Importance of hydrophobic interactions in the single-chained cationic surfactant-DNA complexation

Intercalative binding of two new five-coordinated anticancer Pt(II) complexes to DNA: experimental and computational approaches

Binding interaction of two organoplatinum complexes, [Pt(C^N)Cl(dppa)], 1, and [Pt(C^N)Cl(dppm)], 2, (C^N = N(1), C(2')-chelated, deprotonated 2-phenylpyridine, dppa = bis(diphenylphosphino)amine, dppm = bis(diphenylphosphino)methane), as anti-tumor agents, with calf thymus DNA (CT-DNA) under pseudo-physiological conditions has been investigated using various biophysical techniques viz., UV-Vis and fluorescence spectroscopies, viscosity measurements, and thermal denaturation experiments. A hypochromic shift in UV-Vis absorption titration, fluorescence enhancement of Pt(II) complexes in the presence of CT-DNA, fluorescence quenching in competitive ethidium bromide displacement assay, and an uptrend in the viscosity (η) and melting temperature (Tm) indicated the existence of a tight intercalative interaction of Pt(II) complexes with CT-DNA. The fluorescence quenching of CT-DNA was a combined quenching of static and dynamic with Stern-Volmer quenching constants of 7.520 × 103 M-1 for complex 1 and 5.183 × 103 M-1 for complex 2, at low concentrations of Pt(II) complexes. Besides the experimental studies, computational studies were done. Molecular modeling studies confirmed the intercalation of the studied complexes by the phenyl groups of dppa and dppm, leading to π-π interactions but with a certain steric hindrance because of the size and shape of the considered complexes. The combination of experimental and computational data showed that reported Pt(II) complexes are promising structures and could be developed for cancer therapeutic applications.Communicated by Ramaswamy H. Sarma.

A molecularly informed field-theoretic study of the complexation of polycation PDADMA with mixed micelles of sodium dodecyl sulfate and ethoxylated surfactants

The self-assembly and phase separation of mixtures of polyelectrolytes and surfactants are important to a range of applications, from formulating personal care products to drug encapsulation. In contrast to systems of oppositely charged polyelectrolytes, in polyelectrolyte-surfactant systems the surfactants micellize into structures that are highly responsive to solution conditions. In this work, we examine how the morphology of micelles and degree of polyelectrolyte adsorption dynamically change upon varying the mixing ratio of charged and neutral surfactants. Specifically, we consider a solution of the cationic polyelectrolyte polydiallyldimethylammonium, anionic surfactant sodium dodecyl sulfate, neutral ethoxylated surfactants (C[Formula: see text]EO[Formula: see text]), sodium chloride salt, and water. To capture the chemical specificity of these species, we leverage recent developments in constructing molecularly informed field theories via coarse-graining from all-atom simulations. Our results show how changing the surfactant mixing ratios and the identity of the nonionic surfactant modulates micelle size and surface charge, and as a result dictates the degree of polyelectrolyte adsorption. These results are in semi-quantitative agreement with experimental observations on the same system.

Complexation of Oligo- and Polynucleotides with Methoxyphenyl-Functionalized Imidazolium Surfactants

Interaction between cationic surfactants and nucleic acids attracts much attention due to the possibility of using such systems for gene delivery. Herein, the lipoplexes based on cationic surfactants with imidazolium head group bearing methoxyphenyl fragment (MPI-n, n = 10, 12, 14, 16) and nucleic acids (oligonucleotide and plasmid DNA) were explored. The complex formation was confirmed by dynamic/electrophoretic light scattering, transmission electron microscopy, fluorescence spectroscopy, circular dichroism, and gel electrophoresis. The nanosized lipoplex formation (of about 100-200 nm), contributed by electrostatic, hydrophobic interactions, and intercalation mechanism, has been shown. Significant effects of the hydrocarbon tail length of surfactant and the type of nucleic acid on their interaction was revealed. The cytotoxic effect and transfection ability of lipoplexes studied were determined using M-HeLa, A549 cancer cell lines, and normal Chang liver cells. A selective reduced cytotoxic effect of the complexes on M-HeLa cancer cells was established, as well as a high ability of the systems to be transfected into cancer cells. MPI-n/DNA complexes showed a pronounced transfection activity equal to the commercial preparation Lipofectamine 3000. Thus, it has been shown that MPI-n surfactants are effective agents for nucleic acid condensation and can be considered as potential non-viral vectors for gene delivery.

Calix[4]arene Polyamine Triazoles: Synthesis, Aggregation and DNA Binding

Artificial gene delivery systems are in great demand from both scientific and practical biomedical points of view. In this paper, we present the synthesis of a new click chemistry calix[4]arene precursor with free lower rim and new water-soluble calixarene triazoles with 12 amino-groups on the upper rim (one with free phenol hydroxyl groups and two another containing four butyl or tetradecyl fragments). Aggregation in the series of amino-triazole calixarenes of different lipophilicity (calixarene with free phenol hydroxyl groups or butyl and tetradecyl fragments on the lower rim) was studied using dynamic light scattering and fluorescent pyrene probe. It was found that calix[4]arene with a free lower rim, like alkyl-substituted butyl calix[4]arene, forms stable submicron aggregates 150-200 nm in size, while the more lipophilic tetradecyl -substituted calix[4]arene forms micellar aggregates19 nm in size. Using UV-Vis spectroscopy, fluorimetry and CD, it was shown that amino-triazole calix[4]arenes bind to calf thymus DNA by classical intercalation. According to DLS and TEM data, all studied macrocycles cause significant DNA compaction, forming stable nanoparticles 50-20 nm in size. Among all studied calix[4]arenes the most lipophilic tetradecyl one proved to be the best for both binding and compaction of DNA.

Studies on the interactions of tiny amounts of common ionic surfactants with unsaturated phosphocholine lipid model membranes

In order to provide the fundamental information about the interactions of common anionic surfactants with the basic unsaturated phospholipids the influence of three cationic (dodecyltrimethylammonium bromide, DTAB; tetradecyltrimethylammonium bromide, TTAB and hexadecyltrimethylamonium bromide, CTAB) and one anionic (sodium dodecylsulfate, SDS) surfactants on the properties of the 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) layers was investigated. The studies proved that a tiny amount of the ionic surfactant added to the already synthesized liposome suspension is sufficient to change the zeta potential of the POPC and DOPC liposomes significantly. This impact increases with the surfactant concentration, the alkyl chain length of the surfactant and the degree of lipid saturation. Moreover, this effect is greater for the anionic surfactant than for the cationic one of the same alkyl chain length. The observed findings were confirmed in the course of the research carried out with the use of the corresponding Langmuir monolayers where the surface pressure - mean area isotherms, the compressibility modulus - surface pressure dependences, the monolayer penetration tests, the surface potential - mean molecular area isotherms and Brewster angle microscopy were discussed. It was found that the presence of the surfactants shifts the isotherms towards larger molecular area, to the higher extent for the SDS than DTAB. This effect increases with the increasing surfactant concentration in the subphase. Moreover, the investigated surfactants remain in the monolayer even at high surface pressure. Nevertheless, no effect on the morphology of the POPC and DOPC monolayers was detected from the BAM images. The surface potential and surface charge of the liposomes calculated on the basis of the zeta potential results reflected the interactions between the surfactant and the lipid layers.

Interaction of calf thymus DNA and glucose-based gemini cationic surfactants with different spacer length: A spectroscopy and DLS study

The interactions between calf thymus DNA and a series of glucose-based cationic gemini surfactants 1a-1c with different spacer length, n = 4, 6 and 8, were studied by UV absorption, fluorescence spectroscopy, circular dichroism, FT-IR, dynamic light scattering and zeta potential measurements. The results showed that all the surfactants could interact with DNA efficiently. On addition of increasing concentration of the surfactants, UV absorption hypochromicity with insignificant blue shift were observed, until the DNA signal disappeared. The surfactant 1c was more efficient in the reduction of absorption intensity of DNA. According to the fluorescence quenching experiments by ethidium bromide exclusion, 1c exhibited the highest binding properties, with the binding constant at 3.25 × 10⁸ L·mol^-1. The spectroscopy study indicated that the surfactants bound with the DNA by a non-intercalative mode, mainly electrostatic interaction between the positively charged headgroups of the surfactants and negatively charged phosphate groups of DNA at low concentration, and the hydrophobic interaction among the alkyl chains at high concentration. The conformation of DNA during the interaction process could be kept B-form of DNA. For 1c, the DNA molecules can be compacted to about 103 nm in hydrodynamic diameter at 0.2 mM, while the minimum sizes of DNA were 140 nm and 133 nm, respectively, in the presence of 1a and 1b. The impact of the cationic gemini surfactants on the DNA compaction and condensation would shed light on their potential applications in gene delivery.

Gemini and Bicephalous Surfactants: A Review on Their Synthesis, Micelle Formation, and Uses

The use of surfactants in polymerization reactions is particularly important, mainly in emulsion polymerizations. Further, micelles from biocompatible surfactants find use in pharmaceutical dosage forms. This paper reviews recent developments in the synthesis of novel gemini and bicephalous surfactants, micelle formation, and their applications in polymer and nanoparticle synthesis, oil recovery, catalysis, corrosion, protein binding, and biomedical area, particularly in drug delivery.

Binding between an amine cationic surfactant and DNA and surface properties of the resultant aggregates

Binding between cetyltrimethylammonium bromide, a cationic surfactant, and a variety of lengths of single stranded DNA was measured using fluorescence polarization and a simple cooperative model was used to obtain dissociation constants on the order of 1 × 10^-5 for the aggregates that formed. Aggregation depended on strand length where strands much shorter than 40 nucleotides (for example strands of 24-nucleotides) were too short to form the same size aggregates. Other factors such as salt concentration and temperature also affected aggregate formation: increasing either the salt concentration or performing binding at the highest temperature studied (60 °C) made it more difficult for aggregates to form. Both heating and dilution of aggregates caused the anisotropy signal to decrease, which suggested that the complexes fell apart under these conditions. Force spectroscopy of aggregate surfaces showed that both electrostatic and hydrophobic adhesive forces were present between aggregates and derivatized AFM tips. These findings can be used to better understand the stability of cationic surfactant-DNA aggregates and may provide guidance for lipid nanoparticle design used in vaccine development and therapeutics.

Cationic Single-Chained Surfactants with a Functional Group at the End of the Hydrophobic Tail DNA Compacting Efficiency

The interaction between calf-thymus DNA, ctDNA, and various single-chained surfactants with different functional groups at the end of hydrophobic tail was studied with the goal of investigating the influence of the functional group nature on surfactant DNA compacting efficiency. The surfactants investigated were dodecyltriethylammonium bromide (DTEABr), triethyl(1-phenoxydodecyl)ammonium bromide (12PhBr), triethyl(2-naphthoxydodecyl)ammonium bromide (12NBr) and 11-(isonicotinoyloxy)-N,N,N-triethyl-1-undecanaminium bromide (11PyBr). Results made evident that the surfactants' tendencies to self-aggregation is the key factor determining their efficiency to compact the nucleic acid. Subsequently, DOPE/12NBr/pEGFP-C1 lipoplexes, with different cationic surfactant molar fractions (α) and mass ratios (L/D), were prepared and characterized. DOPE is a zwitterionic phospholipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine, and the plasmid pEGFP-C1 carries a GFP coding sequence with the necessary regulatory elements for constitutive expression of the gene in human cells. 12NBr was chosen because it was the most efficient DNA compacting agent among the surfactants investigated. Finally, the cytotoxicity and transfection efficiency (TE) of DOPE/12NBr/pDNA lipoplexes, with different compositions, were investigated.

Polymer-Colloid Complexes Based on Cationic Imidazolium Amphiphile, Polyacrylic Acid and DNA Decamer

The solution behavior and physicochemical characteristics of polymer-colloid complexes based on cationic imidazolium amphiphile with a dodecyl tail (IA-12) and polyacrylic acid (PAA) or DNA decamer (oligonucleotide) were evaluated using tensiometry, conductometry, dynamic and electrophoretic light scattering and fluorescent spectroscopy and microscopy. It has been established that PAA addition to the surfactant system resulted in a ca. 200-fold decrease in the aggregation threshold of IA-12, with the hydrodynamic diameter of complexes ranging within 100-150 nm. Electrostatic forces are assumed to be the main driving force in the formation of IA-12/PAA complexes. Factors influencing the efficacy of the complexation of IA-12 with oligonucleotide were determined. The nonconventional mode of binding with the involvement of hydrophobic interactions and the intercalation mechanism is probably responsible for the IA-12/oligonucleotide complexation, and a minor contribution of electrostatic forces occurred. The latter was supported by zeta potential measurements and the gel electrophoresis technique, which demonstrated the low degree of charge neutralization of the complexes. Importantly, cellular uptake of the IA-12/oligonucleotide complex was confirmed by fluorescence microscopy and flow cytometry data on the example of M-HeLa cells. While single IA-12 samples exhibit roughly similar cytotoxicity, IA-12-oligonucleotide complexes show a selective effect toward M-HeLa cells (IC50 1.1 µM) compared to Chang liver cells (IC50 23.1 µM).

Potentiometric Study of Carbon Nanotube/Surfactant Interactions by Ion-Selective Electrodes. Driving Forces in the Adsorption and Dispersion Processes

The interaction (adsorption process) of commercial ionic surfactants with non-functionalized and functionalized carbon nanotubes (CNTs) has been studied by potentiometric measurements based on the use of ion-selective electrodes. The goal of this work was to investigate the role of the CNTs' charge and structure in the CNT/surfactant interactions. Non-functionalized single- (SWCNT) and multi-walled carbon nanotubes (MWCNT), and amine functionalized SWCNT were used. The influence of the surfactant architecture on the CNT/surfactant interactions was also studied. Surfactants with different charge and hydrophobic tail length (sodium dodecyl sulfate (SDS), octyltrimethyl ammonium bromide (OTAB), dodecyltrimethyl ammonium bromide (DoTAB) and hexadecyltrimethyl ammonium bromide (CTAB)) were studied. According to the results, the adsorption process shows a cooperative character, with the hydrophobic interaction contribution playing a key role. This is made evident by the correlation between the free surfactant concentration (at a fixed [CNT]) and the critical micellar concentration, cmc, found for all the CNTs and surfactants investigated. The electrostatic interactions mainly determine the CNT dispersion, although hydrophobic interactions also contribute to this process.

Bioinspired pyrimidine-containing cationic polymers as effective nanocarriers for DNA and protein delivery

Cationic polymers have shown great potential in the delivery of nucleic acids and proteins. In this study, a series of pyrimidine-based cationic polymers were synthesized via the Michael addition reaction from pyrimidine-based linkages and low molecular weight polyethyleneimine (PEI). The structure-activity relationship (SAR) of these materials in DNA and protein delivery was investigated. These materials could condense both DNA and protein into nanoparticles with proper sizes and zeta-potentials. In vitro experiments indicated that such polymers were efficient in transporting DNA and proteins into cells. Furthermore, the bioactivity of the genes and proteins encapsulated in these polymers were maintained during the delivery processes. Among the polymers, U-PEI600 synthesized from a uracil-containing linker and PEI 600 Da mediated comparable gene expression to PEI 25 kDa. Moreover, the activities of β-galactosidase delivered by U-PEI600 were well maintained after entering the cells. Evaluation using an immune response assay showed that the U-PEI600/OVA polyplex could stimulate greater production of immune factors with low cytotoxicity. Our study provides a strategy for the construction of cationic polymeric gene and cytosolic protein vectors with high efficiency and low toxicity.

Label-Free Detecting of the Compaction and Decompaction of ctDNA Molecules Induced by Surfactants with SERS Based on a nanoPAA-ZnCl2-AuLs Solid Substrate

DNA molecular compaction/decompaction is of great significance for the exploration of basic life processes, the research of biomedical and genetic engineering, and so forth. However, the detailed mechanism of DNA compaction/decompaction caused by surfactants remains an open and challenging problem that has not been fully solved so far. In this paper, a sort of novel solid substrate, nanoPAA-ZnCl₂-AuLs, with good stability and high sensitivity, was prepared by a self-assembly method. Based on this substrate, the surface-enhanced Raman scattering (SERS) technology was employed to investigate characteristics of interactions between DNA molecules and surfactants at a single molecular level. SERS spectra of calf thymus DNA (ctDNA), cetyl trimethyl ammonium bromide (CTAB), and sodium dodecyl sulfate (SDS) with a concentration as low as 10^-9 M, and SERS spectra of ctDNA-CTAB and ctDNA-CTAB-SDS composites were collected, respectively. The interactions between ctDNA and surfactants were analyzed by changes in SERS spectra, for example, disappearances and appearances of SERS bands and relative changes of peak intensity, in which CTAB resulted in the compaction of the DNA molecule while SDS induced the decompaction of the ctDNA-CTAB complex. Moreover, UV-visible spectrophotometry was employed to demonstrate the compaction/decompaction of ctDNA molecules caused by surfactants. The local binding modes of ctDNA molecules and surfactant molecules were expounded. This work will be helpful for understanding biological processes such as DNA compaction and recombination within nucleus or/and cells and for the development of gene therapy technologies.

Cationic Surfactants: Self-Assembly, Structure-Activity Correlation and Their Biological Applications

The development of biotechnological protocols based on cationic surfactants is a modern trend focusing on the fabrication of antimicrobial and bioimaging agents, supramolecular catalysts, stabilizers of nanoparticles, and especially drug and gene nanocarriers. The main emphasis given to the design of novel ecologically friendly and biocompatible cationic surfactants makes it possible to avoid the drawbacks of nanoformulations preventing their entry to clinical trials. To solve the problem of toxicity various ways are proposed, including the use of mixed composition with nontoxic nonionic surfactants and/or hydrotropic agents, design of amphiphilic compounds bearing natural or cleavable fragments. Essential advantages of cationic surfactants are the structural diversity of their head groups allowing of chemical modification and introduction of desirable moiety to answer the green chemistry criteria. The latter can be exemplified by the design of novel families of ecological friendly cleavable surfactants, with improved biodegradability, amphiphiles with natural fragments, and geminis with low aggregation threshold. Importantly, the development of amphiphilic nanocarriers for drug delivery allows understanding the correlation between the chemical structure of surfactants, their aggregation behavior, and their functional activity. This review focuses on several aspects related to the synthesis of innovative cationic surfactants and their broad biological applications including antimicrobial activity, solubilization of hydrophobic drugs, complexation with DNA, and catalytic effect toward important biochemical reaction.

Use of Ionic Liquids-like Surfactants for the Generation of Unilamellar Vesicles with Potential Applications in Biomedicine

The goal of this work is to understand the influence of the counterion nature on the organized systems formed by 1,4-bis-2-ethylhexylsulfosuccinate surfactants in aqueous solutions and how these aggregates will influence the deoxyribonucleic acid (DNA)-surfactant interactions. With this in mind, two ionic liquid-like surfactants were investigated: 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT) and 1-hexyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (hmim-AOT). Measurements of dynamic light scattering, ζ-potential, transmission electron microscopy, and fluorescence and UV-visible spectroscopy were performed to study the characteristics of the vesicles formed by bmim-AOT and hmim-AOT. Regarding the determination of the interaction of the surfactants with DNA, circular dichroism was used. The results obtained showed that bmim-AOT and hmim-AOT ionic liquid-like surfactants spontaneously form unilamellar vesicles in water at very low surfactant concentrations. The characteristics of these aggregates are dependent on the length of the tail of the counterions. The length of the hydrophobic chains of the counterions also influences the DNA-surfactant interactions through hydrophobic effects.

Influence of the degree of oligomerization of surfactants on the DNA/surfactant interaction

The interaction between calf thymus DNA, ctDNA, and a series of oligomeric surfactants derived from N-benzyl-N,N-dimethyl-N-(1-dodecyl)ammonium chloride is investigated. The influence of the surfactants' degree of oligomerization (2, 3 and 4) on the ctDNA/surfactant interaction is studied, as well as the effect of the structure of the spacer group linking the individual surfactant fragments. In particular, the effect of the distance between the positive charges and the hydrophobic chains within the oligomers on these interactions was examined, by using the three positional isomers (i.e., ortho-, meta-, and para-) with the rigid xylidene moiety as spacer. Results show that the dimeric ("gemini") surfactants are much more efficient in the inversion of the nucleic acid charge than the single-chained (monomeric) surfactant. Whereas the ortho - isomer causes a partial condensation, the meta - and para - isomers can completely condense ctDNA. The meta - and para - isomers of the trimeric surfactants can also completely condense the polynucleotide. In contrast, the tetrameric surfactant investigated does not change the morphology of the nucleic acid from an elongated coil into a compacted form, in spite of effectively inverting the nucleic acid's charge in their complex. Accordingly, the capacity for ctDNA compaction of oligomeric surfactants is not simply correlated to their degree of oligomerization, but depends on a complex balance of the number and relative distance of cationic charges and/or hydrophobic tails in the surfactants for effectively interacting with the nucleic acid to form the appropriate complex. This information will help to design more effective cationic surfactants as non-viral vectors for gene therapy.

Alkyl triphenylphosphonium surfactants as nucleic acid carriers: complexation efficacy toward DNA decamers, interaction with lipid bilayers and cytotoxicity studies

Herein, for the first time the complexation ability of a homological series of triphenylphosphonium surfactants (TPPB-n) toward DNA decamers has been explored. Formation of lipoplexes was confirmed by alternative techniques, including dynamic light scattering, indicating the occurrence of nanosized complexes (ca. 100-150 nm), and monitoring the charge neutralization of nucleotide phosphate groups and the fluorescence quenching of dye-intercalator ethidium bromide. The complexation efficacy of TPPB-surfactants toward an oligonucleotide (ONu) is compared with that of reference cationic surfactants. Strong effects of the alkyl chain length and the structure of the head group on the surfactant/ONu interaction are revealed, which probably occur via different mechanisms, with electrostatic and hydrophobic forces or intercalation imbedding involved. Phosphonium surfactants are shown to be capable of disordering lipid bilayers, which is supported by a decrease in the temperature of the main phase transition, T_m. This effect enhances with an increase in the alkyl chain length, indicating the integration of TPPB-n with lipid membranes. This markedly differs from the behavior of typical cationic surfactant cetyltrimethylammonium bromide, which induces an increase in the T_m value. It was demonstrated that the cytotoxicity of TPPB-n in terms of the MTT-test on a human cell line 293T nonmonotonically changes within the homological series, with the highest cytotoxicity exhibited by the dodecyl and tetradecyl homologs.

Effect of Molecular Composition of Head Group and Temperature on Micellar Properties of Ionic Surfactants with C12 Alkyl Chain

The paper analyses influences of the temperature and hydrophilic groups on micellar properties of ionic surfactants with 12-carbonic hydrophobic chains. The aim is to assess the impact of hydrophilic groups and temperature on thermodynamic parameters and micellization. This knowledge is indispensable for the formulation of new dosage forms. The method uses conductometric measurements. The following hydrophilic groups are analyzed: trimethylammonium bromide, trimethylammonium chloride, ethyldimethylammonium bromide, didodecyldimethylammonium bromide, pyridinium chloride, benzyldimethyl-ammonium chloride, methylephedrinium bromide, cis and trans-[(2-benzyloxy)-cyclohexyl-methyl]-N, N-dimethylammonium bromide, sodium sulphate and lithium sulphate. Except for a few cases, there is a good agreement between values of critical micellar concentrations (CMC) and critical vesicle concentration (CVC) obtained here and those which were obtained by other authors and/or by other physicochemical methods. Values of the CMC are compared with respect to the molar masses of hydrophilic groups. It was found that CMC values increased non-linearly with increasing system temperature. The degrees of counterion binding and thermodynamic parameters, like the standard molar Gibbs energy, enthalpy and entropy of micellization are determined and discussed in detail. The results obtained will be incorporated into in silico processes of modeling and design of optimal dosage forms, a current interdisciplinary research focus of the team.

Zn(ii) coordination to cyclen-based polycations for enhanced gene delivery

Zn²⁺ coordination greatly improved the gene transfection efficiency of cyclen-based polycations.

Insight into the DNA adsorption on nitrogen-doped positive carbon dots

Considerable biosensors have been fabricated on the basis of DNA interaction with carbon nanomaterials, such as graphene oxide (GO) nanosheets. Few studies have focused on the rational design of sensors between carbon dots (CDs) and DNA due to the limited understanding of the real forces behind the adsorption of DNA on CDs. In this work, nitrogen doping-positive CDs (N-CDs), which can quench fluorophore-labeled DNA, were investigated to ascertain the interaction between the CDs and DNA. With reference to DNA adsorption on GO, the adsorption capacity and kinetics of N-CDs for DNA were studied. Desorption of DNA from these surfaces was also measured. Moreover, DNA desorption and anchoring force of N-CDs to DNA were different from those of GO, given that the prepared N-CDs and GO were positively and negatively charged, respectively. Accordingly, DNA was adsorbed on N-CDs mainly via electrostatic adsorption and other forces, such as nucleobase effect, hydrophobic interaction, and van der Waals (vdW) forces. This study enhanced the basic knowledge of DNA adsorption on some CDs for further study in the application of CDs in bioanalysis or biomedicine.

With the reference of DNA adsorption on GO, the adsorption capacity, kinetics of N-CDs to DNA were investigated.

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.