Formation and reactivity of hypophosphite and phosphite radicals and their peroxyl derivatives

Shastri, L.V.; Huie, Robert E.; Neta, P.

doi:10.1021/j100368a033

Cited by 24 publications

(11 citation statements)

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“…The ratio of • OH to H • is influenced primarily by equilibrium reaction 6 with the concentration of H 2 (aq) determined from reaction 7. The photolysis of H 2O requires UV light (Ͻ240 nm), and it is estimated that the amount of water photolyzed reaches a steady-state concentration of Ϸ10 Ϫ11 -10 Ϫ12 M for the top centimeters of water averaged globally over the day-night cycle (70). At these concentrations the rate of production of • OH and H • is balanced by the loss through combination reactions produc- where D is the eddy diffusion coefficient for water (72).…”

Section: Methodsmentioning

confidence: 99%

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Rethinking early Earth phosphorus geochemistry

Pasek

2008

Proc. Natl. Acad. Sci. U.S.A.

240

209

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Phosphorus is a key biologic element, and a prebiotic pathway leading to its incorporation into biomolecules has been difficult to ascertain. Most potentially prebiotic phosphorylation reactions have relied on orthophosphate as the source of phosphorus. It is suggested here that the geochemistry of phosphorus on the early Earth was instead controlled by reduced oxidation state phosphorus compounds such as phosphite (HPO 3 2؊ ), which are more soluble and reactive than orthophosphates. This reduced oxidation state phosphorus originated from extraterrestrial material that fell during the heavy bombardment period or was produced during impacts, and persisted in the mildly reducing atmosphere. This alternate view of early Earth phosphorus geochemistry provides an unexplored route to the formation of pertinent prebiotic phosphorus compounds, suggests a facile reaction pathway to condensed phosphates, and is consistent with the biochemical usage of reduced oxidation state phosphorus compounds in life today. Possible studies are suggested that may detect reduced oxidation state phosphorus compounds in ancient Archean rocks.meteorites ͉ origins of life ͉ phosphonates ͉ prebiotic ͉ redox chemistry P hosphorus (P) is a key biologic element and is the limiting reagent in many ecosystems. Phosphorus is ubiquitous in biochemistry because phosphorylated biomolecules play major roles in replication and information (as RNA and DNA), metabolism (as ATP, NADPH, and other coenzymes), and structure (as phospholipids). Several key properties of P as phosphate make it advantageous to biologic systems, including thermodynamic instability coupled with kinetic stability, charge and coordination state, and a constant oxidation state under typical redox conditions (1). These features are especially critical to the formation of large informational polymers, and hence highly relevant to the origin and development of early life. Phosphorus Geochemistry and CosmochemistryThe major forms of P in life are summarized in Fig. 1. Inorganic P compounds used by life include orthophosphate, pyrophosphate and other condensed phosphates, phosphite, hypophosphite, and phosphine. These inorganic forms are either used by organisms as sources of P for the synthesis of organic-P biomolecules or are possible metabolic by-products of P metabolism (PH 3 ). Additionally, orthophosphate acts as a buffer in many cells, keeping pH constant at Ϸ7. Organic forms of P include compounds with C-O-P linkages and compounds with C-P linkages, and both are formed from inorganic P by using enzymes.Phosphorus is a lithophile element at the redox conditions on the surface of the Earth, and hence orthophosphate is the dominant form of inorganic P on the surface of the Earth today. The concentration of orthophosphate is water-buffered by the solubility of orthophosphate minerals like apatite, Ca 5 (PO 4 ) 3 (OH,F,Cl), on the present-day Earth, and of whitlockite, Ca 9 MgH(PO 4 ) 7 , and brushite, CaHPO 4 ⅐2H 2 O, before the rise of life-mediated apatite deposition (2). Because ...

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Section: Methodsmentioning

confidence: 99%

“…The top profile is based on the estimate of UV flux under a CO 2-rich atmosphere, whereas the bottom profile assumes no CO 2 (70). …”

Section: Biotic Evidencementioning

confidence: 99%

Rethinking early Earth phosphorus geochemistry

Pasek

2008

Proc. Natl. Acad. Sci. U.S.A.

240

209

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“…Hypophosphite salts have proven to be effective hydrogen sources that are often employed in radical-induced reduction and allow facile purification of the resulting polymer products . With an excess of EPHP (15 molar equiv) and under mild UV irradiation (365 nm, 7.0 mW/cm 2 ), trithiocarbonate photolysis liberates the polymer chain end to yield a macroradical that quickly and irreversibly abstracts a hydrogen from the phosphorus–hydrogen bond of the hypophosphite salt . This process was first demonstrated with poly( N , N -dimethylacrylamide) (PDMA) prepared by RAFT polymerization with a trithiocarbonate CTA (PDMA-TTC).…”

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confidence: 99%

Catalyst-Free Photoinduced End-Group Removal of Thiocarbonylthio Functionality

et al. 2017

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An initiator-and catalyst-free method for polymer end-group modification has been designed. Under long-wave ultraviolet irradiation, polymers with thiocarbonylthio end groups undergo photolytic cleavage to reveal an active macroradical capable of irreversible termination with a suitable hydrogen source. This straightforward method was successfully demonstrated by the removal of a range of end groups that commonly result from reversible addition−fragmentation chain transfer or photoiniferter polymerizations, including trithiocarbonate, dithiobenzoate, xanthate, and dithiocarbamate mediating agents. This strategy proved efficient for polymers derived from acrylamido, acrylic, methacrylic, styrenic, and vinylpyrrolidone monomers.

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“…101 The reactions of OH with NH 3 , 97 NH 2 Cl, 102 H 2 PO 2 À , H 2 PO 3 À , and HPO 3 2À are also considered to have hydrogen atom abstraction mechanisms. 10 The sulfate radical was long considered as a virtually obligatory outer-sphere oxidant, but the data in Table 9.10 show that it is also a very powerful hydrogen atom abstractor. Arguments in favor of a HAT mechanism for SO 4 À reactions have been made for a number of reactions with organic substrates.…”

Section: Hydrogen Atom Transfer/proton-coupled Electron Transfermentioning

confidence: 99%

Reactivity of Inorganic Radicals in Aqueous Solution

Stanbury

2010

Physical Inorganic Chemistry

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Formation and reactivity of hypophosphite and phosphite radicals and their peroxyl derivatives

Cited by 24 publications

References 0 publications

Rethinking early Earth phosphorus geochemistry

Rethinking early Earth phosphorus geochemistry

Catalyst-Free Photoinduced End-Group Removal of Thiocarbonylthio Functionality

Reactivity of Inorganic Radicals in Aqueous Solution

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