A geometrical analysis has been performed on π–π stacking in metal complexes with aromatic nitrogen-containing ligands based on a Cambridge Structural Database search and on X-ray data of examples in the recent literature. It is evident that a face-to-face π–π alignment where most of the ring-plane area overlaps is a rare phenomenon. The usual π interaction is an offset or slipped stacking, i.e. the rings are parallel displaced. The ring normal and the vector between the ring centroids form an angle of about 20° up to centroid–centroid distances of 3.8 A. Such a parallel-displaced structure also has a contribution from π–σ attraction, the more so with increasing offset. Only a limited number of structures with a near to perfect facial alignment exists. The term π–π stacking is occasionally used even when there is no substantial overlap of the π-ring planes. There is a number of metal–ligand complexes where only the edges of the rings interact in what would be better described a C–H⋯π attraction.

A critical account on π–π stacking in metal complexes with aromatic nitrogen-containing ligands

Approaches, Derivatives and Applications Vasilios Georgakilas,† Michal Otyepka,‡ Athanasios B. Bourlinos,‡ Vimlesh Chandra, Namdong Kim, K. Christian Kemp, Pavel Hobza,‡,§,⊥ Radek Zboril,*,‡ and Kwang S. Kim* †Institute of Materials Science, NCSR “Demokritos”, Ag. Paraskevi Attikis, 15310 Athens, Greece ‡Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University Olomouc, 17. listopadu 12, 771 46 Olomouc, Czech Republic Center for Superfunctional Materials, Department of Chemistry, Pohang University of Science and Technology, San 31, Hyojadong, Namgu, Pohang 790-784, Korea Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, v.v.i., Flemingovo naḿ. 2, 166 10 Prague 6, Czech Republic

Functionalization of Graphene: Covalent and Non-Covalent Approaches, Derivatives and Applications

The Cationminus signpi Interaction.

Femtosecond filamentation in transparent media

Rydberg atoms with principal quantum number $n⪢1$ have exaggerated atomic properties including dipole-dipole interactions that scale as ${n}^{4}$ and radiative lifetimes that scale as ${n}^{3}$. It was proposed a decade ago to take advantage of these properties to implement quantum gates between neutral atom qubits. The availability of a strong long-range interaction that can be coherently turned on and off is an enabling resource for a wide range of quantum information tasks stretching far beyond the original gate proposal. Rydberg enabled capabilities include long-range two-qubit gates, collective encoding of multiqubit registers, implementation of robust light-atom quantum interfaces, and the potential for simulating quantum many-body physics. The advances of the last decade are reviewed, covering both theoretical and experimental aspects of Rydberg-mediated quantum information processing.

Quantum information with Rydberg atoms

Potential Energy Surface of the Benzene Dimer: Ab Initio Theoretical Study

Hydrogen bonds and their relative strengths in proteins are of importance for understanding protein structure and protein motions. The correct strength of such hydrogen bonds is experimentally known to vary greatly from ≈5–6 kcal/mol for the isolated bond to ≈0.5–1.5 kcal/mol for proteins in solution. To estimate these bond strengths, here we suggest a direct novel kinetic procedure. This analyzes the timing of the trajectories of a properly averaged dynamic ensemble. Here we study the observed rupture of these hydrogen bonds in a molecular dynamics calculation as an alternative to using thermodynamics. This calculation is performed for the isolated system and contrasted with results for water. We find that the activation energy for the rupture of the hydrogen bond in a β-sheet under isolated conditions is 4.76 kcal/mol, and the activation energy is 1.58 kcal/mol for the same β-sheet in water. These results are in excellent agreement with observations and suggest that such a direct calculation can be useful for the prediction of hydrogen bond strengths in various environments of interest.

https://www.phys.sinica.edu.tw/~hydro/journalclub%20data/Yang%20Da-Yen.pdf

Energetics of hydrogen bonds in peptides

A new type of bonding, termed anti-hydrogen bond, is identified in the benzene dimer and other carbon proton donor complexes from correlated ab initio computations. Gradient optimization of the benzene dimer at the MP2/6-31G* and MP2/6-31G** levels shows a shortening of the C−H bond of the proton donor and a blue-shift of the corresponding C−H stretching frequency. The harmonic C−H stretching vibrational frequency shift agrees well with that evaluated for various anharmonic approaches. The blue-shift of the C−H stretching frequency was also found in the case of benzene complexes with other carbon proton donors, CH4 and CHCl3. The anti-H-bonds are expected to be very significant for the structure and dynamics of biomolecules.

Anti-Hydrogen Bond in the Benzene Dimer and Other Carbon Proton Donor Complexes

Structure and Properties of Benzene-Containing Molecular Clusters - Nonempirical Ab-Initio Calculations and Experiments

Isotopically mixed jets of benzene produced the various possible isotopic benzene dimers in a supersonic jet. Mass coincidence in time‐of‐flight multiphoton mass spectra separated the spectra due to the various dimers produced into distinguishable spectra even in the presence of overlap. From the many different isotopic spectral shifts a detailed model of interaction between the two halves of the dimer can be established revealing detailed new information on this interaction. In particular a splitting in the 0–0 transition is reported for the first time indicating an exciton interaction in the dimer of isotropic identical benzene molecules in the gas phase.

Heinrich L. Selzle

Papers

Potential Energy Surface of the Benzene Dimer: Ab Initio Theoretical Study

Energetics of hydrogen bonds in peptides

Anti-Hydrogen Bond in the Benzene Dimer and Other Carbon Proton Donor Complexes

Structure and Properties of Benzene-Containing Molecular Clusters - Nonempirical Ab-Initio Calculations and Experiments

Spectra of isotopically mixed benzene dimers: Details on the interaction in the vdW bond