Dipali N. Lande

Deciphering Noncovalent Interactions Accompanying 7,7,8,8‐Tetracyanoquinodimethane Encapsulation within Biphene[n]arenes: Nucleus‐Independent Chemical Shifts Approach

Binding of novel biphene[n]arene hosts to antiaromatic 7,7,8,8-tetracyanoquinodimethane (TCNQ) are investigated by DFT. Biphene[4]arene favors the inclusion complex through noncovalent interactions, such as hydrogen bonding, π-π stacking, C-H⋅⋅⋅π, and C-H⋅⋅⋅H-C dihydrogen bonding. Donor-acceptor complexation renders aromatic character to the guest through charge transfer. The formation of TCNQ anionic radicals through supramolecular π stacking significantly influences its chemical and photophysical behavior. Electron density reorganization consequent to encapsulation of TCNQ reflects in the shift of characteristic vibrations in the IR spectra. The accompanying aromaticities arising from the induced ring currents are analyzed by employing nucleus-independent chemical shifts based profiles.

Cooperative Hydrogen Bonding, Molecular Electrostatic Potentials, and Spectral Characteristics of Partial Thia-Substituted Calix[4]arene Macrocycles

Structure and spectral characteristics of the 2,14-dithiacalix[4]arene and its homooxa derivatives are obtained employing the dispersion-corrected ωB97X-D-based density functional theory. The conformational behavior of these receptors is governed by the nature and number of substituents at the bridging positions. The partial thia-substituted calix[4]arene scaffolds reveal the electron-rich regions reside near heteroatoms which emerge with deeper minima in molecular electrostatic potential topography. Underlying cooperativity of intramolecular hydrogen bonding manifests in characteristic OH vibrations of their infrared spectra. Moreover, the (1)H NMR reveals that hydrogen-bonded protons are deshielded, unlike those from tertiary butyl substituents. These inferences are in agreement with the experimental data.

Density Functional Investigations on the Selective Binding of an endo-Functionalized Bis-urea Macrocycle

The preferential binding of syn and anti configurational isomers of endo-functionalized bis-urea molecular receptor to 1,2-dinitrobenzene (G1) and 1,4-dioxane (G2) guests has been explained using dispersion-corrected M06-2X-based density functional theory. The host-guest binding is facilitated via hydrogen bonding, C-H···π, dipole-dipole, C···C and O···O (chalcogen-chalcogen) interactions. The formation of an inclusion complex is spontaneous and thermodynamically favorable. The molecular electrostatic potential and quantum theory of atoms in molecules in conjunction with the noncovalent interactions reduced density gradient have been employed to characterize the noncovalent interactions. The encapsulation of G1 or G2 within the π-electron-rich cavity of the bis-urea macrocycle reflects the frequency shift of the characteristic N-H and C-H vibrations of their vibrational spectra. It has also been shown that binding of the bis-urea isomers to G1 and G2 emerges with a signature in the upfield signals of the guest protons confined to the host cavity in 1H NMR spectra.

Host–Guest Interactions Accompanying the Encapsulation of 1,4-Diazabicyclo[2.2.2]octane within endo-Functionalized Macrocycles

The binding of novel endofunctionalized bis-urea/thiourea molecular receptors toward neutral 1,4-diazabicyclo[2.2.2]octane (DABCO) demonstrates stronger binding of the bis-thiourea macrocycles than for their urea analogues by employing M06-2X/6-31+G(d,p)-based density functional theory. The formation of such inclusion complexes is spontaneous, thermodynamically favorable, and facilitated via bifurcated N-H···N···H-N hydrogen bonding and C-H···π, dipole-dipole, and other noncovalent interactions, which are reflected in the frequency shift of their characteristic N-H vibrations in the calculated vibrational spectra of these complexes. The underlying noncovalent interactions are analyzed using the molecular electrostatic potential topography and quantum theory of atoms in molecules in conjunction with the noncovalent interactions reduced density gradient method. It has also been shown that the encapsulation of DABCO within the π-electron-rich cavity of such hosts brings about shielding of the guest protons confined within the host cavity whereas those facilitating hydrogen bonding engender the downfield signals in their calculated 1H NMR spectra.

Bromine substituted aminonaphthoquinones: synthesis, characterization, DFT and metal ion binding studies

Bromine substituted aminonaphthoquinone ligands viz. 2-(2′-aminomethylpyridyl)-3-bromo-naphthalene-1,4-dione; (2MPA), 2-(3′-aminomethylpyridyl)-3-bromo-naphthalene-1,4-dione; (3MPA), 2-(2′-aminoethylpyridyl)-3-bromo-naphthalene-1,4-dione; (2EPA) and 2-(2′-aminomethylthiophenyl)-3-bromo-naphthalene-1,4-dione (2AMT) and 2-(2′-aminoethylthiophenyl)-3-bromo-naphthalene-1,4-dione (2AET) have been synthesized and characterized by single-crystal X-ray diffraction experiments in conjunction with long range corrected density functional theory. The heterocyclic amines on the naphthoquinone ring render diverse crystal structures. It has been shown that bromine substitution influences the planarity and mutual orientation of naphthoquinone and heterocycles in aminonaphthoquinone ligands. The 2MPA, 3MPA, 2EPA, 2AET aminonaphthoquinone ligands crystallize in the monoclinic space group whereas 2AMT led to the triclinic space group P. Furthermore, molecular packing of 2MPA and 2EPA revealed dimeric structures while 3MPA and 2AMT are rendered with ‘stair-case’ arrangements of molecules. 2AET, when viewed down c-axis, showed a ‘butterfly like’ arrangement. A broad charge transfer band (400–600 nm) was observed in the UV-visible spectra of these ligands. Besides 2MPA and 2EPA exhibit remarkable selectivity toward Cu2+ ions, accompanied by a color change from orange to blue in methanol and methanol–water mixture.

Exploring Chimeric Calix[4]tetrolarene Molecular Scaffolds: Theoretical Investigations

The structure and spectral characteristics of the chimeric mixture of calixarene and pyrogallolarene (usually referred to as calix[4]tetrolarene) and its derivatives are studied employing the M06-2X-based density functional theory. Different conformers, viz., cone, partial cone, 1,2-alternate, and 1,3-alternate, were identified as the stationary point structures on their potential energy surfaces. Among these, the symmetric C4 v cone conformer is found to be energetically favorable, which can be attributed to the cyclic array of hydrogen-bonding network in the calix[4]tetrolarene or its thia analogue. The substitution of methoxy groups at the upper rims of calix[4]tetrol- and thicalix[4]tetrol-arenes significantly influences the cooperative hydrogen-bonding network and conformational behavior of these hosts. The methoxy-substituted macrocycles show lowering in symmetry from C4 v to C2 v, engendering the pinched cone conformer to be the lowest energy structure. The enhanced solubility of the modified calix[4]tetrolarene macrocycles has been further explained from diminutive cooperative hydrogen bonding in its top rim compared to the pyrogallolarene, which is evidenced from the quantum theory of atoms in molecule and noncovalent interaction reduce density gradient method. Discernibly, the underlying cooperative hydrogen bonding emerges its signature in the characteristic vibrational patterns of the calixarene-based molecular scaffolds. The chemical shift parameters in their 1H NMR spectra have further been characterized.

Molecular Recognition, Conformational Behavior, and Spectral Characteristics of Oxatub[4]arene Macrocycle

In the present work, we analyze molecular recognition behavior of synthetic hydroxylated oxatub[4]arene (TA4) receptor toward the methyl viologen in different redox states. The supramolecular binding of methyl viologen guest toward TA4 macrocyclic scaffold has been studied employing the dispersion corrected ωB97X-D based density functional theory. The methyl viologen in dicationic and neutral forms revealed distinct features in electronic, 1H nuclear magnetic resonance, and infrared spectra. Quantum theory of atoms in molecules in conjunction with the noncovalent interaction reduced density gradient in real space have been used as tools to characterize the underlying host-guest binding.

Naphthoquinone based chemosensors for transition metal ions: experiment and theory

The synthesis and characterization of 2-((pyridine-2-yl)methylamino)naphthalene-1,4-dione (H-1), 2-((thiophen-2-yl)methylamino)naphthalene-1,4-dione (H-2) and 2-((pyridine/thiophen-2-yl)ethylamino)naphthalene-1,4-dione (H-3 and H-4) have been carried out. Molecular recognition abilities of these ligands toward transition metal ions in methanol, methanol–water, methanol–triethylamine or methanol–water–triethylamine mixtures, stoichiometries and association constants of H-1 and H-3 have been determined. It has been shown that H-1 and H-3 coordinate to metal ions via two nitrogen atoms and oxygen and exhibit remarkable selectivity towards Cu2+ ions in methanol or methanol–water mixtures, the complexation being accompanied by a color change from orange to intense blue. LOD (Limit of Detection) of Cu2+ with H-1, H-3 are 1.48 × 10−8 mol L−1 and 1.59 × 10−8 mol L−1 respectively. The vibrational spectra, 1H NMR chemical shifts and optical properties of H-1 to H-4 derived from density functional theory are also presented.