Ground- and excited-state proton transfers in reversed micelles. Polarity restrictions and isotope effects

Politi, Mário José; Brandt, Ogden; Fendler, János H.

doi:10.1021/j100257a040

Cited by 104 publications

(76 citation statements)

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“…7 The intermolecular proton transfer processes are also found to be markedly affected by cyclodextrins, [8][9][10][11] lipids, 12 and microemulsions. 13 The excited-state double proton-transfer process 15 is also largely modified in microemulsions. 14 In general, the aromatic amines and phenols become more acidic in the excited state and their pK a decreases by several units in the electronically excited state compared to that in the ground state.…”

Section: Introductionmentioning

confidence: 99%

Excited-State Proton Transfer of 1-Naphthol in Micelles

1998

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The fast deprotonation of 1-naphthol, which occurs in 35 ps in aqueous solution, is studied in neutral (triton X 100, reduced, TX-100R), cationic (cetyl trimethylammonium bromide, CTAB), and anionic (sodium dodecyl sulfate, SDS) micelles. Drastically different effects on the proton transfer process and the relative emission intensities of the neutral form (360 nm) and the anion (460 nm) are observed in the three micelles. The intensities of the anion and the neutral emission of 1-naphthol exhibit a break around the reported critical micellar concentration (cmc) of the three micelles. Above cmc, intensity of the neutral emission is enhanced by a factor of nearly 90, 66, and 20 in 20 mM TX-100R, 200 mM SDS, and 96 mM CTAB, respectively. The anion emission is enhanced for CTAB and TX-100R, while for SDS its intensity decreases, compared to water. In CTAB, the rise time of the 460 nm emission (600 ( 100 ps) is similar to the lifetime of decay at 360 nm. However, for TX-100R and SDS, the rise time of the anion emission (at 460 nm) is found to be faster than the decay of the neutral emission (at 360 nm). This indicates that in TX-100R and SDS, there is no parental relation between the normal and the anion emission and they originate from the probe, 1-naphthol molecules, at distinctly different locations. The rise times at 460 nm are 1.8 ( 0.1 ns and 600 ( 100 ps for TX-100R and SDS, respectively, while the corresponding decay times at 360 nm are 2.5 ( 0.1 ns and 1.8 ( 0.1 ns.

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Section: Introductionmentioning

confidence: 99%

Excited-State Proton Transfer of 1-Naphthol in Micelles

1998

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“…Light excitation leads therefore to H + dissociation when starting with a solution containing the undissociated ground-state species. For pyranine it is established that photoacid behavior occurs in water, aqueous urea, and only in a few other highly polar and protic media (25). Since this probe is relatively hydrophilic and bears the same charge as the interface, it will reside in the interior of the aqueous pool (26).…”

Section: Cylindrical Micelle Bicontinuous Structures Bilayersmentioning

confidence: 99%

Effect of urea on biomimetic aggregates

Florenzano¹,

Politi²

1997

Braz J Med Biol Res

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The effect of urea on biomimetic aggregates (aqueous and reversed micelles, vesicles and monolayers) was investigated to obtain insights into the effect of the denaturant on structured macromolecules. Direct evidence obtained from light scattering (static and dynamic), monolayer maximum isothermal compression and ionic conductivity measurements, together with indirect evidence from fluorescence photodissociation, fluorescence suppression, and thermal reactions, strongly indicates the direct interaction mechanism of urea with the aggregates. Preferential solvation of the surfactant headgroups by urea results in an increase in the monomer dissociation degree (when applied), which leads to an increase in the area per headgroup and also in the loss of counterion affinities.

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“…Como sistemas modelos de microcavidade, o estudo da transferência de prótons em micelas reversas (Valeur & Bardez, 1989;Politi et al, 1985) e vesículas (Kotlyar et al, 1994) pode ser útil. O estudo da transferência é feito usando sondas fluorescentes que são mais ácidas no estado excitado do que no estado fundamental (pKa * <pKa).…”

Section: Modelo Simples Para Reprotonaçãounclassified

“…O estudo da transferência é feito usando sondas fluorescentes que são mais ácidas no estado excitado do que no estado fundamental (pKa * <pKa). Depois de excitada, a sonda (S) libera o próton e retorna rapidamente ao seu estado fundamental, seguindo o ciclo abaixo (Förster & Volkers, 1975): A evolução temporal da reprotonação no estado fundamental é acompanhada por meio de absorção UV-VIS da sonda na sua forma ácida ou básica (Kotlyar et al, 1994;Valeur & Bardez, 1989;Politi et al, 1985). No estado excitado, é usada a espectroscopia de fluorescência no domínio do tempo ou freqüência (Kotlyar et al, 1994;Lakowicz et al, 1990;Valeur & Bardez, 1989;Politi et al, 1985).…”

Section: Modelo Simples Para Reprotonaçãounclassified

“…Tanto em micelas reversas como em vesículas, as constantes de velocidade (pseudo-primeira ordem) de reprotonação e deprotonação no estado fundamental e excitado são mais rápidas do que em meio isotrópico (Kotlyar et al, 1994;Valeur & Bardez, 1989;Politi et al, 1985). Sugere-se que o aumento da velocidade esteja relacionado com: um volume menor de reação, pH local mais ácido do que pH bulk, diminuição da constante dielétrica e da atividade da água, partição da sonda entre interface e centro da microcavidade, etc (Valeur & Bardez, 1989;Politi et al, 1985;El Seoud, 1984).…”

Section: Modelo Simples Para Reprotonaçãounclassified

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Aplicação de modelos simples em fenômenos envolvendo monocamadas e micelas

Dias¹

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Dedico este singelo trabalho a minha filhota, Pollyana Hammoud Dias, e a memória de meu pai, Gilberto Luiz Dias. À minha esposa, Nabiha Mohamad Hammoud Dias, pela sua compreensão e pela dedicação com que trata a nossa família.Ao CNPq, pelo apoio financeiro. ii-) Influência da interação eletrostática (neste caso, repulsiva) e tamanho de domínios nas isotermas de monocamadas iônicas insolúveis. Índiceiii-) Influência do tamanho e polaridade do pool aquoso de micelas reversas de AOT na reprotonação de sondas fotoácidas aniônicas. AbstractThe present work focus on the proposition or extension of simple models

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Ground- and excited-state proton transfers in reversed micelles. Polarity restrictions and isotope effects

Cited by 104 publications

References 0 publications

Excited-State Proton Transfer of 1-Naphthol in Micelles

Excited-State Proton Transfer of 1-Naphthol in Micelles

Effect of urea on biomimetic aggregates

Aplicação de modelos simples em fenômenos envolvendo monocamadas e micelas

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