Sandeep Kumar Dey

A selective fluoride encapsulated neutral tripodal receptor capsule: solvatochromism and solvatomorphism.

The dinitrophenyl functionalized tris-(amide) receptor behaves as a selective chemosensor for fluoride by encapsulation within the tripodal pseudocavity in polar aprotic solvents exhibiting solvatochromism and solvatomorphism.

Oxyanion-Encapsulated Caged Supramolecular Frameworks of a Tris(urea) Receptor: Evidence of Hydroxide- and Fluoride-Ion-Induced Fixation of Atmospheric CO2 as a Trapped CO32– Anion

A tris(2-aminoethyl)amine-based tris(urea) receptor, L, with electron-withdrawing m-nitrophenyl terminals has been established as a potential system that can efficiently capture and fix atmospheric CO(2) as air-stable crystals of a CO(3)(2-)-encapsulated molecular capsule (complex 1), triggered by the presence of n-tetrabutylammonium hydroxide/fluoride in a dimethyl sulfoxide solution of L. Additionally, L in the presence of excess HSO(4)(-) has been found to encapsulate a divalent sulfate anion (SO(4)(2-)) within a dimeric capsular assembly of the receptor (complex 2) via hydrogen-bonding-activated proton transfer between the free and bound HSO(4)(-) anions. Crystallographic results show proof of oxyanion encapsulation within the centrosymmetric cage of L via multiple N-H···O hydrogen bonds to the six urea functions of two inversion-symmetric molecules. The solution-state binding and encapsulation of oxyanions by N-H···O hydrogen bonding has also been confirmed by quantitative (1)H NMR titration experiments, 2D NOESY NMR experiments, and Fourier transform IR analyses of the isolated crystals of the complexes that show huge spectral changes relative to the free receptor.

Amidothiourea based colorimetric receptors for basic anions: evidence of anion induced deprotonation of amide –NH proton and hydroxide induced anion⋯π interaction with the deprotonated receptors

Two amidothiourea based receptors (L1 and L2) containing a π-acidic 3,5-dinitrophenyl chromophore have been synthesized in good yields and their anion recognition properties were evaluated both in organic and aqueous organic environment by spectroscopic techniques. Anions such as F−, AcO− and H2PO4− were examined to be suitable analytes for the receptor molecules, displaying optical signaling from colorless to orange/red, whereas anions of lower basicity such as Cl−, Br−, I−, NO3− and HSO4− did not cause any discernable spectral changes. The detailed 1H NMR titration experiments and single crystal X-ray structural analyses revealed that the receptor–anion(s) interaction encourages deprotonation of the amide –NH proton of the amidothiourea function. Interestingly, the highly basic OH− ion showed stepwise color changes with increasing equivalents, from colorless to red to green. The step wise color changes were found to be the outcome of OH− (1 equiv.) induced mono-deprotonation of the individual receptors (colorless to red), followed by anion⋯π interaction (red to green) with the π-acidic 3,5-dinitrophenyl ring of the receptors beyond one equiv. of OH− addition. This anion⋯π interaction between the OH− ion and the synthesized receptors has also been confirmed by monitoring the OH− induced absorption spectral changes of a control receptor (LC).

A subtle interplay of C–H hydrogen bonds in complexation of anions of varied dimensionality by a nitro functionalized tripodal podand

The structural aspects of binding of halides (1 and 2), nitrate (3), perchlorate (4), trifluoroacetate (5) and hexafluorosilicate (6) with the protonated tripodal podand L are examined crystallographically. Anion binding with multiple receptor units is attributable entirely to the (NH)+⋯anion and multiple C–H⋯anion hydrogen bonding interactions in all six complexes. Protonation at the apical nitrogen and presence of nitro functionality renders the methylene and aryl hydrogen sufficiently acidic for their active participation in moderate to weak CH⋯anion interactions are noteworthy. All supramolecular networks of complexes 1–6 are guided by various non-convalent interactions, especially directional CH⋯Onitro hydrogen bonds and π-stacking interactions.

Anion coordinated capsules and pseudocapsules of tripodal amide, urea and thiourea scaffolds

This review aims to deliver a detailed and comparative account of the reported examples of anion (halide and oxyanions) coordinated capsules and pseudocapsules of tripodal receptors that employ hydrogen bonds and/or electrostatic hydrogen bonds offered by specific binding sites from amide, urea and thiourea functionalities. The review discusses both the structural aspects of anion binding and solution-state anion binding affinities of N-bridged and aryl-bridged tripodal receptors. Discussions relating to selective anion recognition and separation, carbondioxide uptake, and transmembrane anion transport, as demonstrated by some of these tripodal receptors have also been included in this review.

Binding discrepancy of fluoride in quaternary ammonium and alkali salts by a tris(amide) receptor in solid and solution states

A dinitrophenyl functionalized tris(amide) receptor, L, showed distinct complexation behaviour towards the F− anion when tetrabutylammonium fluoride (TBAF) and potassium fluoride (KF) salts were individually employed for the recognition of F− with L. X-ray crystallography analyses revealed the formation of a F−–encapsulated complex (1 : 1 host–guest) stabilized by three N–H⋯F− and three C–H⋯F− hydrogen bonds when TBAF was employed as the F− source, whereas in the KF complex of L (1 : 1 host–guest), the receptor is involved in side-cleft binding of a hydrated KF contact ion-pair governed by amide N–H⋯F−, aryl C–H⋯F− and lp(F−)⋯π interactions. The binding of hydrated KF is identical to the side-cleft binding of solvents such as DMSO and DMF via N–H⋯O, aryl C–H⋯O and lp(O) ⋯π interactions, which has been exemplified by X-ray crystallography and a detailed Hirshfeld surface analyses of the crystals. The binding discrepancy of F− in the TBAF and KF complexes of L has also been manifested in the solution state by 1H NMR and 2D NOESY NMR experiments. In the 1H NMR analyses, a huge downfield shift of the coordinating –NH and ortho–CH protons was observed in the TBAF complex in comparison to the KF complex whereas, in the 2D NOESY NMR experiments, a disappearance of the signals corresponding to the through-space NOE coupling between the –NH and ortho–CH protons was observed in the former when compared to the latter and free receptor, L.

Anion specificity induced conformational changes in cresol-based tripodal podands controlled by weak interactions: structural and Hirshfeld surface analysis

N-bridged tripodal receptors have shown a distinct behaviour on their assembly and binding ability towards complexation with inorganic and organic anions. All supramolecular complexes have been structurally authenticated using X-ray diffraction with a detailed analysis of the Hirshfeld surfaces facilitating an understanding of the type and nature of intermolecular interactions present in the complexes and extended structures. The p-substituted podand (L11) crystallized in the symmetric rhombohedral R3c space group to form hemicarcerand in the solid state via intermolecular C–H⋯π interactions. Protonation of L1–31–3 in presence of inorganic anions results in conformational locking of tripodal cavity by N–H⋯Oether trifurcated hydrogen bond formation (1–4) due to the endo-orientation of the bridgehead hydrogen whereas use of organic anions as template leads to the exo-orientation of the apical proton (5–7) and thereby, results into conformational opening of the tripodal arms via the formation of N–H⋯Oanion and π⋯π interactions with the anion. This study also establishes bilayer assembly formation in inorganic anion complexes (2–4) guided primarily by interligand C–H⋯π interactions and multiple C–H⋯anion hydrogen bonds. NMR studies further establish the different orientations of flexible tripodal arms in presence of organic and inorganic counter anions in solution.

Surface-modification-directed controlled adsorption of serum albumin onto magnetite nanocuboids synthesized in a gel-diffusion technique

Magnetite nanocuboids have been synthesized via gel-diffusion technique in agarose gel. Here, the agarose gel matrix has been used as an organic template for formation and growth modification of magnetite. Gel mineralization mimics the membrane-based biomineralization, controls the diffusion process and gives the micro/nano environment for the crystal growth. We also attempt to understand the influence of different surface modifications of synthesized magnetite nanocuboids on protein interaction. For this purpose, magnetite particles were coated with trimesic acid (benzene-1,3,5-tricarboxylic acid) and stearic acid, which generates a hydrophilic and a hydrophobic modified surface, respectively. We report controlled adsorption behavior of bovine serum albumin (BSA) by surface modification of magnetite nanocuboids with different functional groups. The adsorption capacity of BSA increases on trimesic acid-coated surfaces compared to bare magnetite surfaces, while it decreases on stearic acid-coated surfaces. In situ fluorescence spectroscopy has been used to analyze the tertiary protein structure in the adsorbed state on these three surfaces. Partial unfolding in the tertiary structure of BSA was observed upon adsorption onto bare magnetite surfaces. On trimesic acid-coated surfaces, tertiary unfolding of BSA was greater than on bare magnetite surfaces, while BSA undergoes minor tertiary structural change on stearic acid-coated surfaces.

A supramolecular dual-host based ion-pair induced formation of 1D coordination polymer

An N-bridged tripodal urea receptor (L1) in combination with 18-crown-6-ether (LC) has been structurally authenticated to self-assemble into an integrated 1D coordination polymer in the presence of potassium carbonate (K2CO3). The tripodal receptor (L1) encapsulates a carbonate anion within a dimeric capsular assembly. A carbonyl group and a nitro group from each tripodal unit of the dimeric assembly are coordinated to each crown ether bound potassium ion, generating a 1D coordination polymer. Thus, an anion-pair induced 1D integrated polymeric assembly is formed based on two hosts in combination.