A fluorescent probe based on cyclochalcone for detecting peroxynitrite

A novel cyclic chalcone fluorescent probe C-PN was synthesized to detect ONOO-. After reaction with peroxynitrite, the double bond of C-PN in the cyclic chalcone structure was disconnected, which caused the change of intramolecular charge transfer (ICT) effect, emitting blue fluorescence and quenching orange red fluorescence. Visible to the naked eye, the color of the probe solution changed. The probe showed low sensitivity (detection limit = 20.2 nm), short response time (less than 60 s) at low concentration of ONOO-, good visibility, and good selectivity and stability for ONOO-.

Activity-Based Fluorescent Probes for Hydrogen Sulfide and Related Reactive Sulfur Species

Hydrogen sulfide (H2S) is not only a well-established toxic gas but also an important small molecule bioregulator in all kingdoms of life. In contemporary biology, H2S is often classified as a "gasotransmitter," meaning that it is an endogenously produced membrane permeable gas that carries out essential cellular processes. Fluorescent probes for H2S and related reactive sulfur species (RSS) detection provide an important cornerstone for investigating the multifaceted roles of these important small molecules in complex biological systems. A now common approach to develop such tools is to develop "activity-based probes" that couple a specific H2S-mediated chemical reaction to a fluorescent output. This Review covers the different types of such probes and also highlights the chemical mechanisms by which each probe type is activated by specific RSS. Common examples include reduction of oxidized nitrogen motifs, disulfide exchange, electrophilic reactions, metal precipitation, and metal coordination. In addition, we also outline complementary activity-based probes for imaging reductant-labile and sulfane sulfur species, including persulfides and polysulfides. For probes highlighted in this Review, we focus on small molecule systems with demonstrated compatibility in cellular systems or related applications. Building from breadth of reported activity-based strategies and application, we also highlight key unmet challenges and future opportunities for advancing activity-based probes for H2S and related RSS.

H2S Sensors: Synthesis, Optical Properties, and Selected Biomedical Applications under Visible and NIR Light

Hydrogen sulfide (H₂S) is an essential signaling gas within the cell, and its endogenous levels are correlated with various health diseases such as Alzheimer's disease, diabetes, Down's syndrome, and cardiovascular disease. Because it plays such diverse biological functions, being able to detect H₂S quickly and accurately in vivo is an area of heightened scientific interest. Using probes that fluoresce in the near-infrared (NIR) region is an effective and convenient method of detecting H₂S. This approach allows for compounds of high sensitivity and selectivity to be developed while minimizing cytotoxicity. Herein, we report a review on the synthesis, mechanisms, optical properties, and selected biomedical applications of H₂S sensors.

The coumarin-pyrazole dye for detection of hydrogen sulfide in cells

Fluorescent probes for H₂S are often interfered by other thiols. In this work, a coumarin-pyrazole dye with 2,4-dinitrosulfonyl group was designed for the detection of H₂S. The probe exhibits weak fluorescence in water due to the photo induced electron transfer (PET) by 2,4-dinitrosulfonyl. After the sulfonyl group is cleaved off by H₂S, strong fluorescence appears. The probe can specifically detect H₂S without being interfered by other biological thiols, and shows a wide applicable pH range, low detection and wide detection range. The excellent detection properties of the probe can also be used to detect endogenous and exogenous H₂S in cells. In addition, the probes can be made into portable test paper for the detection of H₂S in solutions and can detect H₂S in different water samples.

Theoretical Study on the Atom-Substituted Quinazoline Derivatives with Faint Emission as Potential Sunscreens

Two novel compounds (HQS and HQSe) with excited-state intramolecular proton transfer (ESIPT) properties were designed based on the compound 2-(2-hydroxy-3-ethoxyphenyl)-3H-quinazolin-4-one (HQ). The parameters related to the ESIPT properties and electronic spectra of HQ and its derivatives were calculated using density functional theory and time-dependent density functional theory methods. The obtained geometric configurations, infrared vibrational spectra, and reduced density gradient scatter plots have shown that the intramolecular hydrogen bond O₁···H₁-N₁ has been weakened upon photoexcitation. Moreover, from the scanned potential energy curves, it can be found that the ESIPT processes of the three compounds have no energy barriers. It is noteworthy that HQS and HQSe can strongly absorb light in the UVA region (∼340 nm) and exhibit weak fluorescence emission in the visible light region, which comes from the keto configuration. The special optical properties of HQS and HQSe can promote their application as potential sunscreen agents.

Theoretical study on an intriguing excited-state proton transfer process induced by weakened intramolecular hydrogen bonds

In the present work, we have systematically investigated the dual hydrogen-bonded system 2Z,2'Z-3,3'-(4,4'-methylenebis(4,1-phenylene)bis(azanediyl)bis(1,3-diphenylprop-2-en-1-one)) (abbreviated as L) utilizing quantum chemistry methods, in which the excited-state intramolecular proton transfer (ESIPT) does not conform to the usual stereotype but proceeds along the weakened intramolecular hydrogen bonds (IHBs). Two primary configurations were confirmed to coexist in the ground state (i.e., anti-L and syn-L) by calculating the Boltzmann distribution in three different solvents. Based on the cardinal geometrical parameters involved in IHBs and the interaction region indicator (IRI) isosurface, it can be revealed that the dual IHBs of L were both weakened upon photoexcitation, not least the N₁-H₂⋯O₃ IHB was utterly destroyed in the excited state. The proton-transfer process of anti and syn in three solvents with different polarities has been analyzed by constructing S₀- and S₁-state potential energy surfaces (PESs). It can be concluded that only the single proton transfer behavior along N₁-H₂⋯O₃ occurs in the S₁ state, and the corresponding energy barrier is gradually enlarged with increasing solvent polarity. To further expound the weakened IHB-induced ESIPT mechanism, the scanned PESs connecting the transition state (TS) structures and the initial forms indicate that the ESIPT process is infeasible without the appropriate structural torsion. Our work not only unveils the extraordinary ESIPT process of L, but also complements the results obtained from previous experiments.

Guide to tuning the chalcone molecular properties based on the push-pull effect energy scale created via the molecular tailoring approach

Using the molecular tailoring approach, a total energy scale for the push-pull effect in the range from -40 to 100 kcal/mol is created for the wide series of neutral, charged and doubly charged compounds on the chalcone platform. Taking into account similar energy scale for hydrogen bonds, the strength of the push-pull effect is ranked in the seven categories, ranging from negative (anti-push-pull) to very weak and very strong push-pull effect. It is demonstrated that the molecular properties of chalcone can be tuned prior synthesis due to the created energy scale for the push-pull effect. The single bonds of the π-spacer in the chalcones are shortened, the double ones are lengthened, and the C=O bond vibrations are red shifted when the push-pull effect is enhanced along the energy scale. The HOMO and LUMO energies change systematically while the HOMO-LUMO energy gap narrows as the strength of the push-pull effect increases.