Effect of sodium cholate (NaC) bile salt on the absorption and fluorescence properties of berberine cation was studied in aqueous solution and water-cosolvent mixtures. The alteration of the fluorescent behavior with increasing NaC concentration showed an entirely different trend from that found previously in the presence of sodium dodecylsulfate. Binding to bile salt agglomerates led to significant fluorescence intensity enhancement, and the fluorescence lifetime of berberine proved to be highly sensitive to the structure and size of the aggregates. The dual exponential decay kinetics above 10 mM NaC concentration showed that the probe resided in two totally different binding sites. At 2-10 mM NaC concentrations, only primary aggregates were detected. The aggregate disrupting power of cosolvents decreased in the series of dimethylformamide, acetonitrile, formamide, and methanol. These compounds enhanced the water accessibility of berberine bound to aggregates and diminished the number of secondary aggregates.

Berberine alkaloid as a sensitive fluorescent probe for bile salt aggregates.

The effect of sodium salicylate (Na-sal) and sodium cholate (Na-cholate) on the solvation dynamics in the water pool of aerosol-OT (AOT, sodium dioctylsulfosuccinate) microemulsion in n-heptane is reported. In the absence of any additive, the solvation dynamics of 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) in AOT microemulsions is found to be biexponential with an average solvation time (〈τs〉) of 710 ps. In the water pool, 〈τs〉 decreases to 330 ps on addition of 1 mM Na-sal and increases to 3050 ps in the presence of 100 mM Na-cholate. The spectral width (Γ) of the time-resolved emission spectra of DCM in the water pool is found to be time dependent. This is ascribed to diffusion of the probe (DCM). The Na-sal-induced acceleration of the solvation dynamics is ascribed to the increase in the size of the water pool. In bulk water, in the presence of 100 mM Na-cholate (a bile salt), 〈τs〉 is ∼830 ps. This is 4 times shorter than 〈τs〉 in the presence of Na-cholate in the water pool....

Solvation dynamics in the water pool of an aerosol-OT microemulsion. Effect of sodium salicylate and sodium cholate

Water solvation dynamics of polar species both in the bulk and in the hydration layers of proteins and self-organized assemblies have been discussed. Recent studies have revealed that while water solvation dynamics in the bulk is ultrafast and is mostly complete within 1 ps, this can slow down by as much as 2–3 orders of magnitude in the hydration layers of these systems. In this Report we discuss not only the ultrafast solvation dynamics in bulk water and the slow dynamics in the hydration layers, but also the relevant experimental, theoretical and computer simulation studies on various aspects of water dynamics in self-assemblies and confined geometries

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5 Water solvation dynamics in the bulk and in the hydration layer of proteins and self-assemblies

In this review, bile salt, bile salt–surfactant, and bile salt–drug interactions and their solubilization studies are mainly focused. Usefulness of bile salts in digestion, absorption, and excretion of various compounds and their rare properties in ordering the shape and size of the micelles owing to the presence of hydrophobic and hydrophilic faces are taken into consideration while compiling this review. Bile salts as potential bio-surfactants to solubilize drugs of interest are also highlighted. This review will give an insight into the selection of drugs in different applications as their properties get modified by interaction with bile salts, thus influencing their solution behavior which, in turn, modifies the phase-forming behavior, microemulsion, and clouding phenomenon, besides solubilization. Finally, their future perspectives are taken into consideration to assess their possible uses as bio-surfactants without side effects to human beings.

Solubilization and Interaction Studies of Bile Salts with Surfactants and Drugs: a Review

The solvation dynamics inside an aggregate of a bile salt, sodium deoxycholate (NaDC), in aqueous solution has been studied using picosecond time-resolved emission spectroscopy and two fluorescent probes, 4-(dicyanomethylene)-2-methyl-(p-dimethylaminostyryl)-4H-pyran (DCM) and 2,6-p-toluidinonaphthalenesulfonate (TNS). Addition of NaDC to an aqueous solution causes a nearly 110-fold increase in the emission quantum yield (φf) of TNS. From the variation of φf of TNS, two critical micellar concentrations of NaDC have been detected at around 7 and 60 mM, respectively. The solvation dynamics of TNS in 100 mM NaDC solution is described by three components, 95 ps (17%), 380 ps (16%), and 1.9 ns (67%). The solvation dynamics of DCM bound to 100 mM NaDC is also found to be triexponential with components of 110 ps (19%), 700 ps (17%), and 2.75 ns (64%). The substantially slow solvation dynamics of water in the vicinity of NaDC indicates restricted solvation dynamics of water inside the bile salt aggregate.

Solvation Dynamics in Bile Salt Aggregates

Excited triplet naphthalene and xanthone were employed as probe molecules to study the dynamics of incorporation into sodium cholate, taurocholate, and deoxycholate aggregates. The association and dissociation rate constants and the quenching rate constants for the incorporated probes were recovered from the dependence of the observed triplet decay rate constants on quencher concentrations (nitrite and cupric ions). Triplet naphthalene was incorporated into a site offering a high degree of protection from quenchers and from which dissociation was relatively slow. Triplet xanthone was incorporated into a less protected site from which dissociation was an order of magnitude faster than from the naphthalene site. We propose that naphthalene was incorporated into the hydrophobic site of primary aggregates, and xanthone was located in the region containing the hydroxyl groups in the secondary aggregates.

C. Ju and

Papers

Dynamics of Probe Complexation to Bile Salt Aggregates