Chiral cyclotrisiloxanes

Tanaka, Ryoji; Kowase, Susumu; Unno, Masafumi

doi:10.1039/c0dt00135j

Cited by 7 publications

(3 citation statements)

References 60 publications

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“…Conversion of heme to biliverdin has especially been studied in biological systems − and in models called coupled oxidation during the last two decades. ,− These experimental and theoretical works have shed light on the details of the conversion of heme to oxophlorin and the conversion of verdoheme to biliverdin. − …”

Section: Introductionmentioning

confidence: 99%

Effect of Axial Ligand on the Electronic Configuration, Spin States, and Reactivity of Iron Oxophlorin

2012

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Iron-oxophlorin is an intermediate in heme degradation, and the nature of the axial ligand can alter the spin, electron distribution, and reactivity of the metal and the oxophlorin ring. The structure and reactivity of iron-oxophlorin in the presence of imidazole, pyridine, and t-butyl isocyanide as axial ligands was investigated using the B3LYP and OPBE methods with the 6-31+G* and 6-311+G** basis sets. OPBE/6-311+G** has shown that the doublet state of [(Py)(2)Fe(III)(PO)] (where pyridines are in perpendicular planes and PO is the oxophlorin trianion) is 3.45 and 5.27 kcal/mol more stable than the quartet and sextet states, respectively. The ground-state electronic configuration of the aforementioned complex is π(xz)(2) π(yz)(2) a(2u)(2) d(xy)(1) at low temperatures and changes to π(xz)(2) π(yz)(2) d(xy)(2) a(2u)(1) at high temperatures. This latter electronic configuration is consistently seen for the [(t-BuNC)(2)Fe(II)(PO(•))] complex (where PO(•) is the oxophlorin dianion radical). The complex [(Im)(2)Fe(III)(PO)] adopted the d(xy)(2) (π(xz) π(yz))(3) ground state and has low-lying quartet excited state which is readily populated when the temperature is increased.

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Section: Introductionmentioning

confidence: 99%

Effect of Axial Ligand on the Electronic Configuration, Spin States, and Reactivity of Iron Oxophlorin

2012

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“…It is known that oxophlorin is air sensitive and in the presence of O 2 transforms to verdoheme by releasing carbon monoxide. Balch and co-workers have indeed characterized complexes of oxophlorin macrocycles in model systems called coupled oxidation. − Conversion of heme to biliverdin has been specially studied in biological − and theoretical − systems. The mechanism that converts oxophlorin into verdoheme is, however, the least known step, and especially the role of electron transfer in this process is the subject of challenges.…”

Section: Introductionmentioning

confidence: 99%

Structure and Redox Behavior of Iron Oxophlorin and Role of Electron Transfer in the Heme Degradation Process

2012

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Iron-oxophlorin is an intermediate in heme degradation, and the metal oxidation number can alter spin, electron distribution, and the reactivity of the metal and the oxophlorin ring. The role of electron transfer in the structure and reactivity of [(Py)(2)Fe(III)(PO)] (PO is the oxophlorin trianion) in different redox states has been investigated using the B3LYP and OPBE methods with the 6-31+G* and 6-311+G** basis sets. A computation study has shown that [(py)(2) Fe(III)(PO)] loses one electron from its a(2u) orbital. Thus the oxidized species, [(Py)(2)Fe(III)(PO(•))](+) (where PO(•) is the oxophlorin dianion radical), has an open-shell-singlet ground state with a d(xy)(2) d(xz)(2) a(2u)(1) d(yz)(1) electronic configuration with closely lying triplet and quintet states which are populated at ambient temperature. The aforementioned complex is highly reactive toward O(2). The reduced species [(Py)(2)Fe(II)(POH)] (where POH is the hydroxyheme) has the closed-shell-singlet ground state (π(xz) π(yz))(4) a(2u)(2) d(xy)(2) electronic configuration in which pyridines have a more π-accepting character and, thus, are tightly bound to iron. This reduced form is considerably less reactive toward O(2). The axial ligands effects (Im, t-BuNC) have also been studied in redox reactions of iron oxophlorin complexes. Complex [(Im)(2)Fe(III)(PO)] shows facile oxidation to form a cation radical and a reduction to form hydroxy while the [(t-BuNC)(2)Fe(II)(PO(•))] has high positive oxidation potential.

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“…The chiral enantiomeric pair of cyclotrisiloxanes (5 and 6) were both synthesised and separated. 4 The molecules displayed a three-blade propeller alignment of the phenyl groups which was induced by chiral sec-butyl groups. The enthalpies and entropies of dimerisation were determined for dibutyltin diorgano-oxides (7) by 119 Sn NMR spectroscopic studies and theoretical investigations.…”

Section: Group 14/16 Chemistrymentioning

confidence: 99%