Azo-linked 5-ASA-coumarin prodrug: Fluorescent tracking for colonic drug release in UC treatment

Theranostic prodrugs that enable real-time, non-invasive monitoring of drug release and biodistribution are highly desirable for optimizing therapeutic efficacy and guiding personalized medication. Herein, we report a colon-targeted theranostic prodrug system (P1) for the simultaneous delivery and tracking of 5-aminosalicylic acid (5-ASA) in the treatment of ulcerative colitis (UC). P1 comprises a fluorescent 7-amino-4-methylcoumarin (7-AMC) reporter covalently linked to 5-ASA via an azo bond, which quenches the fluorescence of 7-AMC until P1 is activated by azoreductases in the colonic microenvironment. This selective activation triggers the release of 5-ASA and the revival of 7-AMC fluorescence, enabling real-time monitoring of drug delivery. To improve the solubility and targeted delivery of P1, it was encapsulated within polymeric micelles (PM) that selectively adhere to the positively charged, inflamed colonic tissues. In vitro studies confirmed the stability, biocompatibility, and selective activation of P1 under simulated colonic conditions. Notably, in a mouse model of UC, the P1-loaded PM achieved targeted delivery of 5-ASA to the inflamed colon, resulting in effective attenuation of colitis symptoms. Importantly, the in situ activation of P1 allowed for the real-time, non-invasive visualization of drug release and biodistribution, providing valuable insights for treatment optimization. This theranostic prodrug approach offers a promising strategy for the simultaneous therapy and tracking of 5-ASA delivery in UC treatment, with the potential to facilitate personalized medication and improve therapeutic outcomes.

Storehouse of Peculiar Supramolecular Architecture: Probing the Charge-Transfer Phenomenon and Effect of Altering the pH in a Meta-Oriented Single Donor-Double Acceptor Fluorophore

The investigation of excited-state intramolecular charge transfer (ESICT) has been a fascinating area of research. Although the ESICT events have been studied mostly for para-disubstituted donor-acceptor type molecules, the meta-oriented donor-acceptor type molecules have also shown tremendous potential as ESICT active molecules. In the current work, a small fluorescent probe diethyl 5-amino isophthalate (DE-5A-IPA) was investigated as a potential model to investigate ESICT events in the solution as well as solid phase. DE-5A-IPA was synthesized easily starting from commercially available 5-amino isophthalic acid in excellent yield. In the solid state, differing extents of CH···π-type binding led to formation of fully planar and puckered "cyclobutane" mimic supramolecular architecture, as evidenced from the crystal structure analysis. In addition, the single crystal structure of DE-5A-IPA shows that the donor (-NH2) and acceptor (-CO2Et) are situated in the same plane, thereby assuring the prerequisites of a through-space charge transfer. DE-5A-IPA undergoes noticeable Stokes shift (in cm-1) when the polarity of the medium was changed (4820 cm-1 in hexane; 9375 cm-1 in water). The excited-state dipole moment (μe) was calculated to be 4.0 units higher than the ground-state dipole moment (μg). DE-5A-IPA had an appreciable quantum yield (0.10 ± 0.03 to 0.27 ± 0.04). The ESICT phenomenon was also investigated by ground- and excited-state structural calculations using Gaussian 16 software. The excited-state lifetime measured by the time correlated single photon counting technique was found to vary with the polarity of the solvent, thereby providing further support to the ESICT phenomenon being operative in DE-5A-IPA. Taking advantage of the -NH2 group (which is susceptible to protonation) in DE-5A-IPA, steady state and time-resolved photodynamics were investigated in solutions of varying pH values. Interestingly, the emission quantum yields as well as the emission lifetime increase with an increase in pH value, thereby establishing DE-5A-IPA as a pH-sensitive probe. The current findings shall boost the understanding of meta-oriented ESICT enabled compounds in terms of their excited-state photophysics.

Effective enantioselective recognition by steady-state fluorescence spectroscopy: Towards a paradigm shift to optical sensors with unusual chemical architecture

A series of amino acid-derived 1,2,3-triazoles presenting the amino acid residue and the benzazole fluorophore connected by a triazole-4-carboxylate spacer was studied for enantioselective recognition using only steady-state fluorescence spectroscopy in solution. In this investigation, the optical sensing was performed with D-(-) and L-(+)-Arabinose and (R)-(-) and (S)-(+)-Mandelic acid as chiral analytes. The optical sensors showed specific interactions with each pair of enantiomers, allowing photophysical responses, which were used for their enantioselective recognition. DFT calculations confirm the specific interaction between the fluorophores and the analytes corroborating the observed high enantioselectivity of these compounds with the studied enantiomers. Finally, this study investigated nontrivial sensors for chiral molecules by a mechanism different than turn-on fluorescence and has the potential to broad chiral compounds with fluorophoric units as optical sensors for enantioselective sensing.

Turn-on Fluorescent Biosensors for Imaging Hypoxia-like Conditions in Living Cells

We present the synthesis, photophysical properties, and biological application of nontoxic 3-azo-conjugated BODIPY dyes as masked fluorescent biosensors of hypoxia-like conditions. The synthetic methodology is based on an operationally simple N=N bond-forming protocol, followed by a Suzuki coupling, that allows for a direct access to simple and underexplored 3-azo-substituted BODIPY. These dyes can turn on their emission properties under both chemical and biological reductive conditions, including bacterial and human azoreductases, which trigger the azo bond cleavage, leading to fluorescent 3-amino-BODIPY. We have also developed a practical enzymatic protocol, using an immobilized bacterial azoreductase that allows for the evaluation of these azo-based probes and can be used as a model for the less accessible and expensive human reductase NQO1. Quantum mechanical calculations uncover the restructuration of the topography of the S₁ potential energy surface following the reduction of the azo moiety and rationalize the fluorescent quenching event through the mapping of an unprecedented pathway. Fluorescent microscopy experiments show that these azos can be used to visualize hypoxia-like conditions within living cells.

Azo dyes containing 1,3,4-thiadiazole fragment: synthesis and properties

New 1,3,4-thiadiazole derivatives containing a diazenyl group, as well as simultaneously a diazenyl and an imino group were synthesized.

Proton transfer in fluorescent secondary amines: synthesis, photophysics, theoretical calculation and preparation of photoactive phosphatidylcholine-based liposomes

New proton-transfer lipophilic based benzazoles.

Lophine and pyrimidine based photoactive molecular hybrids. Synthesis, photophysics, BSA interaction and DFT study

New photoactive molecular hybrids containing both lophine and pyrimidine moieties as optical sensors.

Theoretical and experimental study of the ground and excited states of 1,4-dihydropyridine based hexahydroquinoline derivatives achieved by microwave irradiation

The photophysical study indicates ICT state for 1,4-dihydropyridine based hexahydroquinoline derivatives.

Relay proton transfer triggered twisted intramolecular charge transfer

The mechanism for the dual emission of 2-(4′-N,N-dimethylaminophenyl)imidazo[4,5-c]pyridine (DMAPIP-c) in protic solvents was investigated by synthesizing and studying its analogues.

Solvent-tuned dual emission: a structural and electronic interplay highlighting a novel planar ICT (OPICT)

Displaying a dual emission, a Phen-PENMe₂ compound can be foreseen as a new model for fundamental studies.