Liposome-mediated conformation transition of DNA detected by molecular probe: methyl green

Recent studies have focused on the structural features of DNA-lipid assemblies. In this paper, we take methyl green (MG) as a probe molecule to detect the conformational change of DNA molecule induced by dimethyldioctadecylammonium bromide (DDAB) liposomes before the condensation process of DNA begins. DDAB-induced DNA topology changes were investigated by cyclic voltammetry (CV), circular dichroism (CD) and UV-VIS spectrometry. We find that upon binding to DNA, positively charged liposomes induce a conformational transition of DNA molecules from the native B-form to the C motif. Conformational transition in DNA results in the binding modes of MG to DNA, changing and being isolated from DNA to the solution. More stable complexes are formed between DNA and DDAB. That is also proved by the melting study of DNA.     

An insight into the micellization of dodecyldimethylethylammonium bromide (DDAB) in the presence of bovine serum albumin (BSA)

In this work, we report the effect of concentration of bovine serum albumin (BSA) on the micellization of a cationic surfactant, dodecyldimethylethylammonium bromide (DDAB). Several samples covering a wide range of concentrations of protein and surfactant have been investigated. The interactions between the moieties are investigated by measuring fluorescence quenching of BSA molecules. The aggregation number of DDAB micelles is found to be small in the presence of BSA. The formation of DDAB-BSA complex is confirmed by FTIR. Absorbance spectroscopy indicates that at higher concentration, the conformational stability of BSA in DDAB is higher. The viscosity data for protein-surfactant systems confirm conformational changes in protein chains induced by the surfactant. The cmc values for DDAB increase with increasing concentration of BSA. At higher temperatures the micellization-complexation becomes enthalpy-dominated.     

Solubilization and conformational behavior of Zein in aqueous solution of dodecyldimethylethylammonium bromide (DDAB)

The solubilization and conformational behavior of Zein in the presence of cationic surfactant, dodecyldimethylethylammonium bromide (DDAB) have been studied. The colloidal properties of DDAB in the absence and presence of Zein have also been investigated using physico-chemical and spectroscopy methods. The surfactant appears to bind to Zein at concentrations below the critical micelle concentration (cmc) and the binding becomes weaker at concentrations above the cmc. The interaction between DDAB and Zein depends on the chemical structure and molecular parameters (conformation, molar mass, charge) of the protein. The schematic sketches of the molecular mechanisms of the complex formation between like-charged proteins and surfactants have been proposed.     

Optical sensors based on hybrid DNA/conjugated polymer complexes

Single-stranded DNA (ss-DNA) can specifically bind to various targets, including a complementary ss-DNA, ions, proteins, drugs, and so forth. When binding takes place, the oligonucleotide probe often undergoes a conformational transition. This conformational change of the negatively charged ss-DNA can be detected by using a water-soluble, cationic polythiophene derivative, which transduces the complex formation into an optical (colorimetric or fluorometric) signal without any labeling of the probe or the target. This simple and rapid methodology has enabled the specific and sensitive detection of nucleic acids and human thrombin. This new biophotonic tool can easily be applied to the detection of various other biomolecules and is also useful in the high-throughput screening of new drugs.     

Optical sensors based on hybrid aptamer/conjugated polymer complexes

Single-stranded DNA (aptamer) can specifically bind potassium ions or human alpha-thrombin. When binding takes place, the aptamer undergoes a conformational transition from an unfolded to a folded structure. This conformational change of the negatively charged oligonucleotide can be detected by adding a water-soluble, cationic polythiophene derivative, which transduces the new complex formation into an optical (colorimetric or fluorometric) signal without any labeling of the probe or of the target. This simple and rapid methodology has enabled the detection of human thrombin in the femtomole range. This new biophotonic tool can easily be applied to the detection of various other proteins as well as being useful in the high-throughput screening of new drugs.     

Cationic liposomes in mixed didodecyldimethylammonium bromide and dioctadecyldimethylammonium bromide aqueous dispersions studied by differential scanning calorimetry, Nile Red fluorescence, and turbidity

The thermotropic phase behavior of cationic liposomes in mixtures of two of the most investigated liposome-forming double-chain lipids, dioctadecyldimethylammonium bromide (DODAB) and didodecyldimethylammonium bromide (DDAB), was investigated by differential scanning calorimetry (DSC), turbidity, and Nile Red fluorescence. The dispersions were investigated at 1.0 mM total surfactant concentration and varying DODAB and DDAB concentrations. The gel to liquid-crystalline phase transition temperatures (Tm) of neat DDAB and DODAB in aqueous dispersions are around 16 and 43 degrees C, respectively, and we aim to investigate the Tm behavior for mixtures of these cationic lipids. Overall, DDAB reduces the Tm of DODAB, the transition temperature depending on the DDAB content, but the Tm of DDAB is roughly independent of the DODAB concentration. Both DSC and fluorescence measurements show that, within the mixture, at room temperature (ca. 22 degrees C), the DDAB-rich liposomes are in the liquid-crystalline state, whereas the DODAB-rich liposomes are in the gel state. DSC results point to a higher affinity of DDAB for DODAB liposomes than the reverse, resulting in two populations of mixed DDAB/DODAB liposomes with distinctive phase behavior. Fluorescence measurements also show that the presence of a small amount of DODAB in DDAB-rich liposomes causes a pronounced effect in Nile Red emission, due to the increase in liposome size, as inferred from turbidity results.     

Analytical assays based on detecting conformational changes of single molecules.

One common strategy for the detection of biomolecules is labeling either the target itself or an antibody that binds to it. Herein, a different approach, based on detecting the conformational change of a probe molecule induced by binding of the target is discussed. That is, what is being detected is not the presence of the target or the probe, but the conformational change of the probe. Recently, a single-molecule sensor has been developed that exploits this mechanism to detect hybridization of a single DNA oligomer to a DNA probe, as well as specific binding of a single protein to a DNA probe. Biomolecular recognition often involves large conformational changes of the molecules involved, and therefore this strategy may be applicable to other assays.     

聚苯乙烯磺酸钠与阳离子表面活性剂的相互作用和纳米聚集体的生成

在聚苯乙烯磺酸钠(PSS)的水溶液中,引入阳离子表面活性剂(CTAB或DDAB)使与PSS通过静电相互作用实现聚苯乙烯磺酸盐不同程度的中性化,并进而对PSS/表面活性剂复合物在水中的行为特征、特别是PSS因疏水化而产生的聚集行为以及临界聚集浓度等采用多种方法如溶液的透光率;荧光光谱;荧光探针以及扫描电镜观察等进行了研究,得到一些颇为有趣的结果.结果表明PSS-CTAB或DDAB加成物可自发的形成约70 nm的纳米粒子。而中性化程度则对加成物的构型以及体系的透光率等有较大影响。结果还表明所得具有亲水外壳和疏松的疏水内核的聚集体能容易的使疏水分子进入其中。     

Effects of micelle-to-vesicle transitions on the degree of counterion binding

Effects of micelle-to-vesicle transitions on the degree of counterion binding (beta) were investigated on three systems. For the concentration-dependent micelle-to-vesicle transition in the didodecyldimethylammonium bromide (DDAB)/water system, in the region of coexistent micelles and vesicles, less than 3 mM, the beta values increased significantly with DDAB concentration: beta (0.07 mM)=0.35 and beta (3 mM)=0.93. In the coexistent region, activities of the bromide ion, a(Br), were almost independent of the DDAB concentration, suggesting the pseudo-phase nature of both micelles and vesicles. In the concentration-dependent vesicle-to-lamellar transition region above 5 mM, where multilamellar vesicles were prevailing, on the other hand, the beta values were only little affected by this transition. This suggests that the increase in the layer number of DDAB multilamellar vesicles scarcely affects the beta values. This was also supported by the fact that the destruction of multilamellar vesicles by ultrasonication did not change the beta values. These results strongly suggest that the inner and outer monolayers of DDAB multilamellar vesicles are characterized by similar beta values. The second system, cetyltrimethylammonium bromide (CTAB)/DDAB mixtures, showed composition-dependent transitions depending on the mole fraction of DDAB X(DDAB): spherical micelles (0rodlike micelles (0.2vesicles (0.6相似文献   

IGC studies of binary cationic surfactant mixtures

Inverse gas chromatography (IGC) has been used to measure the interaction parameter between two twin-tailed cationic surfactants. Didodecyldimethylammonium (DDAB) and dioctadecyldimethylammonium (DODAB) bromides and their mixtures were used as stationary phases. IGC and DSC techniques have been used for the determination of the temperature zone of working. The activity coefficients at infinite dilution (on a mole fraction basis) were calculated for eleven probe solutes on each pure surfactant column. Values of interaction parameter between surfactants obtained at four weight fractions of the mixtures and at five temperatures are positive and suggested that the interactions is more unfavourable with the increment of DODAB concentration in the mixture. The results are interpreted on the basis of partial miscibility between DDAB and DODAB.     

Direct energy transfer from conjugated polymer to DNA intercalated dye: label-free fluorescent DNA detection

The development of methods for DNA detection is of importance in disease diagnosis, gene-targeted drug discovery and molecular biology field. In this paper, we synthesize a new cationic water-soluble CP containing fluorene moiety and flexible ethylenic moiety in the backbone (PFV) for label-free DNA detection. The conformational freedom of PFV provides stronger interactions with double-stranded DNA (dsDNA) and optimizes the orientation of transition moments between PFV and ethidium bromide (EB) intercalated in dsDNA. The efficient FRET from PFV (donor) to EB (acceptor) intercalated in dsDNA is observed and the emission of EB is amplified by the good light-harvesting ability of conjugated polymers. The interactions between PFV and DNA can also be probed by measuring the FRET ratio between PFV and EB intercalated in DNA. In comparison to other DNA detection assays based on FRET and conjugated polymers, synthesis of dye-labeled DNA probe is avoided in our method, which significantly reduces the cost and the synthetic complexity. The PFV/dsDNA/EB system provides promising applications on DNA detection with a simply, fast and label-free manner.     

Complexation of DNA with cationic surfactants as studied by small-angle X-ray scattering

The phase behaviors of the complex formed by didodecyldimethylammonium bromide(DDAB)and cetyltrimethylammonium bromide(CTAB)interacting with three different types of DNAs,salmon testes DNA(~2000 bp),21-bp double-stranded oligonucleotides(oligo-ds DNA),and 21-nt single-stranded oligonucleotides(oligo-ss DNA)were studied by synchrotron small-angle X-ray scattering.It was found that the DNA length and flexibility,together with the positive/negative charge ratio,determined the final structure.At higher charge ratios,the DNA length exhibited negligible effect.Both oligo-ds DNA and salmon DNA formed inverted hexagonal packing of cylinders with CTAB,as well as bilayered lamella with DDAB.However,at lower charge ratios,oligo-ds DNA formed a distorted hexagonal phase with CTAB and a new structure with DDAB,which was different from the behaviors of salmon DNA.The flexible oligo-ss DNA formed rich structures that were subject to environmental disturbance.Kinetic study also indicated that the structures of the complex formed by oligo-ss DNA took much longer to mature than the structures formed by oligo-ds DNA.We attributed this result to the conformational adjustment of oligo-ss DNA in the complex.     

Interaction of cationic lipid vesicles with model cell membranes--as determined by neutron reflectivity

Transfection of cells by DNA (for the purposes of gene therapy) can be effectively engineered through the use of cationic lipid/DNA "lipoplexes", although the transfection efficiency of these lipoplexes is sensitive to the neutral "helper" lipid included. Here, neutron reflectivity has been used to investigate the role of the helper lipid present during the interaction of cationic lipid vesicles with model cell membranes. Dimethyldioctadecylammonium bromide (DDAB) vesicles were formed with two different helper lipids, 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) and cholesterol, and the interaction of these vesicles with a supported phospholipid bilayer was determined. DOPE-containing vesicles were found to interact faster with the membrane than those containing cholesterol, and vesicles containing either of the neutral helper lipids were found to interact faster than when DDAB alone was present. The interaction between the vesicles and the membrane was characterized by an exchange of lipid between the membrane and the lipid aggregates in solution; the deposition of vesicle bilayers on the surface of the membrane was not apparent.     

Characterization and Aggregation Behaviors of Mixed DDAB/SDS Solution With and Without Poly(4-styrenesulfonic Acid-Co-Maleic Acid) Sodium

Synthetic vesicles are formed by cationic and anionic surfactants, didodecyldimethylammonium bromide (DDAB), and sodium dodecylsulfate (SDS). The morphology, size, and aqueous properties of cationic/anionic mixtures are investigated at various molar ratios between cationic and anionic surfactants. The charged vesicular dispersions made of DDAB/SDS are contacted or mixed with negatively charged polyelectrolyte, poly(4-styrenesulfonic acid-co-maleic acid) sodium (PSSAMA), to form complexes. Depending on DDAB/SDS molar ratio or PSSAMA/vesicle charge ratio, complexes flocculation or precipitation occur. Characterization of the cationic/anionic vesicles or complexes formed by the catanionic vesicles and polyelectrolytes is performed by transmission electron microscope (TEM), dynamic light scattering (DLS), conductivity, turbidity, and zeta potential measurements. The size, stability, and the surface charge on the mixed cationic/anionic vesicles or complexes are determined.     

Binding Mode Multiplicity and Multiscale Chirality in the Supramolecular Assembly of DNA and a π-Conjugated Polymer

Water-soluble π-conjugated polymers are increasingly considered for DNA biosensing. However, the conformational rearrangement, supramolecular organization and dynamics upon interaction with DNA have been overlooked, which prevents the rational design of such detection tools. To elucidate the binding of a cationic polythiophene (CPT) to DNA with atomistic resolution, we performed molecular simulations of their supramolecular assembly. Comparison of replicated simulations show a multiplicity of CPT binding geometries that contribute to the wrapping of CPT around DNA. The different binding geometries are stabilized by both electrostatic interactions between CPT lateral cations and DNA phosphodiesters and van der Waals interactions between the CPT backbone and the DNA grooves. Simulated circular dichroism (CD) spectra show that the induced CD signal stems from a conserved geometrical feature across the replicated simulations, i. e. the presence of segments of syn configurations between thiophene units along the CPT chain. At the macromolecular scale, we inspected the different shapes related to the CPT binding modes around the DNA through symmetry metrics. Altogether, molecular dynamics (MD) simulations, model Hamiltonian calculations of the CD spectra, and symmetry indices provide insights into the origin of induced chirality from the atomic to the macromolecular scale. Our multidisciplinary approach points out the hierarchical aspect of CPT chiral organization induced by DNA.     

Quadruplex-to-duplex transition of G-rich oligonucleotides probed by cationic water-soluble conjugated polyelectrolytes

G-quartet DNA converts to duplex form in the presence of its complementary strand. This conformational change can be detected in real time by a homogeneous assay method based on the signal amplification of conjugated polyelectrolytes and the specific interaction of intercalating dyes with double-stranded DNA (dsDNA). The probe solution contains a cationic, conjugated polymer (CCP), G-quadruplex labeled with a fluorescein at the 5'-terminus (G-quadruplex-Fl), and ethidium bromide (EB). The addition of a complementary target results in the transition from G-quadruplex to duplex (dsDNA-Fl) and EB intercalation within the duplex structure. Excitation of the CCP leads to energy transfer from CCP to dsDNA-Fl (FRET-1) and then energy transfer from dsDNA-Fl to EB (FRET-2). Increasing the number of mismatched bases discourages dsDNA formation, which is detected in the assay.     

Conductivity of water-in-oil microemulsions stabilized by mixed surfactants

The electrical conductivity of D2O-in-n-heptane microemulsions stabilized by cationic/nonionic surfactant mixtures was studied as a function of D2O content, surfactant concentration, and surfactant mixture composition. The surfactants employed were cationic di-n-didodecyldimethylammonium bromide, DDAB, nonionic poly(oxyethylene) monododecyl ethers, C12EJ, with J=3-8 and 23, nonionic polymeric surfactants of the type PEO-PPO-PEO (Pluronic), and the reverse structure analogues (Pluronic R). Qualitative structural information was drawn from a comparison between the measured conductivity and that predicted by the charge fluctuation model for spherical droplets. The conductivity versus water content curves were found to be typical for water-in-oil systems composed of spherical droplets. From the effect of blending nonionic surfactant with DDAB on the measured conductivities, it was concluded that microemulsion conductivity is independent of the concentration of cationic surfactant (DDAB). This finding agrees well with theoretical microemulsion conductivity models.     

The analysis of serum effects on structure,size and toxicity of DDAB–DOPE and DC-Chol–DOPE lipoplexes contributes to explain their different transfection efficiency

The effect of serum on structural properties of dimethyl-dioctadecyl-ammonium bromide (DDAB)–1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) liposomes and DDAB–DOPE/DNA lipoplexes has been investigated by energy dispersive X-ray diffraction (EDXD) technique, at different cationic lipid/DNA weight ratios (ρ). The role of serum on the size of lipoplexes has also been studied by dynamic light scattering. Lipoplex transfection efficiency (TE) as a function of ρ, and lipoplex toxicity to C6 rat glioma cells have been evaluated in Dulbecco's Modified Eagle Medium (DMEM) with and without serum. A multi-parametric analysis concerning the role of size, structure and cytotoxicity on transfection efficiency contributes to explain the experimental observation that 3β-[N-(N′,N′-dimethylaminoethane)carbamoyl]-cholesterol (DC-Chol)–DOPE/DNA transfect C6 cells better than DDAB–DOPE/DNA lipoplexes.     

Binding Gibbs energy of ionic liquids to calf thymus DNA: a fluorescence spectroscopy study

The binding constants and binding Gibbs energies of [C(n)mim]Br (n = 4, 6, 8, 10, 12) and [C(4)mim][BF(4)] to calf thymus DNA-D1501 have been determined by the fluorescence measurements of the pyrene probe. It was found that values of the binding Gibbs energy decrease linearly with the increase of alkyl chain length of the ILs. Based on this observation, Gibbs energies for both the interaction between DNA and -CH(2)- of the ILs and the interaction between DNA and the cationic head group of the ILs have been reported. The result suggests that electrostatic interaction between DNA and the cationic head group of the ILs is predominant for the binding of the ILs with DNA although contribution from the non-electrostatic interaction between DNA and the alkyl chain of the ILs increases with increasing alkyl chain length of the ILs. The information obtained here may have application in the design of novel ILs-based DNA extraction/separation systems.