Félix Freire

University of Santiago de Compostela | USC · Centro Singular de Investigación en Química Biológica y Materiales Moleculares (CIQUS)

Chiral information transmission in helical polymers bearing multi-chiral pendant groups is usually determined by the absolute configuration of the first chiral center. The second chiral residue usually has low-to-null influence in the macromolecular handedness of the polymer, due to its remote position respect to the polyene main chain. Here, we de...

A helical copoly(phenylacetylene) that follows a dynamic chiral accord effect has been designed to further synthesize dynamic chiral nanocomposites. Its two pendants are benzamides of (L)-methionine methyl ester [(L)-1, 20%] and (L)-alanine methyl ester [(L)-2, 80%], the former being responsible for binding the copolymer to metallic nanoparticles (...

Helical polymers such as poly(phenylacetylene)s (PPAs) are interesting materials due to the possibility of tuning their helical scaffold (sense and elongation) once they have been prepared and by the presence of external stimuli. The main limitation in the application of PPAs is their poor photostability. These polymers degrade under visible light...

Helical polymers such as poly(phenylacetylene)s (PPAs) are interesting materials due to the possibility of tuning their helical scaffold (sense and elongation) once they have been prepared and by the presence of external stimuli. The main limitation in the application of PPAs is their poor photostability. These polymers degrade under visible light...

The 3D‐helical structure of a non‐symmetric poly(diphenylacetylene) (PDPA) with dynamic circularly polarized luminescence (CPL) is reported in the Research Article by Félix Freire et al. (DOI: 10.1002/anie.202115070). By conformational changes in the pendant group a helix inversion in the PDPA can be initiated, creating a CPL switch.

Die 3D‐Helixstruktur eines nicht‐symmetrischen Poly(diphenylacetylens) (PDPA) mit dynamischer zirkular polarisierter Lumineszenz (CPL) wird im Forschungsartikel von Félix Freire et al. vorgestellt (DOI: 10.1002/ange.202115070). Durch Konformationsänderungen in der Substituentengruppe kann eine Helixinversion des PDPA ausgelöst werden, wodurch ein C...

Back Cover: In article number 2100616 by Félix Freire and co‐workers, dynamic helical polymers such as poly(phenylacetylene)s interact and respond to external stimuli such as metal ions, due to the formation of a helical polymer metal complex (HPMC), which can further be transformed into a hybrid material by reducing the metal ion. The resulting na...

The 3D helix adopted by a non-symmetric substituted poly(diphenylacetylene) (PDPA) is elucidated, and its ability to self-assemble into nanospheres or fiber-like structures under the right conditions is also demonstrated. Moreover, by conformational changes in the pendant group it is possible to produce a helix inversion in the PDPA and create a ci...

The helical sense control of dynamic helical polymers such as poly(phenylacetylene)s (PPAs) is greatly affected when they are conjugated to AuNPs through a strong thiol-Au connection, which restricts conformational changes at the polymer. Thus, the classical thiol-MNP bonds must be replaced by weaker ones, such as supramolecular amide-Au interactio...

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 stud...

The helical sense and elongation of a helical polymer that bears the 4-ethynylanilide of (R)-α-methoxy-α-phenylacetic acid [m-(R)-1] can be tuned by the action of the two components of tetraalkylammonium-anion salts. Thus, while the supramolecular PPA-anilide/anion interaction creates a chiroptical switch, inducing either P or M helical senses in t...

Light irradiation was used as a structural tool to elucidate the three‐dimensional framework of helical polymers via photochemical electrocyclization of their polyene backbones. Details of this research are reported by Félix Freire et al. in their Research Article (DOI: 10.1002/anie.202014780).

Bestrahlung mit Licht wurde als strukturelles Werkzeug genutzt, um das dreidimensionale Gerüst helikaler Polymere durch photochemische Elektrozyklisierung ihrer Polyen‐Rückgrate aufzuklären. Details dieser Studien werden von Félix Freire et al. in ihrem Forschungsartikel vorgestellt (DOI: 10.1002/ange.202014780).

Aggregation of a short, chiral, and asymmetric oligo(phenyleneethynylene) [OPE, (S)‐1] goes through a competitive pathway in which the two diastereomeric P and M supramolecular helices can be selectively produced by choosing the correct experimental conditions. Thus, while an M supramolecular aggregate is obtained in MCH/DCM [AggII], the diastereom...

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 Agg I aggregate is obtained when a DCM solution of ( S )‐ 1 is diluted with MCH at room temperature, Agg II aggregate is generated only after a slo...

Photochemical electrocyclization of poly(phenylacetylene)s (PPAs) is presented as a new tool for the structural elucidation of a polyene backbone, where important structural information such as w1 can be obtained. This new methodology allows not only the classification of PPAs in cis‐cisoidal (ω1< 90°) or cis‐transoidal structures (ω1> 90°), but al...

The photochemical electrocyclization of poly(phenylacetylene)s in solution was utilized to obtain important structural information that allows determine their helical structures (cis‐cisoidal (ω1<90°) or cis‐transoidal (ω1>90°)) while it also provides an estimated value of ω1. When applied to mixtures, it allows the identification of the different...

Different communication mechanisms can be switched within a copolymer by acting on the conformational composition of the components and their chirality. Thus, a Sergeant and Soldiers effect is produced in two diastereomeric copolymer series -poly[( S )- 1 r - co -( S )- 2 ( 1-r ) ] and poly[( R )- 1 r - co -( S )- 2 ( 1-r ) ]- due to the presence i...

A complete set of communication mechanisms (chiral‐to‐chiral sergeants and soldiers, chiral coalition, chiral conflict, chiral accord, synergistic chiral enhancement) can be activated in a chiral copolymer by acting on the conformational composition and the absolute configuration of the components. Abstract Different communication mechanisms can b...

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 a chiral pendant groups. The chiral moieties induce a positive...

Macromolecular gears composed by helical poly(phenylacetylenes) (PPAs) bearing short oligopeptides as pendant groups are described, where the two structural motifs (framework and substituents) are combined. These gears are obtained by polymerization of the acetylene groups introduced at the C ‐terminus of short oligopeptides formed by achiral (Aib)...

Macromolecular gears composed by helical poly(phenylacetylenes) (PPAs) bearing short oligopeptides as pendant groups are described, where the two structural motifs (framework and substituents) are combined. These gears are obtained by polymerization of the acetylene groups introduced at the C ‐terminus of short oligopeptides formed by achiral (Aib)...

Twist and shout: Poly(phenylacetylene)s are helical polymers where the helical sense of the backbone and the pendant groups can differ. It is shown that a correct assignment of both helical senses can be done using Raman optical activity, which gives more structural insight than electronic circular dichroism alone. Abstract Poly(phenylacetylene)s...

A novel type of stimuli-responsive dynamic helical polymer-metal nanoparticle nanocomposite formed by a helical poly(phenylacetylene) (PPA) combined with gold nanoparticles (AuNPs) is described. Thus, several PPA copolymers containing the ethynyl-4-benzamide of (S)-phenylglycine methyl ester (M1) to dictate the helical structure/sense of the copoly...

The dynamic behaviour of helical polymers bearing pendants with two chiral centers was studied. Controlled conformational changes at the chiral units placed either closer or further to the main chain promote different helical structures. Although the first residue is usually responsible for commanding a specific helicity (P or M), herein it was fou...

The dynamic behaviour of helical polymers bearing pendants with two chiral centers was studied. Controlled conformational changes at the chiral units placed either closer or further to the main chain promote different helical structures. Although the first residue is usually responsible for commanding a specific helicity (P or M), herein it was fou...

A new multi‐sensor material based on helical copolymers showing “Chiral Conflict effect” have been prepared, which can successfully detect and identify diverse metal cations in solution. The design of this novel material has taken into account not only the opposite helical senses induced by the two chiral monomers in the copolymer, but also their d...

Konflikte erkennen: Der Effekt des chiralen Konflikts in chiralen helikalen Copolymeren kann als Werkzeug für die Entwicklung von Multisensor-Materialien genutzt werden. Sein Potential für die Identifizierung monovalenter und divalenter Metallionen wird gezeigt. Abstract A new multi-sensor material based on helical copolymers showing the chiral co...

The introduction of a single chiral substituent with a switchable conformer equilibrium at the poly(phenyl isocyanate) terminus allowed the helical sense of the polymer backbone to be controlled using various...

An unprecedented three-state switchable chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC) was developed using a helical poly(phenylacetylene) bearing a chiral (R)-α-methoxyphenylacetic acid resi-due as the pendant (poly-1). The left- and right-handed helical conformations were induced in poly-1-based CSP upon coordinat...

The role of the main dihedral angles in the electronic circular dichroism (ECD) spectra of poly(phenylacetylene)s (PPAs) was estimated by using time-dependent density functional theory (TD-DFT) for oligo(phenylacetylene)s (n = 12). These studies reveal that in cis-transoidal arrangements, the first Cotton effect is dominated by excitations involvin...

The image is an artistic depiction of the two structural states (helical and elongated) achieved by manipulation at the pendant groups of the poly(phenylacetylene) described in article number 1805413 by Ricardo Riguera, Félix Freire, and co‐workers, and which, after appropriate external stimuli, behaves like a colorimetric sensor that also generate...

Interconversion between extended and bent structures at the pendant groups of a chiral polyene framework [poly(phenylacetylene) with (R)‐(2‐methoxy‐2‐phenylacetyl)glycine residues linked to 4‐vinylanilines] allows the reversible colorimetric transformation from stretched to compressed helical cis‐transoid polyenic structures through manipulation of...

Polyphenylacetylenes bearing prim- and sec-amine groups are barely known due to their poisoning activity towards the polymerization catalyst. Herein we prepare 11 different amino polymers in high yields by direct polymerization of their corresponding ammonium salts in water using [Rh(cod)2] +BF4- as catalyst. They are stable, water soluble, and sho...

A novel approach to the classical Sergeants and Soldiers effect, using chiral Sergeants and chiral Soldiers, allow controlling both axial and external chirality in helical polymers. In the systems here reported it is possible to induce the same helical sense (M or P) from any of the two enantiomers of a chiral pendant group ["chiral Soldier", major...

Several steps of chiral induction have been detected in poly(phenylacetylene)s among their different hierarchical levels of chirality by vibrational circular dichroism, namely: i) from the stereogenic centers to the innermost polyacetylene helical covalent backbone (helixint); ii) from this to the external helix (helixext) formed by the side phenyl...

Teleinduction of chirality, from a distant chiral center in the pendant to the helical backbone of a poly(phenylacetylene) (PPA), was demonstrated by using an achiral, flexible and well-organized spacer. A multistate chiroptical switch was originated as a result. Two PPA series, with pendants formed by one or two consecutive Gly residues C-attached...

The calculated ECD spectrum (time-dependent density functional theory TD-DFT) for small oligomers of poly(phenylacetylene)s (PPAs) show a very good match with the experimental spectra of the PPA polymers, particularly with the first Cotton band associated to the helical sense of the internal polyenic backbone. This has been proven with a series of...

The calculated ECD spectrum (time-dependent density functional theory TD-DFT) for small oligomers of poly(phenylacetylene)s (PPAs) show a very good match with the experimental spectra of the PPA polymers, particularly with the first Cotton band associated to the helical sense of the internal polyenic backbone. This has been proven with a series of...

Both the role of the absolute configuration and the tendency of a chiral monomer to promote a certain helical scaffold in a polyphenylacetylene (PPA) have been evaluated to study the communication between two chiral monomers within a copolymer chain. 19 different PPA copolymer series —47 helical copolymers altogether— were prepared to explore the e...

The great importance of the secondary structure (compressed/stretched) of helical poly(phenylacetylene)s (PPAs) in the formation of nanostructures (nanospheres, nanotoroids) by complexation with metal ions of diverse valence is demonstrated. PPAs bearing the same chelating units [anilide of (R)-methoxyphenylacetic acid] but displaying different hel...

A precise tuning of the four possible states of a helix (P/M helical sense and stretched/compressed helical backbone) is attained by controlling the complexation between Li+ and a poly(phenylacetylene) that bears amide, ester and phenyl ring functionalities at the pendant group. Depending on the MeOH ratio that is present as cosolvent, different co...

The thermoresponsive behavior of an elastin based polymer can be altered by the polymeric macromolecular conformation. Thus, when the elastin basic amino-acid sequence VPGVG is used as a pendant group of a poly(phenylacetylene) (PPA) its thermoresponsivity in water can be remotely detected due to conformational changes on the formed helix. Circular...

The thermoresponsive behavior of an elastin based polymer can be altered by the polymeric macromolecular conformation. Thus, when the elastin basic amino-acid sequence VPGVG is used as a pendant group of a poly(phenylacetylene) (PPA) its thermoresponsivity in water can be remotely detected due to conformational changes on the formed helix. Circular...

A general method for the conversion of a polyphenylacetylene into its P or M helically oriented polymer, and into their corresponding P/M helical nanoparticles via dynamic metal coordination is presented. Addition of Mn+ ions ( e.g., Ca2+, Zn2+, Ag+, among others) to poly(phenylacetylene)s (poly-2 to poly-6), bearing OMe protected amino acids, prod...

Dynamic poly(phenylacetylene)s (PPAs) adopt helical structures with different elongation or helical senses depending on the types of pendants. Hence, a good knowledge of the parameters that define their structures becomes a key factor in the understanding of their properties and functions. Herein, the techniques used for the study of the secondary...

Nanospheres and nanotubes with full control of their size and helical sense are obtained in chloroform from the axially racemic chiral poly(phenylacetylene) poly-(R)-1 using either Ag+ as both chiral inducer and cross-linking agent or Na+ as chiral inducer and Ag+ as cross-linking agent. The size is tuned by the polymer/ion ratio while the helical...

The remarkable consequences in elongation, dynamic character, response to external stimuli (e.g., solvent effects, metal cations) and aggregation observed in helical poly(phenylacetylene)s (PPAs) when either the type of linkage with the pendant groups (i.e., anilide, benzamide) or the aromatic substitution pattern (i.e., ortho, meta, para) of the p...

Poly(phenylacetylene) (PPA) copolymers containing (R)- or (S)-MPA as minor chiral pendant can be forced to selectively adopt the right- o left-handed helix, in the presence of small amounts of Na(+) or Ag(+) ("Sergeants and Soldiers Effect") by addition of a donor cosolvent. The helical sense depends exclusively on the chiral monomer/donor cosolven...

Cation-π interactions determine the helical sense adopted by a polyphenylacetylene bearing (R)-α-methoxy-α-phenylacetamide as pendant group (poly-1). These interactions take place when small amounts of Li+, Na+ and Ag+ salts dissolved in donor cosolvents, are added to the polymer dissolved in a non-donor solvent and the corresponding helical polyme...

The chiral polymer poly-(R)- behaves in solution, despite its chiral pendants, as a dynamic axially racemic (i.e., 1 : 1) mixture of left- and right-handed helices, but its deposition on graphite by a Langmuir-Schaefer (LS) technique leads to a helical sense-selective packing that forms separate enantiomeric domains of left- and right-handed helica...

The interaction of a highly dynamic poly(aryl acetylene) (poly-1) with Li+, Na+, and Ag+ leads to macroscopically chiral supramolecular nanospheres, nanotubes, toroids, and gels. With Ag+, nanospheres with M helicity and tunable sizes are generated, which complement those obtained from the same polymer with divalent cations. With Li+ or Na+, poly-1...

The interaction of a highly dynamic poly(aryl acetylene) (poly-1) with Li+, Na+, and Ag+ leads to macroscopically chiral supramolecular nanospheres, nanotubes, toroids, and gels. With Ag+, nanospheres with M helicity and tunable sizes are generated, which complement those obtained from the same polymer with divalent cations. With Li+ or Na+, poly-1...

Die supramolekulare Assoziation von helikalen Polymeren (Polyarylacetylenen) mit einwertigen Metallkationen (Ag+, Li+ und Na+) führt zu unterschiedlichen makroskopisch chiralen Nanostrukturen, z. B. Nanokügelchen, Nanoröhren, Toroide und Gele, die eine Reihe von organischen und anorganischen Substanzen einkapseln können. Das Titelbild veranschaulic...

The supramolecular assembly of helical polymers, namely poly(aryl acetylenes), with monovalent metal cations (Li+, Na+, and Ag+) leads to a number of different macroscopically chiral nanostructures, such as nanospheres, nanotubes, toroids, and gels, with the capacity to encapsulate a variety of organic and inorganic substances. The cover picture il...

A novel class of stereocomplex is described by interaction of helically complementary poly(phenylacetylene)s (PPAs) carrying a α-methoxy-α-trifluoromethylphenylacetamide group as pendant. The stereocomplex formation requires the presence of exposed cis amide bonds on the polymer helical threads to provide efficient cooperative supramolecular hydrog...

Here we report copolymers where the “Sergeants and Soldiers effect” can be switched ON and OFF by the presence of a metal ion. These copolymers have been prepared by a combination of achiral and chiral monomer units, where the chiral ones are unable to drive the chiral amplification unless a small amount of mono- or divalent metal ions is added. In...

New helical poly(phenylacetylene)s have been successfully designed and synthesised and their properties checked. The new polymers behave as sensors of metal cation valences and/or the polar and donor character of solvents. In the presence of metal salts, poly(phenylacetylene)s form helical polymer–metal complexes (HPMCs) that, in the case of α-meth...

The elasticity (stretched/compressed) and helical sense (clockwise/anticlockwise) of a dynamic helical poly(phenylacetylene) (PPA), bearing (R)-a-methoxytrifluorophenyl acetic acid (MTPA) pendants [poly- (R)-1], can be selectively controlled by the donor and the polar character of the solvent. The basis for this effect lies on the presence in the p...

A new family of nanospheres is made by complexation of divalent metals (i.e., Ca(2+), Ba(2+)) and poly(phenylacetylene) polymers bearing α-methoxyphenylacetic acid (MPA) pendants with high content of the cis isomer responsible for their helical structures. The resulting helical polymer-metal complex (HPMC) nanospheres present two interesting proper...

Ion sensor: A highly dynamic poly(phenylacetylene) bearing α-methoxyphenylacetic acid (MPA) as chiral pendant exhibits selective helix induction and chiral amplification, and gives a material that acts as a sensor for the valence of metal cations. Selective coordination of the pendants with mono- or divalent metal cations determines the right- or l...

Molecular design can be used to investigate whether the parallel-β-sheet secondary structure is subject to length-dependent cooperative stabilization along the strand direction (see picture). Extending strands by adding high-propensity residues (B) leads to a steady increase in parallel-β-sheet stability, but inclusion of low-propensity residues (A...

The conformational compositions of the tris(alpha-methoxy-alpha-phenylacetic acid) ester derivatives of 1,2,3-prim,sec,sec-triols are presented. These conformations have been determined by theoretical and experimental data (i.e., energy- and chemical-shift calculations, circular dichroism (CD) experiments, coupling-constant analysis, enantioselecti...

The absolute configuration of a 1,2-primary/secondary diol can be easily determined by preparation of its bis-(R)- and bis-(S)-9-AMA ester derivatives, followed by comparison of the NMR chemical shifts of the diastereotopic methylene protons in the two derivatives. Alternatively, the assignment can be carried out using only one derivative if the ev...

Pairs of short peptide strands can be induced to adopt an antiparallel beta-sheet secondary structure in aqueous solution via a macrocyclic constraint, as illustrated by many natural and designed peptides. We show that an analogous strategy is successful for creation of small units of parallel beta-sheet secondary structure in aqueous solution. Cyc...

A simple NMR methodology, through the formation of chiral BINOL borates in the NMR tube, and that reunites the advantages of chiral derivatizing (CDAs) and chiral solvating agents (CSAs), is presented for the assignment of the absolute configuration of alpha- and beta-hydroxy acids.

We report the development of diacid units that promote formation of a two-stranded parallel beta-sheet secondary structure between peptide segments attached via their N-termini. These linker units are formed by attaching glycine to one carboxyl group of cis-1,2-cyclohexanedicarboxylic acid (CHDA). Parallel sheet formation in water is observed when...

The absolute configuration of beta-chiral primary alcohols devoid of observable hydrogens on one of the beta-substituents at the asymmetric carbon (L(1)/L(2)) can be determined by comparison of the (1)H NMR of their (R)- and (S)-9-AMA ester derivatives and analysis of the Deltadelta(RS) for the L substituent and the Cbeta-H.

Comparison of the room- and low-temperature 1H NMR spectra of the bis-(R)- or bis-(S)-MPA ester derivative of an open chain sec,sec-1,2-diol allows the easy determination of its relative stereochemistry and in some cases absolute configuration. If the diol is anti, its absolute configuration can be directly deduced from the signs of DeltadeltaT1T2...

Aminoglycosides are clinically relevant antibiotics that participate in a large variety of molecular recognition processes involving different RNA and protein receptors. The 3-D structures of these policationic oligosaccharides play a key role in RNA binding and therefore determine their biological activity. Herein, we show that the particular NH2/...