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Spectroscopic study of porphyrin-caffeine interactions.

Makarska-Bialokoz M - J Fluoresc (2012)

Bottom Line: The association constants were calculated using curve-fitting procedure (K(AC) of the order of magnitude of 10(3) mol(-1)).Whereas the emission spectra point at the presence of the fluorescence quenching effect testifying for the partial inactivation of the porphyrin molecule.The fluorescence quenching constants were calculated from Stern-Volmer plots.

View Article: PubMed Central - PubMed

Affiliation: Department of Inorganic Chemistry, Maria Curie-Sklodowska University, Lublin, Poland. makarska@hektor.umcs.lublin.pl

ABSTRACT
The association between water-soluble porphyrins: 4,4',4″,4'''-(21 H,23 H-porphine-5,10,15,20-tetrayl)tetrakis-(benzoic acid) (H(2)TCPP), 5,10,15,20-tetrakis(4-sulfonatophenyl)-21 H,23 H-porphine (H(2)TPPS(4)), 5,10,15,20-tetrakis[4-(trimethylammonio)phenyl]-21 H,23 H-porphine tetra-p-tosylate (H(2)TTMePP), 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21 H,23 H-porphine tetra-p-tosylate (H(2)TMePyP), the Cu(II) complexes of H(2)TTMePP and H(2)TMePyP, as well as chlorophyll a with caffeine (1,3,7-trimethylxanthine) has been studied analysing their absorption and emission spectra in aqueous (or acetone in case of chlorophyll a) solution. During the titration by caffeine the porphyrins absorption spectra undergo the evolution - the bathochromic effect can be observed as well as the hypochromicity of the Soret maximum. The association constants were calculated using curve-fitting procedure (K(AC) of the order of magnitude of 10(3) mol(-1)). Whereas the emission spectra point at the presence of the fluorescence quenching effect testifying for the partial inactivation of the porphyrin molecule. The fluorescence quenching constants were calculated from Stern-Volmer plots. The results obtained show that caffeine can interact with water-soluble porphyrins and through formation of stacking complexes is able to quench their ability to emission.

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Evolution of chlorophyll a emission spectrum during titration by caffeine. The dependence of fluorescence intensity versus chlorophyll a concentration for titration by caffeine, water and acetone. All the concentrations as in Fig. 4
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Fig5: Evolution of chlorophyll a emission spectrum during titration by caffeine. The dependence of fluorescence intensity versus chlorophyll a concentration for titration by caffeine, water and acetone. All the concentrations as in Fig. 4

Mentions: Both pure water and water solution of caffeine quench the fluorescence of chlorophyll a, as arises from the titration data (Fig. 5). The different mechanism of fluorescence quenching in case of this compound is probably the consequence of its structure, containing the phytol chain, which can hinder to some extent the binding of caffeine, as well as the form of a molecule, changing with the polarity of titrated solution. In acetone solution chlorophyll appears in monomeric form, due to interaction between central Mg in chlorophyll molecule, which acts as electron acceptor and carbonyl group in acetone molecule, which acts as electron donor [48]. Titration by water solution of caffeine increases the polarity of reaction environment, leading to formation of bigger aggregated molecules. Addition of water to acetone solution causes quenching of chlorophyll a fluorescence, what does not exclude the simultaneous interaction with caffeine. It was found that monomeric form of chlorophyll is less stable than dimeric (aggregated) form. In chlorophyll aggregates one chlorophyll may act as an electron donor and the other as electron acceptor via its central magnesium [48]. Therefore the obtained results point in this case at more than one mechanism of quenching and, possibly, more than one quenching centres [49].Fig. 5


Spectroscopic study of porphyrin-caffeine interactions.

Makarska-Bialokoz M - J Fluoresc (2012)

Evolution of chlorophyll a emission spectrum during titration by caffeine. The dependence of fluorescence intensity versus chlorophyll a concentration for titration by caffeine, water and acetone. All the concentrations as in Fig. 4
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3473192&req=5

Fig5: Evolution of chlorophyll a emission spectrum during titration by caffeine. The dependence of fluorescence intensity versus chlorophyll a concentration for titration by caffeine, water and acetone. All the concentrations as in Fig. 4
Mentions: Both pure water and water solution of caffeine quench the fluorescence of chlorophyll a, as arises from the titration data (Fig. 5). The different mechanism of fluorescence quenching in case of this compound is probably the consequence of its structure, containing the phytol chain, which can hinder to some extent the binding of caffeine, as well as the form of a molecule, changing with the polarity of titrated solution. In acetone solution chlorophyll appears in monomeric form, due to interaction between central Mg in chlorophyll molecule, which acts as electron acceptor and carbonyl group in acetone molecule, which acts as electron donor [48]. Titration by water solution of caffeine increases the polarity of reaction environment, leading to formation of bigger aggregated molecules. Addition of water to acetone solution causes quenching of chlorophyll a fluorescence, what does not exclude the simultaneous interaction with caffeine. It was found that monomeric form of chlorophyll is less stable than dimeric (aggregated) form. In chlorophyll aggregates one chlorophyll may act as an electron donor and the other as electron acceptor via its central magnesium [48]. Therefore the obtained results point in this case at more than one mechanism of quenching and, possibly, more than one quenching centres [49].Fig. 5

Bottom Line: The association constants were calculated using curve-fitting procedure (K(AC) of the order of magnitude of 10(3) mol(-1)).Whereas the emission spectra point at the presence of the fluorescence quenching effect testifying for the partial inactivation of the porphyrin molecule.The fluorescence quenching constants were calculated from Stern-Volmer plots.

View Article: PubMed Central - PubMed

Affiliation: Department of Inorganic Chemistry, Maria Curie-Sklodowska University, Lublin, Poland. makarska@hektor.umcs.lublin.pl

ABSTRACT
The association between water-soluble porphyrins: 4,4',4″,4'''-(21 H,23 H-porphine-5,10,15,20-tetrayl)tetrakis-(benzoic acid) (H(2)TCPP), 5,10,15,20-tetrakis(4-sulfonatophenyl)-21 H,23 H-porphine (H(2)TPPS(4)), 5,10,15,20-tetrakis[4-(trimethylammonio)phenyl]-21 H,23 H-porphine tetra-p-tosylate (H(2)TTMePP), 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21 H,23 H-porphine tetra-p-tosylate (H(2)TMePyP), the Cu(II) complexes of H(2)TTMePP and H(2)TMePyP, as well as chlorophyll a with caffeine (1,3,7-trimethylxanthine) has been studied analysing their absorption and emission spectra in aqueous (or acetone in case of chlorophyll a) solution. During the titration by caffeine the porphyrins absorption spectra undergo the evolution - the bathochromic effect can be observed as well as the hypochromicity of the Soret maximum. The association constants were calculated using curve-fitting procedure (K(AC) of the order of magnitude of 10(3) mol(-1)). Whereas the emission spectra point at the presence of the fluorescence quenching effect testifying for the partial inactivation of the porphyrin molecule. The fluorescence quenching constants were calculated from Stern-Volmer plots. The results obtained show that caffeine can interact with water-soluble porphyrins and through formation of stacking complexes is able to quench their ability to emission.

Show MeSH
Related in: MedlinePlus