Soham Samanta

A simple and efficient fluorophoric probe for dual sensing of Fe3+ and F−: application to bioimaging in native cellular iron pools and live cells

A new quinoline functionalized fluorophoric Schiff base L1 was synthesized and its colorimetric and fluorescence responses toward various metal ions in mixed aqueous media were explored. The ligand exhibited high selectivity towards Fe3+ in the presence of a large excess of other competing ions with certain observable optical and fluorescence changes. These spectral changes are significant enough in the visible region of the spectrum and thus enable naked eye detection. The efficiency of L1 in detecting Fe3+ ions was also checked in the presence of relevant complex biomacromolecules viz. methaemoglobin, fetal bovine serum and human serum albumin. L1 was also found to be sensitive enough for visual detection of Fe3+ ions in native iron pools of banana pith. Studies revealed that L1–Fe complex formation is fully reversible in the presence of the fluoride anion with very high selectivity. Furthermore, fluorescence microscopic studies demonstrated that compound L1 could also be used as an imaging probe for detection of uptake of these ions in model human cells. This selective sensing behaviour of L1 towards Fe3+ was explained via the CHEF process where theoretical calculations also supported the premise.

Colorimetric and Fluorometric Discrimination of Geometrical Isomers (Maleic Acid vs Fumaric Acid) with Real-Time Detection of Maleic Acid in Solution and Food Additives

Heterobis imine Schiff base probe L is able to discriminate geometrical isomers (maleic acid vs fumaric acid) through sharp colorimetric as well as fluorogenic responses even conspicuous with the naked eye. Colorimetric as well as fluorogenic sensing of maleic acid among various carboxylic acids was also demonstrated in ethanol-buffer medium. Sensing behavior of L was corroborated by (1)H NMR spectra, mass spectrometry, and theoretical calculations. Subsequently sensing behavior of L was used to probe maleic acid in starch rich food samples.

White-light emission from simple AIE–ESIPT-excimer tripled single molecular system

A simple organic molecule (L3) has been systematically designed and developed to generate white-light emission from a single-component system. It could also tune several emission colors owing to its diverse spectral nature with varying water fractions in methanol–water and acetonitrile–water mixtures. Essentially, the introduction of an aggregation-induced emission (AIE) phenomenon and excimer-forming ability in the molecular system provided the scope for a dual emission, whereas ESIPT (excited state intramolecular proton transfer) coupled-AIE phenomenon acted as an additional means of adjusting the emission wavelength of the corresponding emission peak by varying the solvent polarity. Detailed AFM (atomic force microscopy), DLS (dynamic light scattering) and X-ray crystallographic studies were carried out to validate the mechanism of generation of white-light emission.

A zinc complex of a neutral pyridine-based amphiphile: a highly efficient and potentially therapeutic bactericidal material

The alarming rise in antibiotic-resistant pathogenic bacteria demands a prudent approach in the generation of therapeutic antibacterials. The present study illustrates the development of a potent amphiphilic bactericidal material tailored to leverage interactions with metal-reactive groups (MRGs) present in the bacterial cell surface envelope. Complexation of Zn(ii) with a neutral pyridine-based synthetic amphiphile (C1) generated the cationic C1-Zn, which exhibited manyfold higher membrane-directed bactericidal activity compared to the neutral C1, or the cationic amphiphile bearing two pyridinium head groups (C2). The relevance of MRGs in C1-Zn-bacteria interactions was validated by amphiphile-bacteria binding studies and metal protection assays performed with Mg(ii). C1-Zn retained its bactericidal activity even in simulated gastric fluid (SGF) and the enhanced membrane-directed bactericidal activity of C1-Zn could be garnered in adjuvant applications to increase the efficacy of the therapeutic antibiotic erythromycin. Given the relevance of Zn(ii) in S. aureus biofilm formation, the antibiofilm potential of the amphiphile C1 realized through Zn(ii) complexation could be demonstrated. The lack of resistance in target bacteria coupled with a favorable therapeutic index (IC50/MIC) and non-toxic nature hold significant implications for C1-Zn as a potential antibacterial therapeutic material.

Twisted-Intramolecular-Charge-Transfer-Based Turn-On Fluorogenic Nanoprobe for Real-Time Detection of Serum Albumin in Physiological Conditions

Two cyanine-based fluorescent probes, ( E)-2-(4-(diethylamino)-2-hydroxystyryl)-3-ethyl-1,1-dimethyl-1 H-benzo[ e]indol-3-ium iodide (L) and ( E)-3-ethyl-1,1-dimethyl-2-(4-nitrostyryl)-1 H-benzo[ e]indol-3-ium iodide (L1), have been designed and synthesized. Of these two probes, the twisted-intramolecular-charge-transfer (TICT)-based probe, L, can preferentially self-assemble to form nanoaggregates. L displayed a selective turn-on fluorescence response toward human and bovine serum albumin (HSA and BSA) in ∼100% aqueous PBS medium, which is noticeable with the naked eye, whereas L1 failed to sense these albumin proteins. The selective turn-on fluorescence response of L toward HSA and BSA can be attributed to the selective binding of probe L with HSA and BSA without its interfering with known drug-binding sites. The specific binding of L with HSA led to the disassembly of the self-assembled nanoaggregates of L, which was corroborated by dynamic-light-scattering (DLS) and transmission-electron-microscopy (TEM) analysis. Probe L has a limit of detection as low as ∼6.5 nM. The sensing aptitude of probe L to detect HSA in body fluid and an artificial-urine sample has been demonstrated.

Al 3+ sensing through different turn-on emission signals vis-à-vis two different excitations: Applications in biological and environmental realms

A rationally designed Schiff base chemosensor (L) could render specific detection of Al3+ ions with two distinct turn-on emission signals, separated by over 100 nm upon excitation at two different wavelengths. The utility of the probe lies in facilitating sensing in 80% aqueous medium with an emission close to 600 nm via an intramolecular charge transfer (ICT) mechanism. The biocompatible and cell permeable probe could readily sense Al3+ in live HeLa cells as well. The affinity of the probe for Al3+could be leveraged to specifically study DNA- Al3+ interaction in solution.

CCDC 1536471: Experimental Crystal Structure Determination

Related Article: Utsab Manna, Santanu Kayal, Soham Samanta, Gopal Das|2017|Dalton Trans.|46|10374|doi:10.1039/C7DT01697B