Size-dependent bond dissociation enthalpies in single-walled carbon nanotubes

We report the bond dissociation enthalpy (BDE) and the local electronic properties of Single-Walled Carbon Nanotubes (SWCNT) using density functional theory. Our analysis shows that there is a strong size-dependence of the BDE of these SWCNTs, which is inversely proportional to the radius-squared (1/r2) and the length (1/l) of SWCNT. We derive quantitative relationships from which the BDE can be calculated as a function of size and radius of the SWCNT. We find that the BDE of SWCNT outside the size-dependent region is about 480 kJ mol−1, which can be used for thermochemical calculations

Study of the cap structure of (3, 3),(4, 4) and (5, 5)-SWCNTs: Application of the sphere-in-contact model

We have applied the sphere-in-contact model supported by hybrid Density Functional Theory (DFT) calculations to elucidate the cap geometry of the sub-nanometer in dimension (3,3), (4,4) and (5,5) single-wall carbon-nanotubes (SWCNTs). Our approach predicts certain cap-geometries that do not comprise of the commonly known for their stability combination of pentagonal and hexagonal carbon rings but also tetragonal, trigonal and all-pentagonal structures. Based on hybrid-DFT calculations carbon atoms in these new cap geometries have similar stability to carbon found in other fullerene-like capped zig-zag and arm-chair nanotubes (i.e., (5,5), (6,6), (9,0) and (10,0)) that are known to be stable and synthetically accessible. We find that the cap structure of the (3,3)-CNTs is a pointy carbon geometry comprised of six pentagonal rings with a single carbon atom at the tip apex. In this tip geometry the carbon atom at the tip apex does not have the usual sp2 or sp3 geometry but an unusual trigonal pyramidal configuration. DFT calculations of the molecular orbitals and density-of-states of the tip show that this tip structure apart from being stable can be used in scanning probe microscopies such as STM for very high resolution imaging

Computational inhibition studies of the human proteasome by argyrin-based analogues with subunit specificity

A computational procedure was developed to study the subunit‐specific interactions of the proteasome inhibitors argyrin A and F, with the aim of indentifying the determinants of subunit selectivity. Three‐dimensional models of humanized proteasome active sites β1, β2 and β5 were developed and subsequently used in molecular docking simulations with the argyrin analogues. The subunit selectivity exhibited by each analogue could be explained based on the site‐specific interactions and a probability‐based specificity parameter derived in this study. A rational approach that involved maximizing site‐specific interactions was followed to guide the design of new argyrin analogues as specific inhibitors of the caspase‐like (β1 site) activity

Analysis of binding parameters of HIV-1 integrase inhibitors: correlates of drug inhibition and resistance

This study undertook an exploratory data analysis of the binding parameters of HIV-1 integrase inhibitors. The study group involved inhibitors in preclinical development from the diketo acid, pyrroloquinoline and naphthyridine carboxamide families and the most advanced inhibitors Raltegravir and Elvitegravir. Distinct differences were observed in the energetics of binding between the studied classes of inhibitors that also correlated with drug resistant patterns. Quantitative-property–activity-relationships correlated experimental IC50 values to the binding energy and the logarithm of the partition coefficient between n-octanol and water (clog P). The approach followed here serves as an improved basis for the development of ‘second generation’ integrase inhibitors