International Journal of Quantum Chemistry

For a (molecular) graph G, a spanning tree in G is a tree that has the same vertex set as G. In the cover image, green edges show a spanning tree. The number of spanning trees in a (molecular) graph has lots of intriguing applications in mathematics, computer science, physics, and chemistry. Because of these wide-ranging applications, it is important to develop useful techniques for enumerating the number of spanning trees in various classes of graphs. The paper by Khodakhast Bibak on page 1209 deals with a special case, which might be of particular interest to computational quantum chemistry.

The molecular properties of energetic materials, including bond dissociation energy, electronic structure, and energetic transfer rate, are the main factors that determine the sensitivity of energetic materials, if the aggregation state and environmental conditions are ignored. The sensitivity and thermal stability of these materials can therefore be theoretically predicted. Researchers have conducted many fundamental investigations with regard to theoretical methods that could be used to predict mechanical and spark sensitivity of energetic materials based on quantum chemistry theory or molecular simulation, as reviewed by Qi-Long Yan and Svatopluk Zeman on page 1049.

Theoretical methods used to predict the mechanical and spark sensitivity of energetic materials are compared and discussed in this review. The current ability to predict sensitivity is merely based on a series of empirical rules, such as oxygen balance, molecular properties, and the ratios of carbon and hydrogen to oxygen in explosive compounds. These are valid only for organic classes of explosives, though some models have been also proposed for inorganic materials, such as azides.

Understanding the nature of interactions between metal nanoparticles and conjugated biomolecules is of fundamental importance in the development and design of efficient biosensors. The interaction of D-glucose with neutral and charged metal clusters is modeled with quantum chemical methods to investigate the mechanism of the bonding and the factors that control its efficiency.

β-Glycosidases are able to catalytically hydrolyze the very stable glycosidic bond. Rice BGlu1 enzyme, among the β-glucosidases, more efficiently hydrolyzes cello-oligosaccharides. Using the quantum mechanical/molecular mechanical approach, the deglycosylation step of the rice BGlu1 enzyme is studied, identifying the structure of the transition state, as well as the function of key residues.

The linear dependence of the ensemble ground state energy on particle number is found in expressions for the difference between energy functionals where the particle number differs by one. It is further reflected in the spatial dependence on particle number of the functional derivatives of the mutual electron–electron repulsion and kinetic energy.

Recent computational and experimental studies revealed the paramount importance of proton-transfer processes in phosphine- and amine-catalyzed reactions of unsaturated electrophilic reagents: they can be rate-determining steps and/or require involvement of external proton-donor sources. A similar mechanism was found for quarternization of tertiary phosphines with unsaturated carboxylic acids.

Most of the existing computational methods for protein structure determination with nuclear magnetic resonace (NMR) rely on stochastic and heuristic protocols overlooking the fast analytic-type algebraic methods as unrealistic alternates. An algebraic methodology is here introduced to reinforce this alternate point of view as realistic and effective. A unified and efficient methodology that reduces the computations of protein backbone conformation to a problem of robust, easily soluble, linear and nonlinear equation solving is introduced.

A novel azocompound, 2-(4-phenylazoaniline)-4-phenylphenol: Spectroscopic and quantum-chemical approach.

Generalized local softness is applied not only to predict stereoselectivities of Diels–Alder reactions but also to rationalize the relative magnitudes of the reaction rate constants of said reactions. The approach demonstrated here can be further extended to the study of other types of reactions.

Because of their broad use, primarily in pest control, organophosphorus compounds need to be efficiently and environmentally safely broken down. The mechanisms for atmospheric degradation of a specific compound of this class is investigated here using density functional theory, providing insight into the corresponding potential energy surface profiles and reaction selectivity.

The binding behaviors of eight bivalent metalloporphyrins with NH₃ is investigated by density functional theory. The understanding of the interaction behavior from a theoretical viewpoint is essential to the development of selective and effective gas sensors. As a linear relationship between the magnitude of charge transfer and the binding energy is found for these complexes, it is suggested that the Co porphyrins should interact more strongly with NH₃, making it a promising sensing material.

Glycolaldehyde was recently detected in the interstellar medium. In a nonterrestrial setting the synthetic reaction of this species from formaldehyde and methanol is not expected to be at thermal equilibrium, leaving open the possibility that significant amounts of conformers other than the most stable form could also exist. The vibration-rotation spectra of four stable conformers of Glycolaldehyde and the six reaction paths connecting them are characterized in this work by high-level ab initio calculations.

Cyclopropane carboxaldehyde is studied as an accessible example of the interaction between the electron donor cyclopropyl and the electron acceptor carbonyl. The structure and energetics of its conformers, and the energy barrier between syn and anti forms are determined at the CCSD(T) level of theory. In agreement with experimental data the syn and anti isomers are found to be almost degenerate in energy, with a slight preference for the anti form in gas phase.

β-IEPOX has been suggested as an important intermediate in the reaction of secondary organic aerosol formation from isoprene. Theoretical calculations provide insight into the reaction mechanism. In gas phase reaction, β-IEPOX is decomposed and the secondary organic aerosol is expected to form in aqueous phase. The structure and reactivity of another 2,3-epoxy-1,4-butanediol, BEPOX, is also reported here.

The substituent effects on the stability of benzene derivatives, with and without the formation of intramolecular hydrogen bonding, is evaluated by a variety of computational methods. While high-level quantum chemical approaches (such as correlated and perturbation methods) yield the most accurate energetics, all of the hybrid density functionals showed similar accuracy and could effectively describe the intramolecular hydrogen-bonding interactions of these compounds.

In literature, general expressions for anharmonic constants can be derived only when the cubic and quartic parts of the potential function are considered as perturbations in the calculation of vibrational energies levels. In this work, the general expression is extended to higher, up to the sixth, orders.

Understanding the coordination ability of a transition metal center is fundamental to predict and control their chemistry. Calculations show that up to seven carbonyls can be bonded to the central Sc atom with reasonable binding energies. Thus, the last 18-electron first-row transition metal carbonyls, Sc(CO)₇^{‡‡‡‡‡‡‡‡‡‡−} and Sc(CO)₆^{‡‡‡‡‡‡‡‡‡‡3−}, are stable and could be experimentally accessible. The new Sc-carbonyls predicted in this study add to the hitherto very limited examples of Sc-carbonyls, and welcome future laboratory characterization.

Galanthamine is a tertiary alkaloid extracted from plants that has been studied as an inhibitor of AChE. Inhibition of AChE is considered one of the most promising strategies for the treatment of Alzheimer's and related diseases. The molecular conformation, intermolecular interaction, charge density distribution, and electrostatic properties of galanthamine both in isolated form, and docked in the active site of AChE, are studied here using a combination of computational techniques.

Graphs, among other things, may be thought of as representing the connectivity of the atoms that comprise the (microscopic) conjugation network of an unsaturated molecule. Calculating the number of spanning trees in (i.e., the complexity of) such (labeled) molecular graphs, and their remarkable applications have absorbed much attention. This article, after reviewing some of these applications, gives short proofs for complexities of a semiregular graph and its line graph. The green edges in the figure show a spanning tree.

Poly(amidoamine) (PAMAM) dendrimers have recently been used to modify nano-silicon dioxide by grafting methods. First principle calculations are applied to the study of the interaction of simple NH₂-terminated dendrimers with nano-SiO₂. Spatial hindrance, electrostatic induction force, and hydrogen-bond interaction are all found to play important roles in the complexation process.

yy-Bases are among the size-expanded synthetic nucleobases that have been recently synthetized. Helices formed by such bases are found to be more thermally stable than those of analogous sequences of natural DNA, due to their large aromatic surfaces, which give rise to enhanced π–π stacking interactions and hydrophobicity. The excited-state properties and absorption and emission spectra of the yyG base and its five possible tautomers are studied in this article to aid the interpretation of future experimental data.

The physics of mesoscopic systems are very interesting from the theoretical viewpoint due to the impressive progress of experimental investigations in this domain. A mesoscopic ideal Fermi gas of identical particles confined inside a rectangular box is considered here. Mesoscopic properties, such as the temperature dependence of the chemical potential, the average energy, and the heat capacity before the thermodynamic limit, differ from the corresponding thermodynamic quantities only quantitatively, but are qualitatively similar.