Synthesis and photophysics of benzazole based triazoles with amino acid-derived pendant units. Multiparametric optical sensors for BSA and CT-DNA in solution

Photoactive glycoconjugates with a very large Stokes shift: synthesis, photophysics, and copper(II) and BSA sensing

This study presents the synthesis of novel glycoconjugates by connecting benzazole and carbohydrate units with a 1,2,3-triazole linker. A simple synthetic route employing a copper(I) catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) was utilized. The synthesized compounds exhibit excited-state intramolecular proton transfer (ESIPT), resulting in longer wavelength emission with a significantly large Stokes shift (∼10 000 cm-1). These compounds show potential as chemical sensors due to their ability to detect Cu2+ ions, causing a decrease in fluorescence emission (turn-off effect). Additionally, they demonstrate strong interaction with proteins, exemplified by their interaction with bovine serum albumin (BSA) as a model protein.

Rotamer-Controlled Dual Emissive α-Amino Acids

The synthesis and photoluminescent properties of novel α-amino acids are described in which the biaryl benzotriazinone-containing chromophores were found to display dual emission fluorescence via locally excited (LE) and twisted intramolecular charge transfer (TICT) states. The intensity of each emission band could be controlled by the electronics and position of the substituents, and this led to the design of a 2-methoxyphenyl analogue that, due to twisting, displayed bright TICT fluorescence, solvatochromism, and pH sensitivity.

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.

Fluorine Atoms on C6H5-Corrole Affect the Interaction with Mpro and PLpro Proteases of SARS-CoV-2: Molecular Docking and 2D-QSAR Approaches

The chymotrypsin-like cysteine protease (3CL^pro, also known as main protease—M^pro) and papain-like protease (PL^pro) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been used as the main targets for screening potential synthetic inhibitors for posterior in vitro evaluation of the most promising compounds. In this sense, the present work reports for the first time the evaluation of the interaction between M^pro/PL^pro with a series of 17 porphyrin analogues-corrole (C1), meso-aryl-corrole (C2), and 15 fluorinated-meso-aryl-corrole derivatives (C3–C17) via molecular docking calculations. The impact of fluorine atoms on meso-aryl-corrole structure was also evaluated in terms of binding affinity and physical-chemical properties by two-dimensional quantitative structure–activity relationship (2D-QSAR). The presence of phenyl moieties increased the binding capacity of corrole for both proteases and depending on the position of fluorine atoms might impact positively or negatively the binding capacity. For M^pro the para-fluorine atoms might decrease drastically the binding capacity, while for PL^pro there was a certain increase in the binding affinity of fluorinated-corroles with the increase of fluorine atoms into meso-aryl-corrole structure mainly from tri-fluorinated insertions. The 2D-QSAR models indicated two separated regions of higher and lower affinity for M^pro:C1–C17 based on dual electronic parameters (σ_I and σ_R), as well as one model was obtained with a correlation between the docking score value of M^pro:C2–C17 and the corresponding ¹³C nuclear magnetic resonance (NMR) chemical shifts of the sp² carbon atoms (δ_C-1 and δ_C-2) of C2–C17. Overall, the fluorinated-meso-aryl-corrole derivatives showed favorable in silico parameters as potential synthetic compounds for future in vitro assays on the inhibition of SARS-CoV-2 replication.

Spectroscopic and Computational Study of the Protonation Equilibria of Amino-Substituted benzo[b]thieno[2,3-b]pyrido[1,2-a]benzimidazoles as Novel pH-Sensing Materials

We present the synthesis and analytical, spectroscopic and computational characterization of three amino-substituted benzo[b]thieno[2,3-b]pyrido[1,2-a]benzimidazoles as novel pH probes with a potential application in pH-sensing materials. The designed systems differ in the number and position of the introduced isobutylamine groups on the pentacyclic aromatic core, which affects their photophysical and acid-base properties. The latter were investigated by UV-Vis absorption and fluorescence spectroscopies and interpreted by DFT calculations. An excellent agreement in experimentally measured and computationally determined pKa values and electronic excitations suggests that all systems are unionized at neutral pH, while their transition to monocationic forms occurs at pH values between 3 and 5, accompanied by substantial changes in spectroscopic responses that make them suitable for detecting acidic conditions in solutions. Computations identified imidazole imino nitrogen as the most favorable protonation site, further confirmed by analysis of perturbations in the chemical shifts of 1H and 13C NMR, and showed that the resulting basicity emerges as a compromise between the basicity-reducing effect of a nearby nitrile and a favorable contribution from the attached secondary amines. With this in mind, we designed a system with three amino substituents for which calculations predict pKa = 7.0 that we suggest as an excellent starting point for a potential pH sensor able to capture solution changes during the transition from neutral towards acidic media.

Hybridized 4-Trifluoromethyl-(1,2,3-triazol-1-yl)quinoline System: Synthesis, Photophysics, Selective DNA/HSA Bio-interactions and Molecular Docking

The synthesis, structural analysis, and evaluation of the photophysical properties of twelve novel 2-aryl(heteroaryl)-6-(4-alkyl(aryl)-1H-1,2,3-triazol-1-yl)-4-(trifluoromethyl)quinolines (6-8), where aryl(heteroaryl)=Ph, 4-Me-C₆ H₄ , 4-F-C₆ H₄ and 2- furyl; 4-alkyl(aryl)=-CH₂ OH, -(CH₂ )₅ CH₃ and Ph, are reported. Hybrid scaffolds 6-8 were synthesized at 77-95 % yields by regioselective copper-catalysed azide-alkyne cycloaddition (CuAAC) reaction of unpublished 6-azido-4-(trifluoromethyl)quinolines (2) with selected terminal alkynes (3-5). Azido intermediates 2 were obtained from the reaction of 6-amino-4-(trifluoromethyl)quinolines (1) and sodium azide at good yields (78-87 %). Compounds 6-8 were structurally fully characterized by ¹ H-, ¹³ C- and ¹⁹ F- and ¹ H-¹³ C 2D-NMR (HSQC, HMBC) spectroscopy, X-ray diffraction (SC-XRD) and HRMS analysis. Moreover, the photophysical properties, DNA- and HSA-binding experiments (bio-interactions), and molecular docking studies for compounds 6-8 were performed. These are discussed and compared with similar compounds from recent research.

Synthesis, spectroscopic characterization and DNA/HSA binding studies of (phenyl/naphthyl)ethenyl-substituted 1,3,4-oxadiazolyl-1,2,4-oxadiazoles

Novel 1,3,4-oxadiazolyl-1,2,4-oxadiazole derivatives with promising photophysical and DNA/HSA-binding properties are reported.