Most bacteria in nature exist as biofilms, which support intercellular signalling processes such as quorum sensing (QS), a cell-to-cell communication mechanism that allows bacteria to monitor and respond to cell density and changes in the environment. As QS and biofilms are involved in the ability of bacteria to cause disease, there is a need for the development of methods for the non-invasive analysis of QS in natural bacterial populations. Here, by using surface-enhanced resonance Raman scattering spectroscopy, we report rationally designed nanostructured plasmonic substrates for the in situ, label-free detection of a QS signalling metabolite in growing Pseudomonas aeruginosa biofilms and microcolonies. The in situ, non-invasive plasmonic imaging of QS in biofilms provides a powerful analytical approach for studying intercellular communication on the basis of secreted molecules as signals.

Shape control in metal–organic frameworks still remains a challenge.

The partition of the multicenter electron delocalization indices and the nucleus independent chemical shift indices into alpha and beta contributions in open-shell systems has been performed. In general it is shown that a full understanding of aromaticity in these systems cannot be achieved by restricting the calculations to the global properties but by dissecting these properties into α and β terms. The 4n+2- and 4n-aromaticity rules for singlet and triplet annulenes, respectively, reduce to a general aromaticity rule when the α and β terms are studied separately. This new rule allows us to extend the concept of conflicting aromaticities to radical systems that are simultaneously α-aromatic and β-antiaromatic or vice versa. The existence of such systems is demonstrated here by means of multicenter electron delocalization indices and nucleus independent chemical shifts. Finally, the global aromatic/antiaromatic character of these radical systems is estimated by means of aromatic stabilization energy, which is shown to be either slightly positive or slightly negative, thus reflecting the small aromatic/antiaromatic character of these radicals and reinforcing the conclusions obtained with aromaticity indices.

The suitability of implicitly dispersion-corrected functionals, namely the M06-2X, for the determination of interaction energies and electron polarization densities in adsorption studies of aromatic molecules on carbon allotropes surfaces is analysed by comparing the results with those obtained using explicit dispersion through Grimme’s empirical corrections. Several models of increasing size for the graphene sheet together with one-dimensional curved carbon structures, (5,5), (6,6) and (7,7) armchair single-walled nanotubes, and two-dimensional curved carbon structures, C60 fullerene, have been considered as substrates in this work, whereas pyridine has been chosen as an example for the adsorbed aromatic molecule. Comparison with recent experimental estimations of the adsorption energy and calculations using periodic boundary conditions on a supercell of 72 carbon atoms indicates that a finite model containing ninety six carbon atoms (C96) approaches quite well the adsorption on a graphene sheet. Analysis of the interaction energy components reveals that the M06-2X functional accounts for most of the dispersion energy implicitly, followed far by wB97X and B3LYP, whereas B97 and BLYP do not differ too much from HF. It has been found that M06-2X corrects only the energy component associated to dispersion and leaves the rest, electrostatic, Pauli and induction “unaltered” with respect to the other DFT functionals investigated. Moreover, only the M06-2X functional reflects the effect of dispersion on the electron polarization density, whereas for the remaining functionals the polarization density does not differ too much from the HF density. This makes the former functional more suitable a priori for the calculation of electron density related properties in these adsorption complexes.