Solvation of excess electrons trapped in charge pockets on hydrated molecular surfaces

We have previously computed a set of hypothetical molecular surfaces, which formed charge pockets that were capable of excess electron entrapment. These charge pockets arose due to the fact that the molecular surfaces possessed an extended network of OH groups on one side of the surface and hydrogen atoms on the opposite side. The uneven distribution of the OH groups coupled to the partial positive charge of the hydrogen atoms caused electrons to be attracted to the surface. In the present investigation we will consider the ability of the hydrogen cyanide (HCN)‐water complex in stabilizing excess electrons on molecular surfaces. The computed vertical detachment energy (VDE) values are high, suggesting anion stability. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Localized electron traps on extended molecular surfaces

We have previously alluded to the fact that concentrated charge pockets can form on molecular surfaces that can act to stabilize excess electrons. These charge pockets are formed from systems, which posses a network of hydrogen bonded OH groups on one side of the surface and hydrogen atoms on the opposite side of the molecular surface. In this work, we have increased the size of our recently reported molecular surfaces (Jalbout and Adamowicz, Mol Phys, 2006, 19, 3101) while keeping the number of OH groups constant, to investigate localized charge concentration on extended frameworks. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Stabilization of an excess electron on molecular surfaces by a pair of HF molecules

This work presents the results of solvation of electrons on several hypothetical cyclooctane and cyclohexane molecular surfaces, using the hydrogen fluoride (HF) dimer. These complexes were constructed with extensive OH groups on one side of a hydrocarbon surface (i.e., cyclohexane sheets), which creates hydrogen‐bonded networks that can form, increasing the dipole moment of the system. Concurrently, the hydrogen atoms on the opposite side of the surface form a pocket of positive charge that can attract excess electrons. Two possible orientations for HF dimer solvation on eight molecular surfaces that have been demonstrated to be stable toward electron detachment are examined. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Trapping excess electrons in charge pockets on molecular surfaces in an argon matrix

Recently, we have proposed a series of hydrocarbon molecular surfaces (A.F. Jalbout, L. Adamowicz, Mol Phys 2006, 19, 3101), which had a hydrogen bonded network of OH groups on one side of the surface and hydrogen atoms on the opposite side. The addition of these OH groups increases the dipole moment of the system allowing for excess electrons to attach to the surface in dipole‐bound (DB) anion states. We have used this principle to study the interaction of the DB anions formed from the surfaces and an argon atom. The resulting anions are shown to be stable with respect to electron detachment. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Evolution of lone pair of excess electrons inside molecular cages with the deformation of the cage in e2@C60F60 systems

For unusual e(2)@C(60)F(60)(I(h), D(6h), and D(5d)) cage structures with two excess electrons, it is reported that not only the lone pair in singlet state but also two single excess electrons in triplet state can be encapsulated inside the C(60)F(60) cages to form single molecular solvated dielectrons. The interesting relationship between the shape of the cage and the spin state of the system has revealed that ground states are singlet state for spherical shaped e(2)@C(60)F(60)(I(h)) and triplet states for short capsular shaped e(2)@C(60)F(60)(D(6h)) and long capsular shaped e(2)@C(60)F(60)(D(5d)), which shows a spin evolution from the singlet to triplet state with the deformation of the cage from spherical to capsular shape. For these excess electron systems, the three ground state structures have large vertical electron detachment energies (VDEs (I) of 1.720-2.283 eV and VDEs (II) of 3.959-5.288 eV), which shows their stabilities and suggests that the large C(60)F(60) cage is the efficient container of excess electrons.     

Charge transfer stabilization of an excess electron on a molecular surface

In a developed molecular surface model (Jalbout and Adamowicz, Mol Phys, 2006, 19, 3101), we suggested a series of cyclohexane and cyclooctane systems with a hydrogen‐bonded network of OH groups on one side of the surface and hydrogen atoms on the opposite side. The OH groups in this work increased the dipole moment of the complexes in order to form stable dipole bound anions. In this report we consider the dipole‐bound and solvated anions between a set of hypothetical molecular surfaces and NH₃BF₃. The resulting complexes are stable with respect to vertical electron detachment. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Probing the Properties of Polynuclear Superhalogens without Halogen Ligand via ab Initio Calculations: A Case Study on Double‐Bridged [Mg2(CN)5]−1 Anions

An ab initio study of the superhalogen properties of eighteen binuclear double‐bridged [Mg₂(CN)₅]^?1 clusters is reported herein by using various theoretical methods. High‐level CCSD(T) results indicate that all the clusters possess strong superhalogen properties owing to their high vertical electron detachment energies (VDEs), which exceed 6.8 eV (highest: 8.15 eV). The outer valence Green's function method provides inaccurate relative VDE values; hence, this method is not suitable for this kind of polynuclear superhalogens. Both the HF and MP2 results are generally consistent with the CCSD(T) level regarding the relative VDE values and—especially interesting—the average values of the HF and MP2 VDEs are extremely close to the CCSD(T) results. The distributions of the extra electrons of the anions are mainly aggregated into the terminal CN units. These distributions are apparently different from those of previously reported triple‐bridged isomers and may be the reason for the decreased VDE values of the clusters. In addition, comparisons of the VDEs of binuclear and mononuclear superhalogens as well as studies of the thermodynamic stabilities with respect to the detachment of various CN^?1 ligands are also performed. These results confirm that polynuclear structures with pseudohalogen ligands can be considered as probable new superhalogens with enhanced properties.     

Prediction of solvation free energies from computed properties of solute molecular surfaces

We have shown that the solvation energies of a group of 12 solutes in 7 different solvents can be presented analytically in terms of quantities computed at the density functional B3P86/6‐31+G** level for the isolated solute molecules. These quantities include the molecular surface area and several properties of the electrostatic potential on the surface, e.g., the most positive and negative values, the average deviation of the potential, the positive and negative portions of the surface, and their average potentials. Overall, the average absolute deviation of the predicted from the experimental solvation free energies is 0.25 kcal/mol; the poorest results are obtained for the solute butanone, for which the average absolute deviation is 0.63 kcal/mol. The forms of the relationships reflect the natures of the solute–solvent interactions; for the solvents with low dielectric constants, these are primarily global, involving extended portions of the molecular surfaces, whereas for the more polar solvents, site‐specific interactions also play key roles. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 76: 643–647, 2000     

Magnesium-Based Clusters as Building Blocks of Electrolytes in Lithium-Ion Batteries

Superhalogens, owing to their large electron affinity (EA, exceeding those of any halogen atom), play an essential role in physical chemistry as well as new material design. They have applications in hydrogen storage and lithium-ion batteries. Owing to the unique geometries and electronic features of magnesium-based clusters, their potential to form a new class of lithium salts has been investigated here theoretically. The idea is assessed by conducting ab initio computations on Li⁺/Mg_nF_2n+1-2mO_m⁻ compounds (n=2, 3; m=0-3) and analyzing their performance as potential Li-ion battery electrolytes. The Mg₃F₇⁻ cluster, with large electron binding energy (EA of 7.93 eV), has been proven to serve as a building block for lithium salts. It is shown that, apart from high electronic stability, the new superhalogen-based electrolytes exhibit a set of desirable properties, including a large band gap, high electrolyte stability window, easy mobility of the Li⁺, and favorable insensitivity to water.     

Modeling electrochemical interfaces from ab initio molecular dynamics: water adsorption on metal surfaces at potential of zero charge

The origin of the potential difference between the potential of zero charge of a metal/water interface and the work function of the metal is a recurring issue because it is related to how water interacts with metal surface in the absence of surface charge. Recently ab initio molecular dynamics method has been used to model electrochemical interfaces to study interfacial potential and the structure of interface water. Here, we will first introduce the computational standard hydrogen electrode method, which allows for ab initio determination of electrode potentials that can be directly compared with experiment. Then, we will review the recent progress from ab initio molecular dynamics simulation in understanding the interaction between water and metal and its impact on interfacial potential. Finally, we will give our perspective for future development of ab initio computational electrochemistry.     

Traps for charge carriers in molecular materials formed by dipolar species: towards light-driven molecular switch

The influence of polar species on the transport and trapping of charge carriers is discussed. Calculations performed on a model molecular lattice demonstrate that polar dopants locally modify the polarization energy thus creating traps for charge carriers in the vicinity of the dipole. The presence of polar dopants in disordered solids gives rise to a broadening of the density-of-states function. A scheme of a molecular switch has been put forward, based on electrostatic interactions between photochromic moieties and charge carriers travelling on a molecular wire (conjugated polymer chain).     

Reductive electron transfer and transport of excess electrons in DNA

In principle, DNA-mediated charge transfer processes can be categorized as either oxidative hole transfer or reductive electron transfer. In research on DNA damage, major efforts have focused on the investigation of oxidative hole transfer or transport, resulting in insights on the mechanisms. On the other hand, the transport or transfer of excess electrons has a large potential for biomedical applications, mainly for DNA chip technology. Yet the mechanistic details of this type of charge transfer chemistry were unclear. In the last two years this mechanism has been addressed in gamma-pulse radiolysis studies with randomly DNA-bound electron acceptors or traps. The major disadvantage of this experimental setup is that the electron injection and trapping is not site-selective. More recently, new photochemical assays for the chemical and spectroscopic investigation of reductive electron transfer and electron migration in DNA have been published which give new insights into these processes. Based on these results, an electron-hopping mechanism is proposed which involves pyrimidine radical anions as intermediate electron carriers.     

Studies on molecular interactions of β-cyclodextrin and antiulcer agent

The search for the lowest energy conformation of complex {β-cyclodextrin (β-CD)+chlorambucil} were carried out by molecular mechanics method. Theoretical calculations of molecular interactions of complex were carried out using the molecular orbital method. The correlation between energy changes and molecular structures are discussed. The large interaction energies calculated by the molecular orbital method bears out the inclusion phenomenon.     

Dipole moment enhancement in molecular crystals from X-ray diffraction data.

Although reliable determination of the molecular dipole moment from experimental charge density analyses on molecular crystals is a challenging undertaking, these values are becoming increasingly common experimental results. We collate all known experimental determinations and use this database to identify broad trends in the dipole moment enhancements implied by these measurements as well as outliers for which enhancements are pronounced. Compelling evidence emerges that molecular dipole moments from X-ray diffraction data can provide a wealth of information on the change in the molecular charge distribution that results from crystal formation. Most importantly, these experiments are unrivalled in their potential to provide this information in such detail and deserve to be exploited to a much greater extent. The considerable number of experimental determinations now available has enabled us to pinpoint those studies that merit further attention, either because they point unequivocally to a considerable enhancement in the crystal (of 50 % or more), or because the experimental determinations suggest enhancements of 100 % or more--much larger than independent theoretical estimates. In both cases further detailed experimental and theoretical studies are indicated.