Arresting “Loose Bolt” Internal Conversion from −B(OH)₂ Groups is the Mechanism for Emission Turn-On in <i>ortho</i>-Aminomethylphenylboronic Acid-Based Saccharide Sensors

Different mechanisms for the emission turn-on of <i>ortho</i>-aminomethylphenylboronic acids with appended fluorophores in response to saccharide binding in aqueous media have been postulated, such as photoinduced electron transfer (PET), “p<i>K</i>_a switch”, and disaggregation. However, none of the hypotheses is consistent with all the data for boronic acid–based sensors. To create a unifying theory that can explain the data, we performed a series of experiments to explore the origin of the emission turn-on with several boronic-acid based sensors upon binding fructose. First, we showed that the receptors and their complexes with fructose are solvent-inserted, with no B–N interactions. Second, we verified that the sensors are not aggregated. Third, in pure methanol, that exchanges −B­(OH)₂ to −B­(OMe)₂ groups, we found no fluorescence response upon binding fructose. We propose this occurs via lessening of internal conversion mechanisms. To investigate this proposal further, we performed a solvent isotope effect study. The fluorescence of the probes in D₂O (−B­(OH)₂ → −B­(OD)₂) does not change upon fructose binding. It is well accepted that −OD oscillators are less efficient energy acceptors due to their lower frequency vibrational modes. Thus, our studies reveal that modulating the −B­(OH)₂-induced internal conversion (an example of a “loose bolt effect”) explains how potentially all <i>ortho</i>-aminomethylphenylboronic acid-based fluorescence sensors signal the presence of sugars

Arresting “Loose Bolt” Internal Conversion from −B(OH)₂ Groups is the Mechanism for Emission Turn-On in <i>ortho</i>-Aminomethylphenylboronic Acid-Based Saccharide Sensors

Different mechanisms for the emission turn-on of <i>ortho</i>-aminomethylphenylboronic acids with appended fluorophores in response to saccharide binding in aqueous media have been postulated, such as photoinduced electron transfer (PET), “p<i>K</i>_a switch”, and disaggregation. However, none of the hypotheses is consistent with all the data for boronic acid–based sensors. To create a unifying theory that can explain the data, we performed a series of experiments to explore the origin of the emission turn-on with several boronic-acid based sensors upon binding fructose. First, we showed that the receptors and their complexes with fructose are solvent-inserted, with no B–N interactions. Second, we verified that the sensors are not aggregated. Third, in pure methanol, that exchanges −B­(OH)₂ to −B­(OMe)₂ groups, we found no fluorescence response upon binding fructose. We propose this occurs via lessening of internal conversion mechanisms. To investigate this proposal further, we performed a solvent isotope effect study. The fluorescence of the probes in D₂O (−B­(OH)₂ → −B­(OD)₂) does not change upon fructose binding. It is well accepted that −OD oscillators are less efficient energy acceptors due to their lower frequency vibrational modes. Thus, our studies reveal that modulating the −B­(OH)₂-induced internal conversion (an example of a “loose bolt effect”) explains how potentially all <i>ortho</i>-aminomethylphenylboronic acid-based fluorescence sensors signal the presence of sugars

Synthesis of Amines with Pendant Boronic Esters by Borrowing Hydrogen Catalysis

Amine alkylation reactions of alcohols have been performed in the presence of boronic ester groups to provide products which are known to have use as molecular sensors. The boronic ester moiety could be present in either the alcohol or amine starting material and was not compromised in the presence of a ruthenium catalyst

A Simple Protocol for NMR Analysis of the Enantiomeric Purity of Chiral Hydroxylamines

A practically simple three-component chiral derivatization protocol for determining the enantiopurity of chiral hydroxylamines by ¹H NMR spectroscopic analysis is described, involving their treatment with 2-formylphenylboronic acid and enantiopure BINOL to afford a mixture of diastereomeric nitrono-boronate esters whose ratio is an accurate reflection of the enantiopurity of the parent hydroxylamine

Near-Infrared Colorimetric and Fluorescent Cu²⁺ Sensors Based on Indoline–Benzothiadiazole Derivatives via Formation of Radical Cations

The donor–acceptor system of indoline–benzothiadiazole is established as the novel and reactive platform for generating amine radical cations with the interaction of Cu²⁺, which has been successfully exploited as the building block to be highly sensitive and selective near infrared (NIR) colorimetric and fluorescent Cu²⁺ sensors. Upon the addition of Cu²⁺, an instantaneous red shift of absorption spectra as well as the quenched NIR fluorescence of the substrates is observed. The feasibility and validity of the radical cation generation are confirmed by cyclic voltammetry and electron paramagnetic resonance spectra. Moreover, the introduction of an aldehyde group extends the electron spin density and changes the charge distribution. Our system demonstrates the large scope and diversity in terms of activation mechanism, response time, and property control in the design of Cu²⁺ sensors

Boronic Acid Mediated Coupling of Catechols and <i>N</i>‑Hydroxylamines: A Bioorthogonal Reaction to Label Peptides

An irreversible, three-component assembly with 2-formylphenylboronic acid, catechol, and <i>N</i>-hydroxylamines was achieved in aqueous media. The boronate ester product was formed with substituted catechols including l-DOPA. Assembly was found to be orthogonal to common biological functional groups and both copper­(I)-catalyzed alkyne–azide cycloaddition and aminoether/carbonyl condensations. Boronate ester formation and aminoether condensation were achieved in one pot with a hexameric peptide

A Fluorescent Chemodosimeter for Live-Cell Monitoring of Aqueous Sulfides

Aqueous sulfides are emerging signaling agents implicated in various pathological and physiological processes. The development of sensitive and selective methods for the sensing of these sulfides is therefore very important. Herein, we report that the as-synthesized 1-oxo-1<i>H</i>-phenalene-2,3-dicarbonitrile (OPD) compound provides promising fluorescent properties and unique reactive properties toward aqueous sulfides. It was found that OPD showed high selectivity and sensitivity toward Na₂S over thiols and other inorganic sulfur compounds through a sulfide involved reaction which was confirmed by high-resolution mass spectroscopy (HRMS) and nuclear magnetic resonance (NMR) results. The fluorescence intensity increases linearly with sulfide concentration in the range of 1.0–30 μM with a limit of detection of 52 nM. This novel fluorescent probe was further exploited for the fluorescence imaging sensing of aqueous sulfide in HeLa cells

Highly Efficient Photothermal Semiconductor Nanocomposites for Photothermal Imaging of Latent Fingerprints

Optical imaging of latent fingerprints (LFPs) has been widely used in forensic science and for antiterrorist applications, but it suffers from interference from autofluorescence and the substrates background color. Cu₇S₄ nanoparticles (NPs), with excellent photothermal properties, were synthesized using a new strategy and then fabricated into amphiphilic nanocomposites (NCs) via polymerization of allyl mercaptan coated on Cu₇S₄ NPs to offer good affinities toward LFPs. Here, we develop a facile and versatile photothermal LFP imaging method based on the high photothermal conversion efficiency (52.92%, 808 nm) of Cu₇S₄ NCs, indicating its effectiveness for imaging LFPs left on different substrates (with various background colors), which will be extremely useful for crime scene investigations. Furthermore, by fabricating Cu₇S₄-CdSe@ZnS NCs, a fluorescent-photothermal dual-mode imaging strategy was used to detect trinitrotoluene (TNT) in LFPs while still maintaining a complete photothermal image of LFP

Boronic Acid Mediated Coupling of Catechols and <i>N</i>‑Hydroxylamines: A Bioorthogonal Reaction to Label Peptides

An irreversible, three-component assembly with 2-formylphenylboronic acid, catechol, and <i>N</i>-hydroxylamines was achieved in aqueous media. The boronate ester product was formed with substituted catechols including l-DOPA. Assembly was found to be orthogonal to common biological functional groups and both copper­(I)-catalyzed alkyne–azide cycloaddition and aminoether/carbonyl condensations. Boronate ester formation and aminoether condensation were achieved in one pot with a hexameric peptide

De Novo Green Fluorescent Protein Chromophore-Based Probes for Capturing Latent Fingerprints Using a Portable System

Rapid visualization of latent fingerprints, preferably at their point of origin, is essential for effective crime scene evaluation. Here, we present a new class of green fluorescent protein chromophore-based fluorescent dyes (LFP-Yellow and LFP-Red) that can be used for real-time visualization of LFPs within 10 s. Compared with traditional chemical reagents for LFPs, these fluorescent dyes are completely water-soluble, exhibit low cytotoxicity, and are harmless to users. Level 1–3 details of the LFPs could be clearly revealed through “off–on” fluorescence signal readout. Additionally, the fluorescent dyes were constructed based on an imidazolinone core and so do not contain pyridine groups or metal ions, which ensures that the DNA is not contaminated during extraction and identification after the LFPs are treated with the dyes. Combined with our as-developed portable system for capturing LFPs, LFP-Yellow and LFP-Red enabled the rapid capture of LFPs. Therefore, these green fluorescent protein chromophore-based probes provide an approach for the rapid identification of individuals who were present at a crime scene