Chiral nanostructure in polymers under different deposition conditions observed using atomic force microscopy of monolayers: poly(phenylacetylene)s as a case study

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 structure of PPAs using atomic-force microscopy (AFM) are presented, with special attention directed towards the methods used for the preparation of monolayers, and their consequences in the quality of the AFM images. Thus, monolayers formed by drop casting, spin coating followed by crystallization or annealing, Langmuir–Blodgett and Langmuir–Schaefer methods, onto highly oriented pyrolytic graphite (HOPG) or mica, are described, together with the AFM images and the resulting helical structure obtained for different PPAs. Furthermore, some conclusions are drawn both on the adequacy of the different techniques for the formation of monolayers and on the solid supports utilized to elucidate the secondary structure of different PPAsThis work was supported by grants from MEC (CTQ2014-61470-EXP, CTQ2015-70519-P), ERDF and Xunta de Galicia (GRC2014/040)S

Stereocomplex Nanocomposite Switch Based on Dynamic Helical Polymer-Gold and Silver Nanoparticle Hybrid Materials

Controlled ON/OFF stereocomplexation of dynamic helical polymer-metal nanoparticle nanocomposites─poly(phenylacetylene)-MNP nanocomposites (M = Au or Ag)─is presented. These novel hybrid materials can be found either as well-dispersed metal nanoparticles (MNPs) (stereocomplex OFF) or as fiber-like aggregates (stereocomplex ON) with the metal nanoparticles distributed along the material. A stereocomplex-MNP nanocomposite is formed by the interaction of two complementary and enantiomeric helical polymer-MNP nanocomposites [Poly-(R)-1-M1NPs/poly(S)-1-M2NPs (M1 = M2 or M1 ≠ M2; M = Au, Ag)]. Interestingly, by using dynamic helical polymers, i.e., poly(phenylacetylene)s (PPAs), as coating agents of the metal nanoparticles, it is possible to tune the secondary structure of the polymer─elongation and/or compression─a fact that can trigger the formation/disruption of the stereocomplex. Moreover, the stereocomplexation of these nanocomposites can be controlled in a reversible way (ON/OFF) by playing with the supramolecular interactions that keep the two enantiomeric and complementary helices together, such as hydrogen bondsFinancial support from AEI (PID2019-109733GB-I00), Xunta de Galicia (ED431C 2022/21, Centro Singular de Investigación de Galicia acreditación 2019–2022, ED431G 2019/03, and the European Regional Development Fund (ERDF) and is gratefully acknowledgedS

SEQUENTIAL INDUCTION OF CHIRALITY IN POLY(PHENYLACETYLENE)S

Several hierarchical levels of chirality have been detected in functionalized poly(phenylacetylene)s (PPA).1 In this work we have studied the chirality induction throughout these levels in PPA functionalized with phenylglycine methyl ester groups, Fig. 1.2 These pendant groups force the PPA chain to lose its planar all-transoid shape to form helical structures. The chiral seed of the pendants, [(R)- or (S)-], dictates the preferent handedness of the helices, both the internal polyacetylene helical covalent backbone and the external helix formed by the side pendants which forms a complementary helix or counter-helix. In this work, we afford a full assessment of the interconnection between stereocenter and helix sources of chirality and the action of these polymers as chiral templates of other supra-molecular structures with inherited chiral properties. We then used VCD spectroscoy to demonstrate the chiral induction from the stereogenic centers to the backbone helix and from this to the pendant helix, which are largely promoted by two mechanisms: steric effects and hydrogen bonding. In addition, the VCD spectra supported that the helical setup of the pendants induces the solvent DMSO molecules to adopt a solvation helix around the polymer, thus proving how an achiral solvent becomes chirally organized owing to the template effect of the covalent polymer helices. A similar effect was observed in DMSO solutions of the monomeric units. Interestingly, this resulted in opposite helical sense to the one observed in the polymer with identical enantiomeric form.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

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 agreementThis research was funded by Ministerio de Ciencia e Innovación, grant number PID2019-107307RB-100; Xunta de Galicia, grants number and ED431C 2018/30, ED431C 2017/17 and ED431G 2019/03; and the European Regional Development Fund (ERDF)S

Conformational Kinetics in Chiral Poly(diphenylacetylene)s: A Dynamic P/M Memory Effect

Dynamic P/M (plus/minus) helical memory in chiral dissymmetric poly(diphenylacetylene)s (PDPA) is shown using a PDPA that bears the benzamide of (L)-alanine methyl ester as pendant. For a single chiral polymer, it is possible to obtain either P or M helical structures in a specific solvent without the presence of any chiral external stimuli. To do that, it is necessary to combine the conformational control at the pendant group with a high steric hindrance at the backbone. In this case, by thermal annealing in low-polar solvents, an anti-conformer is stabilized at the pendant which commands a P helix in the PDPA. Next, solvent removal followed by addition of a polar solvent such as dimethyl sulfoxide (DMSO), results in the kinetic conformationally trapped P helix. However, in this medium, the preferred handedness and the thermodynamic macromolecular helix for poly-(L)-1 is M. This process also occurs in the opposite way. Electronic circular dichroism (ECD) and circularly polarized luminescence (CPL) studies show that the dynamic memory effect is present both in ground and excited statesWe thank financial support from AEI (PID2019-109733GB-I00) and Juan de la Cierva Incorporación contract (IJC2020-042689-I, R. R.). Xunta de Galicia (ED431C 2022/21, Centro Singular de Investigación de Galicia acreditación 2019–2022, ED431G 2019/03 and the European Regional Development Fund (ERDF) are gratefully acknowledged. J. J. T. thanks MICINN for an FPU contractS

Dynamic axial‐to‐helical communication mechanism in poly[(allenylethynylenephenylene)acetylene]s under external stimuli

Helix inversion in chiral dynamic helical polymers is usually achieved by conformational changes at the pendant groups induced through external stimuli. Herein, a different mechanism of helix inversion in poly(phenylacetylene)s (PPAs) is presented, based on the activation/deactivation of supramolecular interactions. We prepared poly[(allenylethynylenephenylene)acetylene]s (PAEPAs) in which the pendant groups are conformationally locked chiral allenes. Therefore, their substituents are placed in specific spatial orientations. As a result, the screw sense of a PAEPA is fixed by the allenyl substituent with the optimal size/distance relationship to the backbone. This helical sense command can be surpassed by supramolecular interactions between another substituent on the allene and appropriate external stimuli, such as amines. So, a helix inversion occurs through a novel axial‐to‐helical communication mechanism, opening a new scenario for taming the helices of chiral dynamic helical polymers.Agencia Estatal de Investigación | Ref. PID2019-109733GB-I00Agencia Estatal de Investigación | Ref. PID2021-128057NB-I00Xunta de Galicia | Ref. ED431C 2022/21Xunta de Galicia | Ref. ED431G 2019/0

Stimuli‐Directed Colorimetric Interconversion of Helical Polymers Accompanied by a Tunable Self‐Assembly Process

This is the peer reviewed version of the following article: Rodríguez, R., Quiñoá, E., Riguera, R., Freire, F., Small 2019, 15, 1805413. https://doi.org/10.1002/smll.201805413, which has been published in final form at https://doi.org/10.1002/smll.201805413. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived VersionsInterconversion 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 the flexible spacer. This transformation generates either organogels (stretched helical form) or nanoparticles (compressed helical form) under the control of polar/low polar stimuli respectively and opens the way to the development of new sensors and stimuli‐sensitive materials based on these conceptsFinancial support from MINECO (CTQ2014-61470-EXP, CTQ2015-70519-P), Xunta de Galicia (GRC2014/040, Centro singular de investigación de Galicia accreditation 2016-2019, ED431G/09) and the European Regional Development Fund (ERDF) is gratefully acknowledged. R. R. is grateful to MINECO for a FPI predoctoral fellowshipS

Dynamic Axial-to-Helical Communication Mechanism in Poly[(allenylethynylenephenylene)acetylene]s under External Stimuli

Helix inversion in chiral dynamic helical polymers is usually achieved by conformational changes at the pendant groups induced through external stimuli. Herein, a different mechanism of helix inversion in poly(phenylacetylene)s (PPAs) is presented, based on the activation/deactivation of supramolecular interactions. We prepared poly[(allenylethynylenephenylene)acetylene]s (PAEPAs) in which the pendant groups are conformationally locked chiral allenes. Therefore, their substituents are placed in specific spatial orientations. As a result, the screw sense of a PAEPA is fixed by the allenyl substituent with the optimal size/distance relationship to the backbone. This helical sense command can be surpassed by supramolecular interactions between another substituent on the allene and appropriate external stimuli, such as amines. So, a helix inversion occurs through a novel axial-to-helical communication mechanism, opening a new scenario for taming the helices of chiral dynamic helical polymersWe thank financial support from AEI (PID2019-109733GB-I00, PID2021-128057NB-I00), and Xunta de Galicia (ED431C 2022/21, Centro Singular de Investigación de Galicia acreditación 2019–2022, ED431G 2019/03 and the European Regional Development Fund (ERDF). ML also thanks Xunta de Galicia for a predoctoral contract. We are also thankful for Servicio de Nanotecnología y Análisis de Superficies (CACTI-CINBIO, UVigo) the use of the RIAIDT-USC analytical facilities and CESGA for cpu timeS

Three-State Switchable Chiral Stationary Phase Based on Helicity Control of an Optically Active Poly(phenylacetylene) Derivative by Using Metal Cations in the Solid State

This is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of the American Chemical Society, Copyright © 2019 American Chemical Society after peer review and technical edityng by the publisher. To access the final edited and published work see: https://pubs.acs.org/doi/10.1021/jacs.9b03177An 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 residue as the pendant (poly-1). The left- and right-handed helical conformations were induced in poly-1-based CSP upon coordination with a catalytic amount of soluble sodium and cesium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate salts (MBArF), respectively, which are soluble in the HPLC conditions [hexane–2-propanol (95:5, v/v)]. The switch between the two different helical states of poly-1 can be easily achieved by rinsing the poly-1-based CSP with MeOH and the subsequent addition of the proper MBArF salt. Using this dynamic helical CSP, we demonstrate how changes on the orientation of the secondary structure of a chiral polymer (right-handed, left-handed, and racemic helices) can alter and even invert the elution order of the enantiomers. This study was done without adding chiral additives or changing the mobile phase, which could produce changes on the retention times and make it more difficult to determine the role of the secondary structure during the chiral recognition processThis work was supported by JSPS KAKENHI Grant No. 16H04154 (Grants-in-Aid for Scientific Research (B)) and 17H05361 (Coordination Asymmetry) (K.M.)S

Diastereomeric multi-chiral pendant groups: their key role in stimuli-responsive polymeric responses

Chiral information transmission in helical polymers bearing multi-chiral pen-dant groups is usually determined by the absolute configuration of the first chi-ral center. The second chiral residue usually has low-to-null influence in themacromolecular handedness of the polymer, due to its remote position respectto the polyene main chain. Here, we demonstrate how the stimuli responsiveproperties of diastereomeric polymers, obtained by changing the absolute con-figuration of the second chiral center, are different due to the unlike propertiesof diastereoisomersWe thank financial support from AEI (PID2019-109733GB-I00) and Juan de la Cierva Incorporación contract (IJC2020-042689-I) for R.R., Xunta de Galicia (ED431C 2022/21), Centro Singular de Investigación de Galicia acreditación 2019-2022 (ED431G 2019/03), and the European Regional Development Fund (ERDF)S