Hydration, ion binding and self-aggregation of choline and choline-based surfactants

The present thesis deals mainly with the systematic broadband dielectric relaxation spectroscopy (DRS) of choline, 2-hydroxyethyltrimethylammonium ion, based electrolytes and surfactants. DRS have been performed for aqueous solutions of choline chloride (ChCl), chlorocholine chloride (Cl-ChCl) and ammonium chloride (NH4Cl) over a wide range of frequencies (0.2 ≤ n / GHz ≤ 89) up to reasonable concentration range of each salt at 25°C. The spectra were best described by a superposition of three Debye processes (3D model), except for NH4Cl at c > 1.10 M which is best fitted with a 2D model. The mode centred at ~18 GHz can be assigned to bulk water relaxation. In aqueous ChCl and Cl-ChCl the relaxation process centred at ~12 GHz is assigned to be a composite mode arising due to the incidentally overlapping relaxations of water molecules with reduced dynamics (‘slow water’) hydrating the cations and of the reorienting Ch+ and Cl-Ch+ ions in respective systems. For NH4Cl(aq), however, this intermediate mode is assigned solely to the slow water molecules. The lowest frequency relaxation process detected at ˂1 GHz (in all studied salts) is fairly assigned to the ion-pair and/or ion-cloud relaxation. From the amplitudes of bulk and slow water modes effective hydration numbers of the cations were determined. Both Ch+ and Cl-Ch+ bind ~5 H2O molecules irrotationally at infinite dilution, whereas it turned out that NH4+ ion does not ‘freeze’ water molecules in its vacinity. At infinite dilution, ~18, ~22 and ~13 H2O molecules are found to be slowed down by Ch+, Cl-Ch+ and NH4+ ions, respectively. For the investigations of micellar systems aqueous solutions of two bio-compatible surfactants, namely choline dodecanoate (ChC12) and choline dodecylsulfate (ChDS), and sodium dodecanoate (NaC12) have been studied over a frequencies range of (0.01 ≤ n / GHz ≤ 89) at 25°C. Theory of Grosse have been used to model the dielectric properties of above mentioned colloidal solutions. DR spectra of all studied surfactants were best fitted by a superposition of four Debye (4D) processes. The two low frequency processes, peaking at ≤ 0.1 GHz and ≤0.4 GHz are micelle-related. They can be assigned to the fluctuations of the diffuse ion cloud surrounding the micelle and to the tangential motions of bound counterions, respectively. By applying the Grosse model the distance, RG, of the bound counterions from the micelle centre, the volume fraction of the micelles, mic, and their surface conductance, s, were determined. By rationalizing the Grosse’s parameters it appeared that for NaC12 and ChDS micelles, counterions are directly attached on the micellar surface while in case of ChC12 counterion-headgroup interactions are weak and are water mediated.The relaxation centred at ~20 GHz is due to bulk water. The mode peaking in the range 6 < n / GHz < 9 is regarded as a composite (in ChC12 and ChDS) originating from the incidentally overlapping relaxations of ‘slow’ water molecules hydrating the micelles and their counterions and of the choline cations themselves, whereas in NaC12 this mode is assigned to slow water relaxation. In ChC12(aq) system no irrotational bounding is observed for carboxylate headgroup, whereas in NaC12(aq) and ChDS(aq) micelles, per headgroup, ~5 and ~2.5 H2O molecules are ‘frozen’, respectively. The obtained numbers of slow H2O molecules, per headgroup, were found to be ~18, ~18 and ~50 for ChC12(aq), ChDS(aq) and NaC12(aq), respectively

Hydration and ion association of aqueous choline chloride and chlorocholine chloride

The choline ion (Ch(+)) is ubiquitous in nature and also its synthetic homologue, chlorocholine (ClCh(+)), is widely used. Nevertheless, surprisingly little information on the hydration and counter-ion binding of these cations can be found in the literature. In this contribution we report effective hydration numbers, determined by dielectric relaxation spectroscopy, and ion-pair association constants with Cl-, determined by dilute-solution conductivity measurements. In combination with RISM calculations the obtained data suggest that for Ch(+) water is bound to the hydroxy group via hydrogen bonds whereas for ClCh(+) a rather stiff clathrate-like shell around the chlorine atom seems to be formed. With Cl- both cations form contact ion pairs with association constants of only B2 to 3 M-1

Mixed Micellar Solubilization of Naphthol Green B Followed by Its Removal from Synthetic Effluent by Micellar-Enhanced Ultrafiltration under Optimized Conditions

In this manuscript, the application of cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPC) for the removal of Naphthol Green B (NGB) as a synthetic effluent has been studied. The solubilization of NGB by a single and mixed micellar system using Triton X-100 (TX-100) as a nonionic surfactant has been performed to establish both the extent of the partitioning (kx) of NGB and ultimately their respective Gibbs free energies &Delta;Gp as well. An applied methodology, micellar-enhanced ultrafiltration (MEUF), has also been studied in different micellar media of cationic surfactants by variation in some selective parameters, such as the concentration of surfactant, electrolyte, pressure, pH, and RPM to obtain optimum conditions. The results have been analyzed by a UV/visible double beam spectrophotometer. &Delta;Gp was found to be &minus;39.65 kJ/mol and &minus;47.94 kJ/mol by CTAB and CPC, respectively, in the presence of a nonionic surfactant. The maximum value of Gibbs free energy (&Delta;Gp) of the partition was obtained by CPC. The values of the rejection coefficient (R%) and permeate flux (J) are also calculated. A maximum removal of 99.77% and 98.53% by CTAB and CPC, respectively, was obtained. It has been observed that both of the surfactants are strong candidates for NGB removal

Solubilization of Reactive Red 2 in the Mixed Micelles of Cetylpyridinium Chloride and TX-114

Owing to their surface active properties, surfactants have numerous applications in different fields of life. In the present research work, the solubilization of reactive red 2 (RR2) has been studied in single and mixed micellar systems (MMS) using UV-visible spectroscopy and electrical conductivity measurements. The interaction of RR2 with ionic micelles of cetylpyridinium chloride (CPC) was investigated. In order to probe the interaction of RR2 in MMS, mixtures of CPC and TX-114 (Triton X-114, a nonionic surfactant) were used. UV-visible spectroscopy has been used to obtain the degree of solubilization of RR2 in terms of the partition coefficient (Kc) and Gibbs free energy of partitioning (ΔG°p). Electrical conductivity data have been employed to detect the critical micelle concentration (CMC) of the surfactant systems in the presence of RR2 and, accordingly, to calculate the thermodynamic parameters of the micellization. From the obtained data, it is concluded that the micellization is spontaneous at all studied temperatures. Moreover, the micellization was observed to be driven by both enthalpy and entropy. The results also indicated that MMS have better solubilizing power than single micellar solutions

Analysis of optical properties of diallyldimethylammonium chloride dielectric-coated gold nanospheres for targeted drug delivery

This study theoretically analyzed the optical properties and electric field enhancement of gold nanospheres. Based on numerical analysis, the gold nanospheres were coated experimentally with diallyldimethylammonium chloride (C _8 H _16 ClN) for targeted drug delivery. Numerically, a resonance peak for 10 nm nanospheres was observed at 510 nm. As the radius increased from 10 nm to 100 nm, the resonance peak shifted from 510 nm to 605 nm. The nanosphere radius also affected the extinction cross-section. The resonance peaks showed a red shift as the radius of the nanosphere increased. For experiment analysis, gold nanospheres were synthesized using a seed-mediated technique and then coated with different concentrations of C _8 H _16 ClN. The UV absorbance by the nanospheres increased with an increase in the concentration of C _8 H _16 ClN from 10 mg ml ^−1 to 20 mg ml ^–1 . UV–vis spectrum confirmed a rise in resonance peaks with increasing coating concentration. The coated gold nanospheres were used to deliver the doxorubicin-HCl (DOX-HCl) drug. Maximum drug release was observed when the temperature was set at 50 °C. It was concluded that the nanospheres, coated with 20 mg ml ^–1 of C _8 H _16 ClN, are excellent candidates for drug delivery applications. The gold nanospheres with a radius of 50 nm were best for target drug delivery, and the particles above 50 nm were best for thermal therapies for cancer treatment