Recent Advances in Small Molecule-Based Intracellular pH Probes.

Intracellular pH plays an important role in many biological and pathological processes. Small-molecule based pH probes are found to be the most effective for pH sensing because of ease of preparation, high sensitivity, and quick response. They have many advantages such as small perturbation to the functions of the target, functional adaptability, cellular component-specific localization, etc. The present review highlights the flurry of recent activity in the development of such probes. The probes are categorized based on the type of fluorophore used like quinoline, coumarin, BODIPY, rhodamine, indolium, naphthalimide, etc., and their analytical performance is discussed.

TMSOTf-Mediated Formal [4 + 2] Cycloaddition-Retro-aza-Michael Cascade of Vinylogous Carbamates for the Synthesis of Highly Fluorescent Pyridocarbazoles.

Trimethylsilyl trifluoromethanesulfonate mediated dimerization reaction of vinylogous carbamates of carbazoles gave highly fluorescent pyridocarbazoles through a Povarov-type formal [4 + 2] cycloaddition-retro-aza-Michael cascade. The developed strategy was used to access indolo pyridocarbazole and quinolizinocarbazolone in an expeditious manner. Various coupling reactions were successfully performed on synthesized pyridocarbazoles to study the effect of electronics of substitution on photophysical properties. Synthesized carbazoles possess excellent photophysical properties with high quantum yields (ΦF). Fluorescent carbazole dicarboxylic acid showed potential as a pH probe to give a linear response to pH over a very wide range (7.0-3.0) reflecting high efficiency.

Recent advances in the synthesis of pyrrolo[1,2-a]indoles and their derivatives.

The pyrrolo[1,2-a]indole unit is a privileged heterocycle found in numerous natural products and has been shown to exhibit diverse pharmacological properties. Thus, recent years have witnessed immense interest from the synthesis community on the synthesis of this scaffold. In light of the ever-increasing demand for pyrrolo[1,2-a]indoles in drug discovery, this review provides an overview of recent synthesis methods for the preparation of pyrrolo[1,2-a]indoles and their derivatives. The mechanistic pathway and stereo-electronic factors affecting the yield and selectivity of the product are briefly explained. Furthermore, we have attempted to demonstrate the utility of the developed methods in the synthesis of bioactive molecules and natural products, wherever offered.

Design and Expeditious Synthesis of Quinoline-Pyrene-Based Ratiometric Fluorescent Probes for Targeting Lysosomal pH.

Intracellular pH plays a significant role in many pathological and physiological processes. A series of quinoline-pyrene probes were synthesized in one-step fashion through an oxonium-ion-triggered alkyne carboamination sequence involving C-C, C-O and C-N bond formation for intracellular pH sensing. The quinoline-pyrenes showed significant red shifts at low pH. Fluorescence lifetime decay measurements of the probes showed decreases in lifetime at pH 4. The probes showed excellent selectivity in the presence of various potential interfering agents such as amino acids and cations/anions. Furthermore, the probes were found to show completely reversible emission behaviour in the window between pH 4 and 7. A morpholine-substituted quinoline-pyrene probe efficiently stained lysosomes with high Pearson correlation coefficients (0.86) with Lysotracker Deep Red DND-99 as a reference. A co-localization study of the probe with Lysotracker DND-99 showed selective intracellular targeting and a shift in fluorescence emission due to acidic lysosomal pH.

Highly selective monitoring of metals by using ion-imprinted polymers.

Ion imprinting technology is one of the most promising tools in separation and purification sciences because of its high selectivity, good stability, simplicity and low cost. It has been mainly used for selective removal, preconcentration, sensing and few miscellaneous fields. In this review article, recent methodologies in the synthesis of IIPs have been discussed. For several applications, different parameters of IIP including complexing and leaching agent, pH, relative selectivity coefficient, detection limit and adsorption capacity have been evaluated and an attempt has been made to generalize. Biomedical applications mostly include selective removal of toxic metals from human blood plasma and urine samples. Wastewater treatment involves selective removal of highly toxic metal ions like Hg(II), Pb(II), Cd(II), As(V), etc. Preconcentration covers recovery of economically important metal ions such as gold, silver, platinum and palladium. It also includes selective preconcentration of lanthanides and actinides. In sensing, various IIP-based sensors have been fabricated for detection of toxic metal ions. This review article includes almost all metal ions based on the ion-imprinted polymer. At the end, the future outlook section presents the discussion on the advancement, corresponding merits and the need of continued research in few specific areas. Graphical Abstract IIPs for the selective monitoring of metals.