Youjun Yang

A three-channel fluorescent probe that distinguishes peroxynitrite from hypochlorite.

A novel fluorescent probe for peroxynitrite, PN(600), was rationally designed on the basis of a unique fluorophore assembly approach. PN(600) is a green-emitting coumarin derivative. Upon oxidation by peroxynitrite, PN(600) is transformed into a highly fluorescent red-emitting resorufin derivative via an orange-emitting intermediate. This three-channel signaling capability enables PN(600) to differentiate peroxynitrite from other reactive oxygen and nitrogen species, including hypochlorite and hydroxyl radical. Moreover, PN(600) is membrane-permeable and compatible with common TRITC filter sets and displays low cytotoxicity. Therefore, PN(600) is a promising candidate for in vitro peroxynitrite imaging.

Seminaphthofluorones are a family of water-soluble, low molecular weight, NIR-emitting fluorophores

A readily accessible new class of near infrared (NIR) molecular probes has been synthesized and evaluated. Specific fluorophores in this unique xanthene based regioisomeric seminaphthofluorone dye series exhibit a combination of desirable characteristics including (i) low molecular weight (339 amu), (ii) aqueous solubility, and (iii) dual excitation and emission from their fluorescent neutral and anionic forms. Importantly, systematic changes in the regiochemistry of benzannulation and the ionizable moieties afford (iv) tunable deep-red to NIR emission from anionic species and (v) enhanced Stokes shifts. Anionic SNAFR-6, exhibiting an unusually large Stokes shift of ≈200 nm (5,014 cm−1) in aqueous buffer, embodies an unprecedented fluorophore that emits NIR fluorescence when excited in the blue/green wavelength region. The successful use of SNAFR-6 in cellular imaging studies demonstrates proof-of-concept that this class of dyes possesses photophysical characteristics that allow their use in practical applications. Notably, each of the new fluorophores described is a minimal template structure for evaluation of their basic spectral properties, which may be further functionalized and optimized yielding concomitant improvements in their photophysical properties.

Understanding the Selectivity of a Multichannel Fluorescent Probe for Peroxynitrite Over Hypochlorite

Peroxynitrite is a prominent biological reactive nitrogen species from radical combination of nitric oxide and superoxide and fundamentally involved in broad spectrum physiological and pathological processes. Though redox-inert itself, peroxynitrite anion (OONO(-)) attacks various biological electrophiles to generate an array of potent 2-e(-) or 1-e(-) oxidants, which result in cell injuries. Development of fluorescent probes for peroxynitrite, free from interference from hypochlorite, has been an active endeavor of the chemical community. We previously reported a peroxynitrite probe (PN600), which could differentiate hypochlorite from peroxynitrite through a multichannel signaling mechanism. Herein, this intriguing selectivity was accounted for through a structure-reactivity relationship study. Also, this work, together with rich literature contributions, has allowed a qualitative guideline in the use of electron-rich aromatic moieties to design probes against peroxynitrite and/or hypochlorite. The viability of this guideline was further testified by development of another list of peroxynitrite selective probes.

Structurally Rigid 9-Amino-benzo[c]cinnoliniums Make Up a Class of Compact and Large Stokes-Shift Fluorescent Dyes for Cell-Based Imaging Applications

Classic fluorescent dyes, such as coumarin, naphthalimide, fluorescein, BODIPY, rhodamine, and cyanines, are cornerstones of various spectroscopic and microscopic methods, which hold a prominent position in biological studies. We recently found that 9-amino-benzo[c]cinnoliniums make up a novel group of fluorophores that can be used in biological studies. They are featured with a succinct conjugative push-pull backbone, a broad absorption band, and a large Stokes shift. They are potentially useful as a small-molecule alternative to R-phycoerythrin to pair with fluorescein in multiplexing applications.

Bright, Stable, and Biocompatible Organic Fluorophores Absorbing/Emitting in the Deep Near‐Infrared Spectral Region

Small-molecule organic fluorophores spectrally active in the 800-950 nm region are sought-after for their broad potential in biomedical and material applications. We have developed a new family of brightly fluorescent dyes (ECX) to meet this challenge. ECX dyes are transparent to the visible region, while strongly absorbing in the NIR region at approximately 880 nm. They emit at around 915 nm with a fluorescence quantum yield up to 13.3 %. ECX dyes exhibit high chemostability, high photostability, and low tendency to aggregate. Other merits of ECX dyes include low degree of solvatochromism and facile post-synthetic derivatization. ECX dyes potentially make available the 800-950 nm region for spectroscopic and microscopic applications and are also expected to find broad material applications.

A zero-background fluorescent probe for Hg2+ designed via the “covalent-assembly” principle

We herein report a novel fluorescent probe for Hg2+ based on the deprotection of 1,3-dithiolane, via the covalent assembly principle. Presence of Hg2+ triggers a cascade, which ultimately furnishes the push–pull backbone of a fluorescent dye, rendering a turn-on signal from a zero background and hence high detection sensitivity.

Photocalibrated NO Release from N-Nitrosated Napthalimides upon One-Photon or Two-Photon Irradiation

NO donors are routinely used as the exogenous source in in vitro studies. However, the kinetics or the dose of NO release from the existing donors is not readily monitored. This complicates the elucidation of the involvement of NO in a biological response. We report herein a series of NO donors (NOD545a-g), whose NO release is triggered by UV light at 365 nm or a two-photon laser at 740 nm, and importantly, their NO release is accompanied by a drastic fluorescence turn-on, which has been harnessed to follow the kinetics and dose of NO release in a real-time fashion with spectroscopic methods or microscopic methods in in vitro studies. These merits have rendered NOD545a-g useful molecular tools in NO biology.

A Water-Soluble, Green-Light Triggered, and Photo-Calibrated Nitric Oxide Donor for Biological Applications

Nitric oxide (NO) is a versatile endogenous molecule, involved in various physiological processes and implicated in the progression of many pathological conditions. Therefore, NO donors are valuable tools in NO related basic and applied applications. The traditional spontaneous NO donors are limited in scenarios where flux, localization, and dose of NO could be monitored. This has promoted the development of novel NO donors, whose NO release is not only under control, but also self-calibrated. Herein, we reported a phototriggered and photocalibrated NO donor (NOD565) with an N-nitroso group on a rhodamine dye. NOD565 is nonfluorescent and could release NO efficiently upon irradiation by green light. A bright rhodamine dye is generated as a side-product and its fluorescence can be used to monitor the NO release. The potentials of NOD565 in practical applications are showcased in in vitro studies, e.g., platelet aggregation inhibition and fungi growth suppression.

Mild Chemotriggered Generation of a Fluorophore-Tethered Diazoalkane Species via Smiles Rearrangement.

In situ generation of diazoalkanes under mild conditions is desired. A mechanism based on a Smiles rearrangement has been devised that releases a fluorophore-labeled unstabilized diazoalkane in the presence of various chemical triggers. Notably, the release of this diazoalkane is accompanied by an intense fluorescence turn-on, which calibrates the release of the diazoalkane. Carboxylic acids can trap this short-lived diazoalkane intermediate and yield the corresponding esters. This transformation has potential for broad applications.

A Photo-triggered and photo-calibrated nitric oxide donor: Rational design, spectral characterizations, and biological applications

Abstract Nitric oxide (NO) donors are valuable tools to probe the profound implications of NO in health and disease. The elusive nature of NO bio‐relevance has largely limited the use of spontaneous NO donors and promoted the development of next generation NO donors, whose NO release is not only stimulated by a trigger, but also readily monitored via a judiciously built‐in self‐calibration mechanism. Light is without a doubt the most sensitive, versatile and biocompatible method of choice for both triggering and monitoring, for applications in complex biological matrices. Herein, we designed and synthesized an N‐nitroso rhodamine derivative (NOD560) as a photo‐triggered and photo‐calibrated NO donor to address this need. NOD560 is essentially non‐fluorescent. Upon irradiation by green light (532 nm), it efficiently release NO and a rhodamine dye, the dramatic fluorescence turn‐on from which could be harnessed to conveniently monitor the localization, flux, and dose of NO release. The potentials of NOD560 for in vitro biological applications were also exemplified in in vitro biological models, i.e. mesenchymal stem cell (MSC) migration suppression. NOD560 is expected to complement the existing NO donors and find widespread applications in chemical biological studies. Graphical abstract Authors are required to submit a graphic entry for the Table of Contents (TOC) that, in conjunction with the manuscript title, should give the reader a representative idea of one of the following: A key structure, reaction, equation, concept, or theorem, etc., that is discussed in the manuscript. Consult the journals Instructions for Authors for TOC graphic specifications. Figure. No Caption available. HighlightsNOD560 releases NO upon activation by green‐light.NOD560 is non‐fluorescent with excellent chemostablity.A rhodamine dye is co‐generated stoichiometrically with respective to NO.The potentials of NOD560 as a NO donor were showcased with MSC cells.