BSSE-corrected Interaction Energies Research Articles

Structure and hydrogen bonding of mono-protic ionic liquids composed of N-alkylethylenediaminium cations and trifluoromethanesulfonate anion

The stabilities of some of the possible molecular structures, intermolecular hydrogen bonding interactions, and protonation sites of chelating mono-protic ionic liquids composed of N-alkyl (= Hexyl, Octyl, and 2-Ethylhexyl) ethylenediaminium cations with a trifluoromethanesulfonate anion (TFS), forming [HHex][TFS], [HOct][TFS] and [HEtHex][TFS] were studied using DFT calculations with the M06-2X functional and 6-311G(d, p) basis set. The BSSE-corrected interaction energies (∆E0BSSE) for the investigated structures range from − 98.3 to − 108.3 kcal mol−1. NBO and AIM analyses were applied to quantify the relative strengths of the hydrogen bonding interactions and to account for their effect on the stability of various molecular structures. The values of ∆E0BSSE decrease with increasing alkyl chain length and upon introduction of an ethyl branch in the cation. The second-order perturbation energy and electron density indicate that [HAlkyl]1＋[TFS] (protonated at the primary amine, Form A) are more stable than [HAlkyl]2＋[TFS] (protonated at the secondary amine, Form B).

Carbon nitride 2-D surface as a highly selective electrochemical sensor for V-series nerve agents

Herein, carbon nitride 2-D surface (C2N) was studied as an electrochemical sensor for chemical warfare agents (CWA; A-230, A-232, A-234, and VR). The deep insight of analytes@C2N complexation was obtained by interaction energy, SAPT0, NCI, QTAIM, EED, and FMO analyses. The interaction energies results indicate that these CWAs are physisorbed onto the surface where BSSE corrected interaction energies range from −14.42 kcal/mol to −15.99 kcal/mol. Moreover, SAPT0 analysis revealed that dispersion interactions are the dominant component which amount to nearly 61% of overall SAPT0 interaction energies. SAPT0 analysis results are consistent with interaction energies. The nature of interactions was also quantified by NCI and QTAIMs analysis. NBO analysis showed that the highest amount of charge transfer is observed in A232@C2N (−0.018 e−), while the least amount of charge transfer is seen in VR@C2N. The EDD analysis also verified the results of NCI, QTAIM and NBO analyses. A short recovery time of 0.027 s at 298 K for desorption of VR from C2N surfaces was calculated. VR adsorption onto C2N surface caused the highest change in the HOMO-LUMO energy gap (2.68 eV) compared to bare C2N (3.71 eV), which reveals the potential of C2N as an electrochemical sensor for VR. The complexation of A-230, A-232, and A-234 had a negligible effect on the HOMO-LUMO energy gap. Among all complexes, HOMO-LUMO excitation is associated with charge transfer from analytes to the C2N surface.

Theoretical and experimental spectroscopic studies, XPS analysis, dimer interaction energies and molecular docking study of 5-(adamantan-1-yl)-N-methyl-1,3,4-thiadiazol-2-amine

This research relates to the molecular structure, electronic properties and IR, Raman and XPS analyses of the potential chemotherapeutic agent namely, 5-(adamantan-1-yl)-N-methyl-1,3,4-thiadiazol-2-amine. Another purpose is to explore the structural stabilities and consistencies and, to assess the stable interaction energy and intermolecular hydrogen bond geometry for its dimeric structure. The monomer and dimer optimizations of the molecule have been calculated by the DFT method using various functionals such as B3LYP, B3PW91, mPW1PW91 and M06-2X. Although the minimum energy optimization was calculated at the B3LYP functional, the BSSE-corrected and uncorrected interaction energies of the dimer structure were more effectively obtained with the M062X functional. This assured us a test of the efficiency of M06-Class functional calculations on intermolecular interactions of strongly bound systems. Additionally, the molecular docking study was done between our molecule (ligand) and the previously studied and known as cortisone reductase 11β-Hydroxysteroid dehydrogenase type 1 (receptor, 11-β-HSD1: PDB-2ILT).

Two- and three-body, and relaxation energy terms in water clusters: Application of the hierarchical BSSE corrected decomposition scheme

A detailed analysis of the two- and three-body interaction energy components in water clusters containing up to 30 water molecules is performed at the M05-2X/6-311G** level of theory, using the “hierarchical” basis set superposition error (BSSE)-corrected energy decomposition scheme, VMFC(3), of Valiron and Mayer. We showed that the average BSSE-corrected two- and three-body interaction energy terms are about 74 to 80 and 20 to 26%, respectively, of the total BSSE-corrected interaction energy for all investigated clusters. It was observed that the three-body interaction energy component is significantly negative/positive if there are two H-bonds and one attraction/repulsion interaction energy in the corresponding trimer, respectively. Our calculations also revealed that the deformation energy of water molecules is dependent on their H-bonded environment. To assess the accuracy of the calculations presented here, benchmark calculations were carried out at the high, LNO-CCSD(T)/CBS, level of theory.

Cyclic dimers of formamidine with its N-halogenated formamidine analogues: Structure, energetics, and proton-halonium transfer

Ab initio calculations were carried out to investigate cyclic dimers of formamidine with its N-halogenated analogues, HN = CHNHX (X = Cl, Br, or I). Geometry optimizations and frequency calculations were completed with the MP2 method and both the aug-cc-pVDZ and the aug-cc-pVTZ basis sets. BSSE-corrected interaction energies were calculated at the MP2, QCISD, and CCSD(T) methods. Electron density at relevant critical points, and charge transfers were examined through AIM and NBO analyses respectively. Both the electron density at each of the critical points and the amount of charge transfer correlate with the strength of the dimer interactions. The N-X stretching frequencies and the 15N NMR chemical shifts were also found to correlate with the dimer interaction strengths. Proton-halonium transfer for each of the dimers was also investigated. For any given X, the potential energy profile along the intrinsic reaction coordinate demonstrates that the proton-halonium transfer occurs in one step, without any intermediates. Similarly, the profile of the corresponding force constant (the second derivative of the potential energy) in the transition region indicates that the proton-halonium transfer is a synchronous process. In all cases, the energy barrier for proton-halonium transfer was found to decrease with increasing size of the halogen. Solvent effects were examined using the SMD model with two solvents of differing polarity: tetrahydrofuran and water. Although the proton-halonium transfer remains concerted and synchronous, the energy barrier to proton-halonium transfer increases in solution to the extent that the barrier becomes higher for X = I than it is for X = Br.

Theoretical insights into the metal chelating and antimicrobial properties of the chalcone based Schiff bases

ABSTRACTThe emergence of multi-drug resistant pathogens in infectious disease conditions accentuates the need for the design of new classes of antimicrobial agents that could defeat the multidrug resistance problems. As a new class of molecules, the Heterocyclic Schiff base is of considerable interest, owing to their preparative accessibility, structural flexibilities, versatile metal chelating properties, and inherent biological activities. In the present study, CAM-B3LYP/LANL2DZ and M062X/DEF2-TZVP level of density functional method is used to explore the complexation of chalcone based Schiff base derivatives by Co2+, Ni2+, Cu2+, and Zn2+ metal ions. The HL(1-3)-Co2+, HL(1-3)-Ni2+ and HL(1-3)-Zn2+ complexes formed the distorted tetrahedral geometry. Whereas, the HL(1-3)-Cu2+ complexes prefers distorted square-planar geometry. The BSSE corrected interaction energies of the studied complexes reveals that Cu2+ ion forms the most stable complexes with all three chalcone based Schiff bases. Of the three Schiff bases studied, the HL2 Schiff base acts as a potent chelating agent and forms the active metal complexes than the HL1 and HL3 Schiff bases. Further, the strength of the interaction follows the order as Cu2+ > Ni2+ > Co2+ > Zn2+. The QTAIM analysis reveals that the interaction between the metal ions and coordinating ligand atoms are electrostatic dominant. The metal interaction increases the π-delocalisation of electrons over the entire chelate. Hence, the antimicrobial activity of the metal complexes is more effective than the free Schiff bases. Moreover, the HL(1-3)-Cu2+ complexes shows higher antimicrobial activities than the other complexes studied.

Ni (II) complexes with different ligands express various degree of cytotoxicity

Effect of selected amino acids (glycine, l-histidine, l-cysteine, l-serine, l-tryptophan) and albumin on the spectroscopic properties and photostability of zinc octacarboxyphthalocyanine (ZnPcOC) was explored in the phosphate buffer at a pH of 7.0. The photodegradation of ZnPcOC alone and in the presence of amino acids or albumin has been investigated in aqueous phase using UV-366 nm and daylight irradiation. Kinetic analysis showed that the interaction with amino acids or albumin enhances the photostability of ZnPcOC. To answer the question of how zinc phthalocyanine interacts with amino acids extensive DFT calculations were performed. Analysis of the optimized geometry features of ZnPcOC: amino acids complexes in the gas phase and in water environment as well as the BSSE corrected interaction energies indicates that the more likely is the formation of equatorial complexes in which H-bonds are formed between the COOH groups of the phthalocyanine and carboxyl or amino groups of amino acids. UV–Vis spectra calculated by employing time dependent density functional theory (TD-DFT) are also consistent with this conclusion.

Structural and energetic quantum chemical investigations into how the bioactive thiazolidinedione and rhodanine scaffolds interact with cytosine to form part of DNA

The interaction within biologically active complex configurations composed of thiazolidinedione-cytosine (TC) and rhodanine-cytosine (RC) have been fully investigated using B3LYP and M062X methods in conjunction with various basis sets, including 6-311++G(d,p), 6-311++G(2d,2p), 6-311++G(df,pd) and AUG-cc-pVDZ. Dispersion corrections to interaction energies using M06-2X-GD3 and double hybrid density functionals (B2PLYP-GD2, B2PLYP-GD3 and mPW2PLYP-GD2) have also been taken into account. The results showed that the interaction energies, including long range dispersion corrections obtained using double hybrid density functionals, are about 1–2.5 kcal/mol higher than uncorrected ones. Various combinations of all possible sites around the monomers which could lead to formation of stable complex configurations were considered, and then six double hydrogen bonded interactions which are formed in a cyclic pattern were further investigated for both complex configurations between cytosine-thiazolidinedione and cytosine-rhodanine. The intermolecular hydrogen bonds which are involved in forming of cyclic interaction patterns are of NH⋯O(N) and CH⋯O(N) types.The TCS′2S1 and RCS′2S1 complex configurations were found to have the largest interaction energies within all the complex configurations studied for cytosine-thiazolidinedione and cytosine-rhodanine respectively at all computational levels used for the calculation of interaction energies. These two most stable complex configurations formed between the S1 site of the cytosine monomer and the S′2 site of the thiazolidinedione or rhodanine.The BSSE-corrected interaction energy for six cyclic double hydrogen bonded complex configurations, calculated at M062X/6-311++G(df,pd) level range from −11.26 to −16.22 kcal/mol for TC complexes and −11.04 to −15.59 kcal/mol for RC complexes.The stability order within thiazolidinedione-cytosine (TC) complexes is TCS′2S1 > TCS′1S1 > TCS′2S2 > TCS′1S2 > TCS′3S2 > TCS′3S1 in all levels studied. The same trend was observed for the stability order of rhodanine-cytosine (RC) complexes.The NBO results reveal that the charge transfer occurred from cytosine to thiazolidinedione or rhodanine within complex configurations which are formed at S′1S1, S′1S2, S′2S1 and S′2S2 sites, whereas in the case of complex configurations of cytosine with thiazolidinedione or rhodanine at S′3S1 and S′3S2 sites this order was reversed.The atom in molecule theory (AIM) and natural bond orbital analysis (NBO) were used to understand the nature of the interactions within the complex configurations studied. This showed good consistency with the interaction energies. In addition, good correlations between geometrical parameters, interaction energies, topological AIM data and NBO results were obtained. Based on AIM and NBO results, it is concluded that the H-bond interactions are electrostatic and partially covalent. Finally, the relationship between interaction energies and vibrational frequency changes at involved H-bonds was analyzed.

Comparison of hydrogen- and halogen-bonding interactions in the complexes of the substituted carbonyl compounds with hypohalous acids and monohaloamines

An ab initio study of the complexes formed by hypohalous acids and monohaloamines (designated as HAX where A = O or NH and X = Cl, Br, or I) with RCHO (R = H, CH3, OCH3, and NH2) carbonyl compounds has been carried out at the MP2/aug-cc-pVTZ computational level for comparative study on hydrogen bonds with halogen bonds. Two types of complexes are formed by their combination –RCHO···HAX and RCHO···XAH (A = O or NH) named as hydrogen-bonded and halogen-bonded, respectively, although other weak interactions also coexist in both types of complexes. Analysis of the BSSE-corrected interaction energies reveals that hydrogen bond strength decreases with an increase in size of X atom (i.e., HACl > HABr > HAI) while reverse trend is indicated for halogen-bonded complexes (HACl < HABr < HAI). For the carbonyl compounds, the interaction energies for both hydrogen- and halogen-bonded complexes follow the same order of HCHO < CH3CHO < (CH3O)CHO < (H2N)CHO. Vibrational frequency analysis suggests that both the H-O and H-N bonds are red-shifted while C–H bonds are blue-shifted in hydrogen-bonded complexes. Similarly, the X-O/X-N and C-H bonds are red- and blue-shifted respectively in halogen-bonded; however, the magnitude of red shift for X-O and X-N bonds in halogen-bonded complexes is much smaller than that of H-O and H-N bonds in hydrogen-bonded complexes. The MEP, NBO, and AIMALL methods have been utilized to understand structure, properties, and nature of the interaction stabilizing these two types of the complexes. Relationship of the interaction energies with MEP, charge transfer (CT), and change in % s character obtained from NBO analysis is also drawn for both complexes.

A QM protein–ligand investigation of antipsychotic drugs with the dopamine D2 Receptor (D2R)

The dopamine D2 Receptor (D2R) is a member of the G-Protein-Coupled Receptor family and plays a critical role in neurotransmission activities in the human brain. Dysfunction in dopamine receptor signaling may lead to mental health illnesses such as schizophrenia and Parkinson’s disease. D2R is the target protein of the commonly used antipsychotic drugs such as risperidone, clozapine, aripiprazole, olanzapine, ziprasidone, and quetiapine. Due to their significant side effects and non-selective profiles, the discovery of novel drugs has become a challenge for researchers working in this field. Recently, our group has focused on the interactions of these drug molecules in the active site of the D2R using different in silico approaches. We here compare the performances of different approaches in estimating the drug binding affinities using quantum chemical approaches. Conformations of drug molecules (ligands) at the binding site of the D2R taken from the preliminary docking studies and molecular dynamics simulations were used to generate protein–ligand interaction models. In a first approach, the BSSE-corrected interaction energies of the ligands with the most critical amino acid Asp114 and with the other amino acids closest to ligands in the binding cavity were calculated separately by density functional theory method in implicit water environment at the M06-2X/6-31 g(d,p) level of the theory. In a second approach, ligand binding affinities were calculated by taking into consideration not only the interaction energies but also deformation and desolvation energies of ligands with surrounding amino acid residues, in a radius of 5 Å of the protein-bound ligand. The quantum mechanically obtained results were compared with the experimentally obtained binding affinity values. We concluded that although H-bond interactions of ligands with Asp114 are the most dominant interaction in the binding site, if van der Waals and steric interactions of ligands which have cumulative effect on the ligand binding are not included in the calculations, the interaction energies are overestimated.

Evaluation of the hydrogen adsorption onto Li and Li+ decorated circumtrindene (C36H12): A theoretical study

Circumtrindene as a π-bowl shaped carbon structure decorated by Li and Li+ and examined for H2 adsorption using M06-2X/6-311++G(d,p)//B3LYP/GEN level of theory. All polygons, bonds and various carbon types, in concave and convex sides, were examined to find the best location for Li and Li+. ZPE and BSSE-corrected interaction energy values were calculated for connection of Li or Li+ to circumtrindene and for connection of H2 to LiC36H12 or Li+-C36H12. Better understanding of the adsorption properties were achieved by DOS, PDOS, OPDOS diagrams and NBO analysis. Results showed that in LiC36H12 and Li+-C36H12 complexes, the concave side has more binding energy than the convex ones and Li+-C36H12 has more binding energy than LiC36H12. Also, for LiC36H12, when Li was in center polygon and concave side and for Li+-C36H12, when Li+ was in 6-2 polygon and convex side, the highest interaction energy were obtained. For H2 adsorption, the complexes contain Li and Li+ in center polygon and concave face have the highest binding energy, equal to 15.72 and 16.29 kcal mol−1, respectively. Binding energy values indicated that adsorption of Li or Li+ onto C36H12 and adsorption of H2 onto LiC36H12 or Li+-C36H12 in all positions are chemisorptions, but the connections are not so strong for H2 molecules.

On the thermodynamic stability of the intermolecular association between Lewis acids and Lewis bases: a DFT study

The intermolecular association of twelve combinations of six different Lewis acids and Lewis bases (i.e., R 3 A–BR′3 where A = B and Al; B = N and P; R = H, F, and C6F5; R′ = H, CH3, and C(CH3)3) was theoretically described by means of DFT calculations using the dispersion-corrected ωB97x-D and B97D functionals in conjunction with the 6-311++G(2d,2p) basis set including toluene as solvent through the PCM-SMD implicit solvent scheme. All the studied Lewis pairs appeared to be stable on the basis of computed BSSE-corrected interaction energies; however, the free energies of formation computed in solution (ΔG solv) indicate that three Lewis acid–base combinations can be considered frustrated Lewis pairs (FLPs). Besides, the four features that characterize FLPs are: (1) large distances between the acid and base centers, (2) negligible changes in the geometry of the acid, (3) weak interaction energies, and (4) non-covalent dispersion energy contributing to almost the entire interaction energy. In the present work, we introduce two ad hoc indexes intended to quantify separately the electronic and steric factors, which have a direct effect in the intermolecular association of Lewis acids and Lewis bases and can be used to distinguished FLPs from classical Lewis adducts. Based on the aforementioned ad hoc indexes, the existence of a new kind of complexes that are “intermediate” between classical complexes and FLPs is proposed.

Interactions of zinc octacarboxyphthalocyanine with selected amino acids and with albumin

Effect of selected amino acids (glycine, l-histidine, l-cysteine, l-serine, l-tryptophan) and albumin on the spectroscopic properties and photostability of zinc octacarboxyphthalocyanine (ZnPcOC) was explored in the phosphate buffer at a pH of 7.0. The photodegradation of ZnPcOC alone and in the presence of amino acids or albumin has been investigated in aqueous phase using UV-366nm and daylight irradiation. Kinetic analysis showed that the interaction with amino acids or albumin enhances the photostability of ZnPcOC. To answer the question of how zinc phthalocyanine interacts with amino acids extensive DFT calculations were performed. Analysis of the optimized geometry features of ZnPcOC: amino acids complexes in the gas phase and in water environment as well as the BSSE corrected interaction energies indicates that the more likely is the formation of equatorial complexes in which H-bonds are formed between the COOH groups of the phthalocyanine and carboxyl or amino groups of amino acids. UV–Vis spectra calculated by employing time dependent density functional theory (TD-DFT) are also consistent with this conclusion.

A theoretical investigation of the competition between hydrogen bonding and lone pair⋯π interaction in complexes of TNT with NH3

A theoretical study of the interactions between 2,4,6-trinitrotoluene (TNT) and ammonia (NH3) has been carried out by means of MP2, DFT, and CCSD(T) methods. Eight stable structures of TNT⋯NH3 complexes were identified at the MP2/6-311++G(d,p) level. Various interactions such as lone pair⋯π interaction (lp⋯π interaction), conventional NH⋯O, CH⋯N, N–H···π hydrogen bonds, and novel noncovalent C⋯N carbon bonding, have been observed in the titled complexes. The competition between hydrogen bonding and lp⋯π interaction in the complexes was studied and discussed. The attractive lp⋯π interactions are observed when the lone pair of NH3 points toward TNT π ring. At the CCSD(T)/6-311++G(d,p)//MP2/6-311++G(d,p) level, the corresponding BSSE corrected interaction energy (ΔE) is −3.7kcalmol−1. The calculated results also show that the lp⋯π interaction competes successfully with the NH⋯π and NH⋯O hydrogen bonds. The competition between hydrogen bonding and lp⋯π interaction in TNT⋯NH3 complexes plays important role to affect the structures of complexes. However, the conventional CH⋯N hydrogen bond is stronger than the lp⋯π interaction. The complex I merely with CH⋯N hydrogen bond is the most stable structure among eight complexes. The theoretical studies on UV and IR spectra of the TNT⋯NH3 complexes show that the formations of hydrogen bonding and lp⋯π interaction have small effect on the UV spectra but new IR absorption peaks in range of 100–300cm−1 correlated to interactions between TNT and NH3 have been predicted, which may be helpful for the detection of TNT.

Theoretical studies on an unusual [Ag]+⋯[Au]−⋯[Au]−⋯[Ag]+ metallophilic pattern: Dispersive forces vs. classical coulomb forces

We have studied theoretically the organometallic compound [{Au(C6Cl5)2}Ag([9]aneS3)]2, which displays an unprecedented [Ag]+–[Au]−–[Au]−–[Ag]+ sequence of metals, formed by unsupported Au(I)⋯Au(I) and Au(I)⋯Ag(I) interactions and weaker Cipso⋯Ag and C6Cl5⋯C6Cl5 π-stacking interactions. Density Functional Theory calculations using the pbe functional (DFT/pbe), Hartree–Fock (HF), and second-order Møller Plesset perturbation theory (MP2) calculations have been performed on five model systems based on the X-ray structure. Two dinuclear models (A1 and A2) have been used to estimate the BSSE-corrected interaction energy at HF and MP2 levels between one Ag(I) and one Au(I) fragment and permit to separate the Cipso⋯Ag(I) and Au(I)⋯Ag(I) contribution to the interaction. Three tetranuclear models (B1–B3) have been used to determine the Cipso⋯Ag(I), Au(I)⋯Ag(I), Au(I)⋯Au(I) and π-stacking interactions present in the molecule. The HF level accounts for the ionic component of the interactions and the MP2 level also account for the dispersive contribution; both permits to study the nature and strength of all different types of interactions present in the molecule.

Isolated glyoxylic acid–water 1:1 complexes in low temperature argon matrices

The 1:1 hydrogen bonded complexes between glyoxylic acid (GA) and water are studied in low temperature argon matrices. Four different complex structures were found in deposited matrices. The lowest energy conformer (T1) of GA was found to form complex, where the water molecule was attached to the opposite side of the intramolecular hydrogen bond in the molecule (T1B). Interestingly, this complex was estimated to be+8.0kJmol−1 higher in energy than the most stable structure (T1A), where the water is inserted into the internal hydrogen bond, and also found in solid argon but in smaller abundance. For the second-lowest energy conformer of GA (T2), the two lowest-energy complex structures were identified, with the most stable complex structure (T2A) also being the most abundant in the matrices. The difference between experiment and computational energetic order of the two complex structures of the same GA conformer is explained by contributions of deformation energy upon complexation and the effect of the environment. The computed BSSE-corrected interaction energies are for the two most stable complexes of the two GA conformers for T1A and T2A −42.11 and −45.03kJmol−1, respectively, at the CCSD(T)/aug-cc-pVTZ//B3LYP/aug-cc-pVTZ level of theory.

Strong lone pair⋯π interactions between amine and tri-s-triazine derivatives: A theoretical investigation

For a better understanding of the interesting lone pair⋯π (lp⋯π) interaction, MP2 and CCSD(T) calculations have been carried out to investigate the nitrogen lp⋯π interactions between amine and tri-s-triazine derivatives. New strong attractive lp⋯π interactions are observed when the lone pairs of NH3 and NMe3 point toward the large π system, tri-s-triazine ring. At the CCSD(T)/6-311++G(d,p)//MP2/6-311G(d,p) level, the BSSE corrected interaction energy of the C6N7H3⋯NH3 complex is −6.3kcalmol−1,which is larger than those of the most previously reported lp⋯π systems. The substitution effects on interaction energy of the present studied systems were studied to probe how to manipulate lp⋯π interaction and obtain stronger one. The results indicate that the very strong lp⋯π interaction can form between electron-rich amines and electron-deficient large aromatic ring. But the lp⋯π interactions between the electron-deficient amine such as NF3 and aromatic ring are very weak. The C6N7F3⋯NMe3 complex has interaction energy of −9.8kcalmol−1. This interaction is much stronger than previously reported lp⋯π bindings. The AIM analysis of the nine studied complexes shows that their molecular graphs are obvious different from previously reported benzene⋯amine complexes and X–H/π systems, which may result from the tri-s-triazine ring’s characteristic.

A computational study of the protonation of simple amines in water clusters

The microsolvation study of a group of amines with a variable number of water molecules was performed by conducting a theoretical analysis of the properties of the clusters formed by the amines with up to seven molecules of water. We describe the microsolvation of several amines focusing on the dissociation of a water molecule that transfers a proton to the amine and forms a hydroxide ion. Ab initio calculations were performed on these clusters employing the DFT/B3LYP and MP2 methods with the 6-311++G(2d,p) basis set. Several stationary points for each cluster were thus located and characterized as minima from frequency calculations. Intermolecular BSSE corrected interaction energies were obtained. The protonation mechanism of the amines was examined in terms of some parameters that include the lengths of the bonds involved in the process of proton transfer and the frequencies associated with certain O-H and N-H stretching modes. On the basis of the calculations, all studied amines present similar behavior but trimethylamine, whose limitations to be integrated in the water hydrogen bond network cause the instability of some of their complexes. The cyclic configurations are the most stable structures up to five water molecules due to the presence of cooperative effects associated with the hydrogen bonds of water molecules. However, when the number of water molecules increases the spatial forms become the most stable configurations. The dissociated forms were not found to have the most stable configuration in any of the studied systems but energetic differences between the dissociated and non-dissociated forms decrease with the number of water molecules.

Experimental and Theoretical Characterization of a Lone Pair−π Complex: Water–Hexafluorobenzene

The lone pair-π interaction between H(2)O and C(6)F(6) was studied using matrix isolation infrared spectroscopy and quantum chemical calculations. Co-deposition of H(2)O with C(6)F(6) in a nitrogen matrix at 17 K followed by annealing to 30 K, results in the appearance of multiple new peaks in the infrared spectrum that are shifted from the H(2)O and C(6)F(6) parent absorptions. These peaks only appear when both the H(2)O and C(6)F(6) are present and have been assigned to distinct structures of a 1:1 H(2)O·C(6)F(6) complex. Similar experiments were performed with D(2)O and HDO and the corresponding infrared peaks for the structures of the D(2)O·C(6)F(6) and HDO·C(6)F(6) complexes have also been observed. Theoretical calculations were performed for the H(2)O·C(6)F(6) complex using the B3LYP, MP2, and CCSD(T) methods. Geometry optimizations at the B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVDZ levels of theory located three structural minima, all of which involve the lone pair-π interaction between the H(2)O and the C(6)F(6) ring, but with different relative orientations of the H(2)O and C(6)F(6) subunits. BSSE corrected interaction energies were estimated at the CCSD(T)/aug-cc-pVTZ level and found to be between -11.2 and -12.3 kJ/mol for the three H(2)O·C(6)F(6) structures. Vibrational frequencies for the each of the structures were calculated at the B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVDZ levels. The frequencies calculated with both methods support the assignments of the observed new peaks in the infrared spectra to the structures of the H(2)O·C(6)F(6) complex; however, the B3LYP calculated frequency shifts were found to be in better quantitative agreement with the experimentally observed frequency shifts.

Interactions and Ordering of Ionic Liquids at a Metal Surface.

An atomistic force field for ionic liquids interacting with a metal surface is built on the basis of quantum methods. Density functional calculations of alkylammonium cations and alkylsulfonate anions interacting with a cluster of iron atoms were performed, at a series of distances and orientations, using the M06 functional that represents noncovalent interactions. A site-site potential function was then adjusted to the BSSE-corrected DFT interaction energies. Finally, the polarization of the metal by the ions was taken into account using induced dipoles to reproduce the interaction energy between charges and a conductor surface. When combined with a molecular force field for the ionic liquid and a suitable potential for metals, our model allows the computer simulation of heterogeneous systems containing metal surfaces or nanoparticles in the presence of ionic liquids. Our aim is to study tribological systems with ionic lubricants. We report molecular dynamics results on the structure of the interfacial layer of several alkylammonium alkylsulfonate ionic liquids at a flat iron surface, including analyses of the positional and orientational ordering of the ions near the surface, and charge density profiles. Both anions and cations are found in the first ordered layer of ions near the surface, with the oxygen atoms of the sulfonyl groups interacting more strongly with the metal. The interfacial layer is essentially one ion thick, except for very short chain ionic liquids in which a second layer is observed. The effects of different lengths of the nonpolar alkyl side chains on the cation and the anion are different: whereas butyl chains on the sulfonate anions tend to be directed away from the surface, those on ammonium cations lie more parallel to the surface.