A Fluorescence Sensor Array Based on Zinc(II)-Carboxyamidoquinolines: Toward Quantitative Detection of ATP*.

The newly prepared fluorescent carboxyamidoquinolines (1-3) and their Zn(II) complexes (Zn@1-Zn@3) were used to bind and sense various phosphate anions utilizing a relay mechanism, in which the Zn(II) ion migrates from the Zn@1-Zn@3 complexes to the phosphate, namely adenosine 5'-triphosphate (ATP) and pyrophosphate (PPi), a process accompanied by a dramatic change in fluorescence. Zn@1-Zn@3 assemblies interact with adenine nucleotide phosphates while displaying an analyte-specific response. This process was investigated using UV-vis, fluorescence, and NMR spectroscopy. It is shown that the different binding selectivity and the corresponding fluorescence response enable differentiation of adenosine 5'-triphosphate (ATP), adenosine 5'-diphosphate (ADP), pyrophosphate (PPi), and phosphate (Pi). The cross-reactive nature of the carboxyamidoquinolines-Zn(II) sensors in conjunction with linear discriminant analysis (LDA) was utilized in a simple fluorescence chemosensor array that allows for the identification of ATP, ADP, PPi, and Pi from 8 other anions including adenosine 5'-monophosphate (AMP) with 100 % correct classification. Furthermore, the support vector machine algorithm, a machine learning method, allowed for highly accurate quantitation of ATP in the range of 5-100 µM concentration in unknown samples with error <2.5 %.

Room-Temperature Phosphorescence-active Boronate Particles: Characterization and Ratiometric Afterglow-sensing Behavior by Surface Grafting of Rhodamine B.

We found that boronate particles (BP), as a self-assembled system prepared by sequential dehydration of benzene-1,4-diboronic acid with pentaerythritol, showed greenish room-temperature phosphorescence (RTP). This emission was observed in both solid and dispersion state in water. To understand the RTP properties, X-ray crystallographic analysis, and density functional theory (DFT) and time-dependent DFT at M06-2X/6-31G(d,p) level were performed using 3,9-dibenzo-2,4,8,10-tetraoxa-3,9-diboraspiro[5.5]undecane (1) as a model compound. Our interest in functionalizing the RTP-active particles led us to graft Rhodamine B onto their surface. The resulting system emitted a dual afterglow via a Förster-type resonance energy transfer process from the BP in the excited triplet state to Rhodamine B acting as an acceptor fluorophore. This emission behavior was used for ratiometric afterglow sensing of water content in THF with a detection limit of 0.28 %, indicating that this study could pave the way for a new strategy for developing color-variable afterglow chemosensors for various analytes.

Boronate sol-gel method for one-step fabrication of polyvinyl alcohol hydrogel coatings by simple cast- and dip-coating techniques.

The self-assembly of polyvinyl alcohol (PVA) and benzene-1,4-diboronic acid (DBA) is employed as a sol-gel method for one-step fabrication of hydrogel coatings with versatile functionalities. A mixture of PVA and DBA in aqueous ethanol is prepared as a coating agent. The long pot life of the mixture allows for the coating of a wide range of materials with hydrogel films by simple cast- and dip-coating techniques. The resultant films show negligible dissolution in water and the intrinsic hydrophilicity of PVA provides the films with functional properties, such as improved antifogging property and resistance to protein and cell fouling. The self-assembling process shows adaptive inclusion properties toward nanoscale materials, such as metal-organic coordination polymers and inorganic nanoparticles, affording composite films. Furthermore, the coating film exhibits a unique secondary functionalization reactivity toward boronic acid-appended fluorescent dyes, through which a variety of materials are converted into fluorescent materials.

Anion Sensing by Fluorescent Expanded Calixpyrroles.

Expanded calixpyrrole-type macrocycles, calix[2]benzo[4]pyrroles, bearing fluorescent moieties attached via conjugated vinyl spacers, have been synthesized from the corresponding formyl derivatives through Knoevenagel condensation. The anion-binding properties of the resulting fluorescent macrocycles have been studied by means of NMR, UV/Vis, and fluorescence spectroscopies. Our main focus has been on dicarboxylates matching the size of the binding cavity of the calix[2]benzo[4]pyrrole skeleton. The observed anion-binding properties were compared with those of the regular calix[4]pyrroles bearing identical fluorophores. Surprisingly, the parent calix[4]pyrroles appear to be equally efficient, if not more so, for sensing anions such as dicarboxylates. Affinity constants determined for various anions and dianions show the sensors S1-S5 to be highly cross-reactive. The cross-reactivity of the sensors was utilized in a microchip-based array, which showed perfect (100 %) classification of 18 analytes utilizing only five sensors. Finally, the same array was used to quantitatively analyze dicarboxylates such as oxalate and malonate. The data from the array were subjected to linear regression, allowing the determination of various concentrations of dianions with low error (<2 %).

Fluorescent chirality recognition by simple boronate ensembles with aggregation-induced emission capability.

Chiral ensembles were spontaneously formed in solution through boronate esterification of structurally defined di(boronic acid)-appended tetraphenylethylene (DB-TPE) and commercially available l- or d-tartaric acid, showing enantioselective aggregation behavior for chiral diamines as well as cinchona alkaloids enabling the fluorescent recognition of their chirality.

Surface modification of a polyvinyl alcohol sponge with functionalized boronic acids to develop porous materials for multicolor emission, chemical sensing and 3D cell culture.

Surface modification of a polyvinyl alcohol sponge with functionalized boronic acids led to the formation of porous materials applicable for multicolor emission, chemical sensing and 3D cell culture.

Boronic acid as an efficient anchor group for surface modification of solid polyvinyl alcohol.

We report the use of boronic acid as an anchor group for surface modification of solid polyvinyl alcohol (PVA); the surfaces of PVA microparticles, films, and nanofibers were chemically modified with boronic acid-appended fluorescent dyes through boronate esterification using a simple soaking technique in a short time under ambient conditions.

Quantitative analysis of modeled ATP hydrolysis in water by a colorimetric sensor array.

Self-assembled colorimetric sensors have been prepared from Zn(II)-DPA-attached phenylboronic acid (·Zn) and catechol-type dyes. The ·Zn-dye sensors display selectivity towards oligophosphate over monophosphates. The colorimetric sensor assay (·Zn-dye) is utilized to monitor a model of a metabolic reaction where ATP is hydrolyzed to pyrophosphate (PPi) and AMP.

2,3-Naphtho-Fused BODIPYs as Near-Infrared Absorbing Dyes.

2,3-Naphtho-fused boron-dipyrromethenes (BODIPYs) 1a and 1b, which absorb near-infrared light at 740-770 nm with molar extinction coefficients above 10(5) M(-1) cm(-1) in THF, have been synthesized through a palladium(II)-catalyzed direct acylation of N-BOC hydrazones and subsequent Paal-Knorr pyrrole synthesis. Simple benzo-annulation of dibenzo-BODIPY caused a significant red-shift in the absorption. Subsequent intramolecular B,O-cyclization of 1b gave 2, which exhibited an intense absorption band at 830 nm. The structure-optical property relationship has been investigated using theoretical calculations and cyclic voltammetry.

Thermo-responsive white-light emission based on tetraphenylethylene- and rhodamine B-containing boronate nanoparticles.

Boronate nanoparticles with built-in tetraphenylethylene (TPE) have been prepared. Their emissive color tuning by altering the amount of rhodamine B grafted onto the surface gave white-light emissive nanoparticles. They showed reversible and thermo-responsive emission in the temperature range of 5-65 °C in water, which enabled them to serve as a bright nanothermometer.

Hierarchical supramolecules and organization using boronic acid building blocks.

Current progress on hierarchical supramolecules using boronic acids has been highlighted in this feature article. Boronic acids can participate in "click reactions" with diols and their congeners with dynamic covalent functionality. By comprehensively exploring versatile sequential boronate esterification linkages between plural boronic acid-appended molecules and multiple hydroxyl counterparts, not only versatile supramolecular polymers but also structurally well-defined network nanostructures have been developed. In addition orthogonal interactions such as dative bonds of the boron center with Lewis bases have led to the formation of hierarchical nano/microstructures. Boronate systems have the potential to be used as materials for smart gels, chemosensors, active architectures for electronics, heterogeneous catalysts, chemical-stimulus responsive systems for drug delivery, etc. Here, we fully discuss the feasibility of the structure-directing ability of boronic acids from the standpoint of the generation of new smart materials.

Intramolecular indicator displacement assay for anions: supramolecular sensor for glyphosate.

One of the well-known strategies for anion sensing is an indicator (dye) displacement assay. However, the disadvantage of the dye displacement assays is the low sensitivity due to the excess of the dye used. To overcome this setback, we have developed an "Intramolecular Indicator Displacement Assay (IIDA)". The IIDAs comprise a receptor and a spacer with an attached anionic chromophore in a single-molecule assembly. In the resting state, the environment-sensitive anionic chromophore is bound by the receptor, while the anionic substrate competes for binding into the receptor. The photophysical properties of the dye exhibit change in fluorescence when displaced by anions, which results in cross-reactive response. To illustrate the concept, we have prepared IID sensors 1 and 2. Here, the characterization of sensors and microtiter arrays comprising the IIDA are reported. The microtiter array including IID sensors 1 and 2 is capable of recognizing biological phosphates in water. The utility of the IIDA approach is demonstrated on sensing of a phosphonate herbicide glyphosate and other biologically important anions such as pyrophosphate in the presence of interferent sodium chloride.

Nanospherical aggregation of isothiouronium-terminated amphiphilic polythiophene: preparation and vapor-phase detection of volatile organic compounds.

Cationic isothiouronium-terminated amphiphilic poly(3-octylthiophene) IPOT has been synthesized by the reaction of bromoethylene-terminated poly(3-octylthiophene) with 1-(2-(2-methoxyethoxy)ethyl)-3-methylthiourea. By performing gel-permeation chromatography analysis, we estimated the number-average molecular weight (M(n)) and the polydispersity index (PDI) to be 1.07 x 10(4) and 1.48, respectively. The incorporation of an isothiouronium unit at the terminal position renders the polymer amphiphilic. Well-dispersed spherical aggregates were formed with increasing H2O content in the THF solution and were characterized by FE-SEM and powder XRD measurements. We thus proposed a core/shell-type micelle with a poly(3-octylthiophene) segment as the core and an isothiouronium segment as the shell, exposing the hydrophilic methoxyethoxy pendant. The change in morphology to a spherical shape led to a bathochromic shift of the absorption band with decreasing fluorescence intensity, enabling us to use it as a fluorimetric "off-on" sensor for volatile organic compounds (VOCs) where a quick response to THF was observed on the IPOT aggregate-coated TLC plate.

White-light emitting boronate microparticles for potential use as reusable bright chemosensors in water.

The facile surface functionalization of surfactant-free organic microparticles composed of polymeric 2,4,8,10-tetraoxa-3,9-diboraspiro[5.5]undecane allowed us to develop white-light emissive chemosensors for the real-time visual detection of Cu(2+) in HEPES buffer (pH 7.0) due to a synergistic response of fluorophores grafted onto the particles. A detection limit of 15.4 ppb for Cu(2+) in aqueous media and excellent recyclability were also observed.

Solvent-manipulated guest binding and signaling of a fluorescent resorcin[4]arene cavitand with 1,3,2-benzodiazaboryl D-π-A conjugation flaps.

The conformation of resorcin[4]arene cavitand system 1 was controlled by DMSO through a hydrogen bonding network between benzodiazaborole NHs of the cavitand flaps and DMSO molecules to stabilize the vase form. Subsequently, a guest-binding cavity of 1 was formed to accommodate tetraalkylammonium guest 3, permitting the monitoring of the guest by the unaided eye as a result of a CH-π interaction between the benzodiazaborole π-donor group and the guest.

Sensing of carboxylate drugs in urine by a supramolecular sensor array.

A supramolecular sensor array consisting of eight chemosensors embedded in a hydrogel matrix was used to sense carboxylate drugs. The discriminatory power of the array has been evaluated using principal component analysis and linear discriminant analysis. The eight-member sensor array has been shown to accurately identify 14 carboxylates in water with 100% classification accuracy. To demonstrate the potential for practical utility in the physiological environment, analysis of carboxylate drugs in human urine was also performed achieving 100% correct classification. In addition, the array performance in semiquantitative identification of nonsteroidal anti-inflammatory drugs has been investigated, and the results show that the sensor array is able to differentiate six typical nonsteroidal anti-inflammatory drugs at concentrations of 0.5-100 ppm. This illustrates the potential utility of the designed sensor array for diagnostic and environmental monitoring applications.

Leveraging material properties in fluorescence anion sensor arrays: a general approach.

As the demand for probes suitable for sensor development increases, investigation of approaches that utilize known successful receptors gains in general importance. This study describes a two-prong approach that can be used as a guide to developing sensors from known receptors. First, the conversion of a simple receptor, calix[4]pyrrole, into a fluorescent probe to establish a ratiometric signal is described. Secondly, the sensors that employ an output from a single ratiometric calix[4]pyrrole probe are fabricated by using poly(ether-urethane) hydrogel copolymers. These hydrogels are designed to absorb, internalize and transport aqueous electrolytes. A sensor array of ten different poly(ether-urethane) matrices with varying comonomer proportions were doped with a single probe and were exposed to eight different anions: acetate, benzoate, fluoride, chloride, phosphate, pyrophosphate, hydrogen sulfide, and cyanide, eight urine samples and anti-inflammatory drugs (NSAIDs). The poly(ether-urethane) matrices comprise different proportions of anion-binding urethane moieties and different hydrophilicity given by the ratio between ethylene glycol ether and butylene glycol ether. This diversity in the hydration behavior provides different environment polarity, in which the recognition and self-assembly processes display enough diverse behavior to allow for unique response of the probe to the analytes. Furthermore, a single probe is shown to recognize eight different aqueous anions and eight urine samples when embedded in ten different polyurethanes in an array that displays 100 % classification accuracy. To demonstrate the potential of the concept for quantitative studies, an estimation of non-steroidal anti-inflammatory drugs ibuprofen and diclofenac in water and in saliva was performed. A limit of detection of 0.1 ppm and a dynamic range of 0.1-0.6 and 0.05-60 ppm was observed, respectively. Given the general difficulty of chemosensors to recognize aqueous anions, the fact that one probe recognizes eight different analytes attests to an enormous effect of the polymer environment on the recognition process. This method could be used to generate a variety of sensor arrays for various analyses including species that are difficult to recognize, such as small-molecule- and inorganic anions.

Supramolecular sensor for cancer-associated nitrosamines.

A supramolecular assay based on two fluorescent cucurbit[n]uril probes enables the recognition and quantification of nitrosamines, including cancer-associated nitrosamines, compounds that are difficult to recognize. The cross-reactive sensor leverages weak interactions and competition among the probe, metal, and guest, yielding high information density in the signal output (variance) and enabling the recognition of structurally similar guests.

Near-infrared absorbing boron-dibenzopyrromethenes that serve as light-harvesting sensitizers for polymeric solar cells.

Hexylthiophene-conjugated boron-dibenzopyrromethenes with benzo[1,3,2]oxazaborinine rings, 1, that absorb near-infrared light with relatively high molecular extinction coefficients have been synthesized. The incorporation of 3-hexylthiophene-conjugated dye 1a at a blend ratio of 5 wt % into a polymeric solar cell based on a P3HT/indene-C(70) bisadduct (IC(70)BA) bulk heterojunction structure improved power conversion efficiency from 3.7 to 4.3%. The present work suggests that well-defined near-infrared absorbing BODIPY analogues can potentially be used as photosensitizers in polymeric solar cells.

Boronic acid building blocks: tools for sensing and separation.

In this feature article the use of boronic acids to monitor, identify and isolate analytes within physiological, environmental and industrial scenarios is discussed. Boronic acids recognise diol motifs through boronic ester formation and interact with anions generating boronates, as such they have been exploited in sensing and separation protocols for diol appended molecules such as saccharides and anions alike. Therefore robust molecular sensors with the capacity to detect chosen molecules selectively and signal their presence continues to attract substantial attention, and boronic acids have been exploited with some success to monitor the presence of various analytes. Reversible boronic acid-diol interactions have also been exploited in boron affinity chromatography realising new separation domains through the same binding events. Boronic acid diol and anion interactions pertaining to sensing and separation are surveyed.