Search

The low solubility of α-tocopherol in water and its susceptibility to photodegradation make it difficult for biological systems to absorb this natural antioxidant. To overcome these limitations, α-tocopherol was encapsulated in low-toxicity nanocontainers, namely, niosomes based on Tween 80 and cholesterol. The niosomes were modified with cationic surfactants containing a carbamate fragment. The size and charge of the particles were determined and their stability was assessed using dynamic and electrophoretic light scattering methods. It was found that the introduction of cationic surfactants to niosome formulations significantly improved their physicochemical properties and increased stability due to a positive charge of up to +40 mV being generated. Modified niosomes loaded with α-tocopherol were characterized by a hydrodynamic diameter of 100-120 nm, a narrow particle size distribution, and a high encapsulation efficiency of more than 90%. Testing the photochemical stability of α-tocopherol using a spectrophotometric method demonstrated that niosomes were able to protect this substance from UV irradiation. Luminescence analysis showed that the inclusion of α-tocopherol in niosomes increased their antioxidant activity by 30%. An acute toxicity study has demonstrated the safety of the systems. The LD 50 value for niosomes modified with carbamate-containing surfactants and loaded with α-tocopherol exceeded 10,000 mg·kg -1 (mice, intraperitoneal and oral administration).

This manuscript describes the synthesis, self-assembly, and antibacterial properties of naphthalene-diimide (NDI)-derived cationic π-amphiphiles. Three such asymmetric NDI derivatives with a nonionic hydrophilic wedge and a guanidine group in the two opposite sides of the NDI chromophore were considered. They differ by a single functional group (hydrazide, amide, and ester for NDI-1, NDI-2, and NDI-3, respectively), located in the linker between the NDI and the hydrophilic wedge. For NDI-1, the H-bonding among the hydrazides regulated unilateral stacking and a preferential direction of curvature of the resulting supramolecular polymer, producing an unsymmetric polymersome with the guanidinium groups displayed at the outer surface. NDI-3, lacking any H-bonding group, exhibits π-stacking without any preferential orientation and generates spherical particles with a relatively poor display of the guanidium groups. In sharp contrast to NDI-1, NDI-2 exhibits an entangled one-dimensional (1D) fibrillar morphology, indicating the prominent role of the H-bonding motif of the amide group and flexibility of the linker. The antibacterial activity of these assemblies was probed against Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative). NDI-1 showed the most promising antibacterial activity with a minimum inhibitory concentration (MIC) of ∼7.8 μg/mL against S. aureus and moderate activity (MIC ∼ 125 μg/mL) against E. coli . In sharp contrast, NDI-3 did not show any significant activity against the bacteria, suggesting a strong impact of the H-bonding-regulated directional assembly. NDI-2, forming a fibrillar network, showed moderate activity against S. aureus and negligible activity against E. coli , highlighting a significant impact of the morphology. All of these three molecules were found to be compatible with mammalian cells from the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) and hemolysis assay. The mechanistic investigation by membrane polarization assay, live/dead fluorescence assay, and microscopy studies confirmed the membrane disruption mechanism of cell killing for the lead candidate NDI-1.

Zwitterionic polymers are an emerging family of effective, low-fouling materials that can withstand unintended interactions with biological systems while exhibiting enhanced activity in bacterial matrix deterioration and biofilm eradication. Herein, we modularly synthesized an amphiphilic block copolymer, ZABCP , featuring potential bacteriostatic properties composed of a charge-switchable polyzwitterionic segment and a redox-sensitive pendant disulfide-labeled polymethacrylate block. The leucine-appended polyzwitterionic segment with alternatively positioned cationic amine and anionic carboxylate functionalities undergoes charge alterations (+ve → 0 → -ve) on pH variation. By introducing appropriate amphiphilicity, ZABCP forms distinct vesicles with redox-sensitive bilayer membranes and zwitterionic shielding coronas, enabling switching of surface charge. ZABCP vesicles exhibit 180 ± 20 nm hydrodynamic diameter, and its charge switching behavior in response to pH was confirmed by the change of zeta potential value from -23 to +36 mV. The binding interaction between ZABCP vesicles with lysozyme and pepsin proteins strengthens when the surface charge shifts from neutral (pH 7.4) to either anionic or cationic. This surface-charge-switchable phenomenon paves the way for implementing cationic ZABCP vesicles for bacterial cell growth inhibition, which is shown by the pronounced transition of cellular morphology, including clustering, aggregation, or elongation as well as membrane disruption for both Bacillus subtilis (Gram-positive) and Escherichia coli (Gram-negative). Such enhanced bacteriostatic activity could be ascribed to a strong electrostatic interaction between cationic vesicles and negatively charged bacterial membranes, leading to cell membrane disruption. Overall, this study provides a tailor-made approach to adopt low-fouling properties and potential bacteriostatic activity using zwitterionic polymers through precise control of pH.

Cation-π interaction is one of the most important noncovalent interactions identified in biosystems, which has been proven to play an essential role in the strong adhesion of marine mussels. In addition to the well-known catecholic amino acid, l-3,4-dihydroxyphenylalanine, mussel foot proteins are rich in various aromatic moieties (e.g., tyrosine, phenylalanine, and tryptophan) and cationic residues (e.g., lysine, arginine, and histidine), which favor a series of short-range cation-π interactions with adjustable strengths, serving as a prototype for the development of high-performance underwater adhesives. This work highlights our recent advances in understanding and utilizing cation-π interactions in underwater adhesives, focusing on three aspects: (1) the investigation of the cation-π interaction mechanisms in mussel foot proteins via force-measuring techniques; (2) the modulation of cation-π interactions in mussel mimetic polymers with the variation of cations, anions, and aromatic groups; (3) the design of wet adhesives based on these revealed principles, leading to functional materials in the form of films, coacervates, and hydrogels with biomedical and engineering applications. This review provides valuable insights into the development and optimization of smart materials based on cation-π interactions.

Stabilizing biomolecules under ambient conditions can be extremely beneficial for various biological applications. In this context, the utilization of ionic liquids (ILs) in enhancing the stability and preservation of nucleic acids in aqueous solutions is found to be promising. While the role of the cationic moiety of ILs in the said event has been thoroughly explored, the importance of the anionic moiety in ILs, if any, is rather poorly understood. Herein, we examine the function of anions of ILs in nucleic acid stabilization by examining the stability and structure of calf thymus-DNA ( ct -DNA) in the presence of various ILs composed of a common 1-ethyl-3-methylimidazolium cations (Emim + ) and different anions, which includes Cl - , Br - , NO 3 - , Ac - , HS O 4 - and B F 4 - by employing various spectroscopic techniques as well as Molecular Dynamics (MD) simulation studies. Analysis of our data suggests that the chemical nature of anions including polarity, basicity, and hydrophilicity become an important factor in the overall DNA-IL interaction event. At lower concentrations, the interplay of intermolecular interaction between the IL anions with their respective cations and the solvent molecules becomes a very crucial factor in inducing their stabilizing effect on ct -DNA. However, at higher concentrations of ILs, the ct- DNA stabilization is additionally governed by specific-ion effect. MD simulation studies have also provided valuable insights into molecular-level understanding of the DNA-IL interaction event. Overall, the present study clearly demonstrated that along with the cationic moiety of ILs, the anions of ILs can play a significant role in deciding the stability of duplex DNA in aqueous solution. The findings of this study are expected to enhance our knowledge on understanding of IL-DNA interactions in a better manner and will be helpful in designing optimized IL systems for nucleic acid based applications.

Proteins, in the presence of trivalent cations, exhibit intriguing phase behavior which is contrasting compared to mono- and divalent cations. At room temperature (RT), trivalent cations induce microscopic liquid-liquid phase separation (LLPS) in which a protein-rich phase coexists with a dilute phase. The critical solution temperature related phenomena in these complex fluids are well studied; however, such studies have mostly been restricted below the denaturation temperature ( T M ) of the protein(s) involved. Here, we probe the phase behavior of bovine serum albumin (BSA) incubated at 70 °C (> T M ) in the presence of Na + , Mg 2+ , La 3+ , Y 3+ , and Ho 3+ ions. BSA in the presence of mono- and bivalent ions forms an intense gel phase at 70 °C; however, the trivalent salts offer remarkable thermal resistivity and retain the fluid LLPS phase. We determine the microscopic phase behavior using differential interference contrast optical microscopy, which shows that the LLPS droplet structures in the M 3+ ion-containing protein solutions prevail upon heating, whereas Mg 2+ forms composed cross-linking gelation upon thermal incubation. We probe the interior environment of the protein aggregates by ps-resolved fluorescence anisotropy measurements using 8-anilino-1-naphthalenesulfonic acid (ANS) as an extrinsic fluorophore. It reveals that while the LLPS phase retains the rotational time constants upon heating, in the case of gelation, the immediate environment of ANS gets significantly perturbed. We investigate the explicit protein hydration at RT as well as at T > T M using the ATR THz-FTIR (1.5-22.5 THz) spectroscopy technique and found that hydration shows strong ion specificity and correlates the phase transition behavior.

A catanionic surfactant system is an aqueous solution or dispersion of cationic and anionic surfactants that spontaneously self-assemble into structures such as micelles, vesicles, and coacervates. Their structural diversity varies depending on the ratios of cationic and anionic surfactants (compositions), the chemical structure of the constituent molecules, etc. Herein, two types of catanionic surfactant systems were systematically characterized: (i) cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), both typical ionic surfactants; and (ii) dodecylmethylimidazolium ammonium bromide ([C 12 mim]Br) and SDS, where the former is an ionic liquid. By observing the sample appearance, turbidity, and particle size, the phase state of each system was analyzed according to the total concentration of surfactants and the molar ratio of cationic surfactants to the total concentration. Especially, for specific compositions of catanionic surfactant vesicles (cataniosome), the closed structure of the vesicles was confirmed through calcein entrapment and release detected with a fluorescence assay. The polarities of the interface of the prepared self-assemblies were evaluated using a fluorescence probe, Laurdan. The packing state of the molecules in the formed self-assembly structure was estimated using Raman spectroscopy. The results clearly indicate consistent phase-transition behavior for the CTAB-SDS (i) and [C 12 mim]Br-SDS (ii) systems, depending on the total surfactant concentration and composition, while the membrane properties of the two systems differed. The cataniosome formed in the CTAB-SDS system was in a tightly packed membrane state and more hydrophobic than that formed in the [C 12 mim]Br-SDS system owing to the difference in the structure of the constituting molecule: [C 12 mim]Br has a larger head group and shorter acyl chain than CTAB. The self-assembly properties evaluated in this study were compared with those of typical lipid membranes, liposomes (lipid vesicles), to determine a possible application of the catanionic systems with various self-assembly formulations.

Cholesterol is a major component of many lipid-based drug delivery systems, including cationic lipid nanoparticles. Despite its critical role in the drug release stage, the underlying molecular mechanism by which cholesterol assists in endosomal escape remains unclear. An efficient drug release from the endosome requires endosomal disruption. This disruption is believed to involve a lamellar-to-inverted hexagonal (L α -H II ) phase transition upon fusion of the lipid nanoparticle with the endosomal membrane. We used molecular dynamics simulations to study the structural properties of H II systems composed of an anionic lipid distearoyl phosphatidylserine (DSPS), an ionizable cationic lipid (KC2H), and cholesterol for several hydration levels and molar ratios. This system corresponds to the lipid mixtures in the hypothesized H II structure formed upon fusion and is of interest for the rational design of ionizable cationic lipids, including KC2, for an optimal drug release. Simulations suggest a geometry- and symmetry-driven lipid sorting and cholesterol-DSPS co-location around the water cores. Cholesterol preferentially co-locates with negatively charged saturated DSPS lipids at interstitial angles. The observed cholesterol-DSPS co-location results in an overall increase in the DSPS acyl chains' order parameters, which we propose to assist in stabilizing the H II phase by stretching the DSPS acyl chains for filling the voids formed by three adjacent lipid tubules. Furthermore, a systematic increase in the cholesterol concentration increased the lattice plane spacing and the water core radius but decreased the undulations along the lipid tubule axis. We propose that cholesterol and the degree of saturation/polyunsaturation of the lipid acyl chains, and not the lipid charge, are the main contributors in facilitating the L α -H II phase transition and stabilizing/destabilizing the formed H II phase, whereas the positive charge of the ionizable cationic lipid promotes the LNP-endosomal membrane adhesion and assists in initiating the fusion process at the local contact area. We also propose that the effect of cholesterol on the H II structure and curvature is the main underlying reason for the well-documented H II stabilization and destabilization at low and high molar concentrations of cholesterol, respectively.

In this study, sodium carboxymethyl cellulose/poly(acrylic acid) (CMC/PAA) microgels were successfully synthesized via visible-light-triggered free-radical polymerization to remove methylene blue (MB) from water. The microgels had a loose and porous 3-D network structure, exhibiting excellent adsorption performance. The equilibrium adsorption capacity and the removal efficiency of the microgels reached approximately 1479 mg/g and 97%, respectively, when the initial concentration of MB was 300 mg/L. The adsorption kinetics was well described by the pseudo-second-order model, and the adsorption isotherms followed the Langmuir isothermal model. Notably, CMC/PAA microgels could naturally settle and be separated from the MB solution. Furthermore, the recovery efficiency of the regenerated CMC/PAA microgels reached approximately 94% after five adsorption-desorption cycles. Therefore, the microgels could be used as promising adsorbents due to the advantages of high adsorption capacity, fast removal rate, and reusability.

Carbon-based matter, such as biomolecules and graphitic structures, often form a liquid-solid/soft matter interface in salt solution and continuously affect the surrounding cations through hydrated cation-π interactions. In this Perspective, we revisit the effect of the hydrated cation-π interactions at the interface using statistical physics, which reveals how hydrated cation-π interactions affect every component dynamically and cause a time-dependent statistical effect at the liquid-solid/soft interface. We also highlight several pieces of experimental evidence from a statistical perspective and discuss the remarkable applications related to environmental protection, industrial manufacturing, and biological sciences.

Cationic polymeric micelles that are capable of co-releasing drugs and DNA into cells have attracted considerable interest as combination chemotherapy in cancer treatment. To this effect, we have presently developed a cationic fluorescent amphiphilic copolymer, poly( N , N '-dimethylaminoethylmethacrylate)- b -(poly(2-(methacryloyl)oxyethyl-2'-hydroxyethyl disulfidecholate)- r -2-(methacryloyloxy)ethyl-1-pyrenebutyrate) [PDMAEMA- b -(PMAODCA- r -PPBA)], having pendent cholate moiety linked through a redox-responsive disulfide bond. The amphiphilic nature of the copolymer facilitated the formation of cationic micellar nanoparticles in aqueous medium. The self-assembly of the copolymer to form micelles and subsequent destabilization of the micelles in the presence of glutathione (GSH) was monitored by the change in the fluorescence characteristic of the attached pyrene resulting from alteration in the hydrophobicity of its neighborhood. These micellar nanoparticles were subsequently utilized in encapsulating hydrophobic anticancer drug, doxorubicin (DOX), in the core of the micelles, whereas the cationic shell of the micelles was used for complexation with oppositely charged DNA to form micelleplexes. Gel retardation assays, ethidium bromide (EB) exclusion assay, and DLS and AFM studies confirmed the successful binding of the cationic micelles with DNA. The binding capability of the micelles was higher than corresponding cationic linear PDMAEMA. The kinetics of the simultaneous release of encapsulated DOX and complexed DNA in the presence of glutathione was thoroughly studied using various techniques. All the experiments showed fast and efficient release of DOX and DNA from DOX-loaded micelleplexes. The study implies that these redox-responsive cationic micelles may open up new opportunities toward co-delivery of DNA and anticancer drugs in combinatorial therapy.

The properties of proteins at interfaces are important to many processes as well as in soft matter materials such as aqueous foam. Particularly, the protein interfacial behavior is strongly linked to different factors like the solution pH or the presence of electrolytes. Here, the nature of the electrolyte ions can significantly modify the interfacial properties of proteins. Therefore, molecular level studies on interfacial structures and charging states are needed. In this work, we addressed the effects of Y 3+ and Nd 3+ cations on the adsorption of the whey protein β-lactoglobulin (BLG) at air-water interfaces as the function of electrolyte concentration. Both cations caused very similar but dramatic changes at the interface and in the bulk solution. Here, measurements of the electrophoretic mobility and with vibrational sum-frequency generation (SFG) spectroscopy were applied and consistently showed a reversal of the BLG net charge at remarkably low ion concentrations of 30 (bulk) and 40 (interface) μM of Y 3+ or Nd 3+ for a BLG concentration of 15 μM. SFG spectra of carboxylate stretching vibrations from Asp or Glu residues of interfacial BLG showed significant changes in the resonance frequency, which we associate to specific and efficient binding of Y 3+ or Nd 3+ ions to the proteins carboxylate groups. Characteristic reentrant condensation for BLG moieties with bound trivalent ions was found in a broad concentration range around the point of zero net charge. The highest colloidal stability of BLG was found for ion concentrations <20 μM and >50 μM. Investigations on macroscopic foams from BLG solutions revealed the existence of structure-property relations between the interfacial charging state and the foam stability. In fact, a minimum in foam stability at 20 μM ion concentration was found when the interfacial net charge was negligible. At this concentration, we propose that the persistent BLG molecules and weakly charged BLG aggregates drive foam stability, while outside the bulk reentrant zone the electrostatic disjoining pressure inside foam lamellae dominates foam stability. Our results provide new information on the charge reversal at the liquid-gas interface of protein/ion dispersions. Therefore, we see our findings as an important step in the clarification of reentrant condensation effects at interfaces and their relevance to foam stability.

Drug delivery in cationic liposomes seems to be a promising therapeutic approach in cancer treatment. The rational design of the positively charged lipid vesicles as anticancer drug carriers should be supported by a detailed analysis of the interactions of the carrier components with anticancer drugs. In the present work, 2-hydroxyoleic acid (2OHOA; Minerval), a membrane lipid therapy drug, was incorporated into positively charged mono- and bilayer membranes containing 1-palmitoyl-2-oleoyl- sn-glycero-3-ethylphosphocholine (EPOPC), the synthetic cationic lipid, and 1,2-dioleoyl- sn-glycero-3-phosphocholine (DOPC). The intermolecular interactions, fluidity, and miscibility of the studied monolayers were analyzed by utilizing Langmuir balance experiments. The morphology of two-dimensional films was inspected using a Brewster angle microscopy technique. The properties of the liposomes were investigated by dynamic light scattering (DLS) and zeta potential measurements, steady-state fluorescence anisotropy experiments, and the spectrofluorimetric titration of calcein-encapsulated vesicles with a lysis-inducing agent. According to the collected results, 2OHOA intercalation into films of pure phospholipids or a binary EPOPC/DOPC film is thermodynamically favorable. Surprisingly, no significant effect of the presence of unsaturated 2OHOA chains on the EPOPC/DOPC monolayer order was observed. The experiments carried out for 2OHOA-inserted cationic EPOPC/DOPC (1:4) liposomes indicate effective incorporation of the drug into the liposome bilayer and the formation of stable vesicles without affecting their properties markedly. On the basis of the obtained results, EPOPC/DOPC/2OHOA cationic liposomes with 15% 2OHOA content in the phospholipid bilayer seem to be the most suitable for potential biomedical applications.

Small-molecule cationic amphiphiles (CAms) were designed to combat the rapid rise in drug-resistant bacteria. CAms were designed to target and compromise the structural integrity of bacteria membranes, leading to cell rupture and death. Discrete structural features of CAms were varied, and structure-activity relationship studies were performed to guide the rational design of potent antimicrobials with desirable selectivity and cytocompatibility profiles. In particular, the effects of cationic conformational flexibility, hydrophobic domain flexibility, and hydrophobic domain architecture were evaluated. Their influence on antimicrobial efficacy in Gram-positive and Gram-negative bacteria was determined, and their safety profiles were established by assessing their impact on mammalian cells. All CAms have a potent activity against bacteria, and hydrophobic domain rigidity and branched architecture contribute to specificity. The insights gained from this project will aid in the optimization of CAm structures.

The maintenance of cell membrane fluidity is of critical importance for various cellular functions. At lower temperatures when membrane fluidity decreases, plants and cyanobacteria react by introducing unsaturation in the lipids, so that the membranes return to a more fluidic state. To probe how introduction of unsaturation leads to reduced membrane fluidity, a model cationic lipid dioctadecyldimethylammonium bromide (DODAB) has been chosen, and the effects of an unsaturated lipid monoolein (MO) on the structural dynamics and phase behavior of DODAB have been monitored by quasielastic neutron scattering and time-resolved fluorescence measurements. In the coagel phase, fluidity of the lipid bilayer increases significantly in the presence of MO relative to pure DODAB vesicles and becomes manifest in significantly enhanced dynamics of the constituent lipids along with faster hydration and orientational relaxation dynamics of a fluorophore. On the contrary, MO restricts both lateral and internal motions of the lipid molecules in the fluid phase (>330 K), which is consistent with relatively slow hydration and orientational relaxation dynamics of the fluorophore embedded in the mixed lipid bilayer. The present study illustrates how incorporation of an unsaturated lipid at lower temperatures (below the phase transition) assists the model lipid (DODAB) in regulating fluidity via enhancement of dynamics of the constituent lipids.

A series of anionic, zwitterionic, and cationic lysine-based block copolymers with a thermoresponsive segment were synthesized by the reversible addition-fragmentation chain transfer (RAFT) polymerization of N-acryloyl- N-carbobenzoxy-l-lysine [A-Lys(Cbz)-OH], which contains a carboxylic acid and a protected amine-functionality in the monomer unit. Carboxylic acid-containing homopolymers, poly(A-Lys(Cbz)-OH), with predetermined molecular weights with relatively low polydispersities were initially synthesized by RAFT polymerization of A-Lys(Cbz)-OH. The chain extension of the dithiocarbamate-terminated poly(A-Lys(Cbz)-OH) to N-isopropylacrylamide (NIPAM) via the RAFT process and subsequent deprotection afforded the zwitterionic block copolymer composed of thermoresponsive poly(NIPAM) and poly(A-Lys-OH), which exhibited switchability among the zwitterionic, anionic, and cationic states by pH change. The assembled structures and thermoresponsive and chiroptical properties of these block copolymers were evaluated by dynamic light scattering, circular dichroism, and turbidity measurements. Finally, the cationic block copolymer, poly(A-Lys-OMe)- b-poly(NIPAM), was obtained by the methylation of the carboxylic acid group in the zwitterionic poly(A-Lys-OH) segment. Selective interactions of DNA with the cationic poly(A-Lys-OMe) segment in the lysine-based block copolymer were further evaluated by agarose gel electrophoresis and atomic force microscopy measurements, which revealed characteristic assembled structures and temperature-responsive properties of the polyplexes.

In continuation of previous work, we present a new promising DNA carrier, OO4, a highly effective peptide-mimicking lysine-based cationic lipid. The structural characteristics of the polynucleotide carrier system OO4 mixed with the commonly used co-lipid DOPE and the saturated phospholipid DPPE have been studied in two-dimensional and three-dimensional model systems to understand their influence on the physical-chemical properties. The phase behavior of pure OO4 and its mixtures with DOPE and DPPE was studied at the air-water interface using a Langmuir film balance combined with infrared reflection-absorption spectroscopy. In bulk, the self-assembling structures in the presence and absence of DNA were determined by small-angle and wide-angle X-ray scattering. The amount of adsorbed DNA to cationic lipid bilayers was measured using a quartz crystal microbalance. The choice of the co-lipid has an enormous influence on the structure and capability of binding DNA. DOPE promotes the formation of nonlamellar lipoplexes (cubic and hexagonal structures), whereas DPPE promotes the formation of lamellar lipoplexes. The correlation of the observed structures with the transfection efficiency and serum stability indicates that OO4/DOPE 1:3 lipoplexes with a DNA-containing cubic phase encapsulated in multilamellar structures seem to be most promising.

We investigated the interaction of bulk nanobubbles with cationic liposomes composed of 1,2-dioleoyl- sn-glycero-3-ethylphosphocholine and anionic liposomes assembled from 1-palmitoyl-2-oleoyl- sn-glycero-3-phospho-(1'- rac-glycerol). We employed dynamic light scattering and fluorescence microscopy to investigate both the hydrodynamic and electrophoretic properties of the nanobubble/liposome complexes. These optical techniques permit direct visualization of structural changes as a function of the bubble/liposome ratio. We observed reentrant condensation with cationic liposomes and gas nucleation with anionic liposomes. This is the first report of charge inversion and reentrant condensation of cationic liposomes induced by bulk nanobubbles.

Design of novel and more efficient antibacterial agents is a continuous and dynamic process due to the appearance of new pathogenic strains and inherent resistance development to existing antimicrobial treatments. Metallic nanoparticles (NPs) are highly investigated, yet the role of released ions is crucial in the antibacterial activity of the NP-based systems. We developed herein ion-based, metal/graphene hybrid structures comprising surface-bound Ag and Cu mono-ionic and Ag/Cu bi-ionic species on functionalized graphene, without involvement of NPs. The antibacterial performance of the resulting systems was evaluated against Escherichia coli cells using a series of parametrization experiments of varying metal ion types and concentrations and compared with that of the respective NP-based systems. It was found that the bi-ionic Ag/Cu-graphene materials exhibited superior performance compared to that of the mono-ionic analogues owing to the synergistic action of the combination of the two different metal ions on the surface and the enhancing role of the graphene support, whereas all ion-based systems performed superiorly compared to their NP-based counterparts of the same metal type and concentration. In addition, the materials exhibited sustained action, as their activity was maintained after reuse in repeated cycles employing fresh bacteria in each cycle. The systems developed herein may open new prospects toward the development of novel, efficient, and tunable antibacterial agents by properly supporting and configuring metals in ionic form.

Cationic lipids have attracted much attention because of their potential for biomedical applications, such as gene delivery. The gene transfection efficiency of cationic lipids is greatly influenced by the counterions as well as salt ions. We have systematically investigated the interaction of different monovalent sodium salts with positively charged membrane, composed of 1,2-dioleoyl- sn-glycero-3-phosphocholine (DOPC)/1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) and DOTAP, using dynamic light scattering, zeta potential, isothermal titration calorimetry (ITC), and fluorescence spectroscopy techniques. Our results reveal that the affinity of anions with cationic membranes follows the sequence I - ≫ Br - > Cl - according to descending order of their sizes and is consistent with the Hofmeister series. Interestingly, the electrostatic behavior of the DOTAP membrane in the presence of monovalent anions differs significantly from the DOPC/DOTAP membrane. This difference is due to the strong interplay between phosphocholine and trimethylammonium-propane (TAP) headgroups leading to the reorientation of the TAP group in the membrane. The binding constant of anions, derived from zeta potential and ITC is in agreement with the affinity of anions mentioned above. Among all anions, I - shows strongest affinity, as evidenced from the rapid increase in hydrodynamic radius which eventually leads to the formation of large aggregates. The fluorescence spectroscopy of a lypophilic probe Nile red in the presence of cationic vesicles containing ions complements the I - adsorption onto the membrane. Nonlinear Stern-Volmer plot, consisting of accessible and inaccessible Nile red to I - is consistent with the zeta potential as well as ITC results.

The emergence of antibiotic-resistant bacterial strains has fostered fundamental research to develop alternative antimicrobial strategies. Among the several systems proposed so far, the association complexes (nanoplexes) formed by transcription factor decoys (TFDs), i.e., short oligonucleotides targeting a crucial bacterial transcription factor, and a bolaform cationic amphiphile, 10,10'-(dodecane-1,12-diyl)-bis-(9-amino-1,2,3,4-tetrahydroacridinium) chloride (12-bis-THA), have demonstrated their potential in vitro and in vivo. The application of these nanoplexes is hampered by a scarce colloidal stability, which can be addressed by including the bolaamphiphile in a liposomal carrier, which is then associated to the TFD. The present study reports an investigation on the effects of 12-bis-THA on the structure of synthetic lipid bilayers to assess the morphology of the mixed assemblies, gain insight into the location of the host within the bilayer, and determine the loading capacity of the carrier. Our results demonstrate that 12-bis-THA promptly inserts within 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) bilayers, bending its C-12 spacer chain to adopt a conelike shape and shifting the gel-liquid crystalline transition of the chains to lower temperatures. The host liposomal structure is retained for a bolaamphiphile concentration of up to 3.2% mol to DPPC, whereas higher concentrations lead to the destabilization by means of a detergency-like mechanism, with the simultaneous existence of different lamellar-based structures, such as liposomes, bicelles, and rafts, in which DPPC and 12-bis-THA could be present in different molar ratios. Overall, these results shed light on the interaction of the bolaamphiphile with a lipid bilayer and provide valuable insight to better formulate the antimicrobial amphiphile in liposomal carriers to circumvent the colloidal instability of nanoplexes.

This work studied the interactions of an oppositely charged surfactant mixture of oleyl bis(2-hydroxyethyl)methyl ammonium bromide (OHAB) and sodium dodecyl sulfate (SDS) with 1,2-di-(9Z-octadecenoyl)-sn-glycero-3-phosphocholine (DOPC) vesicles as well as the penetration of the OHAB/SDS mixture through model skin, aimed at understanding the relationship between the ability of different surfactant aggregates in solubilizing phospholipid vesicles and their potential in irritating skin. By changing the molar fraction of OHAB (X OHAB ), five kinds of aggregates are constructed: OHAB and SDS separately form cationic and anionic small micelles, whereas the OHAB/SDS mixtures form cationic and anionic vesicles at X OHAB = 0.30 and 0.70, respectively, and weakly charged vesicles at X OHAB = 0.50. The mixtures have much lower critical micellar concentrations (CMCs) and much larger aggregates than either OHAB or SDS alone, and the CMC and the size of the OHAB/SDS vesicles decrease with the increase in X OHAB . The phase diagrams indicate that the OHAB/SDS mixtures show much stronger ability in solubilizing the DOPC vesicles than individual OHAB and SDS and decrease in the order of X OHAB = 0.30 > 0.50 > 0.70 ≫ 1.00 > 0. However, the ability of the surfactants in penetrating the model skin decreases reversely, and the penetration of the surfactants are significantly reduced by mixing. These results indicate that the surfactant mixture with a larger aggregate size and a smaller CMC value displays much stronger ability in solubilizing the DOPC vesicles but much weaker ability in penetrating the skin.

The effect of cations in the surrounding solutions on the surface degradation of magnesium alloys, a well-recognized biodegradable biomaterial, has been neglected compared with the effect of anions in the past. To better simulate the compressive environment where magnesium alloys are implanted into the body as a cardiovascular stent, a device is designed and employed in the test so that a pressure, equivalent to the vascular pressure, can be directly applied to the magnesium alloy implants when the alloys are immersed in a medium containing one of the cations (K(+), Na(+), Ca(2+), and Mg(2+)) found in blood plasma. The surface degradation behaviors of the magnesium alloys in the immersion test are then investigated using hydrogen evolution, mass loss determination, electron microscopy, pH value, and potentiodynamic measurements. The cations are found to promote the surface degradation of the magnesium alloys with the degree decreased in the order of K(+) > Na(+) > Ca(2+) > Mg(2+). The possible mechanism of the effects of the cations on the surface degradation is also discussed. This study will allow us to predict the surface degradation of magnesium alloys in the physiological environment and to promote the further development of magnesium alloys as biodegradable biomaterials.

The current study is aimed at investigating the effect of cationic charge density and hydrophobicity on the antibacterial and hemolytic activities. Two kinds of cationic surfmers, containing single or double hydrophobic tails (octyl chains or benzyl groups), and the corresponding homopolymers were synthesized. The antimicrobial activity of these candidate antibacterials was studied by microbial growth inhibition assays against Escherichia coli, and hemolysis activity was carried out using human red blood cells. It was interestingly found that the homopolymers were much more effective in antibacterial property than their corresponding monomers. Furthermore, the geminized homopolymers had significantly higher antibacterial activity than that of their counterparts but with single amphiphilic side chains in each repeated unit. Geminized homopolymers, with high positive charge density and moderate hydrophobicity (such as benzyl groups), combine both advantages of efficient antibacterial property and prominently high selectivity. To further explain the antibacterial performance of the novel polymer series, the molecular interaction mechanism is proposed according to experimental data which shows that these specimens are likely to kill microbes by disrupting bacterial membranes, leading them unlikely to induce resistance.

Cationic amphiphiles have received increasing attention as antimicrobials given their unique ability to disrupt bacteria cell membranes. While extensive research has demonstrated that amphiphiles' hydrophobic-to-charge ratio significantly modulates antibacterial activity, less work has focused on elucidating the specific impact of charge location on amphiphile bioactivity. In this study, two series of cationic amphiphiles, termed bola-like and gemini-like, were synthesized with analogous hydrophobic-to-charge ratios yet differing charge location, and their resulting antibacterial activity was assessed. Bola-like amphiphiles exhibited preferential activity against two Gram-positive bacteria, with activity increasing with increasing hydrophobicity, whereas gemini-like amphiphiles were active against both Gram-positive and Gram-negative bacteria, with activity decreasing with increasing hydrophobicity. After identifying lead compounds from each amphiphile series (bola- and gemini-like), biophysical experiments indicated that both amphiphiles were membrane-active; notably, the lead gemini-like amphiphile exhibited a strong dependence on electrostatic interactions for membrane interaction. In contrast, the lead bola-like amphiphile exhibited a reliance on both hydrophobic and electrostatic contributions. These results demonstrate that charge location significantly impacts cationic amphiphiles' antibacterial and membrane activity.

The polysaccharide hyaluronan (HA) is a main component of peri- and extracellular matrix, and an attractive molecule for materials design in tissue engineering and nanomedicine. Here, we study the morphology of complexes that form upon interaction of nanometer-sized amine-coated gold particles with this anionic, linear, and regular biopolymer in solution and grafted to a surface. We find that cationic nanoparticles (NPs) have profound effects on HA morphology on the molecular and supramolecular scale. Quartz crystal microbalance (QCM-D) shows that depending on their relative abundance, cationic NPs promote either strong compaction or swelling of films of surface-grafted HA polymers (HA brushes). Transmission electron and atomic force microscopy reveal that the NPs do also give rise to complexes of distinct morphologies-compact nanoscopic spheres and extended microscopic fibers-upon interaction with HA polymers in solution. In particular, stable and hydrated spherical complexes of single HA polymers with NPs can be prepared when balancing the ionizable groups on HA and NPs. The observed self-assembly phenomena could be useful for the design of drug delivery vehicles and a better understanding of the reorganization of HA-rich synthetic or biological matrices.

Despite long-standing efforts, there is no agreed upon structural model for electrolyte solutions at air-liquid interfaces. We report the simultaneous detection of the near-surface and bulk coordination environments of a trivalent metal cation (europium) in an aqueous solution by use of X-ray absorption spectroscopy. Within the first few nanometers of the liquid surface, the cations exhibit oxygen coordination typical of inner-sphere hydration of an aquated Eu(3+) cation. Beyond that, outer-sphere ion-ion correlations are observed that are otherwise not present in the bulk electrolyte. The combination of near-surface and bulk sensitivities to probe metal ion speciation in electrolyte solutions is achieved by detecting electron-yield and X-ray fluorescence signals from an inverted pendant drop. The results provide new knowledge about the near-surface chemistry of aqueous solutions of relevance to aerosols and ion transport processes in chemical separations and biological systems.

This work presents a study of the association between low molecular weight hyaluronic acid (16 kDa HA) and cationic liposomes composed of egg phosphatidylcholine (EPC), 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP). The cationic liposome/HA complexes were evaluated to determine their mesoscopic structure, average size, zeta potential, and morphology as a function of the amount of HA in the system. Small angle X-ray scattering results revealed that neighboring cationic liposomes either stick together after a partial coating of low concentration HA or disperse completely in excess of HA, but they never assemble as multilamellar vesicles. Cryo-transmission electron microscopy images confirm the existence of unilamellar vesicles and large aggregates of unilamellar vesicles for HA fractions up to 80% (w/w). High concentrations of HA (> 20% w/w) proved to be efficient for coating extruded liposomes, leading to particle complexes with sizes in the nanoscale range and a negative zeta potential.

A stable oil-in-water Pickering emulsion stabilized by negatively charged silica nanoparticles hydrophobized in situ with a trace amount of a conventional cationic surfactant can be rendered unstable on addition of an equimolar amount of an anionic surfactant. The emulsion can be subsequently restabilized by adding a similar trace amount of cationic surfactant along with rehomogenization. This destabilization-stabilization behavior can be cycled many times, demonstrating that the Pickering emulsion is switchable. The trigger is the stronger electrostatic interaction between the oppositely charged ionic surfactants compared with that between the cationic surfactant and the (initially) negatively charged particle surfaces. The cationic surfactant prefers to form ion pairs with the added anionic surfactant and thus desorbs from particle surfaces rendering them surface-inactive. This access to switchable Pickering emulsions is easier than those employing switchable surfactants, polymers, or surface-active particles, avoiding both the complicated synthesis and the stringent switching conditions.

Crystalline vaterite is the most thermodynamically unstable polymorph of anhydrous calcium carbonate (CaCO3), and various morphologies can be controlled in the presence of organic additives. Constructing vaterite with minimal defects, determining its distinctive properties, and understanding the formation mechanism behind a biomimetic process are the main challenges in this field. In this paper, a unique single-crystal-like vaterite hexagonal bifrustum with two hexagonal and 12 trapezoidal faces has been fabricated through a catanionic surfactant-assisted mineralization approach for the first time. Compared with the polycrystalline vaterite aggregates, these bifrustums clearly present a doublet for Raman v1 symmetric stretching mode, a low depolarizaiton ratio for carbonate molecular symmetry, and a high structural stability. These indicate a dominant position of hexagonal phase in each crystallite and confirm the Raman v1 doublet characteristics of synthetic and biomineral-based vaterites. Our finding may provide evidence to distinguish vaterite with different structures and shed light on a possible formation mechanism of vaterite single crystals.

The property of DNA is strongly influenced by counterions. Packing a dense layer of DNA onto a gold nanoparticle (AuNP) generates an interesting colloidal system with many novel physical properties such as a sharp melting transition, protection of DNA against nucleases, and enhanced complementary DNA binding affinity. In this work, the effect of monovalent cation size is studied. First, for free AuNPs without DNA, larger group 1A cations are more efficient in inducing their aggregation. The same trend is observed with group 2A metals using AuNPs capped by various self-assembled monolayers. After establishing the salt range to maintain AuNP stability, the DNA adsorption kinetics is also found to be faster with the larger Cs(+) compared to the smaller Li(+). This is attributed to the easier dehydration of Cs(+), and dehydrated Cs(+) might condense on the AuNP surface to reduce the electrostatic repulsion effectively. However, after a long incubation time with a high salt concentration, Li(+) allows ∼30% more DNA packing compared to Cs(+). Therefore, Li(+) is more effective in reducing the charge repulsion among DNA, and Cs(+) is more effective in screening the AuNP surface charge. This work suggests that physicochemical information at the bio/nanointerface can be obtained by using counterions as probes.

The specificity of carbohydrate-lectin interaction has been reported as an attractive strategy for drug delivery in cancer therapy because of the high levels of lectins in several human malignancies. A novel cationic glucosylated amphiphile was therefore synthesized, as a model system, to attribute specificity toward d-glucose receptors to liposome formulations. Fluorescence experiments demonstrated that the monomeric glucosylated amphiphile is capable of interacting with fluorescently labeled concanavalin A, a D-glucose specific plant lectin. The interaction of concanavalin A with liposomes composed of a phospholipid and the glucosylated amphiphile was demonstrated by agglutination observed by optical density and dynamic laser light scattering measurements, thus paving the way to the preparation of other glycosilated amphiphiles differing for the length of polyoxyethylenic spacer, the sugar moieties, and/or the length of the hydrophobic chain.

Molecular dynamics simulation is applied to investigate the bilayer properties of a novel catanionic vesicle composed of an ion pair amphiphile, hexadecyltrimethylammonium-dodecylsulfate (HTMA-DS), with cholesterol. Structural properties, such as molecular organization, orientation, and conformation, were analyzed from the resulting trajectory. Simulation results showed that cholesterol could induce both condensing and disordering effects on the rigid HTMA-DS bilayer. The condensing effect of cholesterol was ascribed to the maximizing contact between cholesterol ring and the neighboring hydrocarbon chains. Thus, the inserted cholesterol ring restrained the neighboring hydrocarbon chain segments from motion and increased the order of the neighboring hydrocarbon chains. However, the presence of cholesterol would increase the distance between head groups of HTMA-DS and induce a shift of DS(-) head groups toward the inside of the bilayer. This led to the protrusion of the HTMA(+) head groups and conformational disorder in the front segments of HTMA(+) hydrocarbon chains. In addition, the cholesterol-induced void in the hydrophobic core of the HTMA-DS bilayer increased the motion freedom of the terminal segments of the hydrocarbon chains. The cholesterol-induced space in the polar region and void in the nonpolar region of the bilayer led to a conformational disorder. With high cholesterol contents, the conformational disorder effect would overwhelm the condensing effect, resulting in the apparent disordering effect on the rigid HTMA-DS bilayer.

Turbidity titrations are used to study the ion specific aggregation of hemoglobin (Hb) below and physiological salt concentration in the pH range 4.5-9.5. At a salt concentration 50 mM cations promote Hb aggregation according to the order Rb(+) > K(+) ~ Na(+) > Cs(+) > Li(+). The cation series changes if concentration is increased, becoming K(+) > Rb(+) > Na(+) > Li(+) > Cs(+) at 150 mM. We interpret the puzzling series by assuming that the kosmotropic Li(+) will bind to kosmotropic carboxylates groups-according to the law of matching water affinities (LMWA)-whereas the chaotropic Cs(+) will bind to uncharged protein patches due to its high polarizability. In fact, both mechanisms can be rationalized by invoking previously neglected ionic nonelectrostatic forces. This explains both adsorption to uncharged patches and the LMWA as a consequence of the simultaneous action of electrostatic and dispersion forces. The same interpretation applies to anions (with chaotropic anions binding to chaotropic amine groups). The implications extend beyond hemoglobin to other, still unexplained, ion specific effects in biological systems.

Coacervation of cationic gemini surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) (12-6-12) with pH-sensitive N-benzoylglutamic acid (H2Bzglu) has been investigated by potentiometric pH-titration, turbidity titration, dynamic light scattering (DLS), isothermal titration calorimetry (ITC), TEM, (1)H NMR, and light microscopy. Phase boundaries of the 12-6-12/H2Bzglu mixture were obtained over the pH range from 2 to 9 and in the H2Bzglu concentration range from 30.0 to 50.0 mM at pH 4.5. When the H2Bzglu concentration is beyond 30.0 mM, the 12-6-12/H2Bzglu mixed solution undergoes the phase transitions from soluble aggregate, to precipitate, coacervate, and soluble aggregate again as pH increases. The results indicate that coacervation occurs at extremely low 12-6-12 concentration and lasts over a wide surfactant range, and can be enhanced or suppressed by changing pH, 12-6-12/H2Bzglu molar ratio and H2Bzglu concentration. The coacervates present a disorderly connected lay structure. Coacervation only takes place at pH 4-5, where the aggregates are nearly charge neutralized, and a minimum H2Bzglu concentration of 30.0 mM is required for coacervation. In this pH range, H2Bzglu mainly exist as HBzglu(-). The investigations on intermolecular interactions indicate that the aggregation of 12-6-12 is greatly promoted by the strong electrostatic and hydrophobic interactions with the HBzglu(-) molecules, and the interaction also promotes the formation of dimers, trimers, and tetramers of HBzglu(-) through hydrogen bonds. The double chains of 12-6-12 and the HBzglu(-) oligomers can play the bridging roles connecting aggregates. These factors endow the mixed system with a very high efficiency in generating coacervation.

Eumelanin is not only a ubiquitous pigment among living organisms with photoprotective and antioxidant functions, but is also the subject of intense interest in materials science due to its photoconductivity and as a possible universal coating platform, known as "polydopamine films". The structure of eumelanin remains largely elusive, relying either on a polymeric model or on a heterogeneous aggregate structure. The structure of eumelanin as well as that of the closely related "polydopamine films" can be modified by playing on the nature of the oxidant used to oxidize dopamine or related compounds. In this investigation, we show that dopamine-eumelanins produced from dopamine in the presence of either air (O2 being the oxidant) or Cu(2+) cations display drastically different optical and colloidal properties in relation with a different supramolecular assembly of the oligomers of 5,6 dihydroxyindole, the final oxidation product of dopamine. The possible origin of these differences is discussed on the basis of Cu(2+) incorporation in Cu dopamine-eumelanin.

In this paper, the preparation and characterization of an anionic and a cationic surfactant obtained by chemical modifications of a natural bile acid (cholic acid) are reported. The bile acid was modified by introducing a diamine or a dicarboxylic aromatic residue on the lateral chain. The pure cationic surfactant self-assembles in a network of fibers with a cross-section gyration radius of about 15.1 Å, providing hydrogels with a pH-dependent compactness. On the other hand, the anionic molecule gives rise to prolate ellipsoid micelles. Homogeneous catanionic mixtures have also been obtained, with molar fraction of each surfactant ranging from 0.125 to 0.875. At total surfactant concentration of 0.05% (w/v), the mixtures form gels of fibrils partially arranged in secondary twisted superstructures. Comparison of this concentration with the minimum gelation concentration of the pure cationic derivative (0.16% w/v) suggests that, in the mixtures, the presence of the electrostatic component in self-assembly of the molecules allows the formation of gels starting from more dilute samples. In view of these achievements, this work suggests that catanionic mixtures can be exploited to enhance the efficiency of gelators.

We used colloidal probe atomic force microscopy to measure the normal forces between the surface of a silica colloidal particle and a sparse layer of hyaluronan (hyaluronic acid, HA, MW ≈ 10(6) Da) covalently attached to a planar silica surface, both across pure water and following the addition of 1 mM MgCl2. It was found that in the absence of salt the HA layer repelled the colloidal silica surface during both approach and retraction. The addition of the MgCl2, however, changes the net force between the negatively charged HA layer and the opposing negatively charged silica surface from repulsion to adhesion. This interaction reversal is attributed to the bridging effect of the added Mg(2+) ions. Our results provide first direct force data to support earlier simulation and predictions that such divalent cations could bridge between negative charges on opposing surfaces, leading to an overall reversal of force from repulsion to attraction.

Gold nanoparticles stabilized by thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAM-AuNPs) were prepared by surface grafting of thiol-terminated PNIPAM onto citrate-stabilized AuNPs. The color change of the PNIPAM-AuNPs solution from red to blue-purple without precipitation when the solution was heated to 40 °C, above the lower critical solution temperature (LCST) of PNIPAM, indicated the thermoresponsive property of the synthesized AuNPs. PNIPAM-AuNPs were used to detect proteins by chemical nose approach based on fluorescence quenching of fluorophore by AuNPs. An array-based sensing platform for detection of six proteins, namely bovine serum albumin, lysozyme, fibrinogen, concanavalin A, hemoglobin, holo-transferrin human can be successfully developed from the PNIPAM-AuNPs having different molecular weights (4 and 8 kDa) and conformation (varied heat treatment from 25 to 40 °C) in combination with a tricationic branched phenylene-ethynylene fluorophore. From principal component analysis (PCA) followed by linear discriminant analysis (LDA), 100% accuracy of protein classification using a leave-one-out (LOO) approach can be achieved by using only two types of PNIPAM-AuNPs.

The micelle-vesicle-micelle transition in aqueous mixtures of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) and the anionic surfactant-like ionic liquid 1-butyl-3-methylimidazolium octyl sulfate, [C4mim][C8SO4] has been investigated by using dynamic light scattering (DLS), transmission electron microscopy (TEM), surface tension, conductivity, and fluorescence anisotropy at different volume fractions of surfactant. The surface tension value decreases sharply with increasing CTAB concentration up to ∼0.38 volume fraction and again increases up to ∼0.75 volume fraction of CTAB. Depending upon their relative amount, these surfactants either mixed together to form vesicles and/or micelles, or both of these structures were in equilibrium. Fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH), incorporated in this system at different composition of surfactant indicates the formation of micelle and vesicle structures. The apparent hydrodynamic diameter of these large multilamellar vesicles is about ∼200 nm-300 nm obtained by DLS measurement and finally confirmed by TEM micrographs. The large multilamellar vesicles are transformed into small unilamellar ones by sonication using a Lab-line instruments probe sonicator with a diameter of ∼90-125 nm. To investigate the heterogeneity, solvent, and rotational relaxation of coumarin-153 (C-153) have been investigated in these unilamellar vesicles by using picosecond time-resolved fluorescence spectroscopic technique. The solvation dynamics of C-153 in these vesicles is found to be biexponential with average time constant ∼580 ps. This indicates the slow relaxation of water molecules in the surfactant bilayer. In accordance with solvation dynamics, fluorescence anisotropy analysis of C-153 in unilamellar vesicles also indicates hindered rotation compared to bulk water.

Development of high-stability and efficient nonviral vectors with low cytoxicity is important for targeted tumor gene therapy. In this study, cationic polymeric liposomes (CPLs), with similar lipid bilayer structure and high thermal stability, were prepared from polymeric surfactants of quaternized (carboxymethyl)chitosan with different carbon chains (dodecyl, tetradecyl, hexadecyl, and octadecyl). By comparing different factors that influence gene delivery, tetradecyl-quaternized (carboxymethy)chitosan (TQCMC) CPLs, with suitable size (184.4 ± 17.1 nm), ζ potentials (27.5 ± 4.9 mV), and productivity for synthesis TQCMC (weight yield 13.1%), were selected for gene transfection evaluation in various cancer cell lines. Although TQCMC CPLs have lower gene transfection efficiency compared with cationic liposomes (Lipofectamine 2000) in vitro, they displayed higher reporter gene delivery ability for cancer tissues (bearing U87 and SMMC-7721 tumors) in vivo after intravenous injection. TQCMC CPLs also have lower cell cytotoxicity and lower cytokine production or liver injury for BALB/c mice. We conclude that the CPLs are promising gene delivery systems that may be used to target various cancers.

Cationic porphyrin was successfully intercalated into transparent clay membrane by developing the new strategy for the sample preparation conditions. When water:ethanol = 1:2 (v:v) was used as solvent for porphyrin penetration process, high density intercalation of porphyrin into the clay membrane was achieved. In the interlayer space, porphyrin molecules do not aggregate owing to intercharge distance matching effect (size-matching effect), even at high density condition. Judging from XRD and absorption measurements, the orientations of the porphyrins in the clay layers should be almost parallel to the clay nanosheet as monolayer. Because the fluorescence quantum yield did not depend on its loading level, it is turned out that intercalated TMPyP in the clay film keeps the photoactivity even under the high density conditions.

The Gibbs adsorption equation has been indispensable in predicting the surfactant adsorption at the interfaces, with many applications in industrial and natural processes. This study uses a new theoretical framework to model surfactant adsorption at the air/water interface without the Gibbs equation. The model was applied to two surfactants, C14TAB and C16TAB, to determine the maximum surface excesses. The obtained values demonstrated a fundamental change, which was verified by simulations, in the molecular arrangement at the interface. The new insights, in combination with recent discoveries in the field, expose the limitations of applying the Gibbs adsorption equation to cationic surfactants at the air/water interface.

We report the facile one-pot single-phase syntheses of silver nanoparticles stabilized by norbornene type cationic polymers. Silver nanoparticles (AgNPs) stabilized by polyguanidino oxanorbornenes (PG) at 5 and 25 kDa and polyamino oxanorbornenes (PA) at 3 and 15 kDa have been synthesized by the reduction of silver ions with NaBH4 in aqueous solutions at ambient temperature. The four different silver nanoparticles have been characterized by UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and transmission electron microscopy (TEM) for their particle size distributions. Interestingly, PG stabilizes the silver nanoparticles better than PA as evident from our spectroscopic data. Furthermore, the AgNP-PG-5K (5K = 5 kDa) was found to serve as an effective catalyst for the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH4. The reduction has a pseudo-first-order rate constant of 5.50 × 10(-3) s(-1) and an activity parameter of 1375 s(-1) g(-1), which is significantly higher than other systems reported in the literature.

Specific ion effects in surfactant solutions affect the properties of micelles. Dodecyltrimethylammonium chloride (DTAC), bromide (DTAB), and methanesulfonate (DTAMs) micelles are typically spherical, but some organic anions can induce shape or phase transitions in DTA(+) micelles. Above a defined concentration, sodium triflate (NaTf) induces a phase separation in dodecyltrimethylammonium triflate (DTATf) micelles, a phenomenon rarely observed in cationic micelles. This unexpected behavior of the DTATf/NaTf system suggests that DTATf aggregates have unusual properties. The structural properties of DTATf micelles were analyzed by time-resolved fluorescence quenching, small-angle X-ray scattering, nuclear magnetic resonance, and electron paramagnetic resonance and compared with those of DTAC, DTAB, and DTAMs micelles. Compared to the other micelle types, the DTATf micelles had a higher average number of monomers per aggregate, an uncommon disk-like shape, smaller interfacial hydration, and restricted monomer chain mobility. Molecular dynamic simulations supported these observations. Even small water-soluble salts can profoundly affect micellar properties; our data demonstrate that the -CF3 group in Tf(-) was directly responsible for the observed shape changes by decreasing interfacial hydration and increasing the degree of order of the surfactant chains in the DTATf micelles.

We report a simple approach to the ultrasensitive detection of biologically important metal ions using a magnetic nanoemulsion. The nanoemulsion used in our study was an oil-in-water emulsion droplet of average size ∼190 nm containing ferrimagnetic iron oxide nanoparticles of average size ∼10 nm. In a static magnetic field, the emulsion droplets self-assemble into a nanoarray with distinct interdroplet spacing. In the presence of cations in the solution, the nanofluid array shows a large blue shift in the diffracted Bragg peak and a visually perceivable color change due to changes in the electrical double layer upon the diffusion of cations. The colloidal force-distance measurements in the presence of cations show large variations at the onset of repulsion in the presence of cations. The sensor shows good selectivity to Na(+), K(+), Ca(2+), Cu(2+), and Fe(3+) ions and offers a rapid response compared to conventional techniques. This approach can be useful for the recognition of biologically important cations.

The coagulation of sodium montmorillonite by inorganic salts (NaNO3, Ca(NO3)2 and La(NO3)3) was studied by combining classical turbidity measurements with wide-angle-X-ray scattering (WAXS), small-angle-X-ray scattering (SAXS), and transmission X-ray microscopy (TXM). Using size-selected samples, such a combination, associated with an original quantitative treatment of TXM images, provides a true multiscale investigation of the formed structures in a spatial range extending from a few ångstroms to a few micrometers. We then show that, at neutral pH and starting with fully Na-exchanged samples, coagulation proceeds via the formation of stacks of particles with a slight mismatch between layers. These stacks arrange themselves into larger porous anisotropic particles, the porosity of which depends on the valence of the cation used for coagulation experiments. Face-face coagulation is clearly dominant under those conditions, and no evidence for significant face-edge coagulation was found. These structures appear to arrange as larger clusters, the organization of which should control the mechanical properties of the flocs.

Novel π-extended conjugated amphiphiles composed of a hydrophilic section of two quaternary ammonium groups and p-phenylene ethynylene with adjustable alkyl chain hydrophobic section were prepared by a multistep synthesis. These dicationic amphiphiles showed good water solubility and formed a tubular assembly in water. The evidence for the nanotubular comes from direct optical and TEM observations. A strong π-π stacking interaction between neighboring molecules, as evidenced by the red-shift and self-quenching in fluorescence, is proposed for the self-assembly. At the same time, dehydration of the bromide led to strong counterion condensation in headgroups, which resulted in the small curvature structure of the nanotubes. A bilayer lamellar structural model for the organic nanotube is proposed, and a reasonable structural model based on the experimental XRD pattern, as well as cell constants, is proposed.

Three cationic surfactants of the type N(ε)-acyl lysine methyl ester hydrochloride have been studied with respect to solution behavior and adsorption on the air/water interface, as well as the thermolyotropic behavior. The self-assembly of these surfactants, which have the cationic charge on amine protonated groups, was assessed by different physicochemical methods. Depending on the pH value, these surfactants can dissociate in aqueous solutions, losing the cationic charge. Therefore, knowledge of the pK(a) of these compounds is essential to explain their behavior in aqueous solutions. The bulk techniques, conductivity, and nuclear magnetic resonance diffusion (NMR) obtained similar critical micellar concentration (CMC) values, which were well above those obtained from surface tension. Surface tension measurements were strongly dependent on the technique used, namely, Wilhelmy plate and pendant drop. The phase behavior at medium to high concentrations has been studied by optical polarizing microscopy and small angle x-ray scattering (SAXS). The X-ray studies showed that the lysine-based surfactants at low hydration have rich thermotropic liquid crystalline behavior. The results are discussed in terms of the structure of the compounds and the cationic charge of the molecule. We will show how apparently small changes in molecule structure have a large influence on phase behavior.

Palm shell-based adsorbents prepared under five different thermochemical conditions and palm shell powder have been shown to be quite effective for removal of uranium from aqueous solutions. X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), and Fourier transform infrared spectroscopy (FTIR) have been used to determine information about the speciation and binding of uranium on the adsorbents under study. Studies indicate that the uranium which is present as uranyl ion in aqueous solution is present in mixed valence states (U(IV), U(V), and U(VI)) when it is bound to the adsorbents. The mechanism of adsorption is likely to be adsorption-coupled reduction as well as complexation. Adsorption of uranium, cesium, and iron was found to be quantitative in binary as well as ternary mixtures.