Microheterogeneity of Sodium Dodecylsulfate Micelles Probed by Frequency-Domain Fluorometry

Abstract

The microenvironment of sodium dodecylsulfate (SDS) micelles has been examined with the use of two fluorescent probes, 2-anilinonaphthalene-6-sulfonic acid (2,6-ANS) and N-phenyl-naphthylamine (1-AN). The fluorescence lifetimes are recovered from multifrequency phase and modulation data with the use of a global analysis protocol. The fluorescence decay kinetics of 2,6-ANS, which probes the outer-core region (i.e., the palisade layer) of SDS micelles, is characterized by a Lorentzian distribution. In contrast, a single discrete excited-state lifetime is observed for 1-AN, which is expected to position itself in the inner-core region of the micelle. Fluorescence lifetimes of these probes are investigated also as functions of temperature, concentration of counter ions (Na⁺ and Mg²⁺) and linear alcohols (n-BuOH, n-PeOH, n-HeOH, and n-HepOH). The collective results confirm that the outer-core region of SDS micelles is microheterogeneous and the inner core is essentially homogeneous. In addition, the lifetimes and the partitioning of the outer-core probe, 2,6-ANS, appear to be more sensitive to variations in temperature and counter ions in comparison to those of the inner-core probe, 1-AN. The microenvironment of 2,6-ANS is found to be more heterogeneous at high temperature and low salt concentrations. This observation, we propose, is a result of different degrees of water penetration in the outer-core region. In the SDS system, the effects of micelle polydispersity and compositional diversity, on the environmental microheterogeneity of the fluorescent probe, seem to be minimal in comparison to water gradient effects.

Keywords

Micelles Phase and modulation fluorescence Lifetime distributions Water gradients Electrolyte and temperature effects

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References

Kalyanasundaram

, Photochemistry in Microheterogeneous Systems (Academic Press, New York, 1987).

Zana

and Lang

, J. Coll. Surf. 48, 153 (1990).

George

, Spectrochim. Acta Rev. 13, 27 (1990).

George

, Analusis 17, 231 (1989).

Malliaris

, Inter. Rev. Phys. Chem. 7, 95 (1988).

Garcia

M. E. Diaz

and Sanz-Medel

, Talanta 33, 255 (1986).

Gratzel

and Thomas

J. K

, in Modern Fluorescence Spectroscopy, Wehry

E. L.

Jr. Ed. (Plenum Press, New York, 1976), Vol. 2.

Alcala

J. R.

Gratton

and Prendergast

F. G

, Biophys. J. 51, 587 (1987).

Alcala

J. R.

Gratton

and Prendergast

F. G

, Biophys. J. 51, 597 (1987).

10.

Alcala

J. R.

Gratton

and Prendergast

F. G

, Biophys. J. 51, 925 (1987).

11.

Bright

F. V.

Betts

T. A.

and Litwiler

K. S

, C.R.C. Crit. Rev. Anal. Chem. 21, 389 (1990).

12.

Eftink

M. R.

and Ghiron

C. A

, Biophys. J. 52, 467 (1987).

13.

Eftink

M. R.

and Wasylewski

, Biochemistry 28, 382 (1989).

14.

Fiorini

R. M.

Valentino

Wang

Glaser

and Gratton

, Biochemistry 26, 3864 (1987).

15.

Fiorini

R. M.

Valentino

Gratton

Bertoli

and Curatola

, Biochem. Biophys. Res. Commun. 147, 460 (1987).

16.

Fiorini

R. M.

Valentino

Glaser

Gratton

and Curatola

, Biochim. Biophys. Acta 939, 485 (1988).

17.

Huang

and Bright

F. V

, J. Phys. Chem. 94, 8457 (1990).

18.

Bright

F. V.

Catena

G. C.

and Huang

, J. Am. Chem. Soc. 112, 1343 (1990).

19.

James

D. R.

and Ware

W. R

, Chem. Phys. Lett. 120, 455 (1985).

20.

James

D. R.

and Ware

W. R

, Chem. Phys. Lett. 126, 7 (1986).

21.

James

D. R.

Lui

Y. S.

De Mayo

and Ware

W. R

, Chem. Phys. Lett. 120, 460 (1985).

22.

James

D. R.

Turnbull

J. R.

Wagner

B. D.

Ware

W. R.

and Peterson

N. O

, Biochemistry 26, 6272 (1987).

23.

Siemiarczuk

and Ware

W. R

, Chem. Phys. Lett. 167, 263 (1990).

24.

Lakowicz

J. R.

Cherek

Grycznski

Joshi

and Johnson

M. L

, Biophys. Chem. 28, 35 (1987).

25.

Lakowicz

J. R.

Grycznski

Cheung

H. C.

Wang

C. K.

Johnson

M. L.

and Joshi

, Biochemistry 27, 9149 (1988).

26.

Parasassi

Conti

Gratton

and Sapora

, Biochim. Biophys. Acta 898, 196 (1987).

27.

Vincent

Brochon

J. C.

Merola

Jordi

and Gallay

, Biochemistry 27, 8725 (1988).

28.

Williams

B. W.

and Stubbs

C. D

, Biochemistry 27, 1994 (1988).

29.

Williams

B. W.

Scotto

A. W.

and Stubbs

C. D

, Biochemistry 29, 3248 (1990).

30.

Dederen

J. C.

Van der Auweraer

and De Schryver

F. C

, J. Phys. Chem. 85, 1189 (1981).

31.

Rodgers

M. A. J.

da Silva

M. F.

and Wheeler

, Chem. Phys. Lett. 53, 165 (1978).

32.

Catena

G. C.

and Bright

F. V

, Anal. Chem. 61, 905 (1989).

33.

Catena

G. C.

and Bright

F. V

, J. Fluorescence 1, 31 (1991).

34.

Zana

Yiv

Strazielle

and Lianos

, J. Colloid Interface Sci. 80, 208 (1981).

35.

Litwiler

K. S.

Huang

and Bright

F. V

, Anal. Chem. 62, 471 (1990).

36.

Fedderson

B. A.

Piston

D. W.

and Gratton

, Rev. Sci. Instrumn. 60, 2929 (1989).

37.

Spencer

R. D.

and Weber

, J. Chem. Phys. 52, 1654 (1970).

38.

Beecham

J. M.

and Gratton

, Proc. SPIE 909, 70 (1988).

39.

Rosato

Gratton

Mei

and Finazzi-Agro

, Biophys. J. 58, 817 (1990).

40.

Leatherbarrow

R. J.

, Enzfitter: A Non-linear Regression Data Analysis Program (Elsevier Biosoft, Cambridge, UK, 1987).

41.

Menger

F. M.

, Acc. Chem. Res. 12, 111 (1979).

42.

Kosower

Dodiuk

Tanizawa

Ottolenghi

and Orbach

, J. Am. Chem. Soc. 97, 2167 (1975).

43.

Tanford

, The Hydrophobic Effect: Formation of Micelles and Biological Membranes (Wiley, New York, 1980), 2nd ed.

44.

Warr

G. G.

and Grieser

, J. Chem. Soc., Faraday Trans. 1, 82, 1829 (1986).

45.

Larsen

J. W.

and Magid

L. J

, J. Am. Chem. Soc. 96, 5774 (1974).

46.

Hayase

and Hayano

, Bull. Chem. Soc. Japan 50, 83 (1977).

47.

Manabe

Shirahama

and Koda

, Bull. Chem. Soc. Japan 49, 2904 (1976).

48.

Lang

, J. Phys. Chem. 94, 3734 (1990).

49.

Wirth

M. J.

Chou

S.-H.

and Piasecki

D. A

, Anal. Chem. 63, 146 (1991).

50.

Russell

J. C.

and Wild

U. P

, J. Phys. Chem. 90, 1319 (1986).