Oligo(phenyleneethynylene)s: Shape-Tunable Building Blocks for Supramolecular Self-Assembly.

Oligo(phenyleneethynylene)s (OPEs) have attracted widespread attention due to their remarkable (opto)electronic and photophysical properties, which have enabled numerous applications. The versatile functionalization possibilities of OPEs make them unique candidates to form various shape-persistent geometries, including linear, triangular, rectangular, hexagonal and macrocyclic. However, as a result of this structural variety, it is oftentimes challenging to correlate molecular design with self-assembly properties. In this minireview, we have classified OPEs based on their molecular shapes and correlated them with their self-assembly behavior in solution. Particularly, we provide important insights into the aggregation propensity of the different molecular shapes and how to tune the association strength using various non-covalent interactions. Our classification will enable a better understanding of the structure-property correlation in OPEs, which is key to develop supramolecular functional materials.

Exploiting halido ligands to control nucleation pathways and Pt⋯Pt interactions in supramolecular co-polymerizations.

We use different halido ligands to tune metal-metal interactions, nucleation pathways and hetero-seeded growth in supramolecular copolymerizations.

Expanding the Scope of Metastable Species in Hydrogen Bonding-Directed Supramolecular Polymerization.

We reveal unique hydrogen (H-) bonding patterns and exploit them to control the kinetics, pathways and length of supramolecular polymers (SPs). New bisamide-containing monomers were designed to elucidate the role of competing intra- vs. intermolecular H-bonding interactions on the kinetics of supramolecular polymerization (SP). Remarkably, two polymerization-inactive metastable states were discovered. Contrary to previous examples, the commonly assumed intramolecularly H-bonded monomer does not evolve into intermolecularly H-bonded SPs via ring opening, but rather forms a metastable dimer. In this dimer, all H-bonding sites are saturated, either intra- or intermolecularly, hampering elongation. The dimers exhibit an advantageous preorganization, which upon opening of the intramolecular portion of the H-bonding motif facilitates SP in a consecutive process. The retardation of spontaneous self-assembly as a result of two metastable states enables length control in SP by seed-mediated growth.

Elucidating the Supramolecular Copolymerization of N- and C-Centered Benzene-1,3,5-Tricarboxamides: The Role of Parallel and Antiparallel Packing of Amide Groups in the Copolymer Microstructure.

An in-depth study of the supramolecular copolymerization behavior of N- and C-centered benzene-1,3,5-tricarboxamides (N- and C-BTAs) has been conducted in methylcyclohexane and in the solid state. The connectivity of the amide groups in the BTAs differs, and mixing N- and C-BTAs results in supramolecular copolymers with a blocky microstructure in solution. The blocky microstructure results from the formation of weaker and less organized, antiparallel hydrogen bonds between N- and C-BTAs. In methylcyclohexane, the helical threefold hydrogen-bonding network present in C- and N-BTAs is retained in the mixtures. In the solid state, in contrast, the hydrogen bonds of pure BTAs as well as their mixtures organize in a sheet-like pattern, and in the mixtures long-range order is lost. Drop-casting to kinetically trap the solution microstructures shows that C-BTAs retain the helical hydrogen bonds, but N-BTAs immediately adopt the sheet-like pattern, a direct consequence of the lower stabilization energy of the helical hydrogen bonds. In the copolymers, the stability of the helical aggregates depends on the copolymer composition, and helical aggregates are only preserved when a high amount of C-BTAs is present. The method outlined here is generally applicable to elucidate the copolymerization behavior of supramolecular monomers both in solution as well as in the solid state.

Merging Supramolecular and Covalent Helical Polymers: Four Helices Within a Single Scaffold.

Supramolecular and covalent polymers share multiple structural effects such as chiral amplification, helical inversion, sergeants and soldiers, or majority rules, among others. These features are related to the axial helical structure found in both types of materials, which are responsible for their properties. Herein a novel material combining information and characteristics from both fields of helical polymers, supramolecular (oligo(p-phenyleneethynylene) (OPE)) and covalent (poly(acetylene) (PA)), is presented. To achieve this goal, the poly(acetylene) must adopt a dihedral angle between conjugated double bonds (ω1) higher than 165°. In such cases, the tilting degree (Θ) between the OPE units used as pendant groups is close to 11°, like that observed in supramolecular helical arrays of these molecules. Polymerization of oligo[(p-phenyleneethynylene)n]phenylacetylene monomers (n = 1, 2) bearing L-decyl alaninate as the pendant group yielded the desired scaffolds. These polymers adopt a stretched and almost planar polyene helix, where the OPE units are arranged describing a helical structure. As a result, a novel multihelix material was prepared, the ECD spectra of which are dominated by the OPE axial array.

From Oligo(Phenyleneethynylene) Monomers to Supramolecular Helices: The Role of Intermolecular Interactions in Aggregation.

Supramolecular helices that arise from the self-assembly of small organic molecules via non-covalent interactions play an important role in the structure and properties of the corresponding materials. Here we study the supramolecular helical aggregation of oligo(phenyleneethynylene) monomers from a theoretical point of view, always guiding the studies with experimentally available data. In this way, by systematically increasing the number of monomer units, optimized n-mer geometries are obtained along with the corresponding absorption and circular dichroism spectra. For the geometry optimizations we use density functional theory together with the B3LYP-D3 functional and the 6-31G** basis set. For obtaining the spectra we resort to time-dependent density functional theory using the CAM-B3LYP functional and the 3-21G basis set. These combinations of density functional and basis set were selected after systematic convergence studies. The theoretical results are analyzed and compared to the experimentally available spectra, observing a good agreement.

The Competitive Aggregation Pathway of an Asymmetric Chiral Oligo(p-phenyleneethynylene) Towards the Formation of Individual P and M Supramolecular Helical Polymers.

A complex aggregation pathway towards two diastereomeric P and M supramolecular helices arises from the aggregation of a short, chiral, and rigid oligo(phenyleneethynylene) [OPE, (S)-1]. Thus, while AggI aggregate is obtained when a DCM solution of (S)-1 is diluted with MCH at room temperature, AggII aggregate is generated only after a slow heating (353 K)/cooling (273 K) process. Interestingly, during AggI formation (mechanism 1), short P chain oligomers are produced, which have a great tendency to aggregate in plane, yielding brick-like nanostructures that halt the aggregation process. On the other hand, after a heating/cooling cycle, long M type columnar helical aggregates (AggII ) are obtained, formed by individual supramolecular polymer chains (mechanism 2) easily visualized by AFM. The two different P/M orientations obtained for AggI and AggII reveal the dynamic character of the system and its ability to create diastereomeric helical structures under the right conditions. Different experimental protocols were explored to prepare long M type columnar helical aggregates, which are not obtained by using the previous MCH/DCM 99/1 (v/v) solvent mixture. The generation of the desired M oriented supramolecular polymer is achieved when toluene is added to the solvent mixture in a 97/2/1 MCH/Tol/DCM (v/v/v) ratio.

Chiral information harvesting in helical poly(acetylene) derivatives using oligo(p-phenyleneethynylene)s as spacers.

A chiral harvesting transmission mechanism is described in poly(acetylene)s bearing oligo(p-phenyleneethynylene)s (OPEs) used as rigid achiral spacers and derivatized with chiral pendant groups. The chiral moieties induce a positive or negative tilting degree in the stacking of OPE units along the polymer structure, which is further harvested by the polyene backbone adopting either a P or M helix.

Macromolecular helicity control of poly(phenyl isocyanate)s with a single stimuli-responsive chiral switch.

The introduction of a single chiral substituent with a switchable conformer equilibrium at the poly(phenyl isocyanate) terminus allowed the control of the helical sense of the polymer backbone using various external stimuli. Helical sense enhancement was achieved through a domino effect, where the helical sense was assigned by VCD spectroscopy and DFT calculations.

Disminución paradójica del tamaño en dos de 54 masas mamarias no palpables BI- RADS V tras la realización de una PAAF. Análisis de los cambios citohistológicos atribuibles a la PAAF y su posible repercusión mamográfica y ecográfica / Paradoxical decrease in the size of two of 54 BI-RADS category 5 non- Palpable. Breast MASSES after FNA. Analysis of cytohistological changes attributable to FNA and possible mammographic and echographic repurcussions

Objetivos: Analizar los cambios mamográficos y ecográficos apreciados en masas mamarias sospechosas, previamente estudiadas mediante punción aspiración con aguja fina (PAAF) y su hipotética relación con los cambios tisulares atribuibles a dicho procedimiento intervencionista.Material y métodos: Se evaluaron 54 masas no palpables BIRADS V detectadas en mamografías de chequeo, a las que se realizó una biopsia quirúrgica tras la práctica de una PAAF. Se estudiaron los hallazgos mamográficos y ecográficos y el tamaño tumoral de las masas antes y después de la punción. También se revisaron las biopsias quirúrgicas para verificar los cambios histológicos probablemente provocados por la PAAF.Resultados: Se analizaron tres carcinomas ductales in situ, 50 neoplasias infiltrantes y un fibroadenoma. Tan sólo en dos carcinomas infiltrantes observamos cambios paradójicos en la mamografía y ecografía, tales como disminución del tamaño, después de la PAAF. Sin embargo, en los estudios anatomopatológicos encontramos cambios atribuibles a la punción en 18 casos, en todos había reacción inflamatoria y en tres necrosis.Conclusiones: Los fenómenos inflamatorios o la necrosis tumoral que razonablemente pueden ser atribuidos a la practica de una PAAF, infrecuentemente pueden ir asociados con cambios radiológicos tales como la disminución del tamaño de las masas estudiadas (AU)