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Titolo:
Gramicidin A and its complexes with Cs+ and T1(+) ions in organic solvents- A study by steady state and time resolved emission spectroscopy
Autore:
Mondal, S; Ghosh, S;
Indirizzi:
Presidency Coll, Dept Chem, Calcutta 7000073, W Bengal, India Presidency Coll Calcutta W Bengal India 7000073 7000073, W Bengal, India
Titolo Testata:
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY
fascicolo: 1, volume: 60, anno: 2001,
pagine: 12 - 24
SICI:
1011-1344(200104)60:1<12:GAAICW>2.0.ZU;2-9
Fonte:
ISI
Lingua:
ENG
Soggetto:
TRYPTOPHAN RESIDUES; MAGNETIC-RESONANCE; CRYSTAL-STRUCTURE; CHANNELS; CONFORMATION; RESOLUTION; FLUORESCENCE; MEMBRANES; LYSOZYME; CATIONS;
Keywords:
gramicidin A; organic solvents; spectroscopy;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Life Sciences
Citazioni:
58
Recensione:
Indirizzi per estratti:
Indirizzo: Ghosh, S Presidency Coll, Dept Chem, Calcutta 7000073, W Bengal, India Presidency Coll Calcutta W Bengal India 7000073 W Bengal, India
Citazione:
S. Mondal e S. Ghosh, "Gramicidin A and its complexes with Cs+ and T1(+) ions in organic solvents- A study by steady state and time resolved emission spectroscopy", J PHOTOCH B, 60(1), 2001, pp. 12-24

Abstract

Gramicidin A (gr A), a linear pentadecapeptide containing four trp residues has been studied using steady state and time resolved fluorescence (at 298 K) and phosphorescence (at 77 K) in methanol (CH3OH), ethanol (C2H5OH), dimethyl sulfoxide (DMSO), 1,4-dioxane, 2-methyl tetrahydrofuran (2-MeTHF), ethanol/benzene (C2H5OH/C6H6) mixed solvent. Similar studies have also beencarried out in CH3OH containing monovalent cations K+, Cs+. Tl+ and divalent cation Ca2-. lambda (max) of fluorescence is found to be a good signature of the different forms having double helical structure [dh (1) to dh (4)](J. Struct. Biol. 121 (1998) 123-141). Steady state and time resolved quenching studies of gr A by KI in CH3OH and DMSO and life time of the emittingsinglet states of gr A support that gr A exists as a mixture of different forms of double helical (dh) structure [dh (1) to dh (4)] in CH3OH and as arandom coil structure in DMSO. This study further indicates that emitting trp residue in DMSO is better shielded than that in CH3OH. Phosphorescence spectra of gr A at 77 K in CH3OH glass suggests that gr A retains a particular conformation dh (3) in this matrix. The phosphorescence spectra of gr A[conformation db (4)] in 2-MeTHF at 77 K is further red shifted indicatingthat among all the dh forms, dh (4) has the emitting trp residue in most hydrophobic environment. The hydrophobicity of the emitting tryptophan environment is thus found to be in the order: dh (1)<dh (3)<dh (4). Since 2-MeTHF forms a clear glass at low temperature, it is thus possible to study the side chain arrangement of gr A dh (4) as a function of temperature. The phosphorescence spectra in different alcohol glassy matrix are in conformity with the observation of different side chain arrangement of gr A as one changes the polarity of alcohol. Steady state and time resolved quenching studies of gr A using Cs+ ion in CH3OH at 298 K clearly demonstrate the two binding sites for the metal ions and provide the value of equilibrium constant of the 'non-emitting' complex of gr A with Cs+ ion in the ground state. Theobservation of distinct red shift of the (0,0) band of the phosphorescencespectra of the complexes of gr A with K+, Cs+ and Tl+ ions at 77 K compared to that in CH3OH glass confirms the metal ion induced change of conformation in dh (3). The result also suggests that the emitting trp residues in the complexes are in somewhat more hydrophobic environment compared with that in the free gr A in CH3OH glass. The tripler state Life time of these complexes indicate that the heavy metal ions Cs+ and Tl+ are within a Van der Waal's distance of emitting trp residue in gr A in CH3OH glass at 77 K so that they are capable of inducing increased spin-orbit coupling due to a heavy atom effect. (C) 2001 Elsevier Science B.V. All rights reserved.

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Documento generato il 04/04/20 alle ore 09:10:49