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de Visser, S.P.,Rohde, J.U.,Lee, Y.M.,Cho, J.,Nam, W. Elsevier Publishing Company 2013 Coordination chemistry reviews Vol.257 No.2
Iron-oxygen species, such as iron(IV)-oxo, iron(III)-superoxo, iron(III)-peroxo, and iron(III)-hydroperoxo complexes, are key intermediates often detected in the catalytic cycles of dioxygen activation by heme and nonheme iron enzymes. Our understanding of the chemistry of these key intermediates has improved greatly by studies of the structural and spectroscopic properties and reactivities of their synthetic analogues. One class of biomimetic coordination complexes that has proven to be particularly versatile in studying dioxygen activation by metal complexes is comprised of Fe<SUP>IV</SUP>?O and Fe<SUP>III</SUP>?O<SUB>2</SUB>(H) complexes of the macrocyclic tetramethylcyclam ligand (TMC, 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane). Several recent advances have been made in the synthesis and isolation of new iron-oxygen complexes of this ligand, their structural and spectroscopic characterization, and elucidation of their reactivities in various oxidation reactions. In this review, we summarize the chemistry of the first structurally characterized mononuclear nonheme iron(IV)-oxo complex, in which the Fe<SUP>IV</SUP>?O group was stabilized by the TMC ligand. Complexes with different axial ligands, [Fe<SUP>IV</SUP>(O)(TMC)(X)]<SUP>n+</SUP>, and complexes of other cyclam ligands are discussed as well. Very recently, significant progress has also been reported in the area of other iron-oxygen intermediates, such as iron(III)-superoxo, iron(III)-peroxo, and iron(III)-hydroperoxo complexes bearing the TMC ligand. The present results demonstrate how synthetic and mechanistic developments in biomimetic research can advance our understanding of dioxygen activation occurring in mononuclear nonheme iron enzymes.
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de Visser, Sam P.,Nam, Wonwoo American Chemical Society 2008 The Journal of physical chemistry A Vol.112 No.50
<P>Density functional theory studies on the nature of the cis effect and cis influence of ligands on oxoiron nonheme complexes have been performed. A detailed analysis of the electronic and oxidizing properties of [Fe<SUP>IV</SUP>═O(TPA)L]<SUP>+</SUP> with L = F<SUP>−</SUP>, Cl<SUP>−</SUP>, and Br<SUP>−</SUP> and TPA = tris-(2-pyridylmethyl)amine are presented and compared with [Fe<SUP>IV</SUP>═O(TPA)NCCH<SUB>3</SUB>]<SUP>2+</SUP>. The calculations show that the electronic cis effect is determined by favorable orbital overlap between first-row elements with the metal, which are missing between the metal and second- and third-row elements. As a consequence, the metal 3d block is split into a one-below-two set of orbitals with L = Cl<SUP>−</SUP> and Br<SUP>−</SUP>, and the HOMO/LUMO energy gap is widened with respect to the system with L = F<SUP>−</SUP>. However, this larger HOMO/LUMO gap does not lead to large differences in electron affinities of the complexes. Moreover, a quantum mechanical analysis of the binding of the ligand shows that it is built up from a large electric field effect of the ligand on the oxoiron species and a much smaller quantum mechanical effect due to orbital overlap. These contributions are of similar strength for the three tested halogen cis ligands and result in similar reactivity patterns with substrates. The calculations show that [Fe<SUP>IV</SUP>═O(TPA)L]<SUP>+</SUP> with L = F<SUP>−</SUP>, Cl<SUP>−</SUP>, and Br<SUP>−</SUP> have closely lying triplet and quintet spin states, but only the quintet spin state is reactive with substrates. Therefore, the efficiency of the oxidant will be determined by the triplet−quintet spin state crossing of the reaction. The reaction of styrene with a doubly charged reactant, that is, [Fe<SUP>V</SUP>═O(TPA)L]<SUP>2+</SUP> with L = F<SUP>−</SUP>, Cl<SUP>−</SUP>, and Br<SUP>−</SUP> or [Fe<SUP>V</SUP>═O(TPA)NCCH<SUB>3</SUB>]<SUP>3+</SUP>, leads to an initial electron transfer from the substrate to the metal followed by a highly exothermic epoxidation mechanism. These reactivity differences are mainly determined by the overall charge of the system rather than the nature of the cis ligand.</P>
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A Biomimetic Ferric Hydroperoxo Porphyrin Intermediate
de Visser, Sam P.,Valentine, Joan Selverstone,Nam, Wonwoo WILEY-VCH Verlag 2010 Angewandte Chemie Vol.49 No.12
<B>Graphic Abstract</B> <P>OOH, my! The protonation of a side-on high-spin ferric peroxo species yields the corresponding end-on low-spin ferric hydroperoxo intermediate (see picture), which is a precursor of Compound I and has been frequently proposed as a reactive species in heme enzymes. This ferric hydroperoxo complex can be used to study reactivities of similar species in substrate oxygenation and hydroperoxide O&n.bond;O bond cleavage reactions. <img src='wiley_img_2010/14337851-2010-49-12-ANIE200906736-content.gif' alt='wiley_img_2010/14337851-2010-49-12-ANIE200906736-content'> </P>
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de Visser, Sam P.,Tahsini, Laleh,Nam, Wonwoo WILEY-VCH Verlag 2009 Chemistry Vol.15 No.22
<P>How deep is your orbital? Density functional theory studies on the axial ligand effect of aliphatic versus aromatic hydroxylation of ethylbenzene by iron–oxo complexes with a variable axial ligand show that strong (anionic) ligands pull the metal inside the plane of the haeme and destabilise cationic intermediates through orbital interactions (see picture). <img src='wiley_img/09476539-2009-15-22-CHEM200802234-content.gif' alt='wiley_img/09476539-2009-15-22-CHEM200802234-content'> </P><P>The catalytic activity of high-valent iron–oxo active species of heme enzymes is known to be dependent on the nature of the axial ligand trans to the iron–oxo group. In a similar fashion, experimental studies on iron–oxo porphyrin biomimetic systems have shown a significant axial ligand effect on ethylbenzene hydroxylation, with an axial acetonitrile ligand leading to phenyl hydroxylation products and an axial chloride anion giving predominantly benzyl hydroxylation products. To elucidate the fundamental factors that distinguish this regioselectivity reversal in iron–oxo porphyrin catalysis, we have performed a series of density functional theory calculations on the hydroxylation of ethylbenzene by [Fe<SUP>IV</SUP>&n.dbond;O(Por<SUP>+.</SUP>)L] (Por=porphyrin; L=NCCH<SUB>3</SUB> or Cl<SUP>−</SUP>), which affords 1-phenylethanol and p-ethylphenol products. The calculations confirm the experimentally determined product distributions. Furthermore, a detailed analysis of the electronic differences between the two oxidants shows that their reversed regioselectivity is a result of differences in orbital interactions between the axial ligand and iron–oxo porphyrin system. In particular, three high-lying orbitals (π*<SUB>xz</SUB>, π*<SUB>yz</SUB> and a<SUB>2u</SUB>), which are singly occupied in the reactant complex, are stabilised with an anionic ligand such as Cl<SUP>−</SUP>, which leads to enhanced HOMO–LUMO energy gaps. As a consequence, reactions leading to cationic intermediates through the two-electron reduction of the metal centre are disfavoured. The aliphatic hydroxylation mechanism, in contrast, is a radical process in which only one electron is transferred in the rate-determining transition state, which means that the effect of the axial ligand on this mechanism is much smaller.</P> <B>Graphic Abstract</B> <P>How deep is your orbital? Density functional theory studies on the axial ligand effect of aliphatic versus aromatic hydroxylation of ethylbenzene by iron–oxo complexes with a variable axial ligand show that strong (anionic) ligands pull the metal inside the plane of the haeme and destabilise cationic intermediates through orbital interactions (see picture). <img src='wiley_img/09476539-2009-15-22-CHEM200802234-content.gif' alt='wiley_img/09476539-2009-15-22-CHEM200802234-content'> </P>
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Corrosion Fatigue of Austenitic Stainless Steel in Different Hot Chloride Solutions
( A. Visser ),( G. Mori ),( M. Panzenbock ),( R. Pippan ) 한국부식방식학회(구 한국부식학회) 2015 Corrosion Science and Technology Vol.14 No.4
Austenitic stainless steel was investigated under cyclic loading in electrolytes with different chloride contents and pH and at different temperatures. The testing solutions were 13.2 % NaCl (80,000 ppm Cl-) at 80 ¡ÆC and 43 % CaCl2 (275,000 ppm Cl-) at 120 ¡ÆC. In addition to S.N curves in inert and corrosive media, the fracture surfaces were investigated with a scanning electron microscope (SEM) to analyse the type of attack. The experimental results showed that a sharp decrease in corrosion fatigue properties can be correlated with the occurrence of stress corrosion cracking. The correlation of occurring types of damage in different corrosion systems is described.
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de Visser, Sam P,Latifi, Reza,Tahsini, Laleh,Nam, Wonwoo Wiley-VCH 2011 Chemistry - An Asian Journal Vol.6 No.2
<P>Iron(IV)-oxo heme cation radicals are active species in enzymes and biomimetic model complexes. They are potent oxidants in oxygen atom transfer reactions, but the reactivity is strongly dependent on the ligand system of the iron(IV)-oxo group and in particular the nature of the ligand trans to the oxo group (the axial ligand). To find out what effect the axial ligand has on the reactivity of non-heme iron(IV)-oxo species, we have performed a series of density functional theory (DFT) calculations on aliphatic and aromatic hydroxylation reactions by using [Fe(IV) 전(TMC)(L)](n+) (TMC=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane, and L=acetonitrile or chloride). The studies show that the regioselectivity of aliphatic over aromatic hydroxylation is preferred. The studies are in good agreement with experimental product distributions. Moreover, the system with the acetonitrile axial ligand is orders of magnitude more reactive than that with a chloride axial ligand. We have analyzed our results and we have shown that the metal-ligand interactions influence the orbital energies and as a consequence also the electron affinities and hydrogen atom abstraction abilities. Thermodynamic cycles explain the regioselectivity preferences.</P>
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Wilhelmina S Visser,Wouter W te Riele,Djamila Boerma,Bert van Ramshorst,Henderik L van Westreenen 대한대장항문학회 2014 Annals of Coloproctolgy Vol.30 No.3
Purpose: Impaired functional outcome is common after a low anterior resection (LAR). Pelvic floor rehabilitation (PFR) might improve functional outcome after a LAR. The aim of this systematic review is to evaluate the effectiveness of PFR in improving functional outcome. Methods: PubMed, Embase, and the Cochrane Library were searched using the terms fecal incontinence, colorectal neoplasm/surgery, LAR, rectal cancer, anterior resection syndrome, bowel habit, pelvic floor, training, therapy, physical therapy, rehabilitation and biofeedback. Of the 125 identified records, 5 articles were included. Results: The 5 included studies reported on 321 patients, of which 286 patients (89%) underwent pelvic floor training. Three studies included patients with anterior resection syndrome after a LAR while the remaining studies included a series of patients after a LAR. Functional outcome was mostly assessed by using the Wexner incontinence scale. Quality of life was assessed in one study, and in three studies, rectal manometry was performed. After PFR, the functional outcome was improved in four studies, as was the quality of life. Conclusion: This systematic review demonstrated that PFR is useful for improving the functional outcome after a LAR. The data are extracted from studies of limited quality, but the available evidence points to the effectiveness of the procedure.
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