Tryptophan-Containing Block Copolymers Prepared by RAFT Polymerization: Synthesis, Self-Assembly, and Chiroptical and Sensing Properties

Approaching Tryptophan-Derived Polynorbornene Fluorescent Chemosensors: Synthesis, Characterization, and Sensing Ability for Biomedical Applications as Biomarkers for Detecting Fe2+ Ions

We present a novel group of tryptophan (Trp)-based fluorescent polymeric probes synthesized via ring-opening metathesis polymerization (ROMP) of Trp-derived norbornene monomers. These probes, in mono- and disubstituted forms, incorporate amide and ester anchoring groups. The quantity of Trp substituents did not affect fluorescence selectivity but influenced quenching percentage. Poly-diamide-Trp, Poly-monoamide-Trp, Poly-diester-Trp, and Poly-monoester-Trp probes displayed selective detection of Fe2+ and Fe3+ ions with fluorescence on-off characteristics. Poly-diamide-Trp and Poly-monoamide-Trp exhibited a limit of detection (LOD) for Fe2+ and Fe3+ ions of 0.86-11.32 μM, while Poly-diester-Trp and Poly-monoester-Trp showed higher LODs (21.8-108.7 μM). These probes exhibited high selectivity over Fe2+, a crucial metal ion in the body known for its redox properties causing oxidative stress and cell damage. Cell cytotoxicity tests in various cell types confirmed biocompatibility. Additionally, Poly-diamide-Trp displayed excellent cell permeability and iron ion detection in EA.hy926 cells, suggesting potential for bioimaging and clinical applications.

Double hydrophilic copolymers - synthetic approaches, architectural variety, and current application fields

Solubility and functionality of polymeric materials are essential properties determining their role in any application. In that regard, double hydrophilic copolymers (DHC) are typically constructed from two chemically dissimilar but water-soluble building blocks. During the past decades, these materials have been intensely developed and utilised as, e.g., matrices for the design of multifunctional hybrid materials, in drug carriers and gene delivery, as nanoreactors, or as sensors. This is predominantly due to almost unlimited possibilities to precisely tune DHC composition and topology, their solution behavior, e.g., stimuli-response, and potential interactions with small molecules, ions and (nanoparticle) surfaces. In this contribution we want to highlight that this class of polymers has experienced tremendous progress regarding synthesis, architectural variety, and the possibility to combine response to different stimuli within one material. Especially the implementation of DHCs as versatile building blocks in hybrid materials expanded the range of water-based applications during the last two decades, which now includes also photocatalysis, sensing, and 3D inkjet printing of hydrogels, definitely going beyond already well-established utilisation in biomedicine or as templates.

The first tryptophan based turn-off chemosensor for Fe2+ ion detection

In this research work, we have designed and synthesized a novel Tryptophan-Quinoline conjugated turn-off chemosensor 4 for the selective detection of Fe²⁺ ion with high sensitivity (3.06 μM) among 21 metal cations such as Ag⁺, Ca⁺, Cs⁺, Cu⁺, K⁺, Na⁺, NH₄⁺, Ba²⁺, Ca²⁺, Cd²⁺, Co²⁺, Cu²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Zn²⁺, Al³⁺, Au³⁺, Cr³⁺ and Fe³⁺ in DMF-HEPES (1 mM, pH = 7.0, 1:1, v/v) aqueous-organic solvent system. It showed a fluorescence quenching mechanism through the blocked PET process. The optical properties, binding mode of the metal ion with the receptor, plausible electron transfer mechanism, and its practical applications have been discussed. This work will open up a new avenue in amino acid-based Fe²⁺ ion sensors.

d-, l- and d,l-Tryptophan-Based Polyamidoamino Acids: pH-Dependent Structuring and Fluorescent Properties

Chiral polyamidoamino acids were obtained by polyaddition of N,N'-methylenebisacrylamide with d-, d,l- and l-tryptophan (M-d-Trp, M-d,l-Trp and M-l-Trp). l-tryptophan/glycine copolymers, M-G-l-Trp₅, M-G-l-Trp10, M-G-l-Trp20 and M-G-l-Trp40, were prepared from l-tryptophan/glycine mixtures. These polymers were amphoteric, with acid-base properties similar to those of the parent amino acids. The l-tryptophan/glycine copolymers with high glycine content were water soluble in the pH range 2-12. M-G-l-Trp40 showed a solubility gap centred at pH 4.5 and all tryptophan homopolymers were soluble only at pH > 7. Dynamic light scattering measurements performed in their solubility ranges, namely 2-11 M-G-l-Trp₅, M-G-l-Trp10 and M-G-l-Trp20 and 7-11 for M-G-l-Trp40, M-d-Trp, M-l-Trp and M-d,l-Trp, showed that the size of all samples did not significantly vary with pH. Both M-l-Trp and M-G-l-Trp copolymers showed pH-dependent circular dichroism spectra in the wavelength interval 200⁻280 nm, revealing structuring. All samples were fluorescent. Their emission spectra were unstructured and, if normalized for their tryptophan content, almost superimposable at the same pH, providing evidence that only tryptophan governed the photoluminescence properties. Changing pH induced in all cases a slight shift of the emission wavelength maximum ascribed to the modification of the microenvironment surrounding the indole ring induced by different protonation degrees.

Chiral Self-Assembly of Nanoparticles Induced by Polymers Synthesized via Reversible Addition-Fragmentation Chain Transfer Polymerization

Chiral inorganic nanomaterials are of great interest because of their excellent optical properties. Most of the attention has been focused on the utilization of biomolecules or their derivatives as linkers or templates to control the chiral structure of assembled inorganic nanoparticles. Chiral polymers are promising synthetic materials that can be used to replace their biological counterparts. Here, by using poly(methacrylate hydroxyethyl-3-indole propionate) (PIPEMA) and poly(2-hydroxyethyl methacrylate) (PHEMA) synthesized via syndioselective reversible addition-fragmentation chain transfer polymerization, we successfully realized chiral self-assembly of gold nanorods with strong circular dichroism response in the vis-NIR region. Moreover, the intensity of the chiral signal of the assemblies can be regulated by the molecular weight of the polymers. Notably, although the monomers are achiral and no chiral reagents are involved in their synthesis, the main chains of PIPEMA and PHEMA exhibit a preferred-handed helical conformation, which is the origin of chirality of the nanorod assemblies. The preferred-handed helical conformation of polymers is attributed to their syndiotacticity and stabilized by the steric hindrance of the side groups. The addition of chiral carbon atoms at the side groups does not change the preferred-handedness of the polymer main chain, resulting in the assembled nanorod structures with the same chirality. This strategy provides inspiration for the rational design and synthesis of optically active functional synthetic polymers for the preparation of promising chiral nanomaterials.

Tryptophan-based styryl homopolymer and polyzwitterions with solvent-induced UCST, ion-induced LCST and pH-induced UCST

A multi-stimuli responsive tryptophan-based styryl homopolymer and polyzwitterions with solvent-induced UCST, ion-induced LCST and pH-induced UCST under different conditions are presented.

Alternating and random-sequence polyesters with distinct physical properties

Polyesters with alternating or random-sequence arrangements of indole and ethyl pendant groups exhibit distinct physical properties, such as the nature of fluorescence quenching by fluoride ions.

Amino Acid Functional Polymers: Biomimetic Polymer Design Enabling Catalysis, Chiral Materials, and Drug Delivery

Amino acids are the natural building blocks for the world around us. Highly functional, these small molecules have unique catalytic properties, chirality, and biocompatibility. Imparting these properties to surfaces and other macromolecules is highly sought after and represents a fast-growing field. Polymers functionalized with amino acids in the side chains have tunable optical properties, pH responsiveness, biocompatibility, structure and self-assembly properties. Herein, we review the synthesis of amino acid functional polymers, discuss manipulation of available strategies to achieve the desired responsive materials, and summarize some exciting applications in catalysis, chiral particles, and drug delivery.

A recyclable, fluorescent, and colorimetric sensor for fluoride anion in water using a crosslinked polymer functionalized with hydroxyl quinolinium

A crosslinked polymer-based recyclable, fluorescent, and colorimetric sensor for F⁻ in water.

Synthesis and characterization of poly [N-acryloyl-(D/L), (+/−)-phenylalanine-co-(D/L), (−/+)N-methacryloyloxyethyl-N′-2-hydroxybutyl(urea)] copolymers

Two monomers of (D/L), (+/−)-N-methacryloyloxyethyl-N′-2-hydroxybutyl(urea) methacrylate (D/L-MABU) type were prepared and further polymerized through free radical polymerization with optically active monomers containing phenylalanine sequences such as N-acryloyl-(D/L), (−/+)-phenylalanine (A-D/L-Phe). The resulting copolymers, i.e., poly[N-acryloyl-(D/L), (−/+)-phenylalanine-co-(D/L), (+/−)-N-methacryloyloxyethyl-N′-2-hydroxybutyl(urea)], A-D/L-Phe-co-D/L-MABU, were characterized by FT-IR, 1D/2D NMR (1H and 13C), UV-vis, and circular dichroism (CD) spectroscopies, differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). The copolymers obtained with a molar fraction of 0.76: 0.24 / 0.64: 0.36 monomer units had optical rotation values of −25° and +15°, respectively. Upon chemical modification of the phenylalanine-based copolymers with fluorescein-isothiocyanate, new fluorescent copolyacrylates (A-D/L-Phe-co-D/L-MABU-F) were synthesized and further studied for pH measurements in DMF solutions using HCl and NaOH 10−1M. It was found that sterioselectivity of the A-L-Phe-co-L-MABU-F copolymer is higher than of its dextro-form, especially at basic pH.

Side-chain amino-acid-based pH-responsive self-assembled block copolymers for drug delivery and gene transfer

Developing safe and effective nanocarriers for multitype of delivery system is advantageous for several kinds of successful biomedicinal therapy with the same carrier. In the present study, we have designed amino acid biomolecules derived hybrid block copolymers which can act as a promising vehicle for both drug delivery and gene transfer. Two representative natural chiral amino acid-containing (l-phenylalanine and l-alanine) vinyl monomers were polymerized via reversible addition-fragmentation chain transfer (RAFT) process in the presence of monomethoxy poly(ethylene glycol) based macro-chain transfer agents (mPEGn-CTA) for the synthesis of well-defined side-chain amino-acid-based amphiphilic block copolymers, monomethoxy poly(ethylene glycol)-b-poly(Boc-amino acid methacryloyloxyethyl ester) (mPEGn-b-P(Boc-AA-EMA)). The self-assembled micellar aggregation of these amphiphilic block copolymers were studied by fluorescence spectroscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Potential applications of these hybrid polymers as drug carrier have been demonstrated in vitro by encapsulation of nile red dye or doxorubicin drug into the core of the micellar nanoaggregates. Deprotection of side-chain Boc- groups in the amphiphilic block copolymers subsequently transformed them into double hydrophilic pH-responsive cationic block copolymers having primary amino groups in the side-chain terminal. The DNA binding ability of these cationic block copolymers were further investigated by using agarose gel retardation assay and AFM. The in vitro cytotoxicity assay demonstrated their biocompatible nature and these polymers can serve as "smart" materials for promising bioapplications.