Balakrishna Bugga

Well-defined structural changes of molecular units that can be triggered by light are crucial for the development of photoactive functional materials. Herein, we report on a novel switch that has azodicarboxamide as its photo-triggerable element. Time-resolved UV-pump/IR probe spectroscopy in combination with quantum-chemical calculations shows that the azodicarboxamide functionality, in contrast to other azo-based chromophores, does not undergo trans–cis photoisomerization. Instead, a photoinduced pedalo-type motion occurs, which because of its volume-conserving properties enables the design of functional molecular systems with controllable motion in a confined space.

Motion without volume change: By combining time-resolved infrared spectroscopy with quantum-mechanical calculations, a volume-conserving pedalo-type motion was studied in a molecular switch. These azodicaboxamide-based systems have the potential to open a new realm in the achievement of motion in a confined space.

Peptide foldamers have been studied for over two decades and numerous sequence patterns have been shown to form well-defined three-dimensional arrangements in solution. In particular, helices of various geometries have been described. In this article, different concepts concerning the construction of helical foldameric peptides, for which the possibility of governing the sense of the formed helix was evidenced, are presented and discussed.

Left or right? The construction of helical peptide foldamers with the appropriate handedness is possible using either achiral peptides with an element inducing chirality or sequences composed from fragments of alternating chirality.

Multiporphyrin arrays constructed on a pillar[5]arene scaffold adopt a folded conformation owing to an intramolecular complexation of the peripheral Zn^II-porphyrin moieties by 1,2,3-triazole subunits. External stimuli can break the intramolecular coordination at the origin of the folding and the resulting molecular motions mimic the blooming of a flower. An animated version of this Cover Picture is available in the Supporting Information. More information can be found in the Full Paper by E. Maisonhaute, B.  Delavaux-Nicot and J.-F. Nierengarten et al. (DOI: 10.1002/chem.201701622).

In the last five years, we have developed synthetic methods towards encapsulation of single-walled carbon nanotubes (SWNTs) into organic macrocycles, to form rotaxane-type molecules. These are the first examples of mechanically interlocked SWNT derivatives (MINTs). In this article, the motivation to continue developing the chemistry of SWNTs at a time well past their hype is discussed and our synthetic strategy and characterization methodology is explained in detail, stressing the general aspects. In particular, special emphasis is placed on the importance of adequate control experiments and bulk spectroscopic and analytical data to determine the structure of SWNT derivatives, as opposed to relying only (or mostly) on microscopy. Also our experimental results are used as pretext to reflect on more general/conceptual issues pertaining to the chemistry of SWNTs and mechanically interlocked molecules.

If you liked'em then you should've put a ring on them! In this Concept paper it is discussed why it is interesting to make rotaxane-type derivatives of single-walled carbon nanotubes (SWNTs), how to do it, and what they might be useful for.

We combine experimental methods, density functional theory (DFT) calculations, and molecular dynamics (MD) simulations in the quantitative analysis of noncovalent interactions between (6,5)-enriched single-walled carbon nanotubes (SWNTs), as hosts, and a set of pyrene derivatives with different electronic properties and surface areas, as guests. The experiments and calculations were carried out in two solvents with markedly different polarities, namely 1,1′,2,2′-tetrachloroethane (TCE) and N,N-dimethylformamide (DMF). Our results show that dispersion forces govern the supramolecular association of small molecules with (6,5)-SWNTs, with negligible contributions from ground-state charge-transfer effects. In the nonpolar solvent (TCE), the binding constants are highly correlated with the contact area between the SWNT and the guests. In the polar solvent (DMF), the binding constants show a complex dependence on the chemical nature of the pyrene substituents, as demonstrated by MD simulations with the explicit inclusion of solvent molecules. The solvation of the small molecules is shown to play a leading role in the binding process. Remarkably, the binding constants obtained from the MD simulations for the five guest molecules correlate with those derived from experiment. Furthermore, the MD simulations also reveal the structure of the adsorbed guest from low to high SWNT surface coverage.

Discrete interactions: A quantitative multidisciplinary approach to understanding noncovalent interactions between pyrene molecules and single-walled carbon nanotubes involving experimental analyses, DFT, and molecular dynamics calculations is presented (see figure). The results suggest that the pyrene guests interact through π–π forces with additional discrete contacts promoted by the substituents at the periphery of the pyrene core.

We have prepared [2]rotaxanes, the behavior of which as switchable catalysts depends on their pirouetting motion, which can be controlled through the addition and removal of Na⁺ ions. At least three sequential on/off cycles of a Michael reaction can be performed in situ when using the NaTFPB/[2.2.2]cryptand reagent pair to switch “on” and “off” the catalytic ability of the [2]rotaxanes.

Two-way street: The catalytic activity of the [2]rotaxane catalysts can be switched between “on” and “off” states over at least three different cycles through in situ addition and removal of Na⁺ ions.