Debasis Saha

An Ultrahydrophobic Fluorous Metal–Organic Framework Derived Recyclable Composite as a Promising Platform to Tackle Marine Oil Spills

Derived from a strategically chosen hexafluorinated dicarboxylate linker aimed at the designed synthesis of a superhydrophobic metal-organic framework (MOF), the fluorine-rich nanospace of a water-stable MOF (UHMOF-100) exhibits excellent water-repellent features. It registered the highest water contact angle (≈176°) in the MOF domain, marking the first example of an ultrahydrophobic MOF. Various experimental and theoretical studies reinforce its distinctive water-repellent characteristics, and the conjugation of superoleophilicity and unparalleled hydrophobicity of a MOF material has been coherently exploited to achieve real-time oil/water separation in recyclable membrane form, with significant absorption capacity performance. This is also the first report of an oil/water separating fluorinated ultrahydrophobic MOF-based membrane material, with potential promise for tackling marine oil spillages.

Chloride-Mediated Apoptosis-Inducing Activity of Bis(sulfonamide) Anionophores

Transmembrane anion transport modality is enjoying a renewed interest because of recent advances toward anticancer therapy. Here we show bis(sulfonamides) as efficient receptors for selective Cl(-) ion binding and transport across lipid bilayer membranes. Anion-binding studies by (1)H NMR indicate a logical correlation between the acidity of sulfonamide N-H proton and binding strength. Such recognition is influenced further by the lipophilicity of a receptor during the ion-transport process. The anion-binding and transport activity of a bis(sulfonamide) system are far superior compared to those of the corresponding bis(carboxylic amide) derivative. Fluorescent-based assays confirm the Cl(-)/anion antiport as the operational mechanism of the ion transport by bis(sulfonamides). Disruption of ionic homeostasis by the transported Cl(-) ion, via bis(sulfonamide), is found to impose cell death. Induction of a caspase-dependent intrinsic pathway of apoptosis is confirmed by monitoring the changes in mitrochondrial membrane potential, cytochrome c leakage, activation of family of caspases, and nuclear fragmentation studies.

Impact of Ions on Individual Water Entropy

Solutes determine the properties of a solution. In this study, we probe ionic solutions through the entropy of individual water molecules in the solvation shells around different cations and anions. Using a method recently developed by our group, we show the solvation shell entropy stemming from the individual contributions correlates extremely well with experimental values for both polarizable and nonpolarizable force fields. The behavior of water entropy as a function of distance reveals significant (∼20%) contributions from the second solvation shell even for the low concentration considered here. While for the cations, contributions from both translational and rotational entropy loss are similar in different solvation shells, water around anions loses much more rotational entropy due to their ability to accept hydrogen bonds. Most importantly, while charge density of cations or anions correlates with the translational entropy loss, anions with similar charge density as that of cations has a much stronger and long-range effect on water. We also show how the modulation of water entropy by ions is correlated to the structural modifications of hydration shell. This study thus provides a step toward understanding the entropic behavior of water in molecular recognition processes between proteins and drug molecules.

Effect of water and ionic liquids on biomolecules

The remarkable progress in the field of ionic liquids (ILs) in the last two decades has involved investigations on different aspects of ILs in various conditions. The nontoxic and biocompatible nature of ILs makes them a suitable substance for the storage and application of biomolecules. In this regard, the aqueous IL solutions have attracted a large number of studies to comprehend the role of water in modulating various properties of biomolecules. Here, we review some of the recent studies on aqueous ILs that concern the role of water in altering the behavior of ILs in general and in case of biomolecules solvated in ILs. The different structural and dynamic effects caused by water have been highlighted. We discuss the different modes of IL interaction that are responsible for stabilization and destabilization of proteins and enzymes followed by examples of water effect on this. The role of water in the case of nucleic acid storage in ILs, an area which has mostly been underrated, also has been emphasized. Our discussions highlight the fact that the effects of water on IL behavior are not general and are highly dependent on the nature of the IL under consideration. Overall, we aim to draw attention to the significance of water dynamics in the aqueous IL solutions, a better understanding of which can help in developing superior storage materials for application purposes.

Water modulates the ultraslow dynamics of hydrated ionic liquids near CG rich DNA: consequences for DNA stability

Ionic liquids are known to stabilize DNA for much longer than water can. While the source of this stability has commonly been attributed to thermodynamic aspects, we probe the dynamical aspects of the ionic liquids near DNA to further our understanding of this stability. Using molecular dynamics simulation, we calculated the mean residence time (MRT) of the cations of five different ionic liquids (ILs) in the grooves and around phosphate groups of AT and CG rich DNA segments. We find the residence time of different cations next to CG rich DNA to be much higher compared to that next to AT rich DNA, with a negligible difference with the variation of anions. The interaction energy between cations and DNA, however, shows exactly the opposite trend; it is much lower (indicating a stronger interaction) for AT than for CG. Investigation of DNA parameters reveals an insignificant difference for the DNA sequences under consideration. Analysis of water behavior provides a rationale for the long MRTs of cations; water molecules have been found to be denser and to possess higher MRT when next to CG-rich DNA, thus resulting in a crowded environment. Our results indicate that the dynamics influence the binding of ILs to different DNA sequences, possibly by modulating the entropy of the binding process.

Connecting diffusion and entropy of bulk water at the single particle level

The relation between the dynamic (e.g., diffusion) and thermodynamic (e.g., entropy) properties of water and water-like liquids has been an active area of research for a long time. Although several studies have investigated the diffusivity and entropy for different systems, these studies have probed either the configurational entropy or the excess entropy of the overall system. In this study, we focus on the entropy of water at a single molecule level at different temperatures. We have used a method developed in our group to calculate the translational and rotational entropy of individual water molecules at various temperatures. We find that the single water translational and rotational entropy exhibit a transition at around 240 K. The translational entropy of individual water molecules shows a consistent variation with change in temperature whereas the variation in the case of rotational entropy is much smaller at different temperatures. We have also calculated diffusion coefficients of water molecules at these temperatures. We find that diffusion also shows the well-known fragile to strong crossover transition at around the same temperature where transition in entropy values has been seen. We have calculated both kinetic and thermodynamic fragilities and crossover points using diffusion and single water translational entropy values. Finally, we correlate the diffusion and translational entropy of individual water molecules using an analog of the Adam-Gibbs relation.Graphical Abstract:SYNOPSIS Translational and rotational entropy of individual water molecules have been calculated at different temperatures. The thermodynamic fragility in terms of translational entropy has been measured. The thermodynamics have been connected with the dynamics by correlating the diffusion coefficient with translational entropy at different temperatures by using analog of Adam-Gibbs relation.

pH-Gated Chloride Transport by a Triazine-Based Tripodal Semicage

Triazine-based preorganized tripodal receptors are reported as efficient transmembrane Cl- carriers. These receptors were designed based on triazine core and 3,7-diazabicyclo[3.3.1]nonane arms to facilitate preorganized cavity formation. Each bicyclic arm was further functionalized to control protonation and lipophilicity, which are crucial for their efficient anion binding and effective transport through liposomal membranes. The benzyl-substituted receptor was the most effective ion transporter followed by the pentafluorobenzyl-substituted derivative. The nonsubstituted receptor was least active owing to its high polarity. Two active transporters were found to function as mobile carriers for Cl- via an antiport exchange mechanism. Molecular dynamic simulations with the most active receptor show a strong Cl- binding within the cavity by direct and water-mediated H-bonds with its N-H groups.

CCDC 1434995: Experimental Crystal Structure Determination

Related Article: Soumya Mukherjee, Ankit M. Kansara, Debasis Saha, Rajesh Gonnade, Dinesh Mullangi, Biplab Manna, Aamod V. Desai, Shridhar H. Thorat, Puyam S. Singh, Arnab Mukherjee, Sujit K. Ghosh|2016|Chem.-Eur.J.|22|10937|doi:10.1002/chem.201601724