Ditetradecyldimethylammonium Bromide Research Articles

Surface tension studies of binary and ternary mixtures of tetradecyltrimethylammonium bromide, ditetradecyldimethylammonium bromide and synperonic PE/F68

The binary mixtures of the nonionic copolymer Synperonic PE/F68 with the cationic surfactants tetradecyltrimethylammonium bromide (TTAB) and/or the double chain ditetradecyldimethylammonium bromide (di-TDAB) were studied. Mixtures of the three surfactants were also studied. Surface tension studies, using the Wilhelmy plate method, were made. Synergy as well as time dependent hindrance effects were found. The minimum equilibrium surface tension value found, was that obtained for single di-TDAB. At concentrations below cmc, clusters were formed (critical aggregation concentration). Synperonic PE/F68, a very hydrophilic compound, minimized the electrostatic repulsion between the positively charged headgroups of the cationic surfactants. The adsorption constants continuously decreased with time. The results were compared with previous ones, using binary mixtures of some double cationic surfactants with Pluronic F68 and/or hydroxypropylmethylcellulose (HPMC). The observed differences were attributed to the higher hydrophilicity of Synperonic PE/F68.

Enhanced physical stability of positively charged catanionic vesicles: Role of cholesterol-adjusted molecular packing

Abstract A pseudodouble-chain ion pair amphiphile, hexadecyltrimethylammonium-dodecylsulfate (HTMA-DS), and a double-chain cationic surfactant, ditetradecyldimethylammonium bromide (DTDAB), were used as the main materials to form positively charged catanionic vesicles with various cholesterol contents. The effects of cholesterol on physical stability of the charged catanionic vesicles were then investigated by size, zeta potential, and Fourier transform infrared analyses. With the presence of cholesterol, the physical stability of the vesicles was enhanced. The inclusion of cholesterol would increase the distance between the charged headgroups of the vesicle-forming molecules and reduce the tendency of the counterion binding onto the charged vesicle surfaces, leading to a more pronounced charge character of the vesicles. Furthermore, with the incorporation of cholesterol, the sterol ring of cholesterol tended to maximize the contact with neighboring hydrocarbon chains, thus improving the bilayer mechanical strength. In the meantime, the alkyl side-chain of cholesterol together with the segments of the hydrocarbon chains near the ends in the vesicle-forming molecules could form flexible regions within the vesicular bilayers. Thus the presence of cholesterol in the bilayer structures of HTMA-DS/DTDAB catanionic vesicles not only enhanced the inter-vesicular electrostatic repulsion but also adjusted the intra-vesicular molecular packing, resulting in improved physical stability of the vesicles.

Exploring physical stability characteristics of positively charged catanionic vesicle/DNA complexes

Cationic vesicles fabricated from various novel materials have been recently developed for DNA delivery applications, and the physical stability of the vesicle/DNA complexes played an important role in the transfection efficiency. In this study, positively charged catanionic vesicles composed of hexadecyltrimethylammonium-dodecylsulfate (HTMA-DS), ditetradecyldimethylammonium bromide (DTDAB), and cholesterol were prepared in buffer solution by a forced formation approach, and the association behavior of the catanionic vesicles with two types of DNA molecules with the consideration of the vesicle/DNA complex stability was explored by dynamic light scattering, fluorescence polarization, and DNA electrophoresis techniques. In a buffer solution of pH 7.4, HTMA-DS/DTDAB/cholesterol catanionic vesicles with high physical stability and positive charge character were successfully fabricated. A toxicity examination then implied that the catanionic vesicles have the potential of being applied in transfection applications. It is noted that the catanionic vesicle dispersions became unstable as prepared from a concentrated one by dilution due to the less charged vesicle surfaces and the more rigid vesicular bilayers, which could be explained by the enhanced dissolution of HTMA+ from the vesicles. The physical stability and charge character of the catanionic vesicle/DNA complexes were found strongly dependent on the mixing ratio of the vesicle to DNA. The formation of the catanionic vesicle/DNA complexes was also confirmed by an electrophoresis analysis. Moreover, not only the electrostatic repulsion between the vesicle/DNA complexes but also the molecular packing of the vesicular bilayers played roles in governing the physical stability of the vesicle/DNA complexes.

Elucidating the effects of cholesterol on the molecular packing of double-chained cationic lipid langmuir monolayers by infrared reflection-absorption spectroscopy.

Cholesterol has been suggested to play a role in stable vesicle formation by adjusting the molecular packing of the vesicular bilayer. To explore the mechanisms involved in adjusting the bilayer structure by cholesterol, the molecular packing behavior in a mimic outer layer of cationic dialkyldimethylammonium bromide (DXDAB)/cholesterol vesicular bilayer was investigated by the Langmuir monolayer approach with infrared reflection-absorption spectroscopy (IRRAS). The results indicated that the addition of cholesterol in the DXDAB Langmuir monolayers not only restrained the desorption of the DXDAB with short hydrocarbon chains, such as ditetradecyldimethylammonium bromide or dihexadecyldimethylammonium bromide, into the aqueous phase but also induced a condensing effect on the DXDAB monolayers. At a liquid-expanded (LE) state, the ordering effect of cholesterol accompanying the condensing effect occurred in the mixed DXDAB/cholesterol monolayers due to the tendency of maximizing hydrocarbon chain contact between cholesterol and the neighboring hydrocarbon chains. However, for the mixed monolayers containing the DXDAB with long hydrocarbon chains, such as dioctadecyldimethylammonium bromide (DODAB), the disordering effect of cholesterol took place at a liquid-condensed (LC) state. This was related to the molecular structure of cholesterol and hydrocarbon chain length of DODAB. The rigid sterol ring of cholesterol hindered the portion of neighboring hydrocarbon chains from motion. However, the flexible alkyl side-chain of cholesterol along with the corresponding portion of neighboring hydrocarbon chains formed a fluidic region, counteracting the enhanced conformational order induced by the sterol ring of cholesterol. Furthermore, the long hydrocarbon chains of DODAB possessed a more pronounced motion freedom, resulting in a more disordered packing of the monolayers.

Twin-tailed surfactant induced conformational changes in bovine serum albumin: a detailed spectroscopic and physicochemical study

The interactions of a twin-tailed anionic surfactant sodium bis-2-ethylhexyl sulfosuccinate (AOT) and cationic surfactant ditetradecyldimethylammonium bromide (DTDAB) with bovine serum albumin (BSA) has been examined using various spectroscopic and physicochemical techniques such as tensiometry, steady-state fluorescence, potentiometry and isothermal titration calorimetry (ITC). The interactional behavior of the surfactants with BSA at the air–solution interface which depends upon the nature of the surfactant was examined and is discussed in detail. Steady-state fluorescence, and potentiometry combined with ITC measurements provide vital insights into the binding mechanism of the surfactants with BSA. An enhancement in the intrinsic fluorescence intensity and a strong exothermic enthalpy change at low concentrations of AOT demonstrated the crosslinking of AOT monomers between a group of non-polar residues and a positively charged residue located on different helical loops of BSA. The quenching of the intrinsic fluorescence intensity and endothermic enthalpy changes were observed over the whole of the concentration range of DTDAB that was studied indicating powerful interactions between them. The synchronous fluorescence spectra revealed the conformational changes in the peptide backbone of BSA and the altered environment of tryptophan and tyrosine residues. The binding isotherms obtained from intrinsic fluorescence spectroscopy as well as from potentiometry were analyzed using Scatchard plots to obtain insights into the binding mechanism and to evaluate the binding constants and the number of binding sites.

Probing the alkyl chain length effects on molecular packing characteristics of mixed ion pair amphiphile/double-chained cationic surfactant vesicular bilayers with the Langmuir monolayer approach

Alkyl chain length effects of added double-chained cationic surfactants, dialkyldimethylammonium bromides (DXDABs), including ditetradecyldimethylammonium bromide (DTDAB), dihexadecyldimethylammonium bromide (DHDAB), and dioctadecyldimethylammonium bromide (DODAB), on the Langmuir monolayer behavior of a pseudodouble-chained ion pair amphiphile, hexadecyltrimethylammonium-dodecylsulfate (HTMA-DS), were analyzed with the Langmuir monolayer technique, infrared reflection–absorption spectroscopy, and Brewster angle microscopy. It was found that DXDA+ of DXDAB could displace HTMA+ from HTMA-DS and the displaced HTMA+ might desorb into the aqueous subphase, with the extent depending on the alkyl chain length of DXDAB. In the mixed HTMA-DS/DODAB monolayer, DODAB possessing long alkyl chains was capable of restraining HTMA+ from desorption with enhanced intermolecular interaction reflected by the favorable molecule aggregation. As for the mixed monolayers of HTMA-DS and DTDAB with short alkyl chains, incomplete displacement of HTMA+ from HTMA-DS by DTDA+ was detected and ascribed to weak intermolecular attraction exhibited by the fractal-like domain formation. Among the three DXDABs, DHDAB with the best molecular structure match to HTMA-DS in terms of alkyl chain length could form well-packed monolayer structures with HTMA-DS. The finding has the implication on the surface characteristic control of catanionic vesicles composed of ion pair amphiphile with double-chained cationic surfactant.

Fabrication of positively charged catanionic vesicles from ion pair amphiphile with double-chained cationic surfactant

In this study, a pseudodouble-chained ion pair amphiphile, hexadecyltrimethylammonium-dodecylsulfate (HTMA-DS), was prepared from a mixture of cationic surfactant, hexadecyltrimethylammonium bromide, and anionic surfactant, sodium dodecylsulfate. Positively charged catanionic vesicles were then successfully fabricated from HTMA-DS with the addition of cationic surfactants, dialkyldimethylammonium bromide (DXDAB), including ditetradecyldimethylammonium bromide (DTDAB), dihexadecyldimethylammonium bromide, and dioctadecyldimethylammonium bromide (DODAB), with a mechanical disruption approach. The control of charge characteristic and physical stability of the catanionic vesicles through the variations of DXDAB molar fraction and alkyl chain length was then explored by size, zeta potential, and Fourier transform infrared analyses. It was found that the molecular packing and/or molecular interaction of HTMA-DS with DXDAB rather than the electrostatic repulsion between the charged vesicles dominated the physical stability of the mixed HTMA-DS/DXDAB vesicles. The presence of DTDAB, which possesses short alkyl chains, could adjust the packing of the unmatched chains of HTMA+ and DS− and promote the vesicle formation. However, the weak molecular interaction due to the short chains of DTDA+ could not maintain the vesicle structures in long-term storage. With increasing the alkyl chain length of DXDAB, it was possible to improve the vesicle physical stability through the enhanced molecular interaction in the vesicular bilayer. However, the long alkyl chains of DODAB unmatched with those of HTMA-DS, resulting in the vesicle disintegration in long-term storage. For the formation of stable charged catanionic vesicles of HTMA-DS/DXDAB, a good match in hydrophobic chains and strong molecular interaction were preferred for the vesicle-forming molecules.

Aqueous solutions of the double chain cationic surfactants didodecyldimethylammonium bromide and ditetradecyldimethylammonium bromide with Pluronic F68: Dynamic surface tension measurements

The adsorption kinetics of mixtures of the non-ionic copolymer Pluronic F68 with two double chain cationic surfactants didodecyldimethylammonium bromide (di-DDAB) and ditetradecyldimethylammonium bromide (di-TDAB) is studied with dynamic surface tension experiments. A time dependent synergy is observed, in most of the mixtures. In a few cases, hindrance effects are observed. Clusters are formed at concentrations well below the critical micelle concentration (cmc), at the critical aggregation concentration (cac). The presence of the copolymer stabilizes the electrostatic repulsion between the positively charged quaternary ammonium headgroups of di-DDAB and di-TDAB. The electrostatic repulsion between the polar parts of the same and adjacent surfactant molecules is minimized. We compare our results with recently published results, using mixtures of these double chain cationic surfactants with hydroxypropylmethylcellulose.

Dynamic surface tension studies of mixtures of hydroxypropylmethylcellulose with the double chain cationic surfactants didodecyldimethylammonium bromide and ditetradecyldimethylammonium bromide

Dynamic and equilibrium surface tension experiments were carried out to study the adsorption kinetics of mixtures of the nonionic polymer hydroxypropylmethylcellulose (HPMC) with two double chain cationic surfactants, didodecyldimethylammonium bromide (di-DDAB) and ditetradecyldimethylammonium bromide (di-TDAB). Results are obtained concerning the capacity of the surfactants to lower surface tension, the rate of lowering, the extent of adsorption at the interface, the possibility of changing conformation during and after adsorption, and the interactions between the adsorbed molecules. A time-dependent synergy is observed in most of the mixtures, while in a few cases hindrance effects are observed. The interaction of HPMC with the double chain cationic surfactants resulted in complexes with higher surface activity than the two components alone. Two induction times were observed, the second ones being more significant in the presence of di-TDAB. At concentrations well below the critical micelle concentration (cmc), the critical aggregation concentrations (cac), evidence for clusters is observed.

Surface adsorption and mixed micelle formation of surface active ionic liquid in cationic surfactants: Conductivity, surface tension, fluorescence and NMR studies

Here we are reporting the influence of 1-tetradecyl-3-methylimidazolium bromide (C14mimBr), a surface-active ionic liquid (SAIL) on the micellar morphological changes of cationic surfactants such as tetradecyltrimethylammonium bromide (TTAB), dimethylditetradecylammonium bromide (DTDAB), alkane-bis (tetradecyldimethylammonium bromide) (14-2-14 and 14-4-14 gemini). The techniques employed were conductivity, surface tension, fluorescence and 1H NMR. The various micellar and interfacial parameters such as critical micelle concentration (cmc), degree of counterion binding (g), interaction parameter (βm), surface excess concentration (Гmax), minimum area per molecule (Amin), aggregation number (Nagg), Stern–Volmer constant (Ksv) as well as some thermodynamic parameters such as standard Gibbs free energy of adsorption (ΔGads0), excess free energy of micellization (ΔGex) and standard Gibbs free energy of micellization (ΔGm0) have been evaluated. The interactions for IL+ TTAB mixtures are found to be non-ideal and antagonistic. However when the single chain surfactant is replaced by the double chain surfactants the interactions becomes synergistic for the mixtures. The merging and broadening of the peaks for various protons of IL and cationic surfactants suggests the growth of micelles. On comparison between the binary mixtures of IL+ 14-2-14 and IL+ 14-4-14, former one with more hydrophilic spacer promote micellization more easily than 14-4-14.

Interaction of Fe3+meso-tetrakis (2,6-dichloro-3-sulfonatophenyl) porphyrin with cationic bilayers: magnetic switching of the porphyrin and magnetic induction at the interface

An organized multilayer was constructed by the layer-by-layer technique in which alternating layers of metalloporphyrin and dioctadecyldimethylammonium bromide bilayers were deposited onto an indium tin oxide surface electrode. The porphyrin molecules that are organized in the different layers showed a strong electroactivity with a well-defined electrochemical process. In LbL, electroactivity could be explained only by the occurrence of electron hoping. Thus, total Kohn–Sham density functional theory (KS-DFT) was performed to better understand the conditions responsible for the electroactivity of the metalloporphyrin layers intercalated by an insulating material. Total KS-DFT theory involves local density approximation energy calculations based on spin-polarized variant of KS-DFT theory. The results revealed a magnetization switching of the metalloporphyrin induced by the interaction with the surfactant bilayer accompanied by spin polarization of the porphyrin-interacting surfactant molecule. Although discrete, the surfactant magnetization had significant repercussions on the electron conductivity. Calculations also demonstrated loss of porphyrin symmetry promoted by a parent surfactant with a shorter hydrocarbon chain, ditetradecyldimethylammonium bromide. The calculation results were corroborated by experimental results obtained by the electron paramagnetic resonance and magnetic circular dichroism techniques.

Interactional and aggregation behavior of twin tail cationic surfactants with pluronic L64 in aqueous solution

The aqueous mixed systems of twin tail cationic surfactants didodecyldimethylammonium bromide, ditetradecyldimethylammonium bromide, and dihexadecyldimethylammonium bromide with pluronic L64 have been studied to determine the bulk aggregation and interactional behavior. Various experimental techniques, namely small-angle neutron scattering (SANS), fluorescence, conductivity, and surface tension, have been employed to investigate the mixed micellization. The SANS data analysis has been employed to determine the shapes of different aggregates formed. Pure twin tail cationic surfactants form vesicles whereas the micelles of pure pluronic L64 are spherical. The mixed systems (surfactant + L64) also form spherical micelles, and the spherical shape of mixed micelles is predominantly controlled by pluronic L64. Various interfacial parameters such as surface excess (Γ max), minimum area per molecule (A min), and thermodynamic parameters such as the standard Gibbs free energy of micellization (\( \Delta G_{{mic}}^{{0}} \)), Gibbs free energy of adsorption (\( \Delta G_{{ads}}^{{0}} \)), and effective Gibbs free energy (\( \Delta G_{{eff}}^{{0}} \)) have been determined from the surface tension measurements. The results were interpreted on the basis of pseudophase separation model and regular solution theory. The interactions of each surfactant with pluronic L64 are found to be nonideal and antagonistic. The repulsive nature of the interaction is explained on the basis of the changes in the microenvironment of micelles of pluronic L64. Micelles of pluronic L64 are less hydrophobic and contains significant amount of water, and inclusion of hydrophobic alkyl chains of twin tail cationic surfactants disturbs this microenvironment of pluronic L64 micelle.

Electrochemical detection of phenolic compounds using composite film of multiwall carbon nanotube/surfactant/tyrosinase on a carbon paste electrode

A new tyrosinase-based biosensor was developed for detection of phenolic compounds using composite film of multiwall carbon nanotube (MWCNT)/dimethylditetradecylammonium bromide (DTDAB)/tyrosinase (Tyr) on a Nafion-incorporated carbon paste electrode. The biosensor showed a sensitive electrochemical response to the reduction of the oxidation products of different phenolic compounds (phenol, catechol, p-cresol, and p-chlorophenol) by dissolved O2 in the presence of the immobilized enzyme. The effects of pH, operating potential, MWCNT concentration, and the DTDAB/Tyr ratio on electrochemical response were explored for optimum analytical performance. The biosensor exhibited a linear response range of 1.5–25.0, 2.0–15.0, 2.0–15.0, and 2.5–25.0 μM and sensitivity of 2,900, 3,100, 3,100, and 1,500 μA/mM for phenol, catechol, p-cresol, p-chlorophenol, respectively. In addition, the response of the enzyme electrode showed Michaelis–Menten behavior at concentrations of the phenolic compounds higher than 5.0 μM. The stability and the application of the biosensor were also evaluated.

Raman Spectroscopic Characterization of the Interlayer Structure of Na+-Montmorillonite Clay Modified by Ditetradecyl Dimethyl Ammonium Bromide

Raman spectroscopy has been applied for the rapid and nondestructive monitoring of the interlayer structure of sodium montmorillonite (MMT) clay modified by ditetradecyl dimethyl ammonium (DDA+) bromide. This work demonstrates that a detailed analysis of Raman spectra in the fingerprint region (600-1600 cm(-1)), in combination with model simulation, allows one to distinguish different conformational states of DDA+ in the interlayer space of the modified clay, namely, a liquidlike state but rich in trans conformers, disordered conformational states, and a crystallike conformation appearing at increasing modifier content. These conformations differ in the angle between their alkyl chains, the relative content of trans and gauche conformers and the relative length of trans segments. The shape and width of the Raman band at 1300 cm(-1) and the peak intensity ratio I1088/I1064 can be used for a qualitative analysis of the ratio of gauche/trans conformers. The integral intensity ratios I*1064/I*1300 and I*1300/I*705 help to determine the proportion of trans conformers and the content of the modifier in the clay, respectively, thereof providing quantitative characterization of the modified clay (conformational reorganization and modifier content). Noteworthy, the transition from a liquidlike to crystal-like conformation is further supported by the splitting of the symmetric C-C stretching Raman band of the trans segments within the alkyl chains at 1133 cm(-1) (liquidlike conformation) into two modes at 1124 and 1135 cm(-1) corresponding to two parallel trans chains of nonequivalent lengths (crystal-like conformation).

Dimethylditetradecylammonium bromide (2C14DAB) as a self-assembled surfactant coating for detection of protein–dye complexes by CE-LIF

A self-assembled column coating for capillary electrophoresis in conjunction with laser-induced fluorescence detection (CE-LIF) has been evaluated for the separation and quantitation of protein–dye complexes. This semi-permanent coating, composed of dimethylditetradecyl-ammonium bromide (2C14DAB), is inexpensive and easily assembled onto the column and it allows for better peak resolution and greater control over electroosmotic flow. The versatility of long-chained surfactant coatings was determined particularly with respect to their use with fluorescent probes, different pH buffers, and different proteins. Studies were performed to determine the stability of the coating under various pH and buffer conditions. Red-1c, a red luminescent squarylium dye, was used for on-column protein labeling concurrently with the surfactant coating and LIF detection. Protein–Red-1c complexes were excited with a 650-nm diode laser and their emission detected by a photomultiplier tube with a 664-nm filter. A comparison of pre-column labeling and on-column labeling of a two-model protein system (human serum albumin and β-lactoglobulin A) revealed higher efficiencies and greater sensitivities for both proteins using on-column labeling and coated columns. A linear relationship between peak height and protein concentration was obtained by CE-LIF for this on-column labeling method with 2C14DAB-coated columns and the Red-1c probe.

Preparation of pH-sensitive liposomes retaining SOD mimic and their anticancer effect

We prepared an anticancer drug based on a pH-sensitive liposome retaining Fe-porphyrin as an SOD mimic. The liposomes contained cationic/anionic lipid combinations and were composed of Fe-porphyrin, 1,2-dimyristoyl- sn-glycero-3-phosphatidylcholine, dimethylditetradecylammonium bromide, sodium oleate, and Tween-80. The Fe-porphyrin was released from the liposome at low pH, and the cytotoxicity for cancer cells by the liposome depended on the acidic environments of the endosomes in the cells. Furthermore, although the liposome exhibited an excellent anticancer effect on a gastric cancer cell line, the SOD activity of Fe-porphyrin was shown to have a significant influence on the cytotoxicity toward cancer cells. These findings suggest that the pH-sensitive liposome retaining the Fe-porphyrin as an SOD mimic promises to be a novel anticancer drug for endosomal escape.

Off-line coupling of preparative capillary zone electrophoresis with microwave-assisted acid hydrolysis and matrix-assisted laser desorption ionization mass spectrometry for protein sequencing

An off-line coupling of capillary electrophoresis (CE) with microwave-assisted acid hydrolysis/matrix-assisted laser desorption ionization mass spectrometry (MAAH/MALDI) has been developed for protein identification and characterization. Preparative scale protein separations enable collection of 10–50 pmol of purified cytochrome c for subsequent sequencing using MAAH/MALDI. To reduce protein adsorption onto the silica surface, the cationic surfactant-based coatings, dimethylditetradecylammonium bromide and dimethyldioctadecylammonium bromide, are employed. The choice of the buffer conditions is critical for both the preparative CE and MAAH/MALDI method. The use of high buffer concentrations (100 mM Bis–tris) reduces electromigration dispersion, but suppressed MALDI ionization such that a peptide sequence coverage of only 80% was achieved at a sample loading of 40 g L −1 of each cytochrome c. By reducing the buffer concentration to 25 mM Bis–tris, the sequence coverage increased to 95% at a sample loading of 40 g L −1.

Synergistic Effect between Components of Mixtures of Cationic Amphipaths in Transfection of Primary Endothelial Cells

To date, the primary approach to improving the transfection properties of cationic lipids has been the synthesis of new kinds of cationic amphipaths. Recently, however, it was found that combining two cationic lipid derivatives having the same head group but tails of different chain lengths can provide another, and often superior, approach to higher transfection efficiency. For example, the combination of medium-chain and long-chain homologues of O-ethylphosphatidylcholine transfected DNA into primary human umbilical artery endothelial cells (HUAECs) more than 30-fold more efficiently than did either compound separately. Here it is reported that this synergism of mixtures is not limited to O-ethylphosphatidylcholine homologues, but is also exhibited by other common cationic amphipathic transfection reagents; for example, combining DC-Chol (3beta-[N',N'-dimethylaminoethane)-carbamol] cholesterol), dimethylditetradecylammonium bromide, or DMTAP (1,2-dimyristoyl-3-trimethylammonium-propane) with EDOPC increased transfection significantly both in the absence and in the presence of serum. Furthermore, combining a poorer transfection agent-dimethyldioctadecylammonium bromide-with dimethylditetradecylammonium bromide increased transfection by about an order of magnitude with a maximum at an intermediate composition. Lack of synergy occurred with some mixtures, such as DMTAP and DOTAP (1,2-dioleoyl-3-trimethylammonium-propane), in which case transfection activity was a linear function of composition both in the absence and presence of serum. Although the mechanism of enhanced transfection by mixtures is not fully understood, the existence of a number of optimal mixtures with diverse cationic compounds indicates that attention to mixture formulations can lead to greatly improved transfection by cationic amphipathic carriers.

Semipermanent capillary coatings in mixed organic–water solvents for CE

This report describes the creation of semipermanent capillary coatings that are compatible with organic-water solvent systems in CE. The coatings are created by simply rinsing the fused-silica capillary with long double-chain cationic surfactants, such as dimethyl-ditetradecyl ammonium bromide (2C(14)DAB), dihexadecyldimethyl ammonium bromide (2C(16)DAB), and dimethyldioctadecyl ammonium bromide (2C(18)DAB). These surfactants generate semipermanent bilayer coatings on the capillary surface, which display a high degree of stability in buffers containing up to 60% v/v of organic solvents, such as methanol and ACN. The coating stability increases with increasing hydrophobicity of the surfactant, i.e., with increasing chain length. For instance, the EOF changes by only 1.2% in a 2C(18)DAB-coated capillary after 130 capillary volumes of rinsing with 60% v/v methanol containing buffer. The bilayer coatings allow separations to be performed without the need to regenerate the coating between runs or to maintain the EOF modifier in the run buffer. Rapid separations (<2 min) of anions and basic drugs with migration time reproducibility of less than 0.5% RSD and efficiencies of 0.4-0.6 million plates/m are obtained. In addition, selectivity changes for small anions and cationic drugs are also observed when the organic solvent content is adjusted.

PH‐sensitive liposome retaining Fe‐porphyrin as SOD mimic for novel anticancer drug delivery system

AbstractIn this article the novel design of an anticancer drug delivery system is reported based on a pH‐sensitive liposome retaining the Fe‐porphyrin as a superoxide dismutase(SOD) mimic. The liposomes contained cationic/anionic lipid combinations and were composed of Fe‐porphyrin, L‐α‐phosphatidylcholine (DMPC), dimethylditetradecylammonium bromide (DTDAB), sodispdum oleate (OANa), and Tween‐80. The size of the liposome was approximately 30 nm. The EC50 value (the effective concentration of compound required to produce a 50% lethal dose against cells) of the liposome was found to be significantly smaller than that of cisplatin as the control drug, suggesting that the liposome showed a high cytotoxicity toward the cancer cells. This is due to the fact that the pH‐sensitive liposome rapidly corresponds to the acidic environments of the endosomes and is unstable, and the Fe‐porphyrin is delivered into the cytosol. This result suggests that O may be useful as a target molecule to induce the selective death of cancer cells and that a pH‐sensitive liposome retaining Fe‐porphyrin as an SOD mimic is a new class of anticancer agent. Copyright © 2006 John Wiley &amp; Sons, Ltd.