Chiral versus Achiral Assemblies in Multi-Stimuli Responsive Supramolecular Polymerization of Tetra-Substituted Azobenzene Dye.

Incorporating photoswitchable moieties into the molecular design of supramolecular architectures provides unique opportunities for controlling their morphology and functionality via optical stimuli. Harnessing geometrical and electrical changes in response to multiple external stimuli on the molecular level to modulate properties remains a fundamental challenge. Herein, the reversible formation of the aggregates of l-tyrosine E-azobenzene-tetracarboxamide (E-ABT) is shown to be finely controlled by light, solvent, or chemical additives. The resulting products differ not only in their overall morphology and supramolecular interactions, but also in their intrinsic chirality, that is, depending on the conditions applied, self-assembly yields chiral columns or π-stacked "achiral" oligomers. This report shows the potential of rational monomer design to achieve controlled self-assembly by stimuli of choice and paves the way toward the use of multi-responsive, sterically hindered azo-benzene aggregates in materials chemistry and nanotechnology.

Self-assembly of a fluorescent hydrogen-bonded capsule based on an amino-acid functionalised tetraphenylethylene.

Herein we report the self-assembly of an amino-acid substituted tetraphenylethylene (TPE) into a hydrogen-bonded dimeric capsule. Depending on the conditions applied the presented TPE derivative exhibits bluish photoluminescence with QYs up to 24% due to the AIE effect and excimer formation.

Enhanced catalytic performance derived from coordination-driven structural switching between homometallic complexes and heterometallic polymeric materials.

A bifunctional ligand 4,4-dimethyl-1-(pyridin-4-yl)pentane-1,3-dione (HL) able to provide two distinct coordination sites, i.e. anionic ß-diketonate (after deprotonation) and neutral pyridine, has been used in the synthesis of Ag(I), Pd(II) and Pt(II) complexes that then have been applied as metalloligands for the construction of new heterometallic polymeric materials. The ambidentate nature of L- enables switching between different modes of coordination within mononuclear complexes or their conversion into polymeric species in a fully controllable way. The coordination-driven processes can be triggered by various stimuli, i.e. a metal salt addition or acid-base equilibria, and presents an efficient strategy for the generation of metallosupramolecular materials. As a consequence of self-assembly, new multimetallic coordination aggregates have been synthesized and characterized in depth in solution (1H NMR, ESI-MS) as well as in the solid state (XPS, SEM-EDS, FTIR, pXRD, TGA). Furthermore, the Pd-based assemblies have been found to be efficient catalyst precursors in the Heck cross-coupling reaction, demonstrating a direct impact of compositional and morphological differences on their catalytic activity.

Chiral Supramolecular Polymers Assembled from Conformationally Flexible Amino-Acid-Substituted Biphenyldiimides.

Hydrogen-bonded polymers are a class of highly dynamic supramolecular aggregates, whose self-assembly may be tuned by very mild external or internal stimuli. However, the rational design of chiral supramolecules remains challenging especially when flexible components are involved. The combination of the inherent weakness and dynamic nature of the intermolecular bonds that hold together such assemblies with unrestricted molecular motions introduces additional factors which may affect the self-assembly process. In this report, the self-assembly of four amino acid-derived chiral biphenyldiimides into open-chain 1D supramolecular polymers is presented. While the primary driving force, COOH···HOOC hydrogen bonding, is responsible for the polymer growth in all cases, the amino acid side chains play an important role in either stabilizing or destabilizing the assemblies obtained, as deduced from studies of the thermodynamics of the self-assembly process. Furthermore, substantial differences in the structural factors governing the polymerization process between dynamic liquid and static solid are found. This work demonstrates the potential of the rather unexplored class of diimide-based organic dyes in the formation of well-organized chiral supramolecular assemblies with tunable properties.

Why POSS-Type Compounds Should Be Considered Nanomodifiers, Not Nanofillers-A Polypropylene Blends Case Study.

In this work, a series of silsesquioxanes (SSQ) and spherosilicates (SS), comprising a group of cage siloxane (CS) compounds, was tested as functional additives for preparation of isotactic polypropylene (iPP)-based nanocomposites and discussed in the aspect of their rationale of applicability as such additives. For this purpose, the compounds were prepared by condensation and olefin hydrosilylation reactions. The effect of these cage siloxane products on properties of obtained CS/iPP nanocomposites was analyzed by means of mechanical, microscopic (scanning electron microscopy-energy dispersive spectroscopy), thermal (differential scanning calorimetry, thermogravimetry), thermomechanical (Vicat softening point) analyses. The results were compared with the previous findings on CS/polyolefin composites. The role of CS compounds was discussed in terms of plastic processing additives.

A substituent-induced post-assembly modification cascade of a metallosupramolecular imine-type Co-complex.

Here, we report a reaction cascade employing the substituent-induced post-assembly modification of a Co(iii) complex. Unexpectedly, we found that the (triisopropylsilyl)alkynyl moiety introduced to the Sonogashira reaction with the bromo-functionalized Co(iii) assembly plays a "Trojan horse" role, triggering a subsequent, second step of the cascade, i.e. Co(iii) to Co(ii) reduction. The reported substituent-activated Sonogashira-redox cascade reaction might set a new direction in the construction of specific chemical sensors.

The Influence of Mucin-Based Artificial Saliva on Properties of Polycaprolactone and Polylactide.

Polycaprolactone (PCL) and polylactide (PLA) are the two most common biodegradable polymers with potential use in oral applications. Both polymers undergo mainly slow hydrolytic degradation in the human body. However, specific conditions of the oral cavity, like elevated temperature, low pH, and presence of saliva affect the rate of hydrolysis. The study examined the properties of solid samples of PCL and PLA subjected to degradation in phosphate buffered saline (PBS) and artificial saliva (AS) at temperatures of 37 or 42 °C, and pH values 2 or 7.4. A number of tests were performed, including measurement of the degree of swelling, weight loss, molecular weight, differential scanning calorimetry, and thermogravimetry of polymers, as well as hardness and tensile strength. Additionally, topography and stiffness of surfaces using atomic force microscopy are presented. It has been noticed that in the artificial saliva, the processes of polymer degradation occur slightly more slowly, and the effects of temperature and pH are less pronounced. We believe that a layer of porcine gastric mucin from artificial saliva that adsorbed on the surface of polymers may have a key role in the observed differences; this layer resembles protective mucin coating tissues in the oral cavity.

Steering the Self-Assembly Outcome of a Single NDI Monomer into Three Morphologically Distinct Supramolecular Assemblies, with Concomitant Change in Supramolecular Polymerization Mechanism.

Noncovalent self-assembly creates an effective route to highly sophisticated supramolecular polymers with tunable properties. However, the outcome of this assembly process is highly dependent on external conditions. In this work, a monomeric naphthalene diimide (NDI), designed to allow solubility in a wide range of solvents, can assemble into three distinct noncovalent supramolecular species depending on solvent composition and temperature. Namely, while the self-assembly in chlorinated solvents yields relatively short, hydrogen-bonded nanotubes, the reduction of solvent polarity changes the assembly outcome, yielding π-π stacking polymers, which can further bundle into a more complex aggregate. The obtained polymers differ not only in their global morphology but-more strikingly-also in the thermodynamics and kinetics of their supramolecular self-assembly, involving isodesmic or two-stage cooperative assembly with kinetic hysteresis, respectively. Ultimately, three distinct assembly states can be accessed in a single experiment.

Highly efficient one-step microwave-assisted synthesis of structurally diverse bis-substituted α-amino acid derived diimides.

We report herein a facile and widely applicable microwave-assisted protocol for the synthesis of symmetrical diimides based on three structurally distinct aromatic dianhydrides: pyromellitic (PMA), biphenyl-tetracarboxylic acid (BPDA) and benzophenone-tetracarboxylic (BTDA) and five natural amino acids (Phe, Tyr, Ile, Lys, Cys). Fifteen symmetrical diimides with different structural characteristics containing a variety of functional groups can be produced with high yields and on a large scale.

Generation and transformation of a hemi-iminal-based metal-organic Fe(ii) structure obtained via subcomponent self-assembly in water.

We report the synthesis and characterization of a coordination architecture with a Fe(ii) center obtained by subcomponent self-assembly in water. The complex is based on very rare hemi-iminal ligands spontaneously generated from commercially available materials. The complex can be further transformed into another species by oxidation reaction of both the metal center and organic ligand.

Self-organization of amino-acid-derived NDI assemblies into a nanofibrillar superstructure with humidity sensitive n-type semiconducting properties.

The hierarchical self-assembly of l-tyrosine substituted naphthalenediimide has been explored in solution by NMR spectroscopy and in the solid-state by atomic force microscopy. Spontaneous non-covalent polymerisation led to the formation of a three-dimensional fibre-like supramolecular polymer with n-type semiconducting properties.

Generation of Low-Dimensional Architectures through the Self-Assembly of Pyromellitic Diimide Derivatives.

Small π-conjugated molecules can be designed and synthesized to undergo controlled self-assembly forming low-dimensional architectures, with programmed order at the supramolecular level. Such order is of paramount importance because it defines the property of the obtained material. Here, we have focused our attention to four pyromellitic diimide derivatives exposing different types of side chains. The joint effect of different noncovalent interactions including π-π stacking, H-bonding, and van der Waals forces on the four derivatives yielded different self-assembled architectures. Atomic force microscopy studies, corroborated with infrared and nuclear magnetic resonance spectroscopic measurements, provided complementary multiscale insight into these assemblies.

Selective C70 encapsulation by a robust octameric nanospheroid held together by 48 cooperative hydrogen bonds.

Self-assembly of multiple building blocks via hydrogen bonds into well-defined nanoconstructs with selective binding function remains one of the foremost challenges in supramolecular chemistry. Here, we report the discovery of a enantiopure nanocapsule that is formed through the self-assembly of eight amino acid functionalised molecules in nonpolar solvents through 48 hydrogen bonds. The nanocapsule is remarkably robust, being stable at low and high temperatures, and in the presence of base, presumably due to the co-operative geometry of the hydrogen bonding motif. Thanks to small pore sizes, large internal cavity and sufficient dynamicity, the nanocapsule is able to recognize and encapsulate large aromatic guests such as fullerenes C60 and C70. The structural and electronic complementary between the host and C70 leads to its preferential and selective binding from a mixture of C60 and C70.

Photoisomerisation and light-induced morphological switching of a polyoxometalate-azobenzene hybrid.

The functionalization of a spherical Keplerate-type polyoxometalate {Mo72V30} with a cationic azobenzene surfactant has been achieved through ionic self-assembly. The photoisomerisation reaction of this complex, which emerges in a light-triggered aggregation-disaggregation process, has been followed by 1H NMR spectroscopy, dynamic light scattering, absorption spectroscopy and scanning electron microscopy analyses.

Complexation of phosphates by 1,3-bis(3-(2-pyridylureido)propyl)-1,1,3,3-tetramethyldisiloxane.

RATIONALE: Compounds containing a urea or thiourea moiety form complexes with anions thanks to the ability to form quite strong hydrogen bonds. We have synthesized 1,3-bis(3-(2-pyridylureido)propyl)-1,1,3,3-tetramethyldisiloxane (1). Compound 1 contains two urea moieties connected by a long flexible linker; thus, it should be able to adopt a structure suitable for formation of quite stable complexes with anions. METHODS: The ability to form complexes of compound 1 with phosphates was tested by electrospray ionization mass spectrometry (ESI-MS). Full scan ESI mass spectra and collision-induced dissociation tandem mass (CID-MS/MS) spectra of the ions of interest were obtained on a quadrupole time-of-flight (QTOF) mass spectrometer. RESULTS: It has been found that compound 1 is not only much more prone to form complexes with the phosphate anion than with other inorganic anions, but it is also able to form complexes with organic phosphates, namely nucleotides and phospholipids. However, compound 1 is not able to form complexes with organic compounds not containing a phosphate group (e.g. nucleosides, sugars, glycerolipids). CONCLUSIONS: Compound 1 can be regarded as selective towards phosphate-containing organic compounds. Formation of such complexes may have some interesting applications for identification of organic phosphates in crude extracts from biological materials.

Generation of a Multicomponent Library of Disulfide Donor-Acceptor Architectures Using Dynamic Combinatorial Chemistry.

We describe here the generation of new donor-acceptor disulfide architectures obtained in aqueous solution at physiological pH. The application of a dynamic combinatorial chemistry approach allowed us to generate a large number of new disulfide macrocyclic architectures together with a new type of [2]catenanes consisting of four distinct components. Up to fifteen types of structurally-distinct dynamic architectures have been generated through one-pot disulfide exchange reactions between four thiol-functionalized aqueous components. The distribution of disulfide products formed was found to be strongly dependent on the structural features of the thiol components employed. This work not only constitutes a success in the synthesis of topologically- and morphologically-complex targets, but it may also open new horizons for the use of this methodology in the construction of molecular machines.