Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “singlets”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,207 records · Page 67Linked to original sources
PubMed1994

A well resolved ODMR triplet minus singlet spectrum of P680 from PSII particles.

An ADMR T-S spectrum of the primary donor (P680) of photosystem II (PSII) was obtained from anaerobically photoreduced particles. The spectrum is the best resolved obtained so far having a main bleaching band at 684 nm with a linewidth of only 100 cm-1. The view that this spectrum is produced by native homogeneous P680 unlike those obtained before is defended. A small bleaching observed at 678 nm is discussed in terms of the reaction center structure. One possible interpretation of the observations is that P680 is a very loose dimer with an exciton splitting of only 144 cm-1 corresponding to a dimer center-to-center distance of roughly 11.5 A.

Chlorophyll↗
PubMed1993

EPR studies of singlet oxygen (1O2) and free radicals (O2.-, .OH, HB.-) generated during photosensitization of hypocrellin B.

Hypocrellin B(HB), a peryloquinone derivative, is one of the main photosensitive agents, hypocrellin. This pigment, in combination with phototherapy, has been used in human medicine to cure various skin diseases. The photochemistry (Type I and II) of HB has been studied using spin-trapping and spin-counteraction techniques. The results show that the active oxygen (1O2, O2.-, .OH) mechanism of HB photosensitization can be converted into nonoxygen free radical (HB.-) mechanism completely when oxygen is exhausted in the experimental system. Under anaerobic conditions, HB only undergoes Type I reaction, generating nonoxygen free radical (HB.-).

Electron Spin Resonance Spectroscopy↗
PubMed1988

The excited states of covalently linked dimeric porphyrins. I: The excited singlet states.

The ground state absorbance and emission properties of a series of covalently linked biporphyrins were studied, in both their neutral and dicationic forms. The fluorescence quantum yields determined are comparable in value with that obtained from haematoporphyrin IX. Soret band splitting is observed for porphyrin rings separated by a hydrocarbon chain containing 0-3 carbons joined at the beta,beta' ring positions. The biporphyrin linked directly at the meso position shows considerable steric hindrance and behaves like two independent chromophores.

Chemical Phenomena↗
PubMed1992

Excited singlet state properties of anthracenedione photosensitizers.

The absorption, fluorescence and S1 state kinetics of anthracycline antitumour drugs (e.g. daunomycin, adriamycin) and several imino- and/or amino-substituted derivatives are investigated. The study, which includes all anthracyclines which possess photocytocidal activity, is extended to the disubstituted aminoanthracenedione, mitoxantrone, a red-light-absorbing antitumour drug whose activity, both in vitro and in vivo, is enhanced by photoactivation. The S1 state of the anthracycline imino and amino derivatives, in aqueous buffer at pH 7.4, is characterized by bi-exponential decay kinetics which indicates the presence of two ground state populations differing in the extent of hydrogen bonding. The ammonium group of the sugar moiety of anthracyclines contributes to the quenching of the S1 state population through a prototropic mechanism.

Antibiotics, Antineoplastic↗