Enthalpy Of Micellization Research Articles

Thermodynamics of micellisation: Sodium dodecyl sulfate/sodium deoxycholate with polyethylene glycol and model drugs

Variations in the critical micelle concentration (CMC) have been determined for sodium dodecyl sulfate and sodium deoxycholate (NaDC) in the presence of five drugs and polyethylene glycol (PEG) at temperatures (298.2, 304.2 and 310.2)K. From these data, thermodynamic parameters associated with the micellisation process (ΔmicG, ΔmicH and ΔmicS) were calculated. In the presence of some drug-based compounds, the CMC of SDS was affected, for example the presence of PEG dramatically reduced the CMC in all cases. Furthermore, PEG appeared to reduce the enthalpy of micellisation for all scenarios with only comparatively minor variations in the change in Gibbs free energy for the processes observed. For NaDC, the calorimetric results were far less predictable. A primary aggregation event recorded at a comparatively low concentration failed to appear for NaDC in the presence of a secondary compound, such as a drug or PEG. For NaDC, the presence of PEG had little effect on the CMC and corresponding thermodynamic data.

Temperature and pressure based NMR studies of detergent micelle phase equilibria.

Bulk thermodynamic and volumetric parameters (ΔGmic°, ΔHmic°, ΔSmic°, ΔCp,mic°, ΔVmic°, and Δκmic°) associated with the monomer–micelle equilibrium, were directly determined for a variety of common detergents [sodium n-dodecyl sulfate (SDS), n-dodecyl phosphocholine (DPC), n-dodecyl-β-d-maltoside (DDM), and 7-cyclohexyl-1-heptyl phosphocholine (CyF)] via 1H NMR spectroscopy. For each temperature and pressure point, the critical micelle concentration (cmc) was obtained from a single 1H NMR spectrum at a single intermediate concentration by referencing the observed chemical shift to those of pure monomer and pure micellar phases. This permitted rapid measurements of the cmc over a range of temperatures and pressures. In all cases, micelle formation was strongly entropically favored, while enthalpy changes were all positive, with the exception of SDS, which exhibited a modestly negative enthalpy of micellization. Heat capacity changes were also characteristically negative, while partial molar volume changes were uniformly positive, as expected for an aggregation process dictated by hydrophobic effects. Isothermal compressibility changes were found to be consistent with previous measurements using other techniques. Thermodynamic measurements were also related to spectroscopic studies of topology and micelle structure. For example, paramagnetic effects resulting from the addition of dioxygen provided microscopic topological details concerning the hydrophobicity gradient along the detergent chains within their respective micelles as detected by 1H NMR. In a second example, combined 13C and 1H NMR chemical shift changes arising from application of high pressure, or upon micellization, of CyF provided site-specific details regarding micelle topology. In this fashion, bulk thermodynamics could be related to microscopic topological details within the detergent micelle.

Effect of Electrolyte and Temperature on Micellization Behavior of N-Ethyl-N,N-dimethyl-1-hexadecanaminium Bromide

Micellization behavior of aqueous solutions of N-ethyl-N,N-dimethyl-1-hexadecanaminium bromide in the presence of electrolyte sodium bromide, NaBr, was studied at different temperatures. The characterization of the surfactant solutions was done in two electrolytic concentrations of NaBr [(0.001 and 0.005) mol·kg–1] using density, viscosity, ultrasound velocity, and conductivity measurements. Several physicochemical parameters like density, apparent molar volume, ultrasound velocity, isoentropic compressibility, viscosity, Vand and Einstein hydration parameters, conductivity, and thermodynamic parameters were evaluated and compared with the corresponding parameters in aqueous solutions of the surfactant in the absence of electrolyte. In general critical micellar concentration exhibited a decrease in magnitude, apparent molar volumes exhibited an increase in magnitude, and degrees of hydration were lowered upon the addition of salt. Enthalpy of micellization registered a significant decrease in magnitude up...

Determination of the aggregation number for micelles by isothermal titration calorimetry

Isothermal titration calorimetry (ITC) has previously been applied to estimate the aggregation number (n), Gibbs free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) of micellization. However, some difficulties of micelle characterization by ITC still remain; most micelles have aggregation numbers which are too high to be measured by ITC and even when n is sufficiently low, dilution enthalpies can obscure determination. Furthermore, as the parameters are highly correlated, their estimates have been questioned. The traditional approach also involves regression with an implicit model function for n > 4 and its mathematical implementation is therefore not straight-forward. It seems as if all of these difficulties can be traced back to the aggregation number. In this work a new principle of data quantification is derived which is easy to apply, interpret and will provide statistical reliable estimates of the aggregation number even for high values of n. With the aggregation number at hand, the remaining parameters are readily obtained. The proposed method can be used to estimate the heat of dilution and is therefore robust towards this ubiquitous error in ITC. Furthermore, the method offers insight into optimal design of titration protocols for micelle characterization. By applying the new method, the aggregation number of sodium dodecyl sulphate and glycochenodeoxycholate was determined at concentrations around their critical micelle concentration (CMC).

Ionic liquids effect on critical micelle concentration of SDS: Conductivity, fluorescence and NMR studies

The effects of ionic liquids (ILs) 3-methyl-1-pentylimidazolium bromide, [C5mim][Br] and 1-heptyl-3-methylimidazolium bromide, [C7mim][Br] on the physicochemical properties of aqueous sodium dodecylsulfate (SDS) solutions were studied. Various micellar parameters such as critical micelle concentration (cmc), degree of counter ion dissociation (α), aggregation number (Nagg) as well as some thermodynamic parameters such as standard free energy of micellization (ΔGm0), standard enthalpy of micellization (ΔHm0) and standard entropy of micellization (ΔSm0) have been evaluated. Significant increase in cmc and decrease in counter ion binding along with decrease in Nagg was observed. 1H NMR technique was applied to reveal the solubilization site of ILs in the SDS micellar solutions.

Synthesis, Surface Property and Antimicrobial Activity of Cationic Gemini Surfactants Containing Adamantane and Amide Groups

AbstractA series of novel cationic gemini surfactants, namely 1,3‐adamantanedicarboxylic acid bis(alkyldimethyl‐3‐ammoniopropyl amide) dibromide designated as [Ad‐2(amCn)] (n = 12, 14, 16), containing adamantane, two amide groups, and two hydrocarbon chains, were synthesized from 1,3‐adamantanedicarboxylic acid. The surface‐active properties of the surfactants were investigated through surface tension and electrical conductivity measurement. A series of thermodynamic parameters such as standard free energy , enthalpy , and entropy of micellization were evaluated from electrical conductivity measurements in the temperature range from 288 to 308 K. The micellization for [Ad‐2(amCn)] is entropy‐driven at low temperature and enthalpy‐driven at high temperature. Further, the antimicrobial activity of the synthesized gemini surfactants against both Gram‐positive and Gram‐negative bacteria was also investigated, and this study showed that the compound [Ad‐2(amC12)] has excellent antibacterial activity against all studied bacteria.

Photosensitive surfactants: micellization and interaction with DNA.

Recently, photosensitive surfactants have re-attracted considerable attention. It has been shown that their association with oppositely charged biologically important polyelectrolytes, such as DNA or microgels, can be efficiently manipulated simply by light exposure. In this article, we investigate the self-assembly of photosensitive surfactants as well as their interactions with DNA by calorimetric and spectroscopic methods. Critical micelle concentration (CMC), standard micellization enthalpy, entropy, and Gibbs energy were determined in different conditions (ionic strengths and temperatures) for a series of cationic surfactants with an azobenzene group in their tail. It is shown, that aggregation forces of photosensitive units play an important role in the micellization giving the major contribution to the micellization enthalpy. The onset of the aggregation can be traced from shift of the absorption peak position in the UV-visible spectrum. Titration UV-visible spectroscopy is used as an alternative, simple, and sensitive approach to estimate CMC. The titration UV-visible spectroscopy was also employed to investigate interactions (CAC: critical aggregation concentration, precipitation, and colloidal stabilization) in the DNA-surfactant complex.

Cationic gemini and sodium cholate – Following the interaction of oppositely charged surfactants by calorimetry, turbidity and conductivity

The thermodynamics of the process of self-assembly of cationic gemini surfactants, [C12H25(CH3)2N(CH2)SN(CH3)2C12H25]Br2, (the spacer S being 2, 6 or 10, assigned as C12CSC12Br2) and the system of oppositely charged mixture of surfactants formed by C12CSC12Br2 and sodium cholate (NaCA) in aqueous solution has been investigated by isothermal titration calorimetry (ITC), conductivity and turbidity measurements. The critical micelle concentration values (cmc) for the gemini surfactants C12CSC12Br2 obtained from calorimetry and conductivity were found to be consistent with values reported in the literature. The enthalpies of micellization (ΔHmic) of C12CSC12Br2 are all exothermic, presenting a strong negative minimum at S=6, corresponding to the maximum in the cmc values. For the mixed system of oppositely charged surfactants (C12CSC12Br2(S=2,6,10)/NaCA), we did obtain from ITC the critical parameters for different events that take place as the concentration of gemini surfactant increases, such as the formation of NaCA-rich mixed micelles (cmcmix,ΔHmic-mix), the formation of a precipitate (immiscible liquid crystalline (LC) phase) (CP,ΔHP) and its re-dissolution (CR,ΔHR), and finally the formation of positive charge-rich mixed micelles (CM,ΔHM). It should be stressed that the values of cmcmix (gemini) are much smaller than those for pure gemini and pure NaCA. These results also show that there is a stronger synergistic effect between the two surfactants in the NaCA-rich region. The turbidity measurements proved valuable to the determination of the region of immiscible LC phase. The ITC results are combined with those obtained by conductivity and turbidity leading to a thorough discussion of the effect of the gemini spacer length on the aggregation behavior of the mixed systems.

Influence of temperature and organic solvents (isopropanol and 1,4-dioxane) on the micellization of cationic gemini surfactant (14-4-14)

The micellar properties of gemini surfactant, tetramethylene-1,4-bis(dimethyltetradecylammonium bromide) (14-4-14) in binary aqueous mixtures of isopropanol (IP) and 1,4-dioxane (DO) were investigated by tensiometric, conductometric and microcalorimetric methods in the temperature range of 298 to 323 K. The values of both critical micelle concentration (cmc) and degree of dissociation increase with increasing temperature and concentration of cosolvent. The energetics of micellization was determined from the temperature dependence of critical micelle concentration values. The standard Gibbs free energy of micellization (ΔG) was found to be negative and the negative value decreases with both temperature and concentration of cosolvent. The Gibbs free energy of micellization (ΔG) is mainly controlled by tail transfer free energy. The enthalpy of micellization obtained from direct calorimetry, Gibbs-Helmholtz equation and van't Hoff methods are presented and compared. Entropic contribution is found to be larger than the enthalpy and for all the systems, an enthalpy-entropy compensation phenomenon was obtained. Some interfacial parameters, e.g., Gibbs surface excess (Γmax), minimum area per surfactant molecule (Amin), surface pressure (Πcmc) were been calculated. The fluorimetric technique was used to understand the microenvironment of the solution under the influence of cosolvent. The micellar aggregation number of 14-4-14 in a binary mixed solvent was also determined from fluorimetry using pyrene as a probe. Two fluorophores, fluorescein and curcumin delivered the information of the peripheral region of the micellar interface and palisade region. The self-diffusion coefficients of the micellar media were evaluated using the cyclic voltammetry (CV) method. Such multi-technique investigation provides a new look into the role of solvation in micellization.

Thermodynamic and FTIR studies of the interactions between sodium dodecyl sulphate and strong acids – atypical conductivity pattern

Micellisation of sodium dodecyl sulphate (SDS) was studied in the presence of hydrochloric acid (HCl) and perchloric acid (HClO4) using conductometry method. The conductivity-[SDS] plots showed abnormal profile pattern at [HCl] > 0.002 mol dm−3 and [HClO4] > 0.001 mol dm−3. Below these acid concentrations, conductivity pattern was normal, and the critical micelle concentration (CMC) values of SDS were lower in both acids than in water. At high acid concentrations, post-micellar slopes were negative. Fourier transform infrared (FTIR) analysis showed significant shifts in the bands suggesting the formation of dodecyl hydrogen sulphate by SDS at high acid concentrations. Thermodynamic parameters for SDS micellisation at low acid concentrations ([HCl] = 0.002 mol dm−3 and [HClO4] = 0.001 mol dm−3) were determined in the temperature range 15–40°C. As temperature increases, the change in enthalpy and entropy of micellisation becomes less positive, and the change in free energy of micellisation becomes increasingly negative.

Aggregation properties and thermodynamics of micellization of gemini surfactants with diethyl ether spacer in water and water–organic solvent mixed media

The aggregation properties and thermodynamics of micellization of three cationic gemini surfactants (n–EO1–n) containing diethyl ether spacer group with varying carbon number (n=12, 14 and 16) in the hydrophobic tails have been studied in water and water–organic solvents mixed media over the range of temperature (298.15 to 328.15)K using the conductometric method. Ethylene glycol (EG) and 1,4-dioxane (DO) were used as organic co-solvents with three different volume percentages due to their unique nature than other solvents. With increasing tail length, the critical micellar concentration (cmc) of gemini surfactants decreased. The effect of the diethyl ether spacer group on aggregation behaviour has been compared with other reported spacer groups. The micellization process is delayed in the presence of organic co-solvents as compared to pure water giving a positive value for the Gibbs energy of transfer (ΔGtranso). The degree of counter ion dissociation (α) increases with increasing tail length of gemini surfactants. It also increases with increase in the percentage of organic co-solvents and it is more prominent in DO–WR than EG–WR mixed media. The standard Gibbs energy of micellization (ΔGmo) is found to increase with increasing volume percentage of an organic co-solvent and also with decrease in the chain length of gemini surfactants. The ΔGmo has been correlated with Gordon parameter. The ΔGmo increases with increasing temperature which is more prominent in the presence of high percentage of an organic co-solvent and also in the presence of an organic co-solvent with less polarity. The enthalpies of micellization in all cases are exothermic in nature. The compensation between the enthalpy and entropy for the formation of micellar aggregates has been observed.

Colloidal and biological properties of cationic single-chain and dimeric surfactants

The colloidal and biological properties of the two single-chain surfactants N-benzyl-N,N-dimethyl-N-(1-dodecyl)ammonium bromide (PH12) and N-cyclohexylmethyl-N,N-dimethyl-N-(1-dodecyl)ammonium bromide (CH12) and their two dimeric counterparts N,N’-(1,3-phenylenebis(methylene))bis(N,N-dimethyl-N-(1-dodecyl)ammonium dibromide (12PH12) and N,N’-(cyclohexane-1,3-diylbis(methylene))bis(N,N-dimethyl-N-(1-dodecyl)ammonium dibromide (12CH12) were investigated. The thermodynamic functions of the self-aggregation process were estimated by using calorimetric measurements and the micellization enthalpy values, ΔHM, were examined considering the different enthalpic contributions to ΔHM. In the investigation of the structure-property relationship, it was found that the surfactant structure does not influence practically the foamability of the surfactants, but it plays a key role in their solubilization capacity, antimicrobial activity and biodegradability.

The effect of sodium dodecyl sulphate on Furosemide — A cardiovascular drug in water–methanol at different temperature

Different kinds of interactions have been critically assessed in order to understand the effect of methanol (MeOH) on sodium dodecyl sulphate (SDS) containing different concentrations of Furosemide with the help of densimetric and conductometric methods. A number of physico-chemical parameters viz. apparent molar volume, apparent molar adiabatic compressibility, standard enthalpy of micellization, standard entropy of micellization and standard free energy of micellization have been calculated from experimentally measured density, velocity of sound and critical micelle concentration (CMC). The CMC has been calculated from conductivity studies. The behaviour of these parameters suggests hydrophobic hydration of the surfactant molecules in a pre-micellar region and their cooperative self-association in a micellar region. The application of the Lumry–Rajender enthalpy–entropy compensation model to the present thermodynamic parameters has also been done to calculate compensation temperature Tc, which lies in the range 270–300K suggesting solvent induced synergistic behaviour. The plot of apparent molar volume (ϕv) vs. (SDS) at different concentrations of Furosemide in 8.0mol% aqueous solution of MeOH at 303K is shown in Fig. (A) which clearly indicates the dominance of electrostatic interaction in the pre-micellar region. The data were found to be in qualitative accordance indicating the existence of intermolecular hydrophobic as well electrostatic interactions between the surfactant, MeOH and drug.

Cationic Gemini surfactants based on adamantane: Synthesis, surface activity and aggregation properties

A series of novel cationic Gemini surfactants based on adamantane, namely 1,3-bis(alkyldimethylammonioethoxycarbonyl) adamantane dibromide ([CnE-Ad-ECn], n=12, 14, 16) were synthesized from 1-adamantanecarboxylic acid. The surface activity and aggregation properties of the resultant surfactants were investigated by using surface tension, electrical conductivity, dynamic light scattering (DLS), steady-state fluorescence and fluorescence quenching technique. These surfactants have been found to have low critical micelle concentrations (CMC) and large minimum surface area per molecule (Amin) values as compared to other categories of cationic Gemini surfactants. A series of thermodynamic parameters such as standard free energy (ΔGm0), enthalpy (ΔHm0), and entropy (ΔSm0) of micellization were evaluated from electrical conductivity measurements in the temperature range of 288–308K. In addition, the micropolarity and the micelle aggregation number (Nagg) were studied by fluorescence measurements. Particular performances of [CnE-Ad-ECn] such as low CMC, large Amin, and small Nagg, should be attributed to the lipophilic, rigid and bulky adamantane spacer.

Effect of Furosemide on denaturation of lysozyme in the presence of ionic surfactant at different temperatures

The thermodynamics of Furosemide–lysozyme interaction has been studied using conductivity in combination with viscosity, density and speed of sound measurements. Lysozyme binds preferentially with Furosemide in the presence of surfactants, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB). A number of physico-chemical parameters viz. critical micelle concentration (CMC), standard enthalpy of micellization (ΔHm°), standard entropy of micellization (ΔSm°), standard free energy of micellization (ΔGm°), apparent molar volume (ϕv), apparent molar adiabatic compressibility (ϕk) and relative viscosity (ηr) have been calculated from experimentally measured conductivity (κ), density (d), speed of sound (v) and viscosity (η). The critical micelle concentration data were found to pass through a broad minimum at 303K, which tends to become sharp with the increase in the [lysozyme] in case of SDS. Whereas for CTAB, CMC values, in general increase with the temperature and decrease with the increase in concentration of lysozyme. Experiments at different lysozyme concentrations and in the presence of surfactants suggest the predominant involvement of electrostatic interactions in the complexation process of Furosemide with lysozyme in the presence of SDS which induce unfolding of lysozyme as the surfactant concentration approaches its critical micelle concentration value, and non-specific interaction behaviour of Furosemide with lysozyme in the presence of CTAB.

Thermodynamic solution properties of pefloxacin mesylate and its interactions with organized assemblies of anionic surfactant, sodium dodecyl sulphate

This manuscript reports the physicochemical behavior of antibiotic amphiphilic drug pefloxacin mesylate (PFM) and its interaction with anionic surfactant, sodium dodecyl sulfate (SDS). The data of surface tension and electrical conductivity are helpful to detect the CMC as well as to calculate surface parameters, i.e. surface pressure, π, surface excess concentration, Γ, area per molecule of drug and standard Gibbs free energy of adsorption, ΔGads and thermodynamic parameters like standard free energy of micellization, ΔGm, standard enthalpy of micellization, ΔHm and standard entropy of micellization, ΔSm. The interaction of this drug with anionic surfactant, sodium dodecyl sulfate (SDS) was studied by electrical conductivity and UV/visible spectroscopy. This enabled us to compute the values of partition coefficient (Kx), free energy of partition, ΔGp, binding constant, Kb, free energy of binding, ΔGb, number of drug molecules per micelle, n, and thermodynamic parameters of drug–surfactant interaction.

A COMPARATIVE STUDY OF THERMODYNAMIC PROPERTIES OF STRUCTURALLY RELATED PHENOTHIAZINE DRUGS IN AQUEOUS SOLUTION

Association characteristics of amphiphilic phenothiazine drugs Fluphenazine and Trifluperazine dihydrochloride in water have been examined and their thermodynamic parameters have been calculated using conductometry. The electrical conductivity was measured as a function of concentration at various temperatures and cmc was calculated in the temperature range of 20-50C. Thermodynamic parameters i.e. standard free energy of micellization,mG , standard enthalpy of micellization, m H and standard entropy of micellization, m S were calculated from cmc value using closed association model.

The Effect of NaCl on the Krafft Temperature and Related Behavior of Cetyltrimethylammonium Bromide in Aqueous Solution

AbstractThis paper presents the effect of NaCl on the Krafft temperature (TK), surface adsorption and bulk micellization of cetyltrimethylammonium bromide (CTAB) in aqueous solution. The critical micelle concentration (CMC) of CTAB in the presence of NaCl increased and then decreased with increasing temperature. Thus, the CMC–temperature data can be represented by a bell‐shaped curve. The micellar dissociation (fraction of counterion binding) and energetic parameters (free energy, enthalpy and entropy changes) of both adsorption and micellization were calculated. The processes were found to be both enthalpy and entropy controlled and appeared to be more and more enthalpy driven with increasing temperature. An enthalpy–entropy compensation rule was observed for both adsorption and micelle formation. The TK of the surfactant decreased significantly in the presence of NaCl, which is a sharp contrast to the usual behavior of the effect of electrolytes on the TK of classical ionic surfactants. The surface excess concentrations decreased with increasing temperature. However, the values were much higher in the presence of NaCl compared to the corresponding values in pure water. The solubilization behavior of a water‐insoluble dye, Sudan red B (SRB), in the micellar system was studied by the UV–visible spectrophotometric technique. The molar solubilization ratio in the presence of NaCl was found to be about three times higher than that in pure water, indicating that the solubilization of SRB in the CTAB micelles significantly increases in the presence of NaCl.

Amphiphilic activities of anionic sodium cholate (NaC), zwitterionic 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) and their mixtures: A comparative study

Anionic biological surfactant sodium cholate (NaC) and the zwitterionic nontoxic surfactant CHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate) having common steroidal skeleton have not been studied in a comparative level to explore their amphiphilic behaviors separately and in mixed states. Their adsorption at the interface in relation to self-association in solution has been examined in both pure and mixed states with reference to detailed thermodynamic analysis of their surface chemical and solution behaviors. Their head group differences are responsible for the differences in their properties viz. critical micelle concentration (CMC), aggregation number (N), hydrodynamic diameter, Gibbs surface excess (Γmax), minimum head group area (Amin), mixed micelle composition and their mixing ideality/nonideality. Although the CMC values found from tensiometry and isothermal titration calorimetry (ITC) are in good agreement, the standard enthalpy of micellization (ΔHm0) found from ITC at different temperatures are different from that evaluated by the van't Hoff method. This is because van't Hoff rationale is a differential method which estimates the enthalpy of the monomer ↔ micelle equilibrium process whereas calorimetry is an integral process that evaluates all probable/possible processes in addition to monomer to micelle conversion. Results are analyzed, compared and discussed in the light of physicochemical parameters of pure NaC and CHAPS and their mixtures. These fundamental findings are considered prospective in pharmaceutical, biochemical and biomedical applications of the studied bio-friendly amphiphiles.

A physicochemical study of SDS in aqueous solution of Furosemide: Effect of DMSO on surfactant-Furosemide interaction

Micellization behaviour of sodium dodecyl sulphate (anionic surfactant) has been studied in the presence of Furosemide (cardiovascular drug) at two concentrations i.e. 0.001 and 0.002M in 8.0mol% aqueous solution of dimethylsulphoxide using conductance (κ), densities (d), velocities of sound (v) and viscosities (η) studies in the temperature range 20–40°C at an interval of 5°C. The critical micelle concentration (cmc) of sodium dodecyl sulphate (SDS) was determined from the plots of specific conductance (κ) of SDS. The results showed that critical micelle concentration (cmc) values of surfactant decrease with increase in [Furosemide] and increase with the rise in temperature. By using cmc data, various thermodynamic parameters like standard enthalpy of micellization (ΔHmo), standard entropy of micellization (ΔSmo) and standard free energy of micellization (ΔGmo), that have direct bearing on the consequences of such interactions at the molecular level have been calculated. The apparent molar volume (ϕv) and apparent molar adiabatic compressibility (ϕκ) have also been computed using densities and velocities of sound data. The above calculated parameters were found to be sensitive towards the interactions prevailing in Furosemide–SDS–DMSO-water systems.