Substituent and Heteroatom Effects on π-π Interactions: Evidence That Parallel-Displaced π-Stacking is Not Driven by Quadrupolar Electrostatics.

Stacking interactions are a recurring motif in supramolecular chemistry and biochemistry, where a persistent theme is a preference for parallel-displaced aromatic rings rather than face-to-face π-stacking. This is typically explained in terms of quadrupole-quadrupole interactions between the arene moieties but that interpretation is inconsistent with accurate calculations, which reveal that the quadrupolar picture is qualitatively wrong. At typical π-stacking distances, quadrupolar electrostatics may differ in sign from an exact calculation based on charge densities of the interacting arenes.

Video versus Direct Laryngoscopy for Tracheal Intubation Following Cardiac Arrest: a Secondary Analysis of the DEVICE Trial.

Background: Airway management is a critical component of the care of patients experiencing cardiac arrest, but data from randomized trials on the use of video vs direct laryngoscopy for intubation in the setting of cardiac arrest are limited. Current AHA guidelines recommend placement of an endotracheal tube either during CPR or shortly after return of spontaneous circulation but do not provide guidance around intubation methods, including the choice of laryngoscope.

Research Question: Does use of video laryngoscopy improve the incidence of successful intubation on the first attempt, compared to use of direct laryngoscopy, among adults undergoing tracheal intubation after experiencing cardiac arrest?

Study Design And Methods: This secondary analysis of the Direct versus Video Laryngoscope (DEVICE) trial compared video laryngoscopy versus direct laryngoscopy in the subgroup of patients who were intubated following cardiac arrest.

Quick-and-Easy Validation of Protein-Ligand Binding Models Using Fragment-Based Semiempirical Quantum Chemistry.

Electronic structure calculations in enzymes converge very slowly with respect to the size of the model region that is described using quantum mechanics (QM), requiring hundreds of atoms to obtain converged results and exhibiting substantial sensitivity (at least in smaller models) to which amino acids are included in the QM region. As such, there is considerable interest in developing automated procedures to construct a QM model region based on well-defined criteria. However, testing such procedures is burdensome due to the cost of large-scale electronic structure calculations.

Convergent Protocols for Computing Protein-Ligand Interaction Energies Using Fragment-Based Quantum Chemistry.

Fragment-based quantum chemistry methods offer a means to sidestep the steep nonlinear scaling of electronic structure calculations so that large molecular systems can be investigated using high-level methods. Here, we use fragmentation to compute protein-ligand interaction energies in systems with several thousand atoms, using a new software platform for managing fragment-based calculations that implements a screened many-body expansion. Convergence tests using a minimal-basis semiempirical method (HF-3c) indicate that two-body calculations, with single-residue fragments and simple hydrogen caps, are sufficient to reproduce interaction energies obtained using conventional supramolecular electronic structure calculations, to within 1 kcal/mol at about 1% of the computational cost.

Associative learning via eyeblink conditioning differs by age from infancy to adulthood.

Associative learning is a key feature of adaptive behaviour and mental health, enabling individuals to adjust their actions in anticipation of future events. Comprehensive documentation of this essential component of human cognitive development throughout different developmental periods is needed. Here, we investigated age-related changes in associative learning in key developmental stages, including infancy, childhood, adolescence, and adulthood.