Halogen Bonding in Brominated BODIPY Crystals: a Crystallographic and Computational Study.

The study of halogen bonds (XBs) has been a subject of great interest in recent years due to its clear application in catalysis, liquid crystals, and crystal engineering. In this study, we analyzed the intermolecular interactions, in particular halogen bonds in BODIPYs with an increasing number of bromine atoms. The computational study included analyses through three different methods: the first approach of close contacts provided by mercury, then the expanded approach of the electron density partition of the molecules in the crystals provided by the analysis of Hirshfeld surfaces, and finally, the approach of the Quantum Theory of Atoms in Molecules (QT-AIM) to characterize the non-covalent interactions through finding electron density critical points between atoms and between neighboring molecules. The use of different computational methods allowed to gain insight into the interactions directing the crystal packing as the number of bromine atoms increased in the BODIPY moiety. Monocoordinated and bifurcated halogen bonds involving halide/halide were found. The penta-brominated BODIPY showed four-center cyclic nodes where each node is linked via XBs. This kind of motif can be useful in supramolecular chemistry and self-assembly.

Synthesis, complete NMR assignment and structural study of a steroidal dimer of 17α-ethynyl-5α,10α-estran-17ß-ol with diethynylbenzene spacer.

A phenylene-bridged steroidal dimer derived from 17α-ethynyl-5α,10α-estran-17ß-ol with molecular rotor-like architecture was synthesized to investigate the supramolecular interactions directing the crystallization of these systems. Structures with varying importance in complementarity between H-bonding and hydrophobic interactions can be observed directing the packing of the obtained crystals, depending on the synthetic stage, though conserving the same space group for both systems. Such behavior clearly shows the versatility achievable using steroids as crystal packing directors. Alongside this structural study, the complete NMR assignment is presented for the dimer, and precursors, in which the steroids present an unconventional and noteworthy A-B ring fusion.

Experimental-Theoretical Approach to the Adsorption Mechanisms for Anionic, Cationic, and Zwitterionic Surfactants at the Calcite-Water Interface.

The adsorption of surfactants (DTAB, SDS, and CAPB) at the calcite-water interface was studied through surface zeta potential measurements and multiscale molecular dynamics. The ground-state polarization of surfactants proved to be a key factor for the observed behavior; correlation was found between adsorption and the hard or soft charge distribution of the amphiphile. SDS exhibits a steep aggregation profile, reaching saturation and showing classic ionic-surfactant behavior. In contrast, DTAB and CAPB featured diversified adsorption profiles, suggesting interplay between supramolecular aggregation and desorption from the solid surface and alleviating charge buildup at the carbonate surface when bulk concentration approaches CMC. This manifests as an adsorption profile with a fast initial step, followed by a metastable plateau and finalizing with a sharp decrease and stabilization of surface charge. Suggesting this competition of equilibria, elicited at the CaCO3 surface, this study provides atomistic insight into the adsorption mechanism for ionic surfactants on calcite, which is in accordance with experimental evidence and which is a relevant criterion for developing enhanced oil recovery processes.