Intramolecular Hydrogen Bonds in Tip-Functionalized Single-Walled Carbon Nanotubes as pH-Sensitive Gates

Abstract

Since their discovery, carbon nanotubes and other related nanomaterials are in the spotlight due to their unique molecular structures and properties, having a wide range of applications. The cage-like structure of carbon nanotubes is especially appealing as a route to confine molecules, isolating them from the solvent medium. This study aims to explore and characterize, through density functional theory (DFT) calculations, covalent tip-functionalization of single-walled carbon nanotubes (SWCNTS) with carboxymethyl moieties that establish pH sensitive molecular gates. The response of the molecular gate to pH fluctuations arises from variations in the noncovalent interactions between functionalized groups, which depend on the extent of protonation, leading to conformational changes. Overall, the hydrogen bonds present in the molecular models under study, as evaluated through topological analysis and pK a calculations, suggest that functionalized SWCNTs may be suitable for the design of drug delivery systems to enhance the efficiency of some pharmacological treatments, or even in the area of catalysis and separation processes, through their incorporation in nanocomposites.

Implicit and Explicit Solvent Effects on the Global Reactivity and the Density Topological Parameters of the Preferred Conformers of Caespitate

“…Table 5 shows the values of the electron density, ρ(r), the Laplacian of the electron density, ∇ 2 ρ(r), the Lagrangian kinetic energy, G(r), the potential energy density, V(r), the Hamiltonian kinetic energy, H(r), the interaction energy, E In both cases, for implicit and explicit models, it indicates that the first IHB is stronger than the second one. Also, positive values of ∇ 2 ρ(r) on BCPs confirm the existence of weak or medium-strength non-covalent hydrogen bonds, exhibiting a local depletion of density (∇ 2 ρ(r) > 0) [50]. In addition, the positive sign of the H(r) parameter indicates that the accumulation of charge density on the hydrogen bond has a destabilizing effect (H(r) > 0) [51].…”

Developing new derivatives of 3‐X‐4‐hydroxy‐2(1H)‐quinolone as quinoline‐based chemosensors for detecting fluoride: Theoretical study on nucleophilicity and hydrogen‐bonding via various analyses

“…[43][44][45] The atoms in molecules (AIM) analysis give clear evidence of the nature of bond critical points (BCPs) and the strengths of hydrogen bonding. [46][47][48][49] The non-covalent interaction (NCI) or reduced density gradient (RDG) analysis is employed to reveal the nature of intra-and inter-molecular interactions. [50] The Fukui function ( f [r]) and atomic dipole moment corrected Hirshfeld charges (ADCH) studies provide more evidences of electrophilic sites of molecules and possibility of making bonds.…”

Advances in Drug Delivery Nanosystems Using Graphene-Based Materials and Carbon Nanotubes

“…Using density functional theory calculations, Pinto and Magalhaes [260] characterized covalent tip-functionalization of SWCNTs with -CH 2 -COOH groups that create pH-sensitive molecular gates and found that their responses to pH changes relate to the extent of protonation-dependent alternations in the noncovalent interactions between functionalized groups resulting in conformational changes. Thus, functionalized SWC-NTs can be applied as efficient drug delivery systems.…”