Molecular mechanism and thermodynamics study of plasmid DNA and cationic surfactants interactions

Impact of Linker Groups on Self-Assembly, Gene Transfection, Antibacterial Activity, and In Vitro Cytotoxicity of Cationic Bolaamphiphiles

Cationic bolaamphiphiles have gained significant attention in various research fields, including materials science, drug delivery, and gene therapy, due to their unique properties and potential applications. The objective of the current research is to develop more effective cationic bolaamphiphiles. Thus, we have designed and synthesized two cationic bolaamphiphiles (-(CH2)12(2,3-dihydroxy-N,N-dimethyl-N-(3-ureidopropyl)propan-1-aminium chloride))2 (C12(DDUPPAC)2)) and (-(CH2)12(N-(3-(carbamoyloxy)propyl)-2,3-dihydroxy-N,N-dimethylpropan-1-aminium chloride)2 (C12(CPDDPAC)2) containing urea and urethane linkages, respectively. We have investigated their self-assembly properties in water using several techniques, including surface tension, electrical conductivity, fluorescence probe, calorimetry, dynamic light scattering, and atomic force microscopy. Their biological applications, e.g., in vitro gene transfection, antibacterial activity, and cytotoxicity, were studied. Both bolaamphiphiles were observed to produce aggregates larger than spherical micelles above a relatively low critical aggregation concentration (cac). The calorimetric experiments suggested the thermodynamically favorable spontaneous aggregation of both bolaforms in water. The results of interaction studies led to the conclusion that C12(CPDDPAC)2 binds DNA with a greater affinity than C12(DDUPPAC)2. Also, C12(CPDDPAC)2 is found to act as a more efficient gene transfection vector than C12(DDUPPAC)2 in 264.7 cell lines. The in vitro cytotoxicity assay using MTT, however, revealed that neither of the bolaamphiphiles was toxic, even at higher quantities. Additionally, both bolaforms show beneficial antibacterial activity.

Impact of the Hydrocarbon Chain Length of Biodegradable Ester-Bonded Cationic Gemini Surfactants on Self-Assembly, In Vitro Gene Transfection, Cytotoxicity, and Antimicrobial Activity

Gemini surfactants, due to their unique structural features and enhanced properties compared to conventional surfactants, are becoming more popular in the domain of colloid and interface science, drug delivery, and gene delivery science. This distinct class of surfactants forms a wide range of self-assembled aggregates depending on their chemical structure and environmental conditions. The present work aims to develop Gemini with three distinct chain lengths linked through the ester group and quaternary nitrogen head groups that can bind DNA molecules and ultimately serve as vectors for DNA transfection. Thus, we synthesized three distinct cationic Gemini with 12, 14, and 16 carbons in their tails and studied the effect of the hydrocarbon chain length on their physicochemical properties and biological applications. The self-assembly of these Geminis in aqueous solution was investigated by a number of techniques, including surface tension, electrical conductivity, fluorescence probe, calorimetry, dynamic light scattering, and atomic force microscopy. All three Gemini were extremely surface active and self-assembled above a very low critical micelle concentration. Calorimetric studies suggested the formation of thermodynamically favorable aggregates in an aqueous medium. Chain length dependence was observed in the size as well as the morphology of the aggregates. These Gemini ions were found to bind DNA strongly, as indicated by the high binding constant values. In vitro gene transfection studies using the RAW 264.7 cell line suggested that all three cationic Gemini had transfection efficiencies comparable to that of commercial standard turbofectamine. MTT assay was also performed for concentration selection while using these Gemini as transfection vectors. Overall, it was observed that Gemini had very little cytotoxicity within the investigated concentration range, highlighting the significance of the ester link within the structure. When compared with known antimicrobials such as kanamycin and ampicillin, all three Gemini furnished excellent antimicrobial activity in both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) microorganisms.

Strong Synergistic Molecular Interaction in Catanionic Surfactant Mixtures: Unravelling the Role of the Benzene Ring

Noncovalent interactions play a crucial role in driving the formation of diverse self-assembled structures in surfactant systems. Surfactants containing a benzene ring structure are an important subset of surfactants. These surfactants exhibit unique colloid and interfacial properties, which give rise to fascinating transformations in the aggregate structures. These transformations are directly influenced by specific noncovalent interactions facilitated by the benzene ring structure including cation-π and π-π interactions. Investigating catanionic surfactant systems that incorporate benzene ring structures provides valuable insights into the distinct noncovalent interactions observed in mixed surfactant systems. Our approach involved studying the enthalpy change ΔH during the titration process, utilizing isothermal titration calorimetry (ITC). Simultaneously, we employed cryogenic transmission electron microscopy (cryo-TEM) to observe the corresponding self-assembly structures. To gain further insight, we delved into the noncovalent interactions of the mixed systems by analyzing the molecular environments variations through chemical shifts of the aggregates using proton magnetic resonance (1H NMR). The intermolecular interaction was also confirmed by the two-dimensional nuclear Overhauser enhancement spectroscopy (2D NOESY). We conducted a systematic study of the effects of NaCl concentrations, molar ratios, and molecular structures of surfactants on aggregate structures. The existence forms of surfactants are closely linked to the shape of the titration curve and the transition of the aggregate structures. When cationic surfactants were titrated into sodium dodecylbenzenesulfonate (SDBS) micelle solutions, the dominant cation-π interaction leads to the direct formation of vesicle structures. Conversely, when the SDBS system is titrated into benzyldimethyldodecylammonium chloride (DDBAC) micelles, a delicate balance of multiple noncovalent interactions, including cation-π, π-π, hydrophobic, and electrostatic forces, results in a range of aggregate structure transformations such as worm-like micelles and vesicular structures.

Self-Assembly, In Vitro Gene Transfection, and Antimicrobial Activity of Biodegradable Cationic Bolaamphiphiles

Bolaamphiphiles or bolaforms have drawn particular interest in drug and gene delivery, and studies of bolaforms have been growing continuously. Bolaforms, due to their unique structure, exhibit specific self-assembly behavior in water. The present work aims to develop biodegradable cationic bolaforms with a better gene transfection ability. In this work, a novel cationic bolaform (Bola-1) with head groups bearing hydroxyl (OH) functionality was designed and synthesized to investigate self-assembly and gene transfection efficiency. The self-assembly behavior of Bola-1 in water was compared with that of the hydrochloride salt (Bola-2) of its precursor molecule to investigate the effect of the -OH functionality on their solution properties. Several techniques, including surface tension, electrical conductivity, fluorescence probe, calorimetry, dynamic light scattering, and atomic force microscopy, were employed for the physicochemical characterization of Bola-1 and Bola-2. Despite the presence of polar urea groups in the spacer chain, both bolaforms were found to form spherical or elongated micelles above a relatively low critical aggregation concentration (CAC). The presence of the OH group was found to significantly affect the CAC value. The results of calorimetric measurements suggested a thermodynamically favorable aggregate formation in salt-free water. Despite stronger binding efficiency with calf thymus DNA, in vitro gene transfection studies performed using adherent cell Hek 293 suggested that both Bola-1 and Bola-2 have gene transfection efficiency comparable to that of turbofectamine standard. Both bolaforms were found to exhibit significant in vitro cytotoxicity at higher concentrations. Also, the bolaforms showed beneficial antibacterial activity at higher concentrations.

Electrostatic Interactions in the Formation of DNA Complexes with Cis- and Trans-Isomers of Azobenzene-Containing Surfactants in Solutions with Di- and Trivalent Metal Ions

The effect of the presence of divalent and trivalent metal ions in solutions upon DNA packaging induced by the photosensitive azobenzene-containing surfactant is considered. It has been shown that the addition of divalent and trivalent metal ions does not affect the DNA-surfactant interaction for both the cis- and the trans-isomers of the surfactant. At the same time, the ionic strength of the solution, which is provided by a certain concentration of the salt, has a huge impact. It affects the association of surfactant molecules with each other and their binding to DNA. It has been shown by computer simulation that cobalt hexamine is attracted to the N7 atom of guanine in the major groove of DNA and does not penetrate into grooves near the AT base pairs.

In-Membrane Nanostructuring of Cationic Amphiphiles Affects Their Antimicrobial Efficacy and Cytotoxicity: A Comparison Study between a De Novo Antimicrobial Lipopeptide and Traditional Biocides

Cationic biocides have been widely used as active ingredients in personal care and healthcare products for infection control and wound treatment for a long time, but there are concerns over their cytotoxicity and antimicrobial resistance. Designed lipopeptides are potential candidates for alleviating these issues because of their mildness to mammalian host cells and their high efficacy against pathogenic microbial membranes. In this study, antimicrobial and cytotoxic properties of a de novo designed lipopeptide, CH₃(CH₂)₁₂CO-Lys-Lys-Gly-Gly-Ile-Ile-NH₂ (C₁₄KKGGII), were assessed against that of two traditional cationic biocides C_nTAB (n = 12 and 14), with different critical aggregation concentrations (CACs). C₁₄KKGGII was shown to be more potent against both bacteria and fungi but milder to fibroblast host cells than the two biocides. Biophysical measurements mimicking the main features of microbial and host cell membranes were obtained for both lipid monolayer models using neutron reflection and small unilamellar vesicles (SUVs) using fluorescein leakage and zeta potential changes. The results revealed selective binding to anionic lipid membranes from the lipopeptide and in-membrane nanostructuring that is distinctly different from the co-assembly of the conventional C_nTAB. Furthermore, C_nTAB binding to the model membranes showed low selectivity, and its high cytotoxicity could be attributed to both membrane lysis and chemical toxicity. This work demonstrates the advantages of the lipopeptides and their potential for further development toward clinical application.

Repurposing Quaternary Ammonium Compounds as Potential Treatments for COVID-19

The COVID-19 pandemic has highlighted an important role for drug repurposing. Quaternary ammonium compounds such as ammonium chloride, cetylpyridinium and miramistin represent widely accessible antiseptic molecules with well-known broad-spectrum antiviral activities and represent a repurposing opportunity as therapeutics against SARS-CoV-2.

Lipoaminoacids Enzyme-Based Production and Application as Gene Delivery Vectors

Biosurfactant compounds have been studied in many applications, including biomedical, food, cosmetic, agriculture, and bioremediation areas, mainly due to their low toxicity, high biodegradability, and multifunctionality. Among biosurfactants, the lipoplexes of lipoaminoacids play a key role in medical and pharmaceutical fields. Lipoaminoacids (LAAs) are amino acid-based surfactants that are obtained from the condensation reaction of natural origin amino acids with fatty acids or fatty acid derivatives. LAA can be produced by biocatalysis as an alternative to chemical synthesis and thus become very attractive from both the biomedical and the environmental perspectives. Gemini LAAs, which are made of two hydrophobic chains and two amino acid head groups per molecule and linked by a spacer at the level of the amino acid residues, are promising candidates as both drug and gene delivery and protein disassembly agents. Gemini LAA usually show lower critical micelle concentration, interact more efficiently with proteins, and are better solubilising agents for hydrophobic drugs when compared to their monomeric counterparts due to their dimeric structure. A clinically relevant human gene therapy vector must overcome or avoid detect and silence foreign or misplaced DNA whilst delivering sustained levels of therapeutic gene product. Many non-viral DNA vectors trigger these defence mechanisms, being subsequently destroyed or rendered silent. The development of safe and persistently expressing DNA vectors is a crucial prerequisite for a successful clinical application, and it one of the main strategic tasks of non-viral gene therapy research.

Extraction of ferulic acid and vanilla acid by hydrophobic ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate

The study was carried out to evaluate the extraction efficiency of ferulic acid (FA) and vanilla acid (VA) from aqueous phase into IL phase. To achieve the highest extraction efficiency, the influence of varying key parameters was evaluated and optimized by response surface methodology based on Box-Behnken design, including phase volume ratio, extraction temperature and extraction time. FA (or VA) extraction under the optimal conditions were: phase volume ratio of 1.38 (1.28), extraction temperature of 66.34 °C (49.28 °C) and extraction time of 33.83 min (36.64 min) under optimum conditions an average extraction efficiency of 97.11 ± 1.05% for FA was achieved, while VA was 85.43 ± 1.62%. This was very close to the predicted value from the model, 98.05% (86.16%). Additionally, recycling and utilization of ILs were performed well with the recovery ratio for 81.0%. Based on thermodynamic analysis, FTIR and ¹H NMR analysis, the combination of hydrophobic interaction and hydrogen-bond interaction resulted in the real extraction result above. It is desirable to provide a useful reference for the separation and purification of FA, VA, and extend the potential application of ionic liquid in the separation of natural active compounds with great prospects.

DNA Interaction with Head-to-Tail Associates of Cationic Surfactants Prevents Formation of Compact Particles

Cationic azobenzene-containing surfactants are capable of condensing DNA in solution with formation of nanosized particles that can be employed in gene delivery. The ratio of surfactant/DNA concentration and solution ionic strength determines the result of DNA-surfactant interaction: Complexes with a micelle-like surfactant associates on DNA, which induces DNA shrinkage, DNA precipitation or DNA condensation with the emergence of nanosized particles. UV and fluorescence spectroscopy, low gradient viscometry and flow birefringence methods were employed to investigate DNA-surfactant and surfactant-surfactant interaction at different NaCl concentrations, [NaCl]. It was observed that [NaCl] (or the Debye screening radius) determines the surfactant-surfactant interaction in solutions without DNA. Monomers, micelles and non-micellar associates of azobenzene-containing surfactants with head-to-tail orientation of molecules were distinguished due to the features of their absorption spectra. The novel data enabled us to conclude that exactly the type of associates (together with the concentration of components) determines the result of DNA-surfactant interaction. Predomination of head-to-tail associates at 0.01 M < [NaCl] < 0.5 M induces DNA aggregation and in some cases DNA precipitation. High NaCl concentration (higher than 0.8 M) prevents electrostatic attraction of surfactants to DNA phosphates for complex formation. DAPI dye luminescence in solutions with DNA-surfactant complexes shows that surfactant tails overlap the DNA minor groove. The addition of di- and trivalent metal ions before and after the surfactant binding to DNA indicate that the bound surfactant molecules are located on DNA in islets.

Rationally designed mineralization for selective recovery of the rare earth elements

The increasing demand for rare earth (RE) elements in advanced materials for permanent magnets, rechargeable batteries, catalysts and lamp phosphors necessitates environmentally friendly approaches for their recovery and separation. Here, we propose a mineralization concept for direct extraction of RE ions with Lamp (lanthanide ion mineralization peptide). In aqueous solution containing various metal ions, Lamp promotes the generation of RE hydroxide species with which it binds to form hydrophobic complexes that accumulate spontaneously as insoluble precipitates, even under physiological conditions (pH ∼6.0). This concept for stabilization of an insoluble lanthanide hydroxide complex with an artificial peptide also works in combination with stable scaffolds like synthetic macromolecules and proteins. Our strategy opens the possibility for selective separation of target metal elements from seawater and industrial wastewater under mild conditions without additional energy input.

Thermodynamics of complex coacervation

Isothermal titration calorimetry has routinely been used to understand the thermodynamic characteristics of complexation and coacervation. Most commonly, built-in models that assume independent binding sites have been employed in these studies. However, the non-covalent nature of interactions and steric effects accompanying macromolecules require (i) usage of new models such as overlapping binding sites and Satake-Yang's two-state binding models and (ii) reformed interpretations of the data as two-stage structuring. Fitting data with these models, forces driving the interaction of polyelectrolytes with oppositely charged polyelectrolytes, surfactants, and proteins have been identified as electrostatics and/or counterion release with possible contributions from hydrogen bonding and hydrophobic interactions. Additionally, for surfactant-polyelectrolyte coacervation, ITC signals indicated separate regions for formation of polymer-induced micelles and free micelles. Regardless of the type of the coacervation system, thermodynamics of coacervation is affected by the following parameters: pH and ionic strength of the medium, charge density, molecular weight of the polyelectrolyte, concentration, and mixing order of macroions. Lastly, we present a brief comparison between ITC on one hand and surface plasmon resonance or capillary electrophoresis on the other regarding their application in coacervation.

Evidence of a two-step process and pathway dependency in the thermodynamics of poly(diallyldimethylammonium chloride)/poly(sodium acrylate) complexation

Recent studies have pointed out the importance of polyelectrolyte assembly in the elaboration of innovative nanomaterials. Beyond their structures, many important questions on the thermodynamics of association remain unanswered. Here, we investigate the complexation between poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium acrylate) (PANa) chains using a combination of three techniques: isothermal titration calorimetry (ITC), static and dynamic light scattering and electrophoresis. Upon addition of PDADMAC to PANa or vice-versa, the results obtained by the different techniques agree well with each other, and reveal a two-step process. The primary process is the formation of highly charged polyelectrolyte complexes of size 100 nm. The secondary process is the transition towards a coacervate phase made of rich and poor polymer droplets. The binding isotherms measured are accounted for using a phenomenological model that provides the thermodynamic parameters for each reaction. Small positive enthalpies and large positive entropies consistent with a counterion release scenario are found throughout this study. Furthermore, this work stresses the importance of the underestimated formulation pathway or mixing order in polyelectrolyte complexation.

New micellar transfection agents

Two novel micelle-forming amino-functionalized lipids (OT6 and TT6) bearing two alkyl chains connected to a large positively charged hexavalent headgroup, which might be interesting polynucleotide transferring agents with the advantage of an easy and reproducible production of micelle dispersions, have been characterized. The critical micelle concentration (cmc) of both lipids has been determined by two different methods, namely, isothermal titration calorimetry (ITC) and 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence experiments. In addition, the lipid dispersions were studied as a function of temperature using differential scanning calorimetry (DSC), dynamic light scattering (DLS), Fourier-transform infrared (FT-IR) spectroscopy, and cryo-transmission electron microscopy (cryo-TEM). The OT6 and TT6 micelles effectively complex DNA as determined by ITC and DSC measurements. In addition, DLS and ζ-potential measurements were performed to determine lipoplex formulations that exhibit colloidal stability. Finally, the structures of OT6/DNA complexes were investigated by means of X-ray scattering and TEM.

In vitro surfactant structure-toxicity relationships: implications for surfactant use in sexually transmitted infection prophylaxis and contraception

BACKGROUND

The need for woman-controlled, cheap, safe, effective, easy-to-use and easy-to-store topical applications for prophylaxis against sexually transmitted infections (STIs) makes surfactant-containing formulations an interesting option that requires a more fundamental knowledge concerning surfactant toxicology and structure-activity relationships.

METHODOLOGY/PRINCIPAL FINDINGS

We report in vitro effects of surfactant concentration, exposure time and structure on the viability of mammalian cell types typically encountered in the vagina, namely, fully polarized and confluent epithelial cells, confluent but non-polarized epithelial-like cells, dendritic cells, and human sperm. Representatives of the different families of commercially available surfactants--nonionic (Triton X-100 and monolaurin), zwitterionic (DDPS), anionic (SDS), and cationic (C(n)TAB (n = 10 to 16), C(12)PB, and C(12)BZK)--were examined. Triton X-100, monolaurin, DDPS and SDS were toxic to all cell types at concentrations around their critical micelle concentration (CMC) suggesting a non-selective mode of action involving cell membrane destabilization and/or destruction. All cationic surfactants were toxic at concentrations far below their CMC and showed significant differences in their toxicity toward polarized as compared with non-polarized cells. Their toxicity was also dependent on the chemical nature of the polar head group. Our results suggest an intracellular locus of action for cationic surfactants and show that their structure-activity relationships could be profitably exploited for STI prophylaxis in vaginal gel formulations. The therapeutic indices comparing polarized epithelial cell toxicity to sperm toxicity for all surfactants examined, except C(12)PB and C(12)BZK, does not justify their use as contraceptive agents. C(12)PB and C(12)BZK are shown to have a narrow therapeutic index recommending caution in their use in contraceptive formulations.

CONCLUSIONS/SIGNIFICANCE

Our results contribute to understanding the mechanisms involved in surfactant toxicity, have a predictive value with regard to their safety, and may be used to design more effective and less harmful surfactants for use in topical applications for STI prophylaxis.

Probing oppositely charged surfactant and copolymer interactions by isothermal titration microcalorimetry

The complexation between charge-neutral block copolymers and oppositely charged surfactants was investigated by light scattering experiments and by isothermal titration calorimetry (ITC). The copolymer was poly(sodium acrylate)-b-poly(acrylamide) and the surfactant dodecyltrimethylammonium bromide (DTAB). In a previous report, we had shown that the copolymers and the surfactants coassembled spontaneously into colloidal complexes. Depending on the charge ratio, the complexes were either single surfactant micelles decorated by copolymers or core-shell hierarchical structures. ITC was performed in order to investigate the thermodynamics of the complex formation. Titrations of copolymers by surfactants and of surfactants by copolymers revealed that the electrostatic coassembly was an endothermic reaction, suggesting a process dominated by the entropy of the counterions. Here, we found that the thermodynamic quantities associated with the reaction depended on the mixing order. When surfactants were added stepwise to copolymers, the titration was associated with the formation of single micelles decorated by a unique polymer. Above a critical charge ratio, the micelles rearranged themselves into 100 nm colloidal complexes in a collective process which displayed the following features: (i) the process was very slow as compared to the time scale of Brownian diffusion, (ii) the thermodynamic signature was a endothermic peak, and (iii) the stoichiometry between the positive and negative charges was modified from n = 0.48 (single micelles) to 0.75 (core-shell complexes). When copolymers were added stepwise to surfactants, the titration resulted in the formation of the core-shell aggregates only. In both experiments, the amount of polyelectrolytes needed for complex formation exceeded the number required to compensate the net micellar charge, confirming the evidence of overcharging in the complex formation.

DNA binding to zwitterionic model membranes

This study shows that DNA (linearized plasmid, 4331 base pairs and salmon sperm, 2000 base pairs, respectively) adsorbs to model membranes of zwitterionic liquid crystalline phospholipid bilayers in solutions containing divalent Ca(2+) cations, and also in solutions containing monovalent Na(+). The interaction between DNA and surface-supported model membranes was followed in situ using null ellipsometry, quartz crystal microbalance with dissipation, as well as neutron reflectometry. In the presence of Na(+) (in the absence of multivalent ions), DNA adopts an extended coil conformation upon adsorption. The solvent content in the adsorbed layer is high, and DNA is positioned on top of the membrane. In the presence of divalent Ca(2+), the driving force for the adsorption of DNA is electrostatic, and the adsorbed DNA film is not as dilute as in a solution containing Na(+). Cryo-TEM and SANS were further used to investigate the interaction in bulk solution using vesicles as model membrane systems. DNA adsorption could not be identified in the presence of Na(+) using SANS, but cryo-TEM indicates the presence of DNA between neighboring unilamellar vesicles. In the presence of Ca(2+), DNA induces the formation of multilamellar vesicles in which DNA intercalates the lamellae. Possible electrostatic and hydrophobic mechanisms for the adsorption of DNA in solutions containing monovalent salt are discussed and compared to the observations in divalent salt.

A study of interaction of cationic dyes with anionic polyelectrolytes

The interactions of Acridine Orange with Sodium Alginate and Pinacyanol Chloride with Heparin have been investigated by spectrophotometric method. The polymers induce metachromasy in the dye as evidenced from the considerable blue shift in the absorption maxima of the corresponding dyes. The interaction constant and thermodynamic parameters of polymer-dye interactions have been determined. The effect of additives such as alcohols, and urea on the reversal of metachromasy has been studied. The data has been used to determine the stability of the metachromatic complex and the nature of binding. The thermodynamic parameters of interaction revealed that binding between Acridine Orange and Sodium Alginate involved only electrostatic forces while that between Pinacyanol Chloride involved both electrostatic and hydrophobic forces. The reversal studies using surfactants indicated the involvement of both electrostatic and hydrophobic forces in binding. Based on the results it can be concluded that Pinacyanol Chloride is more effective inducing metachromasy than Acridine Orange.

Novel cholesterol-based cationic lipids for gene delivery

Gene therapy based on gene delivery is a promising strategy for the treatment of human disease. Here we present data on structure/biological activity of new biodegradable cholesterol-based cationic lipids with various heterocyclic cationic head groups and linker types. Enhanced accumulation of nucleic acids in the cells mediated by the lipids was demonstrated by fluorescent microscopy and flow cytometry. Light scattering and atomic force microscopy were used to find structure/transfection activity correlations for the lipids. We found that the ability of the lipids to stimulate intracellular accumulation of the oligodeoxyribonucleotides and plasmid DNA correlates well with their ability to form in solution lipid/NA complexes of sizes that do not exceed 100 nm. Screening of the lipids revealed the most promising transfection agents both in terms of low toxicity and efficient delivery: cholesterol-based lipids with positively charged pyridine and methyl imidazole head groups and either the ester or carbamate linker.

A comparative study of polyelectrolyte-dye interactions

The interaction of Azure B with sodium alginate and heparin in aqueous solution has been studied by spectrophotometric method. Absorbance of Azure B at 645 nm decreases and a new band appeared at 545 nm and at 556 nm respectively which indicated that a new metachromatic complex formed. A linear decrease in absorbance is noted. It was found that sodium alginate is more effective than heparin in decreasing the absorbance of Azure B at 645 nm. The stoichiometry of sodium alginate or heparin with Azure B was determined by spectrophotometry. The results suggested that the interaction between Azure B with sodium alginate or heparin was a result of electrostatic forces and the difference between heparin and sodium alginate were attributed to the different negative charge number on repetitive disaccharides unit. Studies on the effect of alcohol or urea indicated that sodium alginate and heparin interacted with the aggregates of Azure B. Thermodynamic parameters of interaction has been evaluated to determine the stability of the metachromatic complex. The effect of surfactants on reversal of metachromasy has also been studied.

Novel gemini pyridinium surfactants: synthesis and study of their surface activity, DNA binding, and cytotoxicity

New pyridinium gemini amphiphiles having ethane-1,2-dithiol spacer have been synthesized by regioselective electrophilic cobromination of alpha-olefins. Ethane-1,2-dithiol (1) and N-bromosuccinimide (6) on reaction with alpha-olefins (dodecene (2), tetradecene (3), hexadecene (4), and octadecene (5)) gave the respective 1,2-bis(2-bromoalkylthio)ethane (7-10). The bromoalkylthio ethers when reacted with pyridine (11) gave the respective gemini bispyridinium bromide (12-15). The surface properties of new geminis were evaluated by surface tension and conductivity measurements. These gemini surfactants have also been found to be having low cytotoxicity by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay on C6 glioma cells. The DNA binding capabilities of these amphiphiles have been determined below as well as above critical micelle concentration. The preliminary studies by agarose gel electrophoresis indicated chain length dependent DNA binding abilities which has further been proved by ethidium bromide exclusion experiments and transmission electron microscopy (TEM).

Electrochemical and spectroscopic study of octadecyltrimethylammonium bromide/DNA surfoplexes

The use of cationic micelles consisting of octadecyltrimethylammonium bromide (C18TAB) to compact calf thymus DNA has been investigated in aqueous buffered solution at 310.15 K by means of conductometry, electrophoretic mobility, and several fluorescence spectroscopy methods. The results indicate that C18TAB micelles, consisting of 44 monomers on average, may compact DNA molecule by an electrostatic interaction that takes place at the cationic spherical micelle surface. The surfoplexes thus formed show a surface density charge that goes from negative to positive values at a Lmic/D mass ratio of around 1.0 (where Lmic and D are the masses of micellized cationic surfactant and DNA), called the isoneutrality ratio (Lmic/D)phi. Values of this characteristic parameter, determined in this work not only from the electrochemical experimental data but also from spectroscopic measurements, are in very good agreement with those ones calculated from molecular parameters and some other properties also obtained in this work. The electrostatic character of the DNA-micelle interaction has been confirmed by analyzing the decrease in fluorescence emission of the fluorophore ethidium bromide, EtBr, initially intercalated between DNA base pairs, as long as the surfoplexes are formed. Fluorescence anisotropy experiments have revealed that micelle packing becomes more rigid in the presence of DNA, but once the surfoplex is formed, the fluidity increases with the Lmic/D mass ratio, attaining its maximum when the isoneutrality ratio is exceeded. This fact, together with the net positive charge of the surfoplexes with the Lmic/D mass ratio over the isoneutrality ratio, makes this regimen of lipid and DNA content the optimum for efficiency in the transfection process.

Modulation of photo-oxidative DNA damage by cationic surfactant complexation

The natural packaging of DNA in the cell by histones provides a particular environment affecting its sensitivity to oxidative damage. In this work, we used the complexation of DNA by cationic surfactants to modulate the conformation, the dynamics, and the environment of the double helix. Photo-oxidative damage initiated by benzophenone as the photosensitizer on a plasmid DNA complexed by dodecyltrimethylammonium chloride (DTAC), tetradecyltrimethylammonium chloride (TTAC), cetyltrimethyammonium chloride (CTAC) and bromide (CTAB) was detected by agarose gel electrophoresis. By fluorescent titration in the presence of ethidium bromide (EB) and agarose gel electrophoresis, we experimentally confirmed the complexation diagrams with a critical aggregation concentration on DNA matrix (CAC DNA) delimiting two regions of complexation, according to the DNA-phosphate concentration. The study of the photo-oxidative damage shows, for the first time, a direct correlation between the DNA complexation by these surfactants and the efficiency of DNA cleavage, with a maximum corresponding to the CAC DNA for DTAC and CTAC, and to DNA neutralization for CTAC and CTAB. The localization of a photosensitizer having low water solubility, such as benzophenone, inside the hydrophobic domains formed by the surfactant aggregated on DNA, locally increases the photoinduced cleavage by the free radical oxygen species generated. The inefficiency of a water-soluble quencher of hydroxyl radicals, such as mannitol, confirmed this phenomenon. The detection of photo-oxidative damage constitutes a new tool for investigating DNA complexation by cationic surfactants. Moreover, highlighting the drastically increased sensitivity of a complexed DNA to photo-oxidative damage is of crucial importance for the biological use of surfactants as nonviral gene delivery systems.