A simple rhodamine hydrazide-based turn-on fluorescent probe for HOCl detection

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

A turn-on fluorescent probe based on N-(rhodamine-B)-thiolactam-2-n-butane with ionic liquids for selective and sensitive detection of mustard gas stimulant

Sulfur mustard (SM) is recognized as one of the most lethal warfare agents. It has the potential to seriously affect public health and safety. To employ appropriate medical countermeasures and treat victims as quickly as possible, the development of a rapid and simple SM detection technique is crucial. The aim of the present study was to explore novel detection systems exhibiting excellent selectivity and high sensitivity. An SM probe, namely N-(rhodamine-B)-thiolactam-2-n-butane (SRB-NB), which was based on a thiolactam structure, was effectively designed and synthesized. The rhodamine and thiourea moieties played the roles of the chromogenic and reacting groups, respectively. Subsequently, using ionic liquids (ILs) as the solvents, a turn-on fluorescence detection system was constructed. Notably, it was found that imidazole-based ILs displayed good solubility for an SM simulant, specifically 2-chloroethyl ethyl sulfide (2-CEES). Moreover, 1-butyl-3-methylimidazolium dicyandiamide ([BMIm]DCA) IL held the maximum amount of 2-CEES (132.5 g/100 g). The SRB-NB probe exhibited better ultraviolet (UV) absorption and fluorescence properties in ILs than in other organic solvents. SRB-NB/IL was able to detect 2-CEES in liquid form with remarkable selectivity and sensitivity. The limit of detection (LOD) was established at 3.0 × 10-6 M. Importantly, SRB-NB/ILs also showed good optical response to gaseous 2-CEES and SM.

Imaging of Hypochlorous Acid by Fluorescence and Applications in Biological Systems

In recent decades, HOCl research has attracted a lot of scientists from around the world. This chemical species is well known as an important player in the biological systems of eukaryotic organisms including humans. In the human body, HOCl is produced by the myeloperoxidase enzyme from superoxide in very low concentrations (20 to 400 μm); this species is secreted by neutrophils and monocytes to help fight pathogens. However, in the condition called "oxidative stress", HOCl has the capability to attack many important biomolecules such as amino acids, proteins, nucleotides, nucleic acids, carbohydrates, and lipids; these reactions could ultimately contribute to a number of diseases such as neurodegenerative diseases (AD, PD, and ALS), cardiovascular diseases, and diabetes. In this review, we discuss recent efforts by scientists to synthesize various fluorophores which are attached to receptors to detect HOCl such as: chalcogen-based oxidation, oxidation of 4-methoxyphenol, oxime/imine, lactone ring opening, and hydrazine. These synthetic molecules, involving rational synthetic pathways, allow us to chemoselectively target HOCl and to study the level of HOCl selectivity through emission responses. Virtually all the reports here deal with well-defined and small synthetic molecular systems. A large number of published compounds have been reported over the past years; this growing field has given scientists new insights regarding the design of the chemosensors. Reversibility, for example is considered important from the stand point of chemosensor reuse within the biological system; facile regenerability using secondary analytes to obtain the initial probe is a very promising avenue. Another aspect which is also important is the energy of the emission wavelength of the sensor; near-infrared (NIR) emission is favorable to prevent autofluorescence and harmful irradiation of tissue; thus, extended applicability of such sensors can be made to the mouse model or animal model to help image internal organs. In this review, we describe several well-known types of receptors that are covalently attached to the fluorophore to detect HOCl. We also discuss the common fluorophores which are used by chemist to detect HOCl, Apart from the chemical aspects, we also discuss the capabilities of the compounds to detect HOCl in living cells as measured through confocal imaging. The growing insight from HOCl probing suggests that there is still much room for improvement regarding the available molecular designs, knowledge of interplay between analytes, biological applicability, biological targeting, and chemical switching, which can also serve to further sensor and theurapeutic agent development alike.

A twist six-membered rhodamine-based fluorescent probe for hypochlorite detection in water and lysosomes of living cells

A novel six-membered rhodamine-based fluorescent probe (6G-ClO) was developed from 2-formyl rhodamine (6G-CHO) and used for hypochlorite detection in water and HUVEC cells. Different from planar penta cycle of rhodamine spirolactam, there was a twist six-membered spirocyclic hydrazone in 6G-ClO optimized by Gaussian software at DFT/B3LYP/6-31G(d) level. The high selectivity, high sensitivity and fast response of 6G-ClO towards ClO^- would be attributed to the twist six-membered spirocycle. Test-strip prepared with 6G-ClO was successfully used to semi-quantitatively indicate the concentration of ClO^- in water. 6G-ClO can also quantitatively detect the concentration of ClO^- in tap water and swimming pool water. The detection limit of 6G-ClO was as low as 12 nM. The co-localization staining of HUVEC cells further verified that 6G-ClO could specifically accumulate in lysosomes and capture exogenous/endogenous ClO^- in living lysosomes. 6G-ClO would be a practical probe for real-time monitoring of ClO^- in the biological and real water samples.