Metallosurfactants: interfaces and micelles

Incorporating a metal cation as an integral component of the headgroup of a surfactant--a metallosurfactant--offers a route to concentrate these ions and their associated functionality at interfaces. To reduce the lability of the metal, various chelating or macrocyclic ligands may be employed leading to a family of homologous series of related metallosurfactants with a structural diversity that is arguably broader than is inherently possible with conventional surfactants. This review discusses the small number of key papers that are quantifying the physico-chemical properties of metallosurfactants and highlights their "classical" as well as "non-classical" surfactant behaviour, providing an insight into the structure of micelles and films formed from these novel materials.     

Remarkable amine-TFA self assembly

Supramolecular assemblies that are formed between amines and trifluoroacetic acid were studied using electrospray ionization mass spectrometry. Distinctive association behavior of primary, secondary, and tertiary amines with trifluoroacetic acid upon identical experimental conditions is observed and indicates that steric effects dominate in the formation of these protonated clusters. Extraordinary complexation behavior is observed in the case of R-(+)-alpha-methylbenzylamine and 4-tert-butyl-cyclohexylamine that form high-order clusters. The strong relation between stereochemistry and assembly results in the specific association characteristics of trans 4-tert-butyl-1-phenylcyclohexylamine when compared with the cis isomer. The cis isomer gives rise to a highly abundant [M(4)TFA(3) + H](+) ion (M = amine molecule, TFA = trifluoroacetic acid), as observed for other primary amines. However, the trans isomer generates higher [M(n)TFA(m) + H](+) cluster ions, the largest and most abundant being an [M(7)TFA(6) + H](+) ion. Collision induced dissociation spectra that were recorded for several [M(n)TFA(m) + H](+) cluster ions typically show the consecutive losses of M.TFA moieties. Density functional theory calculations indicate that the highly abundant [M(4)TFA(3) + H](+) clusters are macrocycles and support the formation of these structures with TFA and not with acetic acid.     

Boronic acid building blocks: tools for self assembly

Dynamic covalent functionality has been acknowledged as a powerful tool for the construction of organised architectures, the reversible nature thermodynamically facilitates self-control and self-correction. The use of boronic acids complexation with diols and their congeners has already shown great promise in realising and developing reversible boron-containing multicomponent systems with dynamic covalent functionality. The structure-directing potential has lead to the development of a variety of self-organisation involving not only macrocycles, cages and capsules, but also porous covalent organic frameworks and polymers. Structure controls as well as remarkable synthesis are highlighted in this feature article.     

Synthesis of ultrathin polymer films by self assembly

Recent progresses in the self assembly of ultrathin polymer films are described. Bilayer membranes of polymeric hydrogen-bond networks are formed in water. Two-dimensional networks of organic and inorganic polymers are formed in cast films of synthetic bilayer membranes to give stable multilayer films upon removal of the matrices. The monolayer at the air-water interface constitutes suitable templates for 2D polymer networks, and it may be either removed or part of the 2D film. Successive adsorption of polycations and polyanions under carefully controlled conditions produces layered polyion complexes in the stepwise manner. Various polymer chains are epitaxially adsorbed onto graphite. All these results indicate that molecularly defined 2D polymer structures are readily available.     

Evaporative micro-particle self assembly influenced by capillary evacuation

As evaporation does not incur energy introduction, the droplet coffee-stain patterning approach is attractive for biochemical tests conducted in the field or in third world environments. A practical strategy uses chemically functionalized microbeads for the coffee stain deposition process. From an application perspective, it will be necessary to minimize the coffee stain deposition time, as evaporation, depending on the volume of the droplet, can be a slow process. The introduction of a porous media will generate a capillary flow (or wicking) that removes any remnant liquid in the droplet, thus permitting it to be done inexpensively and in the field. Using optical profilometry, we were able to establish that polystyrene microspheres developed more copious and defined single ring coffee depositions than silica of the same size and concentration in a suspension. In analyzing the droplet capillary evacuation process with a porous media, we found the liquid bridge formed during the later stages to rupture and leave behind some liquid material for a second stage evaporation process. This was responsible for a two ring structure that was more visible with silica microspheres. A high degree of hysteresis of the contact angle was found to develop at the contact line in which values below 5° could be achieved. Dynamic observations showed the copious and dense packing of polystyrene particles to be more resistant to ring break up from the evacuation flow. Nevertheless, erosion of the back array portions of the ring was evident notwithstanding either type of microsphere used.     

Shape evolution and self assembly of monodisperse PbTe nanocrystals

In this communication, we report our recent achievement in synthesis and self-assembly of both spherical and cubic PbTe nanocrystals using a high-temperature solution-phase synthesis approach. The possible mechanism of nanocrystalline evolution from spherical to cubic structure has also been discussed. It is possible to use the highly orientated PbTe nanocrystals as building blocks to achieve thickness-controlled film for further manipulation into thermoelectric devices.     

Channel architecture via self assembly of oxamide oximes complexes

The nickel(II) and palladium(II) complexes of oxamide oximes substituted with alkyl chains of different length (C4-C8) were synthesized from the reaction of dichloroglyoxime with the corresponding amine derivatives. All compounds have been characterized by X-ray diffraction on single crystals and were found to be centrosymmetric at the metal center which is bound by the four oximic nitrogen atoms of two ligands in a square planar environment. Crystal structure analyses of Ni(II) and Pd(II) complexes showed that all of the Pd(II) complexes but only the hexyl-substituted oxamide oxime Ni(II) complex form infinite tubular channels. Their conformational analyses were carried out in order to understand the role of the chain length and of the metal center in the formation of the tubular channels and it was found that the formation of infinite tubular channels in crystals of Ni(II) and Pd(II) alkyl-substituted oxamide oxime complexes is related to the orientation of the alkyl chains relative to the central core.     

Controlling interfacial interactions for directed self assembly of block copolymers

Over the past 15 years, block copolymer lithography has emerged as its own research field within the broader block copolymer and polymer thin film communities. This distinction is associated with the unique requirements set by the semiconductor device industry, such as low-defect densities, precise feature registration, and complex pattern layouts. To achieve perfection in block copolymer lithography, the surface and substrate interactions must be carefully tuned to control domain ordering in three dimensions. This perspective discusses recent modeling efforts that underline the challenges of predicting interfacial interactions and the resulting block copolymer structures. We emphasize studies that facilitate the design and interpretation of experiments, including materials selection, guiding pattern geometry, and selecting tools for three-dimensional metrology. Finally, we propose that translation of block copolymer lithography to semiconductor manufacturing will require integrated experimental and modeling efforts to interrogate the vast parameter space that controls both lateral and out-of-plane ordering. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 96–102     

Molybdenum complexes of bioinorganic interest. New dioxomolybdenum(VI) complexes of schiff bases derived from salicylaldehydes and salicylhydrazide

Summary New dioxomolybdenum(VI) complexes MoO₂L · H₂O (LH₂=Schiff base) derived from Salicylhydrazide and salicylaldehyde, 5-chloro-, 5-bromo-, 5-nitro-, 3-methoxy, 3-ethoxy-, 3,5-dichlorosalicylaldehyde and 2-hydroxy-1-naphthaldehyde have been synthesized and characterized, together with the MoO₂L · THF adducts. The complexes are monomers, nonelectrolytes and diamagnetic, and contain acis O=Mo=O     

Configuration dependent critical nuclei in the self assembly of magic clusters

Evidence for the formation of various 2-D structures possessing different numbers of Co-Si magic clusters (size approximately 10.0 +/- 0.5 A), configurations and lifetimes are studied in real time on a Si(111)-(7 x 7) surface at elevated temperature in the STM. Observations of individual cluster diffusion, attachment and detachment dynamics resolve unequivocally the question of self assembly over surface reconstruction. The smallest stable structure consisting of seven individual Co-Si magic clusters arranged in a hexagonal closed packed formation (i = 7) is found to retain sufficient cohesive energy to avoid dissociation. A configuration dependent critical 2-D nuclei (i* = 6) is determined to exist in facilitating the self assembly dynamics.     

Molecules to supermolecules and self assembly: a study of some cocrystals of cyanuric acid

The preparation and structure elucidation of cocrystals 1a, 1b, 2a-4a, formed from cyanuric acid (CA) and the aza-donor compounds 4,7-phenanthroline, 1,7-phenanthroline, phenazine and 1,3-bis(4-pyridyl)propane, respectively, have been reported. While CA forms different types of self-assembling modes—monomers (1a), dimers (1b and 4a) and infinite tapes (2a and 3a)—the recognition of the constituents, however, is through a triple hydrogen-bonding pattern, consisting of an N-H?N and two C-H?O hydrogen bonds, except in 4a.     

Core charge distribution and self assembly of columnar phases: the case of triphenylenes and azatriphenylenes

Background  

The relation betweeen the structure of discotic molecules and columnar properties, a crucial point for the realization of new advanced materials, is still largely unknown. A paradigmatic case is that hexa-alkyl-thio substituted triphenylenes present mesogenic behavior while the corresponding azatriphenylenes, similar in shape and chemical structure, but with a different core charge distribution, do not form any liquid crystalline mesophase. This study is aimed at investigating, with the help of computer simulations techniques, the effects on phase behaviour of changes of the charge distribution in the discotic core.     

Polyoxometalate clusters, nanostructures and materials: from self assembly to designer materials and devices

Polyoxometalates represent a diverse range of molecular clusters with an almost unmatched range of physical properties and the ability to form structures that can bridge several length scales. The new building block principles that have been discovered are beginning to allow the design of complex clusters with desired properties and structures and several structural types and novel physical properties are examined. In this critical review the synthetic and design approaches to the many polyoxometalate cluster types are presented encompassing all the sub-types of polyoxometalates including, isopolyoxometalates, heteropolyoxometalates, and reduced molybdenum blue systems. As well as the fundamental structure and bonding aspects, the final section is devoted to discussing these clusters in the context of contemporary and emerging interdisciplinary interests from areas as diverse as anti-viral agents, biological ion transport models, and materials science.     

Metallo-macrocycles with labile coordination sites through self assembly: binuclear phenyl bridged bisbipyridine manganese complexes

Self assembly of phenyl bridged bisbipyridines with manganese perchlorate gave structurally different metallo-macrocycles having cis-labile coordination sites which can catalyse olefin epoxidation with peracetic acid in good yield.     

RPM-2: a recyclable porous material with unusual adsorption capability: self assembly via structural transformations

Structural transformation via deliberate and partial topological changes in a grid network structure has led to a three-dimensional, fully recyclable porous material (RPM-2) with a very high sorption capability.     

Coordination-induced branched self-assembly of porphyrins bearing two redox-active phenylenediamine chains

The porphyrins bearing two three-dimensionally regulated oligoaniline chains with terminal pyridyl groups were synthesized. The self-assembled branched polymer complex by introducing Zn(II) to the porphyrin was achieved in solution, which underwent dropcasting on the surface of mica to result in dome-like nanostructures.     

Coordination-driven self assembly of a brilliantly fluorescent rhomboid cavitand composed of bodipy-dye subunits

The two sp(3) hybridized fluorine atoms of a Bodipy dye have been synthetically replaced with the linear donor ligand 4-ethynylpyridine (-C≡C-Py) to form a rigid and highly symmetrical 109.5° building block in which the fluorophore subunit is vertically aligned to the plane formed by the -C≡C-Py donors. Upon reaction of the above tecton with a 90° organoplatinum acceptor unit, an intensely fluorescent rhomboid cavitand was manifested in solution. In contrast to the vast majority of coordination-driven self-assembled chromophoric systems, the present one fully conserves the excellent photophysical properties of the parent Bodipy dye. These unique features of the present metallosupramolecular entity constitute a fascinating metal-to-ligand self-assembled prototype for building compact and intensely luminescent materials with host-guest capabilities.     

Preparation,Surface, and Biological Activities of Some Novel Metallosurfactants

A series of novel metallosurfactants (III_a-d) was prepared and evaluated as surface active agents. The synthesis was carried out through two steps: the first was the reaction of fatty acids (I_a-d) (lauric, palmitic, myristic and steric acid) with morpholine (tetrahydro-1,4-oxazine) to give morpholin-4-yl-alkan-1-one (II_a-d), respectively. The second step is reaction of product of the first step (compounds II_a-d) with Fe (III) to give (III_a-d) metallosurfactants. The chemical structures of the prepared compounds were elucidated with elemental analysis, FTIR and ¹H NMR spectroscopic tools. The surface properties of the prepared metallosurfactants were determined at different temperature 25, 35, and 45°C. The surface tension (γ), critical micelle concentration (CMC), surface tension at CMC (γ_cmc), effectiveness (π_cmc), efficiency (Pc_2o), maximum surface excess (Γ_max), and minimum surface area (A_min) were determined. Thermodynamic data including, free energy, entropy and enthalpy changes (ΔG, ΔS, ΔH) for adsorption at the air–water interface and also for micellization in the bulk of surfactant solutions were calculated. The antimicrobial activity of the prepared compounds was determined via the inhibition zone diameter technique against Gram-positive, Gram-negative bacteria, and some fungal strains as mold and yeast. The results indicate that the prepared ferrosurfactants have a good surface properties and biological activities against the tested microorganism.     

A zinc(II) amidine complex: tandem synthesis,structure, and self assembly

A five-coordinate zinc(II) amidine complex, [Zn(DEP)(N₃)₂] (DEP = N′-(2-(diethylamino)ethyl)picolinamidine), has been synthesized with 2-cyanopyridine and sodium azide in the presence of zinc(II) acetate dihydrate. The structure of the complex is confirmed by single-crystal X-ray diffraction analysis. The complex crystallizes in triclinic space group P-1 with cell dimensions a = 7.486(5) Å, b = 7.678(5) Å, c = 14.480(5) Å, α?=?96.697(5)°, β = 90.282(5)°, and γ?=?95.716(5)°. The hydrogen bonding interactions in the complex lead to the formation of a 2-D supramolecular network. The complex shows fluorescence with lifetime ~4 ns.