Singlet oxygen



 

Singlet oxygen is the common name used for the two metastable states of molecular oxygen (O2) with higher energy than the ground state triplet oxygen [1]. The energy difference between the lowest energy of O2 in the singlet state and the lowest energy in the triplet state is about 3625 kelvin (Te (a¹Δg <- X³Σg-) = 7918.1 cm-1.)

Molecular antibonding πg-orbitals (see degenerate energy level). The O2(b¹Σg+)-state is very short lived and relaxes quickly to the lowest lying excited state, O2(a¹Δg). Thus, the O2(a¹Δg)-state is commonly referred to as singlet oxygen.

Physics

The energy difference between ground state and singlet oxygen is 94.2 kJ/mol and corresponds to a transition in the near-infrared at ~1270 nm. In the isolated molecule, the transition is strictly forbidden by spin, symmetry and parity selection rules, making it one of nature's most forbidden transitions. In other words, direct excitation of ground state oxygen by light to form singlet oxygen is very improbable. As a consequence, singlet oxygen in the gas phase is extremely long lived (72 minutes). Interaction with solvents, however, reduces the lifetime to microsecond or even nanoseconds.

Direct detection of singlet oxygen is possible through its extremely weak fluorescence of the so-called singlet oxygen dimol (simultaneous emission from two singlet oxygen molecules upon collision) can be observed as a red glow at 634 nm [2].

Chemistry

The chemistry of singlet oxygen is different from that of ground state oxygen. Singlet oxygen can participate in cycloaddition adducts. [4].

Biochemistry

In chlorophyll molecules or quenching the singlet oxygen molecules directly.

In mammalian biology, singlet oxygen is a form of Polyphenol antioxidants can scavenge and reduce concentrations of reactive oxygen species and may prevent such deleterious oxidative effects [5].

Singlet oxygen is the active species photodynamic therapy.

References

  1. ^ David R. Kearns (1971). "Physical and chemical properties of singlet molecular oxygen". Chemical Reviews 71 (4): 395 - 427. doi:10.1021/cr60272a004.
  2. ^ Interpretation of the atmospheric oxygen bands; electronic levels of the oxygen molecule R.S. Mulliken Nature (journal) Volume 122, Page 505 1928
  3. ^ Physical Mechanisms of Generation and Deactivation of Singlet Oxygen C. Schweitzer, R. Schmidt Chemical Reviews Volume 103, Pages 1685-1757 2003
  4. ^ Carey, Francis A.; Sundberg, Richard J.; (1984). Advanced Organic Chemistry Part A Structure and Mechanisms (2nd ed.). New York N.Y.: Plenum Press. ISBN 0-306-41198-9.
  5. ^ Cell and Molecular Cell Biology concepts and experiments Fourth Edition. Gerald Karp. Page 223 2005
 v • d • e Allotropes of oxygen

triplet)
O2

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Ozone (Trioxygen)
O3

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Tetraoxygen
O4

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Metallic oxygen
Ox

 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Singlet_oxygen". A list of authors is available in Wikipedia.