding of experimental trends observed for substrate binding and catalysis. In particular, the methodology is shown to be versatile enough such that experimental observations can be reproduced for such diverse systems as studied herein.

sted, utgiver, år, opplag, sider
Stockholm: Department of Organic Chemistry, Stockholm University, 2017. s. 59
Emneord
density functional theory, catalysis, phosphoester hydrolysis, transesterification, supramolecular chemistry, inclusion complex, host-guest chemistry, cycloaddition
HSV kategori
Forskningsprogram
organisk kemi
Identifikatorer
urn:nbn:se:su:diva-148259 (URN)978-91-7797-016-3 (ISBN)978-91-7797-017-0 (ISBN)
Disputas
2017-12-01, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 14:00 (engelsk)
Opponent
Veileder
Merknad

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Manuscript.

Tilgjengelig fra: 2017-11-08 Laget: 2017-10-19 Sist oppdatert: 2017-11-30bibliografisk kontrollert

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