Use of Fluorescence Probes for Characterization of Solvation Properties of Micelles:  A Linear Solvation Energy Relationship Study

Abstract

Analysis involving the linear solvation energy relationship (LSER) of the energy of maximum fluorescence of seven structurally related probes in a micellar medium has been made to obtain solvation properties of the aqueous micellar phase. Solvation interactions as expressed by the empirical Kamlet-Taft solvatochromic parameters representing dipolarity/polarizability (π*), hydrogen bond donor acidity (R), and hydrogen bond acceptor basicity (β) have been determined for aqueous micelles formed by cetyl trimethylammonium bromide, sodium dodecyl sulfate, and Triton-X 100. The parameters agree well with those reported by other workers using absorption probes. Solvatochromic measurements also allowed the determination of partition coefficient values for the probe molecules between the micellar and the aqueous phase. The observed values have been rationalized in terms of different modes of solute-solvent interaction.

Sensing Micelle Hydration by Proton-Transfer Dynamics of a 3-Hydroxychromone Dye: Role of the Surfactant Headgroup and Chain Length

“…The region of these positively charged −N(CH 3 ) 3 + headgroups in the Stern layer of the cationic micelles is weakly solvated with water molecules because the intervening methyl groups likely inhibit the approach of water molecules close to the positively charged headgroups. 16 This is nicely corroborated from recent results of Kunz et al 17 on micellar hydration by dielectric relaxation spectroscopy, which have shown the surface of the cationic alkyltrimethylammonium halide micelles to be essentially hydrophobic, implying a very poor hydration of the positively charged headgroups. Furthermore, Zana et al 49 and Bales et al 50,51 recently employed electron paramagnetic resonance (EPR) studies and a zeroth-order model to show that the cationic micelles of DTAB are significantly drier than the anionic SDS micelles.…”

“…(1) The Stern layer of the cationic micelles comprises positively charged −N(CH 3 ) 3 + headgroups and a few Br – counterions and is weakly or poorly solvated relative to that of the anionic SDS or STDS micelles. The region of these positively charged −N(CH 3 ) 3 + headgroups in the Stern layer of the cationic micelles is weakly solvated with water molecules because the intervening methyl groups likely inhibit the approach of water molecules close to the positively charged headgroups . This is nicely corroborated from recent results of Kunz et al on micellar hydration by dielectric relaxation spectroscopy, which have shown the surface of the cationic alkyltrimethylammonium halide micelles to be essentially hydrophobic, implying a very poor hydration of the positively charged headgroups.…”

“…In view of the studies in reverse micelles and micelles, , it is quite pertinent to address the issues concerning the sensitivity of the ESIPT dynamics to micelle hydration, the charge of the surfactant headgroup, and the hydrophobic tail length, which have not yet been explored. This is a particularly interesting topic worth addressing because (i) the interfacial region (Figure ) of the micelles is the preferred site for solubilization, even for hydrophobic molecules, (ii) the hydrogen bond donating abilities are different for the cationic, anionic, and neutral micelles , due to a differential solvation of the ionic or polar headgroups in the Stern or palisade layer of the micelle–water interface, (iii) the Stern layer of the anionic sodium dodecyl sulfate micelles with negatively charged −OSO 3 – headgroups was shown recently by dielectric spectroscopy , to be strongly hydrophilic compared to the essentially hydrophobic surface of the cationic alkyltrimethylammonium halide micelles with positively charged −N(CH 3 ) 3 + headgroups, implying a very strong and poor hydration of the anionic and cationic surfactants, respectively, and (iv) the palisade layer of the nonionic micelles comprises at least two water molecules per ethylene oxide (EO) unit tightly associated with the poly(ethylene oxide) (PEO) chains and thus demonstrates a level of hydration intermediate between those of the cationic and anionic micelles. In this context, the fluorescent dye 2-(2′-furyl)-3-hydroxychromone (N, Figure A) is a potential candidate for sensing micelle hydration through the modulation of its ESIPT dynamics because (i) the ESIPT reaction (Figure A) was found to be sensitive to the hydrogen bond donating ability or H-bond acidity of the polar, protic solvents and (ii) the Stern or palisade layer (Figure a,b) of the micelle–water interface is most likely the preferred site for localization of the FHC dye in micelles, as it is highly polar and possesses hydrophilic 4-carbonyl and 3-hydroxy moieties.…”

Electronic spectra and (hyper)polarizabilities of ketocyanine dye complexes with metal ions

“…Due to the presence of electron donor (amino) and electron acceptor (carbonyl) groups in the molecule, the electronic transition is associated with intramolecular charge transfer (ICT) and as such the optical response of the molecule is very much sensitive to the microenvironment. Electronic spectroscopic and photophysical properties of these molecules have been extensively studied in various media in recent years [3][4][5][6][7][8][9][10][11][12][13][14]. These compounds are also used as laser dyes and have industrial application in polymer imaging system [15][16][17].…”

Synthesis and spectroscopic investigation of a novel solvatochromic dye

“…form of the dye exist, the E(F) value can be written as [26][27][28] EðFÞ ¼ x f EðFÞ f þx b EðFÞ b ð7Þ…”