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At least 73 records · Page 4Linked to original sources
PubMed2006

Triplet-triplet energy transfer from naphthalene to biacetyl in the vapor phase.

In principle the optical energy absorbed by a complex molecule raises that molecule to one of its excited states, and afterwards this excitation energy decays through the different relaxation channels. Initially, electronically excited naphthalene emits photons in the phosphorescence band of naphthalene and these emitted photons are absorbed by the acceptor molecule biacetyl, then excited biacetyl phosphoresces. In this investigation, sensitized phosphorescence decay times in different conditions were measured for naphthalene-biacetyl system in the vapor phase. The ultraviolet-visible spectrum of biacetyl vapor at room temperature conditions was broad and structureless.

Diacetyl↗
PubMed2000

Effect of zeolite properties on ground-state and triplet-triplet absorption, prompt and oxygen induced delayed fluorescence of tetraphenylporphyrin at gas/solid interface.

The ground-state and transient absorption, prompt and delayed fluorescence of tetraphenylporphyrin (TPP) adsorbed onto the external surface of different zeolites was monitored using diffuse-reflectance steady-state and laser flash photolysis. The delayed fluorescence (DF) of TPP detected in the presence of O2 is attributed to the energy transfer from 3TPP to 3O2 to form 1O2 and subsequent energy transfer from 1O2 to some other 3TPP within the organised molecular ensembles on the zeolite surface. The spectroscopic and kinetic parameters, namely the yield of DF (2-20% relative to prompt fluorescence), depend on the zeolite properties: the observed differences were correlated with the acid-base properties of the two zeolite series studied in this work (KA, NaA, CaA) and (NaA, NaX, NaY).

Oxygen↗
PubMed2002

Singlet-triplet gap in triplet ground-state biradicals is modulated by substituent effects.

Three S = 1 bis(semiquinone) complexes have been prepared. To ensure ferromagnetic intramolecular exchange coupling, the two semiquinones are attached 1,3 to a 5-substituted phenylene ring. The biradical complexes differ in their meta-substituents: 1-NMe(2)(), X = N,N-dimethylamino; 1-t-Bu, X = tert-butyl; 1-NO(2)(), X = nitro. All three structures have been determined by X-ray crystallography. Results of structural studies indicate that the biradical ligands of all three complexes have nearly identical conformations with average semiquinone ring torsions of 32 degrees +/- 2 degrees relative to the 5-substituted phenylene ring. The exchange parameter, J (Eta = -2JS(1).S(2)), ranges from +31.0 +/- 0.6 cm(-)(1) for 1-NO(2)() to +59.3 +/- 1.2 cm(-)(1) for 1-t-Bu, with J = +34.9 +/- 0.7 cm(-)(1) for 1-NMe(2)(). Since the conformations are nearly identical, the differences in exchange coupling parameter J are due to substituent effects. The experimental results are supported by Hückel theory arguments and previous computational work.

Journal Article↗
PubMed1973

Triplet-triplet energy transfer in alpha-trypsin.

Experiments are reported that demonstrate that light absorbed by ionized tyrosinyl sensitizes the phosphorescence of tryptophanyl residues of native alpha-trypsin. The sensitization effect is abolished when alpha-trypsin is unfolded in guanidine hydrochloride. Under the experimental conditions used, the tryptophan phosphorescence could only have been induced by an electron-exchange interaction. These results, therefore, require that there be at least one ionized tyrosinyl-tryptophanyl pair in the native enzyme and that the distance between the two side chains be sufficiently short to permit electron exchange.

Amidines↗
PubMed1997

Molecular genetics of triplet repeats: unstable expansion of triplet repeats as a new mechanism for neurodegenerative diseases.

Expansion of trinucleotide repeats has been identified as a common mechanism of hereditary neurodegenerative diseases including spinal and bulbar muscular atrophy (SBMA), Huntington's disease, dentatorubral-pallidoluysian atrophy (DRPLA), Machado-Joseph disease (MJD), fragile X syndrome, myotonic dystrophy and Friedreich's ataxia. These diseases share unique features, which are difficult to explain based on Mendelian inheritance. These unique clinical genetic features include genetic anticipation and a broad spectrum of clinical presentations, which have been shown to be associated with the instability of the trinucleotide repeats. Recent studies suggest that gene products with expanded polyglutamine tracts may be toxic to neuronal cells, and the mechanisms of neurotoxicity should be thoroughly investigated. To develop therapeutic measures, creation of animal models or cell culture systems for the investigation of neurotoxicity will be indispensable.

Age of Onset↗