Stimuli-responsive synthetic helical polymers.

Synthetic dynamic helical polymers (supramolecular and covalent) and foldamers share the helix as a structural motif. Although the materials are different, these systems also share many structural properties, such as helix induction or conformational communication mechanisms. The introduction of stimuli responsive building blocks or monomer repeating units in these materials triggers conformational or structural changes, due to the presence/absence of the external stimulus, which are transmitted to the helix resulting in different effects, such as assymetry amplification, helix inversion or even changes in the helical scaffold (elongation, J/H helical aggregates). In this review, we show through selected examples how different stimuli (e.g., temperature, solvents, cations, anions, redox, chiral additives, pH or light) can alter the helical structures of dynamic helical polymers (covalent and supramolecular) and foldamers acting on the conformational composition or molecular structure of their components, which is also transmitted to the macromolecular helical structure.

Size Control of Chiral Nanospheres Obtained via Nanoprecipitation of Helical Poly(phenylacetylene)s in the Absence of Surfactants.

Nanostructuration of dynamic helical polymers such as poly(phenylacetylene)s (PPAs) depends on the secondary structure adopted by the polymer and the functional group used to connect the chiral pendant to the PPA backbone. Thus, while PPAs with dynamic and flexible scaffolds (para- and meta-substituted, ω1<165°) generate by nanoprecipitation low polydisperse nanospheres with controllable size at different acetone/water mixtures, those with a quasi-static behavior and the presence of an extended, almost planar structure (ortho-substituted, ω1>165°), aggregate into a mixture of spherical and oval nanostructures whose size is not controlled. Photostability studies show that poly(phenylacetylene) particles are more stable to light irradiation than when dissolved macromolecularly. Moreover, the photostability of the particle depends on the secondary structure of the PPA and its screw sense excess. This fact, in combination with the encapsulation ability of these polymer particles, allows the creation of light stimuli-responsive nanocarriers, whose cargo can be delivered by light irradiation.

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.

Full Control of the Chiral Overpass Effect in Helical Polymers: P/M Screw Sense Induction by Remote Chiral Centers After Bypassing the First Chiral Residue.

In helical polymers, helical sense induction is usually commanded by teleinduction mechanism, where the largest substituent of the chiral residue directly attached to the main chain is the one that commands the helical sense. In this work, different helical structures with different helical senses are induced in a helical polymer [poly-(phenylacetylene)] when the conformational composition of two different dihedral angles of a pendant group with more than two chiral residues is tamed. Thus, while the dihedral angle at chiral residue 1 [(R)- or (S)-alanine], attached to the backbone, produces an extended or bent conformation in the pendant resulting in two scaffolds with different stretching degree, the second dihedral angle at chiral residue 2 [(R)- or (S)-methoxyphenylacetamide] places the substituents of this chiral center in a different spatial orientation, originating opposite helical senses at the polymer that are induced through a total control of the "chiral overpass effect".

Comparison of screening methods for obstructive sleep apnea in the context of dental clinics: A systematic review.

OBJECTIVE: To review the available bibliographic data to identify the best screening methods to detect potential obstructive sleep apnea (OSA) patients during dental clinical practice. METHODS: Relevant studies published up to April 2020 were sourced from PubMed, Embase, MEDLINE, Cochrane, and LILACS databases. RESULTS: Thirty studies were selected. For adults, the screening methods available to the dentist included questionnaires, scales, indexes, pulse oximetry, and anatomical factors. A combination of questionnaires is potentially the most reliable method to detect OSA risk. For children, only information on questionnaires and anatomical factors was found; two questionnaires accurately identified potential OSA risk cases. Anatomical factors also displayed a significant relation with OSA for both populations. CONCLUSION: Dentists have a fundamental role in early detection of potential OSA cases since they can use the methods identified in this review to perform an initial screening of the population. ABBREVIATIONS: OSA: Obstructive sleep apnea; PSG: Polysomnography; HST: Home sleep study; BMI: Body mass index; PPV: Positive predictive value; NPV: Negative predictive value; AHI: Apnea hypopnea index; RDI: Respiratory disturbance index; ODI: Oxygen desaturation index; PSQ: Pediatric Sleep Questionnaire; SRBD: Sleep-related breathing disorder; CSHQ: Children's Sleep Habits Questionnaire; ESS: Epworth Sleepiness Scale; PSQI: Pittsburgh Sleep Quality Index.

Combined Surgical and Orthodontic Treatments in Children with OSA: A Systematic Review.

Obstructive sleep apnea (OSA) is a sleeping breathing disorder. In children, adenotonsillar hypertrophy remains the main anatomical risk factor of OSA. The aim of this study was to assess the current scientific data and to systematically summarize the evidence for the efficiency of adenotonsillectomy (AT) and orthodontic treatment (i.e., rapid maxillary expansion (RME) and mandibular advancement (MA)) in the treatment of pediatric OSA. A literature search was conducted in several databases, including PubMed, Embase, Medline, Cochrane and LILACS up to 5th April 2020. The initial search yielded 509 articles, with 10 articles being identified as eligible after screening. AT and orthodontic treatment were more effective together than separately to cure OSA in pediatric patients. There was a greater decrease in apnea hypoapnea index (AHI) and respiratory disturbance index (RDI), and a major increase in the lowest oxygen saturation and the oxygen desaturation index (ODI) after undergoing both treatments. Nevertheless, the reappearance of OSA could occur several years after reporting adequate treatment. In order to avoid recurrence, myofunctional therapy (MT) could be recommended as a follow-up. However, further studies with good clinical evidence are required to confirm this finding.