Condensed Fukui Function Research Articles

Study of atomic and condensed atomic indices for reactive sites of molecules

In this paper, we have introduced the atomic descriptors s(f) k to determine the local reactive sites of the molecular systems during electrophilic, nucleophilic and radical attacks. The condensed Fukui function and the newly introduced condensed atomic descriptor have been calculated for six different systems, namely glycine, alanine, aniline, BH2Cl,trans-FC(O)OF andm-anisidine. The individual atomic charges (gross charge) calculated by the MPA scheme have been used to calculate the condensed Fukui functions (f k) and the newly derived condensed atomic descriptors (sf) αk at B1-DZP level of theory. We carried out the calculation using the “stockholders” charge partitioning technique (i.e., Hirshfeld population scheme). The newly derived quantity gives the same reactive sites as the condensed Fukui functions, and the complexities associated with the negative Fukui functions are removed.

Relation between the Fukui function and the Coulomb hole

By using a coarse-grain representation of the molecular electronic density, we demonstrate that the value of the condensed Fukui function at an atomic site is directly related to the polarization charge (Coulomb hole) induced by a test electron removed (or added) from (at) the atom. The link between the formation of an electron-hole pair and the condensed Fukui function provides insights on the possible negativity of the Fukui function which is interpreted in terms of two phenomena: overscreening and over-strengthening.

Theoretical Study of the Interaction of Molecular Oxygen with Copper Clusters

A new method based on frontier orbital theory has been used to investigate the binding site of molecular oxygen to neutral and anion copper clusters. It has been shown that one can make useful predictions of the binding sites based on the knowledge of the donor local reactivity of the cluster using the condensed Fukui function, f(-)(Ff). In this way, it was found that Cu(3), Cu(5), and Cu(5)(-) have the highest reactivity toward molecular oxygen.

Comparison among Four Different Ways to Condense the Fukui Function

Four different ways to condense the Fukui function are compared. Three of them perform a numerical integration over different basins to define the condensed Fukui function, and the other one is the most traditional Fukui function using Mulliken population analysis. The basins are chosen to be the basins of the electron density (AIM), the basins of the electron localization function (ELF), and the basins of the Fukui function itself. The use of the last two basins is new and presented for the first time here. It is found that the last three methods yield results which are stable against a change in the basis set. The condensed Fukui function using the basins of the ELF is not able to give information on the reactivity of an acceptor molecule. In general, the condensed Fukui function using the basins of the density or the basins of the Fukui function describe the reactivity trends well. The latter is preferred, because it only contains information about the Fukui function itself and it gives the right information for donor as well as acceptor centers.

Study of effective hardness and condensed Fukui functions using AIM, ab initio, and DFT methods

The effective chemical hardness for some triatomic molecules has been studied using the ‘atom in a molecule’ approach (AIM). Molecular chemical hardness values calculated from the effective chemical hardness of individual atoms agree with experimental and theoretically calculated molecular hardness values. Condensed Fukui functions have been calculated using Mulliken, NPA and AIM charges calculated by HF and B3LYP methods using the 6-31+G** basis set. All population schemes have predicted few negative Fukui functions, which correlate well with effective chemical hardness values.

Quantum chemical studies on molecular structural conformations and hydrated forms of salicylamide and O‐hydroxybenzoyl cyanide

AbstractAb initio and density functional theory (DFT) methods have been employed to study the molecular structural conformations and hydrated forms of both salicylamide (SAM) and O‐hydroxybenzoyl cyanide (OHBC). Molecular geometries and energetics have been obtained in the gaseous phase by employing the Møller–Plesset type 2 MP2/6‐311G(2d,2p) and B3LYP/6‐311G(2d,2p) levels of theory. The presence of an electron‐releasing group (SAM) leads to an increase in the energy of the molecular system, while the presence of an electron‐withdrawing group (OHBC) drastically decreases the energy. Chemical reactivity parameters (η and μ) have been calculated using the energy values of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) obtained at the Hartree–Fock (HF)/6‐311G(2d,2p) level of theory for all the conformers and the principle of maximum hardness (MHP) has been tested. The condensed Fukui functions have been calculated using the atomic charges obtained through the natural bond orbital (NBO) analysis scheme for all the optimized structures at the B3LYP/6‐311G(2d,2p) level of theory, and the most reactive sites of the molecules have been identified. Nuclear magnetic resonance (NMR) studies have been carried out at the B3LYP/6‐311G(2d,2p) level of theory for all the conformers in the gaseous phase on the basis of the method of Cheeseman and coworkers. The calculated chemical shift values have been used to discuss the delocalization activity of the electron clouds. The dimeric structures of the most stable conformers of both SAM and OHBC in the gaseous phase have been optimized at the B3LYP/6‐311G(2d,2p) level of theory, and the interaction energies have been calculated. The most stable conformers of both compounds bear an intramolecular hydrogen bond, which gives rise to the formation of a pseudo‐aromatic ring. These conformers have been allowed to interact with the water molecule. Special emphasis has been given to analysis of the intermolecular hydrogen bonds of the hydrated conformers. Self‐consistent reaction field (SCRF) theory has been employed to optimize all the conformers in the aqueous phase (ε = 78.39) at the B3LYP/6‐311G(2d,2p) level of theory, and the solvent effect has been studied. Vibrational frequency analysis has been performed for all the optimized structures at MP2/6‐311G(2d,2p) level of theory, and the stationary points corresponding to local minima without imaginary frequencies have been obtained for all the molecular structures. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

Molecular structural conformations and hydration of internally hydrogen‐bonded salicylic acid: Ab initio and DFT studies

AbstractWe studied molecular structural conformations and hydration of internally hydrogen‐bonded salicylic acid using ab initio and density functional theory methods. Molecular geometries and energetical parameters were obtained in gaseous phase using MP2 and B3LYP levels of theory, implementing the 6‐311G(2d,2p) atomic basis set. Chemical hardness and chemical potential were calculated at HF/6‐311G(2d,2p) level of theory for all the optimized structures, and the principle of maximum hardness was tested. The condensed Fukui functions were calculated using the atomic charges obtained through a natural population analysis scheme for all optimized structures at B3LYP/6‐311G(2d,2p) level of theory, and the most reactive sites of the molecules were identified. NMR studies were carried out for all the conformers in gaseous phase on the basis of Cheeseman et al.'s method at B3LYP/6‐311G(2d,2p) level of theory; the calculated chemical shift values are discussed. The self‐consistent reaction field theory (SCRF) was used to optimize all the conformers in aqueous phase (ε = 78.39) at B3LYP/6‐311G(2d,2p) level of theory and the solvent effect was studied. The geometrical and energetical parameters of all the conformers are compared and analyzed. The dimeric structure of the most stable conformer in the gaseous phase was optimized at B3LYP/6‐311G(2d,2p) level of theory and the interaction energy studied. Selected conformers were allowed to interact with water molecule; optimized parameters are discussed. Vibrational frequency analyses were performed at MP2/6‐311G(2d,2p) level of theory and the stationary point corresponding to local minima without imaginary frequencies are obtained for all the optimized structures. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

Study of metal ions (Na+, K+) interaction with different conformations of glycine molecule

AbstractInteraction of metal ions (Na+, K+) with different binding sites, such as amino nitrogen, hydroxyl oxygen, and carbonyl oxygen for all gaseous conformers of glycine molecule were investigated using Density Functional Theory (B3LYP/6‐311++G**, B3PW91/6‐311++G**) methods. It was found that the order of stability of the conformers was changed due to the binding of the metal ion. The relative energy values show that the 7p conformer is more stable than the 1p conformer when a metal ion binds with the carbonyl oxygen. The intensity of interaction on hydroxyl oxygen is very low due to the low basicity of hydroxyl oxygen. The binding affinities of the complexes were calculated using the thermochemical properties. The relative energy and chemical hardness values predicted the most stable complex. The calculated condensed Fukui functions predict the favorable reactive site among the three binding sites. It is concluded that the reactivity of each binding site varies for each conformation due to the presence of intramolecular hydrogen bonding. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

Behavior of the Local Reactivity Descriptors during Complexation: A Case Study of BXX‘X‘ ‘NH3(X, X‘, X‘‘= H, F)

The behavior of local reactivity descriptors such as condensed fukui functions, “relative electrophilicity”, and “relative nucleophilicity” was studied as the complexation reaction of BH3 or fluoroboranes and NH3 proceeds. This study reveals the change of these descriptors of different atoms during the reaction. The case study indicates the general properties of descriptors in a reactive surface.

Synthesis and Spectroscopic Study of a New Lanthanum(III) Complex of 3,3′‐Benzylidenedi‐4‐hydroxycoumarin

The coordination ability of 3,3′‐benzylidenedi‐4‐hydroxycoumarin (H2bhc) has been proved in a complexation reaction with lanthanum(III) ion. The new lanthanum(III) complex of bhc2− was studied by elemental analyses, mass spectra, 1H, 13C NMR, and IR spectroscopy. The data obtained are in agreement with the metal:ligand ratio of 1:l, and the formula La(bhc)(OH)(H2O), where bhc2− = C25H14O6 2−. The calculated condensed Fukui functions for bhc2− predicted that both hydroxyl and carbonyl oxygen atoms are probable reactive sites for coordination to the metal. The vibrational analysis of the lanthanum(III) complex, free H2bhc, bhc2−, and 4‐hydroxycoumarin showed that in the La(III) complex the ligand coordinates to the metal ion through both deprotonated hydroxyl groups. The participation of both carbonyl groups in coordination to the metal ion was confirmed by the significant shift of ν(C˭O) to lower wave number.

Ab initio and DFT studies on tautomerism of indazole in gaseous and aqueous phases

Ab initio and DFT methods have been used to study the five tautomeric forms of indazole (IZT1, IZT2, IZT3, IZT4, IZT5) in gaseous and aqueous phases. The tautomers in gas phase have been optimized at MP2/6-311G(2d,2p), B3LYP/6-311G(2d,2p) and B3PW91/6-311G(2d,2p) levels of theory. The self-consistent reaction field theory (SCRF) has been used to optimize the tautomers in aqueous phase ( ε=78.5) at B3LYP/6-311G(2d, 2p) level of theory and the solvent effect has been studied. The structure, energetics and relative stabilities of the tautomers were compared and analyzed both in gaseous and aqueous phases. The principle of maximum hardness has been tested by calculating chemical hardness and chemical potential at HF/6-311G(2d,2p) level of theory to predict the order of stability of the tautomers. The condensed Fukui functions have been calculated to identify the relative change in most reactive site of the optimized tautomers in gas phase using atomic charges obtained through Mulliken population analysis scheme. 13C-NMR studies have been carried out for these tautomers in the gas phase at B3LYP/6-311G(2d,2p) level of theory on the basis of Cheeseman co-worker's method and the results were discussed.

Intramolecular interactions along the reaction path of keto–enol tautomerism: Fukui functions as local softnesses and charges as local hardnesses

This paper presents an unprecedented analysis of local hard and soft descriptors of the intramolecular reactivity along the reaction path of the keto-enol tautomerism. Different kinds of atomic charges (namely Mulliken, NPA, ESP, Hirschfeld and AIM), as descriptors of local hardness, and different kinds of condensed Fukui functions, as descriptors of local softness are tested in their ability to describe a consistent picture of internal reactivity.

Fukui Indexes Applied to the Reduced and Nonreduced Species of the Nickel(II) Tetraazadinaphtho[14]annulene Complex and Its Protonated Derivative

A first ab initio density functional B3LYP/LACVP theoretical rationalization concerning the determination of the active sites of nickel(II) tetraazadinaphtho[14]annulene (NiN4CH3) and its protonated derivative (NiN4CH3H2trans,trans2+), when they are submitted to a reduction or an oxidation process, is presented. Condensed Fukui functions ( and ) using the approximations given by frozen core (fc) and finite difference (fd) are applied to determine the reductor and oxidant sites. The obtained results of and for the nonreduced NiN4CH3 and reduced NiN4CH3- species, respectively, predict the nickel atom and the four azomethynic carbon atoms as the most probable active sites, in agreement with experimental results using the pulse radiolysis technique. However, in the protonated structure a different result is found. The nickel atom appears as the unique active site, a reductor site in NiN4CH3H2trans,trans2+ and an oxidant site in NiN4CH3H2trans,trans+. We also found that both fc and fd predict the same trend, demonstrating that they are completely valid to be used in the subject of metal complexes and verifying the validity of the partitioning scheme of natural bond orbital used.

Molecular modeling of dipeptide and its analogous systems with water

Intermolecular hydrogen-bond interactions in the monohydrated complexes of formamide, N-methylacetamide and glycylglycine have been studied using ab initio and DFT methods. The geometries were optimized using second-order Møller-Plesset perturbation theory and the B3LYP DFT functional with the 6-311++G** basis set. It is observed that hydrogen-bond interactions at the carbonyl group of the peptide moiety are stronger than those at the amino group of the formamide and N-methylacetamide molecules. Because of the presence of cyclic hydrogen-bonding interactions in glycylglycine, the interaction at the amino group is higher than at the carbonyl. The 13C and 15N NMR shielding values were calculated for the non-hydrated and monohydrated complexes. Condensed Fukui functions have also been calculated for non-hydrated formamide, N-methylacetamide and glycylglycine molecules at the B3LYP/6-311++G** level of theory, and the results are discussed.

Calculation of the Dipole Moment for Polypeptides Using the Generalized Born-Electronegativity Equalization Method: Results in Vacuum and Continuum-Dielectric Solvent

The electronegativity equalization methodology, EEM, is frequently used to calculate the charge distributionand reactivity index (e.g., local softness and hardness, condensed Fukui function) of molecules. However,recent work (Chelli, R. et al., J. Chem. Phys. 1999, 111, 8569) has shown a serious shortcoming of EEM inthe prediction of the polarizability for large molecules. In this paper, our goal is to show that we can obtaina reliable dipole moment for polypeptides in vacuum and continuum-dielectric solvent using the constrainedcharge approximation and the generalized Born-electronegativity equalization method. Different EEMparameterizations were tested and compared to the expected values of the dipole moment vector operator ascalculated at the ab initio B3LYP/6-311G(d,p) level. One EEM parameterization (Bakowies, D., Thiel, W.,J. Comput. Chem. 1996, 17, 87) when used with the constrained charge approximation and the generalizedBorn-electronegativity equalization method was comparable to the CM1 charge model (Storer et al.,J. Comput.-Aided Mol. Des. 1995, 9, 87) in the prediction of the dipole moment vector in vacuum and continuum-dielectric solvent, but was calculated with a much greater computational efficiency.

Experimental and Theoretical Study of the Activity of Substituted Metallophthalocyanines for Nitrite Electro-oxidation

The electrocatalytic activity of various metallophthalocyanines (M-Pc) adsorbed on an ordinary pyrolytic graphite electrode for the oxidation of nitrite has been investigated in aqueous phosphate buffer solution (pH 7.3). A comparison of Pcs of different metals, shows that the activity is influenced by the nature of the central metal but not very significantly. However, the effect of substituents on the periphery of the Pc ligand is more pronounced. Electron-donor substituents of the Pc ligand enhance this activity. At a density functional theoretical level, we found that the calculated condensed Fukui function, associated to a nucleophilic attack, gives a reasonable explanation for the location of the reaction site in the case of the set of M-Pcs. Indeed, for Cr-Pc, Mn-Pc, Fe-Pc, and Co-Pc, the Fukui function predicts that the preferred reactive sites are located on the central metal whereas for Ni-Pc, Cu-Pc, and Zn-Pc it predicts that the reactive sites are located on the ligand, in agreement with the experimental trends observed. © 2003 The Electrochemical Society. All rights reserved.

Effect of solvation on the condensed Fukui function and the generalized philicity index

Condensed Fukui functions (FF) and philicity provide vital information about functionally reactive sites in molecules. The effect of solvation on the condensed FF and philicity has been assessed by computing these local quantities in both gas and solvent media. The various population schemes used to calculate condensed quantities have several limitations viz., computational time, multiplicity problem and interpretation of negative values. To overcome this we used the direct method to evaluate the condensed quantities in both gas and solvent media. Hirshfeld population scheme has also been employed to avoid negative FF values. The implications of the results are discussed.

Application of Condensed Fukui Functions to Cobalt Macrocycle Complexes

A theoretical analysis at the ROB3LYP/3-21G* level of theory of the condensed Fukui function (fk) applied to a set of eight cobalt macrocycles derived of the porphyrine is performed. Two approximations for fk are used, finite difference (fd) and frozen core (fc), and the and indices are evaluated for determining the most probable reaction site for the attack of an electrophile and of a nucleophile, respectively. We found a good agreement between fd and fc calculated for , in the sense that both predict that the cobalt atom is the preferred reaction site receiving an electrophile. In the case of a nucleophilic attack, the comparison between the fd and fc approximations shows that both predict the cobalt atom as the most probable reaction site receiving a nucleophile. We conclude that realistic (fd) as approximate (fc) estimates of the condensed Fukui function used here in general can work very well in diagnosing reactivity trends in cobalt porphyrine and derivatives.

Chemical Reactivity Profiles of Two Selected Polychlorinated Biphenyls

Global reactivity and local selectivity profiles such as electronegativity, hardness, polarizability, electrophilicity index, condensed Fukui function, and local electrophilic power of a selected polychlorinated biphenyl, viz., 2,2‘,5,5‘-tetrachlorobiphenyl have been calculated using the B3LYP/6-31G* method in gas and solution phases in order to gain insight into the toxic nature of this compound and a comparison is also made with 3,3‘,4,4‘,5-pentachlorobiphenyl. It is seen that both global and local electrophilicity helps in understanding the overall toxic nature of the system. The significance of the planarity and electron affinity in determining the toxic nature of the polychlorinated biphenyls is now better understood.

Adsorption of Small Molecules in Zeolites: A Local Hard—Soft Acid—Base Approach.

The interaction of small probe molecules with clusters chosen to represent Brφnsted acid sites in zeolites has been investigated using a local hard−soft acid−base approach. Condensed Fukui functions and local softness values of all the atoms of the probe molecules, namely, CH4, CO, and NH3, have been calculated, and these values are compared with that of the acidic hydrogen atoms of zeolite clusters to find out the most favorable adsorption sites. We calculated the interaction energy of the molecules using local HSAB principle, and the interaction energy values are in good agreement with the experimental results. Density functional and Hartree−Fock methods are used for the calculation of reactivity descriptors. We observed that the intermolecular interaction takes place via the atoms comparable softness values rather than via atoms of equal Fukui functions.