Insights into the CO2 Capture Capacity of Covalent Organic Frameworks.

An inexpensive computational method is designed to demonstrate the efficacy of the complex COF toward CO2 capture. The interaction energy calculations of small repeating units of COF precisely demonstrate CO2 uptake capacity at high pressure and effective dual descriptors values of these repeating units of COFs accurately establish their structure-property relationships under ambient conditions. The computational findings are in consonance with experimental results reported by Yaghi and coworkers. Further, the computationally modelled COFs confirms that the addition of -NH2 increases the effective dual descriptors values of COFs. Whereas an increase in the size of a central aromatic unit of COF6 shows better interactions. Interaction energy and effective dual descriptor calculations demonstrate the CO2 capture abilities of COFs at high pressure and low pressure respectively. The method developed by our group would be useful in high throughput designing and screening of a large number of complex COFs at different pressure.

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.

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.