Synthesis of Bioactive Aminomethylated 8-Hydroxyquinolines via the Modified Mannich Reaction

8-hydroxyquinoline (oxine) is a widely known and frequently used chelating agent, and the pharmacological effects of the core molecule and its derivatives have been studied since the 19th century. There are several synthetic methods to modify this core. The Mannich reaction is one of the most easily implementable examples, which requires mild reaction conditions and simple chemical reagents. The three components of the Mannich reaction are a primary or secondary amine, an aldehyde and a compound having a hydrogen with pronounced activity. In the modified Mannich reaction, naphthol or a nitrogen-containing naphthol analogue (e.g., 8-hydroxyquinoline) is utilised as the active hydrogen provider compound, thus affording the formation of aminoalkylated products. The amine component can be ammonia and primary or secondary amines. The aldehyde component is highly variable, including aliphatic and aromatic aldehydes. Based on the pharmacological relevance of aminomethylated 8-hydroxyquinolines, this review summarises their syntheses via the modified Mannich reaction starting from 8-hydroxyquinoline, formaldehyde and various amines.

Protonation of cyclen-based chelating agents containing fluorescent moieties

The fluorescence emission properties of 1,4,7,10-tetraazacyclododecane-based receptors with appended heteroaromatic fluorophores are tuned by photoinduced electron and proton transfer processes.

Efficient Photodynamic Therapy against Gram-Positive and Gram-Negative Bacteria Using Rose Bengal Encapsulated in Metallocatanionic Vesicles in the Presence of Visible Light

Significant consumption of antibiotics has generated multidrug resistance in bacteria, which is a major menace to human beings. Antibacterial photodynamic therapy (aPDT) is a progressing technique for inhibition of bacterial infection with minimal side effects. Metals and delivering agents play a major role in aPDT efficiency. Herein, we report a formulation to enrich the antibacterial photodynamic therapy utilizing metallocatanionic vesicles (MCVs) against both Gram-positive and Gram-negative bacteria. These MCVs were synthesized by utilizing iron-based double-chain metallosurfactant [FeCPC(II)] as a cationic surfactant and AOT, a double-chain anionic surfactant. These synthesized MCV fractions were characterized by distinct techniques like DLS, zeta potential, FE-SEM, confocal microscopy, SAXS, and UV-Visible spectroscopy. Polyhedral-shaped MCVs with a size of 200 nm were formed, wherein the charge and size of the catanionic vesicle can be controlled by varying the mixing ratios. Both Gram-positive bacteria, i.e., methicillin-resistant Staphylococcus aureus (MRSA), and Gram-negative bacteria, i.e., Escherichia coli (E. coli), were used for aPDT using Rose Bengal (RB) as a photosensitizer (PS) encapsulated in MCVs in the presence of a 532 nm wavelength laser. The aPDT against bacterial cells was evaluated for both dark and light toxicities. Pure MCVs also exhibited good antibacterial properties; however, much enhancement was observed in the presence of RB encapsulated in MCVs under light, where eradication of bacteria (E. coli and MRSA) was achieved in 30 min. The observations demonstrated that it is the presence of metal that enhances the singlet oxygen quantum yield of RB and MCVs help in retarding self-quenching and enhanced solubilization of RB. The cationic surfactant-rich fraction shows strong adhesion toward bacteria via electrostatic interactions. The outcome of this research shows that these newly fabricated metal-based metallocatanionic vesicles were effective against both Gram-positive and Gram-negative bacteria using aPDT and must be exploited for clinical applications as well as an alternative for antibiotics in the future.

8-Hydroxyquinoline Fluorophore for Sensing of Metal Ions and Anions

Among various known hydroxyquinolines, 8-hydroxyquinoline (8-HQ) is the most prevalent moiety due to excellent property for the formation of the complex with different metal ions and anions, and utilized in a wide variety of applications in pharmacological and medicinal fields. 8-Hydroxyquinoline moiety and its analogues acts as fluorophoric ligands on complex formation with alkali and alkaline as well as transition metal ions and anions, thus, considered as an ideal building block in metallo-supramolecular chemistry for recognition, separation, and quantitative investigation of cations. 8-Hydroxyquinoline moiety is also used in various applications for the advancement of novel fluorescent chemosensors in a wide variety of areas viz., material chemistry, bioorganic chemistry, molecular imaging, analytical chemistry, molecular recognition, medical and biological science communities. The present review emphasises on the progress of sensing properties of 8-HQ centred small-molecule fluorescent chemosensors towards several metal ions viz., Fe³⁺ , Al³⁺ , Ag⁺ , Hg²⁺ , Cu²⁺ , Pd²⁺ , Zn²⁺ , Cr³⁺ , Cd²⁺ , Mn²⁺ , Ca²⁺ , and K⁺ and anions such as F^- , CN^- and PPi, from 2008 to 2020, because of their sensitivity and selectivity in terms of diverse colour changes for different species. This critical and comprehensive review might facilitate the improvement of more prevailing chemosensors for future exciting and broad applications.

Carbon Dot Based, Naphthalimide Coupled FRET Pair for Highly Selective Ratiometric Detection of Thioredoxin Reductase and Cancer Screening

The fluorescence resonance energy transfer (FRET) mechanism has been established between carbon dots (CDs) and naphthalimide to monitor the activity of thioredoxin reductase (TrxR), which is often overexpressed in many cancer cells. The naphthalimide moiety was covalently attached to the surface of CDs through a disulfide linkage. In normal cell conditions (when devoid of high concentrations of TrxR), the CDs act as an energy donor and naphthalimide acts as an acceptor, which establishes the FRET pair as interpreted from the emission at λ_em = 565 nm, when excited at λ_ex = 360 nm. However, contrary to this, the elevated levels of TrxR cause the breakage of disulfide bonds and consequently abolishes the FRET pair through the release of the naphthalimide moiety from the surface of CDs. This process was studied by monitoring of fluorescence intensity at λ_em = 565 and 440 nm, when excited at the same wavelength (λ_ex = 360 nm). The TrxR based ratiometric quenching and enhancement of fluorescence intensity offers an interesting opportunity to monitor the enzyme activities and has many advantages over conventional monitoring of fluorescence intensity at a single wavelength to avoid interference of external factors. Fluorescence images of cancer cells in response to the nanosensor were visualized under a confocal microscope. Cytotoxicity study of nanosensor retards the growth of HeLa and MCF-7 cell lines in the presence of visible light. Therefore, the nanosensor also acts as a theranostic agent to diagnose as well as killing of cancer cells.

A Naphthalimide-Based Cd(2+) Fluorescent Probe with Carbamoylmethyl Groups Working as Chelators and PET-Promoters under Neutral Conditions

We have developed a novel naphthalimide-based Cd(2+) fluorescent probe (1), featuring almost no background response, high sensitivity and selectivity toward Cd(2+) through its high association constant [K=(2.10±0.423)×10(6) ], and a practical working pH range. Membrane-permeability was conferred on 1 by replacing the imide and amide substituents with n-butyl groups, and hence the derivative (4) has found practical utility on fluorescent imaging of Cd(2+) in HeLa cells. Comparison of fluorescent properties between various compounds derived from 1 has demonstrated that the carbamoylmethyl groups in 1 function not only as Cd(2+) chelators but also as promoters for photoinduced electron transfer (PET) by lowering the basicity of the two tertiary amino groups. As a result, 1 and 4 exhibited highly practical performance as Cd(2+) probes under neutral conditions.

Fluorescent lactose-derived catanionic aggregates: synthesis, characterisation and potential use as antibacterial agents

The antibacterial properties of catanionic surfactants based on fluorescent lactose-derivative organic salts using low-cost starting materials were investigated towards multi-drug-resistant Gram-positive bacteria.

Highly stable ionic liquid-in-water emulsions as a new class of fluorescent sensors for metal ions: the case study of Fe3+ sensing

A stable fluorescent ionic liquid can act as a fluorescent sensor for metal ion recognition.

A simple highly sensitive and selective TURN-ON fluorescent chemosensor for the detection of cadmium ions in physiological conditions

A very simple fluorophore was synthesized and applied as a chemosensor for Cd²⁺ion detection.