A fluorous-tag-assisted fluorescent probe for simple and selective detection of hydrogen sulfide: application for turbid dyeing solutions.

Accurate hydrogen sulfide (H2S) detection has attracted much attention because its toxicity may affect aquatic environments and human health. However, recognizing H2S levels by conventional fluorescent probes in turbid wastewater has been challenging because the opaque environment interferes with their photophysical properties. To overcome this limitation, a fluorous-tagging strategy can be used for the development of fluorescent sensors to detect H2S in turbid solutions. The use of fluorescent probe assisted with fluorous-tag allowed for easy isolation of the probe using polytetrafluoroethylene (PTFE) material, while disturbing species were eliminated through a simple aqueous wash. This approach enabled the fluorescent probe to effectively quantify H2S, even in opaque solutions containing organic dyes that could interfere with fluorescence emission.

A fluorescent probe for selective detection of boric acids and its application for screening the conversion of the Suzuki-Miyaura coupling reaction.

Boric acid (B(OH)3) plays an important physiological role and is widely used as a food preservative and an antiseptic. Various colorimetric, fluorescent probes have been developed to detect boric acid; however, most of them could not discriminate boric acid over boronic acids (R-B(OH)2) or are limited to boronic acid sensors. Therefore, the development of boric acid-selective probes is necessary. Herein, a salicylimine-based fluorophore, Di-OH, was designed that showed selective fluorescence response to boric acid over boronic acid. Its fluorescence response to boric acid showed a large fluorescence turn-on signal up to 140 fold and excellent selectivity with various analytes. Furthermore, since boric acid is generated in proportion to the consumed boronic acid derivatives during reactions involving oraganoboron compounds, Di-OH allowed the determination of the conversion of the Suzuki-Miyaura coupling reaction using fluorescence spectroscopy and its correlation with the GC conversion was confirmed.

A pH-responsive sensor based on intramolecular internal standard for reproducible detection of strong acids and bases via 19F NMR spectroscopy.

Numerous methods, including pH meters and optical sensors, have been developed for the detection of pH, which is an important indicator in various fields. However, those methods are susceptible to errors in strongly acidic and basic ranges and inaccurate pH measurement due to sample turbidity, hindering their application such as photographic industries and wastewater treatment facilities. Eco-friendly and non-invasive 19F NMR spectroscopy is a promising technique for measurement of strong acids and bases owing to its high sensitivity and little interference; nevertheless, inconsistencies in reproducibility impede its widespread adoption. Herein, we developed a19F NMR-based pH sensor by introducing an intramolecular internal standard strategy into a pH-responsive fluorinated material. Based on the acceptable deviation (ΔδF = 17-19 ppb) in the evaluation of the internal standard signal, this pH-sensing platform enabled reproducible pH measurements in strongly acidic and basic environments. Moreover, its 19F NMR response showed reversibility and high stability to potential interfering factors, and the low absolute difference (0.026-0.086 in pH) for real samples such as diet Coke suggests its potential suitability for various acidic beverages.

Turn-On Fluorescent pH Probes for Monitoring Alkaline pHs Using Bis[2-(2'-hydroxyphenyl)benzazole] Derivatives.

For surveilling human health, industries, and the environment, pH monitoring is important. Numerous studies on fluorescent probes have been conducted to monitor various pH ranges. However, fluorescent probes that are capable of sensing alkaline regions are rare. In this study, we propose turn-on-type fluorescent probes for detecting alkaline pHs using bis[2-(2'-hydroxyphenyl)benzazole] (bis(HBX)) derivatives. These probes have high pKa values (from 9.7 to 10.8) and exhibit strong fluorescence intensity and color changes at alkaline pHs. Probes derived from bis(HBX) exhibit good photostability, reversibility, and anti-interference toward pH variations, which can be identified as a certain fluorescence change toward a basic pH. Therefore, compounds would be advantageous to use fluorescent probes for monitoring alkaline pH changes.

High-Throughput Approach for Facile Access to Hetero-Dinuclear Synergistic Metal Complex for H2O2 Activation and Its Implications.

Hetero-dinuclear synergic catalysis is a promising approach for improving catalytic performance. However, employing it is challenging because the design principles for the metal complex are still not well understood. Further, these complexes have a broader set of possibilities than mononuclear or homometallic systems, increasing the time and effort required to understand them. In this study, we explored a high-throughput approach to obtain a new hetero-dinuclear synergistic metal complex for H2O2 activation. From the 1152 combinations of metal complex candidates obtained by changing three variables (metal ions, unsymmetrical dinucleating ligands, and pH), the lead complex (L3-(Ni, Co)), which has the highest peroxidase activity, was derived using colorimetric parallel analysis. A series of control experiments revealed that L3 plays a crucial role in the formation of active L3-(Ni, Co) complexes, Co2+ acts as a catalytic center, and Ni2+ serves as an assistant catalytic site within L3-(Ni, Co). In addition, the catalytic efficiency of L3-(Ni, Co), which was 125 times that of the homo-bimetallic complex (L3-(Co, Co)), revealed clear hetero-bimetallic synergism in the buffer. The ultraviolet-visible study and electron paramagnetic resonance-based spin-trap experiment provided mechanistic insight into H2O2 activation by the intermediate, which was found to be induced by the reaction of L3-(Ni, Co) and H2O2. Moreover, the intermediate could act as a donor of the hydroperoxyl radical (•OOH) in the buffer. Furthermore, L3-(Ni, Co) demonstrated potential for application as a signal transducer for H2O2 in an enzyme-coupled cascade assay that can be used for the colorimetric detection of glucose.

Oligonucleotide-Chemosensor Conjugate as a Dual Responsive Detection Platform and Its Application for Simultaneous Detection of ATP and Zn2.

Simultaneous detection, which helps understand complex physiological processes and accurately diagnose diseases, has been achieved using dual responsive probes. The dual responsive probe can ideally distinguish four cases, which are a combination of the absence and presence of two analytes, with characteristic fluorescence emissions. Owing to the demanding conditions of its development, most previous studies have focused on the simple linkage between small-molecule chemosensors that have an individual target and spectral range. In this study, a new dual responsive detection platform, oligonucleotide-chemosensor conjugate, was developed using a linkage between versatile oligonucleotide probes and small-molecule chemosensors to expand the applicable scaffold and detectable target for simultaneous detection. As a proof of concept, the ATP aptamer probe and Zn2+ chemosensor were conjugated as the levels of ATP and Zn2+ are intimately correlated in several signaling pathways and diseases. Each probe could detect an analyte independently within a conjugate probe, and simultaneous detection was also demonstrated without spectral crosstalk or interference between the receptors. In addition, the introduced cholesterol modification allowed the developed probe to detect changes in analytes on the plasma membrane of live cells through flow cytometry and confocal microscopy.

Adhesion Improvement of Solvent-Free Pressure-Sensitive Adhesives by Semi-IPN Using Polyurethanes and Acrylic Polymers.

To improve the peel strength and holding time of polypropylene glycol (PPG)-based pressure-sensitive adhesives (PSAs), a semi-interpenetrating polymer network (semi-IPN) was prepared using acrylic polymers. In addition, to prevent air pollution due to volatile organic compound emissions and avoid the degradation of physical properties due to a residual solvent, the PPG-based semi-IPN PSAs were fabricated by an eco-friendly solvent-free method using an acrylic monomer instead of an organic solvent. PPG-based semi-IPN PSAs with different hard segment contents (2.9-17.2%) were synthesized; their holding time was found to depend on the hard segment contents. The peel strength was improved because of the formation of the semi-IPN structure. Moreover, the high degree of hard domain formation in the semi-IPN PSA, derived from the increase in the hard segment content using a chain extender, resulted in a holding time improvement. We believe that the as-prepared PSAs can be used in various applications that require high creep resistance.

Ratiometric Strategy Based on Intramolecular Internal Standard for Reproducible and Simultaneous Fingerprint Recognition of Diols via 19F NMR Spectroscopy.

19F NMR spectroscopy has been widely used as a convenient and noninvasive analytical technique for understanding complex natural phenomena at the atomic level. However, current NMR referencing techniques are most optimized for 1H NMR, which causes some limitations while referencing heteronuclear NMR. Despite its promising advantages, 19F NMR spectroscopy often exhibits large variations in experimental results and lacks consistency compared with 1H NMR. Herein, we propose a new strategy to improve the consistency of 19F NMR referencing using an internal standard method. As a proof-of-concept, BA-Py-TFP was applied as a sensor for diols via 19F NMR spectroscopy. This strategy proved to be a robust and reproducible referencing method with acceptable deviation (ΔδF = 43-58 ppb) across diverse NMR spectrometers at different institutions. In particular, this new strategy allows reliable fingerprint recognition for analytes and enables qualitative and quantitative analyses of mixtures of multiple analytes simultaneously. The high recovery rates for d-glucose in the human serum matrix suggest its potential suitability for a diverse range of applications, such as in diabetes-related diagnostics.

Investigation of a benzodiazaborine library to identify new pH-responsive fluorophores.

The detection of pH is important owing to its significance in various processes, such as clinical and industrial processes. Numerous fluorescent pH probes have been developed using a variety of fluorophores; however, most are only suitable for application in a narrow pH range (between 5 and 8) owing to the lack of diversity of the pH-sensitive units. Furthermore, probes suitable for sensing high pHs have rarely been studied despite the importance of reliable detection of high pH in various industrial processes. In this study, we prepared a benzodiazaborine (bDAB) library consisting of 238 different bDABs through combinatorial synthesis to investigate their suitability as fluorescent pH probes. Informed by the results of a fluorescence-based, high-throughput screening of the library, we identified four bDABs that exhibit promising pH-sensitive ratiometric fluorescence responses. Their pKas vary significantly, ranging from 7.29 to 12.44, indicating their suitability for the detection of basic pHs even in extremely basic environments (pH > 10). Furthermore, their fluorescence responses show high stability, anti-interference, and reversibility under various pH conditions.

pH-guided fluorescent sensing probe for the discriminative detection of Cl- and Br- in human serum.

The fluctuation of the halide ion concentration in human serum is of a high clinical implication. The measurement of Cl- in human serum samples is important because Cl- is a major constituent of human serum and certain Cl- levels are indicators of many acute diseases. Real-time monitoring of Br- levels in human serum samples from patients ingesting Br- salt-based antiepileptic drugs is important to regulate potential adverse drug effects. In this study, we developed a fluorescent probe for the discriminative sensing of Cl- and Br- using a naphthalimide-benzimidazole conjugate-based Ag+ complex (L1-Ag+ complex) by exploiting the strong interaction between Ag+ and halide ions with selectivity control by pH variation. The probe exhibited a dual function of detecting Cl- and Br- at pH levels of 4.5 and 8.0, respectively. Under this two pH conditions, the probe showed a high sensitivity (limit of detection (LOD) = 43 and 5 µM for Cl- and Br-, respectively) and selectivity toward Cl- and Br-. Importantly, the probe could be applied in the quantification of Cl- and Br- levels in human serum samples under two conditions: Cl- in normal human serum and Br- in the serum-mimicking that of epileptic patients during medication.

Aldehyde N,N-dimethylhydrazone-based fluorescent substrate for peroxidase-mediated assays.

Numerous assays based on peroxidase activity have been developed for the detection of analytes due to the various optical peroxidase substrates. However, most substrates are sensitive to light and pH and are over-oxidized in the presence of excess H2O2. In this study, 2-((6-methoxynaphthalen-2-yl)methylene)-1,1-dimethylhydrazine (MNDH), a fluorescent peroxidase substrate prepared from naphthalene-based aldehyde N,N-dimethylhydrazone, was developed. MNDH showed quantitative fluorescence changes with respect to the H2O2 concentration in the presence of horseradish peroxidase (HRP), and the MNDH/HRP assay showed no changes in fluorescence caused by over-oxidation in the presence of excess H2O2. Further, MNDH was thermo- and photostable. Additionally, the assay could be operated over a considerably wide pH range, from acidic to neutral. Moreover, MNDH can be used to detect glucose quantitatively in human serum samples by using an enzyme cascade assay system.

Metal-Free, Rapid, and Highly Chemoselective Reduction of Aromatic Nitro Compounds at Room Temperature.

In this study, we developed a metal-free and highly chemoselective method for the reduction of aromatic nitro compounds. This reduction was performed using tetrahydroxydiboron [B2(OH)4] as the reductant and 4,4'-bipyridine as the organocatalyst and could be completed within 5 min at room temperature. Under optimal conditions, nitroarenes with sensitive functional groups, such as vinyl, ethynyl, carbonyl, and halogen, were converted into the corresponding anilines with excellent selectivity while avoiding the undesirable reduction of the sensitive functional groups.

Effective and prolonged targeting of a nanocarrier to the inflammation site by functionalization with ZnBPMP and chitosan.

Efficient and selective targeting of inflamed tissues/organs is critical for diagnosis and therapy. Although nanomaterials themselves have an intrinsic advantage due to their size for targeting inflammation sites, additional functionalization of the nanomaterials with proper targeting moieties is desired to enhance the targeting efficiency. In this study, we aimed to improve the inflammation targeting characteristics of a pluronic-based nanocarrier, which has advantages as a nanosized delivery cargo for diverse molecules, by conjugating with chitosan and ZnBPMP (two Zn(II) ions chelated 2,6-bis[(bis(2-pyridylmethyl)amino)-methyl]-4-methylphenol) moiety. Specific and significant cellular uptake and interaction between the nanocarrier functionalized with ZnBPMP ligand and chitosan to an apoptosis-induced immune cell line were observed in vitro. An inflammation model in the mouse ear caused by skin hypersensitivity was used to evaluate the effect of functionalization with chitosan and ZnBPMP moiety by comparing with various control groups. Functionalization of the nanocarrier with chitosan greatly enhanced the in vivo circulation time of the nanocarrier, so prolonged targeting ability of the nanocarrier to the inflamed ear was achieved. Additional ZnBPMP functionalization to chitosan-functionalized nanocarrier also resulted in significantly improved initial targeting and further enhancement in the targeting until 5 days to the inflamed ear and the decreased non-specific accumulation of the nanocarrier to the remaining body. Thus, developed nanocarrier has a high potential as a drug delivery carrier as well as a diagnostic agent to the inflammation sites.

An analyte-triggered artificial peroxidase system based on dimanganese complex for a versatile enzyme assay.

We described an analyte-activatable artificial peroxidase system (caged Mn2(bpmp)) by caging a dimanganese complex, exhibiting peroxidase-like activity, with an analyte-reactive trigger. It allowed adjustments of the detection target to be applied depending on the trigger as well as the detection modes, such as fluorescence and colorimetric, as required. This system was successfully applied to a versatile enzyme assay for leucine aminopeptidase and γ-glutamyl transpeptidase based on spectrophotometric change induced from the oxidation of the peroxidase substrate by analyte-triggered peroxidase-like activity.

Photocatalytic carbocarboxylation of styrenes with CO2 for the synthesis of γ-aminobutyric esters.

Metal-free photoredox-catalyzed carbocarboxylation of various styrenes with carbon dioxide (CO2) and amines to obtain γ-aminobutyric ester derivatives has been developed (up to 91% yield, 36 examples). The radical anion of (2,3,4,6)-3-benzyl-2,4,5,6-tetra(9H-carbazol-9-yl)benzonitrile (4CzBnBN) possessing a high reduction potential (-1.72 V vs. saturated calomel electrode (SCE)) easily reduces both electron-donating and electron-withdrawing group-substituted styrenes.

A simple and efficient in situ generated copper nanocatalyst for stereoselective semihydrogenation of alkynes.

Development of a simple, effective, and practical method for (Z)-selective semihydrogenation of alkynes has been considered necessary for easy-to-access applications at organic laboratory scales. Herein, (Z)-selective semihydrogenation of alkynes was achieved using a copper nanocatalyst which was generated in situ simply by adding ammonia borane to an ethanol solution of copper sulfate. Different types of alkynes including aryl-aryl, aryl-alkyl, and aliphatic alkynes were selectively reduced to (Z)-alkenes affording up to 99% isolated yield. The semihydrogenation of terminal alkynes to alkenes and gram-scale applications were also reported. In addition to eliminating catalyst preparation, the proposed approach is simple and practical and serves as a suitable alternative method to the conventional Lindlar catalyst.

Antifibrosis treatment by inhibition of VEGF, FGF, and PDGF receptors improves bladder wall remodeling and detrusor overactivity in association with modulation of C-fiber afferent activity in mice with spinal cord injury.

AIMS: Spinal cord injury (SCI) above the sacral level causes bladder dysfunction and remodeling with fibrosis. This study examined the antifibrotic effects using nintedanib, an inhibitor of vascular endothelial growth factor, fibroblast growth factor, and platelet-derived growth factor receptors, on detrusor overactivity (DO) and bladder fibrosis, as well as the modulation mechanisms of C-fiber afferent pathways. METHODS: Thirty female C57BL/6 mice were divided into group A (spinal intact), group B (SCI with vehicle), and group C (SCI with nintedanib). At 2 weeks after SCI, vehicle or 50 mg/kg nintedanib was administered subcutaneously for 2 weeks. Then, cystometry was conducted, followed by RT-PCR measurements of fibrosis-related molecules, muscarinic, ß-adrenergic, TRP and purinergic receptors in the bladder or L6-S1 dorsal root ganglia (DRG). Trichrome stain and Western blot analysis of transforming growth factor-beta and fibronectin were performed in the bladder. TRPV1 expression in L6 DRG was measured by immunohistochemistry. RESULTS: In cystometry, intercontraction intervals, nonvoiding contractions, voided volume, and voiding efficiency were significantly improved in group C versus group B. RT-PCR, Western blotting, and trichrome staining revealed the fibrotic changes in the bladder of group B, which was improved in group C. Increased messenger RNA levels of TRPV1, TRPA1, P2X2 , and P2X3 in DRG of group B were significantly decreased in group C. TRPV1 immunoreactivity in DRG was increased in group B, but decreased in group C. CONCLUSIONS: Nintedanib improves storage and voiding dysfunctions and bladder fibrosis in SCI mice. Also, nintedanib-induced improvement of DO is associated with reduced expression of C-fiber afferent markers, suggesting the modulation of bladder C-fiber afferent activity.

Hypoxia-inducible factor 2α is a novel inhibitor of chondrocyte maturation.

Hypoxic environment is essential for chondrocyte maturation and longitudinal bone growth. Although hypoxia-inducible factor 1 alpha (Hif-1α) has been known as a key player for chondrocyte survival and function, the function of Hif-2α in cartilage is mechanistically and clinically relevant but remains unknown. Here we demonstrated that Hif-2α was a novel inhibitor of chondrocyte maturation through downregulation of Runx2 stability. Mechanistically, Hif-2α binding to Runx2 inhibited chondrocyte maturation by Runx2 degradation through disrupting Runx2/Cbfß complex formation. The Hif-2α-mediated-Runx2 degradation could be rescued by Cbfß transfection due to the increase of Runx2/Cbfß complex formation. Consistently, mesenchymal cells derived from Hif-2α heterozygous mice were more rapidly differentiated into hypertrophic chondrocytes than those of wild-type mice in a micromass culture system. Collectively, these findings demonstrate that Hif-2α is a novel inhibitor for chondrocyte maturation by disrupting Runx2/Cbfß complex formation and consequential regulatory activity.

Colorimetric discrimination of nucleoside phosphates based on catalytic signal amplification strategy and its application to related enzyme assays.

Selective detection of adenosine monophosphate (AMP) and adenosine diphosphate (ADP) which are less charged molecules than adenosine triphosphate (ATP) or pyrophosphate (PPi) in aqueous solution has been considered challenging because AMP and ADP have relatively low binding affinity for phosphate receptors. In this study, colorimetric discrimination of nucleoside phosphates was achieved based on catalytic signal amplification through the activation of artificial peroxidase. This method showed high selectivity for AMP and ADP over ATP and PPi, unlike previous phosphate sensors that use Zn2+-dipicolylamine-based receptors. High selectivity of the suggested method allowed discrimination of AMP in aqueous solution by the naked eye, and the detection limit was estimated to be 0.5 µM. Mechanism analysis revealed AMP acted as activators in the peroxidation cycle of the Mn2(bpmp)/ABTS/H2O2 system despite having relatively low binding affinity. Additionally, high selectivity and quantitative signal amplification allowed for the development of colorimetric phosphodiesterase and a small molecule kinase assay method. The newly proposed method offers direct, real-time, and quantitative analysis of enzyme activities and inhibition, and is expected to be further applied to high-throughput screening of inhibitors.

A long-term stable paper-based glucose sensor using a glucose oxidase-loaded, Mn2BPMP-conjugated nanocarrier with a smartphone readout.

A simple paper-based analytical device (PAD) for the one-pot detection of glucose was developed herein using an artificial peroxidase-functionalized and glucose oxidase (GOx)-loaded pluronic-based nanocarrier (PNC). Mn2BPMP (BPMP; 2,6-bis[(bis(2-pyridylmethyl)amino)-methyl]-4-methylphenolate), an artificial peroxidase, was conjugated to PNC, allowing GOx to be loaded with a very high encapsulation efficiency. In solution, Mn2BPMP-PNC showed higher peroxidase-like catalytic efficiency than did Mn2BPMP at physiological pH. In addition, glucose detection via enzyme cascade reaction between GOx and Mn2BPMP in the GOx loaded-Mn2BPMP-PNC was more sensitive than the simple combination of Mn2BPMP and GOx with excellent selectivity. Subsequently, a PAD was fabricated using a laser printer with an assay substance containing GOx loaded-Mn2BPMP-PNC and peroxidase chromogenic substrate. The prepared Mn2BPMP-PNC-based PAD quantitatively measured glucose in human serum ranging from normal levels to those typical for diabetics as well as in buffer by obtaining RGB (red, green, and blue) color values through smartphone readout or the naked eye. Importantly, the present PNC-based PAD maintained the detection efficiency during storage at room temperature for 6 weeks in contrast to the rapid decrease in detection efficiency obtained for PAD containing Mn2BPMP and GOx without PNC.