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New approaches to highly sterically encumbered porphyrins as heme active sites.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	New approaches to highly sterically encumbered porphyrins as heme active sites./
作者:	Yeh, Chen-Yu.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 1999,
面頁冊數:	202 p.
附註:	Source: Dissertations Abstracts International, Volume: 62-03, Section: B.
Contained By:	Dissertations Abstracts International62-03B.
標題:	Organic chemistry. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9963436
ISBN:	9780599677340

New approaches to highly sterically encumbered porphyrins as heme active sites.
Yeh, Chen-Yu.

New approaches to highly sterically encumbered porphyrins as heme active sites. - Ann Arbor : ProQuest Dissertations & Theses, 1999 - 202 p.

Source: Dissertations Abstracts International, Volume: 62-03, Section: B.

Thesis (Ph.D.)--Michigan State University, 1999.

This item must not be sold to any third party vendors.

A series of highly hindered β-substituted bis-pocket porphyrins in which both sides of the porphyrin plane are protected to provide a nonpolar environment have been synthesized. The iron(II) complexes of these porphyrins are capable of binding dioxygen irreversibly at room temperature, indicating that the hindered substituents can prevent the irreversible oxidation of the coordination site via the formation of the μ-oxo dimer. Compared to other model porphyrins, the decreased O2 affinities of our system are ascribed to the nonpolar nature of the binding sites. This can be confirmed by the observation that increasing the polarity of solvents increases the O2 affinity. The results are consistent with the fact that in hemoproteins, the polar environments about the active site can stabilize the oxygenated adduct and result in a higher O2 affinity. We have also observed that the polarity of the pockets has little effect on CO binding. The manganese complexes of these sterically hindered bis-pocket porphyrins have also been used as catalysts for shape selective epoxidation of alkenes. The sizes of the substituents at the periphery of porphyrins are responsible for the shape selectivity. The high selectivity of our system is ascribed to increased steric crowding on both face and side ways of the porphyrins. The β-substituted zinc porphyrins show shape-selectivity on ligation with various amines having different sizes and shapes. The hydrophobic pockets of the porphyrins can stabilize the bound ligand, thus showing higher binding constants than Zn(TPP). The size of the pocket of the porphyrin reflects on the selectivity on ligation to small and bulky ligands. A new highly steric β-substituted water-soluble porphyrin has also been synthesized. The spectophotometric data of the iron(III) complex support the absence of μ-oxo dimeric species in the whole range of pH due to the added steric hindered substituents at β-positions. The pKa of the iron complex was estimated to be 8.11 which is the highest of the sulfonated iron porphyrins due to the electron-donating nature of the substituents at β-positions. The synthesis of fully substituted xanthene-bridged chiral porphyrins and their circular dichroism profiles have also been described. The (R) and (S) enantiomers of this series of chiral porphyrins, exhibit a positive and negative split Cotton effect at longer wavelengths in the Soret region, respectively. The CD spectra of the (R) and (S) forms are perfect mirror images of each other. Based on the CD spectra and the X-ray crystal structure, the conformations of this series of single armed fully substituted porphyrins can be assigned and the conformation-circular dichroism relationship can be established. (Abstract shortened by UMI.).

ISBN: 9780599677340Subjects--Topical Terms:

523952
Organic chemistry.
Subjects--Index Terms:

Epoxidation

New approaches to highly sterically encumbered porphyrins as heme active sites.
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020 $a 9780599677340
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100 1 $a Yeh, Chen-Yu. $3 3688785
245 1 0 $a New approaches to highly sterically encumbered porphyrins as heme active sites.
260 1 $a Ann Arbor : $b ProQuest Dissertations & Theses, $c 1999
300 $a 202 p.
500 $a Source: Dissertations Abstracts International, Volume: 62-03, Section: B.
500 $a Publisher info.: Dissertation/Thesis.
500 $a Advisor: Chang, Chi K.
502 $a Thesis (Ph.D.)--Michigan State University, 1999.
506 $a This item must not be sold to any third party vendors.
506 $a This item must not be added to any third party search indexes.
520 $a A series of highly hindered β-substituted bis-pocket porphyrins in which both sides of the porphyrin plane are protected to provide a nonpolar environment have been synthesized. The iron(II) complexes of these porphyrins are capable of binding dioxygen irreversibly at room temperature, indicating that the hindered substituents can prevent the irreversible oxidation of the coordination site via the formation of the μ-oxo dimer. Compared to other model porphyrins, the decreased O2 affinities of our system are ascribed to the nonpolar nature of the binding sites. This can be confirmed by the observation that increasing the polarity of solvents increases the O2 affinity. The results are consistent with the fact that in hemoproteins, the polar environments about the active site can stabilize the oxygenated adduct and result in a higher O2 affinity. We have also observed that the polarity of the pockets has little effect on CO binding. The manganese complexes of these sterically hindered bis-pocket porphyrins have also been used as catalysts for shape selective epoxidation of alkenes. The sizes of the substituents at the periphery of porphyrins are responsible for the shape selectivity. The high selectivity of our system is ascribed to increased steric crowding on both face and side ways of the porphyrins. The β-substituted zinc porphyrins show shape-selectivity on ligation with various amines having different sizes and shapes. The hydrophobic pockets of the porphyrins can stabilize the bound ligand, thus showing higher binding constants than Zn(TPP). The size of the pocket of the porphyrin reflects on the selectivity on ligation to small and bulky ligands. A new highly steric β-substituted water-soluble porphyrin has also been synthesized. The spectophotometric data of the iron(III) complex support the absence of μ-oxo dimeric species in the whole range of pH due to the added steric hindered substituents at β-positions. The pKa of the iron complex was estimated to be 8.11 which is the highest of the sulfonated iron porphyrins due to the electron-donating nature of the substituents at β-positions. The synthesis of fully substituted xanthene-bridged chiral porphyrins and their circular dichroism profiles have also been described. The (R) and (S) enantiomers of this series of chiral porphyrins, exhibit a positive and negative split Cotton effect at longer wavelengths in the Soret region, respectively. The CD spectra of the (R) and (S) forms are perfect mirror images of each other. Based on the CD spectra and the X-ray crystal structure, the conformations of this series of single armed fully substituted porphyrins can be assigned and the conformation-circular dichroism relationship can be established. (Abstract shortened by UMI.).
590 $a School code: 0128.
650 4 $a Organic chemistry. $3 523952
653 $a Epoxidation
653 $a Heme
653 $a Oxygen binding
653 $a Porphyrins
690 $a 0490
710 2 $a Michigan State University. $3 676168
773 0 $t Dissertations Abstracts International $g 62-03B.
790 $a 0128
791 $a Ph.D.
792 $a 1999
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9963436