Ru(II)-based metallosurfactant forming inverted aggregates

Metallosurfactant aggregates: Structures, properties, and potentials for multifarious applications

Metallosurfactants offer important scientific and technological advances due to their novel interfacial properties. As a special class of structures formed by the integration of metal ions into amphiphilic surfactant molecules, these metal-based amphiphilic molecules possess both organometallic and surface chemistries. This review critically examines the structural transitions of metallosurfactants from micelle to vesicle upon metal coordination. The properties of a metallosurfactant can be changed by tuning the coordination between the metal ions and surfactants. The self-assembled behavior of surfactants can be controlled by selecting transition-metal ions that enhance their catalytic efficiency in environmental applications by applying a hydrogen evolution reaction or oxygen evolution reaction. We present the different scattering techniques available to examine the properties of metallosurfactants (e.g., size, shape, structure, and aggregation behavior). The utility of metallosurfactants in catalysis, the synthesis of nanoparticles, and biomedical applications (involving diagnostics and therapeutics) is also explored.

Structural Conversion of Supramolecular Assembly in Solution by Thermally Induced Intramolecular Electron Transfer of [Co2 Fe2 ] Complex

Combining metal complexes with amphiphilic molecules leads to a wide variety of functional self-assembled nanostructures. Metal complexes exhibiting spin transitions can be good candidates as the trigger to cause structural conversion of such assembly because they respond to various external stimuli. In this work, we studied a structural conversion of a supramolecular assembly containing a [Co2 Fe2 ] complex through a thermally induced electron transfer-coupled spin transition (ETCST). With an amphiphilic anion, the [Co2 Fe2 ] complex formed reverse vesicles in solution and showed thermal ETCST. In contrast, thermal ETCST in the presence of a bridging hydrogen-bond donor caused structural conversion from the reverse vesicle structure to entangled one-dimensional chains through hydrogen bond formation.

Molecular fusion of surfactant and Lewis-acid properties for attacking dirt by catalytic bond cleavage

The capability of ordinary surfactants in solubilizing hydrophobic compounds can come to a limit, if the extension of a contaminant is too large. An attractive goal is the development of surfactants which can actively reduce the size of dirt. Because strong Lewis acids are known to catalyze both bond formation and cleavage, an integration into the surfactant's molecular framework is tempting. End-group functionalized hepta-dentate ligands, which coordinate to metal ions preventing deactivation by hydrolysis over a broad range of pH values while maintaining strong Lewis-acidity, are herein presented. After proof of amphiphilicity and surfactant characteristics, catalytic properties are investigated for different reactions including the cleavage of proteins. The compounds perform better than benchmark catalysts concerning the attack of unreactive amide bonds. A study with two Sc³⁺ species as the active site, one non-amphiphilic, the other one being surface-active, underlines the positive effect of surfactant properties for boosting catalytic efficiency.

Cross-Linked Reverse Vesicle as a General and Effective Vehicle for Hydrophobic Drugs

It is well-known that vesicles serve as an excellent delivery platform for hydrophilic drugs. However, there is still a lack of a general and effective platform for hydrophobic drug loading. We herein disclose that water-soluble cross-linked reverse vesicles (cRVs) constructed from anionic surfactant 1, a counterpart of normal vesicles, would be excellent vehicles for hydrophobic drugs, the drug loading content (DLC) for which arrived up to 21.1%, 19.8%, and 25.8%, respectively, for three anticancer drugs, paclitaxel, camptothecin, and carmofur. This represents a general drug carrier with high drug loading content for various hydrophobic drugs without the assistance of other external forces. In addition to drug loading superiority, the cRVs were also characterized by robust stability, specific stimulus response, easy postfunctionalization, and good biocompatibility and thus are promising candidates for drug delivery systems.

Solvent switchable nanostructures and the function of a π-amphiphile

This manuscript reports solvent tunable functional nano-assemblies of an unsymmetrical bola-shaped π-amphiphile (NDI-PY) which consists of a hydrophobic naphthalene-diimide (NDI) chromophore connected to a non-ionic hydrophilic wedge and a pyridine group at its two opposite arms. Importantly, it contains a hydrazide group located at the hydrophobic domain between the NDI-chromophore and the hydrophilic-wedge to drive the supramolecular assembly by directional H-bonding. NDI-PY exhibits spontaneous assembly in water as well as in a highly non-polar solvent like tetra-chloroethylene (TCE) by the synergistic effect of H-bonding and π-stacking interaction. Spectroscopy studies reveal almost identical self-assembly features in water and TCE with critical aggregation concentrations in the range of 0.3 mM, which matches the values obtained from the isothermal calorimetry (ITC) dilution experiment. Differential scanning calorimetry (DSC) experiments reveal a single endothermic peak at 31 °C (ΔH = -12.3 kJ mol^-1) and 40 °C (ΔH = -5.35 kJ mol^-1) for water and TCE, respectively, indicating marginally higher thermal stability in TCE, which is consistent with the FT-IR data, suggesting stronger H-bonding in TCE. Although the molecular assembly features appear to be similar, NDI-PY produces distinctly different mesoscopic structures in water and TCE. In water, it forms vesicles (D_h = 150-180 nm) with the pyridine groups displayed at the outer surface, while in TCE it generates a transparent gel (CGC = 8.0 mM) with a nanotubular (width ∼50 nm, wall thickness ∼10 nm) morphology. Powder X-ray diffraction studies show clearly different packing structures; in water a single sharp peak at the low angle (d = 19.3 Å, a little shorter than the extended length of the molecule) suggests the formation of a monolayer membrane, while in TCE several sharp peaks appear with the d values maintaining a ratio of 1 : 1/√3 : 1/2 : 1/√7 : 1/3 : 1/√12, indicating the formation of a 2D hexagonal lattice. Photoconductivity measurements reveal moderate electronic conduction in both cases. However, it shows a remarkable enhancement of the life time of the charge-carriers for the nanotubular structure compared to the vesicular morphology. On the other hand, the vesicles in water display antimicrobial activity against Gram-positive S. aureus with a highly promising MIC_LB value of 29.4 μg mL^-1. In contrast, it does not lyse human red blood cells even at as high a concentration as 2.5 mg mL^-1 (HC₅₀ > 2.5 mg mL^-1), implying high selectivity of the NDI-PY vesicles towards bacterial cells over mammalian cells. Display of the pyridine groups at the outer surface of the membrane enables molecular recognition by complementary H-bonding with a carboxylic acid group and thereby facilitates uptake of the attached pyrene chromophores in the NDI-membrane by charge-transfer interaction between the NDI acceptor and the pyrene donor. In fact a Job's plot experiment reveals maximum uptake at a 1 : 1 ratio of the NDI-PY and the pyrene guest, indicating all the pyridine groups are accessible at the vesicular surface.

Synthesis, characterisation and self-assembly behaviour of emissive surfactant–ruthenium(ii) complexes

Bipyridine/phenanthroline based dodecylamine/hexadecylamine containing surfactant–ruthenium(ii) complexes form green fluorescent vesicles with an excellent stability in the aqueous medium.

Fabrication of metalosomes (metal containing cationic liposomes) using single chain surfactants as a precursor via formation of inorganic organic hybrids

This work reveals a methodology to modify a single chain surfactant to fabricate a liposome-like assembly by controlling the stoichiometry by virtue of a metallic counter ion. It is a noteworthy advancement in the area of self-assembled molecular structures.

Ag+-induced reverse vesicle to helical fiber transformation in a self-assembly by adjusting the keto–enol equilibrium of a chiral salicylideneaniline

A chiral salicylideneaniline shows Ag⁺-induced reverse vesicle-to-helical nanofiber transformation accompanied by sol-to-gel transition at room temperature.

Polysaccharide-gold nanocluster supramolecular conjugates as a versatile platform for the targeted delivery of anticancer drugs

Through the high affinity of the β-cyclodextrin (β-CD) cavity for adamantane moieties, novel polysaccharide-gold nanocluster supramolecular conjugates (HACD-AuNPs) were successfully constructed from gold nanoparticles (AuNPs) bearing adamantane moieties and cyclodextrin-grafted hyaluronic acid (HACD). Due to their porous structure, the supramolecular conjugates could serve as a versatile and biocompatible platform for the loading and delivery of various anticancer drugs, such as doxorubicin hydrochloride (DOX), paclitaxel (PTX), camptothecin (CPT), irinotecan hydrochloride (CPT-11), and topotecan hydrochloride (TPT), by taking advantage of the controlled association/dissociation of drug molecules from the cavities formed by the HACD skeletons and AuNPs cores as well as by harnessing the efficient targeting of cancer cells by hyaluronic acid. Significantly, the release of anticancer drugs from the drug@HACD-AuNPs system was pH-responsive, with more efficient release occurring under a mildly acidic environment, such as that in a cancer cell. Taking the anticancer drug DOX as an example, cell viability experiments revealed that the DOX@HACD-AuNPs system exhibited similar tumor cell inhibition abilities but lower toxicity than free DOX due to the hyaluronic acid reporter-mediated endocytosis. Therefore, the HACD-AuNPs supramolecular conjugates may possess great potential for the targeted delivery of anticancer drugs.

Green synthesis of gold nanoparticles using Citrus fruits (Citrus limon, Citrus reticulata and Citrus sinensis) aqueous extract and its characterization

This study reports the biological synthesis of gold nanoparticles by the reduction of HAuCl(4) by using citrus fruits (Citrus limon, Citrus reticulata and Citrus sinensis) juice extract as the reducing and stabilizing agent. A various shape and size of gold nanoparticles were formed when the ratio of the reactants were altered with respect to 1.0mM chloroauric acid solution. The gold nanoparticles obtained were characterized by UV-visible spectra, transmission electron microscopy (TEM) and X-ray diffraction (XRD). TEM studies showed the particles to be of various shapes and sizes and particle size ranges from 15 to 80 nm. Selected-area electron diffraction (SAED) pattern confirmed fcc phase and crystallinity of the particles. The X-ray diffraction analysis revealed the distinctive facets (111, 200, 220 and 222 planes) of gold nanoparticles. Dynamic light scattering (DLS) studies revealed that the average size for colloid gp(3) of C. limon, C. reticulata and C. sinensis are 32.2 nm, 43.4 nm and 56.7 nm respectively. The DLS graph showed that the particles size was larger and more polydispersed compared to the one observed by TEM due to the fact that the measured size also includes the bio-organic compounds enveloping the core of the Au NPs. Zeta potential value for gold nanoparticles obtained from colloid gp(3) of C. limon, C. reticulata and C. sinensis are -45.9, -37.9 and -31.4 respectively indicating the stability of the synthesized nanoparticles. Herein we propose a novel, previously unexploited method for the biological syntheses of polymorphic gold nanoparticles with potent biological applications.

Preparation and characterization of doxorubicin functionalized gold nanoparticles

In this paper, we have presented the demonstration of gold nanoparticles (Au NPs) functionalized with an anticancer drug, doxorubicin. Doxorubicin was assembled on gold via amino group. The reaction proceeded under mild acidic conditions. Au NPs could not be adsorbed on doxorubicin in alkaline solution because amino group was not protonated. However, under acidic conditions, protonation created a positively charged amino group thus adsorption was easier. The interaction between Au colloids and doxorubicin is believed to be electrostatic. High-resolution TEM was used for visualization of nanoparticles, which were found to retain their average size and shape. The method, demonstrated that doxorubicin could be attached to Au NPs in a controlled manner. Our research laid the foundation of a linking methodology through which hybrid multi drug and receptor labeled NPs could be created, which might serve as an alternative design for nanosized drug-delivery systems.

Alkylsulfides of Ag(I) and Au(I) as metallosurfactants

Several representative, interfacially active silver(I) nitrate alkylsulfide complexes were synthesized and characterized in detail. The complexes form extended structures in the solid state and in solution. Interestingly, a two-phase approach, in which aqueous silver nitrate is combined with organically dissolved sulfides, leads to the in situ formation of the complexes at the water-organic interface and a strong reduction of the surface tension. Despite their low solubility in water or organic solvent, these complexes are capable of stabilizing eicosane emulsions and dispersions in water. Thus, these silver nitrate alkyl sulfides represent a new class of metallosurfactants in which the metal ion is crucial for the interfacial activity. Gold(I) chloride alkyl sulfides show the same effect to a lesser extent.

New surfactant phosphine ligands and platinum(II) metallosurfactants. Influence of metal coordination on the critical micelle concentration and aggregation properties

We have prepared the first platinum(II) metallosurfactants from a new family of linear surfactant phosphines Ph(2)P(CH(2))(n)SO(3)Na {1 (n = 2), 2 (n = 6), and 3 (n = 10)}, which were synthesized by reaction between the halosulfonates X(CH(2))(n)SO(3)Na and sodium diphenylphosphide. The metallosurfactants cis-[PtCl(2)L(2)] (L = 1-3) were obtained after reaction between the phosphines and PtCl(2) in dimethylsulfoxide. All compounds were fully characterized by the usual methods {NMR ((1)H, (13)C, (31)P, (195)Pt), IR, MS-ESI and HRMS}. By exploring the surfactant properties of phosphines 1-3 and their respective platinum metallosurfactants cis-[PtCl(2)L(2)] (L = 1-3) through surface tension measurements, dynamic light scattering spectroscopy, and cryo-TEM microscopy, we were able to analyze the influence of the metal coordination on the critical micelle concentration (cmc) and the aggregation properties. The cmc values of platinum metallosurfactants were considerably lower than those obtained for the free phosphines 1-3. This behavior could be understood by an analogy between the structure of cis-[PtCl(2)L(2)] complexes and bolaform surfactants. The calculated values of area per molecule also showed different tendencies between 1-3 and cis-[PtCl(2)L(2)] complexes, which could be explained on the basis of the possible conformations of these compounds in the air-water interface. The study of aggregates by dynamic light scattering spectroscopy and cryo-TEM microscopy showed the formation of spherical disperse medium size vesicles in all cases. However, substantial differences were observed between the three free phosphines (the population of micellar aggregates increased with long chain length) and also between phosphines and their respective metallosurfactants.

Self-assembly of a triangle-shaped, hexaplatinum-incorporated, supramolecular amphiphile in solution and at interfaces

The self-assembly and characterization of a novel supramolecular amphiphile built from a new 60 degree amphiphilic precursor that incorporates hydrophilic platinum(II) metals and hydrophobic dioctadecyloxy chains is reported. The amphiphilic macrocycle and its precursor compound have been characterized by multinuclear NMR spectroscopy, ESI-MS, and other standard techniques. The coacervate morphology of the amphiphile at the liquid-liquid interface has been studied by using confocal optical microscopy and in situ Raman spectroscopy. The self-assembly of the amphiphilic macrocycle at the air-water interface has been investigated through Langmuir-trough techniques. The study indicates the possible formation of surface micelle-like aggregates. The disparity between the experimental molecular areas and those derived from molecular models support the idea of aggregation. AFM images of the surface aggregates show the formation of a flat topology with arbitrary ridgelike patterns. Reasonable molecular-packing arrangements are proposed to explain the molecular organization within the observed structures.

Aqueous solutions of transition metal containing micelles

Incorporation of d- or f-block metals into ligand systems that renders a metal complex surface-active or drives its partitioning into surfactant phases enables the localisation of chemical functionality at interfaces. This article discusses a number of fundamental aspects of these interesting materials and examines potential applications.

Giant micelles of organoplatinum(II) gemini amphiphiles

Organoplatinum(II) gemini amphiphiles with two different chain lengths are synthesized and characterized. Self-assembly at the air-water interface is investigated as a function of chain length and reduction in surface area by using Langmuir-trough techniques. The Langmuir-trough experiments lead to a conjecture that surface aggregates may be the adsorbing units. Atomic force microscopy on the transferred Langmuir-Schaefer films reveals spontaneous formation of wormlike micellar aggregates. A shear-induced transition and alignment are proposed for the observed effects.