Cationic Cetyltrimethylammonium Chloride Research Articles

Cationic surfactant-assisted foam fractionation enhances the removal of short-chain perfluoroalkyl substances from impacted water

Several studies have demonstrated that air-bubbling and foam fractionation techniques can efficiently remove long-chain PFAS from contaminated water. However, removing short-chain PFAS is challenging due to its lower surface activity and inability to form self-assembly structures at the air-water interface. In this study, we tested various additives, including salts, surfactants, and polymers, to improve short-chain PFAS (e.g., perfluorobutanesulfonic acid (PFBS) and perfluorobutanoic acid (PFBA)) removal in non-foaming solutions using a bench-scale system. We found that in the presence of cetyltrimethylammonium chloride (CTAC) and salt, air-bubbling can significantly remove 0.5 μg L−1 of PFBS and PFBA in deionized water by >99% (15 min) and 81% (60 min), respectively. The decline of surface tension and the formation of thin foam-like layers during bubbling, controlled by the concentration of CTAC, significantly improved the removal of short-chain PFAS. Adding anionic and neutral surfactants showed no removal of short-chain PFAS during bubbling, suggesting the importance of the electrostatic interactions between short-chain PFAS and the cationic CTAC. We observed a 1:1 M ratio between CTAC and PFBS removed from the solution, suggesting the formation of ion pairs in the solution and enhancing the surface activity of the overall neutral (PFAS-CTAC) complex. A mass balance of the system revealed that the primary mechanism by which PFAS was removed from non-foaming waters was through aerosol generation (70−100%). Using the optimized condition, PFAS mixtures (short- and long-chain PFAS, including five recently regulated PFAS by USPEA, 2 nM each) in deionized water and natural groundwater were successfully removed to below detection (>99% removal; <2 ng L−1), except for PFBA (25−73% removal). These results provide an improved understanding of the mechanism by which PFAS is removed during foam fractionation and highlight the need for capturing aerosols enriched with PFAS to prevent secondary contamination.

Hierarchical Polyimide Microparticles with Controllable Morphology.

Hierarchical polyimides (PIs) not only show outstanding thermal stability and high mechanical strength but also have great advantages in terms of microstructure and surface area, which makes them highly valuable in various fields such as aerospace, microelectronics, adsorption, catalysis, and energy storage. However, great challenges still remain in the synthesis of hierarchical PIs with well-defined microstructure. Herein, polyamide acid salts (PAAS) with tunable ionization degree are synthesized first via the polymerization of dianhydride and diamine monomers in deionized water with 1,2-dimethylimidazole (DMIZ). Then cationic cetyltrimethylammonium chloride (CTAC) is added to the PAAS aqueous solution to induce the formation of polyelectrolyte-surfactant complexes based on electrostatic interaction. After a typical hydrothermal reaction (HTR) procedure, hierarchical PIs with different microstructures such as urchin-like PI microparticles, flower-like PI microparticles, and lamellar PI petals can be fabricated simply by changing the additive amount of DMIZ and CTAC. The nanostructure self-assemblies of PAAS are dominated by the charges on macromolecular chains and the formation of hierarchical structures of polymers is ascribed to a geometrical selection process during crystal growth. This work provides valuable insights into the self-assembly behaviors of polyelectrolyte systems for synthesizing well-defined hierarchical polymers.

In Situ Assay of Interfacial Interaction between ZnO Nanoparticles and Live Cell Disturbed by Surfactants.

The interfacial interaction between pollutants and organisms is a critical process in controlling the environmental fates of pollutants; however, in situ assay of the interaction is still a great challenge. Here, in situ determination of dissociation constants (Kd) for ZnO nanoparticles (ZnO NPs) from live algal cells disturbed by different-charged surfactants was established using microscale thermophoresis (MST). Moreover, in situ measurement of the adhesion force between the ZnO NPs probe and live single cell was performed using an atomic force microscope (AFM). Results showed that the cationic cetyltrimethylammonium chloride (CTAC) and anionic sodium dodecylbenzenesulfonate (SDBS) increased but nonionic Triton X-100 (TX-100) decreased the adhesion of ZnO NPs on cells. However, the force signature exhibited a smooth single retracted peak at short distances in the SDBS- and TX-100-treated groups, distinguished from the "see-saw" pattern peak in the CTAC-treated groups. The extended Derjaguin-Landau-Verway-Overbeek (XDLVO) calculation further confirmed that SDBS and TX-100 mainly disturbed the short-range hydration on the NP-cell interface, while CTAC reduced the long-range electrostatic repulsion. Furthermore, an excellent linear correlation between Zn bioaccumulation and two parameters (Kd and adhesion force) indicated that NP-cell interfacial interactions affected Zn bioaccumulation. Thus, in situ assay provides a quantitative basis for the pollutant-organism interfacial interaction to evaluate the environmental fate and ecological risk of pollutants.

Surfactant-Controlled Mobility of Oil Droplets in Mineral Nanopores.

Polymer flooding is one of the widely used enhanced oil recovery (EOR) methods. However, tuning polymer properties to achieve improved performance in porous mineral rocks of diverse oil reservoirs remains one of the challenges of EOR processes. Here, we use molecular dynamics (MD) simulations to examine decane/water mixtures with surfactant additives in calcite and kaolinite mineral nanopores and characterize surfactant properties associated with increased fluid mobility and improved wettability in planar and constricted nanopore geometries. Cetyltrimethylammonium chloride (CTAC) and sodium dodecyl sulfate (SDS) surfactants are found to modulate the contact angles of decane droplets and reduce the decane density on mineral surfaces. CTAC can enhance and unblock the flow of decane droplets through narrowing nanopores with constricted geometries while aiding in decane droplet shape deformation, whereas SDS leads to decane droplets stalling in front of constrictions in nanopores. We hypothesize that the inability of the cationic CTAC headgroup to form hydrogen bonds is one of the key factors leading to enhanced CTAC-coated decane flow through constricted nanopores. The obtained molecular view of equilibrium and dynamic properties of complex fluids typical of oil reservoirs can provide a basis for the future design of new molecules for EOR processes.

Nonmonotonic Scission and Branching Free Energies as Functions of Hydrotrope Concentration for Charged Micelles.

Using coarse-grained molecular dynamics simulations and an umbrella sampling method that uses local surfactant density as a reaction coordinate, we directly calculate, for the first time, both the scission and branching free energies of a model charged micelle [cationic cetyltrimethylammonium chloride (CTAC)] in the presence of inorganic and organic salts (hydrotropes). We find that while inorganic salt only weakly affects the micelle scission energy, organic hydrotropes produce a strong, nonmonotonic dependence of both scission energy and branching on salt concentration. The nonmonotonicity in scission energy is traced to a competition between electrostatic screening of the repulsions among the surfactant head groups and thinning of the micellar core, which result from attachment of the hydrotropes to the micelle surface. We are able to correlate the nonmonotonicity in the scission energy of CTAC micelles with the peak observed experimentally in viscosity versus hydrotrope concentration and the location of this peak in CTAC solutions.

Quenching of fluorene fluorescence by single-walled carbon nanotube dispersions with surfactants: application for fluorene quantification in wastewater.

The fluorescence of fluorene in aqueous solutions of surfactants of different natures, anionic sodium dodecylsulphate (SDS), cationic cetyltrimethyl ammonium chloride (CTAC) and non-ionic polyoxyethylene-23-lauryl ether (Brij 35), as well as in single-walled carbon nanotube (SWCNT) dispersions in these surfactants, has been studied and compared. A fluorescence quenching phenomenon has been observed in the presence of SWCNT, the effect being stronger for dispersions in CTAC, related to the improved dispersion capability of this surfactant as revealed by microscopic observations and its stronger adsorption onto the SWCNT surfaces as inferred from the Raman spectra. SWCNT interact with fluorene causing a fluorescence quenching. The fluorescence intensity ratio, calculated in the absence and in the presence of SWCNT, follows the Stern-Volmer equation. For the CTAC concentration that provides the highest quenching effect, the analytical characteristics of the fluorimetric method like sensitivity, detection and quantification limits, repeatability, reproducibility and robustness have been calculated. Results demonstrate that it is possible to determine fluorene in a fortified wastewater sample in aqueous solutions of CTAC and SWCNT/CTAC dispersions, showing recoveries close to 100 %. The quenching effect found in this work could be useful for the development of an optical device that uses SWCNT-based receptors for fluorene detection and quantification in aqueous surfactant solutions. Graphical abstract Distribution of fluorene between single-walled carbon nanotubes and micelles.

양쪽성 메조 포러스 실리카에 의한 수용액 속의 MX의 흡착

Mesoporous silica was synthesized in a water solvent and in an ethanol solvent with the non and cationic cetyltrimethyl ammonium chloride (CTAC) by varying the amount of the amphiphilic acrylic urethane oligomer (AAU) and the pH of the solution. The adsorption of the MX (3-chloro-4 (dichloromethyl)-5-hydroxy-2-(5H)-furanone) in drinking water was studied using the synthesized mesoporous silica as an adsorbent. The most appropriate silica was synthesized in acidic conditions in the water solvent and in alkali conditions in the ethanol solvent. The average pore sizes of the synthesized mesosilica were 3 ㎚ and more. The mesoporous silica synthesized by the addition of the AAU oligomer showed excellent adsorption characteristics. With respect to the co-surfactant, the best adsorption characteristics were obtained when the P64,a non-ionic surfactant with a high molecular weight, was used to synthesize the silica than when other co-surfactants were used. The adsorption rate decreased as the MX concentration in the water increased. Different adsorption equilibrium conditions were reached depending on the adsorbate MX concentration in the adsorbent and the solution. It was seen that perfect adsorption does not occur due to such equilibrium conditions.

On the origin of the stability of foams made from catanionic surfactant mixtures

Using mixtures of the anionic myristic acid (C13COOH) and the cationic cetyl trimethylammonium chloride (C16TA+Cl−) in aqueous solutions at a 2:1 ratio, we show that the outstanding stability of foams generated from sufficiently concentrated “catanionic” surfactant mixtures can be explained by a synergy effect between two fundamentally different mechanisms. Applying a multi-scale approach, in which we link static and dynamic properties of the bulk solutions, isolated gas/liquid interfaces, thin liquid films and foams, we identify these two mechanisms to be as follows: firstly, cationic mixtures create tightly packed surfactant layers at gas/liquid interfaces, which are strongly viscoelastic and also confer high disjoining pressures when two interfaces are approaching each other to form a thin liquid film. Foams created with such kind of interfaces tend to be extremely stable against coalescence (film rupture) and coarsening (gas exchange). However, typical time scales to cover the interfaces are much longer than typical foaming times. This is why a second mechanism plays a key role, which is due to the presence of micron-sized catanionic vesicles in the foaming solution. The bilayers of these vesicles are in a gel-like state, therefore leading to nearly indestructible objects which act like elastic micro-spheres. At sufficiently high concentrations, these vesicles jam in the presence of the confinement between bubbles, slowing down the drainage of liquid during the initial foaming process and therefore providing time for the interfaces to be covered. Furthermore, the tightly packed vesicles strongly reduce bubble coalescence and gas transfer between bubbles.

Surfactant dispersed multi-walled carbon nanotube/polyetherimide nanocomposite membrane

Carbon nanotube based nanocomposite membranes have been fabricated through solution casting by embedding multi-walled carbon nanotubes (MWCNTs) within polyetherimide (PEI) polymer host matrix. In order to achieve fine dispersion of nanotubes and facilitate strong interfacial adhesion with the polymer matrix, the nanotubes were first treated with surfactants of different charges, namely anionic sodium dodecyl chloride, cationic cetyl trimethyl ammonium chloride and non-ionic Triton X100, prior to the dispersion in the PEI dope solution. Dispersion of MWCNTs in N-methyl-2-pyrrolidone solvent showed that the agglomeration and entanglement of the nanotubes were greatly reduced upon the addition of Triton X100. Scanning electron microscopy and atomic force microscopy examination has evidenced the compatibility of Triton X100 dispersed MWCNTs with the polymer matrix in which a promising dispersion and adhesion has been observed at the MWCNT-PEI interface. The increase in both thermal stability and mechanical strength of the resulting Triton X100 dispersed MWCNT/PEI nanocomposite indicated the improved interaction between MWCNTs and PEI. This study demonstrated the role of Triton X100 in facilitating the synergetic effects of MWCNTs and PEI where the resulting composite membrane is anticipated to have potential application in membrane based gas separation.

Interaction of pyrimethamine and sulfadiazine with ionic and neutral micelles: Electronic absorption and fluorescence studies

The binding of two antitoxoplasmosis drugs, pyrimethamine (PYR) and sulfadiazine (SDZ) to cationic cetyltrimethylammonium chloride (CTAC), anionic sodium dodecylsulfate (SDS), zwiterionic N-hexadecyl- N, N-dimethyl-2-ammonium-1-propanesulfonate (HPS) and neutral polyoxyethylene-dodecyl-ether (Brij-35 ®) micelles was studied using absorption and fluorescence spectroscopic methods. The p K a of PYR changed in the presence of charged anionic, cationic and zwiterionic micelles, indicating that interaction is influenced by the micellar charge. For SDZ, p K a changes were lower than 1 for all micelles, suggesting the occurrence of low binding constants in addition to a reasonable influence of the micellar charge. The values of binding constants K b, obtained from fluorescence measurements, for PYR to CTAC micelles were very low at pH 4.0, where the drug is in a complete protonated state, increasing at pH 9.0 to long-chained CTAC and HPS micelles since this factor also favors accomodation of the neutral drug in the hydrophobic compartments. For SDZ the binding constants were determined from optical absorption measurements. Low binding constants were observed to charged surfactant micelles, with influence of micellar charge. It must be stated however that those values can be underestimated due to the relatively low sensitivity of the method based on absorption measurements.

Fluorescence Studies on the Properties of the Nanoaggregates of Poly(ethylene oxide)-b-polymethacrylate Copolymer Formed by Binding of Cationic Surfactants to Polymethacrylate Block

Fluorescence measurements have been applied to the characterization of the nanoaggregates of poly(ethylene oxide)-b-polymethacrylate (PEO-b-PMA) copolymer with the cationic surfactant cetyltrimethylammonium chloride (CTAC). It was found that the formation of the aggregates is dependent on two factors: the concentration of the block copolymer and the degree of electric charge neutralization (DN) of the carboxylate anion with cationic CTAC. The critical aggregation concentration of the complex was determined at various levels of DN. The micropolarity of the nanoaggregates was investigated by vibronic fine structure of the monomer fluorescence of pyrene (so-called I1/I3 ratio). It was revealed that the micropolarity of the aggregate particles is close to that of acetic acid or ethyl acetate. The microviscosity of the aggregates was elucidated from excimer formation of pyrene and fluorescence polarization of rhodamine B. The interior of the aggregate particle is not rigid, so that the incorporated pyrene can...

Interaction of Fe(III)- and Zn(II)-tetra(4-sulfonatophenyl) porphyrins with ionic and nonionic surfactants: aggregation and binding.

Interactions of the water soluble Fe(III)- and Zn(II)-tetra(4-sulfonatophenyl) porphyrins, FeTPPS(4) and ZnTPPS(4), with ionic and nonionic micelles in aqueous solutions have been studied by optical absorption, fluorescence, resonance light-scattering (RLS), and 1H NMR spectroscopies. The presence of three different species of both Fe(III)- and Zn(II)TPPS(4) in cationic cetyltrimethylammonium chloride (CTAC) solution has been unequivocally demonstrated: free metalloporphyrin monomers or dimers (pH 9), metalloporphyrin monomers or aggregates (possibly micro-oxo dimers) bound to the micelles, and nonmicellar metalloporphyrin/surfactant aggregates. The surfactant:metalloporphyrin ratio for the maximum nonmicellar aggregate formation is around 5-8 for Fe(III)TPPS(4) both at pH 4.0 and 9.0; for Zn(II)TPPS(4) this ratio is 8, and the spectral changes are practically independent of pH. In the case of zwitterionic N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) and non-ionic polyoxyethylene lauryl ether (Brij-35) and t-octylphenoxypolyethoxyetanol (Triton X-100), the nonmicellar aggregates were not observed in the pH range from 2.0 to 12.0. Binding constants were calculated from optical absorption data and are of the order of 10(4) M(-1) for both CTAC and HPS, values which are similar to those previously obtained for the porphyrin in the free base form. For Brij-35 and Triton X-100 the binding constant for ZnTPPS(4) at pH 4.0 is a factor of 3-5 lower than those for CTAC and HPS, while in the case of FeTPPS(4) they are two orders of magnitude lower. Our data show that solubilization of ZnTPPS(4) within nonpolar regions of micelles is determined, in general, by nonspecific hydrophobic interactions, yet it is modulated by electrostatic factors. In the case of FeTPPS(4), the electrostatic factor seems to be more relevant. NMR data indicated that Fe(III)TPPS(4) is bound to the micelles predominantly as a monomer at pH 4.0, and at pH 9.0 the bound aggregated form (possibly micro-oxo dimers) remains. The metalloporphyrins were incorporated into the micelles near the terminal part of their hydrocarbon chains, as evidenced by a strong upfield shift of the corresponding peaks of the surfactants.

Interaction of chlorpromazine and trifluoperazine with ionic micelles: electronic absorption spectroscopy studies

The characteristics of binding of two phenothiazine antipsychotic drugs, namely, chlorpromazine (CPZ) and trifluoperazine (TFP), to cationic cetyltrimethylammonium chloride (CTAC), zwitterionic N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS), neutral t-octylphenoxypolyethoxyethanol (TRITON X-100) and polyoxyethylene dodecyl ether (Brij-35) micelles were investigated using electronic absorption spectroscopy. Binding constants Kb and pKa values of drugs in micelles were estimated using the red shifts of the maximum absorption upon alkalization or in the presence of detergents. The pKa of TFP seems to be shifted by 2.5–4.1 units to lower values in the presence of different surfactants as compared to the experimental value of pKa obtained in buffer which is around 7.0. Consideration of the second pKa around 4.0 reported in the literature for TFP leads to a better rationalization of pKa changes for this compound. The changes in pKa contributed by electrostatic effects are all positive, small for CTAC (+0.2), and greater for HPS (+0.9). For CPZ the pKa shift due to its interaction with micelles is in the 0.7–2.3 range, the direction of the shift depending on the charge of the polar head. The electrostatic contribution for the shift is great for CTAC (−0.8) and smaller for HPS (+0.2). This result suggests a more polar localization in the micelle of CPZ as compared to TFP. The values of binding constants Kb for TFP and CPZ in different protonation states show that electrostatic interactions are essential in the affinity of the drugs to micelles bearing different charges on their headgroups (CTAC, HPS). Data for Brij-35 demonstrate that the additional charge on the TFP ring at pH 2.0 leads to a decrease of binding constant probably due to the repulsion of the phenothiazine ring from the protons accumulated at the polar head of the micelle at acidic pH values. For this micelle at pH 5.0 TFP has a Kb 3-fold greater than that for CPZ while at pH 2.0 Kb for TFP is 3-fold less than that for CPZ. So, for more hydrophobic TFP electrostatic interactions due to protonation of the ring are quite important even considering its deeper penetration into the micelle interior as compared to CPZ.

Interaction of the Tetra(4-sulfonatophenyl)porphyrin with Ionic Surfactants: Aggregation and Location in Micelles

Interactions of the water-soluble tetra(4-sulfonatophenyl)porphyrin (TPPS4) with ionic micelles in aqueous solutions have been studied by optical absorption, fluorescence, resonance light-scattering (RLS), and 1H NMR spectroscopies. The presence of three different species of TPPS4 in cationic cetyltrimethylammonium chloride (CTAC) solution has been unequivocally demonstrated: free porphyrin monomers, monomers bound to micelles, and nonmicellar porphyrin/surfactant aggregates. This result is similar to our previous findings for TPPS4 interactions with biomacromolecules (serum albumin and DNA). The surfactant:porphyrin ratio for maximum aggregate formation is around 4:1−5:1 and 14:1 at pH 3.0 and pH 7.5, respectively. In the case of zwitterionic N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) the aggregates were not observed. Binding constants estimated from these data were of the order of 104 M-1 for CTAC and HPS. Our data show that solubilization of porphyrins within nonpolar regions of micelles is determined, in general, by nonspecific hydrophobic interactions, yet it is significantly modulated by electrostatic factors. NMR chemical shift, T1, and nuclear Overhauser effect data indicate that TPPS4 is located mainly in the hydrophobic core in CTAC and HPS micelles, while in lysophosphatidylcholine its involvement in the polar area is more significant.

Aggregation of Fe(III)TPPS(4) on Biological Structures Is pH-Dependent, Suggesting Oxo-Bridging in the Aggregates.

Interaction of the Fe(III) derivative of tetra(4-sulfonatophenyl)porphyrin (TPPS(4)), and diamagnetic ZnTPPS(4) and metal-free TPPS(4), with the simplest models for membranes and protein reaction centers, aqueous (AM) and reversed (RM) ionic micelles, was studied by high-resolution (1)H NMR and proton magnetic relaxation measurements. AM were much more sensitive than RM to the bulky porphyrins, seemingly, because of the more restricted motion of surfactant chains in AM. TPPS(4) and its derivatives were incorporated into the AM of cationic cetyltrimethylammonium chloride (CTAC) or zwitterionic lysophosphatidylcholine (LPC) near the terminal part of their hydrocarbon chains, as evidenced by a strong upfield shift of the corresponding peaks. At a FeTPPS(4)/CTAC molar ratio greater than 0.05 and a pH > 4, FeTPPS(4) partly formed nonparamagnetic aggregates, which dissociated into monomers at pH < 4. In CTAC RM, FeTPPS(4) was predominantly aggregated, the transition to the monomer form occurring upon acidification of the water RM interior to about pH -1. No similar pH dependencies were found for ZnTPPS(4) and TPPS(4). It is supposed that charged porphyrins may interact with cellular membranes. Characteristic pH dependence of the FeTPPS(4) aggregation in micelles suggests that aggregated units are bound through a &mgr;-oxo-bridge. Similar mechanisms may be operative in other systems, such as porphyrin-protein.

Different Micellar Packing and Hydrophobicity of the Membrane Probes TEMPO and TEMPOL Influence Their Partition Between Aqueous and Micellar Phases Rather than Location in the Micelle Interior

We report the investigation of the distribution of two stable nitroxyl radicals, 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) and 4-hydroxy-TEMPO (TEMPOL), between aqueous and micellar phases and in the micelle interior by quenching of fluorescence of dipyridamole (DIP) and by1H NMR, ESR, and optical absorption spectroscopies. Cationic cetyltrimethylammonium chloride (CTAC), anionic sodium dodecylsulfate (SDS), zwitterionicN-hexadecyl-N,N-dimethyl 3-ammonio-1-propanesulfonate (HPS), and non-ionic octylphenoxypolyethoxyethanol (Triton X-l00) micelles were used. In all types of micelles the binding constants for more hydrophobic TEMPO appear higher than those for TEMPOL. At the same time the1H NMR and optical absorption data show that the distribution of both radicals in the micelle interior is practically the same: The paramagnetic fragments are localized in the interface between the polar headgroup region and the hydrophobic interior of micelles. There is no clear correlation betweenKband the micelle charge. Indeed,Kbfor TEMPO with SDS (2150 M−1) is lower than with CTAC (3250 M−1), but higher than with Triton X-l00 (1300 M−1) or HPS (1000 M−1). TheKbvalues correlate quite well with the packing of the monomers in the micelle, being higher for the loosely packed micelles (higher cmc). Besides, the micelle headgroup hydration water seems to decrease the binding constant.

Low K Mesoporous Silica Films Through Template-Based Processing

AbstractLow dielectric-constant mesoporous silica films were prepared by condensation of a silicate network around surfactant micellar structures. Adherent, porous films 0.5–1.0 μm in thickness, and containing an ordered assemblage of ≈2 nm diameter pores were synthesized by spin-coating water/ethanol-based solutions containing a silica precursor and surfactant template. In this paper, film deposition conditions are described, and film thickness, porosity, refractive index and dielectric constant measured by ellipsometry are presented. Using a coating solution containing tetraethyl orthosilicate (TEOS) and a cationic cetyltrimethylammonium chloride (CTAC) surfactant template, the film porosity and dielectric properties were controlled over a wide range by adjusting the CTAC/TEOS molar ratio. With the CTAC/TEOS ratio between 0.1 and 0.15, the pores were highly ordered in hexagonal arrays after heat treatment at 550 °C. With a CTAC/TEOS ratio of 0.21, films with a pore volume of ≈64% (≈36 vol% silica) could be synthesized. The measured index of refraction for these highly porous films at 500 nm wavelength was 1.16, indicating that these films are potentially useful as low K interlayer dielectrics.

Synthesis, characterization and interaction with ionic micelles of tetraacetylated dipyridamole

Tetraacetylated dipyridamole (Ac-DIP) was synthesized by reaction of dipyridamole (DIP) with acetic anhydride in a quantitative yield. Infrared and NMR spectra showed that the acetylation was complete, yielding the expected new bands and the disappearance of hydroxyl bands in the IR and NMR spectra. Tetraacetylated DIP was analyzed by electronic absorption and fluorescence emission in different solvents. The solubility of Ac-DIP in water is considerably lower than that of DIP, and both the absorption and emission are shifted to the blue denoting a less efficient relaxation to the solvent. Extinction coefficients and quantum yields in ethanol, chloroform and dimethyl sulfoxide are very similar for Ac-DIP and DIP. 1H and 13C NMR spectra were obtained in deuterated chloroform and dimethyl sulfoxide and a complete assignment of peaks was obtained. In order to obtain more insight into the properties of Ac-DIP, the interaction of DIP and Ac-DIP with cationic cetyltrimethylammonium chloride (CTAC) and anionic sodium dodecyl sulfate (SDS) micelles was studied. In the presence of micelles the p K a of DIP changes considerably from its value in water: from 5.8 to 4.3 in CTAC and to 7.3 in SDS indicating a considerable interaction with micelles. The p K a of Ac-DIP in SDS is 5.8. For both compounds the interaction with micelles is predominantly hydrophobic in nature but for Ac-DIP it is less sensitive to the charge on the micelle and the degree of ionization of the drug. All the results suggest that Ac-DIP is significantly more hydrophobic than DIP, being probably quite efficient in the interaction with membrane systems. This could be quite relevant for its effect at the cellular level.

Localization of dipyridamole molecules in ionic micelles: effect of micelle and drug charges

The localization of the coronary vasodilator dipyridamole (DIP) in cationic cetyltrimethylammonium chloride (CTAC), anionic sodium dodecylsulfate (SDS) and zwitterionic N-hexadecyl- N, N-dimethyl-3-ammonio-1-propanesulfonate and lysophosphatidylcholine (HPS and LPC) micelles was investigated using fluorescence quenching by quenchers with known localization in the micelle (TEMPO and 5-doxyl and 12-doxyl stearic acids). The use of fluorescence quenching jointly with fluorescence and 1H-NMR spectral measurements shows that DIP molecules in both protonated and nonprotonated forms are localized in micelles near the region which separates their polar and nonpolar parts, the polarizable heteroaromatic cycle of DIP being close to the polar part and the nonpolar substituents penetrating the hydrophobic interior of the micelle. The electrostatic interaction between the protonated DIP molecules and micelle charges either moves DIP into the micelle interior (for cationic and zwitterionic micelles) or draws it closer to the micelle surface (for anionic ones). Our results could be relevant to the mechanism of DIP action since many data indicate the interaction of the drug with cell membranes. The ability of DIP to localize near the membrane surface with the substituents immersed into a hydrophobic moiety could be essential for the drug interaction with P-glycoprotein, which is responsible for mediation of the effects of several antitumour drugs.

Proton Relaxation and Spin Label Studies of Papaverine Localization in Ionic Micelles

The localization of papaverine (PAV) in micelles of zwitterionic N-hexadecyl- N, N-dimethyl-3-ammonio-1-propanesulfonate (HPS), cationic cetyltrimethylammonium chloride (CTAC), and anionic sodium dodecyl sulfate (SDS) in D 2O was studied by 1H NMR and ESR in the presence and absence of 5-doxyl- or 12-doxyl-stearic acid. PAV, surfactants, and spin probes are characterized by restricted anisotropic motion in micelles. The rotational correlation time of doxyl fragment was in the range of 0.2 to 0.5 nanoseconds. Binding of PAV to micelles decreases the mobility of both probes, suggesting the localization of PAV inside the hydrophobic part of micelles near the micelle-water interface. According to the NOE data, the methoxy groups of PAV are located in the vicinity of the nitrogen atom in CTAC and HPS micelles, the methoxy groups of the PAV heterocycle being immersed slightly deeper inside the micelle. The T 1 relaxation enhancements by two different spin probes show that the H5 and methoxy substituents of the PAV heterocycle are in close proximity to the α-CH 2 of acyl chains in all types of micelles, whereas H3 and H12 are the most distant from the α-CH 2. No significant differences were found for the protonated and neutral PAV in SDS micelles at pD 4.9 and 11.2. These data show that the geometry of the PAV-micelle complex is practically independent of the PAV charge and surfactant headgroup.