Dynamics of solvation and rotational relaxation in neutral Brij 35 and Brij 58 micelles

Protolytic equilibria of ACE inhibitors in micellar solution of nonionic surfactant Brij 35

The acid-base equilibria of six ACE inhibitors (ACEIs), captopril, cilazapril, enalapril, lisinopril, quinapril, and ramipril, were investigated in the presence of micelles of nonionic surfactant Brij 35. The pKa values were potentiometrically determined at 25 °C and at a constant ionic strength (0.1 M NaCl). The obtained potentiometric data were evaluated in the computer program Hyperquad. On the basis of the shift in the pKa values (ΔpKa) determined in micellar media in relation to the pKa values previously determined in "pure" water, the effect of Brij 35 micelles on ACEIs ionization was estimated. The presence of nonionic Brij 35 micelles caused a shift in the pKa values of all ionizable groups of the investigated ACEIs (ΔpKa from - 3.44 to + 1.9) while shifting the protolytic equilibria of both acidic and basic groups toward the molecular form. The Brij 35 micelles expressed the most pronounced effect on the ionization of captopril among the investigated ACEIs and stronger effect on the ionization of amino than on the ionization of carboxyl groups. The obtained results suggest that ionizable functional groups of ACEIs are involved in interactions with palisade layer of nonionic Brij 35 micelles, which potentially can be considered in physiological conditions. Distribution diagrams of the investigated ACEIs equilibrium forms as a function of pH indicate that the change in distribution is most strongly expressed in pH range 4-8, which includes biopharmaceutically important pH values.

Graphical abstract

Tailoring Niosomes- Implications for Controlled Cargo Release and Function as Nanoreactors

Nonionic surfactant vesicles (Niosomes) were prepared using polyoxyethylene alkyl ether (Brij 58).The impact of variation of the Brij: cholesterol molar ratio on the niosomal structure was studied. Fluorescence studies performed with the membrane probe 1,6-Diphenyl-1,3,5-triene (DPH) gave important insight on the bilayer integrity of the niosomes in response to environmental perturbations. The aim of the work being assessment of the efficacy of the niosomes as "drug release vehicles", release studies were performed with a xanthene dye Carboxyfluorescein (CF). Further, the vesicles were used as nanoreactors for the synthesis of gold nanoparticles (GNPs) as it is often useful to house nanoparticles in biological /biomimicking environments. Stable, spherical GNPs of diameter 6-10 nm were formed in these vesicles. As the vesicular bilayer mimics the cell membrane, the present work is relevant to the use of the GNPs for diagnostic and therapeutic purpose. It has also been established that fluorescence resonance energy transfer (FRET) effectively occurs between DPH and CF in the niosomes. The FRET studies provide important insight on the location of dyes within the vesicles thus indicating the prospective applications of this fluorescence technique for tracking the location of probes in biomimicking systems which maybe extrapolated to in vivo biological systems in future.

A real-time and in-situ monitoring of the molecular interactions between drug carrier polymers and a phospholipid membrane

The dynamic interactions between drug carrier molecules and a cell membrane can not be ignored in their clinical use. Here a simple, label-free and non-invasive approach, photo-voltage transient method, combined with the atomic force microscopy, dynamic giant unilamellar vesicle leakage assay and cytotoxicity method, was employed for a real-time monitoring of the interaction process. Two representative polymer molecules, polyoxyethylene (35) lauryl ether (Brij35) and polyvinylpyrrolidone (PVPk30), were taken as examples to interact with a phospholipid bilayer membrane in a low ionic strength and neutral pH condition. Brij35 demonstrated an adsorption-accumulation-permeabilization dominated process under the modulation of polymer concentration in the solution. In contrast, PVPk30 performed a dynamic balance between adsorption-desorption of the molecules and/or permeabilization-resealing of the membrane. Such difference explains the high and low cytotoxicity of them, respectively, in the living cell tests. Briefly, through combining the photo-voltage approach with conventional fluorescent microscopy method, this work demonstrates new ideas on the time and membrane actions of polymer surfactants which should be taken into account for their biomedical applications.

Optimization of a fluorogenic assay to determine caspase 3/7 activity in meat extracts

Usefulness of general-purpose fluorogenic assay kits to determine caspase 3/7 activity of biological extracts is highly compromised in meat-based samples due to their scarce enzyme concentration. In the present work, a straightforward protocol is presented with two main purposes: 1) to enhance sensitivity of the fluorogenic approach addressing caspase 3/7 activity in tissues showing scarce enzyme concentration such as skeletal muscle, and 2) to reduce/economize the volume of employed reagents. The enzyme extraction procedure, peptide substrate, dithiothreitol concentration and detection settings were appropriately optimized for use in microtiter-plate fluorometers. As a result, low to high enzyme activity extracts (from 10,000 to 260,000 relative fluorescence units) can be measured under developed sampling and experimental conditions. The fact that enzyme reactions took place in 96-microtiter well plates reduces the consumption of chemical compounds when analysing a high number of samples, thus contributing to environment sustainability.

Role of Different States of Solubilized Water on Solvation Dynamics and Rotational Relaxation of Coumarin 490 in Reverse Micelles of Gemini Surfactants, Water/12-s-12.2Br- (s = 5, 6, 8)/n-Propanol/Cyclohexane

The present study demonstrates how the different states of solubilized water viz. quaternary ammonium headgroup-bound, bulklike, counterion-bound, and free water in reverse micelles of a series of cationic gemini surfactants, water/12-s-12 (s = 5, 6, 8).2Br^-/n-propanol/cyclohexane, control the solvation dynamics and rotational relaxation of Coumarin 490 (C-490) and microenvironment of the reverse micelles. The relative number of solubilized water molecules of a given state per surfactant molecule decides major and minor components. A rapid increase in the number of bulklike water molecules per surfactant molecule as compared to the slow increase in the number of each of headgroup- and counterion-bound water molecules per surfactant molecule with increasing water content (W _o) in a given reverse micellar system is responsible for the increase in the rate of solvation and rotational relaxation of C-490. The increase in the number of counterion-bound water molecules per surfactant molecule and the concomitant decrease in the number of bulklike water molecules per surfactant molecule with increasing spacer chain length of gemini surfactants at a given W _o are ascribed to the slower rates of both solvation and rotational relaxation. Relative abundances of different states of water have a role on the microenvironment of the reverse micelles as well. Thus, a comprehensive effect of different states of water on dynamics in complex biomimicking systems has been presented here.

Facile synthesis of hollow dendritic Ag/Pt alloy nanoparticles for enhanced methanol oxidation efficiency

Hollow dendritic Ag/Pt alloy nanoparticles were synthesized by a double template method.

Effect of Polymethylene Spacer of Cationic Gemini Surfactants on Solvation Dynamics and Rotational Relaxation of Coumarin 153 in Aqueous Micelles

The present work demonstrates the solvation dynamics and rotational relaxation of Coumarin 153 (C-153) in the micelles of a series of cationic gemini surfactants, 12-s-12, 2Br(-) containing a hydrophobic polymethylene spacer with s = 3, 4, 6, 8, 12. Steady-state and time-correlated single-photon counting (TCSPC) fluorescence spectroscopic techniques have been used to carry out this study. Steady-state and TCSPC fluorescence data suggest that C-153 molecules are located at the Stern layer of micelles. While probe molecules feel more or less the same micropolarity in the micellar phase, the microviscosity of micelles decreases with spacer chain length. Solvation dynamics at the Stern layer is bimodal in nature with fast solvation as a major component. Counter ions and water molecules bonded with the polar headgroups of surfactant molecules are responsible for the slow component. Average solvation time increases with spacer chain length because of the increased degree of counter ion dissociation. Some water molecules are involved in the solvation of counter ions themselves, resulting in the decrease in "free" water molecules to be available for the solvation of C-153. The hydrophobic spacer chain also has an effect on increasing the solvation time with increasing chain length. The average rotational relaxation time for C-153 decreases with spacer chain length with a rapid decrease at s > 4. The anisotropy decay of C-153 in micelles is biexponential in nature. The slow rotational relaxation is due to the lateral diffusion of C-153 in micelles. Lateral diffusion is much faster than the rotational motion of a micelle as a whole. The rotational motion of the micelle as a whole becomes faster with the decreasing size of micelles.

The effect of membrane fluidity on FRET parameters: an energy transfer study inside small unilamellar vesicle

The fluorescence resonance energy transfer (FRET) in a lipid bilayer system containing two different donors and one common acceptor at below and above transition temperature has been studied and all the FRET parameters are analyzed using steady state and time-resolved fluorescence spectroscopy. Using dynamic light scattering measurement, we have followed the process of preparation of small unilamellar vesicles, and by following the FRET parameters of C-153-Rh6G and C-151-Rh6G pairs inside SUVs at 16 °C and 33 °C (T(m) = 23.9 °C) we have noticed that there is greater effect of temperature on the FRET parameters in case of the C-153-Rh6G pair than that of the C-151-Rh6G pair. Finally we have concluded that this difference is due to their different location inside the lipid bilayer in which fluidity of the long alkyl chain markedly affects the FRET parameters for C-153-Rh6G pair embedded inside a small unilamellar vesicle of size 20-50 nm.

The use of solvent relaxation technique to investigate headgroup hydration and protein binding of simple and mixed phosphatidylcholine/surfactant bilayer membranes

The subject of this report was to investigate headgroup hydration and mobility of two types of mixed lipid vesicles, containing nonionic surfactants; straight chain Brij 98, and polysorbat Tween 80, with the same number of oxyethylene units as Brij, but attached via a sorbitan ring to oleic acid. We used the fluorescence solvent relaxation (SR) approach for the purpose and revealed differences between the two systems. Fluorescent solvent relaxation probes (Prodan, Laurdan, Patman) were found to be localized in mixed lipid vesicles similarly as in pure phospholipid bilayers. The SR parameters (i.e. dynamic Stokes shift, Deltanu, and the time course of the correlation function, C(t)) of such labels are in the same range in both kinds of systems. Each type of the tested surfactants has its own impact on water organization in the bilayer headgroup region probed by Patman. Brij 98 does not modify the solvation characteristics of the dye. In contrast, Tween 80 apparently dehydrates the headgroup and decreases its mobility. The SR data measured in lipid bilayers in presence of Interferon alfa-2b reveal that this protein, a candidate for non-invasive delivery, affects the bilayer in a different way than the peptide melittin. Interferon alfa-2b binds to mixed lipid bilayers peripherally, whereas melittin is deeply inserted into lipid membranes and affects their headgroup hydration and mobility measurably.

Dynamics of Solvent and Rotational Relaxation of Coumarin-153 in Room-Temperature Ionic Liquid 1-Butyl-3-methyl Imidazolium Tetrafluoroborate Confined in Poly(oxyethylene glycol) Ethers Containing Micelles

We have investigated solvent and rotational relaxation of coumarin 153 (C-153) in room-temperature ionic liquid (RTILs) 1-butyl-3-methyl-imidazolium tetrafluoroborate ([bmim][BF(4)]) and the ionic liquid confined in alkyl poly(oxyethylene glycol) ethers containing micelles. We have used octaethylene glycol monotetradecyl ether (C(14)E(8)) and octaethylene glycol monododecyl ether (C(12)E(8)) as surfactants. In the [bmim][BF(4)]-C(14)E(8) micelle, we have observed only a 22% increase in solvation time compared to neat [bmim][BF(4)], whereas in the [bmim][BF(4)]-C(12)E(8) system, we have observed approximately 57% increase in average solvation time due to micelle formation. However, the slowing down in solvation time on going from neat RTIL to RTIL-confined micelles is much smaller compared to that on going from water to water confined micellar aggregates. The 22-57% increase in solvation time is attributed to the slowing down of collective motions of cations and anions in micelles. The rotational relaxation times become faster in both the micelles compare to neat [bmim][BF(4)].

Dynamics of Solvent and Rotational Relaxation of Glycerol in the Nanocavity of Reverse Micelles

The dynamics of solvent and rotational relaxation of Coumarin 480 and Coumarin 490 in glycerol containing bis-2-ethyl hexyl sulfosuccinate sodium salt (AOT) reverse micelles have been investigated with steady-state and time-resolved fluorescence spectroscopy. We observed slower solvent relaxation of glycerol confined in the nanocavity of AOT reverse micelles compared to that in pure glycerol. However, the slowing down in the solvation time on going from neat glycerol to glycerol confined reverse micelles is not comparable to that on going from pure water or acetonitrile to water or acetonitrile confined AOT reverse micellar aggregates. While solvent relaxation times were found to decrease with increasing glycerol content in the reverse micellar pool, rotational relaxation times were found to increase with increase in glycerol content.

Dynamics of Solvent and Rotational Relaxation of Coumarin 153 in Room-Temperature Ionic Liquid 1-Butyl-3-methylimidazolium Hexafluorophosphate Confined in Brij-35 Micelles: A Picosecond Time-Resolved Fluorescence Spectroscopic Study

The dynamics of solvent and rotational relaxation of Coumarin 153 (C-153) in ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and in the ionic liquid confined in Brij-35 micellar aggregates have been investigated using steady-state and time-resolved fluorescence spectroscopy. We observed slower dynamics in the presence of micellar aggregates as compared to the pure IL. However, the slowing down in the solvation time on going from neat IL to IL-confined micelles is much smaller compared to that on going from water to water-confined micellar aggregates. The increase in solvation and rotational time in micelles is attributed to the increase in viscosity of the medium. The slow component is assumed to be dependent on the viscosity of the solution and involves large-scale rearrangement of the anions and cations while fast component is assumed to originate from the initial response of the anions during excitation. The slow component increases due to the increase in the viscosity of the medium and increase in fast component is probably due to the hydrogen bonding between the anions and polar headgroup of the surfactant. The dynamics of solvent relaxation was affected to a small extent due to the micelle formation.

Solvent Relaxation Study of pH-Dependent Hydration of Poly(oxyethylene) Shells in Polystyrene-block-poly(2-vinylpyridine)-block-poly(oxyethylene) Micelles in Aqueous Solutions

The hydration of the poly(oxyethylene) shell in polystyrene-block-poly(2-vinylpyridine)-block-poly(oxyethylene) micelles was investigated by monitoring the solvent relaxation response of a solvent-sensitive fluorophore (patman). It has been found that the relaxation occurs on the nanosecond time scale. Results for triblock copolymer micelles have been compared with those obtained for polystyrene-block-poly(2-vinylpyridine) micelles in order to evaluate the effect of the outer polyoxyethylene layer. Considerable pH-dependent changes in the hydration of poly(oxyethylene) units at the poly(2-vinylpyridine)/polyoxyethylene interface were observed. Additionally, the paper shows that the solvent relaxation technique is a suitable tool for studying polymeric nanoparticles and that the measurement of time-dependent half-width of the emission spectrum allows for estimation of the extent of relaxation process observed by a given experimental setup.

Fluorescence probe assisted post-column detection for lipid analysis in microbore-LC

A general approach, still few exploited so far and never associated with microbore-LC, consisting of detection of various lipid classes (i.e. phospholipids, triglycerides, ceramides and glycosphingolipids) by non-covalent association with 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence probe is developed. This mode of detection was coupled with non-aqueous reversed-phase microbore-LC (C18) by using classical post-column fluorescence detection. The classical LC system was first adapted to microbore-chromatography (internal diameter 1 mm) without apparatus miniaturization of the solvent delivery system and the detection cell. For this purpose, the detection parameters (probe concentration, post-column flow rate, post-column reactor length and post-column system temperature) were optimized by a central composite design (CCD) using a mixture of phosphatidylcholine (PC) species as a lipid model and DPH (lambda(ex) = 350 nm, lambda(em) = 430 nm) as a fluorescence probe. The optimal conditions of detection for the various molecular species of PC were determined for a DPH concentration of 3.35 micromol/L, a post-column flow rate of 0.5 mL/min, a reactor length of 1.4 m and a temperature of 35 degrees C. The fluorescence response was linear over a wide range of PC species from 5 microg/mL to 100 microg/mL and the lower limit of detection (signal/noise = 3) was about 1 microg/mL, that is equivalent to evaporative light scattering detection (ELSD). Others molecular species of various classes of lipids, i.e. triglycerides, ceramides and glycosphingolipids were also easily detected. Thus, this study demonstrated the versatility of the proposed system of detection which was shown to be sensitive, easy to perform, non-destructive and allowed, in contrast to ELSD, for a linear response with various polarity lipid classes.

Study of Energy Transfer from 7-Amino Coumarin Donors to the Rhodamine 6G Acceptor in Lecithin Vesicles and Sodium Taurocholate−Lecithin Mixed Aggregates

The energy transfer using 7-amino coumarin dyes as the donor and rhodamine 590 (Rh6G) as the acceptor was investigated in lecithin vesicles and sodium taurocholate (NaTC)-lecithin mixed aggregates using steady-state and time-resolved fluorescence spectroscopy. All energy transfer parameters were calculated. The coumarin 153-Rh6G pair is the most efficient donor-acceptor pair as reflected by the value of k(ET). With addition of NaTC in lecithin, in the case of the coumarin 153-Rh6G pair, the energy transfer rate or efficiency does not change very much, whereas in the case of the coumarin 151-Rh6G pair, the energy transfer rate decreases 2-fold upon going from lecithin vesicles to NaTC-lecithin mixed aggregates where the molar ratio is 2.5. It is mainly due to the deeper location of coumarin 153 in the lipid bilayer or in mixed aggregates. Rotational relaxation data also support this idea.

Effect of alkyl chain length and size of the headgroups of the surfactant on solvent and rotational relaxation of Coumarin 480 in micelles and mixed micelles

The effect of alkyl chain length and size of the headgroups of the surfactant on the solvation dynamics and rotational relaxation of Coumarin 480 (C-480) has been investigated using dynamic Stokes' shift of C-480 in different types of alkyltrimethylammonium bromide micelles and mixed micelles. The rotational relaxation time increases with increase in alkyl chain length of the surfactant. The increase in the number of alkyl chains of the surfactant leads to the more close packed micelles, hence the microviscosity of the micelles increases and consequently rotational relaxation time increases. Solvation time also increases due to the increase in number of alkyl chains of the surfactant. The change in solvation and rotational relaxation time is more prominent in micelles compared to mixed micelles. The solvation and rotational relaxation time also increase with the increase in size of the headgroup of the surfactant.

Solvation dynamics in aqueous anionic and cationic micelle solutions: sodium alkyl sulfate and alkyltrimethylammonium bromide

Solvation dynamics of the fluorescence probe, coumarin 102, in anionic surfactant, sodium alkyl sulfate (C(n)H(2n+1)SO(4)Na; n = 8, 10, 12, and 14), and cationic surfactant, alkyltrimethylammonium bromide (C(n)H(2n+1)N(CH(3))(3)Br; n = 10, 12, 14, and 16), micelle solutions have been investigated by a picosecond streak camera system. The solvation dynamics in the time range of 10(-10)-10(-8) s is characterized by a biexponential function. The faster solvation time constants are about 110-160 ps for both anionic and cationic micelle solutions, and the slower solvation time constants for sodium alkyl sulfate and alkyltrimethylammonium bromide micelle solutions are about 1.2-2.6 ns and 450-740 ps, respectively. Both the faster and the slower solvation times become slower with longer alkyl chain surfactant micelles. The alkyl-chain-length dependence of the solvation dynamics in both sodium alkyl sulfate and alkyltrimethylammonium bromide micelles can be attributed to the variation of the micellar surface density of the polar headgroup by the change of the alkyl chain length. The slower solvation time constants of sodium alkyl sulfate micelle solutions are about 3.5 times slower than those of alkyltrimethylammonium bromide micelle solutions for the same alkyl-chain-length surfactants. The interaction energies of the geometry optimized mimic clusters (H(2)O-C(2)H(5)SO(4)(-) and H(2)O-C(2)H(5)N(CH(3))(3)(+)) have been estimated by the density functional theory calculations to understand the interaction strengths between water and alkyl sulfate and alkyltrimethylammonium headgroups. The difference of the slower solvation time constants between sodium alkyl sulfate and alkyltrimethylammonium bromide micelle solutions arises likely from their different specific interactions.