John Sydney Lomas

Planktonic bacteria can be eliminated by gold nanoparticles photothermia.

Complexes of three aromatic diols, catechol, naphthalene‐1,8‐diol, and fluorene‐4,5‐diol, with a series of hydrogen bond acceptors (HBAs) that have oxygen, nitrogen, and sulfur acceptor atoms, have been studied by density functional theory (DFT) at the B3LYP/6‐311+G(d,p) level. Binding energies, geometries, infrared spectroscopic (IR) frequencies, nuclear magnetic resonance (NMR) shifts, and measures of the electron density distribution from the Quantum Theory of Atoms in Molecules (QTAIM) are evaluated and compared with data for the corresponding monohydroxy compounds (monols), phenol, naphth‐1‐ol, and fluorene‐4‐ol, in order to assess the importance of cooperativity between intramolecular and intermolecular hydrogen bonding. All measures for all complexes show positive cooperativity whereby both the intermolecular and intramolecular hydrogen bonds are strengthened upon complexation. Cooperativity is weak for catechol and strong for the other two diols and, for all diols, increases with the hydrogen bond basicity of the acceptor. Correlations of IR and NMR metrics against binding energies for a single HBA and all six monols and diols are excellent, but attempts to correlate the same metrics for all HBAs and a single donor are frustrated by differences in intermolecular hydrogen bonding, depending notably on the identity of the acceptor atom in the HBA. Atom–atom interaction energies, calculated by the Interacting Quantum Atoms approach, are used to discuss the covalency of both types of hydrogen bond.

Cooperativity between intermolecular and intramolecular hydrogen bonds is an important factor determining the strength of donor‐acceptor complexes. Its impact in poly‐1,2‐diols, notably polyhydroxybenzenes, is subject to debate. Density functional theory calculations have been performed on complexes of phenol, catechol, pyrogallol and 1,2,3,4‐tetrahydroxybenzene with pyridine, trimethylamine and trimethylphosphine oxide. Binding energies, proton NMR shifts, Quantum Theory of Atoms in Molecules analysis and Interacting Quantum Atoms (IQA) interaction energies reveal a positive cooperative effect of a topological intramolecular hydrogen bond (IMHB) in catechol relative to phenol, with insignificant or small negative effects of further HO groups. Except for catechol complexes, there are no topological IMHBs in any donors or their complexes, although all show Non‐Covalent Interaction isosurfaces. The absence of a topological IMBH in catechol itself is explained by electron density contour plots. Complexes of Me₃N and Me₃PO with catechol, pyrogallol and 1,2,3,4‐tetrahydroxybenzene display additional intermolecular hydrogen bonds, C‐H^…H‐C and C‐H^…O=P, respectively, with the hydrogen atomorthoto the bound HO group. The predominantly covalent or electrostatic character of the various hydrogen bond types is discussed in terms of the IQA energy partition scheme, which is also useful for characterising IMHBs in the absence of a bond critical point. These results further our understanding of the nature and the limits of cooperative hydrogen bonding in donor‐acceptor complexes.

A corona, consisting of 18 carbon atoms bearing 12 hydroxy groups in a continuous hydrogen‐bonded chain, is built up by alternating degenerate conformations of alternating alkane‐1,2‐diol and 1,3‐diol motifs. Geometries, proton nuclear magnetic resonance shifts and interaction energies for the dodecahydroxycyclo‐octadecane and selected fragments are determined by density functional calculations at the B3LYP/6‐311+G(d,p) level. Cooperative effects of O–H⋯O–H bonding are evident from the simple juxtaposition of these two motifs with a common OH group in butane‐1,2,4‐triol conformers. Bracketing a 1,2‐diol motif with two 1,3‐diol motifs in hexane‐1,3,4,6‐tetrol leads to a structure in which the 1,2‐diol motif displays a bond critical point for hydrogen bonding. This is associated with enhancement of the shift of the hydrogen‐bonded OH proton and of the corresponding H⋯O interaction energy. The full corona has a complete outer ring of O–H⋯O–H bond paths, and an inner ring of bond paths, due to C–H⋯H–C hydrogen–hydrogen bonding, which result in a central ring critical point. The topological O–H⋯O–H hydrogen bond, never seen in simple alkane‐1,2‐diols, is associated with cooperative enhancement of the H⋯O interaction energy, but this is not a necessary condition for a bond path: values for topological C–H⋯H–C hydrogen–hydrogen bonds can be as low as −0.4 kcal mol⁻¹.

Proton nuclear magnetic resonance chemical shifts and atom–atom interaction energies for alkanepolyols with 1,2‐diol and 1,3‐diol repeat units, and for their 1:1 pyridine complexes, are computed by density functional theory calculations. In the 1,3‐polyols, based on a tG'Gg' repeat unit, the only important intramolecular hydrogen bonding interactions are O─H^…OH. By quantum theory of atoms in molecules analysis of the electron density, unstable bond and ring critical points are found for such interactions in 1,2‐polyols with tG'g repeat units, from butane‐1,2,3,4‐tetrol onwards and in their pyridine complexes from propane‐1,2,3‐triol onwards. Several features (OH proton shifts and charges, and interaction energies computed by the interacting quantum atoms approach) are used to monitor the dependence of cooperativity on chain length: This is much less regular in 1,2‐polyols than in 1,3‐polyols and by most criteria has a higher damping factor. Well defined C─H^…OH interactions are found in butane‐1,2,3,4‐tetrol and higher members of the 1,2‐polyol series, as well as in their pyridine complexes: There is no evidence for cooperativity with O─H^…OH bonding. For the 1,2‐polyols, there is a tenuous empirical relationship between the existence of a bond critical point for O─H^…OH hydrogen bonding and the interaction energies of competing exchange channels, but the primary/secondary ratio is always less than unity.

Hydrogen–hydrogen C─H^…H─C bonding between the bay‐area hydrogens in biphenyls, and more generally in congested alkanes, very strained polycyclic alkanes, and cis‐2‐butene, has been investigated by calculation of proton nuclear magnetic resonance (NMR) shifts and atom–atom interaction energies. Computed NMR shifts for all protons in the biphenyl derivatives correlate very well with experimental data, with zero intercept, unit slope, and a root mean square deviation of 0.06 ppm. For some congested alkanes, there is generally good agreement between computed values for a selected conformer and the experimental data, when it is available. In both cases, the shift of a given proton or pair of protons tends to increase with the corresponding interaction energy. Computed NMR shift differences for methylene protons in polycyclic alkanes, where one is involved in a very short contact (“in”) and the other is not (“out”), show a rough correlation with the corresponding C─H^…H─C exchange energies. The “in” and “in,in” isomers of selected aza‐ and diaza‐cycloalkanes, respectively, are X─H^…H─N hydrogen bonded, whereas the “out” and “in,out” isomers display X─H^…N hydrogen bonds (X = C or N). Oxa‐alkanes and the “in” isomers of aza–oxa‐alkanes are X─H^…O hydrogen bonded. There is a very good general correlation, including both N─H^…H─Y (Y = C or N) and N─H^…Z (Z = N or O) interactions, for NH proton shifts against the exchange energy. For “in” CH protons, the data for the different C─H^…H─Y and C─H^…Z interactions are much more dispersed and the overall shift/exchange energy correlation is less satisfactory.

Carbon Dots (CDs) are innovative materials which have potential applications in many fields, including nanomedicine, energy and catalysis. Here CDs were produced by the alkali-assisted ultrasonic route and characterized by several techniques to determine their composition and properties. Fluorescence nanoscopy using single-molecule localization microscopy shows that they have very good photophysical properties and a remarkable blinking behaviour at 405 nm. Moreover, these CDs are a safe material, non-toxic towards different cell lines (cancer and non-cancer cells) even at very high concentration, reflecting an excellent biocompatibility. Photothermia, i.e. their heating capacity under laser irradiation, was evaluated at two wavelengths and at several power densities. The resulting temperature increment was high (5 < ΔT < 45 °C) and appropriate for biomedical applications. Bioimaging and photothermia were then performed on E. coli, a Gram(−) bacterium, incubated with CDs. Remarkably, by photothermia at 680 nm (0.3, 1 and 1.9 W cm⁻²) or 808 nm (1.9 W cm⁻²), CDs are able to eradicate bacteria in their exponential and stationary phases. Images obtained by 3D super-resolution microscopy clearly show the different CD distributions in surviving bacteria after mild photothermal treatment. These results confirm that CDs are multifunctional materials with a wide range of biomedical applications.

Isosurfaces appearing in three‐dimensional Non‐Covalent Interactions (NCI) representations of molecules are attributed to bonding interactions (sign(λ ₂ )*ρ < 0) or to non‐bonding interactions, often referred to as “steric clashes” and typical of ring systems (sign(λ ₂ )*ρ > 0). Since the second eigenvalue of the Hessian of the electron density, λ ₂ , is positive for a ring or a cage critical point and negative for a bond critical point, in many cases NCI isosurfaces simply surround QTAIM critical points, which means that the attribution of positive‐λ ₂ isosurfaces to steric clashes in rings or cages is not justified. Examples are given for sterically congested hydrocarbons, where isosurfaces associated with C–H … H–C interactions enclose bond and ring critical points. In the same way, their appearance in the absence of critical points can be attributed to a variation of λ ₂ . It is shown that for small, very strained rings, positive‐λ ₂ isosurfaces are not found when the recommended plot parameters are used.

Density functional theory calculations are used to compute proton nuclear magnetic resonance (NMR) chemical shifts, interatomic distances, atom–atom interaction energies, and atomic charges for partial structures and conformers of α‐D‐glucopyranose, β‐D‐glucopyranose, and α‐D‐galactopyranose built up by introducing OH groups into 2‐methyltetrahydropyran stepwisely. For the counterclockwise conformers, the most marked effects on the NMR shift and the charge on the OH1 proton are produced by OH2, those of OH3 and OH4 being somewhat smaller. This argues for a diminishing cooperative effect. The effect of OH6 depends on the configuration of the hydroxymethyl group and the position, axial or equatorial, of OH4, which controls hydrogen bonding in the 1,3‐diol motif. Variations in the interaction energies reveal that a “new” hydrogen bond is sometimes formed at the expense of a preexisting one, probably due to geometrical constraints. Whereas previous work showed that complexing a conformer with pyridine affects only the nearest neighbour, successive OH groups increase the interaction energy of the N⋯H1 hydrogen bond and reduce its length. Analogous results are obtained for the clockwise conformers. The interaction energies for C―H⋯OH hydrogen bonding between axial CH protons and OH groups in certain conformers are much smaller than for O―H⋯OH bonds but they are largely covalent, whereas those of the latter are predominantly coulombic. These interactions are modified by complexation with pyridine in the same way as O―H⋯OH interactions: the computed NMR shifts of the CH protons increase, the atom–atom distances are shorter, and interaction energies are enhanced.