Highly sensitive detection of saccharides under physiological conditions with click synthesized boronic acid-oligomer fluorophores

A Portrait of the OPE as a Biological Agent

Oligophenylene ethynylenes, known as OPEs, are a sequence of aromatic rings linked by triple bonds, the properties of which can be modulated by varying the length of the rigid main chain or/and the nature and position of the substituents on the aromatic units. They are luminescent molecules with high quantum yields and can be designed to enter a cell and act as antimicrobial and antiviral compounds, as biocompatible fluorescent probes directed towards target organelles in living cells, as labelling agents, as selective sensors for the detection of fibrillar and prefibrillar amyloid in the proteic field and in a fluorescence turn-on system for the detection of saccharides, as photosensitizers in photodynamic therapy (due to their capacity to highly induce toxicity after light activation), and as drug delivery systems. The antibacterial properties of OPEs have been the most studied against very popular and resistant pathogens, and in this paper the achievements of these studies are reviewed, together with almost all the other roles held by such oligomers. In the recent decade, their antifungal and antiviral effects have attracted the attention of researchers who believe OPEs to be possible biocides of the future. The review describes, for instance, the preliminary results obtained with OPEs against severe acute respiratory syndrome coronavirus 2, the virus responsible for the COVID-19 pandemic.

Well-Defined Conjugated Macromolecules Based on Oligo(Arylene Ethynylene)s in Sensing

Macromolecules with well-defined structures in terms of molar mass and monomer sequence became interesting building blocks for modern materials. The precision of the macromolecular structure makes fine-tuning of the properties of resulting materials possible. Conjugated macromolecules exhibit excellent optoelectronic properties that make them exceptional candidates for sensor construction. The importance of chain length and monomer sequence is particularly important in conjugated systems. The oligomer length, monomer sequence, and structural modification often influence the energy bang gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the molecules that reflect in their properties. Moreover, the supramolecular aggregation that is often observed in oligo-conjugated systems is usually strongly affected by even minor structural changes that are used for sensor designs. This review discusses the examples of well-defined conjugated macromolecules based on oligo(arylene ethynylene) skeleton used for sensor applications. Here, exclusively examples of uniform macromolecules are summarized. The sensing mechanisms and importance of uniformity of structure are deliberated.

Preparation of lactic acid- and glucose-responsive poly(ε-caprolactone)-b-poly(ethylene oxide) block copolymer micelles using phenylboronic ester as a sensitive block linkage

The present study describes the synthesis, self-assembly and responsiveness to glucose and lactic acid of biocompatible and biodegradable block copolymer micelles using phenylboronic ester as the linkage between hydrophobic poly(ε-caprolactone) (PCL) and hydrophilic poly(ethylene oxide) (PEO). The PCL block with pendant phenylboronic acid (PCLBA) was synthesized by combining ε-caprolactone (ε-CL) ring-opening polymerisation (ROP), using 4-hydroxymethyl(phenylboronic) acid pinacolate as the initiator, and pinacol deprotection. The glucose-terminated PEO (PEOGlc) was prepared by 1,3-dipolar, Cu(i)-catalysed, alkyne-azide cycloaddition of α-methoxy-ω-propargyl poly(ethylene oxide) and 1-azido-1-deoxy-d-glucopyranose. All new compounds were evaluated by 1H NMR spectroscopy and by SEC analysis. PCLBA and PEOGlc blocks were linked in NaOH acetone solution, which was indirectly confirmed by Alizarin Red S fluorescence and directly by 1H NMR spectroscopy. Dialysis against Milli-Q water induced the self-assembly of PCLBA-b-PEOGlc nanoparticles, which were characterised by static (SLS) and dynamic (DLS) light scattering and by cryogenic transmission electron microscopy (cryo-TEM). Furthermore, the microscopic properties of the charged interface between the hydrophobic PCLBA core and the hydrophilic PEOGlc shell were examined by electrophoretic light scattering (zeta potential) and by fluorescence spectroscopy using the fluorescent probe 5-(N-dodecanoyl)aminofluorescein (DAF) as a pH indicator. Subsequently, the nanoparticles were transferred to a phosphate buffer saline (PBS) solution supplemented with different concentrations of glucose to simulate the physiological conditions in blood or lactic acid to simulate acidic cytosolic or endosomal conditions in tumour cells. Adding a surplus of glucose or lactic acid, which competitively binds to PBA, removes the stabilising hydrophilic PEOGlc blocks, thereby triggering marked nanoparticle aggregation. However, the rate of aggregation induced by lactic acid is considerably faster than that induced by glucose, as confirmed by light scattering. Thus, this novel block copolymer may contribute to the field of selective, lactic acid- and/or glucose-responsive drug delivery vehicle design under both pathological and physiological conditions.

Glucose selective bis-boronic acid click-fluor

Four novel bis-boronic acid compounds were synthesised via copper catalysed azide-alkyne cycloaddition (CuAAC) reactions. Glucose selectivity was observed for a particular structural motif. Moreover, a new glucose selective fluorescent sensor was designed and synthesised as a result.

“Click-fluors”: triazole-linked saccharide sensors

A series of boronic acid-containing saccharide receptors was synthesised via copper catalysed azide–alkyne cycloaddition (CuAAC) reactions.

A new fluorescence and colorimetric sensor for highly selective and sensitive detection of glucose in 100% water

A new naphthalimide derivative containing hexanoic acid and boronate groups was designed and synthesized.

RAFT polymerization of 4-vinylphenylboronic acid as the basis for micellar sugar sensors

Well-defined homo and mPEGylated block (co)polymers of the commercially available unprotected 4-vinylphenylboronic acid (4-VBA) monomer are reported based on reversible addition-fragmentation chain transfer (RAFT) polymerization. The polymerization kinetics are studied in detail for homo and block (co)polymerizations with different chain transfer agents (CTAs) to optimize the preparation of well-defined polymer structures, eventually leading to comparatively low dispersities (Đ ≤ 1.25). Subsequently, block (co)polymers with methoxy poly(ethylene glycol) mPEG-b-P(4-VBA) are prepared using a mPEG-functionalized CTA. The formed block copolymer mPEG114 -b-P(4-VBA)30 is demonstrated to be pH and glucose responsive as its micellization behavior is dictated by pH as well as the presence of glucose. The glucose-responsive pH window of mPEG114 -b-P(4-VBA)30 is found to be pH 9-10 based on the DLS and TEM measurement.

Study of boron-nitrogen dative bonds using azetidine inversion dynamics

A method for probing the strength of B-N dative bonds is reported. The activation parameters for nitrogen inversion in a series of azetidines tethered to boronate esters have been quantified by VT-NMR and the measured barriers correlated with data obtained by (11)B NMR, X-ray crystallography and MP2 calculations.

The development of boronic acids as sensors and separation tools

Synthetic receptors for diols that incorporate boronic acid motifs have been developed as new sensors and separation tools. Utilizing the reversible interactions of diols with boronic acids to form boronic esters under new binding regimes has provided new hydrogel constructs that have found use as dye-displacement sensors and electrophoretic separation tools; similarly, molecular boronic-acid-containing chemosensors were constructed that offer applications in the sensing of diols. This review provides a somewhat-personal perspective of developments in boronic-acid-mediated sensing and separation, placed in the context of the seminal works of others in the area, as well as offering a concise summary of the contributions of the co-authors in the area.

Tetrathiafulvalene vinylogues as versatile building blocks for new organic materials

Although tetrathiafulvalene (TTF) and its derivatives have been extensively studied as important organic electronic materials over the past half century, tetrathiafulvalene vinyl-ogues (TTFVs) still remain a relatively underdeveloped branch in the family of TTF derivatives. Our recent work has investigated the synthesis and characterization of a class of diphenyl-substituted TTFVs carrying alkynyl functionality. The unique conformational and redox properties of such TTFV derivatives along with the versatile chemistry enabled by acetylenic groups (e.g., metal-catalyzed coupling and click reactions) have led us to a variety of functional molecular architectures ranging from oligoynes, polymers, and molecular tweezers, to macrocycles. Property studies of these new TTFV-based molecular materials point to appealing applications in molecular electronics and optoelectronics.