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

Novel PEPPSI-Type NHC Pd(II) Metallosurfactants on the Base of 1H-Imidazole-4,5-dicarboxylic Acid: Synthesis and Catalysis in Water-Organic Media

Carrying out organic reactions in water has attracted much attention. Catalytic reactions in water with metallosurfactants, which have both a metallocenter and the surface activity necessary for solubilizing hydrophobic reagents, are of great demand. Herein we proposed new approach to the synthesis of NHC PEPPSI metallosurfactants based on the sequential functionalization of imidazole 4,5-dicarboxylic acid with hydrophilic oligoethylene glycol and lipophilic alkyl fragments. Complexes of different lipophilicity were obtained, and their catalytic activity was studied in model reduction and Suzuki-Miyaura reactions. A comparison was made with the commercial PEPPSI-type catalytic systems designed by Organ. It was found that the reduction reaction in an aqueous solution of the metallosurfactant with the tetradecyl lipophilic fragment was three times more active than the commercially available PEPPSI complexes, which was associated with the formation of stable monodisperse aggregates detected by DLS and TEM.

Design and applications of metallo-vesicular structures using inorganic-organic hybrids

In advanced biomedical diagnosis, various supramolecular assemblies based on inorganic-organic hybrids have found great interest as functional materials. These assemblies describe a new field of metallovesicles where the introduction of metal ions enables the chemical manipulation of assemblies in terms of their structural stability, redox activity, and pH stability. Additionally, they mimic the elaborative architecture of natural liposomal assemblies and exhibit hierarchical morphologies, and promise novel functions. With the constant developments in this field, various supramolecular assemblies such as MCsomes, Polymersomes, and Metallosomes, etc. came into existence. These hybrid assemblies have been utilized for several applications such as drug delivery, MRI contrasting, DNA delivery, and catalytic activity. The key advantage of these assemblies is their ability to deliver therapeutics to specific locations due to their biomimetic properties and release their contents at the desired time. Hence, they provide a valuable platform for the treatment of a variety of diseases. Through the present article, we intend to provide insights into the latest developments made in this field. This modularity underscores the tremendous promise of supramolecular assemblies as an emerging interdisciplinary research branch at the interface of chemistry and biological sciences.

Metallosurfactants Consisting of Amphiphilic Ligands and Transition Metals: Structure, Bonding, Reactivity, and Self-assembling Property

Metallosurfactants are emerging as a relatively new class of surfactants whose ligand moieties bind to various transition metals. Because transition metal centers are incorporated into the surfactant frameworks, they can form various self-assembled structures with metallic interfaces such as micelles, vesicles, and lyotropic liquid crystals. To reduce the lability of transition metal complexes under aqueous conditions, various amphiphilic ligands have been developed as surfactant frameworks. This review discusses some aspects of the design and chemical structures of amphiphilic ligands, as well as focus on various functions and types of chemical bonds present in metallosurfactants.

Direct Synthesis of Rhenium and Technetium-99m Metallosurfactants by a Transmetallation Reaction of Lipophilic Groups: Potential Applications in the Radiolabeling of Liposomes

A new zinc dithiocarbamate functionalized with palmitoyl groups is described as a useful tool for the preparation of metallosurfactants through a transmetallation reaction with the transition metals rhenium and technetium. An amphiphilic rhenium complex is synthesized by a transmetallation reaction with the zinc complex in presence of the polar phosphine sodium triphenylphosphine trisulfonate, which leads to a rhenium complex with a lipophilic dithiocarbamate and a polar phosphine ligand. The study of this rhenium complex has shown that it self-aggregates, leading to the formation of aggregates that have been analyzed by dynamic light scattering and cryotransmission electron microscopy (cryo-TEM). In addition, this amphiphilic rhenium complex is incorporated into soy phosphatidylcholine liposomes, whether liposomes are prepared by mixing phospholipid and the rhenium complex or by the incorporation of the rhenium complex into preformed liposomes. The one-pot reaction of the radiocompound [^99mTc(H₂O)₃(CO)₃]⁺ with the above-mentioned zinc dithiocarbamate, the phosphine sodium triphenylphosphine trisulfonate and the phospholipid soy phosphatidylcholine, leads to liposomes labeled with a Tc-99m homologous complex of the rhenium complex, in accordance with the high-performance liquid chromatography (HPLC) data.

Assessment of the aggregation and adsorption behavior of newly synthesized tetradecylpyridinium-based metallosurfactants and their interaction with bovine serum albumin

Tetradecylpyridinium (TP) based metallosurfactants, TP₂[MCl₄] (M = Mn, Co, Ni, Cu, Zn): synthesis, aggregation behavior and interaction with bovine serum albumin.

Genesis of electron deficient Pt1(0) in PDMS-PEG aggregates

While numerous single atoms stabilized by support surfaces have been reported, the synthesis of in-situ reduced discrete metal atoms weakly coordinated and stabilized in liquid media is a more challenging goal. We report the genesis of mononuclear electron deficient Pt1(0) by reducing H2PtCl6 in liquid polydimethylsiloxane-polyethylene glycol (PDMS-PEG) (Pt1@PDMS-PEG). UV-Vis, far-IR, and X-ray photoelectron spectroscopies evidence the reduction of H2PtCl6. CO infrared, and 195Pt and 13C NMR spectroscopies provide strong evidence of Pt1(0), existing as a pseudo-octahedral structure of (R1OR2)2Pt(0)Cl2H2 (R1 and R2 are H, C, or Si groups accordingly). The weakly coordinated (R1OR2)2Pt(0)Cl2H2 structure and electron deficient Pt1(0) have been validated by comparing experimental and DFT calculated 195Pt NMR spectra. The H+ in protic state and the Cl- together resemble HCl as the weak coordination. Neutralization by a base causes the formation of Pt nanoparticles. The Pt1@PDMS-PEG shows ultrahigh activity in olefin hydrosilylation with excellent terminal adducts selectivity.

Self-assembling Properties of an N-Heterocyclic Carbene-based Metallosurfactant: Pd-Coordination Induced Formation of Reactive Interfaces in Water

In this study, an N-heterocyclic carbene (NHC)-based metallosurfactant (MS), NHC-PdMS, was synthesized, where Pd(II) was bound to the NHC framework via a robust Pd-carbene bond with NEt₃ as a co-ligand. Surface tension measurements revealed that the critical micelle concentration (CMC) of NHC-PdMS (1.8×10^-4 M) was one order of magnitude lower than that of its MS precursor (imidazolium bromide). Coordination of the MS precursor and NEt₃ to Pd(II) also influenced micelle size; the hydrodynamic diameters of NHC-PdMS and the MS precursor were observed to be 25.8±5.6 nm and 2.5±0.3 nm, respectively. Furthermore, small angle X-ray scattering measurements indicated that NHC-PdMS exhibited liquid crystalline behavior above 26 wt%, with a spacing ratio of 1:2:3 for the first, second, and third Bragg peaks. To understand the role of the reactive interface, NHC-PdMS was also applied to aqueous catalytic reactions. Owing to its low CMC value, a catalytic amount of NHC-PdMS (3 mol%) provided the reactive interface, which facilitated the aqueous Mizoroki-Heck reaction of various aryl iodides and styrene in good yields (72-95%). These results suggest that MS formation results in a drastic change in selfassembling properties, which are important for the development of highly reactive chemical interfaces in water.

Advancing the Pharmaceutical Potential of Bioinorganic Hybrid Lipid-Based Assemblies

Bioinspired lipid assemblies that mimic the elaborate architecture of natural membranes have fascinated researchers for a long time. These lipid assemblies have gone from being just an imperative platform for biophysical research to a pharmaceutical delivery system for biomedical applications. Despite success, these organized nanosystems are often subject to the mechanical instability and limited theranostic capability without adding any inconvenient modifications. To reach their advanced pharmaceutical potential, various bioinorganic hybrid lipid-based assembles, which provide new opportunities to synergistically complement and improve therapeutic/diagnostic potential of existing lipid-based nanomedicine with distinct mechanisms containing inorganic embedded surfactants, have recently been developed.

In vitro assessment of antimicrobial and genotoxic effect of metallosurfactant based nickel hydroxide nanoparticles against Escherichia coli and its genomic DNA

In the present study, we have synthesized nickel hydroxide nanosuspensions (Ns) using microemulsion technique. This approach is eco-friendly and makes use of Tween 80 (a non-ionic biocompatible surfactant) and newly synthesized metallosurfactants for the formation of uniform nanoparticles in the form of nanosuspensions (Ns). The nickel hydroxide Ns's were derived from three different metallosurfactants i.e. NiCTAC (Bishexadecyltrimethylammonium nickel tetrachloride), NiDDA (Bisdodecylamine nickel dichloride) and NiHEXA (bishexadecylamine nickel dichloride). Three different nickel-based metallosurfactants were synthesized and characterized using various methods such as CHN, ¹HNMR, and FTIR. Fabrication of nanosuspension was confirmed using different characterization methods such as Transmission electron microscopy (TEM), Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray Spectroscopy (EDX), X-ray Diffraction (XRD), pH and Zeta potential. These particles were further investigated for their genotoxic and cytotoxic effects on gram-negative bacteria, Escherichia coli (E. coli). Effect of nanosuspensions on E. coli was confirmed using colony forming unit count, agar well diffusion, and gram staining method. Through colony forming unit count method, nanosuspensions influence on the colony-forming capacity of E. coli cells was confirmed. Agar well diffusion method provides the estimation of antimicrobial activity, and the largest inhibition zone was observed for NiCTAC Ns and smallest for NiHEXA Ns which is related to maximum and minimum bactericidal properties of Ns, respectively. The interaction behavior of bacterial DNA with Ni nanosuspension was analyzed using agarose gel electrophoresis and circular dichroism. Along with, the role of different chemical scavengers was also evaluated in DNA damage using gel electrophoresis. Furthermore, the antioxidant activity of Ni nanosuspension was also confirmed using DPPH assay.

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.

Aggregation and surface behavior of aqueous solutions of cis-bis(1,3-diaminopropane)bis(dodecylamine)cobalt(iii) nitrate. A double-chained metallosurfactant

Metallosurfactants or amphiphilic metal complexes are emerging as a new class of material with a range of properties inherent to both metal complexes and surfactants.

Iron-Carbonyl Aqueous Vesicles (MCsomes) by Hydration of [Fe(CO){CO(CH2)5CH3}(Cp)(PPh3)] (FpC6): Highly Integrated Colloids with Aggregation-Induced Self-Enhanced IR Absorption (AI-SEIRA)

Self-assembly of hydrophobic molecules into aqueous colloids contradicts common chemical intuition, but has been achieved through hydration of [Fe(CO){CO(CH2)5CH3}(Cp)(PPh3)] (FpC6). FpC6 has no surface activity, no NMR signals in D2O and no critical aggregation concentration (CAC) in H2O. The molecule, however, contains both acyl and terminal CO groups that are prone to being hydrated. By adding water to a solution in THF, self-assembly of FpC6 can be initiated through water-carbonyl interactions (WCIs) with the highly polarized acyl CO groups. This aggregation subsequently enhances the hydration of the acyl CO groups and also induces the WCI of otherwise unhydrated terminal CO groups. The resultant metal-carbonyl aggregates have been proved to be bilayer vesicles with iron complexes exposed towards water and alkyl chains forming inner walls (MCsomes). These MCsomes show high structure integration upon dilution due to the hydrophobic nature of the building blocks. The highly polarized CO groups on the surface of the MCsomes result in a negative zeta potential (-65 mV) and create a local electric field, which significantly enhances the IR absorption of CO groups by more than 100-fold. This is the first discovery of aggregation-induced self-enhanced IR absorption (AI-SRIRA) without the assistant of external dielectric substrates. Highly integrated MCsomes are, therefore, promising as a novel group of materials, for example, for IR-based sensing and imaging.

The formation of host-guest complexes between surfactants and cyclodextrins

Cyclodextrins are able to act as host molecules in supramolecular chemistry with applications ranging from pharmaceutics to detergency. Among guest molecules surfactants play an important role with both fundamental and practical applications. The formation of cyclodextrin/surfactant host-guest compounds leads to an increase in the critical micelle concentration and in the solubility of surfactants. The possibility of changing the balance between several intermolecular forces, and thus allowing the study of, e.g., dehydration and steric hindrance effects upon association, makes surfactants ideal guest molecules for fundamental studies. Therefore, these systems allow for obtaining a deep insight into the host-guest association mechanism. In this paper, we review the influence on the thermodynamic properties of CD-surfactant association by highlighting the effect of different surfactant architectures (single tail, double-tailed, gemini and bolaform), with special emphasis on cationic surfactants. This is complemented with an assessment of the most common analytical techniques used to follow the association process. The applied methods for computation of the association stoichiometry and stability constants are also reviewed and discussed; this is an important point since there are significant discrepancies and scattered data for similar systems in the literature. In general, the surfactant-cyclodextrin association is treated without reference to the kinetics of the process. However, there are several examples where the kinetics of the process can be investigated, in particular those where volumes of the CD cavity and surfactant (either the tail or in special cases the head group) are similar in magnitude. This will also be critically reviewed.

Synthetic ion transporters: pore formation in bilayers via coupled activity of non-spanning cobalt-cage amphiphiles

Three amphiphilic cobalt-cage congeners bearing a diaza-crown bridge and varying alkyl chains (1:2:3; n = 12, 16, 18) have been assessed for their ion transport across planar lipid bilayer membranes. In symmetrical electrolyte solutions, a range of ion transport activity is provoked: 1 disrupts painted (fluid) bilayers in a detergent-like mode of action; 2 forms conducting "pores" in folded (rigid) membranes with long open lifetimes (>2 min) while 3 requires the larger auxiliary solvent volume and lower lateral stress of painted membranes to effect ion transport via long-lived pores. Hill analysis of the conductance variation with monomer concentration yields coefficients (2:3; n = 2.3, 1.9) in support of dimeric (n = 2) membrane-active structures, for which the derived "pore" radii are correlated with charge-density of the transported cations and their affinity for the crown moiety. A toroidal-pore model is invoked to account for the flux of guest ions through planar bilayer membranes without a fast-diffusing intermediary or direct membrane-spanning structure.

Interfacial assembly of a series of cinnamoyl-containing bolaamphiphiles: spacer-controlled packing, photochemistry, and odd-even effect

A series of bolaamphiphiles with 4-hydroxycinnamoyl head groups and different length of the alkyl spacers (n = 6-12) were designed to investigate their photochemistry in the organized films obtained from the air/water interface. It has been found that both the length and odd-even number of the spacers can finely tune the molecular packing as well as the photochemistry. When the spacer length was changed from 6 to 12 methylene units, the assemblies changed from J aggregate to H aggregate. The molecules with even-numbered polymethylene spacer tend to form three-dimensional nanorod structure at the air/water interface. For the assembly of derivatives with odd-numbered spacers, diverse morphologies such as nanospirals and nanofibers were observed depending on the chain length and the surface pressures. The different packing of bolaamphiphiles could subsequently affect the photochemistry of the cinnamoyl groups in the organized films. The spacer effect in the assembly can be understood from the cooperation between H-bond of the phenolic hydroxyl and the amide groups, π-π stacking as well as the hydrophobic interactions of the alkyl spacer. A packing model was proposed to explain the phenomenon.