Interaction between 14mer DNA oligonucleotide and cationic surfactants of various chain lengths

Biocompatible Catanionic Vesicles from Arginine-Based Surfactants: A New Strategy to Tune the Antimicrobial Activity and Cytotoxicity of Vesicular Systems

Their stability and low cost make catanionic vesicles suitable for application as drug delivery systems. In this work we prepared catanionic vesicles using biocompatible surfactants: two cationic arginine-based surfactants (the monocatenary Nα-lauroyl-arginine methyl ester-LAM and the gemini Nα,Nϖ-bis(Nα-lauroylarginine) α, ϖ-propylendiamide-C3(CA)2) and three anionic amphiphiles (the single chain sodium dodecanoate, sodium myristate, and the double chain 8-SH). The critical aggregation concentration, colloidal stability, size, and charge density of these systems were comprehensively studied for the first time. These catanionic vesicles, which form spontaneously after mixing two aqueous solutions of oppositely charged surfactants, exhibited a monodisperse population of medium-size aggregates and good stability. The antimicrobial and hemolytic activity of the vesicles can be modulated by changing the cationic/anionic surfactant ratio. Vesicles with a positive charge efficiently killed Gram-negative and Gram-positive bacteria as well as yeasts; the antibacterial activity declined with the decrease of the cationic charge density. The catanionic systems also effectively eradicated MRSA (Methicillin-resistant Staphylococcus Aureus) and Pseudomonas aeruginosa biofilms. Interestingly, the incorporation of cholesterol in the catanionic mixtures improved the stability of these colloidal systems and considerably reduced their cytotoxicity without affecting their antimicrobial activity. Additionally, these catanionic vesicles showed good DNA affinity. Their antimicrobial efficiency and low hemolytic activity render these catanionic vesicles very promising candidates for biomedical applications.

Binding of 12-s-12 dimeric surfactants to calf thymus DNA: Evaluation of the spacer length influence

Several cationic dimeric surfactants have shown high affinity towards DNA. Bis-quaternary ammonium salts (m-s-m) have been the most common type of dimeric surfactants investigated and it is generally admitted that those that posses a short spacer (s≤3) show better efficiency to bind or compact DNA. However, experimental results in this work show that 12-s-12 surfactants with long spacers make the surfactant/ctDNA complexation more favorable than those with short spacers. A larger contribution of the hydrophobic interactions, which control the binding Gibbs energy, as well as a higher average charge of the surfactant molecules bound to the nucleic acid, which favors the electrostatic attractions, could explain the experimental observations. Dimeric surfactants with intermediate spacer length seem to be the less efficient for DNA binding.

Interaction between a cationic bolaamphiphile and DNA: The route towards nanovectors for oligonucleotide antimicrobials

Bacterial resistance to antimicrobials is a global threat that requires development of innovative therapeutics that circumvent its onset. The use of Transcription Factor Decoys (TFDs), DNA fragments that act by blocking essential transcription factors in microbes, represents a very promising approach. TFDs require appropriate carriers to protect them from degradation in biological fluids and transfect them through the bacterial cell wall into the cytoplasm, their site of action. Here we report on a bolaform cationic surfactant, [12-bis-THA]Cl2, with proven transfection activity in vivo. By studying the physical-chemical properties of its aqueous solutions with light scattering, cryo-TEM, ζ-potential, absorption and fluorescence spectroscopies, we prove that the bolaamphiphiles associate into transient vesicles which convert into one-dimensional elongated structures over time. These surfactant assemblies complex TFDs with extremely high efficiency, if compared to common cationic amphiphiles. At Z+/-=11, the nanoplexes are stable and have a size of 120nm, and they form independently of the original morphology of the [12-bis-THA]Cl2 aggregate. DNA is compacted in the nanoplexes, as shown through CD spectroscopy and fluorescence, but is readily released in its native form if sodium taurocholate is added.

Magnetic Surfactants and Polymers with Gadolinium Counterions for Protein Separations

New magnetic surfactants, (cationic hexadecyltrimethlyammonium bromotrichlorogadolinate (CTAG), decyltrimethylammonium bromotrichlorogadolinate (DTAG), and a magnetic polymer (poly(3-acrylamidopropyl)trimethylammonium tetrachlorogadolinate (APTAG)) have been synthesized by the simple mixing of the corresponding surfactants and polymer with gadolinium metal ions. A magnetic anionic surfactant, gadolinium tri(1,4-bis(2-ethylhexoxy)-1,4-dioxobutane-2-sulfonate) (Gd(AOT)3), was synthesized via metathesis. Both routes enable facile preparation of magnetically responsive magnetic polymers and surfactants without the need to rely on nanocomposites or organic frameworks with polyradicals. Electrical conductivity, surface tensiometry, SQUID magnetometry, and small-angle neutron scattering (SANS) demonstrate surface activity and self-aggregation behavior of the magnetic surfactants similar to their magnetically inert parent analogues but with added magnetic properties. The binding of the magnetic surfactants to proteins enables efficient separations under low-strength (0.33 T) magnetic fields in a new, nanoparticle-free approach to magnetophoretic protein separations and extractions. Importantly, the toxicity of the magnetic surfactants and polymers is, in some cases, lower than that of their halide analogues.

Self-assembly and biophysical properties of gemini 3-alkyloxypyridinium amphiphiles with a hydroxyl-substituted spacer

New gemini pyridinium amphiphiles having alkyl chain lengths of C10, C12, C14 , and C16 and appended with hydroxyl-substituted spacers have been synthesized, characterized, and investigated for their self-assembly as well as adsorption behavior by state-of-the-art techniques such as conductometry, tensiometry, isothermal titration calorimetry (ITC), and spectrofluorometry. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) have provided excellent acumen with respect to the micellar size distribution of investigated dicationics in aqueous media. Furthermore, the interaction of these dicationics with plasmid DNA, at different charge ratios (N/P), has been studied by DLS, agarose gel electrophoresis, and ethidium bromide exclusion measurements. The cytotoxicity of these geminis has been evaluated by using an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay on BV2 (microglial) and C6 glioma cell lines. It was found that the varying alkyl chain length, fashioned by ether linkage close to the headgroup, and the presence of a polar linker significantly altered the physicochemical properties of these new dicationics as compared to the properties of nonfunctionalized gemini surfactants.

Fluorescence and Förster resonance energy transfer investigations on DNA oligonucleotide and PAMAM dendrimer packing interactions in dendriplexes

Considering the importance of short oligonucleotide packing in dendriplex-mediated gene delivery, a direct insight into the 14-mer oligonucleotide and dendrimer interactions using fluorescence and FRET techniques is the focus of this study. Fluorometric titrations of various fluorophore-tagged oligonucleotides with the first three PAMAM dendrimer generations showed a decrease in the fluorescence intensity with two break points, namely Z and Z, for each titration. The first break point for each dendrimer was identical to the neutralization point observed by basic biophysical studies for the corresponding dendrimer generations. Additionally, FRET studies on dual tagged oligonucleotide (DFT) molecules revealed a third break point at the charge ratio (Z) where there was the highest fluorescence energy transfer from the donor to the acceptor fluorophores. Altogether, dendriplex formation was considered to take place via three steps with an increase in the dendrimer concentration, where initially there was monomeric complexation at the neutralization point (Z) followed by loosely held molecular aggregation of the dendrimer (Z). In the final step, dendrimer molecular aggregates were held tightly together for the closest possible packing of the oligonucleotide molecules onto their surface. The effective molecular packing is identified by the highest FRET intensity for the dendrimer of generation 2 at a charge ratio of 0.34 (Z±).

Drastic stabilization of parallel DNA hybridizations by a polylysine comb-type copolymer with hydrophilic graft chain

Electrostatic interactions play a major role in protein-DNA interactions. As a model system of a cationic protein, herein we focused on a comb-type copolymer of a polycation backbone and dextran side chains, poly(L-lysine)-graft-dextran (PLL-g-Dex), which has been reported to form soluble interpolyelectrolyte complexes with DNA strands. We investigated the effects of PLL-g-Dex on the conformation and thermodynamics of DNA oligonucleotides forming various secondary structures. Thermodynamic analysis of the DNA structures showed that the parallel conformations involved in both DNA duplexes and triplexes were significantly and specifically stabilized by PLL-g-Dex. On the basis of thermodynamic parameters, it was further possible to design DNA switches that undergo structural transition responding to PLL-g-Dex from an antiparallel duplex to a parallel triplex even with mismatches in the third strand hybridization. These results suggest that polycationic molecules are able to induce structural polymorphism of DNA oligonucleotides, because of the conformation-selective stabilization effects.

Conformational changes of DNA in the presence of 12-s-12 gemini surfactants (s=2 and 10). Role of the spacer's length in the interaction surfactant-polynucleotide

A multifaceted study on the interaction of calf-thymus DNA with two different cationic gemini surfactants alkanediyl-α-ω-bis(dodecyldimethyl-amonium)bromide, 12-s-12,2Br(-) (with s=2, G2, and 10, G10) was carried out. The measurements were done at different molar ratios X=[surfactant]/[DNA]. Results show two different conformational changes in DNA: a first compaction of the polynucleotide corresponding to a partial conformational (not total) change of DNA from an extended coil state to a globular state that happens at the lower molar ratio X. A second change corresponds to a breaking of the partial condensation, that is, the transition from the compacted state to a new more extended conformation (for the higher X values) different to the initial extension. According to circular dichroism spectra and dynamic light scattering measurements, this new state of DNA seems to be similar to a ψ-phase. Measurements confirm that interactions involved in the compaction are different to those previously obtained for the analog surfactant CTAB. X values at which the conformational changes happen depend on the length of the spacer in the surfactant along with the charge of the polar heads.

Interaction between DNA and trimethyl-ammonium bromides with different alkyl chain lengths

The interaction between λ--DNA and cationic surfactants with varying alkyl chain lengths was investigated. By dynamic light scattering method, the trimethyl-ammonium bromides-DNA complex formation was shown to be dependent on the length of the surfactant's alkyl chain. For surfactants with sufficient long alkyl chain (CTAB, TTAB, DTAB), the compacted particles exist with a size of ~60-110 nm at low surfactant concentrations. In contrast, high concentration of surfactants leads to aggregates with increased sizes. Atomic force microscope scanning also supports the above observation. Zeta potential measurements show that the potential of the particles decreases with the increase of surfactant concentration (CTAB, TTAB, DTAB), which contributes much to the coagulation of the particles. For OTAB, the surfactant with the shortest chain in this study, it cannot fully neutralize the charges of DNA molecules; consequently, the complex is looser than other surfactant-DNA structures.

Self-assembly, DNA binding and cytotoxicity trends of ether functionalized gemini pyridinium amphiphiles

Six new ether functionalized gemini pyridinium amphiphiles have been synthesized having dodecyl, tetradecyl alkyl chain lengths and three different spacers (i.e. -(CH2)n-, where n is 4, 5 and 6) and investigated for their self-assembling behavior by state of the art techniques such as tensiometry, conductivity and spectrofluorometry. These new pyridinium gemini surfactants exhibit lower cmc values as compared to other gemini surfactants reported in literature. These amphiphiles form stable complexes with DNA as established by agarose gel electrophoresis and ethidium bromide exclusion experiments. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay was carried out in vitro on C6 glioma cell line for cytotoxicity assessment of new pyridinium geminis. The dynamic light scattering (DLS) and transmission electron microscopy (TEM) have been used to measure the micellar size of gemini surfactants. Further, thermal stability of these amphiphiles has been evaluated by thermogravimetric analysis (TGA). The dependence of self-assembly behavior and other properties on spacer as well as alkyl chain length has been established.

Magnetizing DNA and proteins using responsive surfactants

DNA chains and their movement in solvent may now be controlled simply by surfactant binding and the switching "on" and "off" of a magnetic field adding a new paradigm to the study and control, condensation and manipulation of DNA (and other biomolecules). Such control is essential for biotechnological applications such as transfection and the regulation of gene suppression, as well as in materials science concerning soft molecular self-assemblies.

Compaction and decompaction of DNA induced by the cationic surfactant CTAB

A multifaceted study on the interaction of the cationic surfactant CTAB with calf thymus DNA was carried out by using different techniques. The measurements were done at different molar ratios X = [CTAB]/[DNA]. Results show the conformational change that DNA suffers due to the interaction with surfactant molecules at low molar ratios: the condensation of the polynucleotide, from an extended coil state to a globular state. The effect observed at the higher molar ratios is worth noting: the decondensation of DNA, that is, the transition from a compact state to a more extended conformation. Experimental data obtained confirm that this latter state is not exactly the same as that found in the absence of the surfactant. Attractive interactions between different parts of the molecule by ion correlation effects are the driving force to produce both the compaction and decompaction events. Results also show the importance of choosing both a proper system for the study and the most seeming measuring technique to use. The study demonstrates that, in some cases, the use of several techniques is desirable in obtaining reliable and accurate results.

Structure and stability of the complex formed by oligonucleotides

Polycations and cationic lipids have been widely used as non-viral vectors for the delivery of plasmid DNA, siRNA and anti-sense oligonucleotides. To demonstrate that one polycation can form a complex with several types of DNA, we conducted a comparative study on the complexation of poly(L-lysine) (PLL) with 2000 bp salmon testes DNA (dsDNA), 21 bp double-stranded oligonucleotides (ds-oligo), and 21 nt single-stranded oligonucleotides (ss-oligo) in PBS buffer. The complexes are prepared by a titration method and the process is monitored by laser light scattering. It was found that in most cases, ss-oligo and ds-oligo form complexes with higher molecular weights than the complex formed by dsDNA at the same +/- ratio immediately after mixing. More importantly, the complexes formed by oligonucleotides are not stable, the scattered intensity gradually decreases to the level of the solvent in weeks. Atomic force microscopy measurements also indicate that the freshly prepared complex is subject to environmental changes and could dissociate very quickly. The behaviour of oligonucleotides cannot be predicted by the classical polyelectrolyte theories.

Synthesis, characterization and comparative evaluation of phenoxy ring containing long chain gemini imidazolium and pyridinium amphiphiles

Two series of phenoxy ring containing long chain imidazolium and pyridinium based gemini amphiphiles have been synthesized from renewable cardanol oil having different spacers (i. e. -S-(CH(2))(n)-S-, where n is 2, 3, 4 & 6). Critical micelle concentration (cmc) of these new gemini amphiphiles has been determined by conductivity method. Further, these new cationic amphiphiles have been evaluated for their DNA binding capability by agarose gel electrophoresis, ethidium bromide exclusion experiments and transmission electron microscopy (TEM). The cytotoxicity of these new amphiphiles have been evaluated by MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. Comparative studies of these phenoxy ring containing long chain gemini imidazolium amphiphiles and their pyridinium analogues depicted low cmc values of the later but greater DNA interaction capability and low cytotoxicity of the former series of amphiphiles.

Characterization of the nanostructure of complexes formed by single- or double-stranded oligonucleotides with a cationic surfactant

We report the use of dynamic light scattering (DLS), small-angle neutron scattering (SANS), and small-angle X-ray scattering (SAXS) to characterize the nanostructure of complexes formed by either single- or double-stranded oligonucleotides with a cationic surfactant (cetyltrimethylammonium bromide, CTAB) in aqueous solution (1 mM Li(2)SO(4)). For single-stranded oligonucleotides 5'-A(20)-3' and 5'-CCCCATTCTAGCAGCCCGGG-3', both the appearance of two Bragg peaks (at 0.14 and 0.28 Å(-1)) in SAXS spectra with a spacing of 1:2 and form factor fits to SANS spectra are consistent with the presence of multilamellar vesicles (with, on average, 6-9 layers with a periodicity of 45-48 Å). Some samples showed evidence of an additional Bragg peak (at 0.20 Å(-1)) associated with periodic packing (with a periodicity of 31 Å) of the oligonucleotides within the lamellae of the nanostructure. The nucleotide composition of the single-stranded oligonucleotides was also found to impact the number and size of the complexes formed with CTAB. In contrast to 5'-A(20)-3' and 5'-CCCCATTCTAGCAGCCCGGG-3', 5'-T(20)-3' did not change the state of aggregation of CTAB (globular micelles) over a wide range of oligonucleotide:CTAB charge ratios. These results support the proposition that hydrophobic interactions, as well as electrostatics, play a central role in the formation of complexes between cationic amphiphiles and single-stranded oligonucleotides and thus give rise to nanostructures that depend on nucleotide composition. In contrast to the single-stranded oligonucleotides, for double-stranded oligonucleotides mixed with CTAB, three Bragg peaks (0.13, 0.23, and 0.25 Å(-1)) in SAXS spectra with a spacing ratio of 1:√3:√4 and characteristic changes in SANS spectra indicate formation of a hexagonal nanostructure. Also, the composition of the double-stranded oligonucleotides did not measurably impact the nanostructure of complexes formed with CTAB, suggesting that electrostatic interactions dominate the formation of these complexes. Overall, these results provide insights into the intermolecular interactions that occur between cationic amphiphiles and oligonucleotides and establish that single and double-stranded oligonucleotides form complexes with cationic surfactants that differ in nanostructure. The results also provide guidance for the design of oligonucleotide complexes with cationic amphiphiles.

Fluorescence dynamics of double- and single-stranded DNA bound to histone and micellar surfaces

The study of structure and dynamics of bound DNA has special implications in the context of its biological as well as material functions. It is of fundamental importance to understand how a binding surface affects different positions of DNA with respect to its open ends. Because double-stranded (ds) and single-stranded (ss) DNA are the predominant functional forms, we studied the site-specific dynamics of these DNA forms, bound to the oppositely charged surface of histones, and compared the effects with that of DNA bound to cetyltrimethyl ammonium bromide micelles. We utilized a time-resolved fluorescence technique using fluorescent base analogue 2-aminopurine located at specific positions of synthetic poly-A DNA strands to obtain fluorescence lifetime and anisotropy information. It is observed that the binding leads to overall rigidification of the DNA backbone, and the highly flexible ends show drastic dampening of their internal dynamics as well as the fraying motions. In the case of ds-DNA, we find that the binding not only decreases the flexibility but also leads to significant weakening of base-stacking interactions. An important revelation that strong binding between DNA and the binding agents (histones as well as micelles) does not dampen the internal dynamics of the bases completely suggests that the DNA in its bound form stays in some semiactive state, retaining its full biological activity. Considering that the two binding agents (histones and micelles) are chemically very different, an interesting comparison is made between DNA-histones and DNA-micelle interactions.

An investigation on interaction between 14mer DNA oligonucleotide and CTAB by fluorescence and fluorescence resonance energy transfer studies

Possible interaction mechanisms between oligonucleotide (DNA) of 14 base pairs with cetyl trimethyl ammonium bromide (CTAB) were postulated based on fluorescence and fluorescence resonance energy transfer (FRET) studies. Detailed FRET investigations were carried out by fluorometric titrations of the surfactant with various oligonucleotide duplexes with 5'-tagged fluorescein (donor) (D(D)), 5'-tagged TAMRA (acceptor) (D(A)) and both (D(DA)). In general, fluorescence spectra of the duplexes (D(D), D(A) and D(DA)) revealed a reduction in the fluorescence intensities of 5'-fluorescein as well as 5'-TAMRA and thereafter an attainment of saturation with increase in the surfactant concentration. The observed changes in the oligonucleotide fluorescence intensities for the duplexes under investigation could be attributed to the microenvironmental changes during the oligonucleotide-CTAB interaction. Considering together, it appeared that the interaction is a three-stage process, wherein the initial addition of surfactant caused neutralization of the 14mer at Z(+/-)(1) = 0.8, which is manifested by a slight reduction in fluorescence intensity. Further, addition of the surfactant molecules sharply reduced the fluorescence intensity of the oligonucleotide depicting oligonucleotide induced self-assembly until the second break point (Z(+/-)(2) = 1.7). From the second break point, a striking resonance energy transfer was observed from donor to acceptor, which revealed shortening of distance between 5' ends of the oligonucleotides that attained a saturation at Z(+/-)(3) = 2.5. Similar three-stage interaction of oligonucleotide with the surfactant has also been observed through fluorometric titrations in the presence of NaCl. However, in the presence of the salt, neutralization of oligonucleotide, surfactant aggregation and FRET occurred at higher charge ratios due to the screening effect of Na+ ions followed by an increase in critical association concentration (CAC) of the surfactant. Overall, investigations probe possible structural changes in the 14mer oligonucleotide-CTAB complex upon increase in the surfactant concentration.

Swelling properties of cross-linked DNA gels

This work represents our contribution to the field of physical chemistry of DNA gels, and concerns the synthesis and study of novel chemically cross-linked DNA gels. The use of covalent DNA gels is a very promising way to study DNA-cosolute interactions, as well as the dynamic behaviour of DNA and cationic compacting agents, like lipids, surfactants and polycations. Manipulating DNA in new ways, like DNA networks, allows a better understanding and characterization of DNA-cosolute complexes at the molecular level, and also allows us to follow the assembly structures of these complexes. The use of responsive polymer gels for targeted delivery of toxic and/or labile drugs has, during the past few years, shown to be a promising concept. The features found in the proposed system would find applications in a broader field of gel/drug interaction, for the development of controlled release and targeted delivery devices.

Role of linker groups between hydrophilic and hydrophobic moieties of cationic surfactants on oligonucleotide-surfactant interactions

The interaction between DNA and amino-acid-based surfactants with different linker groups was investigated by gel electrophoresis, ethidium bromide exclusion assays, circular dichroism, and melting temperature determinations. The studies showed that the strength of the interaction between the oligonucleotides and the surfactants is highly dependent on the linker of the surfactant. For ester surfactants, no significant interaction was observed for surfactant-to-DNA charge ratios up to 12. On the other hand, amide surfactants were shown to interact strongly with the oligonucleotides; these surfactants could displace up to 75% of the ethidium bromide molecules bound to the DNA and induced significant changes in the circular dichroism spectra. When comparing the headgroups of the surfactants, it was observed that surfactants with more hydrophobic headgroups (proline vs alanine) interacted more strongly with the DNA, in good agreement with previous studies.

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).