Reaction-based fluorometric analysis of N-bromosuccinimide by oxidative deprotection of dithiane.

In this study, a fluorescent probe is developed for the first time for N-bromosuccinimide (NBS), a synthetically and analytically important compound. Pyrene-dithiane-based probe 1 showed prominently selective and sensitive signaling behavior toward NBS owing to the oxidative cleavage of the dithiane protecting group of 1-pyrenecarboxaldehyde. The NBS-selective signaling of the probe was possible under competitive conditions in the presence of common metal ions and anions as a background. The detection limit of the probe for NBS was found to be 5.6 × 10-8 M (10.0 ppb). The signaling product was sufficiently stable under the oxidative stress of NBS in contrast to another tested compound, 6-methoxy-2-naphthaldehyde-based dithiane derivative 2, which showed a gradually decaying response because of the reaction of the signaling product with the residual NBS. In the practical application of the probe, a smartphone was used as a stand-alone device, and the fluorometric assays of the commercial NBS reagents could be conducted rapidly and in a convenient manner.

A simple hypochlorous acid signaling probe based on resorufin carbonodithioate and its biological application.

A novel hypochlorous-acid-selective signaling probe based on the carbonodithioate derivative of resorufin (RT-1) was developed. Probe RT-1 showed prominent colorimetric and turn-on type fluorescence signaling behavior exclusively toward hypochlorous acid, induced by oxidative hydrolysis, to regenerate resorufin dye. Hypochlorous acid signaling was not affected by the presence of common metal ions and anions as background, except for the redox active bromide and iodide anions. The detection limit of RT-1 for hypochlorous acid was found to be 2.18 × 10-9 M (0.11 ppb), and the signaling was completed within 3 min. It was also confirmed that hypochlorous acid signaling by the carbonodithioate-based probe RT-1 was superior to that of the closely related carbonothioate derivative RT-2. This was rationalized by density functional theory calculations, which demonstrated that the C[double bond, length as m-dash]S sulfur atom of the former is more negatively charged than that of the latter. Finally, as a biological application of the probe, visualization of hypochlorous acid in RAW 264.7 murine macrophages and HeLa cells was successfully conducted to detect the cellular response to hypochlorous acid.

Electronic Effect on the Molecular Motion of Aromatic Amides: Combined Studies Using VT-NMR and Quantum Calculations.

Rotational barrier energy studies to date have focused on the amide bond of aromatic compounds from a kinetic perspective using quantum calculations and nuclear magnetic resonance (NMR). These studies provide valuable information, not only regarding the basic conformational properties of amide bonds but also the molecular gear system, which has recently gained interest. Thus, we investigate the precise motion of the amide bonds of two aromatic compounds using an experimental rotational barrier energy estimation by NMR experiments and a theoretical evaluation of the density functional theory calculation. The theoretical potential energy surface scan method combined with the quadratic synchronous transit 3 method and consideration of additional functional group rotation with optimization and frequency calculations support the results of the variable temperature ¹H NMR, with deviations of less than 1 kcal/mol. This detailed experimental and theoretical research strongly supports molecular gear motion in the aromatic amide system, and the difference in kinetic energy indicates that the electronic effect from the aromatic structure has a key role in conformational movements at different temperatures. Our study provides an enhanced basis for future amide structural dynamics research.

Ratiometric Signaling of Hypochlorite by the Oxidative Cleavage of Sulfonhydrazide-Based Rhodamine-Dansyl Dyad.

A reaction-based probe 1 for hypochlorite signaling was designed by the conjugation of two fluorophores, rhodamine and dansyl moieties, by the reaction of rhodamine B base with dansylhydrazine. Probe 1 exhibited pronounced hypochlorite-selective chromogenic and fluorescent signaling behavior over other oxidants used in practical applications, such as hydrogen peroxide, peracetic acid, and ammonium persulfate, as well as commonly encountered metal ions and anions. Signaling was attributed to the hypochlorite-induced oxidative cleavage of the sulfonhydrazide linkage of the probe. In particular, favorable ratiometric fluorescence signaling was possible by utilizing the emissions of the two fluorophores. A detection limit of 1.13 × 10(-6) M (0.058 ppm) was estimated for the determination of hypochlorite. A paper-based test strip was prepared and was used as a semiquantitative indicator for the presence of hypochlorite in aqueous solutions. The probe was also successfully applied for the determination of hypochlorite in practical tap water samples.

Modulation of quinone PCET reaction by Ca2+ ion captured by calix[4]quinone in water.

Calix[4]arene-triacid-monoquinone (CTAQ), a quinone-containing water-soluble ionophore, was utilized to investigate how proton-coupled electron transfer (PCET) reactions of quinones were influenced by redox-inactive metal ions in aqueous environment. This ionophoric quinone derivative captured a Ca(2+) ion that drastically altered the voltammetric behavior of quinone, showing a characteristic response to pH and unique redox wave separation. Spectroelectrochemistry verified significant stabilization of the semiquinone, and electrocatalytic currents were observed in the presence of Ca(2+)-free CTAQ. Using digital simulation of cyclic voltammograms to clarify how the thermodynamic properties of quinones were altered, a simple scheme was proposed that successfully accounted for all the observations. The change induced by Ca(2+) complexation was explained on the basis of the combined effects of the electrostatic influence of the captured metal ion and hydrogen bonding of water molecules with the support of DFT calculation.

Reaction-based dual signaling of fluoride ions by resorufin sulfonates.

We developed new reaction-based probes for the dual signaling of fluoride ions. Selective fluoride-assisted deprotection of resorufin nosylate to generate resorufin fluorochrome was used for signaling. Resorufin nosylate exhibited selective colorimetric and fluorogenic signaling of fluoride ions in acetonitrile. The response from sulfide ions was effectively masked by using the TPEN-Cu(2+) complex as a source of Cu(2+) ions for masking sulfide. Selective optical signaling of fluoride was possible in the presence of commonly encountered anions with a detection limit of 1.9 × 10(-6) M.

Dual signaling of hydrazine by selective deprotection of dichlorofluorescein and resorufin acetates.

The highly selective chemosignaling behaviors for hydrazine by a reaction-based probe of dichlorofluorescein and resorufin acetates were investigated. Hydrazinolysis of latent dichlorofluorescein and resorufin acetate fluorochromes caused prominent chromogenic and fluorescent turn-on type signals. The probes selectively detected hydrazine in the presence of commonly encountered metal ions and anions as background. Dichlorofluorescein and resorufin acetates selectively detected hydrazine with detection limits of 9.0 × 10(-8) M and 8.2 × 10(-7) M, respectively. Furthermore, hydrazine was selectively detected over other closely related compounds, such as hydroxylamine, ethylenediamine, and ammonia. As a possible application of the acetate probes, hydrazine signaling in tap water was tested.

A colorimetric and fluorescent signaling probe for assaying Pd2+ in practical samples.

We developed an optical signaling probe to detect Pd2+ ions in Pd-containing catalyst and drug candidate. The Pd2+ signaling probe (Res-DT) was readily prepared by reacting the versatile fluorochrome resorufin with phenyl chlorodithioformate. In a phosphate-buffered saline solution (pH 7.4) containing sodium dodecyl sulfate (SDS) as a signal-boosting surfactant, Res-DT exhibited a pronounced colorimetric response with a chromogenic yellow to magenta shift, leading to a substantial increase in the fluorescence intensity. The Pd2+ signaling performance of Res-DT was attributed to the Pd2+-promoted hydrolysis of the dithioate moiety. The probe displayed high selectivity toward Pd2+ ions and remained unaffected by commonly encountered coexisting components. Moreover, the detection limit of Res-DT for Pd2+ ions was 10 nM, and the signaling was achieved within 7 min. Furthermore, to demonstrate the real-world applicability of Res-DT, a Pd2+ assay was performed in Pd-containing catalyst and drug candidate using an office scanner as an easily accessible measurement device. Our results highlight the prospects of Res-DT as a tool to detect Pd2+ ions in various practical samples, with potential applications in catalysis, medicine, and environmental science.

Colorimetric and fluorescent signaling of Au3+ by desulfurization of thiocoumarin.

We investigated the chemosignaling of Au(3+) by the selective desulfurization of thiocoumarin. In the presence of a heavy metal ion chelator N,N,N',N'-tetrakis-(2-pyridylmethyl)ethylenediamine, thiocoumarin was selectively converted to its oxo analogue by reaction with Au(3+), resulting in a pronounced chromogenic and fluorescent signaling. Selective signaling of Au(3+) was possible in the presence of common alkali, alkaline earth, and transition metal ions, as well as Au(+) in a mixed aqueous environment. The colorimetric determination of Au(3+) was possible by the color change from pink to yellowish green of the designed probe. The detection limit for the determination of Au(3+) in 50% aqueous acetonitrile was 1.1 × 10(-7) M.

Fluorescence signaling of Zr4+ by hydrogen peroxide assisted selective desulfurization of thioamide.

Thioamide derivative with a pyrene fluorophore was smoothly transformed to its corresponding amide by Zr(4+) ions in the presence of hydrogen peroxide. The transformation was evidenced by (1)H NMR spectroscopy and the signaling was completed within 10 min after sample preparation. Interference from Ag(+) and Hg(2+) ions in Zr(4+)-selective fluorescence signaling was readily suppressed with the use of Sn(2+) as a reducing additive. Discrimination of Zr(4+) from closely related hafnium, which is a frequent contaminant in commercial zirconium, was not possible. Prominent Zr(4+)-selective turn-on type fluorescence signaling was possible with a detection limit of 4.6 × 10(-6) M in an aqueous 99% ethanol solution.

Colorimetric screening of elevated urinary mercury levels by a novel Hg2+-selective probe of resorufin phosphinothioate.

Urinary mercury levels are the most reliable indicators of mercury exposure but identifying them requires complex techniques and heavy instruments. In this research, we reported a simple and convenient urinary mercury analysis method using a readily available office scanner. Probe MP-1 synthesized by the reaction of resorufin and dimethylthiophosphinoyl chloride revealed Hg2+-selective chromogenic and fluorescent signaling behavior. Signaling was realized through Hg2+-induced deprotection of the phosphinothioate protecting group in the resorufin-based probe MP-1 to yield the parent fluorochrome. A pronounced colorimetric response of color change from light yellow to pink alongside a turn-on type fluorescence enhancement was perceived exclusively toward Hg2+ ions over other metal ions and anions. The colorimetry provided a more advantageous ratiometric approach than the simple fluorometric analysis exhibiting an off-on type response, with a detection limit of 12 nM (2.4 ppb). The Hg2+ signaling of the MP-1 probe was not disturbed by the presence of coexisting metal ions and anions. The sensitive and convenient diagnosis of clinically important neurological symptoms and fatal inorganic mercury levels in urine was successfully demonstrated using a standard office scanner.

Signaling of hypochlorous acid by selective deprotection of dithiane. [corrected].

The selective signaling of hypochlorous acid by dithiane-protected [corrected] pyrene-aldehyde was investigated. Dithiolane derivative of pyrene-aldehyde was efficiently deprotected by hypochlorous acid to its corresponding aldehyde, which resulted in a prominent UV-vis and turn-on type fluorescence signaling. The signaling was not affected by the presence of other common alkali, alkaline earth metal ions, and anions. Interference from Hg(2+) ions could be successfully circumvented by using Chelex-100 resin. Dithiane [corrected] also provided selectivity toward hypochlorous acid over other commonly used oxidant of hydrogen peroxide.

Hg2+ -selective chromogenic and fluorogenic chemodosimeter based on thiocoumarins.

The highly selective chemodosimetric behavior of thiocoumarins toward Hg(2+) ions was investigated; significant chromogenic and fluorogenic signaling of Hg(2+) ions occurs from the transformation of thiocoumarin to coumarin by Hg(2+)-induced selective desulfurization.

The first hydride-Meisenheimer adduct of electron-deficient 3-nitronaphthalimide: application to colorimetric borohydride determination.

The first hydride-Meisenheimer adduct of 3-nitronaphthalimide was used for the colorimetric borohydride assay. To explain the regioselectivity of the adduct, the reaction enthalpies of the two most plausible Meisenheimer adducts were obtained via computational calculation. Using the adduct formation, the assay of borohydride reagents was successfully conducted.

Novel Hg2+-Selective Signaling Probe Based on Resorufin Thionocarbonate and its µPAD Application.

In this study, a novel resorufin thionocarbonate-based Hg2+-selective signaling probe (RT) for microfluidic paper-based analytical device (µPAD) applications is reported. The designed probe, RT, was readily synthesized by the one-step reaction of resorufin with phenyl thionochloroformate. The RT probe displayed a prominent color change from yellow to pink and a marked turn-on fluorescence signaling behavior exclusively toward the Hg2+ ion. The signaling of RT was due to Hg2+-induced hydrolysis of the phenyl thionocarbonate moiety to form the parent resorufin dye, which restored its spectroscopic properties. In addition, RT exhibited the Hg2+-selective signaling behavior without interference by coexisting environmentally relevant metal ions. The detection limit for Hg2+ in simulated wastewater samples was estimated to be 5.8 × 10-8 M. In particular, an RT-equipped µPAD prepared using a wax printing technique enabled simple and convenient determination of Hg2+ ions in simulated wastewater samples, with a detection limit of 5.9 × 10-6 M.

Ratiometric determination of Hg2+ ions based on simple molecular motifs of pyrene and dioxaoctanediamide.

A new podand-type dioxaoctanediamide-based chemosensor having two pyrene moieties was prepared, and its fluoroionophoric behaviors toward transition-metal ions were investigated. Pyrene-appended dioxaoctanediamide 1 showed a selective fluorescence quenching toward Hg2+ ions over other transition-metal ions in an aqueous methanol solution. Unique responses in pyrene monomer and excimer emissions allowed selective ratiometric determination of Hg2+ ions in aqueous environments, and the detection limit was found to be 1.6 x 10(-6) M. [structure: see text]

Magnetic resonance microscopic imaging based on high-order intermolecular multiple-quantum coherences.

Most imaging studies using intermolecular multiple-quantum coherences (iMQCs) have focused on the two-spin dipolar interactions--zero and double quantum coherences. Here, we report the results of various experimental studies to assess the feasibility of magnetic resonance microscopy with high-order iMQCs in model systems at 7 and 14 T. Experimental results demonstrated that the iMQC microscopic images with high coherence orders are readily observable at high field and have unique contrast depending on the sample microstructure and coherence order.

Hg2+-selective OFF-ON and Cu2+-selective ON-OFF type fluoroionophore based upon cyclam.

[structure: see text]. A new cyclam derivative having two different fluorophores of pyrene and NBD subunits was prepared, and its Hg2+- and Cu2+-selective signaling behaviors were investigated. The detection limits for the analysis of Hg2+ and Cu2+ ions were found to be 7.9 x 10(-6) and 2.6 x 10(-7) M in aqueous acetonitrile solution (H2O-CH3CN = 10:90, v/v), respectively. The compound also exhibited a selective Hg2+/Cu2+-induced OFF-ON-OFF type of signaling pattern that can be utilized for the construction of functional supramolecular switching systems.

Fluorogenic Hg2+-selective chemodosimeter derived from 8-hydroxyquinoline.

[reaction: see text] A new thioamide derivative of 8-hydroxyquinoline-benzothiazole was prepared, and its fluorogenic chemodosimetric behaviors toward transition-metal ions were investigated. The thioamide derivative showed highly Hg2+-selective fluorescence enhancing properties (167-fold) in 30% aqueous acetonitrile solution. The selective and sensitive signaling behaviors were found to originate from the Hg2+ ion induced transformation of the very weak fluorescent thioamide derivative into a highly fluorescent amide analogue.

Visible-light-induced regioselective synthesis of polyheteroaromatic compounds.

A method for visible-light-induced synthesis of polyheteroaromatics from 2-heteroaryl-substituted anilines and heteroarylalkynes was developed. The process, which uses fac-Ir(ppy)3 as the photocatalyst and (t)BuONO as the diazotization reagent, is highly regioselective.