Sequence,Stoichiometry, and Dimensionality Control in Porphyrin/Bis‐calix[4]arene Self‐Assemblies in Aqueous Solution

The use of a water‐soluble octacationic bis‐calix[4]arene with divergent cavities (BC₄) as a templating agent for the assembly of a tetraanionic porphyrin (CuTPPS) has allowed the noncovalent synthesis of 2D or 3D multiporphyrin assemblies. Self‐assembly of CuTPPS and BC₄ molecules proceeded under hierarchical control in a stepwise fashion to yield discrete and isolable supramolecular nanostructures containing up to 33 molecular elements (i.e., the CuTPPS/BC₄ 17:16 assembly, obtained in less than three hours). The formation of these species could be conveniently monitored by means of UV/Vis spectroscopy by following the absorbance of the Soret band at 412 nm. In particular, the attainment of the pivotal CuTPPS/BC₄ 5:4 species with a cruciform structure, as the key fork‐point intermediate for the subsequent formation of the higher 2D and 3D assemblies, has been demonstrated by light‐scattering studies and by an unequivocal synthesis of mixed‐porphyrin/calixarene 5:4 species involving the use of two different types of metallated porphyrins, namely CuTPPS and MnTPPS. The remarkable stability of these assemblies permits a stepwise synthesis that makes it possible to choose the desired porphyrin sequence.     

Stepwise synthesis and selective dimerisation of bis- and trisloop tetra-urea calix[4]arenes

Tetra-urea calix[4]arenes substituted with four mono- or bisalkenyl residues have been converted into bis- or tetraloop compounds by intramolecular olefin metathesis, with use of a tetratosylurea calix[4]arene as template. The same strategy has now been used to synthesise trisloop compounds and bisloop compounds with adjacent loops, completing the series of the loop-containing tetra-urea derivatives. A tetra-urea calix[4]arene of the AABB type, where A stands for a bisalkenyl- and B for a monoalkenyl-substituted urea unit, was used as precursor for the three loops. It was easily synthesised from a tetraamino calix[4]arene in which two adjacent amino groups were Boc-protected. The ABCB-type precursor for the two adjacent loops was prepared through protection of two opposite amino functions with trityl groups. The capabilities of the novel macrocyclic tetra-ureas for the selective formation of hydrogen-bonded dimers were studied.     

Polyelectrolyte-induced self-assembly of positively charged alkynylplatinum(II)-terpyridyl complexes in aqueous media

Polyelectrolytes carrying multiple negative charges were found to induce the aggregation and self-assembly of the positively charged platinum(II)-terpyridyl complexes in aqueous media. The aggregation and self-assembly of the complexes were driven by electrostatic interactions between the polymer and the complex, and by terpyridine ligand pi-pi stacking and platinum-platinum (metal-metal) interactions. As a result, remarkable UV/Vis and emission spectral changes were observed. The spectroscopic property changes were related to the structural properties of the metal complexes as well as the polyelectrolytes. The induced self-assembly of the platinum complexes was also strongly affected by the solution properties of the aqueous media, for example, the solution pH, ionic strength, and the percentage of organic solvent added.     

Noncovalent Assembly of Picket‐Fence Porphyrins on Nitrogen‐Doped Carbon Nanotubes for Highly Efficient Catalysis and Biosensing

A water‐insoluble picket‐fence porphyrin was first assembled on nitrogen‐doped multiwalled carbon nanotubes (CN_x MWNTs) through Fe? N coordination for highly efficient catalysis and biosensing. Scanning electron micrographs, Raman spectra, X‐ray photoelectron spectra, UV/Vis absorption spectra, and electrochemical impedance spectra were employed to characterize this novel nanocomposite. By using electrochemical methods on the porphyrin at low potential in neutral aqueous solution, the presence of CN_x MWNTs led to the direct formation of a high‐valent iron(IV)–porphyrin unit, which produced excellent catalytic activity toward the oxidation of sulfite ions. By using sulfite ions, a widely used versatile additive and preservative in the food and beverage industries, as a model, a highly sensitive amperometric biosensor was proposed. The biosensor showed a linear range of four orders of magnitude from 8.0×10^?7 to 4.9×10^?3 mol L^?1 and a detection limit of 3.5×10^?7 mol L^?1 due to the highly efficient catalysis of the nanocomposite. The designed platform and method had good analytical performance and could be successfully applied in the determination of sulfite ions in beverages. The direct noncovalent assembly of porphyrin on CN_x MWNTs provided a facile way to design novel biofunctional materials for biosensing and photovoltaic devices.     

Size‐Regulable Vesicles Based on Anion–π Interactions

Taking tetraoxacalix[2]arene[2]triazine as a functionalization platform, a series of new amphiphilic molecules were synthesized in 18 to 53 % yields by using a fragment coupling protocol. These amphiphilic molecules self‐assembled into stable vesicles in a mixture of THF and water, with the surface of the vesicles engineered by electron‐deficient cavities. Various anions are able to selectively influence the size of self‐assembled vesicles, following the order of F^?<ClO₄^?<SCN^?<BF₄^?<Br^?<Cl^?<NO₃^?, as revealed by DLS measurements. Such a sequence was independent with the hydration cost and in agreement with the binding strength of anions with tetraoxacalix[2]arene[2]triazine host molecule, indicating that the anion–π interaction most probably competed over other possible weak interactions and accounted for this interesting selectivity. In addition, the chloride permeation process across the membrane of the vesicles was also preliminarily studied by means of fluorescent experiments. This study, in addition to providing the potentiality of heteracalixaromatics as new models to construct functional vesicles, opens a new avenue to study the anion–π interactions in aqueous and also potentially in living systems.     

Hydrophobic Self‐Assembly Affords Robust Noncovalent Polymer Isomers

In covalent polymerization, a single monomer can result in different polymer structures due to positional, geometric, or stereoisomerism. We demonstrate that strong hydrophobic interactions result in stable noncovalent polymer isomers that are based on the same covalent unit (amphiphilic perylene diimide). These isomers have different structures and electronic/photonic properties, and are stable in water, even upon prolonged heating at 100 °C. Such combination of covalent‐like stability together with structural/functional variation is unique for noncovalent polymers, substantially advancing their potential as functional materials.     

High‐Fidelity Noncovalent Synthesis of Hydrogen‐Bonded Macrocyclic Assemblies

A hydrogen‐bonded cyclic tetramer is assembled with remarkably high effective molarities from a properly designed dinucleoside monomer. This self‐assembled species exhibits an impressive thermodynamic and kinetic stability and is formed with high fidelities within a broad concentration range.     

Adaptive Correction from Virtually Complex Dynamic Libraries: The Role of Noncovalent Interactions in Structural Selection and Folding

The hierarchical self‐assembling of complex molecular systems is dictated by the chemical and structural information stored in their components. This information can be expressed through an adaptive process that determines the structurally fittest assembly under given environmental conditions. We have set up complex disulfide‐based dynamic covalent libraries of chemically and topologically diverse pseudopeptidic compounds. We show how the reaction evolves from very complex mixtures at short reaction times to the almost exclusive formation of a major compound, through the establishment of intramolecular noncovalent interactions. Our experiments demonstrate that the systems evolve through error‐check and error‐correction processes. The nature of these interactions, the importance of the folding and the effects of the environment are also discussed.     

Mesoporous carbon materials: synthesis and modification

Porous carbon materials are of interest in many applications because of their high surface area and physicochemical properties. Conventional syntheses can only produce randomly porous materials, with little control over the pore-size distributions, let alone mesostructures. Recent breakthroughs in the preparation of other porous materials have resulted in the development of methods for the preparation of mesoporous carbon materials with extremely high surface areas and ordered mesostructures, with potential applications as catalysts, separation media, and advanced electronic materials in many scientific disciplines. Current syntheses can be categorized as either hard-template or soft-template methods. Both are examined in this Review along with procedures for surface functionalization of the carbon materials obtained.     

A Porphyrin Coordination Cage Assembled from Four Silver(I) Triazolyl‐Pyridine Complexes

The synthesis of a zinc(II) porphyrin 1 with four appended triazolyl–pyridine chelates is reported. Complexation of the porphyrin peripheral ligands with Ag^I ions in a 1:2 binding stoichiometry afforded quantitatively the coordination cage [Ag₄( 1 )₂]⁴⁺. The assembly and disassembly processes of the cage were investigated in solution using UV/Vis spectroscopy. The mathematical analysis of the data obtained in the UV/Vis titration of 1 with Ag^I confirmed the assembly in CH₂Cl₂/MeOH (90:10) solution of a species having a 1:2 porphyrin/silver stoichiometry and assigned to it an overall stability constant of 5.0×10²⁶ M ^?5. The use of a model system allowed an independent assessment of a microscopic binding constant value (K_m) for the interaction between the triazolyl‐pyridine ligand and Ag^I. The coincidence that existed between the K_m values extracted from the model system and the titration of 1 provided an indication of the quality and fit of the data analysis. It also allowed the calculation of the average effective molarity (EM) value for the three intramolecular processes that led to the cage assembly as 2.6 mM . Simulated speciation profiles supported the conclusion that at millimolar concentration and working under strict stoichiometric control of the silver/porphyrin ratio, the cage [Ag₄( 1 )₂]⁴⁺ was the species exclusively assembled in solution. On the other hand, when the concentration of added Ag^I was approximately 2.6 mM , 50 % of the coordination cage disassembled into open aggregates.