Reactivity and Functionalization of β‐Substituted Porphyrins and Chlorins

Vicente, Maria da Graça H.

doi:10.1002/chin.200317267

“…Et 2 O was added, and the mixture was filtered (to remove triethylammonium iodide). The filtrate was concentrated and treated with hexanes (30 mL 4 (17.6 mg, 0.0152 mmol, 20 mol%) were weighed in a 25 mL Schlenk flask. The flask was pump-purged with argon three times.…”

Section: Methodsmentioning

confidence: 99%

“…Three approaches generally have been employed for the synthesis of model (bacterio)chlorins. (i) Reduction or derivatization of porphyrins: This approach is the simplest yet least versatile, typically affording mixtures of isomers with porphyrins that bear distinct patterns of substituents (4,5). (ii) Semisynthesis: The chemical modification of naturally occurring (bacterio)chlorophylls takes advantage of ample quantities of naturally available starting materials.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Photophysical Characterization of Porphyrin, Chlorin and Bacteriochlorin Molecules Bearing Tethers for Surface Attachment

Muthiah

¹

,

Taniguchi

²

,

Kim

³

et al. 2007

Photochem & Photobiology

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The ability to tailor synthetic porphyrin, chlorin and bacteriochlorin molecules holds promise for diverse studies in artificial photosynthesis. Toward this goal, the synthesis and photophysical characterization of five tetrapyrrole compounds is described. Each compound bears a surface attachment group. One set contains three meso-substituted porphyrins that differ only in the nature of a surface-binding tether-isophthalic acid, ethynylisophthalic acid or cyanoacrylic acid. The other set includes a porphyrin, chlorin and bacteriochlorin each of which bears an ethynylisophthalic acid tether. The ester derivative of each compound was prepared for solution photophysical characterization studies. The photophysical studies include determination (in toluene or acetonitrile) of the electronic absorption and fluorescence spectra, fluorescence yield and lifetime of the lowest excited singlet state. The excited-state lifetimes range from 1 to 5.6 ns for the five compounds. The radiative rate constant for the excited-state decay was estimated from the photophysical data (fluorescence yield and excited-state lifetime) and from Strickler-Berg analysis of the absorption and fluorescence spectra. The synthesis and characterization of the tetrapyrrole compounds underpin their use as sensitizers in molecular-based solar cells.

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“…Our results above suggest that a different explanation should be given to the role of the core metal in dechlorination reactions and that the entire metalloporphyrin should be considered as an integral system in which the organic portion of the macrocycle plays an indispensable role in the reaction. Porphyrin macrocycles are known to have conjugated systems that allow significant electron delocalization [33]; hence, they are capable of transferring electrons not only through the core metal but also through the entire macromolecular system. Upon considering the concept of a reactive macromolecular system, the van der Waal space-filling molecular model shows that the available vitamin B 12 surface has pockets of sufficient size (diameter Ͼ4.5 Å ) to facilitate interaction and subsequent reaction with chlorinated organic molecules, even for the limiting case that considers only the porphyrin and core metal portions of the macrocycle as the reactive sites.…”

Section: Tetrapyrrole Macrocycle Structure Considerations For Dechlormentioning

confidence: 99%

Role of metalloporphyrin core metals in the mediated reductive dechlorination of tetrachloroethylene

Dror

¹

,

Schlautman

²

2003

Enviro Toxic and Chemistry

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A promising approach to abiotically dechlorinate a variety of chlorinated organic contaminants under reducing conditions is to utilize porphyrins or other tetrapyrrole macrocycles as electron transfer mediators/shuttles for catalyzing their reduction. In this study, various experimental approaches were used to elucidate the role of porphyrin core metals in the reductive dechlorination of tetrachloroethylene (PCE). The importance of specific core metals for the reactivity of a porphyrin and its mediated reaction mechanisms was demonstrated by inserting different metals into metallo tetrakis (N-methyl-4-4 pyridiniumyl) porphyrin (TMPyP). No PCE dechlorination was observed when the free-base (i.e., no core metal) and iron core metal forms of TMPyP were utilized. When using nickel or cobalt TMPyP, reductive dechlorination of PCE occurred but appeared to follow different pathways for the two metals based on product analyses. Physical (e.g., steric) considerations suggest that direct contact between a porphyrin core metal and PCE may be limited and therefore that the entire metalloporphyrin molecule should be viewed as a functional system in which the organic macrocycle has an active part in reductive dechlorination reactions. This view is supported by the fact that slight changes in the functional groups on a porphyrin macrocycle, particularly those far removed from the core metal itself, greatly affected the reactivity and mechanism of the porphyrin. Solution conditions also had a major effect on porphyrin reactivities, to the extent that a nonreactive metalloporphyrin could be activated merely by adjusting the pH of the solution or by adding a small amount of cosolvent. The collective results of this study suggest that fine tuning of naturally occurring metalloporphyrin complexes and/or their environments can enhance the catalyzed detoxification of chlorinated contaminants in many natural and engineered environmental systems.

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“…Porphyrin macrocycles are known to have conjugated systems that allow significant electron delocalization [33]; hence, they are capable of transferring electrons not only through the core metal but also through the entire macromolecular system. Porphyrin macrocycles are known to have conjugated systems that allow significant electron delocalization [33]; hence, they are capable of transferring electrons not only through the core metal but also through the entire macromolecular system.…”

Section: Tetrapyrrole Macrocycle Structure Considerations For Dechlormentioning

confidence: 99%

Role of Metalloporphyrin Core Metals in the Mediated Reductive Dechlorination of Tetrachloroethylene

Dror¹,

Schlautman²

2003

Environ Toxicol Chem

2

15

0

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A promising approach to abiotically dechlorinate a variety of chlorinated organic contaminants under reducing conditions is to utilize porphyrins or other tetrapyrrole macrocycles as electron transfer mediators/shuttles for catalyzing their reduction. In this study, various experimental approaches were used to elucidate the role of porphyrin core metals in the reductive dechlorination of tetrachloroethylene (PCE). The importance of specific core metals for the reactivity of a porphyrin and its mediated reaction mechanisms was demonstrated by inserting different metals into metallo tetrakis (N-methyl-4-4 pyridiniumyl) porphyrin (TMPyP). No PCE dechlorination was observed when the free-base (i.e., no core metal) and iron core metal forms of TMPyP were utilized. When using nickel or cobalt TMPyP, reductive dechlorination of PCE occurred but appeared to follow different pathways for the two metals based on product analyses. Physical (e.g., steric) considerations suggest that direct contact between a porphyrin core metal and PCE may be limited and therefore that the entire metalloporphyrin molecule should be viewed as a functional system in which the organic macrocycle has an active part in reductive dechlorination reactions. This view is supported by the fact that slight changes in the functional groups on a porphyrin macrocycle, particularly those far removed from the core metal itself, greatly affected the reactivity and mechanism of the porphyrin. Solution conditions also had a major effect on porphyrin reactivities, to the extent that a nonreactive metalloporphyrin could be activated merely by adjusting the pH of the solution or by adding a small amount of cosolvent. The collective results of this study suggest that fine tuning of naturally occurring metalloporphyrin complexes and/or their environments can enhance the catalyzed detoxification of chlorinated contaminants in many natural and engineered environmental systems.

show abstract

Reactivity and Functionalization of β‐Substituted Porphyrins and Chlorins

Abstract: For Abstract see ChemInform Abstract in Full Text.

Cited by 15 publications

References 0 publications

Synthesis and Photophysical Characterization of Porphyrin, Chlorin and Bacteriochlorin Molecules Bearing Tethers for Surface Attachment

Synthesis and Photophysical Characterization of Porphyrin, Chlorin and Bacteriochlorin Molecules Bearing Tethers for Surface Attachment

Role of metalloporphyrin core metals in the mediated reductive dechlorination of tetrachloroethylene

Role of Metalloporphyrin Core Metals in the Mediated Reductive Dechlorination of Tetrachloroethylene

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